CASI image of Blue Lagoon, Rangiroa atoll, French Polynesia

Image courtesy of HDI , collected at low altitude in 1998 from the small seaplane Golden Eye from vessel Golden Shadow.
These are 10 bands images; pixel resolution is1 meter.
Flight #2 is 7 km long 4SM license cost is 1050 Euros
Flight #4 is 9 km long 4SM license cost is 1169 Euros
-WL0435/462/490/525/547/577/654/666/680/850 in nanometers
Unfortunately, this dataset lacks bands in the red-yellow region of the solar spectrum.
This does not help for an optimal deglinting, and also for calibrating/modeling!
A difficult case, interpretation is questionable.

Work done in 2005

rangiroa_SPOT
rangiroa_ETM
rangiroa_OLIP
rangiroa_CASI



 
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
 
 
SPOT XS image_RGB at Blue_Lagoon
SPOT XS, image_Z in grey-shades at Blue_Lagoon
One-band case: deeper than 4-6 m, dark bottomed areas are mapped with depths in great excess:
this explains the apparent "moat" around the coral growths.

 
 

  Casi flights #2 & 4 false color composites
 

Casi flights #2 & 4 false color composites, histeq enhancement
Please notice numerous -and ominous- cloud shadows,
and also skyglint -or is it cloudglint, at the far right?
Deglinting quite efficient though: see below.

 


Casi flights #2 & 4 image_Z
 

 
 
Casi flights #2 & 4 image_B

Please refer to Rangiroa_ETM: this dark-bottomed area is present also in the ETM image
A difficult case, interpretation is questionable.
It is reassuring to see bright bottomss reappearing at depth inside the main lagoon in Flight #4!

 

Casi flights #2 & 4 Color composite of normalized bottom reflectance, 490-557-645 nm
 

 
Flight #2: a close-up view of the shadowed/glinted area
These shadows/glint, combined with complex bottom topography/history,
make for a challenging interpretation!

 


Jerlov's water type inside the atoll lagoon is OII+0.15
waters are very clear


 
Flight #2: false color composite, 
histeq enhancement

 
 Flight #2: image_B
The "sandy plain" at depth is mapped 
in excess of 30 m at the base of the outer reef slope

 
 Flight #2: image_Z

Local "spurr and groove" morphology appears
to be the result of erosion of the reef outer slope:
this cause the reef rim to move back by approx 20 m

Many coral growths grace most of theBlue_Lagoon floor, except inside the three basins
 
Flight #2: normalized bottom reflectance
 

3D views of Blue_Lagoon flight #2
(processed in 1999)

 
  • 3D_1: Blue Lagoon

  • 3D_2: towards Deep Lagoon


3D_1


3D_2

  • 3D_1: Deep Lagoon

  • 3D_2: Deep Lagoon

3D_1
3D_2