Clear Skies in Birr for Radio Astronomy

/in /by

The Trinity Solar Physics Group has been working hard over the past three years setting up instruments to measure the causes and effects of solar storms from their observatory in Birr in the Irish midlands. To date, they they have installed a number of antennas to monitor solar radio bursts at 10-400 MHz, a magnetometer, and most recently, a 4-element LOFAR Low Band Antenna (LBA) test array. But this is just the start, and a collaboration of Irish universities now plan on installing a LOFAR station in Birr. To assess the suitability of Birr as a site for a LOFAR station, the LOFAR team in Holland kindly lent us a LOFAR High Band Antenna (HBA) in spring/summer 2013. The first radio frequency interference (RFI) survey was carried out in May 2013 using the HBA, which is sensitive to frequencies in the range 100 – 300 MHz. The results shown in the figure below are impressive showing that Birr has relatively clean spectrum in this range, making it a good site for a LOFAR station.

A survey covering the LOFAR LBA range of 10-80 MHz was also undertaken in April 2013 using our Schwarzbeck bicone antenna. As can be seen below, the spectrum at very low frequencies is also quite clean:

Shown below are spectral overviews taken in June 2009 at the Rosse Observatory (blue) compared with Bleien Radio Observatory in Switzerland (red; offset by 10 dB) and Potsdam Bornim (green; offset by 20 dB). The Rosse Observatory spectrum is quiet at all frequencies! It appears the RFI situation has changed little at the Rosse Observatory since this survey was undertaken by Christian Monstien for the Callisto network which placed the observatory among the most RFI free sites surveyed worldwide in the frequency range of 45-870 MHz.
For a more technical description of our LBA and HBA RFI surveys of Birr, check out the July 2013 CRAF Newsletter.