Effect of frequency dependence of sea-bottom attenuation on the optimum frequency for acoustic propagation in shallow water

Abstract

The optimum frequency for acoustic propagation in shallow water is controlled by a number of physical effects and environmental parameters. This article concentrates on the effect of a nonlinear frequency dependence of the sea-bottom attenuation on the optimum frequency. Experimental data on low-frequency acoustic propagation in shallow water are presented, for which, over the frequency range where the optimum frequency should occur, no apparent optimum frequency is observed. If there is an optimum frequency for these sea areas, it is much lower than predicted by existing theories. It is demonstrated that the nonoccurrence, or lowering, of the optimum frequency can be easily explained if the sea bottom is assumed to have a nonlinear frequency dependence. Excellent agreement between theory and experiment is achieved for a site in the Yellow Sea for three different seasons using values for sediment attenuation (with nonlinear frequency dependence) and sediment sound speed which were measured independently at the same site [J. X. Zhou, J. Acoust. Soc. Am. 78, 1003-1009 (1985) ]. The sea-bottom attenuation used for the calculations was proportional to frequency to about the 1.8 power.

Effects of East China Sea shallow-water environment on acoustic propagation

“…Attenuation (1), provided in Section III, has the classical dependence and this, of course, would seem to recommend it. Attenuation (2) has a nonclassical frequency dependence, but is consistent with transmission observations by others in the general area [1]- [5] and is used in the remainder of the paper. This is not the place to adjudicate the sand-attenuation issue, but it does illustrate how disparate inputs to an otherwise competent propagation model can affect the prediction.…”

“…10. 5 A detailed discussion of the periodic ridge hypothesis is inappropriate in this paper. Note, however, that this directional mechanism can include not only scattering, but also transmission into the uplifted plates.…”

“…In contrast, TL data along B-to-A (propagation up the bathymetric contours) are much less influenced by the ridges, because the latter present small-angle planes to the sound wave and, thus, are consistent with the B-to-A data, which do not have periodic transmission troughs. 5 The difference between the TLs along the opposing tracks C-to-A and D-to-C also could be explained with appeal to the foregoing ridge mechanism. If the 8-km spacing signifies spatial periodicity, as Fig.…”

Low-frequency geoacoustic model for the effective properties of sandy seabottoms

“…The ratio of the sound speed in the bottom to the water sound speed at the water/sediment interface is about 1.056. [33][34][35] With this sound speed ratio, the best match between the measured LF Q values and the predictions of Eq. ͑4͒ requires that the bottom attenuation at sites 1-3 is…”

Analysis and model/data comparison of broadband acoustic propagation at the Atlantic Generating Station (AGS) site

“…[2][3][4][5][6][7][8][9][10] The first work on broadband acoustic propagation by Pekeris proposed a simple model to analyze the experimental results of explosive charges in shallow-water regions. 2 This work was later extended by Tolstoy 3 who obtained a solution using a fluid bottom first 11 and later for elastic media with attenuation.…”