Co-registration of an Antarctic digital elevation model with SSM/I brightness temperatures

Abstract

The Special Sensor Microwave/Imager (SMM/I) instrument provides daily measures of microwave brightness temperatures Tb over the polar regions. Data are available from 1987 to the present and have a demonstrated utility for sea-ice studies. In this paper we investigate applications to polar ice sheets with a view towards correlating patterns of Tb with ice-sheet elevation. We go on to discuss the Tb signature of processes linked to temperature anomalies and accumulation zone boundaries. Our approach consists of combining SSM/I Tb values provided on CD-ROM by the National Snow and Ice Data Center (NSIDC) with a digital elevation model (DEM) of Antarctica derived originally from the Scott Polar Research Institute Antarctic Map Folio. We focused on 37 GHz data which is mapped onto a 316 × 332 polar stereographic grid at 25 km resolution. The DEM consists of a 281 × 281 array of elevation values with a 20 km resolution. The DEM was resampled to be compatible with the SSM/I data by transforming the elevation data from the original projection place to geodetic coordinates. The elevation data were than transformed onto the SSM/I projection plane. Elevation data were interpolated to yield ice-sheet surface heights at 25 km intervals coinciding with SSM/I point Tb assignments. By co-registering the two data sets, it is possible to “drape” the brightness temperature data over the elevation data. The resulting image highlights the relationship (and variations) between ice-sheet topography and brightness temperature.