Assessment of Hydroacoustic Propagation Using Autonomous Hydrophones in the Scotia Sea

• Main Authors: Matsumoto, Haru, Bohnenstiehl, Del R, Dziak, Robert P, Embley, Robert W, Park, Minkyu
• Other Authors: OREGON STATE UNIV NEWPORT OR COOPERATIVE INST FOR MARINE RESOURCES STUDIES
• Format: Text
• Language: English
• Published: 2010
• Subjects: Acoustics; *HYDROPHONES; *UNDERWATER ACOUSTICS; ACOUSTIC CHANNELS; ACOUSTIC SIGNALS; ACOUSTIC SURVEILLANCE; ANTARCTIC REGIONS; ARRAYS; BACKGROUND NOISE; CLOCKS; CONTINUITY; CRYSTAL OSCILLATORS; DEEP DEPTH; DEPLOYMENT; DUCTS; ENVIRONMENTS; HIGH LATITUDES; ICEBERGS; INSTRUMENTATION; INTERACTIONS; ISLANDS; LOW FREQUENCY; MODELS; MONITORING; MOORING; NATURAL RESOURCES; OCEAN BOTTOM; OCEANS; PENINSULAS; POLAR REGIONS; PROPAGATION; REFLECTION; REGIONS; RIDGES; SAMPLING; SANDWICH CONSTRUCTION; SELF OPERATION; SHALLOW DEPTH; SHIFTING; SIGNALS; SLOPE; SOUND; SOUND GENERATORS; SOUND TRANSMISSION; SOURCES; SURFACES; TIME; TRANSMISSION LOSS; TRANSMITTANCE; UNDERWATER; UNDERWATER SOUND; SCOTIA SEA; Antarctic; The Antarctic; Antarctic Peninsula; Scotia Sea; Sandwich Islands; South Sandwich Islands; Antarc*; Iceberg*
• Online Access: http://www.dtic.mil/docs/citations/ADA569258; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA569258

The remote area of the Atlantic Ocean near the Antarctic Peninsula and the South Scotia Sea is a region where acoustic surveillance by International Monitoring System hydrophones is at best limited. Sound originating in this area is either blocked or hindered by the South Georgia, South Sandwich Islands and the associated seafloor ridge system, making the region a potential hydroacoustic blind spot. To investigate the sound propagation and interferences affected by these landmasses in the vicinity of the Antarctic polar front, an array of autonomous hydrophones (AUHs) was deployed in the Scotia Sea in December 2007. In January 2009, five AUHs were recovered, completing a 13-month-long acoustic monitoring operation. Four of the recovered instruments continuously recorded low-frequency acoustic signals (1?110 Hz) at a sampling rate of 250 Hz, with one instrument sampling at a rate a rate of 1000 Hz (1?440 Hz band-passed). The submerged moorings utilized autonomous crystal oscillator clocks, with small time shifts that average 2 seconds per year. Despite the fact that the high-latitude ocean lacks a deep sound channel, low-frequency sound tends to travel relatively efficiently. Regional seismo-acoustic signals (bottom sources) and episodic tremors from large icebergs (near-surface sources) were utilized as natural sound sources. Surface sound sources, e.g., ice-related events, tend to suffer less transmission loss (TL) and dominate the background noise as a result of surface duct transmission and less interaction with seafloor features. On the other hand, earthquake-generated signals (bottom sources) interact more strongly with the shallow arc, and TL tends to be larger. The RAM PE-code (Collins, 1993a,b) was used to model TL, and the AUH data were used to compare with these modeling results. Both the observational and model results indicate a unique acoustic environment of the Scotia Sea, including the evidences of reflected T-waves by the steep slope of the South Ge Published in Proceedings of the 2010 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 21-23 September 2010, Orlando, FL. Volume II. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License