Bathymetry and water column correction
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

scene LC80120442013202LGN00, July 21th 2013
Work done september 2016

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.
Smoothing applied

July 21rst 2013    vs   Jan 29th 2014
This is a test of the robustness of 4SM

ZR-0.50m - ZC
Jan 29th 2014 - July 21rst 2013
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
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

BOA TCC deglinted image

Deglinted TCC
  • Please note the distinct negative bopttom contrast  between waypoints 2 and 3 along Red Profile
  • With Laswir1 =Lswswir1 at ~10 under the cloud shadows, it is seen that the atmosphere in this scene exhibits a lot of aerosols
  • ?The atmospheric path radiance is set at 17 in the SWIR1 band: this is observed under could shadows, while the lowest sea-surface signal under sun illumination is 10 DNs stronger.
    • this must be accomodated in the optical calibration!
Deglinting of PURPLE and SWIR1 bands
  along Profile Red
  • Please note the pronounced and steady increase of the signal in the SWIR1 band from West to East: "deglinting"  removes it efficiently
  • The negative bottom contrast in the Purple band is quite pronounced between waypoints 2 and 3 along Red Profile

16U data are scaled to allow for comfortable screen display

Calibration diagram for the whole scene
for bands Blue, Green, Red and NIR
KBLUE/KGREEN=0.46 => Jerlov water type OIB+0.1


Calibration diagram for the whole scene
for bands Blue, PAN, Red, NIR


Ready for modeling

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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