JBOMD at Jodrell Bak Observatory

Image credit: Megan Argo

What is a radio meteor?

Visually, we see meteors because of the heat generated through ram pressure as the particles fly through the atmosphere. The heat causes the stripping of electrons from atoms in the atmosphere producing a trail of ionised gas in the wake of the meteor. This ionised gas acts like a mirror to radio waves and transmissions from the ground, which would normally pass out of the atmosphere and into space, are instead reflected back down to the ground.

In order to detect meteors with radio waves, astronomers in the 1950s used radar equipment. They sent radio transmissions up into the sky and then listened for the reflected echoes in a technique known as back-scatter. Using these echoes, the astronomers could determine the range and speed of the meteors and then calculate an orbit.

A modern experiment to look for echoes from ionised meteor trails uses a similar technique, but relys on someone else to be the transmitter. This technique is known as forward-scatter. The antenna shown in the image (left) is a simple dipole which listens for signals from a television station which is too far away to detect normally. When there is a patch of ionised air created by a meteor, the signal gets reflected back down to the Earth and can be picked up by the receiver situated, in this case, at Jodrell Bank Observatory in the UK.

The equipment is simple: a basic dipole, a commercial scanning receiver and a small amplifier. Each time an echo happens, the scanner produces a "ping". The sound is fed into the soundcard of a computer where a graphical representation is generated and the reflections are counted. This technique, used by amateur astronomers around the world, can detect meteors 24 hours a day, 365 days a year.

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