Laser-Doppler-based acoustic-to-seismic detection of buried mines

Abstract

Airborne acoustic waves coupled into the surface of the ground excite Biot Type I and II compressional and shear waves. This coupling of airborne sound into the ground is termed acoustic-to-seismic coupling. If a land mine or other inhomogeneity is presented below the surface, the ground surface vibrational velocity or S/A ratio will increase due to reflection and scattering of the Type II compressional wave. The dispersion characteristics of this wave in solids determines the mine detection limits. The S/A ratio is read with a laser doppler vibrometer (LDV). The loud speaker and LDV were mounted onto a large forklift at Fort AP Hill. This system was used to scan patches of ground at the Fort AP Hill calibration mine lanes. An investigation on the variability of surface velocity over different background types and mine types is described. The results of these initial field exercises are described.