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A Multi-Layer Phoswich Radioxenon Detection System

Description: Laboratory radioactive sources were used to characterize the phoswich detector. The CaF{sub 2} scintillator has a low light-yield and slow decay time, thus produces very small signals due to low-energy gamma rays or X-rays. Therefore, detection of 30 keV X-rays (from the xenon radioisotopes) using this layer and discriminating its very small signals from electronic noise was a challenging task. Several solutions were considered and experimentally evaluated. We found that the best solution would be extending the fast triangular filter from 10 taps to 30 taps. This will extend the peaking time of this filter from 25 nsec to 75 nsec. The digital filter is implemented in FPGA on our DPP2.0 and is used to trigger the detection system. Functionality of the new filter in capturing and discriminating 30 keV X-rays was confirmed by using a {sup 133}Ba gamma-ray source. Development of the DPP GUI software has continued with the addition of two new panels to display histograms of beta/gamma and beta/x-ray coincidence events. This includes coincidence events from a single channel, as well as two-channel, coincidence event. A pileup rejection algorithm has been implemented in the FPGA code, and controls to adjust its sensitivity have been added to the GUI. Work has begun on a new prototype system to develop a USB host interface between the PC and the FPGA to end reliance on Opal Kelly prototyping boards; the hardware for this system has been completely assembled, and the PC-side software is currently in development.
Date: July 14, 2008
Creator: Hamby, David M.
Partner: UNT Libraries Government Documents Department

Modeling laser wakefield accelerators in a Lorentz boosted frame

Description: Modeling of laser-plasma wakefield accelerators in an optimal frame of reference is shown to produce orders of magnitude speed-up of calculations from first principles. Obtaining these speedups requires mitigation of a high-frequency instability that otherwise limits effectiveness in addition to solutions for handling data input and output in a relativistically boosted frame of reference. The observed high-frequency instability is mitigated using methods including an electromagnetic solver with tunable coefficients, its extension to accomodate Perfectly Matched Layers and Friedman's damping algorithms, as well as an efficient large bandwidth digital filter. It is shown that choosing the frame of the wake as the frame of reference allows for higher levels of filtering and damping than is possible in other frames for the same accuracy. Detailed testing also revealed serendipitously the existence of a singular time step at which the instability level is minimized, independently of numerical dispersion, thus indicating that the observed instability may not be due primarily to Numerical Cerenkov as has been conjectured. The techniques developed for Cerenkov mitigation prove nonetheless to be very efficient at controlling the instability. Using these techniques, agreement at the percentage level is demonstrated between simulations using different frames of reference, with speedups reaching two orders of magnitude for a 0.1 GeV class stages. The method then allows direct and efficient full-scale modeling of deeply depleted laser-plasma stages of 10 GeV-1 TeV for the first time, verifying the scaling of plasma accelerators to very high energies. Over 4, 5 and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV and 1 TeV class stages, respectively.
Date: June 15, 2010
Creator: Vay, J.-L.; Geddes, C.G.R.; Cormier-Michel, E. & Grotec, D. P.
Partner: UNT Libraries Government Documents Department

Nonlinear image filtering within IDP++

Description: IDP++, image and data processing in C++, is a set of a signal processing libraries written in C++. It is a multi-dimension (up to four dimensions), multi-data type (implemented through templates) signal processing extension to C++. IDP++ takes advantage of the object-oriented compiler technology to provide ``information hiding.`` Users need only know C, not C++. Signals or data sets are treated like any other variable with a defined set of operators and functions. We here some examples of the nonlinear filter library within IDP++. Specifically, the results of MIN, MAX median, {alpha}-trimmed mean, and edge-trimmed mean filters as applied to a real aperture radar (RR) and synthetic aperture radar (SAR) data set.
Date: February 9, 1995
Creator: Lehman, S.K.; Wieting, M.G. & Brase, J.M.
Partner: UNT Libraries Government Documents Department

Lossless compression of weight vectors from an adaptive filter

Description: Techniques for lossless waveform compression can be applied to the transmission of weight vectors from an orbiting satellite. The vectors, which are a part of a hybrid analog/digital adaptive filter, are a representation of the radio frequency background seen by the satellite. An approach is used which treats each adaptive weight as a time-varying waveform.
Date: August 1, 1994
Creator: Bredemann, M. V.; Elliott, G. R. & Stearns, S. D.
Partner: UNT Libraries Government Documents Department

Comparison of filter predictions with satellite observations

Description: Satellite observations of meteor entry are used to calibrate a filter model of fragmentation. Predicted sizes and masses compare favorably with data and analytic interpretations for objects of all sizes. However, objects that fragment into many large objects should be treated by the decomposition of the radiation signal into the contributions from the different fragments.
Date: October 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department

Block-classified bidirectional motion compensation scheme for wavelet-decomposed digital video

Description: In this paper the authors introduce a block-classified bidirectional motion compensation scheme for the previously developed wavelet-based video codec, where multiresolution motion estimation is performed in the wavelet domain. The frame classification structure described in this paper is similar to that used in the MPEG standard. Specifically, the I-frames are intraframe coded, the P-frames are interpolated from a previous I- or a P-frame, and the B-frames are bidirectional interpolated frames. They apply this frame classification structure to the wavelet domain with variable block sizes and multiresolution representation. They use a symmetric bidirectional scheme for the B-frames and classify the motion blocks as intraframe, compensated either from the preceding or the following frame, or bidirectional (i.e., compensated based on which type yields the minimum energy). They also introduce the concept of F-frames, which are analogous to P-frames but are predicted from the following frame only. This improves the overall quality of the reconstruction in a group of pictures (GOP) but at the expense of extra buffering. They also study the effect of quantization of the I-frames on the reconstruction of a GOP, and they provide intuitive explanation for the results. In addition, the authors study a variety of wavelet filter-banks to be used in a multiresolution motion-compensated hierarchical video codec.
Date: August 1, 1997
Creator: Zafar, S.; Zhang, Y.Q. & Jabbari, B.
Partner: UNT Libraries Government Documents Department

Statistical signal processing and artificial intelligence applications in the nondestructive assay of U/Pu bearing materials

Description: Over the years a number of techniques have been developed to determine the quantity and distribution of radiative isotopes contained in given assay samples through the measurement and analysis of penetrating characteristic radiations. An active technique of particular utility when assaying samples containing very small quantities of fissionable material or when high gamma ray backgrounds are encountered is the delayed neutron nondestructive assay (DN-NDA) technique. Typically, analysis of the delayed neutron signal involves relating the gross delayed neutron count observed following neutron irradiation of an assay sample to total fissionable material present via a linear calibration curve. In this way, the technique is capable of yielding the mass of a single dominant fissionable isotope or the total fissionable mass contained in a sample. Using this approach the only way to determine the mass of individual fissionable isotopes contained in a sample is to correlate total fissionable mass to individual isotopics via calculations or other means, yielding an indirect measure of isotopics. However, there is isotope specific information in the temporal delayed neutron signal due to differences in the delayed neutron precursor yields resulting from the fissioning of different isotopes. The authors present the results of an analysis to evaluate the feasibility of using Kalman filters and genetic algorithms to determine multiple specific fissionable isotopic masses contained in an assay sample from a cumulative delayed neutron signal measured following neutron irradiation of the sample.
Date: October 1, 1997
Creator: Aumeier, S.E. & Forsmann, J.H.
Partner: UNT Libraries Government Documents Department

Construction of filter vectors for the information-efficient spectral imaging sensor

Description: The information-efficient spectral imaging sensor (ISIS) seeks to improve system performance by processing hyperspectral information in the optical hardware. Its output may be a gray scale image in which one attempts to maximize the contrast between a given target and the background. Alternatively, its output may be a small number of images, rather than a full data cube, that retain the essential information required in the application. The principal advantage of ISIS is that it offers the discrimination of hyperspectral imaging while achieving the signal-to-noise ratio of multispectral imaging. The paper focuses on construction of the filter vectors that are needed to program ISIS. The instrument produces an image which is essentially a dot product of the scene and the filter vector. Both single vector and multiple vector approaches are considered. Also, they discuss some subtle points related to optimizing the filter vectors.
Date: December 1, 1998
Creator: Stallard, B.R. & Gentry, S.M.
Partner: UNT Libraries Government Documents Department

Peak finding using biorthogonal wavelets

Description: The authors show in this paper how they can find the peaks in the input data if the underlying signal is a sum of Lorentzians. In order to project the data into a space of Lorentzian like functions, they show explicitly the construction of scaling functions which look like Lorentzians. From this construction, they can calculate the biorthogonal filter coefficients for both the analysis and synthesis functions. They then compare their biorthogonal wavelets to the FBI (Federal Bureau of Investigations) wavelets when used for peak finding in noisy data. They will show that in this instance, their filters perform much better than the FBI wavelets.
Date: February 1, 2000
Creator: Tan, C.Y.
Partner: UNT Libraries Government Documents Department

Salvaging transient data with overloads and zero offsets

Description: The authors are sometimes presented with data with serious flaws, like overloads, zero shifts, and impulse noise, including much of the available pyrotechnic data. Obviously, these data should not be used if at all possible. However, they are sometimes forced to use these data as the only data available. Methods to salvage these data are discussed. Using the methods requires judgment, and the results must be accepted with the understanding that the answers are credible, not necessarily correct. None of the methods will recover information lost due to overloads or non-linearities of the data system. The best that can be accomplished is the recovery of data, after the data system has recovered from the overload. Several correction methods are discussed: high pass filtering of the data, correction with two forms of an exponential function, and a correction with the form t exp({minus}{alpha}t). Examples showing the results of the methods will be given using flawed pyrotechnic data.
Date: October 21, 1997
Creator: Smallwood, D.O. & Cap, J.S.
Partner: UNT Libraries Government Documents Department

Automatic feature detection and identification in digital point-ordered signals

Description: A computer-based automated method to detect and identify features in digital point-ordered signals. The method is used for processing of non-destructive test signals, such as eddy current signals obtained from calibration standards. The signals are first automatically processed to remove noise and to determine a baseline. Next, features are detected in the signals using mathematical morphology filters. Finally, verification of the features is made using an expert system of pattern recognition methods and geometric criteria. The method has the advantage that standard features can be located without prior knowledge of the number or sequence of the features. Further advantages are that standard features can be differentiated from irrelevant signals features such as noise, and detected features are automatically verified by parameters extracted from the signals. The method proceeds fully automatically without initial operator set-up and without subjective operator feature judgment.
Date: December 31, 1995
Creator: Oppenlander, J.E.; Loomis, K.C.; Brudnoy, D.M. & Levy, A.J.
Partner: UNT Libraries Government Documents Department

A wavelet phase filter for emission tomography

Description: The presence of a high level of noise is a characteristic in some tomographic imaging techniques such as positron emission tomography (PET). Wavelet methods can smooth out noise while preserving significant features of images. Mallat et al. proposed a wavelet based denoising scheme exploiting wavelet modulus maxima, but the scheme is sensitive to noise. In this study, the authors explore the properties of wavelet phase, with a focus on reconstruction of emission tomography images. Specifically, they show that the wavelet phase of regular Poisson noise under a Haar-type wavelet transform converges in distribution to a random variable uniformly distributed on [0, 2{pi}). They then propose three wavelet-phase-based denoising schemes which exploit this property: edge tracking, local phase variance thresholding, and scale phase variation thresholding. Some numerical results are also presented. The numerical experiments indicate that wavelet phase techniques show promise for wavelet based denoising methods.
Date: July 1, 1995
Creator: Olsen, E.T. & Lin, B.
Partner: UNT Libraries Government Documents Department

Edge and line enhancement by adaptive lattice filtering. [Haar transform]

Description: Digitized images were two-dimensionally transformed to the Haar sequency domain. High-sequency boosting was performed, and the inverse Haar two-dimensional transform, applied. The resulting image was then raster-scanned with a continuously adaptive lattice filter. This procedure was applied to a simple image of a photographic step tablet and a complex scene. All of the lines of the step tablet were well defined over the whole dynamic range. Useful definition of lines in the complex scene was obtained. 10 figures.
Date: January 1, 1979
Creator: Brolley, J.E.
Partner: UNT Libraries Government Documents Department

Image restoration with a locally variable Wiener filter

Description: The parametric Wiener filter is often used to deblur images that are relatively noise-free.If noise is more severe, the restored image may be obscured by a granular pattern that results when the noise is subjected to the deblurring filter. This effect may be reduced by using a larger noise parameter, but this leads to a restoration that is less sharp. Variation of the noise parameter from pixel to pixel so that it is larger only where noise is greater is described. Pixels with low singnal-to-noise ratios are identified by a thresholding process and comparison with nearest neighbors. The effects of the estimated Wiener spectra on the restored image are discussed. 14 figures.
Date: January 1, 1979
Creator: Lahart, M.J.
Partner: UNT Libraries Government Documents Department

A real-time MPEG software decoder using a portable message-passing library

Description: We present a real-time MPEG software decoder that uses message-passing libraries such as MPL, p4 and MPI. The parallel MPEG decoder currently runs on the IBM SP system but can be easil ported to other parallel machines. This paper discusses our parallel MPEG decoding algorithm as well as the parallel programming environment under which it uses. Several technical issues are discussed, including balancing of decoding speed, memory limitation, 1/0 capacities, and optimization of MPEG decoding components. This project shows that a real-time portable software MPEG decoder is feasible in a general-purpose parallel machine.
Date: December 31, 1995
Creator: Kwong, Man Kam; Tang, P.T. Peter & Lin, Biquan
Partner: UNT Libraries Government Documents Department

Partial removal of correlated noise in thermal imagery

Description: Correlated noise occurs in many imaging systems such as scanners and push-broom imagers. The sources of correlated noise can be from the detectors, pre-amplifiers and sampling circuits. Correlated noise appears as streaking along the scan direction of a scanner or in the along track direction of a push-broom imager. We have developed algorithms to simulate correlated noise and pre-filter to reduce the amount of streaking while not destroying the scene content. The pre- filter in the Fourier domain consists of the product of two filters. One filter models the correlated noise spectrum, the other is a windowing function e.g. Gaussian or Hanning window with variable width to block high frequency noise away from the origin of the Fourier Transform of the image data. We have optimized the filter parameters for various scenes and find improvements of the RMS error of the original minus the pre-filtered noisy image.
Date: April 1, 1996
Creator: Borel, C.C.; Cooke, B.J. & Laubscher, B.E.
Partner: UNT Libraries Government Documents Department

Comparison of filter with Prairie and European Network data

Description: Earlier notes derived a model for the hydrodynamics, ablation, and radiation of meteor impacts at the level needed to infer meteor parameters from observations and extended it to objects that fragment during entry, using models based on related cometary studies. This note completes the comparison of the resulting filter model to European and Prairie Network (EN and PN) data and models of meteor impact. In cases of mutual applicability, US and European models give broadly consistent results. The quantitative analysis of the EN and PN data is best discussed in conjunction with the Russian program of its analysis, because the Russian program has bypassed the large reported photometrically based masses to derive more plausible estimates of sizes, masses, and radiation efficiencies, which are the primary quantities of concern here. This note completes the discussion of the PN and EN data begun earlier, uses the data to produce filter predictions, and compares it with observations and the predictions of the Russian analytic effort. The overall agreement is useful in that the Russian efforts have employed more complex models that use observational data directly, while the filter model is at a level of simplification much better suited to data inversion.
Date: October 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department

Detecting discontinuities in time series of upper air data: Demonstration of an adaptive filter technique

Description: The issue of global climate change due to increased anthropogenic emissions of greenhouse gases in the atmosphere has gained considerable attention and importance. Climate change studies require the interpretation of weather data collected in numerous locations and/or over the span of several decades. Unfortunately, these data contain biases caused by changes in instruments and data acquisition procedures. It is essential that biases are identified and/or removed before these data can be used confidently in the context of climate change research. The purpose of this paper is to illustrate the use of an adaptive moving average filter and compare it with traditional parametric methods. The advantage of the adaptive filter over traditional parametric methods is that it is less effected by seasonal patterns and trends. The filter has been applied to upper air relative humidity and temperature data. Applied to generated data, the filter has a root mean squared error accuracy of about 600 days when locating changes of 0.1 standard deviations and about 20 days for changes of 0.5 standard deviations. In some circumstances, the accuracy of location estimation can be improved through parametric techniques used in conjunction with the adaptive filter.
Date: November 1, 1997
Creator: Zurbenko, I.; Chen, J. & Rao, S.T.
Partner: UNT Libraries Government Documents Department

Space-variant filtering for correction of wavefront curvature effects in spotlight-mode SAR imagery formed via polar formatting

Description: Wavefront curvature defocus effects can occur in spotlight-mode SAR imagery when reconstructed via the well-known polar formatting algorithm (PFA) under certain scenarios that include imaging at close range, use of very low center frequency, and/or imaging of very large scenes. The range migration algorithm (RMA), also known as seismic migration, was developed to accommodate these wavefront curvature effects. However, the along-track upsampling of the phase history data required of the original version of range migration can in certain instances represent a major computational burden. A more recent version of migration processing, the Frequency Domain Replication and Downsampling (FReD) algorithm, obviates the need to upsample, and is accordingly more efficient. In this paper the authors demonstrate that the combination of traditional polar formatting with appropriate space-variant post-filtering for refocus can be as efficient or even more efficient than FReD under some imaging conditions, as demonstrated by the computer-simulated results in this paper. The post-filter can be pre-calculated from a theoretical derivation of the curvature effect. The conclusion is that the new polar formatting with post filtering algorithm (PF2) should be considered as a viable candidate for a spotlight-mode image formation processor when curvature effects are present.
Date: December 31, 1996
Creator: Jakowatz, C.V. Jr.; Wahl, D.E.; Thompson, P.A. & Doren, N.E.
Partner: UNT Libraries Government Documents Department

General application of rapid 3-D digitizing and tool path generation for complex shapes

Description: A system for automatic tool path generation was developed at Sandia National Laboratories for finish machining operations. The system consists of a commercially available 5-axis milling machine controlled by Sandia developed software. This system was used to remove overspray on cast turbine blades. A laser-based, structured-light sensor, mounted on a tool holder, is used to collect 3D data points around the surface of the turbine blade. Using the digitized model of the blade, a tool path is generated which will drive a 0.375 inch grinding pin around the tip of the blade. A fuzzified digital filter was developed to properly eliminate false sensor readings caused by burrs, holes and overspray. The digital filter was found to successfully generate the correct tool path for a blade with intentionally scanned holes and defects. The fuzzified filter improved the computation efficiency by a factor of 25. For application to general parts, an adaptive scanning algorithm was developed and presented with simulation and experimental results. A right pyramid and an ellipsoid were scanned successfully with the adaptive algorithm in simulation studies. In actual experiments, a nose cone and a turbine blade were successfully scanned. A complex shaped turbine blade was successfully scanned and finished machined using these algorithms.
Date: September 1, 1997
Creator: Kwok, K.S.; Loucks, C.S. & Driessen, B.J.
Partner: UNT Libraries Government Documents Department

Robust tracking with spatio-velocity snakes: Kalman filtering approach

Description: Using results from robust Kalman filtering, the author presents a new Kalman filter-based snake model for tracking of nonrigid objects in combined spatio-velocity space. The proposed model is the stochastic version of the velocity snake, an active contour model for combined tracking of position and velocity of nonrigid boundaries. The proposed model uses image gradient and optical flow measurements along the contour as system measurements. An optical-flow based measurement error is used to detect and reject image measurements which correspond to image clutter or to other objects. The method was applied to object tracking of both rigid and nonrigid objects, resulting in good tracking results and robustness to image clutter, occlusions and numerical noise.
Date: June 1, 1997
Creator: Peterfreund, N.
Partner: UNT Libraries Government Documents Department

General formulation for wavefront curvature correction in polar-formatted spotlight-mode SAR images using space-variant post-filtering

Description: In this paper, the authors introduce a general formulation for wavefront curvature correction in spotlight-mode SAR images formed using the polar-formatting algorithm (PFA). This correction is achieved through the use of an efficient, image domain space-variant filter which is applied as a post-processing step to PFA. Wavefront curvature defocus effects occur in certain SAR collection modes that include imaging at close range, using low center frequency, and/or imaging very large scenes. The formulation is general in that it corrects for wavefront curvature in roadside as well as squinted collection modes, with no computational penalty for correcting squint-mode images. Algorithms such as the range migration technique (also known as seismic migration), and a recent enhancement known as frequency domain replication, FReD, have been developed to accommodate these wavefront curvature effects. However, they exhibit no clear computational advantage over space-variant post-filtering in conjunction with polar formatting (PF2). This paper will present the basic concepts of the formulation, and will provide computer results demonstrating the capabilities of space-variant post-filtering.
Date: October 1997
Creator: Doren, N. E.; Jakowatz, C. V., Jr.; Wahl, D. E. & Thompson, P. A.
Partner: UNT Libraries Government Documents Department

A novel algorithm for real-time adaptive signal detection and identification

Description: This paper describes a novel digital signal processing algorithm for adaptively detecting and identifying signals buried in noise. The algorithm continually computes and updates the long-term statistics and spectral characteristics of the background noise. Using this noise model, a set of adaptive thresholds and matched digital filters are implemented to enhance and detect signals that are buried in the noise. The algorithm furthermore automatically suppresses coherent noise sources and adapts to time-varying signal conditions. Signal detection is performed in both the time-domain and the frequency-domain, thereby permitting the detection of both broad-band transients and narrow-band signals. The detection algorithm also provides for the computation of important signal features such as amplitude, timing, and phase information. Signal identification is achieved through a combination of frequency-domain template matching and spectral peak picking. The algorithm described herein is well suited for real-time implementation on digital signal processing hardware. This paper presents the theory of the adaptive algorithm, provides an algorithmic block diagram, and demonstrate its implementation and performance with real-world data. The computational efficiency of the algorithm is demonstrated through benchmarks on specific DSP hardware. The applications for this algorithm, which range from vibration analysis to real-time image processing, are also discussed.
Date: April 1, 1998
Creator: Sleefe, G. E.; Ladd, M. D.; Gallegos, D. E.; Sicking, C. W. & Erteza, I. A.
Partner: UNT Libraries Government Documents Department