Detection of buried objects at low grazing angles: preliminary experimental results

Abstract

This report considers the acoustic detection of objects buried in the seabed, and especially the possibility of using subcritical insonification geometries in order to increase coverage rate.

Experimental results are presented for acoustic transmissions in the approximate frequency range 2-

16 kHz both above and below the nominal critical angle of the sediment. The buried objects studied

are a solid aluminum sphere of radius a, = 0.3 m and a 2 m long water-filled cylindrical steel shell with

radius a, = 0.25 m. Preliminary processing of the data has shown that gains in signal-to-noise ratio

can be obtained for subcritical cases by emphasizing the lower frequency components (in this case, f

< 3 kHz) where models predict that the target echo is strongest due to the evanescent nature of the

incident acoustic wave.