Indian Ocean Hydroacoustic Wave Propagation Characteristics

• Main Authors: Piserchia, Pierre-Franck, Dordain, Pierre-Mathieu
• Other Authors: COMMISSARIAT A L'ENERGIE ATOMIQUE PARIS (FRANCE)
• Format: Text
• Language: English
• Published: 2000
• Subjects: Seismic Detection and Detectors; Acoustics; *TRANSMISSION LOSS; *UNDERWATER ACOUSTICS; *SEISMIC DETECTION; INDIAN OCEAN; HYDROPHONES; UNDERWATER EXPLOSIONS; FRANCE; WAVE PROPAGATION; SYMPOSIA; SEISMIC WAVES; T-PHASE STATIONS; HYDROACOUSTICS; HYDROACOUSTIC WAVE PROPAGATION; INDIAN OCEAN PROPAGATION; DEEP SOUND CHANNEL; SOFAR CHANNEL; CTBT(COMPREHENSIVE NUCLEAR TEST BAN TREATY); SOUND SPEED IMS(INTERNATIONAL MONITORING SYSTEM); HYDROPHONE STATIONS; NUMERICAL ESTIMATIONS; FOREIGN REPORTS; Antarctic; Antarctic Ocean; Indian; Orleans; The Antarctic; Antarc*; South Atlantic Ocean
• Online Access: http://www.dtic.mil/docs/citations/ADA526959; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA526959

The channeling efficiency of the Deep Sound Channel (often referred as the Sofar channel) allows long range propagation of hydroacoustic waves over a few thousands of kilometers. Strong T-waves, referring to a third arrival on seismic waves, are commonly observed on underwater receivers (hydrophones stations) and on coastal receivers (T-phase stations), when an oceanic earthquake or an underwater explosion occurs, even for small events. Consequently, to insure the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the hydroacoustic network of the International Monitoring System (IMS) uses five T-phase stations and six hydrophones. At the end of 2001, three hydrophone stations--HA1 at Cape Leeuwin, HA4 at Crozet, and HA8 at Diego Garcia will continuously send their data to the IMS. These data will also be available at National Data Centers. Then, using these data it will be possible 1) to refine the network detection capability 2) to estimate the network localization precision and 3) to estimate the transmission loss of the hydroacoustic propagation and the hydroacoustic-to-seismic conversion at the T-phase stations. To prepare this evaluation, we are studying the underwater propagation in the region of the Indian Ocean and in the South Atlantic Ocean using modeling approaches. The first part of this paper gives a general view of the variation of the bathymetry, the sound speed propagation and the Sofar channel axis in the Indian Ocean. In particular, it is shown that there is a strong sound speed profile variation, from the North to South Indian Ocean, due to a cold water front coming from the Sub-Antarctic Ocean. In a second part, three areas are defined in the region of the Indian Ocean and in the Antarctic Ocean. In each of them, a typical sound speed profile has been considered to estimate numerically the underwater transmission loss characteristics. The underwater blockage effect due to underwater seamounts are also investigated in this part. Published in Proceedings of the Annual DoD/DOE Seismic Research Symposium: Planning for Verification of and Compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) (22nd), held in New Orleans, LA on 13-15 Sep 2000. U.S. Government or Federal Rights. The original document contains color images.