A comparison of predictions and measurements of the radiation field in a shallow water layer

Abstract

The problem of solar radiation transfer in a body of water is complicated by several factors, which include the directional distribution of the incident radiation, reflection and refraction at the air‐water interface, absorption and multiple scattering within the water, and reflection off the bottom surface. Although theoretical methods have been developed to treat the problem, little has been done to test the accuracy of the methods through a comparison of predictions with measurements under controlled laboratory conditions. In this study, measurements of the directional and spatial distribution of the spectral radiation have been made in a diffusely irradiated aqueous medium, and the results have been compared with predictions based on the discrete ordinate and three‐flux methods. For the prescribed laboratory conditions the radiation is concentrated within a cone of half angle θ ≈ 0.85 rad, and for this region, good agreement is obtained between intensity measurements and predictions based on the discrete ordinate method. Good agreement is also obtained between radiation fluxes measured for the forward direction and predictions based on both the discrete ordinate and three‐flux methods. Discrepancies between predicted and measured results for θ ≳0.85 rad are attributed to uncertainties in the radiation intensity and phase function measurements.