HR: 10:50h
AN: C12A-03    [Abstracts]
TI: Field-based Measurements of 37-GHz Microwave Extinction Length at Summit, Greenland
AU: * Koenig, L S
EM: lorak@u.washington.edu
AF: University of Washington, Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195,
AU: Grenfell, T C
EM: tcg@atmos.washington.edu
AF: University of Washington, Department of Atmospheric Sciences, Box 351640, Seattle, WA 98195,
AU: Winebrenner, D P
EM: dpw@apl.washington.edu
AF: University of Washington, Applied Physics Laboratory, 1013 NE 40th Street Box 355640, Seattle, WA 98105,
AU: Steig, E J
EM: steig@u.washington.edu
AF: University of Washington, Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195,
AB: Microwave emission from ice sheets is related to both firn temperature and other firn properties, including density and grain size. To better understand the relationship between microwave emission, temperature and firn properties, we use a convolution model that relates surface temperatures to microwave brightness temperatures. The convolution model is constructed by using the thermal diffusivity equation to solve for a temperature profile in the radiative transfer equation. The model is fit using a timescale, the extinction-diffusion time, which is physically related to the extinction length, or e-folding depth, of the microwave emission and the thermal diffusivity of the firn. The success of the extinction-diffusion time model at predicting the microwave signal motivated this investigation of the spatial variation of microwave extinction lengths with firn properties on ice sheets. Here we present a method for collecting field-based measurements of microwave extinction lengths and present results from Summit, Greenland. We measure microwave extinction lengths by placing a radiometer at the bottom of undisturbed snow pits looking upwards through different snow depths. This provides a direct measurement of the microwave optical depth as a function of snow thickness. We measured microwave extinction lengths at 5 snow pits within a 25-km radius of Summit and recorded values ranging from 1.4 to 1.8 m at 37 GHz. These measured values are slightly larger than those predicted by an existing model, 1.0 to 1.4 m, using similar firn properties as recorded at Summit.
DE: 0726 Ice sheets
DE: 0758 Remote sensing
SC: Cryosphere [C]
MN: 2007 Fall Meeting