Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries

Full CASI mosaic at Mahone Bay, 2001
image courtesy of HDI
14350*10140 17-bands CASI image, pixel size 1 metre : 4SM license cost is 4974 Euros,   processed january 2006

WL/442.5/464.6/490.5/510.1/520.3/529.7/540.0/555.0/565.3/574.7/585.1/595.5/605.0/624.8/654.3/684.8/850.3 in nanometers

In spite of radiometric quality problems which are poorly controlled and still under investigation,


to show that 4SM is capable of processing a VERY VERY large image



 
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
 
raw image

equalized image

 

computed depth

 

TCC of "normalized" spectral bottom reflectance

 


 


Bottom typing at Mahone Bay,
as of 04 septembre 2005

 
Image balancing has been slightly improved
(still not satisfactory though)


it is presented as a true color composite
of deglinted image, histeq enhancement

 Spectral Water-Column-Corrected
Shallow Bottom Reflectance


it is presented as a true color composite,
histeq enhancement
 
Spectral Shallow Bottom Reflectance

it is composited into a 3 bands BGR true color composite
through a process that optimizes the visual aspect
 Shallow bottoms are classified by 4SM
into 7 bottom types
and less than 1% unclassified


image_Z250


image_B


 


Optical Calibration Diagrams : 
a humbling experience for a hardy practitioner

One of the things I have learned lately: the BPL must be made 
to be parallel to the observed BPL pixels, rather than to match it closely: 
this is because the shallow bottom at BPL pixels is actually far from being spectrally neutral,
as it is now well known that "supposedly clean sands" actually harbour a host of "cyanobacterial biofilm" material
which is quite alive and active (this particularly applies to Tracady Bay dataset, as I recall).

This results is the Optical Water Type OIII+0.2 here,
which really belongs toJerlov's familly of curves of attenuation coefficients at all visible wavelengths,
as demonstrated in the calibration diagrams below.

It is quite clear that an orderly set of operational K values has been established,
although some further and minor refinements are still in order.

 


mb4_17_16_15_14


mb4_16_15_14_13


mb4_15_14_13_12


mb4_14_13_12_11


mb4_13_12_11_10


mb4_12_11_10_9


mb4_11_10_9_8


mb4_11_7_6_5


mb4_11_4_3_2


mb4_11_4_3_1

  
 

Calibration of bands_16_14_10_3
[up]



 
Bandset for MAHONE BAY 2001==============================
# 1 [16U] 420.5nm+/- 10.2nm (rows 272-282) DNSRU:1000.000000    NOT USED
# 2 [16U] 442.5nm+/- 10.3nm (rows 260-270) DNSRU:1000.000000
# 3 [16U] 464.6nm+/- 10.3nm (rows 248-258) DNSRU:1000.000000
# 4 [16U] 490.5nm+/- 10.4nm (rows 234-244) DNSRU:1000.000000
# 5 [16U] 510.1nm+/-  5.8nm (rows 226-231) DNSRU:1000.000000
# 6 [16U] 520.3nm+/-  4.8nm (rows 221-225) DNSRU:1000.000000
# 7 [16U] 529.7nm+/-  4.8nm (rows 216-220) DNSRU:1000.000000
# 8 [16U] 540.0nm+/-  5.8nm (rows 210-215) DNSRU:1000.000000
# 9 [16U] 555.0nm+/-  5.8nm (rows 202-207) DNSRU:1000.000000
#10 [16U] 565.3nm+/-  4.9nm (rows 197-201) DNSRU:1000.000000
#11 [16U] 574.7nm+/-  4.9nm (rows 192-196) DNSRU:1000.000000
#12 [16U] 585.1nm+/-  5.8nm (rows 186-191) DNSRU:1000.000000
#13 [16U] 595.5nm+/-  4.9nm (rows 181-185) DNSRU:1000.000000
#14 [16U] 605.0nm+/-  4.9nm (rows 176-180) DNSRU:1000.000000
#15 [16U] 624.8nm+/-  5.8nm (rows 165-170) DNSRU:1000.000000
#16 [16U] 654.3nm+/-  4.9nm (rows 150-154) DNSRU:1000.000000
#17 [16U] 684.8nm+/-  4.9nm (rows 134-138) DNSRU:1000.000000
#18 [16U] 850.3nm+/- 25.0nm (rows  37- 62) DNSRU:1000.000000
#19 [16U] 922.0nm+/- 22.1nm (rows   1- 23) DNSRU:1000.000000    NOT USED