Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
WorldView 2 image Marmion Marine Park, Western Australia
June 2nd 2012, 2875*4096, 2 m ground resolution, 5.7 km * 8.2 km,   courtesy of Simon Allen, CSIRO
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Marmion in Simon's image below
Marmion in Perth twin stripes mosaic

This dataset, courtesy of Simon Allen, is comprised of
  • tiles R1C1 and R2C1 12JUN02025339-M2AS_R1C1-052749202010_01_P002 Multi
  • tiles R1C1 and R2C1 12JUN02025339-P2AS_R1C1-052749202010_01_P002 Panchro 0.5 m resolution

bands 1, 2, 3, Panchro, 4, 5, 6, 7 and 8        
bands 1, 2, 3, 4, 5, 6, 7, 8 and 9
Panchromatic band was not used here

The data
Optical calibration

Sewage outfall

System noise and pollution

Nov 23rd 2012

Simon, I beg for indulgence,

as I lack the deep water coverage
which is required for estimating deep water radiances.

When I get some seatruth data, then I can use it to ascertain blue-green deep water radiances.

The deeper/darker the bottom, the more hazardous the results.
The least bands usable, 
the more hazardous the results.

No tide correction applied.
Smart-smoothing applied.

FinalZ = CoefZ * ComputedZ - HTide
CoefZ and Htide to be derived from seatruth regression

  • I used only the MULTI bands, so far
  • I used all the experience gained since november 2011 when I pocessed a Geraldton W2 image: this involves
    •  estimating the spectral deep water radiances Lsw for the purple, blue and green bands
    • estimating the spectral water volume reflectances Lw for the purple, blue, green and yellow bands
    • estimating operational wavelenghts for the yellow and red bands
  • This was made possible thanks to the absence of adverse surface glint 
    • and lso needed masking all  those countless alien objects that populate the image: boats and wakes, all sorts of objects at the sea surface in this Marine Park
  • The nice radiometic quality of the image allowed me to operate the smart smoothing scheme
    • It shall be observed that the smart smoothing does a good job of smoothing homogeneous features while respecting their sharp limits

Existing depth data

  • As a general rule, keeping secret the existing depth data does not serve any purpose
  • By making it available along with the image data, the end user can save the practioner a lot of time and anguish, particularly when the image is a hard case

No optically deep waters

  • The lack of optically deep waters is a real pain for operating the simplified RTE

    • as it relies on the estimation of the so-called "bottom contrast" LsB-Lsw, or LB-Lw, where the deep water radiance takes a dominant role over darker or deeper bottoms

    • TOA : Ls=Lsw + (LsB-Lsw)/exp(K*Z)           or BOA : L=Lw + (LB-Lw)/exp(K*Z)


    • Deep water radiances Lsw in the blue-green range are pure fantasy

  • So it would be required that the dataset extends farther seaward so as to reach areas where the water is optically deep in the blue-green range, where to ascertain the value of Lsw for these bands (and therefore also the value of Lw)

  • It would also be desirable that the dataset extends a bit further inland, so that I can get a more reliable Soil Line


Sewage outfall


  • Panchro band : up to now, I failed to obtain consistent results

Dark vs Bright

  • The big question is: very dark features, probably rock constructs, would be expected to raise a bit higher than surrounding sedimentary areas.

    • I feel uncomfortable that those dark  features are mapped ~2 m deeper than surrounding bright features 


  • Thorough masking of those aliens yields a more secure and much less clear water type

    • This takes an awful lot of time

    • Sorry for that: very high ground resolution in a popular marine park requires a lot of learning

  • All manners of radiometric aliens yield fancy depth results: beware of that when running a seatruth regression!!

    • this includes fancy pixels all around the 4x4 sum-aggregated Panchro image

    • I masked them out of the calibration process, but they do appear in the modeling results, lest I would punch holes to weed them out, like they were clouds

    • you may use the value of 1 in this mask

I can get NOOO sa-tis-fac-tion!

  • A frustrating experience, like at Geraldton.

  • After days of battling, I give up: the results are hazardous, to say the least; although the southern part of the image might be less of a problem because the pollution does not seem to affect it.

  • The data is not at its best:

    • system noise

    • pollution: water quality is NOT homogeneous

    • lack of optically deep water coverage

    • lack of land coverage

  • The site is a difficult one:

    • most of the shallow area is deeper than 6 m: the Yellow band is of little help over those very dark bottoms, even more as it needs a high threshold because it is affected by pollution.

    • most bottom substrates are very dark, even the "bright" one, apart from a few small areas.

    • the topography is quite hard to guess: dark vs bright. Seems we have a dark rocky platform upon which stand hydraulic sandwaves a few meters higher.

  • Essential calibration parameters cannot be estimated to satisfaction:

    • deep water radiances Lsw for the Purple, Blue and Green bands: I need optically deep water coverage.

    • atmospheric path radiance La: La=Lsw-Lw : I need more land coverage.


Nov 23rd 2012

The data

mosaic FCC bands 7, 3 and 2

mosaic Panchro


Purple band 1 at 427 nm


Blue band 2 at 477 nm

Green band 3 at 546 nm

Yellow band 5 at 596 nm

  • In the clearest waters, Yellow does not show bottom detection in excess of ~12 m of depth over very bright bottoms.

  • So we can infer that "bright" bottoms here are quite deep in most of the image: this is a precious indication, and I used it when picking calibration details.

Red band 6 at 641 nm
this band is rotten
things do happen!

NIR1 band 8 at 831 nm
No glint
No adjacency effect

Nov 23rd 2012
 Optical calibration 

Calibration diagram for bands 2, 3, 5 and 6
Waters are quite clear: ~OIB water type of Jerlov

Calibration diagram for bands 1, 3, 5 and 8




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