Experimental tests of a new method to monitor sea medium by analyzing ambient noise and reradiating it from a distant point

Abstract

In-sea experiments show a possibility to estimate parameters of the water column by analyzing space-time characteristics of the natural ambient noise. If the noise is reradiated by sound transponder located at a distance from the receiver, a regenerative monitoring scheme can be implemented. In such scheme a feedback is present that increases the contrast of the spectrum maximums to higher accuracy. By increasing the amplification gain of the whole circuit (including the feedback loop of the underwater channel), one comes to a self-sustained oscillator, its frequency deviations are indicating variations of the medium parameters. Experimental examples are presented to confirm feasibility of the proposed monitoring technique for measuring temperature variations, current velocity, periods of internal waves, and other features of the water column. The method is especially applicable to small sea areas like straits, harbors, and lakes to monitor their environmental equilibrium or manifestations of human activity. [Work supported by RFBR, Project No. 00-05-64226.]