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

Bathymetry and water column corection
A 1500*2100 series of Landsat ETM/TM  4-bands images 

of Ras Hatibah, Saudi Arabia

work done in march 2010



 
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
 
 


ETM_2000-11-01 TCC


ETM_2000-11-01 FCC
   


rashatibahCZ11.pix: Channel 16

Final averaged depth
in decimeters



Average Depth


for each shallow pixel:

 
  • Average (N=11): 11 depths in decimeters are averaged 
  • Standard deviation (N=11) is also computed
 
  • images which yield depth outside Average+/-STD are rejected
  • ==> N images survive
  • Channel_16: Final average depth is written 
  • Channel_15: Final standard deviation is written 
  • Channel_14: Final N is written

==Two champions==
  • 7 ZCombiner: 14.4 percents of shallow pixels of image ETM_2003-01-10 are rejected while averaging depth
  • 2 ZCombiner: 15.5 percents of shallow pixels of image ETM_1999-11-15 are rejected while averaging depth


rashatibahCZ11.pix: Channel 15

Standard deviation 
on final averaged depth 
in decimeters

rashatibahCZ11.pix: Channel 14

N on final averaged depth
 

Maximum Depth


rashatibahCZ11.pix: Channel 13

Deepest depth over 11 images
in decimeters

Maximum Depth


rashatibahCZ11.pix: Channel 12

Shows which image is deepest

2 - blue for ETM_1999-11-15
11 - purple for TM_1990-11-06
...

   



TM at Ras Hatibah


TM at Ras Hatibah


 

K[blue]/K[green]=0.55

Calibration using Mid waveband

  • WL[blue  ]=485.0 nm at mid waveband 
  • WL[green]=569.5 nm at mid waveband 
  • WL[red   ]=658.5 nm at mid waveband 

is not acceptable as seen in the plot of X[1_2] vs X[3] 

This yields 

  • ZM[blue  ]=45.6 m
  • ZM[green]=25.2 m
  • ZM[red   ]=  7.2 m

option A

One way to alleviate the problem is:

  • keep WL[green]=569.5 nm at mid waveband 
  • relocate WL[red] at 624.7 nm
This yields
  • ZM[blue  ]=45.6 m
  • ZM[green]=25.2 m
  • ZM[red   ]=  9.1  m

All Ras Hatibah ETM and TM images 
were processed 
using this way:
this yields depths 
1.4 times deeper than option B

We'll see then!!

option B

Another way to alleviate the problem is:

  • relocate WL[green] at 578.4 nm 
  • keep WL[red] at 658.5 nm at mid waveband  
This yields
  • ZM[blue  ]=33.3 m
  • ZM[green]=18.4 m
  • ZM[red   ]=  6.9 m
All Tanzania TM and ETM images
were processed using this way,

with the result that depths
were underestimated
by a factor of 1.5!

The same is observed
with ETM images

 
The same is observed
with ETM images
.
.
.
.