Algorithms for radio interference detection and removal

PhD ceremony: Mr. A.R. Offringa, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Algorithms for radio interference detection and removal

Promotor(s): prof. A.G. de Bruyn, prof. S. Zaroubi, prof. M. Biehl

Faculty: Mathematics and Natural Sciences

This project concerns the effects of interference on radio astronomy caused by human devices. Radio astronomy is a challenging astronomical application and with its help, many surprising details of our Universe have been discovered. Modern radio telescopes can observe the sky with an enormous sensitivity and resolution. To achieve this, observatories are often composed of large dishes. Because of several technological advancements, on low frequenties it has become very efficient to synthesize many small antennas into one large telescope. LOFAR is a new telescope that makes use of this idea. It consists of tens of antenna fields, which are spread over the Netherlands and several neighbouring countries. LOFAR’s centre is near the city of Exloo in the Dutch province of Drenthe.

Human devices can interfere with radio astronomical observations. Therefore, telescopes are often build in remote areas with a very low population density. However, building telescopes at remote locations is costly. LOFAR has taken a different approach by building antenna fields all over populated areas of the Netherlands. This has raised concerns about the harmful effects that human hardware could cause.

This thesis addresses these concerns. We have designed several automated methods that can filter interference from radio observations. The techniques remove the interference from the data with an unprecendented accuracy. We extensively analyse the resulting data and conclude that after the application of our filters, we can make very sensitive sky maps with LOFAR. Consequently, it appears it was an excellent decision to build LOFAR in the Netherlands.