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

Bathymetry and water column corection
WV2 at Saint Croix and Buck Island Reef,
US Virgin Islands, 14_JAN_2012
8967*8805, MULTI, UTM zone 20, 2 m resolution
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Watch DigitalGlobe's bathymtery webinar 2013

For the work below, I had to mosaic two tiles
and I also used file "depth_v2_final.tif"

Another view is also available in two tiles

This is red-hot!    Proteus
         www.thsoa.org/hy13/pdf/0328A_03_07.pdf         GEBCO cookbook 2013



WV2 radiances along Profile Green
for bands 1, 2, 3, 4, 5 and 8

There appears to be a northern body
of optically deep waters
with radiances slightly higher in Blue-Green bands
than in southern clearer open waters

This is accounted for in the commandline:

Glint regressions are taken from clouds


Optical Calibration

Optical calibration for bands 6, 5, 3 and 2
  • Note that WLgreen had to be specified at 550.9 nm
    • cWL/0.500/0.500/0.570/0.500/0.5....
  • This results in a remarkably nice fit of the BPL pixels with Jerlov's optical model for OIB water type for the pairs K2/K3, K2/K5 and K3/K5
  •  K2/K3=0.50 yields operational spectral 2K:
    • 2K 0.093 0.075 0.150 0.536 0.800 ...
    • Jerlov's water type OIB+0.12

Optical calibration for bands 6, 5, 4 and 1
  • Note that bands 1, 2, 4, 5 and 6 are specified at mid-wavelength
    • -cWL/0.500/0.500/0.570/0.500/0.500/0.500/0.500/0.500
  • Bands 1 to 6 are seen to exhibit a very strong and consistant set of Ki/Kj ratios
    • This is a remarkable proof that Jerlov's data may safely be used for optical calibration to derive spectral values of the effective spectral diffuse attenuation coefficient 2K over the visible range

Go, tell it in the mountain,
over the hills, and everywhere


No need for field data


Profile Red

Computed depth
and water column corrected radiances
along Profile Red
  • For a comparison, the red depth profile exhibits the depths read from file depth_v2_final.tif
    • I assume this is results obtained by an anonymous researcher
    • Of course, a LIDAR seatruth DTM would be required
    • I downloaded file buis_bathy_3m.zip from NOAA website, but was unable to read it
  • Red profiles are shown
  • TIF file depth_v2_final.tif is displayed
  • My 4SM results and those by anonymous quite remarkably exhibit a reasonable fit
    • this again shows that the operational spectral K values derived by 4SM using just the image data are closely consistant with those derived by anonymous through a probably most elaborate path
  • 4SM results are smoothed by a smart-smoothing scheme, (while it would appear that anonymous results are not smoothed?)
  • My 4SM results and those by anonymous quite remarkably exhibit distinct local offsets, possibly over specific bottom types
    • comparing those results on a detailed and local basis should be quite enlightening
    • of course 4SM and anonymous both have to operate some assumption as regards the spectral bottom signature at each shallow pixel
    • it might be that a more acceptable end result would be obtained by averaging both depth estimates at each shallow pixel

How nice if I could use the PANchromatic band!

Computed depth in centimeters
4SM results as a backdrop
depth_v2_final is overlayed

Computed depth in centimeters
4SM result only


Average bottom reflectance

NDR : Normalized Difference Ratio


Watercolumn corrected bottom reflectance
RGB CC : a "low tide" view


Watercolumn corrected bottom reflectance
RGB CC normalized

Command Line
Totally blind test

nice -20  4SM.4.13  -Process  -Origin/DigitalGlobe           
-B/tclNe/cLM1 .5                           

This test is totally blind
By use of a proper seatruth LIDAR DTM, I'll be able to investigate

  • whether spectral K should be modified
  • whether spectral deep water radiances should be modified
  • whether NDR feature in 4SM should be tweaked in order to accomodate this image
  • etc


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