The Echometer: An acoustic sound speed profiler

Preliminary experimental results are presented which demonstrate the feasibility of an acoustic technique for remote sensing of ocean sound speed profiles. A three-dimensional acoustic interference pattern was produced in the water column by a ship-mounted active linear array. The scattered returns from the interference pattern were interrogated by a narrow-beam receiver displaced laterally from the source array. A dual-frequency technique employing signals differing by 1 percent in frequency produced calculable shifts in acoustic path lengths and hence, measurable travel time differences. The differences in path lengths and measured travel times (phase) were combined in an iterative process to calculate the sound speed at discrete depths, i.e., at the intersections of the constructive interference lines and the beam of the receiver.