A theoretical investigation has been made into the effect on acoustic propagation of oceanic fronts at the edge of warm-core eddies. The investigation utilized modeling of acoustic propagation using the parabolic approximation to the wave equation. Propagation was examined using typical parameters for a wintertime warm-core eddy in the Tasman Sea. Propagation across the eddy boundary (at a frequency of 100 Hz) is shown to create a second series of convergence zones, in addition to the normal series. This occurred for propagation both into and out of the eddy. For a source outside the eddy, energy is shown to strongly couple from deep refracted paths to mixed layer paths within the eddy. The eddy boundary was found to have significant effects on convergence zone properties. Acoustic propagation was also modeled using parameters from a particular realization of a summertime warm-core eddy in the Tasman Sea (for which realization there was environmental and acoustic data available). This eddy had a surface duct and a separate subsurface duct. Reasonable agreement between model and experiment was found for source and receiver both in the subsurface duct at frequencies from 50 to 1000 Hz; disagreement occurred at 25 Hz. However, for source in surface duct but receiver in subsurface duct, the agreement was poor at most frequencies. The effect of minor variations in oceanic and experimental parameters was examined to determine the experimental resolution required of these parameters.
A global hydroacoustic monitoring system is being implemented for use in verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). This system will provide hydroacoustic monitoring of all the world’s oceans for 24 h a day, every day of the year, into the indefinite future. This unique resource will utilize two types of station. One type will be based on a hydrophone at the SOFAR axis depth, cabled back to shore. The other will be based on a seismometer on a small island using detection of the T-phase signal. This latter station relies on a signal which has propagated predominantly through the ocean, but has been converted to seismic energy at the margin of the island. This new application of hydroacoustics highlights a number of scientific questions which have not been adequately addressed. Progress in implementation of this network will be described.
Hydroacoustics is one of the four monitoring technologies of the International Monitoring System (IMS') established under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The hydroacoustic network, designed to monitor the major world oceans, contains eleven stations located with an emphasis on the vast ocean areas of the Southern Hemisphere. Two different sensing techniques are employed; hydrophone sensors, which effectively cover large ocean areas, but are quite complex and expensive, and seismic detectors on small islands which are less effective, but considerably simpler and cheaper. The hydroacoustic stations transmit data in real time via satellite to the International Data Centre (IDC). The IDC analyses the hydroacoustic data in combination with the other three technologies to produce bulletins of detected events for the States Party to the Treaty.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.