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Updated:
14 February 2003
Disclaimer:With all these enhancements and algorithms, it must be noted that the satellite sensor is broad band and the unique discrimination of surface materials is often limited. At best the presented algorithms are an indication of occurrence of the labelled features and some will be more definitive than others. While we have presented a powerful on-line remote sensing analysis tool, there are limitations of algorithms in terms of accuracy. An understanding of the properties of marine and coastal materials and their interaction to produce a complex signal at the satellite sensor is required to properly analyse the processed imagery. Variability in scene contents will always result in subjective and relative accuracies of imagery.
Substrate AlgorithmThis is a shallow marine sea-floor enhancement. This algorithm displays a colour enhancement for shallow water areas only and places band 5 data in land areas using the masking thresholds described above. The 'substrate algorithm' is described as:
Red = b3/(b1+b2+b3) The first three bands of Landsat TM are the best for water penetration of light. Dividing these bands by the sums helps to reduce contrast effects due to water depth and brightens the colours. This is conceptually similar to the more rigorous Shallow Water Image Mapping (SWIM) substrate algorithm (Bierwirth et al, 1993) but different in that the colours for the 'substrate' algorithm will change for similar substrates at varying depths. Unfortunately the SWIM algorithm was seen to be too complex for on-line processing. As with the depth algorithm, substrate mapping is impossible in 'thick' waters where the on-line results will be in error. |
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