The Transarctic Acoustic Propagation Experiment and climate monitoring in the Arctic

Abstract

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 Experiment (TAP), 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. 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. 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 Arctic Ocean temperature. The TAP data provided propagation loss measurements to compare with the models to be used for correlating modal scattering losses 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 C, which has been confirmed by direct measurement from icebreakers 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 the Greek o &, meaning "listen!") is underway to carry out the first installations of sources and receivers in the Arctic Ocean. ACOUS is a joint project being executed under a bilateral memorandum of understanding with Russia and is part of the Gore-Chernomyrdin (now Gore-Primakov) Commission, Science and Technology Committee.

Multipurpose Acoustic Networks in the Integrated Arctic Ocean Observing System

“…In the 1994 TAP experiment, transmissions from a source located north of the Svalbard Archipelago to receivers in the Lincoln Sea (1000 km distant) and the Beaufort Sea (2600 km distant) revealed, for the first time, basin-scale warming of the AIW (Mikhalevsky et al, 1999), which was then confirmed by submarine measurements . In the ACOUS experiment in 1998 -99, transmissions from a source deployed in Franz Victoria Strait to receivers in the Lincoln Sea and the Chukchi Sea measured continued basin-scale warming of the AIW and detected a rapid warming in a broadly dispersed mass of Atlantic water with a maximum temperature that exceeded 2.5˚C crossing the Nansen Basin north of the Franz Victoria Strait in August -December 1999 ).…”

“…The 1988 -89 Greenland Sea Experiment (Worcester et al, 1993;Morawitz et al, 1996a, b) and the six-year Labrador Sea experiment (Avsic et al, 2005) successfully observed deep-water formation processes. In the High Arctic, the 1994 Transarctic Acoustic Propagation (TAP) experiment (Mikhalevsky et al, 1999) and the Arctic Climate Observations Using Underwater Sound (ACOUS) experiment in 1998 -99 ) observed basin-scale warming of the Arctic Intermediate Water (AIW).…”

“…Higher modes sample greater depths. With the vertically stratified major water masses of the Arctic basin, acoustic modes can selectively sample specific water masses, such as the AIW (Mikhalevsky et al, 1999;Mikhalevsky, 2001) and the deep Arctic water.…”

Low frequency active sonar performance in the Arctic Beaufort Lens

“…The PSD of the noise is estimated using actual measured noise from the TAP Experiment in 1994 [5], ICEX data, and simulated noise from OASN. arrival.…”

Variational assimilation of ocean tomographic data: Twin experiments in a quasi-geostrophic model

“…These methods rely on a combination of data, statistics and stationary conservation constraints. Such methods were applied to study local phenomena as convection events (Send et al 1995;Morawitz et al 1996;Gaillard et al 1997) as well as to estimate basinscale temperature fields over the Pacific Ocean (Dushaw 1999), or over an unaccessible region such as the Arctic (Mikhalevsky et al 1999). The range of scales resolved by the data is determined by the size of the cells defined by the sections of the observational array.…”