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Computational Complexity of Subspace Detectors and Matched Field Processing

Description: Subspace detectors implement a correlation type calculation on a continuous (network or array) data stream [Harris, 2006]. The difference between subspace detectors and correlators is that the former projects the data in a sliding observation window onto a basis of template waveforms that may have a dimension (d) greater than one, and the latter projects the data onto a single waveform template. A standard correlation detector can be considered to be a degenerate (d=1) form of a subspace detector. Figure 1 below shows a block diagram for the standard formulation of a subspace detector. The detector consists of multiple multichannel correlators operating on a continuous data stream. The correlation operations are performed with FFTs in an overlap-add approach that allows the stream to be processed in uniform, consecutive, contiguous blocks. Figure 1 is slightly misleading for a calculation of computational complexity, as it is possible, when treating all channels with the same weighting (as shown in the figure), to perform the indicated summations in the multichannel correlators before the inverse FFTs and to get by with a single inverse FFT and overlap add calculation per multichannel correlator. In what follows, we make this simplification.
Date: December 1, 2010
Creator: Harris, D B
Partner: UNT Libraries Government Documents Department

Numerical Calculation of the Spectrum of the Severe (1%) Lighting Current and Its First Derivative

Description: Recently, the direct-strike lighting environment for the stockpile-to-target sequence was updated [1]. In [1], the severe (1%) lightning current waveforms for first and subsequent return strokes are defined based on Heidler's waveform. This report presents numerical calculations of the spectra of those 1% lightning current waveforms and their first derivatives. First, the 1% lightning current models are repeated here for convenience. Then, the numerical method for calculating the spectra is presented and tested. The test uses a double-exponential waveform and its first derivative, which we fit to the previous 1% direct-strike lighting environment from [2]. Finally, the resulting spectra are given and are compared with those of the double-exponential waveform and its first derivative.
Date: February 12, 2010
Creator: Brown, C G; Ong, M M; Perkins, M P & Speer, R D
Partner: UNT Libraries Government Documents Department

Monitoring microbe-induced physical property changes using high-frequency acoustic waveform data: Toward the development of a microbial megascope

Description: A laboratory investigation was undertaken to determine the effect of microbe generated gas bubbles in controlled, saturated sediment columns utilizing a novel technique involving acoustic wave propagation. Specifically, the effect of denitrifying bacteria on saturated flow conditions was evaluated in light of the stimulated production of N{sub 2} gas and the resulting plugging of the pore throats. The propagation of high frequency acoustic waves through the sediment columns was used to locate those regions in the column where gas accumulation occurred. Over a period of six weeks, regions of gas accumulation resulted in the attenuation of acoustic wave energies with the decreases in amplitude typically greater than one order of magnitude.
Date: May 20, 2002
Creator: Williams, Kenneth Hurst
Partner: UNT Libraries Government Documents Department

3-D full waveform inversion of seismic data; Part I. Theory

Description: Full waveform inversion of seismic data is a challenging subject partly because of the lack of precise knowledge of the source. Since currently available approaches involve some form of approximations to the source, inversion results are subject to the quality and the choice of the source information used. A new full waveform inversion scheme has been introduced (Lee and Kim, 2003) using normalized wavefield for simple two-dimensional (2-D) scalar problems. The method does not require source information, so potential inversion errors due to source estimation may be eliminated. A gather of seismic traces is first Fourier-transformed into the frequency domain and a normalized wavefield is obtained for each trace in the frequency domain. Normalization is done with respect to the frequency response of a reference trace selected from the gather, so the complex-valued normalized wavefield is source-independent and dimensionless. The inversion algorithm minimizes misfits between measured normalized wavefield and numerically computed normalized wavefield. In this paper the full waveform inversion is extended to three-dimensional (3-D) problems.
Date: May 12, 2003
Creator: Lee, Ki Ha
Partner: UNT Libraries Government Documents Department

Source-independent full waveform inversion of seismic data

Description: A rigorous full waveform inversion of seismic data has been a challenging subject partly because of the lack of precise knowledge of the source. Since currently available approaches involve some form of approximations to the source, inversion results are subject to the quality and the choice of the source information used. We propose a new full waveform inversion methodology that does not involve source spectrum information. Thus potential inversion errors due to source estimation can be eliminated. A gather of seismic traces is first Fourier-transformed into the frequency domain and a normalized wavefield is obtained for each trace in the frequency domain. Normalization is done with respect to the frequency response of a reference trace selected from the gather, so the complex-valued normalized wavefield is dimensionless. The source spectrum is eliminated during the normalization procedure. With its source spectrum eliminated, the normalized wavefield allows us construction of an inversion algorithm without the source information. The inversion algorithm minimizes misfits between measured normalized wavefield and numerically computed normalized wavefield. The proposed approach has been successfully demonstrated using a simple two-dimensional scalar problem.
Date: March 20, 2002
Creator: Lee, Ki Ha & Kim, Hee Joon
Partner: UNT Libraries Government Documents Department

A Multisensor system for the detection and characterization of UXOMM-0437

Description: A prototype active electromagnetic system has been developedfor detecting and characterizing UXO. The system employs two orthogonalvertical loop transmitters and a pair of horizontal loop transmittersspaced apart vertically by 0.7 m. Eight vertical field detectors aredeployed in the plane of each of the horizontal loops and are arranged tomeasure offset vertical gradients of the fields. The location andorientation of the three principal polarizabilities of a target can berecovered from a single position of the transmitter-receiver system.Further characterization of the target is obtained from the broadbandresponse. The system employs a bipolar half sine pulse train currentwaveform and the detectors are dB/dt induction coils designed to minimizethe transient response of the primary field pulse. The target transientis recovered in a 40 mu-sec to 1.0 msec window. The ground responseimposes an early time limit on the time window and system/ambient noiselimits the late time response. Nevertheless for practical transmittermoments and optimum receivers the size and the ratio of conductivity topermeability canbe accurately recovered. The prototype system hassuccessfully recovered the depths and polarizabilities of ellipsoidaltest targets.
Date: June 1, 2006
Creator: Gasperikova, Erika; Becker, A.; Morrison, H.F. & Smith, J.T.
Partner: UNT Libraries Government Documents Department

ADVANCED WAVEFORM SIMULATION FOR SEISMIC MONITORING EVENTS - REPORTING PERIOD AUGUST 1, 2007-OCTOBER 31, 2007

Description: We have developed a forward modeling technique to retrieve rupture characteristics of small earthquakes (3<M<5), including rupture propagation direction, fault dimension, and rupture speed.
Date: September 30, 2007
Creator: Helmberger, Donald V.; Tromp, Jeroen & Rodgers, Arthur J.
Partner: UNT Libraries Government Documents Department

Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

Description: Repeating earthquakes (REs) are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. We investigate the occurrence of these REs along faults in central California to determine which faults exhibit creep and the spatio-temporal distribution of this creep. At the juncture of the San Andreas and southern Calaveras-Paicines faults, both faults as well as a smaller secondary fault, the Quien Sabe fault, are observed to produce REs over the observation period of March 1984-May 2005. REs in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time. Cumulative slip over the observation period at individual sequence locations is determined to range from 5.5-58.2 cm on the San Andreas fault, 4.8-14.1 cm on the southern Calaveras-Paicines fault, and 4.9-24.8 cm on the Quien Sabe fault. Creep at depth appears to mimic the behaviors seen of creep on the surface in that evidence of steady slip, triggered slip, and episodic slip phenomena are also observed in the RE sequences. For comparison, we investigate the occurrence of REs west of the San Andreas fault within the southern Coast Range. Events within these RE sequences only occurred minutes to weeks apart from each other and then did not repeat again over the observation period, suggesting that REs in this area are not produced by steady aseismic creep of the surrounding fault surface.
Date: July 9, 2007
Creator: Templeton, D C; Nadeau, R & Burgmann, R
Partner: UNT Libraries Government Documents Department

The Response of Long-Span Bridges to Low Frequency, Near-Fault Earthquake Ground Motions

Description: Historical seismic hazard characterizations did not include earthquake ground motion waveforms at frequencies below approximately 0.2 Hz (5 seconds period). This resulted from limitations in early strong motion instrumentation and signal processing techniques, a lack of measurements in the near-field of major earthquakes and therefore no observational awareness, and a delayed understanding in the engineering community of the potential significance of these types of motions. In recent years, there is a growing recognition of the relevance of near-fault, low frequency motions, particularly for long-period structures such as large bridges. This paper describes a computationally based study of the effects of low frequency (long-period) near-fault motions on long-span bridge response. The importance of inclusion of these types of motions for long span cable supported bridges is demonstrated using actual measured broad-band, near-fault motions from large earthquakes.
Date: February 27, 2009
Creator: McCallen, David; Astaneh-Asl, A.; Larsen, S.C. & Hutchings, Larry
Partner: UNT Libraries Government Documents Department

Spherical Wave Propagation in a Nonlinear Elastic Medium

Description: Nonlinear propagation of spherical waves generated by a point-pressure source is considered for the cases of monochromatic and impulse primary waveforms. The nonlinear five-constant elastic theory advanced by Murnaghan is used where general equations of motion are put in the form of vector operators, which are independent of the coordinate system choice. The ratio of the nonlinear field component to the primary wave in the far field is proportional to ln(r) where r is a propagation distance. Near-field components of the primary field do not contribute to the far field of nonlinear component.
Date: July 1, 2009
Creator: Korneev, Valeri A.
Partner: UNT Libraries Government Documents Department

Up-conversion time microscope demonstrates 103x magnification of an ultrafast waveforms with 300 fs resolution

Description: We have demonstrated a system for the temporal expansion of arbitrarily shaped ultrafast optical waveforms based on the principle of temporal imaging. This system has demonstrated 103x magnification of an input signal with 300 fs resolution, thus allowing ultrafast phenomena to be recorded with slower conventional technology. The physics of temporal imaging work on a single shot basis, thus it is expected that this technology will lead to a new class of single transient recorders with ultrafast resolution.
Date: October 17, 1998
Creator: Bennett, C. V. & Kolner, B. H.
Partner: UNT Libraries Government Documents Department

Analysis of seismic events in and near Kuwait

Description: Seismic data for events in and around Kuwait were collected and analyzed. The authors estimated event moment, focal mechanism and depth by waveform modeling. Results showed that reliable seismic source parameters for events in and near Kuwait can be estimated from a single broadband three-component seismic station. This analysis will advance understanding of earthquake hazard in Kuwait.
Date: May 11, 1999
Creator: Harris, D B; Mayeda, K M; Rodgers, A J & Ruppert, S D
Partner: UNT Libraries Government Documents Department

Zeroth-order inversion of transient head observations

Description: A high-frequency, asymptotic solution for transient head,appropriate for a medium containing smoothly varying heterogeneity,provides a basis for efficient inverse modeling. The semi analyticsolution is trajectory based, akin to ray methods used in modeling wavepropagation, and may be constructed by post processing the output of anumerical simulator. For high frequencies, the amplitude sensitivities,the relationship between changes in flow properties and changes in headampliude, are dominated by the phase term which may be computed directlyfrom the output of the simulator. Thus, transient head waveforms may beinverted with little more computation than is required to invert arrivaltimes. An applicatino to synthetic head values indicates that thetechnique can be used to improve the fit to waveforms. An application totransient head data from the Migration experiment in Switzerland revealsa narrow, high conductivity pathway within a 0.5 m thick zone offracturing.
Date: August 15, 2007
Creator: Vasco, D.W.
Partner: UNT Libraries Government Documents Department

Accurate iterative analytic solution of theKapchinskij-Vladimirskij equations for the case of a matched beam

Description: The well-known Kapchinskij-Vladimirskij (KV) equations are difficult to solve in general, but the problem is simplified for the matched-beam case with sufficient symmetry. They show that the interdependence of the two KV equations is eliminated, so that only one needs to be solved--a great simplification. They present an iterative method of solution which can potentially yield any desired level of accuracy. The lowest level, the well-known smooth approximation, yields simple, explicit results with good accuracy for weak or moderate focusing fields. The next level improves the accuracy for high fields; they previously showed how to maintain a simple explicit format for the results. That paper used expansion in a small parameter to obtain the second level. The present paper, using straightforward iteration, obtains equations of first, second, and third levels of accuracy. For a periodic lattice with beam matched to lattice, they use the lattice and beam parameters as input and solve for phase advances and envelope waveforms. They find excellent agreement with numerical solutions over a wide range of beam emittances and intensities.
Date: August 6, 2006
Creator: Anderson, Oscar A.
Partner: UNT Libraries Government Documents Department

A Five-Level Cascade Multilever Invertor Three-Phase Motor Drive Using a Single DC Source

Description: A method is presented showing that a 5-level cascade multilevel inverter for a three-phase permanent magnet synchronous motor drive can be implemented using only a single DC link to supply a standard 3-leg inverter along with three full H-bridges supplied by capacitors. It is shown that the capacitor voltages can be regulated while achieving an output voltage waveform that is 20% greater than that obtained using the standard 3-leg inverter alone. Finally conditions are given in terms of the power factor and modulation index that determine when the capacitor voltage can regulated.
Date: September 15, 2006
Creator: Chiasson, J.N. (Univ. Tennessee-Knoxville)
Partner: UNT Libraries Government Documents Department

Dynamic Response of the Suspension Spans of the San Francisco-Oakland Bay Bridge

Description: The dynamic response of the suspension spans of the San Francisco-Oakland Bay Bridge (SFOBB) have been numerically modeled in a case-study to investigate the effects of long-period, near-field ground motions on flexible suspension bridges. The structural simulation model used in the study was developed as a special purpose computer program tailored to efficiently simulate the nonlinear response of cable supported bridges. The simulation model includes a number of special element technologies and solution algorithms that enable efficient nonlinear analysis of suspension bridges. The ground motions used in the study were site specific synthetic records for a Mw=7.25 earthquake along the Hayward fault at 12-15 km distant, and actual measured near-field records from the Izmit Turkey (1999) and Chi-Chi Taiwan (1999) earthquakes. These records include near- and far-field broad-band motions for three components. The results of the numerical simulations indicate that low frequency waveforms associated with near-field motions can place a significant demand on the structural systems of suspension bridges, and must be accounted for in suspension bridge analysis and design.
Date: November 3, 2005
Creator: McCallen, D; Astaneh-Asl, A; Larsen, S & Hutchings, L
Partner: UNT Libraries Government Documents Department

Evaluation of Porous Medium Permeability by Acoustic Logging Finds Geothermal Applications

Description: In a well, after an acoustic waveform has circulated through the surrounding porous media, the study of its alteration can help in evaluating their permeability. The treatment of the acoustic compressional wave's first three cycles yields a unique parameter called I-c. The recording of this I-c log all along any open hole interval is now possible by respecting some practical rules known by logging companies. Large flows of fluid found in geothermal low-enthalpy operations have provided an opportunity to check the validity of this method. Cumulative I-c derived permeability with depth (''EXAFLO'' log) correlates with the flowmeter log, as examples will show. Some new aspects of the theory underlying the I-c/permeability relationship have been developed and are described here.
Date: January 21, 1986
Creator: Conche, B.; Lebreton, F. & Rojas, J.
Partner: UNT Libraries Government Documents Department

Evaluation of Inter-Mountain Labs infrasound sensors : July 2007.

Description: Sandia National Laboratories has tested and evaluated three Inter Mountain Labs infrasound sensors. The test results included in this report were in response to static and tonal-dynamic input signals. Most test methodologies used were based on IEEE Standards 1057 for Digitizing Waveform Recorders and 1241 for Analog to Digital Converters; others were designed by Sandia specifically for infrasound application evaluation and for supplementary criteria not addressed in the IEEE standards. The objective of this work was to evaluate the overall technical performance of the Inter Mountain Labs (IML) infrasound sensor model SS. The results of this evaluation were only compared to relevant noise models; due to a lack of manufactures documentation notes on the sensors under test prior to testing. The tests selected for this system were chosen to demonstrate different performance aspects of the components under test.
Date: October 1, 2007
Creator: Hart, Darren M.
Partner: UNT Libraries Government Documents Department

An Application of the Coda Methodology for Moment-Rate Spectra Using Broadband Stations in Turkey

Description: A recently developed coda magnitude methodology was applied to selected broadband stations in Turkey for the purpose of testing the coda method in a large, laterally complex region. As found in other, albeit smaller regions, coda envelope amplitude measurements are significantly less variable than distance-corrected direct wave measurements (i.e., L{sub g} and surface waves) by roughly a factor 3-to-4. Despite strong lateral crustal heterogeneity in Turkey, we found that the region could be adequately modeled assuming a simple 1-D, radially symmetric path correction for 10 narrow frequency bands ranging between 0.02 to 2.0 Hz. For higher frequencies however, 2-D path corrections will be necessary and will be the subject of a future study. After calibrating the stations ISP, ISKB, and MALT for local and regional distances, single-station moment-magnitude estimates (M{sub w}) derived from the coda spectra were in excellent agreement with those determined from multi-station waveform modeling inversions of long-period data, exhibiting a data standard deviation of 0.17. Though the calibration was validated using large events, the results of the calibration will extend M{sub w} estimates to significantly smaller events which could not otherwise be waveform modeled due to poor signal-to-noise ratio at long periods and sparse station coverage. The successful application of the method is remarkable considering the significant lateral complexity in Turkey and the simple assumptions used in the coda method.
Date: February 3, 2004
Creator: Eken, T; Mayeda, K; Hofstetter, A; Gok, R; Orgulu, G & Turkelli, N
Partner: UNT Libraries Government Documents Department

xdamp Version 6 : an IDL-based data and image manipulation program.

Description: The original DAMP (DAta Manipulation Program) was written by Mark Hedemann of Sandia National Laboratories and used the CA-DISSPLA{trademark} (available from Computer Associates International, Inc., Garden City, NY) graphics package as its engine. It was used to plot, modify, and otherwise manipulate the one-dimensional data waveforms (data vs. time) from a wide variety of accelerators. With the waning of CA-DISSPLA and the increasing popularity of Unix(reg sign)-based workstations, a replacement was needed. This package uses the IDL(reg sign) software, available from Research Systems Incorporated, a Xerox company, in Boulder, Colorado, as the engine, and creates a set of widgets to manipulate the data in a manner similar to the original DAMP and earlier versions of xdamp. IDL is currently supported on a wide variety of Unix platforms such as IBM(reg sign) workstations, Hewlett Packard workstations, SUN(reg sign) workstations, Microsoft(reg sign) Windows{trademark} computers, Macintosh(reg sign) computers and Digital Equipment Corporation VMS(reg sign) and Alpha(reg sign) systems. Thus, xdamp is portable across many platforms. We have verified operation, albeit with some minor IDL bugs, on personal computers using Windows 7 and Windows Vista; Unix platforms; and Macintosh computers. Version 6 is an update that uses the IDL Virtual Machine to resolve the need for licensing IDL.
Date: April 1, 2012
Creator: Ballard, William Parker
Partner: UNT Libraries Government Documents Department

Observing muon decays in water Cherenkov detectors at the Pierre Auger Observatory

Description: Muons decaying in the water volume of a Cherenkov detector of the Pierre Auger Observatory provide a useful calibration point at low energy. Using the digitized waveform continuously recorded by the electronics of each tank, we have devised a simple method to extract the charge spectrum of the Michel electrons, whose typical signal is about 1/8 of a crossing vertical muon. This procedure, moreover, allows continuous monitoring of the detector operation and of its water level. We have checked the procedure with high statistics on a test tank at the Observatory base and applied with success on the whole array.
Date: August 1, 2005
Creator: Allison, P.; Arneodo, F.; Bertou, Xavier; Busca, N.; Ghia, P.L.; Medina, C. et al.
Partner: UNT Libraries Government Documents Department