Angular Dependence of Cloud Property Retrievals from Satellite Data

Satellite cloud retrievals and products are the basis for GCM validation and future assimilation over large spatial domains. Cloud retrievals and products are derived from many satellite instruments and platforms. Geostationary satellites provide the capability for performing coincident retrievals of cloud properties from different viewing geometries. The amount of variation in a given retrieved property resulting from view angle differences is a method for validating cloud property retreivals. A perfect retrieval would result in no differences in the same cloud property measured at two different angles. Some of the difference may be due to 3-D cloud structure and variances in the phase functions that are not captured in the simple retrieval models. By viewing the same clouds simultaneously from different directions, it is possible to estimate the model uncertainties caused by 3-D effects and model assumptions. By altering the model characteristics that minimize parameter differences, due to view angles, it is possible to make improvements to the model and minimize the impacts of the model assumptions. This study utilizes GOES-12 (75° W), GOES-10 (135° W) and GOES-11 (~115° W) data during July 2005 and some areas with dual coverage during 2004. The Visible Infrared Solar-infrared Split-window Technique is used to retrieve cloud optical depth, phase, particle size, water path and height and temperature. Angular biases of cloud properties will be quantified by scattering angle, diurnally and seasonally. Modifications of ice crystal phase functions and water droplet distribution models are tested by changing particle shapes and size distributions, respectively. The results are compared to surface observations of liquid water path.