Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-07-19
2001-05-15
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S600000, C073S170240, C073S384000, C702S003000
Reexamination Certificate
active
06232882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and systems for detecting tornadoes by means of their electromagnetic signatures, and more particularly, to such methods and systems which are capable of distinguishing between electromagnetic signals caused by tornadoes per se and other electromagnetic signals which are either manmade or associated with common lightning.
2. Description of the Related Prior Art
Tornado detection systems which operate based on the identification of drastic changes in ambient atmospheric pressure, and more particularly rapid reductions in atmospheric pressure, have been previously proposed. One such system is disclosed, for example, by U.S. Pat. No. 3,029,422 to Wilson. Such systems have been found to have certain shortcomings, including a preponderance of false alarms, since low atmospheric pressures, and even the sudden onset of such low atmospheric pressures, can be associated not only with tornadoes, but also with other storm systems of varying severity. As a result, merely detecting the presence or onset of low atmospheric pressures is not a reliable indicator of tornadoes.
On the other hand, a system disclosed in U.S. Pat. No. 3,646,540 to Cooper makes use of the well known phenomenon that approaching tornadoes can cause the appearance of “static” on the screen of a TV monitor, particularly when the monitor is tuned to a lower part (typically channel
2
or about 55 MHz) of the broadcast frequency range. Moreover, such a system is used in conjunction with an aneroid switch which closes when ambient atmospheric pressure falls below a predetermined limit. However, this system also has disadvantages, including the need to employ a miniature TV screen, a light detector and an aneroid switch, making the system expensive and bulky. Furthermore, this system also suffers from an unacceptable rate of false alarms when used in areas where manmade electromagnetic signals from TV stations are prevalent. Although such problems can be alleviated to some extent by fine tuning and frequent calibration of the system to account for the presence of manmade signals which can occur within the same spectral range as that used for detecting tornadoes, as a practical matter, such calibration has to be carried out at each site for which the warning device is intended, and cannot be done during production of the system at the factory.
Bacon et al. in U.S. Pat. No. 3,810,137 propose an alarm system employing a receiver which is tuned to a single frequency in a range of between 20 MHz to 60 MHz, and preferably to 53.25 MHz. The system is additionally coupled to an audio frequency detector for detecting and amplifying the amplitude modulations of a carrier signal in the range of 5 to 2000 Hz which are hopefully caused only by the presence of an oncoming tornado. However, manmade signals within the disclosed frequency range (i.e. TV channel
2
or 55 MHz) can also include amplitude modulations, making calibration of the system for given areas difficult. Essentially, a threshold for the system must be set at which the system will activate an alarm, however, such a calibration can be carried out accurately only for certain limited locations where manmade signals are present only intermittently and not at a constant intensity. Furthermore, in order to be useful, such calibration and threshold settings must be carried out in the presence of an approaching tornado, so as not to result in false alarms (when the threshold is set too low) or result in missing actual threatening tornadoes (when the threshold is set too high). Furthermore, such calibration must take into account the local nature of manmade RF signals, and thus this system cannot be used as a mobile alarm system. The system also suffers from false alarms generated due to normal lightning associated with approaching storms which may not necessarily generate tornadoes, but which can nevertheless activate the alarm too frequently.
Finally, Kennedy et al. in U.S. Pat. No. 4,812,825 describe a tornado alarm system in which an RF receiver is designed to receive an amplitude modulated signal within a broad range of 1 MHz to 100 MHz. Such a receiver is used in conjunction with a wide band amplifier and an integrator which activates a tornado alarm if and only if the amplitude modulation, generated by an approaching tornado, exceeds a minimum threshold for a minimum period not shorter than 3 seconds and, in most instances, between 10 to 25 seconds. The long term integration is designed to differentiate between the continuous electromagnetic noise generated by a tornado and intermittent electromagnetic noises generated by less severe storms, particularly lightning events. However, such long integration periods severely cut the time available for seeking shelter. Furthermore, this system, as with the system described in U.S. Pat. No. 3,810,137, requires the setting of threshold levels, through an automatic gain control, to prevent activation by manmade signals, and these thresholds are necessarily location dependent as well.
To the extent that U.S. Pat. Nos. 3,646,540, 3,810,137 and 4,812,825 demonstrate the well known fact that tornadoes generate electromagnetic noise, and describe means for detecting such noise within certain regions of the electromagnetic spectrum, the disclosures of these patents are hereby expressly incorporated into the present disclosure by reference.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to provide a method and system for the detection of tornadoes which overcomes the deficiencies of the aforementioned prior art.
Yet another object of the present invention is to provide a tornado detection system and method which utilizes algorithms for differentiating between manmade EM signals and naturally occurring EM signals associated with tornadoes.
A further object of the present invention is to provide a tornado detection system and method which is capable of distinguishing between lightning and electromagnetic signals generated by tornadoes.
A still further object of the present invention is to provide a tornado detection system which can be maintained calibrated even in a mobile environment.
A still further object of the present invention is to provide a tornado detection system and method utilizing a network of detectors and associated warning systems for population centers.
To achieve the above objects, the present invention is based on the well known fact that tornadoes generate electromagnetic noise, particularly around the TV broadcasting channel
2
(i.e. about 54 to 60 MHz). However, the present invention also takes into account that it is difficult to electronically distinguish between the noise actually generated by tornadoes and manmade electromagnetic signals occurring within the same frequency range. It is also difficult to avoid triggering false tornado alarms which can occur in the prior art systems as a result of electrical storms which are not necessarily associated with tornadoes.
To overcome such difficulties, the system and method of the present invention provides for a time and site variable calibration of the threshold values of the electromagnetic noise to be detected. Furthermore, according to one embodiment, such noise is detected at two independent frequencies, at least one of which does not typically bear an AM signal in the manmade part of the spectrum. More specifically, at least one of the frequencies is in the range of 54 to 60 MHz, where white noise generated by tornadoes is known to be prevalent, whereas the second frequency is selected to be either within the same range but where broadcasting only of FM signals is practiced, specifically at 59.75 MHz where the audio signal is carried solely on an FM carrier, or in the range of 30 to 50 MHz, which is the frequency band assigned by the FCC to tactical FM only communications.
Surprisingly, the inventors have discovered that in order to differentiate between lightning strikes and tornado generated electromagnetic signals, integration pe
Aisenberg Sol
Freedman George
Hed Aharon Ze'ev
Pavelle Richard
Greigg Edwin E.
Greigg Ronald E.
Spectrum Electronics, Inc.
Wu Daniel J.
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