Listen to the Leonids with ESA scientists|
This Wednesday, a team of ESA scientists will listen to the sound of
Leonid meteors as they silently sweep across the night sky.
Instead of using cameras or simply observing with the naked eye, their aim
is to try an experiment using new digital signal processing to make audible
the impact of the myriads of shooting stars as they hit the Earth's upper atmosphere.
During the nights of 16 - 18 November, as the annual Leonid meteor shower
reaches its peak, the group from ESA's Solar System Division at ESTEC,
will be glued to a radio receiver and their computer screens.
"The ionised meteor trails act like mirrors and reflect high frequency
radio signals from stations that are below the horizon," explained ESA's Jean-Pierre Lebreton, "so we're going to listen to suitable
signals from various radio stations around the world."
Listening to these radio signatures of the meteors is one of the popular ways of observing them.
All over the world amateurs will be using radio techniques to observe the Leonids during the forthcoming encounter.
"But we will be trying something different", says fellow team member Trevor Sanderson. "We will detect the minute changes in the signal frequency
caused by the motion of the meteor trail in the upper atmosphere, using advanced signal processing techniques," explained Sanderson. "We will
also try to turn these small changes into an audible signal so that we can hear a "ping" or some such sound every time a meteor hits the atmosphere"
"The technique employed relies on measuring the frequency of the signal after it has been reflected by the trail of ionisation left by the meteor. The motion
of the meteor trail due to the upper atmosphere winds changes the frequency of the reflected signal due to the Doppler effect. The change is so small that
we have to use advanced signal processing techniques to detect it."
Spectrogram received in Portugal on 14 November, courtesy of Bev Ewan-Smith, COAA, Portugal.
"We will analyse the signals in real time, and also record them on digital audio tape so that we can analyse them later," said Lebreton. "We're also
hoping to put the recording on the Web so that everyone can hear the sound of shooting stars!"
"I got interested in the Leonids after I saw last year's fireballs which
came the night before the predicted peak. I was fortunate enough not to trust the
predictions and was up early on the morning of 17 November to observe the fireball display in
the Dutch sky!" explained Jean-Pierre Lebreton.
We were inspired by a new method developed by a UK communications expert Peter Martinez. We will be using his software, as well as software developed
by the Centro de Observação Astronómica no Algarve in Portugal", said Sanderson.
So why are they going to all this trouble?
"We're hoping to complement the optical observations that are planned by some of our colleagues," said Lebreton. "And we
wanted to do something that would be of interest to the public". One of the advantages of radio observing is that meteors can be detected when skies are
cloudy or during daylight. Radio observing has some advantages at night, too. The human eye can only see shooting stars brighter than 6th magnitude, but
radio methods can detect meteors that are at least 5 times dimmer.
Do it yourself
Have a go and let us here at ESA Science know how you get on! If you get a good result send the .wav
file to us and we'll include it in our Leonids reports.
The Doppler method can be tried by anyone with a good shortwave receiver and a PC. Suitable software and a description of the method can be downloaded from http://sapp.telepac.pt/coaa/r_meteor.htm. which includes a description of the method.
This software uses the sound card of the PC to analyse the signal. All that is needed is a connection from the headphone output of the receiver to the PC's sound card input. Download the software, install, read the help file and you are ready to go. Tune to a station around 500 km or so away. Switch to SSB mode, and start the software. All you need now are the Meteors!
A simpler experiment
For this you use your FM receiver with an external aerial. Try to find a station a long way away (that's the difficult bit, as usually a nearby station gets in the way). Under normal circumstances the transmission should be difficult or impossible to detect, but when a meteor intervenes the signal jumps over the horizon and
a brief fragment of the transmission can be heard. Depending on the type of transmission, it might sound like a tone, a fragment of music or voice, or simply noise.
Contact lasts for as long as the meteor train persists, usually from 100 milliseconds to a few seconds.
What's so special about this new radio experiment?
For further information visit the International Meteor Organisation Web
site at: http://www.imo.net/radio/index.html