Research Article Correcting Positional Errors in Shore ...downloads.hindawi.com/journals/jmb/2014/267917.pdf750 1000 750 1000 750 1000 1500 1250 250 500 500 500 250 50 50 Kaikoura

Research ArticleCorrecting Positional Errors in Shore-Based TheodoliteMeasurements of Animals at Sea

Opheacutelie Sagnol1 Femke Reitsma2 Christoph Richter3 and Laurence H Field1

1 School of Biological Sciences University of Canterbury Christchurch 8140 New Zealand2Department of Geography University of Canterbury Christchurch 8140 New Zealand3Department of Biology University of Toronto at Mississauga Mississauga ON Canada L5L 1C6

Correspondence should be addressed to Ophelie Sagnol opheliesagnolhotmailfr

Received 30 September 2013 Revised 3 December 2013 Accepted 9 December 2013 Published 22 January 2014

Academic Editor Nobuyuki Miyazaki

Copyright copy 2014 Ophelie Sagnol et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Determining the position of animals at sea can be particularly difficult and yet accurate range and position of animals at seaare essential to answer a wide range of biological questions Shore-based theodolite techniques have been used in a number ofstudies to examine marine mammal movement patterns and habitat use offering reliable position measurements In this study weexplored the accuracy of theodolite measurements by comparing positional information of the same objects using two independenttechniques a shore-based theodolite station and an onboardGPS over a range of 25 km from the shore-based stationThe techniquewas developed to study the habitat use of sperm whales (Physeter macrocephalus) off Kaikoura New Zealand We observed that theposition accuracy fell rapidly with an increase in range from the shore-based station Results showed that the horizontal angle wasaccurately determined but this was not the case for the vertical angle We calibrated the position of objects at sea with a regression-based correction to fit the difference in distance between simultaneously recorded theodolite fixes andGPS positionsThis approachrevealed the necessity to calibrate theodolite measurements with objects at sea of known position

1 Introduction

Knowing the accurate geographical position is essential forstudying the spatial behaviour of animals at sea Accuratepositional data can answer a wide range of biological ques-tions related to their movement patterns habitat use and theeffects of human activities [1 2]

A number of tracking methods can be used in order toobtain the position of animals at sea including recoverabledata loggers satellite tags [3ndash8] acoustic monitoring [9ndash12] and boat surveys [13ndash16] All of these methods requireexpensive equipment and time to collect data and theobserver can be a source of potential disturbance [17] Asa result the geographical coordinates of animals at sea areideally determined from shore using a surveyorrsquos theodolitefirst introduced byRoger Paine in 1972 (Describe inWursig etal 1991) [18] Shore-based theodolite tracking is a techniqueoffering an inexpensive and nondisturbing alternative toother tracking techniques

By tracking animals at sea from land a small amount ofequipment is required and a larger area can be monitoredin a shorter amount of time compared to boat-based stationThe theodolite readings (horizontal and vertical angle) can beconverted into longitude and latitude when exact theodoliteposition and height above sea level are known [18 19]However shore-based tracking can only occur with animalspassing close enough to the coastline to be sighted fromthe shore-based station Previous studies using theodolitetracking have focused on coastal species such as dolphinswithin 5 km from shore [2 17 20 21] Shore-based trackinghas also been used to monitor whales during their migrationwhen their course passes close to shore [22ndash29] or to examinethe effects of human activities on whales [30ndash34]

A number of parameters can influence the accuracy of thecalculated position from theodolite fixes such as the accuracyinherent to the theodolite weather parameters (heat haze orswell) and the experience of the observer One of the main

Hindawi Publishing CorporationJournal of Marine BiologyVolume 2014 Article ID 267917 8 pageshttpdxdoiorg1011552014267917

2 Journal of Marine Biology

1250

750

1000

750

1000

750

1000

1500

1250

250

500

500

500

250

50

50

Kaikoura peninsula

N

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

Figure 1 Bathymetry of the study area and location of the shore-based station (pentagon)

problems with shore-based theodolite data is the increasingerror in positional fixes with increasing distance In order toimprove the accuracy of theodolite readingsWursig et al [18]summarized several of the necessary elements to organizea shore-based study Errors in the calculation of the stationelevation will bias the calculations of the animalrsquos positionTherefore the theodolite station height should be greater than45m and errors in the elevation calculation should be withinplusmn10 cm Thus far a better understanding of the calculationof the elevation has been the focus to improve theodoliteaccuracy [18 35]

Previous boat-based platform studies have assessed theaccuracy of distance measurements of animals at sea atclose range (0ndash2 km) using video cameras and binocularsGordon [36] compared the photogrammetric technique withlaser rangefinding binoculars and nondifferential GPS anddetermined that there was a good agreement for rangesmeasured between these three techniques Kinzey and Ger-rodette [37] identified the accuracy with which distances canbe measured from ships using the reticles in binoculars ata range of 0ndash8 km They determined that the accuracy ofdistance measurements decreased with the distance of theobject at sea [37] Concerning shore-based tracking Denardoet al [1] established and calibrated a shore-based technique tomeasure interanimal spacing using a theodolite and a videocamera over a 2 km range from the station

In this paper we compare positional information of thesame objects from two independent techniques a shore-based theodolite station and an onboard vessel GPS Byanalysing how the difference in the positions from bothtechniques relates to the distance of themeasured object fromthe shore-based station we build amodel to correct positionsestimated from theodolite measurements The objective ofthis study is mainly to describe a protocol that should beusedwhen tracking animals at sea from a shore-based station

This protocol will offer the possibility to easily correct thepositional error arising in such shore-based data

2 Method

The theodolite accuracy correction was developed for asperm whale (Physeter macrocephalus) habitat study withinthe Kaikoura submarine canyon in New Zealand The prox-imity of the Kaikoura submarine canyon to the coast of theSouth Island makes it one of the few places in the worldwhere male sperm whales are found close to the shoreline[38 39] offering the opportunity to track sperm whales fromshore A shore-based station was set up on a hill situatedat the east end of the Kaikoura peninsula (42∘25101584047 110158401015840 S173∘41101584054 610158401015840E) (Figure 1) at a height of 9988m (plusmn004m)above sea level (method described byWursig et al [18])Thislocation provided a good vantage point overlooking the studyarea encompassing the Kaikoura canyon and surroundingnearshore habitat

3 Data Collection

To determine the theodolitersquos accuracy we needed inde-pendently derived and accurate geographical positions ofthe same objects taken at the same time as recorded bythe shore-based theodolite station During our study tworesearch boats were operating inside our study area One ofthe research vessels was a 6m aluminium monohull usedfor behavioural and acoustic observation on sperm whalesThe second vessel was a 55m rigid-hull inflatable vessel usedfor a study on dusky dolphins (Lagenorhynchus obscurus)Both vessels were equipped with a GPS (accuracy within3m) and recorded the vesselrsquos position every 15 secondsFrom shore we collected the positions of these researchvessels using a Sokkia Set4000 theodolite (accuracy of anglemeasurement plusmn5

10158401015840

and measuring time less than 05 sec)For consistency we fixed the boat positions by placing thetheodolite crosshair at the waterline at the centre of thevessel We connected the theodolite to a laptop running thetracking program Pythagoras [19] The software transformedreal-time theodolite readings into GPS coordinates correctedfor curvature of the Earth and tide level and stored them foranalysis [19]

4 Results

During the study period we recorded a total of 347 theodolitefixes of research vessels (Table 1) The positions recordedwere between 2 km and up to 26 km from the theodolitestation (Table 1) and were distributed along the whole studyarea (Figure 2) For each research vessel position recordedwith the theodolite we extracted the time related positionrecorded with the vesselsrsquo onboard GPS

We compared vessel positions based on theodolite read-ings with the time-related positions extracted from thevesselsrsquo onboard GPS (Figure 3) Theodolite and GPS posi-tions appeared to be on the same line as seen from thetheodolite stationwhen viewing fromplan view (Figure 4(a))

Journal of Marine Biology 3

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(a)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

0 5 10

(km)

(b)

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(c)

Figure 2 Research vessels locations recorded by onboard GPS by year (a) and (b) are fixes from the sperm whale research vessel (2010 and2011) and (c) is fixes from the dolphin research vessel (2012) (pentagon shore-based station grey dot research vessel positions)

However when seen from the side theodolite and GPSpositions differed (Figure 4(b)) We hypothesized that whilehorizontal angles recorded with the theodolite were accuratevertical angles were inaccurately determinedWe investigatedthis hypothesis by separately examining the relationshipsbetween horizontal and vertical angles measured by GPS andtheodolite

To compare the accuracy all theodolite fixes and onboardGPS positions were converted to a Cartesian system using thetool ldquocalculate geometryrdquo in ArcGIS 101 We also convertedthe geographic coordinates of the theodolite station in orderto centre all the positions with the theodolite station In order

to calculate an angle towards a given position wemade use ofthe fact that we know the length of the vertical distance (119910 islatitude converted to theCartesian system) and the horizontaldistance (119909 is longitude converted to the Cartesian system) tothis position

The horizontal angle (120579119867) to the research boat position

(GPS) or theodolite position (TH) can be calculated using therelationship

tan(120579119867-GPS) =119910GPS119909GPS

tan(120579119867-TH) =119910TH119909TH

The vertical angle (120579119881) to the research boat position

(GPS) or theodolite position (TH) can be calculated using the


1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265

minus4270

Figure 3 Comparison of all research vessel positions over all yearsrecorded by theodolite (red dots) and by onboard GPS (black dots)

Table 1 Distance summary of the two research vessels from thetheodolite station (plusmnSE)

Sperm whale researchvessel positions

Dolphinresearch vessel

positions2010

(119873 = 66)2011

(119873 = 137) 2012 (119873 = 144)

Mean distance(km) 1299 (plusmn074) 1193 (plusmn039) 793 (plusmn028)

Maximum distance(km) 2585 2522 1852

Minimum distance(km) 296 476 245

relationship using the distance from the position (119863) and thetheodolite station height (ℎ)

tan(120579119881-GPS) =119863GPSℎ = (119910GPScos(120579119867-TH))ℎ

tan (120579119881-TH) =119863THℎ = (119910THcos(120579119867-TH))ℎ

The error in distance (Δ119863) is given by subtracting thedistances recorded from the GPS positions (119863GPS) and thedistances recorded from the theodolite (119863TH)

Δ119863 = 119863TH minus 119863GPS (1)

We then determined the distance of the object at sea Asexpected 119863 differed significantly between theodolite andonboard GPS positions (Mann Whitney 119880 test 119875 = 0013)While the 120579

119867is resolved very accurately with the theodolite

(MannWhitney 119880 test ns) 120579119881is not (MannWhitney 119880 test

119875 = 0013)Since distance from the platform can influence accu-

racy of theodolite readings we examined the relationshipbetween distance from shore and the distance error betweensimultaneously recorded theodolite fixes and GPS positions(Figure 5)We tested a couple ofmodels to determine the bestfitted model and we used the Akaike Information Criterion

Table 2 Results of models analyses (AIC = Akaike InformationCriterion Δ

119894

(AIC) = AIC119894

minusminAIC)

Model AIC ΔAICy sim alowast xandb 5138896 0119910 sim 119909 lowast 119887 5502441 363545119910 sim 119909 + 119887 6722799 1583903119910 sim 119909 5267642 128746119910 sim minus1 + 119909 5502441 363545

(AIC) to select the best model A quadratic model of the form119910 = 119886lowast 119909and 119887 fitted the data best (Table 2) and we plotted thebest curve fitting for visualization (Figure 5)

The best model (119910 sim 119886 lowast 119909 and 119887) was used to correcttheodolite fixes based on their distance from the theodolitestation After applying this correction to our data the verticalangles of the theodolite fixes did not differ from the GPSpositions (Mann Whitney 119880 test ns) After calibrationtheodolite positions did not differ from GPS positions any-more (Figure 6 MannWhitney 119880 test ns)

The corrected positions showed normal distributions oferrors in distance suggesting no evidence of overall bias indistance after the correction (Figure 7)

5 What Is Influencing This Error

A number of parameters can influence the accuracy oftheodolite positions such as the observer experience the sizeof the boat incorrect calibration imprecision in measuringthe theodolite height above sea level (waves swell and tidalestimation) and the refraction [36 37]

We illuminated the possibility of an error coming froman imprecision in measuring the height of the shore-basedstation In order to avoid such an error we determined theheight of the theodolite station twice during our study Wealso checked the height of the theodolite eyepieces duringthe day to make sure that it did not vary To determine thepossible effect of the observers on the theodolite fixes wemodelled separately the error with distance depending onthe year During 2010 different people collected the datathrough the year and data collected from mid-2011 and 2012were entirely collected by the same observer By comparingthe distance error on the annual dataset with the generaldistance error on the whole dataset we could assess whetherexperienced versus inexperienced observer influenced theaccuracy in theodolite fixes We hypothesized that a presenceof observer bias will be described by a better accuracy oftheodolite fixes towards the end of the fieldwork Howeverthere was no significant difference in the theodolite fixescorrected by years or corrected using the complete database(Mann Whitney 119880 test ns) We also compared the error indistance from data collected from the same observer withthe distance error in the whole dataset and there was nosignificant difference (MannWhitney 119880 test ns) After theseanalyses we determined that in our study the observer didnot significantly influence the accuracy of theodolite fixes


120579H

(a)

h

120579VminusGPS

DGPS ΔD

(b)

Figure 4 (a) Plan view and (b) side view schematic for theGPS position of a particular position recorded by the theodolite (red dot) comparedto the position collected with the onboard GPS (black dot) extracted from Figure 3 The blue dot is the shore-based station

5000 10000 15000 20000 25000

0

1000

2000

3000

4000

5000

6000

Distance from theodolite station (m)

Erro

r in

dist

ance

(m)

Figure 5 Error in measurements of distance between theodolitefixes and GPS positions Red line best fitting curve (119910 sim 119886 lowast 119909 and 119887)

We then looked at the possible impact of the size ofthe object being tracked Analysis showed that there was nosignificant influence of the boat size on the fixes accuracy(Mann Whitney 119880 test ns) Therefore neither observerexperience nor object size influenced accuracy of theodolitepositions

Because data were collected from a shore-based stationit was not possible to obtain accurate values for the swellheight and the Beaufort sea state Data were collected onlyduring favourable weather conditions limiting the effect ofswell and Beaufort sea state on research vesselsspermwhalesdetection Consequently it was unlikely that these conditionsinfluenced our results

The possibility of an error in positioning the theodolitecrosshair on the waterline can be one of the factors causing anoverestimation of the distance from the shore-based stationSince size of the object will decrease with the distance it

1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265

Figure 6 Comparison of the corrected positions of the researchvessel over all years recorded by theodolite (green dots) and byonboard GPS (black dots)

minus900minus650minus400minus150 150 400 650 900 1150 1400 1650

Error in range by categories (m)

Num

ber o

f mea

sure

men

ts

0

20

40

60

80

100

Figure 7 Distribution of Δ119863 after correction


became increasingly difficult for the observer to establish theposition of the object waterline In addition the size of thetheodolite crosshair remained constant covering up distantand thus small objects making it difficult to accurately locatethewaterlineTherefore the error can come from the difficultyby the observer to accurately position the theodolite crosshairon the waterline which leads to an error that increases withdistance

6 Discussion

This study presented the accuracy in determining the positionof object at sea using a surveyor theodolite over a distancerange of 25 km from the shore-based station Our resultsindicated that themodel we provided can successfully correctthe positional error in shore-based theodolite measurementsof animals at sea

The particularity of this study was to focus on objectsfound at large distance from the shore-based station Theaccuracy and precision of determining the distance of objectsat sea has been previously studied for a range up to 8 km fromthe shore [1 36 37] Studies using a surveyor theodolite formarine mammals tracking avoided collecting data at largedistances because of the likelihood of inaccuracy in the dis-tance estimation These studies limited their data collectionto a critical distance from the theodolite station in orderto ensure consistent data [1 26 27 40] By having knownGPS positions over the whole study area we significantlyimproved our theodolite measurements and this allowed usto collect data to the limit of the visual capacity The methodpresented here could easily be used in other locations in orderto accurately survey a larger study area from a shore-basedstation

Theodolite estimation has been shown to be biased by theobserver experiences Our results showed that this factor wasnot significantly influencing the error Our observers weretrained before the fieldwork and one main observer was incharge of most of the theodolite data collection

Previous studies found that the swell and Beaufort seastate were important factors influencing the accuracy ofdistance estimates for sightings of marine mammals [37 41]In our case it was not possible to access a database providinginformation on swell and Beaufort sea state We looked at theyear effect and it was not statistically significant in ourmodelwhich suggests that the weather factors did not explain thebias in overestimation of the theodolite measurements

The effect of refraction was not directly tested duringour study Light does not travel in straight lines whenlight travels through the Earthrsquos atmosphere it is subjectto refraction Mirages and other refraction events are theresult of the bending of rays in the Earthrsquos atmosphere Forrange measurement studies the effect of refraction will resultin an angular error and the distance estimates of distantobjects will be seriously affected Several studies integrateda correction for the refraction for surveys using binocularsand video camera [36 37 42] based on the air temperatureand pressure measured daily during their data collection Ifthe rangemeasurements are not corrected with the refraction

correction distances will be negatively biased In our resultsthe error increase with the distance rejecting the possibilityof an impact caused by the refraction In addition byregularly collecting the position of an object at known rangeduring fieldwork all the parameters influencing the error canbe corrected

Optical errors can be an important factor in theodoliteaccuracy and can be affected by the fact that theodolitescopes are composed of a monocular scope with a singleeyepiece Therefore it is harder to see the object due to thedecreasing field of view increasing the possibility of an opticalerror Parallax errorwas also consideredwhenpositioning thetheodolite crosshair This error is caused by a change in theposition of the eye which will change the point of aim of thescope If the parallax error was important it should influenceboth vertical and horizontal angles and should differ betweenobservers and days However in our study we determinedthat the horizontal angle was accurately determined by thetheodolite

The last andmore probable error came from the crosshairpositioning error This study showed that the observer wasable to accurately determine the general position of theobject described with an accurate horizontal angle but whatappeared to be difficult was to establish the exact verticalangle the position where the object met the waterline Asthe object became smaller with distance it was harder forthe observer to define the waterline Moreover the large sizeof the theodolite crosshair made it difficult to position iton small objects In conclusion with increasing distanceobservers tended to place the theodolite crosshair on theobject instead of on the waterline creating a bias in thepositioning crosshair Positioning the crosshair on the objectrather than the waterline will overestimate the distanceand may cause the positive bias in distance estimation weobserved

During our study it was not possible to have constantobjects found at different distances within our study areaand collecting opportunistic vessel positions was the onlyapproach to estimate positional error Thus the protocolwe propose could be improved by using objects at constantpositions such as buoysThe difficulty will be to have enoughsuch objects across the study area

7 Conclusion

This study revealed the necessity of calibrating theodolitemeasurements when tracking animals at sea Known GPSpositions of objects within the study area should be used in alltheodolite studies in order to correct the error with distanceOne of the most important applications of this technique isits potential to improve the use of shore-based stations forhabitat and abundance studies at the limit of visual detection

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper


Acknowledgments

Equipment was provided by the Department of Conserva-tion New Zealand The authors thank Dara Orbach andManuel C Fernandes who provided the data from theonboard GPS They are grateful to the many volunteersthat have given their time to this project Finally they alsothank Kathy Walter from the National Institute of Water andAtmosphere Research (NIWA) who provided data on tidelevels

References

[1] C Denardo M Dougherty G Hastie R Leaper B Wilsonand P M Thompson ldquoA new technique to measure spatialrelationships within groups of free-ranging coastal cetaceansrdquoJournal of Applied Ecology vol 38 no 4 pp 888ndash895 2001

[2] H Bailey and PThompson ldquoQuantitative analysis of bottlenosedolphin movement patterns and their relationship with forag-ingrdquo Journal of Animal Ecology vol 75 no 2 pp 456ndash465 2006

[3] M Amano and M Yoshioka ldquoSperm whale diving behaviormonitored using a suction-cup-attached TDR tagrdquo MarineEcology Progress Series vol 258 pp 291ndash295 2003

[4] M P Heide-Jorgensen E S Nordoy N Oien et al ldquoSatellitetracking of minke whales (Balaenoptera acutorostrata) off thecoast of northen Norwayrdquo Journal of Cetacean Research ampManagement vol 3 no 2 pp 175ndash178 2001

[5] WAWatkinsMADaherNADimarzio et al ldquoSpermwhalesurface activity from tracking by radio and satellite tagsrdquoMarineMammal Science vol 15 no 4 pp 245ndash267 1999

[6] G L Kooyman Diverse Divers Physiology and BehaviorSpringer New York NY USA 1989

[7] M A Hindell D J Slip and H R Burton ldquoThe divingbehaviour of adult male and female southern elephant sealsMirounga leonina (Pinnipedia Phocidae)rdquo Australian Journalof Zoology vol 39 no 5 pp 595ndash619 1991

[8] R L DeLong B S Stewart and R D Hill ldquoDocumentingmigrations of northern elephant seals using day lengthrdquoMarineMammal Science vol 8 pp 155ndash159 1992

[9] M R Heupel J M Semmens and A J Hobday ldquoAuto-mated acoustic tracking of aquatic animals scales design anddeployment of listening station arraysrdquo Marine and FreshwaterResearch vol 57 no 1 p 113 2006

[10] S M Wiggins and J A Hildebrand ldquoHigh-frequency AcousticRecording Package (HARP) for broad-band long-term marinemammal monitoringrdquo in International Symposium on Under-water Technology and Workshop on Scientific Use of SubmarineCables and Related Technologies pp 551ndash557 April 2007

[11] W A Watkins andW E Schevill ldquoSperm whale codasrdquo Journalof the Acoustical Society of America vol 62 no 6 pp 1485ndash14901977

[12] KM Stafford C G Fox andD S Clark ldquoLong range detectionand localization of bluewhale calls in the northeast Pacific usingmilitary hydrophone arraysrdquo Journal of the Acoustical Society ofAmerica vol 104 no 6 pp 3616ndash3625 1998

[13] L T Ballance ldquoHabitat use patterns and ranges of the bottlenosedolphin in the Gulf of California Mexicordquo Marine MammalScience vol 8 no 3 pp 262ndash274 1992

[14] A Canadas R Sagarminaga and S Garcıa-Tiscar ldquoCetaceandistribution related with depth and slope in the Mediterranean

waters off southern SpainrdquoDeep-Sea Research vol 49 no 11 pp2053ndash2073 2002

[15] M C Ferguson J Barlow S B Reilly and T Gerrodette ldquoPre-dicting Cuvierrsquos (Ziphius cavirostris) and Mesoplodon beakedwhale population density from habitat characteristics in theeastern tropical Pacific Oceanrdquo Journal of Cetacean Researchand Management vol 7 no 3 pp 287ndash299 2006

[16] G D Hastie R J Swift G Slesser P M Thompson andW R Turrell ldquoEnvironmental models for predicting oceanicdolphin habitat in the Northeast Atlanticrdquo ICES Journal ofMarine Science vol 62 no 4 pp 760ndash770 2005

[17] K Barr and E Slooten ldquoEffects of tourism on dusky dolphinsat Kaikourardquo New Zealand Journal of Marine and FreshwaterResearch vol 35 pp 277ndash287 1999

[18] B Wursig F Cipriano and M Wursig ldquoDolphin movementpatterns information from radio and theodolite tracking stud-iesrdquo in Dolphin Societies Discoveries and Puzzles K Pryor andK S Norris Eds pp 79ndash111 University of California PressBerkeley Calif USA 1991

[19] G A Gailey and J Ortega-Ortiz ldquoA note on a computer-basedsystem for theodolite tracking of cetaceansrdquo Journal of CetaceanResearch amp Management vol 4 no 2 pp 213ndash218 2002

[20] S Harzen ldquoUse of an electronic theodolite in the study ofmovements of the bottlenose dolphin (Tursiops truncatus) inthe Sado Estuary Portugalrdquo Aquatic Mammals vol 28 no 3pp 251ndash260 2002

[21] T Photopoulou P B Best P S Hammond and K P FindlayldquoMovement patterns of coastal bottlenose dolphins in thepresence of a fast-flowing prevailing current shore-basedobservations at Cape Vidal South Africardquo African Journal ofMarine Science vol 33 no 3 pp 393ndash401 2011

[22] N J Patenaude Southern Right Whales Wintering in the Auck-land Islands vol 321 of Conservation Advisory Science NotesDepartment of Conservation Wellington New Zealand 2000

[23] P B Best K Sekiguchi and K P Findlay ldquoA suspendedmigration of humpback whales Megaptera novaeangliae on thewest coast of South AfricardquoMarine Ecology Progress Series vol118 no 1ndash3 pp 1ndash12 1995

[24] M E Morete A Freitas M H Engel R M Pace III and P JClapham ldquoA novel behavior observed in humpback whales onwintering grounds at Abrolhos Bank (Brazil)rdquoMarineMammalScience vol 19 no 4 pp 694ndash707 2003

[25] A Schaffar B Madon C Garrigue and R ConstantineldquoAvoidance of whale watching boats by humpback whales intheir main breeding ground in New Caledoniardquo SC61WW6Paper SC34WW6 IWC Scientific Committee 2009

[26] K P Findlay P B Best and M A Meyer ldquoMigrations ofhumpback whales past Cape Vidal South Africa and anestimate of the population increase rate (1988ndash2002)rdquo AfricanJournal of Marine Science vol 33 no 3 pp 375ndash392 2011

[27] T K Boye M Simon and P T Madsen ldquoHabitat use ofhumpback whales in Godthaabsfjord West Greenland withimplications for commercial exploitationrdquo Journal of theMarineBiological Association of the United Kingdom vol 90 pp 1529ndash1538 2010

[28] J Barendse P B BestMThornton C Pomilla I Carvalho andH C Rosenbaum ldquoMigration redefined seasonality move-ments and group composition of humpback whales megapteranovaeangliae off the west coast of South AfricardquoAfrican Journalof Marine Science vol 32 no 1 pp 1ndash22 2010

[29] M EMorete T L Bisi RM Pace III and S Rosso ldquoFluctuatingabundance of humpback whales (Megaptera novaeangliae) in


a calving ground off coastal Brazilrdquo Journal of the MarineBiological Association of the United Kingdom vol 88 no 6 pp1229ndash1235 2008

[30] G Gailey B Wursig and T L McDonald ldquoAbundance behav-ior and movement patterns of western gray whales in relationto a 3-D seismic survey Northeast Sakhalin Island RussiardquoEnvironmental Monitoring and Assessment vol 134 no 1ndash3 pp75ndash91 2007

[31] D W Funk T M Markowitz and R R Rodrigues EdsBaseline Studies of Beluga Whale Habitat Use in Knik ArmUpper Cook Inlet Alaska 2004-2005 LGL Alaska ResearchAssociates HDR for the Knik Arm Bridge and Toll AuthorityDepartment of Transportation and Public Facilities and theFederal Highway Administration Anchorage Alaska USA2005

[32] T M Markowitz and T L McGuire Temporal-Spatial Dis-tribution Movements and Behavior of Beluga Whales Nearthe Port of Anchorage Alaska Alaska Research Associatesfor Integrated Concepts and Research Corporation and theUS Department of Transportation Maritime AdministrationAnchorage Alaska USA 2007

[33] D Lundquist M Sironi B Wursig and V Rowntree ldquoBehav-ioral responses of southern right whales to simulated swim-with-whale tourism at Penınsula Valdes Argentinardquo Journal ofCetacean Research amp Management SC60WW4 2006

[34] F Ollervides Effects of boat traffic on the behavior of gray whalesEschrichtius robustus in Bahia Magdalena Baja California SurMexico [MS thesis] Texas AampM University 1997

[35] H Bailey andD Lusseau ldquoIncreasing the precision of theodolitetracking modified technique to calculate the altitude of land-based observation sitesrdquo Marine Mammal Science vol 20 no4 pp 880ndash885 2004

[36] J Gordon ldquoMeasuring the range to animals at sea from boatsusing photographic and video imagesrdquo Journal of AppliedEcology vol 38 no 4 pp 879ndash887 2001

[37] D Kinzey and T Gerrodette ldquoDistance measurements usingbinoculars from ships at sea accuracy precision and effects ofrefractionrdquo Journal of Cetacean Research ampManagement vol 5no 2 pp 159ndash171 2003

[38] J Gordon R Leaper F G Hartley and O Chappell ldquoEffects ofwhale-watching vessels on the surface and underwater acousticbehaviour of sperm whales off Kaikoura New Zealandrdquo Sci-ences and Research Series 52 Department of ConservationWellington New Zealand 1992

[39] N Jaquet S Dawson and E Slooten ldquoSeasonal distribution anddiving behaviour of male sperm whales off Kaikoura foragingimplicationsrdquo Canadian Journal of Zoology vol 78 no 3 pp407ndash419 2000

[40] R Williams A W Trites and D E Bain ldquoBehavioural resp-onses of killer whales (Orcinus orca) to whale-watching boatsopportunistic observations and experimental approachesrdquo Jour-nal of Zoology vol 256 no 2 pp 255ndash270 2002

[41] J Barlow T Gerrodette and J Forcada ldquoFactors affectingperpendicular sighting distances on shipboard line-transectsurveys for cetaceansrdquo Journal of Cetacean Research and Man-agement vol 3 no 2 pp 201ndash212 2001

[42] R Leaper and J Gordon ldquoApplication of photogrammetricmethods for locating and tracking cetacean movements at seardquoJournal of Cetacean Research and Management vol 3 no 2 pp131ndash141 2001

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


1250

750

1000

750

1000

750

1000

1500

1250

250

500

500

500

250

50

50

Kaikoura peninsula

N

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

Figure 1 Bathymetry of the study area and location of the shore-based station (pentagon)

problems with shore-based theodolite data is the increasingerror in positional fixes with increasing distance In order toimprove the accuracy of theodolite readingsWursig et al [18]summarized several of the necessary elements to organizea shore-based study Errors in the calculation of the stationelevation will bias the calculations of the animalrsquos positionTherefore the theodolite station height should be greater than45m and errors in the elevation calculation should be withinplusmn10 cm Thus far a better understanding of the calculationof the elevation has been the focus to improve theodoliteaccuracy [18 35]

Previous boat-based platform studies have assessed theaccuracy of distance measurements of animals at sea atclose range (0ndash2 km) using video cameras and binocularsGordon [36] compared the photogrammetric technique withlaser rangefinding binoculars and nondifferential GPS anddetermined that there was a good agreement for rangesmeasured between these three techniques Kinzey and Ger-rodette [37] identified the accuracy with which distances canbe measured from ships using the reticles in binoculars ata range of 0ndash8 km They determined that the accuracy ofdistance measurements decreased with the distance of theobject at sea [37] Concerning shore-based tracking Denardoet al [1] established and calibrated a shore-based technique tomeasure interanimal spacing using a theodolite and a videocamera over a 2 km range from the station

In this paper we compare positional information of thesame objects from two independent techniques a shore-based theodolite station and an onboard vessel GPS Byanalysing how the difference in the positions from bothtechniques relates to the distance of themeasured object fromthe shore-based station we build amodel to correct positionsestimated from theodolite measurements The objective ofthis study is mainly to describe a protocol that should beusedwhen tracking animals at sea from a shore-based station

This protocol will offer the possibility to easily correct thepositional error arising in such shore-based data

2 Method

The theodolite accuracy correction was developed for asperm whale (Physeter macrocephalus) habitat study withinthe Kaikoura submarine canyon in New Zealand The prox-imity of the Kaikoura submarine canyon to the coast of theSouth Island makes it one of the few places in the worldwhere male sperm whales are found close to the shoreline[38 39] offering the opportunity to track sperm whales fromshore A shore-based station was set up on a hill situatedat the east end of the Kaikoura peninsula (42∘25101584047 110158401015840 S173∘41101584054 610158401015840E) (Figure 1) at a height of 9988m (plusmn004m)above sea level (method described byWursig et al [18])Thislocation provided a good vantage point overlooking the studyarea encompassing the Kaikoura canyon and surroundingnearshore habitat

3 Data Collection

To determine the theodolitersquos accuracy we needed inde-pendently derived and accurate geographical positions ofthe same objects taken at the same time as recorded bythe shore-based theodolite station During our study tworesearch boats were operating inside our study area One ofthe research vessels was a 6m aluminium monohull usedfor behavioural and acoustic observation on sperm whalesThe second vessel was a 55m rigid-hull inflatable vessel usedfor a study on dusky dolphins (Lagenorhynchus obscurus)Both vessels were equipped with a GPS (accuracy within3m) and recorded the vesselrsquos position every 15 secondsFrom shore we collected the positions of these researchvessels using a Sokkia Set4000 theodolite (accuracy of anglemeasurement plusmn5

10158401015840

and measuring time less than 05 sec)For consistency we fixed the boat positions by placing thetheodolite crosshair at the waterline at the centre of thevessel We connected the theodolite to a laptop running thetracking program Pythagoras [19] The software transformedreal-time theodolite readings into GPS coordinates correctedfor curvature of the Earth and tide level and stored them foranalysis [19]

4 Results

During the study period we recorded a total of 347 theodolitefixes of research vessels (Table 1) The positions recordedwere between 2 km and up to 26 km from the theodolitestation (Table 1) and were distributed along the whole studyarea (Figure 2) For each research vessel position recordedwith the theodolite we extracted the time related positionrecorded with the vesselsrsquo onboard GPS

We compared vessel positions based on theodolite read-ings with the time-related positions extracted from thevesselsrsquo onboard GPS (Figure 3) Theodolite and GPS posi-tions appeared to be on the same line as seen from thetheodolite stationwhen viewing fromplan view (Figure 4(a))


0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(a)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

0 5 10

(km)

(b)

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(c)







tan(120579119867-GPS) =119910GPS119909GPS

tan(120579119867-TH) =119910TH119909TH




1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265

minus4270





positions2010

(119873 = 66)2011

(119873 = 137) 2012 (119873 = 144)








Δ119863 = 119863TH minus 119863GPS (1)







119894

(AIC) = AIC119894

minusminAIC)









120579H

(a)

h

120579VminusGPS

DGPS ΔD

(b)


5000 10000 15000 20000 25000

0

1000

2000

3000

4000

5000

6000


Erro

r in

dist

ance

(m)





1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265




Num

ber o

f mea

sure

men

ts

0

20

40

60

80

100




6 Discussion










7 Conclusion





Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(a)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

0 5 10

(km)

(b)

0 5 10

(km)

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

173∘50

9984000998400998400E173

∘40

9984000998400998400E173

∘30

9984000998400998400E

42∘209984000998400998400

S42∘309984000998400998400

S

42∘209984000998400998400

S42∘309984000998400998400

S

N

(c)







tan(120579119867-GPS) =119910GPS119909GPS

tan(120579119867-TH) =119910TH119909TH




1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265

minus4270





positions2010

(119873 = 66)2011

(119873 = 137) 2012 (119873 = 144)








Δ119863 = 119863TH minus 119863GPS (1)







119894

(AIC) = AIC119894

minusminAIC)









120579H

(a)

h

120579VminusGPS

DGPS ΔD

(b)


5000 10000 15000 20000 25000

0

1000

2000

3000

4000

5000

6000


Erro

r in

dist

ance

(m)





1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265




Num

ber o

f mea

sure

men

ts

0

20

40

60

80

100




6 Discussion










7 Conclusion





Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265

minus4270





positions2010

(119873 = 66)2011

(119873 = 137) 2012 (119873 = 144)








Δ119863 = 119863TH minus 119863GPS (1)







119894

(AIC) = AIC119894

minusminAIC)









120579H

(a)

h

120579VminusGPS

DGPS ΔD

(b)


5000 10000 15000 20000 25000

0

1000

2000

3000

4000

5000

6000


Erro

r in

dist

ance

(m)





1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265




Num

ber o

f mea

sure

men

ts

0

20

40

60

80

100




6 Discussion










7 Conclusion





Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


120579H

(a)

h

120579VminusGPS

DGPS ΔD

(b)


5000 10000 15000 20000 25000

0

1000

2000

3000

4000

5000

6000


Erro

r in

dist

ance

(m)





1735 1736 1737 1738 1739Longitude

Latit

ude

minus4245

minus4250

minus4255

minus4260

minus4265




Num

ber o

f mea

sure

men

ts

0

20

40

60

80

100




6 Discussion










7 Conclusion





Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



6 Discussion










7 Conclusion





Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Acknowledgments


References





















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology























Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Research Article Correcting Positional Errors in Shore ...downloads.hindawi.com/journals/jmb/2014/267917.pdf750 1000 750 1000 750 1000 1500 1250 250 500 500 500 250 50 50 Kaikoura