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
 
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 
and 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 LC80090452014216LGN00, Aug 4th  2014
work done august 2016
This is summer time in the Bahamas

home





DTM seatruth  RMSE=0.59 m
    
ZDTM - Z4SM in centimeters
tide correction applied 0.8m
see legend
   
Z4SM vs ZDTM regression

tide correction applied 0.8m

Z4SM and ZDTM along profile_green
no tide correction applied
see location of this profile

Z4SM vs ZDTM along profile_green
no tide correction applied
see location of this profile




Data and Deglinting

TOA FCC: raw image
linear enhancement
density of the atmosphere increases dramatically
from NW to SE

TOA TCC: raw image

This is a low-tide image:
no tide correction needed

 

From NW to SE
accross the whole imge
  • NIR increases from 30 to 60
    • this is a lot of "glint" that mudst be subtracted
  • NIR is as low as 14 under cloud shadow
    • this is a dense atmosphere: LaNIR~=14

Glint regressions are excellent
  • this is a feature of very dense atmospheres

BOA TCC deglinted
linear enhancement




Optical calibration, optimized
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 is modeled
decreasing
from 0.68 (0-6 m) to 0.47 at depth


This is done through four -CP... arguments

 

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


 
Reflectance (0-1)
of the path radiance Ra for this scene
0.108 0.086 0.056 0.051 0.038 0.024 0.012

 
Reflectance (0-1)
of the water volume Rw for this scene
0.010 0.007 0.001 0.001 0.0 0.0 0.0

 







Now ready for Modeling
Smoothing applied
PAN solution applied

BOA TCC water column corrected
scaled 0-250
no enhancement

 

Retrieved depth




 






Bottom typing
   
SAM classified image
This is August 2014

see legend for SAM

ImageB: average bottom brightness
This is August 2014