scholarly journals The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

2015 ◽  
Vol 32 ◽  
Author(s):  
A. R. Offringa ◽  
R. B. Wayth ◽  
N. Hurley-Walker ◽  
D. L. Kaplan ◽  
N. Barry ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Low Frequency ◽  
Digital Tv ◽  
Frequency Resolution ◽  
Interference Detection ◽  
Radio Frequency Interference ◽  
Receiver Design ◽  
Square Kilometre Array ◽  
Atmospheric Propagation ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

scholarly journals A Census of Southern Pulsars at 185 MHz

2017 ◽  
Vol 34 ◽  
Author(s):  
Mengyao Xue ◽  
N. D. R. Bhat ◽  
S. E. Tremblay ◽  
S. M. Ord ◽  
C. Sobey ◽  
...  
Keyword(s):  
Phase 1 ◽  
Low Frequency ◽  
Frequency Component ◽  
Frequency Resolution ◽  
Large Field ◽  
Initial Time ◽  
Wide Field ◽  
Processing Load ◽  
Square Kilometre Array ◽  
Murchison Widefield Array

AbstractThe Murchison Widefield Array, and its recently developed Voltage Capture System, facilitates extending the low-frequency range of pulsar observations at high-time and -frequency resolution in the Southern Hemisphere, providing further information about pulsars and the ISM. We present the results of an initial time-resolved census of known pulsars using the Murchison Widefield Array. To significantly reduce the processing load, we incoherently sum the detected powers from the 128 Murchison Widefield Array tiles, which yields ~10% of the attainable sensitivity of the coherent sum. This preserves the large field-of-view (~450 deg2 at 185 MHz), allowing multiple pulsars to be observed simultaneously. We developed a WIde-field Pulsar Pipeline that processes the data from each observation and automatically folds every known pulsar located within the beam. We have detected 50 pulsars to date, 6 of which are millisecond pulsars. This is consistent with our expectation, given the telescope sensitivity and the sky coverage of the processed data (~17 000 deg2). For 10 pulsars, we present the lowest frequency detections published. For a subset of the pulsars, we present multi-frequency pulse profiles by combining our data with published profiles from other telescopes. Since the Murchison Widefield Array is a low-frequency precursor to the Square Kilometre Array, we use our census results to forecast that a survey using the low-frequency component of the Square Kilometre Array Phase 1 can potentially detect around 9 400 pulsars.

Radio frequency interference detection based on the AC-UNet model

2021 ◽  
Vol 21 (5) ◽  
pp. 119
Author(s):  
Rui-Qing Yan ◽  
Cong Dai ◽  
Wei Liu ◽  
Ji-Xia Li ◽  
Si-Ying Chen ◽  
...  
Keyword(s):  
Radio Frequency ◽  
Interference Detection ◽  
Radio Frequency Interference

scholarly journals Radio Frequency Interference Detection from Space

1991 ◽  
Vol 112 ◽  
pp. 198-200
Author(s):  
William E. Howard
Keyword(s):  
Radio Frequency ◽  
Low Cost ◽  
Simple Solution ◽  
Geostationary Orbit ◽  
Interference Detection ◽  
Radio Frequency Interference ◽  
The Cost ◽  
Communications Satellites

Occasional interference experienced in the channels of communications satellites has prompted an analysis to see how radio frequency interference (RFI) might be detected from space. RFI may be experienced on any type of satellite, including commercial and scientific satellites. For a satellite in geostationary orbit that interference may come from anywhere in the hemisphere under the satellite. Because the location of an interfering transmitter is so uncertain, traditional means for geolocating it is not effective. “Down-looking” detectors are needed to detect the “up-looking” interference. Moreover, a low cost, simple solution to the problem – one in which the cost to geolocate is small relative to the cost of the downtime in the channel – is required in order to make the solution tractable.

Low-frequency technology for a lunar interferometer

2020 ◽  
Vol 379 (2188) ◽  
pp. 20190575 ◽  
Author(s):  
Kristian Zarb Adami ◽  
I. O. Farhat
Keyword(s):  
Radio Frequency ◽  
Signal Detection ◽  
Radio Astronomy ◽  
Lunar Surface ◽  
Low Frequency ◽  
Radio Interferometer ◽  
Radio Frequency Interference ◽  
The Moon ◽  
Single Antenna ◽  
Global Signal

This work sketches a possible design architecture of a low-frequency radio interferometer located on the lunar surface. The design has evolved from single antenna experiments aimed at the global signal detection of the epoch of reionization (EoR) to the square kilometre array (SKA) which, when complete, will be capable of imaging the highly red-shifted H 1 -signal from the cosmic dawn through to the EoR. However, due to the opacity of the ionosphere below 10 MHz and the anthropogenic radio-frequency interference, these terrestrial facilities are incapable of detecting pre-ionization signals and the moon becomes an attractive location to build a low-frequency radio interferometer capable of detecting such cosmological signals. Even though there are enormous engineering challenges to overcome, having this scientific facility on the lunar surface also opens up several new exciting possibilities for low-frequency radio astronomy. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades’.

scholarly journals A New Restoration Method for Radio Frequency Interference Effects on AMSR-2 over North America

2019 ◽  
Vol 11 (24) ◽  
pp. 2917 ◽  
Author(s):  
Wangbin Shen ◽  
Zhengkun Qin ◽  
Zhaohui Lin
Keyword(s):  
Radio Frequency ◽  
Land Surface ◽  
Interpolation Method ◽  
Low Frequency ◽  
Principal Component ◽  
New Method ◽  
Radio Frequency Interference ◽  
Data Restoration ◽  
Order Of Magnitude ◽  
Restoration Method

Observations from spaceborne microwave imagers are important sources of land surface information. However, the low-frequency channels of microwave imagers are easily interfered with by active radio signals with similar frequencies. Radio frequency interference (RFI) signals are widely distributed because of the lack of frequency protection, which seriously hinders the application of microwave imager data in data assimilation and retrieval research. In this paper, a new data restoration method is proposed based on principal component analysis (PCA). Both the ideal and real reconstruction experiments show that the new method can effectively repair abnormal observations interfered by RFI compared with the commonly used Cressman interpolation method because observation information over the whole selected domain is used for restoration in the new method, whereas Cressman interpolation uses only a selection of data around the target observation. The observation errors in the data with RFI can be reduced by one order of magnitude by means of the new method and little artificial information is introduced. One-week restoration validation also proves that the new method has a stable accuracy and broad application prospects.

scholarly journals Source counts and confusion at 72–231 MHz in the MWA GLEAM survey

2019 ◽  
Vol 36 ◽  
Author(s):  
T. M. O. Franzen ◽  
T. Vernstrom ◽  
C. A. Jackson ◽  
N. Hurley-Walker ◽  
R. D. Ekers ◽  
...  
Keyword(s):  
Thermal Noise ◽  
Low Frequency ◽  
Radio Continuum ◽  
Large Area ◽  
Design Study ◽  
Array Design ◽  
Square Kilometre Array ◽  
Noise Limit ◽  
Murchison Widefield Array ◽  
Extended Emission

Abstract The GaLactic and Extragalactic All-sky Murchison Widefield Array survey is a radio continuum survey at 72–231 MHz of the whole sky south of declination +30º, carried out with the Murchison Widefield Array. In this paper, we derive source counts from the GaLactic and Extragalactic All-sky Murchison data at 200, 154, 118, and 88 MHz, to a flux density limit of 50, 80, 120, and 290 mJy respectively, correcting for ionospheric smearing, incompleteness and source blending. These counts are more accurate than other counts in the literature at similar frequencies as a result of the large area of sky covered and this survey’s sensitivity to extended emission missed by other surveys. At S154 MHz > 0.5 Jy, there is no evidence of flattening in the average spectral index (α ≈ −0.8 where S ∝ vα) towards the lower frequencies. We demonstrate that the Square Kilometre Array Design Study model by Wilman et al. significantly underpredicts the observed 154-MHz GaLactic and Extragalactic All-sky Murchison counts, particularly at the bright end. Using deeper Low-Frequency Array counts and the Square Kilometre Array Design Study model, we find that sidelobe confusion dominates the thermal noise and classical confusion at v ≳ 100 MHz due to both the limited CLEANing depth and the undeconvolved sources outside the field-of-view. We show that we can approach the theoretical noise limit using a more efficient and automated CLEAN algorithm.

scholarly journals Science with the Murchison Widefield Array

2013 ◽  
Vol 30 ◽  
Author(s):  
Judd D. Bowman ◽  
Iver Cairns ◽  
David L. Kaplan ◽  
Tara Murphy ◽  
Divya Oberoi ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Early Universe ◽  
Western Australia ◽  
Space Weather ◽  
Time Domain ◽  
Angular Resolution ◽  
Low Frequency ◽  
Performance Properties ◽  
Square Kilometre Array ◽  
Murchison Widefield Array

AbstractSignificant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the southern hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21-cm emission from the EoR in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives.

scholarly journals A morphological algorithm for improving radio-frequency interference detection

2012 ◽  
Vol 539 ◽  
pp. A95 ◽  
Author(s):  
A. R. Offringa ◽  
J. J. van de Gronde ◽  
J. B. T. M. Roerdink
Keyword(s):  
Radio Frequency ◽  
Interference Detection ◽  
Radio Frequency Interference
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