[LINK] Nokia lightning detector patent application
stephen at melbpc.org.au
stephen at melbpc.org.au
Fri May 25 23:55:17 AEST 2007
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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