Water pollution has become a very serious problem in big cities and in offshore areas along industrial zones. Water quality monitoring is one of the typical applications of remote sensing.
Figure 12.4.1 shows the characteristics of reflection, absorption and scattering on the water surface, beneath the surface water and from the bottom. The sea color depends on the absorption and scattering due to water molecules and suspended particles or plankton.
Figure 12.4.2 shows various curves of spectral attenuation with respect to various types of water. As seen in the figure, clear water has a peak of minimum attenuation around 0.5 m, while turbid water with suspended solid (SS) has larger attenuation with a minimum peak around 0.55
m. In other word, radiation can penetrate into deep clear water and is scattered by the water volume, causing the typical bluish color. Turbid waters cannot be penetrated and radiation is scattered near the surface, giving a greenish or yellowish color.
The sea color depends on not only on suspended solids but also the chlorophyll of plankton within the water body.
Figure 12.4.3 shows an example of the measurement for spectral reflectance of various amounts of chlorophyll. As seen in the figure, chlorophyll in the sea can be detected in the region of 0.45 - 0.65 m.
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