Comparison of linear and nonlinear experiments for landmine detection

When airborne sound couples into the ground, so‐called ‘‘slow’’ compressional waves can interact with a target buried in the soil and effect the vibration velocity of the surface. Donskoy [SPIE Proc. 3392, 211 (1998); 3710, 239 (1999)] has suggested a nonlinear technique that can detect an acoustically compliant buried mine that is insensitive to relatively noncompliant targets. A VS 1.6 inert antitank mine (23 cm diam) was buried in the natural loess soil at the test site. In the linear experiment, a pair of subwoofers were sinusoidally swept from 70 to 600 Hz. The geophone’s response was measured along a 1 m scan segment across the mine. A 107 Hz resonance was chosen and the nonlinear experiment was performed by driving the woofers at f1=300 Hz and f2=407 Hz and detecting at the difference frequency. Nonlinear scan profiles over the mine have more relative sensitivity than the linear profiles. When a 30 cm diam, 4 cm thick concrete disk was buried, it could be detected ‘‘linearly’’ but not ‘‘nonlinearly’’ in agreement with Donskoy. Nonlinear theories will be discussed. [Work supported by the United States Army Communications‐Electronics Command Night Vision and Electronic Sensors Directorate.]