Abstract
This paper describes recent developments in the design of a coded acoustic signal for the study of outdoor sound propagation. Low signal-to-noise ratio is a common limitation in outdoor propagation investigations, and time variance of the air limits the amount of averaging. Recent work by the authors presented a coded acoustic signal approach consisting of a frequency carrier biphase-modulated by a specially designed pseudo-random code sequence to overcome these limitations. The Inner and Outer code sequence was specially designed for environmental sound propagation investigations, combining simultaneous fine time resolution and large range ambiguity, together with an ability to average and probe the propagation path. This approach is extended to multiple acoustic sources for the study of outdoor sound propagation, with the design of signals using orthogonal correlation sequences. The results illustrate that combinations of orthogonal coding and multiple carrier frequencies can permit continuous sound speed measurements in numerous vertical and horizontal directions, and might therefore be useful for acoustic tomographic applications.
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