Passive range estimation and range rate detection

The problem of interest is a rapidly closing object (e.g. a torpedo) emitting broadband and narrowband acoustic signatures. A high negative range rate is indicative of a torpedo threat, and good range-bearing estimates provide good target localization. A linear, towed hydrophone array is used as a receiver, and in many cases the received signals will display high signal-to-noise ratio. It is desirable to detect at ranges greater than the near field range of the array. High-resolution range-bearing estimators have been developed using narrowband signatures and broadband signatures. The range difference to the target across an array causes target signals to display a wave-front curvature. Range estimation is based on wave-front curvature determination using a matched-filtering post beamformer approach. First a target is selected for range estimation in which a subset of beams is chosen for sector inverse beamforming. Curvature pattern replicas over range and bearing are computed and used in a Capon form beamformer. Simulations and experiments with in-water data compare the algorithm performance to a derived benchmark. In addition, a cepstrum-based range rate indicator was demonstrated using experimental data displaying multipath propagation (Lloyd mirror).