Deglint and investigate your image
 next to Extract calibration data

Activity: use LINE_2

Smoothed and Deglinted image

Extraction window
for a comparison -and some fun-,
these illustrations show raw_data inside a -E70/610/150/320 subwindow.
In order to produce the above image
  • First run the script as it is with  -Deglint/vRbaD/GlintM13
    • with a @E70/610/150/320 subwindow disabled
    • so that the whole image is deglinted (backdrop)
  • Then run the script with
    • with  -Deglint/vRbaD/GlintM0.0 
      • so that no deglinting is performed at all: GlintMax=0
    • with  -E70/610/150/320 subwindow enabled,  

Image result for tarawa mudflat
Near Infra Red and Linearity
  • This Tarawa_XS image is the best image I know which demonstrates clearly,
  • This is because of the extremely gently sloping of the sea bottom
    • over a very clean, fine-grained and very bright carbonate mud:
    • please google tarawa mud flat.
  • Just 15 cm of water is enough to attenuate the BOA NIR radiance 
    • to about half its reference value at null depth:
    •  200/exp(2K*Z)=200/exp(4.5*0.15)=101
  • Claims that shallow water optics -as rendered through radiance measurements in remote sensing imagery- might not be used for water column correction get severely beaten!
    • we shall see for ourselves that everything looks very much linear indeed after "linearization".
    • therefore multiple reflection, inelastic scattering   -and the like-   do not appear to scramble things beyond reasonable for our operational application: the simplified RTE seems to be applicable.

Activity : use LINE_3
  • Run profile_1
    • to investigate further on specifying spectral Lsw

LINE 3: Run the Profiler
Run a profile
  • please append a copy of #LINE_3 into your script
  • then: follow the instructions

  How to use the glint regressions to choose spectral Lsw 
A windy scene
Deglinting may not generate radiances Ls<La!
  profile_1           profile_2
  • Over open waters: the water surface exhibits strong wind/swell-modulated sea-surface glint
  • Inside the lagoon: the water surface is not affected by swell/wave-modulated glint
  • Cloud shadow: from South to North, the profile runs through cloud shadows at km 5 and 16
    • LswNIR was estimated ~=6.5 under the cloud shadow
    • but we know that the radiance of darkest shadow is at 6
    • this is the path radiance LaNIR

try with -smooth/5/Smart+


try with -smooth/5/Smart+
  • Note the 8-bits quantization noise
  • See at km 13 that radiances under the cloud shadow are too low in all three bands
  • Lsw values must be decreased:
  • Change for -dLsw000/0000/0-1.0
  • By application of  
    • -dLsw000/0000/0-1.0
  • Lsw is now adjusted to
    • Lswgreen=25.9
    • Lswred=13.9
    • LswNIR=5.5
  • ?After deglinting, all three bands now exhibit approx atmospheric path  radiance even over the darkest shadow

From now on:              -dLsw/000/000/-1.0
back to Tarawa tutorial      
back to Prepare  your image

next to Deglint page 3


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