Visual representation of the effects of spatial and frequency filters applied in passive sonars

The operator of a passive sonar should be able to discern the direction (bearing) of a submerged, noise-producing object. Interference to bearing comes from reverberations, noise from the sea, man-made noise and noise generated by other objects. The article presents methods of spatial and frequency filtration designed to provide various forms of display of those fragments of the spectrum that are of interest to the operator. The operator makes his selection on the basis of many spectrograms that are produced during the successive listening cycles, displayed on the monitor. The amplitudes of spectral lines in the spectrograms are presented as lines of various lengths and colours. The summation spectrum of the displayed listening cycles is presented, too. The lines from a selected spectral range are shown on the panoramic amplitude graph in the function of the bearing angle. Thanks to that the determination of the location of the source of sound is significantly improved. The source of sound can also be discerned by using a reverse technique whereby a group of spectral lines is determined on the basis of a selected sector of angular observation