Low grazing angle radar imaging experiments over the South Falls sandbank
Abstract:A number of X-band radar data collection exercises have been conducted in the area of the South Falls sandbank, which were supported by two deployments with a research vessel that directly measured the tidal flow and water depth. Results from a total of 12 low grazing angle airborne radar data collections are presented. Nine sorties were flown with the Enhanced Surveillance Radar, using a synthetic aperture radar (SAR) mode. The other three aircraft sorties were flown using a real aperture scanning radar mode. For the scanning radar experiment, data were collected from around the sandbank on three successive days with grazing angles of 0.5°–4°. The wind speed remained relatively constant at 7–9?m?s -1 during this experiment. The radar cross-section modulation was found to have a linear relationship with the estimated surface strain rate, and the constant of proportionality was found to be 500?s when the radar was pointing downwind or crosswind, and around 200?s when looking upwind. For the SAR mode data collection, a similar look-direction dependence was observed as the scanning mode data, and a strong wind speed dependence on the visibility of the sandbank was also seen. At 6° grazing angle and a peak strain rate of 5×10 -4 ?s -1 , the strength of the radar contrast decreased by approximately 1.7?dB for unit increase in the wind speed, and the radar contrast vanished for wind speeds much beyond 10?m?s -1 .
Document Type: Research Article
Affiliations: TW Research, Harcourt Barn, Harcourt Lane, Malvern, Worcestershire WR14 4DW, UK
Publication date: March 1, 2005