| Popis: |
An experiment was performed in a deep‐ocean basin to investigate the reflectivity of the ocean surface. Acoustic pulses were produced at depths ranging from 500 to 3000 ft and received on hydrophones at a variety of depths and horizontal ranges. The pulses were produced by gating 60‐msec bursts of sine waves into sources having resonant frequencies of 170, 400, 600, and 1300 cps. Simultaneous measurements of the ocean‐surface waves were made with light buoys (Splashniks) which carried accelerometers. The level of the reflected acoustic energy varies markedly from pulse to pulse. Autocorrelation of successive levels yields a power spectrum which resembles that of the ocean waves. Defining fluctuation as the ratio of the standard deviation of ∫ρ2dt to the average value of ∫ρ2dt, we find that fluctuation increases with acoustic frequency, approaching a saturation value of about 100% when the acoustic wavelength is 4 times the product of the rms height of the ocean waves and the cosine of the angle of inciden... |
