Acoustic backscattering from uniform Arctic Sea ice

The purpose of this study was to determine the acoustic backscattering produced from the bottom of flat, first-year sea ice. Most under-ice reverberation measurements have been made at low frequencies, using explosive sources. Our measurements were made with 60- kHz pulses, and should be of special importance to the higher frequency sonar systems. The experiment site was a first-year ice floe with a large flat area of uniform thickness, about 90 cm. The bottom was considered characteristic of first-year ice. Under-ice reverberation measurements were made at four locations beneath this flat area, using 60-kHz, 4- ms pulses from a directional transducer. Analysis of the measurements shows that the scattering strength varied from -40 dB at a grazing angle of10to -30 dB at a grazing angle of45with a standard deviation of about 5 dB. There was an appreciable spread in the measurements at the four locations; however, the dependence on grazing angle appears to be similar to that of the open sea surface with a light wind.