Bathymetry and water column correction
at SanLorenzoChannel, Baja california
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

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
I keep digging
until suitable data
become available


The assumptions commonly used in operational shallow water modeling are the following.
  • Simplified RTE: shallow water modeling is only possible because the very complex radiative transfer equation of sun and sky light through atmosphere and water has been extensively simplified for sake of operationality.
  • Homogeneity: the optical properties of the atmosphere column and of the water column are assumed to be horizontally homogeneous.
  • Operational K: the various specific diffuse attenuation coefficients for downwelling and upwelling irradiances, Kup and Kdown, which compound into the depth-dependent diffuse attenuation coefficients for irradiance Kd are conveniently rounded up into an effective two-way diffuse attenuation coefficient for near-nadir radiances, denoted K, for sake of operationality.
  • Multiple scattering in the water column is neglected, as is multiple reflection at the water-air interface.
  • Dark target assumption: in 4SM, the radiance measured in the imagery at the longer wavelength available (possibly a NIR -or Red- band) over an optically deep water area is assumed to be representative of the radiance of the atmospheric path at that wavelength.
  • For all these reasons, bathymetry modeling is best conducted using images, or part of them, which exhibit a very high radiometric quality standard, and it should be considered a safe precaution that certain images or part of them may not be used for this specific purpose.