HR: 11:08h
AN: A32B-04    [Abstracts]
TI: Snow Optical Properties for Different Particle Shapes with Application to Snow Grain Size Retrieval and Simulation of MODIS/CERES Radiances Over the Antarctic Plateau
AU: * Jin, Z
EM: zhonghai.jin-1@nasa.gov
AF: SSAI, 1 Enterprise PKWY, Hampton, VA 23666, United States
AU: Charlock, T
EM: Thomas.P.Charlock@nasa.gov
AF: NASA Langley Research Center, Mail Stop 420, Hampton, VA 23681, United States
AU: Yang, P
EM: pyang@csrp.tamu.edu
AF: Texas A&M University, Dept of Atmospheric Sciences, College Station, TX 77843, United States
AU: Xie, Y
EM: xieyu@ariel.met.tamu.edu
AF: Texas A&M University, Dept of Atmospheric Sciences, College Station, TX 77843, United States
AB: We investigated the single scattering optical properties of snow for different particle shapes and roughness. These optical properties were implemented and tested in a coupled atmosphere-snow radiative transfer model. The modeled surface spectral albedo and radiance distribution were compared with surface measurements. The results show that the usual equivalent sphere assumption rather significantly overestimates the forward reflected radiances and underestimates the backscattering radiances around the principal plane. On average, the aggregate shape assumption has the best agreement with the measured radiances. Optical properties with the aggregate assumption were used to retrieve snow grain size over the Antarctic plateau. The retrieved grain sizes showed similar and large seasonal variations in all years, and smaller interannual variation; our results for 2000-2005 are consistent with in situ measurements reported in the literature. Using the retrieved snow grain sizes based on MODIS channels 1 and 6, the modeled radiances agreed well with measurements for other MODIS channels and for broadband CERES. Except for the MODIS 2.13um channel, the mean relative model-observation differences are only few percent. The modeled MODIS radiances using measured surface reflectance at Dome C (Hudson et al.) also showed good agreement in visible channels, where radiation is not sensitive to snow grain size and the measured surface bidirectional reflectance is generally representative of the Antarctic plateau. But modeled radiances using measured reflectance in near infrared presented large errors because of the high sensitivity to the snow grain size, which varies spatially and temporally. The broadband shortwave radiance is moderately sensitive to the snow grain size, comparable to the MODIS 0.86um channel.
DE: 0736 Snow (1827, 1863)
DE: 3349 Polar meteorology
DE: 3359 Radiative processes
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting