Measurement of transmission loss using an inexpensive mobile source on the Upper Slope of the South China Sea
Graessle, Samuel W.
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During the 2014 South China Sea Upper-Slope Sand Dunes Experiment, an inexpensive, expendable mobile sound source was deployed to investigate potential use of such a device to acquire quality transmission loss (TL) data and yield additional spatial information of the complex acoustic environment. The mobile source was programmed to maintain depth, speed, and to transmit a tonal signal followed by a short linear-sweep timing/ranging pulse every minute. A vertical hydrophone array and other receivers recorded the signals. The methodology and related mathematical tools to analyze the received acoustic data for coherence time (optimum integration time) and consequently TL were developebcd. Specifically, coherence times were estimated based on a tolerance of one-dB degradation in the measured SPL of the tone. It is shown that a time segment is coherent when 50% of the segment has phase fluctuations within ± 45° about the linear trend of the phase. The optimum integration time was applied to the data to obtain TL estimates versus range using spectral estimation techniques. Measured coherence time and TL were compared to model results from the National Taiwan University to gain insights into the quality, limitations, and attainable future advances of this measurement method.
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