Maintaining RADARSAT-1 image quality performance in extended mission

This paper discusses the synthetic aperture radar (SAR) calibration and image quality monitoring of RADARSAT-1 in its extended mission, as evolved from the earlier phases of the calibration plan, after its launch in 1995 and the start its routine operation in 1996. Since the early qualification period of the mission, both single beams and ScanSAR operating modes are monitored routinely, based on Amazon Rainforest images for radiometric calibration performance, and on images of Precision Transponders for image quality performance. After an initial calibration phase, radiometric monitoring showed changes in the characteristics of several previously calibrated elevation antenna patterns and compensation for these changes were, and are still made in the image processor. In addition, a major upgrade of the ScanSAR processor completed at the Canadian Data Processing Facility (CDPF) in 2002 provided significant improvements in image quality and radiometry. Through the five-year nominal mission which ended in 2001 and the four years of the current extended mission, radiometrically and geometrically calibrated imagery products were continuously provided to worldwide users. In late October 2000 however, concerns began to rise of the possibility of failure of the Horizon Scanner 1 (HS1), which would result in operating the spacecraft in a degraded attitude control mode, compared to the current primary operation. Experiments were conducted to better understand the impact on image quality when operating in backup attitude control mode. In mid 2002, aging considerations for the On-Board Recorder also led to survey natural sites within Canadian data reception masks for their potential to support radiometric analyses, as an alternative to the Amazon Rainforest, where images are recorded.