Since its launch on November 4,1995 and the start of the routine operation on April 1, 1996, RADARSAT-1, the first Canadian SAR remote sensing satellite, is providing calibrated data to worldwide users for their intended applications. This paper discusses the calibration and image quality perspectives of RADARSAT-1 in its extended mission, as evolved from the earlier phases of the calibration plan. At the early qualification stages of the mission, the RADARSAT-1 calibration and image quality plan integrated two sets of measurements still in use today: both single beams and ScanSAR are monitored routinely using images of the Amazon Rainforest for calibration performance, and using images of RADARSAT-1 Precision Transponders for quality performance. Following the Antarctic Mapping Mission in 1997, systematic calibration measurements showed changes in the characteristics of several previously calibrated elevation antenna patterns. Compensations for these changes are made in the processor by re-calibrating the beams. In addition, a major upgrade of the ScanSAR processor completed at CDPF in 2002 made significant improvements in image quality and radiometry. Through the 2 years of successful image quality maintenance of RADARSAT-1 in extended mission, the provision of radiometrically and geometrically calibrated products to users by the Canadian Data Processing Facility (CDPF) has also fostered specific efforts to prevent image quality to be affected by aging and potential failure of spacecraft subsystems. In late October 2000, concerns began to rise of the possibility of failure of the Horizon Scanner 1, which would result in operating the spacecraft in a mode known as 'Attitude Determination Method 3' (ADM3), causing a decrease in attitude control performance of spacecraft compared to the current operation in ADM1.Experiments were conducted to better understand the impact on processing and image quality when in ADM3 mode. No major impact on image quality was noticed with adapted re-processing. In mid 2002, due to aging considerations for the On-Board Recorder, sites within Canadian mask have been envisioned for their ability to support radiometric analyses, as a potential alternative for the Amazon Rainforest, where images are recorded. From several sites, a Boreal Forest location near Hearst, Ontario, was chosen for testing radiometric measurements, using specific beams to cover the entire range of incidence angles. In parallel, new methods and software tools are developed to improve image quality operational efficiency and to perform new measurements. A database tool has been developed for tracking performance of image quality parameters and radiometric measurements over Amazon and Hearst regions. Downloaded by 128.70.15.31 on June 20, 2016 | http://arc.aiaa.org |
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