Publications
Mode coherence at megameter ranges in the North Pacific Ocean
Abstract
This article analyzes the coherence of low mode signals at ranges of 3515 km and 5171 km using data from the Acoustic Thermometry of Ocean Climate (ATOC) and Alternate Source Test (AST) experiments. Vertical line arrays at Hawaii and Kiritimati received M-sequences transmitted from two sources: the 75 Hz bottom-mounted ATOC source on Pioneer Seamount and the near-axial dual-frequency (28/84 Hz) AST source deployed nearby. This study demonstrates that the characteristics of the mode signals at 5171-km range are quite similar to those at 3515-km range. At 75 Hz the mode time spreads are on the order of 1.5 s, implying a coherence bandwidth of 0.67 Hz. The time spread of the 28-Hz signals is somewhat lower, but these signals show significantly less frequency-selective fading than the 75-Hz signals, suggesting that at the lower frequency the multipaths are temporally-resolvable. Coherence times for mode 1 at 75 Hz are on the order of 8 min for the 3515-km range and 6 min for 5171-km range. At 28 Hz mode 1 is much more stable, with a magnitude-squared coherence of greater than 0.6 for the 20-min transmission period.
© 2005 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires the permission of the authors and the Acoustical Society of America. The article (PDF) appeared in the Journal of the Acoustical Society of America, vol. 117(3), pt. 2, pp. 1565-1581, March 2005 and may also be found on the JASA website.