On the potential of using sound sources of opportunity recorded on the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic network for historical ocean thermometry

Abstract

The globally distributed CTBT hydrophones form an existing network to measure temperature structure of the world oceans. Ocean tomography (or thermometry, asserting the primary driver in sound speed variability is temperature) typically operates by deploying active sources in precisely known locations and projecting signals at precisely known times. Ocean temperature is inferred from the travel time to distributed receivers. Here, we investigate the potential for using sound sources of opportunity within the nearly 20 year record of CTBT recordings. While some of these historical events have known locations and time, multiple hydroacoustic stations can localize the origin of intense sounds without this information. This study will focus primarily on sounds generated by seismic events detected on the CTBT station Diego Garcia in the central Indian Ocean. Hydroacoustic-based localization is possible through the consideration of multiple refracted and diffracted arrivals caused by the complicated bathymetry near this archipelago. These multiple arrivals are used to form ‘virtual’ stations to precisely triangulate the sound origin and establish the event time. Comparison of sound source locations to the event epicenters, determined by land-based seismic stations, are discussed in terms of sound generation mechanisms and uncertainties relevant to ocean thermometry.The globally distributed CTBT hydrophones form an existing network to measure temperature structure of the world oceans. Ocean tomography (or thermometry, asserting the primary driver in sound speed variability is temperature) typically operates by deploying active sources in precisely known locations and projecting signals at precisely known times. Ocean temperature is inferred from the travel time to distributed receivers. Here, we investigate the potential for using sound sources of opportunity within the nearly 20 year record of CTBT recordings. While some of these historical events have known locations and time, multiple hydroacoustic stations can localize the origin of intense sounds without this information. This study will focus primarily on sounds generated by seismic events detected on the CTBT station Diego Garcia in the central Indian Ocean. Hydroacoustic-based localization is possible through the consideration of multiple refracted and diffracted arrivals caused by the complicated bathymetry ...