Spectra of short-term fluctuations of line-of-sight signals: Electromagnetic and acoustic

Theoretical expressions for the spectral density of amplitude, amplitude-difference, and phase-difference fluctuations of waves propagating over a line-of-sight path in a weakly scattering turbulent medium are derived. Experimental observations made at radio (35 GHz) and acoustic (3 kHz) frequencies are in good agreement with the theoretical predictions under a variety of meteorological conditions. Comparison of experimental and theoretical spectra yields a measure of the average across-the-path wind velocity and the average refractive-index structure constant Cn. In general, wind speeds and refractive-index structure constants inferred from simultaneous meteorological measurements agree with those obtained from propagation data.

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