Sun glint removal


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The effect of sun glint may be reduced / removed by a special processing, which however leads to changes in spectral signatures. The basic requirement is that a band in the near-infrared region which is not affected by chlorophyll.

The basic idea can be described as follows:

1 The near-infrared radiance is practically totally absorbed in the water, thus the observed radiance can be considered to have an origin either as reflected from the surface or as scattered in the atmosphere.
2 The atmospherically scattered radiance is considered to be the lowest radiance value found under a water mask.
3 The proportion of the incoming radiation being reflected by surface is the calculated for each pixel as the observed pixel radiance minus the atmospherically scattered divided by the downwelling total radiance in the spectral band.
4 The surface reflectance is considered as being the same for all bands (a perfect mirror), and each band and pixel is now corrected by subtracting the proportion, found under 3., of the downwelling radiance from the observed radiance.



In the example found below an infrared band around 755 nm was used to determine the surface reflectance. The correction was done using the spectral distribution of the extra-terrestrial radiance although it must be considered to be more correct to use downwelling radiance measured at the surface.

 

Raw image Sunglint corrected
 

 


National
Environmental
Research
Institute

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This page was updated: 19. September 1999
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