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Illustration of the deglinting process
 
Cloud and its shadow  
Cloud and its shadow
at Caicos Bank
Inter-band correlation is very strong.
Glint and Cloud at Tarawa
  Glint and Cloud at Tarawa
part of the cloud has been added
to the scatter plot
 
Sea-surface glint,  
and haze that surrounds the cloud,  
seem to exhibit very similar correlation here,  
as they both mostly tell us  
about Mie scattering in the atmosphere. 
They both may be removed  
through the same "deglinting" process.
false color composite


deglinting at Tarawa
Sea-surface glint 
is fairly strong
in this wind-swept SPOT image  
Inter-band correlation is reasonable. 
Smoothing can greatly improve this correlation.
Deglinting at Tarawa removes
  • specular reflection at the sea surface : 
    • the sky glint from the sky dome
    • the sun glint from direct sun light
  • isolated lumps of haze, 
  • and the haze that surrounds the clouds





<== Here a rectangular window   has been left untouched 
in order to illustrate
the -E extraction window feature of 4SM.
Deglinting blandly transfers the noise 
from the NIR band into other bands!
Deglinting at Caicos Bank
  • Upper : modeling on raw data
    • note the presence of a faint lump of haze
    • and the corresponding artifact in the form of underestimated depth and bottom brightness
Deglinting at  Caicos Bank
  • Lower : modeling on deglinted data
    • see how deglinting has removed the haze (while its shadow is still there)
    • and the corresponding improvement in the final result
 
Deglinting at Lee Stocking Island, Bahamas (Ikonos)
  • CENTRAL     :  raw data
  • BACKDROP : smoothed-deglinted data
Deglinting  at MahoneBay,
Nova Scottia, Canada (CASI) 
  • Sunglint affect this area.
    • poor correlation between the Nir band ond other bands
    • deglinting based on the red bands over this fairly deep area.
  • Removing the sunglint also removes the skyglint.
  • The profile compares
    • RAW in blue
    • DEGLINTED in red
    • Smart-Smoothed in green
    • FINAL in black


Smart-Smoothing
preserves the edges
at MahoneBay, Nova Scottia, Canada (CASI) 
  • No sunglint here
  • Smart-Smoothing preserves the edges of the dark and shallower patch
  • The profile compares
    • RAW in blue
    • DEGLINTED in red
    • Smart-Smoothed in green
    • FINAL in black
 
Deglinting of a CASI mosaic  
at Gezirat Siyul Reef, Red Sea 


  
delimb_derow_deglint
This  image preparation is done
"on the fly" while modeling,
as 4SM reads the raw U8 or U16 data
and applies all the required improvements
on a pixel wise basis prior to modeling.
Radiometric improvements:
The Delimbing/Deglinting process
on a 512 pixels wide raw CASI flight line
    from bottom to top:
  • Raw data: the limb brightening is very obvious: it must be removed prior to geocoding of the image
  • Delimbed/Derowed: note that in spite of the derowing of individual rows, there remains groups of adjacent rows which are slightly brighter or darker: this shows how important for shallow water work that the imaging instrument  be optimally tuned
  • Delimbed/Derowed/Deglinted/Smart-smoothed
  • Delimbed/Derowed/Deglinted/NOT-smoothed: in spite of all efforts, there remains all sorts of noise features and also remnants of imperfect deglinting: therefore it is very important that the data be smoothed prior to modeling
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