Passive localization of an underwater acoustic source using directional sensors

This thesis studies the passive localization (bearing estimation and range and depth estimation) of a single stationary underwater acoustic source in a two-path (direct and surface-reflected path) environment. The main objective of the study is to synthesize and then analyze a passive localization system with a two-receiver (vertically separated) structure that can be supported by a single sonobuoy. Each of the two receivers consists of a cluster of directional sensors uniformly located on a small circle in a horizontal plane. The gain profile of the directional sensors is such that it depends only on bearing of source.;Source bearing is estimated from the average signal powers received at two adjacent sensors in one of the two clusters. The focus in the study of bearing estimation is on the feasibility of energy-based bearing estimators. The range and depth information of the source is extracted from the 6 estimated time differences of arrivals (TDOAs) at the two receivers. The emphasis in the study of range and depth estimation is on the correlation among the multipath TDOA estimators and its effect on the prediction of the variance of the time delay-based range and depth estimators.;Two algorithms for energy-based bearing estimation are developed. Expressions for the bias and variance of both energy-based bearing estimators are derived. They reveal a fairly simple relationship between the performance of the two bearing estimators and the design parameters (the omnidirectional signal-to-noise ratio and the two receiver parameters). Using the developed expressions can provide good predictions of the bias and variance of the two energy-based bearing estimators in the case of reasonable signal-to-noise ratios.;The range and depth estimators are investigated with time delay techniques. Fifteen expressions for the covariance among the six multipath TDOA estimators are derived. It is shown that all six multipath TDOA estimators are correlated and the degree of the correlation depends on the power spectral density of the source signal and that of the ocean noise, and only two multipath TDOAs--the time difference of arrival between the direct and the surface-reflected path for each receiver. A generalized covariance equation is developed for each category. Thus, the fifteen covariance expressions can be obtained from three compact expressions.;The effect of correlation among the multipath TDOA estimators on range and depth estimators is investigated. The least squares range and depth estimators, based on all six TDOA estimators, are proposed. Expressions for the variance and bias of the range and depth estimators are derived. The results in the study of range and depth estimation show that the expressions for the variance of the range and depth estimators can be in error by as much as a factor of 2.5 without the correlation among the TDOA estimators. Including the correlation provides significantly better predicted range and depth variance. Also, the range and depth estimators are nearly unbiased. (Abstract shortened by UMI.).