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.

Application of line-scan CMOS camera in multi-beam heterodyne differential laser Doppler vibration sensor.

The possibility of using a line-scan digital CMOS camera as a photodetector in a multi-beam heterodyne differential laser Doppler vibration sensor has been investigated. Application of the line-scan CMOS camera allows for selection of a different number of beams for a particular application in the sensor design, and for a compact design of the sensor. It was demonstrated that a limitation of the maximum measured velocity caused by the camera limited line rate can be overcome by selecting the beams separation on the object and the value of shear between images on the camera.

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.

Multi-beam heterodyne laser Doppler vibrometer based on a line-scan CMOS digital camera.

Multi-beam laser Doppler vibrometers (MB-LDVs) have an advantage over scanning single-beam laser Doppler vibrometers (LDVs) due to the reduction in measurement time and their ability to measure non-stationary and transient events. However, the number of simultaneously interrogated points in current MB-LDVs is limited due to the complexity of the electronic hardware, which increases with the number of measurement channels. Recent developments of high-speed line-scan CMOS cameras suggest that their use in MB-LDVs can reduce the hardware complexity and increase the number of measurement channels. We developed a MB-LDV based on a digital line-scan CMOS camera that simultaneously measures vibrations on a linear array of 99 points. The experimental setup and performance of the developed MB-LDV are discussed in this paper.