Ground excitation associated with acoustic and seismic sources

Abstract

Acoustic detection of buried objects, such as mines, has proven itself as a technique that provides high probability of detection and very low false alarm rate. The method consists of exciting ground vibrations and measuring the vibration characteristics of the ground at many points with a non-contact vibration sensor, for example a laser Doppler vibrometer (LDV). The interaction of a buried object with the elastic waves in the ground causes the object to vibrate, resulting in a vibration anomaly at the ground surface above the object. The performance of the methods depends on many factors, such as: type of object, object emplacement, soil type, and the type of ground excitation. The use of airborne sound from loudspeakers or seismic waves created by mechanical shakers are the two common sources of ground excitation. In this paper, we investigate the ground deformation versus range and frequency using airborne acoustic sources and mechanical contact sources. Measurements on a grass covered loess soil and a compacted gravel lane are analyzed to evaluate the differences in: modes of propagation, signal attenuation with range, and the three-component surface deformation.