A Correlation Sonar System for Recording Ice Cover Movement

The use of correlation sonar for the determination of reflector movement involves the processing of echoes resulting from two short pulses of sound of a known time separation. These echoes are received by a number of hydrophones in the plane of anticipated movement. Numerical cross correlation is used to compare the echo pulse waveforms in the search for the best match between the first and the second pulses among the various hydrophones. The physical displacement of the hydrophones for this best match represents the movement of the reflector in the interpulse time. This instrument, designed specifically for the measurement of ice cover movement, is self contained in that it is battery operated, self controlled and records results for later recovery. Projector and hydrophones mount on the end of a cylindrical pressure case; the enclosed electronic amplifiers and computing elements are based in the STD bus card system. Correlations are performed on captured echo waveshapes by the internal processor, and the results stored. Testing to date has involved downward looking movements over the sea bottom to verify the hardware operation and the software algorithms. Future test programs involve accuracy measurements over bottom, and under ice verification. Operational deployment is scheduled for 1987.