Distance Measurement Uncertainty Research Articles

A Multi-Sensor Fusion Approach Based on PIR and Ultrasonic Sensors Installed on a Robot to Localise People in Indoor Environments.

This work illustrates an innovative localisation sensor network that uses multiple PIR and ultrasonic sensors installed on a mobile social robot to localise occupants in indoor environments. The system presented aims to measure movement direction and distance to reconstruct the movement of a person in an indoor environment by using sensor activation strategies and data processing techniques. The data collected are then analysed using both a supervised (Decision Tree) and an unsupervised (K-Means) machine learning algorithm to extract the direction and distance of occupant movement from the measurement system, respectively. Tests in a controlled environment have been conducted to assess the accuracy of the methodology when multiple PIR and ultrasonic sensor systems are used. In addition, a qualitative evaluation of the system's ability to reconstruct the movement of the occupant has been performed. The system proposed can reconstruct the direction of an occupant with an accuracy of 70.7% and uncertainty in distance measurement of 6.7%.

Evidence for baryon acoustic oscillations from galaxy–ellipticity correlations

The baryon acoustic oscillation feature in the clustering of galaxies or quasars provides a ‘standard ruler’ for distance measurements in cosmology. In this work, we report a 2–3σ signal of the baryon acoustic oscillation dip feature in the galaxy density–ellipticity cross-correlation functions using the spectroscopic sample of the Baryon Oscillation Spectroscopic Survey CMASS, combined with the deep Dark Energy Spectroscopic Instrument Legacy Imaging Surveys for precise galaxy shape measurements. We measure the galaxy–ellipticity correlation functions and model them using the linear alignment model. We constrain the distance DV/rd to redshift 0.57 to a precision of 3–5%, depending on the details of modelling. The galaxy–ellipticity measurement reduces the uncertainty of distance measurement by ~10% on top of that derived from the galaxy–galaxy correlation. More importantly, for future large and deep galaxy surveys, the independent galaxy–ellipticity measurements can help sort out the systematics in the baryon acoustic oscillation studies.

Improved uncertainty evaluation for a long distance measurement by means of a temperature sensor network

The aim of the research described in this paper was to more accurately determine the measurement uncertainty of an interferometric long distance measurement. The chosen method was to install a temperature sensor network in the laboratory to measure in more detail the ambient temperature profile to more accurately determine the local values of the refractive index on the path travelled by the laser light. The experimental measurements were supplemented by a theoretical analysis of the mathematical model being used. The outcome of the performed work was that the claimed measurement uncertainty of the distance measurement, which is based on using only 5 temperature sensors, was justified. However, if in the future a lower uncertainty would be needed, a sensor network like the one that was temporarily installed would be needed. During the measurement campaign an offset in the mean temperature of 0.2 °C was found, which was equal to the maximum allowed bias in view of the claimed uncertainty for the long distance measurement. At a more general level, it was concluded that such sensor networks provide a useful new tool to increase the understanding of other measurements, to validate assumptions and optimize existing measurements.

Application of a Space-based Optical Interferometer Toward Measuring Cosmological Distances of Quasars

Measuring quasar distance through joint analysis of spectroastrometry and reverberation mapping observations is a new method for driving the development of cosmology. In this paper, we carry out detailed simulation and analysis to study the effect of four basic observational parameters (baseline length, exposure time, equivalent diameter and spectral resolution) on the data quality of differential phase curves (DPCs), and furthermore on the accuracy of distance measurement. In our simulation, we adopt an axisymmetrical disk model of a broad line region (BLR) to generate differential phase signals. We find that the differential phases and their Poisson errors could be amplified by extending the baseline, while the influence of optical path difference errors can be reduced during fitting the BLR model. Longer exposure time or larger equivalent diameter helps reduce the absolute Poisson error. Therefore, the relative error of DPCs could be reduced by increasing any of the above three parameters, then the accuracy of distance measurement could be improved. In contrast, the uncertainty of absolute angular distances (D A) could be improved with higher spectral resolution, although the relative error of DPCs would be amplified. We show how the uncertainty of distance measurement varies with the relative error of DPCs. For our specific set of model parameters, without considering more complicated structures and kinematics of BLRs in our simulation, it is found that the relative error of DPCs < 20% is a limit for accurate distance measurement. The relative error of DPCs has a lower limit (roughly 5%) and the uncertainty in distance measurement can be better than 2%.

Learning of uncertainty in an introductory astronomy course in remote asynchronous delivery during Covid-19 lockdown

The teaching of an introductory astronomy course in remote delivery during Covid-19 lockdown encountered a unique issue in terms of a mixture of three student groups. They are the science majors, science-interested students, and non-science majors to satisfy science requirement in our Two-year community college located in New York City. The learning of how to assess uncertainty would be of a universal concern in the three groups. Uncertainty examples includes shoe size selection experience in daily life for non-science majors, distance measurement uncertainty for science-interested students who are parents, and simulation uncertainty for science majors. Reciting or memorizing a narrative in remote learning should be supplemented with a discussion using an alternative perspective with intellectual maturity, and the uncertainty theme would fit well for the learning of any chapters in an astronomy textbook. Assessment exercise questions are developed. The strategy to discourage rote learning and plagiarism in the remote asynchronous delivery of introductory astronomy at the college level is discussed.

Quantification of source-to-site distance uncertainty in ground motion models

Among different input data, source-to-site distance plays a major role in the results of ground motion models (GMMs). In order to determine the source-to-site distance, geometric characteristics of the seismic source need to be specified. This can be challenging when the seismic source is not known thoroughly. Empirical relationships themselves which are used to determine the geometric characteristics of seismic sources contain large degree of uncertainty. In this paper, a simple algorithm based on Monte Carlo (MC) simulation method which quantifies the uncertainties in distance metric and geometric characteristics of seismic sources is proposed. The jointly effects of magnitude and distance are considered in the proposed algorithm for uncertainties modeling. Also, this algorithm has been used to quantified errors resulted from inputting inaccurate source-to-site distance metrics in the GMMs. NGA-West2 global GMMs and event-specific isotropic and non-isotropic GMMs are used in the analysis. The results demonstrate that the uncertainty in the measurement of different source-to-site distance definitions depends on the magnitude and on the location of site with respect to the seismic source. It is also observed that the distance measurement uncertainty has a direct effect on the outcomes of GMMs. GMMs’ coefficient of variation maps demonstrate that the amount of uncertainty is higher around the fault; for large magnitudes, outcome variation of GMMs reaches as high as 40% of the average predictions. The coefficient of variation in GMM results decreases with the increase in distance metrics considered where at a distance beyond 30 km, the coefficient of variation of GMM estimates drops from 40 to 10%.

Reconstruction of a Deformed Tumor Based on Fiducial Marker Registration: A Computational Feasibility Study

Interstitial photodynamic therapy has shown promising results in the treatment of locally advanced head and neck cancer. In this therapy, systemic administration of a light-sensitive drug is followed by insertion of multiple laser fibers to illuminate the tumor and its margins. Image-based pretreatment planning is employed in order to deliver a sufficient light dose to the complex locally advanced head-and-neck cancer anatomy, in order to meet clinical requirements. Unfortunately, the tumor may deform between pretreatment imaging for the purpose of planning and intraoperative imaging when the plan is executed. Tumor deformation may result from the mechanical forces applied by the light fibers and variation of the patient’s posture. Pretreatment planning is frequently done with the assistance of computed tomography or magnetic resonance imaging in an outpatient suite, while treatment monitoring and control typically uses ultrasound imaging due to considerations of costs and availability in the operation room. This article presents a computational method designed to bridge the gap between the 2 imaging events by taking a tumor geometry, reconstructed during preplanning, and by following the displacement of fiducial markers, which are initially placed during the preplanning procedure. The deformed tumor shape is predicted by solving an inverse problem, seeking for the forces that would have resulted in the corresponding fiducial marker displacements. The computational method is studied on spheres of variable sizes and demonstrated on computed tomography reconstructed locally advanced head and neck cancer model. Results of this study demonstrate an average error of less than 1 mm in predicting the deformed tumor shape, where 1 mm is typically the order of uncertainty in distance measurements using magnetic resonance imaging or computed tomography imaging and high-quality ultrasound imaging. This study further demonstrates that the deformed shape can be calculated in a few seconds, making the proposed method clinically relevant.

Three-dimensional temperature field compensation technology for large-scale ultrasonic positioning system

Large-scale ultrasonic positioning systems have recently shown substantial improvement, according to the current great interest concerning large-scale metrology applications in many different fields of manufacturing industry. However, the sound velocity is greatly influenced by the ambient temperature especially in large-scale applications. The traditional sound velocity compensation method mainly uses the average temperature in measurement space based on an assumption that the temperature field is uniform and stable. As the assumption is invalid in most cases, especially in industrial measurement environments, the traditional compensation method will bring obvious errors. To reduce these errors caused by sound velocity, this article proposes a novel compensation method by constructing a three-dimensional temperature field of measurement space through heat transfer theory as well as the finite element method, and then estimating the distance accurately using a couple iterating algorithm. Verification experiments demonstrate that the ranging deviation estimated through the proposed method may keep within 0.5 mm in 5.4×2 m measurement space, whereas the average distance measurement uncertainty is about 0.25 mm.

The MCCB Electrical Clearance and Creepage Distance Measurement Uncertainty Evaluation

The electrical clearance and creepage distance are two key parameters for the design of MCCB (molded case circuit breaker, MCCB), which directly influences the electrical safety performance of MCCB. In this paper, the electrical clearance and creepage distance measurement uncertainty were evaluated through the uncertainty sources analysis, the mathematical model establishment and the components uncertainty calculation, to ensure the accuracy of the measurement results.

Precision of frequency scanning interferometry distance measurements in the presence of noise

A lower limit-the Cramér-Rao bound-on the variance of frequency scanning interferometry (FSI) distance measurements in the presence of noise is presented. We show that, with a suitable analysis method, the variance of experimental measurements almost reaches this limit. In particular, the variance of results with a simple analysis method was 1.54 times the limit over a range of signal-to-noise ratios. This bound aids the understanding of FSI distance measurement uncertainty, and provides a benchmark against which to compare FSI analysis algorithms.

UTILITY OF GALAXY CATALOGS FOR FOLLOWING UP GRAVITATIONAL WAVES FROM BINARY NEUTRON STAR MERGERS WITH WIDE-FIELD TELESCOPES

The first detections of gravitational waves from binary neutron star mergers with advanced LIGO and Virgo observatories are anticipated in the next five years. These detections could pave the way for multi-messenger gravitational-wave (GW) and electromagnetic (EM) astronomy if GW triggers are successfully followed up with targeted EM observations. However, GW sky localization is relatively poor, with expected localization areas of ~10--100 square degrees; this presents a challenge for following up GW signals from compact binary mergers. Prioritizing wide-field follow-ups based on the probability of successful imaging is important when it is impossible to tile the entire gravitational-wave localization region. Galaxy catalogs were effective at narrowing down regions of the sky to search in initial attempts at joint GW/EM observations. The next generation of GW detectors will have a ten-fold increase in range thereby increasing the expected number of galaxies per unit solid angle a thousand-fold. As an additional complication, catalogs may be highly incomplete. We show how to quantify the advantages of using galaxy catalogs as a function of only two parameters: the three-dimensional volume within the field of view of a telescope after accounting for the GW distance measurement uncertainty, and the fraction of the GW sky localization uncertainty region that can be followed up. We find that the use of galaxy catalogs can improve success rates by ~10% to a factor of 4 relative to follow-up strategies that do not utilize such catalogs for the scenarios we considered. We determine that catalogs with a 75% completeness perform comparably to complete catalogs in most cases, while 33%-complete catalogs can lead to lower follow-up success rates than complete catalogs for small fields of view, though still providing an advantage over strategies that do not use a catalog at all.

Quasistatic microscanner with linearized scanning for an adaptive three-dimensional laser camera

This paper reports on a gimbaled MEMS scanning mirror with quasistatic resonant actuation, specially developed for adaptive raster scanning in an innovative three-dimensional (3-D) time-of-flight (ToF) laser camera with real-time foveation. Large quasistatic deflections of ±10 deg are provided by vertical comb drives in the vertical direction in contrast to resonant horizontal scanning. This mirror is 2.6×3.6 mm and operates at 1600 Hz with an 80-deg optical scan range. For position feedback, piezo-resistive position sensors are integrated on chip for both axes. To guarantee the full reception aperture of effectively 5 mm, a synchronized driven MEMS scanner array—consisting of five hybrid assembled MEMS devices—is used in an innovative 3-D ToF laser scanner. This enables a distance measuring rate of 1 MVoxel/s with an uncertainty in distance measurement of 3 to 5 mm for a 7.5-m measuring range for a gray target. Flatness-based open loop control is used for driving control of quasistatic axis in order to compensate for the dynamics of the low damped MEMS system.

Estimation of distance error by fuzzy set theory required for strength determination of HDR (192)Ir brachytherapy sources.

Verification of the strength of high dose rate (HDR) 192Ir brachytherapy sources on receipt from the vendor is an important component of institutional quality assurance program. Either reference air-kerma rate (RAKR) or air-kerma strength (AKS) is the recommended quantity to specify the strength of gamma-emitting brachytherapy sources. The use of Farmer-type cylindrical ionization chamber of sensitive volume 0.6 cm3 is one of the recommended methods for measuring RAKR of HDR 192Ir brachytherapy sources. While using the cylindrical chamber method, it is required to determine the positioning error of the ionization chamber with respect to the source which is called the distance error. An attempt has been made to apply the fuzzy set theory to estimate the subjective uncertainty associated with the distance error. A simplified approach of applying this fuzzy set theory has been proposed in the quantification of uncertainty associated with the distance error. In order to express the uncertainty in the framework of fuzzy sets, the uncertainty index was estimated and was found to be within 2.5%, which further indicates that the possibility of error in measuring such distance may be of this order. It is observed that the relative distance li estimated by analytical method and fuzzy set theoretic approach are consistent with each other. The crisp values of li estimated using analytical method lie within the bounds computed using fuzzy set theory. This indicates that li values estimated using analytical methods are within 2.5% uncertainty. This value of uncertainty in distance measurement should be incorporated in the uncertainty budget, while estimating the expanded uncertainty in HDR 192Ir source strength measurement.

Set-Membership Adaptive Localization Algorithm with Time-Varying Error Bounds for Underwater Wireless Sensor Networks

This paper presents a set-membership adaptive localization algorithm with time-varying error bounds for underwater wireless sensor networks (UWSNs). In large-scale UWSNs, the nonstationary underwater environments, the insufficient prior information of hybrid noise, the small sample size of available distance measurements, and the node mobility all pose severe challenges for localization, and most current schemes are not applicable. Unlike most of the existing approaches, we tackle the multihop localization problem in a set-membership framework based on the consideration that the distance measurement uncertainty can be cast into an unknown but bounded (UBB) context. The principle of our scheme is firstly to use the bootstrap method to build confidence intervals and error bounds from a small sample set of distance measurements and then to determine the positions by a low-complexity interval analysis method as well as an adaptive localization update specification with time-varying error bounds. Simulation results show that our proposed scheme is an effective and efficient localization approach in large-scale UWSNs.

Displacement, distance, and shape measurements of fast-rotating rough objects by two mutually tilted interference fringe systems

The precise distance measurement of fast-moving rough surfaces is important in several applications such as lathe monitoring. A nonincremental interferometer based on two mutually tilted interference fringe systems has been realized for this task. The distance is coded in the phase difference between the generated interference signals corresponding to the fringe systems. Large tilting angles between the interference fringe systems are necessary for a high sensitivity. However, due to the speckle effect at rough surfaces, different envelopes and phase jumps of the interference signals occur. At large tilting angles, these signals become dissimilar, resulting in a small correlation coefficient and a high measurement uncertainty. Based on a matching of illumination and receiving optics, the correlation coefficient and the phase difference estimation have been improved significantly. For axial displacement measurements of recurring rough surfaces, laterally moving with velocities of 5 m/s, an uncertainty of 110 nm has been attained. For nonrecurring surfaces, a distance measurement uncertainty of 830 nm has been achieved. Incorporating the additionally measured lateral velocity and the rotational speed, the two-dimensional shape of rotating objects results. Since the measurement uncertainty of the displacement, distance, and shape is nearly independent of the lateral surface velocity, this technique is predestined for fast-rotating objects, such as crankshafts, camshafts, vacuum pump shafts, or turning parts of lathes.

Set‐membership localisation algorithm based on adaptive error bounds for large‐scale underwater wireless sensor networks

Proposed is a new set-membership approach based on adaptive error bounds to solve multi-hop localisation problems in the cases where the prior information is insufficient and only a very few distance measurements are available, which are commonly encountered in large-scale underwater wireless sensor networks. Unlike most of the existing schemes, the localisation problem is solved in a set-membership framework which is based on the consideration that the distance measurement uncertainty can be cast into an unknown but bounded context. For the first time, an adaptive bounds specification is introduced into multi-hop localisation for eliminating the risk of overbounding or underbounding. To reduce the computational burden, boxes are utilised to approximate the irregular intersection of all feasible solutions. Then the feasible sets and coordinates of ordinary nodes are obtained by using the interval analysis method. Simulation results confirm the effectiveness of the algorithm.

MID-INFRARED PERIOD-LUMINOSITY RELATIONS OF RR LYRAE STARS DERIVED FROM THEWISEPRELIMINARY DATA RELEASE

Interstellar dust presents a significant challenge to extending parallax-determined distances of optically observed pulsational variables to larger volumes. Distance ladder work at mid-infrared wavebands, where dust effects are negligible and metallicity correlations are minimized, have been largely focused on few-epoch Cepheid studies. Here we present the first determination of mid-infrared period-luminosity (PL) relations of RR Lyrae stars from phase-resolved imaging using the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE). We present a novel statistical framework to predict posterior distances of 76 well-observed RR Lyrae that uses the optically constructed prior distance moduli while simultaneously imposing a power-law PL relation to WISE-determined mean magnitudes. We find that the absolute magnitude in the bluest WISE filter is M_W1 = (-0.421+-0.014) - (1.681+-0.147)*log(P/0.50118 day), with no evidence for a correlation with metallicity. Combining the results from the three bluest WISE filters, we find that a typical star in our sample has a distance measurement uncertainty of 0.97% (statistical) plus 1.17% (systematic). We do not fundamentalize the periods of RRc stars to improve their fit to the relations. Taking the Hipparcos-derived mean V-band magnitudes, we use the distance posteriors to determine a new optical metallicity-luminosity relation which we present in Section 5. The results of this analysis will soon be tested by HST parallax measurements and, eventually, with the Gaia astrometric mission.

Absolute interferometry with a 670-nm external cavity diode laser

In the past few years there has been much interest in use of tunable diode lasers for absolute interferometry. Here we report on use of an external cavity diode laser operating in the visible (lambda approximately 670 nm) for absolute distance measurements. Under laboratory conditions we achieve better than 1-microm standard uncertainty in distance measurements over a range of 5 m, but significantly larger uncertainties will probably be more typical of shop-floor measurements where conditions are far from ideal. We analyze the primary sources of uncertainty limiting the performance of wavelength-sweeping methods for absolute interferometry, and we discuss how errors can be minimized. Many errors are greatly magnified when the wavelength sweeping technique is used; sources of error that are normally relevant only at the nanometer level when standard interferometric techniques are used may be significant here for measurements at the micrometer level.

A generic coordinate transformation uncertainty assessment approach and its application in machine vision metrology

A measurement result is complete only when accompanied by a quantitative statement of its uncertainty [1]. However, there is no unified approach to the expression and computation of uncertainty, especially when coordinate transformations are involved. A generic approach to the uncertainty analysis of coordinate transformations based on constrained optimization uncertainty analysis is presented in this paper. The nonlinear constrained optimization algorithm used in this paper is a more generic algorithm for coordinate referencing than conventional 3-2-1 nesting method. We performed analysis on two types of uncertainty computation that relate to the final measurement: uncertainty of a single point in a world frame and uncertainty of distance measurement. The proposed method provides a mechanism for on-line assessment of measurement uncertainties on any coordinate measuring machines, mechanical or optical. Results of Monte Carlo simulation from a structured-light optical coordinate measurement machine (CMM) show that under normal machine operation conditions the approximations are valid.

Laser triangulation: fundamental uncertainty in distance measurement

We discuss the uncertainty limit in distance sensing by laser triangulation. The uncertainty in distance measurement of laser triangulation sensors and other coherent sensors is limited by speckle noise. Speckle arises because of the coherent illumination in combination with rough surfaces. A minimum limit on the distance uncertainty is derived through speckle statistics. This uncertainty is a function of wavelength, observation aperture, and speckle contrast in the spot image. Surprisingly, it is the same distance uncertainty that we obtained from a single-photon experiment and from Heisenberg's uncertainty principle. Experiments confirm the theory. An uncertainty principle connecting lateral resolution and distance uncertainty is introduced. Design criteria for a sensor with minimum distanc uncertainty are determined: small temporal coherence, small spatial coherence, a large observation aperture.