Bathymetry and water column correction
LANDSAT 8 OLIP 
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
 
So
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  


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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