Abstract
A sound record measured by a moored hydrophone in the South China Sea basin was analyzed. Sampled at a rate of 1.6 kHz and with a duty cycle of approximately 1-min-on and 14-min-off, the measured time series captures the spectral characteristics and variability of the ambient noise in the less-than-800-Hz band over an annual cycle. Using a combination of automated and manual screening methods, the dominant regular and transient noise sources were identified and categorized, which include shipping, wind waves, seismic air-gun surveys, shots/explosives and sonar. Intermittent self noise (squeaking sounds) that prevailed at times during the passage of the very large-amplitude internal waves was also identified. In addition to the noise budget, the variability in the daily and monthly means and variances of the measured noise spectrum and band levels were examined. In order to gain insights into the predictability of the ambient noise field in this marginal sea, the interpretation of the data was facilitated with temperature records measured with moored instruments, wind and precipitation time series from the US Naval Operational Global Atmospheric Prediction System (NOGAPS), and vessel motion simulation based on historical shipping density and lane structure. [Research sponsored by the Office of Naval Research.]
Published Version
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