105 lines
3.4 KiB
Markdown
105 lines
3.4 KiB
Markdown
+++
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title = "Sferics"
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description = "Hunting for the voice of lightning from thousands of kilometers away"
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date = 2024-06-20
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authors = ["Aron Petau"]
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[taxonomies]
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tags = [
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"antenna",
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"electronics",
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"geosensing",
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"lightning",
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"radio",
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"sferics",
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"vlf",
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"university of the arts berlin"
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]
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[extra]
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show_copyright = true
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show_shares = true
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+++
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## What the Hell are Sferics?
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> A radio atmospheric signal or sferic (sometimes also spelled "spheric") is
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> a broadband electromagnetic impulse that occurs as a result of natural
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> atmospheric lightning discharges. Sferics may propagate from their lightning
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> source without major attenuation in the Earth–ionosphere waveguide, and can
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> be received thousands of kilometres from their source.
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*Source: [Wikipedia](https://en.wikipedia.org/wiki/Radio_atmospheric_signal)*
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## Why Catch Them?
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[Microsferics](https://microsferics.com) is a fascinating reference project—a
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network of sferics antennas used to detect lightning strikes. Through
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triangulation (not unlike GPS mathematics), they can determine the
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more-or-less exact location of each strike. This proves useful for weather
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prediction and detecting forest fires, which are often caused by lightning.
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When converted to audio, sferics frequencies fall within the audible range,
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making it possible to actually *listen* to lightning strikes. The sound is
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usually a crackling noise, though sometimes surprisingly melodic—reminiscent
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of a Geiger counter.
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### The Technical Challenge
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Sferics live in the VLF (Very Low Frequency) range, around 10 kHz—a problem
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for most radios not designed for such low frequencies. That's why we built our
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own antenna.
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At 10 kHz, we're dealing with *insanely* large waves: a single wavelength
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stretches roughly 30 kilometers. This scale demands a sizable antenna. A
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special property of such massive waves is their tendency to reflect between
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the ionosphere and Earth's surface—effectively bouncing around the globe
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several times before absorption. This means we can pick up sferics from all
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over the world, even Australian lightning strikes!
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Without proper triangulation math, we can't determine exact directions, but
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the "tweeks" we captured typically originate from at least 2,000 km away.
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## The Build
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We constructed several "long-loop" antennas—essentially a coil of wire with a
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capacitor at the end. A specific balun is needed (depending on wire length) to
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output an electrical signal via XLR cable.
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Loosely following instructions from
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[Calvin R. Graf](https://archive.org/details/exploringlightra00graf), we built
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a 26-meter antenna looped multiple times around a wooden frame.
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## The Result
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We captured several hours of sferics recordings, which we're currently
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investigating for further potential.
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### Listen to the Lightning
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{{ youtube(id="2YYPg_K3dI4") }}
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As you can hear, there's a noticeable 60 Hz ground buzz in the recording.
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This likely stems from improper grounding or our proximity to the bustling
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city. Still, it's surprising we achieved such clear results so close to
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Berlin. Let's see what the countryside yields!
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{% gallery() %}
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[
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{
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"file": "./sferics1.jpg",
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"alt": "Listening to sferics at night",
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"title": "Night session capturing atmospheric signals"
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},
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{
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"file": "./sferics2.jpg",
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"alt": "The Drachenberg location",
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"title": "Recording location at Drachenberg"
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},
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{
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"file": "./sferics3.jpg",
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"alt": "The long-loop antenna",
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"title": "Our 26-meter VLF antenna setup"
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}
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]
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{% end %}
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