Passive sonic detection and ranging for locating sound sources

A passive sonic detection and ranging (SODAR) technology is developed to locate sound sources that emit arbitrarily time-dependent signals in a typical environment encountered in practice in real time. This passive SODAR is built on a comprehensive approach including the pre-processing of input data to enhance the signal-to-noise ratio, acoustic modeling of sound radiation from a point source, iterative triangulations, and post-processing of output data to ensure the accuracy in source localization. Moreover, it employs an optimization process to extend the source detection range and improve the source localization accuracy in a highly non-ideal environment that involves a large number of unspecified reflected and diffracted sound waves. This is accomplished through computations based on the source locations predicted by the individual units of four microphones that are not lying on the same plane. Experimental results confirm that passive SODAR works for arbitrarily time-dependent signals that include continuous, transient, impulsive, random, narrow-, and broadband sounds with frequencies above 20 Hz. The minimum number of microphones that are required in passive SODAR is six. These microphones can be mounted anywhere as long as they are not on the same plane and the lines of sight from sound sources remain unblocked.