Metrologia - IOPscience

Metrologia - IOPscience
Metrologia
The International Bureau of Weights and Measures (BIPM)
was set up by the Metre Convention and has its headquarters near Paris, France. It is financed jointly by its Member States and operates under the exclusive supervision of the CIPM.
Its mandate is to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI). This task takes many forms, from direct dissemination of units (as in the case of mass and time) to coordination through international comparisons of national measurement standards (as in electricity and ionizing radiation).
The BIPM has an international staff of over 70 and its status vis-à-vis the French Government is similar to that of other intergovernmental organizations based in Paris.
SUPPORTS OPEN ACCESS
The leading international journal in pure and applied metrology, published by IOP Publishing on behalf of
Bureau International des Poids et Mesures (BIPM)
Metrologia
is now a fully open access journal as of January 2026. For more information about the move, please visit the
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The following article is
Open access
Redetermination of the gravitational constant with the BIPM torsion balance at NIST
Stephan Schlamminger
et al
2026
Metrologia
63
025012
View article
, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
PDF
, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
We report the first replication of a high-precision measurement of the gravitational constant,
. The experiment employed the torsion balance originally designed and constructed at the International Bureau of Weights and Measures (BIPM) approximately three decades ago. Using the same apparatus and geometry, with several modifications documented in this work, we determined
, corresponding to a relative standard uncertainty of
. The result is lower by
relative to the BIPM determination. This replication provides an independent verification of one of the most precise torsion-balance determinations of
and contributes to assessing the reproducibility limits of current experimental techniques in measurements of the gravitational constant.
The following article is
Open access
Improved systematic evaluation of a strontium optical clock with uncertainty below
Zhi-Peng Jia
et al
2026
Metrologia
63
025002
View article
, Improved systematic evaluation of a strontium optical clock with uncertainty below
PDF
, Improved systematic evaluation of a strontium optical clock with uncertainty below
We report a systematic uncertainty of
for the Sr1 optical lattice clock at the University of Science and Technology of China (USTC), achieving accuracy at the level required for the roadmap of the redefinition of the SI second. A finite-element model with
in situ
-validated, spatially-resolved chamber emissivity reduced blackbody radiation (BBR) shift uncertainty to
. Concurrently, the externally mounted lattice cavity, by providing a larger beam waist, reduced the atomic density and thereby suppressed the density shift. Enhanced lattice depth modulation consolidated lattice light shift uncertainty to
by enabling simultaneous determination of key polarizabilities and magic wavelength. Magnetic shifts were resolved below 10
−18
via precision characterization of the second-order Zeeman coefficient. Supported by a clock laser stabilized on an ultralow-expansion glass cavity with crystalline-coated mirrors and refined temperature control suppressing BBR fluctuations, the clock also achieves a frequency stability better than
at 30 000 s averaging time. These developments collectively establish a new benchmark in USTC Sr1 clock performance and pave the way for high-accuracy applications in metrology and fundamental physics.
The following article is
Open access
Roadmap towards the redefinition of the second
N Dimarcq
et al
2024
Metrologia
61
012001
View article
, Roadmap towards the redefinition of the second
PDF
, Roadmap towards the redefinition of the second
This paper outlines the roadmap towards the redefinition of the second, which was recently updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of optical frequency standards (OFS) call for reflection on the redefinition of the second, but open new challenges related to the performance of the OFS, their contribution to time scales and UTC, the possibility of their comparison, and the knowledge of the Earth’s gravitational potential to ensure a robust and accurate capacity to realize a new definition at the level of 10
−18
uncertainty. The mandatory criteria to be achieved before redefinition have been defined and their current fulfilment level is estimated showing the fields that still needed improvement. The possibility to base the redefinition on a single or on a set of transitions has also been evaluated. The roadmap indicates the steps to be followed in the next years to be ready for a sound and successful redefinition.
The following article is
Open access
Lunar reference timescale
A Bourgoin
et al
2026
Metrologia
63
015003
View article
, Lunar reference timescale
PDF
, Lunar reference timescale
Setting up a relativistic lunar reference frame is of a prime importance in the context of future exploration missions to the Moon. If the procedure for building a consistent reference frame within the framework of the general theory of relativity is well established (see resolutions B.3 of International Astronomical Union 2000), there is still some freedom in the choice of the coordinate timescale to be adopted as reference in the lunar region. In this paper, we review the orders of magnitude of the relativistic effects resulting from (i) the gravitational redshift of a clock on the lunar surface and (ii) the time transformations between a clock on the surface of the Moon and a clock on the surface of the Earth. We then discuss possible options for a lunar reference timescale with their advantages and drawbacks, taking note that the solution which is adopted for the Moon shall then be reemployed for Mars and other planets. Finally, we propose possible realizations of the lunar reference timescale as well as its traceability to UTC.
The following article is
Open access
The Coordinated Universal Time (UTC)
G Panfilo and F Arias 2019
Metrologia
56
042001
View article
, The Coordinated Universal Time (UTC)
PDF
, The Coordinated Universal Time (UTC)
Coordinated Universal Time (UTC) has considerably changed in recent years. The evolution of UTC follows the scientific and industrial progress by developing appropriate models, more adapted calculation algorithms, more efficient and rapid dissemination processes and a well defined traceability chain. The enormous technical progress worldwide has resulted in an impressive number of atomic clocks now available for UTC calculation. The refined time and frequency transfer techniques are approaching the accuracy requested for the new definition of the SI second. The more regular operation of primary frequency standards (PFS) increases the accuracy of UTC and opens a possible new development for time scale algorithms. From the metrological point of view all the ingredients are available for major improvements to UTC. Dissemination of UTC is done by the monthly publication of results in BIPM
Circular T
. This document makes a quality evaluation of local representations of UTC, named UTC(
), in national institutes, and other organizations, by giving the evolution of their offsets relative to UTC and their respective uncertainties. The clock models adopted and the time transfer techniques have progressively improved over the years, assuring the long-term stability of UTC. Each computation of UTC processes data over one month with five-day sampling and publication. A rapid solution of UTC (UTCr) has existed since 2013, and consists of the processing of daily sampled data over four consecutive weeks, computed and published weekly. It gives quick access to UTC, and allows participating laboratories to better monitor the offsets of their realizations to the reference UTC. The traditional monthly publication, containing results of all the laboratories contributing data to the BIPM for the computation of UTC was complemented after the establishment of the Mutual Recognition Arrangement of the International Committee on Weights and Measures (CIPM MRA). This time comparison, which has been the responsibility of the BIPM since 1988, added as a complement the key comparison on time defined by the Consultative Committee for Time and Frequency (CCTF) in 2006 as CCTF-K001.UTC, where the results published are those of national metrology institutes (NMIs) signatories of the CIPM MRA, or designated institutes (DIs). The traceability issues are formalized in the framework of the CIPM MRA. The development of time metrology activities in the different metrology regions, supports the actions of the BIPM time department to improve the accuracy of [UTC–UTC(
)], where the coordination with the Regional Metrology Organizations (RMOs) has a key role. This paper presents an overview of UTC.
The following article is
Open access
The revision of the SI—the result of three decades of progress in metrology
Michael Stock
et al
2019
Metrologia
56
022001
View article
, The revision of the SI—the result of three decades of progress in metrology
PDF
, The revision of the SI—the result of three decades of progress in metrology
On 16 November 2018 a revision of the International System of Units (the SI) was agreed by the General Conference on Weights and Measures. The definitions of the base units were presented in a new format that highlighted the link between each unit and a defined value of an associated constant. The physical concepts underlying the definitions of the kilogram, the ampere, the kelvin and the mole have been changed. The new definition of the kilogram is of particular importance because it eliminated the last definition referring to an artefact. In this way, the new definitions use the rules of nature to create the rules of measurement and tie measurements at the atomic and quantum scales to those at the macroscopic level. The new definitions do not prescribe particular realization methods and hence will allow the development of new and more accurate measurement techniques.
The following article is
Open access
The uncertainty of the half-life
S Pommé 2015
Metrologia
52
S51
View article
, The uncertainty of the half-life
PDF
, The uncertainty of the half-life
Half-life measurements of radionuclides are undeservedly perceived as ‘easy’ and the experimental uncertainties are commonly underestimated. Data evaluators, scanning the literature, are faced with bad documentation, lack of traceability, incomplete uncertainty budgets and discrepant results. Poor control of uncertainties has its implications for the end-user community, varying from limitations to the accuracy and reliability of nuclear-based analytical techniques to the fundamental question whether half-lives are invariable or not. This paper addresses some issues from the viewpoints of the user community and of the decay data provider. It addresses the propagation of the uncertainty of the half-life in activity measurements and discusses different types of half-life measurements, typical parameters influencing their uncertainty, a tool to propagate the uncertainties and suggestions for a more complete reporting style. Problems and solutions are illustrated with striking examples from literature.
The following article is
Open access
The CODATA 2017 values of
, and
for the revision of the SI
D B Newell
et al
2018
Metrologia
55
L13
View article
, The CODATA 2017 values of h, e, k, and NA for the revision of the SI
PDF
, The CODATA 2017 values of h, e, k, and NA for the revision of the SI
Sufficient progress towards redefining the International System of Units (SI) in terms of exact values of fundamental constants has been achieved. Exact values of the Planck constant
, elementary charge
, Boltzmann constant
, and Avogadro constant
from the CODATA 2017 Special Adjustment of the Fundamental Constants are presented here. These values are recommended to the 26th General Conference on Weights and Measures to form the foundation of the revised SI.
The following article is
Open access
Comparison of thin-film thickness measurements using ellipsometry and reflectometry with uniform samples
Masoud Rastgou
et al
2026
Metrologia
63
015006
View article
, Comparison of thin-film thickness measurements using ellipsometry and reflectometry with uniform samples
PDF
, Comparison of thin-film thickness measurements using ellipsometry and reflectometry with uniform samples
This study evaluates spectroscopic ellipsometry and reflectometry using high-quality SiO
and Al
thin-films on Si substrates, thereby facilitating a detailed assessment of consistency of measurement results and uncertainty analyses. The results with detailed uncertainty budgets indicate good agreement between the two methods across a broad layer thickness range from 10 nm to 2000 nm, with deviations remaining well within the measurement uncertainties. Ellipsometry results have lower uncertainty than reflectometry results especially with the thinner layers, whereas reflectometry uncertainties are lower with the thickest layers studied. This work underscores the importance of rigorous thickness characterization and reliable uncertainty evaluation as critical factors in advancing both modeling and measurement practices in thin-film metrology.
The following article is
Open access
171
Yb optical lattice clock with uncertainty below 5×10
−18
Tao Zhang
et al
2026
Metrologia
63
025004
View article
, 171Yb optical lattice clock with uncertainty below 5×10−18
PDF
, 171Yb optical lattice clock with uncertainty below 5×10−18
We report improved performance of the
171
Yb optical lattice clocks at East China Normal University, achieving a total uncertainty of 4.4×10
−18
for the Yb2 clock through high-precision synchronous frequency comparisons with the similar Yb1 clock. A 578 nm laser for the
clock transition is cavity-stabilized using a newly developed ultra-stable laser system, featuring a reduced thermal-noise limit compared to its predecessor. Through systematic optimization, including suppression of technical noise in the laser system and detailed evaluation of frequency shifts, such as collision, blackbody radiation, lattice, and Zeeman shifts, we achieved stable clock-transition spectra for the
= ± 1/2 spin states using 400 ms interrogation pulses, obtaining a Fourier-limited linewidth of 2 Hz. Based on these optimizations, synchronous comparisons between two
171
Yb clocks enable a fractional frequency instability for each clock to average at a rate of 2.0×10
−16
, reaching
×10
−18
at 8000 s, which provides the resolution necessary for high-precision systematic evaluation. Furthermore, a complementary asynchronous comparison accounting for the Dick noise yields an instability of 4.0×10
−18
at 8000 s. The combination of these high-precision comparisons and rigorous frequency shift evaluations validates the total systematic uncertainty below 5×10
−18
The following article is
Open access
CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026
Metrologia
63 013001)
Andrew J Lewis and Timothy J Coveney 2026
Metrologia
63
029502
View article
, CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026 Metrologia 63 013001)
PDF
, CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026 Metrologia 63 013001)
In this corrigendum we correct some numerical and symbol errors in table 2 found in the original manuscript. These errors were independently detected by the authors and a reader during the final production of the paper, but too late for consideration as proof corrections. Table 2 is our version of a table from a paper by Lehman
et al
showing how our proposal for the radian would fit with their scheme. We took their table and extended it to include the radian, taking into account their later published corrigendum. However additional errors, which persisted after the corrigendum by Lehman
et al
were not noticed until the final stages of publication of our paper. This corrigendum fixes these errors and doing so has required a small additional change to the symbols in tables 1 and 2. Of our corrected lines in table 2 for the entries for m, kg, A and rad, the first three would also suffice as corrections to the Lehman paper. We thank the reader for informing us of the errors.
The following article is
Open access
Angles in the SI—a practical dimensional metrologist viewpoint
Andrew J Lewis and Timothy J Coveney 2026
Metrologia
63
023002
View article
, Angles in the SI—a practical dimensional metrologist viewpoint
PDF
, Angles in the SI—a practical dimensional metrologist viewpoint
The International System units of plane angle (radian) and solid angle (steradian) have been the subject of much international debate and discussion, stretching back over several decades. This letter presents the viewpoint from practising dimensional metrologists for whom the realisation of angular units is their responsibility.
The following article is
Open access
Second generation room-temperature dual-mode photodiodes with record-low uncertainties
Johanne Heitmann Solheim
et al
2026
Metrologia
63
025013
View article
, Second generation room-temperature dual-mode photodiodes with record-low uncertainties
PDF
, Second generation room-temperature dual-mode photodiodes with record-low uncertainties
The dual-mode method enables self-calibration of photodiodes by combining a photocurrent measurement with an electrical-substitution measurement of the absorbed optical power. Recent developments have focused on reducing thermal non-equivalence between optical and electrical heating, which limits accuracy through unwanted dependencies on beam position, power level and operating temperature. In this work, we present a new generation of dual-mode modules designed to improve thermal symmetry through a backside resistive heater, a redesigned thermal conduction path and an assembly approach optimized for manufacturability. The new design also facilitates the implementation of the dual-mode method with photodiodes based on materials other than silicon. We characterize the modules experimentally and with finite-element simulations. The measurements show a substantial reduction in position-dependent non-equivalence, from 230 ppm mm
−1
for the previous generation to no significant dependency for the new generation. The measurements also reveal a clearly measurable dependence on optical power and relative temperature. These two effects are quantified and used to correct the apparent internal quantum deficiency (IQD). The resulting corrected IQD when measuring at the center of the diode with 748
W optical power is −73 ppm ± 34 ppm (
= 1), consistent with simulations and representing the lowest uncertainty achieved with room-temperature dual-mode photodiodes to date. Remaining discrepancies between simulations and measurements highlight the need for improved thermal modeling, particularly regarding radiative coupling. The results demonstrate that the revised module design provides a robust pathway toward compact self-calibrating photodiodes with uncertainties equivalent to those of cryogenic radiometers.
The following article is
Open access
Redetermination of the gravitational constant with the BIPM torsion balance at NIST
Stephan Schlamminger
et al
2026
Metrologia
63
025012
View article
, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
PDF
, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
We report the first replication of a high-precision measurement of the gravitational constant,
. The experiment employed the torsion balance originally designed and constructed at the International Bureau of Weights and Measures (BIPM) approximately three decades ago. Using the same apparatus and geometry, with several modifications documented in this work, we determined
, corresponding to a relative standard uncertainty of
. The result is lower by
relative to the BIPM determination. This replication provides an independent verification of one of the most precise torsion-balance determinations of
and contributes to assessing the reproducibility limits of current experimental techniques in measurements of the gravitational constant.
The following article is
Open access
Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
Salim Ferhat
et al
2026
Metrologia
63
025011
View article
, Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
PDF
, Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
State-of-the-art spectral solar irradiance measurements are performed using spectroradiometers, devices that require regular laboratory calibration for traceability to the SI. Typically, these calibrations involve transfer standard light sources, calibrated at National Metrology Institutes against primary standards. However, these transfer standards have disadvantages, and their uncertainties are significantly higher than primary optical standards. In this study, we suggest a novel optical facility for spectroradiometer calibration of spectral responsivity based on predictable quantum efficient detector (PQED) and an ultra-stable, homogeneous monochromatic light beam. This approach is a proof-of-concept for a cost-effective, in-lab primary standard alternative based spectral irradiance facility with significantly reduced uncertainties than the traditional calibration methods. The performance of the system was evaluated at two laser wavelengths, 473 nm and 633 nm using three spectroradiometers calibrated with standard tungsten halogen lamps traceable to the SI. The relative difference in measured irradiances obtained with both methods was consistently below 0.8%, which is well within the combined uncertainties attributed to state-of-the-art spectroradiometer calibration methods. We suggest that combining the PQED with a temporally stable and spatially homogeneous monochromatic light beam can provide a system useable as a primary reference of spectral irradiance in the 400 nm–800 nm spectral range, directly in-lab, significantly shortening the traceability chain to the SI.
The following article is
Open access
Developing calibration and measurement capabilities for atmospheric CH
stable isotope ratios at NMIs/DIs: metrology for global comparability
Abneesh Srivastava
et al
2025
Metrologia
62
032001
View article
, Developing calibration and measurement capabilities for atmospheric CH4 stable isotope ratios at NMIs/DIs: metrology for global comparability
PDF
, Developing calibration and measurement capabilities for atmospheric CH4 stable isotope ratios at NMIs/DIs: metrology for global comparability
To establish robust calibration and measurement capabilities (CMCs) for atmospheric methane (CH
) stable isotope ratios, National Metrology Institutes (NMIs) and Designated Institutes (DIs) need a comprehensive understanding of the underlying measurement techniques, reference materials (RMs), calibration hierarchies, value assignment, uncertainty evaluation, and inter-laboratory comparison activities. This review, developed by the CH
Task Team within the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) Gas Analysis Working Group (GAWG) and the Isotope Ratio Working Group (IRWG), provides key insights for developing these capabilities at NMIs/DIs. The World Meteorological Organization (WMO) recommended network compatibility goals for atmospheric methane stable isotope ratio monitoring, expressed as isotope delta values, are 0.02‰ for the stable carbon isotope delta (
13
C) value and 1‰ for the stable hydrogen isotope delta (
H) value, with extended targets of 0.2‰ for
13
C and 5‰ for
H. Global inter-laboratory comparisons have revealed offsets of up to 0.5‰ for
13
C and 13‰ for
H measurements, substantially exceeding the WMO targets. To address these discrepancies, steady progress is being made, particularly by expert isotope laboratories, with increasing engagement from NMIs/DIs. Improved measurement techniques and the use of common RMs are bringing measurements closer to the WMO goals. This overview not only reviews the components necessary for establishing NMI/DI CMCs but also provides actionable recommendations to further align global measurements, including the development of standardized protocols, adoption of the VPDB carbon isotope delta scale for atmospheric data harmonization, and international comparison studies to support NMI/DIs in their CMC claims. These actions are critical for achieving long-term consistency and advancing global standards for atmospheric methane stable isotope ratio measurements.
The following article is
Open access
Practical realisation of the kelvin by Johnson noise thermometry
Samuel P Benz
et al
2024
Metrologia
61
022001
View article
, Practical realisation of the kelvin by Johnson noise thermometry
PDF
, Practical realisation of the kelvin by Johnson noise thermometry
Johnson noise thermometry (JNT) is a purely electronic method of thermodynamic thermometry. In primary JNT, the temperature is inferred from a comparison of the Johnson noise voltage of a resistor at the unknown temperature with a pseudo-random noise synthesized by a quantum-based voltage-noise source (QVNS). The advantages of the method are that it relies entirely on electronic measurements, and it can be used over a wide range of temperatures due to the ability of the QVNS to generate programmable, scalable, and accurate reference signals. The disadvantages are the requirement of cryogenic operation of the QVNS, the need to match the frequency responses of the leads of the sense resistor and the QVNS, and long measurement times. This review collates advice on current best practice for a primary JNT based on the switched correlator and QVNS. The method achieves an uncertainty of about 1 mK near 300 K and is suited to operation between 4 K and 1000 K.
The following article is
Open access
Roadmap towards the redefinition of the second
N Dimarcq
et al
2024
Metrologia
61
012001
View article
, Roadmap towards the redefinition of the second
PDF
, Roadmap towards the redefinition of the second
This paper outlines the roadmap towards the redefinition of the second, which was recently updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of optical frequency standards (OFS) call for reflection on the redefinition of the second, but open new challenges related to the performance of the OFS, their contribution to time scales and UTC, the possibility of their comparison, and the knowledge of the Earth’s gravitational potential to ensure a robust and accurate capacity to realize a new definition at the level of 10
−18
uncertainty. The mandatory criteria to be achieved before redefinition have been defined and their current fulfilment level is estimated showing the fields that still needed improvement. The possibility to base the redefinition on a single or on a set of transitions has also been evaluated. The roadmap indicates the steps to be followed in the next years to be ready for a sound and successful redefinition.
Ode to Bayesian methods in metrology
Juris Meija
et al
2023
Metrologia
60
052001
View article
, Ode to Bayesian methods in metrology
PDF
, Ode to Bayesian methods in metrology
Bayesian statistical methods are being used increasingly often in measurement science, similarly to how they now pervade all the sciences, from astrophysics to climatology, and from genetics to social sciences. Within metrology, the use of Bayesian methods is documented in peer-reviewed publications that describe the development of certified reference materials or the characterization of CIPM key comparison reference values and the associated degrees of equivalence. This contribution reviews Bayesian concepts and methods, and provides guidance for how they can be used in measurement science, illustrated with realistic examples of application. In the process, this review also provides compelling evidence to the effect that the Bayesian approach offers unparalleled means to exploit all the information available that is relevant to rigorous and reliable measurement. The Bayesian outlook streamlines the interpretation of uncertainty evaluations, aligning their meaning with how they are perceived intuitively: not as promises about performance in the long run, but as expressions of documented and justified degrees of belief about the truth of specific conclusions supported by empirical evidence. This review also demonstrates that the Bayesian approach is practicable using currently available modeling and computational techniques, and, most importantly, that measurement results obtained using Bayesian methods, and predictions based on Bayesian models, including the establishment of metrological traceability, are amenable to empirical validation, no less than when classical statistical methods are used for the same purposes. Our goal is not to suggest that everything in metrology should be done in a Bayesian way. Instead, we aim to highlight applications and kinds of metrological problems where Bayesian methods shine brighter than the classical alternatives, and deliver results that any classical approach would be hard-pressed to match.
The CIPM MRA—success and performance
Olav Werhahn
et al
2023
Metrologia
60
042001
View article
, The CIPM MRA—success and performance
PDF
, The CIPM MRA—success and performance
The CIPM Mutual Recognition Arrangement (CIPM MRA) provides a technical framework to the measurement community for comparability of measurement results and international recognition of metrological capabilities declared by the national metrology institutes throughout the globe. Since its founding in 1999, the participating institutes have now published more than 25 700 peer-reviewed calibration and measurement capabilities (CMCs) in the CIPM MRA database (Key Comparison Database (KCDB)). It is these capabilities and the technical evidence behind them that underpin the international acceptance of measurements around the world. The success and wide adoption of the CIPM MRA indicate the maturity of the arrangement, however, the accompanying increased workload for the participants motivated a review of the practices with the aim to increase the efficiency while maintaining the technical rigor. This review identified a number of key factors that formed the basis of the revision of the
modus operandi
, including the procedures and the database. The review resulted in recommendations for the CIPM Consultative Committees (CCs), regional metrology organizations (RMOs), participating institutes, as well as the BIPM. The revamped KCDB incorporated the whole lifecycle of CMCs, familiarizing with the new system being supported by the Capacity Building and Knowledge Transfer Programme of the BIPM. The result was an improvement in not only efficiency of the CIPM MRA, but also its effectiveness. For example, the time required for the Joint Committee of the RMOs and the BIPM (JCRB) review of CMCs has dropped by more than 50% to 59 d (median) in 2022, and the number of uncompleted key comparisons (KCs) have been reduced by a factor of three to a total of 38 in March 2023, representing now less than 3% of the total KCs. In this paper we look at the key factors through the various metrological areas addressing practices by each CCs.
The following article is
Open access
The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
Montillet et al
View accepted manuscript
, The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
PDF
, The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
The Project for On-Board Autonomy-3 (PROBA3) is the fourth satellite technology development and demonstration mission within the European Space Agency General Support Technology Program (ESA’s GSTP). The mission has started on the 5th of December 2024 with the launch of the two satellites. One of the two PROBA3 satellites includes the Digital Absolute Radiometer (DARA) to acquire total solar irradiance observations. Developed and manufactured in Switzerland by the PMOD/WRC, DARA features three black cavity receivers designed to measure total solar irradiance. The pre-flight calibration campaign and the data analysis has been completed for these three cavities at the facilities in Davos (PMOD/WRC) and the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, USA. We discuss several parameters used to transform the raw measurements into irradiance observations. Due to improvements in the electrical design of the cavities, the estimated lead-heating value is significantly lower for the DARA radiometer compared to previous instruments. An system-level calibration of DARA against a NIST traceable radiometer at LASP allowed us to estimate the DARA-to-SI ratio in both power and irradiance modes. We found the ratio to be closer to 1 in power mode than in irradiance mode. Additionally, our comparison with the World Radiometric Reference indicates that the calibration factors for optical power and irradiance are compatible at that the calibration factors for optical power and irradiance are compatible within a k = 2 confidence interval.
The following article is
Open access
Monte Carlo Uncertainty Evaluation of Gravimetric Gas Mixture with Asymmetric Distributions
Li et al
View accepted manuscript
, Monte Carlo Uncertainty Evaluation of Gravimetric Gas Mixture with Asymmetric Distributions
PDF
, Monte Carlo Uncertainty Evaluation of Gravimetric Gas Mixture with Asymmetric Distributions
Gravimetric preparation is internationally recognized as the primary method for producing calibration gas mixtures, and its uncertainty is commonly evaluated using the law of propagation of uncertainty within the GUM uncertainty framework (GUF). For impurities in parent gases with amount fractions close to or below the limit of detection (LOD), ISO 19229 indicates that symmetric distributional assumptions may yield unphysical results and requires the use of asymmetric probability density functions, such as the beta distribution. However, the quantitative impact of such assumptions in gravimetric gas mixture preparation has not yet been systematically reported. In this work, a Monte Carlo method (MCM) was implemented to propagate asymmetric input distributions in accordance with ISO 19229. A representative multi-stage gravimetric dilution case study was designed, including major components, significant impurities and trace impurities, to systematically compare the uncertainty evaluation results obtained using the GUF and the MCM. The results show that, for target gas mixtures prepared through three dilution stages, the GUF and the MCM yield highly consistent results, with deviations between the estimates below 0.02% and relative differences in standard uncertainties below 0.2% for most components, increasing to about 6% for 1,3-butadiene due to the limited purity of the parent gas. By contrast, for intermediate mixtures prepared through at most two dilution stages, components dominated by beta-distributed uncertainty contributions exhibit asymmetric output distributions. In these cases, differences between mean-based and mode-based estimates exceed 40%, and differences in standard uncertainties exceed 8%. The MCM further provides asymmetric coverage intervals and additional statistical descriptors such as skewness and kurtosis. These results demonstrate the MCM as a practical approach for complying with ISO 19229 in gravimetric preparation. Furthermore, this framework holds broader significance for uncertainty evaluation in trace-level monitoring tasks characterized by asymmetric distributional assumptions.
The following article is
Open access
Low-Frequency Calibration of Accelerometers by Rotation in the Gravitational Field at NIST
Strait et al
View accepted manuscript
, Low-Frequency Calibration of Accelerometers by Rotation in the Gravitational Field at NIST
PDF
, Low-Frequency Calibration of Accelerometers by Rotation in the Gravitational Field at NIST
We present a low-frequency accelerometer calibration system based on rotation in the gravitational field. Example characterizations of three accelerometers from (0.01 to 1.5) Hz with an uncertainty analysis demonstrate k = 2 magnitude and phase uncertainty of <0.1 % and <0.2
, respectively. This rotational system complements the linear shakers in the NIST Primary Vibration Calibration Laboratory by improving uncertainty in the range of overlap and extending accelerometer calibration capability to lower frequencies. We demonstrate a magnitude comparison between the linear and rotational approaches, showing agreement to within the rotational calibration uncertainty of <0.1 %.
The following article is
Open access
CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026
Metrologia
63 013001)
Andrew J Lewis and Timothy J Coveney 2026
Metrologia
63
029502
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, CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026 Metrologia 63 013001)
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, CORRIGENDUM: Angles in the SI—a practical dimensional metrologist viewpoint (2026 Metrologia 63 013001)
In this corrigendum we correct some numerical and symbol errors in table 2 found in the original manuscript. These errors were independently detected by the authors and a reader during the final production of the paper, but too late for consideration as proof corrections. Table 2 is our version of a table from a paper by Lehman
et al
showing how our proposal for the radian would fit with their scheme. We took their table and extended it to include the radian, taking into account their later published corrigendum. However additional errors, which persisted after the corrigendum by Lehman
et al
were not noticed until the final stages of publication of our paper. This corrigendum fixes these errors and doing so has required a small additional change to the symbols in tables 1 and 2. Of our corrected lines in table 2 for the entries for m, kg, A and rad, the first three would also suffice as corrections to the Lehman paper. We thank the reader for informing us of the errors.
The following article is
Open access
Angles in the SI—a practical dimensional metrologist viewpoint
Andrew J Lewis and Timothy J Coveney 2026
Metrologia
63
023002
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, Angles in the SI—a practical dimensional metrologist viewpoint
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, Angles in the SI—a practical dimensional metrologist viewpoint
The International System units of plane angle (radian) and solid angle (steradian) have been the subject of much international debate and discussion, stretching back over several decades. This letter presents the viewpoint from practising dimensional metrologists for whom the realisation of angular units is their responsibility.
The following article is
Open access
The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
Jean-Philippe Montillet
et al
2026
Metrologia
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, The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
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, The DARA-PROBA3 Radiometer: Results from the Pre-Flight Calibration Campaign
The Project for On-Board Autonomy-3 (PROBA3) is the fourth satellite technology development and demonstration mission within the European Space Agency General Support Technology Program (ESA’s GSTP). The mission has started on the 5th of December 2024 with the launch of the two satellites. One of the two PROBA3 satellites includes the Digital Absolute Radiometer (DARA) to acquire total solar irradiance observations. Developed and manufactured in Switzerland by the PMOD/WRC, DARA features three black cavity receivers designed to measure total solar irradiance. The pre-flight calibration campaign and the data analysis has been completed for these three cavities at the facilities in Davos (PMOD/WRC) and the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, USA. We discuss several parameters used to transform the raw measurements into irradiance observations. Due to improvements in the electrical design of the cavities, the estimated lead-heating value is significantly lower for the DARA radiometer compared to previous instruments. An system-level calibration of DARA against a NIST traceable radiometer at LASP allowed us to estimate the DARA-to-SI ratio in both power and irradiance modes. We found the ratio to be closer to 1 in power mode than in irradiance mode. Additionally, our comparison with the World Radiometric Reference indicates that the calibration factors for optical power and irradiance are compatible at that the calibration factors for optical power and irradiance are compatible within a k = 2 confidence interval.
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Open access
Second generation room-temperature dual-mode photodiodes with record-low uncertainties
Johanne Heitmann Solheim
et al
2026
Metrologia
63
025013
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, Second generation room-temperature dual-mode photodiodes with record-low uncertainties
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, Second generation room-temperature dual-mode photodiodes with record-low uncertainties
The dual-mode method enables self-calibration of photodiodes by combining a photocurrent measurement with an electrical-substitution measurement of the absorbed optical power. Recent developments have focused on reducing thermal non-equivalence between optical and electrical heating, which limits accuracy through unwanted dependencies on beam position, power level and operating temperature. In this work, we present a new generation of dual-mode modules designed to improve thermal symmetry through a backside resistive heater, a redesigned thermal conduction path and an assembly approach optimized for manufacturability. The new design also facilitates the implementation of the dual-mode method with photodiodes based on materials other than silicon. We characterize the modules experimentally and with finite-element simulations. The measurements show a substantial reduction in position-dependent non-equivalence, from 230 ppm mm
−1
for the previous generation to no significant dependency for the new generation. The measurements also reveal a clearly measurable dependence on optical power and relative temperature. These two effects are quantified and used to correct the apparent internal quantum deficiency (IQD). The resulting corrected IQD when measuring at the center of the diode with 748
W optical power is −73 ppm ± 34 ppm (
= 1), consistent with simulations and representing the lowest uncertainty achieved with room-temperature dual-mode photodiodes to date. Remaining discrepancies between simulations and measurements highlight the need for improved thermal modeling, particularly regarding radiative coupling. The results demonstrate that the revised module design provides a robust pathway toward compact self-calibrating photodiodes with uncertainties equivalent to those of cryogenic radiometers.
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Open access
Redetermination of the gravitational constant with the BIPM torsion balance at NIST
Stephan Schlamminger
et al
2026
Metrologia
63
025012
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, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
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, Redetermination of the gravitational constant with the BIPM torsion balance at NIST
We report the first replication of a high-precision measurement of the gravitational constant,
. The experiment employed the torsion balance originally designed and constructed at the International Bureau of Weights and Measures (BIPM) approximately three decades ago. Using the same apparatus and geometry, with several modifications documented in this work, we determined
, corresponding to a relative standard uncertainty of
. The result is lower by
relative to the BIPM determination. This replication provides an independent verification of one of the most precise torsion-balance determinations of
and contributes to assessing the reproducibility limits of current experimental techniques in measurements of the gravitational constant.
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Open access
Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
Salim Ferhat
et al
2026
Metrologia
63
025011
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, Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
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, Laser-based primary standard for absolute spectral irradiance calibration with predictable quantum efficient detectors
State-of-the-art spectral solar irradiance measurements are performed using spectroradiometers, devices that require regular laboratory calibration for traceability to the SI. Typically, these calibrations involve transfer standard light sources, calibrated at National Metrology Institutes against primary standards. However, these transfer standards have disadvantages, and their uncertainties are significantly higher than primary optical standards. In this study, we suggest a novel optical facility for spectroradiometer calibration of spectral responsivity based on predictable quantum efficient detector (PQED) and an ultra-stable, homogeneous monochromatic light beam. This approach is a proof-of-concept for a cost-effective, in-lab primary standard alternative based spectral irradiance facility with significantly reduced uncertainties than the traditional calibration methods. The performance of the system was evaluated at two laser wavelengths, 473 nm and 633 nm using three spectroradiometers calibrated with standard tungsten halogen lamps traceable to the SI. The relative difference in measured irradiances obtained with both methods was consistently below 0.8%, which is well within the combined uncertainties attributed to state-of-the-art spectroradiometer calibration methods. We suggest that combining the PQED with a temporally stable and spatially homogeneous monochromatic light beam can provide a system useable as a primary reference of spectral irradiance in the 400 nm–800 nm spectral range, directly in-lab, significantly shortening the traceability chain to the SI.
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Open access
Explicit ensemble mean clock synchronization for optimal atomic time scale generation
Takayuki Ishizaki
et al
2026
Metrologia
63
025010
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, Explicit ensemble mean clock synchronization for optimal atomic time scale generation
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, Explicit ensemble mean clock synchronization for optimal atomic time scale generation
This paper presents a novel theoretical framework, called explicit ensemble mean synchronization. This framework unifies time scale generation, clock synchronization, and oscillator frequency regulation within the systems and control theory paradigm. By exploiting the observable canonical decomposition of a standard atomic ensemble clock model, the system is decomposed into two complementary components: the observable part, which represents the synchronization error, and the unobservable part, which captures the synchronization destination. Within this structure, we mathematically prove that standard Kalman filtering, which is widely used in current time scale generation, not only performs observable state estimation, but also significant unobservable state estimation, and it can be interpreted as a special case of the proposed framework that optimizes long-term frequency stability in terms of the Allan variance. Furthermore, applying state feedback control based on Kalman filtering to each component achieves optimal time scale generation, clock synchronization, and oscillator frequency regulation in a unified manner. The proposed framework provides a foundation for developing explainable timing systems.
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Open access
Control of the blackbody radiation shift in hydrogen and hydrogen-like optical computable clocks using a magic temperature
O Amit
et al
2026
Metrologia
63
025009
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, Control of the blackbody radiation shift in hydrogen and hydrogen-like optical computable clocks using a magic temperature
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, Control of the blackbody radiation shift in hydrogen and hydrogen-like optical computable clocks using a magic temperature
The blackbody radiation (BBR) shift is a significant systematic shift for atomic clocks on the 10
−18
scale. We investigate the BBR shift of the hydrogen and hydrogen-like systems and present a method to reduce the uncertainty due to the BBR shift of the 1S–2S clock transition to the 10
−21
range. This feature is due to the single-electron system’s energy level structure and a close dipole-allowed resonance to the excited 2S state. We present detailed calculations and analyses of the magic temperature where the BBR shift mathematically cancels. We also present the operational magic temperature, a stationary point where the shift becomes insensitive to the temperature. This shift is precisely calculable, in contrast to all other optical clocks.
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Open access
On a definition of the SI second based on several transitions
Petr Křen 2026
Metrologia
63
023001
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, On a definition of the SI second based on several transitions
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, On a definition of the SI second based on several transitions
The redefinition of the System of Unit (SI) second is expected in the near future due to progress in time and frequency metrology. One promising option is to use several transitions to define the SI second. However, the proposed definitions use a ‘constant’ that is unnecessary for such a definition, is not a constant in value between possible redefinitions and has no physical meaning, which may be controversial properties. Therefore, this paper proposes alternative wording for the definition of the SI second that does not directly use such a constant, in order to improve a possible definition based on several transitions.
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Open access
Enhancing the UTCr algorithm: performance improvements and optimization
Gianna Panfilo
et al
2026
Metrologia
63
025008
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, Enhancing the UTCr algorithm: performance improvements and optimization
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, Enhancing the UTCr algorithm: performance improvements and optimization
Considering the evolving needs of time metrology and the importance of providing contributing laboratories with more frequent access to a realization of Coordinated Universal Time (UTC) than through the monthly BIPM Circular T, the Time Department introduced a rapid realization of UTC (UTCr), officially published on a weekly basis since July 2013. The algorithm used to compute UTCr was first published in 2014, and since then only minor mathematical adjustments have been applied. In the initial paper, it was stated that UTCr could be maintained within ±2 ns of UTC. An improved UTCr calculation method is proposed in this paper and it has recently been implemented, reducing deviation from UTC to within ±1 ns.
More Open Access articles
The following article is
Open access
Roadmap towards the redefinition of the second
N Dimarcq
et al
2024
Metrologia
61
012001
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, Roadmap towards the redefinition of the second
PDF
, Roadmap towards the redefinition of the second
This paper outlines the roadmap towards the redefinition of the second, which was recently updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of optical frequency standards (OFS) call for reflection on the redefinition of the second, but open new challenges related to the performance of the OFS, their contribution to time scales and UTC, the possibility of their comparison, and the knowledge of the Earth’s gravitational potential to ensure a robust and accurate capacity to realize a new definition at the level of 10
−18
uncertainty. The mandatory criteria to be achieved before redefinition have been defined and their current fulfilment level is estimated showing the fields that still needed improvement. The possibility to base the redefinition on a single or on a set of transitions has also been evaluated. The roadmap indicates the steps to be followed in the next years to be ready for a sound and successful redefinition.
High-precision gravity measurements using atom interferometry
A Peters
et al
2001
Metrologia
38
25
View article
, High-precision gravity measurements using atom interferometry
PDF
, High-precision gravity measurements using atom interferometry
We have built an atom interferometer that can measure
, the local acceleration due to gravity, with a resolution of Δ
= 2 × 10
−8
after a single 1.3 s measurement cycle, 3 × 10
−9
after 1 min and 1 × 10
−10
after two days of integration time. The difference between our value for
and one obtained by a falling corner-cube optical interferometer is (7 ± 7) × 10
−9
. The atom interferometer uses velocity-selective stimulated Raman transitions and laser-cooled caesium atoms in an atomic fountain. We extend previous methods of analysing the interferometer to include the effects of a gravitational gradient. We also present detailed experimental and theoretical studies of potential systematic errors and noise sources.
JILA SrI optical lattice clock with uncertainty of
Tobias Bothwell
et al
2019
Metrologia
56
065004
View article
, JILA SrI optical lattice clock with uncertainty of
PDF
, JILA SrI optical lattice clock with uncertainty of
We report on an improved systematic evaluation of the JILA SrI optical lattice clock, achieving a nearly identical uncertainty compared to the previous strontium record set by the JILA SrII optical lattice clock at
. This improves upon the previous evaluation of the JILA SrI optical lattice clock in 2013, and we achieve a more than twenty-fold reduction in systematic uncertainty to
. A seven-fold improvement in clock stability, reaching
for an averaging time
in seconds, allows the clock to average to its systematic uncertainty in under 10 min. We improve the systematic uncertainty budget in several important ways. This includes a novel scheme for taming blackbody radiation-induced frequency shifts through active stabilization and characterization of the thermal environment, inclusion of higher-order terms in the lattice light shift, and updated atomic coefficients. Along with careful control of other systematic effects, we achieve low temporal drift of systematic offsets and high uptime of the clock. We additionally present an improved evaluation of the second order Zeeman coefficient that is applicable to all Sr optical lattice clocks. These improvements in performance have enabled several important studies including frequency ratio measurements through the boulder area clock optical network (BACON), a high precision comparison with the JILA 3D lattice clock, a demonstration of a new all-optical time scale combining SrI and a cryogenic silicon cavity, and a high sensitivity search for ultralight scalar dark matter.
The International Temperature Scale of 1990 (ITS-90)
H Preston-Thomas 1990
Metrologia
27
107
View article
, The International Temperature Scale of 1990 (ITS-90)
PDF
, The International Temperature Scale of 1990 (ITS-90)
A strontium lattice clock with both stability and uncertainty below
Jie Li
et al
2024
Metrologia
61
015006
View article
, A strontium lattice clock with both stability and uncertainty below
PDF
, A strontium lattice clock with both stability and uncertainty below
We report the realization of the closed-loop operation of an optical lattice clock based on
87
Sr atoms. A cavity-stabilized 698 nm laser is used to probe the
clock transition of strontium atoms trapped in optical lattices. Therein, we obtain a Fourier-limited Rabi spectrum with 0.6 Hz linewidth. The two transitions from
ground states are alternatively interrogated to realize the closed-loop operation of the clock, and the clock laser light is frequency-stabilized to the center of the two transitions. Based on the interleaved measurement, the frequency instability of a single optical clock is optimized for the Dick effect, which is demonstrated to be
, with
being the averaging time for measurement. Further, we build another similar setup of the strontium lattice clock, which is used for the asynchronous comparison between the two clocks, where the stability is measured as
at 47 000 s. Moreover, we carefully calibrate the systematic effects of the Sr1 optical clock, and the total uncertainty is evaluated as
The following article is
Open access
The Coordinated Universal Time (UTC)
G Panfilo and F Arias 2019
Metrologia
56
042001
View article
, The Coordinated Universal Time (UTC)
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, The Coordinated Universal Time (UTC)
Coordinated Universal Time (UTC) has considerably changed in recent years. The evolution of UTC follows the scientific and industrial progress by developing appropriate models, more adapted calculation algorithms, more efficient and rapid dissemination processes and a well defined traceability chain. The enormous technical progress worldwide has resulted in an impressive number of atomic clocks now available for UTC calculation. The refined time and frequency transfer techniques are approaching the accuracy requested for the new definition of the SI second. The more regular operation of primary frequency standards (PFS) increases the accuracy of UTC and opens a possible new development for time scale algorithms. From the metrological point of view all the ingredients are available for major improvements to UTC. Dissemination of UTC is done by the monthly publication of results in BIPM
Circular T
. This document makes a quality evaluation of local representations of UTC, named UTC(
), in national institutes, and other organizations, by giving the evolution of their offsets relative to UTC and their respective uncertainties. The clock models adopted and the time transfer techniques have progressively improved over the years, assuring the long-term stability of UTC. Each computation of UTC processes data over one month with five-day sampling and publication. A rapid solution of UTC (UTCr) has existed since 2013, and consists of the processing of daily sampled data over four consecutive weeks, computed and published weekly. It gives quick access to UTC, and allows participating laboratories to better monitor the offsets of their realizations to the reference UTC. The traditional monthly publication, containing results of all the laboratories contributing data to the BIPM for the computation of UTC was complemented after the establishment of the Mutual Recognition Arrangement of the International Committee on Weights and Measures (CIPM MRA). This time comparison, which has been the responsibility of the BIPM since 1988, added as a complement the key comparison on time defined by the Consultative Committee for Time and Frequency (CCTF) in 2006 as CCTF-K001.UTC, where the results published are those of national metrology institutes (NMIs) signatories of the CIPM MRA, or designated institutes (DIs). The traceability issues are formalized in the framework of the CIPM MRA. The development of time metrology activities in the different metrology regions, supports the actions of the BIPM time department to improve the accuracy of [UTC–UTC(
)], where the coordination with the Regional Metrology Organizations (RMOs) has a key role. This paper presents an overview of UTC.
Recommended table for the density of water between 0 °C and 40 °C based on recent experimental reports
M Tanaka
et al
2001
Metrologia
38
301
View article
, Recommended table for the density of water between 0 °C and 40 °C based on recent experimental reports
PDF
, Recommended table for the density of water between 0 °C and 40 °C based on recent experimental reports
Experimental results from four recent research reports on the determination of the density/temperature relationship of Standard Mean Ocean Water (SMOW) under a pressure of 101 325 Pa are analysed and a new formula is recommended for metrological applications. This paper determines the formulae of density and relative density, with their uncertainties, in the temperature range 0 °C to 40 °C. The uncertainty estimation of one of the reports included in the analysis has been re-evaluated. Effects on water density due to isotopic mixtures other than SMOW, ambient pressures different from 101 325 Pa, and the presence of dissolved air, are also reviewed.
The following article is
Open access
171
Yb
optical clock with
systematic uncertainty and absolute frequency measurements
A Tofful
et al
2024
Metrologia
61
045001
View article
, 171Yb+ optical clock with systematic uncertainty and absolute frequency measurements
PDF
, 171Yb+ optical clock with systematic uncertainty and absolute frequency measurements
A full evaluation of the uncertainty budget for the ytterbium ion optical clock at the National Physical Laboratory (NPL) was performed on the electric octupole (E3)
transition. The total systematic frequency shift was measured with a fractional standard systematic uncertainty of
. Furthermore, the absolute frequency of the E3 transition of the
171
Yb
ion was measured between 2019 and 2023 via a link to International Atomic Time (TAI) and against the local caesium fountain NPL-CsF2. The absolute frequencies were measured with fractional standard uncertainties between
and
, and all were in agreement with the 2021 BIPM recommended frequency.
1 × 10
−16
frequency transfer by GPS PPP with integer ambiguity resolution
Gérard Petit
et al
2015
Metrologia
52
301
View article
, 1 × 10−16 frequency transfer by GPS PPP with integer ambiguity resolution
PDF
, 1 × 10−16 frequency transfer by GPS PPP with integer ambiguity resolution
For many years, the time community has been using the precise point positioning (PPP) technique which uses GPS phase and code observations to compute time and frequency links. However, progress in atomic clocks implies that the performance of PPP frequency comparisons is a limiting factor in comparing the best frequency standards. We show that a PPP technique where the integer nature of phase ambiguities is preserved consitutes significant improvement of the classical use of floating ambiguities. We demonstrate that this integer-PPP technique allows frequency comparisons with 1  ×  10
−16
accuracy in a few days and can be readily operated with existing products.
Radionuclide metrology using liquid scintillation counting
Ryszard Broda
et al
2007
Metrologia
44
S36
View article
, Radionuclide metrology using liquid scintillation counting
PDF
, Radionuclide metrology using liquid scintillation counting
Liquid scintillation counting (LSC) techniques can be used for radionuclide standardization when the calculation of detection efficiency is possible. This is done using a model of the physicochemical processes involved in light emission and also of the statistics of photon emission: the free parameter model. This model can then be applied in two ways: by deducing the free parameter from the measurement of a tracer (the CIEMAT/NIST method) or by calculating this free parameter from coincidence ratio in a specific LS counter (the TDCR method). The purpose of this paper is to describe both these models and some practical issues that need to be addressed if LSC is to be effectively used in radionuclide metrology.
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Metrologia
doi: 10.1088/issn.0026-1394
Online ISSN: 1681-7575
Print ISSN: 0026-1394