Acoustic–seismic coupling model for the Short-Distance detection of Ultra-Low-Altitude aircraft

When using seismic signals to detect ultra-low-altitude aircraft at short distances, inappropriately designed filters reduce the signal quality and detection accuracy. To solve this problem, continuous acoustic signals generated by standard sound sources were used to induce vibrations in soil. Based on the assumed incidence of spherical wavefronts, we found that frequency bands of strengthened and weakened coupling are caused by interference between acoustic coupled waves and precursory seismic waves. We estimated the seismic properties at the experimental site by scanning various parameters to optimize the similarity coefficient. Based on the model, we discussed the relationship among soil velocities, layer thicknesses, and the amplitude of the coupled signal with frequency and provided a basis for the design of filters for detecting ultra-low-altitude aircraft.