Surface and bottom backscattering strengths measured from midrange reverberation in the CEAREX 89 arctic experiment.

Abstract

Acoustic reverberation data from SUS explosions collected during the CEAREX 89 experiment in the Norwegian–Greenland Seas are analyzed to estimate both under-ice and bottom backscattering strengths. Data from the 1230-m vertical array were previously used to measure scattering strengths from short-range (<3 km) under-ice reverberation returns [T. J. Hayward and T. C. Yang, J. Acoust. Soc. Am. 89, 1941 (A) (1991)]. The analysis here concentrates on midrange (up to 20 km) reverberation, and extracts the backscattering strengths from single and double bottom bounced data. The high-angle returns backscattered from the ice (and bottom) and specularly reflected from the bottom are recognized in the display of vertical-array beam response vs vertical arrival angle and time. Bottom losses are inferred from comparison of the single-bounce and double-bounce data using modeled transmission losses. This method provides both a larger scattering-area sample and higher incident/scattered angle backscattering strengths compared with the direct-path measurements. These results are compared with the short-range measurements. [Work supported by ONR Arctic Sciences Program.]