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High-resolution interferometric diagnostics for ultrashort pulsesAustin, Dane R. January 2010 (has links)
I present several new methods for the characterisation of ultrashort pulses using interferometry. A generalisation of the concatenation algorithm for spectral shearing interferometry enables interferograms taken at multiple shears to be combined. This improves the precision of the reconstructed phase in the presence of detector noise, and enables the relative phase between disjoint spectral components to be obtained without decreasing the spectral resolution. The algorithm is applied to experimental data from two different implementations of spectral shearing interferometry for ultrashort optical pulses. In one, the shears are acquired sequentially, and in the other they are acquired simultaneously. I develop a form of spatio-temporal ultrashort pulse characterisation which performs both spatial and spectral shearing interferometry simultaneously. It requires a similar geometrical setup to common implementations of spectral phase interferometry for direct electric-field reconstruction, but provides complete amplitude and phase characterisation in time and one spatial dimension. I develop the theory of lateral shearing interferometry for spectrally resolved wavefront sensing of extended ultraviolet and soft x-ray pulses generated using high-harmonic generation. A comprehensive set of wavefront measurements of harmonics 13-25 in Krypton show good agreement with theory, validating the technique. I propose and numerically demonstrate quantum-path interferometry mediated by a weak control field for high harmonic generation. This is a general technique for measuring the amplitude and relative phases of each contributing quantum path. The control field perturbatively modulates the phase of each path. The differing sensitivity of each path to the parameters of the control field allows their contributions to be distinguished from one another.
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Quantiative biological microsocopy by digital holographyMann, Christopher J 01 June 2006 (has links)
In this dissertation, improved techniques in digital holography, that have produced high-resolution, high-fidelity images, are discussed. In particular, the angular spectrum method of calculating holographic optical field is noted to have several advantages over the more commonly used Fresnel transformation or Huygens convolution method. It is observed that spurious noise and interference components can be tightly controlled through the analysis and filtering of the angular spectrum. In the angular spectrum method, the reconstruction distance does not have a lower limit, and the off-axis angle between the object and reference waves can be lower than that of the Fresnel requirement, while still allowing the zero-order background to be cleanly separated. Holographic phase images are largely immune from the coherent noise commonly found in amplitude images. With the use of a miniature pulsed laser, the resulting images have 0.5um diffraction-limited lateral resolution and the phase profile is accurate to about several nanometers of optical path length. Samples such as ovarian cancer cells (SKOV-3) and mouse-embryo fibroblast cells have been imaged. These images display intra-cellular and intra-nuclear organelles with clarity and quantitative accuracy. This technique clearly exceeds currently available methods in phase-contrast opticalmicroscopy in both resolution and detail and provides a new modality for imaging morphology of cellular and intracellular structures that is not currently available. Furthermore, we also demonstrate that phase imaging digital holographic movies provide a novel method of non-invasive quantitative viewing of living cells and other objects. This technique is shown to have significant advantages over conventional microscopy.
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Combining body wave tomography, surface wave inversion, seismic interferometry and laboratory measurements to characterize the black shales on Bornholm at different scalesBaumann-Wilke, Maria January 2013 (has links)
Black shales are sedimentary rocks with a high content of organic carbon, which leads to a dark grayish to black color. Due to their potential to contain oil or gas, black shales are of great interest for the support of the worldwide energy supply. An integrated seismic investigation of the Lower Palaeozoic black shales was carried out at the Danish island Bornholm to locate the shallow-lying Alum Shale layer and its surrounding formations and to characterize its potential as a source rock. Therefore, two seismic experiments at a total of three crossing profiles were carried out in October 2010 and in June 2012 in the southern part of the island. Two different active measurements were conducted with either a weight drop source or a minivibrator. Additionally, the ambient noise field was recorded at the study location over a time interval of about one day, and also a laboratory analysis of borehole samples was carried out. The seismic profiles were positioned as close as possible to two scientific boreholes which were used for comparative purposes.
The seismic field data was analyzed with traveltime tomography, surface wave inversion and seismic interferometry to obtain the P-wave and S-wave velocity models of the subsurface. The P-wave velocity models which were determined for all three profiles clearly locate the Alum Shale layer between the Komstad Limestone layer on top and the Læså Sandstone Formation at the base of the models. The black shale layer has P-wave velocities around 3 km/s which are lower compared to the adjacent formations. Due to a very good agreement of the sonic log and the vertical velocity profiles of the two seismic lines, which are directly crossing the borehole where the sonic log was conducted, the reliability of the traveltime tomography is proven. A correlation of the seismic velocities with the content of organic carbon is an important task for the characterization of the reservoir properties of a black shale formation. It is not possible without calibration but in combination with a full 2D tomographic image of
the subsurface it gives the subsurface distribution of the organic material.
The S-wave model obtained with surface wave inversion of the vibroseis data of one of the profiles images the Alum Shale layer also very well with S-wave velocities around 2 km/s. Although individual 1D velocity models for each of the source positions were determined, the subsurface S-wave velocity distribution is very uniform with a good match between the single models. A really new approach described here is the application of seismic interferometry to a really small study area and a quite short time interval. Also new is the selective procedure of only using time windows with the best crosscorrelation signals to achieve the final interferograms. Due to the small scale of the interferometry even P-wave signals can be observed in the final crosscorrelations.
In the laboratory measurements the seismic body waves were recorded for different pressure and temperature stages. Therefore, samples of different depths of the Alum Shale were available from one of the scientific boreholes at the study location. The measured velocities have a high variance with changing pressure or temperature. Recordings with wave propagation both parallel and perpendicular to the bedding of the samples reveal a great amount of anisotropy for the P-wave velocity, whereas the S-wave velocity is almost independent of the wave direction. The calculated velocity ratio is also highly anisotropic with very low values for the perpendicular samples and very high values for the parallel ones. Interestingly, the laboratory velocities of the perpendicular samples are comparable to the velocities of the field experiments indicating that the field measurements are sensitive to wave propagation in vertical direction.
The velocity ratio is also calculated with the P-wave and S-wave velocity models of the field experiments. Again, the Alum Shale can be clearly separated from the adjacent formations because it shows overall very low vP/vS ratios around 1.4. The very low velocity ratio indicates the content of gas in the black shale formation. With the combination of all the different methods described here, a comprehensive interpretation of the seismic response of the black shale layer can be made and the hydrocarbon source rock potential can be estimated. / Schwarzschiefer sind Sedimentgesteine, die einen hohen Gehalt an organischem Kohlenstoff aufweisen, was zu einer dunkelgrauen bis schwarzen Färbung führt. Da Schwarzschiefer das Potenzial besitzen, Öl oder Gas zu enthalten und somit zur weltweiten Energieversorgung beitragen könnten, sind sie von großem Interesse. Mit Hilfe der Kombination verschiedener seismischer Messverfahren wurden die Schwarzschiefer des Unteren Paläozoikums auf der dänischen Insel Bornholm untersucht um den oberflächennahen Alaunschiefer und dessen Umgebungsgestein dort zu lokalisieren und sein Potenzial als Muttergestein abzuschätzen. Dafür wurden im Oktober 2010 und im Juni 2012 im südlichen Teil der Insel zwei seismische Experimente auf insgesamt drei sich kreuzenden Profilen durchgeführt. Für zwei aktive seismische Messungen wurden ein Fallgewicht und ein Minivibrator als Quellen genutzt. Zusätzlich wurde im Messgebiet noch das Wellenfeld des umgebenden Rauschens über einen Zeitraum von etwa einem Tag aufgezeichnet. Außerdem wurden Labormessungen an Bohrkernen aus dem Alaunschiefer durchgeführt. Die seismischen Messprofile befanden sich so nah wie möglich an zwei wissenschaftlichen Bohrungen, die für Vergleichszwecke genutzt wurden.
Um die P- und S-Wellengeschwindigkeitsmodelle des Untergrundes zu erhalten wurden die seismischen Felddaten mittels Laufzeittomographie, Oberflächenwelleninversion und seismischer Interferometrie ausgewertet. Die P-Wellenmodelle, die für alle drei seismischen Profile erstellt wurden, zeigen den Alaunschiefer zwischen dem Komstad Kalkstein, der den Alaunschiefer überdeckt, und der Læså Sandsteinformation, die die Basis der Modelle bildet. Für die Schwarzschieferschicht ergeben sich mit rund 3 km/s deutlich geringere P-Wellengeschwindigkeiten als für die umgebenden Gesteine. Zwei seismische Profile liegen direkt an einer der Bohrungen, für die verschiedene Bohrloch-Logs durchgeführt wurden. Der Vergleich des Sonic-Logs mit den vertikalen Geschwindigkeitsprofilen beider Modelle am Bohrpunkt zeigt eine sehr gute übereinstimmung aller Geschwindigkeiten. Dies ist ein Indiz für die Plausibilität der durchgeführten Laufzeittomographie. Um die Reservoireigenschaften der
Schwarzschieferschicht einordnen zu können, wurde versucht, die seismischen Geschwindigkeiten mit dem Gehalt an organischem Material zu korrelieren. Ohne geeignete Kalibrierung ist diese Korrelation schwierig, kann aber mit Hilfe der Tomographieergebnisse ein zweidimensionales Abbild der Verteilung des organischen Materials im Untergrund liefern.
Auch das S-Wellengeschwindigkeitsmodell, welches mit der Oberflächenwelleninversion der Vibroseisdaten erstellt wurde, bildet den Alaunschiefer gut ab. Hierbei zeigen sich S-Wellengeschwindigkeiten um 2 km/s. Obwohl jeweils nur 1D-Modelle für jede Quellposition bestimmt wurden, ergibt sich für die gesamte Untergrundstruktur des untersuchten Profils ein einheitliches Bild der Geschwindigkeiten. Einen sehr neuen Ansatz bildet die Anwendung der seismischen Interferometrie auf ein sehr kleines Untersuchungsgebiet und über einen sehr kurzen Zeitraum. Neu ist außerdem, dass für die Bestimmung der endgültigen Interferogramme nur Zeitfenster der Kreuzkorrelationen ausgewählt werden, in denen die Signalqualität hinreichend gut ist. In den berechneten Kreuzkorrelationen sind sogar P-Wellen enthalten, was auf die geringen Abstände der seismischen Rekorder zurück zu führen ist.
Bei den Labormessungen wurden die Raumwellen für verschiedene Drücke und Temperaturen aufgezeichnet. Die Messungen der Geschwindigkeiten sowohl parallel als auch senkrecht zur Schichtung der Proben zeigen eine starke Anisotropie für die P-Welle. Dagegen scheint die S-Wellengeschwindigkeit fast unabhängig von der Ausbreitungsrichtung der Wellen zu sein. Auch das Verhältnis der Geschwindigkeiten weist starke Anisotropie auf. Für die Wellenausbreitung senkrecht zur Schichtung zeigen sich sehr niedrige Werte, die Werte für die Messungen parallel zur Schichtung sind dagegen deutlich erhöht. Ein interessanter Aspekt der aus den Labormessungen resultiert ist, dass die Geschwindigkeit der Messungen senkrecht zur Schichtung mit den Geschwindigkeitswerten der Feldmessungen übereinstimmen. Damit scheinen die Feldmessungen besonders die Ausbreitung der Wellen in vertikaler Richtung zu registrieren.
Das Geschwindigkeitsverhältnis wurde auch mit den P- und S-Wellenmodellen der Feldexperimente berechnet. Auch hier hebt sich der Alaunschiefer mit deutlich verringerten Werten um 1.4 vom Umgebungsgestein ab. Solch geringe Werte für das Verhältnis der Geschwindigkeiten deutet auf den Gehalt von Gas im Schwarzschiefer. Mit der Kombination der verschiedenen Methoden ist es möglich, die seismische Antwort der Schwarzschieferschicht umfassend zu beschreiben und Schlussfolgerungen darüber zu ziehen, ob die hier untersuchte Schwarzschieferschicht das Potenzial hat als Kohlenwasserstofflagerstätte zu fungieren.
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Untersuchungen zu gezeitenbedingten Höhenänderungen des subglazialen Lake Vostok, Antarktika / Investigation of tidal induced height variations of the subglacial Lake Vostok, AntarcticaWendt, Anja 08 May 2004 (has links) (PDF)
Lake Vostok, der größte der über 70 subglazialen Seen in der Antarktis, ist derzeit einer der Forschungsschwerpunkte der geowissenschaftlichen Polarforschung. Der See erstreckt sich unter einer 4 000 m dicken Eisschicht auf über 250 km Länge mit einer Wassertiefe von bis zu 1 000 m. Ziel der hier vorliegenden Arbeit ist die Untersuchung des Einflusses der Gezeiten auf den Wasserstand des Sees, die eine bisher nicht betrachtete Komponente in der Zirkulation im See darstellen. Auf Grund seiner Ausdehnung ist das Gezeitenpotential an verschiedenen Punkten auf dem See nicht gleich, sondern weist differentielle Unterschiede auf. Unter der Annahme, dass sich die Seeoberfläche entlang einer Äquipotentialfläche ausrichtet, ergeben sich Gleichgewichtsgezeiten des Sees mit Amplituden von bis zu 4,6 mm für die größte ganztägige Tide K1 und 1,8 mm für die größte halbtägige Tide M2. Differenzen des Luftdruckes zwischen Nord- und Südteil des Sees rufen zusätzlich einen differentiellen inversen Barometer-Effekt hervor. Der inverse Barometer-Effekt besitzt im wesentlichen die spektralen Eigenschaften eines roten Rauschens. Die Variationen erreichen bis zu +/- 20 mm. Zum messtechnischen Nachweis derartiger Höhenänderungen an der Eisoberfläche über dem See wurden drei unterschiedliche Verfahren herangezogen. Differentielle GPS-Messungen zwischen einem Punkt auf aufliegendem Eis und einem zweiten in der südlichen Seemitte bestätigen die Modellvorstellungen und zeigen sowohl mit der Luftdruckdifferenz korrelierte Höhenänderungen als auch Höhenänderungen mit ganz- und halbtägigen Perioden. Die SAR-Interferometrie als flächenhaft arbeitende Methode zur Bestimmung von Höhenänderungen lässt den räumlichen Verlauf der Deformation erkennen. Dabei zeigt sich, dass sich die Aufsetzzone auf dem etwa 50 km breiten See bis in die Seemitte ersteckt. Erdgezeitenregistrierungen, die im Jahr 1969 in der Station Vostok durchgeführt wurden, zeigen zwar Auffälligkeiten wie etwa einen stark erhöhten Luftdruckregressionskoeffzienten und einen Phasenvorlauf der K1-Tide, diese können jedoch nicht eindeutig als Resultat von Höhenänderungen der Seeoberfläche identifiziert werden. Auf Grund der Lage der Station Vostok nahe dem Ufer des Sees ist die Deformation dort schon stark gedämpft. Die zu erwartenden Effekte liegen daher unterhalb der Auflösung der damaligen Messungen. Damit sind die theoretischen Grundvorstellungen über die Reaktion des subglazialen Sees auf Gezeiten- und Luftdruckanregungen herausgearbeitet, sowie diese Effekte mit zwei unabhängigen und komplementären Messverfahren nachgewiesen. / Lake Vostok, the largest of more than 70 subglacial lakes in the Antarctic, is one of the prominent topics of recent geoscientific polar research. The lake extends beneath the 4,000 m thick ice sheet to a length of more than 250 km with a water depth of up to 1,000 m. This thesis aims to investigate the influence of tides on the lake level which has not been considered so far in the discussion of water circulation within the lake. Due to the extent of the lake the tidal potential at different positions on its surface is not equal but exhibits a differential effect. Under the assumption of the lake level to be parallel to an equipotential surface the equilibrium tides of the lake yield amplitudes of up to 4.6 mm for the largest diurnal tidal constituent K1 and 1.8 mm for the largest semi-diurnal wave M2. In addition, differences in air pressure between the northern and the southern part of the lake result in a differential inverse barometric effect. This effect shows red noise characteristics with variations of up to +/- 20 mm. Three different types of measurements were used to verify corresponding height changes of the ice surface above the lake. Differential GPS measurements between one station on grounded ice and one in the southern centre of the lake confirm the concept and show height changes correlated to air pressure differences as well as changes with diurnal and semi-diurnal periods. SAR interferometry as a spatial method to determine height changes reveals the areal extent of the deformation with a grounding zone extending to the centre of the about 50 km wide lake. Gravimetric earth tide data recorded at Vostok Station in 1969 show pecularities such as an increased regression with air pressure and a phase lead of the K1 tide. However, these effects cannot be explicitly attributed to height changes of the lake surface. Due to the position of the station near the edge of the lake the effect is highly attenuated and below the noise level of these measurements. This work introduces the concept of the response of the subglacial lake to the tidal potential and to air pressure forcings and presents evidence for the effect by two different techniques proving the validity of the model.
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Development of confocal optical holographic microscopyMcLeod, Robert A. 06 September 2006 (has links)
Optical Confocal Holography is a combination of two well known concepts: confocal
microscopy and optical (laser) holography. Confocal microscopy places an aperture at a
conjugate focus to the specimen focus. This filters any rays that are not on the focus
plane, allowing a 3-dimensional image of the specimen to be built up over a set of planes.
Holography is the measurement of both the amplitude and phase characteristics of light.
Typically most methods only measure the amplitude of the image. The phenomenon of
interference allows the determination of the phase shift for a coherent source as well. The
phase information is directly related to the index of refraction of a material, which in turn
is a function of the temperature and composition. As a technique, confocal holography
holds promise to better characterize many physical processes in materials science, such as
combustion and convection. It also may contribute to the biological sciences by imaging
low-contrast, weak-phase objects. Thanks to the ongoing, continued improvement in
computer processing speed, it has recently become practical to interpret data from
confocal holography microscopy with a computer. The objective of the microscope is to
non-invasively measure the three-dimensional, internal temperatures and compositions
(e.g. solute/solvent gradient) of a specimen.
My contributions over the course of two years to the project were: generation and
optimization of an optical design with a software package known as Zemax; sourcing and
purchasing all components; formation of a CAD model of the microscope; experiments to
characterize building vibrations and air currents; and the development of software in
Visual Basic to simulate holograms and execute reconstruction algorithms for the specific
application of confocal holography.
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Confocal acoustic holography for non-invasive 3D temperature and composition measurementAtalick, Stefan 03 May 2007 (has links)
This thesis summarizes my work at the University of Victoria to design and evaluate
a proof-of-concept instrument called the Confocal Acoustic Holography Microscope (CAHM).
The instrument will be able to measure small changes in temperature and composition in a
fluid specimen, which can be indirectly measured via small fluctuations in the speed of sound.
The CAHM combines concepts of confocal microscopy, interferometry, and
ultrasonic imaging. This recent work in confocal acoustic holography has progressed from our previous research in confocal laser holography.
The prototype CAHM design uses a frequency of 2.25 MHz, and can measure sound
speed changes of 16 m/s, temperature changes of 5°C, with a spatial resolution of 660 μm.
With future improvements to the CAHM, utilizing the latest technologies such as 2D array detectors, MEMS, and acoustic lenses, we expect resolutions of 1 m/s, 0.5°C, and 150 μm.
The design of the CAHM involved the production of a 3D CAD layout of the optomechanical components and ray tracing simulations using Zemax optical design software. Simulated acoustic holograms and fringe shifts were produced and they were found to match up very well with theoretical calculations. A simplified acoustic holography instrument was built and tested. Speed of sound measurements were made for several test specimens, while keeping temperature constant. Specimens of ethanol, isopropanol, acetic acid, glycerine, and mineral oil were measured. Holograms were collected for acetic acid and mineral oil and were compared to the reference case (distilled water). The fringe spacing and phase shifts measured experimentally matched up well with the Zemax simulations and the theoretical calculations. Hence, the popular Zemax optical software can be effectively used to design acoustic instruments. To our knowledge, this is the first use of Zemax for acoustic designs.
Based on the successful results of the simulations and experiments, the CAHM is
expected to have many useful applications, especially in medical diagnostics where it could be used to measure density and temperature within the human body. Phase contrast images could also be used to help identify suspicious lesions, such as those found in prostate or breast tissue. Other applications include non-destructive testing of electronic and mechanical parts, measurements of fluid samples, material science experiments, and microgravity experiments, where non-invasive examination is required.
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Integrated optical interferometric sensors on silicon and silicon cmosThomas, Mikkel Andrey 14 October 2008 (has links)
The main objective of this research is to fabricate and characterize an optically integrated interferometric sensor on standard silicon and silicon CMOS circuitry. An optical sensor system of this nature would provide the high sensitivity and immunity to electromagnetic interference found in interferometric based sensors in a lightweight, compact package capable of being deployed in a multitude of situations inappropriate for standard sensor configurations. There are several challenges involved in implementing this system. These include the development of a suitable optical emitter for the sensor system, the interface between the various optically embedded components, and the compatibility of the Si CMOS with heterogeneous integration techniques. The research reported outlines a process for integrating an integrated sensor on Si CMOS circuitry using CMOS compatible materials, integration techniques, and emitter components.
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Medium frequency radar studies of meteorsGrant, Stephen Ian January 2003 (has links)
This thesis details the application of a medium frequency (MF) Doppler radar to observations of meteoroids entering the Earth's atmosphere. MF radars make possible a greater height coverage of the meteor region (70 to 160 km) than conventional meteor radars. However this type of radar has generally been under-utilised for meteor observations, primarily due to the less than ideal radio environment associated with MF systems. This situation demanded selection of the most appropriate radar meteor techniques and in this respect a variety of techniques are evaluated for application at this frequency. The 2 MHz radar system used in this study is located at the Buckland Park research facility (35.6 deg. S, 138.5 deg. E), near Adelaide, South Australia and is operated by the Department of Physics of the University of Adelaide. This radar has the largest antenna of any MF radar with 89 crossed dipoles distributed over an area of about 1 km in diameter. Beam forming is achieved by varying the phase to groups of elements of the array. The array was constructed in the 1960's, and while having several upgrades, a preliminary examination of the array and associated systems indicated that a significant amount of maintenance work would be required to enable the system to be used for meteor observations. It was also apparent that the software used with the radar hardware for atmospheric studies was not suitable for processing meteor data. Thus a major refurbishment of the radar hardware, as well as the development of appropriate software, was initiated. The complete radar system was divided into its constituent components of antenna array, transmitter, receiver and computer systems. The transmitter and receiver systems were examined and various improvements made including increasing total output power and enhancing beam steering capability. Time domain reflectometry (TDR) techniques were extensively used on the antenna array, as many feed cables showed the presence of moisture. New hardware in the form of a portable power combining system was designed, constructed and tested to further increase radar experimental capabilities. Techniques were developed that verified system performance was to specification. Extensive night time observations of sporadic and shower meteor events were made over a two and a half year period. A particular study was made of the Orionids shower as well as other meteor activity on the night of 22 October 2000. Using the upgraded beam swinging features of the array, a narrow radar beam was used to track the shower radiant in an orthogonal sense so as to maximise the number of shower meteors detected. From each echo, various intrinsic meteoroid parameters were determined, including meteor reflection point angle-of-arrival using a five-element interferometer, echo duration and height; meteoroid speeds were determined using the Fresnel phase time technique. Meteor echoes belonging to the Orionids radiant were selected using a coordinate transform technique. The speed was then used as an additional discriminant to confirm the Orionid shower members. A second radiant, observed at a slightly higher declination is classified as also part of the Orionid stream. The sporadic meteor component in the data set was examined and found to exhibit speeds much higher than expected for sporadic meteors at the time of the observations. However, these results are consistent with a selection bias based on meteoroid speed, that is inherent in radar observations. The Orionid observations indicate that the refurbishment of the radar system and the introduction of new software for meteor analysis has been successfully achieved and that radar meteor studies can now be carried out routinely with the Buckland Park 2 MHz radar. Moreover it has been shown for the first time that meteoroid speeds can be determined with a MF radar operating on a PRF as low as 60 Hz. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.
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A parallel model for the heterogeneous computation of radio astronomy signal correlationHarris, Christopher John January 2009 (has links)
The computational requirements of scientific research are constantly growing. In the field of radio astronomy, observations have evolved from using single telescopes, to interferometer arrays of many telescopes, and there are currently arrays of massive scale under development. These interferometers use signal and image processing to produce data that is useful to radio astronomy, and the amount of processing required scales quadratically with the scale of the array. Traditional computational approaches are unable to meet this demand in the near future. This thesis explores the use of heterogeneous parallel processing to meet the computational demands of radio astronomy. In heterogeneous computing, multiple hardware architectures are used for processing. In this work, the Graphics Processing Unit (GPU) is used as a co-processor along with the Central Processing Unit (CPU) for the computation of signal processing algorithms. Specifically, the suitability of the GPU to accelerate the correlator algorithms used in radio astronomy is investigated. This work first implemented a FX correlator on the GPU, with a performance increase of one to two orders of magnitude over a serial CPU approach. The FX correlator algorithm combines pairs of telescope signals in the Fourier domain. Given N telescope signals from the interferometer array, N2 conjugate multiplications must be calculated in the algorithm. For extremely large arrays (N >> 30), this is a huge computational requirement. Testing will show that the GPU correlator produces results equivalent to that of a software correlator implemented on the CPU. However, the algorithm itself is adapted in order to take advantage of the processing power of the GPU. Research examined how correlator parameters, in particular the number of telescope signals and the Fast Fourier Transform (FFT) length, affected the results.
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Medium frequency radar studies of meteorsGrant, Stephen Ian January 2003 (has links)
This thesis details the application of a medium frequency (MF) Doppler radar to observations of meteoroids entering the Earth's atmosphere. MF radars make possible a greater height coverage of the meteor region (70 to 160 km) than conventional meteor radars. However this type of radar has generally been under-utilised for meteor observations, primarily due to the less than ideal radio environment associated with MF systems. This situation demanded selection of the most appropriate radar meteor techniques and in this respect a variety of techniques are evaluated for application at this frequency. The 2 MHz radar system used in this study is located at the Buckland Park research facility (35.6 deg. S, 138.5 deg. E), near Adelaide, South Australia and is operated by the Department of Physics of the University of Adelaide. This radar has the largest antenna of any MF radar with 89 crossed dipoles distributed over an area of about 1 km in diameter. Beam forming is achieved by varying the phase to groups of elements of the array. The array was constructed in the 1960's, and while having several upgrades, a preliminary examination of the array and associated systems indicated that a significant amount of maintenance work would be required to enable the system to be used for meteor observations. It was also apparent that the software used with the radar hardware for atmospheric studies was not suitable for processing meteor data. Thus a major refurbishment of the radar hardware, as well as the development of appropriate software, was initiated. The complete radar system was divided into its constituent components of antenna array, transmitter, receiver and computer systems. The transmitter and receiver systems were examined and various improvements made including increasing total output power and enhancing beam steering capability. Time domain reflectometry (TDR) techniques were extensively used on the antenna array, as many feed cables showed the presence of moisture. New hardware in the form of a portable power combining system was designed, constructed and tested to further increase radar experimental capabilities. Techniques were developed that verified system performance was to specification. Extensive night time observations of sporadic and shower meteor events were made over a two and a half year period. A particular study was made of the Orionids shower as well as other meteor activity on the night of 22 October 2000. Using the upgraded beam swinging features of the array, a narrow radar beam was used to track the shower radiant in an orthogonal sense so as to maximise the number of shower meteors detected. From each echo, various intrinsic meteoroid parameters were determined, including meteor reflection point angle-of-arrival using a five-element interferometer, echo duration and height; meteoroid speeds were determined using the Fresnel phase time technique. Meteor echoes belonging to the Orionids radiant were selected using a coordinate transform technique. The speed was then used as an additional discriminant to confirm the Orionid shower members. A second radiant, observed at a slightly higher declination is classified as also part of the Orionid stream. The sporadic meteor component in the data set was examined and found to exhibit speeds much higher than expected for sporadic meteors at the time of the observations. However, these results are consistent with a selection bias based on meteoroid speed, that is inherent in radar observations. The Orionid observations indicate that the refurbishment of the radar system and the introduction of new software for meteor analysis has been successfully achieved and that radar meteor studies can now be carried out routinely with the Buckland Park 2 MHz radar. Moreover it has been shown for the first time that meteoroid speeds can be determined with a MF radar operating on a PRF as low as 60 Hz. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.
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