A new hybrid-beam data acquisition strategy to support ScanSAR radiometric calibration

Wide-swath synthetic aperture radar (SAR) coverage is provided by RADARSAT using a multiple-beam scanning strategy called ScanSAR. Each beam covers a different range, and is allocated a fixed period of time in which to transmit and receive radar pulses. During SAR processing, the data from each beam must be "stitched" together to form a complete image of the scanned area. This data must be radiometrically calibrated to compensate for antenna beam patterns. However, incorrect measurements of the satellite roll angle cause errors in radiometric calibration, and can lead to visible artifacts in the image (e.g. banding). A new ScanSAR data acquisition technique is proposed that improves roll angle estimation through the use of radar pulses, transmitted by one beam and received by another. The new data are called "hybrid beam data" and can be utilized with modified versions of existing roll estimation algorithms. This paper shows how the hybrid beam data are collected, accommodating pulse repetition frequency, range gate delay, and other timing changes as beams are switched.