4SM on OLI at Caicos Bank, Bahamas

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_1, Blue_2, Green_3, PAN_4, Red_5, NIR_6 and SWIR1_7

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

home

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! 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! Deglinted BOA TCC Deglinting is far from perfect: lots of clouds, complex atmosphere

Maximum bottom detection

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

Deglinted Pan band
exhibits bottom detection
in excess of 30 m

We shall see below how 2K_PAN 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