Syntax_LsM
Specify the Maximum Shallow Water Radiance at null depth

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1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
 
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
 
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
 
So
I keep digging
until suitable data
become available
 

 

How to Choose LsM

  • -LsM/188.7/177.2/164.1
  • Spectral LsM is intended to sit as the intersection of the Brightest Pixels Line and the Soil Line.
    • this choice is not very sensitive
  • LsM is adjusted so as to obtain a satisfactory fit of depths computed for BPL pixels in the calibration diagram: see big star on tarawa-subset_calibration_1_CP
    • LsM and CP are adjusted manually in order to obtain a satisfactory fit
  • CoefLM : this spectral LsM value may be altered using the CoefLM parameter in the -B argument
    • a value higher or lower than 1.0 is used to slide spectral LsM up or down the observed Soil Line
    • this does not affect the computed depth, while it widens or narrows the range of computed bottom reflectances (one more priviledge of a ratio method)