The transarctic acoustic propagation experiment and climate monitoring in the Arctic

In April 1994, coherent acoustic transmissions were propagated across the e ntire Arctic basin for the first time. This experiment, known as the Transa rctic Acoustic Propagation Experiment (TAP), was designed to determine the feasibility of using these signals to monitor changes in Arctic Ocean tempe rature and changes in sea ice thickness and concentration. CW and maximal l ength sequences (MLS) were transmitted from the source camp located north o f the Svalbard Archipelago 1000 km to a vertical line array in the Lincoln Sea and 2600 km to a two-dimensional horizontal array and a vertical array in the Beaufort Sea. TAP demonstrated that the 19.6-Hz 195-dB (251-W) signa ls propagated with both sufficiently low loss and high phase stability to s upport the coherent pulse compression processing of the MLS and the phase d etection of the CW signals. These yield time-delay measurements an order of magnitude better than what is required to detect the estimated 80-ms/year changes in travel time caused by interannual and longer term changes in Arc tic Ocean temperature. The TAP data provided propagation loss measurements to compare with the models to be used for correlating modal scattering loss es with sea ice properties for ice monitoring, The travel times measured in TAP indicated a warming of the Atlantic layer in the Arctic of close to 0. 4 degrees C, which has been confirmed by direct measurement from icebreaker s and submarines, demonstrating the utility of acoustic thermometry in the Arctic. The unique advantages of acoustic thermometry in the Arctic and the importance of climate monitoring in the Arctic are discussed. A four-year program, Arctic Climate Observations using Underwater Sound (ACOUS, from th e creek alpha kappa o upsilon sigma, meaning "listen!") is underway to carr y out the first installations of sources and receivers in the Arctic Ocean, ACOUS is a joint project being executed under a bilateral memorandum of un derstanding with Russia and is part of the Gore-Chernomyrdin (now Gore-Prim akov) Commission, Science and Technology Committee.