Estimating Water Depth from Satellite Images
As an alternative to ship-borne water depth surveys, water depth can be directly estimated from the Landsat and SPOT images (Nordman et al., 1990; references in Appendix C are included in the reference list at the end of Part 1). Water absorbs light exponentially with increasing depth, so assuming that the sea bottom has constant reflectance and that the water quality is the same everywhere, then the log of the brightness measured by the satellite is linearly proportional to the water depth.
In other words, if we proceed from the beach toward progressively deeper water offshore, the brightness sensed by a satellite in blue, green, and red visible light will decrease exponentially. The rate of the exponential decrease is greatest for the red, less so for the green, and slowest for the blue light. That is, the blue light will penetrate deeper than green or red light.