Retrieval of Water-Ice Cloud Opacity at the Phoenix Mars Landing Site from Radiative Transfer in Thermal and Visible Wavelengths

Water-ice clouds at the Phoenix landing site are investigated by considering radiative transfer in thermal and visible wavelengths. First, we reconstruct a record of water-ice clouds at the Phoenix landing site by examining the radiative contribution to the surface energy balance and compare our results to the Phoenix lidar. We find that clouds, radiating between 0 and 30 W m^-2, were present earlier in the mission than previously known and that optically thicker clouds emitted more radiation toward the surface. Next, we use a doubling-and-adding radiative transfer model to derive the visible opacities of the water-ice clouds in images. The derived opacities are consistent with prior studies during the daytime, but give higher opacities between 2:00 - 10:00 LTST. This work allows us to make a direct comparison between the visible opacity of the cloud and the thermal radiation emitted by the cloud to better constrain their effect on the atmosphere.