4SM moorea french polynesia

SPOT
ALI

Please refer to Stephane Maritorena,
"Remote sensing of water attenuation in coral reefs: a case study in French Polynesia":
IJRS, vol 17, no 1, pp 155-166, 1996

**SPOT 1986 image**
This is the image that MARITORENA could not calibrate using Lyzenga's method in his PhD work.	Please see below that the 4SM method allows for an easy and reliable optical calibration of shallow areas for this image.
	DGPS navigated precision depth profiling courtesy of SHOM (Tahiti, 1994) An average seatruth depth has been computed manually from SHOM's precision depth sounding profiles at each 20*20 m seatruth pixel for Temae, Nuupere and Orau lagoons (IFREMER-SPT, Tahiti, 1994).
Image_B	Image_Z
N=1073, RMS=0.45 m Smart-Smoothing does a good job here on all seatruth pixels Too many seatruth depths in the 2-3.0 m depth range result in biased regression line Optical calibration is optimal needs no adjustments	N=1046, RMS=0.67 m No Smoothing yield poor results here on all seatruth pixels Too many seatruth depths in the 2-3.0 m depth range result in biased regression line
Smart-Smoothing does a good job particularly here only on darkest pixels 0<B<100 Too many seatruth depths in the 2-3.0 m depth range result in biased regression line Most darker pixels are affected by coral growths amid sandy bottoms: this makes their "seatruth depth" a delicate concept.	No Smoothing yields poor results particularly here only on darkest pixels 0<B<100 Too many seatruth depths in the 2-3.0 m depth range result in biased regression line Most darker pixels are affected by coral growths amid sandy bottoms: this makes their "seatruth depth" a delicate concept.
SPOT	SPOT WL[green]=550 nm, WL[red]=650 nm K[green]/K[red]~=0.26 an optical water type OII+0.75 of Jerlov 2K[green]=0.225 ==> ZMax=23.3 m 2K[red]=0.867 ==> ZMax= 6.1 m
	The 1986 SPOT image data is affected by electronic system noise: striping , crosstalk in the NIR band (right) adjacency effect in the NIR band (right) <== Green, Red and NIR bands, histeq enhancement <== RGB, Image_Z and Image_B This limits the potential of the image for a shallow water application

**ALI 2003 image**
	The 2003 ALI image data is of excellent radiometric quality Processing this image hardly requires any smoothing Only the glint require proper attention
ALI	ALI WL[blue]=482.5 nm, WL[green]=576.0 nm WL[red]=666.0 nm K[blue]/K[green]~=0.56 an optical water type OII+0.11 of Jerlov 2K[blue ]=0.140 ==> ZMax=39 m 2K[green]=0.248 ==> ZMax=23 m ALI seatruth regression for Temae lagoon
Seatruth TEMAE lagoon Stability: these profiles exhibit remarkable stability over the years Clear waters: the southern channel has clear waters in the 2003 ALI image	Seatruth Seatruth regression for Temae lagoon
NUUPERE lagoon RIGHT: seatruth profiles from West to East Stability: these profiles exhibit remarkable stability over the years Nothing will do: the northern channel has turbid waters in the 2003 ALI image; results there are artifacts
ORAU RIGHT: seatruth profiles from West to East Stability: these profiles exhibit remarkable stability over the years Nothing will do: the southern channel has turbid waters in the 2003 ALI image, much more than in the 1986 SPOT image; results there are artifacts
ALI True Color Composite of the normalized bottom reflectance	ALI Classified into seven shallow bottom types unclassified shallow pixels are in red

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