The August 2011 Meteors as observed by the Amateur Radio Astronomers of the Michelbach observatory

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Oct 03

2011

by NÖ Volkssternwarte Austria

By Fritz Lensch, OE3 FLB. This article was also published in “Der Sternbote” 8/2011

As the Perseids were not well observable visually this year – due to the full moon – we decided to count the meteors using our radio telescope. The principle is based on Radar, but with spatially separated emitters and receivers (so called forward scattering). Detecting radio reflections of meteors requires a powerful emitter located approximately 300 to 1000 km away sending with high power in the direction of the meteors. We used the station GRAVES (http://www.satellitenwelt.de/spaceradar.htm#GRAVES), which is a French space surveillance system used for gauging satellite orbits. The emitter very well suited for our location in Lower Austria. The radar station is located southwest of Paris and sends 24 hours with a power of several 100 kW. The emitter cannot be heard at our location under normal propagation conditions. If however a meteorite burns up in the earth’s atmosphere the emitter’s signal is reflected at the plasma trail and partially scattered back to earth.

As a receiving antenna we used a 2 times 8 element Kreuzyagi which was set to an elevation of 7°. Following a highly sensitive preamplifier a VHF receiver is tuned to the frequency of the 22m band. The AF signal of the receiver (CW or SSB) is digitally processed using the computer’s sound card. The software RadioSkyPipe was used for registering the noise of the receiver and the signal of the emitter.

The horizontal axis shows the time in UTC whereas the y axis gives the potentia
l in mV. To the left we see a meteor with a reflection time of approx. 30 s, which would be visible to the naked eye. The smaller signals to the right are rapidly vaporized comet dust, which cannot be observed visually. The software used is freely available in the internet at http://radiosky.com/skypipeishere.html

In order to make an assertion on the number of meteors per hour the software ColorgrammeRMOB is used (http://217.169.242.217/rmob/download.php?lng=en). This program allows to determining the maximum of a meteor stream by creating a color graphics depicting a month’s overview. At the same time the program sends the result to a central server to provide a possibility for research to anyone interested. This possibility is used all over the world.

Meteors with a diameter smaller than 1mm are not visible to the naked eye, but are detected by a radio telescope. In order to compare our measurements to optical observations (IMO)we only count meteors with sizes above 1 mm.

In December 2010 we registered the Geminids using the same technique.

Using ColorgrammeRMOB we produced this figure, which shows the unusually sharp maximum of the Geminids 2010. Of special interest is the echo showing a twelve hour cycle. This is obviously related to the rise and set of the radiant.

One has to mention that within the registered meteors some sporadic ones are found, which may not be attributed to the current stream. The direction where meteors originate from can only derived via Fourier transform of every meteor when using radio astronomy, which is very elaborate procedure.

The region covered by our radio telescope is approximately 10 to 15° in width and is located between emitter and receiver. The best reflection conditions lie directly in the middle. Meteors at other locations result in reflections of inferior quality. Therefore the region between Salzburg and Switzerland delivers the best conditions for our setup. The emitter selected by us works at a wavelength of 2m, which is the upper limit. Most of our colleagues use wavelengths around 6m, as the conditions for reflections at meteors are way better. Due to TV stations sending from the east we experience too much interference to use the better conditions at low frequencies in Lower Austria.

On Aug 12^th we scheduled a public observation night at our observatory in Michelbach, as we do every year. Despite beginning rain, cloud cover and full moon we were allowed to welcome around 70 visitor including children, for whom we organized a special crafting workshop. The evening started with a special lecture on the origin of meteors with focus on the Perseids. Using a projector we displayed the meteors registered by our radio telescope onto the wall of the observatory building. Therefore our visitors could follow the meteor shower “live and in action”. We also stayed connected with our colleagues participating in this project via internet. Overall we could observe only very few of the meteors visually. However, using radar we were able to observe the meteors all over Europe and even over Canada.

In the morning of Aug 15 the analysis of our data showed a preliminary maximum of 124 meteors per hour at the 3^rd hour of Aug 13 (UTC)

The x axis in the plots show the hour and the y axis denote the detected meteors.