Low grazing angle radar imaging experiments over the South Falls sandbank

• Published in: International journal of remote sensing Vol. 26; no. 5; pp. 937 - 966
• Main Authors: Lamont-smith, T., Jackson, A. M., Shepherd, P. W., Hill, R. D.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 10.03.2005; Taylor and Francis
• Subjects: Applied geophysics; Earth sciences; Earth, ocean, space; Exact sciences and technology; Internal geophysics; Marine geology; Northeast Atlantic; North Atlantic; North Sea; strain rates; Atlantic Ocean; ERS; data processing; remote sensing; velocity; synthetic aperture radar; airborne methods; depth; winds; sand ridges; imagery; radar methods; direction
• ISSN: 0143-1161; 1366-5901
• DOI: 10.1080/01431160512331316441

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 .