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

home
 
 

scene LC80120442015224LGN00, August 12th 2015
Work done september 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
August 8th 2015    vs   Jan 29th 2014
This is a test of the robustness of 4SM

ZR+0.70m - ZC
Jan 29th 2014    -   August 8th 2015
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
very dense and variable atmosphere

BOA TCC deglinted image
logaritmmic enhancement

No discolouration in august 2016
Some vegetation beds are not to be confused
with areas of discoloured waters

Strong discolouration in august 2016
Bottom features are seen
through
discoloured waters

Strong discolouration in august 2016
Bottom features are seen
through
discoloured waters
Such discoloured waters
should exhibit the following optical properties:
  • Increased KCOASTAL and KBLUE 
    • with KCOASTAL~=KBLUE ,
    • i.e. ratio KCOASTAL/KBLUE ~=1 
  • Decreased LwCOASTAL   and LwBLUE
  •  



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

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

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

 




 



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