[TangerineSDR] Lightning Stroke/TLE Analysis with VLF Receiver

[Jonathan]

Thanks Bob! I'll monitor that thread for ELVES events to see if I can find
ELF tails.

I still owe you the vlfrx-tools startup script. Be mindful that the cameras
don't generate any interference for the VLF receiver.

Jonathan
KC3EEY

On Fri, Jan 27, 2023 at 10:36 AM Bob Stricklin via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:

> Johnathan,
>
> The Global Meteor Network (GMN)
>
> Has a few TLE researches involved. They have posted on this topic in the
> past as well.
>
> See if this link will work for you without being listed in the Groups.io:
>
> https://globalmeteornetwork.groups.io/g/main/topic/91046167#6266
>
> The GMN cameras are excellent for recording these and you can get the time
> data needed.
>
> My VLF system with be sitting next to my cameras.
>
> This is an image captured by Damir Šegon in France on On Fri, May 13,
> 2022 at 6:41 PM. If the image is used in a publication then we should get
> his permission.
>
>
>
> the image has aircraft meteors and probably some bugs.
>
> There has been additional discussion on this but it is a minor topic on
> GMN. The GMN cameras have good information on the exact location
> (especially if multiple cameras)  and brightness of the light produced as
> well.
>
> Bob N5BRG
>
>
>
>
> On Jan 27, 2023, at 7:41 AM, Jonathan via TangerineSDR <
> tangerinesdr at lists.tapr.org> 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, it's 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: Inline image]
>
> 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 indicitive
> as that "little wavy line" after the sferic's impulse. The plot below
> show's 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: Inline image]
>
> 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 captured by Paul:
> [image: Inline image]
>
> This is the time domain plot with the ELF tail easier to see because there
> are much less high frequency components:
> [image: Inline image]
>
> 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: Inline image]
>
> 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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