[TangerineSDR] [HamSCI] Lightning Stroke/TLE Analysis with VLF Receiver (Post with Missing Images)

Sun Jan 29 16:26:37 EST 2023

Gerry,

No worries. Why do you prefer to use TDOA instead of TOGA?

Also, how does one characterize the stroke in VLF? Will looking at the
analytic magnitude indicate anything?

In vlfrx-tools software, lightning location works in the following manner:
the utility vttoga will identify impulsive signals and measure their TOGA
(whether they are sferics, rain static, or local interference). It can also
measure other parameters, such as ground wave and sky wave identification,
analytic magnitude, frequency spectra, and unwrapped absolute phase. Still,
vttoga just sees the impulse. To determine whether it came from a stroke or
some other interference source, vttoga data from multiple receivers
(including lat/long coordinates of the VLF receivers) is fed into the
utility vtspot which computes a solution for the stroke using
trilateration. Rain static and local interference won't yield a solution,
but sferics will if it's within a location between the VLF receivers.
vtspot is not perfect, but it generates pretty accurate solutions when fed
with good data. You can read about how to use vttoga and vtspot for
lightning location here
<http://abelian.org/vlfrx-tools/notes.html#Lightning%20location>. The hope
is to build a dense network of VLF receivers for an overdetermined
solution, but this will be volunteer based, so it'll take time to build.

Using VLF receivers with vlfrx-tools, do you feel it would be a good start?
With the signal processing utilities available in vlfrx-tools, I think
quite a lot can be done.

Jonathan
KC3EEY

On Sun, Jan 29, 2023 at 10:20 AM Robert McGwier <rwmcgwier at gmail.com> wrote:

> Where in Maryland would you locate one?
>
> Bob
> N4HY
>
>
> On Fri, Jan 27, 2023 at 12:41 PM Jonathan <emuman100 at gmail.com> wrote:
>
>> Kerry,
>>
>> ELVES and sprites occur in the mesosphere above thunderstorms.
>>
>> Gerry,
>>
>> I'm still looking to create a network of VLF receivers and one of the
>> functions would be lightning location. Other than impulse duration, what
>> are the characteristics of a CG and intracloud stroke at VLF and how would
>> distance from the receiver affect that? The vlfrx-tools software I use is
>> very versatile in terms of signal processing, so what were you looking to
>> do?
>>
>> Jonathan
>> KC3EEY
>>
>> On Fri, Jan 27, 2023 at 10:35 AM Gerald Creager <gcreager at cap.gov> wrote:
>>
>>> Jonathon,
>>>
>>> Your network of receivers is similar in concept to the network I
>>> presented several years ago at the TAPR DCC. Let's talk. Your ELF tail and
>>> EVLE work suggest some things to me. A lot of work has been done in other
>>> spectral ranges than VLF, and there are data to capture at higher
>>> frequencies. Think "Citizen Weather Observer Network" but for lightning.
>>> I've also got some ideas on central processing for geolocation for GC and
>>> CC/IC impulses.
>>>
>>> 73
>>> Gerry N5JXS
>>>
>>> Maj Gerry CreagerNational Health Services Advisory TeamCivil Air Patrol, U.S. Air Force Auxiliary
>>>
>>> (M) 979.229.5301
>>>
>>> GoCivilAirPatrol.com <https://www.gocivilairpatrol.com/>
>>>  <https://www.gocivilairpatrol.com/>
>>>
>>> Volunteers serving America's communities, saving lives, and shaping futures.
>>>
>>>
>>>
>>> On Fri, Jan 27, 2023 at 7:35 AM Jonathan <emuman100 at gmail.com> wrote:
>>>
>>>> Sometimes lightning strokes produce what are called transient luminous
>>>> events, or TLEs. They are commonly known as sprites and jets. Not much is
>>>> known about them but they are continuously studied. Columns and regions of
>>>> atmosphere are ionized so much by the electric potentials caused by the
>>>> lightning stroke that the air glows red. It’s present for a split second
>>>> when the stroke occurs, so you need a quick eye and a camera to capture an
>>>> image. Many enthusiasts who capture these beautiful events often use timed
>>>> video and photography and use lightning stroke data to identify the
>>>> specific lightning stroke, its channel current, and polarity. The "channel"
>>>> is the conductive channel of ionized air where lightning current either
>>>> flows upwards or downwards. VLF receivers detect the radio emissions from
>>>> lightning strokes, called sferics. The sferic signal characteristics are
>>>> fed into models that calculate stroke polarity and channel current.
>>>>
>>>> An enthusiast and photographer, Paul, captured a double TLE, showing
>>>> both a sprite (the dendritic structure) and an ELVE (the upper dim region
>>>> of red glowing air above the sprite). ELVEs are often, but not always,
>>>> indicative of what is called a "continuing current", or a residual current
>>>> flowing through the channel with ELF frequency components.
>>>> [image: thumbnail1.png]
>>>>
>>>> Using a VLF receiver connected to a soundcard and vlfrx-tools software,
>>>> it is possible to look at the sferic's impulse in a time domain plot. A
>>>> continuing current will often show up as an "ELF tail" right after the
>>>> initial impulse. This tail has ELF frequency components and is indicative
>>>> of that "little wavy line" after the sferic's impulse. The plot below shows
>>>> the sferic from the stroke that created the TLE above. The ELF tail is hard
>>>> to see because it has some high frequency components on it, but it is
>>>> there. Running the following signal processing chain in vlfrx-tools
>>>> software produced the plot below:
>>>>
>>>> vtread -T2022-12-14_02:09:20,+30s /data/vlf_96k | vtfilter -a th=5 |
>>>> vtresample -r32000 | vtcat -T2022-12-14_02:09:38.2,+0.1 | vtplot -t "+266kA
>>>> Stroke Nice Sprite/ELVE Combo"
>>>>
>>>> [image: thumbnail2.png]
>>>>
>>>> The farther the VLF receiver is from the lightning stroke, the longer
>>>> the ELF tail is. If this stroke occurred in Europe, it would be much
>>>> longer, but it was captured in the US, closer to the VLF receiver. Here is
>>>> another example of an ELVE:
>>>> [image: thumbnail5.png]
>>>>
>>>> This is the time domain plot with the ELF tail easier to see because
>>>> there are much less high frequency components:
>>>> [image: thumbnail3.png]
>>>>
>>>> In recording these millisecond events, it is essential to use precision
>>>> timing, which is why I use a GPS receiver to enable accurate and precision
>>>> timestamping. I used the signal processing chain above to pull the spectrum
>>>> data from the data store, filter out mains hum, resample to 32k to remove a
>>>> lot of high frequency components, then feed the specific spectrum chunk
>>>> into the plotting program.
>>>>
>>>> With vlfrx-tools software and a network of VLF receivers, you can do
>>>> lightning location as well. Here is a lightning map from a network of VLF
>>>> receivers in India:
>>>> [image: pn221206a.png]
>>>>
>>>> The red dots indicate the location of a stroke and the circles indicate
>>>> VLF receiver locations.
>>>>
>>>> Eventually, I would like to have a network of VLF receivers collecting
>>>> sferic data for lightning location.
>>>>
>>>> Jonathan
>>>> KC3EEY
>>>>
>>>> --
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>>>>
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> --
> Dr. Robert W McGwier, Ph.D.
> Adjunct Faculty, Virginia Tech
> Affiliated Faculty, University of Scranton
> ARDC Member of Board
> N4HY: ARRL, TAPR, AMSAT, EARC, CSVHFS
> Sky: AAVSO, Sky360, explorescu.org, Skyscrapers
>
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