Seismic detection of a target is obtained with a geophone detecting earth vibrations caused by the actions of the target. The vibrations are wide band amplified and band-passed filtered with the pass bands being fed to the threshold detectors. The outputs of the threshold detectors are fed to a diode...http://www.google.com.mx/patents/US4337528?utm_source=gb-gplus-sharePatent US4337528 - Moving vehicle seismic target detector
