HICO at Lee Stocking Island, Bahamas
This is the June image: lsihico_20100616
Level 1B, in ENVI format downloaded from http://hico.coas.oregonstate.edu/datasearch on december 17th, 2014
go to the november image
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1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
 
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
 
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
 
So
I keep digging
until suitable data
become available
 

The data
TCC
 
TCC
logarithmic enhancement
Note several extremely dark areas
FCC
logarithmic enhancement
PANCHRO
logarithmic enhancement
407 nm
logarithmic enhancement
Note: negative bottom contrast area
Note: variable deep water radiance

 
476 nm
logarithmic enhancement
Note: negative bottom contrast area
Note: variable deep water radiance
 
544 nm
logarithmic enhancement


 
648 nm
logarithmic enhancement
Note: no bottom detection under the negative botttom contrast area


 

No surface glint is observed






 
  
Radiances along Profile_red
See Profile Red locator
  • data is scaled so that the brightest shallow bottoms score a BOA radiance ~290
  • a "glint regression" file represents the cloud/shadows; it is used for an approximate estimation of the spectral deep water radiances Lsw
  • profile crosses small clouds at km 24 and km 27
  • profile crosses negative bottom contrast between waypoints 2 and 3: see that the Red band is extinct (which for a very dark bottom might actually be quite shallow bottoms)
  • waypoint 4 is located where extinction of the Green band may be assumed
  • this kind of plot allows to operate a Lsw=Lsw+dLsw correction, a very delicate and all-important step in 4SM,
    • as Lsw is expected to remain constant all over the scene
  • NO smoothing applied: the low level of system noise is quite obvious; no banding is observed
   May I say:
everything seems to behave as expected by the simplified radiative transfer equation...?
          
 
 
 


Optical calibration

Calibration diagram for the whole scene
for Blue, Green, Red and NIR bands
  • bidim histogram only shows marine and cloud pixels
  • ratio Kblue/Kgreen=0.64 is a solid estimation
    • waters are just slightly less clear in june than in november    where a ratio Kblue/Kgreen=0.60 is observed
  • June vs november:
    • OIB+0.6 water type of Jerlov in june
    • OIB+0.4 water type of Jerlov in november
    • this change is quite small indeed
  • note that, for the Blue vs Red and Green vs Red pairs, there is not an acceptable fit of the BPL pixels with a direct application of Jerlov's diffuse attenuation coefficient model: 
    • 2Kred=0.767 m-1 we would welcome a lower estimate of 2K for the Red band
    • this actually is observed for the whole region from band_15_567 nm onwards

Calibration diagram for the whole scene
for Blue, Green, Red and NIR bands

2K not corrected

2K corrected