nb_20190813

LANDSAT 8 OLIP
A time series of Landsat 8 OLIP images
at Nosy Be, Madagascar
work done in january 2021 at 15 m GSD

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

peer-reviewed and published in 2017

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image acquired on August 13th 2019

The data

TCC TOA	TCC TOA deglinted, no smoothing
Glint regressions, based on SWIR band quite low level of glint/haze R2 values are acceptable Deglinting is far from perfect	PAN BOA deglinted the atmosphere is thick and homogeneous water volume reflectance is near null everywhere
UltraBlue BOA deglinted the atmosphere is thick and heterogeneous water volume reflectance over deep waters is mostly at ~25, variable but decreases to 4 where Coastal 5 waters are observed at the end of Ampasindava Bay	BLUE TOA deglinted the atmosphere is thick and heterogeneous water volume reflectance over deep waters is mostly at ~20, variable but decreases to 9 where Coastal 5 waters are observed at the end of Ampasindava Bay

Optical calibration over the whole image

Calibration 6,5,3,2 whole image 0-15 m: K2/K3=0.60 OIB+0.8 >15 m: K2/K3=0.50 OIB+0.4	Calibration 6,5,3,1 whole image the UltraBlue band_1 behaves as expected
Calibration 6,5,4,2 whole image the panchromatic band_4 is under control	The calibration over the full image captures the optical properties of the clearest waters But, zooming on local ROIs reveals distinct spatial heterogeneity: as documented below: this cannot be overlooked while inverting the simplified RTE.

**Optical calibration under 8 local ROIs**
Calibration under mask_E1_white K2/K3~0.55 The Grand Serpent shoal is ~10 m deep	Calibration under mask_E2_red 0-6 m: K2/K3 decreases from 1.0 to 0.8 6-~15 m: K2/K3 stable at ~0.8 >15 m: K2/K3 clearer at ~0.7
Calibration under mask_E3_turquoise K2/K3~0.58 The Grand Banc de l'Entree shoal is ~10 m deep	Calibration under mask_E4_green K2/K3~=1.0 down to ~5 m becomes clearer at depth this case is humbling!
Calibration under mask_E5_black Baie des Russes K2/K4=K3/K4~=0.38 therefore: K2/K3~=1.0 down to >6 m bottoms are fairly dark	Calibration under mask_E6_purple down to ~5 m :K2/K4=K3/K4~=0.38 therefore: K2/K3~=1.00 deeper than 5 m: K2/K3~=0.70 waters become clearer at depth bottoms are fairly dark
Calibration under mask_E7_yellow K2/K4~=0.18 K3/K4~=0.29 therefore: K2/K3~=0.6 this water type OIB+0.8 is present over the whole depth range in the vicinity of Nosy Iranja island bottoms are fairly bright	Calibration under mask_E8_pink K2/K4~=0.9 K3/K4~=0.7 Kblue>Kgreen! therefore: K2/K3~=1.3 this is water type Coastal C5 of Jerlov in Ampasindava Bay