awebsite/content/project/2024-06-20-sferics/index.md

+++
title = "Sferics"
description = "Hunting for the voice of lightning from thousands of kilometers away"
date = 2024-06-20
authors = ["Aron Petau"]

[taxonomies]
tags = [
  "antenna",
  "electronics",
  "geosensing",
  "lightning",
  "radio",
  "sferics",
  "vlf",
  "university of the arts berlin"
]

[extra]
show_copyright = true
show_shares = true
+++

## What the Hell are Sferics?

> A radio atmospheric signal or sferic (sometimes also spelled "spheric") is
> a broadband electromagnetic impulse that occurs as a result of natural
> atmospheric lightning discharges. Sferics may propagate from their lightning
> source without major attenuation in the Earth–ionosphere waveguide, and can
> be received thousands of kilometres from their source.

*Source: [Wikipedia](https://en.wikipedia.org/wiki/Radio_atmospheric_signal)*

## Why Catch Them?

[Microsferics](https://microsferics.com) is a fascinating reference project—a
network of sferics antennas used to detect lightning strikes. Through
triangulation (not unlike GPS mathematics), they can determine the
more-or-less exact location of each strike. This proves useful for weather
prediction and detecting forest fires, which are often caused by lightning.

When converted to audio, sferics frequencies fall within the audible range,
making it possible to actually *listen* to lightning strikes. The sound is
usually a crackling noise, though sometimes surprisingly melodic—reminiscent
of a Geiger counter.

### The Technical Challenge

Sferics live in the VLF (Very Low Frequency) range, around 10 kHz—a problem
for most radios not designed for such low frequencies. That's why we built our
own antenna.

At 10 kHz, we're dealing with *insanely* large waves: a single wavelength
stretches roughly 30 kilometers. This scale demands a sizable antenna. A
special property of such massive waves is their tendency to reflect between
the ionosphere and Earth's surface—effectively bouncing around the globe
several times before absorption. This means we can pick up sferics from all
over the world, even Australian lightning strikes!

Without proper triangulation math, we can't determine exact directions, but
the "tweeks" we captured typically originate from at least 2,000 km away.

## The Build

We constructed several "long-loop" antennas—essentially a coil of wire with a
capacitor at the end. A specific balun is needed (depending on wire length) to
output an electrical signal via XLR cable.

Loosely following instructions from
[Calvin R. Graf](https://archive.org/details/exploringlightra00graf), we built
a 26-meter antenna looped multiple times around a wooden frame.

## The Result

We captured several hours of sferics recordings, which we're currently
investigating for further potential.

### Listen to the Lightning

{{ youtube(id="2YYPg_K3dI4") }}

As you can hear, there's a noticeable 60 Hz ground buzz in the recording.
This likely stems from improper grounding or our proximity to the bustling
city. Still, it's surprising we achieved such clear results so close to
Berlin. Let's see what the countryside yields!

{% gallery() %}
[
  {
    "file": "./sferics1.jpg",
    "alt": "Listening to sferics at night",
    "title": "Night session capturing atmospheric signals"
  },
  {
    "file": "./sferics2.jpg",
    "alt": "The Drachenberg location",
    "title": "Recording location at Drachenberg"
  },
  {
    "file": "./sferics3.jpg",
    "alt": "The long-loop antenna",
    "title": "Our 26-meter VLF antenna setup"
  }
]
{% end %}