Meteor scatter observations during the 2013 Perseid meteor shower
2013 November 27
2013 August 12 and Aug 13 provided a number of strong radio reflections from meteor trails, several of which showed detail in the dispersal of the plasma created by the meteor. In these images the time scale is UTC with markers at 2 second intervals. The vertical scale is frequency with markers at 100Hz intervals.
At the observing frequency of 143.05MHz these markers correspond to variations in velocity of approximately 200 metres per second, relative to the observer. These frequency variations are the result of Doppler shift imparted by the moving plasma during the reflection of the original radio signal. For the series of observations shown here an indicated frequency of 4350Hz represents static plasma (with reference to the observer) whilst frequencies higher than this value are a result of motion towards the observer. Lower frequencies arise from plasma moving away from the observer.
Several vertical ‘spikes’ can be seen at 0.8 second intervals; these are believed to be artefacts introduced by the Fast Fourier Transform process used to derive the spectrograms. The source transmitter is a radar system located near Dijon, France, which sweeps the sky in discrete steps. Each step introduces a discontinuity in the received signal which will affect the FFT calculation at that point. The spikes should thus be ignored, though they may offer potential as a time synchronisation mechanism for future observations from multiple locations.
There are six steps in the sweep, each illuminating a different portion of the meteor trail. The sequence repeats every 4.8 seconds and this can be seen in some of the images.
The equipment used was a simple Yagi antenna manufactured with aluminium angle and copper pipe mounted on a wooden boom; suitable antennas can also be purchased for around £30. The support consisted of two 2.4m garden posts with the lower post securely anchored using ‘Postcrete’ or similar. The receiver was a FUNcube Dongle which can be purchased for £150 inclusive of postage.
The Radio Astronomy Group has one of these receivers available for short term loan to BAA members. The software used for capturing images was the freely available SpectrumLab application. For further information please contact myself or look at the papers on the RAG website (http://www.britastro.org/radio)
Paul Hyde, Coordinator, Radio Astronomy Group