SIGNAL PROCESSOR

• US 3,696,369 A
• Filed: 12/02/1970
• Issued: 10/03/1972
• Est. Priority Date: 12/02/1970
• Status: Expired due to Term

• Current Assignee: Jerome D. Mccoy, Marvin D. Laymon, Millard F. Schewe
• Original Assignee: Jerome D. Mccoy, Marvin D. Laymon, Millard F. Schewe
• Inventors: Laymon, Marvin D., McCoy, Jerome D., Schewe, Millard F.
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Slobasky, Michael
• Application Number:
  US05/094,405
• Time in Patent Office: 671 Days
• Field of Search: 340/261,258D,258R,15,15.5GG,16,276
• US Class Current: 367/136
• CPC Class Codes: G08B 13/1663 using seismic sensing means

Abstract

Seismic vibrations sensed by a geophone in a protected area are converted to an electrical seismic signal that is applied to an envelope detector. The detected signal is coupled directly and through an integrator which inverts the polarity thereof to a summing network. The zero crossings of the seismic signal are detected to generate a train of pulses that are integrated to produce a signal having an amplitude that is related to the fundamental frequency of the seismic signal and of the opposite polarity with respect to the detected signal and which is applied to the summing network. The output of the summing network is applied to a threshold circuit which produces an alarm indicating intrusion of the protected area when the magnitude of the sum signal exceeds a prescribed threshold level.

Claims

1. A seismic signal processor for discriminating between burst seismic signals such as are produced by a walking man and continuous seismic signals such as are produced by aircraft, comprising first means responsive to a seismic signal for producing a first signal having an amplitude that is an indication of the difference between the instantaneous amplitude of and the time varying average value of the envelope of said seismic signal, said average value being that value that is related to a time interval that is longer than the rise time of the value of a burst seismic signal and shorter than the rise time of the envelope of a continuous seismic signal, second means responsive to the first signal for producing a second signal indicating that said seismic signal is a burst seismic signal when the value of the amplitude of the first signal is greater than the prescribed value, and third means responsive to the seismic signal for producing a third signal having an amplitude that is proportional to and an indication of the fundamental frequency of said seismic signal, said second producing means including means for comparing said first and third signals, said second producing means generating the second signal indicating that said seismic signal is a burst seismic signal when the operation of said comparing means indicates that the amplitude of the first signal exceeds the amplitude of the third signal by a prescribed amount.

2. The processor according to claim 1 wherein said third producing means comprises fourth means responsive to said seismic signal for producing pulses indicating crossings of a prescribed level by the amplitude of the seismic signal, and means for integrating said pulses over a time interval that is shorter than the duration of a continuous signal for producing said third signal.

3. The processor according to claim 2 wherein said first producing means comprises a second envelope detector responsive to the seismic signal for producing an output signal having an amplitude that is proportional to the instantaneous amplitude thereof, said second envelope detector having a time constant controlling the operation thereof that is shorter than the rise time of the envelope of a burst signal, and a third reactive network responsive to the output signal of said second envelope detector, said third reactive network having a time constant that is long compared to the rise time of the envelope of a burst signal and short compared to the rise time of the Envelope of a continuous signal.

4. The processor according to claim 3 wherein said third reactive network has a low pass frequency response and produces the first signal.

5. The processor according to claim 3 wherein said third reactive network averages the output of said second envelope detector over the specified time interval, said first producing means including a second difference circuit responsive to the outputs of said second envelope detector and said third reactive network for producing the first signal.

6. The processor according to claim 2 wherein said fourth producing means comprises a zero crossing detector, pulses from said fourth producing means indicating zero crossings of the amplitude of the seismic signal.

7. The processor according to claim 2 wherein said fourth producing means comprises a first threshold circuit detecting crossings of a threshold level by the seismic signal, said threshold level being greater than the zero reference-level of the seismic signal and less than the prescribed amount specifying the operation of said comparing means.

8. The processor according to claim 2 wherein said third producing means comprises a second differentiator circuit and a first full wave rectifier.

9. The processor according to claim 1 wherein said comparing means comprises a third difference circuit producing an output signal having an amplitude proportional to the difference between the amplitudes of the first and third signals, said second producing means including a second threshold circuit responsive to the output signal of said third difference circuit.

10. The processor according to claim 1 wherein said comparing means comprises a third threshold circuit having a variable threshold level, said third threshold circuit being responsive to the output of said third producing means for varying the threshold level of said third threshold circuit an amount related to the fundamental frequency of said seismic signal and operatively receiving the first signal for producing the second signal indicating that the seismic signal is a burst seismic signal when the amplitude of the first signal exceeds the variable threshold level.

11. The processor according to claim 5 wherein said integrating means integrates pulses over a time interval that is longer than that over which said third reactive network averages the seismic signal.

12. The processor according to claim 3 wherein said second envelope detector comprises a second full wave rectifier and a low pass filter.

13. A seismic signal processor for discriminating between burst and continuous seismic signals comprising an envelope detector responsive to a seismic signal for producing a first signal having an amplitude that is a measure of the instantaneous amplitude of the envelope of the seismic signal, said envelope detector having a time constant controlling the operation thereof that is shorter than the rise time of the envelope of a burst signal, a reactive network receiving the first signal for producing a second signal having an amplitude that is a measure of the difference between the instantaneous amplitude of and the average value of the envelope of the seismic signal, said reactive network having a low pass frequency response and a time constant controlling the operation thereof that is long compared to the rise time of the envelope of a burst signal and short compared to the rise time of the envelope of a continuous signal, means responsive to the seismic signal for producing a third signal having an amplitude that is a measure of the fundamental frequency of said seismic signal, said producing means comprising a first threshold circuit producing pulses indicating crossings of a prescribed level by the amplitude of the seismic signal, and an integrator circuit responsive to the operation of said first threshold circuit for integrating pulses over a time interval that is shorter than the duration of a continuous signal for producing said third signal, aNd means comparing said second and third signals for producing an indication that said seismic signal is a burst seismic signal when the amplitude of the second signal exceeds the amplitude of the third signal by a prescribed amount.

14. The processor according to claim 13 wherein the time constant of said envelope detector is less than the period of a burst signal fundamental frequency of 30 Hz and the time constant of said reactive network is approximately equal to the duration of a burst signal.

15. The processor according to claim 14 wherein said reactive network comprises a first differentiator circuit having a time constant that is approximately 0.3 second, said integrator circuit having a time constant which is greater than that of said first differentiator circuit.

16. The processor according to claim 15 wherein said producing means comprises a second differentiator circuit and a full-wave rectifier.

17. The processor according to claim 15 wherein said comparing means comprises a difference circuit.

18. The processor according to claim 15 wherein said comparing means comprises a second threshold circuit having a variable threshold level, said second threshold circuit having a first input receiving the third signal for varying the threshold level thereof and having a second input receiving the second signal, said second threshold circuit producing an output signal indicating that the seismic signal is a burst seismic signal when the second signal exceeds the variable threshold level of a prescribed amount.

19. The method of detecting burst seismic signals comprising the steps of producing an indication of the difference between the instantaneous amplitude of and the average value of the envelope of seismic signals, producing an indication of the fundamental frequency of said seismic signal, comparing the difference and frequency indications, and indicating that the seismic signal is a burst seismic signal when the difference indication exceeds the frequency indication by a prescribed amount.

20. The method according to claim 19 wherein said step of producing the difference indication includes the steps of producing separate indications of the instantaneous amplitude of and and average value of the envelope of the seismic signal.

21. The method of detecting burst seismic signals comprising the steps of producing a first indication of the instantaneous amplitude of the envelope of a seismic signal, producing a second indication of the average value of the envelope of a seismic signal, producing a third indication that is a measure of the fundamental frequency of the seismic signal, comparing said first, second and third indications, and indicating that the seismic signal is a burst seismic signal when the difference between the instantaneous amplitude of the envelope of the seismic signal and the sum of the average value of the envelope of and the measure of the fundamental frequency of the seismic signal is a prescribed value.

22. In a seismic intrusion detection system including a seismic sensor for sensing vibrations in a medium for producing associated electrical seismic signals, a seismic signal processor for discriminating between burst seismic signals such as are produced by a walking man and continuous seismic signals such as are produced by low flying aircraft, comprising first means receiving a seismic signal for producing a first signal having an amplitude that is an indication of the instantaneous amplitude of the envelope of the seismic signal, second means receiving the first signal for producing a second signal having an amplitude that is an indication of the difference between the instantaneous amplitude of and the average value of the envelope of the seismic signal, third means receiving the seismic signal for producing a third signal having an amplitude that is an indication of the fundamental frequency of the seismic signal, and means For comparing the second and third signals for producing an indication that said seismic signal is a burst seismic signal when the difference between the instantaneous amplitude of and the average value of the envelope of the seismic signal exceeds the indication of the fundamental frequency of the seismic signal by a prescribed amount.

23. The processor according to claim 22 wherein said third producing means comprises a first threshold circuit producing pulses indicating crossings of a prescribed threshold level by the amplitude of the seismic signal, and an integrator circuit responsive to the operation of said first threshold circuit for integrating pulses for producing the third signal.

24. The processor according to claim 23 wherein said first producing means comprises a first envelope detector and said second producing means comprises a first reactive network having a low pass frequency response, said first reactive network receiving the first signal for producing the second signal, the threshold level of said first threshold circuit being greater than a zero-reference level of the seismic signal.

25. The processor according to claim 24 wherein said comparing means comprises a second threshold circuit having a variable threshold level, said second threshold circuit being responsive to the third signal from said integrator circuit for varying the threshold level of said second threshold circuit an amount that is a measure of the fundamental frequency of the seismic signal and responsive to the second signal for producing an indication that the seismic signal is a burst signal when the amplitude of the second signal exceeds the variable threshold level.

26. The processor according to claim 23 wherein said first producing means comprises a second envelope detector producing the first signal, and said second producing means comprises a second reactive network for averaging the first signal and producing a fourth signal that is a measure of the average value of the envelope of the seismic signal, said comparing means being responsive to the first, third and fourth signals.