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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

A study of the pyramid sensor : analytic theory, simulation and experiment

LeDue, Jeffrey Matthew. 10 April 2008 (has links)
The Pyramid Sensor (PS) is a promising wavefront sensor (WFS) for astronomical adaptive optics (AO) due to its potential to increase the number of accessible scientific targets by more efficiently using guide star (GS) photons. This so-called magnitude gain, as well as the key role played by the PS in several novel multi-reference wavefront sensing schemes have generated intense interest in the device. The diffraction based theory of PS and the underlying optical shop test, the Foucault knife-edge test, is reviewed. The theory is applied to calculate the magnitude gain. The impact of the magnitude gain on the number of galaxies accessible to observation with classical A0 on a TMT sized telescope for the Virgo Cluster Catalogue is assessed via simulations. Additional simulation results are shown to elucidate the impact of various parameters of the pyramidal prism on the magnitude gain. The results of experiments conducted in the UVIC A0 lab with a prototype Id PS are discussed. The Id PS uses a novel optical element called a holographic diffuser to linearize the response of the PS to wavefront tilt. The results of calibrating the sensor are given as well as caveats to the use of such a device. The results of using the Id PS to measure a static aberration as well as spatial and temporal characterization of turbulence produced by the UVIC A0 lab's Hot-Air Turbulence Generator are given.

Optimising alignment of a multi-element telescope

Kamga, Morgan M. 23 April 2013 (has links)
A thesis submitted to the Faculty of Science in fulfillment of the requirements of the degree of Doctor of Philosophy School of Computational and Applied Mathematics University of the Witwatersrand September 20, 2012 / In this thesis, we analyse reasons for poor image quality on the Southern African Large Telescope (SALT) and we analyse control methods of the segmented primary mirror. Errors in the control algorithm of SALT (circa 2007) are discovered. More powerful numerical procedures are developed and in particular, we show that singular value decomposition method is preferred over normal equations method as used on SALT. In addition, this method does not require physical constraints to some mirror parameters. Sufficiently accurate numerical procedures impose constraints on the precision of segment actuator displacements and edge sensors. We analyse the data filtering method on SALT and find that it is inadequate for control. We give a filtering method that achieves improved control. Finally, we give a new method (gradient flow) that gives acceptable control from arbitrary, imprecise initial alignment.

An investigation of the fine-pointing control system of a soft-gimbaled orbiting telescope /

Morrell, Frederick R. January 1970 (has links) (PDF)
Thesis (M.S. in Electrical Engineering)--University of Virginia, March 1968. / "June 1970." Submitted in partial fulfillment of the requirements for the degree Master of Electrical Engineering, University of Virginia, Charlottesville, Virginia, March 1968.--Report documentation page. "NASA TN D-5829." "L-6988." Includes bibliographical references (p. 17). Also available online in PDF from NASA Technical Reports Server Web site.

Techniques in high resolution observations from the ground and space, and imaging of the merging environments of radio galaxies at redshift 1 to 4

Steinbring, Eric 03 August 2018 (has links)
High resolution imaging and spectroscopy are invaluable tools for extragalactic astronomy. Galaxies with redshifts of 1 or more subtend a very small angle on the sky—typically, only about an arcsecond. Unfortunately, this is also approximately the angular resolution achieved with a ground-based telescope regardless of its aperture. Atmospheric turbulence ruins the image before it reaches the telescope but the emerging technology of adaptive optics (AO) gives the observer the possibility, within limitations, of correcting for these effects. This is the case for instruments such as the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) and the Gemini North Telescope (Gemini) Altitude-Conjugate Adaptive Optics for the Infrared (Altair) systems. The alternative is to rise above the limitations of the atmosphere entirely and put the telescope in space, for example, the Hubble Space Telescope (HST) and its successor, the Next-Generation Space Telescope (NGST). I discuss several techniques that help overcome the limitations of AO observations with existing instruments in order to make them more comparable to imaging from space. For example, effective dithering and flat-fielding techniques as well as methods to determine the effect of the instrument on the image of, say, a galaxy. The implementation of these techniques as a software package called AOTOOLS is discussed. I also discuss computer simulations of AO systems, notably the Gemini Altair instrument, in order to understand and improve them. I apply my AO image processing techniques to observations of high-redshift radio galaxies (HzRGS) with the CFHT AOB and report on deep imaging in near-infrared (NIR) bands of 6 HzRGs in the redshift range 1.1 ≤ z ≤ 3.8. The NIR is probing the restframe visible light—mature stellar populations—at these redshifts. The radio galaxy is resolved in all of these observations and its ‘clumpier’ appearance at higher redshift leads to the main result—although the sample is very small—that these galaxy environments are undergoing mergers at high redshift. Finally, I look to the future of high resolution observations and discuss simulations of imaging and spectroscopy with the NGST. The computer software NGST VI/MOS is a ‘virtual reality’ simulator of the NGST observatory providing the user with the opportunity to test real observing campaigns. / Graduate

Extremely large segmented mirrors: dynamics, control and scale effects

Bastaits, Renaud 11 June 2010 (has links)
All future Extremely Large Telescopes (ELTs) will be segmented. However, as their size grows, they become increasingly sensitive to external disturbances, such as gravity, wind and temperature gradients and to internal vibration sources. Maintaining their optical quality will rely more and more on active control means. This thesis studies active optics of segmented primary mirrors, which aims at stabilizing the shape and ensuring the continuity of the surface formed by the segments in the face of external disturbances.<p><p>The modelling and the control strategy for active optics of segmented mirrors are examined. The model has a moderate size due to the separation of the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary, or residual response). The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty.<p><p>Scaling laws allowing the extrapolation of the results obtained with existing 10m telescopes to future ELTs and even future larger telescopes are addressed and the most relevant parameters are highlighted. The study is illustrated with a set of examples of increasing sizes, up to 200 segments. This numerical study confirms that scaling laws, originally developed with simple analytical models, can be used in confidence in the preliminary design of large segmented telescopes. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Next generation of wide field adaptive optics

Stoesz, Jeffrey A. 20 January 2010 (has links)
In the last decade, adaptive optics systems have been implemented on all the major ground based telescopes and have proven reliable tools for correcting the image to near the diffraction limit. However, the correction from these systems is limited to a narrow field of view. This dissertation address the challenges of widening the corrected field of single conjugate adaptive optics by properly using statistical information on the optical turbulence profile of the atmosphere above the telescope, and by optimizing the trade-off between image quality and field of view. Altair is the facility adaptive optics system for the 8-meter Gemini North telescope and marks the historical beginning of wide field adaptive optics. Its performance evaluation in Part One is the first on-sky comparison of sparse field images from an altitude-conjugated and a ground-conjugated deformable mirror. All of the other basic aspects of Altair's performance are characterized for use by the Gemini community to plan observations. We also study and report. on techniques for extrapolating the edge of the deformable mirror, a critical step in altitude-conjugated mode. In Part Two we develop a point spread function model for Ground Layer Adaptive Optics (GLAO) that is based on analytic forms of the phase power spectral density. This model has been used for feasibility studies of GLAO on Gemini, and the Thirty Meter Telescope (TMT), currently the most advanced extremely large telescope project. The TMT will be an adaptive telescope that has science goals for the huge 81 square arcminute field of the Wide Field Optical Spectrograph (WFOS). We will show that WFOS-GLAO provides useful gains and will operate in the very wide GLAO (VWGLAO) regime, which has no additional overhead for seeing improved operation. To identify the VWGLAO regime we use statistical turbulence profile models and examine anisoplanatism in terms of image quality metrics relevant to the science that GLAO will likely assist. The VWGLAO regime is where there are useful gains over the theoretical seeing limit for wide field science that measure data collection efficiency as proportional to the product of image quality and the field of view (solid angle). We also show that for many cases VWGLAO will not be impacted by lag anisoplanatism nor by wavefront sensor noise.

Cabling and interfaces for Karoo Array telescopes : modelling and metrology

Van der Merwe, Paul Stephanus 03 1900 (has links)
Thesis (DPhil (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Karoo Array Telescope (KAT) will be used by South Africa in its bid to host the international Square Kilometre Array (SKA). As the SKA will have orders of magnitude greater sensitivity than existing radio telescopes, it will also be concomitantly more sensitive to radio frequency interference (RFI). The influence of RFI on a differential mode (DM) KAT conductive system is an unavoidable phenomenon. In this context, the conductive or galvanic system can, in its most basic form, consist of a source, a load, and connecting conductors. It can also, in the case of the KAT-7 seven-dish interferometer, consist of each telescope, its functional cabling, and the main correlator connecting the telescopes together. However, additional connections between the system and the environment exist. These might be an intentional connection made to the earthing layout, or unintentional connections due to parasitic capacitances and inductive connections. As a result of this, additional conductive systems are created which carry common mode (CM) currents. Interference present in such CM paths enters the DM system through the transfer impedance (Zt) between them. To reduce or eliminate this interference in the DM system, Zt has to be minimised. The use of an earthed parallel conductor (EPC as commonly referred to) in the form of a cable tray is considered to be one of the principal methods to reduce Zt. The properties of cable trays as EPCs at wavelengths which are greater than the tray length are well documented. One main focus in this dissertation is on cable tray mid-span and end connections. They are not well described in the literature over the wide range of frequencies that is expected for KAT developments. The influence of the most common connections on the measured and computed Zt of the cable tray is determined. Computer Simulation Technology’s Microwave Studio (CST MWS) is employed to validate the measured results and also to enable visualisation of the fields and currents. Recommendations for the best connection to use for any cable tray installation is given. The overall shielding ability of optimally-connected cable trays has been evaluated using a physical and computational model. In both cases the induced voltage on a victim conductor, and far-field gain functions for varying angles of incidence onto the model, are determined. The results also show that for certain scenarios, most of the coupling to the victim conductor, takes place inside the end enclosure and not the cable tray. In general, properly-connected cable trays do provide protection to their enclosed conductors, even at frequencies were the wavelength is much shorter than the width of the tray. The second main focus arises from an on-site radio frequency (RF) current audit undertaken on two of the seven KAT-7 telescopes. Shielding measures, such as interface barriers at the floor and roof of the lower telescope pedestal, are studied. The investigation is facilitated by the development of an accurate physical and computational scale model of the dish. Direct current injection and plane wave illumination methods are used to excite the system. The measured CM current distributions are compared and comments made regarding the validity of the measurement procedure. The CM currents, measured around the outside of the lower pedestal show higher levels when a direct current path to ground is established, as opposed to when no clear path exists. This finding suggests at least two methods of preventing CM interference entering or leaving the pedestal: harden the floor and roof barriers, or manage current paths outside the telescope. Related to this, CM currents measured either side of the telescope interface barriers, are used to determine the level of shielding the interface provides. When compared to the common definition of shielding effectiveness, the current measurement provides more conservative shielding estimates. The research in this dissertation has influenced, and will continue to influence, the layout of galvanic systems for the present KAT-7 structures and the anticipated developments to MeerKAT. / AFRIKAANSE OPSOMMING: Die Karoo Array Telescop (KAT) sal gebruik word deur Suid-Afrika in sy poging om die bod te kry om die internasionale Square Kilometre Array (SKA) te huisves. Aangesien die SKA ordes meer sensitief sal wees as bestaande radioteleskope, sal dit terselfdertyd ook meer sensitief wees vir radio frekwensie steurnisse. Die invloed van radio frekwensie steurnisse op die differentiëlemodus KAT geleidende netwerk is iets onvermydeliks. Binne hierdie konteks kan die geleidende netwerk, in sy mees basiese vorm, bestaan uit ʼn bron, ʼn las, en verbindingsgeleiers. Dit kan ook, in die geval van die KAT-7 sewe-teleskoop interferometer, bestaan uit elke teleskoop, sy funksionele bekabeling, en die korrelator wat die verbinding is tussen al die teleskope. Daar is egter, addisionele verbindings tussen die netwerk en die onmiddellike omgewing rondom dit. Hierdie verbindings kan opsetlik gemaak word deur byvoorbeeld, verbinding van die netwerk se aardkabel aan die res van die beaarding, of onopsetlik deur parasitiese kapasitansies en induktiewe verbindings. As gevolg hiervan word addisionele geledende netwerke geskep waarin gemenemodus strome kan vloei. Indien daar wel strome in die gemenemodus netwerk vloei, word dit oorgedra aan die differentiëlemodus netwerk deur ʼn oordragimpedansie (Zt) wat teenwoordig is tussen die twee. Om dus die steurnisse in die differentiëlemodus netwerk te verminder of te elimineer, moet Zt tot ʼn minimum beperk word. Die gebruik van ʼn geaarde parallelle geleier in die vorm van ʼn kabelkanaal, word beskou as een van die mees doeltreffendste metodes om Zt te verminder. Die eienskappe van kabelkanale as geaarde parallelle geleiers by frekwensies waar die golflengtes langer is as die van die kabelkanaal, is volledig gedokumenteer. Een van die belangrikste fokuspunte in hierdie verhandeling is rakende die kabelkanale se middel en eindpuntverbindings. Hulle word nie goed beskryf in die beskikbare literatuur nie, en weliswaar vir wyeband doeleindes wat vir KAT ontwikkelinge verwag word. Die invloed van die mees algemeenste kabelkanaal verbindings op gemete en berekende Zt word bepaal. Computer Simulation Technology’s Microwave Studio (CST MWS) word eerstens, gebruik om die akkuraatheid van die gemete resultate te bewys en tweedens, deur visualisering van E-veld en gemenemodus oppervlak strome. Aanbevelings vir die beste verbindings vir enige kabelkanaal opstelling word gegee. Die algemene afskerminsvermoeë van ʼn idiaal-verbinde kabelkanaal word bepaal deur middel van metings en simulasies. In beide gevalle word die geïnduseerde spanning op ʼn slagoffer kabel, en die verveld aanwins funksie bepaal vir verskillende invalshoeke op die model. Die resultate toon verder dat vir spesifieke gevalle wat beskou word, die meeste koppeling binne die kabinet aan die einde van die kabelkanaal plaasvind. Oor die algemeen verskaf goed verbinde kabelkanale wel ʼn sekere vlak van beskerming aan kabels binne die kabelkanaal, selfs by frekwensies waar die golflengte baie korter is as die breedte van die kabelkanaal. Die tweede belangrike fokuspunt spruit voort uit ʼn radio frekwensie stroomoudit, wat twee van die KAT-7 teleskope evalueer het. Afskermingsmatreëls soos die kabelhindernisse op die vloer en dak van die onderste teleskoop voetstuk, word bestudeer. Tesame met die metings op die werklike teleskoop wat geneem is, word ʼn akkurate fisiese en simulasie skaalmodel geskep om die metings beter te analiseer. Direkte stroominspuitings metode en platvlakgolf beligting word gebruik om gemenemodus strome op die teleskoop se struktuur te induseer. Die gemenemodus stroomverspreiding vir beide tegnieke word vergelyk in ʼn poging om kommentaar te lewer rakende die geldigheid van die meettegniek. Die gemenemodus strome wat aan die buitekant van die teleskoop voetstuk gemeet word, is hoër wanneer ʼn direkte stroompad na grond op die voetstuk geskep word in vergelyking met ʼn ongedefinieerde pad. Hierdie verskynsel dui daarop dat ten minste twee metodes bestaan om die ongevraagde gemenemodus strome te verhoed om aan die binnekant van die teleskoop voetstuk te vloei. Die een is die verbetering van die vloer en dak kabelhindernisse, en die ander is verbetering van die stroompad (stroompaaie) aan die buitekant van die voetstuk sodat ʼn meer direkte pad na grond geskep word. Die gemiddelde gemenemodus strome weerskante van die kabelhindernis, kan gebruik word op te bepaal hoeveel afskerming die hindernis bied. Indien die berekende waardes by verskillende frekwensies vergelyk word met die tradisionele filter doeltreffendheid (Zt), word ʼn meer konserwatiewe beraming verkry. Die navorsing in hierdie verhandeling het alreeds, maar sal ook die toekomstige uitleg van galvaniese stelsels vir KAT-7 asook die verwagte MeerKAT beïnvloed.

Novel architectures for broadband free-space optical communications: deep-space and terrestrial optical links

Hashmi, Ali Javed 22 April 2010 (has links)
The main objective of this research is to design, simulate, and evaluate telescope array-based receiver architectures for the inter-planetary optical communication links, which is able to provide broadband data support for future deep-space and universe exploration missions. The major aspects of this research are as follows: (1) evaluation and performance comparison of telescope arrays-based receiver with a large, monolithic telescope-based receiver, (2) mathematical modeling and analysis of the impact of various limiting factors (i.e., background noise, atmospheric turbulence, synchronization and tracking errors) on the performance of optical array receiver, (3) design and evaluation of subsystems and adaptive signal processing algorithms for the mitigation of the above-mentioned deleterious effects, and (4) development of an end-to-end simulation and analysis platform for an optical communication link between a transmitter in Mars orbit and an Earth-based array receiver after integration of the proposed sub-systems. In the second part of this research, I aim to extend the analysis to the free-space, short-range, terrestrial optical communication links. In this part, the objective is the development of the efficient simulation tools for the analysis of receiver performance and optical beam propagation through turbulent atmospheric channel. In the experimental part of the research, the investigation of the use of adaptive optics (AO) subsystems for turbulence and background noise compensation in the deep-space optical communication links will be carried out.

Astronomical submillimetre Fourier transform spectroscopy from the Herschel Space Observatory and the JCMT

Jones, Scott Curtis, University of Lethbridge. Faculty of Arts and Science January 2010 (has links)
Fourier transform spectroscopy (FTS) is one of the premier ways to collect source information through emitted radiation. It is so named because the principal measurement technique involves the analysis of spectra determined from the Fourier transform of a time-domain interference pattern. Given options in the field, many space- and ground-based instruments have selected Fourier transform spectrometers for their measurements. The Herschel Space Observatory, launched on May 14, 2009, has three on-board instruments. One, SPIRE, comprises a FTS paired with bolometer detector arrays. SCUBA-2 (Submillimetre Common User Bolometer Array) and FTS-2 have recently been commissioned and will be mounted within the collecting dish of the James Clerk Maxwell Telescope by Fall, 2010. The use of FTS in these two observatories will be examined. While work towards each project is independently useful, the thesis is bound by the commonality between the two, as each seeks similar answers from vastly different viewpoints. / xvii, 123 leaves : ill. (some col.) ; 29 cm

Lightning protection and radio frequency interference mitigation for the Karoo Array Telescope

Wiid, P. Gideon 03 1900 (has links)
Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa and Australia are now the two remaining countries bidding for the Square Kilometre Array (SKA), the biggest and most sensitive project ever undertaken in radio astronomy. The South African SKA is demonstrating its technology capabilities through the Karoo Array Telescope (KAT or MeerKAT). The development of KAT is taking place in stages to optimise design and minimise risks at each stage. An array of seven 12 m antennas will be complete by the end of 2009, called KAT-7. The following phase will see the construction of MeerKAT, which will lead to eighty arrayed dishes. Lightning and RFI studies for KAT-7 are the focus of this dissertation. Due to the extent and complexity of the South African demonstrator project, these studies have largely been conducted on a single structure. Parameters for the dish antenna and pedestal design changed throughout their development. To be effective, the doctoral research had to track these changes appropriately. A Method of Moments frequency domain computational electromagnetic code, FEKO, is used throughout the study. The consequences of direct and indirect lightning strikes are examined for the KAT-7 structure. Important FEKO model verification is achieved through measurement of physical scale models in an anechoic chamber. The microwave simulation code, CST, gives direct comparison of FEKO results by using a finite volume time domain method of calculation. Using frequency domain analysis on these models, the lightning down conductor design over the dish antenna bearings is optimised with cost-effectiveness as one driving parameter. RFI coupling levels for different designs are compared to each other to identify areas requiring RFI mitigation. Analysis of resonances enables evaluation of the mitigation at frequencies sensitive to radio astronomy. A Sommerfeld integral ground plane is used together with the computational model to investigate the use of the concrete foundation steel reinforcing as part of the lightning earthing electrode system. Different interconnections of the steel reinforcing elements are critically evaluated. The KAT-7 design incorporated clear lightning protection and RFI mitigation policies derived from recommendations contained within this dissertation. / AFRIKAANSE OPSOMMING: Suid-Afrika en Australie is nou die oorblywende twee lande wat bie vir die Vierkante Kilometer Reeks (SKA), die grootste en mees sensitiewe projek nog ooit in radio astronomie onderneem. Die Suid Afrikaanse SKA demonstreer sy tegnologiese bekwaamheid met die Karoo Reeks Teleskoop (KAT of MeerKAT). Die ontwikkeling van KAT vind plaas in fases om die ontwerp te optimaliseer en risikos te minimaliseer met elke fase. ’n Reeks van sewe 12 m antennas, genaamd KAT-7, sal teen die einde van 2009 klaar wees. Die volgende fase behels die konstruksie van MeerKAT, wat sal lei tot ’n tagtig-skottel reeks. Die fokus van hierdie proefskrif hanteer weerlig en radiofrekwensie steurings (RFS) vir KAT-7. As gevolg van die omvang en kompleksiteit van die Suid-Afrikaanse demonstreerder projek, is die studies hoofsaaklik op een struktuur gedoen. Parameters vir die antenna-skottel en -voetstuk ontwerp het met hul ontwikkeling deurgaans verander. Om effektief te wees, moes die doktorale navorsing hierdie veranderinge toepaslik volg. ’n Metode-van-Momente frekwensiedomein rekenaar elektromagnetiese kode, FEKO, is deurgaans met die studie gebruik. Die gevolge van direkte en indirekte weerligslae vir die KAT-7 struktuur is ondersoek. Belangrike FEKO model bevestiging is bereik met metings van skaalmodelle in ’n anego¨ıse kamer. Die mikrogolf-simulasie kode, CST, gee ’n direkte vergelyking met die FEKO resultate deur ’n eindige-volume-tyd-domein metode van berekening te gebruik. Met behulp van frekwensiedomein analise van hierdie modelle, is die weerligafleierontwerp oor die antenna-skottel laers ge-optimaliseer, met koste-effektiwiteit as een van die drywingsparameters. RFS koppelingsvlakke vir onderskeie ontwerpe is teen mekaar opgeweeg om areas te identifiseer wat RFS tempering benodig. Analise van resonansies stel die evaluering van die tempering in staat teen frekwensies wat sensitief is vir radio astronomie. ’n Sommerfeld integrale grondvlak word saam met die rekenaarmodel gebruik om die insluiting van die beton se staalversterking as deel van die aardingselektrodestelsel te ondersoek. Verskillende bindmetodes van die onderlinge staalversterkingselemente word krities ge¨evalueer. Die KAT-7 ontwerp inkorporeer duidelike weerligbeveiligings- en RFS temperingstrategie ¨e, komende van aanbevelings in hierdie proefskrif omskryf

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