A far distance wideband geoacoustic parameter inversion method based on a modal dispersion curve

Abstract

Acoustic propagation in shallow water is greatly influenced by the properties of the sea bottom. The dispersion characteristics of modes are relatively sensitive to the bottom parameters and have been used to invert the bottom parameters. Since the inversion error using a single wideband sound source increases with increasing range, a far distance inversion method based on the modal dispersion curve using a single hydrophone with two wideband sound sources is presented in this paper, in which a warping transform is applied so that it can accurately extract the modal dispersion curve from the warped signal spectrum. Experimental data used for the inversion are acquired using a hydrophone of vertical array in the South Sea of China during the Autumn in 2012. The transmitted signals are explosive signals, and the bottom sound speed and density are inverted by matching the theoretical arrival time differences of various modes and frequencies with those calculated using the experimental data. The attenuation coefficient is deduced using the transmission loss data recorded in the experiment. A genetic algorithm (GA) is used for optimization search for the parameter bounds. Inversion results demonstrate that the arrival time difference when using the bottom sound speed and density show a high consistency with those obtained using the experimental data. Moreover, the attenuation coefficient is nonlinear over the frequency band from 100 to 315 Hz. The validity of inverted parameters is evaluated by the posteriori probability distributions, and the numerical results of arrival time differences calculated using the inverted sound speed and density are in good agreement with those extracted from the other two wideband explosive signals at different distances. In addition, the theoretical transmission loss calculated using the inverted attenuation coefficient matches the experiment data very well. It is shown that the inversion scheme can provide a valid and stable environmental estimation.