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 for water column correction

home


 
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 LC80090452014008LGN00, Jan 8th 2014
Work done august 2016





DTM sea truth   RMSE=0.57 m
No need for field data
  
Seatruth regression
Zcomputed vs Zseatruth
RMSE=0.57 m
Tide correction applied: 1.0 m

Difference ZDTM - Z4SM - 1.0m
Tide correction applied: 1.0 m
see legend

Profile GREEN regression

It would appear that a CoefZ~=0.88 is needed?
This would yield
Zfinal=0.88*Z-0.5 in meters

Profile GREEN

 

Profile GREEN location
Tide correction applied: 0.50 m

see legend

Profile GREEN location
DTM by Harris-Ellis

see legend










The data

Seven bands are used: Purple, Blue, Green, PAN, Red, NIR and SWIR1

Panchromatic band
sum-aggregated to 30 m,
exhibits excellent radiometric quality

TCC
Landsat OLI exhibits excellent radiometric quality

Glint regression based on NIR band
 

Glint regression based on SWIR1 band
 
Deglinting based on SWIR1 band
is excellent!

caicosOLI_20140108_FCC_BOA_deglinted
Deglinted BOA FCC
Very shallow areas are well deglinted,
thanks to near-null water penetration
of the SWIR band
Deglinting based on SWIR1 band
is excellent!
caicosOLI_20140108_TCC_BOA_deglinted
Deglinted BOA TCC
  • Deglinting is far from perfect:
    • lots of clouds,
    • complex atmosphere






Maximum bottom detection
caicosOLI_20140108_RED_deglinted
Deglinted Red band
exhibits bottom detection
in excess of 10 m
Yellow is optically deep

Following study of hyperspectral data,
we shall see below that this requires manually decreasing 2K
for the RED band
caicosOLI_20140108_PAN_deglinted
Deglinted Pan band
exhibits bottom detection
in excess of 30 m



We shall see below how 2KPAN  is established

 





Optical calibration for the whole image
Whole image

Calibration diagram for whole image
for bands Blue, Green, Red and NIR
Water type OIB+0.35 of Jerlov
slightly less clear in the 0-6 m depth range
Whole image

Calibration diagram for whole image
for bands Coastal, Blue, Green, and Red

 






Modeling
using the PAN solution


Retrieved depth
see legend


BOA TCC water column corrected
pinkish areas denote an excess of RED radiance
is it some "whiting"?
or suspended particles?
or pinkish oolith bottoms?

Average bottom brightness
very bright in january 2014


 
   
Spectral Angle mapping
january 2014
this is a done using a spectral angle scheme (SAM)

see legend for SAM