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

Various illustrations of Computed Depth

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Remopte Sensing
can be quite useful
in inaccessible locations!!

   

Remote sensing
can be quite useful
for very large scale projects!

DTM at Caicos Bank, Bahamas

180 km accross

This "combines" computed depths obtained 16 SLCOFF ETM images:

  • clouds have "disappeared"

  • and no-data stripes as well

One band case
can be quite useful
in slightly murky waters

Computed depth
at Tarawa atoll
Kiribati, Central Pacific
SPOT XS image

 

Making this was only possible
because shallow bottoms
deeper than 3-5 m
are assumed to be
very bright bottoms.

This is a reasonable assumption,
as the bottom is known
to be littered
with coral/halimedas sand/mud.

Certain parts of the lagoon
obviously have foul waters:
this shows badly in this map,
like in the SE end of the lagoon.

 
 



 

Detail of the above map
 

  • The use of the NIR band can provide very fine bathymetric features
 
 

 

One band case 
can be quite useful 
in slightly murky waters


Computed depth
at Arcachon Inlet
France
SPOT XS image

 

 
Making this was only possible
because shallow bottoms
deeper than 3-5 m
are assumed to be
fairly bright sandy bottoms.

This is a reasonable assumption
in this highly dynamic environment.

 


 
 

LEFT : potential error on computed depth                      RIGHT : computed depth
Potential error, alias "uncertainty" can be mapped along with computed depth

Computed depth
at Caicos Bank
Bahamas
Landsat TM image

  • Right : computed depth in dm
  • Left : image of sensitivity on computed depth, in dm
This is a representation of the degree of uncertainty caused by the 8-bits quantization noise, i.e. by a +/- 0.5 DN uncertainty for all bands used.
   

4SM can process
all sorts of  
multispectral imageries



AAHIS at Kaneohe Bay
Oahu, Hawaii
work done in 1998

image courtesy of Eric HOCHBERG
 

   
CASI at Mahone Bay,
Nova Scottia, Canada


Shallow dark features
are mapped to shallow depth,
as expected here:


 

<==Upper left
BGR composite of raw data








<==Lower left
computed depths






Accounting for water volume reflectance is key to this achievement



 

  

TM at Geraldton, Western Australia





Bright bare sand dunes

stand a few meters
above a 
very dark
vegetated bottoms surrounding




Accounting for water volume reflectance is key to this achievement








 

   



Sand dunes at Prince Edward Island, Nova Scottia, Canada


Using Jerlov's data
to calibrate the diffuse attenuation coefficients 2K
 is a safe process in the St Laurent Estuary


Remember:
No field data
was used
for this calibration!

   

CASI at Gezirat Reef, Red Sea

 

<==watercolumn corrected





<==computed depth






 

 



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