Abstract: A dual mode sensor having a seismic channel and an RF channel with a logic circuit recognizing both channels. The seismic channel detects disturbances with a geophone and determines the spacing and the density of the impulses while the RF channel radiates electromagnetic energy and detects impedance changes in the oscillator circuit driving the antenna when the target is in the field. The rates of changing impedances and their thresholds are determined.

Abstract: 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 AND logic circuit, the output thereof indicating the presence of a target.

Abstract: Threshold count pulses, the number of which being proportional to the slope of an impedance curve of a radiating antenna in an RF detection system, are counted in a first counter and, upon receipt of a read pulse representing a threshold of impedance, are transferred to a memory counter while the read pulse delayed resets the first counter. The values in these two counters are compared in a first comparator which emits a pulse if the value of the first counter is greater than that of the memory counter and in the absence of these pulses a sequencer emits a signal indicating a target is moving outwardly. The threshold count pulses also feed an AND gate together with pulses from the first comparator with the AND gate output being fed to a third counter. The third counter is compared in a second comparator which emits a pulse upon equality indicating the target has approached an inner boundary. The third counter is reset with delayed read pulses.