Optimum Frequency for Detection of Acoustic Sources in the Upper Atmosphere

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Abstract
Frequency-selective detection of acoustic sources in the upper atmosphere is shown to offer advantages over a broad-band detector in improving signal-to-noise ratio. A model for an optimum frequency is developed using simplified assumptions: i.e., a source with a Fourier spectrum of uniform amplitude; attenuation by absorption during propagation; local turbulence as the noise source. An optimum frequency is found where the signal-to-noise ratio is maximum as a function of altitude. Experimental evidence confirms that a peak in the signal-to-noise ratio exits for acoustic sources in the upper atmosphere.