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18 pags., 15 figs., 16 tabs., We report new developments in instrumentation and techniques for both acoustic (speed of sound) and radiometric primary thermometry methods. These include both new cylindrical resonators for extending acoustic gas thermometry to higher temperatures and absolute radiation thermometers incorporating InGaAs detectors to extend primary radiometry to lower temperatures than can be achieved using Si-detector based instruments. These new approaches have been established in order to determine the difference between thermodynamic temperature, T, and the International Temperature Scale of 1990 (the ITS-90), T90, over the temperature range from 430 K to 1358 K as part of the three-year EMPIR project `Implementing the new kelvin 2¿ (InK2). This paper describes the facilities and measurement methodologies for measuring T¿T90 at each of the different institutes, along with an assessment of the target uncertainties. The work is ongoing, but we anticipate that the results of these measurements will ultimately be pooled to provide consensus values of T¿T90 with associated estimated uncertainties. These consensus values will initially feed into the technical annex of the mise en pratique for the definition of the kelvin (MeP-K-19) and, if required, will be used to help to provide a foundation for any future temperature scale., This work has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 R&I programme through the InK2 project. NIM’s research was supported by the National Key R&D Program of China (number 2016YFF0200101)

Previously (Underwood et al 2015 Meteorol. Appl. 22 830) we reported first tests of a device capable of simultaneous, non-contact, temperature and humidity (NCTAH) measurements in air. The device used an acoustic thermometer and a tuneable diode laser absorption spectrometer (TDLAS), a combination which should be capable of an extremely rapid response to changes in humidity as it does not require moisture in a solid-state matrix to equilibrate with the surrounding air. In this paper we report recent developments of the instrument focussed on reducing its response time so that it can be used as a reference instrument for assessing the response time of conventional humidity sensors. In addition, the interdependence of the temperature and humidity estimates is now accounted for in real-time using an iterative procedure, which eliminates the need for data post-processing. The TDLAS measures water molecule number density based on the transmission of an infrared beam (approximate wavelength 1360 nm) through a 0.6 m path length. The acoustic thermometer is based around a fixed-path acoustic interferometer. The improved NCTAH device now produces estimates of the water molecule number density every 20 ms and the temperature output displays an RC filter-like response, with a time constant of approximately 30 ms. The instrument has been tested in a climatic chamber through a temperature range of −40 °C to +40 °C and a dew point range of −43 °C to +38 °C, at atmospheric pressure, comparing the instrument readings with those from a calibrated hygrometer and four platinum resistance thermometers. In steady-state conditions, the instrument readings are in good agreement with the conventional sensors, with temperature differences less than 1 °C (repeatability 0.1 °C), and humidity differences mostly within 5% of mixing ratio. Under transient conditions, we demonstrate how the instrument can be used to evaluate the response times of conventional sensors.

HadISDH.2.0.0 is the first gridded, multi-variable humidity and temperature in situ observations-only climate-data product that is homogenised and annually updated. It provides physically consistent estimates for specific humidity, vapour pressure, relative humidity, dew point temperature, wet bulb temperature, dew point depression and temperature. It is a monthly mean gridded (5° by 5°) product with uncertainty estimates that account for spatio-temporal sampling, climatology calculation, homogenisation and irreducible random measurement effects. It provides a tool for the long-term monitoring of a variety of humidity-related variables which have different impacts and implications for society. It is also useful for climate model evaluation and reanalyses validation. HadISDH.2.0.0 is shown to be in good agreement both with other estimates and with theoretical understanding. The data set is available from 1973 to the present. The theme common to all variables is of a warming world with more water vapour present in the atmosphere. The largest increases in water vapour are found over the tropics and the Mediterranean. Over the tropics and high northern latitudes the surface air over land is becoming more saturated. However, despite increasing water vapour over the mid-latitudes and Mediterranean, the surface air over land is becoming less saturated. These observed features may be due to atmospheric circulation changes, land–sea warming disparities and reduced water availability or changed land surface properties.

The study describes significant outcomes of the Metrology for Meteorology' project, MeteoMet, which is an attempt to bridge the meteorological and metrological communities. The concept of traceability, an idea used in both fields but with a subtle difference in meaning, is at the heart of the project. For meteorology, a traceable measurement is the one that can be traced back to a particular instrument, time and location. From a metrological perspective, traceability further implies that the measurement can be traced back to a primary realization of the quantity being measured in terms of the base units of the International System of Units, the SI. These two perspectives reflect long-standing differences in culture and practice and this project - and this study - represents only the first step towards better communication between the two communities. The 3 year MeteoMet project was funded by the European Metrology Research Program (EMRP) and involved 18 European National Metrological Institutes, 3 universities and 35 collaborating stakeholders including national meteorology organizations, research institutes, universities, associations and instrument companies. The project brought a metrological perspective to several long-standing measurement problems in meteorology and climatology, varying from conventional ground-based measurements to those made in the upper atmosphere. It included development and testing of novel instrumentation as well as improved calibration procedures and facilities, instrument intercomparison under realistic conditions and best practice dissemination. Additionally, the validation of historical temperature data series with respect to measurement uncertainties and a methodology for recalculation of the values were included.

Temperature and humidity measurements in the upper atmosphere are of critical importance for understanding the climate of the Earth. However such measurements are difficult for several reasons. Firstly, measurements are typically made on a rising sonde which carries moisture upwards with it, compromising measurements in the dry stratospheric environment. Secondly, the difference in the time-constants of thermometers and hygrometers on a rising sonde leads to difficulties in determining the extent of saturation of the air - a critical variable for understanding cloud formation. Finally the effects of insolation and the poor thermal contact with the air compound the other measurement problems. To address these issues we have designed a new combined temperature and humidity sensor which makes rapid measurements in approximately 10 litres of air of without requiring thermal contact. The temperature measurements are made using an acoustic interferometer which is servo-controlled at around 15 kHz to keep a fixed number of wavelengths in the measurement volume. The volume being measured is that between a parabolic dish 20 cm in diameter and an acoustic mirror 50 cm away. These elements are held together in a carbon-fibre open frame. Humidity measurements are made using a Tuneable Diode Laser Absorption Spectrometer (TDLAS) which interrogates the same volume of air through holes in the mirror and parabola. Here we report tests on the device at NPL at a pressure of 1 atmosphere, and from simulated ascents through the atmosphere at the MARS Simulation facility at the University of Aarhus, Denmark.

International audience; The International Committee for Weights and Measures (CIPM), at its meeting in October 2017, followed the recommendation of the Consultative Committee for Units (CCU) on the redefinition of the kilogram, ampere, kelvin and mole. For the redefinition of the kelvin, the Boltzmann constant will be fixed with the numerical value 1.380 649 × 10−23 J K−1. The relative standard uncertainty to be transferred to the thermodynamic temperature value of the triple point of water will be 3.7 × 10−7, corresponding to an uncertainty in temperature of 0.10 mK, sufficiently low for all practical purposes. With the redefinition of the kelvin, the broad research activities of the temperature community on the determination of the Boltzmann constant have been very successfully completed. In the following, a review of the determinations of the Boltzmann constant k, important for the new definition of the kelvin and performed in the last decade, is given.

There is overwhelming evidence that the climate system has warmed since the instigation of instrumental meteorological observations. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change concluded that the evidence for warming was unequivocal. However, owing to imperfect measurements and ubiquitous changes in measurement networks and techniques, there remain uncertainties in many of the details of these historical changes. These uncertainties do not call into question the trend or overall magnitude of the changes in the global climate system. Rather, they act to make the picture less clear than it could be, particularly at the local scale where many decisions regarding adaptation choices will be required, both now and in the future. A set of high-quality long-term fiducial reference measurements of essential climate variables will enable future generations to make rigorous assessments of future climate change and variability, providing society with the best possible information to support future decisions. Here we propose that by implementing and maintaining a suitably stable and metrologically well-characterized global land surface climate fiducial reference measurements network, the present-day scientific community can bequeath to future generations a better set of observations. This will aid future adaptation decisions and help us to monitor and quantify the effectiveness of internationally agreed mitigation steps. This article provides the background, rationale, metrological principles, and practical considerations regarding what would be involved in such a network, and outlines the benefits which may accrue. The challenge, of course, is how to convert such a vision to a long-term sustainable capability providing the necessary well-characterized measurement series to the benefit of global science and future generations.

To provide new determinations of the Boltzmann constant, k, which has been asked for by the International Committee for Weights and Measures concerning preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project has coordinated the European activities in this field. In this major European research project the Boltzmann constant has been determined by various methods to support the new definition of the kelvin. The final results of the project are reviewed in this paper. Determinations of the Boltzmann constant k were achieved within the project by all three envisaged methods: acoustic gas thermometry, Doppler broadening technique, and dielectric constant gas thermometry. The results were exploited by the interdisciplinary Committee on Data for Science and Technology (CODATA) in their 2010 adjustment of recommended values for fundamental constants. As a result, the CODATA group recommended a value for k with a relative standard uncertainty about a factor of two smaller than the previous u(k)/k of 1.7×10−6.

Recent advances in primary acoustic gas thermometry (AGT) have revealed significant differences between temperature measurements using the International Temperature Scale of 1990, $$T_{90}$$ , and thermodynamic temperature, T. In 2015, we published estimates of the differences $$(T-T_{90})$$ from 118 K to 303 K, which showed interesting behavior in the region around the triple point of water, $$T_\mathrm{TPW}=273.16$$ K. In that work, the $$T_{90}$$ measurements below $$T_\mathrm{TPW}$$ used a different ensemble of capsule standard platinum resistance thermometers (SPRTs) than the $$T_{90}$$ measurements above $$T_\mathrm{TPW}$$ . In this work, we extend our earlier measurements using the same ensemble of SPRTs above and below $$T_\mathrm{TPW}$$ , enabling a deeper analysis of the slope $$\mathrm{d}(T-T_{90})/\mathrm{d}T$$ around $$T_\mathrm{TPW}$$ . In this article, we present the results of seven AGT isotherms in the temperature range 258 K to 323 K. The derived values of $$(T-T_{90})$$ have exceptionally low uncertainties and are in good agreement with our previous data and other AGT results. We present the values $$(T-T_{90})$$ alongside our previous estimates, with the resistance ratios W(T) from two SPRTs which have been used across the full range 118 K to 323 K. Additionally, our measurements show discontinuities in $$\mathrm{d}(T-T_{90})/\mathrm{d}T$$ at $$T_\mathrm{TPW}$$ which are consistent with the slope discontinuity in the SPRT deviation functions. Since this discontinuity is by definition non-unique, and can take a range of values including zero, we suggest that mathematical representations of $$(T-T_{90})$$ , such as those in the mise en pratique for the kelvin (Fellmuth et al. in Philos Trans R Soc A 374:20150037, 2016. doi: 10.1098/rsta.2015.0037 ), should have continuity of $$\mathrm{d}(T-T_{90})/\mathrm{d}T$$ at $$T_\mathrm{TPW}$$ .

We have measured the internal volume of a 1 litre, diamond-turned copper quasispherical resonator with a fractional uncertainty of approximately 1 part in 106 using two independent techniques. This is in response to the need for a uniquely accurate measurement of resonator volume, for the purpose of measuring the Boltzmann constant in pursuit of the redefinition of the kelvin. The first technique is a pyknometric measurement using water as a liquid of known density. We describe the development of a procedure that results in stable, reproducible volume measurements. We provide a detailed discussion of the factors that affect the water density, such as dissolved gases. The second technique is microwave resonance spectroscopy. Here, we measure the resonant frequencies of the TM1n modes and relate them to the dimensions of the resonator. We evaluate the frequency perturbations that arise from the coupling waveguides and the electrical resistivity of the copper surface. The results of the microwave measurements show evidence of a dielectric coating on the surface. We propose that this is an oxide layer and estimate its thickness from the microwave data. Finally, we compare the volume estimates from the two methods, and find that the difference is within the combined uncertainty.

Earth’s atmosphere is used as a standard reference gas for mass spectrometric determinations of argon (Ar) isotopes used principally in geochronology. There are three published independent determinations of the Ar isotope composition of modern atmosphere that differ subtly. We have made new high-precision measurements of Ar isotope ratios of five different sources of air using a high-sensitivity multi-collector noble gas mass spectrometer in order to distinguish between them. The isotope ratios, corrected only for backgrounds, reside on a inverse square-root mass law fractionation line that passes through the air value proposed by Lee et al. [Lee J. Y., Marti K., Severinghaus J. P., Kawamura K., Yoo H. S., Lee J. B. and Kim J. S. (2006) A redetermination of the isotopic abundances of atmospheric Ar. Geochim. Cosmochim. Acta 70, 4507–4512]. They are distinct from both the other proposed compositions and provide the first independent confirmation of the atmospheric Ar isotope composition. We suggest that the revised values should now be in routine employment.

In situ measurements of humidity, temperature, and pressure are demon- strated for a polymer electrolyte membrane (PEM) fuel cell of interdigitated gas flow channel layout. Sensors are embedded at the flowfield edges, sampling air, and hydro- gen at several positions along the flow channels. The measurements provide, for the first time, real-time localized data for this configuration of fuel cell. The results show that, for the interdigitated flowfield, moisture freely permeates through the membrane electrode assembly (MEA). This is in contrast to lower net moisture transmission through the same MEA used in a serpentine flowfield.

Fiber-coupled radiometry allows for the radiometric measurement of high temperatures in environments where there is no line of sight to the target. However, transmission through conventional silica optical fibers degrades rapidly at elevated temperatures, and exotic fibers—such as sapphire fibers—typically cannot be bent. As part of a project to investigate the performance of solid oxide fuel cells, the feasibility of using an alternative fiber, solid-core silica photonic crystal fiber (PCF), was tested. The test system used an Inconel blackbody as a source, and a detection system based on an InGaAs array spectrometer with a wavelength range of 907 nm to 1681 nm. The temperature was determined from the spectrometer signal at particular wavelengths using the Planck relationship. Two tests were performed: (1) long-term high temperature soak tests to measure the drift and noise in thermal radiation levels, in which spectra are sequentially recorded over a long period of time with the blackbody cavity at a constant temperature and (2) temperature dependence tests, whereby thermal radiation spectra are recorded with the blackbody cavity at several temperatures. At 934 °C, the transmission of the PCF decreased at a rate of 0.078 % per hour corresponding to a temperature error of −0.12 °C per hour. The transmission of conventional silica fiber decreased at a rate of 0.5 % per hour corresponding to a temperature error of −0.8 °C per hour. While the PCF represents a significant improvement over conventional fiber, it is still not good enough for most practical purposes. At 600 °C there was no observable decline in transmission and there may be applications for PCF in that regime.

We describe the dimensional characterization of copper quasisphere NPL-Cranfield 2. The quasisphere is assembled from two hemispheres such that the internal shape is a triaxial ellipsoid, the major axes of which have nominal radii 62.000 mm, 62.031 mm and 62.062 mm. The artefact has been manufactured using diamond-turning technology and shows a deviation from design form of less than ±1 µm over most of its surface. Our characterization involves both coordinate measuring machine (CMM) experiments and microwave resonance spectroscopy.We have sought to reduce the dimensional uncertainty below the maximum permissible error of the CMM by comparative measurements with silicon and Zerodur spheres of known volume. Using this technique we determined the equivalent radius with an uncertainty of u(k = 1) = 114 nm, a fractional uncertainty of 1.8 parts in 106. Due to anisotropy of the probe response, we could only determine the eccentricities of the quasihemispheres with a fractional uncertainty of approximately 2%.Our microwave characterization uses the TM11 to TM18 resonances. We find the equivalent radius inferred from analysis of these modes to be consistent within ±4 nm with an overall uncertainty u(k = 1) = 11 nm. We discuss corrections for surface conductivity, waveguide perturbations and dielectric surface layers.We find that the CMM radius estimates derived from each hemisphere cannot be used to accurately predict the equivalent radius of the assembled resonator for two reasons. Firstly, the equatorial flanges are flat only to within ±1 µm, leading to an equatorial 'gap' whose dimension cannot be reliably estimated. Secondly, the resonator undergoes significant elastic distortion when the bolts connecting the hemispheres are tightened. We provide CMM and microwave measurements to support these conclusions in addition to finite-element modelling.Finally, we consider the implications of this work on a forthcoming experiment to determine the Boltzmann constant with a relative uncertainty below 1 part in 106.

Acoustic thermometry using a gas-filled quasi-spherical resonator (QSR) is one of the most promising techniques for measuring the Boltzmann constant kB with low uncertainty. Dimensional metrology with coordinate measurement machines (CMMs) can be used to determine the resonator's volume, either directly or in combination with measurements of the resonator's microwave spectra. We assessed the uncertainty achievable when using a CMM to characterize the shape and volume of three QSRs. The resonators differed significantly in their design and construction: their inner volumes ranged between 524?cm3 and 2225?cm3, while the QSR geometries ranged from a diamond-turned triaxial ellipsoid to the variable misalignment of spheroidal hemispheres. Comparative coordinate measurements of two solid spherical density standards were used to identify and estimate type B uncertainties.We tested the regression of the CMM data to spherical harmonic expansions and determined the volume of a QSR directly with a relative uncertainty uR < 30 parts in 106. Additionally, spherical harmonic regression of the CMM data can place uncertainty bounds on the eccentricity parameters, ?1 and ?2, typically with a relative uncertainty uR ? 0.02. This is sufficient to determine corrections to both the acoustic and the microwave resonance frequencies of the QSR with a relative uncertainty uR < 1 part in 106 for all resonances. These figures assume that the enclosed volume of an assembled QSR is equal to the sum of the volumes of its two component 'hemispheres'. In practice this cannot be strictly true and the additional uncertainties in the volume of the assembled QSR are discussed.

Acoustic thermometry is capable of phenomenal accuracy, but is a difficult technique to apply in many practical situations. Here, we describe a modification of the technique, which permits robust temperature measurements to be made, potentially with millikelvin resolution, over a temperature range extending from cryogenic temperatures to over 1000 °C. The technique uses measurements of the time of flight of acoustic pulses in tubes, usually filled with an inert gas such as argon. The tubes—typically made of stainless steel with an outer diameter of 6mm—act as acoustic waveguides and can be several meters long and bent into complex shapes. The time of flight is determined by the average temperature along the entire length of the tube. Local temperature information can be inferred in several ways. Typically a second shorter tube is used and the difference in time of flight reflects the temperature in the region at the end of the first tube. If the measurement length is sufficiently long—typically 1m of tube—then a measurement resolution of less than 1mK is achievable. The technique is well suited to measurements in harsh environments in which conventional sensors degrade. Results from early tests are shown, which highlight the strengths and weaknesses of the technique.

Piezoelectric materials are used in many applications, at increasingly smaller scales. Methods of measuring their hydrostatic properties have been developed where the piezoelectric charge is produced as a result of a varying hydrostatic pressure generated within a sealed chamber. In this paper, the authors explore an anomalous generation of charge in thin laminar samples and show this is a result of the pyroelectric effect. The authors model the change in temperature in the sealed chamber caused by the adiabatic expansion of the gas and relate this to the observed generation of charge, using finite element modelling to investigate the temperature profile through the material. The implications of these results are relevant for the successful integration of piezoelectric thin and thick films into MEMS devices.

In this work a procedure is described to prepare SI-traceable argon isotope amount ratios in high purity argon. Following a gravimetric approach, a total of three synthetic isotope mixtures have been prepared, from argon gases enriched in (36)Ar, (38)Ar and (40)Ar, close to the natural isotopic composition of argon. These synthetic mixtures serve as reference gases to calibrate ion current ratio measurements in argon. In this way SI-traceable measurements of argon isotope amount ratios can be performed without any assumptive correction. On a high purity argon gas separated from air the absolute argon isotope amount ratios R(36/40) = 0.00334774 (93) and R(38/40) = 0.00063529 (57) were measured. From these ratios, the average molar mass of argon gas can be determined with a total relative combined uncertainty of 0.09 x 10(-6). (C) 2010 Elsevier B.V. All rights reserved.

Miniature temperature/humidity sensors are incorporated into the graphite flowplates of a single cell polymer electrolyte membrane fuel cell (PEMFC) in order to measure the humidity profile along the serpentine channels of both anode and cathode in real time. The sensors show robust performance and importantly are able to recover after saturation. The key observation is a significant increase in relative humidity along the anode gas channel due to back diffusion of water from cathode to anode. Such measurements may be used to determine the water balance in the cell under a range of operating conditions to facilitate model validation and system optimisation.

Ongoing work to improve the uniformity of vertically mounted furnaces, manufactured by Carbolite (e.g., Type TZF12/75—three-zone furnace capable of 1200 °C, with 75 mm inner bore) along the axis and across the working tube and/or equalizing block is reported. This involves adjusting the size of the end zones, the position of the control thermometers, and the use of cascade-control methods. Means regularly used at NPL to reduce electrical noise in some commercially available ac furnaces through a reduction in the voltage used to “fire” the heaters, and better use of thyristor controllers (by extending their cycle time) are described. The need to shield the controllers from local magnetic fields is described. With these measures, the electrical noise from ac furnaces can approach that of dc furnaces, without the large cost of a dc power supply. The application of new data analysis techniques (Allan deviation) will be shown to improve the representation of uninterrupted fixed-point traces (as used in ingot verification rather than PRT calibration). Reduction of statistical noise on the temperature measurements has been achieved for data on the freezing plateau by determining the statistically optimum averaging time. This shows that the statistical uncertainty in the determination of the temperature of a particular freezing plateau is less than 25 μK and that noise (drift) from other sources, possibly due to variations in room temperature, starts to become appreciable over periods longer than a few tens of minutes. The measurement of freezing and melting plateaux at this level is aided by the introduction of new ASL-F900 bridge(s), and quieter/larger standard resistor baths.

We report progress in the development of an apparatus to compare the thermodynamic temperature of a gas with the temperature as determined by the International Temperature Scale of 1990 (ITS-90). The apparatus uses the Rayleigh scattering of light from a gas to provide an intensive measure of gas density, thus avoiding the need for corrections for dead volumes or wall adsorption required in conventional gas thermometry. A laser beam is shone through gas in two cells which are at the same pressure but different temperatures, and the measured ratio of the Rayleigh scattering signals from the two cells can be related to the ratio of the gas density in the cells. From the density ratio, the thermodynamic temperature of one cell can be inferred if the other cell is held close to the triple point of water. However, the Rayleigh scattering is weak and signals are small, making measurements with sufficiently small uncertainty extremely challenging. Since previous reports, the apparatus has been significantly modified and we describe these changes along with indicative results. In this paper we present results of measurements in the range 211 K to 292 K using both argon and xenon. The results suffer from large systematic errors due to presence of contamination in one of the measurement cells. However, although the results do not provide reliable estimates of T -T90, they do indicate that the measurements with uncertainties below 1 mK are feasible.

Accurate measurement of high temperatures in a nuclear environment presents unique challenges. All secondary techniques inevitably drift because the thermometric materials in thermocouples and resistance sensors are sensitive not just to temperature, but also their own chemical and physical composition. The solution is to use primary methods that rely on fundamental links between measurable physical properties and temperature. In the nuclear field the best known technique is the measurement of Johnson Noise in a resistor (See Paper 80 at this conference). In this paper we describe the measurement of temperature in terms of the speed of sound in a gas confined in a tube — an acoustic waveguide. Acoustic thermometry is the most accurate technique of primary thermometry ever devised with the best uncertainty of measurement below 0.001 °C. In contrast, the acoustic technique described in this work has a much larger uncertainty, approximately 1 °C. But the cost and ease of use are improved by several orders of magnitude, making implementation eminently practical. We first describe the basic construction and method of operation of thermometers using twin-tubes and single tubes. We then present results using a twin-tube design showing long-term stability (i.e. no detectable drift) at 700 °C over periods of several weeks. We then outline how the technique may be developed for different nuclear applications.

Launched in 2011 within the European Metrology Research Programme (EMRP) of EURAMET, the joint research project ‘MeteoMet’—Metrology for Meteorology—is the largest EMRP consortium; national metrology institutes, universities, meteorological and climate agencies, research institutes, collaborators and manufacturers are working together, developing new metrological techniques, as well as improving existing ones, for use in meteorological observations and climate records. The project focuses on humidity in the upper and surface atmosphere, air temperature, surface and deep-sea temperatures, soil moisture, salinity, permafrost temperature, precipitation, and the snow albedo effect on air temperature. All tasks are performed using a rigorous metrological approach and include the design and study of new sensors, new calibration facilities, the investigation of sensor characteristics, improved techniques for measurements of essential climate variables with uncertainty evaluation, traceability, laboratory proficiency and the inclusion of field influencing parameters, long-lasting measurements, and campaigns in remote and extreme areas. The vision for MeteoMet is to take a step further towards establishing full data comparability, coherency, consistency, and long-term continuity, through a comprehensive evaluation of the measurement uncertainties for the quantities involved in the global climate observing systems and the derived observations. The improvement in quality of essential climate variables records, through the inclusion of measurement uncertainty budgets, will also highlight possible strategies for the reduction of the uncertainty. This contribution presents selected highlights of the MeteoMet project and reviews the main ongoing activities, tasks and deliverables, with a view to its possible future evolution and extended impact.

Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met. © 2013 AIP Publishing LLC.

In preparation for the new challenges posed by the higher temperature environments which are likely to be encountered in the next generation of nuclear power plants, to maintain the safety and to ensure the long-term reliability of such plants, it is crucial that new temperature sensors and methods for in-situ measurement are investigated and developed. This is the general objective of the first workpackage of the joint research project, ENG08 MetroFission, funded in the framework of the European metrology research program. This paper will review the results obtained in developing and testing new temperature sensors and references during the course of the project. The possible continuation of these activities in the future is discussed.

Acoustic thermometry is the most accurate technique of primary thermometry ever devised. However, resonator based techniques are not practical and are rarely used in practice. Previously we have demonstrated the basic functionality of an acoustic thermometer operating at up to 1000 °C based on the time-of-flight measurements of short pulses in an acoustic waveguide. Here we report progress in assessing the practical and theoretical performance limitations of such a device. In this paper we report improvements in timing techniques which significantly improve the signal-to-noise ratio, a feature likely to be important in many industrial settings. We discuss the inference of the free field speed of sound from timing measurements and report results from a simple twin tube thermometer operating up to 500 °C. Finally we consider the shortcomings of current designs and prospects for future improvements including frequency domain analysis of the system.

The aim of International Surface Temperature Initiative is to create an end-to-end process for analysis of air temperature data taken over the land surface of the Earth. The foundation of any analysis is the source data. Land surface air temperature records have traditionally been stored in local, organizational, national and international holdings, some of which have been available digitally but many of which are available solely on paper or as imaged files. Further, economic and geopolitical realities have often precluded open sharing of these data. The necessary first step therefore is to collate readily available holdings and augment these over time either through gaining access to previously unavailable digital data or through data rescue and digitization activities. Next, it must be recognized that these historical measurements were made primarily in support of real-time weather applications where timeliness and coverage are key. At almost every long-term station it is virtually certain that changes in instrumentation, siting or observing practices have occurred. Because none of the historical measures were made in a metrologically traceable manner there is no unambiguous way to retrieve the true climate evolution from the heterogeneous raw data holdings. Therefore it is desirable for multiple independent groups to produce adjusted data sets (so-called homogenized data) to adequately understand the data characteristics and estimate uncertainties. Then it is necessary to benchmark the performance of the contributed algorithms (equivalent to metrological software validation) through development of realistic benchmark datasets. In support of this, a series of successive benchmarking and assessment cycles are envisaged, allowing continual improvement while avoiding over-tuning of algorithms. Finally, a portal is proposed giving access to related data-products, utilizing the assessment results to provide guidance to end-users on which product is the most suited to their needs. Recognizing that the expertise of the metrological community has been under-utilized historically in such climate data analysis problems, the governance of the Initiative includes significant representation from the metrological community. We actively welcome contributions from interested parties to any relevant aspects of the Initiative work.

The European metrology research programme (EMRP) allows funding for metrology-oriented projects in the frame of targeted calls aimed at improving metrology for important contemporary and future needs in different fields such as energy, environment and industry. A joint research project (JRP), called "MetroFission", was selected for funding in the "Energy" call of 2010. This JRP, led by NPL (UK), aims to anticipate and to start addressing the metrological needs of the next generation of nuclear power plants. The need for improving the accuracy and reliability of temperature measurements at temperatures higher than those currently measured in nuclear power plants is dealt with in the first workpackage of the project. This project started in September 2010 and will last for three years. This paper summarizes the activities of the first half of the project and the expected final achievements, which will be essentially oriented towards new temperature references and new devices, adapted to the high temperature range as well as the particularly harsh working conditions.

The use of a combined microwave and acoustic resonator to determine the Boltzmann constant, kB, permits several checks on the internal consistency of the data. Using measurements in argon gas in the NPL-Cranfield quasispherical copper resonator (NPLC-2), we describe four distinct types of internal consistency check. Firstly, we estimate kB using six distinct acoustic resonances varying in frequency from 3.55 kHz to 21.77 kHz. We thus span a wide range of systematic corrections, most notably in the effect of the thermal boundary layer (TBL), which varies strongly with mode. Secondly, the same theory which predicts the TBL corrections to the acoustic resonance frequencies also predicts the widths of the resonances. By comparing the measured and theoretically-expected widths we can place limits on the effect of any un-modeled physics. Thirdly, the equivalent radius of the resonator (∼62.03 mm) is inferred from analysis of 8 TM microwave resonances and the spread of the radius values inferred from each mode is a measure of how well the resonator has been modeled. Finally, the microwave data can be used to check the inferred density of gas within the resonator. Based on measurements of the dielectric permittivity of the argon gas, pressure discrepancies greater than ±6 Pa can be detected at all pressures up to 700 kPa. Taken together, these four checks improve confidence in the final estimate for kB and restrict the types of systematic error which may affect the result.

HadISDH is a near-global land surface specific humidity monitoring product providing monthly means from 1973 onwards over large-scale grids. Presented herein to 2012, annual updates are anticipated. HadISDH is an update to the land component of HadCRUH, utilising the global high-resolution land surface station product HadISD as a basis. HadISD, in turn, uses an updated version of NOAA's Integrated Surface Database. Intensive automated quality control has been undertaken at the individual observation level, as part of HadISD processing. The data have been subsequently run through the pairwise homogenisation algorithm developed for NCDC's US Historical Climatology Network monthly temperature product. For the first time, uncertainty estimates are provided at the grid-box spatial scale and monthly timescale. HadISDH is in good agreement with existing land surface humidity products in periods of overlap, and with both land air and sea surface temperature estimates. Widespread moistening is shown over the 1973–2012 period. The largest moistening signals are over the tropics with drying over the subtropics, supporting other evidence of an intensified hydrological cycle over recent years. Moistening is detectable with high (95%) confidence over large-scale averages for the globe, Northern Hemisphere and tropics, with trends of 0.089 (0.080 to 0.098) g kg−1 per decade, 0.086 (0.075 to 0.097) g kg−1 per decade and 0.133 (0.119 to 0.148) g kg−1 per decade, respectively. These changes are outside the uncertainty range for the large-scale average which is dominated by the spatial coverage component; station and grid-box sampling uncertainty is essentially negligible on large scales. A very small moistening (0.013 (−0.005 to 0.031) g kg−1 per decade) is found in the Southern Hemisphere, but it is not significantly different from zero and uncertainty is large. When globally averaged, 1998 is the moistest year since monitoring began in 1973, closely followed by 2010, two strong El Niño years. The period in between is relatively flat, concurring with previous findings of decreasing relative humidity over land.

The magnetization of NdCu2 has been measured from 0.3 to 7.0 K, in fields up to 12 T. The correspondence of the magnetization with a zero-field neutron diffraction study is considered. A model is proposed in order to explain the various magnetic phases observed in the magnetization data.

Using exceptionally accurate measurements of the speed of sound in argon, we have made estimates of the difference between thermodynamic temperature, T , and the temperature estimated using the International Temperature Scale of 1990, T 90 , in the range 118 K to 303 K. Thermodynamic temperature was estimated using the technique of relative primary acoustic thermometry in the NPL-Cranfield combined microwave and acoustic resonator. Our values of ( T − T 90 ) agree well with most recent estimates, but because we have taken data at closely spaced temperature intervals, the data reveal previously unseen detail. Most strikingly, we see undulations in ( T − T 90 ) below 273.16 K, and the discontinuity in the slope of ( T − T 90 ) at 273.16 K appears to have the opposite sign to that previously reported.

Substantial improvements in high temperature measurement have been made in the last few years at national measurement institutes, which can be of benefit to the nuclear industry. In this article some of these developments are summarised. In addition, the temperature aspects of a major European project, ‘MetroFission’, to build on these improvements and disseminate these developments are described. Novel aspects include new temperature calibration techniques and artifacts, new thermocouple types with much improved stability and low neutron absorption cross-section, self-calibrating thermocouples and practical acoustic thermometry - a driftless technique for measuring absolute temperature.

The low-temperature specific heat of CeNixPt1-x compounds has been investigated from x=0 to X=1. These compounds evolve from a Pauli paramagnet (CeNi) to a Kondo ferromagnet (CePt), with a crossover around x=0.90. The reduction of the magnetic entropy at T(C) has been used to illustrate the increasing 4f-sd hybridization with increasing Ni content, related to a decrease of the cell volume. This effect has been confirmed by the results obtained on Y and La diluted compounds which have opposite volume effects. The relations between the jump in the specific heat at T(C), the magnetic moment, and the ratio T(K)/T(C) have been analyzed. The values of the electronic heat capacity gamma vary as almost-equal-to 1/T(K) in the nonmagnetically ordered compounds in accord with the standard theory. However in the magnetically ordered compounds gamma increases with T(K) in accord with the resonance-level model developed by Bredl et al. [Z. Phys. B 29, 327 (1978)].

We present details of a Practical Acoustic Thermometer (PAT), in which temperature is inferred from measurements of the speed of sound along acoustic waveguides. We describe both the theory of operation, and measurements on three devices at temperatures up to 1000 °C. Because the relationship between the speed of sound in a simple gas and absolute temperature is well understood, the mean temperature along a tube may be estimated from measurements of the frequency-dependent propagation constant. A PAT device made from two tubes of different lengths allows the temperature measurement region to be localised, creating an instrument functionally similar to conventional contact thermometers. Three twin-tube PAT devices were constructed and tested. PAT-A, made of silica, served to validate the technique with differences between the acoustic thermometer and a reference thermocouple of less than 2 °C at temperatures in the range from 100 °C to 1000 °C. PAT-B and PAT-C were made of Inconel-600, potentially more suitable for use in harsh environments. The Inconel devices deviated from expected behaviour in a reproducible manner, which after calibration allowed measurements with errors of less than ±1 °C in the range to 700 °C. No drift was observed up to 700 °C. The drift observed during prolonged exposure to higher temperatures is described and its likely causes discussed. In the longer term, similar technology may provide a means for the measurement of temperature in harsh environments such as those found in the nuclear industry.

The results of calorimetry from 2 to 12 K on single crystals of localised-moment UPd3 in magnetic fields of zero and 6 T applied along the crystallographic c-direction are presented. Three anomalies in the specific heat were observed which coincide with anomalies in magnetic thermal expansion. The different field-dependencies of these transitions are reported. Combining the two measurements we are able to map the changes in the zero-field Gruneisen parameter across the three transitions.

Heat capacity measurements on the orthorombic compounds CePt and LaPt are presented between 0.7 K and 300 K. Measurements over this large temperature range allow a good estimate of the crystalline electric field (CEF) levels derived from the J = 5 2 ground multiplet of the Ce3+ ion lying in a low symmetry site. The subtraction of the corresponding Schottky anomaly allows an accurate value for the electronic coefficient γ to be obtained, which is clearly enhanced compared with previous estimates made without considering CEF effects. The thermal expansion anomaly can be explained with the CEF level scheme deduced from the specific heat results.

Magnetization and resistivity studies show the evolution of the physical properties of the ferromagnet UPt ( T c = 27 K) when Pt is substituted by Ni. Magnetic order remains for compounds with x > 0.5, while for higher Ni content we find a mainly delocalized behaviour. The resistivity exhibits interesting features, including a negative thermal coefficient for T > T c in the ferromagnetic compounds and a Kondo-like minimum in UNi.

We report the first measurements of a quasi-spherical microwave resonator used as a dew-point hygrometer. In conventional dew-point hygrometers, the condensation of water from humid gas flowing over a mirror is detected optically, and the mirror surface is then temperature-controlled to yield a stable condensed layer. In our experiments we flowed moist air from a humidity generator through a quasi-spherical resonator and detected the onset of condensation by measuring the frequency ratio of selected microwave modes. We verified the basic operation of the device over the dew-point range 9.5–13.5 °C by comparison with calibrated chilled-mirror hygrometers. These tests indicate that the microwave method may allow a quantitative estimation of the volume and thickness of the water layer which is condensed on the inner surface of the resonator. The experiments reported here are preliminary due to the limited time available for the work, but show the potential of the method for detecting not only water but a variety of other liquid or solid condensates. The robust all-metal construction should make the device appropriate for use in industrial applications over a wide range of temperatures and pressures.

The perturbing effect of a waveguide on the boundary of a quasispherical cavity resonator is investigated both theoretically and experimentally. Expressions for the frequency perturbation to the triply degenerate TM1mn and TE1mn modes are derived using cavity perturbation theory. The fields in and around the waveguide are calculated in the static limit using finite-element software. Experiments performed using quasispherical and cylindrical cavity resonators confirm the accuracy and generality of the approach. The impact of this study on attempts to re-determine the Boltzmann constant (kB) by an acoustic resonance technique is briefly considered.

We report heat capacity measurements on annealed polycrystalline samples of UNi x Pt 1 − x ( x = 1, 0.8, 0.6, 0.4, 0.2, 0) in zero field and in a 6 T magnetic field, over the temperature range 2 to 70 K. Anomalies are seen in UPt and UNi 0.2 Pt 0.8 , at 26.2 and 14.8 K. UNi and UNi 0.8 Pt 0.2 show no signs of magnetic order. Weak transitions have been noted in several compounds, but their behaviour on annealing and correlation between compounds indicates their origin is probably due to mixed phases. An applied field of 6 T has no effect on the transition temperatures. The electronic heat capacity term γ decreases roughly linearly from 80 mJ K −2 mol −1 for UPt to 25 mJ K −2 mol −1 for UNi and is unaffected by an applied field of 6 T.

We report the study of the magnetisation of CeCo2 at temperature below 1 K, in which a superconducting transition (TC = 0.82 K) is observed. Field cooling the sample from above TC in a 5 mT field suppressed the superconducting transition for temperatures down to 0.4 K. Magnetisation measurements below TC show behaviour typical of a type II superconductor, except for an unusual feature below Hc2, with Hc1 = 7.5 mT and Hc2 = 0.275 T at 0.4 K.

We have measured the magnetic susceptibility of UPd3 along the a-, b- and c-axes from 0.4 to 80 K. With decreasing temperature, the c-axis susceptibility shows a sharp drop, and the a-and b-axis results show increases, at the antiferroquadrupolar and magnetic transitions, at 6.8 and 4.5 K, respectively.