Seismic-acoustic low-flying aircraft detector

Details Seismic-acoustic low-flying aircraft detector Seismic-acoustic low-flying aircraft detector

1984-06-22

1986-12-16

Terapane, John F.

Communications, electrical: acoustic wave systems and devices

Receiver circuitry

367 45, 367 46, 367124, 367125, 367126, 367136, 340522, 340566, H04B 110, G01S 382, G08B 1900, G08B 1326

Patent

active

046302468

ABSTRACT:
The detection of low-flying aircraft is accomplished using both a microphone and geophone as sensors and a signal processing system for measuring the correlation between the seismic and acoustic signals. The signal processing system contains two amplification and band-limiting circuits, a delay circuit, an adaptive noise cancelling circuit, two signal smoothing circuits and a comparison circuit. The two amplification and bandlimiting circuits enhance a selected portion of the seismic and acoustic signals received by the sensors. The optional delay circuit is applied to the input acoustic signal, allowing the user the option of sensing or rejecting the detection of jet aircraft. The adaptive noise cancelling circuit generates an error signal by subtracting the signal components which are correlated between the seismic and acoustic signals from the input seismic signal. The first signal smoothing circuit improves the quality of the input seismic signal for comparison. The second signal smoothing circuit improves the quality of the error signal generated by the adaptive noise cancelling circuit. Finally, the comparison signal compares the smoothed seismic signal with the error signal. Low-flying aircraft have seismic and acoustic signatures which are highly correlated while other sources (wind, seismic events and motor vehicles) have little correlation. Therefore, if the error signal resembles the seismic signal there occured little correlation and the causing the event was not an aircraft. Dissimilar error signals and seismic signals occur when aircraft are detected, an event which is indicated by the output signal from the comparison circuit.

REFERENCES:
patent: 3573817 (1971-04-01), Akers
patent: 3774190 (1973-11-01), Kyle, Jr.
patent: 3852706 (1974-12-01), Barney et al.
patent: 4083031 (1978-04-01), Pharo, Jr.
patent: 4223304 (1980-09-01), Barowitz et al.
patent: 4408533 (1983-10-01), Owen et al.

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