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INTERNATIONAL HYDROGRAPHIC REVIEW MAY 2013

THE

INTERNATIONAL

HYDROGRAPHIC

REVIEW

INTERNATIONAL HYDROGRAPHIC BUREAU

MONACO

No. 9 MAY 2013

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By Ian HALLS, Editor

- The Caris Engineering Analysis Module - Assisting in the Management of Queensland’s Waterways.

by : Owen CANTRILL (Australia) Daniel KRUIMEL (Australia)

□ Editorial

□ Articles

- A technical method on calculating the length of coastline for comparison purposes.

by : Laurent LOUVART (France)

□ Notes

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777

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373737

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- The GE.N.ESIS project - Georeferenced Depiction and Synthesis of Marine Archaeological Survey Data in Greece.

by : Panagiotis GKIONIS (Greece)

- Results of operational sea-wave monitoring with radar gauges.

by : Sebastian RÜTTEN (Germany) Stephan MAI (Germany) Jens WILHELMI (Germany) Theodor ZENZ (Germany) Hartmut HEIN (Germany) Ulrich BARJENBRUCH (Germany)

- Anomalous ECDIS Operations.

by : Dr Mohamed I. MOHASSEB (Egypt)

- New scientific contribution to the King Abdulaziz University.

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616161

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Editorial

This edition comprises four Articles and two Notes.

The first Article outlines how Maritime Safety Queensland (MSQ) in Australia is using state of the art CARIS software to assist in the management of their waterways. The paper uses test results from surveys to identify improvements to volume calculations, sur-vey conformance analysis, shoal detection and survey reference models.

The second Article describes the field work, processing and reporting for a new project in Greece to assist with mapping, visualisation and synthesis of underwater archaeologi-cal data. The author describes the fieldwork procedures and the GIS capabilities used to prepare the collected data in order to provide a potential model for the sustainable management of Greek maritime archaeology. Ed. Note - as this model is developed, it is hoped that S-100 may provide a suitable geodatabase model for managing such data and information as discussed by Masetti, Calder and Alexander in the IHR November 2012 edition.

Our third Article discusses the development of a low cost, non-contact sea wave monitoring system based on radar sensors. The results to date are promising in terms of estimating wave heights and direction.

The final Article is a summary of issues relating to anomalies in ECDIS equipment in terms of displaying recent changes to ENC data encoding and display standards including complex symbology. These ongoing issues are not new, however the IHB has been proactive in identifying the issues and raising awareness through several recent Circular Letters. Using the IHB’s test data, the author runs the data through a couple of ENC visualisation tools to determine the ability for them to display the symbols correctly. Given that ECDIS has been operational for 20 years it is disappointing that interpretation issues with S-52 display still exist. Hopefully, the work of the IHB in conjunction with the IMO will soon rectify the issues. Ultimately, it is the responsibility of the type approval agencies to ensure that ECDIS equipment conforms and perhaps there are more deep seated issues regarding training and competencies in these areas. The maintenance of software should not even be an issue today and manufacturers have the responsibility to conform whilst users have the responsibility to understand the capability. “Buyer beware” and “minimum performance specifications” are simply not acceptable with mandatory car-riage requirements now in effect. This Edition also includes two Notes :

The first Note describes the findings of an IHO Correspondence Group attempting to harmonise the way in which IHO Member States define and measure the length of their national coastlines.

The second Note provides a brief technical description of a new hydrographic survey vessel for the King Abdulaziz University in Saudi Arabia.

On behalf of the Editorial Board, I hope that this edition is of interest to you. Thank you to all the authors for your contributions and to my colleagues who provided peer reviews for the Articles in this edition. My thanks also go to the IHB staff who finalise the publication and provide translations.

Ian W. Halls Editor

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THE CARIS ENGINEERING ANALYSIS MODULE ASSISTING IN THE MANAGEMENT OF QUEENSLAND’S WATERWAYS

By Owen CANTRILL (Maritime Safety Queensland - Australia) & Daniel KRUIMEL (Caris Asia Pacific - Australia)

Abstract

Résumé

Resumen

Maritime Safety Queensland (MSQ) is responsible for protecting Queensland's waterways and the people who use them providing safer, cleaner seas. MSQ first incorporated CARIS products into their workflow in 2009 with HIPS and SIPS and BASE Editor and in 2012 are looking to utilize the new functionality of the Engineering Analysis module to assist them in the management of their ports and waterways throughout Queensland. This paper will look into how BASE Editor and the Engineering Analysis Module are being utilized in the Ports and Waterways environment, with a focussed case study on the application with MSQ. In-cluded in this will be a detailed comparison of techniques for volume computation (such as end area volumes, hyperbolic and TIN volumes), a summary of the results that can be achieved and the associated advantages/disadvantages with each method.

La sécurité maritime du Queensland (MSQ) est chargée de la protection des voies navigables du Queensland et des personnes qui les utilisent en leur procurant des eaux plus sûres et plus propres. La MSQ a d’abord incorporé des produits CARIS dans son plan de travail en 2009 avec HIPS et SIPS et BASE Editor et, en 2012, elle a cherché à utiliser la nouvelle fonctionnalité du module d’analyse bathymétrique afin d’aider à la gestion de ses ports et de ses voies navigables à travers le Queensland. Cet article examine la manière dont BASE Editor et le module d’analyse bathymétrique sont utilisés à l’intérieur des ports et des voies navigables avec une étude de cas consacrée aux applications à la MSQ. Il comprend une comparaison détaillée des techniques de calculs de volumes (tels que les volumes finis, les volumes hyperboliques et TIN), un résumé des résultats qui peuvent être obtenus et des avantages/inconvénients de chaque méthode.

La Autoridad de la Seguridad Marítima de Queensland (MSQ) es responsable de la protección de las vías navegables de Queensland y de las personas que las utilizan, proporcionando mares más seguros y más limpios. La MSQ incluyó los productos CARIS por primera vez en su proceso de trabajo en el 2009, con HIPS y SIPS y el Editor BASE y en el 2012 esperaban utilizar la nueva funcionalidad del Módulo de Análisis de Ingeniería, como ayuda para la gestión de sus puertos y vías navegables en la totalidad del Queensland. Este artículo profundizará sobre cómo el Editor BASE y el Módulo de Análisis de Ingeniería están siendo utilizados en el entorno de los Puertos y las Vías Navegables, con el estudio de un caso centrado en la aplicación de la MSQ. En dicho estudio se incluirá una comparación detallada de técnicas para el cálculo de volumen (tales como los volúmenes finales de áreas los volúmenes hiperbólicos y TIN) y un resumen de los resultados que pueden obtenerse y las ventajas/desventajas asociadas a cada método.

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INTRODUCTION Maritime Safety Queensland (MSQ) is a division of the Department of Transport and Main Roads within the Queensland State Government. MSQ's role is to protect Queensland's waterways and the people who use them - providing safer and cleaner seas. Within the corporate structure of MSQ, the Hydrographic Services section carries out hydrographic surveys on behalf of clients. Current clients include North Queensland Bulk Ports (Ports of Hay Point, Weipa, Abbot Point and Mackay), Ports North (Cape Flat-tery, Thursday Island), Gladstone Ports Corporation and Boating Infrastructure and Waterways Manage-ment (recreational boating facilities). These various sites are spread over 1700Nm of coastline. OVERVIEW OF OPERATIONS MSQ utilize a variety of survey equipment, such as a Kongsberg Simrad EM 3002D multi-beam echo sounder, Klein 3000 Sidescan, Starfish 452f sides-can, SEA Swath plus 234 kHz interferometry system, Echotrak MK III dual frequenciy single beam, Deso 300 single beam, Applanix POS MV 320, Applanix POS MV Wavemasters and Lecia RTK DGPS. Surveys range from boat ramps that integrate land survey and a small hydrographic component, through to high precision surveys for Under Keel Clearance systems. A permanent installation of the EM3002D exists on the vessel QGNorfolk, with other mobile systems deployed on vessels of opportunity, such as the QG Bellara used during rapid response surveys in the 2011 Brisbane floods. MSQ ensures a high quality of work through the use of experienced and competent personnel. There are six surveyors certified at Level 1 by the Australasian Hydrographic Surveyors Certification Panel (AHSCP) and five surveyors (including graduates) that work under direct supervision. In an effort to improve acquisition to processing ratios, MSQ first incorporated CARIS Ping-to-Chart products into their workflow early in 2009, turning to HIPS and SIPS for processing their bathymetric data. Later that year, BASE Editor was also brought on board to assist in bathymetric data compilation and QC. Staff from MSQ have stayed well versed in the latest functionality for the software packages through participation in open training courses held in the region by the CARIS Asia Pacific office. After attending a training course on the new Engineering Analysis Module (compatible with BASE Editor) in August of 2011, MSQ sought to expand on their

current functionality and utilize the new module to assist them in the management of their ports and waterways throughout Queensland. THE ENGINEERING ANALYSIS MODULE The Engineering Analysis Module features under the 'Analysis' pillar of the Ping-to-Chart workflow, as part of the Bathy DataBASE suite of products. Recognis-ing the fact that different users have different requirements, Bathy DataBASE is a scalable solution. In order to provide more functionality for users in the ports and waterways environment, the Engineering Analysis module was introduced to the Bathy DataBASE product suite. The module works with either BASE Editor or BASE Manager, and includes many functions migrated from an existing CARIS application (BEAMS - Bathymetry and Engineering Management System). These functions include volume computations, shoal management, confor-mance analysis and reference model creation and maintenance. VOLUME CALCULATION METHODS FOR HYDROGRAPHIC SURVEYING The calculation of volumes in hydrographic survey-ing is frequently used in dredging applications and reservoir analysis (for example, sedimentation). A number of different methods can be utilized in determining a volume. The 'best' method to use is determined by factors such as the technique of sounding for the data (single beam, multi-beam, LiDAR etc.) and also the nature of the material (smooth, sandy bottom is quite different to an undulating, rocky terrain).

"Accurate volume estimates are important for the choice of dredging plant, production estimates and ultimately project costs." (Sciortino J.A., 2011)

In addition to the volume of material, the type of material is another important factor. The cost of dredging rock will be much higher compared to the same amount of material in sand. End Area Volumes End Area volumes have been derived from land-based methods used in railroad and roadway construction. They involve calculating the volume from cross sections of a channel, surveyed at regular intervals (see Figure 1).

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The key components in computing the volume are the cross sectional area (an average is taken of the two areas) and the length between the cross sections. This method assumes that the cross sectional area is relatively constant between two successive cross sections. If this assumption is not true, the volume produced will realistically just be an approximation.

TIN Volumes Triangulated Irregular Network (TIN) Volumes are based on the true positions of depths to calculate the volume of a surface. This calculation involves modelling the surface as a collection of small planes. TIN's can either be derived from a gridded bathym-etry source (i.e. surface) or from a point cloud. One advantage in using the TIN method (particularly for point data) is that the true position of the source depths will be utilized in the volume calculation. This is the historically preferred method for most dredging type applications where volume is critical.

Hyperbolic Volumes For this method, a hyperbolic cell is created from the centres of every four adjacent grid cells. The depths from the grid cells are used as the depths for the corners of the hyperbolic cell. For this calculation, the surface is modelled as a collection of hyperbolic paraboloid sections, with a hyperbolic paraboloid created to smoothly pass through the points of each hyperbolic cell (see Figure 2). This gives a smooth approximation of the surface and good volume results, but is processing intensive and can be time consuming.

Rectangular Volumes In this method, a single depth value from each cell (or bin) in the surface is used to calculate the volume. The surface is modelled as a collection of disjointed rectangular prisms, with the depth for each grid cell becoming the depth of the prism (see Figure 3). In comparison to the previous hyperbolic method, this results in a much more 'simple' volume calculation which is processed much faster, however the accuracy of the computed volume may not be as reliable.

One limitation on the rectangular volume method is the inability to perform a volume calculation against a sloped or non-horizontal surface in a reference model (for example the bank of a channel). This is because by definition, a rectangular prism cannot have a sloped edge, so only horizontal reference surfaces are supported.

Figure 1: Calculation of End Area Volumes (USACE, 2001).

Figure 2: Representation of the hyperbolic paraboloid volume method

Figure 3: Representation of the rectangular volume method

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VOLUME COMPARISONS As previously outlined, there are a number of different methods available to the hydrographer for volume determination. So this leads to the next question - which method should be used? This will largely be dependent on what technology is available to conduct the survey. If the user only has access to a single beam echo sounder, they will be limited to end area volumes and TIN volumes. For a full den-sity multibeam survey, rectangular and hyperbolic volumes can also be taken into consideration. The nature of the seafloor (or riverbed/reservoir) could be another factor in determining which is the most suitable volume method to be used. If the bottom topography is smooth (such as with sand), hyperbolic volumes, which produce a smooth estimate of the terrain using constructed hyperbolic paraboloids could yield the best results. For a harsher, rocky terrain, TIN volumes utilizing the true positions of each depth may be the most robust answer.

Case Study in Weipa In order to test the results produced by the various methods of volume calculation, a case study was carried out using survey data collected by MSQ at the Port of Weipa in October, 2011. The data was provided as an ASCII XYZ file that had already been binned at 1m. A reference model for the Port of Weipa was also used in the calculations. The test area used is a section of channel located just to the east of beacons 7 and 8 in the south channel. Volumes were calculated in the test area to determine the amount of material that would need to

be removed to bring the channel down to a declared depth of 16m (Note: this is just an arbitrary value chosen for testing purposes). The methods used for comparison were hyperbolic, rectangular and TIN volumes. Simulated end area volumes were also calculated by extracting profiles from the multi-beam bathymetry at intervals of 25m, 50m and 100m. The results can be seen in Table 1. (Note: In this case, the hyperbolic volume has been used as the bench-mark for determining volume difference and error for other methods. This does not mean that there is zero error in the hyperbolic volume result). The results displayed in Table 1 yield some interest-ing results. As could be expected, the two volumes closest to each other are the hyperbolic and TIN volumes. What is probably most surprising are the results achieved through the use of end area volumes. One would generally assume that profile spacing would be inversely proportional to the volume difference/error (i.e. the lesser distance between profiles, the greater the accuracy of the computed volume). This is not reflected in these results, where the error actually decreases as the interval increases.

This may be due to the nature of the seabed. The data used was a pre dredge data set following the wet season. The channel is typically smooth and shaped in a reasonably consistent V shape due to the amount of siltation and the effect of significant shipping movements which assist in keeping the centreline clear of siltation. Validation of Case Study As the results produced in the Weipa case study did not reflect expected results, an additional independ-ent case study was sought out. One was found by Dunbar J.A and Estep H of the Baylor University

METHOD VOLUME (m³) DIFFERENCE (m³) VOLUME ERROR (%)

Hyperbolic Volume 794,912.5 0 0

Rectangular Volume 805,090.2 10,177.7 1.280

TIN Volume 798,654.4 3,741.9 0.471

End Area (25m Interval)

803,019.1 8,106.5 1.020


802,755.3 7,842.7 0.987


802,022.8 7,110.2 0.894

Table 1: Comparison of volume results for the test area in Weipa

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Department of Geology (BU) in Texas, USA. The project undertaken by BU was to study the hydro-graphic surveying methods utilized by the Texas Water Development Board (TWDB) in determining water and sediment volume in reservoirs throughout Texas. Whilst the project also investigated sub bottom profiling and sediment surveys, the volume comparison was carried out in Lake Lyndon Baines Johnson (LBJ), a Highland Lake on the Texas Colorado River. As part of the project, Hydrographic Consultants Inc collected and processed a multi-beam survey in Lake LBJ. In order to evaluate the influence of survey profile spacing on volume accuracy:

"BU extracted simulated profiles at spacing’s ranging from 100 to 2000 ft from a high-density multi-beam survey collected by an independent contractor. Volume calculations based on the extracted profile sets were compared to the volume based on the full multi-beam survey. " (Dunbar, J.A, Estep, H, 2009)

The results produced in the study by BU can be seen in Table 2. They are also shown graphically in Figure 4. When extracting the profile sets to produce simulated volumes, BU did this in two runs (Run 1 and Run 2). This meant that for each simulated profile spacing, two independent sets of profiles were extracted from the multi-beam bathym-etry.

By undertaking a statistical analysis of the BU Volume comparison results, values from Run 1 have a coefficient of correlation of 0.884 and 0.936 for Run 2. This indicates a strong positive correlation between profile spacing and volume error, which is what we would generally expect. However despite the strong correlation, there are inconsistencies in the data. Such as the very low value of 0.14 % for 1000 ft profile spacing in Run 1, and a difference of 0.696% in Run 1 and Run 2 error for 300 ft profile spacing. This is because the Volume Error of 0.718% for 300 ft profile spacing in Run 1 is higher than expected in contrast to other results.

Table 2: Results of BU Volume Comparisons (Dunbar, J.A, Estep, H, 2009)

Figure 4: Scatter plot and 3D line graph of BU volumes comparisons.

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From these results, a conclusion can be drawn that when increasing the population size of our sample dataset, the error values do display a tendency for strong positive correlation. In the Weipa Case Study, the population size was only three (25m, 50m and 100m spacing) so these results were not apparent. If further intervals were added and multiple runs (as in the BU example), perhaps we could expect to see similar results. It could therefore be argued that while there is a trend for volume error to increase with profile spacing, for any given dataset based on one set of profiles (i.e. a single beam survey) the accuracy of the volume is essentially down to 'luck.' In their report, Dunbar J.A and Estep H state that "Reducing the profile spacing to less than 500 ft does not guar-antee improved volume accuracy. " (Dunbar, J.A, Estep, H, 2009) VOLUME COMPUTATIONS AT MSQ MSQ have traditionally used the TIN method to compute volumes for their hydrographic surveys. As part of an evaluation for the Engineering Analysis Module in 2011, MSQ ran a comparison of TIN volume computations using the module against their existing capability. Results from the comparison can be seen in Table 3. The Engineering Analysis Module produced the same TIN volume results, in less time across all cases, as well as having the ability to compute a volume for the entire channel (which the existing capability was not able to achieve).

CONCLUSION The Engineering Analysis Module is able to greatly assist users in managing Ports and Waterways through the use of conformance analysis, sophisti-cated volume computations, shoal detection/

management and the creation, editing and mainte-nance of reference models. When computing vol-umes, users should consider what type of volume will deliver the most accurate results. While End Area volumes have traditionally been widely used, this paper presents evidence that TIN volumes and hyperbolic volumes should be taken into considera-tion as they are capable of producing volume results that are reliable and repeatable. The Engineering Analysis Module has provided MSQ with the ability to compute volumes faster and on much larger data sets than their existing capability, along with new functionality for advanced visualiza-tion techniques. The ability to increase the data sets reduces the trade off historically required between precise volumes (e.g. 0.5m spaced data) with practi-cal processing limits. (Data generalised to 2.5m) REFERENCES Cantrill, O, (2012) General Aspects of Port Survey-ing and Shallow Water Bathymetry, Proceedings of SWPHC Ports & Shallow Water Bathymetry Techni-cal Workshop, Brisbane, Australia, March 13-14. Dunbar, J.A, Estep, H, (2009) Hydrographic Survey Program Assessment Contract No 0704800734, Baylor University Department of Geology, Waco, TX. Kruimel, D, Fellinger, C, (2011) Bathymetric Data Management: The Ports and Waterways Environ-ment, Proceedings of Hydro 2011 Conference, Fre-mantle, Australia. November 7-10.

Sciortino, J.A, (2011) Fishing Harbour Planning, Construction And Management: FAO Fisheries And Aquaculture Technical Paper No. 539

USACE, (2001) Hydrographic Surveying, Engineer-ing Manual 1110-2-1003, United States Army Corps of Engineers, Washington, DC.

CARIS Engineering Analysis Module Existing capability

Area Time to Process

(hh:mm:ss) Volume to Dredge (m³)

Time to Process (hh:mm:ss)

Volume to Dredge (m³)

Whole Channel 0:47:00 116,724 Not enough mem-

ory to compute

Not enough memory to com-

pute

BN16 - BN18 0:01:57 2,234 0:03:14 2,233.8

BN6 - BN 8 0:05:50 31,015 0:19:34 31,016.2

BN 8 - CH15500 0:02:00 19,049 0:02:45 19,048.8

BN2 - BN4 0:05:52 10,492 > 1 hr 9867

Table 3: Volume results and processing times at MSQ

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BIOGRAPHIES Owen Cantrill is a Level 1 Certified Hydrographic Surveyor having gained certification in 2000. He gained a Bachelor of Surveying with honours from the University of Melbourne in 1989. He is currently employed as the manager of the Hydrographic Services section of Maritime Safety Queensland (MSQ). [email protected] Daniel Kruimel is an active member of the Spatial Industry and is currently a member on the SSSI Regional Committee of South Australia, as well as the Hydrography Commission National Committee. At the start of 2011, Daniel took up a role with CARIS Asia Pacific as a Technical Solutions Provider. [email protected]

mailto:[email protected]


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THE GE.N.ESIS PROJECT Georeferenced Depiction and Synthesis of Marine

Archaeological Survey Data in Greece

By Panagiotis GKIONIS (Hellenic Navy Hydrographic Service with Plymouth University - UK)

Abstract

Résumé

Resumen

Through the GE.N.ESIS project, the Hellenic Ephorate of Underwater Antiquities (EUA) is introduced to a digital tool for visualisation and synthesis of underwater archaeological data. A marine geoarchaeological survey was conducted at the Methoni underwater archaeological site (Greece) in the summer of 2012 utilising geophysical instruments. The acquired data together with archival archaeological data was managed through a Geographical Information System (GIS). The survey results present the ruins of a submerged prehistoric settlement, the Methoni ancient harbour and submerged breakwater, wrecks, cannons and artefacts/features – all of which are of potential archaeological interest. The project outcomes provide the genesis of a new baseline capability for the cultural management of the Greek archaeological sites.

Dans le cadre du projet GE.N.ESIS, l’éphorat grec des antiquités sous-marines (EUA) est présenté via un outil numérique de visualisation et de synthèse des données archéologi-ques sous-marines. Un levé géo-archéologique marin a été réalisé sur le site d’archéolo-gie marine de Méthone (Grèce) au cours de l’été 2012 à l’aide d’instruments de géophysique. Les données acquises ainsi que les données archéologiques d’archives ont été gérées via un système d’information géographique (SIG). Les résultats du levé présentent les ruines d’une zone de peuplement préhistorique submergée, l’ancien port de Méthone et des brise-lames, épaves, canons et artefacts/éléments submergés – tous d’intérêt archéologique potentiel. Les résultats du projet fournissent la génèse d’une nouvelle capacité de base pour la gestion culturelle des sites archéologiques grecs.

Gracias al Proyecto GE.N.ESIS, le ha sido presentada al “Hellenic Ephorate of Underwater Antiquities” (EUA) una herramienta digital para la visualización y la síntesis de datos arqueológicos submarinos. Un levantamiento geoarqueológico marino fue efectuado en el sitio arqueológico submarino de Methoni (Grecia) durante el verano del 2012, utilizando instrumentos geofísicos. Los datos adquiridos, junto con los datos de los archivos arqueológicos, fueron administrados a través del Sistema de Información Geográfica (SIG). Los resultados del levantamiento presentan las ruinas de un emplaza-miento prehistórico sumergido, el antiguo Puerto de Methoni y el rompeolas sumergido, restos de naufragios, cañones y artefactos/objetos, todos ellos de un interés arqueológi-co potencial. El resultado del proyecto proporciona la génesis de una nueva capacidad de referencia para la gestión cultural de los sitios arqueológicos griegos.

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INTRODUCTION Methoni is a Greek seaside town at the south-western extremity of the Messenia Peninsula (Fig.1), also known as Pylia Region. There is archaeological evidence supporting that the human presence in the area which nowadays forms the Methoni Bay, dates back to the Bronze Age (Spondylis, 1996).

In the historical periods that followed, the vigorous activities of the local population and the naval battles fought off Methoni were prominent themes through the literature. The harbour of Methoni was strategi-cally significant (Biris, 2002) and this is evident from the successive improvements of the initial fortifica-tion of the ancient town which took place following the second Messenian War and the town’s inde-pendence around 369 B.C. Methoni’s strategic role through the centuries is evident from the repeated predatory raids/expeditions of Romans, Venetians, Turks and the French in the area from the 12

th to the

19th century. Its importance is mainly evident through

the existence of its harbour dating from the Archaic Period of Ancient Greece according to Homer’s Iliad (UoA, 2012) and the successive improvement works on the harbour’s breakwater (Lianos, 1987) by some of the above mentioned expeditionary forces. Al-though in the 18

th century the capacity of the harbour

was enough to accommodate 7 or 8 galleys (Lianos, 1987), nowadays its breakwater is submerged lying just below the sea surface and the harbour has not been used commercially since a new breakwater was constructed in the 19

th century closing its en-

trance (Fig. 2 and 3).

Figure 1. Pylia Region in Greece and the Methoni Bay (ESRI, 2012)

Figure 2. The town of Methoni, the

fortification of the ancient town, the ancient submerged breakwater and the latest breakwater which closes the entrance of the ancient harbour.

Figure 3. The 19th century break-

water over the (nowadays sub-merged) ancient breakwater.

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Since 1993, the archaeological surveys and excava-tions undertaken by the Hellenic Ministry of Culture / Ephorate of Underwater Antiquities (EUA) confirmed the glorious historical past of Methoni, bringing to light numerous antiquities at the site. Prehistoric settlement ruins have been discovered lying on the seabed at a depth of 3.5-5m (Fig. 4). Together with parts of a medieval coastal stone fresh-water pipeline, they have been documented with the use of land survey methods. A number of wrecks, pottery, a prehistoric stone anchor (Fig. 5) and other antiqui-ties have also been discovered in the same area revealing the maritime roots of the local population through the millennia (Spondylis, 2000).

Previous to the summer of 2012 and from pure archaeological surveys, no marine geophysical sur-vey had ever been conducted off Methoni. All governmental survey records concerning Methoni and other underwater sites were archived in either paper form or simple electronic means in no specific format (Spondylis, 2011). Hence, the Greek govern-ment archaeologists could only make archival site investigations from distinctive sources of conven-tional data (maps / architectonic plans) with very few options of further data correlation spatially referenced. Further, it was difficult to analyse survey data provided by external partners in sophisticated formats, mainly because of format incompatibility with existing EUA IT suites or inefficiency in spatial correlation of existing data with the data provided.

Figure 4. Ruins of a square

building at the prehistoric submerged town of Methoni.

Figure 5. Prehistoric stone

anchor, discovered at Methoni Bay in 2000.

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The GE.N.ESIS Project (GEoreferenced depictioN and synthESIS of marine archaeological survey data in Greece) introduced the Ephorate of Underwater Antiquities (EUA) to a digital management tool for visualisation, synthesis and analysis of underwater archaeological data. Within the objectives of the pro-ject were (a) the conduct of a marine geophysical survey of the ruins of the prehistoric submerged town of Methoni, the submerged breakwater of the town’s ancient harbour and potentially of other local underwater antiquities and (b) the visualisation, geo-reference, synthesis, analysis and management of existing archival archaeological data and survey data acquired during the survey using a GIS. The information presented in the following sections includes a brief background of the EUA’s underwater geo-archaeological surveys and site management, the methodology implemented for the survey, the survey and the project results, leading to the recorded features of potential archaeological interest and a spatial synthesis and depiction of results through a GIS. Discussed will be issues of further scientific concern which qualify and quantify the data reliability and support the interpretation of results. Finally, conclusions and recommendations for further research and project development will be addressed. Further information about the project can be found on the web at www.methoni-genesis.blogspot.com.

BACKGROUND

Underwater Archaeology and Marine Geophysi-cal Surveys in Greece off Methoni

The EUA is the governmental agency for marine ar-chaeology in Greece. It was founded in 1976 and together with the Hellenic Institute of Marine Archae-ology are the only bodies that systematically conduct pure marine archaeological surveys in Greece. How-ever, in the light of the particularities of underwater archaeological investigations, the need for integrated scientific collaboration during surveys was early identified and Spondylis (1996) had early addressed the need for multi-scientific research to be conducted off the southwest coasts of Greece. Since 1976, the EUA in collaboration with other research Institutes, industrial partners and universi-ties, has undertaken numerous surveys sponsored by the survey collaborators off the Greek coasts where remote sensing techniques and often state-of-the-art geophysical instruments were utilised. Despite ongoing discussion amongst geologists and archaeologists about the reasons that led the prehis-toric town of Methoni being submerged (Spondylis, 1996), until this project, no geophysical survey had been conducted off Methoni.

GIS in Maritime Archaeology

GIS have growing applications in maritime archae-ology (Green, 2004). They allow the display, synthe-sis and analysis of archaeological and relevant data in geographical space and in such a form that spatial and/or chronological trends of a site can be visual-ised (NAS, 2009). Layering of ortho-images and datasets from sonar traces or archaeological records is a typical GIS application. A fieldwork oriented GIS can be interfaced with geophysical and positioning systems, to allow survey planning, the provision of real-time positioning information during data acquisi-tion phase and pure archaeological data recording (3H Consulting, 2012). Moreover, GIS facilitates the determination of legal aspects during surveys through the monitoring of archaeological site bound-ary delimitation. Most significantly, GIS can be used as a data manipulation tool for digital storage and database creation as well as a decision support tool for site and holistic cultural heritage management. The EUA has neither implemented an office-based nor a real-time data monitoring/collection GIS, so even when EUA survey partners use one for data acquisition, the post visualisation and analysis of data is inadequate or non-existent.

Legislation – Legal Issues

The Nautical Archaeology Society (2009) provides a good guide for a study on International Law concern-ing underwater archaeological surveys. Greek Legis-lation is applied according to the Greek Law No 3028/2002 (‘’On the Protection of Antiquities and Cultural Heritage in general’’) and relevant Govern-mental Directives for licensing issues. The participa-tion of the EUA in all maritime archaeological sur-veys off the Greek coasts and literally the direction of all surveys by the EUA are legal prerequisites. Ilias Spondylis was assigned by the EUA as the Survey Director Archaeologist.

METHODS

Preparatory Tasks

Locating resources for the project was a major factor for the best possible project outcome. Staffing the project adhered to the general rules of Green (2004). Apart from the author, the participation of Gwyn Jones (Plymouth University, MSc Hydrography programme Leader) as Project Supervisor and Kon-stantinia Tranaka, a professional administrator and nurse, provided enhanced expertise for handling sophisticated geophysical hardware/software and dealing with Health and Safety issues. The EUA granted the provision of the Director Archaeologist, divers and a coxswain for the survey boats.

http://www.methoni-genesis.blogspot.com

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Aris Paleokrassas contributed to the project as a marine surveyor. Financial resources were secured by the Plymouth University funding scheme and the author’s personal budget. All assets used are presented in the next sections. A preliminary site reconnaissance took place in Methoni in early April 2012 for familiarisation with the site, to undertake coastlining and for definition of minimum depth inside the ancient harbour ensuring the safety of boat operations. Since the ancient harbour is now enclosed, a passage had to be located over the submerged breakwater crest (Fig. 6) so that the survey boat could enter the harbour with a safe clearance depth under its keel.

Laboratory tests (Fig. 7) were conducted during early June 2012 to familiarise the operator with the survey equipment and software and to investigate methods for very-shallow-water towfish deployment. Sea trials were conducted in Plymouth Sound during June 2012. The aim was to simulate the imminent survey tasks expected at the site, so that problems related to the actual survey and its specifics could be identified at an early stage. The objectives of the sea trials were to set up the survey instruments for sea (Fig. 8), to test very-shallow-water deployment techniques of sidescan sonar and magnetometer towfishes (Fig. 9, 10) and to evaluate acquired data samples for definition of the optimum towing tech-nique. Towing the towfishes by the stern with a float rigidly attached on top of them proved to be the opti-mum deployment method (Fig. 10a) at that stage.

Figure 6. Preliminary underwater reconnaissance of the

harbour’s breakwaters. A measuring pole was used for detection of a point of maximum depth over the submerged breakwater and the definition of minimum depth inside the ancient harbour.

Figure 7. Laboratory tests.

Figure 8. Magnetometer setup afloat.

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Figure 9. Investigation of optimum ultra shallow water deployment technique for towfishes : Testing the attachment of a towfish on a custom-built catamaran at Plymouth Sound.

Figure 10. Investigation of optimum ultra shallow water deployment technique for sidescan towfish.

Left (a): A float rigidly attached to the towfish. Right (b): A float attached to the towfish cable.

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System checks were conducted prior to mobilisation overseas to verify good operational condition and integration of all survey instruments. The Hemi-sphere Crescent VS110 GPS was initially chosen for positioning. It utilises EGNOS differential corrections and according to ESSP (2012a), the expected horizontal accuracy over the Methoni site area should be in the order of 3m (95% of the time). However, during the system checks it became apparent that Open Service differential corrections were not available for prolonged periods due to Signal-In-Space (SIS) outage for both EGNOS PRNs (120, 126). The history of SIS outages highlighted a recent period of significant signal instability (ESSP, 2012b). In the light of this fact, the use of the C-Nav 2050G DGNSS was decided. After software updates for the C-Navigator I unit and firmware updates for the receiver unit, the reception of RTG (C1) corrections marked the end of system checks.

All the surveying equipment was mobilised early July 2012 across Europe by car. The project team settled in a Ministry of Culture guesthouse at the Pylos fortress 10km away from Methoni. Reconnaissance During the period between the team settling in and the start of the fieldwork, reconnaissance took place in Methoni ashore, underwater and afloat. Although it was conducted in a rather informal way, the team discovered a cannon (Fig. 11a) probably linked to a wreck which was simultaneously discovered nearby (Fig. 12). Another cannon had been discovered by a local resident in the same area a few days previous (Fig. 11b).

Figure 11. Cannons on the seabed of Methoni Bay.

Left (a): The cannon that was discovered by the team.

Right (b): The cannon that was discovered a few days before the start of fieldwork.

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Fieldwork The fieldwork took 7 days between the 11

th and 27

th

of July 2012. Sidescan sonar, magnetometer and sub-bottom profiler were used for the survey, provid-ing a wide range of remote sensing techniques to be implemented for the underwater investigation of the site and the potential of data correlation for artefact identification. The first phase of the fieldwork (sidescan sonar and magnetometer survey) was conducted utilising a 5.50m RHIB provided by EUA. For the second phase (seismic survey) the EUA mobilised a 6.85m RHIB from Athens to Methoni.

Four areas off Methoni (Fig. 13) were identified to be surveyed: (a) area ‘A’ for the visualisation of the submerged prehistoric settlement ruins and its sub-seabed profile, the estimation of its potential extent under and over the seabed and for artefact detection and identification (b) area ‘B’ for the visualisation of the submerged ancient harbour and breakwater as well as for artefact detection and identification (c) area ‘C’ due to the recent findings on the seabed (a wreck and two cannons), for artefact detection/identification both on and under the seabed and (d) area ‘D’ for artefact detection only under the seabed due to low equipment avail-ability at the final stage of the project.

Figure 12. Cannonballs on top of the ballast load of a wreck.

Figure 13. The four survey areas off Methoni.

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For data acquisition, processing and rendering, the following geodetic parameters were used: For Horizontal control, UTM Grid/Projection (34N, 18-24E zone) and ITRF2005 Datum (ITRF2005 coordinates coincide with WGS84 coordinates at the decimetre level (ITRF, 2012)). Vertical control was not applied since no bathymetric survey was conducted and the maximum tidal range for the nearby Kalamata port is 0.58m (HNHS, 1991). The observed tidal range during the survey period never exceeded 0.15m (IOC, 2012). For positioning information the C-Nav® Precise Point Positioning (PPP) System was chosen (sourced by Plymouth University). It is a dynamic DGNSS which provides worldwide positioning of decimetre level accuracy (C&C Technologies, 2012). Its 2050G receiver integrates a 24-channel, dual frequency GPS receiver, a 2-channel Satellite Based Augmen-tation System (SBAS) receiver and a C-Nav Correc-tion Service L-Band receiver. The raw data latency is less than 20ms and the receiver outputs up to 5Hz raw measurement data in the standard configuration. The C-Nav world DNGSS division of C&C Technolo-gies, Inc. provided free worldwide access to the C1

Correction Service for the project through Plymouth Univesity, hence distribution of satellite based differential GNSS corrections with no additional equipment required (reference/base stations). The C-Nav Correction Service has 99% availability and EGNOS Open Service corrections can also be accessed. The C-Navigator I Control and Display unit was used as a quality control tool for monitoring performance, data quality and accuracy of the receiver. The GeoAcoustics SS941 dual frequency Sidescan Sonar Transceiver combined with the Model 159D dual channel towfish were sourced by Plymouth University and used for artefact detection and seabed feature mapping. The SS941 Transceiver operated at 410 KHz was triggered externally and the operational parameters were controlled remotely by the Coda DA1000 acquisition system. The acquisition range was 32-38m. The 159D towfish was initially deployed by the stern of the RHIB hav-ing a float attached to it, but soon a noisy data acqui-sition became apparent and the towfish was de-ployed from the bow (Fig. 14) resulting in improved data acquisition.

Figure 14. The GeoAcoustics sidescan sonar towfish deployed by the bow of the survey boat.

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The Geometrics G-882 Cesium magnetometer, provided by Plymouth University, was utilised for artefact magnetic detection (Fig. 15). Being small and lightweight, it provided flexibility for the RHIB survey operations. The G-882 performs at an abso-lute accuracy of better than 3nT throughout range and its typical operating sensitivity for the actual survey sample rate (10Hz) is better than 0.002 nT P-P (Geometrics, 2012). The towfish was deployed by the RHIB stern having attached a float on top of it. During and after the magnetometer survey, all vessels anchored in the area were positioned so as their magnetic anomalies could be identified and excluded from the dataset during post-process.

For the seismic survey, the GeoAcoustics GeoPulse Pinger was provided by Akti Engineering. It is a flexible sub-bottom profiler (SBP) allowing operation as an ‘over-the-side mount’ system onboard small boats (Fig. 16). The system utilises the Model 5430A Transmitter (which controls the output power, frequency and transmit repetition rate), the Model 5210A Receiver and the over-the-side Transducer Mount Model 132B which houses a four transducers array. The SBP was operated at a 3.5 kHz central frequency and at a variable output power according to the depth and sub-seabed structure. Areas ‘A’, ‘C’ and ‘D’ were investigated by the SBP.

Figure 15. The Geometrics

G-882 magnetometer.

Figure 16. System checks of

the GeoAcoustics GeoPulse Pinger.

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For magnetometer data acquisition, processing and helmsman’s guidance along navigation lines, the Site Searcher software was used, provided by 3H Consulting Ltd. The HYPACK® MAX software was used for navigation planning, helmsman’s guidance and recording control during the seismic survey, sourced by Akti Engineering. Geodetic transforma-tion parameters of both systems were found to be coincident maintaining seamless datasets. For sidescan sonar data acquisition, processing and SBP data processing, the Coda DA1000 hardware and the Coda GeoSurvey software were used, both sourced by Plymouth University. The SonarWiz Map suite, sourced by Akti Engineering, was used for seismic data acquisition integrated with the HYPACK® MAX Software. Following the geophysical survey, a precise position-ing task was conducted. Two wrecks, two cannons and various artefacts were precisely positioned. For this task, a diver had to attach a float to one edge of a line and hold the other edge on top of the point to

be recorded while keeping the line under tension to achieve verticality. Simultaneously, a snorkeler had to attach the C-Nav antenna on top of the float and keep it there until the position was recorded (Fig. 17). Post-survey Tasks The survey team returned to the UK either by road or air transportation. The survey instrumentation was demobilised largely by freight service provided by Teletrans SA without charge and partly by private car / road. After returning back to the UK, the GEo-referenced depictioN and synthESIS (GE.N.ESIS) of marine archaeological survey data was conducted utilising the Site Recorder (SR) software sourced by 3H Consulting Ltd. SR is a GIS suite used for integration of information either recorded during an archaeological survey or post synthesised. It combines mapping, finds database, survey processing program, dive log and image manage-ment tools (3H Consulting, 2012).

Figure 17. Precise positioning of a wreck.

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RESULTS

Sidescan Sonar Survey

Table 1 (see p. 25-27) presents a selection of detected small scale features of potential archaeo-logical interest through sonograph imagery. Feature dimensions are given as horizontal by vertical length and numbering retains the originally logged values. Mosaics of acoustical seabed imagery of survey areas and imagery of large scale features are presented through the synthesis of archaeological data in the following paragraph. The sidescan sonar data post-process procedure included manual sea-bed tracking corrections, navigation editing, and Time Variable Gain adjustments.

Magnetometer Survey

Following the 1st-stage magnetometer data post-

processing (normalisation and filtering), magnetic anomaly plots were mapped using the GIS. Fig. 18 and 19 present the magnetic anomaly plots in the vicinity of the submerged settlement (area ‘A’) and the ancient harbour (area ‘B’) on a different basemap. Strongest anomalies are referred to deeper red and green data samples/points.

Figure 18. Magnetic plot of area ’A’ after 1st stage data post-process (SR screen dump).

Figure 19. An introduction to data synthesis: Magnetic plot of area ’B’ (the ancient harbour and

the submerged breakwater) on a Google Earth basemap (SR screen dump).

27


Table1. Selection of detected small scale sidescan sonar features.

28


Table1. Selection of detected small scale sidescan sonar features.

29


During the 2nd

-stage data post-processing, the magnetic profiles of survey areas were created after further normalisation of data by filtering excessive yaw effect, instrument noise and turning points (Fig. 20, 21). Subsequently, wherever necessary, magnetic anomaly maps of the above mentioned areas were created following a 3

rd-stage data post-

process, namely parasite/contamination removal (Fig. 22). In the following maps, all magnetic anom-aly map projections are perspective and Grid North coincides with y (Northings) axis. The Krigging data interpolation method was used for the magnetic model creation.

Table1. Selection of detected small scale sidescan sonar features (continuation).

Figure 20. Magnetic profile of survey area ‘C’ after 2nd-stage

data process. The large spikes at the northeast extremity of the area were caused by cannons, wreck artefacts and unknown features. Unknown features also caused the spikes at the north-west extremity of the area.

Figure 21. Magnetic profile of survey area ‘A’ after 2nd-stage

data process. The two large spikes correspond to anomalies caused by the keels of sailing vessels at anchor.

Figure 22. Magnetic profile of survey area ‘A’ after 3rd-stage

data process. Among others, the two spikes caused by vessels at anchor are filtered.

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Seismic Survey

In this section, selected subsea-bed features detected during the survey and deemed to be of potential archaeological interest, are presented. For the SBP data post process, sub-bottom sections around potential targets were created after sea-bed tracking and applying a separate set of 3-zone (water column zone, seabed zone and sub-seabed zone) time varying frequency filters to

the data for each section.

In the following list of SBP features (Table 2), ex-tended profiling sections were not possible to be at-tached. All sections run from West (left) to East (right) and depth values are below sea surface.

Table 2. Selection of detected small

scale SBP features.

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Synthesis of Marine Archaeological Data

In this section, selected data elements of the synthe-sised digital GIS project are presented, highlighting the potential of findings’ evaluation through data synthesis. The following project elements/datasets where synthesised through the GIS as geographical information layers: Navigational charts, aerial ortho-photos, coastline boundary (sourced from the Hellenic Navy Hydrographic Service), Google Earth imagery, archaeological site and survey area boundaries, survey lines, sidescan sonar mosaics, magnetometer data, precise positioning information, architectonic plans, position of anchored vessels during the survey and detected sidescan sonar and SBP features. Fig. 23 depicts the synthesis of post-processed magnetometer data in the area ‘C’ and positioning information of a wreck and two cannons (derived during the precise positioning task). Fig. 24 shows the synthesis of post-processed magnetome-ter and sidescan sonar data in the same area. The two cannons are visible, as well as the extent of the wreck and the strong backscatter from the cannon-balls. Fig. 25 depicts the same findings, post-processed magnetometer data superimposed on a marine chart basemap, a SBP survey line and the sub-seabed profile of the wreck along the line.

Fig. 26 presents the synthesis of sidescan sonar data of the ancient harbour and the submerged breakwater, archaeological site delimitation data (site boundaries) and coastline information. Clearly defined are the extent of the submerged breakwater and the shape of the harbour entrance of which nowadays is closed. Sand depositions are visible all over the harbour seabed. The west breakwater rocky slope is steep and its shape seems to be well preserved, while the east rocky slope is gentle and its stones are showing marks of inconsistency. Interesting geological and habitat features are evident east of the submerged breakwater where hard sediments and sea grass exist. Fig. 27 and 28 refer to the same area (in the vicinity of the submerged prehistoric settlement) and highlight the potential of data correlation through the synthesis of data from existing architectonic plans, magnetometer data, precise positioning data of a wooden wreck, SBP survey lines and sidescan sonar mosaic. Magnetic anomalies are evident over the wreck and the settlement ruins. Clearly defined is the extent of the north block of settlement ruins while the ruins of the south blocks are rather spread over the area to an extent greater than what is recorded till now. In the sidescan mosaic, a wreck is readily apparent as well as a number of small scale features. Figure 23. Synthesis of post-processed magnetometer data

and positioning data of two cannons and a wreck.

Figure 24. Synthesis of post-processed magnetometer and sidescan sonar data. The blue ellipsis includes a wreck and the two white ones two cannons within area ‘C’. Strong backscatter within the blue ellipsis is caused by cannonballs.

Figure 25. Synthesis of precise positioning data (cannons and wreck) in the Area ‘C’, SBP and magnetometer data (survey line and wreck profile) superimposed on a chart.

Figure 26. Synthesis of sidescan sonar data (mosaic of the ancient harbour and the submerged breakwater), archaeologi-cal site delimitation data (the violet dashes form part of the site boundaries) and coastline information.

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DISCUSSION

The archaeological site of Methoni lies in the shallow waters of the homonymous bay and is exposed to heavy waves of almost all directions due to wave diffraction. Consequently, the wave energy along the coasts is high. The wave energy turbidity combined with the littoral drift action causes sediment transport and deposition towards the north-west part of the bay, as well as erosion of the east coast and the shallow patches of seafloor. The revelation of the two cannons and even the stones on top of one of them (Fig. 11) are indicative of the seabed erosion. Indicative of the sand transport along the surf zone and the consequent covering and uncovering of the settlement ruins is the fact that the same blocks of ruins, depicted at different data acquisition periods, do not spatially match. This offset cannot be ex-plained solely by limitations of the survey system positional accuracy.

The positional accuracy of the integrated sidescan sonar system is considered at a 1.5m level. Although the daily checked decimetre accuracy of the C-Nav DGNSS, in situ measurements (running survey lines in opposite directions over a distinctive feature) high-lighted a 1.5m horizontal accuracy.

The accuracy degradation was caused by yaw/pitch/roll effects of the towfish not being adequately filtered by the navigation smoothing algorithm of the processing software together with the variation in the apparent bearing of targets. This variation was caused by fluctuation of water temperature due to water column patches of inhomogeneties (sand) that provoked fluctuation of transmitted sound amplitude and phase (Urick, 1983). To verify the system positional accuracy, observed positions of features during the sidescan survey were checked against their derived positions from precise positioning. The horizontal accuracy close to the breakwater slope is considered further degraded due to ranging distortion (Russell-Cargill, 1982). The positional accuracy of the integrated magnetometer system is considered at a 3.5m level, estimated through in situ measurements (running survey lines in opposite directions over a distinctive ferrous feature). Towfish layback issues are believed to have largely contributed to the stated accuracy due to boat yawing and engine shut-offs. To verify the horizontal accuracy, observed positions of features during the magnetometer survey were checked against the derived positions from precise positioning.

Figure 27. Synthesis of data in the vicinity of the settlement ruins from existing architectonic plans, magnetometer data, pre-cise positioning data (wreck 1) and SBP survey lines. The potential of data corre-lation is clear.

Figure 28. Synthesis of data in the vicinity of the settlement ruins from existing architec-tonic plans, magne-tometer data, precise positioning data (wreck 1), SBP survey lines and sidescan sonar mosaic. Large scale features are evident (wreck 1 in the white ellipsis and settlement ruins in the white circles).

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The horizontal accuracy of SBP integrated system within the archaeological site is considered at a 1m level due to roll/pitch motion of the survey boat. During the first day of fieldwork, the shallow waters of Methoni Bay proved to be noisier than those of Plymouth Sound. Hence, a by-the-bow deployment of the sidescan towfish was tested and applied. Although this alteration decreased the sidescan sonar susceptibility to noise, the excessive pitch motion of the boat caused heaving effects to be evident throughout the sidescan sonar dataset and especially across the area ‘C’. These effects are readily apparent especially through the raw sidescan sonar dataset and deteriorated the depiction of small scale features creating an apparent topography through replication of previous and next swath lines (Russell-Cargill, 1982). However, the main consid-eration during the sidescan sonar survey was acous-tic interferences. These were apparent in three forms, namely transducer channel interference (Fig. 29), where occasionally a mirror image in sidescan sonar channels is evident, multipath reflection inter-ference (Fig. 30), where multiple acoustic signal reflections from the seabed and the sea surface resulted in depiction of non-existing artefacts close to existing ones, and finally noise. The latter is mostly evident in the area ‘C’. Through the literature (Blondel, 2009), noise is explained by the dense particle suspension in the water column, air bubbles in the surf zone, interference fringes, sea tempera-ture inversion and speckle. Fig. 31 is an example of problematic data due to a combination of interfer-ence effects namely multi-path reflection interference (false targets), air bubbles in the surf zone (parasite backscatter close to the transducer) and speckle or temperature inversion (shoal like patches in the data). Since part of the area ‘C’ together with all other survey areas were surveyed the previous days or the same day without such problems but using lower sonar range, it is believed that reasons for these effects were the sea conditions and the relatively increased sonar range that was used for achieving a good data coverage in area ‘C’. These effects were dealt with through wide stencilling and gain histogram manipulation / TVG equalisation during sidescan data post-process.

The magnetometer was also affected by the shallow water environment. The seafloor contamination, the regional influences from anchored vessels and the movement of the sensor due to turbulence / boat wake (Green, 2004) led to the collection of a noisy dataset. However, after a 3-stage data post-process, potential targets are distinctive. The GeoPulse SBP, when operated in water depth less than 3m, defi-nitely reached its operational limitations. The SBP recordings were found to be readable up to a mini-mum water depth of 3m and the maximum seabed penetration was about 15m depending on Power and Recording Length settings. The seabed and sub-seabed investigation, on the base of the geological background, confirms the existence of the sub-merged prehistoric settlement and highlights its wider extent. The walls of the settlement as recorded through the sidescan dataset, compared with their depiction through the existing architectonic plans, seem to be widely scattered due to the wave/longshore drift energy or human activities.

Figure 29. Sidescan sonar transducer channel interference effect. A mirror image of the ancient breakwater from the starboard to the port channel is clear (Coda screen dump).

Figure 30. False sidescan sonar artefacts due to multipath reflection effect.

Figure 31. Coda screen dump showing problematic sidescan sonar data due to multipath reflection interference (false targets in red circles), air bubbles in water column (parasite backscatter close to the transducer in the green circle) and speckle or tem-perature inversion (shoal like patches in the data where they do not really exist, in the yellow circles).

34


Fig. 32 shows the scouring effects of sea current energy around the ruins which degrade their physical support. Fig. 33 shows not only the presence of an-chored vessels inside the officially declared archaeo-logical site but especially on top of a wooden wreck. CONCLUSIONS The Hellenic Ephorate of Underwater Antiquities (EUA) now has a digital tool for the sustainable man-agement of the Methoni underwater archaeological site, through the visualisation of synthesised geo-archaeological information. Moreover, the Ephorate has a full report of features of potential archaeologi-cal interest within the site. Apart from small-scale artefacts, highlighted are the submerged breakwater of the ancient harbour and the ruins of the sub-merged prehistoric settlement of Methoni. According to the project results, the settlement ruins are se-verely scattered due to environmental and possibly anthropogenic factors and many of the already known settlement walls are buried while new ones are revealed due to sediment transport. The EUA may evaluate the project results and implement the proposed management suite on the Methoni under-water archaeological site and even on all of the

Greek underwater archaeological sites, setting the basis for a holistic management of the underwater cultural wealth. Furthermore, the suite can be mobi-lised onboard the survey boats so as to provide the EUA staff, information about the spatial distribution of underwater antiquities on the seabed, thus reduc-ing the time spent on a site underwater. Additionally, the suite facilitates the determination of legal aspects during archaeological surveys providing site bound-ary monitoring. The GE.N.ESIS project, as a new start for Greek maritime archaeology, has the potential for further development. A thorough study and correlation of the numerous recorded features/artefacts in the Methoni Bay may provide the EUA with a priority list of features to be further investigated for years to come. This study will have even better results if further data post-processing is conducted. For the sidescan sonar dataset, further filtering, gain histo-gram equalisation, reflection removal and additional process applications can improve information about a target’s 3D dimensions and its potential of being artefacts. The theoretical investigation of recorded profiles / time series of magnetic anomalies and the removal of magnetic regional variations may improve information about a target’s depth, size, weight and description. A further insight to the sub-bottom sections can provide a clearer estimation and even a map of the settlement extent and evidence for the geological evolution that caused the settlement submersion. A combined study of the above mentioned datasets will boost the archaeological knowledge of the Methoni site. At a more technical level, the investigation of optimum towfish deployment techniques according to various dominating factors, as well as the investi-gation of interference factors and optimum sonar parameterisation in the ultra-shallow water environ-ment may provide useful results for future surveys. A further multibeam echo-sounder and a high-resolution sidescan sonar survey of the site would provide the EUA with 3D and updated bathymetric information as well as updated seabed imagery which would facilitate the monitoring of natural processes / erosion patterns. This would enhance the estimation of the site evolution and the promotion of an efficient site preservation management. It is recommended that the Hellenic Ministry of Environ-ment, Energy and Climate Change, together with the Hellenic Navy and the EUA, implement a Delimita-tion Scheme for Marine Archaeological Sites for the protection of underwater antiquities off the Greek coasts. Information about the archaeological site boundaries and any navigational restrictions can be released through the nautical charts. Finally, the EUA is recommended to publish a Governmental

Figure 32. Sidescan sonar mosaic of settlement ruins showing halos around the ruins and close to the coast.

Figure 33. SR screen capture showing the presence of anchored vessels (red crosses) inside the officially declared archaeological site (bounded by the coast and the violet lines) and especially on top of a wreck (black dashed circle) during the survey.

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Directive providing data submission guidelines for Project Managers conducting externally commis-sioned projects involving GIS, so that data submitted to the EUA can be beneficial for the evolved GE.N.ESIS project.

REFERENCES Biris, J. (2002) A road in the South. Chora–Pylos

–Methoni. Nestor’s realm and the Mothon stone, Athens: Ultrasound.

Blondel, P. (2009) The Handbook of Sidescan Sonar, Chichester: Praxis.

C&C Technologies (2012) About C-Nav, viewed 1 Sep 2012, http://www.cnavgnss.com/site.php.

3H Consulting (2012) Site Recorder 4 Software, viewed 5 Sep 2012, http://www.3hconsulting.com/ProductsRecorderMain.html.

European Satellite Services Provider (2012a)

‘‘EGNOS Helpdesk - EGNOS Open Service Avail-ability and Accuracy’’, personal communication (email), 29 June 2012

European Satellite Services Provider (2012b) His-torical of Signal in Space Outages, viewed 25 June 2012, http://egnos-user-support.essp-sas.eu/egnos_ops/data_gaps

ESRI (2012) World Imagery, viewed 4 Sep 2012, http://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer

Geometrics (2012) G-882 Marine Magnetometer, viewed 1 Sep 2012, http://www.geometrics.com/geometrics-products/geometrics-magnetometers/g-882-marine-magnetometer/

Green, J. (2004) Maritime Archaeology. A tech-

nical Handbook, 2nd

ed., California: Elsevier Inc. HNHS (1991) Tidal Information for Hellenic Har-

bours, Athens: HNHS.

International Oceanographic Commission (2012) Sea Level Station Monitoring Facility, viewed 1 Sep 2012, http://www.ioc-sealevelmonitoring.org/station.php?code=kala.

ITRF (2012) ITRS and WGS84, viewed 5 Sep 2012, ftp://itrf.ensg.ign.fr/pub/itrf/WGS84.TXT.

Lianos, N. (1987) ‘’A study of the ancient harbour

works of Methoni’’, pp.129-135, in ARF (eds.) Re-construction-Conservation-Preservation of Monu-ments, Athens: ARF.

Nautical Archaeology Society (2009) Underwater Archaeology. The NAS guide to principles and practice, 2

nd ed., Chichester: Blackwell Publishing.

Russell-Cargill, W. (1982) Recent Developments in Side Scan Sonar Techniques. Cape Town: University of Cape Town.

Spondylis, I. (1996) ‘‘Contribution in the study of coastal formation in relation to the location of new archaeological sites’’, ENALIA, IV (3/4), pp.30-37.

Spondylis, I. (2000) ‘‘Messenia county – Methoni’’, pp.1225-1226, in ARF (eds.) Archaeological Re-view 55/2000. Athens: ARF

Spondylis, I. (2011) ‘‘EUA archive’’, personal com-munication (discussion), Dec. 2011.

University of Athens (2012) Homer’s Ilias, viewed 4 Sep 2012, http://users.uoa.gr/~nektar/arts /tributes/omhros/il.htm

Urick (1983) Principles of Underwater Sound, 3rd

ed., California: Peninsula Publishing.

BIOGRAPHY

Panagiotis Gkionis has been working for the Hellenic Navy for 18 years. Following training at the Hellenic Naval Academy, he embarked on his seagoing career as a Deputy Navigating Officer in 1998. For the next 14 years he found himself within a wide range of warfare appointments onboard Hellenic frigates and gunboats, qualifying as a Navi-gating Officer and Operational Training Officer. He took up his current appointment as an Assistant Head of the Research and Planning Department onboard the Hellenic Navy Hydrographic Service, following the completion of an ‘MSc Hydrography’ programme in 2012. ([email protected])

http://www.cnavgnss.com/site.php

http://www.3hconsulting.com/ProductsRecorderMain.html

http://www.3hconsulting.com/ProductsRecorderMain.html

http://egnos-user-support.essp-sas.eu/egnos_ops/data_gaps

http://egnos-user-support.essp-sas.eu/egnos_ops/data_gaps

http://services.arcgisonline.com/ArcGIS/rest/%20services/World_Imagery/MapServer

http://services.arcgisonline.com/ArcGIS/rest/%20services/World_Imagery/MapServer

http://www.geometrics.com/geometrics-products/geometrics-magnetometers/g-882-marine-magnetometer/



http://www.ioc-sealevelmonitoring.org/station.php?code=kala

http://www.ioc-sealevelmonitoring.org/station.php?code=kala

ftp://itrf.ensg.ign.fr/pub/itrf/WGS84.TXT

http://users.uoa.gr/~nektar/arts%20/tributes

http://users.uoa.gr/~nektar/arts%20/tributes


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RESULTS OF OPERATIONAL SEA-WAVE MONITORING WITH RADAR GAUGES

By Sebastian RÜTTEN, Stephan MAI, Jens WILHELMI, Theodor ZENZ, Hartmut HEIN and Ulrich BARJENBRUCH

(German Federal Institute of Hydrology (BfG))

Abstract

Résumé

Resumen

The German Federal Institute of Hydrology (BfG) developed a low-cost, non-contact sea-wave monitoring system based on a single radar sensor. A short description of the measuring system and the analysis of wave parameters is given. Furthermore, long-term wave measurements with this system, in combination with wind-measurements and statistics, are used to analyse possible future changes in wave heights. The results are in good agreement with those of other methods. Due to the good results achieved with the single radar sensor, an extension of the system which will be capable of recording directional information, is now under development. First results are presented in this study.

L’Institut fédéral allemand d’hydrologie (BfG) a élaboré un système peu onéreux de surveillance à distance des vagues à partir d’un unique sondeur radar. Une brève description du système de mesure ainsi que l’analyse des paramètres des vagues est donnée. De plus, les mesures à long-terme des vagues avec ce système, combinées avec les mesures du vent et les statistiques sont utilisées pour analyser les changements futurs possibles des hauteurs de vagues. Les résultats concordent avec ceux établis au moyen d’autres méthodes. Du fait des bons résultats de l’unique sondeur radar, une extension du système qui pourrait enregistrer des informations relatives à la direction, est actuellement en cours de développement. Les premiers résultats sont présentés dans cette étude

El Instituto Federal Alemán de Hidrología (BfG) ha desarrollado un sistema de seguimiento de bajo coste, que no tiene contacto con la ola, basado en un sensor con un único radar. Se proporciona en el presente artículo una breve descripción del sistema de medición y del análisis de los parámetros de las olas. Además, las mediciones de olas por periodos largos efectuadas con este sistema, en combinación con las medidas del viento y las estadísti-cas, se utilizan para analizar los posibles cambios futuros en las alturas de las olas. Los resultados concuerdan con aquellos obtenidos mediante otros métodos. Debido a los buenos resultados obtenidos con el sensor de radar único, una extensión del sistema, que está ahora en fase de desarrollo, podrá registrar la información direccional. En este estudio se presentan los primeros resultados.

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1. Introduction New construction projects off the German coasts such as offshore wind farms, require the operational monitoring of waves nearby such offshore structures. While much research on the consequences of cli-mate change has been carried out with respect to the change of the sea level, only a few studies ana-lyse its impact on waves. This may relate to the fact that no long-term records of wave parameters are available. Accordingly, several authors (Mai, 2008), emphasized the need for reliable, continuous wave measurements. Therefore, the German Federal Insti-tute of Hydrology (BfG) (in cooperation with the Ger-man Federal Waterways and Shipping Administra-tion (WSV) developed a monitoring system based on a radar liquid-level sensor. To date, four systems have proven their functionality and robustness at different locations, covering a wide range of sea-state conditions. The first test as-sembly has been in operation at the gauge “Borkum Südstrand” close to the North-Sea island of Borkum since 2002. In 2006 an additional monitoring system was mounted at the gauge “Lighthouse Alte Weser” in the estuary of the rivers Jade and Weser (see Fig-ure 1). To further analyse the functionality under off-shore wave conditions, another system was installed in 2008 at the research platform “FINO 1” (http://www.fino1.de), which is approx. 45 km off the island of Borkum. In an international context, it is used in conjunction with the flood-defence project “Mose” in the lagoon of Venice, Italy (Wilhelmi and Barjen-bruch, 2008).

Measurements of the radar monitoring system at the “Lighthouse Alte Weser” are considered within this study to analyse possible future changes in wave heights. The estimation of future changes includes the following steps: a) Analysis of current and future wind statistics from results of a global climate model (see Section 3)

b) Derivation of a transfer function of wind speed to wave height (see Section 4)

c) Applying the transfer function to map the changes of the wind statistics to the changes in wave heights (see Section 5)

A description of the monitoring system at the “Lighthouse Alte Weser”, data acquisition and proc-essing is discussed in the next Section, while the extension towards an array of four radar sensors is described in Section 6. 2. Data and Methods The data used as a basis for this study consists of wave and wind measurements recorded in the period from May 2006 until August 2011. Further-more, wind data that were generated by the climate model” ECHAM5” were assessed for the years 1970-2090. 2.1 Wave measurements Many of the sensors that are commonly used to monitor the water-surface elevations (e.g. wave-rider buoys or pressure gauges) have to be installed directly in the water. This requires much mainte-nance as those systems are permanently exposed to harsh environmental sea conditions such as wave attack and corrosion. For long-term measuring campaigns, sensors that are not directly in contact with the water are much more easily operated and maintained. The described monitoring system, developed by the German Federal Institute of Hydrology (BfG) in cooperation with the Federal Waterways and Shipping Administration (WSV) and the German Federal Maritime and Hydrographic Agency (BSH) meets this criterion. The measuring setup consists of a commercial radar liquid-level sensor, which is fixed to the end of a joist that is attached to a coastal or offshore structure (as illustrated with the “Lighthouse Alte Weser” in Figure 1). The radar sensor emits electromagnetic pulses at a frequency of 26 GHz twice a second and, in turn, detects these pulses when they are backscattered at the water surface. The water surface elevation can be easily calculated since the distance between the radar and the water surface is proportional to the

Figure 1: The operational sea-wave monitoring system at the gauge “Lighthouse Alte Weser”.

http://www.fino1.de/

http://www.fino1.de/

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travelling time of each pulse. This allows the meas-ure of water-level oscillation and, in turn, to derive wave parameters such as the significant wave height. For further information see Mai, S. and Zimmermann, C. (2000).

In order to optimise the results, a very important first step is to detect outliers and replace them by interpolated values. This is particularly important because the commercial radar sensors were originally designed for level measuring in processing industries. The outliers are located by using physical criteria, by evaluating the possible maxima of velocity and acceleration of the water surface, as well as a statistical outlier test procedure. The removed data points are then replaced by applying a hermite polynomial which does not add artificial extremes (Wilhelmi and Barjenbruch, 2008). The sea-state parameters can then be calculated adopting the Wave Analysis for Fatigue and Oceanography (WAFO) Matlab toolbox for the analysis of random waves and loads, developed by the University Lund/Sweden (WAFO, 2005). One example of long-term recordings of the significant wave height is illustrated in Figure 2 (c).

The precision of this system was tested under labo-ratory conditions as well as in the field (Wilhelmi and

Barjenbruch, 2008). The results of the wave-flume experiments reveal an accuracy of less than 0.5 cm for 95% (σ = 0.017 cm) of the recorded significant wave heights. Other field tests were also run on the offshore platform “FINO 1” in the North Sea. There, the radar gauge is mounted close to the pillars of the platform. For reference, a wave-rider buoy is anchored at a distance of 100 meters. The compari-son of the calculated significant wave heights shows only slight deviations without a significant trend. Thus, interactions of the sea with the structure that might affect the wave-height measurements seem unlikely. 2.2 Wind measurements The monitoring programme at the “Lighthouse Alte Weser” also includes wind parameters. A meteoro-logical station of the Deutscher Wetter Dienst (DWD – German national meteorological service) records wind speed (Figure 2 b) and direction (Figure 2 a) every minute at a height of 30m above the mean sea level. For pre-processing, the data are converted to local Cartesian coordinates (U=zonal wind compo-nent, V=meridional wind component) with respect to a reference level of 10m above the mean sea level, following Kleemann und Meliss (1993).

Figure 2: Illustration of the mean (bin size 1 week) wind direction (a), wind speed (b), and significant wave height (c) during the considered period. The shaded patches indicate the standard deviation.

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2.3 Climate data To predict future changes in significant wave heights, additional wind-data of the Global Climate Model “Echam5” are used. This comprehensive general circulation model of the atmosphere was developed by the Max Planck Institute for Meteorol-ogy (Roekner et al., 2003). The data are given on a rotated pole grid with hourly resolution. As the “Lighthouse Alte Weser” is not located directly on a grid point of the model, the data needed to be inter-polated linearly to the exact position. Analyses of the interpolation methods indicate only slight differences (average deviation of 0.1 m/s for U and V) when choosing the nearest-neighbour method instead of linear interpolation. The average variation of the wind speed is calculated with regard to its direction-ality to include directional changes. This is of particu-lar importance, as the wave height at the “Lighthouse Alte Weser” strongly depends on the wind direction. 3. Transfer function Besides wind speed and direction (or more precisely: wind stress and fetch), various additional factors in-fluence the wave generation at the “Lighthouse Alte Weser”. Amongst them, wind duration and water depth are commonly assumed to be the dominant parameters. However, at this particular observation site, some additional aspects may also play an important role. As the structure is located within the estuary of the River Weser, wind-current interactions could be relevant. Moreover, the water depth at the site (about 11m) is strongly tide-dependent. Due to the complexity of the processes involved, a determi-nistic calculation of the significant wave heights is almost impossible. Assuming that all time-dependent differences will average out due to the long time period of the recorded parameters, this study presents a simple transfer function for the location at “Lighthouse Alte Weser”, which depends only on the zonal (U in m/s) and meridional (V in m/s) wind components:

(1)

One possible interpretation of this function is that the wind stress, which is proportional to the square of the wind speed, is the fundamental impulse, whereas the linear correction terms include directional dependencies. The constant offset is partly caused by a lower measuring threshold of the radar gauge. A comparison of the calculated and measured significant wave heights is shown in Figure 3, resulting in a correlation coefficient c=0.84 with an R

2 goodness of fit of 0.71. Besides the

expected scatter, there are only few wider devia-tions. A comparison of the times series (Figure 2 c) shows an overall good agreement as well. For a wind speed of 16 m/s at 240°, a significant wave height of Hsig =2.06m is estimated by the transfer function (1). This is in good agreement with the results given by Mai (2008), who derived a signifi-cant wave height between 1.80m and 2.20m by adopting the phase-averaged wave model SWAN. Assuming that the transfer function will continue to hold under the possible future climate as projected by the model, the variability of the exceedance prob-ability of the significant wave height and the wind speed can be predicted.

4. Prediction of wave-height changes As a first step, a quantile-mapping-based bias cor-rection for the considered location was made for the wind statistics of the global climate model. There-upon, exceedance probabilities of wind speed and, by applying the transfer function, wave heights were calculated. A general increase of the wind speed along with an increase of the significant wave height within the next coming years is suggested by the model (see Figure 4). For the period from 2006 to 2045, an av-erage increase of the 99% quantile of the significant wave height by 0.33 cm/year is indicated. In the sub-sequent 30 years, the model predicts an average increase that is slightly lower (0.17 cm/year). On the average of the period from 2006 to 2075, the derived change of the significant wave height at the ”Lighthouse Alte Weser” suggests an increase of the 99% quantile by 0.26 cm/year.

Figure 3: Scatter plot of the comparison of significant wave heights.

http://en.wikipedia.org/wiki/Global_Climate_Model

http://en.wikipedia.org/wiki/Global_Climate_Model

http://en.wikipedia.org/w/index.php?title=Max_Planck_Institute_for_Meteorology&action=edit&redlink=1

http://en.wikipedia.org/w/index.php?title=Max_Planck_Institute_for_Meteorology&action=edit&redlink=1

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The uncertainty of the predicted wind speed distribu-tion can lead to wide discrepancies in the results. Mai and Zimmermann (2004) examined a climate scenario for the year 2050 near Solthörn, which is approximately 50 km east of the observation site. They determined an increase of the 99% quantile of the significant wave height by 0.4cm/year, which is close to the results estimated in this study. The slight difference may be attributed to the fact that the water depth near Solthörn is less than at the ”Lighthouse Alte Weser”. Therefore, climate-change related rise of water level causes an increased change in wave height. In contrast to the aforementioned good agreement, Weisse et al. (2003) proposed a trend of 1.2cm/year increase for the years 1958-2001 as de-termined by wind wave hind casts. This spread in the estimates of changes in significant wave height em-phasizes the need for more continuous monitoring of sea-state parameters, including not only significant wave height and wave period but also wave direc-tion. 5. Extension of the existing monitoring system by measurements of directional information Precise recordings of wave direction would improve, on the one hand, numerical modelling of sea states (Haver and Nyhus, 1986) and, on the other hand, the design of coastal and offshore structures. Bowers et al. (2000) underline that the maximum hawser ten-sion at some structures may occur when wind and waves are at 60-90°. They point out that the simple assumption of an aligned wind and wave direction is often invalid. They monitored a difference up to 60° before the storm is fully developed. Even at the peak of a storm, differences of 10-30° are common. Therefore the radar based wave-gauging stations,

which monitor water surface elevation at one point and thus, sea state parameters, as wave heights and wave periods, is enlarged towards monitoring wave direction. This development of the German Federal Institute of Hydrology (BfG) makes use of an array of commercial radar sensors. The technique is based on simultaneous recordings of wave profiles at several fixed positions. Basically, the cross-covariance spectral densities between these records are used to estimate the directional spectrum. Further information is given in the literature, e.g. Benoit et al. (1997). While designing such an array, the following relevant guidelines should be taken into account (Goda, 1985) - to fully exploit the information of all sensor locations, the duplication of vector distances should be avoided. Furthermore, the array size is limited, on the one hand, by the smallest wavelength for which the directional analysis is to be made, because the minimum separation distance between a pair of wave gauges has to be less than one half of this wavelength. On the other hand, the directional resolution of the array increases as the maximum distance between the wave gauges increases. However, the maximum size of the array is often limited by the construction of the offshore or coastal structure to which it is attached. For an operational use of radar arrays, the number of sensors should be limited to three or four in order to keep it as sim-ple and cost-effective as possible. 5.1 Laboratory tests and PC based simulations The applicability of an array of three commercial radar liquid-level sensors to measure the directional wave spectrum under the constraints mentioned

Figure 4: Exceedance probabilities of wind speed and significant wave heights at the “Lighthouse Alte Weser” within three time periods.

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above was tested by numerical simulations and laboratory experiments. Since the cross-covariance method (Goda, 1985) presumes simultaneous records of the water-surface elevation at all sensor locations, the impact of the uncertainty in the simultaneity of measurements within the used array-dimension was analysed under laboratory conditions. The laboratory experiment is set up in such a way that all commercial radar sensors record a distance to a reflector, moving along a known track. There-fore, the difference in the measured distance can be assigned to a time lag. The resulting uncertainty of the measuring time of all sensors was found to be Gaussian-distributed with a standard deviation of =0.05s. In addition to the uncertainty in measuring time, a standard deviation of the distance measured by the radar sensors of 0.5 cm (see Section 3.1) was considered. With these uncertain-ties in measuring time and distance, the optimal design of the radar gauge array was derived using the following numerical methodology: The starting point was a measured time series of water-level elevations ( ) at the location of one radar sensor within the array. This time series was then assigned to the other sensor locations within the array prescribing wave velocity ( ) and the vectorial distance of each sensor location to the lo-cation of the first sensor ( ) using:

(2)

Afterwards, the time series of these simulated surface elevations of all sensor positions were digitized with a frequency of 2 Hz, including possible uncertainties in time and distance of the measure-ment. The resulting dataset was used to calculate the directional spectral density, adopting the DIWASP Matlab toolbox, developed at the Coastal Oceanography Group, Centre for Water Research, at the University of Western Australia, Perth (Johnson, 2002). Within this toolbox, the extended maximum entropy method (Hashimoto et al., 1993) was selected for data analysis. As the simulated wave field is unidirectional, only the dominant wave direction is evaluated for accuracy examination. For the analysis of directional resolu-tion, the mean absolute deviation ( ) of the estimated direction from the prescribed direction is regarded:

(3)

With each parameter setting, 100 simulation runs ( ) were performed. Figure 5 illustrates the resolu-tion of a delta array, consisting of three sensors at the apexes of an equilateral triangle, as proposed by Goda (1985), for different edge lengths. On the x-coordinate, the standard deviation of an as-sumed Gaussian-distributed uncertainty in time is shown.

The directional resolution of the simulated radar gauge array increases as the distance between the sensor locations increases or the time lag between all measuring devices becomes smaller. For a standard deviation of 0.05s a mean absolute deviation of e=5.2° was found for the smallest considered edge length of 2m. The resolution further improved to e=3.2° for a length of 3m and e=2.8° for an edge length of 4m. An expansion of the array size to 5m or 7m leads to a mean absolute deviation of e=2.0°. Despite the measuring time delay of the chosen radar liquid-level sensors, sufficiently accurate results will probably be achieved for edge lengths larger than 3m. On this basis, a triangular array design with edge lengths larger than 3m is recommended.

)(1 t

v

in

e

outin

N

Figure 5: Resolving power of the radar gauge array, determined by adopting simulated computer data. The mean absolute deviation of the estimated direction is shown for Gaussian-distributed time lags with standard deviations up to 0.6 s. Additionally, the dependence on the edge length can be examined.

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5.2 Onsite implementation of the radar array system For a first field test of the radar array, an edge length of 3.5m was chosen. The prototype system was mounted at the gauge “Borkum Südstrand” in July, 2012. This location is particularly suitable as it is close to a revetment. Since information about direc-tionality is necessary for revetment design, it is a potential operational site. Here, the wind blows predominantly from North-west. From this direction, the sea state is not influenced by obstacles like islands or shoals, while passing ships may generate waves there (Wilhelmi and Barjenbruch, 2008). The water depth at this site is approximately 8m (Mai et al., 2010). The arrangement of the radar gauge array is illus-trated in Figure 6. A star array (an extension of the delta shaped array with an additional sensor in the centre) was preferred for the first test assembly to further improve the directional resolution, since numerical results revealed that the error in wave direction, described in this study by the mean absolute deviation ( ), further decreases by 59%.

This choice is also supported by Mobarek (1965), who states that a four-detector array of wave gauges

is sufficient to yield a good estimate of the two dimensional spectrum, provided the spacings between the probes were chosen carefully. In addition, a fourth sensor can be particularly advanta-geous in situations in which one sensor records erroneous data or even stops working. 5.3 First results of the extended monitoring system First measurements of the extended monitoring system were analyzed for a time period of 30 minutes starting on 03.11.2012 at 11 pm. The recorded significant wave height is Hsig =0.76m with a mean wave period of Tm=3.57s. Figure 7 presents both the normalized spectral density, on the one hand, and, on the other hand, the direction as a function of frequency.

The dominant energy input is induced by wind-generated waves. The peak frequency is approx. 0.19Hz. Swell contributes only a small amount of energy to this sea state (small peak at approx. 0.07Hz). The directional information is estimated by applying the direct Fourier transformation method. For comparison, the mean wind direction ind=250° at a mean wind speed of 12m/s is delineated in black. In the presented case, the wave direction coincides with the wind direction in the range of their mean intensities, since the wave approach is almost perpendicular to the beach and this is also the predominant wind direction at this particular site. Wider differences were found only in those frequency components of the wave spectrum that contain very little energy.

e

Figure 6: First test assembly at the gauge "Borkum Südstrand". The specially developed triangular extension of the gauge is equipped with four radar liquid-level sensors.

Figure 7: First results from the radar gauge array. The normalized spectral density (blue) and the direction of the waves (red) are illustrated as functions of frequency. The black dotted line denotes the mean wind direction.

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6. Conclusion

As demonstrated in this study, the monitoring system based on a radar liquid-level sensor, developed by the German Federal Institute of Hydrology (BfG) has proven its suitability for long-term measurements. In combination with wind statistics from a global climate model, this data was successfully used to examine possible future changes in sea-wave heights. De-spite the simplicity of the presented transfer function from wind speed to wave heights, the results are in good agreement with that of other methods. The de-rived change in the significant wave height at the “Lighthouse Alte Weser” suggests an average in-crease of the 99% quantile by 0.26 cm/year until the year 2075. To detect long-term trends more accu-rately, continuous monitoring of sea-state parame-ters is indispensable. Special emphasis shall be given to the fact that the system can be extended towards gathering direc-tional information of the sea state, while the advan-tages (e.g. low costs and maintenance and high reli-ability) are retained. The first test assembly consist-ing of a star-shaped array of four radar sensors pro-duced encouraging results. 7. Outlook

The comparison of the directions of the waves to that of the wind can only be considered as a first indica-tion for the efficiency of the new developed direc-tional measurement system, as significant deviations are often noted in the literature. To evaluate its accu-racy more precisely, a Datawell Directional Wa-verider buoy MKIII will be deployed near to the gauge “Borkum Südstrand”. In addition, a second test assembly is planned to be installed at the re-search platform “FINO 1”. This observation site is located close to the German offshore wind farm “Alpha Ventus”, approximately 45 km offshore, where sea states conditions differ considerably from those at the gauge “Borkum Südstrand”. Moreover, there are hardly any obstacles such as islands in the vicinity of this site that might influence the sea state in any direction. Furthermore, larger waves and crossing seas are likely to occur at “FINO 1”. Acknowledgement

The results of this study are partly taken from the “KLIWAS” research programme and from the BfG project “RiseARaF”, both funded by the Federal Ministry of Transport, Building and Urban Develop-ment (BMVBS). The authors thank Anette Ganske (Deutscher Wetterdienst, Hamburg) for support. The authors would also like to thank the Water and Ship-ping offices (WSA) Bremerhaven and Emden for the installation and maintenance of the radar gauges.

REFERENCES

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Bowers, J.A., Morton, I.D. and Mould, G.I. (2000). “Directional statistics of the wind and waves”. Ap-plied Ocean Research 22. 13-22.

Haver,S. and Nyhus, K.A. (1986). “A wave climate description for long term response calculations”. Pro-ceedings of the fifth international offshore mechanics and Arctic engeneering symposium, Vol 4, 27-34.

Goda, Y. (1985). “Random seas and design of maritime structures”. Univ. Tokyo Press. Hashimoto, N., Nagai, T., Asai, T., Sugahara, K., (1993). “Extension of the maximum entropy principle method for estimating directional ocean wave spectrum”. Report of the Port and Harbour Research Institute 32 (1), 3 –25.

Johnson, D. (2002). “DIWASP, a directional wave spectra toolbox for MATLAB®: User Manual”. Re-search Report WP-1601-DJ, Centre for Water Re-search, University of Western Australia.

Kleemann, M. and Meliss, M. (1993). Regenerative Energiequellen. Springer Verlag.

Mai, S. and Zimmermann, C. (2000). “Applicability of Radar Level Gauges in Wave Monitoring”. Proc. of the 2nd Int. Conf. Port Development & Coastal Envi-ronment. Varna, Bulgaria.

Mai, S. and Zimmermann, C. (2004). “Veränderung der Seegangsbedingungen an den Küsten von Jade und Weser als Folge der Klimaänderung”. Coastline Reports 1. 93 – 100.

Mai, S. (2008). “Statistics of Waves in the Estuaries of the Rivers Ems and Weser-Measurement vs. Nu-merical Wave Model”. COPEDEC VII, Dubai.

Mai, S., Wilhelmi, J., Barjenbruch, U. (2010). “Wave height distributions in shallow waters”. Proceedings of 32nd International Conference on Coastal Engi-neering, Shanghai, China. Mobarek, I.E.S., (1965), Directional wave spectra of laboratory wind waves. Proceedings A.S.C.E., WW 3, 91-116. Roeckner, E., Bäuml, G., Bonaventura, L., Brokopf,

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R., Esch, M., Giorgetta, M., Hagemann, S.,Kirchner, I., Kornblueh, L., Manzini, E., Rhodin, A., Schlese, U., Schulzweida, U., and Tompkins,A. (2003). “The atmospheric general circulation model ECHAM5. PART I: Model description”,Tech. rep., Max Planck Institute for Meteorology, MPI-Report 349.

WAFO. (2005). “A Matlab toolbox for analysis of random waves and loads" Version 2.1.1, The WAFO Group, Lund Institute of Technology, Lund University, 2005. Wang, X. L., Zwiers, F. W. and Swail, V. R. (2003). “North Atlantic Ocean Wave Climate Change Scenarios for the Twenty-First Century”. J. climate, Vol. 17.

Weisse, R., Feser, F. and Günther, H. (2003), “Wind-und Seegangsklimatologie 1958-2001 für die südliche Nordsee basierend auf Modellrechnungen”, GKSS Report.

Wilhelmi, J. and U. Barjenbruch. (2008). “Application of Radar gauges to measure the water level and the state of the sea”. Proceedings of 31st International Conference on Coastal Engineering, Hamburg, Germany. CONTACT DETAILS Sebastian Rütten Federal Institute of Hydrology (BfG) Department of Hydrometry and Hydrological Survey Am Mainzer Tor 1 56068 Koblenz Germany Tel.: +49 261 1306 5336 Email: [email protected] BIOGRAPHIES Sebastian Rütten is a Physicist and since 2012 has been at the Federal Institute of Hydrology in Koblenz, Germany. He studied Physics at the University of Cologne, a Diploma thesis in Oceanog-raphy at the University of Bremen and during 2007 to 2009, was a student research assistant at the University of Cologne. From 2009 to 2011, Sebastian was engaged as a student research assis-tant at the University of Bremen and participated in two North Atlantic expeditions on the research ves-sel Meteor. (Email: [email protected]) Dr.-Ing. Stephan Mai is a Physicist and Civil Engineer and since 2005 has been at the Federal Institute of Hydrology in Koblenz, Germany. He studied Physics at the University of Bremen and Civil Engineering at the University of Hannover in

Germany. His Ph.D. thesis was in the field of coastal engineering. From 1989 to 1995, he was a student research assistant at the Alfred-Wegener Institute for Maritime and Polar Research. From 1990 to 1994 he was a student research assistant at the University of Bremen and between 1995 and 2004, Stephan was a research assistant at the Franzius-Institute for Wa-terways and Coastal Engineering. (Email: [email protected]) Jens Wilhelmi is a Physics engineer and since 2000, has been employed at the German Federal Institute of Hydrology evaluating new measurement techniques and data transmission. (Email: [email protected]) Ted Zenz is a Civil Engineer and electronic techni-cian with studies in electronics and Civil Engineering at the University of Applied Science in Koblenz. He has been with the Federal Institute of Hydrology in Koblenz, Germany since 1989. (Email: [email protected]) Dr. Hartmut Hein is a Hydrographic Surveyor with studies in surveying at the University of Applied Science Hamburg. He has a Ph.D. with his thesis in the field of oceanography. In the period 2003 to 2009, he was a research assistant at the University of Hamburg. Since 2009, Hartmut has been at the Federal Institute of Hydrology in Koblenz, Germany. (Email: [email protected]) Dr. Ulrich Barjenbruch is a Physicist with studies in Electrical Engineering and Physics at the University of Hannover. His Ph.D. thesis was in the field of solid state Physics. Ulrich has been the Chief of Department: Hydrometry and Hydrological Survey at the German Federal Institute of Hydrology since 2006.

His previous experience follows:

- 1984 to 1988: research associate at the Institute

of solid-state physics, Technical University of Hannover

- 1989: research associate at the institute of

physical and theoretical chemistry, University of Tübingen

- 1989 to 1995: research associate at the section of

measurement and technology, University of Kassel

- 1995: state doctorate in “Electrical measurement

technology”, theme: “Highly sensitive measure-ment of magnetic fields”

- 1995: self-employed (engineering office), construc-

tion and application of highly sensitive magnetic field sensors






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- 1995 to 1997: assistant professor at the University

of Kassel (section of measurement and technology)

- 1997 to 2006: Chief of Department Physics,

Instruments and Measurements at the German Federal Institute of Hydrology.

(Email: [email protected])


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ANOMALOUS ECDIS OPERATIONS

By Dr. Mohamed I. MOHASSEB (Navigation Division in the Egyptian Naval Hydrographic Office &

Arab Academy for Science and Technology and Maritime Transport - Alexandria, Egypt)

Abstract

Résumé

Resumen

The Electronic Chart Display and Information System (ECDIS), in conjunction with other recent technologies such as Radar and Automatic Information System (AIS) has practical benefits to facilitate safe navigation and bridge watchkeeping. The ECDIS capability however is suffering from ongoing issues including Electronic Navigation Chart (ENC) data encoding inconsistencies, differences between the content shown on paper charts and the corresponding ENC, overlapping and conflicting ENC coverage and the interpretation and application of the IHO’s S-52 Presentation Library to display ENC symbols. This paper addresses the International Hydrographic Organization’s (IHO) effort to collect, analyze and resolve these problems so that they can be addressed by the appropriate agencies and organizations in order to maintain safety of navigation.

Le système de visualisation des cartes électroniques et d’information (ECDIS), conjointement avec d’autres technologies récentes, telles que le radar et les AIS, présente des avantages pratiques qui favorisent la sécurité de la navigation et les pratiques de veille sur la passerelle. La capacité de l’ECDIS souffre toutefois de problèmes récurrents y compris des incohérences dans le codage des données des cartes électroniques de navigation (ENC), des différences entre le contenu qui apparaît sur les cartes papier et les ENC correspondantes, ou de l’existence de chevauchements et de couverture ENC contradictoires et de l’interprétation et de l’application de la Bibliothèque de présentation de la S-52 de l’OHI pour présenter les symboles des ENC. Cet article aborde les efforts de l’Organisation hydrographique internationale pour rassembler, analyser et résoudre ces problèmes afin qu’ils puissent être résolus par les agences et organes appropriés dans le but de maintenir la sécurité de la navigation.

El Sistema de Información y de Visualización de la Carta Electrónica (ECDIS), junto con otras tecnologías recientes como el radar y el Sistema de Identificación Automática (AIS), tiene beneficios prácticos para facilitar una navegación segura y para las tareas de guardia en el puente. Sin embargo la capacidad del ECDIS se ve afectada por temas en desarolloque incluyen: incoherencias en la codificación de datos de la Carta Electrónica de Navegación (ENC), diferencias entre el contenido mostrado en las cartas de papel y la ENC correspondiente, el solapamiento y una cobertura discordante de ENCs y la interpretación y aplicación de la Publicación S-52 de la OHI – Biblioteca de Presentación, para representar los símbolos ENC. Este artículo trata sobre el esfuerzo de la Organiza-ción Hidrográfica Internacional para reunir, analizar y resolver estos problemas, de modo que puedan ser tratados por las agencias y organizaciones adecuadas para mantener la seguridad de la navegación.

48


Importance of ECDIS

Numerous studies have been conducted concerning the importance of Electronic Chart Display and Information System (ECDIS). Some of these studies concern the physical state of the mariner whilst other studies related the mental state whilst using the ECDIS technology. A study conducted by the Russian Federation [2], found a reduction in a user's pulse rate by some 10-12% when using ECDIS compared with others who were not using it. The mariner’s ability to handle navigationally-challenging areas such as maneuvering to avoid a collision with other vessels in close proximity, is significantly improved when using ECDIS. Another important benefit is the intelligent integration of the radar image and Automatic Identification System (AIS) information with the ECDIS display brings further practical benefits to facilitate safe navigation and bridge watch keeping. ECDIS is also used for pre-sailing activities such as voyage planning, execution and monitoring. [1] ECDIS Anomalies

Because of the benefits that ECDIS provides, several concerns have been raised about identified ECDIS anomalies. These anomalies could be that ECDIS equipment at sea does not perform optimally or as expected because of shortcomings in the nature of the ENC data, the ECDIS software implementation, the implementation of current IHO ECDIS-related standards, and/or various combina-tions of these and other factors.

International Efforts

Several efforts have taken place internationally to address these ECDIS anomalies. Examples of these efforts are listed below: At the 88th session of the International Maritime

Organization (IMO) Maritime Safety Committee (MSC), Japan, Norway, the United Kingdom, the International Chamber of Shipping (ICS), and the International Federation of Shipmasters’ Asso-ciations (IFSMA) submitted document MSC88/25/6 on “Operating anomalies identified within ECDIS”. [3]

UK made a presentation entitled “ECDIS Anoma-lies and Safety Implications”. [3]

The UKHO and the UK Maritime and Coastguard Agency co-hosted a technical workshop in London attended by invited experts to review the current situation with reported ECDIS issues. The participants comprised 23 leading ECDIS experts from IHO Member States, ECDIS manu-

facturers, type-approval laboratories, training establishments, professional mariner and indus-try bodies, and maritime Administrations. [4]

The International Hydrographic Bureau (IHB) hosted the workshop in Monaco on 15-16 February 2011. The workshop was attended by 37 leading representatives from stakeholder groups including the IMO Secretariat, IHO and IMO Member States, Intergovernmental Organizations, Non-Governmental International Organizations, data service providers, ECDIS manufacturers and type-approval authorities. The Chair and Vice-Chairs of IHO HSSC and TSMAD working groups also attended the workshop. [5]

UKHO has found over 900 differences between paper charts and their equivalent ENC product that have potential significant implications for navigation safety. These differences cover 400 ENC cells from 30 different producer nations. [6]

IHO Standards for ECDIS

IHO Circular Letter 46/2011 [7] identified the current status of the IHO ECDIS related Standards and these are listed in Table 1.

Based on the above standards, any ECDIS purchased before 1 January 2008 will not have been built or type-tested in accordance with the latest IHO chart standards. Mariners, whose ECDIS software is not up to date, should contact the manufacturer or the service agent for assistance. [7] One of the main concerns is that the ECDIS software is not conforming to the latest IHO standards. It should be possible to interrogate the operating software in any ECDIS to determine if the latest standards have been implemented by the manufac-turer. However, the method for finding this information differs from system to system and is not always easy to locate. In any case, it does not nec-essarily guarantee that the latest IHO standards have been comprehensively implemented. For these reasons, the IHO developed a test data set in the

IHO Standard Name Effective date of latest edition

S-57 Edition 3.1 IHO Transfer Stan-dard for Digital Hydrographic Data

November 2000

S-52 Presentation Library Edition 3.4

IHO Presentation Library for ECDIS

January 2008

S-63 Edition 1.1 IHO Data Protection Scheme

March 2008

Table 1. IHO ECDIS Standards

49


form of three dummy ENCs that mariners can use to check if the latest IHO Standards have been implemented in their equipment. All together, there are six different tests designed to check the status of the ECDIS [7]. The tests require that you load the three dummy ENC cells. The six tests involve looking carefully at various chart objects contained in the ENC cells. For this paper, 5 of the 6 tests have been consoli-dated into 3 Checks as follows:

Check 1 – Display of navigation areas recently

recognized by the IMO.

Check 2 – Display of complex lights.

Check 3 – Display of underwater features and isolated dangers.

A final test involving the detection of objects by route checking in voyage planning mode was not included in a Check as the software being tested are not ECDIS equipment but ENC viewing software. Check Results

Even though these tests are designed to check ECDIS performance, they have been run on two ENC viewers. The ENC viewers are HYPACK ENC Editor 12.0.0.0 and CARIS Easy View 2 (freely available from the CARIS home site). The tests were conducted on 16

th June 2012.

Check 1 – Display of navigation areas recently recognized by the IMO Figure 1 illustrates four symbols that should be displayed to highlight navigation areas that were recently adopted by the IMO and resulted in changes to S-57. These areas include:

Archipelagic Sea Lane (ASL)

Environmentally Sensitive Sea Area (ESSA)

Particularly Sensitive Sea Area (PSSA)

Also included in this Test is an encoding of a new IHO object called NEWOBJ which will display as a black square and have labeled text “Presentation Library 3.4”. This test is to display a new chart object without any change to the IHO Presentation Library.

Figures 2 and 3 illustrate how the HYPACK ENC Editor 12.0.0.0 and CARIS Easy View 2 display the features.

Figure 1. Correct display of 4 objects based on the S-52 Presentation Library edition 3.4

Figure 2. HYPACK ENC Editor 12.0.0.0 depiction of the 4 objects

Figure 3. CARIS Easy View 2 depiction of the 4 objects

As shown in Figures 2 and 3, HYPACK ENC Editor 12.0.0.0 managed to show Archipelagic Sea Lane, Environmentally Sensitive Sea Area and Particularly Sensitive Sea Area symbology correctly but CARIS Easy View 2 could not. However, CARIS Easy View 2 shows the Presentation Library 3.4 symbology but HYPACK ENC Editor 12.0.0.0 doesn't show it.

50


Check 2 – Display of complex lights Figure 4 shows how complex light should be shown along with light characteristics.

Figure 4. Correct display of complex lights objects.

Figure 5. HYPACK ENC Editor 12.0.0.0 depiction of the complex light objects.

Figure 6. CARIS Easy View 2 depiction of the complex light objects

As shown in Figures 5 and 6, both packages fail to depict the correct sector light symbol meanwhile both depict the light characteristics correctly.

Check 3 – Display of underwater features and isolated dangers

The display of obstructions and isolated dangers in ECDIS is complex. Unfortunately, not all ECDIS equipment performs as intended by the IHO Standards. This test is intended to confirm that the more common display issues are not present in the ECDIS display.

Figure 7. Correct display of isolated dangers in OTHER mode with 10m safety contour/safety depth

Figure 8. HYPACK ENC Editor 12.0.0.0 depiction of the isolated dangers.

Figure 9. . CARIS Easy View 2 depiction of the isolated dangers.

51


According to Figures 8 and 9, both packages depict the isolated dangerous symbols labeled 9 and 10 correctly. The results of these tests have been sent to both software manufactures. HYPACK Company upgraded its ENC Editor 12.0.0.0 to comply with IHO standards and will be released in the next version. ECDIS Validation Test Results

The IHO’s ENC Data Presentation and Performance Check was issued in October 2011. By the end of February 2012, 500 reports from testing parties had been received. These reports covered 15 out of approximately 25 recognized and widely used type‐approved ECDIS manufacturers. The results were divided into three major findings; One third of the systems fulfill the check and

function as expected;

A further third display all significant underwater features, including underwater obstructions, but the isolated danger symbol required to be shown under certain conditions is not always used; and

Most of the remaining third failed to display some significant underwater features in the "Standard" display mode. All these features are however displayed in the “Full display” or “All display” modes. [8]

The analysis of results that were received by IHO shows that:

A significant number of ships reported that they were unable to clearly identify the recently IMO-adopted ASL, PSSA or ESSA objects on the ECDIS display;

Ships reported that lights with complex charac-teristics such as multiple colored sectors were not displayed as intended by the IHO standards;

The display of underwater features and isolated dangers was reported as variable across the different manufacturers’ systems. However in most cases the display gave a safe, if not entirely correct, interpretation of the ENC data;

A high proportion of ships reported that naviga-tionally significant objects, such as certain land features, “area to be avoided” and marine aqua-culture installations, did not raise an appropriate warning in the route checking mode of ECDIS;

Few ships in the nearly 500 reports received by the IHB, appear to have an ECDIS that success-fully passed all parts of the IHO checks;

The checks that have produced negative results vary between manufacturers and different soft-ware versions from the same manufacturer.

No check reveals the same failure across all 15 manufacturers’ systems reported to the IHB. This appears to confirm that certain parts of the requirements of the ECDIS standards have been interpreted and implemented in different ways by different manufacturers. [9]

ECDIS Non-Conformance – recommended actions If after applying the IHO test and finding that the

ECDIS is not complying, the mariner should contact the manufacturer to upgrade the ECDIS software. Untill ECDIS has been upgraded it is recommended to perform certain actions depending on what test your ECDIS fails to satisfy.

During the test, the following areas should be displayed - ASL, ESSA, PSSA, as well as the New Object. If these areas are not displayed on the ECDIS screen, and the borders contain “?” marks, interrogate all “?-?-?” type borders or “?” symbols, using the function usually known as Chart Query or Chart Pick. If any symbol could not be seen at all, it is essential to consult other nautical publications during the route planning phase including Sailing Directions and Mariners‟ Routing Guides, to identify the existence of ESSA, PSSA and ASL and then include them manually as Mariners Objects in the ECDIS.

Symbols of different sector light and light characteristics should be displayed. If they are not shown at all or not shown correctly, notes should be recorded.

During the voyage planning phase, cross-check the information about lights shown on ECDIS with the information shown in the relevant List of Lights.

Among the objects that should be displayed during the test, are underwater and isolated dangers. If any of the objects are not displayed, it is essential to consult other sources of informa-tion such as paper charts and publications to ensure that all underwater dangers and isolated dangers are identified.

The last check on this test is the detection of objects by route checking in voyage planning, mode. If hazardous objects don't raise alarms in voyage planning, it is recommended to carry out a visual examination so as to detect them and to highlight them manually in ECDIS as "manual updates".

52


Conclusions ECDIS is an important enabling technology to improve navigation safety. ECDIS software, just like any system on the ship's bridge, must be maintained and kept up to date. The mariner’s awareness of the need to upgrade ECDIS software should be improved. In using ECDIS systems that fail to adequately show underwater features, the mariner must navigate in conjunction with the paper chart to ensure that all wrecks and underwater obstructions can be properly identified.

References

[1] DEVELOPMENT OF CARRIAGE REQUIREMENTS FOR ECDIS, Proposal to amend regulation 19 of SOLAS chapter V.

[2] DEVELOPMENT OF CARRIAGE RE-QUIREMENTS FOR ECDIS, IMO, NAV 54/14, 2008.

[3] International Hydrographic Organization, Circular Letter, 83/2010, Monaco, 2010.







Biography

Dr. Mohasseb is currently the head of the Naviga-tion Division in the Egyptian Naval Hydrographic Office and a Hydrographic survey instructor at the Arab Academy for Science and Technology and Maritime Transport (AASTMT), Alexandria, Egypt. He received his CAT B certificate from US Naval Oceanographic Office in 1998, his Master of Science degree from AASTMT in 2001 and a PhD degree from AASTMT in 2006 with the award of best dissertation. He then achieved CAT A certification and his Master of Science with the award of Outstanding Academic and Practical Performance from the University of Southern Mississippi in 2009. e-mail : [email protected] cell phone: (+201001448673)

Note from IHB : At the time of publication, IHB can report significant progress has been made by ECDIS manufacturers and software producers to address the anomalies identified. As a result of discussions between IHO, IMO and various key stakeholders, considerable efforts have been made by manufacturers to contact system users to provide up-grades which meet the IHO Standards. Performance monitoring remains an ongoing task. For further information see the IHO website: ENC & ECDIS.


http://www.iho.int/srv1/index.php?option=com_content&view=article&id=331&Itemid=430

53


A TECHNICAL METHOD ON CALCULATING THE LENGTH OF COASTLINE FOR COMPARISON PURPOSES

Laurent LOUVART (Eng. Corps & Hydrograph., SHOM - FRANCE) on behalf of the IHO Correspondence Group

Abstract

A quick web search illustrates the wide variation in the quoted lengths of the coastline of a unique State, with ratios from 1 to 100 and in some examples, even more. This illustrates the need for a common measuring method. The length of a coastline, for the purpose of compari-son between States, can be calculated according to the guidance and specifications described in this paper. This specification describes a harmonized approach to determining the length of a coastline. It may only be relevant for comparison purposes and should not to be regarded as definitive nor suitable for all purposes. Based on official ENC datasets, the advantage of this method is that it gives comparable results that can be easily verified.

Background

Following a request from the European Commission, the 20th IHO CHRIS Meeting (November 2008) encouraged the creation of a Correspondence Group (CG) aimed at harmonizing the way Member States define and measure the length of their national coastlines.

France volunteered to coordinate such a CG to study the feasibility of such standardization and members were invited to join the group. The HSSC-2 meeting in October 2010 invited the CG on the Definition and Length of Coastline to complete its work by HSSC-3.

The CG met on 30-31 March 2011 in Brest, France, with participation from Germany, Finland, Spain, Cyprus, USA, Slovenia and France. A first draft method was proposed to HSSC-3 in 2011. This last version clarified the aspects related to determinations between S-57 Usage Band ENC’s.

Users’ need and purposes for length of coastline

The CG found that there are no clear legal, or other obligations to define how the length of coastline is determined. It is possible to define the length for various different purposes such as, administrative and comparison purposes (allocating fishing quotas, referencing aquacul-ture production statistics, coastal zone management, defining “hydrographic interest”, etc.), environmental protection (for example, evaluating response capacity requirements) and scientific purposes.

It was found that there are often several lengths available for the calculated or estimated length of coastlines, but only few metadata is associated with these values. There are many worldwide digital source data sets available. There also exist several GIS software tools available to make the calculations.

The CG recognized that the coastline is by nature a fractal object, so it is not possible to provide an unambiguous length. The length may be calculated in as much detail as is desired and the length may therefore grow to infinity. There is never one simple solution (see Appendix 1).

However, the CG noted that there are often requirements to be able to compare the length of coastlines between States for certain administrative purposes. Thus a standardised method for calculating these lengths is required.

54


General requirements

The CG noted that in order to develop a harmonised approach, there are many issues that must be clarified before the length of a coastline can be calculated for a given purpose. Among these are:

Requirements on the level of detail Sources to be used Scale of the sources Method to be used Generalisation What to be included (islands, inland waters, artificial structures…) How far do we measure river mouths Dynamic aspects and evolution of coastline

The CG identified some general requirements, specifications and guidance for those who may need to cal-culate the length of a coastline:

Have a common definition of what is used in calculations

Sufficient metadata should be associated with the calculated length. These include information on the methods used, source data, purpose of the calculation, what is included in the calculation, specifications used, expected use of the results

The calculated results should be repeatable

The results should be auditable

Coastline Length calculation for comparison purposes based on ENCs

The CG has developed a specification on a harmonised approach to define the length of a coastline for comparison purposes, based on official, standardised and available data: S-57 Electronic Navigational Charts (ENC).

The ENC coverage at Navigation Purpose code 1 (Overview), which is almost complete, is recommended as the basis for the calculation. Where this coverage is not available or suited for comparison purposes, Navigation Purpose code 2 or largest existing scales should be used. The key concept here is that the ini-tial selection of equivalent scale products is fundamental to appropriately comparing lengths of coastline between two or more States.

The CG noted the following benefits of using ENC as the basis for the calculations:

ENCs are officially produced under the authority of national Hydrographic Offices (HOs).

The coverage of small scale ENCs is effectively complete.

The ENC product specification does not allow overlaps in the same navigation purpose code – hence a single unambiguous source of data should normally be available.

It is possible to identify the Producer State from the ENC data for each coastline segment.

Data is already in a consistent structure and in a uniform format and associated with a unique geodetic datum

There are tools to extract coastlines from unencrypted ENC data sets.

The following specification identifies the sources to be used for the calculation, what elements should be included and the metadata to be associated with the results. Appendix 1 provides examples of calculated lengths together with relevant metadata.

Calculation details

1. For the purposes of this method, the coastline is defined as the High Water Line as represented by the Coastline, Shoreline Construction and Causeway object classes of the applicable Electronic Navigation Charts (ENC).

55


2. The length of the coastline between two points is the sum of the lengths of the three Coastline, Shoreline Construction and Causeway object classes between those points.

3. Equivalent scale and vintage products are recommended for the calculation to support comparative analysis. The following approaches are recommended:

The relevant lengths obtained from Navigation Purpose code 1 (overview) ENC cells should be considered first for the calculation.

If Navigation Purpose code X ENC cells have not been published or are not suited for compari-son purposes, data from Navigation Purpose code X+1 ENC cells (largest scales) should be used.

In cases where data from Navigation Purpose code X ENC cells is supplemented by data from Navigation Purpose code X+1 ENC cells, the latter is counted from the vertex closest to the last

vertex of the code X ENC corresponding curve (see Appendix 2).

4. River mouths should be included in the calculation to the point where they become a line feature in the ENC band that is used for the calculation. When the chart ends first or when there is no great-est ENC scale to complete the river, a straight line is drawn across the mouth and included in the measurement of the length of coastline.

5. Water bodies, such as inland lakes, which may be upstream of a river line should not be included in the calculation of coastline (for example: in the case of inland water linked to the sea by a canal).

6. The end of each State coastline will be at the agreed or declared border line.

Data and descriptive metadata

Whatever the way of calculation of the length of coastline, the results should at least include the following metadata:

Country name Two-letter Country code (IHO S-62) Length Unit of Measure (UoM)

Some metadata should be also included with the result of the calculation.

Note: elements marked * are repeatable.

Any comments

Point of contact of the organisation responsible for the calculation (such as the postal address or web addresses of the HO)

Method of calculation (e.g. International Hydrographic Review reference)

Date of calculation (YYYY/mm/dd)

Identifier of the ENC cell(s) used for the calculation *

Edition date of the ENC(s) *

Producer code of the ENC(s) (IHO S-62) *

Scale of the line segment(s) used *

Object Classes included in the calculation *

Conclusions

France achieved some tests to validate this method and results are shown in Appendix 3. Now, it is up to nations or interested readers to complete it.

56


Biography of the Author

Laurent LOUVART

He is currently deputy director of research & innovation department, SHOM Headquarters. Amongst other duties, he is responsible for managing the survey fleet renewal project and representing SHOM at the IHO’s Hydrographic Services & Standards Committee (HSCC).

e-mail : [email protected]


57


Appendix 1 - Examples of different calculations for the same State

This example is based on a quick web search. It illustrates the wide variation in the quoted lengths of the coastline of Finland - from 1,100 km to 314,604 km, thus illustrating the need for a common metric and minimum metadata.

Length [km] What is included Metadata Source

1100 Only sea border line. No metadata available Unspecified document

1250 No metadata available CIA World Fact book: Worldwide list of lengths of coastlines

2774

Shoreline only. Based on 1:4.5M. No other metadata available

Unspecified document

4600 No metadata available Unspecified document

6299 Coastal shorelines. No metadata available Finnish Environmental Centre

31119 No metadata available NGA World Vector Shoreline

39125

Basic topographic map 1:10.000. No other metadata available

Unspecified document

46198

Coastal shorelines includ-ing shorelines of islands and of lakes on islands.

No metadata available Finnish Environmental Centre

314604

Coastal shorelines and shorelines of lakes includ-ing shorelines of islands and of lakes on islands.

No metadata available Finnish Environmental Centre

58


Appendix 2 - An Example of how incorporate rivers using Navigation Purpose codes 1 and 2 ENC cells

Below is an illustrated example on how Navigation Purpose codes 1 and 2 ENC cells should be handled so that the latter supplement the former.

Fig.1 : Navigation Purpose code 1 ENC (blue), classes Coastline, Shoreline construction and Causeway The line presents a discontinuity that can be supplemented by Navigation Purpose code 2 ENC data (red). The next figure displays the cropped area (dashed box).

Fig.2 : Crop on the discontinuity.Navigation Purpose code 1 data is supplemented by Navigation Purpose code 2 data from the vertex closest to the last vertex of the code 1 ENC curve (arrows).

Fig.3 : Calculation can now be based on the composite coastline.

59


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60



61


The King Abdulaziz University of Saudi Arabia is to be newly equipped with a new ultra sophisticated vessel in the field of research and scientific exploitation. This vessel, to be delivered early 2014, is a composite built by a French shipyard renowned for this type of construction, appropriate for the conditions of the Red Sea, is specialised in all maritime areas :

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NEW SCIENTIFIC CONTRIBUTION TO THE KING ABDULAZIZ UNIVERSITY

62


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NOUVELLE CONTRIBUTION SCIENTIFIQUE DE L’UNIVERSITE « KING ABDULAZIZ»

63


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