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
 
Activity
Calibrate and Model under Mask_3

 
LINE_6

LINE 6: Calibrate under mask_3
 
Please, append a copy of #LINE_6 into your script,
then follow the instructions, step by step
MapBPL color composite
Syntax_Extract

Map BPL under Mask 4

Map BPL under Mask 3
Most BPL pixels are located 
at a well protected shallow beach
Most BPL pixels are located
in/around shallow steams of oceanic waters
entering the lagoon from the reef

 


Bulge and saturation:
very shallow bottoms are much brighter
 

Calibration under Mask_3
 
<<==The large bulge in Ls1 vs Ls2 diagram
points to  very shallow areas which are  
up to 1.35 times brighter than under mask_4.


This bulge represents the saturated areas 
that we already noted.


This obviously happens
where very clear oceanic waters flow
from the reef into the lagoon,
through the hoas.

This might signal precipitation
of calcium carbonate particles
in very warm and shallow waters.
Particulate inorganic carbon (PIC)
This time again,
the Ghost pixels confirm 

that this bulge is not an artifact of sort.
 
 


Bad fit   /   Good fit
Kgreen/Kred changes from 0.29 to 0.46
 
Calibration under Mask_3
KIKJ=0.29: Jerlov water type Oceanic II
This area exhibits a ratio KIKJ much higher than 0.29.
Waters under Mask_3 are
distinctly less clear than under Mask_4.

 
 
Calibration under Mask_3
KIKJ=0.46: Jerlov water type Coastal 1+0.3
The ratio KIKJ=0.46 suits very well this area. 
Waters under Mask_4 are
under the influence of Oceanic waters.
Waters under Mask_3 are less clear:
South-East lagoon waters are confined.

 
 
Comparing two models
LINE 5 by Mask_4                    and
                    LINE 6 by Mask_3

A compromise between the two models  would possibly be useful

Computed depth Zcm
by LINE 5                      by LINE 6
Point Querry 
14.68 m         11.73 m

 

Bottom brightness B
by LINE 5                     by LINE 6





   
 
Activity
Extract and plot bi-dimensional histograms for Calibration
Learn about using the -Recode/... argument

 
LINE 7 
LINE 7: Extract and plot bidim histograms
 
BiDimensional histograms
For the optical calibration, much insight can be gained by studying bidim histograms,
as they reflect all aspects of the various processes which affect spectral radiance,
  • through the atmosphere,
  • at the water surface,
  • through the water column,
  • and at the shallow bottom.
Please append #LINE_7... to your script, and follow the instructions
 

BiDimensional histograms
over glint area
 

BiDimensional histograms
over glint/cloud/shadow area

 

mSE=10 under black areas
Using a mask_10 shapefile,
the -Recode/... argument recodes
all marine pixels to 10 in mask mSE

BiDim histogram under black areas
recoded to mSE=10