The LOFAR radio environment
Journal article, 2012
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.
filtering techniques
methods: data analysis
removal
interference mitigation
telescopes
astronomy
instrumentation: interferometers
techniques: interferometric
telescopes
rfi
Author
A. R. Offringa
University of Groningen
A. G. de Bruyn
University of Groningen
S. Zaroubi
University of Groningen
G. van Diepen
Netherlands Institute for Radio Astronomy (ASTRON)
O. Martinez-Ruby
University of Groningen
P. Labropoulos
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Brentjens
University of Groningen
B. Ciardi
S. Daiboo
University of Groningen
G. Harker
V. Jelic
S. Kazemi
University of Groningen
L. V. E. Koopmans
University of Groningen
G. Mellema
V. N. Pandey
R. F. Pizzo
J. Schaye
H. Vedantham
University of Groningen
V. Veligatla
University of Groningen
S. J. Wijnholds
S. Yatawatta
P. Zarka
A. Alexov
J. Anderson
A. Asgekar
M. Avruch
University of Groningen
R. Beck
M. Bell
M. R. Bell
M. Bentum
G. Bernardi
University of Groningen
P. Best
L. Birzan
A. Bonafede
F. Breitling
J. W. Broderick
M. Brueggen
H. Butcher
Netherlands Institute for Radio Astronomy (ASTRON)
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
M. de Vos
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. Dettmar
J. Eislöffel
H. Falcke
R. Fender
W. Frieswijk
M. Gerbers
J. M. Griessmeier
A. W. Gunst
T. E. Hassall
G. Heald
J. Hessels
M. Hoeft
A. Horneffer
A. Karastergiou
V. Kondratiev
Y. Koopman
M. Kuniyoshi
Max Planck Society
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
P. Maat
G. Mann
J. McKean
H. Meulman
M. Mevius
J. D. Mol
R. Nijboer
J. Noordam
M. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
Argelander-Institut für Astronomie
M. Pandey
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. Polatidis
D. Rafferty
S. Rawlings
W. Reich
H. Rottgering
A. P. Schoenmakers
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. Smirnov
Netherlands Institute for Radio Astronomy (ASTRON)
C. Sobey
B. Stappers
M. Steinmetz
J. Swinbank
M. Tagger
Y. Tang
Netherlands Institute for Radio Astronomy (ASTRON)
C. Tasse
Paris Observatory
Arnold van Ardenne
Chalmers, Earth and Space Sciences, Onsala Space Observatory
W. van Cappellen
Netherlands Institute for Radio Astronomy (ASTRON)
A. P. van Duin
Netherlands Institute for Radio Astronomy (ASTRON)
M. van Haarlem
Netherlands Institute for Radio Astronomy (ASTRON)
J. van Leeuwen
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. van Weeren
Netherlands Institute for Radio Astronomy (ASTRON)
R. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Ramj Wijers
M. Wise
O. Wucknitz
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 549 A11Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201220293