Reflectance Anisotropy Comparison of Marine Stratocumulus and Trade Cumulus Using MISR-MODIS Synergy

The applicability of 1D radiative transfer theory to remote sensing of cloud properties is examined through synergistic use of the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) onboard NASA's EOS-Terra satellite. A variety angular consistency metrics derived from retrieved BRF, albedo and optical depth are explored over the stratocumulus off the California coast and trade cumulus off of Antigua. For example, 1D optical depths retrieved at the nine MISR viewing angles, through MODIS-MISR synergy, are reasonably consistent 85% of the time for the stratocumulus and 35% for the cumulus. Angular signatures of the BRF difference between simulated 1D calculations and MISR observations show that the stratocumulus achieves higher consistency than the cumulus. The magnitude of the difference increases with increasing viewing angle and is more prominent in the forward direction than in the backward direction. The difference is positive for thick clouds and for pixels with large sub-pixel BRF variation. However, it is negative for thin clouds and for pixels with small sub-pixel BRF variation. Factors contributing to the metrics' magnitude and its angular signature are explored. The results serve as observational evidences for the further theoretical studies to understand physical mechanisms of the 3D effects on cloud optical property retrievals.