Common Calibration Research Articles

Measurement of Hubble constant: were differences in secondary distance indicators apparent as early as the HST Key Project?

Different measurements of the Hubble constant (H 0) are not consistent, and a tension between the CMB based methods and cosmic distance ladder based methods has been observed. Measurements from various distance based methods are also inconsistent. To aggravate the problem, the same cosmological probe (Type Ia SNe for instance) calibrated through different methods also provides different values of H 0. We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope (HST). Our analysis is based on parametric (t-test) as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test. Our results show that different methods provide different values of H 0 and the differences are statistically significant. The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme. The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.

Quantitative analysis and benchmarking of positional accuracies of neutron strain scanners

Positional accuracy is an important parameter in residual stress investigations with neutron diffraction, considering that precise measurements of strains at the same localised position along a number of sample orientations are required, including investigations of complete complex shaped engineering components. This study reports the development of a standardised approach for quantitative analysis of positional accuracy on neutron strain scanners that builds on previous campaigns. The approach uses standardised sample sets with specific geometries that enable quantitative assessment of instrumental and sample alignment procedures and associated accuracies. This method has been implemented on four participating instruments: ENGIN-X (United Kingdom), MPISI (South Africa), SALSA (France) and STRESS-SPEC (Germany), to render results representative of monochromatic and time-of-flight strain scanners. The benchmarking results show comparable performance between the instruments with positional accuracies around 100 μm readily achieved. This standardised approach confirms the high positional precision attainable for non-destructive stress determination, to unequivocally benefit utilisation by academia and industry alike. It is envisaged that this common calibration protocol and reporting template that conforms to the newly developed Neutron Quality Label for Internal Stress Characterisation be adopted by other facilities to facilitate expansion of the supportive network.

Calibration of river hydrodynamic models: Analysis from the dynamic component in roughness coefficients

Hydrodynamic modelling is an important tool for several studies, such as flood forecasting and analysis of energy and mass transport. In rivers, the most common calibration parameter is the roughness coefficient, that accounts for the friction term. However, while uncertainties are associated to this parameter definition, it is often defined as constant over time or space. Even though sophisticated techniques are available for model calibration, unsteady flow routing applications usually involve simplified methods, such as trial-and-error and Monte Carlo strategies. These practices can be subjective, time consuming and dependent on user experience; on the other hand, automatic approaches may generate unrealistic values and require large computational efforts. This study introduces a new strategy to calibrate one-dimensional hydrodynamic models, accounting for temporal and spatial variation while maintaining computational thrift. Among multiple random roughness coefficients, a time series is generated according to a linear relationship with observed water depths or flow for five control sections; the resulting daily series of parameters are the set for simulation inputs. The algorithm was combined with the hydrodynamic module in the SihQual model (Hydrodynamic and Water Quality Simulation); when compared to observed data, it showed to be suitable to predict discharges and water levels for different years over 85 km of the Iguaçu river, located in Paraná (Brazil). Compared to Monte Carlo and trial-and-error techniques for calibration, the HTC method (Hydrodynamic Temporal Calibration) was able to match their results or even improve simulations in some cases, requiring less user interaction than the other approaches. The study highlights the relevance of including a temporal component in model calibration, aiming to reduce the overall inherent uncertainty of this process.

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Revised application of copper ion selective electrode (Cu-ISE) in marine waters: A new meta-calibration approach

Copper (Cu) is a bio-essential trace element that is of concerns due to its potential toxicity at concentrations commonly encountered in coastal waters. Here, we revisit the applicability of Cu(II) ion selective electrode (Cu-ISE) based on a jalpaite membrane for the measurement of Cufree in seawater. At high total Cu concentration (>0.1 mM), (near)Nernstian slope was obtained and determination of Cufree down to fM levels was possible. However, this slope decreases with decreasing total Cu concentration (e.g. 7 mV/decade at 15 nM total Cu) making the use of a common single calibration approach unreliable. To solve this problem, we carried out several calibrations at different levels of total Cu (15 nM - 1 mM) and ethylenediamine (EN: 5 μM - 15 mM) and fitted the calibration parameters (slope and intercept) as a function of total Cu using the Gompertz function (a meta-calibration approach). The derived empirical equations allowed the determination of Cufree at any total Cu concentration above 20 nM (determination of Cufree at lower total Cu levels is prevented by the dissolution of the electrode). We successfully tested this meta-calibration approach in UV digested seawater in presence of a synthetic ligand (EN), isolated natural organic matter (humic acid, HA) and in a natural estuarine sample. In each case, our meta-calibration approach provided a good agreement with modeled speciation data (Visual MINTEQ), while standard single approach failed. We provide here a new method for the direct determination of the free Cu ion concentration in seawater at levels relevant for coastal waters.

Antenna Array Calibration Using a Sparse Scene

In radar systems, antenna arrays acquire direction-dependent information to localize targets or create images of the environment. However, because of unknown complex amplitudes per channel and mutual coupling, a calibration is necessary for good performance. Common calibration approaches measure to targets under known angles in a multipath-free far-field environment, which often can only be provided by anechoic chambers. Therefore, this process is not suitable for low-cost and frequent calibration. To overcome these limitations, this paper proposes a novel calibration approach using an unknown but sparse target scene. Multiple measurements at known relative positions of the radar are combined to a synthetic aperture. Then, the full mutual coupling matrix is estimated simultaneously with the unknown target scene. The method requires neither target position information, far-field conditions, nor an anechoic chamber because multipath propagation can be suppressed easily for targets located in the near-field. The proposed calibration approach is validated by measurements of a commercial 77GHz radar. The performance is evaluated by comparing the achieved image quality using the calibration results of this work and the radar’s ex-factory calibration data. The proposed novel calibration procedure improves the image quality, while considerably lowering the demands on the calibration measurements and environment.

Analytical considerations and plans to standardize or harmonize assays for the reference bone turnover markers PINP and β-CTX in blood

Procollagen type I N-propeptide (PINP) and the C-terminal telopeptide of type I collagen (β-CTX) in blood have been designated as reference bone turnover markers in osteoporosis by the International Osteoporosis Foundation (IOF) and International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The IFCC Committee on Bone Metabolism (C-BM) has examined current commercial assays and performed a multicentre study to examine the agreement between assays for PINP and β-CTX in serum and plasma. The results of these studies will inform our work towards the harmonization of PINP assays and the standardization of β-CTX assays in blood, with the development of common calibrators and reference measurement procedures in collaboration with the reagent manufacturing industry. Successful achievement of these goals will help develop universally acceptable practice guidelines for the management of osteoporosis with the inclusion of common reference intervals and treatment targets for PINP and β-CTX.

Interference from alkenes in chemiluminescent NO<sub><i>x</i></sub> measurements

Abstract. Nitrogen oxides (NOx=NO+NO2) are critical intermediates in atmospheric chemistry and air pollution. NOx levels control the cycling and hence abundance of the primary atmospheric oxidants OH and NO3 and regulate the ozone production which results from the degradation of volatile organic compounds (VOCs) in the presence of sunlight. They are also atmospheric pollutants, and NO2 is commonly included in air quality objectives and regulations. NOx levels also affect the production of the nitrate component of secondary aerosol particles and other pollutants, such as the lachrymator peroxyacetyl nitrate (PAN). The accurate measurement of NO and NO2 is therefore crucial for air quality monitoring and understanding atmospheric composition. The most commonly used approach for the measurement of NO is the chemiluminescent detection of electronically excited NO2 (NO2∗) formed from the NO + O3 reaction within the NOx analyser. Alkenes, ubiquitous in the atmosphere from biogenic and anthropogenic sources, also react with ozone to produce chemiluminescence and thus may contribute to the measured NOx signal. Their ozonolysis reaction may also be sufficiently rapid that their abundance in conventional instrument background cycles, which also utilises the reaction with ozone, differs from that in the measurement cycle such that the background subtraction is incomplete, and an interference effect results. This interference has been noted previously, and indeed, the effect has been used to measure both alkenes and ozone in the atmosphere. Here we report the results of a systematic investigation of the response of a selection of commercial NOx monitors to a series of alkenes. These NOx monitors range from systems used for routine air quality monitoring to atmospheric research instrumentation. The species-investigated range was from short-chain alkenes, such as ethene, to the biogenic monoterpenes. Experiments were performed in the European PHOtoREactor (EUPHORE) to ensure common calibration and samples for the monitors and to unequivocally confirm the alkene levels present (via Fourier transform infrared spectroscopy – FTIR). The instrument interference responses ranged from negligible levels up to 11 %, depending upon the alkene present and conditions used (e.g. the presence of co-reactants and differing humidity). Such interferences may be of substantial importance for the interpretation of ambient NOx data, particularly for high VOC, low NOx environments such as forests or indoor environments where alkene abundance from personal care and cleaning products may be significant.

Improving the calibration process of inertial measurement unit for marine applications

Marine navigation systems have very accurate sensors, such as 0.01deg/hr gyro drift stability and 0.1mg/year accelerometer bias stability. Common calibration methods and equipment do not meet the accuracy required. In this paper, a systematic method for calibration of an inertial measurement unit (IMU) for marine applications is proposed which is not based on the accuracy of the calibration turn table and only requires one specific plate to determine the initial attitude of the IMU and functions independently of the turn table. The first contribution of this paper is to derive a model for systematic calibration of IMU that expresses the rotation matrix error and velocity as a linear function of the calibration parameters at any time. As the second contribution, this paper proposes a calibration algorithm with only using an initial, specific plate. Using the actual data, it was found that the proposed algorithm provides a good estimation of the parameters.

MiniVO: Minimalistic Range Enhanced Monocular System for Scale Correct Pose Estimation

Monocular vision systems allow compact and resource-constrained vehicles to perform online state estimation through Structure from Motion approaches. However, it is needed to integrate additional information to obtain a metric scale for the estimated trajectory. We propose a minimalistic approach based on the sensor fusion between a monocular camera and a 1D LiDAR (LIght Detection And Ranging) rangefinder. A classical visual front-end, in charge of tracking the camera pose with respect to a map of landmarks, is paired with an optimization back-end where depth measurements constrain the distance between cameras and 3D points. The fusion methodology is based on a keyframe-wise search of correspondences between visual landmarks and projections of altimeter points. The differences between triangulated landmark depths and associated altimeter measurements are minimized using the iSAM2 incremental smoother. We test our algorithm in a variety of datasets comprising an outdoor scenario with accurate D-GPS ground truth evaluating both tracking accuracy and computational effort. Results show that our algorithm provides comparable performances to scale-aware RGB-D vision systems and obtains relative trajectory errors close to 0.5%. Furthermore, we propose and validate an extrinsic calibration pipeline to refer range measurements in the camera reference system which differs from common LiDAR-camera calibration algorithms due to the 5 Degrees of Freedom (DoF) nature of the single-point rangefinder and camera system.

Vanishing Cantilever Calibration Error with Magic Ratio Atomic Force Microscopy

AbstractAn analysis is presented of the error propagation through a simplified contact model for atomic force microscopy (AFM) static force spectroscopy, one that is meant to be intuitive and pedagogically informative rather than maximally realistic. It is shown that an important dimensionless ratio appears in several critical locations in the closed form error equation, and that under common calibration methods there exists a ``magic'' ratio where an important class of systematic calibration errors cancel out completely. This argument is extended to more complex contact models and the presence of a magic ratio is demonstrated using real data. A method is shown to identify and operate at optimal conditions in commercial AFMs. Targeting this magic ratio provides a simple, comprehensive guideline for cantilever selection, system calibration, and imaging parameter selection.

Scaling relations and baryonic cycling in local star-forming galaxies

Metallicity and gas content are intimately related in the baryonic exchange cycle of galaxies, and galaxy evolution scenarios can be constrained by quantifying this relation. To this end, we have compiled a sample of ∼400 galaxies in the local Universe, dubbed “MAGMA” (Metallicity And Gas for Mass Assembly), which covers an unprecedented range in parameter space, spanning more than 5 orders of magnitude in stellar mass (Mstar), star-formation rate (SFR), and gas mass (Mgas), and it has a factor of ∼60 in metallicity [Z, 12 + log(O/H)]. Stellar masses and SFRs were recalculated for all of the galaxies using IRAC, WISE, and GALEX photometry, and 12 + log(O/H) was transformed, where necessary, to a common metallicity calibration. To assess the true dimensionality of the data, we applied multidimensional principal component analyses (PCAs) to our sample. We find that even with the vast parameter space covered by MAGMA, the relations between Mstar, SFR, Z, and Mgas (MHI + MH2) require only two dimensions to describe the hypersurface, which confirms the findings of previous work. To accommodate the curvature in the Mstar–Z relation, we applied a piecewise 3D PCA that successfully predicts observed 12 + log(O/H) to an accuracy of ∼0.1 dex. MAGMA is a representative sample of isolated star-forming galaxies in the local Universe, and it can be used as a benchmark for cosmological simulations and to calibrate evolutionary trends with redshift.

Consistent frequency-matching calibration procedure for electromechanical shunt absorbers

Electromagnetic and piezoelectric shunt damping can be represented by an equivalent mechanical vibration absorber with a spring, dashpot, and inerter in series. A common calibration procedure for multiple electromechanical shunt absorbers is obtained by this equivalence, including a correction for the influence from residual vibration modes by additional modal terms, whose coefficients are consistently identified by frequency matching for the system with rigid absorber dashpots. The accuracy and robustness of the calibration procedure are verified numerically for an unsupported truss structure with rigid body modes.

On the application of neural networks for temperature field measurements using thermochromic liquid crystals

This study presents an investigation regarding the applicability of neural networks for temperature measurements using thermochromic liquid crystals (TLCs) and discusses advantages as well as disadvantages of common calibration approaches. For the characterization of the measurement technique, the dependency of the color of the TLCs on the temperature as well as on the observation angle and, therefore, on the position within the field of view of a color camera is analyzed in detail. In order to consider the influence of the position within the field of view on the color, neural networks are applied for the calibration of the temperature measurements. In particular, the focus of this study is on analysis of the error of temperature measurement for different network configurations as well as training methods, yielding a mean absolute deviation and a mean standard deviation in the range of 0.1 K for instantaneous measurements. On the basis of a comparison of this standard deviation to that of two further calibration approaches, it is shown that neural networks are suited for temperature measurements via the color of TLCs. Finally, the applicability of this measurement technique is illustrated at an exemplary temperature measurement in a horizontal plane of a Rayleigh–Bénard cell with large aspect ratio, which clearly shows the emergence of convective flow patterns by means of the temperature field.Graphic abstract

An IMM-UKF Aided SINS/USBL Calibration Solution for Underwater Vehicles

To improve the efficiency of the calibration process and enhance the adaptability of the calibration method, an interacting multiple model and unscented Kalman filter (IMM-UKF) aided strapdown inertial navigation system (SINS)/Ultra-Short Base Line (USBL) calibration solution is proposed for the common calibration procedure, where only one transponder is employed without pre-locating. Firstly, construct the SINS/USBL calibration mechanism, where the transponder's position, level-arm and misalignment angle are estimated simultaneously utilizing the slant range, inclination angles of USBL and depth information from depthometer. Second, to mitigate the decreasing calibration accuracy caused by the single filtering parameter under the complex underwater environment, an IMM-UKF algorithm is presented to support the proposed calibration mechanism. Simulation results indicate that the proposed mechanism earns faster convergence rate and better calibration results than other solutions. Besides, the proposed solution can maintain its robustness when the observation quality changes.

Improvement in spectral library-based quantification of soil properties using representative spiking and local calibration – The case of soil inorganic carbon prediction by mid-infrared spectroscopy

Mid-infrared reflectance spectroscopy (MIRS) is time- and cost-effective. It was used for quantifying soil inorganic carbon (SIC) concentration in France based on a national library, and performances were evaluated on an independent regional set. Our objective was to improve the accuracy of MIRS predictions based on common multivariate regression, through spiking (enrichment of the national library with some representative target samples) with possible extra-weighting (replication of spiking samples) and local calibration (only using calibration samples that are spectral neighbours of each target samples), which have not been fully explored yet, in combination especially.Global (i.e. common) calibration yielded accurate prediction (standard error of prediction, SEP, was ≈5 g kg−1), which could be improved when the library was completed with spiking samples (optimally 10samples extra-weighted 40times; SEP = 3.3 g kg−1). Using spiking samples only (without the library) yielded slightly less accurate results (SEP = 3.6 g kg−1). Prediction was more accurate using local calibration without spiking, but on a validation set that was reduced because some validation samples lacked calibration neighbours (SEP = 2.5–2.7 g kg−1). Local calibration with spiking (optimally 10samples without extra-weight) yielded somewhat less accurate prediction but for the full validation set when few calibration neighbours were required (SEP = 2.7 g kg−1), or higher accuracy on the reduced validation set when many neighbours were required (SEP = 2.3 g kg−1).These accurate predictions demonstrated the usefulness of representative spiking and local calibration for rendering large soil spectral libraries fully operational, while extra-weighting had no additional benefit. Along with more exhaustive spectral libraries, this paves the way for extensive use of MIRS for SIC determination.

Self-calibration of rotary axis and linear axes error motions by an automated on-machine probing test cycle

Efficient, precise and automated in-process calibration schemes are essential to improve the accuracy and productivity of five-axis machine tools. This paper presents a new calibration approach, which combines an on-machine measurement cycle and self-calibration techniques, to evaluate the position errors and the error motions of a rotary axis using a touch trigger probe and an uncalibrated cylindrical artefact. This significantly reduces the downtime of machine tools required for the calibration process. In contrast to many common calibration strategies for rotary axes of five-axis machine tools, the presented self-calibration concept does not neglect the positioning errors of the linear axes when identifying the position errors and the error motions of the rotary axis. The self-calibration procedure is able to separate the positioning errors of the linear axes in radial direction, and the radial error motions and the position errors of a rotary axis, as well as the errors related to the uncalibrated artefact. This error separation is realized by a test cycle consisting of four tests in which the measurements are conducted by particular axis movements. Furthermore, an uncertainty analysis of the self-calibration concept is conducted to visualize the uncertainty propagation within the mathematical model. The self-calibration procedure is analyzed by an experimental evaluation, which includes a comparison between the results of the self-calibration approach and an R-Test. This comparison shows that the results of both measurement procedures are consistent.

Analytical effects on clumped isotope thermometry: Comparison of a common sample set analyzed using multiple instruments, types of standards, and standardization windows.

Carbonate clumped isotope geothermometry is being increasingly used in multiple disciplines in the geosciences. However, potential interlaboratory issues are arising from different standardization procedures that may contribute to the multiple Δ47 -temperature calibrations reported in the literature. We investigate this issue by comparing a common temperature calibration sample set across three different mass spectrometers, using multiple standardization methods. The same temperature calibration sample set was analyzed on three different mass spectrometers. Several standardization methods were utilized, including the use of carbonate versus gas standards, and different types of background correction were applied to the raw data. All standardization types applied resulted in statistically indistinguishable Δ47 -temperature slopes, with the exception of standardization calculations that did not correct for background effects. Some instruments and standardizations showed different intercepts relative to each other. The use of carbonate standards improved comparability between different instruments relative to gas standards. Our results show that background effects are the largest factor potentially affecting Δ47 results, and there may be an improvement in interlaboratory precision using carbonate standards. Critically, all techniques used for standardizing Δ47 results converge on a common slope as long as background effects are properly corrected. The use of carbonate standards is recommended as a component of standardization procedures.

Implementation of metrological traceability in laboratory medicine: where we are and what is missing.

Background The Joint Committee on Traceability in Laboratory Medicine (JCTLM) has recently created the Task Force on Reference Measurement System Implementation (TF-RMSI) for providing guidance on traceability implementation to in vitro diagnostics (IVD) manufacturers. Using serum creatinine (sCr) as an example, a preliminary exercise was carried out by checking what type of information is available in the JCTLM database and comparing this against derived analytical performance specifications (APS) for measurement uncertainty (MU) of sCr. Content APS for standard MU of sCr measurements were established as a fraction (≤0.75, minimum quality; ≤0.50, desirable quality; and ≤0.25, optimum quality) of the intra-individual biological variation of the measurand (4.4%). By allowing no more than one third of the total MU budget for patient samples to be derived from higher-order references, two out of the four JCTLM reference materials (RMs) at least allow minimum APS to be achieved for the MU of patient samples. Commutability was explicitly assessed for one of the JCTLM-listed matrixed RMs, which was produced in compliance with ISO 15194:2009 standard, whereas the remaining three RMs were assessed against the ISO 15194:2002 version of the standard, which only required the extent of commutability testing to be reported. Regarding the three listed reference methods, the MU associated with isotopic dilution-mass spectrometry coupled to gas chromatography (ID/GC/MS) and isotopic dilution-mass spectrometry coupled to liquid chromatography (ID/LC/MS) would allow APS to be fulfilled, while the isotope dilution surface-enhanced Raman scattering (ID/SERS) method displays higher MU. Summary The most recently listed RM for sCr in the JCTLM database meets the ISO 15194:2009 requirements with MU that would allow APS to be fulfilled and has had commutability demonstrated for use as a common calibrator in implementing traceability of sCr measurements. Splitting clinical samples with a laboratory performing ID/GC/MS or ID/LC/MS provides an alternative but would also require all components of uncertainty of these materials to be assessed. Outlook Using appropriately derived APS to judge whether reference measurement system components are fit for purpose represents a novel approach. The TF-RMSI is planning to review a greater number of measurands to provide more robust information about the state of the art of available reference measurement systems and their impact on the ability of clinical measurements to meet APS.

Stereo calibration of binocular ultra-wide angle long-wave infrared camera based on an equivalent small field of view camera

ABSTRACTIn this paper, a stereo calibration method for binocular ultra-wide angle long-wave infrared camera is proposed on the basis of an equivalent small field of view camera. Extrinsic parameters are calibrated through the corrected images from the left and right cameras. They can be viewed as images taken by a small field of view camera. The calibration procedure consists of three steps: monocular calibration, distortion correction and extrinsic parameters calibration. In order to evaluate the accuracy of the method, stereo vision of the camera is modelled and a 3D reconstruction approach is presented. A series of experiments, including intrinsic parameters, extrinsic parameters and 3D reconstruction, are conducted to validate the proposed method. The results show that the baseline length error decreases to 0.67%, and the relative error for the 3D reconstruction of corners is smaller than 8.11%. In contrast to the common stereo calibration method, it improves calibration accuracy.