Laser Doppler multi-beam differential vibration sensor for real-time continuous visualization of buried objects in multiple frequency bands.

Laser-acoustic detection of buried objects, such as landmines, uses elastic waves in the ground and a laser vibrometer to create a vibration image of the ground surface. A decision on the presence of a buried object is made by analyzing vibration images for multiple vibration frequencies. With traditionally used laser Doppler vibrometers, the vibration imaging data are saved to a computer memory to be analyzed, which increases the detection time. A novel laser multi-beam differential interferometric sensor (LAMBDIS) that provides simultaneous real-time visualization of vibration images for multiple frequencies has been developed. The sensor is capable of displaying vibration images for up to 32 frequency bands simultaneously in real time. The sensor employs a digital line-scan complementary metal-oxide semiconductor camera and field programmable gate arraysbased real-time signal processing and is capable of operating continuously by scanning an object with a linear array of laser beams. Performance of the sensor has been verified experimentally. The ability of the LAMBDIS for real-time continuous vibration imaging of the ground surface in multiple frequency bands for laser-acoustic detection of buried objects has been demonstrated.