Laboratory study of ultrasonic pulse reflection from freshwater ice

This paper presents the results of a laboratory study of ultrasonic pulse reflection from freshwater ice during a complete freeze-thaw cycle of the ice cover. Measurements were conducted in a small ice tank at the Arctic and Antarctic Research Institute. The maximum ice thickness was 57 cm, and the freeze-thaw cycle lasted 90 days. A sonar with a carrier frequency of 200 kHz operated continuously at the bottom. The transceiver antenna was oriented vertically upward toward the water surface. The underwater sonar measured and stored the reflected pulses throughout the experiment. Analysis of the reflected pulse data made it possible to study ice thickness dynamics and to obtain estimates of the average speed of sound in ice and the sound attenuation coefficient in ice over the entire measurement period. A simple empirical model for the shape of an acoustic pulse reflected from a freshwater ice cover is proposed. In this model, the reflected signal is represented as the sum of reflections from the undisturbed water surface, shifted by the travel time of the acoustic wave in the ice, with the reflection from the upper boundary of the ice cover additionally multiplied by the sound attenuation coefficient in ice.