ScanSAR Processing Algorithm for Space borne SAR - Results with Radarsat-1 Data

摘要

ScanSAR mode of SAR operation is a very important mode with which range swath can be increased multifold. This operation is based on burst mode of operation, in which raw data is collected for a fraction of the SAR aperture time, and different bursts are considered corresponding to different contiguous range-swaths, so that we can get an equivalent swath width, which is much larger than what we can get with normal strip map-mode SAR imaging. This is achieved by re-orienting the antenna beam in the elevation direction to different sub-swaths for each burst-duration. Hence, this mode is called ScanSAR mode. Of course the penalty paid in the process, is degraded resolution. This paper presents the ScanSAR operation philosophy and the development of its processing algorithm. The algorithm is tested using Radarsat-1 data in the ScanSAR narrow mode. Different parameters like variable Doppler rate and variable PRF across the sub-swaths are estimated from the data set. In the case of ScanSAR processing, estimation of Doppler Centroid is very crucial, as burst times are very limited and hence it needs a different technique to estimate this parameter from the small burst of data. The estimation algorithm is elaborated. Another important phenomenon called the "scalloping effect" is observed in the case of ScanSAR images. The genesis of this effect and its compensation are also discussed. Also due to the unique mode of imaging in bursts, mosaicing of the sub swaths in both the range as well as the azimuth direction is required in the processed image. The overall design strategy followed for processing the Radarsat-1 data is explained, and results are presented.