Bottom mounted active sonar for detection, localization, and tracking

Abstract

A bottom-mounted, wideband active sonar system designed to detect unfriendly vessels entering a closed area is described. Wepresent signal-proeessingalgorithms for target detection, classiAcation, locallzation, and tracking, and present performance predictions based on simulations. These algorithms are shown to be effective With state of the art, reallzable sonar systems.The signals are binary phase shift keyed (BPSK) with a range resolution of approximately 0.01 m and Doppler resolution of 0.5 d s . Received signals from multiple directional receive beams are basebanded and Hilbert transformed to obtain a complex representation. These signals are correlated with replicas of the transmitted signal time comprplsed or dilated to represent a number of different hypothetical target Dopplers, giving a processed signal with three dimensions: time, chauneI, and target Doppler.. . Background interference is estimated wing a blocktrunsversal Alter. The processed signal is dlvtded by the estimated backgronnd to obtain signal-to-interference ratio (SIR) and SIR threshold crossings. are detected and contiguous detections are clustered. Range Is estimatedusing arrival time.Bearing :is estimated using an amplitude comparison for adjacent receivebeam. Elevation is estimated using split beam phase between signals from elements separated vertIdly. Finally, the crossings are clustered by location and Doppler.Clusters are classified based on amplitude and estimated physical extent and shape. Clnsters with sufficiently high classification are passed to a tracking algorithm that compntm a Kalman liiter track using clusters derived from sequential traosmissions. This filter operates using linked line of sight (LOS) coonlinates, a technique long used in radar. The LOS coordinates used in this application are range, range rate, hearing, add elevation;Use of such coordinates Is advantageous in thlr appiication because the errors in the coordinates are nearly Independent of one another.Performajxe of thls 'algorithm was investigated using active acoustic signals synthesized by the Sonar Simnlation Toolset (SST), a digital program written by Robert Goddard at the AppUed Physics Laboratory. This program. generates a complex baseband representation of the acoustic signal In eacb chinneL This 'sigdal is pmcessed by the detectlou,classificatIon, and track@g algorithms. SST simulates effects of aconstic propagation ihclnding .refraction and scanering and reflection from a target. Several simulated encounters with different target geometries are presented to illustrate detection, localization, and tracking performance.

Submarine Location Estimation Via a Network of Detection-Only Sensors

“…In this paper, we focus on localization with active sonar systems, as those studied in [3], [4], [9], and [15]. Traditional active sonar systems rely on one or a few source-receiver pairs.…”

“…As depicted in Fig. 3, we compute as (4) There is no ambiguity in determining from (4) when , and, thus, belongs to the range of . Whether the sensor is in the zone or outside the zone depends on the angle difference between and .…”

Exact simulation of complex-valued Gaussian stationary processes via circulant embedding

“…Specific applications include time series of (i) reverberation measurements recorded in an underwater environment [10,16], (ii) passive radar returns from the ionosphere [17] and (iii) ultrasound measurements of blood flow [8]. One reason that such models are of interest is that they can be used to generate realistic simulated time series for studying signal processing algorithms.…”