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Air-borne broadband interference detection by LOFAR

Submitter: Hans van der Marel/Olaf Wucknitz
Description: During LOFAR observation L2011_23410 of 13/14 February 2011 on the Crab Nebula some peculiar interference was detected. For a period of about 30 minutes a pulsing signal was measured with a frequency from less than 115 MHz up to 141 MHz. The autocorrelation plot of station RS106 shows this very nicely.

Olaf analysed the data carefully and he found that the source of the interference was at an altitude of 10200 m. With that information the whole track of the source from about the position that it came above the horizon in Denmark until it passed the city of Zwolle could be reconstructed.

Comparison of the reconstructed track with information about the air traffic resulted in a perfect match in 3 dimensions! The source of the interference appears to be an Airbus A319-111 from Aeroflot with registration VP-BUO at flight AFL231 from Moscow to Brussels.

According to information that we received from the German air traffic control via our German colleagues (the Dutch air traffic control did not answer to our questions) it appears that this problem is known since January 2005. From then on Eurocontrol and ATC have reported non systematic audio pertubations. The source of the interference is the VHF Data Radio (a Honeywell RTA-44D). Problems with this device only appear at Aeroflot Airbuses (at least 14 are affected). 'Airbus is deeply concerned and is very actively analyzing the interference events.'

This case shows that LOFAR can act as a passive radar, even if the beam(s) of LOFAR are pointing at astrononmical objects. This property makes LOFAR a versatile tool for many types of observations, and at the same time its sensitivity in many directions are a threat for astronomical observations of weak objects.
Copyright: Hans van der Marel/Olaf Wucknitz
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