The LOFAR radio environment
Abstract
Aims: This paper discusses the spectral occupancy for performing radio astronomy with the Low-Frequency Array (LOFAR), with a focus on imaging observations. Methods: We have analysed the radio-frequency interference (RFI) situation in two 24-h surveys with Dutch LOFAR stations, covering 30-78 MHz with low-band antennas and 115-163 MHz with high-band antennas. This is a subset of the full frequency range of LOFAR. The surveys have been observed with a 0.76 kHz / 1 s resolution. Results: We measured the RFI occupancy in the low and high frequency sets to be 1.8% and 3.2% respectively. These values are found to be representative values for the LOFAR radio environment. Between day and night, there is no significant difference in the radio environment. We find that lowering the current observational time and frequency resolutions of LOFAR results in a slight loss of flagging accuracy. At LOFAR's nominal resolution of 0.76 kHz and 1 s, the false-positives rate is about 0.5%. This rate increases approximately linearly when decreasing the data frequency resolution. Conclusions: Currently, by using an automated RFI detection strategy, the LOFAR radio environment poses no perceivable problems for sensitive observing. It remains to be seen if this is still true for very deep observations that integrate over tens of nights, but the situation looks promising. Reasons for the low impact of RFI are the high spectral and time resolution of LOFAR; accurate detection methods; strong filters and high receiver linearity; and the proximity of the antennas to the ground. We discuss some strategies that can be used once low-level RFI starts to become apparent. It is important that the frequency range of LOFAR remains free of broadband interference, such as DAB stations and windmills.
Keywords
Cite
@article{arxiv.1210.0393,
title = {The LOFAR radio environment},
author = {A. R. Offringa and A. G. de Bruyn and S. Zaroubi and G. van Diepen and O. Martinez-Ruby and P. Labropoulos and M. A. Brentjens and B. Ciardi and S. Daiboo and G. Harker and V. Jelic and S. Kazemi and L. V. E. Koopmans and G. Mellema and V. N. Pandey and R. F. Pizzo and J. Schaye and H. Vedantham and V. Veligatla and S. J. Wijnholds and S. Yatawatta and P. Zarka and A. Alexov and J. Anderson and A. Asgekar and M. Avruch and R. Beck and M. Bell and M. R. Bell and M. Bentum and G. Bernardi and P. Best and L. Birzan and A. Bonafede and F. Breitling and J. W. Broderick and M. Bruggen and H. Butcher and J. Conway and M. de Vos and R. J. Dettmar and J. Eisloeffel and H. Falcke and R. Fender and W. Frieswijk and M. Gerbers and J. M. Griessmeier and A. W. Gunst and T. E. Hassall and G. Heald and J. Hessels and M. Hoeft and A. Horneffer and A. Karastergiou and V. Kondratiev and Y. Koopman and M. Kuniyoshi and G. Kuper and P. Maat and G. Mann and J. McKean and H. Meulman and M. Mevius and J. D. Mol and R. Nijboer and J. Noordam and M. Norden and H. Paas and M. Pandey and R. Pizzo and A. Polatidis and D. Rafferty and S. Rawlings and W. Reich and H. J. A. Rottgering and A. P. Schoenmakers and J. Sluman and O. Smirnov and C. Sobey and B. Stappers and M. Steinmetz and J. Swinbank and M. Tagger and Y. Tang and C. Tasse and A. van Ardenne and W. van Cappellen and A. P. van Duin and M. van Haarlem and J. van Leeuwen and R. J. van Weeren and R. Vermeulen and C. Vocks and R. A. M. J. Wijers and M. Wise and O. Wucknitz},
journal= {arXiv preprint arXiv:1210.0393},
year = {2012}
}
Comments
Accepted for publication in A&A. 15 figures, 16 pages