Peter N. Mikhalevsky
Ocean Sciences Group, Science Applications International Corp., McLean, VA
Long-term observations over many years of the changes in acoustic phase, travel time, and amplitude for many trans-Arctic paths could provide synoptic measurements of Arctic Ocean temperature and sea ice properties (particularly average ice thickness), crucial elements of the Arctic climate that plays a significant role in the Earth's climate system as well as being a sensitive indicator of global climate change. The response of acoustic phase and amplitude to changes in Arctic Ocean temperature, and changes in sea ice coverage and thickness have been estimated for a trans-Arctic path of 2700 km at 30 Hz. Low frequencies (<40 Hz) are required in the Arctic due to the large scattering losses from the ice (indeed, one of the observables). The travel time and phase ``noise'' caused by ``short-term'' mesoscale and internal wave modulation of the Arctic Ocean temperature are calculated to be negligible. Phase measurements made in the Arctic over a 320-km path at 30 Hz [P. N. Mikhalevsky, J. Acoust. Soc. Am. 70, 1717--1722 (1981)] demonstrated phase detection to better than one hundredth of a cycle with observed short-term phase fluctuations consistent with the mesoscale calculations. However, these observations were too short in time and in range for any definitive conclusions regarding trans-Arctic paths. An experiment is planned in late April to transmit signals at 20 Hz from a Russian ice camp off Spitzbergen to a vertical array in the Lincoln Sea, and horizontal and vertical arrays at an ice camp in the Beaufort Sea.