Dispersion bandwidth deduced from coherency of wave recordings from spatially separated sites

Abstract

In an earlier paper it was pointed out that temporal variability in the dispersive properties of the propagation medium can cause a band of wave velocities to be associated with each frequency component in the time series of a sampled quantity. This results in degrading the coherence between stations separated in the direction of propagation and can cause significant error in the apparent wave velocity as deduced from the phase of the cross spectra. This bandwidth is complementary to the concept of beamwidth, which principally degrades the coherence between stations separated perpendicular to the direction of propagation. The present paper uses numerical procedures to extend the earlier results to larger beamwidths and bandwidths.

Understanding and Designing Military Organizations for a Complex Dynamic Environment

“…It seems clear that the optimal design of an infrasonic monitoring array will depend critically on a good understanding of the properties of infrasonic signal correlation as a function of frequency and distance between the array elements. The spatial coherence of infrasonic signals has been studied extensively since the pioneering work of Gossard (1969), Gossard and Sailors (1970) (see also Gossard and Hooke, 1975) and Mack and Flinn (1971). Mack and Flinn (1971) have provided convincing evidence to show that the observed loss of signal coherence along the direction of wave propagation is due to a small variation, ± c Δ , in the velocity of the waves while the observed loss of coherence along the wavefront is due to a small variation, ± θ Δ , in the azimuth of the waves.…”

Detection of Nuclear Explosions Using Infrasound Techniques

“…It seems clear that the optimal design of an infrasonic monitoring array will depend critically on a good understanding of the properties of infrasonic signal correlation as a function of frequency and distance between the array elements. The spatial coherence of infrasonic signals has been studied extensively since the pioneering work of Gossard (1969), Gossard and Sailors (1970) (see also Gossard and Hooke, 1975) and Mack and Flinn (1971). Mack and Flinn (1971) have provided convincing evidence to show that the observed loss of signal coherence along the direction of wave propagation is due to a small variation, ± c Δ , in the velocity of the waves while the observed loss of coherence along the wavefront is due to a small variation, ± θ Δ , in the azimuth of the waves.…”

Remote sensing of the troposphere

“…Criteria for judging the significance levels of coherence in terms of sampling parameters are beyond the scope of this introductory discussion but are covered by Gossard and Noonkester (1967). Gossard (1969) and Gossard and Sailors (1970) also show that the behavior of coherence as sensor spacing varies can be used to deduce (a) temporal variability of the dispersive properties of the source or the propagation medium, in the case of stations separated in the direction of propagation, and (b) effective beamwidths or angular dispersion of arriving waves, in the case of stations separated perpendicular to the direction of wave travel.…”