Algorithm development for a two-stream irradiance model for layered environmental media

The transfer of solar radiation is the prime physical process that drives the circulation of the atmosphere and oceans. Consequently, an evaluation of the modeling of the physical processes of radiative transfer is very important to the understanding of the phenomena resulting from this transfer. The primary goal of this research was to develop a model that describes the radiative transfer of the sun's electromagnetic energy utilizing a solution to the modified two-flow equations that generated fast and accurate estimates of light distributions in any layered media, while retaining the essence of the physics that have the greatest impact on the radiative transfer model. A model was developed which solves the modified two-flow equations by an iterative technique. This model is unique in that it uses an iterative method to converge on a solution to the layered, two-flow radiative transfer equations, it accounts for diffuse and specular (collimated) irradiance below the water's surface and utilizes boundary conditions that allow the absorption, backscatter, beam attenuation, and conversion (from specular irradiance to diffuse irradiance) coefficients to vary as a function of depth. The model utilizes constant absorption and backscatter coefficients in each layer. The upwelling irradiance at the surface and the reflectances both below and above the water's surface were compared with values obtained from the two-flow computer model described by Ma (1997) that assumes constant absorption and backscatter throughout the water column to within ±0.44% RMS error. The model was compared with the layered, singly scattered irradiance (SSI) model by Philpot (1987) to within ±0.10% RMS error.