Tuesday, 16 January 2007
A validation for retrieving cloud optical and microphysical properties in the IR region with MODIS and AIRS
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Knowing the spatial and temporal distribution of clouds at nighttime is paramount in determining their role in climate. The scope of cloud properties retrieved during the nighttime from satellite is limited in comparison with daytime cloud property retrievals due to the necessary dependence on only infrared (IR) measurement. Recent and emerging technologies point to the possibility of expanding the scope of nighttime cloud property retrievals to include particle size and optical thickness, and detailed feasibility studies are necessary. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS) level 2 atmospheric cloud products, along with Atmospheric Infrared Sounder (AIRS) atmospheric profile are combined and used to simulate radiances in selected IR channels at 8.5-, 11- and 12-Ám with the Discrete Ordinates Radiative Transfer model (DISORT). Gaseous absorption is calculated with the correlated-k distribution method. The simulated radiances are then compared to observed radiances from MODIS for cases of clear sky and for single-layer ice and water clouds. Results show that cloud retrieval methods for optically thin clouds are practical; however sensitivity to cloud effective particle size is lost as clouds become optically thick (black) in the selected IR channels.