Forward scatter radio observations, Leonids, 2006
The carriers of Band 1 TV transmitters in Western Europe provide
a convenient source of radio illumination of the atmosphere, allowing
the use of modest receiving equipment to effectively observe the
incoming meteors. These observations from northern England make use of
transmitters in Norway and Belgium. See  for a good introduction to the
physics of forward scatter meteor observation.
This year, Europe was well placed to observe the Earth's encounter with
a dust trail left behind by the 1932 passage of comet 55P/Tempel-Tuttle.
A peak of activity was predicted (David Asher ) for Nov 19th 04:45 UT
geocentric, with a +4 minute topocentric correction for the UK, and a ZHR
of around 120. Some very graphic and detailed computer predictions of the
2006 encounter with 55P/Tempel-Tuttle dust trails are available at .
A simple wire turnstile antenna, tuned to 55Mhz and placed about 1/4 wavelength
above flat ground, points towards the zenith to provide omnidirectional
coverage of the sky. An AR8200 receiver in USB mode delivers an audio
signal to a PC
soundcard for recording to disk. A receiver frequency of 55.2493Mhz places
several distant TV carriers in the passband, two of which are used for these
observations. This arrangement collects around a dozen meteor 'pings' per
minute under background conditions, as well as reflections from aircraft
Previous attempts to count individual pings during Leonid showers have not
been successful due to the large number of strong overlapping reflections from
overdense meteor trails, which can persist for several minutes. The simplest
way to gauge activity seems to be to report the average signal level
received in a narrow bandwidth centered on the carrier frequencies. Software
analyses the data stream from the soundcard to determine the relative power
in each carrier, using 50Hz-wide filters and applies a normalisation using a
nearby empty band to compensate for receiver AGC action and broadband noise.
Unfortunately, it is not feasible to provide a calibration capable of
converting average signal strength into the ZHR estimates which are of
most interest to astronomers studying the dynamics and structure of
comet dust trails. One problem is that the signal level can be dominated
by a small number of long lasting overdense returns. Another difficulty is
that radio and visual observations are likely to be sensitive to different
Daily Results, Nov 15th to 21th
The following daily charts use an integration time of 2 minutes and combine
the results from the two most reliable TV carriers.
Leonid activity is present for several days, characterised by short bursts
of fairly strong activity set against an elevated background consisting
of a large number of faint pings.
Raw data files are available - email.
A total of eight visual meteors were seen between 04:15 and 04:45 on the 19th,
through about 50% cloud cover with LM around 5 or 6.
Five occurred in the first 15 minutes, two of which were coincident with
1932 Trail Encounter
Below is a closer look at the morning of the 19th.
There is a complete
absence of any peak of activity near the predicted time of 04:49, although
a period of increased activity begins at about 04:55 and continues for about
an hour. An earlier burst of activity lasting 15 minutes was centered at 04:18
and coincident visual observation suggested a temporary ZHR of perhaps 70 or
It was disappointing not to see a clear peak of activity resulting from the 1932
trail. This was most likely due to the forward scatter system responding to
a rather smaller particle size than the visual meteors for which the
predictions were made (smaller particles are much more susceptible to radiation
Early results (for example ) suggest that
visual observers had more success. The recording process worked well, with
no interference or breakdowns, but the signal analysis needs to be improved.
The 'spikey' character of the charts suggests that the signal
strength average is probably quite a non-linear function of meteor activity.
Some ingenuity will be needed to extract a proportional count of meteor pings
from beneath the strong overdense returns.
In these examples, time runs left to right, frequency from bottom to top.
Two meteors arriving about a second apart. The slanting lines are the
Doppler-shifted reflections from the rapidly decelerating head of the meteor,
which in this example last for about 2 seconds each. The broken horizontal
lines are rapidly decaying reflections from the almost stationary underdense
The dark vertical bands are caused by the receiver AGC responding to the
strong trail returns.
Orbit number 45733 of the International Space Station appears in this
spectrogram as the broken slanting lines and the faint curved line.
The horizontal lines are drifting
overdense trails, here showing up five distinct TV carriers. Fresnel
oscillations of the trail returns are clearly visible by the way they
modulate the background noise via receiver AGC action. This spectrogram
spans 50 seconds.
An example sound sample is available from the 2002 Leonids, which illustrates
a typical mix of meteor returns during shower activity .
 Wislez J.-M.,Proceedings of the International Meteor Conference,
Brandenburg 14-17 September 1995,
"Forward Scattering of Radio Waves off Meteor Trails".
 Armagh Observatory
The Leonid Meteors 2006
 Jeremie Vaubaillon, IMCCE,
MP3 sample (215kB, 70 seconds) from Leonids 2002,