Study of Tropospheric Propagation Effects in Sace-borne SAR Remote Sensing: Lates Results from TerraSAR-X

Abstract

TerraSAR-X, the first civil German space-borne synthetic aperture radar (SAR) satellite, has been successfully launched on 15th of June, 2007. The main purpose of Synthetic aperture radar systems is to map the Earth-surface in high resolution and synthetic aperture radars are often considered as day/night and all-weather imaging systems. Whereas the first argument is true, the second does not hold in every case depending on the operating frequencies for the applied system. Indeed, recent examples of typical rain-induced signature modification have been recorded with the X-band TerraSAR-X system. It is well known that the specific attenuation of the signals may be around 1 dB/km assuming a rain-rate of 40 mm/hr and such an occurrence may frequently take place for tropical areas over rain-forest. Attenuation up to 20 dB and beyond may occur through the precipitation volumes in the cases of heavy precipitation, such as the Brazilian rainforest. However, as will be shown, even the northern latitudes are vulnerable to precipitation induced distortions. During the commissioning phase, a total of 12000 SAR-images (scenes) have been investigated for potential “propagation effects” and some scenes have been selected that revealed visible atmospheric effects. In this contribution, we will present a particularly interesting example acquired over New York, where the SAR image will be compared with weather-radar data acquired nearly simultaneously (within the same minute). The comparison of the images show a good overall agreement and it can be clearly shown that reflectivities in the weather radar image of 50 dBz may cause visible artefacts in the SAR images. In addition, several recent examples of SAR-images with from precipitation induced signatures around the globe will given.