Evaluation of the Plane-Parallel Model from MISR Measurements
Horvath, A.(a), Davies, R.(b), and Diner, D.J.(b), University of Arizona (a), Jet Propulsion Laboratory (b)
Thirteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting
Due to its simplicity and computational speed, the 1-D plane-parallel model enjoys widespread popularity in the satellite remote sensing of cloud microphysical properties. Just how well this model describes real clouds is a question rather difficult to answer with traditional single-angle observations. With the advent of near-simultaneous multiangle measurements, it is possible to evaluate the validity of the plane-parallel approach. This study used data from the Multiangle Imaging SpectroRadiometer (MISR) on NASA's TERRA (EOS-AM) platform. Only liquid clouds over oceans were considered. The multiangle radiances were coregistered using automated stereo matching. Atmospheric correction included Rayleigh scattering and ozone absorption, and used actual cloud top pressure (MISR/MODIS) and column ozone (TOMS) measurements. Ice and mixed-phase clouds were excluded using MODIS cloud phase information. The measured anisotropy of the reflected radiation was compared to that of the plane-parallel model DISORT. In order to account for the limitations of the employed surface BRDF model (Lambertian ocean with 5% albedo), the thinnest clouds were excluded from the study. Angular homogeneity rates, defined as the percent of pixels within 5% of the plane-parallel model at all angles, are presented for 1 day of MISR data (14 orbits). The effects of spatial scale, effective radius, and number of used angles on the results are considered. The relevance of our findings to a column radiation model is also discussed.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
