RADIO METEOR DETECTION AT THE NLO

by Andy SmithG7IZU

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v.1.0 2010-07-28

Meteors can be detected by receiving radio signals reflected from

their trails

What do we need to detect meteors?

A powerful transmitter located at some distance from the receiver that transmits a clean carrier wave signal.

An aerial. A suitable receiver (single side-band

mode) A PC with suitable software. We use a freeware package called

“Spectrum Lab” to display results.

Which transmitter do we use?

We make use of a powerful satellite tracking radar in eastern France called “Graves”.

It transmits a carrier wave on 143.050 MHz.

It wasn’t designed to detect meteors, but we find that it’s very good for that purpose!

It’s so powerful that we can also detect the moon and the International Space Station passing through its beam! You’ll see images of these reflections later in this presentation.

The Graves transmitter is located near Dijon in eastern France .It transmits a fan shaped beam to the south which meets the

ionosphere at 80-110km altitude (the area shown in red).This area can be “seen” from NLO.

Other views of the fan beam showing a meteor passing through

How do we detect meteors?

As a meteor enters the atmosphere at 80-110km altitude, it burns up. It collides with molecules in the atmosphere, leaving a trail of super-heated, electrically charged plasma, which we briefly see as a bright streak in the sky.

The plasma is made from electrons that have been knocked free from their atoms by the meteor. If the plasma is dense enough, it will reflect radio signals. The plasma will quickly dissipate and stop reflecting radio signals after a short time.

How do we detect meteors?

We have an aerial and radio receiver on-site. The receiver is tuned to the radar, and every time a meteor passes through its beam we hear a “ping” as the signal is reflected back to us.

The sound from the receiver is fed into Spectrum Lab on a PC, which creates a 3D spectrogram showing the signal strength against audio frequency and time.

We can also hear sound from the receiver.

We can sometimes hear a very rapid Doppler- shifted whistle where the head of a meteor, shrouded in plasma, reflects the signal, followed by a more steady whistle as the signal reflects off of the trail.

Usually, we just hear a brief “ping”! Most meteors occur in the early morning.

What you see in the spectrograms

Examples of “head echoes”and “trail echoes”

Head echoes

Trail echoes

Satellite and moon echoes

The International Space Station

Moon echoes

What else can systems like this receive?

Some detection systems use lower frequencies where other interesting things can be detected.

Lower frequencies, such as the 48-68 MHz VHF band, can reflect a signal for longer than the higher frequencies. Intense meteor showers can over-saturate the system with signals.

Solar coronal mass ejections hitting the earth can cause auroras which can also be detected.

An intense meteor shower can look like this when using transmitters on 48 and 55 MHz.

This 2D view shows one hour of activity from the 2008 Perseids shower.

The sound is from a recording of a part of the 2009 Perseids shower.

This is a spectrogram of an aurora in 2003.

The colours are a representation of the signal strength of the received signal, not the colour of the actual aurora in the sky!These signals were received in Devon, south-west UK.

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