Radar/Visible Optical Depth Retrieval of Stratus Microphysics in Preparation for CloudSat

Dr. Richard Austin, Colorado State University

The CloudSat mission, scheduled for launch in March 2003, will carry a 94 GHz cloud radar and an oxygen A-band spectrometer together on a space platform, providing the first vertical profiling of cloud from a space-borne cloud radar. CloudSat will fly in formation with PICASSO-CENA, the NASA aerosol and cloud lidar mission, and Aqua (formerly EOS-PM), NASA's multi-sensor platform that is part of the EOS program. These three spacecraft (the "EOS Constellation") will concurrently profile the atmosphere with a radar, lidar, A-band spectrometer, microwave and millimeter-wave radiometers, and multi-spectral imagers, producing a rich data set for the study of clouds, aerosols, and radiation processes. In addition to conventional single-instrument retrievals, there is great potential for new multi-instrument and multi-platform retrievals of cloud properties.

Numerous algorithms exist for the vertical profiling of cloud microphysical properties from radar data, often in combination with a passive sensor (e.g., Frisch et al. [1995], Sassen et al. [1999], etc.) These are often intended for radars with Doppler capability and are therefore unsuitable for CloudSat. This presentation will outline the development of a new retrieval using radar reflectivity and visible optical depth derived from measurements of passive sensors. The retrieval is cast in an estimation theory framework, providing for the explicit inclusion of a priori information, estimates of uncertainty in the retrieved parameters, and quantification of the relative influence of a priori, forward model, and measurement information on the retrieval and its uncertainties. An important feature of the algorithm is that it can be readily expanded to include additional data streams, allowing for the development of complementary combined algorithms using data from MODIS, AMSR, and other sensors of the EOS Constellation.

Validation efforts for the retrieval are underway and will be described in the seminar. The primary validation activity to date has been the CloudSat Antecedent Validation Experiment (CAVEX), which featured remote and in situ measurements of maritime stratus off the Pacific Coast near Monterey, CA in June-July 1999. Comparisons have also been conducted using data and retrievals of cloud liquid water in continental stratus over the Atmospheric Radiation Measurement Program's Southern Great Plains site in Oklahoma.