A time series of Landsat 8 OLIP images
at Nosy Be, Madagascar

work done in may 2020 at 15 m GSD
Using the Panchromatic band for water column correction
to derive water depth and spectral bottom signature:

Landsat 8 OLIP bandset used for this work

Purple=1Blue=2Green=3PAN=4Red=5NIR=6 and SWIR1=7

   peer-reviewed and published in 2017    


Presentation of 4SM for the busy executive

Shallow water depth and bottom type from satellite image


  • Further to Lyzenga's and Stumpf's methods, most existing empirical methods still need the following and only deliver shallow water depths
    • atmospheric correction
    • conversion into units of reflectance
    • an existing depth sounding dataset that covers faithfully the whole ranges of bottom brightnesses and shallow depths
    • segmentation of shallow areas into several bottom brightness classes, irrespective of depth
    • specify a, b and c for each class: Z= aX + bY + C through multiple linear regressions
  • With 4SM, in order to get the same result,
    • no need for atmospheric correction
    • no need for calibration into units of reflectance
    • no need for any field data for calibration of the optical model
  • With 4SM, a water column corrected image is produced AS WELL AS the computed depth in meters
    • fully supervised, "on the fly",
    • starts by reading raw data,
    • ends up writing computed depth and water column corrected spectral  bottom signatures ready for bottom typing,
    • line after line, for a "same day" low cost comprehensive service
  • All that bounty
    • One single executable code, ~50000 lines compiled in C, in an opensource LINUX environment
    • well ahead of any field work
  • With 4SM, seatruth data is only needed to 
    • DTM : specify Htide and CoefZ in 
      • FinalZ = Htide+CoefZ*computedZ
    • Habitats : document and label the bottom types that have been mapped

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