by Andy Smith G7IZU This PowerPoint presentation will play automatically in a few seconds. v

 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.

 We make use of a powerful satellite tracking radar in eastern France called “Graves”.  It transmits a carrier wave on 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.

 As a meteor enters the atmosphere at km 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.

 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.

Head echoes Trail echoes

The International Space Station Moon echoes

 Some detection systems use lower frequencies where other interesting things can be detected.  Lower frequencies, such as the 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.

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

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. [This is the last slide]