Robust Ellipsoid Fitting Using Axial Distance and Combination

In random sample consensus (RANSAC), the problem of ellipsoid fitting can be formulated as a problem of minimization of point-to-model distance, which is realized by maximizing model score. Hence, the performance of ellipsoid fitting is affected by distance metric. In this paper, we proposed a novel distance metric called the axial distance, which is converted from the algebraic distance by introducing a scaling factor to solve nongeometric problems of the algebraic distance. There is complementarity between the axial distance and Sampson distance because their combination is a stricter metric when calculating the model score of sample consensus and the weight of the weighted least squares (WLS) fitting. Subsequently, a novel sample-consensus-based ellipsoid fitting method is proposed by using the combination between the axial distance and Sampson distance (CAS). We compare the proposed method with several representative fitting methods through experiments on synthetic and real datasets. The results show that the proposed method has a higher robustness against outliers, consistently high accuracy, and a speed close to that of the method based on sample consensus.Comment: 13 page

Radio transients: Surveys and Techniques

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

Investigations into a multiplexed fibre interferometer for on-line, nanoscale, surface metrology

Current trends in technology are leading to a need for ever smaller and more complex featured surfaces. The techniques for manufacturing these surfaces are varied but are tied together by one limitation; the lack of useable, on-line metrology instrumentation. Current metrology methods require the removal of a workpiece for characterisation which leads to machining down-time, more intensive labour and generally presents a bottle neck for throughput. In order to establish a new method for on-line metrology at the nanoscale investigation are made into the use of optical fibre interferometry to realise a compact probe that is robust to environmental disturbance. Wavelength tuning is combined with a dispersive element to provide a moveable optical stylus that sweeps the surface. The phase variation caused by the surface topography is then analysed using phase shifting interferometry. A second interferometer is wavelength multiplexed into the optical circuit in order to track the inherent instability of the optical fibre. This is then countered using a closed loop control to servo the path lengths mechanically which additionally counters external vibration on the measurand. The overall stability is found to be limited by polarisation state evolution however. A second method is then investigated and a rapid phase shifting technique is employed in conjunction with an electro-optic phase modulator to overcome the polarisation state evolution. Closed loop servo control is realised with no mechanical movement and a step height artefact is measured. The measurement result shows good correlation with a measurement taken with a commercial white light interferometer

Probing Power-Absorbing Structures at Near-Infrared Wavelengths using Energy Absorption Interferometry

Energy Absorption Interferometry was recently proposed as an interferometric technique capable of fully characterizing the optical response of single-mode, few-mode and multi- mode power-absorbing structures, such as near-infrared detectors. A detector’s output can be written as the full spatial contraction of the external field correlation tensor and detector response correlation tensor representing their respective spatial coherence states; EAI recovers the latter, solely using power measurements. EAI is essentially a generalization of holography, and allows the reconstruction of the individual degrees of freedom through which the device under test can absorb energy, including their relative sensitivities and spatial forms. The natural modes of the detector response are intimately related to its optical coupling mechanisms and the underlying solid-state phenomena responsible for power absorption: their study therefore has direct applications in improving current infrared detector technology. In particular, device properties dependent on its geometry and material are directly obtained, such as the absorber’s spatial coherence length. EAI yields an experimental procedure where the system under test is excited with two external coherent sources, and the fringe in the total power dissipated is measured as the relative phase between the sources is varied. Iterating for multiple source positions, the fringes’ complex amplitudes allow the two-point detector response function to be retrieved: this correlation function can then be decomposed into a set of natural modes. In this thesis, we demonstrate the application of EAI at near-infrared wavelengths. We describe the theoretical basis of EAI and numerically investigate its feasibility at infrared wavelengths. We present for the first time the design of a room-temperature, fiber-based, 1550 nm-wavelength experiment and its performance. We report the first measurement of the complex-valued DRF of fiber-coupled photodetectors, with single-mode, few-mode and multi-mode behaviors; this includes extending the experimental system to suppress environmental phase drift in optical fibers. We recover the natural modes of the devices under test, and compare their spatial forms to numerical simulations. Finally, we discuss the application of EAI to many-body structures as varied as spin systems and energy-harvesting absorbers, and its extension to measure quantum correlation functions using a pair of probes creating generalized forces

Pathfinding Fast Radio Bursts Localizations using Very Long Baseline Interferometry

Fast radio bursts (FRBs) are millisecond-duration, bright radio transients of extragalactic origin. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope’s CHIME/FRB instrument and other radio telescopes across the globe have detected hundreds of FRBs. Their origins are a mystery. Precise localization within the host is critical to distinguish between progenitor models. This can be achieved through Very Long Baseline Interferometry (VLBI). Until now, VLBI localizations have only been carried out in targeted follow-up observations of some repeating sources which comprise a small fraction of the FRBs. For this work, an interferometric array of 6m dishes was constructed at the Green Bank Observatory as a pathfinder to develop the necessary systems, technology, and techniques to enable VLBI on FRBs. This array called TONE has 8 instrumented dishes and works as a VLBI outrigger for CHIME on a \SI{\sim3300}{\kilo\meter} baseline. This involved construction, commissioning, and integration of the custom analog chains and digital system. TONE is pointed to shadow a portion of the CHIME primary beam at a fixed declination of \SI{22}{\deg}. Upon detection of a single dispersed pulse such as an FRB or a giant pulse from the Crab pulsar, CHIME alerts TONE, triggering a recording of buffered data to disk. In addition to TONE, a single 10-m dish at Algonquin Radio Observatory (ARO10) is set up with a similar infrastructure. Together they form the pathfinders for conducting VLBI for FRBs. We used these VLBI pathfinders to localize FRB 20210603A at the time of detection. The baseband data from CHIME and TONE are used to synthesize single beams at each telescope. The single-beam data from TONE and data from ARO10 are each cross-correlated with the single beam data from CHIME. We use the Crab pulsar for astrometric calibration and additionally correct for clock errors. The calibrated and corrected cross-correlated data is sampled with a likelihood function of the sky location and ionospheric effects using a Markov Chain Monte Carlo method to estimate the Right Ascension and Declination of the FRB. We localize the burst to SDSS J004105.82+211331.9, an edge-on quiescent lenticular galaxy at redshift z $\approx 0.177$. The localization, dispersion measure, rotation measure (RM), and temporal broadening are consistent with an observed line-of-sight through the host galactic disk, suggesting a progenitor from a population coincident with the host galactic plane. The development of the TONE telescope has enabled the localization of the FRB within the host. This is a key stepping stone towards constraining the origins and host environments of FRBs

Transverse Diagnostics For High Energy Hadron Colliders

The Large Hadron Collider (LHC) is a circular synchrotron accelerator that will explore new Physics at the higher energies ever achieved, aiming to find the Higgs boson. The LHC is being built at CERN and by 2007 it will be ready to produce head-on collisions of protons at a centre-of-mass energy of 14 TeV. The employment of superconducting magnets for achieving high energies, the high luminosity required for physics, the limited dynamic aperture and the large energy stored in the beams will make the machine very challenging to operate, especially during the injection process and the energy ramp. Two particular problems will be a high sensitivity to beam losses and a relatively poor field quality requiring the use of many types of magnetic correction elements. This may lead to the inclusion of certain beam measurements in feedback loops, making special demands on the control system. The injection and acceleration of the LHC proton beams without particle losses and emittance blow up will require an accurate control of the beam parameters. The value of the betatron tune is about 63 units and needs to be controlled to a level of $\Delta Q = ±0.003$. Orbit excursions should be limited to less than 0.5 mm. The linear chromaticity should be limited to some units (nominal value $Q'_HV = 2$). This Thesis will be focused on the improvement of new instrumentation for the measurement of beam parameters that is compatible with LHC high intens ity running. In this sense, the importance for the performance of the accelerator of terms such as tune or chromaticity will be pointed out. This work can be considered to be divided into two differentiated parts: the tests performed to a potentially beam diagnostics device and the improvement of the sensitivity of an already existing monitor. However, behind both subjects there is a common objective: the need of implementing new sensitive and non destructive methods for measuring parameters of major importance to keep the beam within the tight tolerances imposed to the superconducting and high energy accelerator LHC

Contributions to GNSS-R earth remote sensing from nano-satellites

Premi extraordinari doctorat UPC curs 2015-2016, àmbit de CiènciesGlobal Navigation Satellite Systems Reflectometry (GNSS-R) is a multi-static radar using navigation signals as signals of opportunity. It provides wide-swath and improved spatio-temporal sampling over current space-borne missions. The lack of experimental datasets from space covering signals from multiple constellations (GPS, GLONASS, Galileo, Beidou) at dual-band (L1 and L2) and dual-polarization (Right Hand Left Hand Circular Polarization: RHCP and LHCP), over the ocean, land and cryosphere remains a bottleneck to further develop these techniques. 3Cat-2 is a 6 units (3 x 2 elementary blocks of 10 x 10 x 10 cm3) CubeSat mission ayming to explore fundamentals issues towards an improvement in the understanding of the bistatic scattering properties of different targets. Since geolocalization of specific reflections points is determined by the geometry only, a moderate pointing accuracy is still required to correct for the antena pattern in scatterometry measurements. 3Cat-2 launch is foreseen for the first quarter 2016 into a Sun-Synchronous orbit of 510 km height using a Long March II D rocket. This Ph.D. Thesis represents the main contributions to the development of the 3Cat-2 GNSS-R Earth observation mission (6U CubeSat) including a novel type of GNSS-R technique: the reconstructed one. The desing, development of the platform, and a number of ground-based, airborne and stratospheric balloon experiments to validate the technique and to optimize the instrument. In particular, the main contributions of this Ph.D. thesis are: 1) A novel dual-band Global Navigation Satellite Systems Reflectometer that uses the P(Y) and C/A signals scattered over the sea surface to perform highly precise altimetric measurements (PYCARO). 2) The first proof-of-concept of PYCARO was performed during two different ground-based field experiments over a dam and over the sea under different surface roughness conditions. 3) The scattering of GNSS signals over a water surface has been studied when the receiver is at low height, as for GNSS-R coastal altimetry applications. The precise determination of the local sea level and wave state from the coast can provide useful altimetry and wave information as "dry" tide and wave gauges. In order to test this concept an experiment has been conducted at the Canal d'Investigació i Experimentació Marítima (CIEM) wave channel for two synthetic "sea" states. 4) Two ESA-sponsored airborne experiments were perfomed to test the precision and the relative accuracy of the conventional GNSS-R. 5) The empirical results of a GNSS-R experiment on-board the ESA-sponsored BAXUS 17 stratospheric balloon campaign performed North of Sweden over boreal forests showed that the power of the reflected signals is nearly independent of the platform height for a high coherent integration time. 6) An improved version of the PYCARO payload was tested in Octover 2014 for the second time during the ESA-sposored BEXUS-19,. This work achieved the first ever dual-frequency, multi-constellation GNSS-R observations over boreal forests and lakes using GPS, GLONASS and Galileo signals. 7) The first-ever dual-frequency multi-constellation GNSS-R dual-polarization measurements over boreal forests and lakes were obtained from the stratosphere during the BEXUS 19 using the PYCARO reflectometer operated in closed-loop mode.Global Navigation Satellite Systems Reflectometry (GNSS-R) es una técnica de radar multi-estático que usa señales de radio-navegación como señales de oportunidad. Esta técnica proporciona "wide-swath" y un mejor sampleado espacio-temporal en comparación con las misiones espaciales actuales. La falta de datos desde el espacio proporcionando señales de múltiples constelaciones (GPS, GLONASS, Galileo, Beidou) en doble banda (L1 y L2) y en doble polarización (RHCP y LHCP) sobre océano, tierra y criosfera continua siendo un problema por solucionar. 3Cat-2 es un cubesat de 6 unidades con el objetivo de explorar elementos fundamentales para mejorar el conocimiento sobre el scattering bi-estático sobre diferentes medios dispersores. Dado que la geolocalización de puntos de reflexión específicos está determinada solo por geometría, es necesario un requisito moderado de apuntamiento para corregir el diagrama de antena en aplicaciones de dispersometría. El lanzamiento del 3Cat-2 será en Q2 2016 en una órbitra heliosíncrona usando un cohete Long March II D. Esta tesis representa las contribuciones principales al desarrollo del satélite 3Cat2 para realizar observación de la tierra con GNSS-R incluyendo una nueva técnica: "the reconstructed-code GNSS-R". El diseño, desarrollo de la plataforma y un número de experimentos en tierra, desde avión y desde globo estratosférico para validar la técnica y optimizar el instrumento han sido realizados. En particular, las contribuciones de esta Ph.D. son: 1) un novedoso Global Navigation Satellite Systems Reflectometer que usa las señales P(Y) y C/A después de ser dispersadas sobre la superficie del mar para realizar medidas altimétricas muy precisas. (PYCARO). 2) La primera prueba de concepto de PYCARO se hizo en dos experimentos sobre un pantano y sobre el mar bajo diferentes condiciones de rugosidad. 3) La disperión de las señales GNSS sobre una superfice de agua ha sido estudiada para bajas altitudes para aplicaciones GNSS-R altimétricas de costa. La determinación precisa del nivel local del mar y el estado de las olas desde la costa puede proporcionar información útil de altimetría e información de olas. Para hacer un test de este concepto un experimento en el Canal d'Investigació i Experimentació Marítima (CIEM) fue realizado para dos estados sintéticos de rugosidad. 4) Dos experimentos en avión con esponsor de la ESA se realizaron para estudiar la preción y la exactitud relativa de cGNSS-R. 5) Los resultados empíricos del experimento GNSS-R en BEXUS 17 con esponsor de la ESA realizado en el norte de Suecia sobre bosques boreales mostró que la potencia reflejada de las señales es independiente de la altitud de la plataforma para un tiempo de integración coherente muy alto. 6) Una versión mejorada del PYCARO fue testeada en octubre del 2014 por segunda vez durante el BEXUS 19 que también fue patrocidado por la ESA. Este trabajo proporcionó las primeras medidas GNSS-R sobre bosques boreales en doble frecuencia usando varias constelaciones GNSS. 7) Las primeras medidas polarimétricas (RHCP y LHCP) de GNSS-R sobre bosques boreales también fueron conseguidas durante el experimento BEXUS 19.Award-winningPostprint (published version

Optical direct detection of thermal vibrations of ultralow stiffness micro-nano structures.

A direct detection optical vibrometer is constructed around an 850 nm laser and a quadrant photodetector (QPD). The limit of detection is 0.2 fW which corresponds to a minimum amplitude of 0.1 Å. The vibrometer is used to measure the thermal vibration spectra of low stiffness micromechanical structures have nanometer features. One structure measured is a cantilevered 30 μm diameter glass fiber. Vibration amplitudes as low as 1.1 Å are measured. The thermal vibration spectra show fundamental resonances at 80-250 Hz and a signal to noise ratio (SNR) of 23-55 dB. Young’s modulus of glass in the cantilevers, estimated from the spectra, agree to within 3 % of the manufacturer’s value, which is somewhat more accurate than force-elongation measurements made of 50-100 mm long fibers which differ by 5 %. Mass changes due to adhering small drops of liquids to the tip of the fiber cantilevers shifts the resonant frequency with a sensitivity of 120 ng. The mass detection limit would decrease by 2-3 orders by increasing the length of the time series data. The intended purpose of the vibrometer development is the measurement of the thermal vibration of polymer bead-on-string (BOS) fibers with enough sensitivity to detect time-varying changes in the spectra that relate to molecular-level and temperature dependent changes, such as evaporation, solidification, crystallization and strain-dependent chain reorganizations of the polymer material. Time dependent variations in the BOS spectra are observed in vibrometer measurements that, if attributable to material properties, would represent 2.5-5.2 % change in elastic modulus, 20-40 % loss in water mass due to evaporation, with the minimum detectable change in these properties being 0.06 % for the measured spectra. The vibrometer provides an important tool for the real-time study of changing properties of BOS fibers, as well as other low stiffness microstructures, especially those composed of polymers and other soft mater