MICROWAVE EMISSION FROM DENSITY-STRATIFIED ANTARCTIC FIRN AT 6 CM WAVELENGTH

Previous observations have shown spatial covariances between microwave emission from Antarctic firn at 6 cm wavelength, physical firn temper ature and firn-density stratification. Such observations motivate us t o understand the physics underlying such covariances and, based on the understanding, to develop estimation methods for firn temperature and layering parameters. We present here a model for 6 cm emission from f irn in which density, and therefore dielectric permittivity, varies ra ndomly in discrete layers with mean thicknesses on the order of centim eters. The model accounts for depth profiles of the physical temperatu re, mean density and variance of random density fluctuations from laye r to layer. We also present a procedure to estimate emission-model inp ut parameters objectively from in situ density-profile observations, a s well as uncertainties in the input parameters and corresponding unce rtainties, as well as uncertainties in the input parameters and corres ponding uncertainties in theoretical brightness-temperature prediction s. We compare emission-model predictions with ground-based observation s at four diverse sites in Antarctica which span a range of accumulati on rates and other parameters. We use coincident characterization data to estimate model inputs. At two sites, layered-medium emission-model predictions based on the most probable input parameters (i.e. with no model tuning) agree with observations to within 3.5% for incidence an gles less than or equal to 50 degrees. Corresponding figures for the o ther two sites are 7.5% and 10%. However, uncertainties in the input p arameters are substantial due to the limited length and depth resoluti on of the characterization data. Uncertainties in brightness-temperatu re predictions are correspondingly substantial. Thus brightness-temper ature predictions for the last-mentioned sites based on only slightly less probable input parameters are also in close agreement with observ ations. The significance of agreements and discrepancies could be clar ified using characterization measurements with finer depth resolution.