Bathymetry and water column correction
LANDSAT 8 OLIP 
at Lee Stocking Island, Bahamas
Image courtesy of the U.S. Geological Survey
7671*7841 30 m pixel size, UTM zone 18


 
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
see also using IKONOS at LSI
see also using WV2 at LSI
see also using HICO at LSI

home


 
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
 

scene LC80120442016131LGN00, May 10th 2016
Work done october 2016


Robustness
As I don't have seatruth data, apart from the above speaker_harris_fig_01.png,
I used results obtained on
lsiOLI_20140129 as a seatruth DTM
The result is astounding,
knowing that part of the fuzziness is caused by slight misregistration of the PAN band.
No smoothing applied

Regression
February 4th 2016    vs   Jan 29th 2014
This is a test of the robustness of 4SM

ZR-0.50m - ZC
February 4th 2016   -   Jan 29th 2014
Discrepancies
Three specific sources of discrepancies must be considered
  • Cloud shadows: they cause over-estimation of retrieved depths. I could not find a way to avoid it.
  • Misregistration: the 30 m re-sampled PAN band is misregistrated by one pixel in both row and line. This causes fuzziness, and overestimated depths on occasion.
  • Variation of water optical properties: they cause local over -or under- estimation of retrieved depth
Robustness
The results are much more robust than I expected!
I intend to produce
a Combined Depth raster
 out of all these results.




Data and Deglinting

TOA TCC: raw image
logaritmmic enhancement

BOA TCC deglinted image
logaritmmic enhancement
Discoloured waters
not whiting!
  • Clear atmosphere, strong glint
  • Radiance in the Red band is seen to be flat:
    • no bottom detection,
    • no sign of backscatter as woul cause a whiting
  • Radiance of the Green band is low, but remains above deep water radiance
    • bottom detection all through the discoloured area
    • except between waypoints A1 and A2
  • Deglinted radiance for the Coastal and Blue bands is seen to decrease well below deep water radiance:
    • this is the cause of the discolouration
    • negative bottom contratst



Calibration
16U data are scaled to allow for comfortable screen display
OPTIMIZED CALIBRATION

Calibration diagram for the whole scene
for bands Blue, Green, Red and NIR
OPTIMIZED CALIBRATION

Calibration diagram for the whole scene
for bands Coastal, PAN, Red and NIR




Ready for modeling
No Smoothing

BOA TCC: water column corrected
 

Retrieved depth
see legend

 



Bottom typing

SAM classified image
see legend for SAM

Average bottom brightness