A Direct Method for the Estimation of Sediment Sound Speed With a Horizontal Array in Shallow Water

Abstract

In this paper, a fast approach for estimating sediment sound speed in a shallow-water environment is developed. Under certain assumptions, this algorithm recovers the seabed sound-speed profile using pressure field measurements at low frequencies. The geometry of the problem involves measuring the pressure at horizontally placed hydrophones in the water column. The Deift–Trubowitz integral equation is then solved. This work introduces two methods for this task. The first is a modified Born approximation that builds upon a standard first-order approximation; the second is based on interpolating the integrand. It is shown with synthetic data that these methods work well with successful sound-speed estimation and identification of sharp discontinuities in sound speed. Although the methods are stable and effective with noise-free data, problems arise when noise contaminates the acoustic field. Regularization approaches, reducing the disruptive effect of singular points and smoothing a measured reflection coefficient, are developed to remedy this problem, leading to improved results in noisy environments. In addition to providing sound-speed estimates, the method also computes sediment thickness. This feature is of particular interest, since it makes the method suitable as a preprocessing step providing useful information to other inversion methods. Sensitivity analyses demonstrate that some assumptions required for the approach implementation are not restrictive.