Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
CASI image of Gezirat Siyul Reef, Red Sea
Work updated in 2006

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Image courtesy of HDI . This is a 12 bands image, 2800 x 5900, pixel resolution 1 meter.

Bandset : -WL410/430/451/470/490/509/523/538/550/565/608/850 in nanometers

Unfortunately, this dataset lacks bands in the red and green region of the solar spectrum.

Glint parameters appear to change in a subtle way from start to end of data collection.
And the mosaic includes oblique viewing which fades out at some locations.

A very good dataset anyway: lots of photons!

see CASI presentation for U. of Hawai in year 2000 (6 MB)


1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
I keep digging
until suitable data
become available

bottom profile

bottom typing

Work below was done in 2000, then may 2008


Bottom typing: 32 types are mapped by 4SM
White: 4% of shallow pixels are UnClassified
review the statistics of bottom typing
see the location of training sites
see modal filtered image:

Bottom typing legend
Clearly, bottom types should be re-numbered
and possibly binned into less super bottom types

review How To Classify

before filtering

Bottom typing details

after filtering
see a slightly modal filtered image: WinRadMod=2
A wider filter window (
WinRadMod up to 5)
would wipe out many small coral growths


Calibration diagram

Optical calibration diagram
for the whole reef

for 490, 550, 608 and 850 nm

Water type is ~OIB+0.3 of Jerlov

Optical calibration diagram
for the whole reef

for 451, 565, 608 and 850 nm

Water type is ~OIB+0.3 of Jerlov

Optical calibration diagram
for the reef lagoon only

for 490, 550, 608 and 850 nm

Water type is the same
See that water depth is limited to ~10 m


   work below was done in nov 2006 

BGR color composite
of bands at 470, 550 and 608 nm

Left: raw, 16U data
Right: deglinted, not smoothed, 16U data
Zooms: at location shown

is absolutely necessary here.
Deglinting is quite efficient over shallower bottoms, but does not solve all problems over deeper bottoms!

Glint correlation decreases...

...for two bands farther apart