Seismic/acoustic detection of ground and air traffic for unattended ground sensor technology

Abstract

Human footfall and vehicle traffic create surface waves in soil media that can easily be detected by seismic sensors. Field measurement data have been acquired with a triaxial geophone at several experimental sites. The in-plane-surface wave components dominate the response and decay at a rate of approximately 1/R, where R is distance. This decay rate is due to the combined effect of spreading (1/sqrt(R)) and damping losses in the soil. Further, the detection range is dependent upon the level of environmental noise, soil compliance, moisture content, and topography. Human detection was achieved in rural environments at distances up to ∼30–40 m, and vehicle detection was possible at much greater distances. Seismic signals due to aircraft are small when compared to the acoustic signature. Ground-based microphone measurements clearly show the blade passage frequency tones of propeller airplanes and the broader band signature of turbojet aircraft. Time- and frequency-domain signal-processing methods for the detection and identification will also be introduced. These experimental results will be discussed with particular emphasis placed on wave phenomenon, detection and identification algorithms, and the related physics.