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. © 2012 ESO.
The LOFAR radio environment / Offringa, A.R.; De Bruyn, A.G.; Zaroubi, S.; Van Diepen, G.; Martinez-Ruby, O.; Labropoulos, P.; Brentjens, M.A.; Ciardi, B.; Daiboo, S.; Harker, G.; Jelić, V.; Kazemi, S.; Koopmans, L.V.E.; Mellema, G.; Pandey, V.N.; Pizzo, R.F.; Schaye, J.; Vedantham, H.; Veligatla, V.; Wijnholds, S.J.; Yatawatta, S.; Zarka, P.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, M.; Beck, R.; Bell, M.; Bell, M.R.; Bentum, M.; Bernardi, G.; Best, P.; Birzan, L.; Bonafede, A.; Breitling, F.; Broderick, J.W.; Brüggen, M.; Butcher, H.; Conway, J.; De Vos, M.; Dettmar, R.J.; Eisloeffel, J.; Falcke, H.; Fender, R.; Frieswijk, W.; Gerbers, M.; Griessmeier, J.M.; Gunst, A.W.; Hassall, T.E.; Heald, G.; Hessels, J.; Hoeft, M.; Horneffer, A.; Karastergiou, A.; Kondratiev, V.; Koopman, Y.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Mann, G.; McKean, J.; Meulman, H.; Mevius, M.; Mol, J.D.; Nijboer, R.; Noordam, J.; Norden, M.; Paas, H.; Pandey, M.; Pizzo, R.; Polatidis, A.; Rafferty, D.; Rawlings, S.; Reich, W.; Röttgering, H.J.A.; Schoenmakers, A.P.; Sluman, J.; Smirnov, O.; Sobey, C.; Stappers, B.; Steinmetz, M.; Swinbank, J.; Tagger, M.; Tang, Y.; Tasse, C.; Van Ardenne, A.; Van Cappellen, W.; Van Duin, A.P.; Van Haarlem, M.; Van Leeuwen, J.; Van Weeren, R.J.; Vermeulen, R.; Vocks, C.; Wijers, R.A.M.J.; Wise, M.; Wucknitz, O.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - ELETTRONICO. - 549:(2012), pp. A11.A11-A11.25. [10.1051/0004-6361/201220293]
The LOFAR radio environment
Offringa, A. R.; De Bruyn, A. G.; Zaroubi, S.; Van Diepen, G.; Martinez-Ruby, O.; Labropoulos, P.; Brentjens, M. A.; Ciardi, B.; Daiboo, S.; Harker, G.; Jelić, V.; Kazemi, S.; Koopmans, L. V. E.; Mellema, G.; Pandey, V. N.; Pizzo, R. F.; Schaye, J.; Vedantham, H.; Veligatla, V.; Wijnholds, S. J.; Yatawatta, S.; Zarka, P.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, M.; Beck, R.; Bell, M.; Bell, M. R.; Bentum, M.; Bernardi, G.; Best, P.; Birzan, L.; Bonafede, A. ;Breitling, F.; Broderick, J. W.; Brüggen, M.; Butcher, H.; Conway, J.; De Vos, M.; Dettmar, R. J.; Eisloeffel, J.; Falcke, H.; Fender, R.; Frieswijk, W.; Gerbers, M.; Griessmeier, J. M.; Gunst, A. W.; Hassall, T. E.; Heald, G.; Hessels, J.; Hoeft, M. ;Horneffer, A.; Karastergiou, A.; Kondratiev, V.; Koopman, Y.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Mann, G.; McKean, J.; Meulman, H.; Mevius, M.; Mol, J. D.; Nijboer, R.; Noordam, J.; Norden, M.; Paas, H.; Pandey, M.; Pizzo, R.; Polatidis, A.; Rafferty, D.; Rawlings, S.; Reich, W.; Röttgering, H. J. A.; Schoenmakers, A. P.; Sluman, J.; Smirnov, O.; Sobey, C.; Stappers, B.; Steinmetz, M.; Swinbank, J.; Tagger, M.; Tang, Y.; Tasse, C.; Van Ardenne, A.; Van Cappellen, W.; Van Duin, A. P.; Van Haarlem, M.; Van Leeuwen, J.; Van Weeren, R. J.; Vermeulen, R.; Vocks, C.; Wijers, R. A. M. J.; Wise, M.; Wucknitz, O.
2012
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. © 2012 ESO.
Citazione
The LOFAR radio environment / Offringa, A.R.; De Bruyn, A.G.; Zaroubi, S.; Van Diepen, G.; Martinez-Ruby, O.; Labropoulos, P.; Brentjens, M.A.; Ciardi, B.; Daiboo, S.; Harker, G.; Jelić, V.; Kazemi, S.; Koopmans, L.V.E.; Mellema, G.; Pandey, V.N.; Pizzo, R.F.; Schaye, J.; Vedantham, H.; Veligatla, V.; Wijnholds, S.J.; Yatawatta, S.; Zarka, P.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, M.; Beck, R.; Bell, M.; Bell, M.R.; Bentum, M.; Bernardi, G.; Best, P.; Birzan, L.; Bonafede, A.; Breitling, F.; Broderick, J.W.; Brüggen, M.; Butcher, H.; Conway, J.; De Vos, M.; Dettmar, R.J.; Eisloeffel, J.; Falcke, H.; Fender, R.; Frieswijk, W.; Gerbers, M.; Griessmeier, J.M.; Gunst, A.W.; Hassall, T.E.; Heald, G.; Hessels, J.; Hoeft, M.; Horneffer, A.; Karastergiou, A.; Kondratiev, V.; Koopman, Y.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Mann, G.; McKean, J.; Meulman, H.; Mevius, M.; Mol, J.D.; Nijboer, R.; Noordam, J.; Norden, M.; Paas, H.; Pandey, M.; Pizzo, R.; Polatidis, A.; Rafferty, D.; Rawlings, S.; Reich, W.; Röttgering, H.J.A.; Schoenmakers, A.P.; Sluman, J.; Smirnov, O.; Sobey, C.; Stappers, B.; Steinmetz, M.; Swinbank, J.; Tagger, M.; Tang, Y.; Tasse, C.; Van Ardenne, A.; Van Cappellen, W.; Van Duin, A.P.; Van Haarlem, M.; Van Leeuwen, J.; Van Weeren, R.J.; Vermeulen, R.; Vocks, C.; Wijers, R.A.M.J.; Wise, M.; Wucknitz, O.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 0004-6361. - ELETTRONICO. - 549:(2012), pp. A11.A11-A11.25. [10.1051/0004-6361/201220293]
Tutti gli autori
Offringa, A.R.; De Bruyn, A.G.; Zaroubi, S.; Van Diepen, G.; Martinez-Ruby, O.; Labropoulos, P.; Brentjens, M.A.; Ciardi, B.; Daiboo, S.; Harker, G.; Jelić, V.; Kazemi, S.; Koopmans, L.V.E.; Mellema, G.; Pandey, V.N.; Pizzo, R.F.; Schaye, J.; Vedantham, H.; Veligatla, V.; Wijnholds, S.J.; Yatawatta, S.; Zarka, P.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, M.; Beck, R.; Bell, M.; Bell, M.R.; Bentum, M.; Bernardi, G.; Best, P.; Birzan, L.; Bonafede, A.; Breitling, F.; Broderick, J.W.; Brüggen, M.; Butcher, H.; Conway, J.; De Vos, M.; Dettmar, R.J.; Eisloeffel, J.; Falcke, H.; Fender, R.; Frieswijk, W.; Gerbers, M.; Griessmeier, J.M.; Gunst, A.W.; Hassall, T.E.; Heald, G.; Hessels, J.; Hoeft, M.; Horneffer, A.; Karastergiou, A.; Kondratiev, V.; Koopman, Y.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Mann, G.; McKean, J.; Meulman, H.; Mevius, M.; Mol, J.D.; Nijboer, R.; Noordam, J.; Norden, M.; Paas, H.; Pandey, M.; Pizzo, R.; Polatidis, A.; Rafferty, D.; Rawlings, S.; Reich, W.; Röttgering, H.J.A.; Schoenmakers, A.P.; Sluman, J.; Smirnov, O.; Sobey, C.; Stappers, B.; Steinmetz, M.; Swinbank, J.; Tagger, M.; Tang, Y.; Tasse, C.; Van Ardenne, A.; Van Cappellen, W.; Van Duin, A.P.; Van Haarlem, M.; Van Leeuwen, J.; Van Weeren, R.J.; Vermeulen, R.; Vocks, C.; Wijers, R.A.M.J.; Wise, M.; Wucknitz, O.
Eventuali allegati, non sono esposti
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
Sei sicuro che questo prodotto debba essere cancellato?
Il report seguente simula gli indicatori relativi alla propria produzione scientifica in relazione alle soglie ASN 2023-2025 del proprio SC/SSD. Si ricorda che il superamento dei valori soglia (almeno 2 su 3) è requisito necessario ma non sufficiente al conseguimento dell'abilitazione.
