An MlS Method for Non-Stationary and Outdoor Acoustic Paths
The correlation properties of a directly carrier-modulated code sequence modulation signal are exploited to investigate sound propagation in turbulent air. An experiment is described in which the correlation properties of the spread spectrum signal are demonstrated and are used to calculate accurate times of flight that compare well with sonic anemometer measurements of speed of sound. The results illustrate that a directly carrier-modulated code sequence modulation system can provide significantly improved ways of measuring sound propagation outdoors. Moreover, the technique directly measures wind speed. This can be used to compensate the time of flight thus allowing the measurement of acoustic impulse responses in non-stationary media, for example outdoors, where reliable measurements have previously been difficult to obtain.
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