Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
Four Landsat ETM 4-bands images of Andros, Bahamas

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



This work was done in 4 hours, including the preparation of this web page

True color composite of raw data

this image exhibits extensive greennish areas
which are likely to be dense seagrass beds


False color composite of raw data




Computed depth
most of this image exhibits
bottom detection in the red band

Bottom brightness

Lots of vegetation

Water column corrected image :  a "low tide view"


OII water type
Note the bad saturation in the blue band

Fairly good, hey!






Obviously, the upper profile requires
some alteration of calibration

in order to increase depths computed
by the two-bands case
in the eastern half of the image:

seagrass is greener there

==> -Z/MSL0.00/n_1/RLBgb1.300_0.500/Mask_3

Z and spectral bottom reflectance
along profile_purple

Location pf profile_purple

The water column corrected image
probably depicts the variations
of seagrass cover density


nice -20  4SM.4.08  -Process  -Origin/BILKO   
-B/tclNe/Bmin0/cLM1 .6 0.88 .60           
-Model /mask_3               
@-E1/7764/1/7096    -E4300/7764/800/6000_Mask_3               
@-DN300/100/3/comment  @-DD550/125/4/comment