Warning system and method for detection of tornadoes

• US 6,232,882 B1
• Filed: 07/19/2000
• Issued: 05/15/2001
• Est. Priority Date: 07/19/2000
• Status: Expired due to Fees

• Current Assignee: Spectrum Electronics Incorporated
• Original Assignee: Spectrum Electronics Incorporated
• Inventors: Hed, Aharon Zeʼev, Aisenberg, Sol, Pavelle, Richard, Freedman, George
• Primary Examiner(s): Wu, Daniel J.
• Application Number:
  US09/619,690
• Time in Patent Office: 300 Days
• Field of Search: 340/600, 340/601, 340/690, 731/706.6, 733/84, 702/3
• US Class Current: 340/601
• CPC Class Codes: G01W 1/10 Devices for predicting weather conditions computers per se G06; display devices G09
• CPC Class Codes: G01W 1/16 Measuring atmospheric potential differences, e.g. due to electrical charges in clouds measuring potentiels in general G01R
• CPC Class Codes: Y02A 50/00 in human health protection, e.g. against extreme weather

Abstract

To differentiate between lightning strikes and tornado generated electromagnetic signals, a tornado detection system and method is made up of RF receiving circuits which receive signals at two frequencies, while implementing a time variable automated calibration and the use of special algorithms, to reliably detect tornado events and to signal an alarm. A network of such systems can be implemented, using a plurality of antennas which are capable of discerning a directional vector, and integrating the directional information from multiple units by effecting a triangulation calculation in a server terminal to determining a position and path of an approaching tornado.

Claims

1. A system for detecting tornadoes, comprising:

a first RF receiving circuit adapted to be connected to an antenna and comprising a resonant circuit tuned to receive an RF signal at a first predetermined frequency;

a second RF receiving circuit adapted to be connected to an antenna and comprising a resonant circuit tuned to receive an RF signal at a second predetermined frequency;

memory means storing a pair of predetermined threshold values and an algorithm to distinguish between an electromagnetic signature of a tornado, intermittent electromagnetic signals and manmade signals; and

processing means connected to said first and second RF receiving circuits, for receiving respective amplitude signals indicating amplitudes of the RF signals at said first and second predetermined frequencies, said processing means further comprising means for applying said algorithm to said amplitudes of the RF signals at said first and second frequencies to detect a tornado, said processing means further comprising means to emit a signal when said algorithm detects a tornado.

2. The system according to claim 1, further comprising alarm and/or display means and said emitted signal activates said alarm and/or display.

3. The system according to claim 1, wherein said predetermined threshold values are continuously updated according to the background electromagnetic noise prevailing at the system site at said two frequencies.

4. The system according to claim 1, wherein the algorithm comprises the steps of:

comparing the RF amplitudes received at said two frequencies to their respective threshold values;

updating said threshold value to exceed background noise and manmade signals at said frequencies; and

determining the presence of a tornado if and only if both amplitudes are greater than their respective threshold values for a period greater than a predetermined time interval, said interval being longer than that of natural intermittent signals such as lightening.

5. The system according to claim 1, wherein said first and second frequencies are both within a range of from 30 MHz to 60 MHz.

6. The system according to claim 5, wherein said first frequency is set within a range of a frequency spectrum publicly used for carrying AM video image signals, and said second frequency is set within a range of the frequency spectrum publicly used for carrying FM audio signals.

7. The system according to claim 6, wherein said first frequency is set at 55.25 MHz and said second frequency is set at 59.75 MHz.

8. The system according to claim 4, wherein said processing means further comprises:

means for sampling said respective amplitudes of said first and second frequencies for a predetermined sampling interval; and

means for counting a predetermined number of consecutive sampling intervals during respective measurement cycles at which said RF amplitudes at said first and second frequencies exceed said predetermined threshold values, wherein said predetermined time interval is determined by said predetermined number.

9. The system according to claim 8, wherein said sampling interval is between 0.1 ms and 50 ms.

10. The system according to claim 8, wherein said respective amplitudes are sampled simultaneously.

11. The system according to claim 8, wherein a standby time interval, during which sampling is not performed, occurs between sampling of said respective amplitudes.

12. The system according to claim 4, wherein said threshold values comprise first and second threshold values each comprising the product of an average of previously received amplitude signals times a scaling constant.

13. The system according to claim 12, further comprising default threshold values T₁(d) and T₂(d) associated with each of said first and second threshold values, wherein said first and second threshold values T₁ and T₂ are calculated according to the following equations:

14. The system according to claim 13 wherein said respective averages are updated during each measurement cycle, unless during the preceding measuring cycle said amplitude values for both of said first and second frequencies have exceeded the first and second threshold values, respectively.

15. A method of detecting tornadoes by distinguishing the electromagnetic signature of a tornado from manmade signals and intermittent natural signals comprising the steps of:

setting a first RF receiving circuit, adapted to be connected to an antenna and comprising a resonant circuit, to be tuned at a first predetermined frequency;

setting a second RF receiving circuit, adapted to be connected to an antenna and comprising a resonant circuit, to be tuned at a second predetermined frequency;

storing a pair of predetermined threshold values that are greater than present ambient manmade signals;

receiving with said first and second RF receiving circuits, respective amplitude signals indicating amplitudes of the RF signals at said first and second predetermined frequencies;

comparing said amplitude signals with said predetermined thresholds values; and

emitting a signal indicating detection of a tornado when both of said amplitude signals exceed said predetermined threshold values for a predetermined duration of time.

16. A method according to claim 15, further comprising an alarm means and/or display means, and said signal activates said alarm means and/or display means.

17. A method according to claim 15, wherein said predetermined threshold values are continuously updated according to the background electromagnetic noise prevailing at the system site at said two frequencies.

18. The method according to claim 15, wherein said first and second frequencies are both within a range of from 30 MHz to 60 MHz.

19. The method according to claim 15, further comprising the steps of:

setting said first RF receiving circuit to be tuned to said first frequency within a range of a frequency spectrum used publicly for carrying AM video image signals; and

setting said second RF receiving circuit to be tuned to said second frequency within a range of the frequency spectrum used publicly for carrying FM audio signals.

20. The method according to claim 19, wherein said first frequency is set at 55.25 MHz and said second frequency is set at 59.75 MHz.

21. The method according to claim 15, further comprising the steps of:

sampling said respective amplitudes of said first and second frequencies for a predetermined sampling interval; and

counting a predetermined number of sampling intervals during respective measurement cycles at which both of said first and second frequencies exceed said predetermined threshold values, wherein said predetermined duration of time is determined by said predetermined number.

22. The method according to claim 21, wherein said sampling interval is between 0.1 ms and 50 ms.

23. The method according to claim 21, wherein said respective amplitudes are sampled simultaneously.

24. The method according to claim 21, wherein a standby time interval, during which sampling is not performed, occurs between sampling of said respective amplitudes.

25. The method according to claim 17, further comprising setting said threshold values as first and second threshold values, wherein said first and second threshold values each comprise the product of an average of previously received amplitude signals times a scaling constant.

26. The method according to claim 25, further comprising the steps of:

setting default threshold values T₁(d) and T₂(d) associated with each of said first and second threshold values;

calculating said first and second threshold values T₁ and T₂ according to the following equations;

27. The method according to claim 26, further comprising the step of updating respective averages during each measurement cycle, unless during a prior measuring cycle said amplitude values for both of said first and second frequencies have exceeded the first and second threshold values, respectively.

28. A system for detecting tornadoes, comprising:

a plurality of tornado detectors, wherein each of said tornado detectors comprises;

a first RF receiving circuit adapted to be connected to an antenna and comprising a resonant circuit tuned to receive an RF signal at a first predetermined frequency;

a second RF receiving circuit adapted to be connected to an antenna and comprising a resonant circuit tuned to receive an RF signal at a second predetermined frequency;

memory means storing a pair of predetermined threshold values and an algorithm to distinguish between an electromagnetic signature of a tornado, intermittent electromagnetic signals and manmade signals; and

processing means connected to said first and second RF receiving circuits, for receiving respective amplitude signals indicating amplitudes of the RF signals at said first and second predetermined frequencies, said processing means further comprising means for applying said algorithm to said amplitudes of the RF signals at said first and second frequencies to detect a tornado, said processing means further comprising means to emit a signal when said algorithm detects a tornado;

a digital communications network interconnecting said RF receiving units and a server terminal,

wherein said tornado detectors each further comprise processing means for determining the direction of maximum signal, when a tornado is detected, and means for emitting a signal indicating a directional vector at which an amplitude of the RF signal is maximum, and

wherein said directional vectors from each of said tornado detectors are transmitted through said communications network to said server terminal, said server terminal having means for determining an intersection of at least two directional vectors for detecting a position of the detected tornado.

29. The system according to claim 28, wherein said antennas associated with each tornado detector comprise directional loop antennas.

30. The system according to claim 28, wherein at least one of said tornado detectors is mobile and the said threshold values associated with each said tornado detector are updated at least once every 5 seconds.