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Multi-Sensor Hydrographic LiDAR Operations

Multi-Sensor Hydrographic LiDAR Operations. Mark Sinclair – Tenix LADS Dushan Arumugam – BLOM Aerofilms (Carl-Johan Stigermark BLOM Aerofilms) Sean Cullen – Geological Survey of Ireland (Fergal McGrath – Marine Institute).

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Multi-Sensor Hydrographic LiDAR Operations

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  1. Multi-Sensor Hydrographic LiDAR Operations Mark Sinclair – Tenix LADS Dushan Arumugam – BLOM Aerofilms (Carl-Johan Stigermark BLOM Aerofilms) Sean Cullen – Geological Survey of Ireland (Fergal McGrath – Marine Institute)

  2. INtegrated Mapping FOr the sustainable development of Ireland’s MArine Resource (INFOMAR) Program • Successor to Continental Shelf Delineation project 1995 – 1996 and Irish National Seabed Survey (INSS) 1999 – 2005 which mapped all Irish designated waters > 200 m deep and collected bathymetric, magnetic, gravity and ancillary datasets to support a range of activities and research • INSS also included ground truthing to acquire seabed samples, video transects and photographic evidence • In 2002, INSS included an initial trial airborne laser survey in Clew Bay

  3. INFOMAR Program • INFOMAR program commenced in 2006 • priority to inshore areas • Joint management by Irish Marine Institute and Geological Survey of Ireland (GSI) • Program to collect, integrate and supply data to support a number of value added products and projects, including nautical charting, habitat mapping, infrastructure support and research • 20 year initiative, with first 10 years to map 26 priority bays and 3 offshore areas • In the initial 3 years a multi-platform mapping strategy has been adopted using vessels offshore and lidar in inshore areas and over the shoreline

  4. INFOMAR 2008 LiDAR project • Areas surveyed included Donegal, N side Galway Bay, NW coast Aran Islands, Tralee Bay, Sligo Bays, Blacksod Bay and Lough Foyle • Nature of areas: • Donegal and Sligo bays, shallow and mostly intertidal • Galway bay, shallow sandy inter-tidal bay with moderate turbidity & west of Galway, steep-to rocky coastal area with kelp • Aran I and Blacksod Bay, sand and rock • Tralee Bay, sandy inter-tidal bay with extensive high ground close south • Lough Foyle, highly turbid bay on international border between Northern Ireland (UK) and Republic of Ireland

  5. Strategy for LiDAR survey • Multi-sensor approach using 2 complementary LiDAR systems • In general, areas were allocated to each sensor as follows: • Hawk Eye 2 (BLOM Aerofilms) to survey shallow inter-tidal areas and small rocky bays • LADS Mk II (Tenix LADS) to survey larger coastal areas where the water was deeper and areas in vicinity of high ground. Shallow inter-tidal bays with turbidity were also surveyed.

  6. General GSI Requirements • IHO order 1 position and depth accuracy • Depths to 20 meters (minimum of 10 meters) • 5x5 meters laser spot spacing • Caris readable data • Data to Malin Head datum in ASCII format (CZM) and to LAT datum in CARIS readable format (navigation / charting) • Data to ellipsoidal datum for checking new separation models • Seabed reflectivity data for interpretation of bottom-type

  7. Hawk Eye – survey areas • Data capture in 3 areas • Donegal Bay • Sligo Bays • Greatmans & Cashla Bays (west of Galway) • Data captured from coastline down to the 10m contour

  8. Hawk Eye – system description

  9. Hawk Eye – calibrations • Factory Calibrations • Laser alignment • Pixel range calibration • Absolute range calibration Hydro Laser Pixels Topo Laser Pixels

  10. Hawk Eye – calibrations • Field Calibrations • Pitch, Roll and Heading • Absolute range in water and on land • Terramatch • Identify Heading, Roll and Pitch misalignments • Apply corrections to point cloud

  11. Hawk Eye – verification • Sea Control Areas (SCA) • 2 SCAs at each area • Singlebeam echo-sounder survey • 30mx30m area • Ground Control Areas (GCA) • 2 GCAs at each area • PPK Survey • 10mx10m area

  12. Hawk Eye – data collection

  13. Hawk Eye – data processing • Applanix POSPac • Process trajectories • AHAB Coastal Survey Studio (CSS) • Bottom detection algorithm processing • Export point clouds to TerraScan cleaning software run on Microstation • TerraSolid (extension for MicroStation) • Data cleaning and output CARIS • Orthophoto production • CARIS • Creation of final data products

  14. Hawk Eye – datums • Data was initially processed on the ellipsoid and then transformed to Malin Head datum and LAT • Ellipsoid to orthometric height using OSGM02 geoid model • Orthometric height to Malin head using a static offset at each bay (0.13m – 0.17m) • Orthometric height to LAT using a static offset at each bay (2.09m – 2.68m) • The static offsets were determined for each bay using tidal benchmarks and tide gauge data

  15. Hawk Eye – Donegal coverage

  16. Hawk Eye – Sligo coverage

  17. Hawk Eye – Greatmans coverage

  18. LADS – survey areas • Data capture in 3 areas: • Galway Bay (N side) including Aran Islands • Tralee Bay – operations near high ground • Blacksod Bay • Data was captured from coastline down to the 10 - 20m contour (depending on water clarity in respective areas)

  19. LADS – additional survey area • INFOMAR also engaged other stakeholders for a potential survey of Lough Foyle. • GSI, Marine Institute, Loughs Agency, Port of Londonderry, Environment NI and AFBI (Department of Agriculture) are relevant agencies • Lough Foyle is an environmentally sensitive marine habitat in a cross border region • Survey was extended to include this area • Turbidity management in this area was crucial

  20. LADS – data collection • Data collected relative to the instantaneous mean sea surface • Data reduced to LAT and Malin Head datums through tide models using observed tides • Variable height capability important in managing low cloud and high ground, particularly on the south side of Tralee Bay • Flexibility to move between areas significantly separated

  21. LADS – calibrations • Static and dynamic position checks and checks over known features were conducted • Benchmarks used for depth checking – common SCAs used in areas where both systems operated • Cross line comparisons • Analysis of overlapping data in common survey areas

  22. LADS – operations • Operations based primarily on managing water clarity in the most turbid areas • When conditions unsuitable, diverted to alternative areas • Management of water clarity significantly impacted by flood / ebb and spring / neap tides • Wind strength and direction also significantly impacted selection of survey area • Cloud height and the vicinity of high terrain also had to be considered

  23. LADS – survey life cycle including data processing • Data processing during field operations to keep up to date • Pre-validation to progressively appraise quality of data collected and identify where additional data is needed • Detailed validation and checking in depot following field operations • Approval of data by IHO cat A surveyor following quality control

  24. LADS – coverage • Galway Bay and N coast

  25. LADS – coverage • Aran Islands – west of Galway Bay

  26. LADS – coverage • Tralee Bay

  27. LADS – coverage • Blacksod Bay

  28. LADS – coverage • Lough Foyle

  29. Integration - datums • Typically Malin Head datum is determined at tide gauge sites. • LAT values are defined by software PolPred for each survey area relative to Malin Head datum • An important challenge for this survey has been the integration of data from an both an ellipsoidal datum (ETRF89 / GRS80)and geoidal datums (Malin Head / LAT) • This has been complicated by weaknesses in geoid / ellipsoid separation models in the survey areas on the west coast of Ireland • New software provides a model for this (VORF), but it has not been extensively verified

  30. Integration – datums / formats • Malin Head datum in ASCII format • LAT datum in Caris readable format • Ellipsoidal datum – customer requested fields for ETRF89 / GRS80to be added to ASCII format records • Hawk Eye 2 ASCII Data Format • One file for each survey run • One record per sounding • Space separated fields for: • Latitude • Longitude • Depth • Easting • Northing

  31. Integration - formats • LADS in CARIS Export Format (CAF), readable by CARIS and Fledermaus: One ASCII file for each area containing: • Survey summary data • Area Bounds • Spheroid • UTM zone etc • For each sounding • Sounding ID (run, frame, scan, sounding numbers) • Latitude • Longitude • Depth • Easting • Northing • Possible contending depth and positions

  32. Integration - formats • ASPRS (The American Society for Photogrammetry and Remote Sensing) LAS Version 1.1 One binary file for each line containing: • Public header block • System Information • Total number of records • Min / max values • Variable length records • Developer defined (Project Info etc) • Point data • XYZi • Return number • Number of returns • Scan information • Classification (e.g. Ground, Low / Medium / High Vegetation, Buildings, Water)

  33. Integration - checks • Comparisons between datasets • Datasets available for each area: • Seabed and Ground Control Areas (SCAs & GCAs) • Hawk Eye 2 Lidar data • LADS MKII Lidar data • A “mean” 1m grid was created for all datasets • Artefacts excluded (eg cars over GCA) • Compared using CARIS Base Editor – Surface Difference functionality

  34. Integration - datums • Integration is still in progress and results are preliminary only Example of Hawk Eye 2 data against SCAs and GCAs in Sligo Bay

  35. Integrating data and products • Preliminary results from Greatmans / Cashla between LADS and SCAs and Hawk Eye 2 data

  36. Integrating data and products • QC • Area based reviews of each survey area conducted on ASCII data for both systems • Emphasis on: • Datums • Excessive noise spread due to artefacts e.g. turbidity • Data coverage • Anomalous soundings (large depth difference with respect to surroundings) • Primary tool used was QCTools (LADS proprietary software)

  37. Integrating data and products • QC (Cont) • Key functions: • Depth difference grids • Profiles • Tinned 3-D images • Tinned contours • 3-D Editor in Fledermaus and CARIS also used • Queries logged and forwarded to respective survey teams for comment / action

  38. Integrating data and products • Combined image of vicinity of Greatmans / Cashla (Hawk Eye) and Galway / Aran Islands (LADS)

  39. Comments on management of turbidity

  40. Overall comments on multi-sensor approach

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