Ice Cloud Optical Thickness, Effective Radius, And Ice Water Path Inferred From Fused MISR and MODIS Measurements Based on a Pixel-Level Optimal Ice Particle Roughness Model

The Multi-angle Imaging SpectroRadiometer (MISR) provides measurements over a wider scattering-angle range for a given location than a cross-track scanning sensor such as the MODerate resolution Imaging Spectroradiometer (MODIS). Based on a full year (2013) of fused MISR-MODIS datasets, we develop a variable surface roughness model for ice particles with the goal of identifying the optimal degree of roughness in the ice model for a given pixel containing single-layer ice clouds. For the MISR-MODIS observations over oceans, severe roughness values are often selected for a pixel when optical thickness (tau) and particle effective radius (R-eff) are large in conjunction with larger cloud heterogeneity index (H-sigma) or a warmer cloud top temperature. Furthermore, tau, R-eff, and ice water path are retrieved with the optimal model and compared to operational MODIS Collection 6 (MC6) products that assume a constant roughness. In general, the retrievals based on the present optimal model lead to greater consistency with MISR measurements, and result in larger median tau by 10.1% and smaller median R-eff by 6.5% but almost identical ice water path in comparison with the MC6 counterparts. The higher average tau value is caused by a slightly larger number of large tau cases, but the smaller average R-eff value is due to the shifting of the retrieved R-eff value toward smaller values by approximately 2-4 mu m in comparison to the MC6 distribution over all seasons. Both tau retrievals have similar regional and monthly variations, but a larger annual cycle of R-eff is associated with the optimal model.