Application of maximum entropy to statistical inference for inversion of data from a single track segment.

In this paper an approach is presented to estimate the constraint required to apply maximum entropy (ME) for statistical inference with underwater acoustic data from a single track segment. Previous algorithms for estimating the ME constraint require multiple source track segments to determine the constraint. The approach is relevant for addressing model mismatch effects, i.e., inaccuracies in parameter values determined from inversions because the propagation model does not account for all acoustic processes that contribute to the measured data. One effect of model mismatch is that the lowest cost inversion solution may be well outside a relatively well-known parameter value's uncertainty interval (prior), e.g., source speed from track reconstruction or towed source levels. The approach requires, for some particular parameter value, the ME constraint to produce an inferred uncertainty interval that encompasses the prior. Motivating this approach is the hypothesis that the proposed constraint determination procedure would produce a posterior probability density that accounts for the effect of model mismatch on inferred values of other inversion parameters for which the priors might be quite broad. Applications to both measured and simulated data are presented for model mismatch that produces minimum cost solutions either inside or outside some priors.

A two-way coupled mode formalism that satisfies energy conservation for impedance boundaries in underwater acoustics.

This paper shows that energy conservation and the derivation of the two-way coupled mode range equations can be extended in three dimensions to complex mode functions and eigenvalues. Furthermore, the energy in the coupled mode formulation is conserved for finite thickness fluid ocean waveguides with a penetrable bottom boundary beneath any range dependence. The derivations rely on completeness and a modified orthonormality statement. The mode coupling coefficients are specified solely and explicitly by the waveguide range dependence. The statement of energy conservation is applied to a numerical coupled mode calculation.

Scattering in a Pekeris waveguide from a rough bottom using a two-way coupled mode approach.

Scattering from a rough ocean bottom is described numerically with a two-way coupled-mode formalism that contains scattering effects to all orders and provides an exact solution to the wave equation. Both scattered field and direct blast components are computed within the formalism framework. A comparison of the scattered component solution from the coupled mode with the Born approximation (BA) solution for scattering from a rough bottom Pekeris waveguide shows that the BA predicts correctly the scattered field levels but not detailed structure. The transition from direct blast to scattered field dominance is identified in the total field time series.

Geoacoustic inversions and localizations with adaptively beamformed data from a surface ship of opportunity source.

A technique has been developed for incorporating adaptively beamformed (ABF) data into geoacoustic inversions and source localizations based on matched-field processing. Rather than adaptively adjusting matched-field weights, for this paper ABF processing is applied to construct subaperture beam data from which the inversions and localizations are derived. This application of ABF processing to inversion and localization is successfully demonstrated with data collected on a horizontal line array from a surface ship of opportunity source (SSOS). When measured data representing noise from one or more interfering sources at various levels are injected into the data collected from the SSOS, the inversion processing with ABF subaperture data is successful at interferer noise levels exceeding the SSOS levels by 10-13 dB and for which the inversion processing with conventionally beamformed data fails.

Rough surface scattering in a Born approximation from a two-way coupled-mode formalism.

Scattering from a rough surface in an ocean waveguide is described in a new derivation from a two-way coupled-mode representation. The general formalism, which contains scattering effects to all orders, is truncated to the first-order terms of an iterative (Born) expansion. Both two- and three-dimensional ocean waveguide geometries are discussed. By reducing the mode functions in terms of plane wave reflection coefficients, the off-diagonal components of the scattering kernel that is derived are shown to be consistent with a standard solution, but the diagonal components are different from the standard solution.

Coupled-mode solutions in generalized ocean environments.

This paper presents the application of the differential equation approach to solving the second-order coupled-mode equations in inhomogeneous ocean environments. The model incorporates sound velocity profile points to construct depth-dependent, piecewise linear, ocean and bottom environments along a range grid. Modal solutions are evaluated in terms of Airy functions. The formalism to evaluate analytically the mode-coupling coefficients is presented. Comparisons to conventional expressions of the coefficients are made. The integro-differential form of the coupled equations is solved using an approach developed in nuclear theory that incorporates the Lanczos method [Knobles, J. Acoust. Soc. Am. 96, 1741-1747 (1994)]. Demonstration of the practicality of this approach is made by applying the results in actual calculations with realistic ocean environments. The formalism to evaluate analytically the mode-coupling coefficients is presented. Several benchmark examples were examined in order to validate the model and are discussed, including propagation over a hill, benchmark wedge problems, and a range-varying sound speed profile benchmark. The importance of this model is also demonstrated by the physical insight gained in having a coupled-mode approach to solving range-dependent problems.