Coherence of Sound using Navy Sonars: Deep Water Acoustics
Abstract
The long term goals are to 1) determine when methods can be used to reliably and accurately predict the temporal and spatial coherence of sound at low frequencies in the sea, 2) develop reliable and accurate methods to make such predictions and, 3) determine the physical mechanisms affecting coherence. The first two goals are to be achieved without tuning with data in any way whatsoever. The primary objective is to determine when the temporal and spatial scales of coherence are accurately predicted by solving an approximation of the acoustic wave equation for climatological conditions in the ocean perturbed by a time-evolving field of internal gravity waves following a standard spectrum. These waves have long been thought responsible for coherence in the deep ocean at low frequencies. Despite decades of theoretical work to predict coherence, theoretical models to date are highly unreliable, often being inaccurate by several orders of magnitude. We are comparing numerical predictions for coherence with data collected with Navy sonars. A secondary objective is to understand how to quantify the regions of the ocean that influence acoustic signals that are measured at a receiver. The classic picture of such regions is described by ray paths, which are solutions of the wave equation at high frequency. Modern theories of diffraction have the ability to quantify the regions exactly for any finite frequency and bandwidth (Spiesberger, 2011b). Since the exact regions that influence sound look very different than where rays propagate at low frequency, it may turn out in the long-term that the modern theory will replace the use of rays for many applications in basic research and surveillance.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2012
- Accession Number
- ADA575109
Entities
People
- John L. Spiesberger