Assessing the Effect of Satellite Viewing Geometry on Retrieved Ice Cloud Particle Surface Roughness Using MISR Satellite Observations

The Multi-angle Imaging SpectroRadiometer (MISR) instrument measures reflectivity at nine angles along the satellite track. For the each observation reflectivity, estimated spherical albedo are computed based on results of radiative transfer calculation with randomly oriented hexagonal ice particle model and chosen roughness value. The spherical albedo difference (SAD) is defined as the difference between estimated spherical albedo at any angle and the average of them. If the assumed roughness is correct, SAD values should be close to zero at all scattering angles. By analyzing SAD values as a function of solar angles, viewing angles, and latitudes, we attempt to estimate the effect of satellite viewing geometry on retrieved ice particle surface roughness. The angular profiles of SAD values with several roughness values are calculated in different latitude bands on December and June solstice days. We found the variations in the SAD patterns on these two dates have different characteristics even when subsolar points are aligned by a latitudinal shift. In addition, by stratifying clouds by cloud top pressure, we discuss the sensitivity of SAD distributions to cloud top pressure assumptions.