Application of Compressive Sensing to Weather Radars

The capability and importance of weather radar are proven for hazardous weathers detection, monitoring, and prediction in both research and operations. Continuous efforts have been made in improving radar performance in terms of spatial and temporal resolutions, data quality, new capabilities, etc. On the other hand, compressive sensing (CS) theory has been developed for solving underdetermined problems using l1-norm minimization. It has been shown that CS is capable of reconstructing the sparse images from a limited number of measurements. In this work, CS is specifically applied to two weather radar problems of (1) refractivity retrieval using a network of radars, and (2) retrieving reflectivity and velocity from an imaging radar. In the first study, CS is proposed to improve the refractivity retrieval since the performance of a conventional constraint least squares method can be degraded significantly by the measurement noise and the limited number of high-quality ground returns. The application of CS to refractivity retrieval is formulated using a linear model and subsequently the feasibility is demonstrated and verified using simulations. In the second study, the problem of digital beamforming (DBF) is posed as an inverse problem and formulated using a linear model for both reflectivity and velocity estimation for CS. The application of CS is investigated using both simulation and real data. In simulations, the performance of CS is quantified and compared to the traditional Fourier beamforming and high resolution Capon beamforming for various conditions. The feasibility of CS to weather observations is further demonstrated using the data collected by the Atmospheric Imaging Radar (AIR), developed at the Advanced Radar Research Center (ARRC) of the University of Oklahoma, on 15 April 2012

Image Quality Modeling and Optimization for Non-Conventional Aperture Imaging Systems

The majority of image quality studies have been performed on systems with conventional aperture functions. These systems have straightforward aperture designs and well-understood behavior. Image quality for these systems can be predicted by the General Image Quality Equation (GIQE). However, in order to continue pushing the boundaries of imaging, more control over the point spread function of an imaging system may be necessary. This requires modifications in the pupil plane of a system, causing a departure from the realm of most image quality studies. Examples include sparse apertures, synthetic apertures, coded apertures and phase elements. This work will focus on sparse aperture telescopes and the image quality issues associated with them, however, the methods presented will be applicable to other non-conventional aperture systems. \\ In this research, an approach for modeling the image quality of non-conventional aperture systems will be introduced. While the modeling approach is based in previous work, a novel validation study will be performed, which accounts for the effects of both broadband illumination and wavefront error. One of the key image quality challenges for sparse apertures is post-processing ringing artifacts. These artifacts have been observed in modeled data, but a validation study will be performed to observe them in measured data and to compare them to model predictions. Once validated, the modeling approach will be used to perform a small set of design studies for sparse aperture systems, including spectral bandpass selection and aperture layout optimization

Coded aperture breast tumour imaging using a full-size clinical gamma camera

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Improvements to the alignment process in electron-beam lithography

Electron beam lithography is capable of defining structures with sub-10 nm linewidths. To exploit this capability to produce working devices with structures defined in multiple 'lithographic steps' a process of alignment must be used. The conventional method of scanning the electron beam across simple geometrically shaped markers will be shown inherently to limit the alignment accuracy attainable. Improvements to alignment allow precise placement of elements in complex multi-level devices and may be used to realise structures which are significantly smaller than the single exposure resist limit. Correlation based alignment has been used previously as an alignment technique, providing improvements to the attainable accuracy and noise immunity of alignment. It is well known that the marker pattern used in correlation based alignment has a strong influence on the magnitude of the improvements that can be realised. There has, to date, however, been no analytical study of how the design of marker pattern affects the correlation process and hence the alignment accuracy possible. This thesis analyses the correlation process to identify the features of marker patterns that are advantageous for correlation based alignment. Several classes of patterns have been investigated, with a range of metrics used to determine the suitability and performance of each type of pattern. Penrose tilings were selected on this basis as the most appropriate pattern type for use as markers in correlation based alignment. A process for performing correlation based alignment has been implemented on a commercial electron beam lithography tool and the improvements to the alignment accuracy have been demonstrated. A method of measuring alignment accuracy at the nanometer scale, based on the Fourier analysis of inter-digitated grating has been introduced. The improvements in alignment accuracy realised have been used to facilitate the fabrication of 'nanogap' and 'nanowire' devices - structures which have application in the fields of molecular electronics and quantum conduction. Fabrication procedures for such devices are demonstrated and electrical measurements of such structures presented to show that it is a feasible method of fabrication which offers much greater flexibility than the existing methods for creating these devices

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

The Space and Earth Science Data Compression Workshop

This document is the proceedings from a Space and Earth Science Data Compression Workshop, which was held on March 27, 1992, at the Snowbird Conference Center in Snowbird, Utah. This workshop was held in conjunction with the 1992 Data Compression Conference (DCC '92), which was held at the same location, March 24-26, 1992. The workshop explored opportunities for data compression to enhance the collection and analysis of space and Earth science data. The workshop consisted of eleven papers presented in four sessions. These papers describe research that is integrated into, or has the potential of being integrated into, a particular space and/or Earth science data information system. Presenters were encouraged to take into account the scientists's data requirements, and the constraints imposed by the data collection, transmission, distribution, and archival system

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

MATLAB

A well-known statement says that the PID controller is the "bread and butter" of the control engineer. This is indeed true, from a scientific standpoint. However, nowadays, in the era of computer science, when the paper and pencil have been replaced by the keyboard and the display of computers, one may equally say that MATLAB is the "bread" in the above statement. MATLAB has became a de facto tool for the modern system engineer. This book is written for both engineering students, as well as for practicing engineers. The wide range of applications in which MATLAB is the working framework, shows that it is a powerful, comprehensive and easy-to-use environment for performing technical computations. The book includes various excellent applications in which MATLAB is employed: from pure algebraic computations to data acquisition in real-life experiments, from control strategies to image processing algorithms, from graphical user interface design for educational purposes to Simulink embedded systems