Optimized constraints for the linearized geoacoustic inverse problem

Abstract

A geoacoustic inversion scheme to estimate the depth-dependent sound speed characteristics of the shallow-water waveguide is presented. The approach is based on the linearized perturbative technique developed by Rajan et al. [J. Acoust. Soc. Am. 82, 998-1017 (1987)]. This method is applied by assuming a background starting model for the environment that includes both the water column and the seabed. Typically, the water column properties are assumed to be known and held fixed in the inversion. Successful application of the perturbative inverse technique lies in handling issues of stability and uniqueness associated with solving a discrete ill-posed problem. Conventionally, such problems are regularized, a procedure which results in a smooth solution. Past applications of this inverse technique have been restricted to cases for which the water column sound speed profile was known and sound speed in the seabed could be approximated by a smooth profile. In this work, constraints that are better suited to specific aspects of the geoacoustic inverse problem are applied. These techniques expand on the original application of the perturbative inverse technique by including the water column sound speed profile in the solution and by allowing for discontinuities in the seabed sound speed profile.

Accounting for Ocean and Seabed Variability in Oceanic Waveguide Parameter Estimation

“…Although the amplitudes for individual wave number peaks were not-equal, only wave numbers corresponding to locations of the peaks are used in the inversion, so there is little impact on the results. These data, expressed in terms of modal eigenvalues as determined by the peak locations were used in a linearized inversion scheme [2]. The resulting sound speed fields inferred from data collected on the two systems were remarkably consistent as indicated in Fig.…”

“…To date this work has resulted in multiple publications in refereed journals [2][3][4][5][6], conference proceedings, and conference presentations. In FY11, experimental work with operational assets was carried out in March 2011 on the R.V.…”

“…Alternative regularlization methods [2] were adapted and exploited to better constrain inverse solutions and account for layering in the seabed. The perturbative method was also expanded for use with broadband data.…”

“…They were also applied to estimate range-dependent water column sound speed. [2][3][4][5] (2) The application of high-resolution wave number estimation techniques was optimized for extracting range-dependent modal information used in the inversion algorithms.…”

Inversion for range-dependent water column sound speed profiles on the New Jersey shelf using a linearized perturbative method

“…Therefore, an accurate estimate of the water column sound speed profile can be obtained even when seabed properties are not well known. 24 Although application of the perturbative inverse technique for estimation of water column sound speed profiles is relatively straightforward, some complications do arise. Specifically, difficulty occurs because the wave number data are insufficient to determine water column properties in some portions of the waveguide.…”