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

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

 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

Toau lagoon:  deglinted, smoothed, BOA

 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!!!
  • 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

  • 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


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