Long-Range Shallow-Water Signal-Level Fluctuations and Frequency Spreading

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Abstract
The fluctuation of the received sound for frequencies of 350, 700, 1200, and 2400 cps was studied for transmission over flat 60-fathom sand and 50-fathom sandstone bottoms out to ranges of 15 miles. The received sound fluctuated over a range of 50 db. In general, the amplitude distribution was neither Gaussian nor Rayleigh. No significant correlation was found between the outputs of the receiving hydrophones which were separated vertically by 90 or more feet. The frequency was spread due to transmission and the relative power P is related to the half-width of the spectra |f − f0| from 350 to 2400 cps by P = bf0|f − 0|−3, where b = (7.7±0.8)×10−6 (cps)2 for the sand bottom and (3.9±2.7)×10−6 (cps)2 for the sandstone bottom. Special measurements indicated no significant asymmetry between the spectra above f0 from that below f0.

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