COMPARISON OF MICROWAVE BACKSCATTER ANISOTROPY PARAMETERISATIONS OVER THE ANTARCTIC ICE SHEET

Abstract

The Antarctic Ice Sheet exhibits a strong anisotropy in microwave backscatter, both as a function of azimuth angle and incidence angle. This anisotropy arises as a result of i) the alignment of roughness elements and other wind-related surface and sub-surface features, as well as ii) internal layers and snow grain size gradient within the snowpack. As a result of its antenna configuration, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Advanced SCATterometer (ASCAT) satellite instrument is able to observe much of the continent with a large azimuth and incidence angle diversity. A lack of azimuth and incidence diversity has restricted previous backscatter parameterisations to relatively simple bi-sinusoidal (azimuth angle) and linear (incidence angle) parameterisations. Using ASCAT, we show that a better fit can be obtained using a cubic incidence angle function and a Fourier series of up to four terms for parameterisation of the azimuth angle anisotropy. Scatterometer instruments have previously been used in Greenland to retrieve accumulation rate by observing the change in backscatter as a function of incidence angle. Here we present preliminary results of an empirical study linking the isotropic component and incidence angle dependence to snow accumulation rate in Antarctica, using snow stake measurements as ground truthing.