Abstract
Observations of the CW acoustic propagation between a fixed source and receiver in the Florida Straits have revealed fluctuations in both phase and amplitude with frequencies corresponding to surface waves. Comparison of the spectra of acoustic phase and amplitude to the spectra of surface wave height show proportionally more energy in the acoustic signal in the frequency range of sea swell than in the frequency range of wind-driven waves. To investigate the effects of sound-speed structure and wind speed and direction upon the surface modulation, online digital processing has been employed. Phase coherent demodulation and filtering followed by fast Fourier transform provide nearly continuous spectra of the acoustic signal. A spectrum is obtained every 3 min with a frequency resolution of 0.005 Hz from ±0.5 Hz about the 420-Hz carrier. Three dimensional displays of frequency, intensity, and time are presented for several 2-h samples on selected days having varying conditions of wind speed and direction. The presented data are discussed in light of single reflection experiments (Roderick) and known seasonal characteristics of acoustic propagation in the Florida Straits.
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