The LOFAR radio environment
Journal article, 2013

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.

telescopes

instrumentation: interferometers

interference mitigation

filtering techniques

rfi

removal

techniques: interferometric

telescopes

methods: data analysis

astronomy

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 A11

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201220293

More information

Latest update

1/24/2020