Radio Interferometric Techniques Research Articles

Radio interferometry applied to the observation of cosmic-ray induced extensive air showers

We developed a radio interferometric technique for the observation of extensive air showers initiated by cosmic particles. In this proof-of-principle study we show that properties of extensive air showers can be derived with high accuracy in a straightforward manner. When time synchronisation below sim 1 ns between different receivers can be achieved, direction reconstruction resolution of < 0.2^circ and resolution on the depth of shower maximum of <10 g/cm^2 are obtained over the full parameter range studied, with even higher accuracy for inclined incoming directions. In addition, by applying the developed method to dense arrays of radio antennas, the energy threshold for the radio detection of extensive air showers can be significantly lowered. The proposed method can be incorporated in operational and future cosmic particle observatories and with its high accuracy it has the potential to play a crucial role in unravelling the composition of the ultra-high-energy cosmic-particle flux.

Expected performance of air-shower measurements with the radio-interferometric technique

Interferometric measurements with arrays of radio antennas are a powerful and widely used technique in astronomy. Recently, this technique has been revisited for the reconstruction of extensive air showers []. This “radio-interferometric technique” exploits the coherence in the radio emission emitted by billions of secondary shower particles to reconstruct the shower parameters, in particular the shower axis and depth of the shower maximum X max. The accuracy previously demonstrated on simulations with an idealized detector is very promising. The prospect of an accurate X max measurement for inclined air showers combined with measurements of the electromagnetic energy (also with radio antennas) and the muonic shower content (via ground particle detectors) is very intriguing as it would provide a high sensitivity to the mass of cosmic rays, key information to study their origin. In this article we evaluate the potential of interferometric X max measurements using (simulated) inclined air showers with sparse antenna arrays under realistic conditions. To determine prerequisites for the application of the radio-interferometric technique with various antenna arrays, the influence of inaccuracies in the time synchronisation between antennas and its inter-dependency with the antenna density is investigated in detail. We find a strong correlation between the antenna multiplicity (per event) and the maximum acceptable time jitter, i.e., inaccuracy in the time synchronisation. For data recorded with a time synchronisation accurate to within 1 ns in the commonly used frequency band of 30 MHz to 80 MHz, an antenna multiplicity of >50 is needed to achieve an X max resolution of g cm−2. For data recorded with 2 ns accuracy, already ≳ 200 antennas are needed to achieve this X max resolution. Furthermore, we find no advantage reconstructing X max from data simulated at higher observation frequencies, i.e., up to several hundred MHz. Finally, we provide a generalisation of our results from very inclined air showers to vertical geometries.

Differential Bearing Estimation for RF Tags

Fusing spatially distributed observations in wireless sensor networks or asset tracking in a shipyard are just two-example applications where the location of radio nodes needs to be known. Localization and tracking of wireless nodes have been an active research area, yet a universal solution has not emerged so far. This paper introduces a novel method for bearing estimation based on a rotating antenna generating a Doppler shifted RF signal. The small frequency change can be measured even on low-cost resource constrained nodes using a radio interferometric technique introduced previously. Bearing information between anchors nodes at known locations and RF tags at unknown positions can be derived. A few such measurements provide enough information to enable accurate node localization.

The Integrated Global Geodetic Observing System (IGGOS) viewed from the perspective of history

Abstract Towards the end of the 19th century, geodetic observation techniques allowed it to create geodetic networks of continental size. The insight that big networks can only be set up through international collaboration led to the establishment of an international collaboration called “Central European Arc Measurement”, the predecessor of the International Association of Geodesy (IAG), in 1864. The scope of IAG activities was extended already in the 19th century to include gravity. At the same time, astrometric observations could be made with an accuracy of a few tenths of an arcsecond. The accuracy stayed roughly on this level, till the space age opened the door for milliarcsecond (mas) astrometry. Astrometric observations allowed it at the end of the 19th century to prove the existence of polar motion. The insight that polar motion is almost unpredictable led to the establishment of the International Latitude Service (ILS) in 1899. The IAG and the ILS were the tools (a) to establish and maintain the terrestrial and the celestial reference systems, including the transformation parameters between the two systems, and (b) to determine the Earth's gravity field. Satellite-geodetic techniques and astrometric radio-interferometric techniques revolutionized geodesy in the second half of the 20th century. Satellite Laser Ranging (SLR) and methods based on the interferometric exploitation of microwave signals (stemming from Quasars and/or from satellites) allow it to realize the celestial reference frame with (sub-)mas accuracy, the global terrestrial reference frame with (sub-)cm accuracy, and to monitor the transformation between the systems with a high time resolution and (sub-)mas accuracy. This development led to the replacement of the ILS through the IERS, the International Earth Rotation Service in 1989. In the pre-space era, the Earth's gravity field could “only” be established by terrestrial methods. The determination of the Earth's gravitational field was revolutionized twice in the space era, first by observing geodetic satellites with optical, Laser, and Doppler techniques, secondly by implementing a continuous tracking with spaceborne GPS receivers in connection with satellite gradiometry. The sequence of the satellite gravity missions CHAMP, GRACE, and GOCE allow it to name the first decade of the 21st century the “decade of gravity field determination”. The techniques to establish and monitor the geometric and gravimetric reference frames are about to reach a mature state and will be the prevailing geodetic tools of the following decades. It is our duty to work in the spirit of our forefathers by creating similarly stable organizations within IAG with the declared goal to produce the geometric and gravimetric reference frames (including their time evolution) with the best available techniques and to make accurate and consistent products available to wider Earth sciences community as a basis for meaningful research in global change. IGGOS, the Integrated Global Geodetic Observing System, is IAG's attempt to achieve these goals. It is based on the well-functioning and well-established network of IAG services.

AGN Selection by Size of Dominant Emission

AbstractThe potential of AGN surveys extends to structure-related objectives: e.g. to study the size and properties of the NLR in AGN. From a complete sample of 1665 radio sources, we selected fifty-five with features on ~0.2-2 kpc scales (core/jet flux ratio &lt;7:1) for further study. Here, we summarize the radio interferometric selection technique used and speculate on the prospects for optical surveys (using a size criterion).

Limitations of the tangent plane approximation for wide-field imaging using the mauritius radio telescope

The Mauritius Radio Telescope (MRT) is a Fourier synthesis, non-coplanar T array. The primary objective of the telescope is to survey the southern sky at 151.5 MHz in the declination range -70° to -10°. Due to non-coplanarity, wide-field imaging and deconvolution of wide field images made using MRT are challenging problems in applications of radio interferometric techniques. This paper discusses the usefulness and limitations of the tangent plane approximation in transforming the measured visibilities to wide field images and in estimating the point spread function (PSF) required for the deconvolution.

Water Masers toward Low-Luminosity Young Stellar Objects

A review of the importance of water maser observations toward young stellar objects (YSOs) is presented. Also, we present recent, differing types of observations of water masers near YSOs. Single antenna observations, taken regularly, characterize the variability of the masers and allow estimates of time and spatial scales. High resolution (∼ 1 mas) multi-epoch observations allow proper motions to be studied. Detailed analysis of such proper motions will allow the placement of the masers in the circumstellar (a disk) or near-stellar environment at the base of the outflow. Radio interferometric techniques are the best method of making estimates of the kinematics of the gas in these regions.

Hubble Space Telescope observations of synchrotron jets

view Abstract Citations (36) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Observations of Synchrotron Jets Sparks, W. B. ; Biretta, J. A. ; Macchetto, F. Abstract The Hubble Space Telescope for the first time enables optical and UV images of jets to be obtained with spatial resolution comparable to radio interferometric techniques. Because synchrotron emission at these wavelengths is a diagnostic of particles several orders of magnitude higher in energy and correspondingly shorter in lifetime than those probed by radio, the sites of particle acceleration may be more readily identified in the optical and UV. Short-lifetime optical synchrotron emission in the SE inner radio lobe of M87 argues strongly for the presence of an invisible counterjet. A detailed comparison of HST and VLA images of the M87 jet shows there are very strong similarities in overall morphology, but that there are also significant differences. The optical and UV radiation is more localized within the knots than the radio emission and appears more confined toward the jet center. These differences may arise from localized shocks, sited at the optical knots with diffusion of relativistic particles away from those knots, or else they may be due to nonuniform magnetic fields and distributed acceleration processes. The UV fluxes of the knots are consistent with a single power law from optical to X-ray. Optical jets in other radio galaxies show diverse properties-the jet of PKS 0521-36 is smoothly resolved by HST while that of 3C 66B shows previously unsuspected filmentary structure. Likewise, the jet of 3C 273 shows newly observed optical filaments and an intensity distribution quite unlike that of the radio emission. Like M87, the optical jet of 3C 273 is narrower than the radio jet. The serendipitous discovery of a new optical synchrotron jet in 3C 264 suggests that optical jets may be relatively common. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1994 DOI: 10.1086/191924 Bibcode: 1994ApJS...90..909S Keywords: Hubble Space Telescope; Particle Acceleration; Plasma Jets; Spaceborne Astronomy; Synchrotron Radiation; Electron Distribution; Faint Object Camera; Radio Interferometers; Spatial Resolution; Ultraviolet Astronomy; Very Large Array (Vla); Astrophysics; GALAXIES: JETS full text sources ADS | data products SIMBAD (5) NED (5) MAST (1) ESA (1)

Hubble Space Telescope Observations of Synchrotron Jets

AbstractThe Hubble Space Telescope for the first time enables optical and UV images of jets to be obtained with spatial resolution comparable to radio interferometric techniques. Because synchrotron emission at these wavelengths is a diagnostic of particles several orders of magnitude higher in energy and correspondingly shorter in lifetime than those probed by radio, the sites of particle acceleration may be more readily identified in the optical and UV. Short-lifetime optical synchrotron emission in the SE inner radio lobe of M87 argues strongly for the presence of an invisible counterjet. A detailed comparison of HST and VLA images of the M87 jet shows there are very strong similarities in overall morphology, but that there are also significant differences. The optical and UV radiation is more localized within the knots than the radio emission and appears more confined toward the jet center. These differences may arise from localized shocks, sited at the optical knots with diffusion of relativistic particles away from those knots, or else they may be due to nonuniform magnetic fields and distributed acceleration processes. The UV fluxes of the knots are consistent with a single power law from optical to X-ray. Optical jets in other radio galaxies show diverse properties—the jet of PKS 0521–36 is smoothly resolved by HST while that of 3C 66B shows previously unsuspected filmentary structure. Likewise, the jet of 3C 273 shows newly observed optical filaments and an intensity distribution quite unlike that of the radio emission. Like M87, the optical jet of 3C 273 is narrower than the radio jet. The serendipitous discovery of a new optical synchrotron jet in 3C 264 suggests that optical jets may be relatively common.Subject heading: galaxies: jets

Evaluation of catalogues of extragalactic radio sources

A combined catalogue is constructed from the observations of extragalactic radio sources compiled in independent catalogues providing precise positions determined by radio interferometric techniques. Positions and catalogue differences are derived and discussed. The average precision of the combined catalogue is at the level of 0.7 mas in right ascension and 1.3 mas in declination. For the more recent catalogues the systematic differences amount to a fraction of a millisecond of arc.

Japan-US time comparison experiment for realizing better than 1-ns accuracy by using a radio interferometric technique

A zero baseline interferometry (ZBI) experiment was conducted to determine the differential instrumental delay between two stations (Kashima, Japan, and Richmond, USA). It enabled the authors to find an absolute time comparison with an accuracy of better than 1 ns. ZBI experiments in Japan were conducted in winter and summer to find the delay dependency on temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Principles of Imaging Using Arrays

Since diffraction-limited imaging with a single aperture yields angular resolution ~ λ/D, the attainment of high angular resolution with single apertures requires the construction of correspondingly large monolithic apertures, the whole surface of which must be figured to much less than a wavelength. At the longer wavelengths, it is impossible to build a sufficiently large single aperture: for example, at λ21 cm, arcsecond resolution requires an aperture of diameter ~ 50 km. At the shorter wavelengths, the atmosphere imposes a natural limit in resolution of about one arcsecond. However, another route is possible: that of using synthetic apertures to image the sky. The problem of figuring synthetic apertures is considerably simpler, and can be implemented in a computer. Synthetic apertures are now in use in many fields, e.g. radio-interferometry, radar imaging, magnetic resonance imaging. Radio-interferometric techniques developed in radio-astronomy over the past forty years are now being applied to optical and IR astronomical imaging by a number of groups.

Two‐dimensional interferometric positions of VHF lightning sources

Using a new radio interferometric technique, we present observations of VHF lightning radiation source positions. The crossed base line interferometer provides the directions of arrival (azimuth and elevation) of VHF lightning radiation. Much flexibility exists in the choice of instrument parameters such as operating frequency and sampling interval. The present instrument operates at 34.3 MHz and provides an average position for every 2.5 μs of lightning radiation. Observations indicate that each 2.5 μs position should be attributed to a single discrete source in the sky. The positions of such sources define the temporal and spatial development of breakdown and rapid charge acceleration during the lightning flash. We have obtained VHF source positions correlated in time with electric field measurements. This allows us to identify the various processes occurring during a discharge and to compare the VHF phenomena with previously observed lightning phenomena. We have analyzed six flashes completely and portions of others. All six flashes contained ground strokes and two had intracloud discharges following the ground flash. We present data from three flashes that showed features common to the flashes we analyzed. The initial (preceding the first return stroke) and intracloud portions consisted of a large number of bursts of 20 μs average duration occurring on the average every 100 μs. The positions within each burst developed in a systematic, nearly linear, sequence with apparent speeds of ∼107 m/s. The relative positions from burst to burst drifted through the sky with speeds ∼105 m/s. In intracloud portions this drift was predominantly horizontal. In ground flashes the VHF sources drifted downward, in effect the leader for the first return stroke. They terminated at the return stroke.

The National Geodetic Survey project “POLARIS”

Abstract The National Geodetic Survey (N.G.S.) of the National Ocean Survey has undertaken a new project called POLar-motion Analysis by Radio Interferometric Surveying (POLA-RIS). The premier goal of the project is to establish a fully operational polar motion monitoring network, with a spatial resolution and accuracy of 10 cm and a temporal resolution of 24 hours. The new network will utilize radio interferometric techniques. The fixed POLARIS observatories may also serve as base stations to be used in conjunction with small-aperture, 3–10-m, mobile units for positional surveys for geodetic and geo-dynamic applications. The N.G.S. plans to cooperate fully with other governmental organizations having related responsibilities and interest in polar motion, earth rotation and geodynamics [e.g., National Aeronautics and Space Administration (NASA), United States Geological Survey (U.S.G.S.), United States Naval Observatory (U.S.N.O.)] as well as academic and private researchers.

The Application of Radio Interferometric Techniques to the Determination of Earth Rotation

Radio interferometric techniques for the determination of Earth rotation are described.

The NAVOBSY/NRL Program for the Determination of Earth Rotation and Polar Motion

The joint program of NAVOBSY/NRL is discussed.The United States Naval Observatory (NAVOBSY) and the Naval Research Laboratory (NRL) are collaborating in a program to apply radio interferometric techniques to the determination of variations in Earth rotation, polar motion, and improved astronomical position reference systems. Investigations of VLBI and connected interferometer techniques and radio sources for astrometic application have been in progress for several years as part of the NRL radio astronomy program, and currently NRL and NAVOBSY are carrying out experimental programs to investigate VLBI time transfer techniques and UT determination using the connected element interferometer of the NRAO in Green Bank. Some previous results of observations using the Green Bank interferometer and proposed plans for operation as a dedicated system over a period of time to evaluate effectiveness for precise determination of Earth rotation parameters are discussed.

Determination of an Extragalactic Radio Source Position Catalogue Suitable for Use in Monitoring Geophysical Phenomena

The use of radio interferometric techniques to monitor geophysical phenomena such as UTI-UTC variations, polar motion, and tectonic plate motion requires that there be available a fairly uniform distribution of extragalactic radio sources whose relative positions are known to better than 0″.01. These sources must also have very small proper motion, and not be subject to asymmetric changes in radio structure or to very large variations in intensity. In addition, to facilitate tying this frame of reference to the optical star frames, it is desirable that many of these radio objects have optical counterparts. This paper describes our progress in obtaining such a frame and sets forth our desiderata for further work by radio and optical astronomers.

Geodetic Ties Between Continents by Means of Radio Telescopes

The basic principles and formulas involved in measuring intercontinental distances to very high accuracy using a radio interferometer are expounded. Measurements and results from a Canadian experiment are reported with the difficulties and limitations encountered. The possibility of virtually eliminating the effect of ionospheric refraction, which is the largest source of error, is examined. It is concluded that the radio interferometric technique may give higher accuracies than any other technique for making geodetic ties between continents.