Land mine detection measurements using acoustic-to-seismic coupling

During the early 1980s, the phenomenon of acoustic-to-seismic coupling was used to detect buried objects or mines. In these early measurements, large 2 Hz geophones measured the low frequency (50-300 Hz) normal component of the soil particle velocity over buried targets. Several different, naturally-occurring ground types were studied in these measurements, including grass-covered ground; bare, sandy soil surfaces; and “dirt” roads. Since the large geophone averages the particle velocity over the area of the sensor case, acoustic-to-seismic transfer function measurements were made with new, smallersized (10 Hz) geophones. Higher frequency (1-10 kHz) measurements were made using accelerometers. Three-dimensional maps of the surface particle velocity were made using measured seismic/acoustic transfer function data. Recognizing the need for a non-contact sensor and the need to investigate the geophone/soil coupling effect in the acoustic-to-seismic transfer function, additional measurements were made using a laser Doppler vibrometer (LDV). This paper explains the acoustic-toseismic coupling mine detection measurement technique using both geophones and an LDV. The early measurements of the acoustic-to-seismic coupling transfer function for mine-like targets are discussed as well as some recent measurements using a LDV.