Constrained comparison of ocean waveguide reverberation theory and observations

Abstract

Measurements of long-range ͑order 10 4 m͒ shallow-water reverberation in the Straits of Sicily at 900 and 1800 Hz are compared with theoretical predictions. All of the required environmental inputs for the theory are obtained independently, that is to say there are no free parameters. The reflection coefficient and the scattering strength are measured by direct path methods; both quantities show strong frequency dependence. The theoretical reverberation predictions using these measurements are in good agreement with directional reverberation data, i.e., within the expected uncertainty bounds. The good agreement suggests that the supporting environmental measurement techniques are robust and that the physics associated with reverberation in a waveguide is reasonably well understood, at least in simple environments. The ability to independently measure the seabed scattering strength and reflection coefficient is a crucial step for the advancement of inverse methods using reverberation ͑e.g., rapid environmental assessment͒ inasmuch as it provides the means for quantitatively measuring the robustness of those methods.

Low frequency seabed scattering at low grazing angles

“…[6][7][8][13][14][15][16] Due to its simplicity and intuitive nature, the energy flux method has further been developed and widely used for SW reverberation calculations, 17-30 mainly due to works by Harrison,Holland and Ainslie. 18,20,21,[23][24][25][26][27][28][29][30] All the closed-form expressions in isovelocity shallow water, derived by Zhou, 6 Harrison, 18 Ainslie 27,30 and Holland, 24 are almost identical, having only minor differences in constant coefficients. In this paper, Zhou's closed-form expressions for reverberation in isovelocity water are used to extract the frequency and angular dependence of the BBS at LF&LGA from long-range reverberation data.…”

“…Harrison, 18 Ainslie 27 and Holland 24 have derived expressions for an isovelocity SW that are similar to Eq. (23) and Eq.…”

“…11 The IRRL data were obtained from 4 sites. Equation (24) shows that in the three-halves law region, if the bottom scattering obeys the Lambert law (n ¼ 2), the reverberation intensity is independent of water depth, H. Using the IRRL data shown in Figs. If both wideband TL and RL are well measured, or if both RL data and the seabed geoacoustic model are available, then Eqs.…”

A waveguide invariant adaptive matched filter for active sonar target depth classification

“…For scatterers on the ocean floor, an empirical model for the T mn ðxÞ can be used to form s(t, r, z b ) which has been shown to accurately model reverberation (e.g., in the Malta plateau area) 20 and is given by…”

Distant bottom reverberation in shallow water

“…The channel effect of bottom reverberation had been investigated by many authors (Bucker and Morris, 1968;Holland, 2006;Mackenzie, 1962;Zhou and Zhang, 1977), but in most of these researches, bottom reverberation had been described as the sound field formed by distributed secondary sources on boundary, and results obtained in such way sometimes will contradict with principle of reciprocity in bi-static cases (Wang and Shang, 1981). It is desirable to give a method for computation of reverberation, which directly using the scattering effect of stochastic characteristics of water channel, and can give results obeying the principle of reciprocity in any case.…”