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

Fri Jan 27 12:41:33 EST 2023

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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