Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
Bathymetry and water column correction
LANDSAT 8 OLIP 
at Caicos Bank, Bahamas
4018*4149, 30 m pixel size, UTM zone 18, downloaded from USGS
Image courtesy of the U.S. Geological Survey
 
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

Please refer to Bora Bora and Sanaa
for use of the PANchromatic band for water column correction


 
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 LC80090452014312LGN00, Nov 8th  2014
This is autumn time in the Bahamas
Work done july 2016

home





DTM SeaTruth RMSE=0.59 m
   
Z4SM vs ZDTM
tide correction applied: 1.7m
RMSE=0.59 m

 

ZDTM-Z4SM
tide correction applied: 1.7m

see legend




Data and Deglinting

TOA TCC: raw image
logaritmic enhancement

TOA TCC deglinted image
same logaritmic enhancement

 




Optical calibration, optimized
16U data are scaled to allow for comfortable screen display

Calibration diagram under mask_3
for bands Blue, Green, Red and NIR
KBLUE/KGREEN=0.55 => Jerlov water type OIB+0.54

This calibration is fairly secure,
but results shall show that
bottoms are green and dark everywhere.

Calibration diagram under mask_3
for bands Coastal, Blue, Green, and PAN

[X1 & 2] vs [X3]
This plot justifies that
KCOASTAL   must be significantly reduced
from  K1=0.115 m-1  to   K1=0.096 m-1  
This is done through the -CP... argument

 
Reflectance (0-1)
of the path radiance Ra for this scene
0.106 0.079 0.045 0.038 0.024 0.009 0.001 

 
Reflectance (0-1)
of the water volume Rw for this scene
0.022 0.019 0.003 0.002 0.0 0.0 0.0

 



Now ready for Modeling
No smoothing applied
PAN solution applied
  
BOA TCC water column corrected
scaled 0-250
Linear enhancement

Quite remarkable:
bottoms everywhere exhibit
a fairly GREEN and dark signature

BOA TCC deglinted
scaled 0-250
Same scaling and linear enhancement





 







Bottom typing
  
SAM classified image
This is November 2014

see legend for SAM
  
ImageB: average bottom brightness
This is November 2014