ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3aUW13. Shallow-water backscatter reduction through selective mode excitation.

D. F. Gingras

SACLANT Undersea Res. Ctr., Viale San Bartolomeo, 400, 19038 La Spezia, Italy

In shallow-water areas the utilization of active sonar is complicated by the fact that in these environments the performance of active sonar systems is degraded by backscatter generated by source signal interaction with channel boundaries. In this paper knowledge about the shallow-water acoustic channel, namely the normal-mode structure, is used to design vertical source arrays which minimize source signal boundary interaction. The boundary signal interaction is minimized for many environments by exciting only the first mode. Mode one excitation is accomplished by weighting the array sources by the amplitude and polarity of the mode one eigenfunction. Simulations across the frequency range from 200 to 700 Hz using a two-way PE backscatter model were conducted. It was shown that a vertical array of sources, containing only 15 elements, can reduce bottom generated backscatter by as much as 15--20 dB.