Underwater Acoustic Scattering and Its Effect on Binary Decoding
PENNSYLVANIA STATE UNIV UNIVERSITY PARK ORDNANCE RESEARCH LAB
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The paper is based on an experimental study of the amplitude fluctuation in underwater acoustic pulses and its dependence on range, acoustic frequency, and pulse length. The fluctuation is assumed to be a result of spatial variation in the refractive index field. The coefficient of variation, a measure of the relative amplitude fluctuation, is used to compare experimental results with theoretical predictions. For large values of the wave parameter, the theoretical coefficient of variation has a first-power dependence on the acoustic frequency and a 12-power dependence on the range. Experimentally, this quantity was found to display a 710-power relation and a 12-power relation with the acoustic frequency and range, respectively. The variance of the signal portion of a correlator output is shown to be proportional to the mean-square value of the signal amplitude fluctuation which, according to theory, is proportional to the square of the acoustic frequency and the first power of the range. Because the effective scatterers are highly directional, the major contribution of scattered energy comes from the region of a cone whose axis lies along a line joining the source and receiver and whose apex is located at the receiver. It is reasoned that the increment in pulse length served to intensify scatterers outside the cone, thereby producing scattered energy not directed to the receiver.
- Non-Radio Communications