Abstract:

Acoustic backscatter data were collected from the ocean bottom at four sites on the Sohm Abyssal Plain. Using a simple array consisting of a free-flooding ring projector, omnidirectional in azimuth, and an omnidirectional hydrophone, data were collected over the frequency range of 800 to 1700 Hz. To obtain sufficient signal-to-noise ratio without impairing spatial resolution, 200-Hz-wide linear FM pulses were employed. The array was deployed 500 m above the seabed and bottom backscatter data were obtained at grazing angles down to 4(degrees) before the onset of the first surface return. For data arriving after the first-bottom first-surface interaction, the geometry approximates an in-plane bistatic experiment. Therefore, the in-plane bistatic data and the monostatic data can be compared to examine the validity of using the separable and half-angle approximations used in some bistatic scattering models [J. Acoust. Soc. Am. 89 (1991)]. In this paper the bistatic geometry is explained and the data are interpreted in light of the bistatic arrivals. Then, an algorithm is presented for extracting the in-plane bistatic scattering strength from the data. Finally, bistatic and monostatic data are compared using the separable and half-angle approximations.