Laser Doppler multi-beam differential vibration sensor based on a line-scan CMOS camera for real-time buried objects detection

Laser Doppler vibrometers (LDVs) traditionally used for ground vibration sensing in laser-acoustic detection of buried objects are limited to operation from a stationary platform due to their sensitivity to the motion of the LDV itself. In order to overcome this limitation a novel Laser Multi-Beam Differential Interferometric Sensor (LAMBDIS), has been developed. The LAMBDIS allows for measurements of vibration fields with interferometric sensitivity, while having low sensitivity to the motion of the sensor itself. The LAMBDIS described in this paper is based on a digital line-scan CMOS camera and FPGA based real-time signal processing. The principle of operation of the LAMBDIS employs the interference of light reflected from different points on the object surface illuminated with an array of laser beams. The Doppler shift induced by the sensor motion is canceled out thereby allowing for measurements from a moving vehicle. The ability of the LAMBDIS to detect buried objects in real time from a moving vehicle has been confirmed in field experiments.