Www.sea.co.uka Cohort plc company SWATHplus Interferometric Sonar Co-registered Bathymetric Mapping and Seafloor Imaging 26 th May 2009

www.sea.co.uk a Cohort plc company

SWATHplus Interferometric SonarCo-registered Bathymetric Mapping and

Seafloor Imaging

26th May 2009


• Why SWATHplus?

• advantages over multibeam systems

• advantages over other interferometric systems

• Principles of Interferometry

• System Performance

• data quality and analysis

• error analysis

• analysis results, 234 kHz

• uncertainty analyses

• accuracy & resolution: summary

• range limits

• System Features

• data formats

• interfaces

Contents

• System Components

• sonar transducers & universal mounting kit

• transducer interface unit (TIU)

• laptop with data acquisition/processing software

• Operations

• calibration

• data acquisition

• data processing

• Users & Applications

• coastal surveys

• pipeline inspection survey

• civil engineering support

• seamless water/land survey

• Contact Details


• Wide swath width in shallow water or low altitude:

USGS: “Operating Swath of the bathymetric system ranged

from 15 to 20 times water depth in depths less than 15m.”

• Co-registered, high quality bathymetry and seafloor imagery

• High data count gives high special resolution up to the swath edge

• Low cost of ownership compared with most beamforming multibeams

• Lightweight, compact, lower power requirement and highly portable - facilitates simple and rapid deployment

• Reduced survey effort and data turn-around times

• Data exportable to industry-standard applications, such as CARIS

• Meets tight international data standards, such as IHO survey requirements

Submetrix

Multibeam

Why SWATHplus?


advantages over multibeam echosounders

• Wide swath width:

• Greatly reduces survey durations

• Provides total insonification of the seafloor at typical survey speeds

• Portability

• Low power requirements – less than 25W

• High resolution and accuracy - multibeam systems suffer from poor resolution at far ranges

• Simultaneous, co-registered seafloor imagery

• Simplicity

• Multibeam systems have angular restrictions while SWATHplus can survey a full 300o sector in standard configuration

• Multibeam swath coverage is affected by roll which can lead to un-surveyed areas at the swath edges


advantages other interferometric systems

• Simultaneous pinging

– Double the productivity and along track coverage of alternate pinging systems

• Portability

– Does not require rack mounting

• CAATI systems do not perform well in shallow waters; SWATHplus is:

– Capable of producing a wider swath width

– More cost-effective

– Lighter, more compact and robust


Principles of Interferometry

• Transmits short acoustic pulse in beam: • narrow along track

• wide across track

• Receives backscattered signal

• Measurement of range and angle:

• Range from timing

• Angle by comparing phases at vertically-spaced transducer staves

• Depth calculated from range, angle and transducer motion

• Similar range coverage and data density to a sidescan sonar system

• Amplitude image is equal to that of a sidescan-only sonar system

Transducer

Sediment

Sea surface


System Performance

• Interferometric swath bathymetry systems give 2000-8000 raw data points per side, with uncertainties (standard deviation) greater than that of multibeam systems (only producing 100-200 points per side)

• Software filtering reduces uncertainty to internationally acceptable survey limits but at the expense of survey resolution

• SWATHplus has been used and quality checked in surveys at all International Hydrographic Organisation (IHO) S44 accuracy orders, including Special Order

• Accuracy is defined by IHO S44:

• Total propagated uncertainty (TPU),

• Resolution (detection of small objects)

• Data coverage (accepted points per metre)

• SWATHplus is essentially an angle-measuring instrument, so that depth accuracy reduces with horizontal range

• It may therefore be necessary to restrict range for accuracy control


data quality and analysis

• Statistical composition of interferometric data is different to that of MBES, and so data quality is sometimes questioned

• Analysis of real data and mathematical modelling demonstrate that interferometers can meet tight international data standards

• Analysis process:

– Establish the statistical data quality requirement (IHO S44)

– Use two key criteria which can be traded off against each other, using statistical processing:

• Depth accuracy

• Spatial resolution

– Analyse real data to see whether it can fall within stated limits for these two parameters

– Create an error model and validate it against the real data

– Use the error model to explore the limits of conformity with IHO S44 accuracy requirements

• Real data taken from SWATHplus “Shallow Survey 08” Common Data Set, (http://www.shallowsurvey2008.org):

– Collected by USGS, using their own SWATHplus systems and normal operational survey procedures (speed, line spacing, etc.)

– All three SWATHplus frequencies used: 468 kHz, 234 kHz & 117 kHz

– Most common commercially-available swath bathymetry systems, MBES and interferometers, were used over the same data area, in similar survey conditions


error analysis

• Analysis of data from SWATHplus “Shallow Survey 08” data set:

• random component of horizontal and vertical uncertainties in processed SWATHplus output.

• Raw data smoothed with a sliding Gaussian window:

• scale size selected to maintain IHO S44 resolution (samples per metre)

• Calculated standard deviations of overall vertical and horizontal variations

• 95% confidence level uncertainties (as defined by S44) as a function of range (using a second sliding window)

• Error model developed for SWATHplus, based on Sonar Equation analysis

• Uncertainties measured from raw data compared with error model

• Calculated maximum range at which IHO accuracy is achieved


analysis results, 234 kHz

Typical “Ping”

• Depth versus horizontal range

• Raw data: Blue

• Smoothed to IHO S44 resolution requirement: Red

Raw Data Estimated Vertical Error

• Vertical uncertainty (error) in raw data estimated using depth variance from highly smoothed profile


uncertainty analyses

95% Uncertainty, 234 kHz

• Data smoothed at a level to maintain IHO points-per-m2 criterion

• Represented as 95% uncertainty, in line with IHO S44 specification, over a second sliding window

95% Uncertainty Averaged and Compared with Model, 234 kHz

95% Uncertainty Averaged and Compared with Model, 468 kHz


accuracy & resolution: summary

• Statistical variance of raw, un-processed interferometric data is in excess of IHO S44 requirements

• However, spatial resolution of interferometric data is far in excess of that called for in S44

• Simple statistical processing, as provided by SWATHplus and third-party software, brings interferometric data within S44 accuracy and resolution envelopes at swath width limits

• So: SWATHplus can meet IHO S44 accuracy requirements

Range versus Depth for IHO S44 Special Order

•Computed from validated model

•Marked points derived from real data


range limits

• Horizontal range is limited by two factors

– Grazing angle

– Spreading loss

• Grazing-angle:

– limit is dominant in shallow water, typically 7.5 times water depth

– total swath width 15 times water depth

– better in less that 10m depth, but reduced in poor conditions

• Spreading loss depends on sonar frequency:

– affects bathymetry more than sidescan data

– generally visible at greater ranges, about 20% - 50% more than the depth data

1

7

Effect 468 kHz 234 kHz 117 kHz

Grazing angle limit (typical) 1:7.5 1:7.5 1:7.5

Spreading limit (typical) 100m 200m 500m

Grazing angle limit (poor conditions)

1:5 1:5 1:5

Spreading limit (poor conditions) 50m 100m 200m


System Features

• Worldwide sales with systems currently operating in 5 continents

• Available in 117 kHz, 234 kHz and 468 kHz operating frequencies for shallow water surveys up to 350 metres water depth:

• 468 kHz available as AUV/ROV option (SWATHplus ‘Compact’)

• Double-sided pinging

• USB interface to any modern laptop or computer

• Wide swath to depth ratio:

• 10:1 on average

• 20:1 in shallow water

• Compact and portable: easy, rapid deployment on vessels of opportunity

• Interface with real-time applications such as Fugro Starfix, QINSy, Hypack and PDS2000

• Inputs:

• GPS, motion heading, speed of sound, echosounders etc.

• Outputs:

• Ethernet sonar records to third party software

• SEA formats file

• XTF imagery files


data formats

Software Vendor Notes

Starfix Fugro Proprietary acquisition and processing software

CARIS, HIPS & SIPS CARIS Inc. A widely used hydrographic processing package

Fledermaus IVS Inc. A processing tool with excellent visualisation

Hypack Hypack Inc. Navigation & survey planning/processing software

PDS2000 Reson Navigation & survey planning/processing software

QINSy QPS BV Navigation, positioning and surveying package

QTC Sideview QTC Sidescan sonar processing package

SonarWeb Chesapeake Sidescan processing & mosaicing software

Some of the systems that have been used with SWATHplus:

It is possible to interface to other company in-house systems if required


interfaces

• Real time interfaces to other survey suite sensors including:

• Motion (attitude)

• Speed of sound

• Position and height (e.g. DGPS / RTK DGPS)

• Heading

• Echosounder

• Arbitrary data streams

• Tide height measurement can be input

• From telemetry system

• In post processing

• Interfaces supported using RS232 serial ports & Ethernet UDP ports

• Data timing from GPS/sensor time, using 1PPS input, or PC time


1. Sonar transducers and Universal Mounting Kit

2. Transducer Interface Unit (TIU)

3. Laptop computer with SWATHplus sonar data acquisition & processing software

System Components


sonar transducers & universal mounting kit

Hull:

• Permanent installation of transducers

• Solid fixture providing:

• Less motion

• Ease of calibration

• Good for long-term deployment

Side-pole & Bow-mount:

• Ideal for Vessels of Opportunity

• Rapid deployment far from base

• Requires calibration on installation


transducer interface unit (TIU)

• Compact & highly portable

• USB interface

• Integrated power supply

• 1PPS timing Input


laptop with data acquisition/processing software

• Real-time software:

• Allows for control and set-up of the system

• Processes and displays data

• Gives quality control and error diagnostic information

• Stores raw and processed data

• Provides first pass of post-processing

• Post processing software:

• Converts processed data files into digital depth models

• Supports automatic patch-test calibration

• 3D visualisation & data cleaning

• Automated data cleaning

• Users may select SEA post processing software or third-party programs


Operations

• Calibration

• Data acquisition

• Data processing


calibration

• Self-calibration process built in to SWATHplus electronics

• Pre-survey: auxiliary sensor and sonar offsets and alignments measured and entered into the SWATHplus software

• During survey:

• Run auxiliary sensor calibration processes

• Run a pattern of overlapping lines: “patch test”

• After survey:

• Use the patch test results to refine sensor offsets and alignments: supported by functions in the SWATHplus post-processing software

• Approximately 3 hours required to collect and process the patch test


• All real-time functions via the laptop computer including:• Controlling the sonar electronics system

• Acquiring data from the sonar electronics system

• Acquiring data from the auxiliary systems, through the PC's serial ports

• Storing all the raw data

• Converting the raw data to depth, position and amplitude (xyza)

• Combining auxiliary data, such as motion, position, heading, tide and speed of sound.

• Filtering the data to remove noise and unwanted targets

• Displaying the data

• Storing processed xyza data in a range of formats

data acquisition


• Grid program runs off-line and performs the following functions:

• Places all the processed data into a gridded digital terrain model (DTM)

• Displays depth and amplitude for each node of the grid

• Displays statistical information about depths in each node of the grid

• The data for each ping and line of the survey are stored separately in the grid, allowing simple comparison of overlapping data sets.

• The data from overlapping survey lines are compared to provide automatic post processing calibration.

• Filtering and moving the data in the grid, to enable the operator to quickly and easily clean and correct the processed data.

• 3D views of the data in the grid, allowing the operator to see the seabed in three dimensions.

• The grid can be edited in the 3D mode.

• Grid data can be stored in “point cloud” format

• Every data point from the Swath program is retained in the grid allowing for high resolution views

• Typically 1 day’s data acquisition can be processed in ⅓ to ½ day.

data processing


Users and Applications

• Research and education

• Survey companies

– Navigable depth mapping

– Cable route surveys

– Oil & gas support surveys

• Utility companies

– Pipeline survey

• Marine science organisations

– Habitat survey

• Civil engineering

– Bridge, harbour structural surveys

• Oil & gas

– Pipeline route surveys

– Pipeline integrity inspections


coastal surveys

Mola di Bari, Italy

• SWATHplus-H Survey

• Monitor cliffs and caves

• Water depths 0-30 m

• Survey undertaken in 1 day with 1 day’s preparation and mobilisation

• Motion sensing and positioning using a CodaOctopus F180

• Sidescan imagery shows a pipeline


pipeline inspection survey

Sally Bayou and Atchafalaya Bay, Louisiana, USA

• SWATHplus-H with CodaOctopus F190

• 2 day survey to look at pipeline crossings

• Offshore and Bayou survey

• Bayou area 2.5 km x 90 m

• Offshore area 750 m x 100 m

• Shows anchor drag scarring

• 3-4 metres water depth


civil engineering support

Lougher Bridge, Wales,

• SWATHplus-H survey of train bridge footings, 250m by 100m, depths 0 to 10m to visualise wooden bridge piles.

• RTK positioning and height control with a Seatex MRU6 motion sensor.

• Survey undertaken within a 2 hour period as a test and no patch test undertaken.


seamless water/land survey

All images courtesy of Codevintec Italy

Integration of SWATHplus and scanning laser data


Contact Details

Systems Engineering & Assessment Limited

Offshore Division

SEA House

Building 660

Bristol Business Park

Coldharbour Lane

Bristol BS16 1EJ

Telephone: +44 (0) 1373 852000

Fax: +44 (0) 117 937 5088

www.sea.co.uk

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Www.sea.co.uka Cohort plc company SWATHplus Interferometric Sonar Co-registered Bathymetric Mapping and Seafloor Imaging 26 th May 2009