A model of underwater spectral irradiance accounting for wave focusing

Abstract

The downwelling irradiance in water usually shows very high short-time variability due to focusing and defocusing of the sun and sky light by the wave-modulated water surface. Since the direct and diffuse components are affected differently by wave focusing, not only intensity is highly variable, but also the spectral shape is fluctuating. A depth dependent analytic model was developed which calculates the direct and diffuse components separately. By assigning weights to the intensities of the two components, measurements performed at arbitrary surface conditions can be analysed using inverse modeling by treating the weights as fit parameters. The model was validated against Hydrolight and field measurements and implemented into the public domain software WASI for the simulation and analysis of downwelling irradiance measurements.