Measurements of mid-frequency boundary scattering on the New Jersey Shelf and in the Straits of Sicily

Abstract

During joint trials with the SACLANTCEN, direct-path monostatic scattering measurements were conducted at 18 sites across the New Jersey Shelf (Boundary Characterization 2001) and at 9 sites in the Straits of Sicily (Boundary Characterization 2002). Using combinations of short duration cw and LFM signals, both the mean (scattering strength) and statistical (probability density function) characteristics of the bottom- and surface-interaction zones were measured at each site. Bottom-zone scattering strength results show that many sandy and rocky sites exhibited a generally flat dependence on grazing angle (over 20–70 deg) and a moderate dependence (∼5 dB) on frequency over 2.5–5 kHz. In contrast, the measured surface-zone scattering strengths exhibited a strong dependence on grazing angle (and a mild dependence on frequency), consistent with scattering from the rough air–sea interface. Using physics-based scattering models, coupled with the supporting environmental measurement results, estimates of both the relative contributions of different bottom-zone scattering mechanisms (water-sediment interface, sediment volume and, at low grazing angles, near-bottom fish) and geophysical quantities (such as bottom roughness spectral parameters) were derived and will be presented along with the acoustic data results. [Work supported by ONR.]