Short range acoustic transmission in the Chukchi Sea

Short range acoustic transmission measurements were made in the summer of 1972 between two stations on a drifting ice floe in the marginal ice zone of the Chukchi Sea. The measurements were accomplished by transmitting short 60 kHz pulses from a transmitter placed at a fixed depth and then raising and lowering a receiving hydrophone 220 yd away at hourly intervals. At the same time, temperature profiles were measured at four stations on the ice floe and salinity profiles at one station. At the northern edge of the marginal ice the sound velocity profile was nearly constant, but within the zone a very irregular profile resulted from the intrusion of Pacific water. Analysis of the results of the study shows temperature layers of
0.1\deg
C that extend hundreds of yards and result in sound velocity variations which cause a considerable variation in acoustic transmissions at low angles (
\pm5
dB). Such thermal structure, as well as larger, more persistent layers, are common in the marginal ice zone of the Chukchi Sea.