Bathymetry and water column correction
a time series of 14
LANDSAT 8 OLIP   scenes 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

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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
 


download from Explorer-in-Nobeltec-TZ-2.png


I used the above image for fine-tuning the optical calibration:   speaker_harris_fig_01.png


   
Final combined depth result,
using 14 scenes 
GSD 30 m
all artifacts have disappeared (clouds, discoloured waters)
very fine details are preserved
No smoothing at all


Lesser & Mobley 2007 at LSI
Bathymetry, water optical properties, and benthic classification of coral reefs
using hyperspectral remote sensing imagery

 
see depth legend


 

Combined depth from 14 scenes
NO SMOOTHING AT ALL
Dunes

 
Lee Stocking Island







On March 21rst 2015, discoloured waters are flushed
away from the platform into the Tongue Of The Ocean


 
Discoloured waters in the Bahamas
I hypothesize that, 

under soft modern sedimentation, there is a giant karst system
and a fresh water lens which is subject to tidal pumping,
through a great number of dolines, sinkholes and fractures.
Black waters seep up here and there from below
and might even entertain some kind of transient blooms.
This is the cause of bad artifacts in 4SM results.

 
July 2013
 
SAM mapping
Robustness: RMSE=1.47 m 
September 2013 
A bad image remains a bad image
Robustness: RMSE=2.18 m
 
 
 
 
November 2013
Robustness: RMSE=0.85 m
Winter is the time of choice
reference image reference image January 2014
Reference image
 
 
October 2014
Bad image
Robustness: RMSE=1.29 m
November 2014
Black hole discoloured water
Robustness: RMSE=0.87 m
December 2014
Almost no discoloured waters
Vegetation is dormant

Robustness: RMSE=0.96 m
Very low tide

 
February 2015
Robustness: RMSE=1.53 m
March 2015 
Robustness: RMSE=0.93 m
August 2015
Extremely dense and variable atmosphere
Robustness: RMSE=2.14 m
BAD, DISCOLOURED
 
October 2015
Robustness: RMSE=1.07 m
February 2016
Winter time of choice
Thin homogeneous atmosphere
Homogeneous waters 
Very low tide RMSE=1.02 m
Best calibration
April 2016
Poor deglinting by NIR
Robustness RMSE=1.12 m
May 2016
Robustness RMSE=1.27 m
  Freeport December 2014
 Freeport South December 2014
Whitings cause artifacts
Ooid sands look pinkish  
 
Achieved the optimization of the calibration SAM results through the seasonal cycle appear to make sense Now ready for computing
a Combined Depth raster
for LSI scene
Collected good reflectance signatures for coral sand enmember  Streamlined the processing of Landsat 8 (or WV2) data