Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
A 600*750 SPOT-1 XS+P image of Bora Bora Island, French Polynesia (1986)
Work done in 2007
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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
 
Please refer to Stephane Maritorena,
"Remote sensing of water attenuation in coral reefs: a case study in French Polynesia":
IJRS, vol 17, no 1, pp 155-166, 1996

This study case compares modeling without and with an additional Panchromatic waveband.

Using a panchromatic band where available should be profitable,
even with a 4 multispectral band like Ikonos, Formosat or Quickbird.

for another such comparison, see sanaa

The 10*10 m Panchromatic band has been decimated to a 20*20 m resolution,
and then added as channel 2 of the raw image: ch1=Green, ch2=Pan, ch3=Red, ch4=Nir .

 

 


Green, Red, NIR false color composite

 

Green, Pan, Red true color composite
Green, Pan, Red true color composite

 


Image_Z

 


Image_Z using the Pan channel

 


Image_B

 


Image_B using the Pan channel

 

Calibration using a Pan channel

  • 4 bands are used in this calibration:
    Green=XS1, Pan, Red=XS2, Nir=XS3

  • This diagram reveals bad saturation of the Green channel

  • Optical water type OIB+0.74 calibration is derived using the Green/Red pair of bands: very clear waters indeed!

  • Maximum penetration of the Pan channel is ~19 m over very bright bottom substrate in this image: this extends the maximum depth of the bathymetry from 6.6 m with the Green/Red pair to 19 m with the Green/Pan pair in these very clear waters.

  • The Green/Pan Brightest Pixels Line is a distinctly curved line

    • K[green], K[red] and K[nir] are constant with depth

    • K[pan] decreases markedly as depth increases.

   

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