Acoustical Society of America 2013

Ocean Networks Canada presents at the 166th Meeting of the Acoustical Society of America in San Francisco, 2-6 December 2013

Presentations of Note

Protocols for acoustic devices on cabled ocean observatories

Session 1aAO1: Richard K. Dewey, Steve Mihaly, and Tom Dakin (Ocean Networks Canada, Univ. of Victoria, 2300 McKenzie Ave., Victoria, BC V8N 5M7, Canada)

Cabled ocean observatories offer an unprecedented opportunity for marine acoustic devices. With continuous power and high bandwidth, long-term broadband measurements from both passive and active systems are possible over a wide range of oceanographic environments. In particular, the cabled ocean observatories VENUS and NEPTUNE operated by Ocean Networks Canada offer a unique set of possibilities for acoustic research, ranging from littoral to mid-ocean ridge installations. Since 2006 fiber optic telecommunication cables have provided high power and up to GB data rates from nine distributed observatory Nodes across marine provinces, which include fjords, tidal straits, river deltas, continental shelves, slopes and rises, abyssal plains, and spreading margins. Experience from passive hydrophones as well as both mono- and bi-static active systems including echo-sounders, sonars, and many acoustic Doppler current devices will be discussed. This paper will review our experiences, provide examples, and propose protocols, or at least our suggested best practices, for many active and passive acoustic devices, including calibration, configuration, interference reduction techniques, bandwidth considerations, data handling, and data analysis and delivery methods.

Hydrophone data management at Ocean Networks Canada

Session 1aAO2: Benoit Pirenne, John Dorocicz, and Tom Dakin

In this contribution, we describe the seabed cabled observatory networks managed by Ocean Networks Canada (ONC). The focus is on the hydrophone hosting capabilities of ONC’s advanced science infrastructure and on the assets already in place, together with their scientific objectives. We describe the data acquisition and archival principles and methods, as well as the derived products available to users. We also elaborate on the concerns of the United States and Canadian Navies with quasi real-time, public data and on the mitigation measures in place to balance security needs with the scientific and public safety goals of the instrumentation. Finally, we describe the potential for instrument development and testing that ONC offers on its networks.

Remote performance assessment of cabled observatory hydrophone systems

Session 1aAO3: Nathan D. Merchant Univ. of Bath, Bath, United Kingdom), Tom Dakin, John Dorocicz (Ocean Networks Canada, Univ. of Victoria, Ocean Networks Canada, Victoria, Canada), and Philippe Blondel (Univ. of Bath, Bath, United Kingdom)

The increasing expansion of cabled undersea observatories worldwide presents a unique opportunity to develop and deploy hydrophone systems for long-term monitoring of underwater noise. Among the first such observatories, the NEPTUNE and VENUS networks operated by Ocean Networks Canada (ONC) have been pioneering in their implementation of acoustic monitoring systems and are projected to continue operation with an anticipated lifetime of 25 years. One challenge that arises from decades-long deployments is the need to assess the consistency of data quality from operational instruments. Since the replacement or in situ calibration of instruments can be costly and problematic, it is expedient if such performance assessment can be conducted remotely. Here, we present methods of detecting deterioration in the performance of cabled hydrophone systems and assessing the suitability of the dynamic range to the prevailing noise conditions. Approaches are proposed based on tracking variability in the primary mode, detection and classification of persistent tonal components, and automatic detection of dynamic range exceedance. Scenarios based on data from ONC observatories are presented.

Measurement of hydrothermal heat flux using a sonar deployed on the Canadian Neptune cabled observatory

Session 1aAO4: Guangyu Xu, Peter A. Rona, Karen G. Bemis (Inst. of Marine and Coastal Sci., Rutgers Univ., New Brunswick, NJ), and Darrell R. Jackson (Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105, drj@apl.washington.edu)

The Cabled Observatory Vent Imaging Sonar (COVIS) was deployed at the Main Endeavour Field node of the Canadian NEPTUNE cabled observatory in September 2010 and has acquired long time series on plume and diffuse hydrothermal flows. This talk will focus  on recent efforts by the Rutgers-APL collaboration to invert sonar data to determine heat flux from the Grotto plume complex. Inversion employs plume theory to relate velocity as determined by Doppler shift to buoyancy flux, hence heat flux. The primary uncertainties have to do with plume bending due to ambient current and short sampling times relative to dynamic changes in plume shape. These uncertainties have been quantified by means of special high-statistics experiments using COVIS. Time series for heat flux will be compared with ground truth obtained by thermometry using an ROV. [Work supported by NSF Grants OCE-0824612 and OCE-0825088.]