Urban and Coastal Impacts Geoscience Australia

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.

Water Chlorophyll

Organic suspended matter can consist of living and decaying biota containing living pigmented algal cells and weakly pigmented particles (Dekker, 1993). The pigment chlorophyll-a dominates in oceans mainly due to phytoplankton and decaying organic matter is also common and is often referred to as yellow stuff or aquatic humus. Figure 3 shows absorption spectra for varying concentrations of chlorophyll. The top curve represents high chlorophyll and the high values of absorption between 450- 520nm means that TM band 1 values will be low.

Figure 3. Spectral values (nm) of absorption coefficient (m-1) for stations in chlorophyll-rich green oceanic waters (from Morel and Prieur, 1977). aw is the absorption spectrum for clear water.

For TM band 2 (520-600nm), Figure 3 shows less variation in chlorophyll absorption of light. Therefore we have used (b2/b1) as an estimation of chlorophyll content in the marine environment. This is generally effective in most waters but again the accuracy will decrease in waters with high SSC where band 2 will increase more rapidly relative to band 1. The effect of aquatic humus is to decrease reflectance toward shorter wavelengths (Dekker, 1993) so that an increase in this ratio may reflect aquatic humus concentrations.

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