Acoustic excitation of landmines and remote sensing from a moving truck

Abstract

The U.S. Department of Defense developed a 960 pixel laser Doppler vibrometer to capture seismic vibration and detect buried landmines. The sensor relied on a loudspeaker to create the seismic disturbances. This system captured seismic spatial responses while advancing at 1 m/s at 30 m standoff. Automated target recognition algorithms quickly processed the spatial vibration data to warn operators of threats. Sensor noise was highly variable, but on the order of .05mm/s in a band 50–400 Hz over which the sensor operated. Inertial sensing reduced gross Doppler components common to all channels. Even with these corrections, channel dropouts remained a challenge, so filtering of erroneous samples in time and space was required to improve the data quality, which is possible due to 960 simultaneous spatial samples. The large pixel count permitted road scans of 2 m × 1 km in less than 30 min. The system proved effective at finding buried threats that produced seismic anomalies at the surface, but additional challenges lie in differentiating target responses from clutter. This presentation will introduce the system and display high-resolution seismic images excited acoustically. It will also illustrate an acoustic wave captured directly by the lasers as the air's index-of-refraction fluctuated.