Spurious Tonals in Intensity Time Series Associated with Long Range Propagation

One of the commonly examined characteristics of received underwater acoustic signals has been the spectrum of intensity fluctuations in the internal wave frequency range which extends from several cycles per hour (cph) up to tidal frequencies and beyond. In some cases, it is anticipated that the internal waves may induce tonal components in these spectra, for example at a tidal frequency, or at the frequency of some other coherent individual internal wave source. Our results show that periodic components can be generated in the intensity fluctuation spectra, at internal wave frequencies, as a result of the end point motion and multipath interference. Thus, observed tonals in such data should not be ascribed to an internal wave process until this effect has been considered.