HR: 11:20h
AN: C31D-05    [PDF]
TI: Calibration of the Geoscience Laser Altimeter System (GLAS) 1064 nm Atmospheric Channel
AU: * Palm, S P
EM: spp@virl.gsfc.nasa.gov
AF: Science Systems and Applications Inc, 10210 Greenbelt Rd., Lanham, MD 20706 United States
AU: Hlavka, D L
EM: sgdlh@virl.gsfc.nasa.gov
AF: Science Systems and Applications Inc, 10210 Greenbelt Rd., Lanham, MD 20706 United States
AU: Hart, W D
EM: billhart@virl.gsfc.nasa.gov
AF: Science Systems and Applications Inc, 10210 Greenbelt Rd., Lanham, MD 20706 United States
AU: Spinhirne, J D
EM: James.D.Spinhirne@nasa.gov
AF: Code 912, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Mahesh, A
EM: mahesh@agnes.gsfc.nasa.gov
AF: Goddard Earth Sciences and Technology Center, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: McGill, M J
EM: Matthew.J.McGill@nasa.gov
AF: Code 912, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Welton, E J
EM: Ellsworth.J.Welton@nasa.gov
AF: Code 912, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AB: In order to obtain quantitative information on clouds and aerosols from earth orbiting backscatter lidars, accurate calibration is of fundamental importance. For lidar wavelengths in the visible and UV portion of the spectrum, molecular scattering from the atmosphere in regions devoid of cloud or aerosol can be used as a calibration `target'. However, at 1064 nm, the signal from molecular scattering is too small to be detected from space. In this case alternate calibrated backscatter targets such as clouds, aerosols or the earth's surface must be used. This paper uses co-located measurements of cloud and aerosol backscatter obtained from a well calibrated airborne lidar system to obtain the lidar calibration constant for the 1064 nm channel of the Geophysics Laser Altimeter System (GLAS). In January, 2003 GLAS was launched into a near polar orbit aboard the Ice, Cloud and land Elevation Satellite (ICESat). In addition to a high resolution altimetry channel, GLAS contains both 1064 and 532 nm backscatter lidar channels. After a month long engineering checkout phase, the first laser (GLAS has 3 lasers) was turned on and GLAS began obtaining atmospheric and surface returns at 1064 nm. The 532 nm channel was not activated at this time due to engineering concerns. In this paper we describe the methodology used to calibrate the GLAS 1064 lidar channel using validation measurements acquired by the Cloud Physics Lidar (CPL) during the THORpex (THe Observing-system Research and predictability experiment) campaign in February-March 2003. The CPL is a compact and versatile 3 wavelength (1064, 532 and 355 nm) lidar system that flies on the NASA ER-2 aircraft and serves as the primary validation instrument for the GLAS atmospheric measurements. On three days during THORpex, the ER-2 was flown directly underneath the GLAS track for 20 to 30 minutes as GLAS flew overhead at roughly the mid point of the ER-2 flight leg. The GLAS under flights were performed in regions that contained varying cloud types with one day obtaining mainly marine boundary layer aerosol. The talk will present a short overview of the GLAS instrument, the derivation of the GLAS theoretical calibration based on the system parameters, and the use of the CPL data to obtain the GLAS 1064 nm calibration.
UR: http://glo.gsfc.nasa.gov
DE: 0394 Instruments and techniques
SC: Cryosphere [C]
MN: 2003 Fall Meeting