Showing papers on "Noise reduction published in 1992"

Nonlinear anisotropic filtering of MRI data

Abstract: In contrast to acquisition-based noise reduction methods a postprocess based on anisotropic diffusion is proposed. Extensions of this technique support 3-D and multiecho magnetic resonance imaging (MRI), incorporating higher spatial and spectral dimensions. The procedure overcomes the major drawbacks of conventional filter methods, namely the blurring of object boundaries and the suppression of fine structural details. The simplicity of the filter algorithm permits an efficient implementation, even on small workstations. The efficient noise reduction and sharpening of object boundaries are demonstrated by applying this image processing technique to 2-D and 3-D spin echo and gradient echo MR data. The potential advantages for MRI, diagnosis, and computerized analysis are discussed in detail. >

Theory and Performance of Narrow Correlator Spacing in a GPS Receiver

Abstract: Historically, conventional GPS receivers have used 1.0 chip early-late correlator spacing in the implementation of delay lock loop s (DLLs), However, there are distinct advantages to narrowing this spacing, especially in C/A-code tracking applications. These advantages are the reduction of tracking errors in the presence of both noise and multipath. The primary disadvantage i s that a wider precorrelation bandwidth is required, coupled with higher sample rates and higher digital signal processing rates. However, with current CMOS technology, this is easily achievable and well worth the price. Noise reduction is achieved with narrower spacing because the noise components of the early and late signals are correlated and ten d to cancel, provided that early and late processing are simultaneous (not dithered). Multipath effects are reduced because the DLL discriminator is less distorted by the delayed multipath signal. This paper presents the derivation of these narrow correlator spacing improvements, verified by simulated and tested performance.

Noise and vibration control engineering - Principles and applications

Abstract: Preface. Contributors. 1. Basic Acoustical Quantities: Levels and Decibels (Leo L. Beranek). 2. Waves and Impedances (Leo L. Beranek). 3. Data Analysis (Allan G. Piersol). 4. Determination of Sound Power Levels and Directivity of Noise Sources (William W. Lang, George C. Maling, Jr., Matthew A. Nobile, and Jiri Tichy). 5. Outdoor Sound Propagation (Ulrich J. Kurze and Grant S. Anderson). 6. Sound in Small Enclosures (Donald J. Nefske and Shung H. Sung). 7. Sound in Rooms (Murray Hodgson and John Bradley). 8. Sound-Absorbing Materials and Sound Absorbers (Keith Attenborough and Istvan L. Ver). 9. Passive Silencers (M. L. Munjal, Anthony G. Galaitsis and Istvan L. Ver). 10. Sound Generation (Istvan L. Ver). 11. Interaction of Sound Waves with Solid Structures (Istvan L. Ver). 12. Enclosures, Cabins, and Wrappings (Istvan L. Ver). 13. Vibration Isolation (Eric E. Ungar and Jeffrey A. Zapfe). 14. Structural Damping (Eric E. Ungar and Jeffrey A. Zapfe). 15. Noise of Gas Flows (H. D. Baumann and W. B. Coney). 16. Prediction of Machinery Noise (Eric W. Wood and James D. Barnes). 17. Noise Control in Heating, Ventilating, and Air Conditioning Systems (Alan T. Fry and Douglas H. Sturz). 18. Active Control of Noise and Vibration (Ronald Coleman and Paul J. Remington). 19. Damage Risk Criteria for Hearing and Human Body Vibration (Suzanne D. Smith, Charles W. Nixon and Henning E. Von Gierke). 20. Criteria for Noise in Buildings and Communities (Leo L. Beranek). 21. Acoustical Standards for Noise and Vibration Control (Angelo Campanella, Paul Schomer and Laura Ann Wilber). Appendix A. General References. Appendix B. American System of Units. Appendix C. Conversion Factors. Index.

The origin and reduction of acoustic noise in doubly salient variable-reluctance motors

Abstract: An experimental study of the acoustic noise emitted from an inverter-driven doubly salient variable-reluctance motor (VRM) is presented. A list of possible noise sources is given. Through a series of experiments, all but one source is eliminated as being important, and the remaining source is shown to be dominant. The dominant noise source is the ovalizing deformation of the stator due to its radial magnetic attraction to the rotor. The emitted noise is particularly strong when the frequency of deformation coincides with that of a natural mechanical resonance of the stator. Several methods of reducing acoustic noise emission are studied. One successful method is the introduction of dither into the control of the motor in order to spread the spectrum of noise excitation and reduce its coupling to the mechanical resonance of the stator. >

The sliding-frequency guiding filter: an improved form of soliton jitter control

Abstract: By gradually translating the peak frequency of guiding filters along its length, we create a fiber transmission line that is substantially opaque to noise while remaining transparent to solitons. This trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise from the excess gain required to overcome filter loss.

Acquisition and processing of wide-aperture ground-penetrating radar data

Abstract: A 40-channel wide‐aperture ground penetrating radar (GPR) data set was recorded in a complicated fluvial/aeolian environment in eastern Canada. The data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence (filtering, static corrections, common‐midpoint gathering, velocity analysis, normal‐ and dip‐moveout corrections, stacking and depth migration). The results show significant improvements, over single‐channel recordings, in noise reduction and depth of penetration (by stacking), and in spatial positioning and reduction of diffraction artifacts (by migration). These characteristics increase the potential for reliable interpretation of structural and stratigraphic details. Thus, without having to develop any new software, GPR data processing technology is brought to the same level of capability, flexibility, and accessibility that is current in seismic exploration.

Apparatus and method for smoothing images

Abstract: Improved spatial, temporal, and spatio-temporal noise reduction apparatus (10) and also apparatus for noise reduction in conjunction with one or several of the following functions: edge enhancement, spatial interpolation, magnification adjustment by spatial interpolation, and dynamic range compression (DRC). An embodiment of apparatus (10) comprises an image preprocessing unit (12), an estimation gain parameter computation unit (14) and a two-directional processor (16).

Local-geometric-projection method for noise reduction in chaotic maps and flows.

Abstract: We describe a method for noise reduction in chaotic systems that is based on projection of the set of points comprising an embedded noisy orbit in R d toward a finite patchwork of best-fit local approximations to an m-dimensional surface M'⊂R d , m≤d

Characteristics and reduction of coherent fading noise in Rayleigh backscattering measurement for optical fibers and components

Abstract: The characteristics of fading noise in Rayleigh backscattering measurements made with coherent lightwaves such as in coherent-OTDR (optical time-domain reflectometry) and coherent-OFDR (optical frequency-domain reflectometry) are studied. The effects of frequency shift averaging on fading noise reduction are clarified theoretically, and the relationships between measurement accuracy and other parameters, such as spatial resolution and frequency variation range are derived. The calculated results of loss measurement accuracy are in good agreement with experimental data. The formula can also be applied to low-coherence interferometric OTDR. >

Noise reduction in recursive digital filters using high-order error feedback

Abstract: The problem of solving the optimal (minimum-noise) error feedback coefficients for recursive digital filters is addressed in the general high-order case. It is shown that when minimum noise variance at the filter output is required, the optimization problem leads to set of familiar Wiener-Hopf or Yule-Walker equations, demonstrating that the optimal error feedback can be interpreted as a special case of Wiener filtering. As an alternative to the optimal solution, the formulas for suboptimal error feedback with symmetric or antisymmetric coefficients are derived. In addition, the design of error feedback using power-of-two coefficients is discussed. The efficiency of high order error feedback is examined by test implementations of the set of standard filters. It is concluded that error feedback is a very powerful and versatile method for cutting down the quantization noise in any classical infinite impulse response (IIR) filter implemented as a cascade of second-order direct form sections. The high-order schemes are attractive for use with high-order direct form sections. >

Noise reduction of image sequences using adaptive motion compensated frame averaging

Abstract: A scheme for noise reduction of image sequences by adaptively switching, on a block-by-block basis, between simple (nondisplaced) frame averaging and motion-compensated frame averaging is represented. The resulting noise reduction approaches that achievable with simple frame averaging, while maintaining the good image resolution achievable for motion compensated frame averaging. >

Fading noise reduction in coherent OTDR

Abstract: The authors describe a reduction in fading noise which causes amplitude fluctuation on a backscattered trace in coherent OTDR (optical time-domain reflectometry). In order to reduce the fading noise, the optical frequency of the DFB-LD (distributed feedback laser diode) is changed by changing the LD temperature during the integrations of the backscattered signals. At the same time, the state of polarization of the launched signal pulses is changed. The amplitude fluctuation has been reduced to as low as 0.06 dB. Measurements were performed on a 10 km length of conventional single-mode fiber. >

Registration-noise reduction in difference images for change detection

Abstract: Two methods are introduced and evaluated for the reduction of registration noise in difference images: image smoothing and adaptive grey-scale mapping. Landsat Thematic Mapper (TM) data obtained on two different dates over an urban and urban-fringe area depicting significant change were geometrically registered and then subtracted from each other. The TM band 3 difference image was used to test the registration noise reduction algorithms. Results indicate that adaptive grey scale mapping is more appropriate to use for registration noise reduction.

Noise rejection for ultrasonic sensors in mobile robot applications

Abstract: The authors categorize different types of noise and discuss methods for rejecting each type of noise. They introduce a method called error eliminating rapid ultrasonic firing (EERUF). EERUF combines different noise rejection techniques and optimizes them for rapid firing. EERUF almost completely rejects crosstalk. Its unique noise rejection capability allows multiple mobile robots to collaborate in the same environment, even if their ultrasonic sensors operate at the same frequencies. For each noise category methods are described to identify and reject the resulting errors. These individual rejection measures were combined into one error rejection method which was then combined with a fast firing algorithm. The resulting combination was EERUF. The EERUF method was implemented on a mobile robot and experimental results are presented. With EERUF, a mobile robot was able to traverse an obstacle course of densely spaced, pencil-thin poles at up to 1 m/s. >

Using the coherence function for noise reduction

Abstract: With the development of hands-free radio communications there is great interest in noise cancelling or speech enhancement in a car. The authors assume that M observations are available; each one is composed of signal and noise (s/sub i/+b/sub i/), and s/sub 1/ is the signal to be estimated. Whatever the distance between microphones is, the signals are strongly correlated, while the correlation between noises becomes rather weak for a sufficiently great distance. The coherence function is then a pertinent criterion to know whether a speech signal exists or not. The three methods presented use the coherence function to filter the observations so giving an estimate of the signal s/sub 1/. The procedures presented are first shown for M=2. Then, a generalisation of these procedures is offered. The performances of the three methods have been evaluated on real noisy speech signals by objective tests (gain on the signal-to-noise ratio, distance measures) and informal listening tests.< >

Neural network method and apparatus for retrieving signals embedded in noise and analyzing the retrieved signals

Abstract: An apparatus for retrieving signals embedded in noise and analyzing the signals. The apparatus includes an input device for receiving input signals having noise. At least one noise filter retrieves data signals embedded in the input signals. At least one adaptive pattern recognition filter generates coefficients of a polynomial expansion representing the pattern of the filtered data signals. A storage device stores the coefficients generated. It is determined when an event has occurred, the event being located at any position within the data signals. An adaptive autoregressive moving average pattern recognition filter generates coefficients of a polynomial expansion representing an enhanced pattern of filtered data signals. At least one weighting filter compares the stored patterns with the enhanced pattern of data signals.

Simulation of substrate coupling in mixed-signal MOS circuits

Abstract: The use of device simulations to examine substrate-coupling noise induced by the switching of the transistor drain voltages is examined. Methods for reducing such noise are reported. The noise resulting from internal and external parasitics in the path of the substrate current flow is examined for structures with substrate contacts and additional guard rings and for both epitaxial and nonepitaxial substrates. A p/sup +/ guard ring, or substrate contact, between the digital circuits and noise sensitive components is found to be effective for reducing the substrate noise. In heavily doped substrates, a backside contact is an alternative method for noise reduction. >

An adaptive controller for the active absorption of sound

Abstract: An adaptive system is presented that allows a secondary acoustic source to become an active absorber of sound at the end of a closed duct. The system can also be generalized in order to achieve other termination impedances. The system consists of a loudspeaker, two microphones, and signal processing hardware including a digital signal microprocessor. The signals from the microphones are processed to obtain an error signal that represents the difference between the actual and the desired acoustic impedance of the termination. An absorbing termination requires, for example, that the microphone pair acts as a unidirectional probe picking up the sound reflected from the active termination only. This signal is used as the error signal that the digital controller is required to minimize. A simple analysis shows that this can be done adaptively using the ‘‘filtered‐X’’ LMS algorithm. A simple experimental setup is used to obtain an absorbing termination which is shown to work with periodic, random, and transient input signals.

Two-dimensional joint process lattice for adaptive restoration of images

Abstract: The two dimensional (2D) joint process lattice (TDJPL) and its implementations for image restoration applications are examined. A 2D adaptive lattice algorithm (TDAL) is first developed. Convergence properties of the algorithm are covered for the 2D adaptive lattice least mean squares (TDAL-LMS) case. The complexity of the normalized algorithm is slightly more than that of the TDAL-LMS, but it is a faster-converging algorithm. Implementations of the proposed TDJPL estimator as a 2D adaptive lattice noise canceler and as a 2D adaptive lattice line enhancer are then considered. The performance of both schemes is evaluated using artificially degraded image data at different signal-to-noise ratios (SNRs). The results show that substantial noise reduction has been achieved, and the high improvement in the mean square error, even at very low input SNR, is ensured. The results obtained consistently demonstrate the efficacy of the proposed TDJPL implementations, and illustrate the success in its use for adaptive restoration of images. >

Noise reduction with a multiscale edge representation and perceptual criteria

Abstract: The wavelet multiscale edge representation of signals developed by S.G. Mallat and S. Zhong (1991) provides a new tool for signal and image processing. A tree structure was built from wavelet-transform (WT) maxima, and metrics for analyzing the WT maxima tree were developed. These metrics fall into two classes corresponding to two perceptual criteria (scaling and spatial stabilities) for discriminating features from background noise. Identified noisy branches are trimmed off the WT maxima tree. This technique of noise reduction preserves edges well while suppressing noise. The results of processing simulated and medical images with this technique are presented. >

Decoupling capacitor effects on switching noise

Abstract: The experimental procedures and test vehicles used for the characterization of the decoupling capacitor efficiency in reducing the power supply differential switching noise of the multichip-module (MCM) package structure employed in the IBM ES/9000 system are described. The experimental results are summarized for various switching elements. It is demonstrated that careful design of the test vehicles, tester systems, and probes makes the accurate measurement of Delta-1 noise feasible. Experimental results on the BOBCAT tester show that the decoupling capacitor efficiency in reducing the peak of the differential Delta-1 noise is 50-67%. This efficiency can be increased by reducing the effective inductance in the decoupling capacitor current return path. >

Method and apparatus for processing images

Abstract: A method and apparatus for reducing noise and enhancing the dynamic range of an image data set gather from an array (12) of transducers (T). The method includes the step of processing the image data set in a digital computer (17) by a noise reduction technique, such as deconvolving the noise component by means of a CLEAN or other algorithm. Thereafter the artifact image data introduced by the noise reduction technique is reduced by masking the processed image data set with the original image data set. This masking is done by multiplying each data value in the processed image data set by the corresponding data value in the original image data set. The method further includes scaling and normalizing the masked data and finally displaying the same on an image display device (42). Additionally, for imaging apparatus (10) not having a cross-correlator (16), phase aberration is reduced by performing a coordinate transformation step prior to noise reduction using a non-standard set of coordinate transformation algorithms.

An adaptive impulse noise canceler for digital subscriber lines

Abstract: An adaptive impulse noise cancellation device is described. It is expected to substantially reduce the impact of impulse noise in asymmetrical digital subscriber lines (ADSLs) and will also benefit any digital transmission systems. It is capable of cancelling any of several different impulse shapes on a given loop, and the shapes can be learned by the device after it is installed. The canceler uses a relatively simple neuromorphic network. >

Reduction of semiconductor laser intensity noise by feedforward compensation: experiment and theory

Abstract: The authors have recently demonstrated that an optical feedforward compensation technique can be used to reduce distortion and intensity noise in semiconductor laser transmitters. In the present work, an experimental demonstration of noise reduction by feedforward compensation and a theoretical estimation of noise limitations of the optical feedforward system are described. It is shown that in an optimized feedforward system using state-of-the-art components the relative intensity noise (RIN) can be as low as -160 dB/Hz. >

Acoustic noise reduction in the MK 49 ship's inertial navigation system (SINS)

Abstract: Sperry Marine has devised a passive structure-borne noise isolation system that reduces the noise generated by dithered ring laser gyroscopes to levels below the requirements of MIL-STD-740-2. Descriptions of some of the analytical and experimental processes required to develop this system are presented, together with structure-borne noise test results. Results show that a 47-dB structure-borne noise reduction has been achieved with a noise isolation system that is compatible with the stability and repeatability required by navigation systems. The noise reduction techniques presented have enabled Sperry Marine to develop a dithered ring laser gyroscope navigator feasible for naval applications, the MK 49. >

A study of the generalized morphological filter

Abstract: A new class of morphological filters is proposed for image enhancement The filter, known as the generalized morphological filter (GMF), uses multiple structuring elements and combines linear and morphological operations The GMF can be designed to suppress various types of noise yet preserve geometrical structure in an image A study of several aspects of the performance of the filter is presented The study includes geometrical feature preservation, noise suppression, structuring element selection, and the root signal structure For the sake of comparison, averaging and median filters are also used in the experiments and corresponding figures of merit of the performance of the filter The empirical study shows that the generalized morphological filter possesses effective noise suppression with reduced geometrical feature blurring

Multiple widths yield reliable finite differences (computer vision)

Abstract: A finite difference edge finder in which the finite difference is computed at a range of widths, i.e. a range of distances between data points, is introduced. Wide operators report low-amplitude responses more reliably than narrow operators, so if wide operators are used to fill gaps in narrow operator responses, each operator can be restricted to report only statistically reliable responses without losing many real features. This sharply reduces the noise in the final output. Theoretical bounds on spurious responses in the finite difference outputs, given only weak assumptions about the signal and noise, are presented. The expected response of the edge finder to an ideal straight step edge is also analyzed. These performance measures are compared with those of a standard algorithm based on Gaussian smoothing and those of a second algorithm that also considers the spatial structure of noise. The algorithms prove equally good at suppressing noise, but are better able to detect faint or blurred features. These predictions are confirmed by empirical tests on real images. >

Resolving time-series structure with a controlled wavelet transform

Abstract: Wavelet transforms are powerful techniques that can decompose time series into both time and frequency components. Their application to experimental data has been hindered by the lack of a straightforward method to handle noise. A noise reduction technique, developed recently for use in wavelet cluster analysis in cosmology and astronomy, is adapted here for time-series data. Noise is filtered using control surrogate data sets generated from randomized aspects of the original time series. The method is a powerful extension of the wavelet transform that is readily applied to the detection of structure in stationary and nonstationary time series.