Numerical Modeling of the Underwater Light Field

The fundamental principles of all optical processes are incorporated within Radiative Transfer of Energy theory (RT). RT explains how the radiometric properties, i.e. the radiance and irradiance, change in the water column due to the optical properties of the medium. Mobley (1994) and the software package Hydrolight based on that book are the current state-of-the-art tools for exact modeling of the underwater light field. The Hydrolight model does require accurate input on sun position and atmospheric conditions (including wind speed at the surface), inherent optical properties of each of the optical components and substratum or benthic vegetation reflectance. Once these are available, it will calculate all apparent optical properties such as attenuation coefficients, reflectances from just above the substratum to those above the air-water interface, and so on. The average cosines and diffuse inherent optical properties can also be calculated. Since the user may define many layers of water with differing optical properties, all conceivable permutations of water columns can be calculated.

Unfortunately, it is not possible to directly invert an RT model to derive the variables of interest because the calculations involve tracing the fates of fluxes of photons through few to many interactions with the pure water, its constituents and the substratum and its vegetation cover.

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