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Hydrographic Mapping by Combined Operations UsingBathymetric LIDAR and Multibeam Echosounder in Alaska

Dean Moyles, Andy Orthmann, Carol Lockhart

Fugro Pelagos, Inc. San Diego, CA

Jana DaSilva Lage

Fugro Pelagos, Inc. Anchorage, AK

ABSTRACT

During the 2004 field season, the National Oceanic and Atmospheric Administration awardedFugro Pelagos, Inc. (FPI) the first task order ever, to require simultaneously collected AirborneLIDAR Bathymetry (ALB) and ship based multibeam bathymetry. The survey area, in the vicinityof Sitka, Alaska, consisted of a single 20.7 NM2sheet containing a highly irregular shoreline withmany islets, rocks, foul areas, and kelp.

The primary objective of the survey was to provide data in support of nautical charting fornavigation safety in this intricate area of islands and drying reefs. To complete this complextask, FPI utilized different survey platforms to support the necessary equipment, which includedthe SHOALS-1000T ALB system, as well as the Reson 8101 and Reson 8111 multibeamsystems.

The SHOALS-1000T provides both bathymetric and topographic LIDAR mapping capabilities. Inaddition to the LIDAR bottom reflectivity, an integral part of the FPI ALB data acquisitionincludes geo-referenced digital ortho-photos, which are used to produce a detailed aerialmosaic of the survey area.

Nautical charting in the Sitka region of Alaska was successfully and economically completedusing integrated ALB and ship-based multibeam echosounding (MBES) operations. The use ofthese methods results in the fusion of airborne and acoustic data co-registered with high-resolution terrain mapping. Navigation safety and scientific information for this area aresignificantly enhanced by the high-resolution, 100% coverage of MBES plus 200% ALB dataover the shoal zones surrounding the numerous islets.

Introduction

Fugro Pelagos, Inc. (FPI), formerly Thales GeoSolutions (Pacific), Racal Pelagos, and Pelagos,has been performing contract hydrographic work in Alaska for the National Oceanic andAtmospheric Administration (NOAA) since 1998. The majority of this survey work has been

conducted with multibeam echosounders and has included areas of extreme tides (Cook Inlet:Richards et al, 1999) and remote areas with challenging navigation issues (Castle Bay and theKenai Fjords). However, FPIs extensive hydrographic experience under contract to NOAA alsoincludes the following work with subcontractors to collect hydrographic LIDAR data:

Semidi Islands, 2001, Tenix LADS

Pribilof Islands in the Bering Sea, 2002, US Army Corps of Engineers (USACE), usingthe Scanning Hydrographic Operational Airborne LIDAR Survey (SHOALS) system

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owned by the Joint Airborne LIDAR Bathymetry Technical Center of Expertise(JALBTCX)

During these surveys, the subcontractor was responsible for all LIDAR data collection andpreliminary data processing, including initial quality control. FPI managed the projects, providedfinal data processing, quality control, smooth sheet preparation and reporting. Additionally,

during a recent survey in the Shumagin Islands, FPI was tasked to compare their collectedmultibeam data with previously collected LIDAR data and to investigate and verify numerousLIDAR targets.

In 2004, FPI purchased an Optech SHOALS-1000T LIDAR system, which provides thecapability to perform a complete (shoreline and bathymetry) hydrographic survey. In fact, theproject described within this paper is the first NOAA contracted hydrographic survey toincorporate both hydrographic LIDAR and multibeam data collected by the same contractor.

Location

The survey limits encompass a 20.7NM2area in the vicinity of Sitka, Alaska, which is locatedin

the inland passage of Southeast Alaska (Figure 1). The area contained a highly irregularshoreline (Figure 2) with many rocks, foul areas, and kelp. The field staff worked out of Sitka, inan office leased from the local Native Corporation, providing a positive economic impact on thetown.

Figure 1. Sheet U Location

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Figur e 2. Aerial view of Sitka with the approximate survey area boundaries

Objectives

The primary objective of this Alaska survey was nautical charting for navigation safety in an

intricate area of islands and drying reefs. However, as this project was the first of its kind, thesecond objective was to fully integrate multiple survey platforms to provide the best dataavailable for nautical charting, and to illustrate the efficiency and benefits of performing such asurvey.

Methodology

All data were collected to meet or exceed the requirements set forth in the Statement of Workand the NOS Hydrographic Surveys Specifications and Deliverables March 2003 edition. Due tothe complexity of the area, this unique survey was completed in the following four phases usingdifferent survey platforms and equipment:

LIDAR Survey

A Beechcraft King Air 90 (Figure 3) was equipped with a SHOALS-1000T Bathymetric andTopographic LIDAR System, to collect data in the land / sea interface areas from 15m waterdepth (WD) up to and including the shoreline. As with the two previously collected LIDAR datasets mentioned above, the SHOALS-1000T LIDAR system was flown over NOAAs Shilsholetesting area in Seattle for system verification. A review of the data from this test showed it to bewell within NOAA hydrographic survey standards (See Millar et al, 2005). Following this, thesystem was deployed to Sitka to survey in conjunction with our multibeam vessels.

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Figur e 3. The SHOALS-1000T survey platform, a Beechcraft King Air 90, at the Sitka airport with MountEdgecumbe in the background

The 1 kHz bathymetric laser (or hydro laser) was used to collect data over the entire surveyarea. The laser was operated to achieve 4m x 4m spot spacing flying near 400m altitude atapproximately 160 knots. The survey lines were planned with 20% overlap and flown two times,once at MLW and once at MHW, in opposing directions to achieve 200% coverage.

The topographic data were also collected using the 1 kHz bathymetric laser operated to achieve4m x 4m spot spacing flying at the above specifications. The survey lines were planned with20% overlap and flown two times in opposing directions to achieve 200% coverage.

In addition to collecting LIDAR data, a DuncanTech DT4000 digital camera was also used toacquire one 24-bit color photo per second. The camera, mounted in a bracket at the rear of thesensor, captured imagery of the area being flown; these photos can be used during post-processing.

Flight planning, data processing and editing, quality control, and data export were conducted in

the SHOALS Ground Control System. CARIS was contracted to write a converter to bringSHOALS-1000T data and waveforms into CARIS HIPS for quality control; this also allowed theLIDAR data to be effectively merged with the multibeam data for production of smooth sheets.As with the converters that FPI had written for the two older systems, this CARIS converter willbe provided to NOAA to enable meaningful quality review of SHOALS-1000T data.

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Near Shore Survey

The near shore data, up to 100m water depths, were collected from the R/V Quicksilver(Figure 4). The R/V Quicksilver, which is 32 feet in length with a draft of 3 feet, was equippedwith a hull-mounted Reson SeaBat 8101 multibeam system with option 033 (pseudo SideScan).The Reson 8101 system operates at a frequency of 240 kHz with 101 horizontal beams

centered 1.5 apart (150 across-track beam width) and 1.5 along-track beam width. Ittransmits and receives a sonar signal to measure the relative water depth over the 150 swath.The range scale, gain, power level, ping rates, etc. were a function of water depth and dataquality. The vessel was also equipped with two AML sound velocity and pressure sensors forsound velocity profiles. Vessel attitude and position were measured using an Applanix Positionand Orientation System for Marine Vessel (POS/MV) with XTF files logged in ISIS V 6.24.

The line orientation for the Quicksilver was generally parallel to the coastline and bathymetriccontours in the area. The line spacing depended on the water depth and data quality, but neverexceeded three times the water depth.

Figur e 4. Survey vessel R/V Quicksilver

Offshore Survey

The deeper offshore data were collected from the R/V Kvichak Surveyor I, a catamaranspecifically modified for hydrographic survey operations (Figure 5). The Kvichak Surveyor I, 67feet in length with a draft of 5.5 feet, was equipped with a pole mounted Reason 8111 (Figure 6)with option 033 (pseudo SideScan). The Reson 8111 system operates at a frequency of 100kHz with 101 horizontal beams centered 1.5 apart (150 across-track beam width) and 1.5along-track beam width. It transmits and receives a sonar signal to measure the relative waterdepth over the 150 swath. The range scale, gain, power level, ping rates, etc. were a functionof water depth and data quality. Two AML sound velocity and pressure sensors were used forsound velocity profiles. Vessel attitude and position were measured using an Applanix Positionand Orientation System for Marine Vessel (POS/MV) with XTF files logged in ISIS V 6.24.

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The line orientation for the Kvichak Surveyor I was generally parallel to the bathymetric contoursin the area. The line spacing depended on the water depth and data quality, but never exceededthree times the water depth.

Figur e 5. Survey vessel R/V Kvichak Surveyor I at the dock in Sitka

Figur e 6. Reson 8111 on pole mount on R/V Kvichak Surveyor I

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Investigations and Shoreline Verifications

All LIDAR investigations and shoreline verifications (Figure 7) were completed with the 15-footskiff, referred to as the DP skiff, which has a draft of a half foot. The DP skiff could generallysafely navigate in any area where it could maintain 0.5 meters of under-keel clearance, exceptin locations of heavy swells near shore. The skiff was equipped with a CSI GBX-PRO DGPS

receiver, WinFrog v3.4.0 data acquisition system (operated on a Panasonic laptop) and a Sonydigital camera. In addition, the NOAA charts were displayed as a layer in WinFrog for reference.The DP skiff was outfitted with a Hummingbird Piranha Max15 fish finding sounder, to assist thehydrographer in location of targets near the surf zone or areas of limited visibility. However, allsoundings on submerged features were conducted with a lead line.

Figur e 7. Rocky coastal area investigated during skiff operations

Software Developments

During the course of hydrographic surveying for NOAA, FPI has developed the followingsoftware devices to enhance the quality of hydrographic data collection and processing; these

systems were employed for this study:

The Shoreline Correlator add-on in ArcMap v8.2 (now v9.0) was created to aid in theprocessing of the Shoreline Verification results. It is an integrated system that creates anindividual Detached Position (DP) form, which includes the data log, tide, photos, NOAAchart (largest scale available), T-sheet data, smooth sheet soundings, multibeamcoverage files and now photo-mosaics from the LIDAR system (see results section).

Pelagos Precise Timing was developed as a new timing scheme; it allows data to be timestamped when it is created, not when it is logged (i.e. to XTF). It uses a single clock /

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epoch (POS/MV UTC Epoch) to time stamp all data. This new scheme was a precursor toTrue Heave technology, which FPI developed with the assistance of Applanix, Caris, andTriton Elics. There are numerous benefits to using the Precise Timing and True Heavesuch as reducing timing errors, facility in diagnosing mechanically induced artifacts,increasing operational weather window, reducing heave component in error budget,shorter turn times, line changes, and easier shoreline surveys.

Building upon the Pelagos Precise Timing development, FPI collected dual frequency POSGPS data during 2004. This new technology was implemented in POS Pac, CARIS, andISIS. The dual frequency GPS data were post-processed for both the LIDAR andmultibeam system and are being evaluated as a tool for enhancing or replacing the needfor installing multiple tide gauges in remote locations (Lockhart et al, 2005).

Results

The ability to view the photos taken by the system during data editing is an enormous qualitycontrol and efficiency advantage over the previous LIDAR systems (Figure 8).

Figur e 8. Photo taken during LIDAR operations helped delineate areas of rock and kelp

While the individual digital photographs are extremely useful to the hydrographer, thecombination of the photos to create a digital ortho-photo mosaic is an incredible breakthrough inQuality Control during data post-processing. The ortho-photo mosaics have aided in shorelinedelineation where the shoreline was unclear on the LIDAR data due to an overhanging tree lineor wash. Both the Mean High Water and Mean Low Water lines were precisely defined duringthis survey. The following images illustrate various scales available with the ortho-photo mosaicand an example of the photo mosaic draped over the DTM (Figures 9-14).

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Figur e 9. Ortho-photo mosaic in the vicinity of Belknap Island and Mertz Island, superimposed overNOAA chart no. 17327

Figure 10. Ortho-photo mosaic showing Belknap Island and vicinity, superimposed over NOAA chart no.17327

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Figure 11. Ortho-photo mosaic in the vicinity of Belknap Island with visible kelp beds, rocks, and small

islets, superimposed over NOAA chart no. 17327

Figure 12. Ortho-photo mosaic showing Mertz Island, superimposed over NOAA chart no. 17327

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Another benefit of the ortho-photo mosaic is the ability to derive cultural or man-made featuressuch as houses and docks.

Figure 13. Ortho-photo mosaic in the vicinity of Mertz Island, superimposed over NOAA chart no. 17327.

In this photo mosaic, it is easy to see houses with docks and other structures.

Figure 14. Ortho-photo mosaic drape over DTM in the vicinity of Mertz Island

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During this project, the ortho-photos were also incorporated into the Shoreline Correlator add-on

in ArcMap v9.0 developed and modified by the Fugro Pelagos GIS Department (Figure

15). Thistool allows the hydrographer to perform Quality Control on all detached positions (DP) collectedduring the survey. The software was developed during surveys in the Northern Clarence Straitarea where FPI recorded 880 DPs and 190 Dangers to Navigation. While not every survey

needs to use this tool, it proved useful during the Sitka survey where the field crew documented256 DPs and reported 55 Dangers to Navigation.

Figure 15. Example of a DP sheet from the Sitka project

It takes many steps to produce a smooth sheet that meets NOAAs quality standards. FPI

recognizes the quality and precision necessary to provide deliverables that meet or exceedNOAAs specifications. During this survey, FPI took the following steps to provide NOAA withthe best available hydrographic data from a combined multibeam / LIDAR survey:

Collected high quality data using the proper tools for such a complex area: a SHOALS-1000T ALB, Reson 8101, Reson 8111, and leadline for shallow investigations

Utilized technology advancements: previously developed - Pelagos Precise Timing;modified - Shoreline Correlator tool; and newly developed - dual frequency POS GPSdata and ortho-photo mosaics

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Post-processed the data using all the tools available, from the Shoreline Correlator tothe ortho-photo mosaic, to produce the first seamless hydrographic survey incorporatingmultibeam bathymetry and ALB data (Figure 16).

Figure 16. Sheet U sun-illuminated image of combined multibeam and ALB data over a nautical chart

Conclusions

FPI has successfully completed the first ever multibeam / ALB survey contracted by NOAA.Employment of the LIDAR in conjunction with multibeam on a NOAA charting project is aconsiderable milestone for FPI and the future of charting. FPI will deliver a seamless data set

from the shoreline to depth in the time it takes to complete a survey incorporating onlymultibeam data. Performing a combined survey decreases the time needed to update the chartby a year. Previous LIDAR surveys have been collected during one field season, andinvestigated during a multibeam survey the subsequent season, resulting in two years of datacollection prior to final completion of a survey area.

FPI, as a leader in surveying and mapping, continually strives to improve data collection andprocessing, and willingly shares breakthrough developments with the hydrographic communityto better the field as a whole. This is another example of FPIs industry-leading position in

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hydrographic surveying. FPI sees combined multibeam and bathymetric LIDAR operations asthe way of the future in hydrographic surveying. The combined survey results in a faster turn-around time for updating the nautical chart and thus decreasing the survey backlog.

References

Lockhart, D., Lockhart, C. Orthmann, A., and Arumugam, D., 2005. MLLW and the NAD83Ellipsoid: An Investigation of Local Offsets and Trends Using PPK and Gauge Derive WaterSurfaces. Proceedings of the U.S. Hydrographic Conference.

Millar, D., Lockhart, C., and Arumugam, D., 2005. Meeting Hydrographic Charting Specificationswith the SHOALS-1000T Airborne LIDAR Bathymeter. Proceedings of the U.S. HydrographicConference.

NOAA, 2003, NOS Hydrographic Surveys Specifications and Deliverables:http://chartmaker.ncd.noaa.gov/hsd/specs/specs.htm.

Richards Jr., R.J., Lockhart, D., and Oswald J. 1999. Tidal Zoning of Upper Cook Inlet, Alaska

in support of NOAA Nautical Charting Program. Proceeding of the U.S. HydrographicConference.