Multipurpose acoustic networks in the integrated arctic ocean observing system

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory

A decade of acoustic thermometry in the North Pacific Ocean

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94643/1/jgrc11250.pd

Applications of Underwater Acoustics in Polar Environments

The unique feature of the Arctic and Antarctic polar oceans that affects underwater acoustics, both the propagation of sound and the ambient noise, is the presence of sea ice that seasonally expands and retreats and ice shelves extending from the land into the ocean. They also have important differences. In the last two decades there has been a significant reduction of both the extent and thickness of the ice in the Arctic while there has been an increase in the extent of the sea ice in the Antarctic. The Arctic Ocean is a Mediterranean basin with limited communication to the world’s oceans while the Southern Ocean surrounds the continent of Antarctica and is contiguous with the south Atlantic, south Pacific, and Indian Oceans and acoustically linked to the deep sound channel of the world’s oceans

Low-frequency acoustic propagation loss in the Arctic Ocean: results of the Arctic climate observations using underwater sound experiment

Acoustic data from the Arctic climate observations using underwater sound (ACOUS) experiment are analyzed to determine the correlation between acoustic propagation loss and the seasonal variability of sea ice thickness. The objective of this research is to provide long-term synoptic monitoring of sea ice thickness, an important global climate variable, using acoustic remote sensing. As part of the ACOUS program an autonomous acoustic source deployed northwest of Franz Josef Land transmitted tomographic signals at 20.5 Hz once every four days from October 1998 until December 1999. These signals were received on a vertical array in the Lincoln Sea 1250 km away. Two of the signals transmitted in April 1999 were received on a vertical array at ice camp APLIS in the Chukchi Sea north of Point Barrow, Alaska, at a distance of approximately 2720 km from the source. Temporal variations of the modal propagation loss are examined. The influence of ice parameters, variations of the sound speed profile, and mode-coupling effects on the propagation losses of individual modes is studied. The experimental results are compared to the results of the earlier experiments and the theoretical prediction using numerical modeling

The Transarctic Acoustic Propagation Experiment and Climate Monitoring in the Arctic

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 temper- ature 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 degrees, 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 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

Measured and modeled acoustic propagation underneath the rough Arctic sea-ice

A characteristic surface duct beneath the sea-ice in the Marginal Ice Zone causes acoustic waves to be trapped and continuously interact with the sea-ice. The reflectivity of the sea-ice depends on the thickness, the elastic properties, and its roughness. This work focuses on the influence of sea-ice roughness on long-range acoustic propagation, and on how well the arrival structure can be predicted by the full wave integration model OASES. In 2013, acoustic signals centered at 900 Hz were transmitted every hour for three days between ice-tethered buoys in a drifting network in the Fram Strait. The experiment was set up to study the signal stability in the surface channel below the sea-ice. Oceanographic profiles were collected during the experiment, while a statistical description of the rough sea-ice was established based on historical ice-draft measurements. This environmental description is used as input to the range independent version of OASES. The model simulations correspond fairly well with the observations, despite that a flat bathymetry is used and the sea-ice roughness cannot be fully approximated by the statistical representation used in OASES. Longrange transmissions around 900 Hz are found to be more sensitive to the sea-ice roughness than the elastic parameters