Through the sensor estimation of sound speed profiles

Abstract

A through-the-sensor method to sense the local sound speed profile (SSP) using measured acoustic wave numbers via an array of hydrophones is proposed. Ocean sounds can be treated as acoustic energy trapped as discrete modes within the water column. A Fredholm integral equation of the first kind relates the linearized (perturbative) sound speed corrections to the wave number differences between the measured values and those calculated from an acoustic kernel. Thus, a method to exploit environmental information deduced from different in situ sonar systems is proposed. Though this inversion can be unstable and non-unique, recent improvements in sparse inversions can lead to robust estimates even without an accurate starting SSP. An iterative algorithm using multiple acoustic frequencies is beneficial to achieve convergence and stability for larger sound speed corrections. This paper will compare broadband incoherent L2- and coherent L1-inversion results. Careful consideration must be made of the acoustic frequency, number of modes, a priori environmental information (e.g., water depth), and array length. The method will be first demonstrated on simulations and recordings from the Littoral Depth Discrimination Experiment 2012 (LIDDEX12) data set.