Rapid high-spatial-resolution imaging of buried landmines using ESPI

Recent work in acoustic landmine detection has shown that many landmines exhibit a multi-mode vibration pattern. To fully map the vibration pattern of these modes requires spatial resolutions on the order of millimeters. An optical technique that lends itself to such vibration sensing is an electronic speckle pattern interferometer (ESPI). In this work the double-pulse ESPI system has been used for the vibration measurement of the ground surface. The principle of method is based on recording two specklegrams of the object with two laser pulses synchronized with the vibration peak and the vibration valley respectively. The 2D vibration amplitude spatial distribution is obtained by subtracting two specklegrams and processing the received correlation fringe pattern. The experimental setup uses a mechanical shaker to excite vibrations in the ground to significantly increase the vibration amplitudes at the spot of interest and a laser Doppler vibrometer to detect the resonant frequency of the mine. Experimental results are presented from laboratory experiments. The spatial maps of the vibrating ground over buried antitank and antipersonnel landmines are studied. The effect of the vibration of a granular material like sand on the speckle decorrelation is discussed. 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.