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
 
Panchromatic band
Using the Panchromatic band for water column correction to derive water depth and spectral bottom signature:

Landsat 8 OLIP bandset used for this work

Coastal_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 LC80090452015299LGN00
Nov 11th 2015

Work done september 2016
home


DTM seatruth RMSE=0.62 m
    Z4SM vs ZDTM+1.7m
 
  
ZDTM+1.7m and Z4SM
  ZDTM+1.7m-Z4SM
Z_final=Z4SM-1.7m
 
  • Spectral K is under satisfactory control
  • Tide correction 1.7 m is too much
    • Something is not under control
    • Likely the Soil Line model for the PAN band, i.e. the reference value of the reflectamce of Coral Sands





Data and Deglinting

TOA TCC: raw image
logaritmic enhancement

TOA TCC deglinted image
same logaritmic enhancement

 




Optical calibration
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=0.44 => Jerlov water type OIB+0.1
CoefK=0.8

Calibration diagram for the whole scene
for bands Coastal=1, Blue=2, Green=3 and PAN=4

 
  • see that KCOASTAL~=KBLUE



Now ready for Modeling
No smoothing applied
RED threshold=2.3
PAN solution was used here
A threshold of 2.3 was specified for the RED band,
in order to avoid local artifacts caused by turbidity
  
BOA TCC water column corrected
No enhancement
   
Retrieved depth in centimeters 
see legend for retrieved depth in cm





Bottom typing
caicosOLIP_20151111_signature_types
  
SAM classified image
see legend for SAM
  
ImageB: average bottom brightness