fakaravaOLI_20170919

Investigating a LUT approach using Landsat 8 data

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OLIP 19_september_2017 at Fakarava atoll, French Polynesia
work done may 2021
**Taiaro Atoll:** a hypersaline lagoon
**Toau Atoll:** a layered water column
**Aratika Atoll:** ebbing tide through the pass
TCC	<<<==clockwise Fakarava, Toau Aratika Kauehi Faaite Tahanea Raraka Taiaro +++++++++++++++++++++++++ Excellent glint regressions based on the SWIR band over open waters
Raw Coastal band at 440 nm Toau and Taiaro atolls exhibit very low deep water reflectance: this smacks of "coastal waters"	Glint in the SWIR band

Taiaro lagoon: deglinted, smoothed, BOA
TCC		Ratio Kblue/Kgreen*100 see legend Kblue/Kgreen ranges 0.75 to ~1.30 inside the lagoon Taiaro lagoon is reported to be hyper-saline
null reflectance (lagoon) optically deep 440 nm	very low reflectance optically deep 480 nm	faint bottom detection?? optically deep? 560 nm	null reflectance optically deep Panchromatic

Toau lagoon: deglinted, smoothed, BOA
TCC		Ratio Kblue/Kgreen*100 see legend ocean: Kblue/Kgreen~=0.50 lagoon: Kblue/Kgreen ranges 0.70 to ~0.80 reef flat: Kblue/Kgreen ranges 0.90 to ~1.30
vast optically deep area 440 nm	smaller optically deep area 480 nm	any optically deep area? 560 nm	striping sucks!!! Panchromatic
Kblue>Kgreen>Kgreen This must be K[2]/K[3]=1.1 Jerlov Type Coastal 1 with 2K 0.59 0.33 0.29 in m-1 It could even be K[2]/K[3]=1.3 Jerlov_Type Coastal 3 with 2K 0.90 0.56 0.42 in m-1
The problem is: The LUT algorithm reports ratios Kblue/Kgreen=0.70 to 0.80 for the upper layer of the water column, say 0-10 m this is OII to OII water type of Jerlov Threfore, the lower layer of the water column would be much less clear Think of phytoplancton migrating down around noon time, in order to optimize their chlorophyll assimilation business This might explain the odd results obtained in many atolls so far

Aratika atoll: deglinted, smoothed, BOA
TCC the atoll is surrounded by a slightly turbid halo ebbing tide through the pass		Ratio Kgreen/Kblue*100 see legend Ebbing tide through the pass: turbid lagoon waters discharged away to the ocean reef flat exhibits turbid waters

Work in progress, may 2021