Harley H. Cudney

Verification of Acoustic Propagation Over Natural and Synthetic Terrain

In this paper we review the theoretical basis for the PSTOP3D acoustic propagation code and the added features for acoustic source modeling and propagation over porous surfaces. We then present results from verification efforts for free-field propagation, propagation over porous surfaces, and comparison with experimental data for reflections from a wall. Finally, we review efforts to extend the modeling capabilities in the code, as well as continuing modeling efforts.

Spatial Processing of Urban Acoustic Wave Fields from High-Performance Computations

Future US Army ground sensors in urban terrain will process acoustic signals to detect, classify, and locate sources of interest. Optimal processing will require understanding of the effects of the urban infrastructure on sound propagation. These include multi-path phenomena that will complicate sensing, and must be accounted for in sensor placement and performance algorithms. The objective of this work is to develop spatial processing techniques for acoustic wave propagation data from three-dimensional high-performance computations to quantify scattering due to urban structures and develop reduced-order models of wave-field data. The work applies Fourier analysis to urban acoustic wave-field data to generate measures of signal fading caused by scattering. The work calculates these measures from ratios of Fourier transforms of wave-field signals with and without scattering to isolate the structure-induced scattering. In addition, we calculate impulse response functions of acoustic wave-field data, and use these functions as the input to a system realization algorithm to produce reduced-order wave-field models. The results include signal fading as functions of distance and frequency for an urban acoustic model that includes structures like those in a small-city periphery. The results also include predicted acoustic wave-field signals from reduced-order models in comparison with full-model signals. We conclude that the spatial processing of urban acoustic wave fields from high-performance computations produces broadly useful measures for understanding and modeling urban wave propagation.

Reduced-Order Wave-Propagation Modeling Using the Eigensystem Realization Algorithm

This paper presents a computationally efficient version of the Eigensystem Realization Algorithm (ERA) to model the dynamics of large-domain acoustic propagation from High Performance Computing (HPC) data. This adaptation of the ERA permits hundreds of thousands of output signals to be handled at a time. Once the ERA-derived reduced-order models are obtained, they can be used for future simulation of the propagation accurately without having to go back to the HPC model. Computations that take hours on a massively parallel high performance computer can now be carried out in minutes on a laptop computer.

Superstable Models for Short-Duration Large-Domain Wave Propagation

This paper introduces a superstable state-space representation suitable for modeling short-duration wave propagation dynamics in large domain. The true system dimensions and the number of output nodes can be extremely large, yet one is only interested in the propagation dynamics during a relatively short time duration. The superstable model can be interpreted as a finite-time version of the standard state-space model that is equivalent to the unit pulse response model. The state-space format of the model allows to user to take advantage of extensive state-space based tools that are widely available for simulation, model reduction, dynamic inversion, Kalman filtering, etc. The practical utility of the new representation is demonstrated in modeling the acoustic propagation of a sound source in a complex city center environment.

Signal fading curves from computed urban acoustic wave fields

Future US Army ground sensors in urban terrain will process acoustic signals to detect, classify, and locate sources of interest. Optimal processing will require understanding of the effects of the urban infrastructure on sound propagation. These include multi-path phenomena that must be accounted for in sensor placement and performance algorithms. This work applies Fourier analysis to urban acoustic wave-field data from three-dimensional high-performance computations to generate statistical measures of signal fading caused by scattering. The work calculates these measures from ratios of Fourier transforms of wave-field signals with and without scattering to isolate the structure-induced scattering.

Implementing statistical acoustic characterization of urban terrain into a decision support tool

Statistics-based characterizations of acoustic propagation, namely, fading and coherence, are being developed as functions of urban terrain zones. The fading and coherence curves are characterized for each of several urban terrain zones of interest, and the resulting curves are parameterized as a function of frequency and distance from the source. With the parameters for signal fading and coherence as a function of frequency, distance to source, and urban terrain zone type, the decision support tool SPEBE (Sensor Performance Evaluator for Battle-space Environments) is extended to urban areas. Combined with a separate effort characterizing background noise levels as functions also of urban terrain zones, a tool for predicting probability of detection for various sources in urban areas is demonstrated.