Bathymetry and water column correction
at Mulroy Bay, Ireland
Image courtesy of the U.S. Geological Survey
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

Work done july 2018
GSD 15 m

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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