Characterization and Simulation of an Acoustic Source Moving through an Oceanic Waveguide

Abstract

EXECUTIVE SUMMARYThe processing of acousti,; energy produced in an oceanic waveguide by a moving source in a near-field scenario is a challenging task statistically due to the nonstationarity of the data induced by the source motion. Many techniques of time series analysis require the estimation of at least second-order moments of the data received at a sensor or an array of sensors. The inherent assumption is made that statistically consistent estimates can be determined from sufficiently long segments of data. However, data of adequate length may not be available in the near-field scenario and so reliable estimates are difficult to obtain.In the first part of this report, we introduce a statistical characterization of the moving source via a time-varying linear-syste" :;.,_:'retation that inherently accounts for source motion. This approach demonstrates how sp% ,-.-. ,erence, which is indicative of temporally nonstationary data, is dependent on various envirn -mertal and source parameters. In the second part, wc present a technique that uses this interpretatioa to simulate the acoustic time series received at a sensor or an array of sensors of arbitrary geometry due to an acoustic source moving through an oceanic waveguide. This simulation can be L~ed tn test how source motion affects the performance of signal and array processing algorithms. We further ciLmonstrate the utility of this algorithm by comparing simulation results with experimental data.Ao6s3t1on 7OUW

Spectral Correlation Properties of Time Series Due To An Acoustic Source Moving Through An Oceanic Waveguide.

“…The impulse response and the bifrequency system function G(w, u) of a time-varying linear system are related by the Fourier transform pair (Reuter, 1994;Zadeh, 1950) …”

“…If NJ y 1 (t) Nj and NJ y 2 (t) Nj are the outputs of two real, stable linear systems driven by the same real, wide sense stationary process NJ x(t) Nj , then the 2-D spectrum between NJ y 1 (t) Nj and NJ y 2 (t) Nj is given by Reuter (1994) S 12 (a, b) + 1 2p…”

“…Hawker (1979) originally derived the pressure field generated by an acoustic source moving through an oceanic waveguide. We related Hawker's results to time-varying linear system theory and used them as a basis for an acoustic time series simulation (Reuter, 1994). In this section, we briefly review these results.…”