Defense applications of acoustic signal time delay estimation

Abstract

Measurements of the differences in the times of arrival (or time delays) of a signal at spatially-separated sensors can be used to provide localization information about a source. For continuous broadband signals, the time delay for a given pair of sensors is estimated using the generalized cross-correlation method. The time delay estimate corresponds to the time lag at which the cross-correlation function attains its maximum value. The variance of the time delay estimates depends on the signal-to-noise ratio, signal bandwidth, and integration time. Errors in the source localization parameters depend on the variance of the time delay estimates as well as on the source-sensor geometry, stationarity of the sound propagation medium, uncertainty in the actual sensor positions, and the presence of multipath arrivals. Numerous practical examples of time delay estimation and the instantaneous localization of sources of military interest are presented for acoustic sensors deployed on land and under water. Also, localization performance is observed to degrade when the sound propagation medium becomes nonstationary, the direct path and multipath arrivals are unresolvable, or the differential Doppler effect is significant. Finally, the results of source motion parameter estimation using sequences of time delay estimates from pairs of sensors are presented.