Optical calibration, bathymetry, water column correction and bottom typing of shalClipperton Atoll, Francelow marine areas, using passive remote sensing imageries
Landsat 8 at Clipperton Atoll, France
 
 








Landsat January 19th 2020, 360*374 pixels, 15 m GSD

 
TOA TCC

 
BOA deglinted TCC
glint regressions

 
calibration Nir, Red, Green, Blue

 
calibration Red, Pan, green, blue

 
map of the ratio 100*Kblue/Kgreen

 
satellite derived bathymetry, in cm

 
BOA TCC of water column corrected radiances 
Ublue, Green, Blue RGB
 







Landsat December 2nd 2020
work done june 2021
 
Clipperton atoll
Deglinted/smoothed data: Red->Pan->Green->Blue->UltraBlue

 Blue waters in the ocean  
 Green waters inside the lagoon
Red, Pan, and Green bands glow, bur Blue and UltraBlue bands are depressed
 

The purpose of the LUT approach is, among other things, 
to account for such variations  of the optical properties of the shallow waters

 upon operating the water column correction, pixel-wise
With Coastal C5 water type, the central lagoon is most probably optically deep
Red glows slightly PAN glows strongly Green glows strongly Blue is depressed UBlue more depressed
         



 
  
TCC 
a neat and very small scene 

image size: 360*374, 15m GSD
  
Glint regressions based on SWIR
shows PAN vs SWIR

a good start: regressions are excellent
  
  
calibration NIR, Red, Green, Blue
full image, clear oceanic waters
K2/K3=0.65 related to Oceanic II water type

  
calibration Red, Pan, Green, Blue
full image, under satisfactory control

 
Map of the ratio Kblue/Kgreen
oR1

 

  
TCC BOA deglinted

 
SDB in cm
Relates reasonably well with existing bathymetric maps

 
TCC BOA WCC Ublue, Green, Blue RGB 
TCC of water column corrected radiances:
the ultimate goal



 



A 1371*1160 IKONOS 4 bands image of Clipperton atoll
Wavelengths at midresponse curve are 480, 551, 665 and 805 nm
Strong sky and sun glints. Clouds not masked. Confined fresh waters in the lagoon 
 Work done in 2000, updated in 2005, image courtesy of S.  Andrefouet


Raw image, BGR TCC
histeq enhancement


Raw image, full resolution
histeq enhancement


Deglinted image, BGR TCC
histeq enhancement
No smoothing over the deep ocean


Deglinted image, full resolution
histeq enhancement
No smoothing over the deep ocean


image_Z


image_B


image_LBS normalized


image_LBS
histeq enhancement

   

Blue vs Green
natural

Blue vs Green
linearized
   



Optical calibration
of outer slopes


Fairly straightforward, although 
2K[red]=0.38 at 665 nm is a physical nonsense,
therefore the range of computed depths is problematic
  • Wavelengths must be set so that all ratios Ki/Kj fit nicely the slopes observed in this calibration diagram
  • Kblue/Kgreen=0.762
  • Kblue/Kred and Kgreen/Kred are very easy to check
  • Quite likely WLgreen must be increased and WLred must be decreased

Optical calibration
inside the lagoon

Quite difficult, as the lagoon bottom substrates
would appear to be extremely dark

The following is adopted:
Jerlov water type Coastal 3+0.14
2Kblue~=0.54
2Kgreen~=0.38
Kblue/Kgreen~=1.42







 



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