Transarctic Acoustic Propagation (TAP) Experiment: Sea Ice Mechanics Initiative

In April 1994, coherent acoustic transmissions were propagated across the entire Arctic basin for the first time.

This experiment, known as the Transarctic Acoustic Propagation (TAP) Experiment, was designed to determine the feasibility of using these signals to monitor changes in Arctic Ocean temperature and changes in sea-ice thickness and concentration. Continuous waves (CW) and maximal length sequences (MLS) were transmitted from the source camp located north of 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) signals propagated with both sufficiently low loss and high phase stability to support the coherent pulse-compression processing of the MLS and the phase detection of the CW signals. The travel times measured in TAP indicated a warming of the Atlantic layer in the Arctic of close to 0.4 deg C, which has been confirmed by direct measurements from icebreakers and submarines, demonstrating the utility of acoustic thermometry in the Arctic. A four-year program, Arctic Climate Observations, using Underwater Sound (ACOUS, from the Greek, meaning “listen!”), has been proposed to carry out the first installation of sources and receivers in the Arctic Ocean. ACOUS is a joint project being executed under a bilateral memorandum of understanding with Russia. The Chief Scientist for the TAP component of SIMI (Sea Ice Mechanics Initiative) who worked with Professors Baggeroer and Schmidt was Dr. Peter N. Mikhalevsky of SAIC. He is also leading the ACOUS effort.