Selection of modes by time reversal in a shallow sea

Modes of the waveguide are selected from signals of individual receivers by time reversing them with the use of the frequency response of a plane wave. The experimental distribution of the modes on the “arrival time — mode number” plane corresponds to the model of an ideal waveguide, differing in that higher modes advance lower ones in the experiment. A modification of the frequency response, which eliminates that contradiction, is proposed, the modification accounting for the dependence of the effective thickness of the waveguide on the frequency. As a result, a method of determining the distance between the sound source and receiver is proposed and tested, and the interpretation of the noise immunity of signal reception on the basis of the time reversal is presented. The experimental data are obtained in the Barents Sea, at depths of about 100 m and distances of 7, 10.5, and 12 km, with the signals in a band of 100–300 Hz.