Sea ice characterization with a correlation sonar

A prototype correlation sonar has been developed for the measurement of both ice motion and acoustical backscatter strength in polar seas. The device was deployed for three winters in the Beaufort Sea near a Doppler current meter, which measured ice velocities over one cm/s, and an ice profiling system, which monitored the underside topography of sea ice. The bistatic 100 kHz sonar transmits with 204 dB source level, at 20 degree full beamwidth. The sonar receiver contains four arrays, each with eight elements orientated in steps of 45 degrees. It operates in the very-shallow-water mode as a two-pulse spatial correlation log, measuring shifts in acoustical interference patterns. Four components of velocity are measured independently and combined to provide speed and direction of ice motion from 0.02 cm/s to 50 cm/s. The sonar and electronic components were calibrated using a standard sphere. Time series for raw acoustic echoes were recorded, from which acoustical backscatter strengths for ice can be calculated.