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
500*2000 HICO image of Bahrain, oct 21rst 2013
scene iss.2013294.1021.093734.L1B.Bahrain.v04.14946.20131021200925.100m.hico     courtesy of OSU
HICO: Hyperspectral Imager for the Coastal Ocean: GSD 100 m
work done march 2016  


Optical calibration

  • Calibration is outstanding
  • Kblue/Kbgreen=0.740
  • Kblue=0.130 m-1 , Kgreen=0.176 m-1
  • See that it is necessary to decrease markedly the operational attenuation coefficients in the Yellow-Red-NIR range
  • this is now recognised to be systematic, probably under control of the path radiance (overcast skies, here)
  • it is a remarkable feature of the diffuse underwater light field observed from above by a remote sensing imager
  • see HYPERION at Fakarava
  • 7=Blue
  • 13=Green
  • 22=Red
  • 28=NIR
  • X[7]/X[13]: the ratio Kblue/Kgreen is well secured at K7/K13=0.74 over the whole depth range
  • X[7]/X[22]=0.280 and X[13]/X[22]=0.378 are fairly secure
  • 280/378=0.741: this system is consistent
  • it actually is consistent over the whole visible range: this is remarkable
  • WL[7]=475 nm
  • WL[11]=522 nm
  • WL[20]=625 nm
  • Channel 27 is PANchromatic
  • X[7] vs X[27]: calibration of the PAN channel is under tight control