Cloud and Aerosol Retrieval for the 2001 GLAS Satellite Lidar Misson

The Geoscience Laser Altimeter System (GLAS) is scheduled for launch in July of 2001 aboard the Ice, Cloud and land Elevation Satellite (ICESAT). In addition to being a precision altimeter, GLAS will be an atmospheric lidar, sensitive enough to detect gaseous, aerosol, and cloud backscatter signals. GLAS will be the first lidar to produce temporally continuous atmospheric backscatter profiles with nearly global coverage (94 degree orbital inclination). The projected operational lifetime for GLAS is five years. A fundamental question is what is the observational potential of GLAS in relationship to atmospheric constituents that affect global climate. What can be learned about clouds and aerosols from a long-term global observational program? In this presentation, we show what we expect based upon modeling studies and our long term body of aircraft lidar observations using the NASA ER-2 Cloud Lidar System(CLS).

We demonstrate that GLAS will routinely be able to detect certain atmospheric constituents. The conclusions are based upon results of lidar signal modeling using the engineering specifications of GLAS and the characteristic scattering values of atmospheric particles. For instance, the CLS found extensive layers of tropical tropopause cirrus during the 1993 TOGA/COARE and CEPEX deployments. These clouds had typical backscatter coefficients of 1e-3/km-sr and optical depth of less than 0.04 and were found to have horizontal extents of thousands of kilometers. We show that GLAS will readily find these clouds, which will permit development of climatologies of typical frequency of occurrence, altitude, and optical depth. Another type of interesting observation we expect from GLAS are Polar Stratospheric Clouds (PSC). These very high altitude aerosol-type layers occur on a seasonal basis in Polar Regions. The existing observational record of PSC's is quite limited. GLAS will expand that record dramatically. We present simulations for boundary layer, tropospheric, and stratospheric aerosol layers, biomass-burning smoke layers, mesoscale and synoptic scale cirrus layers, marine stratocumulus layers, and other significant cloud or aerosol features. This presentation will demonstrate to the atmospheric monitoring community the efficacy of GLAS observations in the development of improved and expanded global climatological records and models.