Estimation of bottom attenuation in shallow water with changing depth using intensity fluctuations due to moving nonlinear internal waves

Abstract

The use of analysis of intensity fluctuations in the presence of non-linear internal waves (NIWs) for estimating the bottom attenuation is demonstrated in (JASA, v.140, p.3980, 2016) using data of Shallow Water 2006. Key objects of this analysis are the time dependence and spectrum of the total intensity (summed over the entire depth of the waveguide, in other words, over all hydrophones of the vertical line array—VLA). In this paper, we consider data on the measurement of field fluctuations (frequency 224 Hz) on an acoustic track ∼ 30 km long in the presence of NVWs, obtained in the ASIAEX 2001 experiment. The acoustic track consists of two parts: “deep,” (∼ 270 m) and “shallow” (∼ 120 m). This feature leads, first, to variation of NIW parameters, propagating toward the coast, and second, it gives reason to assume different bottom properties for these sub-tracks. The paper proposes a technique for estimating the attenuation coefficients independently for two parts based on the study of spectrograms at the VLA and spectrum of total intensity, and the following fitting between experimental data and theoretical modeling. The obtained attenuation coefficients are compared with the data of other authors for the same area.