Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
A 3294*3012 IKONOS 4 bands image of Dubai
 
 
Seatruth
Thanks to excellent seatruth provided by Sam Purkis, NCRI in January 2009,
which was kindly  converted into a 4x4 m DTM by FUGRO-NPA
I now can investigate further this adverse case.

 
Please refer to 
"Integration of Satellite Remote Sensing of Subtidal Habitats with Vessel-based Video Survey (Dubai, United Arab Emirates, Arabian Gulf", Bernhard Riegl, Ryan Moyer, Brian Walker, Serge Andrefouet
Presented at the 7th International Conference on Remote Sensing for Marine and Coastal Environments, Miami, Florida, 20-22 May 2002

   "An Ikonos satellite imagery scene was obtained for the area between Ras Ghantoot and Jebel Ali in the United Arab Emirates
(Emirate of Dubai) in July 2001, concentrating on coverage of the immediately
offshore marine area.
Ikonos imagery was delivered in two resolutions:
4m pixel resolution in the red (632-
698nm), green (506-595nm), blue (445-515nm) and near infrared bands (757-853nm),
and 1m pixel
resolution in the panchromatic band.
The actual ground sampling distance of the sensor is 3.2m to 4.8m,
which is resampled for a 4.0m map increment.
Only the RGB bands were used for classification of marine
bottom types."

"Multi-site evaluation of IKONOS data for classification of tropical coral reef environments"

 ANDREFOUET, Serge ; KRAMER, Philip et al Remote sensing of environment, 2003 vol. 88, no 1-2, pp 

"Corals in a non-reef setting in the Arabian Gulf (Dubai, UAE):
Fauna and community structure in response to recurring mass mortality
". Riegl, B. (1999). Coral Reefs, 18, 63 – 73.


 


 
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
 
 

Wavelengths at mid-response curve are 480, 551, 665 and 805 nm
but wavelengths are set to 480, 582, 640 and 805 nm for sake of consistency in optical calibration:
Quite a challenge: no optically deep water coverage and very strong adjacency effect

WARNING: not for beginners!

Given the amount of adjacency effect, the estimation of an operational path radiance is a real challenge!
29 July 2001 is mid-summer in Dubai:

  • photons aplenty
  • aerosols aplenty
  • water clarity, well, would have been more favorable in winter
  • glint: lucky, there is no sea-surface swell-modulated sun/sky glint to worry about