Scintillation statistics of broadband acoustic transmissions in the Gulf of Maine.

Abstract

Broadband acoustic transmissions from a vertical source array in the 300–1200 Hz frequency range of 1 s duration, with source‐receiver separations ranging from 2 to 20 km measured in the Gulf of Maine, are analyzed. The received signal intensity is shown to follow the gamma distribution, implying that the field has been fully saturated by independent multimodal propagation contributions. The gamma distribution depends on the mean intensity and the number of independent statistical fluctuations of the received signal. The standard deviations of the received broadband signal intensities are found to be a function of center frequencies and bandwidths. For a fixed center frequency, the standard deviation decreases with increasing bandwidth, implying that there are more independent fluctuations in larger bandwidth signals. The measured scintillation statistics are verified with a range‐dependent numerical Monte‐Carlo propagation model incorporating linear internal wave fluctuations in the random waveguide. Further analysis with the model indicates the range‐dependence of broadband signal intensity standard deviations, which increase rapidly from deterministic at the source location to a maximum at roughly 3‐km range and decay gradually afterward. The standard deviation of a short‐duration monotonic signal remains constant at between 5 and 6 dB after a 3‐km range since it contains only one independent fluctuation.