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An investigation into multipath resolution for outdoor sound propagation is done using spread spectrum acoustic signals. A low-frequency sinusoid is bi-phase modulated using a pseudorandom sequence with period 2M−1. The ‘‘chip rate’’ fc in Hz is the number of bits per second used in the bi-phase modulation. The shape of the spread spectrum sinusoid is in the form of sin(x)/x, where the peak is at the sinusoid frequency and the adjacent nulls are at ±fc in Hz. Faster chip rates result in broader spectra. Cross correlating the received acoustic signals with the transmitted signals provides a time delay and amplitude estimate for each path in the propagation channel. A field experiment in a strong 15-kn wind revealed a clear direct path and ground reflection appropriate for the profile conditions and confirmed by ray tracing. [Work supported by DARPA.]

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