207,097 research outputs found

    Aspects of real-time digital spectral analysis

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    In the field of control engineering there is a need to study the dynamic behaviour of systems which are subjected to random disturbances. A technique which is of great practical use is to describe the dynamic properties as a function of frequency. This involves determining the frequency content, or spectrum, of the disturbances, and the frequency response function of the system. There are many analogue and digital techniques which are designed for this type of spectral analysis. However, digital computer techniques are often avoided because they are slow, and data must be collected 'off-line'. A recently discovered computational method, termed the fast- Fourier-transform (FFT), enables digital spectral analysis to be carried- out in a much shorter time than was previously possible. In view of this discovery it was decided to develop digital computer programmes which would overcome the disadvantages of conventional digital spectral analysis. Using these programmes a computer would be connected, via an analogue to digital interface, to the signal source, and would process the data as it entered the computer. In the jargon of computing, the computer would be 'on-line' and analyzing the spectra in 'real-time'. The first part of the project consisted of an investigation of the FFP when programmed for an on-line digital computer. The results of this investigation showed that a rapid, accurate, and compact FFT could be programmed by using fixed-point arithmetic, and coding in an assembly language. The speed of the transform was sufficient to allow spectral analysis over a frequency range useful in control applications. Two on-line computer programmes based upon the YPP were then written; one for 'real-time' spectral analysis of a single record, and another for the 'real-time' estimation of the frequency response function relating two signals. In order that the results of these programmes could be sensibly interpreted, a statistical study was made of the spectral estimators used in the programmes. Arising from this study, several contributions to the field of digital spectra. analysis were made. These were : - 1) A more general covariance relationship for cross-spectral estimators. 2) An examination of aliasing in digital spectral estimators. 3) Some theoretical results concerning spectral estimators for closed loop systems with random disturbances inside the loop, Some experimental work was conducted with the real-time' spectral analysis programmes, and it was concluded that the tec: inique is more powerful than conventional digital. methods because it is on- line, and can provide estimates with improved resolution and statistical stability. Real-time digital spectral analysis methods also have the advantage that they may be simply and quickly modified to suit specific applications

    Rapid Frequency Estimation

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    Frequency estimation plays an important role in many digital signal processing applications. Many areas have benefited from the discovery of the Fast Fourier Transform (FFT) decades ago and from the relatively recent advances in modern spectral estimation techniques within the last few decades. As processor and programmable logic technologies advance, unconventional methods for rapid frequency estimation in white Gaussian noise should be considered for real time applications. In this thesis, a practical hardware implementation that combines two known frequency estimation techniques is presented, implemented, and characterized. The combined implementation, using the well known FFT and a less well known modern spectral analysis method known as the Direct State Space (DSS) algorithm, is used to demonstrate and promote application of modern spectral methods in various real time applications, including Electronic Counter Measure (ECM) techniques

    Recovering galaxy star formation and metallicity histories from spectra using VESPA

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    We introduce VErsatile SPectral Analysis (VESPA): a new method which aims to recover robust star formation and metallicity histories from galactic spectra. VESPA uses the full spectral range to construct a galaxy history from synthetic models. We investigate the use of an adaptative parametrization grid to recover reliable star formation histories on a galaxy-by-galaxy basis. Our goal is robustness as opposed to high resolution histories, and the method is designed to return high time resolution only where the data demand it. In this paper we detail the method and we present our findings when we apply VESPA to synthetic and real Sloan Digital Sky Survey (SDSS) spectroscopic data. We show that the number of parameters that can be recovered from a spectrum depends strongly on the signal-to-noise, wavelength coverage and presence or absence of a young population. For a typical SDSS sample of galaxies, we can normally recover between 2 to 5 stellar populations. We find very good agreement between VESPA and our previous analysis of the SDSS sample with MOPED.Comment: In press MNRAS, minor revisions to match accepted version by the journa

    SSME propellant path leak detection real-time

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    Included are four documents that outline the technical aspects of the research performed on NASA Grant NAG8-140: 'A System for Sequential Step Detection with Application to Video Image Processing'; 'Leak Detection from the SSME Using Sequential Image Processing'; 'Digital Image Processor Specifications for Real-Time SSME Leak Detection'; and 'A Color Change Detection System for Video Signals with Applications to Spectral Analysis of Rocket Engine Plumes'
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