HR: 08:45h
AN: C21B-04 INVITED     [Abstracts]
TI: Global and Polar Cloud Cover from the Geoscience Laser Altimeter System, Observations and Implications
AU: * Spinhirne, J D
EM: james.spinhirne@nasa.gov
AF: NASA, Goddard SFC/912, Greenbelt, MD 20771 United States
AU: Palm, S P
EM: spp@virl.gsfc.nasa.gov
AF: SSAI, Goddard SFC/912, Greenbelt, MD 20771 United States
AU: Hlavka, D L
EM: sgdlh@virl.gsfc.nasa.gov
AF: SSAI, Goddard SFC/912, Greenbelt, MD 20771 United States
AU: Hart, W D
EM: billhart@virl.gsfc.nasa.gov
AF: SSAI, Goddard SFC/912, Greenbelt, MD 20771 United States
AU: Mahesh, A
EM: mahesh@agnes.gsfc.nasa.gov
AF: UMBC, Goddard SFC/912, Greenbelt, MD 20771 United States
AB: The Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and Land Elevation Satellite provides space-borne laser observations of atmospheric layers. The GLAS laser profiling permits unambiguous detection of clouds with high sensitivity and direct height profiling. Climatologies of clouds in the high latitudes in particular are compiled to much greater accuracy than passive satellite observations where clouds and snow surfaces appear similar at both infrared and visible wavelengths. Since its launch in early 2003, GLAS has obtained a substantial sample of cloud observations by space borne lidar. In addition to the detection of the coverage and height distribution of clouds, the GLAS data algorithms also derive the optical thickness and scattering cross sections for transmissive clouds. A substantial fraction of clouds are sufficiently transmissive that a laser pulse from surface scattering is obtained. The accurate results for cloud coverage and distribution obtained from GLAS may be contrasted with previous climatologies and other satellite observations. Overall GLAS has detected a 70 percent average global cloud cover with 45 percent of the total being single layered. For many parameters there is good agreement with MODIS and other passive cloud retrievals but in some cases, especially night time and polar clouds, there are significant discrepancies. Polar clouds and aerosol are an important factor for the accuracy of the altitude measurements of ice sheet elevation change. Multiple scattering through even the thinnest clouds introduces an effective pulse spreading and altitude bias. Pulse spreading up to 10 of meters is observed in data. The GLAS mission was designed so that cloud clearing and corrections would permit centimeter accuracies for surface elevation change. Results showing the adequacy the cloud detection and clearing for surface measurements are presented.
UR: http://glo.gsfc.nasa.gov/
DE: 9805 Instruments useful in three or more fields
DE: 1863 Snow and ice (1827)
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0933 Remote sensing
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting