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12th NIOHC, Colombo, 20-23 March 2012 1/30 Céline Roux
Satellite Bathymetry
12th NIOHC, Colombo, 20-23 March 2012 2/30 Céline Roux
SHOM nautical navigation canvas
Charting coral reefs before 1982
The Landsat Thematic Mapper breakthrough
SHOM’s « Spacechart » (from 1988 until today)
Latest improvements
12th NIOHC, Colombo, 20-23 March 2012 3/30 Céline Roux
Example of Ari atoll space chart produced in 2011
12th NIOHC, Colombo, 20-23 March 2012 4/30 Céline Roux
Satellite images
Orthoimages
Depths layers (0-5m, 5-10m…), Foreshore and Land Masks
Space chart
Ground Control Points
Geometric Processing
Bathymetric Processing
Edition
Production flow chart
Additional Info (place names,boundaries, existing surveys, Gebco…)
Ground Truth (Echosounder, Lidar)
12th NIOHC, Colombo, 20-23 March 2012 5/30 Céline Roux
The RapidEye constellation
5 identical satellites
Orbital altitude: 630 km in sun-synchronous orbit
12th NIOHC, Colombo, 20-23 March 2012 6/30 Céline Roux
RapidEye satellite
Ground sampling distance (nadir): 6.5mPixel size (orthorectified): 5mDynamic range: up to 12 bits (4096 levels, instead of SPOT’s 255 DN)5 spectral bandsSwath width: 77 kmImage up to 1 500 km longSpacecraft roll angle: +/- 25 degreesRevisit time: Daily off-nadir / 5.5 days at nadirImage capture capacity: 4 million km2/day2 billion km2 archived since launch in 2009
12th NIOHC, Colombo, 20-23 March 2012 7/30 Céline Roux
RapidEye coverage
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Initial attempt with Spot 5 Images
Tasking from 08/2010 to 01/2011
No image available within SHOM stringent specifications
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Ari Atoll – RapidEye images attempts
Several attempts made and rejected
12th NIOHC, Colombo, 20-23 March 2012 10/30 Céline Roux
Final images selection
2 images selected
06/02/201114/02/2011
12th NIOHC, Colombo, 20-23 March 2012 11/30 Céline Roux
Block Adjustment
Ground control points on
existing mosaic of aerial
images
12th NIOHC, Colombo, 20-23 March 2012 12/30 Céline Roux
Orthorectification
Processing of the 2 orthoimages:
Images projected in Mercator WGS
84 to meet mariners’ requirement
Pixel size = 5m
12th NIOHC, Colombo, 20-23 March 2012 13/30 Céline Roux
Perfect superimposition of
overlapping areas
Final Accuracy = 2 m
Overlaps check
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GLOSS tide gauges
12th NIOHC, Colombo, 20-23 March 2012 15/30 Céline Roux
Tidal range determination
http://easytide.ukho.gov.uk/EASYTIDE/EasyTide/SelectPort.aspx
<http://easytide.ukho.gov.uk/EASYTIDE/EasyTide/SelectPort.aspx>
Mixed tide – maximum tidal range: 1.2 metre
12th NIOHC, Colombo, 20-23 March 2012 16/30 Céline Roux
Field determination of chart datum
He Sounding datum:-95,570 m
Mean level of live reef face (after 38 measurements): - 95.37 m (σ = 0.057 m)
Sounding datum
Mean level of live reef faceTidal range
Benchmark (x,y,z)
HWS
LWS
Water level at time of check
HBenchmark above sounding datum
Hreef
HBenchmark above water level at time of check
20 cm
Ellipsoid
HBenchmark (ellipsoid height) He live reef face: - 95.370 m
12th NIOHC, Colombo, 20-23 March 2012 17/30 Céline Roux
ARI ~ Mahibadhoo observed tide
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Male (GLOSS)
ARI / M
ahibad
hoo(Project)
Tide-by-tide simultaneous comparison
22nd to 29th July 2010 – Heights in metres
12th NIOHC, Colombo, 20-23 March 2012 19/30 Céline Roux
Processing
Harmonizing Image radiometry same colour of deep water everywhere
Generating Land Mask and coastline RapidEye band 5 (NIR)
Generating Inter-tidal Mask RapidEye band 4 (RedEdge)
Computing the Bathymetric Model (depth contours):
Processing performed by applying thresholds to RapidEye band 2 (Green)
Transformation of image by using the Lyzenga algorithm (elimination of influence
of water column) : Z = A . ln(R-Rinf) + B, where Z: calculated depth, R: pixel value,
Rinf: deep water value
Model calibration by using precise sensors (Lidar or echosounders)
12th NIOHC, Colombo, 20-23 March 2012 20/30 Céline Roux
Threshold Contour determination
Threshold
Shoreline determination Inter‐tidal mask by Band4 threshold
Depth contour
Threshold
12th NIOHC, Colombo, 20-23 March 2012 21/30 Céline Roux
Depth Processing
5 layers:
Land
Inter-tidal
0-5 m
5-10 m
10-15 m
12th NIOHC, Colombo, 20-23 March 2012 22/30 Céline Roux
Resulting space charts
1/100 000 chart covering
Alifu & Rasdhoo atolls
1/50 000 chart of South Alifu
1/50 000 chart of North Alifu &
Rasdhoo
1/10 000 chart of Hangnaameedhoo
12th NIOHC, Colombo, 20-23 March 2012 23/30 Céline Roux
Cartographic overlayLatitude, longitude & UTM 43 N
Detailed chart legend
Compass rose & magnetic variation
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Conspicuous objects & topography
Using IHO publication 1 D
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Surface to be covered : 32 200 km²
Step 1: Choice of satellite
RapidEyedefinition = 5m1 pixel = 0.03 mm (for chart scale 1:175 000)
Step 2: Fieldwork
• GPSReference stations & control points (WGS 84) Reference : Betio/DORIS
• TideReference : Betio Tide GaugeTide by tide simultaneous comparison withtemporary tide gauges
Example of Admiralty chart BA700
12th NIOHC, Colombo, 20-23 March 2012 26/30 Céline Roux
Step 3: Production of a minimum cartographic base
• Geometric processing• Bathymetric processing• Overlaying additional information• Quality checks
Example of Ari atoll
Total production time = 7 months
Average cost per spacechart = 100 k€
Cost per km2 = 40 €(vs 1 000 € with other survey methods)
12th NIOHC, Colombo, 20-23 March 2012 27/30 Céline Roux
1- Main tanker route before piracy
2 - Diverted route used by tankers and bulk traffic in case of persistent piracy
3 - Route variant in case of stable or declining rates of piracy
in 2
012
Possible limit of piracy
Farthest attack to the south
Farthest attack to the
northFarthest
attack to the east
2
3
1
Spacecharts for the marine highways
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Spacecharts index
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Lakshadweep,Maldives and
the British Indian Ocean
Territory
2
77 km
0 200
600
800
1200
400
1000 1600 km
1400
Aldabra group
Geyzer & Zélée reefs
1
CosmoledoFarquhar
Coetivy
Amirantes
Agalega
St BrandonTromelin
Rodrigues
3
2
Available satellite images for the marine highways
12th NIOHC, Colombo, 20-23 March 2012 30/30 Céline Roux
Thank you for your attention.