Azimuth variation in microwave scatterometer and radiometer data over Antarctica

While designed for ocean observation, scatterometer and radiometer data have proven very useful in a variety of cryosphere studies. Over large regions of Antarctica, ice sheet and bedrock topography and the snow deposition, drift, and erosional environment combine to produce roughness on various scales. Roughness ranges from broad, basin scale ice-sheet topography at 100 km wavelengths, to large spatially coherent dune fields at 10 km wavelengths, to erosional features on the meter scale known as sastrugi. These roughness scales influence the microwave backscattering and emission properties of the surface, combining to introduce azimuth-angle dependencies in the satellite observation data. In this paper we explore the use of NSCAT data, ERS AMI scatterometer mode data, and SSM/I data to study surface roughness effects in Antarctica. All three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and resulting katabatic wind flow regime. Due to its broad azimuth coverage, NSCAT data appears to be the best suited for azimuth-angle observations. A simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from NSCAT data at a fine scale is presented. Results indicate relationships exit between the azimuthal variation of the data and the orientation of the surface slope and small-scale roughness relative to the sensor look direction. Keywords— radar, radiometer, scatterometer, ice sheet, azimuthal anisotropy, surface roughness, sastrugi, backscattering, emissitivity.