RADARSAT ScanSARRoll Angle Estimation

Wide-swath SAR imagery obtained by the RADARSAT ScanSAR mode can suffer from radiometric artifacts. These artifacts arise from improper application of Range Dependent Gain Corrections (RDGCs), mainly due to insufficient knowledge of the satellite’s roll angle. Specifically, roll angle estimation errors as small as 0.1 degrees can cause noticeable gain errors of 1 dB or more. Beam-stitching techniques exist which can reduce, but not eliminate, these errors in the beam overlap region Current roll angle estimation algorithms do not consistently provide adequate results. These algorithms are susceptible to RDGC uncertainties in terms of pattern shape and gain offsets. This paper proposes a new data acquisition method, in which signal data is obtained during the beam switchover by transmitting pulses through one beam and receiving them with another beam. This “2-beam data” is then used in a modified algorithm to provide a more accurate and robust roll estimate. The logistics of acquiring 2-beam data are also explored. The effects of various roll angle estimation errors on different beam combinations are simulated. The algorithm results from a current and two proposed algorithms are compared. Algorithms using this 2-beam data can tolerate an overall lower mean scene σ◦ and more RDGC uncertainty than standard data.