Abstract

A concept, practical realization and applications of the passive acoustic radar for localization and continuous tracking of fixed and mobile sound sources such as: cars, trucks, aircrafts and sources of shooting, explosions were presented in the paper. The device consists of the new kind of multi-channel miniature three dimensional sound intensity sensors invented by the Microflown company and a group of digital signal processing algorithms developed in the Multimedia System Department, Gdansk University of Technology. Contrarily to active radars, the passive acoustic radar does not emit any scanning beam but "listens to" surrounding sounds and in result it provides information about the directions of arriving acoustical waves. Hence, monitoring of the acoustic field in this way remains unnoticeable. For the sound source localization the two independent 3D sound intensity probes and triangulation technique were used. In order to increase accuracy of the sound source localization an additional algorithm of the resonant narrow-band filtration of acoustic signals was applied. The practical examinations of the sensitivity and accuracy of the developed PAR were conducted in an anechoic chamber and in typical reverberant conditions. The functionality and acoustic properties of the passive radar were examined in details using three types of signals for given environmental conditions: broadband sounds, pure-tones and impulsive sounds. Taking the obtained results of the realized experiments into consideration it was ascertained that even the inconsiderable value of the signal to noise ratio was sufficient to localize sound source suitably. The obtained measurement results including real sounds samples can be remotely sent to the control station. The passive radar can be operated both automatically as a stand-alone unit and in manual mode. The proposed technology can provide the operator with many essential data representing the activity of objects and targets in a given area. Moreover, the automatic and continuous tracking of the selected sound source movement is also possible. Additional procedures such as: sound source classification module or automatic control of the digital PTZ (Pan Tilt Zoom) camera can be used to extend the usefulness of the presented device.

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