Amplitude Fluctuations of the Sound from a Low-Frequency Moving Source in the Deep Sea.

摘要

The sound from a steady source in the sea fluctuates in amplitude on reaching a distant receiver. One way to express the fluctuation is by means of its power spectrum,normalized to the mean level of the carrier frequency. Such spectra have been obtained for three minute samples of the signals from 142and 275Hz CW sources towed together in range as far as the first convergence zone from sonobuoy hydrophones at 90 300feet. At all ranges and at both depths,the spectra in the band 0.01to 0.5Hz (periods two to 100seconds) show a broad peak near 0.1Hz. The integral under the spectrum,equalling the square of the modulation coefficient,ranges from less than one to about 50percent,with a strong dependence on carrier level. That is,the fluctuation is low when the mean level in high,and vice versa,so that the fluctuation power tends to be constant. These 'fast'fluctuations are doubtless caused by ocean waves. At the other end of the frequency range of interest, 'slow'fluctuations are found having periods from 10seconds to one hour that are probably caused by the range movement of the source. (Modified author abstract)