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UBC Theses and Dissertations

ScanSAR radiometric calibration based on roll angle Estimatiru Bast, Daniel Christopher

Abstract

Wide-area SAR imagery obtained by the RADARSAT-1 ScanSAR mode can suffer from various radiometric artifacts. Some of these artifacts arise from the incorrect application of Range Dependent Gain Corrections due to insufficient knowledge of satellite 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 that can reduce these errors in the beam overlap region; however, accurate roll information is required for optimum radiometric calibration across the entire range swath. Current roll angle estimation algorithms do not provide consistent results even on routine scenes. These algorithms are susceptible to uncertainties in the range beam patterns, overall scene a°, and other system variables. Currently, the Canadian Data Processing Facility does not implement an automated roll angle estimator. Compensation for range gain errors is performed in the post-processing stage. This thesis 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 "hybrid data" is then used in a new (hybrid peak detection) and modified (three beam) algorithm to provide a more accurate and robust roll estimate. Algorithms using this hybrid data are more tolerant to lower mean scene σ°, gain uncertainty, and other variables than algorithms using normal data. As this data is not currently acquired, the algorithm is tested using simulated data. The logistics of acquiring hybrid data are also explored. The implementation of hybrid data acquisition on RADARSAT-1 would not require any significant software changes. The effects of various roll angle estimation errors on different beam combinations are simulated. The new data and algorithms offer significant potential for improving roll estimates. Results suggest that the three beam algorithm can generally tolerate 3-4 dB lower σ° and 0.2 to 0.4 dB more uncertainty in the beam pattern gain than a current algorithm, while meeting required radiometric accuracy. The hybrid peak detection algorithm did not meet stringent roll requirements, but was shown to produce consistent coarse roll estimates while remaining independent of the mean scene σ and beam gain uncertainty. Other current algorithms can also be modified to use the hybrid data for potentially greater accuracy.

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