HYPERION
A 762*1934 EO1 HYPERION 26 bands image of Tarawa atoll, Kiribati, July 11th 2002
A 393*651 EO1 HYPERION 26 bands image of Tarawa atoll, Kiribati, May 25th 2003


a case where the waters are
not worthy of shallow water work inside the Tarawa lagoon

return to Kiribati
 
 
A 762*1934 EO1 HYPERION 26 bands image of Tarawa atoll, Kiribati, July 11th 2002
A 393*651 EO1 HYPERION 26 bands image of Tarawa atoll, Kiribati, May 25th 2003



EO1H0800592002192110PZ at high tide, processed may 2010


FCC                                         TCC

 


TCC deglinted


 




Normalized true color composite 
of computed bottom reflectance




Hard to beleive that the lagoon bottom 
is all covered in dark vegetation!
 
 
Average computed bottom reflectance

The very dark patch at the center of the lagoon 
seems dubious.
More probably, 
the waters there are much less clear than further west
where open ocean waters move in and out with the tide.
The close study of the calibration diagrams
shall help us ascertain that


Computed depth is in excess of 14 m in the lagoon


 












It is quite clear that these computed water depths
are far too shallow: an average of ~5 m

  
Healthy coconut groove
  • These are BOA radiances scaled so that a bright sandy beach would plot at 200 for all bands
  • The specification of blue bands, green bands and red bands is derived from this sort of plot: the average BOA blue reflectance is approximately equal to the average BOA red reflectasnce
    • ==> BlueGreen=500 nm
    • ==> GreenRed=625 nm
    • this is entered in the -KK... argument: -KK4_21_0.200/Knir5.499/Bm440_BG500_GR625_RN700
 
 Bright green shallow bottom: Z=1.77 m

These are BOA radiances scaled so that a bright sandy beach would plot at 200 for all bands 


Darker blue shallow bottom: Z=2.63 m
 


Darker green deeper bottom: Z=5.57 m
 


Calibration diagram
for bands Blue=4, Green=11, Red=21 and Nir=26

Calibration

  • BPL assumption: the most remarquable feature of this calibration is that the BPL assumption is demonstrated to apply, as this atoll exhibits clean bright shallow bottom substrates from null depth down to optically deep waters in the Tarawa lagoon
    • this substrate is a fine grained snow-white mud which mostly comes from the green algae Halimeda which is coated with a thin white calcium carbonate shell
  • Water type ~OII+0.2: the BPL model  is seen to fit quite closely to Jerlov's  estimaded water type
  • K[nir]~=5.5 here


Calibration diagram
for bands 23, 24, 25 and 26

 


Calibration diagram
for bands 10, 15, 20 and 25







EO1H0800592003147110PY at low tide, processed may 2010


TCC

 

TCC deglinted and smoothed


Normalized true color composite 
of computed bottom reflectance


Average computed bottom reflectance

 

Computed depth is in excess of 14 m in the lagoon

 
 

Water volume reflectance

  • Lw:  note that as of 4SM.3.29 version, Lw is specified instead of La,   then La is computed as La=Lsw-Lw
    • Lw is required to be null higher than ~640 nm
    • Lw is required to increase as wavelength decreases below ~640 nm
    • healthy dark vegetated pixels are very usefull for assessing Lw for the blue bands




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