COMPARISON OF PRECIPITATION EFFECTS IN SPACE-BORNE X- AND KA-BAND SAR IMAGING A. Danklmayer German Aerospace Center (DLR) Microwaves and Radar Institute Oberpfaffenhofen, Germany M. Chandra Chemnitz University of Technology Dept. of Microwave Eng. and Photonics Chemnitz, Germany ABSTRACT As the operating frequencies of SAR-systems are increasing, the visible distortions due to precipitation in SAR-images are becoming more frequent. This holds especially for the case of convective rain events. The German space-borne satel- lite TerraSAR-X has delivered a series of measurement exam- ples, which were used to study precipitation effects in SAR- images. Based on these valuable data takes and simultane- ous weather radar measurements, a quantitative estimation of precipitation effects in SAR-images is presented.In a further step, an attempt is made to extrapolate the observed effects to systems operating at higher nominal frequency-bands, i.e. Ka-band, being taken under consideration for future SAR- systems. Index Terms— Synthetic-aperture radar (SAR), Mi- crowave imaging, Propagation effects, Signal attenuation, Precipitation 1. INTRODUCTION Since 2007, TerraSAR-X is ready to deliver outstanding data, day and night, and during almost all weather conditions. Mi- crowave SAR imaging at X-band frequencies is sometimes affected by propagation effects due to heavy rain, as can be seen in Fig. 1. The physical processes involved are • reflection at the precipitation volume • attenuation through the precipitation volume • change of the surface due to the wetness and for water- surfaces due to the impinging rain drops or due to the influence by the wind Today, a considerable body of literature exists on propa- gation effects in SAR imaging and how to make use of SAR data to deduce meteorological information [1][2][3]. Range & Illumination Azimuth 10 km Fig. 1. An example of a SAR image with rain-cell signatures recorded with TerraSAR–X in the US close to Baton Rouge. The white shading is due to direct reflections from the rain region (shown as volume ’A’ in Fig.2). Whereas the darkly shaded areas are due to rain attenuated (blocked) signals from the ground; this effect is shown as region ’B’ in Fig. 2. 2. ANALYSIS OF DATASETS AND PHYSICAL INTERPRETATION OF ARTEFACTS IN SAR IMAGES DUE TO PRECIPITATION A physical interpretation of how rain cells affect SAR im- ages is shown in Fig. 2. The sketch shows an imaging sce- nario, where the transmitted waves interact with a precipita- tion cell. It can be observed that area ’A’, which corresponds to time instant τ A in the amplitude/time diagram, is due to strong backscattering from large hydrometeors. Time instant τ B , which corresponds to the region ’B’ proves that signals have been heavily attenuated. By comparing the dark patch in Fig. 1 and the amplitude/time diagram in Fig. 2, the veil in Fig.1 corresponds to area ’A’(τ A ), and the shadowlike black areas close to this veil in Fig. 1 corresponds to the region ’B’ (τ B ) in Fig. 2.