Coherence analysis of air - and mechanically-coupled ground vibrations

The coherence function between the microphone and vertical geophone is investigated for air-coupled and mechanically-coupled sources and offers new insights into air vs. ground source discrimination. This aids one in the understanding of air-coupled sounds from airborne and ground sources and mechanically-coupled vibrations from ground sources. Air borne sources provide energy that, that is measured by microphone and, as this energy is coupled into the ground, by geophone. This measured energy, obtained by using co-located sensors (microphone and geophone), will have common amplitude and phase information Ground sources produce mechanically-coupled ground waves that arrive at the geophone with unique amplitude and phase information, independent of any acoustic signal they may radiate. Data analyzed at an Army test site is compared to experimental results.