Robin J. Beaman. School of Earth and Environmental Sciences, James Cook University, Cairns, Qld 4870, Australia.

Transcription

1 Robin J. Beaman School of Earth and Environmental Sciences, James Cook University, Cairns, Qld 4870, Australia. Seminar to SSSI Qld Hydrography Coping with Nature, Brisbane, QLD, Australia, 14 March

2 ... and found 2

3 Seminar outline AUV platform specifications Hydrographic surveying with AUVs Stereo image odometry Case study NE Myrmidon Reef Other data products Other AUV sensors 3

4 Flexible, mobile, high resolution data collection device Sensors include - Vision (stereo) - Sonar (multibeam, and fwd obstacle avoidance) - Doppler velocity log - Compass - Pressure - Water chemistry Mission time up to 12 hours 2 km AUV Sirius 4

5 AUV platform Vehicle Specifications Depth rating Size Mass Maximum Speed Batteries Propulsion 700 m 2.0 m(l) x 1.5 m(h) x 1.5 m(w) 200 kg 1.2 m/s 1.6 kwh Li-ion pack 3 x 150 W brushless DC thrusters Navigation Attitude/Heading Tilt (±0.5 o ), Compass (±2 o ) Depth Paroscientific pressure sensor, (0.01 %) Velocity RDI Navigator ADCP (1-2mm/s) Altitude RDI Navigator USBL TrackLink 1500 HA (0.2m range, 0.25 o ) GPS Ashtech A12 Optical Sensing Camera Proslica 12bit 1360 x 1024 CCD Lighting 2 x 200 Ws strobe Separation ~1 m between camera and light Acoustic Sensing Multibeam sonar Imaging sonar Obstacle Avoidance Other Sensors CT Fluorometer Communications RF Modem Acoustic Modem Imagenex Delta T Profiling Tritech Seaking lmagenex 852 Echo Sounder Seabird 37SBI Wetlab Ecopuck chlorophyll-a, CDOM, scattering (r) FreeWave TrackLink 5

6 Imagenix Delta T: 260 khz 120 beams 0.75 beam width 120 swath angle 2.49 kg 6

7 Hydrographic surveying with AUVs d (AUV depth) Water level W Sounding equipment Chart datum (cd) D cd D (sounding depths) D cd = D + d - W Seabed 7

8 Error sources in AUV hydrography AUV depth accuracy: Pressure sensor measurement accuracy Pressure to depth conversion Dynamic pressure field due to waves or swell Sounding depth accuracy: Sounding equipment measurement accuracy Ray-bending and the sensitivity to temporal and spatial variations in the SVP Transducer mounting alignment relative to AUV attitude sensor Depth reduction accuracy: Determination of water level relative to the desired datum Datum uncertainty AUV position accuracy: Position measurement accuracy Survey vessel attitude and installation accuracy in the case of USBL Performance of the integrated navigation system to enhance accuracy Sounding position accuracy: AUV attitude accuracy Transducer mounting alignment relative to AUV attitude sensor 8

9 Stereo image odometry Find features in left image Measure altitude and bound search for features in right image Estimate feature locations Check consistency with epipolar geometry Use DVL displacement to estimate motion to next pair. Find correspondences Confirm consistency using RANSAC Bundle adjustment to refine estimate 9

10 Simultaneous Localisation and Mapping 10

11 Case study: NE Myrmidon Reef GBR201107: July seagrass missions 5 reef missions AIMS/JCU/MCI/USyd NE Myrmidon Reef Thimble Shoal Helix Reef seagrass habitats 11

12 Caris HIPS and SIPS NE Myrmidon: 23 July x 10 min lines 30 m x 200 m 2 x dense boxes kn 12

13 Profile-view AUV depths sounding depths 3D-view 13

14 Profile-view sounding depths 3D-view 14

15 Subset Editor 15

16 Don t show rejected soundings 16

17 Show rejected soundings very little noise 17

18 Subset Editor 18

19 Coloured by lines 19

20 Coloured by depth roll/pitch/latency(?) issues geolocated points a few tens of cm apart in horizontal and vertical planes 20

21 influence of height above seafloor sandwaves slight artefact in overlap swell or wave influence 21

22 Other data products 22

23 Other data products georeferenced image mosiac with 3D relief 23

24 Bathymetry from stereo images 24

25 Other AUV sensors 25

26 Hydrographic surveying with AUVs Stable platform Low platform noise High-performance navigation and positioning solutions Possibility to operate below difficult water layers Increased mapping resolution Increased mapping efficiency (speed) compared to tow-fish and ROV Simultaneous recording of full geophysical sensor suite and oceanographic data Only solution for demanding applications, e.g. deep-water, under ice survey, naval 26

27 Acknowledgments Thomas Bridge, CoE Coral Reef Studies JCU John Guinotte, Marine Conservation Institute Stefan Williams, ACFR Uni of Sydney Rick Morton, Kongsberg Hydroid 27