Detection and Mitigation of Strong Azimuth Ambiguities in High Resolution SAR Images

Azimuth ambiguities of bright point-like targets become more pronounced in case of high resolution SAR imaging. When improving the spatial resolution, the compression gain in SAR image formation becomes larger, which increases the dynamic range of SAR images. The increased point target intensity also implies a correspondingly higher azimuth ambiguity power, which often exceeds the reflectivity of the surrounding homogeneous areas. This paper proposes a new approach to identifying and mitigating azimuth ambiguities of bright targets within areas of distributed homogeneous backscattering. The method makes use of two independent range looks. While the main signal in the two looks is considered nearly identical, the ambiguous signal becomes mis-registered, i.e. the azimuth position shifts as a function of the range look center frequency. This property is used to derive a suitable mitigation approach. It is tested with X-band data acquired by DLR's F-SAR sensor in step-frequency mode.