Time-updating IAA-based spectral estimates with missing samples using data interpolation

In this work, we propose a computationally efficient time-updating algorithm for estimating the spectral content of a signal with missing samples. The algorithm extends earlier work on the topic by formulating a data-interpolation scheme reducing the required complexity to a fraction of the earlier efficient implementation, without resulting in any noticeable loss of performance for even a quite large degree of missing samples

DATAMAP upgrade version 4.0

The changes made on the data analysis and management program DATAMAP (Data from Aeromechanics Test and Analytics - Management and Analysis Package) are detailed. These changes are made to Version 3.07 (released February, 1981) and are called Version 4.0. Version 4.0 improvements were performed by Sterling Software under contract to NASA Ames Research Center. The increased capabilities instituted in this version include the breakout of the source code into modules for ease of modification, addition of a more accurate curve fit routine, ability to handle higher frequency data, additional data analysis features, and improvements in the functionality of existing features. These modification will allow DATAMAP to be used on more data sets and will make future modifications and additions easier to implement

Reaction Wheels Fault Isolation Onboard 3-Axis Controlled Satellite using Enhanced Random Forest with Multidomain Features

With the increasing number of satellite launches throughout the years, it is only natural that an interest in the safety and monitoring of these systems would increase as well. However, as a system becomes more complex it becomes difficult to generate a high-fidelity model that accurately describes all the system components. With such constraints using data-driven approaches becomes a more feasible option. One of the most commonly used actuators in spacecraft is known as the reaction wheel. If these reaction wheels are not maintained or monitored, it could result in mission failure and unwarranted costs. That is why fault detection and isolation, which is detecting anomalies in real-time and finding the root cause of the failure, is crucial. This work proposes a novel approach for a data-driven machine learning technique for detecting and isolating multiple in-phase faults in nonlinear systems, with a case-study for an in-orbit closed loop-controlled satellite with reaction wheels as actuators. The proposed method uses a hierarchical approach with automated feature ex-traction, feature reduction and model selection. The method is also studied on three different datasets and three configurations. The results yield a performance accuracy of 98.91%, 97.87%, and 98.02% for all three configurations, respectively. Further-more, sensitivity analysis which includes missing values, missing sensors, and noise, are applied against the proposed method to test its robustness

Advanced Signal Processing For Multi-Mission Airborne Radar

With the technological advancement of the 21st century, functions of different radars are being merged. A multi-functional system brings the technology of remote sensing to a wide array of applications while at the same time reduces costs of implementation and operation. Ground-based multi-mission radars have been studied in the past. The airborne counterpart deserves a through study with additional and stringent requirements of cost, size, weight, and power.In this dissertation, multi-mission functions in an airborne radar is performed using modular, software-based architecture. The software-based solution is chosen instead of proposing new hardware, primarily because evaluation, validation, and certification of new hardware is onerous and time consuming. The system implementations are validated using simulations as well as field measurements. The simulations are carried out using Mathworks® Phased Array System Toolbox. The field measurements are performed using an enhanced commercial airborne radar system called Polarimetric Airborne Radar Operating at X-band Version 1 (PARADOX1), which is an X-band, vertically polarized, solid state, pulsed radar.The shortcomings of PARADOX1 originate from small aperture size and low power. Various signal processing algorithms are developed and applied to PARADOX1 data to enhance the data quality. Super-resolution algorithms in range, angle, and Doppler domains, for example, have proven to effectively enhance the spatial resolution. An end-to-end study of single-polarized weather measurements is performed using PARADOX1 measurements. The results are compared with well established ground-based radars. The similarities, differences as well as limitations (of such comparisons) are discussed. Sense and Avoid (SAA) tracking is considered as a core functionality and presented in the context of safe integration of Unmanned Aerial Vehicles (UAV) in national airspace. A "nearly" constant acceleration motion model is used in conjunction with Kalman Filter and Joint Probabilistic Data Association (JPDA) to perform tracking operations. The basic SAA tracking function is validated through simulations as well as field measurements.The field-validations show that a modular, software-based enhancement to an existing radar system is a viable solution in realizing multi-mission functionalities in an airborne radar. The SAA tracking is validated in ground-based tests using an x86 based PC with a generic Linux operating system. The weather measurements from PARADOX1 and the subsequent data quality enhancements show that PARADOX1 data products are comparable to those of existing ground based radars

Earth Resources: A continuing bibliography with indexes (Issue 37)

This bibliography lists 512 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1 and March 31, 1983. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Discrete-time optimal preview control

There are many situations in which one can preview future reference signals, or future disturbances. Optimal Preview Control is concerned with designing controllers which use this preview to improve closed-loop performance. In this thesis a general preview control problem is presented which includes previewable disturbances, dynamic weighting functions, output feedback and nonpreviewable disturbances. It is then shown how a variety of problems may be cast as special cases of this general problem; of particular interest is the robust preview tracking problem and the problem of disturbance rejection with uncertainty in the previewed signal. . (', The general preview problem is solved in both the Fh and Beo settings. The H2 solution is a relatively straightforward extension ofpreviously known results, however, our contribution is to provide a single framework that may be used as a reference work when tackling a variety of preview problems. We also provide some new analysis concerning the maximum possible reduction in closed-loop H2 norm which accrues from the addition of preview action. / Name of candidate: Title of thesis: I DESCRIPTION OF THESIS Andrew Hazell Discrete-Time Optimal Preview Control The solution to the Hoo problem involves a completely new approach to Hoo preview control, in which the structure of the associated Riccati equation is exploited in order to find an efficient algorithm for computing the optimal controller. The problem tackled here is also more generic than those previously appearing in the literature. The above theory finds obvious applications in the design of controllers for autonomous vehicles, however, a particular class of nonlinearities found in typical vehicle models presents additional problems. The final chapters are concerned with a generic framework for implementing vehicle preview controllers, and also a'case study on preview control of a bicycle.Imperial Users onl

Contribution of the internet towards sustainable development through its economic growth, social capital and environmental effects

Spectacular growth in the use of the Internet has revolutionised many aspects of nations and human lives, including the key pillars of sustainable development such as economic, social and environmental aspects, among others. However, such phenomenal growth in the use of this enabling technology has also led to different forms of social inequalities, popularly known as ‘digital divide’. However, it is not merely the access divide that haunts the digital landscapes of the world today. With the rapid diffusion of the Internet technology, other forms of divide resulting from various factors such as age, education, speed and e-skills are emerging as potential threats to achieving the expected benefits from this general purpose technology. Empirical literature on the effects of the Internet support the view that digital divide potentially hampers the positive effects of the Internet. Currently, this is the central focus of the debate with regards to the potential economic, social and environmental effects of the Internet and the burning question is whether the Internet significantly impacts these three key parameters of sustainable development. This thesis seeks to answer this question through economic growth, social capital and environmental effects of the Internet – in the context of Organization of Economic Cooperation and Development (OECD) countries and in Australia, in particular. To accomplish this aim, this study is guided by four research questions: i) Does Internet use affect economic growth in OECD countries, and in Australia, in particular? ii) Does Internet use affect social capital in OECD countries and in Australia and regional Australia, in particular? iii) Does Internet use have any effect on electricity consumption in OECD countries, and in Australia, in particular? and iv) Does Internet use have any effect on CO2 emissions in OECD countries, and in Australia, in particular? In order to addressing these research questions, this study uses panel macro data for OECD countries, annual time series macro data for Australia, and quantitative survey data from regional Australia. Secondary data are obtained from the World Development Indicators Database of the World Bank. Data on social capital are gathered from the World Values Survey. An advanced panel data econometric estimation technique – the Pooled Mean Group (PMG) regression technique – is applied for panel data analysis, while the Autoregressive Distributed Lag (ARDL) model is used for analysis of time series data. Summated scale method is applied to quantify the social capital variable and multivariate regression technique is employed to examine the Internet–social capital nexus at a regional level. This PhD by publication thesis consists of seven chapters. The Introduction and Conclusions are presented in Chapter one and Chapter seven, respectively. A total of nine research outputs delivered by this research are presented in the remaining five chapters. Research question one is addressed in paper one and paper two. Research question two is addressed in papers three, four and five. Papers six and seven deal with research question three while research question four is addressed in papers eight and nine. Paper one and paper two examine economic growth effects of the Internet for OECD countries and for Australia respectively. In addition to enriching the existing literature on Internet-growth association, these two papers make a contribution by identifying the weaknesses of previous studies. Findings suggest that the Internet stimulates economic growth both for the panel of OECD countries and for Australia as well. Internet use data is analysed for the first time for Australia in paper two. To address research question two, the potential of the Internet in generating social capital is examined in papers three, four and five. Findings from both OECD panel and Australian time series investigations indicate that the Internet reduces social capital in the long run, while it slightly enhances social capital in the short run. Paper five analyses survey data to explore the relationship between the Internet and social capital in regional Australia. The survey data was collected from the Western Downs Region of Queensland. The social capital variable was constructed from five theoretically supported and statistically tested dimensions of social capital concept using summated scale method. These dimensions are; bonding social capital, bridging social capital, trust, neighbourhood effects and community engagement. This is believed to be a novel contribution to the existing literature on social capital measurement which suffers from intense debate on the topic. This paper also provides a conceptual framework on Internet-social capital relationship that may be a useful guideline for similar studies in future in regional context. The key finding indicates a positive relationship between Internet use and social capital implying that Internet-enabled network connectivity stimulates social capital in regional Australia. Research questions three and four deal with the environmental effects of the Internet. Research question three is addressed in papers six and seven – these papers investigate the effect of Internet use on electricity consumption for a panel of OECD countries and for Australia, respectively. In both studies, the Internet is found to cause an increase in electricity consumption. Such findings enforced the development of research question four, which investigates the CO2 emissions effect of the Internet. This is addressed in papers eight and nine. Both investigations found that Internet use does not have any significant effect on CO2 emissions. In other words, the growth in Internet use is still environmentally sustainable for these countries. All of papers six, seven, eight and nine are believed to make important empirical contributions to the literature on the environmental effects of the Internet. The findings from these studies are expected to provide stimuli for future researchers to examine such effects for other regions and countries. The conceptual framework of this study is believed to be a contribution by itself as it studies the effects of the Internet in all three key aspects of sustainable development (economic, social and environmental). Also, the massive literature review of all the three areas will enable future researchers identify research gaps in a relatively easier way for further investigations. This study offers a number of policy recommendations. To ensure expected economic benefits from Internet use, it is recommended in paper one and paper two that demand-side issues – such as education and skills – need more attention from policymakers responsible for framing and revising digital divide policies. Despite mixed findings on the Internet-social capital relationship from papers three, four and five, the inclusion of the social capital issue in digital divide policy should not be ruled out in the process of ensuring long-run success in addressing the digital divide. To achieve energy efficiency gains from the Internet and to exploit its emissions abatement potential, ‘green Internet’ and ‘Internet for green’ are strongly recommended in papers six, seven, eight and nine in order to combat future negative environmental effects of this technology. Finally, the overall findings from the investigations undertaken by this thesis confirm that the growth in the use of the Internet contributes towards sustainable development for the OECD countries as well as for Australia in particular

Colocated multiple-input multiple-output radars for smart mobility

In recent years, radars have been used in many applications such as precision agriculture and advanced driver assistant systems. Optimal techniques for the estimation of the number of targets and of their coordinates require solving multidimensional optimization problems entailing huge computational efforts. This has motivated the development of sub-optimal estimation techniques able to achieve good accuracy at a manageable computational cost. Another technical issue in advanced driver assistant systems is the tracking of multiple targets. Even if various filtering techniques have been developed, new efficient and robust algorithms for target tracking can be devised exploiting a probabilistic approach, based on the use of the factor graph and the sum-product algorithm. The two contributions provided by this dissertation are the investigation of the filtering and smoothing problems from a factor graph perspective and the development of efficient algorithms for two and three-dimensional radar imaging. Concerning the first contribution, a new factor graph for filtering is derived and the sum-product rule is applied to this graphical model; this allows to interpret known algorithms and to develop new filtering techniques. Then, a general method, based on graphical modelling, is proposed to derive filtering algorithms that involve a network of interconnected Bayesian filters. Finally, the proposed graphical approach is exploited to devise a new smoothing algorithm. Numerical results for dynamic systems evidence that our algorithms can achieve a better complexity-accuracy tradeoff and tracking capability than other techniques in the literature. Regarding radar imaging, various algorithms are developed for frequency modulated continuous wave radars; these algorithms rely on novel and efficient methods for the detection and estimation of multiple superimposed tones in noise. The accuracy achieved in the presence of multiple closely spaced targets is assessed on the basis of both synthetically generated data and of the measurements acquired through two commercial multiple-input multiple-output radars

Earth resources: A continuing bibliography with indexes, issue 50

This bibliography lists 523 reports, articles and other documents introduced into the NASA scientific and technical information system between April 1 and June 30, 1986. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis