Acoustic-to-seismic coupling technology using an LDV as a vibration sensor has proved itself as a potential confirmatory sensor for buried landmine detection. One of the most important objectives of this technology is to increase the speed of measurements over traditional point-by-point scanning LDVs. A moving cart that uses 16 LDVs as well as a continuously-scanning single beam LDV have recently been demonstrated to increase the speed of detection. Recently a multi-beam LDV simultaneously probing 16 positions on the ground has been developed and successfully used for landmine detection. In this work, we report on a continuously-scanning multi-beam LDV as a confirmatory sensor for acoustic landmine detection. The multi-beam LDV simultaneously illuminates the ground in 16 points spread over a 1 meter line. A scanning mirror moves all 16 laser beams across the line. The system enables scanning a 1 meter square area in a much shorter time than previous scanning techniques. This material is based upon work supported by the U. S. Army Communications-Electronics Command Night Vision and Electronic Sensors Directorate under Contract DAAB15-02-C-0024.
This paper discusses the performance and experimental results of a multiple beam laser Doppler vibrometer designed to locate buried landmines with the laser-acoustic technique. The device increases the speed of landmine detection by simultaneously probing 16 positions on the ground over a span of 1 meter, and measuring the ground velocity at each of these positions. Experimental results are presented from controlled laboratory experiments as well as from landmine test lanes at the University of Mississippi. In the mine lanes, the multiple beam system is raised to a height of 2.5 meters with a forklift, with the 16 beams spread over a 1 meter line along the mine lane. A motor system then allows the 16 beams to be translated across the mine lane, enabling the system to scan a 1 x 1 meter area in a much shorter time than with previous scanning techniques. The effects of experimental parameters such as platform motion, angle of incidence, speckle dropout, and system depth-of-field will be presented and discussed.
This paper discusses the development and performance of a multi-beam laser Doppler vibrometer specifically designed to locate buried landmines with a laser-acoustic technique. The device aims at increasing the speed of landmine detection with this technique by at least one order of magnitude. The present system is capable of simultaneously probing sixteen positions on the ground over a span of one meter, and of measuring the ground velocity at each of these positions with a velocity resolution of about 1 micrometers /s. This architecture could also be scaled to a larger number of beams or into two dimensions. The present system uses a low (100 kHz) carrier frequency, which enables digital signal processing in a simple architecture. This paper also discusses a numerical model to simulate and predict the performance of the multi-beam vibrometer. In particular, the model attempts to address issues associated with speckle dropout, signal/noise, and maximum scanning velocity.