A SIMPLIFIED METHOD FOR IDENTIFICATION AND EXTRACTION OF NORMAL MODES

A simplified method for filtering normal modes in shallow water has been developed.During the experiment a single hydrophone,placed at different depths,received the explosive signals at a certain distance.In the laboratory the received signals were filtered in octave band centred at a higher frequency (8 kHz) and in 1/3 octave bands centred at several lower frequencies (<800 Hz),and the high-frequency signal was used as the trigger to start sampling the signals at lower frequencies.The theoretical calculation and the experimental results showed that for these lower frequencies the depth dependence of the signals received at different depths by the single hydrophone was similar to that for the case when a vertical hydrophone array was used.And the filtering of the first two modes has been realized by adding up the signals received at different depths with the weighting coefficients determined according to the mode eigenfunctions or their signs at the corresponding depths.