A test of three‐dimensional radiative transfer simulation using the radiance signatures and contrasts at a high latitude coastal site

Abstract

A three‐dimensional Monte Carlo radiation code is used to analyze surface observations of sky radiance at a high latitude coastal site. Observations were made at Palmer Station, Antarctica, under uniform marine stratus clouds during both ice‐free and iced‐in ocean conditions. The model results using actual snow/ocean area coverage show good qualitative agreement with all‐sky images and high spectral resolution radiometer scans. When viewing over the island, toward the northeast, observations and modeling indicate that sky radiance in the visible bands is up to a factor of two greater than for directions toward the southwest, viewing out over open ocean. Owing to a decrease in snow reflectance at longer wavelengths, modeled and observed radiance distributions in the near infrared tend to be much more symmetric. Results of the modeling study indicate that details of the snow BRDF, or island topography, have a very small effect on model predictions. In addition, the model indicates that the angular distribution of sky radiance is fairly insensitive to cloud optical depth (assumed homogeneous) and is independent of cloud height as long as cloud layer thickness is not much larger than the cloud base height.