Reduce Measurement Noise Research Articles

Ballistocardiography and seismocardiography: a review of recent advances.

In the past decade, there has been a resurgence in the field of unobtrusive cardiomechanical assessment, through advancing methods for measuring and interpreting ballistocardiogram (BCG) and seismocardiogram (SCG) signals. Novel instrumentation solutions have enabled BCG and SCG measurement outside of clinical settings, in the home, in the field, and even in microgravity. Customized signal processing algorithms have led to reduced measurement noise, clinically relevant feature extraction, and signal modeling. Finally, human subjects physiology studies have been conducted using these novel instruments and signal processing tools with promising results. This paper reviews the recent advances in these areas of modern BCG and SCG research.

A degree of dispersion-based damage localization method

We present an efficient and robust damage localization method. Its applications therefore include defect location in shear buildings and beam structures. The proposed method is based on the knowledge of the difference of curvatures, computed for a structure before and after damage occurs. However, instead of using modal shapes for this purpose, as is frequently performed, the present method computes the curvature directly from acceleration signals, without identifying modal shapes of the structure. Additionally, the accelerations are subjected to averaging, which reduces measurement noise, and logarithm extraction, which renders the method independent of the amplitude of the loading impulse used for damage location. Another important feature of the method is that it does not require any calibration of numerical models, because it is solely based on measurement data. The presented method of damage location is illustrated with two examples, which involve experimental tests on laboratory-scale structures. The first example concerns defect location in a shear-building structure, and the second one in a spatially excited simply supported steel beam. Both cases confirm the effectiveness of the method, and its robustness to measurement noise. Copyright © 2015 John Wiley & Sons, Ltd.

Recent progress in laser-based trace gas instruments: performance and noise analysis

We review our recent results in development of high-precision laser spectroscopic instrumentation using mid-infrared quantum cascade lasers, interband cascade lasers and antimonide diode lasers. These instruments are primarily for high-precision and high-sensitivity measurements of atmospheric trace gases, as required for atmospheric research. The instruments are based on direct absorption spectroscopy with rapid sweeps, integration and precision fitting, under the control of high-capability software. By operating in the mid-infrared with long absorption path lengths at reduced pressure, we achieve excellent sensitivity. Some instruments have demonstrated a fractional precision of 10−4 for atmospheric trace gases at ambient concentration, allowing real-time isotopologue measurements of CO2, CO, CH4, N2O and H2O. Trace gas detection in ambient air at the low part-per-trillion levels is feasible. We also describe signal processing methods to identify and reduce measurement noise. Analysis of spectral information is largely based on loading spectra into arrays and then applying block operations such as filters, Fourier analysis, multivariate fitting and principal component analysis. We present mathematical expressions for averaged spectra in arrays and note different ways frequency aliasing can occur. We present an extended example of analysis of instrument noise and find an electronic signal mixing with an interference fringe.

Development of a mobile tracer correlation method for assessment of air emissions from landfills and other area sources

A standardized version of a mobile tracer correlation measurement method was developed and used for assessment of methane emissions from 15 landfills in 56 field deployments from 2009 to 2013. Using cavity ring-down spectroscopy and acetylene tracer gas, this method has potential implementation and cost advantages over other mobile tracer correlation approaches. The field deployment, data acquisition and analysis procedures, and a range of use conditions are discussed. To test real-world method application, the field studies were conducted by engineering technician-level personnel under randomly-encountered daytime atmospheric conditions. A total of 1876 mobile tracer correlation measurement transects were attempted over 131 field sampling days. Of these, 1366 transect (73%) were successfully completed and passed basic data acceptance criteria as valid measurement attempts. Invalid data were caused primarily by equipment failures, transect execution errors, or poor plume transport conditions. Valid transects were further analyzed using signal-to-noise ratio, plume correlation, and emission rate difference method quality indicators described here. Encountered scenarios that can result in high emission measurement uncertainty or bias are discussed in term of these indicators. Reasonable values for the acceptance levels of the method quality indicators that help protect against method errors and reduce measurement noise are discussed. The application of a default indicator set to the valid data yield 456 transects (33%) that pass data acceptance criteria. Transects that fail were associated with insufficient advected plume transport, poor correlation between the tracer and source plumes, and potential emissions pooling conditions.

Improved retrieval of nitrogen dioxide (NO<sub>2</sub>) column densities by means of MKIV Brewer spectrophotometers

Abstract. A new algorithm to retrieve nitrogen dioxide (NO2) column densities using MKIV ("Mark IV") Brewer spectrophotometers is described. The method includes several improvements, such as a more recent spectroscopic data set, the reduction of measurement noise, interference by other atmospheric species and instrumental settings, and a better determination of the zenith sky air mass factor. The technique was tested during an ad hoc calibration campaign at the high-altitude site of Izaña (Tenerife, Spain) and the results of the direct sun and zenith sky geometries were compared to those obtained by two reference instruments from the Network for the Detection of Atmospheric Composition Change (NDACC): a Fourier Transform Infrared Radiometer (FTIR) and an advanced visible spectrograph (RASAS-II) based on the differential optical absorption spectrometry (DOAS) technique. To determine the extraterrestrial constant, an easily implementable extension of the standard Langley technique for very clean sites without tropospheric NO2 was developed which takes into account the daytime linear drift of stratospheric nitrogen dioxide due to photochemistry. The measurement uncertainty was thoroughly determined by using a Monte Carlo technique. Poisson noise and wavelength misalignments were found to be the most influential contributors to the overall uncertainty, and possible solutions are proposed for future improvements. The new algorithm is backward-compatible, thus allowing for the reprocessing of historical data sets.

Designing and optimizing a healthcare kiosk for the community

Investigating new ways to deliver care, such as the use of self-service kiosks to collect and monitor signs of wellness, supports healthcare efficiency and inclusivity. Self-service kiosks offer this potential, but there is a need for solutions to meet acceptable standards, e.g. provision of accurate measurements. This study investigates the design and optimization of a prototype healthcare kiosk to collect vital signs measures. The design problem was decomposed, formalized, focused and used to generate multiple solutions. Systematic implementation and evaluation allowed for the optimization of measurement accuracy, first for individuals and then for a population. The optimized solution was tested independently to check the suitability of the methods, and quality of the solution. The process resulted in a reduction of measurement noise and an optimal fit, in terms of the positioning of measurement devices. This guaranteed the accuracy of the solution and provides a general methodology for similar design problems.

NOISE IMMUNITY RESEARCH FOR NONLINEAR DYNAMICAL SYSTEMS IDENTIFICATION BASED ON VOLTERRA MODEL IN FREQUENCY DOMAIN

The accuracy and noise immunity of the interpolation method of nonlinear dynamical systems identification based on the Volterra model in the frequency domain is studied in this paper. The polyharmonic signals are used for the testing the method. The algorithmic and software toolkit in Matlab is developed for the identification procedure. This toolkit is used to construct the informational models of test system and communication channel. The model is built as a first-, second- and third-order amplitude–frequency and phase–frequency characteristics. The comparison of obtained characteristics with previous works is given. Wavelet denoising is studied and applied to reduce measurement noise.

Noise reduction capacity of a composite pavement system

Rapid economic development has induced massive road construction, due to increased traffic and travel speeds. However, this development has produced numerous social problems, such as air pollution, traffic noise and road vibration. By applying the theory of Helmholtz resonators to asphalt pavement, special concrete blocks in the base course of asphalt pavement can be used to alleviate various types of traffic noise, such as noise produced by vehicle engines and tire. This research examines two laboratory tests on the sound absorption effect of concrete block and base concrete block, and their applicability in the construction of quiet pavements. The noise reduction effects of the specimens, which are constructed with a fixed size, space, and depth for each hole, are analyzed using different vehicle noise levels. Based on the test results for vehicle noise volume, measurement distance, and form and size of the hole in which the base concrete block is placed, the use of special concrete base and quiet asphalt surface was determined to be a good alternative solution for traffic noise levels in the range of 4 dB to 9 dB. Noise reduction effects were separated into two parts:, a different Hot Mix Asphalt (HMA) on the same base concrete block, and a different base block with the same HMA. HMA 3 on the same base concrete block exhibited optimum noise reduction effects with measured noise reduction values in the range of 3 dB to 6 dB. The measured noise reduction values of different base concretes, using the same HMA, ranged e dB to 4 dB. This result means that a quiet asphalt surface exhibited a greater noise reduction effect than a hole in the concrete base block. Based on the test results, the use of HMA 3 in Base D exhibited optimal performance.

Improved light collection and wavelet de-noising enable quantification of cerebral blood flow and oxygen metabolism by a low-cost, off-the-shelf spectrometer

Broadband continuous-wave near-infrared spectroscopy (CW-NIRS) is an attractive alternative to time-resolved and frequency-domain techniques for quantifying cerebral blood flow (CBF) and oxygen metabolism in newborns. However, efficient light collection is critical to broadband CW-NIRS since only a small fraction of the injected light emerges from any given area of the scalp. Light collection is typically improved by optimizing the contact area between the detection system and the skin by means of light guides with large detection surface. Since the form-factor of these light guides do not match the entrance of commercial spectrometers, which are usually equipped with a narrow slit to improve their spectral resolution, broadband NIRS spectrometers are typically custom-built. Nonetheless, off-the-shelf spectrometers have attractive advantages compared to custom-made units, such as low cost, small footprint, and wide availability. We demonstrate that off-the-shelf spectrometers can be easily converted into suitable instruments for deep tissue spectroscopy by improving light collection, while maintaining good spectral resolution, and reducing measurement noise. The ability of this approach to provide reliable cerebral hemodynamics was illustrated in a piglet by measuring CBF and oxygen metabolism under different anesthetic regimens.

Reduction of Noise in Measurements of Phasor Angles by Using Two Digital Filters

An electric power system is monitored and controlled on the basis of its phasor information, such as amplitude, phase angle, and frequency. This phasor can be measured through discrete Fourier transform (DFT) coefficients of its positive nominal frequency. Then, the frequency estimate can be calculated from time variation of the measured phasor angle. The accuracy of the phasor-angle measurement and the frequency estimation are severely affected by noise in the power system signal and the leakage of the negative fundamental frequency in DFT. This paper proposes a DFT-based phasor-angle measurement algorithm to cope with both the noise effect and the leakage effect. In addition, a frequency estimation algorithm is developed to use the same technique in the phasor-angle measurement algorithm. These algorithms introduce two digital filters for the reduction of the noise effect. The effectiveness of the proposed algorithm in the noise effect reduction is verified through simulations.

DTIPrep: quality control of diffusion-weighted images.

In the last decade, diffusion MRI (dMRI) studies of the human and animal brain have been used to investigate a multitude of pathologies and drug-related effects in neuroscience research. Study after study identifies white matter (WM) degeneration as a crucial biomarker for all these diseases. The tool of choice for studying WM is dMRI. However, dMRI has inherently low signal-to-noise ratio and its acquisition requires a relatively long scan time; in fact, the high loads required occasionally stress scanner hardware past the point of physical failure. As a result, many types of artifacts implicate the quality of diffusion imagery. Using these complex scans containing artifacts without quality control (QC) can result in considerable error and bias in the subsequent analysis, negatively affecting the results of research studies using them. However, dMRI QC remains an under-recognized issue in the dMRI community as there are no user-friendly tools commonly available to comprehensively address the issue of dMRI QC. As a result, current dMRI studies often perform a poor job at dMRI QC. Thorough QC of dMRI will reduce measurement noise and improve reproducibility, and sensitivity in neuroimaging studies; this will allow researchers to more fully exploit the power of the dMRI technique and will ultimately advance neuroscience. Therefore, in this manuscript, we present our open-source software, DTIPrep, as a unified, user friendly platform for thorough QC of dMRI data. These include artifacts caused by eddy-currents, head motion, bed vibration and pulsation, venetian blind artifacts, as well as slice-wise and gradient-wise intensity inconsistencies. This paper summarizes a basic set of features of DTIPrep described earlier and focuses on newly added capabilities related to directional artifacts and bias analysis.

Study of self-calibration and multilateration in machine tool volumetric verification for laser tracker error reduction

This article aims to present the influence of the measurement uncertainty of a commercial laser tracker on the volumetric verification of a machine tool through the study of verification procedures that are affected by measurement uncertainty, multilateration and laser tracker self-calibration. Self-calibration provides relative positioning between measuring coordinate systems (laser trackers) and the reference system from the measured points of the same mesh. The measured points are affected by the noise of each laser tracker; therefore, they provide positions that are different from the real positions of the laser trackers. By applying the technique of multilateration and by knowing the positions of the laser trackers, the measurement noise can be reduced. The range of the measurement noise reduction is influenced by the radial measurement noise of the laser tracker, the distance between the laser tracker and the measured point and the techniques that multilateration and laser tracker self-calibration employs. This article presents different laser tracker self-calibration procedures, a least squares adjustment, trilateration and quadrilateration as well as the scope and appropriateness of each method relative to the laser tracker measurement noise. Moreover, the influences of radial laser tracker noise on the trilateration and quadrilateration techniques are described as well as the influence of the distance between the laser tracker and the measured point on multilateration.

Efficient application of encapsulated bubbles and foam elements to mitigate offshore piling noise

The very high noise levels of offshore piling noise during the installation of offshore wind converters are dangerous to marine life like harbor porpoises and fishes. Encapsulated bubbles and foam elements are successfully used to reduce the very high noise levels. There are different physical effects such as impedance mismatch, resonance and scattering effects and material damping effects that are responsible to the measured noise reduction between about 10 dB (SEL) and 23 dB (SEL). The radiation of underwater noise from the pile surface, the propagation and the reflections of the radiated waves are investigated together with the influence of encapsulated bubbles and foam elements in the near field of the pile. Only a very small part of the impact energy is radiated directly from the pile into the surrounding water. Most of the hammer energy is driven into the ground. A small part from this is radiated indirectly from the ground into the water. The efficiency of encapsulated bubbles and foam elements in underwater noise mitigation is investigated by theoretical studies, laboratory measurements, and by offshore measurements with different elements and combinations.

Quantitative evaluation of spatio-temporal heat transfer to a turbulent air flow using a heated thin-foil

Spatial and temporal variation of heat transfer to a turbulent air flow was evaluated experimentally, employing a technique from high-speed infrared thermography that records temperature fluctuation on a heated thin-foil. Although the temperature variation on the foil attenuated in time and space due to the thermal inertia and lateral conduction, it was possible to restore the quantitative heat transfer by solving the inverse heat conduction equation. In this paper, the experimental technique and the procedure to evaluate the heat transfer coefficient are described which includes low-pass filtering to reduce measurement noise and inverse heat conduction analysis inside the test surface. The time-spatial variation of the heat transfer evaluated here was confirmed to be reliable by comparing the statistics with the existing experimental and numerical results. In addition, a unique feature of the spatio-temporal heat transfer for the turbulent boundary layer is observed that correlates with flow features in the near-wall region such as the streak structure.

Sensorless enhancement of an atomic force microscope micro-cantilever quality factor using piezoelectric shunt control

The image quality and resolution of the Atomic Force Microscope (AFM) operating in tapping mode is dependent on the quality (Q) factor of the sensing micro-cantilever. Increasing the cantilever Q factor improves image resolution and reduces the risk of sample and cantilever damage. Active piezoelectric shunt control is introduced in this work as a new technique for modifying the Q factor of a piezoelectric self-actuating AFM micro-cantilever. An active impedance is placed in series with the tip oscillation voltage source to modify the mechanical dynamics of the cantilever. The benefit of using this control technique is that it removes the optical displacement sensor from the Q control feedback loop to reduce measurement noise in the loop and allows for a reduction in instrument size.

An innovative neural forecast of cumulative oil production from a petroleum reservoir employing higher-order neural networks (HONNs)

Abstract Precise and consistent production forecasting is indeed an important step for the management and planning of petroleum reservoirs. A new neural approach to forecast cumulative oil production using higher-order neural network (HONN) has been applied in this study. HONN overcomes the limitation of the conventional neural networks by representing linear and nonlinear correlations of neural input variables. Thus, HONN possesses a great potential in forecasting petroleum reservoir productions without sufficient training data. Simulation studies were carried out on a sandstone reservoir located in Cambay basin in Gujarat, India, to prove the efficacy of HONNs in forecasting cumulative oil production of the field with insufficient field data available. A pre-processing procedure was employed in order to reduce measurement noise in the production data from the oil field by using a low pass filter and optimal input variable selection using cross-correlation function (CCF). The results of these simulation studies indicate that the HONN models have good forecasting capability with high accuracy to predict cumulative oil production.

Influence of measurement noise and laser arrangement on measurement uncertainty of laser tracker multilateration in machine tool volumetric verification

Abstract This paper aims to present different techniques and factors that affect the measurement accuracy of a commercial laser tracker responsible for capturing checkpoints used in machine tool volumetric verification. This study was conducted to uncover various sources of error affecting the measurement uncertainty of the laser tracker, additional sources of error that further contributed to the uncertainty, and the factors influencing these techniques. We also define several noise reduction techniques for the measurements. The improvement in the accuracy of captured points focuses on a multilateration technique and its various resolution methods both analytically and geometrically. Similarly, we present trilateration and least squares techniques that can be used for laser tracker self-calibration, which is an essential parameter in multilateration. This paper presents the influence of the spatial distribution of laser trackers (LTs) in measurement noise reduction by multilateration, which produces an improvement in volumetric error machine tool reduction. A study of the spatial angle between LTs, the distance and the visibility of the point to be measured are presented using a synthetic test. All of these factors limit the scope of multilateration. Similarly, a comparison of self-calibration techniques using the least squares and trilateration methods with which to determine the relative position of the laser tracker employees is presented. We also present the influence of the relationship between the radial and angular measurement noise self-calibration processes as it relates to the volumetric error reduction achieved by the machine tool with multilateration. All studies were performed using synthetic tests generated using a synthetic data parametric generator.

CFD analysis of a transfer matrix of exhaust muffler with mean flow and prediction of exhaust noise

A multi-dimensional computational fluid dynamics (CFD) approach was proposed in this study aiming to calculate the transfer matrix of an engine exhaust muffler in the conditions with and without mean flow. The CFD model of the muffler with absorptive material defined as porous zone was calibrated with the measured noise reduction without mean flow, and was further employed to study the effect of the mean flow on the acoustic performance of the muffler. Furthermore, the exhaust acoustical source was derived from the calculated transfer matrices of six different additional acoustic loads obtained by the proposed CFD approach as well as the measured tail noise based on a multiload least squares method. Finally, the exhaust noise was predicted based on Thevenin’s theorem. The proposed CFD approach was suggested to be able to predict the acoustic performance of a complex muffler considering mean flow (without and with mean flow) and heat transfer, and provide reasonable results of the exhaust noise.

Image processing for three-dimensional scans generated by time-of-flight range cameras

Time-of-flight (TOF) full-field range cameras use a correlative imaging technique to generate three-dimensional measurements of the environment. Though reliable and cheap they have the disadvantage of high measurement noise and errors that limit the practical use of these cameras in industrial applications. We show how some of these limitations can be overcome with standard image processing techniques specially adapted to TOF camera data. Additional information in the multimodal images recorded in this setting, and not available in standard image processing settings, can be used to improve reduction of measurement noise. Three extensions of standard techniques, wavelet thresholding, adaptive smoothing on a clustering based image segmentation, and an extended anisotropic diffusion filtering, make use of this information and are compared on synthetic data and on data acquired from two different off-the-shelf TOF cameras. Of these methods, the adapted anisotropic diffusion technique gives best results, and is implementable to perform in real time using current graphics processing unit (GPU) hardware. Like traditional anisotropic diffusion, it requires some parameter adaptation to the scene characteristics, but allows for low visualization delay and improved visualization of moving objects by avoiding long averaging periods when compared to traditional TOF image denoising.

A novel easy-to-use phantom for the determination of MTF in SPECT scanners

To evaluate modulation transfer function (MTF) in single photon emission computed tomography (SPECT) systems using the line spread function (LSF) method and a novel flood source which can be easily fabricated with materials accessible in hospital facilities. A Tc-99m-based flood source (E(γ) = 140 keV) consisting of a radiopharmaceutical bound to the grains of a radiographic film was prepared in laboratory. Various films and radiopharmaceuticals were examined, in order to obtain a thin homogenous and reproducible flood source. The source showing best uniformity and reproducibility was placed between two PMMA blocks and images were obtained by using the brain tomographic acquisition protocol (brain) and the myocardial perfusion tomographic acquisition protocol (heart). MTF was evaluated by determining the LSF for various reconstruction methods and filters. MTF calculation was obtained by the utilization of a custom made software in which a method similar to the one proposed by Boone [Med. Phys. 28, 356-360 (2001)] was implemented. All imaging experiments were performed in a Siemens e-Cam γ-camera. Furthermore, MTF was assessed through the point spread function (PSF) following conventional methods. The optimum homogeneity was obtained by immersing an Agfa MammoRay HDR Medical x-ray film in a solution of dithiothreitol (DTT, 10(-3) M)/Tc-99m(III)-DMSA (DMSA: trivalent technetium-99m-dimercapto-succinic acid, 40 mCi/40 ml) for 30 min in the dark. These films exhibited better uniformity (CV < 1.9%). Higher MTF values were obtained for the brain scan protocol with iterative 3D with eight iterations reconstruction method. MTF of the brain protocol was in all cases better than the heart protocol. MTFs derived from LSF were more precise compared with those obtained from PSF since their reproducibility was better in all cases, providing a mean standard deviation of 0.0065, in contrary to the PSF method which gave 0.0348. The method presented here is novel and easy to implement, requiring materials commonly found in clinical practice. Furthermore, this technique which is based on the LSF method reduces measurement noise levels due to the larger amount of data averaging than in the conventional PSF method. Furthermore, MTF can be assessed easily, in three dimensions (3D), by placing the flood source either in sagittal or coronal direction.