Acoustic methods detect hollow underground cavities near infantry by exploiting differences in sound wave propagation, reflection, and resonance between solid soil and voids. These techniques generate vibrations that reveal anomalies through altered echoes or seismic responses.[mit +1]
Primary Techniques
Parametric acoustic arrays (PAAs) direct high-intensity sound beams to couple acoustic energy into the ground, inducing vibrations in cavities measurable by laser Doppler vibrometers from standoff distances up to 30 meters. Hammer impacts on nearby surfaces, like plates or ground, produce measurable reflections captured by microphones, with signal analysis estimating cavity size based on resonance frequencies.[pmc.ncbi.nlm.nih +1]