4SM tutorial
on a 500*500 Landsat TM
4 bands image (1985)
of Negril Shores, Jamaica,

UTM georeferenced with sea-truth dataset

Courtesy of Tomy Lindell, University of Upsala, Sweden.    

Also refer to work done in 1998: Erim Marine 98

work in progress


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
I keep digging
until suitable data
become available
back to 4SM tutorial        next to Prepare your image           
    Quite a difficult image
  • too small, not enough shallow pixels
  • 30 m pixels are very large; only 70 pixels from beach to deep waters
  • fairly dark TM2 band: low dynamic range
  • striping
  • faithful bright sandy pixels fairly scarce
  • 0-5 m depth range poorly represented
  • possibly turbid waters along the beach
  • heterogeneous open waters
  • no swell-modulated glint
  • non-DGPS sea-truth data




First let's take a look at the results I finally obtaned
through an intnsive use of seatruth field data



Sea truth correlation: r 2=0.73 RMS=1.40 m
This improves markedly on results obtained in 1998.

neg85 mapZ   is the depth contour map obtained in 1998.


Three depth profile

Red: computed depth
Black: Sea-truth depth
Then we shall try to see, step by step, whether it is possible,
 to reach there without using that field dataset.

Several key points have to be addressed:

        • Which pair of bands for measuring the ratio KiKj?
        • What wavelengths?
        • What Lsw values?
        • What La values?
        • Is the water body homogeneous? 
        • What smoothing scheme?
        • What about the electronic noise?
        • SIG or not SIG?
Flow chart
Bottom typing was the ultimate goal of this venture.
Whether it can be of any help for coastal management remains to be seen.