Characterization of a Low-Frequency Radio Astronomy Prototype Array in Western Australia
Adrian SutinjoT. ColegateR. B. WaythPeter J. HallEloy de Lera AcedoT. BoolerA. J. FaulknerL. FengN. Hurley‐WalkerBudi JuswardyS.K. PadhiN. Razavi‐GhodsM. SokołowskiS. J. TingayJ.G. Bij de Vaate
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We report characterization results for an engineering prototype of a next-generation low-frequency radio astronomy array. This prototype, which we refer to as the Aperture Array Verification System 0.5 (AAVS0.5), is a sparse pseudo-random array of 16 log-periodic antennas designed for 70-450 MHz. It is co-located with the Murchison Widefield Array (MWA) at the Murchison Radioastronomy Observatory (MRO) near the Australian Square Kilometre Array (SKA) core site. We characterize the AAVS0.5 using two methods: in-situ radio interferometry with astronomical sources and an engineering approach based on detailed full-wave simulation. In-situ measurement of the small prototype array is challenging due to the dominance of the Galactic noise and the relatively weaker calibration sources easily accessible in the southern sky. The MWA, with its 128 "tiles" and up to 3 km baselines, enabled in-situ measurement via radio interferometry. We present array sensitivity and beam pattern characterization results and compare to detailed full-wave simulation. We discuss areas where differences between the two methods exist and offer possibilities for improvement. Our work demonstrates the value of the dual astronomy-simulation approach in upcoming SKA design work.Keywords:
Radio Astronomy
Virtual Observatory
Aperture synthesis
The study of celestial objects through radio astronomy has enhanced our understanding of a gamut of astronomical phenomena that are often invisible or faintly observable in other portions of the electromagnetic spectrum. A number of new sources of radio emission have been identified that include radio galaxies, quasars, pulsars, masers etc. Radio astronomy uses either single telescope or a number of telescopes that are linked together and utilizes the techniques of radio interferometry. Typically, the signals encountered in radio astronomy have very low signal-noise ratio, and hence radio telescopes usually tend to be very sensitive and large. As a result, they also have high angular resolution. The mechanical constraints of building even larger telescopes led to the use of radio interferometer to achieve higher resolution that can be achieved through a single telescope. Radio astronomy receivers use cryogenically cooled low-noise amplifiers and low-loss components in the RF path. High gain, low spillover, low crosspolarization, low far-out sidelobes, etc. are important features of a radio telescope.
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Abstract The low loss and ease of use of optical fibres for data transmission offers a number of advantages over traditional methods of bringing signals from radio telescopes together. Aperture synthesis techniques involve the correlation of signals from each pair of telescopes in the array. The requirements of radio astronomy systems, where the broad-band noise-like signals from each telescope have to be brought together coherently over distances as large as hundreds of km or greater in some cases, are discussed in this paper. A number of arrays around the world currently use fibres for data transmission and also for the coherent transfer of local oscillator signals. Further developments in the use of optical fibres in radio astronomy are described as well as new instruments planned for the next millennium, where fibre interconnections will be an essential part of their design.
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One of the first scientific justifications of building the Mauritius Radio Telescope (hereafter referred to as MRT) was to complement the Cambridge 6C survey, which is a radio map of most of the northern sky at 150 MHz [1]; the MRT would then be the equivalent of the 6C survey for the southern sky and together we would obtain a whole sky radio map at 150 MHz. When the MRT was built, there were no radio surveys of the southern sky at frequencies less than 408 MHz; the frequency of 150 MHz was also chosen to complement the other radio surveys of the southern sky, which have been done at higher frequencies. Furthermore low radio frequencies like 150 MHz are bound to see new sources that would have been missed at higher frequencies due to the form of their spectra. Interesting features of resolved objects can also be studied in more details. In this paper, a brief description of the MRT will be made as well as the observations and imaging with the MRT data, and some astrophysical results obtained since its commissioning in 1992 (20 years of existence this year 2012).
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I summarize the current spectroscopic sky surveys and some of the scientific results, emphasizing the largest sky survey to-date, the Sloan Digital Sky Survey (SDSS). Techniques used commonly in spectral analyses are discussed, followed by the present needs and challenges for solving some of the unknown problems. I discuss how the Virtual Observatory (VO) can help astronomers in carrying out related research.
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The Square Kilometer Array is an ambitious project aiming to tackle some of the most fundamental scientific questions of our time and revolutionize our understanding of the Universe. The SKA is made up of two world-leading complementary radio telescopes on two continents, and will cover a very wide frequency range from 50 MHz up to 15 GHz+. These telescopes represent a game-changer for radio astronomy and, to achieve the science goals, precise prediction and knowledge of the telescopes' performance and behavior are essential. This contribution provides insights into the importance of electromagnetic models in prediction, support, and verification of astronomical observations with the Square Kilometer Array.
Radio Astronomy
Kilometer
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A recent development in radio astronomy is to replace traditional dishes with many small antennas. The signals are combined to form one large, virtual telescope. The enormous data streams are cross-correlated to filter out noise. This is especially challenging, since the computational demands grow quadratically with the number of data streams. Moreover, the correlator is not only computationally intensive, but also very I/O intensive. The LOFAR telescope, for instance, will produce over 100 terabytes per day. The future SKA telescope will even require in the order of exaflops, and petabits/s of I/O. A recent trend is to correlate in software instead of dedicated hardware. This is done to increase flexibility and to reduce development efforts. Examples include e-VLBI and LOFAR.
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This paper serves as an introduction to the contributions in this Special Issue on ldquoAdvances in Radio Telescopes.rdquo After a very short historical view of the emergence of Radio Astronomy, we refer to earlier IEEE special issues on this subject and mention recent instruments in the domain of millimeter wavelength radio telescopes, developments in very long baseline interferometry and the planned Square Kilometre Array (SKA). After a short discussion of site selection aspects for the new telescopes we conclude with a summary of the major astronomical and astrophysical problems which will be studied by the new instruments described in the following papers.
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Methods of radio frequency interference suppression in radio astronomy are considered. Estimations of signal-to-noise ratio for temporal and frequency methods of RFI rejection are made. Implementation of these methods in real-time digital signal processing could be an effective mean for supporting radio astronomy observations in worsening radio ecology environment. Radio telescope RATAN-600 experience shows the advantages of such a processing.
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