Radiometric measurements of the Canadian boreal forest using RADARSAT-1 beam patterns

This paper describes exploratory work in evaluating the use of the Canadian boreal forest in potential support to radiometric calibration of the RADARSAT-1 Synthetic Aperture Radar (SAR) sensor. The primary site for SAR calibration performance and monitoring, in the Amazon rain forest, requires the use of the spacecraft's On-Board Recorder (OBR) to store the images until they can be downloaded to a Canadian data reception facility. In mid 2002, aging considerations for the OBR led to the survey of natural sites within data reception mask of Canadian ground stations. Several boreal forest and mixed Tundra-Taiga sites were tested for their ability to support radiometric analyses in case of an OBR failure. A boreal forest-type area, near Hearst, in the province of Ontario, was chosen for a more comprehensive study. Radiometric measurements covering the entire incidence angle range of RADARSAT-1 were performed using an elevation pattern measurement method adapted from the existing methodology used for Amazon image analyses. Radiometric measurements over the chosen area are reported, examining temporal and seasonal variations. Antenna gain pattern shape determination is also attempted, based on seasonal backscattering profiles of the region. The differences between extracted pattern shapes and their corresponding calibrated patterns then provide indications on the mean term, across swath backscattering behavior of the boreal forest, confirming its potential suitability for radiometric calibration monitoring.