Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries

A 824*1494 Landsat ETM 4 bands image of Davies Reef
Great Barrier Reef, Australia

4SM licensekey is 42 US$ for this image

Work updated in 2005

Wavelengths used are 477.6, 576.3 and 661.3 nm
Not easy, as there is absolutely no dryland at high tide :
average height of water is ~ 1 m above the reef crest

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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
 
So
I keep digging
until suitable data
become available
 

 


True color composite, raw data


True color composite, deglinted data

 


image Z

 


image B

 


image BSC


image LBS

Optical calibration

Not easy,
as there is absolutely no dryland at high tide
average height of water is ~ 1 m above the reef crest

Optical water type OIB+0.8

for wavelengths 477.6, 576.3 and 661.3 nm

Zoom window


True color composite, raw data

Zoom window


True color composite, deglinted dat


image


image Z
Smart-smoothing does a good job
at preserving the geomorphology


image LBS

 


image BSC

 


image WR


image WZ