Geoacoustic Inversion Using Simple Hand-Deployable Acoustic Systems

Abstract

This article proposes the use of a simple, low-cost, hand-deployable pair of experimental assets to conduct geoacoustic inversion at sea. The system consists of an expendable, fully mechanical acoustic source called a rupture induced underwater sound source (RIUSS) and a new ropeless passive acoustic mooring called a TOSSIT (not an acronym). Used together, RIUSS and TOSSIT enable the collection of acoustic data suitable to perform single-hydrophone geoacoustic inversion. The method is illustrated using data collected on the New England Mud Patch in May 2021 from a relatively small (22 m) and inexpensive chartered fishing vessel. Modal time-frequency dispersion from 15 to 385 Hz is extracted from the TOSSIT/RIUSS data using warping, and used as input for Bayesian transdimensional geoacoustic inversion. The inversion results compare favorably to results obtained with data collected on the same track with traditional assets (e.g., a vertical line array) during the 2017 Seabed Characterization Experiment, even when jointly inverting for the water-column sound speed profile and seabed geoacoustic parameters. This further demonstrates inversion repeatability in a given location using data sets collected years apart, and under different (and potentially unknown) oceanographic conditions.

Trans-dimensional Bayesian Inversion for Seabed and Water-column Models

“…The subbottom depth of this layer in the inversion results corresponds closely to that of a seismic reflector interpreted to represent the transition from mud to a sand layer [9]. The seabed profiles agree well with other geoacosutic inversion results (computed with known SSPs) at the NEMP, e.g., [5,11,12].…”

“…Hence, this paper considers an approach to geoacoustic inversion that accounts for lack of knowledge of the water column by carrying out joint trans-D Bayesian inversion for both the water SSP and the seabed geoacoustic model. The approach is validated here by application to modal-dispersion data collected on the New England Much Patch (NEMP) [5].…”

A Multi-Objective Geoacoustic Inversion of Modal-Dispersion and Waveform Envelope Data Based on Wasserstein Metric

“…To minimize uncertainties in the estimation of seabed parameters, researchers have developed signal processing techniques to derive pertinent details from acoustic field data, such as sound pressure or amplitude phase [9], waveguide invariants [10], reflection coefficient versus angle [11,12] data, etc. The inversion methods using modal amplitude ratio [13], green function [14,15], modal group speed dispersion [16] and vertical coherence [17] have been discussed by Zhou et al [18], while the most widely used characteristic of propagating normal modes is modal group speed dispersion [19][20][21].…”