Effects of Variability Associated with the Antarctic Circumpolar Current on Sound Propagation in the Ocean

• Main Authors: Groot-Hedlin, Catherine de, Blackman, Donna K., Jenkins, C. S.
• Other Authors: SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA
• Format: Text
• Language: English
• Published: 2008
• Subjects: Acoustics; *ACOUSTIC WAVES; *ANTARCTIC REGIONS; *ACOUSTIC SIGNALS; *PROPAGATION; TRANSMISSION LOSS; CONVERSION; PREDICTIONS; MODELS; MONITORING; UNDERWATER SOUND SIGNALS; NUMERICAL ANALYSIS; TRAVEL TIME; CALIBRATION; GROUND BASED; HYDROPHONES; CLIMATOLOGY; NUCLEAR EXPLOSIONS; FREQUENCY; DATA BASES; SYMPOSIA; *CIRCUMPOLAR CURRENT; Antarctic; Indian; Pacific; The Antarctic; Antarc*; Antarctica
• Online Access: http://www.dtic.mil/docs/citations/ADA516246; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA516246

Our objectives were to conduct a series of calibration shots within and to the south of the ACC that would generate acoustic signals at frequencies f > 30 Hz and to analyze the signals recorded at hydrophone stations operated by the IMS. The overall goal was to compare observed source-receiver travel times to the IMS hydrophone stations to those predicted by numerical models for paths crossing the Antarctic convergence zone and to use these results to determine the accuracy to which sources may be located within the ACC. A second goal was to compare observed vs. modeled transmission losses. The results of the second goal were reported last year; it was found that transmission loss is nearly uniform as a function of frequency for the shots examined in this study (de Groot-Hedlin et al., 2007; de Groot-Hedlin et al., 2008). Acoustic propagation for sources within the ACC is complicated by the sharp temperature gradient at the northern boundary. The ACC boundary separates cold waters that flow eastward around Antarctica from warmer subtropical waters to the north. The abrupt spatial variation in temperature and salinity results in strong gradients in the speed of acoustic waves through the ocean, which in turn deflects the path of propagating acoustic waves near the northern boundary of the ACC (Heaney et al., 1999). Furthermore, south of the ACC boundary, the low-velocity oceanic "sound channel" axis, that is typically 100's to 1,000-m-deep shoals and the overlying higher velocity layer thins to nothing over a short distance, resulting in sea surface-limited propagation. Therefore, the detailed structure of the ACC boundary is strongly affected by seasonal temperature variations that extend to depths of over 1 km. Dushaw et al., (1999) showed that this type of seasonal variability produces considerable seasonal differences in acoustic travel times for paths through the North Pacific. We conducted an experiment in December, 2006, to determine how well acoustic wave tra Presented at the Conference on Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (30th), held in Portsmouth, VA, on 23-25 Sep 2008. Published in the proceedings of the conference, p715-724, 2008. Prepared in cooperation with Naval Surface Warfare Center, Indian Head Division. Sponsored in part by the National Nuclear Security Administration (NNSA) and by the Army Space and Missile Defense Command. The original document contains color images.