When a meteor strikes Earth’s
atmosphere it decelerates rapidly. The friction created by the air causes the
meteor to burn up at extremely high temperatures creating the white “shooting
star” that we are all familiar with. This process also ionises the air along the
trail making it possible to reflect radio waves.
Utilising a high powered VHF radar
signal sent into the sky, we are able to detect reflected waves from these
ionisation trails. Because the meteor is moving, the reflected signal is shifted
in frequency from the original, by an amount according to it’s speed. This shift
is also heard as an audible ping by the station operator.
Our system translates the reflected
wave into three main parameters - Amplitude (strength), Frequency shift
(Doppler shift) and decay time. This allows us to determine the relative size of
the meteor strike (vertical scale) and the relative approximate speed and
deceleration (amount of shift and width of the trace).
You can see the output from our system
above in real time (approximately 1 minute delay on the Internet) This view is a
2D view over approximately the last five minutes, to see a 3D view please use
the links at the top of this page. During a
meteor shower this trace will be full of strike traces, but it is also
surprising how many meteors are striking Earth’s atmosphere all of the
Here you can see what a typical meteor
strike looks like. The trace starts high in frequency and rapidly drops to the
radar carrier frequency as the meteor decelerates in the atmosphere, increasing
in strength (ionisation) as it burns up. This creates this typical triangular
shape you can see here. The width, height and shape tell us a lot about the
meteor strike. The blue is the baseline atmospheric noise.