We have seen that most of the solar photons which enter the water are absorbed. Many of these photons - most, in some waters - undergo scattering one or more times before they are absorbed. Scattering does not by itself remove light - a scattered photon is still available for photosynthesis. The effect of scattering is to impede the vertical penetration of light. It makes the photons follow a zig-zag path as they ricochet from one scattering particle to the next. This increases the total path-length that the photons must follow in traversing a certain depth, and so increases the probability of their being captured by one of the absorbing components of the medium. In addition, some of the photons are actually scattered back in an upwards direction. Thus the effect of scattering is to intensify the vertical attenuation of the light.
In this chapter we shall consider the nature of the scattering process and the scattering properties of natural waters.
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