[LINK] Nokia lightning detector patent application

[stephen at melbpc.org.au]

There's a new Nokia (US) Patent Office application for:

"A lightning detector and a lightning detection method.."

<http://appft1.uspto.gov/netacgi/nph-Parser?
Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%
2Fsrchnum.html&r=1&f=G&l=50&s1=%2220070085525%
22.PGNR.&OS=DN/20070085525&RS=DN/20070085525>
 
BACKGROUND OF THE INVENTION 

[0002] Thunderstorms are a major weather hazard, but are difficult to 
predict. They can travel at speeds of 20 km/h to 40 km/h, and lightning 
strokes may occur more than 10 km in front of the rain clouds and equally 
some distance behind the rain clouds. While a lightning stroke is 
produced by a cloud or a weather front, many of the most dangerous 
lightning strokes actually occur when no visible clouds are present above 
as a warning of a thunderstorm. Thus, a system that warns of possibility 
harmful thunderstorms, even if only approximately proximately ten minutes 
before they become visible, can be considered a major safety feature. 

[0003] There is a large population that would benefit from such a safety 
feature. To some persons, it might provide only a nice-to-know everyday 
knowledge. To a considerable number of persons, however, storm and 
lightning originated threats have significant implications in the form of 
an increased risk, loss of property or even fatal consequences. A 
lightning alerting system is of particular interest, for instance, for 
persons spending much time outdoors, and equally for aviators, navigators 
or the like. A system providing a warning of lightning even when the 
weather seems to be perfectly calm and clear may enable a person to take 
suitable safety measures in time, for instance seek shelter etc. 

[0004] From the state of the art, many single-purpose lightning detectors 
are known, but they have some disadvantages from a commercial 
perspective. Scientific lightning detectors, which are used in 
meteorology, are very large and their range is hundreds of kilometers. 

[0005] Also other high-end lightning detectors using a single radio 
frequency (RF) band are large and relatively expensive, compared for 
instance to mobile phones. Moreover, they are usually required to have a 
specific orientation, for instance standing on a wall or on a desk stand, 
in order to gain the required accuracy or directionality. They are thus 
not well suited for a truly mobile use. These devices typically have 
further to be positioned in a certain way and held stationary for several 
minutes before a reliable detection of a thunderstorm becomes possible. 

[0006] In addition, there are now existing rather inexpensive low end 
lightning detectors which are completely portable in size and which do 
not require a specific orientation. These detectors, however, are 
extremely susceptible to man-made electromagnetic compatibility (EMC) 
emissions and thus tend to cause spurious alarms especially in an urban 
setting or near highways 

[0007] Currently most of commercially available mobile lightning 
detectors detect lightning strokes by measuring the electromagnetic 
emission caused by lightning at very low frequencies (VLF: 3-30 kHz). In 
addition, it has been known for decades that lightning strokes can 
be "heard" by using a traditional AM broadcast radio receiver, which 
operates at longwave frequencies (150 to 300 kHz), mediumwave frequencies 
(500 to 1700 kHz) and shortwave frequencies (SW: 2 to 30 MHz). However, 
numerous publications exist where lightning have been detected and 
measured by its emission at HF and VHF frequencies between 3-300 MHz and 
even at higher (UHF) frequencies. 

SUMMARY OF THE INVENTION 

[0008] The present invention proceeds from the consideration, that a 
lightning stroke is a single flash which produces besides a visual signal 
and a partly audible pressure signal as well a brief but strong 
electromagnetic pulse extending over a wide variety of wavelengths. 
Typical electromagnetic pulses caused by a lightning stroke cover the 
frequencies between 10 Hz and 5 GHz with a peak around 500 Hz, i.e. in 
the audio frequency range. At a normalized distance of 10 km, the 
amplitudes of such pulses range from 107 mV/m to 1 mV/m in a bandwidth of 
1 kHz. the strongest signal of the electromagnetic pulse is the induced 
electric field caused by the vertical current in the lightning stroke, 
and this is the parameter that is most commonly measured in large-scale 
distance-bearing devices. 

[0009] However, due to the complexity of the lightning stroke phenomenon, 
there are also strong signals in the extremely low frequency (ELF) range 
of a few hundred Hz or less, and weaker signals extending up to the GHz 
range and above. 

[0010] It is a well-known fact that the exact characteristics and time 
spectra of the electromagnetic interference (EMI) signatures are 
different in the MHz range that in the kHz and Hz ranges due to the 
slightly different meteorological mechanisms causing them. 

[0011] For the purposes of the present invention it is sufficient to note 
that at all frequencies of interest, a lightning stroke is accompanied by 
an EMI pulse that can be identified at a distance of many kilometers. 

[0012] As a result of the lightning stroke generated EMI pulse, RF 
channels are briefly interfered during a lightning stroke in the 
vicinity. The impairment of RF receivers due to an EMI caused by a 
lightning stroke can be experienced in using an AM/FM radio, TV or over 
power supply lines in form of statics, clicks, scratches, noise or loss 
of sound or picture. Disturbances in RF channels due to a lightning 
stroke can be sensed at very large distances. Specialized and large-scale 
lightning detectors are able to detect lightning disturbances, so-called 
sferics, at a distance of several hundreds of kilometres from a lightning 
stroke, although these detectors typically operate by measuring the 
induced electric or magnetic field rather than the interferences in an 
audio or RF signal as the present invention. 

[0013] Ordinary AM radios are known to suffer from EMI disturbances at a 
distance up to 30 km or more from a lightning stroke, which can even be 
heard directly in an audio signal as various clicks. At higher 
frequencies than the AM bands the signal is typically much weaker due to 
both atmospheric attenuation and different causation mechanisms, but is 
nevertheless detectable at large distances. 

[0014] While in known mobile RF devices, such as ordinary mobile phones, 
electromagnetic interference in received RF signals are eliminated 
immediately by filtering, it is proposed in the present invention that 
such electro-magnetic interferences in a monitored RF channel are 
evaluated. If a detected interference seems to be caused by a lightning 
stroke, a user of for example a mobile phone can be alerted. An 
interference can be assumed to be caused by a lightning stroke, for 
example, if it exceeds a predetermined threshold value or if it has a 
frequency spectrum which is characteristic of a lightning stroke. The 
lightning detection can be on as long as the RF detection is on. 

[0015] The present invention thus provides a new security feature that 
can be implemented in a mobile RF device, for example a cellular phone. 

[0016] While in many case, the desire to detect lightning strokes in the 
vicinity may not be large enough to justify the costs and the difficulty 
of carrying along a dedicated lightning detector, many people would 
appreciate a low-cost sensing system that could be integrated with a 
device that they are already carrying along in any case, especially like 
a mobile phone. The known art does not provide for such an integration of 
a lightning detection as a new functionality in known mobile RF devices. 

[0018] The present invention is based on the idea that the incoming 
spectrum generated by a thunderstorm is studied using all or many 
available RF channels available in a mobile RF device, such as a cellular 
phone. Because of the many radio interfaces (i.e. hundreds of channels in 
each of the three bands in a tri-band receiver, the Bluetooth receiver 
frequencies, the FM radio including the pilot tone channel, the Wi-Fi 
radio local area receiver, the RFID tag reader and even the RDS and/or 
DARC receivers) the present invention provides a new and feasible method 
for lightning detection. 

[0019] Thus according to the first aspect of the invention, the present 
invention is based on the use of at least two channels, at least one of 
which is a telecom channel, for lightning detection.


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