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1
Van, Tonder Vereese. "Beamforming for radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96126.
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Thesis (MEng) -- Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: Beamforming is a technique used to combine signals from an array of antennas to effectively
synthesize a single aperture and beam. In the Radio Astronomy community the
technique is used to obtain a desirable beam pattern as well as to electronically point the
beam of an array. Next generation radio telescopes such as the Square Kilometre Array
(SKA) surpass current technology and will extensively make use of beamforming techniques.
Various factors determine the output of a beamformer; however, given an array with a
fixed configuration only the weights applied to the incoming signals affect the synthesized
aperture and beam. Furthermore, the incoming data must be processed in real-time, at a
rate equal to the input-output rate of the processor. Both the weighting function and the
real-time implementation of beamforming, are the primary subjects of this thesis.
In this thesis various deterministic weighting functions are investigated. The algorithms
are implemented in a matlab program, serving as a simulation tool for investigating the
techniques. The program is verified by comparing the expected theoretical outcomes to
the simulated output. For the program the following functionalities are included: a steering
technique, spectral weighting, Dolph-Chebychev, and the Least Square Error algorithm. Applications
of these techniques is investigated and their prominence in the Radio Astronomy
community is established.
For the real-time beamformer implementation, the UniBoard platform configured with
beamformer firmware, is investigated. This is important as the UniBoard is an excellent
example of a beamformer implementation within the Radio Astronomy community. The
architecture is used to emulate a linear array by implementing a python control script,
where the output corresponded accurately with the expected theoretical values.
The thesis also constitutes the design and implementation of a digital frequency domain
beamformer on the ROACH board. This processing board is employed by the Karoo Array
Telescope (KAT-7) in South Africa. This work is therefore important as it demonstrates a
beamformer implementation on an architecture in use by the Radio Astronomy community.
An antenna array is designed and built for the verification of the beamformer design. Results
with a good degree of accuracy were obtained and where errors exist they are discussed.<br>AFRIKKANSE OPSOMMING: Bundelvorming is ’n tegniek waarmee die seine van ’n antenna samestelling gekombineer
word om ’n enkele effektiewe stralingsvlak en stralingspatroon te sintiseer. In die Radio Astronomie
gemeenskap word die tegniek gebruik om ’n gewenste stralingspatroon te sintiseer
sowel as om die rigting van die patroon elektronies te beheer. Die Square Kilometre Array
(SKA) is ’n toekomstige radioteleskoop en sal grootliks gebruik maak van bundelvorming
tegnieke.
Die uitset van bundelvormers word geaffekteer deur verskeie faktore, maar vir ’n gegewe
samestelling is dit net die gewigsfunksies wat toegepas word op die inkomende seine wat
die gesintiseerde patroon kan beheer. Verder moet die inkomende data verwerk word teen
’n tempo gelykstaande aan die inset-en-uitsetkoers van die verwerker. Die gewigsfunksie so
wel as die implementasie van die bundelvormer is albei primêre onderwerpe van die tesis.
’n Verskeindenheid van deterministiese bundelvormingstegnieke sal ondersoek word in
hierdie tesis. Die algoritmes is in ’n matlab program geïmplementeer vir simulasie doeleindes.
Die program is geverifieër deur die uitset te vergelyk met die verwagte teoretiese
waardes. Die program sluit die volgende funksies in: ’n rigting beheer algoritme, spektraalgewigte,
Dolph-Chebychev, en die minste vierkantsfout algoritme. Hierdie tegnieke is van
belang weens hul toepassing in die Radio Astronomie gemeenskap.
Vir die implementasie van ’n bundelvormer is die UniBoard hardeware, geprogrameer in
’n bundelvormings modus, van gebruik gemaak. Hierdie aspek is belangrik omdat die Uni-
Board ’n goeie voorbeeld van ’n geïmplementeerde bundelvormer in die Radio Astronomie
gemeenskap is. Die UniBoard word gebruik om ’n lineêre samestelling te emuleer deur in
python ’n beheer skrip te skryf, waar die uitset van die emuleerder akkuraat ooreenstem
met die verwagte waardes.
Die tesis behels ook die ontwerp en implementasie van ’n digitale frekwensiegebied bundelvormer
op die ROACH platform. Hierdie verwerker word tans gebruik in die Karoo Array
Telescope (KAT-7) in Suid-Afrika. Hierdie werk is dus belangrik omdat dit die implementasie
van ’n bundelvormer op tegnologie wat huidiglik in die Radio Astronomie gemeenskap
gebruik word demonstreer. Daarbenewens is ’n antenna samestelling ontwerp en gebou om
die bundelvormer te verifieër. Die resultate is akkuraat tot ’n redelike mate. Waar daar ’n
fout onstaan het word dit in die tesis bespreek.
2
Junklewitz, Henrik. "Statistical inference in radio astronomy." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-177457.
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This thesis unifies several studies, which all are dedicated to the subject of statistical data
analysis in radio astronomy and radio astrophysics.
Radio astronomy, like astronomy as a whole, has undergone a remarkable development in the past twenty years in introducing new instruments and technologies. New telescopes like the upgraded VLA, LOFAR, or the SKA and its pathfinder missions offer unprecedented sensitivities, previously uncharted frequency domains and unmatched survey capabilities.
Many of these have the potential to significantly advance the science of radio astrophysics and cosmology on all scales, from solar and stellar
physics, Galactic astrophysics and cosmic magnetic fields, to Galaxy cluster astrophysics
and signals from the epoch of reionization.
Since then, radio data analysis, calibration and imaging techniques have entered a similar phase of new development to push the boundaries and adapt the field to the new instruments and scientific opportunities.
This thesis contributes to these greater developments in two specific subjects, radio interferometric imaging and cosmic magnetic field statistics.
Throughout this study, different data analysis techniques are presented and employed
in various settings, but all can be summarized under the broad term of statistical infer-
ence. This subject encompasses a huge variety of statistical techniques, developed to solve
problems in which deductions have to be made from incomplete knowledge, data or measurements. This study focuses especially on Bayesian inference methods that make use of a subjective definition of probabilities, allowing for the expression of probabilities and statistical knowledge prior to an actual measurement.
The thesis contains two different sets of application for such techniques. First, situations
where a complicated, and generally ill-posed measurement problem can be approached by
assuming a statistical signal model prior to infer the desired measured variable. Such
a problem very often is met should the measurement device take less data then needed
to constrain all degrees of freedom of the problem. The principal case investigated in
this thesis is the measurement problem of a radio interferometer, which takes incomplete
samples of the Fourier transformed intensity of the radio emission in the sky, such that it is
impossible to exactly recover the signal. The new imaging algorithm RESOLVE is presented,
optimal for extended radio sources. A first showcase demonstrates the performance of the
new technique on real data. Further, a new Bayesian approach to multi-frequency radio
interferometric imaging is presented and integrated into RESOLVE.
The second field of application are astrophysical problems, in which the inherent stochas-
tic nature of a physical process demands a description, where properties of physical quanti-
ties can only be statistically estimated. Astrophysical plasmas for instance are very often in a turbulent state, and thus governed by statistical hydrodynamical laws. Two studies are presented that show how properties of turbulent plasma magnetic fields can be inferred from radio observations.
3
Thompson, Nicholas Christopher. "RFI mitigation in radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86637.
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Thesis (MEng)--Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: Technical advances in electromagnetics, signal processing and processing power
have led to a significant increase in sensitivity and accuracy in radio telescopes.
With this increase in sensitivity, radio frequency interference (RFI) has become a
much larger problem. The notable growth in wireless communication as well as
self generated RFI has further escalated this problem. In order to utilise the full
capabilities of modern radio telescopes, RFI mitigation is required on the captured
signals. With the enormous data rates of modern radio telescopes, managing RFI
has become increasingly difficult, and in order to utilise the full captured radio
spectrum, more accurate RFI mitigation strategies will be necessary.
The use of different RFI mitigation strategies is studied in the form of online
and offline techniques. This includes Spectral Kurtosis, Spectral Flatness and the
Var/SumThreshold method. The special case for RFI mitigation in timing pulsars
will also be studied. These techniques are well known in the radio astronomy community;
here, spectral kurtosis and spectral flatness will be implemented on the raw
data as well as the post correlated data. System speed and accuracy will be the
deciding factors when testing these methods as possible solutions to this problem.<br>AFRIKAANSE OPSOMMING: ‘n Toename in die sensitiwiteit van hedendagse radioteleskope kan toegedra word
aan die tegniese bevordering in elktromagnetika en seinverwerking. Die toename
in sensitiwiteit het egter tot die gevolg dat radiofrekwensiesteuring ‘n groter rol
speel in hedendaagse radioteleskope. Die groei in die gebruik van radioverbindings
asook die gevolge van self gei¨nduseerde radiofrekwensiesteuring dra ook verder
by tot hierdie probleem. Radiofrekwensiesteuring matiging word toegepas op die
opgevangde seine, om sodoende gebruik te maak van die volle kapasiteit van moderne
radioteleskope. Die bestuur van radiofrekwensiesteuring word bemoeilik deur
die groot hoeveelheid intydse data van die radioteleskope. Meer akurate radiofrekwensiesteuring
matigingstegnieke word vereis om die bandwydte ten volle te hanteer.
Daar word op ‘n aantal verskillende matingstegnieke gefokus. Hierdie tegenieke
kan in twee kategorieë verdeel word, naamlik aanlyn- en aflyntegenieke. Onderafdelings
van hierdie kategorieë sluit in: spektrale kurtose, spektrale matheid en
“Var/SumThreshold”. Daar word ook na ‘n spesiale geval van radiofrekwensiesteuring
matiging gekyk, in die opmeeting van tydsberekening-pulsars. Alhoewel
hierdie tegnieke bekend is in die radioastronomie gemeenskap, word spektrale kurtose
en spektrale matheid egter toegepas op die rou data sowel as postgekorreleerde
data. Daar sal op stelsel spoed en akuratheid gefokus word, om vas te stel of hierdie
metodes wel moontlike oplossings bied tot die probleem bespreek.
4
Mitchell, Daniel Allan. "Interference Mitigation in Radio Astronomy." Thesis, The University of Sydney, 2004. http://hdl.handle.net/2123/693.
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This thesis investigates techniques and algorithms for mitigating radio frequency interference (RFI) affecting radio astronomy observations. In the past radio astronomy has generally been performed in radio-quiet geographical locations and unused parts of the radio spectrum, including small protected frequency bands. The increasing use of the entire spectrum and global transmitters such as satellites are forcing the astronomy community to begin implementing active interference cancelling. The amount of harmful interference affecting observations will also increase as future instruments such as the Square Kilometre Array (SKA) are required to use larger bandwidths to reach up to 100 times the current sensitivity levels, and as spectral line observations require observing in bands licensed to other spectrum users. Particular attention is paid to interference cancellation algorithms which make use of reference beams. This has proven to be successful in removing interference from the contaminated astronomical data. Reference antenna cancellers are closely analysed, leading to filters and techniques that can offer improved RFI excision for some important applications. It is shown that pre- and post-correlation reference antenna cancellers give similar results, and an important aspect of the cancellers is the use of a second reference signal when the reference interference-to-noise ratio is low. These modified filters can theoretically offer infinite interference suppression in the voltage domain, equivalent to that of post-correlation interference cancellers, and their internal structure can offer an understanding of the residual RFI and added receiver noise components of a variety of reference antenna techniques. The effect of variable geometric delays is also considered and various filters are compared as a function of the geometric fringe rate.
5
Mitchell, Daniel Allan. "Interference Mitigation in Radio Astronomy." University of Sydney. Physics, 2004. http://hdl.handle.net/2123/693.
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This thesis investigates techniques and algorithms for mitigating radio frequency interference (RFI) affecting radio astronomy observations. In the past radio astronomy has generally been performed in radio-quiet geographical locations and unused parts of the radio spectrum, including small protected frequency bands. The increasing use of the entire spectrum and global transmitters such as satellites are forcing the astronomy community to begin implementing active interference cancelling. The amount of harmful interference affecting observations will also increase as future instruments such as the Square Kilometre Array (SKA) are required to use larger bandwidths to reach up to 100 times the current sensitivity levels, and as spectral line observations require observing in bands licensed to other spectrum users. Particular attention is paid to interference cancellation algorithms which make use of reference beams. This has proven to be successful in removing interference from the contaminated astronomical data. Reference antenna cancellers are closely analysed, leading to filters and techniques that can offer improved RFI excision for some important applications. It is shown that pre- and post-correlation reference antenna cancellers give similar results, and an important aspect of the cancellers is the use of a second reference signal when the reference interference-to-noise ratio is low. These modified filters can theoretically offer infinite interference suppression in the voltage domain, equivalent to that of post-correlation interference cancellers, and their internal structure can offer an understanding of the residual RFI and added receiver noise components of a variety of reference antenna techniques. The effect of variable geometric delays is also considered and various filters are compared as a function of the geometric fringe rate.
6
Bock, Douglas Carl-Johan. "Wide Field Aperture Synthesis Radio Astronomy." University of Sydney. Physics, 1998. http://hdl.handle.net/2123/377.
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This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
7
Ngongoni, Chipo Nancy. "Neural cross-correlation for radio astronomy." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11427.
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Includes abstract.<br>Includes bibliographical references (leaves 56-62).<br>Correlation engines are essential elements of most signal processing systems. Areas of applicability include image processing, speech synthesis and analysis, high energy physics, wireless and mobile communication systems, spread spectrum communication systems and even prosthetics. Finding cost effective and computationally less intensive engines is the thrust of most research. Neural networks have also been used as aids in making complex tasks relatively easy to process.
8
Manley, Jason Ryan. "A scalable packetised radio astronomy imager." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15573.
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Includes bibliographical references<br>Modern radio astronomy telescopes the world over require digital back-ends. The complexity of these systems depends on many site-specific factors, including the number of antennas, beams and frequency channels and the bandwidth to be processed. With the increasing popularity for ever larger interferometric arrays, the processing requirements for these back-ends have increased significantly. While the techniques for building these back-ends are well understood, every installation typically still takes many years to develop as the instruments use highly specialised, custom hardware in order to cope with the demanding engineering requirements. Modern technology has enabled reprogrammable FPGA-based processing boards, together with packet-based switching techniques, to perform all the digital signal processing requirements of a modern radio telescope array. The various instruments used by radio telescopes are functionally very different, but the component operations remain remarkably similar and many share core functionalities. Generic processing platforms are thus able to share signal processing libraries and can acquire different personalities to perform different functions simply by reprogramming them and rerouting the data appropriately. Furthermore, Ethernet-based packet-switched networks are highly flexible and scalable, enabling the same instrument design to be scaled to larger installations simply by adding additional processing nodes and larger network switches. The ability of a packetised network to transfer data to arbitrary processing nodes, along with these nodes' reconfigurability, allows for unrestrained partitioning of designs and resource allocation. This thesis describes the design and construction of the first working radio astronomy imaging instrument hosted on Ethernet-interconnected re- programmable FPGA hardware. I attempt to establish an optimal packetised architecture for the most popular instruments with particular attention to the core array functions of correlation and beamforming. Emphasis is placed on requirements for South Africa's MeerKAT array. A demonstration system is constructed and deployed on the KAT-7 array, MeerKAT's prototype. This research promises reduced instrument development time, lower costs, improved reliability and closer collaboration between telescope design teams.
9
Bock, Douglas Carl-Johan. "Wide Field Aperture Synthesis Radio Astronomy." Thesis, The University of Sydney, 1997. http://hdl.handle.net/2123/377.
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This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
10
Carozzi, Tobia. "Radio waves in the ionosphere : Propagation, generation and detection." Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
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We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
11
Zhang, Guoyong. "Superconducting microwave components for radio astronomy applications." Thesis, University of Birmingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435303.
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12
Janes, Clinton C. "The Impact of Telemetry on Radio Astronomy." International Foundation for Telemetering, 1995. http://hdl.handle.net/10150/608408.
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International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada<br>The National Radio Astronomy Observatory (NRAO) operates the Very Large Array
(VLA) Radio Observatory in New Mexico, and the Very Long Baseline Array
(VLBA) with 10 radio antenna in locations from Hawaii to St. Croix, as well as other
radio telescopes at Green Bank, West Virginia, and the 12 meter radio antenna near
Tucson, AZ. Although radio frequency (RF) bands have been set aside for passive use
by these radio telescopes, harmful interference from increased demands on the radio
spectrum is a growing problem for earth-based radio astronomy. For example, locating
a radio observatory in a remote area is little defense from satellite downlink telemetry.
This paper describes why the operation of the radio telescopes is susceptible to RF
telemetry interference, what bands are particularly vulnerable and at what power
levels, and how data collection and centralized control of the arrays are accomplished
without RF telemetry.
13
Kennedy, Paul Robert. "Superconducting devices for millimetre-wavelength astronomy." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386169.
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14
Mena, Juan. "A radio-frequency-over-fiber link for large-array radio astronomy applications." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121390.
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The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a specialized array of cylindrical radio telescopes that will study the nature of dark energy by mapping the three-dimensional distribution of neutral hydrogen gas in the universedetected from redshifted 21 cm radiation. CHIME will measure the characteristic Baryon Acoustic Oscillation (BAO) scale across the key redshift range z~0.8 to z~2.5 where the expansion history of the universe changes from one dominated by the attractive force of ordinary gravity to one dominated by dark energy. While characterizing the CHIME analog receiver, the implementation of a Radio-Frequency-over-Fiber (RFoF) link to transport the signals from the antennas to the processing room has been investigated as an alternative to traditional coaxial cable. In this thesis, a prototype version of a custom-built RFoF link for CHIME is presented, as well as tests on its dynamic performance and gain and phase stability. We demonstrate that RFoF can be successfully used as a cost-effective solution for analog signal transport on the CHIME telescope and in other large-array radio astronomy applications.<br>L'expérience CHIME (Canadian Hydrogen Intensity Mapping Experiment) est un réseau de radiotélescopes cylindriques qui vont cartographier la distribution tridimensionnelle des atomes d'hydrogène neutres dans l'univers en détectant directement leurs émissions radio à 21 cm décalées vers le rouge afin d'étudier la nature de l'énergie sombre. CHIME mesurera l'échelle spatiale des oscillations acoustiques baryoniques (BAO) sur une plage de décalage vers le rouge allant de z~0.8 à z~2.5 dans les directions radiales and angulaires, là où se trouve la transition entre la décélération de l'expansion de l'univers dominée par les forces gravitationnelles, vers son accélération dominée par l'énergie sombre. Nous étudions dans cette thèse la possibilité d'utiliser un lien optique pour transmettre les signaux radio du télescope au lieu des câbles coaxiaux traditionnels. Nous présentons une version prototype du lien radio optique de CHIME ainsi que les résultats des tests de performance dynamique et de stabilité de gain et de phase du lien. Ces tests démontrent que des liens radio optiques ont les performances nécessaires pour être utilisés avec succès dans le transport à faible coût des signaux astronomiques du télescope de CHIME et d'autres télescopes de radioastronomie.
15
Price, Daniel Charles. "Radio astronomy instrumentation for redshifted hydrogen line science." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:3185b622-9aba-4c0f-995b-eceb50a5a49c.
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This thesis presents instrumentation with which to measure the abundance of neutral hydrogen gas in the Universe. Measuring where the Universe’s hydrogen is, and tracing how its distribution evolves with time, holds the key to understanding how galaxies evolve, the nature of dark energy, and how the first cosmic structures formed. In particular, this thesis looks at instrumentation for 21-cm intensity mapping telescopes. In 21-cm intensity mapping, the collective emission of many galaxies is measured, without individual detections. This technique promises to allow detection of the baryonic acoustic oscillation peaks in the power spectrum of the Universe’s matter distribution. Such a detection would increase constraints on cosmological parameters. There are two main approaches to designing a 21-cm intensity mapping instruments: using a filled aperture instrument such as a single-dish telescope, or using a sparse aperture instrument such as an interferometric array of dipoles. This thesis investigates analogue components for a sparse aperture instrument operating at 1.0-1.5 GHz. As part of this work, a 16-element sparse aperture array was designed and constructed. To test the array’s performance, field testing was conducted; the results of which are presented here. In addition to this, I have designed a new digital spectrometer for redshifted hydrogen line science, named HISPEC. A copy of this spectrometer has been installed on the Parkes 64 m telescope, as a digital signal processor for the 21-cm multibeam receiver. HISPEC has increased instantaneous bandwidth, higher interchannel isolation, and improved quantization efficiency as compared to the existing backend, MBCORR. The HISPEC equipped multibeam receiver is an ideal instrument for 21-cm intensity mapping at redshifts z<0.2.
16
Hugo, Benjamin. "Fast online predictive compression of radio astronomy data." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/21225.
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This report investigates the fast, lossless compression of 32-bit single precision
floating-point values. High speed compression is critical in the context of
the MeerKAT radio telescope currently under construction in Southern Africa and
Australia, which will produce data at rates up to 1 Petabyte every 20 seconds.
The compression technique being investigated is based on predictive compression,
which has proven successful at achieving high-speed compression in previous research.
Several different predictive techniques (which includes polynomial extrapolation),
along with CPU- and GPU-based parallelization approaches are discussed.
The implementation successfully achieves throughput rates in excess of 6 GiB/s
for compression and much higher rates for decompression using a 64-core AMD
Opteron machine, achieving file-size reductions of, on average 9%. Furthermore
the results of concurrent investigations into block-based parallel Huffman encoding
and Zero-length Encoding are compared to the predictive scheme and it was found
that the predictive scheme obtains approximately 4%-5% better compression ratios
than the Zero-Length Encoder and is 25 times faster than Huffman encoding on
an Intel Xeon E5 processor. The scheme may be well-suited to address the large
network bandwidth requirements of the MeerKAT project.
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Mootoovaloo, Arrykrishna. "Bayesian model selection with applications to radio astronomy." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27492.
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This thesis consists of two main parts, both of which focus on Bayesian methods and the problem of model selection in particular. The first part investigates a new approach to computing the Bayes factor for model selection without needing to compute the Bayesian evidence, while the second part shows, through an analytical calculation of the Bayesian evidence, that Bayesian methods allow two point sources to be distinguished from a single point source at angular separations that are much smaller than the naive beam size at high signal to noise. In the first part, the idea is to create a supermodel by combining two models using a hyperparameter, which we call α. Setting α = 0 or 1 switches each of the models off. Hence, the ratio of the posterior of α at the two end points (0 or 1) gives the Bayes Factor. This effectively converts the problem of model selection into a Bayesian inference problem. One can then use a standard Markov Chain Monte Carlo method to map the posterior distribution of α and compute the Bayes factor. In the second part of this thesis, the Bayesian radio interferometry formalism of Lochner et al. (2015) is extended to take into account the gains of the antennae using the StEFCal algorithm, an important part of the calibration pipeline. Finally we study the case of a pair of sources and show that they can be resolved using an analytical computation of the Bayesian evidence. This demonstrates that Bayesian methods allow super-resolution: the pair of sources can be distinguished from a single source at arbitrarily small scales compared to the naive beam size, as long as the measurements have sufficient signal to noise.
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McMahon, Peter Leonard. "Adventures in radio astronomy instrumentation and signal processing." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5165.
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Includes abstract.<br>Includes bibliographical references (leaves 117-119).<br>This thesis describes the design and implementation of several instruments for digitizing and processing analogue astronomical signals collected using radio telescopes. Modern radio telescopes have significant digital signal processing demands that are typically best met using custom processing engines implemented in Field Programmable Gate Arrays. These demands essentially stem from the ever-larger analogue bandwidths that astronomers wish to observe, resulting in large data volumes that need to be processed in real time. We focused on the development of spectrometers for enabling improved pulsar² science on the Allen Telescope Array, the Hartebeesthoek Radio Observatory telescope, the Nançay Radio Telescope, and the Parkes Radio Telescope. We also present work that we conducted on the development of real-time pulsar timing instrumentation.
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Van, Vuuren Lukas Martin. "Design of a receiver system for use in radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96800.
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Choeysakul, Chittawan. "Small reverberation chambers for radio frequency emission measurements: a radio astronomy feasibility study." Thesis, Curtin University, 2015. http://hdl.handle.net/20.500.11937/2136.
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To use a Reverberation Chamber (RC) below the Lowest Usable Frequency, this thesis applies: multiple receiving antennas; multiple EUT positions; and a modified validation procedure. Emission measurements are then possible down to the first cavity resonance. The design is based on theory and simulations, and validated by on a prototype. The longer measurement times, compare to conventional RCs are acceptable where sensitivity is of concern, e.g. in radio astronomy or defence applications.
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Roberts, Paul Philip. "Components for Wide Bandwidth Signal Processing in Radio Astronomy." University of Sydney. Electrical Engineering, 2003. http://hdl.handle.net/2123/603.
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In radio astronomy wider observing bandwidths are constantly desired for the reasons of improved sensitivity and velocity coverage. As observing frequencies move steadily higher these needs become even more pressing. In order to process wider bandwidths, components that can perform at higher frequencies are required. The chief limiting component in the area of digital spectrometers and correlators is the digitiser. This is the component that samples and quantises the bandwidth of interest for further digital processing, and must function at a sample rate of at least twice the operating bandwidth. In this work a range of high speed digitiser integrated circuits (IC) are designed using an advanced InP HBT semiconductor process and their performance limits analysed. These digitiser ICs are shown to operate at up to 10 giga-samples/s, significantly faster than existing digitisers, and a complete digitiser system incorporating one of these is designed and tested that operates at up to 4 giga-samples/s, giving 2 GHz bandwidth coverage. The digitisers presented include a novel photonic I/O digitiser which contains an integrated photonic interface and is the first digitiser device reported with integrated photonic connectivity. In the complementary area of analogue correlators the limiting component is the device which performs the multiplication operation inherent in the correlation process. A 15 GHz analogue multiplier suitable for such systems is designed and tested and a full noise analysis of multipliers in analogue correlators presented. A further multiplier design in SiGe HBT technology is also presented which offers benefits in the area of low frequency noise. In the effort to process even wider bandwidths, applications of photonics to digitisers and multipliers are investigated. A new architecture for a wide bandwidth photonic multiplier is presented and its noise properties analysed, and the use of photonics to increase the sample rate of digitisers examined.
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Foster, Griffin. "Large-N correlator systems for low frequency radio astronomy." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:2bca41ff-ec75-4a41-a634-c5bbbceae434.
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Low frequency radio astronomy has entered a second golden age driven by the development of a new class of large-N interferometric arrays. The low frequency array (LOFAR) and a number of redshifted HI Epoch of Reionization (EoR) arrays are currently undergoing commission and regularly observing. Future arrays of unprecedented sensitivity and resolutions at low frequencies, such as the square kilometer array (SKA) and the hydrogen epoch of reionization array (HERA), are in development. The combination of advancements in specialized field programmable gate array (FPGA) hardware for signal processing, computing and graphics processing unit (GPU) resources, and new imaging and calibration algorithms has opened up the oft underused radio band below 300 MHz. These interferometric arrays require efficient implementation of digital signal processing (DSP) hardware to compute the baseline correlations. FPGA technology provides an optimal platform to develop new correlators. The significant growth in data rates from these systems requires automated software to reduce the correlations in real time before storing the data products to disk. Low frequency, widefield observations introduce a number of unique calibration and imaging challenges. The efficient implementation of FX correlators using FPGA hardware is presented. Two correlators have been developed, one for the 32 element BEST-2 array at Medicina Observatory and the other for the 96 element LOFAR station at Chilbolton Observatory. In addition, calibration and imaging software has been developed for each system which makes use of the radio interferometry measurement equation (RIME) to derive calibrations. A process for generating sky maps from widefield LOFAR station observations is presented. Shapelets, a method of modelling extended structures such as resolved sources and beam patterns has been adapted for radio astronomy use to further improve system calibration. Scaling of computing technology allows for the development of larger correlator systems, which in turn allows for improvements in sensitivity and resolution. This requires new calibration techniques which account for a broad range of systematic effects. And, a deep integration between DSP hardware and software data reduction into a single backend.
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Staats, Kai. "Genetic programming applied to RFI mitigation in radio astronomy." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/23703.
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Genetic Programming is a type of machine learning that employs a stochastic search of a solutions space, genetic operators, a fitness function, and multiple generations of evolved programs to resolve a user-defined task, such as the classification of data. At the time of this research, the application of machine learning to radio astronomy was relatively new, with a limited number of publications on the subject. Genetic Programming had never been applied, and as such, was a novel approach to this challenging arena. Foundational to this body of research, the application Karoo GP was developed in the programming language Python following the fundamentals of tree-based Genetic Programming described in "A Field Guide to Genetic Programming" by Poli, et al. Karoo GP was tasked with the classification of data points as signal or radio frequency interference (RFI) generated by instruments and machinery which makes challenging astronomers' ability to discern the desired targets. The training data was derived from the output of an observation run of the KAT-7 radio telescope array built by the South African Square Kilometre Array (SKA-SA). Karoo GP, kNN, and SVM were comparatively employed, the outcome of which provided noteworthy correlations between input parameters, the complexity of the evolved hypotheses, and performance of raw data versus engineered features. This dissertation includes description of novel approaches to GP, such as upper and lower limits to the size of syntax trees, an auto-scaling multiclass classifier, and a Numpy array element manager. In addition to the research conducted at the SKA-SA, it is described how Karoo GP was applied to fine-tuning parameters of a weather prediction model at the South African Astronomical Observatory (SAAO), to glitch classification at the Laser Interferometer Gravitational-wave Observatory (LIGO), and to astro-particle physics at The Ohio State University.
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Pollak, Alexander Werner. "Receiver technology for radio astronomy and deep space communications." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:c37da004-c428-49ca-8097-deae9f1ed8f7.
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This thesis presents the design and development of a complete receiver system for a conversion project, which replaces the commercial receiver of a telecommunication antenna with a cryogenically cooled radio astronomy receiver. Part of the project is to explore the synergy between radio astronomy and deep-space communications, which share many technical requirements, but also have technical conflicts. Therefore, this thesis attempts to solve some of these technological issues and provides a design for a receiver system, where radio astronomy and communication applications can successfully share the same hardware and infrastructure. The receiver system employs a FPGA-based digital signal processing backend, which enables the instrument to be used in three different operational modes, single-dish observation, interferometer observation, and deep-space communication. The architecture of the receiver system includes a novel technical solution to stabilise gain drift when used in single-dish observation mode. Two stabilisation methods are discussed in detail, and their performance is verified by measurements. The white-noise stabilisation approach uses a modulated reference noise signal and the continuous-wave stabilisation approach uses a narrowband reference signal to track the change in amplification. Both stabilisation methods showed excellent performance and are implemented to stabilise the gain drift of the receiver system. A number of analogue signal components were specially designed for the receiver system in order to meet the requirements of the conversion project. One of these components is the compact quad-ridged orthomode transducer, which provides the transmission between the feed horn and the coaxial cables. Its design uses a novel approach to reduce significantly the transition length, while retaining a wide operational bandwidth. Finally we present the design of the complete receiver system, which includes the development work and verification of the components that were built for this project.
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Bukilic, Nino. "Wide bandwidth focal plane array receiver for radio astronomy." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/2331.
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Reflective antennas equipped with phase array feeds (PAFs) have been proposed as part of the Square Kilometre Array reference design, since they offer a wide Field of View (FoV) and large collecting area. To achieve a contiguous FoV, and to cancel spill-over radiation, the Focal Plane Array (FPA) must sample the focal field of the reflector at least every half-wavelength at the upper operating frequency. Low-noise operation over a wide bandwidth requires appropriate impedance matching to the low-noise amplifiers, and this is a challenging research problem since the input impedance of the FPA elements can vary strongly with frequency.Advanced broadband design techniques for antenna arrays have resulted in antenna shapes getting more complex. Modelling of these antennas can only be carried out using numerical computational electromagnetic methods (CEM), and accurate modelling of complex antennas demand the full-wave analysis with fields and currents that vary in three dimensional space. The Frequency Domain Integral Equation model is adopted in this study and used via the Method of Moments (MoM) technique for simulation and modelling of the FPA. The "MoM Antenna Development Toolbox" (MoMADT), 64 bit version of the modelling software, is specifically developed in this study for designing, building and modelling of complex antenna and electromagnetic structures. MoMADT utilizes surface and volume integral equations and provides functions for generating precise meshes and accurate method of moments solutions. MoMADT enables structures to be assembled in an array formation to consist of conductive or dielectric materials, or a combination of both.Study of the wide bandwidth FPA receiver was achieved through analysis of broadband planar antenna structures. This research investigates a unique design solution for a FPA utilizing the diamond planar strip antenna elements arranged to provide three vectors of polarization (triple-polarized FPA). The most promising FPA identified is the 77 Hexagonal Diamond Tripole (HDT) array. This array yields an operating frequency range of 550 to 2100 MHz, providing bandwidth ratio of 3.8:1. It is shown that adequate impedance match can be achieved across the indicated frequency range with desired directivity and gain. In addition, the 77 HDT array offers optimized efficiency and allows the polarization to be distinguished at any angle about the axis normal to the antenna plane to within a theoretical uncertainty of ± 2.2°. This is also true for any function of the FoV allowed by the surface area of the FPA.
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Maciel, Tamela. "Radio source evolution." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708637.
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Sihlangu, Isaac. "The MeerKAT Radio Frequency Interference Environment." Master's thesis, Faculty of Science, 2019. https://hdl.handle.net/11427/31748.
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Radio signals from astronomical sources are extremely weak and easily distorted/- corrupted or overwhelmed by man-made radio signals such as cellphones, satellites, aircraft and telescope electronics. These Radio Frequency Interference (RFI) are increasingly threatening radio observatories due to our increasingly technological world. To detect and mitigate RFI, observatories need to understand their RFI environment, what contributes to it and how it is changing. While there are few dedicated RFI monitoring systems on the MeerKAT site, the most sensitive RFI detector is the MeerKAT array itself. In this thesis we use approximately 1500 hours of MeerKAT observations to create a multi-dimensional view of the RFI at the MeerKAT site. Here we investigate a probabilistic approach to characterise the RFI environment around the MeerKAT radio telescope. In order to achieve our goal, we propose the MeerKAT Historical Probability of RFI (KATHPRFI) framework. We produced the high level requirements of the KATHPRFI framework driven by the needs of the MeerKAT users. The design approach and the design decision of the framework is presented that cover both the software and hardware constraints. The KATHPRFI produces a 5-dimensional array of the RFI probability as measured by the MeerKAT telescope during the commissioning phase (May 2018 - December 2018) for each observation file. From the 5-D array, we extracted various statistics and characterised the RFI environment around MeerKAT site. We found that there is a correlation between RFI occupancy and the time of the day which is most probably related to human activities. Furthermore, we found a correlation between the time of the day and flights passing over a region of site. Our results showed that the highest probability of RFI points towards a region including nearby towns. The results obtained are consistent with the argument that the major RFI sources for MeerKAT site are the Global Positioning System (GPS) satellite, flight Distance Measurement Equipment (DME) and the Global System for Mobile Communications (GSM). Our data also showed that the RFI occupancy decreases with an increase of baseline length, this is a result of moving RFI sources with respect to the static sky. Therefore, the phase of the RFI changes rapidly on long baselines compared to short baselines. As a result when a correlation is carried out the RFI amplitude will vanish less on short baselines compared to the long baselines. Our results provide the first highly detailed view of the MeerKAT RFI environment allowing us to track the historical evolution of the RFI, both on average, and as a function of frequency, baseline and direction. With historical baselines known, one can also provide alerts about sudden changes. This could be due to new sources of RFI or stem from any outliers in the data, which could signal telescope or correlator issues. Hence the KATHPRFI framework also provides a window into the operational health of the telescope.
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Abdalla, Filipe B. "Cosmological constraints with future radio surveys." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711600.
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Wu, Nailong. "The maximum entropy method and its application in radio astronomy." Thesis, The University of Sydney, 1985. https://hdl.handle.net/2123/27440.
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This thesis consists of seven chapters, two appendices and a bibliography. In addition, three publications are included. The first digit in the page numbers refers to the chapter or appendix, and the second one or two digits are the serial numbers of the page in the chapter or appendix. For equations, figures and tables, the first digit and the second one or two digits refer respectively to the chapter and section; the third one or two digits refer to its serial occurrence in the chapter. The references in the bibliography are listed in alphabetical order by the author. Mathematical symbols are defined when they are first introduced. All abbreviated terms in the text are given in full at the first mention, with the abbreviations in parentheses; thereafter, the abbreviations are used. However, words in full may be repeated for readability.
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Junklewitz, Henrik [Verfasser], and Simon [Akademischer Betreuer] White. "Statistical inference in radio astronomy / Henrik Junklewitz. Betreuer: Simon White." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1065610122/34.
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Lukic, Vesna [Verfasser], and Marcus [Akademischer Betreuer] Brüggen. "Deep learning in Radio Astronomy / Vesna Lukic ; Betreuer: Marcus Brüggen." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1201821282/34.
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Agar, Jon. "Screening science : spatiality and authority at a radio astronomy observatory." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309750.
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Goodrick, Lee. "Image reconstruction in radio astronomy with non-coplanar synthesis arrays." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96902.
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Thesis (MEng)--Stellenbosch University, 2015.<br>ENGLISH ABSTRACT: Traditional radio astronomy imaging techniques assume that the interferometric array is
coplanar, with a small field of view, and that the two-dimensional Fourier relationship
between brightness and visibility remains valid, allowing the Fast Fourier Transform to be
used. In practice, to acquire more accurate data, the non-coplanar baseline effects need
to be incorporated, as small height variations in the array plane introduces the w spatial
frequency component. This component adds an additional phase shift to the incoming signals.
There are two approaches to account for the non-coplanar baseline effects: either the full
three-dimensional brightness and visibility model can be used to reconstruct an image, or the
non-coplanar effects can be removed, reducing the three dimensional relationship to that of the
two-dimensional one.
This thesis describes and implements the w-projection and w-stacking algorithms. The aim of
these algorithms is to account for the phase error introduced by non-coplanar synthesis arrays
configurations, making the recovered visibilities more true to the actual brightness distribution
model. This is done by reducing the 3D visibilities to a 2D visibility model. The algorithms
also have the added benefit of wide-field imaging, although w-stacking supports a wider field
of view at the cost of more FFT bin support. For w-projection, the w-term is accounted for in
the visibility domain by convolving it out of the problem with a convolution kernel, allowing
the use of the two-dimensional Fast Fourier Transform. Similarly, the w-Stacking algorithm
applies a phase correction in the image domain to image layers to produce an intensity model
that accounts for the non-coplanar baseline effects.
This project considers the KAT7 array for simulation and analysis of the limitations and
advantages of both the algorithms. Additionally, a variant of the Högbom CLEAN algorithm
was used which employs contour trimming for extended source emission flagging. The CLEAN
algorithm is an iterative two-dimensional deconvolution method that can further improve image
fidelity by removing the effects of the point spread function which can obscure source data.<br>AFRIKAANSE OPSOMMING: Tradisionele beeldvormingstegnieke in radio-astronomie aanvaar dat die interferometriese
skikking samevlakkig is. Dit beteken dat die twee-dimensionele Fourier verhouding tussen
helderheid en sigbaarheid geldig bly en dat die Vinnige Fourier Transform aangewend kan
word. Klein hoogtevariasies in die skikkingsvlak bring die w-ruimtelike frekwensiekomponent
mee, wat ’n faseverskuiwing in die inkomende seine tot gevolg het. Dus, in praktyk, moet
die bydrae van die nie-samevlakkige basislyneffekte in ag geneem word om sodoende
die akkuraatheid van die data te verhoog. Twee benaderings kan gevolg word om die
nie-samevlakkige basislyneffekte in ag te neem: Metodes wat die volle drie dimensionele
helderheid en sigbaarheidsmodel gebruik kan toegepas word om ’n beeld te herbou, andersins
kan die nie-samevlakkige effekte verwyder word om sodoende die drie-dimensionele
verhouding te verminder tot ’n twee-dimensionele verhouding.
Hierdie tesis beskryf en implementeer die ‘w-projeksie’ en ‘w-stapel’ algoritmes. Die doel van
hierdie algoritmes is om die fasefout wat deur nie-samevlakkige sinteseskikkingskonfigurasies
veroorsaak word, reg te stel. Hierdie regstelling maak die herwinde sigbaarheid van die beeld
meer getrou aan die werklike helderheidsverspreidingsmodel. ’n Bykomende voordeel van
die algoritmes is beeldvorming van wye-veld ruimtewaarnemings. In ‘w-projection’ word die
w-term in die sigbaarheidsdomein in ag geneem deur die ruimtelike frekwensiekomponent met
behulp van ’n konvolusiekern vanuit die probleem te verwyder. Die twee-dimensionele Vinnige
Fourier Transform kan gevolglik toegepas word. Soortgelyk hieraan, wend die ‘w-Stacking’
algoritme ’n fasekorreksie aan tot ’n reeks beeldlae, om sodoende ’n beeld te verkry wat die
nie-samevlakkige basislyneffekte in ag neem.
Die KAT7 teleskoop is gebruik in die simulasie en analiese van die tekortkominge en voordele
van beide algoritmes. ’n Hibriede weergawe van die Högbom CLEAN algoritme is bykomend
oorweeg. Hierdie algoritme is ’n iteratiewe twee-dimensionele dekonvolusiemetode wat die
betroubaarheid van beelde verbeter deur die verskansingseffek van puntverspreidingsfunksies
te verwyder. Verder gebruik die Högbom CLEAN algoritme kontoersnoeiing om uitgebreide
bron-emisies te identifiseer.
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Poulsen, Andrew Joseph. "Real-time Adaptive Cancellation of Satellite Interference in Radio Astronomy." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd238.pdf.
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Diao, Junming. "High-Sensitivity Phased Arrays for Radio Astronomy and Satellite Communications." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6546.
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Radio astronomy is used to study stars, galaxies, black holes and gas clouds radiation at radio frequencies. Detecting extremely weak signals from deep space radio sources requires high sensitive feed system associated with large dish antennas. The key figure of merit is survey speed, or the time required to map a region of the sky to a given source flux density. Survey speed is proportional to the frequency bandwidth, the field of view or observable region of the sky, and the squared sensitivity, where sensitivity is related to reflector aperture efficiency and system noise temperature. Compared to the traditional single feed, phased array feeds with significantly expanded field of view are considered as the next generation feed for radio telescope. This dissertation outlines the design, analysis and measurement of high sensitivity L-band and mm-wave phased array feeds for the 100-meter Green Bank Telescope. Theoretical works for radio astronomy includes design guideline for high sensitivity phased array feed, fundamental frequency bandwidth limit, array antenna loss influenced by mutual coupling and beamformer coefficients and possibility of superdirectivity for radio telescopes and other antennas. These study are helpful to understand and guide the design of a phased array feed system. In the absence of dish antennas, sparse phased arrays with aperiodic structure have been developed for satellite communications. A compromise between the peak side lobe level, array element density, directivity and design complexity is studied. We have found that the array peak side lobe level can be reduced by enhancing the array element direction at the main lobe direction, increasing the array element density and enlarging the array size. A Poynting streamline approach develops to understand the properties of a receiving antenna and the mutual coupling effects between array elements. This method has been successfully used to generate effective area shape for many types of antennas and guide the design of a superdirective antenna. Motivated by this method, a superdirective antenna is experimental demonstrated.
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Alvear, Cabezón Andrés Arturo. "Ultra-pure digital detection of polarization for radio astronomy applications." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/167849.
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Magíster en Ciencias de la Ingeniería, Mención Ingeniería Eléctrica<br>Polarization is a key measurement within radio astronomy because its state can give insight as to the physical conditions of the source and the medium the radiation has traveled through.
In radio astronomy receivers, the device used to separate the polarization is known as an Ortho-Mode Transducer (OMT). The OMT is a passive component that separates signals into two orthogonal components.
Using available millimeter-wave analog technology, wideband heterodyne receiver systems generally obtain polarization isolation ratios of 15dB to 20dB, insufficient for modern astronomical applications. That low polarization isolation ratio is due to the presence of leakage from one polarization contaminating the other, which is known as cross-polarization.
In order to improve polarization isolation and reduce cross-polarization, a new approach called Digital OMT has been proposed, based on passing one given functionality from the analog domain to the digital domain using digital signal processing techniques.
Digital techniques were studied to improve OMT performance, which led to the design of a polarimeter based on the Fast Fourier Transform (FFT). The polarimeter was implemented on a Field Programmable Gate Array (FPGA), including the implementation of a Ku-band analog front-end to characterize the design and measure the synthesized polarization.
This thesis introduces a prototype of a DOMT created for real-time processing and continuous integration, suitable for radio astronomy observations. The configuration used is based on the architecture of a compact four-port OMT. The outputs are downconverted using mixers and then directly digitalized using four 8bit ADC sampling at 1.2 GSPS. A 180° hybrid was implemented on the FPGA together with a set of calibration vectors, with the purpose of compensating the amplitude and phase imbalance typical of analog radio astronomy front-ends.
This calibrated Digital OMT exhibits a polarization isolation ratio of more than 40 dB for the entire RF bandwidth, representing an improvement factor of 100 over its analog counterpart.<br>Este trabajo ha sido parcialmente financiado por Centro de Astrofísica y Tecnologías Afines (CATA-BASAL-PBF 06), FONDECYT 11140428 y 1121051, y ALMA-CONICYT 31150012. Agradecemos a Xilinx Inc. por la donación de circuitos integrados y licencias de software y a la comunidad de CASPER por el apoyo brindado.
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Buchan, James. "Mitigating Electromagnetic Interference in Power Converters for Radio Astronomy Applications." Thesis, Curtin University, 2021. http://hdl.handle.net/20.500.11937/88250.
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Computational studies and a prototype half-bridge DC-DC converter capable of logistic-shaped switching transitions to achieve high-frequency electromagnetic interference mitigation is presented. The logistic-shaped transition provides steep spectral content roll-off, which is desirable for low noise outcomes. The research demonstrates that shaped switching transitions can be integrated into power converters operating with pulse with modulation control strategies, which is desirable for low noise applications such as radio astronomy.
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Rees, Nicholas Peter. "The 38 MHz radio survey." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315316.
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Woermann, Beate. "Radio observation of the Gum Nebula Region." Thesis, Rhodes University, 1997. http://hdl.handle.net/10962/d1005271.
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This thesis describes the results of an investigation of the physical properties of the Gum Nebula. For this investigation a radio continuum map of the region was made at 2326 MHz and resolution ⅓° with the HartRAO antenna. This map was used to generate spectral index images and an infrared to radio flux density ratio (IRR) image. The latter image shows that the IRR of the nebula is in the range 20 to 250, identifying it as an old SNR. Several spectral index images of this region were generated using two different methods, one based on the isolation of the nebula from its background radiation, the other based on TT-plots (Turtle et al., 1962). The two methods yield similar results, which show that the nebula has a thermal shell with a non-thermal region in its interior. Below the galactic plane the thermal region dominates and above the plane the nonthermal region. These results suggest a model of an old SNR with an H II region shell. Spectral line observations of hydrogen recombination lines and hydroxyl (OH) were made with the HartRAO and the Mopra telescopes. The detection of hydrogen recombination lines at four positions in the thermal regions of the nebula give electron temperatures and emission measures in the ranges 4000 to 6000 K and 220 to 460 pc.cm⁻⁶ respectively. The turbulent velocities are of the order of 20 km/s. A search for shocked OH lines at 1667 MHz and 1720 MHz in the Gum Nebula gave results that were negative, but numerous unshocked 1667 MHz OH lines were detected. The latter were used in a test for an expansion of the nebula. The most plausible fit to the data gives an expansion centre at l = 260.5°, b = -2.5° and at a distance of 0.7 kpc from us. The front face angular radius and expansion velocity are 10.5° and 16 km/s respectively. The back face angular radius and expansion velocity are 8.50 and 7 km/s respectively.
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Unewisse, Anne Margaret. "Radio emission from southern clusters of galaxies." Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26671.
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Radio, optical, far-infrared and X-ray sources lying towards galaxy clusters listed in the southern portion of the Abell, Corwin and Olowin rich cluster catalogue (ACO) are presented. The bulk of the observational work is a radio survey of 39 nearby (distance class D < 3) southern ACO clusters undertaken at 843MHz with the Molonglo Observatory Synthesis Telescope. Also included are studies of 408MHz MRC radio sources and 60 pm IRAS far-infrared sources in the direction of ACO clusters.
The survey results are presented in two forms:
i) as a series of radio images, centred on each surveyed cluster with optical images from
the COSMOS database superimposed and IRAS far-infrared and Einstein X-ray
source positions marked, and
ii) in a table of positions, flux densities and optical identifications of the 682 radio
sources detected within the projected boundaries of the cluster sample.
The 207 optical identifications, 50 non-stellar IRAS sources and 20 Einstein sources falling
in the mapped regions are outlined in individual tables. Supplementary Very Large Array
and Australia Telescope Compact Array observations of selected sources are also presented.
The main results of the thesis are:
i) the number of far-infrared sources detected in the direction of a given cluster sample
depends on both the median redshift of the sample and the number of gas rich
galaxies in the clusters,
ii) the fractional radio luminosity fimction (RLF) of first ranked cluster galaxies is found
to flatten at a radio power of around log P(843) = 23 which corresponds power gap
in the differential RLF and an abrupt change in radio morphology, y
iii) a comparison with the RLF of a sample of non-cluster ellipticals suggests that, for
log P(843) > 23, first ranked cluster members are more likely to produce radio
emission than field galaxies and
iv) the radio—infrared correlation appears to hold regardless of cluster membership.
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West, Craig James, and cwest@astro swin edu au. "Development of disk-based baseband recorders and software correlators for radio astronomy." Swinburne University of Technology. Centre for Astrophysics and Supercomputing, 2004. http://adt.lib.swin.edu.au./public/adt-VSWT20050804.143155.
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This thesis details work undertaken in the field of radio astronomy instrumentation. Specific components of the data collection and processing systems used by radio astronomers have been implemented using non-traditional approaches. Traditionally, the correlation of radio astronomy data has taken place on dedicated,
specific hardware. This thesis deals with the implementation of equivalent correlators
using software running on generic clusters of personal computers - the software approach to radio astronomy. Toward this end a system has been developed that records the raw telescope output onto computer hard drives, allowing
easy access to the data on cluster supercomputers. Part of this thesis describes the design, construction, testing and utilisation of these data recording systems. The correlator software used to process these data
on supercomputers is also fully described, including extensive tests of the software
and a detailed comparison between its output and the output of an existing hardware correlator. The software correlator is shown to produce output that agrees extremely well with the hardware correlator, verifying its accuracy and performance. Finally, results of on-going scientific investigations that use the software correlators described in this thesis are outlined, illustrating the flexibility and usefulness of the software approach to radio astronomy.
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Clark, Neil Edward. "Jet-cloud interactions in powerful radio galaxies." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389730.
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McGilchrist, Mark Mungo. "The first 7C survey of radio sources." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303245.
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Campbell, Jacob L. "The Development of a Small Scale Radio Astronomy Image Synthesis Array for Research in Radio Frequency Interference Mitigation." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1014.pdf.
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45
Breton, René. "Radio pulsars in binary systems." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40755.
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This thesis focuses on the study of binary radio pulsars, their evolution and some specific use of their properties to investigate fundamental physics such as general relativity and other gravitational theories. The work that we present here is organized in three main parts. First, we report on the study of PSR J1744-3922, a binary pulsar presenting a peculiar `flickering' flux behavior as well as spin and orbital properties that do not correspond to the expectations of standard evolution scenarios. We investigated the nature of this flux behavior. We also studied the pulsar's properties in relationship to the binary radio pulsar population and proposed the existence of an as yet unidentified class of binary pulsars. Second, we conducted an in-depth analysis of the eclipses in the relativistic double pulsar system PSR J0737-3039A/B. During these eclipses, the `A' pulsar partly disappears for ~30 s behind its companion, `B'. The eclipse light curve displays a complex structure of flux modulation that is synchronized with the rotation of pulsar B. We worked on improving our understanding of the eclipse phenomenology and more particularly the modulation phenomenon. From our modeling of the eclipses, we precisely determined the geometry of pulsar B in space and used this information to study the temporal behavior of the eclipses, which revealed that pulsar B precesses around the angular momentum of the system in a way that is consistent with the prediction of general relativity. Third, we searched for the signature of latitudinal aberration in the pulse profile of pulsar A in PSR J0737-3039A/B. This relativistic effect should cause a periodic variation in the separation between the two pulse components of pulsar A on an orbital time scale. The non-detection of this effect allows us to put an upper limit on its amplitude, which constrains the geometry of pulsar A with respect to our line of sight as well as its emission geometry.<br>Cette thèse se concentre sur l'étude des pulsars en systèmes binaires, leur évolution, ainsi que certains usages de leurs propriétés pour comprendre la physique fondamentale dont la relativité générale et les théories gravitationnelles alternatives. Le travail de cette thèse comprend trois parties principales.En premier lieu, nous présentons l'étude de PSR J1744-3922, un pulsar binaire démontrant d'étranges fluctuations d'intensité lumineuse ainsi que des propriétés orbitales et de rotation qui ne correspondent pas aux prédictions des scénarios évolutifs conventionnels. Nous analysons d'abord les fluctuations d'intensité lumineuse. Nous étudions ensuite la nature de ce pulsar en relation avec la population de pulsars radio en systèmes binaires et proposons l'existence d'une classe de pulsars binaires qui n'avait pas encore été mise à jour.Deuxièmement, nous avons réalisé une analyse en profondeur des éclipses du pulsar double relativiste PSR J0737-3039A/B. Durant ces éclipses, le pulsar `A' disparaît partiellement pendant une trentaine de secondes derrière son compagnon, `B'. La courbe de lumière des éclipses montre une complexe structure de modulation d'intensité qui est synchronisée avec la rotation du pulsar B. Les travaux présentés ici ont pour but de mieux comprendre la phénoménologie des éclipses et visent plus particulièrement le phénomène de modulation. La modélisation des éclipses nous a permis de précisément déterminer la géométrie du pulsar B dans l'espace et d'en déduire son évolution temporelle. Nous concluons que le pulsar B subit une précession de son axe de rotation autour du moment angulaire du système selon un taux et une direction en accord avec la prédiction de la relativité générale.Pour conclure, nous avons recherché la présence d'aberration latitudinale dans le profil du pulse du pulsar A, toujours dans le double pulsar PSR J0737-3039A/B. Cet effet relativiste devrait causer une
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Bannister, Keith. "Radio transients: Surveys and Techniques." Thesis, The University of Sydney, 2011. http://hdl.handle.net/2123/13293.
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I present two pilot surveys and a range of new algorithms to aid in planning and implementing wide-field radio surveys for transient and variable sources. The first pilot survey is a blind survey for transient and variable radio sources with the Molonglo Observatory Synthesis Telescope at 843~MHz. This survey discovered 53 highly variable sources and 15 transient sources and determined surface densities of $0.268 \unit{deg^{-2}}$ for variable sources and $1.3 \times 10^{-2} \unit{deg^{-2}}$ for transient sources, with associated timescales of between one day and three years. I also propose two new techniques which were developed for this survey. The first technique provides a post-imaging calibration for image gain. The second technique is a statistical method for verifying whether flux error measurements agree with the scatter in light curves over a population of sources. I also describe a follow-up survey for prompt radio emission from gamma ray bursts (GRBs) at 1.4~GHz. This survey used a single-dish telescope to automatically slew to a GRB position within 2~min of the gamma ray trigger and performed single-pulse, repeating and low-time resolution searches for variability. This survey discovered single, dispersed pulses following two long GRBs, which are possibly related to the delayed formation of a black hole at the centre of the GRBs. The high-time resolution measurements from this survey are some of the most constraining limits on prompt radio emission from GRBs to date. I also present two efficient new algorithms for detecting dispersed radio emission in interferometric data: the Chirpolator and the Chimageator. These two techniques excel in the regime of sparse arrays, where they both require substantially lower data rates, and the Chirpolator requires a much lower post-integrator operation rate than the existing algorithms. These techniques are well matched to future supercomputing architectures, where the arithmetic capability is outstripping the bandwidth capa! bility, and are therefore suitable for use by interferometer-based fast transient surveys. The surveys and techniques described in this thesis will have immediate application to upcoming surveys with the next generation of wide-field radio telescopes, such as the two transients surveys proposed for the Australian Square Kilometre Array Pathfinder.
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Mauch, Thomas. "Radio Sources in the Local Universe." University of Sydney, 2006. http://hdl.handle.net/2123/928.
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Doctor of Philosophy<br>This thesis presents a census of radio sources selected from the NRAO (National Radio Astronomy Observatory) VLA (Very Large Array) Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS) catalogues which have also been observed in the first data release of the 6 degree Field Galaxy Survey (6dFGS), a galaxy redshift survey of the local universe. Radio detections were found for 4,506 galaxies in the 6dFGS near-infrared-selected primary sample, a radio detection rate of 16%. A further 1,196 radio sources were observed by 6dF which were missing from the 6dFGS primary sample either because their host galaxies were too blue in colour or they appeared stellar on optical plates. The full sample comprises the largest and most homogeneous set of spectra and redshifts of radio sources in the local universe ever obtained. Results from the study of these objects form an accurate benchmark from which their cosmic evolution may be understood. 6dF spectra of galaxies have been used to determine the physical cause of radio emission from each object as either star formation or an active galactic nucleus powered by a super-massive black hole. These two classes of radio source have been characterised via a determination of the local radio luminosity function at 1.4 GHz; plotting the variation in their space density with luminosity. The star-formation density of the universe at the present epoch has been determined, the value of which which turns out to be in excellent agreement with previously published values. Fractional luminosity functions have also been determined showing that more massive galaxies have higher star-formation rates and are more likely to host a radio-loud AGN. The large-scale structure of star-forming galaxies and radio-loud AGN in the local universe has been studied by determining their clustering properties via the two-point correlation function. Radio-loud AGN are found to cluster more strongly than star-forming galaxies confirming that these objects are biased tracers of the underlying matter distribution. Both star-forming galaxies and AGNs cluster similarly to the underlying host galaxy population in which they reside. This thesis also describes the 843 MHz SUMSS catalogue, made by fitting elliptical Gaussians to sources in images. The catalogue contains radio sources to a limiting peak brightness of 6 mJy/beam at declination less than -50 degrees and 10 mJy/beam at declination greater than -50 degrees. Image artefacts have been classified using a novel technique involving a decision tree, which correctly identifies and rejects spurious sources in over 96% of cases and has ensured the catalogue is more than 95% complete and 90% reliable over most of its flux density range.
48
Mauch, Thomas. "Radio Sources in the Local Universe." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/928.
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This thesis presents a census of radio sources selected from the NRAO (National Radio Astronomy Observatory) VLA (Very Large Array) Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS) catalogues which have also been observed in the first data release of the 6 degree Field Galaxy Survey (6dFGS), a galaxy redshift survey of the local universe. Radio detections were found for 4,506 galaxies in the 6dFGS near-infrared-selected primary sample, a radio detection rate of 16%. A further 1,196 radio sources were observed by 6dF which were missing from the 6dFGS primary sample either because their host galaxies were too blue in colour or they appeared stellar on optical plates. The full sample comprises the largest and most homogeneous set of spectra and redshifts of radio sources in the local universe ever obtained. Results from the study of these objects form an accurate benchmark from which their cosmic evolution may be understood. 6dF spectra of galaxies have been used to determine the physical cause of radio emission from each object as either star formation or an active galactic nucleus powered by a super-massive black hole. These two classes of radio source have been characterised via a determination of the local radio luminosity function at 1.4 GHz; plotting the variation in their space density with luminosity. The star-formation density of the universe at the present epoch has been determined, the value of which which turns out to be in excellent agreement with previously published values. Fractional luminosity functions have also been determined showing that more massive galaxies have higher star-formation rates and are more likely to host a radio-loud AGN. The large-scale structure of star-forming galaxies and radio-loud AGN in the local universe has been studied by determining their clustering properties via the two-point correlation function. Radio-loud AGN are found to cluster more strongly than star-forming galaxies confirming that these objects are biased tracers of the underlying matter distribution. Both star-forming galaxies and AGNs cluster similarly to the underlying host galaxy population in which they reside. This thesis also describes the 843 MHz SUMSS catalogue, made by fitting elliptical Gaussians to sources in images. The catalogue contains radio sources to a limiting peak brightness of 6 mJy/beam at declination less than -50 degrees and 10 mJy/beam at declination greater than -50 degrees. Image artefacts have been classified using a novel technique involving a decision tree, which correctly identifies and rejects spurious sources in over 96% of cases and has ensured the catalogue is more than 95% complete and 90% reliable over most of its flux density range.
49
Botai, Ondego Joel. "Ionospheric total electron content variability and its influence in radio astronomy." Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005258.
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Ionospheric phase delays of radio signals from Global Positioning System (GPS) satellites have been used to compute ionospheric Total Electron Content (TEC). An extended Chapman profle model is used to estimate the electron density profles and TEC. The Chapman profle that can be used to predict TEC over the mid-latitudes only applies during day time. To model night time TEC variability, a polynomial function is fitted to the night time peak electron density profles derived from the online International Reference Ionosphere (IRI) 2001. The observed and predicted TEC and its variability have been used to study ionospheric in°uence on Radio Astronomy in South Africa region. Di®erential phase delays of the radio signals from Radio Astronomy sources have been simulated using TEC. Using the simulated phase delays, the azimuth and declination o®sets of the radio sources have been estimated. Results indicate that, pointing errors of the order of miliarcseconds (mas) are likely if the ionospheric phase delays are not corrected for. These delays are not uniform and vary over a broad spectrum of timescales. This implies that fast frequency (referencing) switching, closure phases and fringe ¯tting schemes for ionospheric correction in astrometry are not the best option as they do not capture the real state of the ionosphere especially if the switching time is greater than the ionospheric TEC variability. However, advantage can be taken of the GPS satellite data available at intervals of a second from the GPS receiver network in South Africa to derive parameters which could be used to correct for the ionospheric delays. Furthermore GPS data can also be used to monitor the occurrence of scintillations, (which might corrupt radio signals) especially for the proposed, Square Kilometer Array (SKA) stations closer to the equatorial belt during magnetic storms and sub-storms. A 10 minute snapshot of GPS data recorded with the Hermanus [34:420 S, 19:220 E ] dual frequency receiver on 2003-04-11 did not show the occurrence of scintillations. This time scale is however too short and cannot be representative. Longer time scales; hours, days, seasons are needed to monitor the occurrence of scintillations.
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Van, der Merwe Carel. "Culprit and victim management RFI environment for a radio astronomy site." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19987.
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Thesis (MScEng)--Stellenbosch University, 2012.<br>ENGLISH ABSTRACT: A methodology is developed to manage the large number of RFI Culprits on a new Radio
Telescope location such as the South African site being developed in the Karoo, both during
construction and ongoing operations. The requirement for RFI control is presented, with brief
reference to the more traditional methods used by other Radio Telescope observatories. The new
approach is then presented, based on methods used in the engineering field of Logistic
Engineering. Three case studies are used to illustrate how the approach can be applied. Finally,
recommendations are made on how the approach can be implemented for new Radio Telescope
projects.<br>AFRIKAANSE OPSOMMING: ‘n Metodolgie word ontwikkel vir die beheer van die groot aantal Radiofrekwensiesteurings
oortreders by ‘n nuwe Radio Teleskoop terrein, soos die Suid Afrikaanse terrein wat huidiglik in die
Karoo ontwikkel word. Die metodolgie geld beide gedurende konstruksie en gedurende bedryf.
Die behoefte vir RFS beheer word aangebied, met kortlikse melding van die meer tradisionele
metodes wat ander Radio Teleskoop Sterrewagte gebruik. ‘n Nuwe aanslag, gebaseer op die
metodolgieë van Logistieke Ingenieurswese, word dan aangebied. Drie gevallestudies wys hoe
hierdie nuwe aanslag toegepas kan word. Laastens word aanbevelings gemaak om hierdie nuwe
aanslag met nuwe Radio Teleskoop projekte te implimenteer.