scholarly journals Accurate radiometry from space: an essential tool for climate studies

2011 ◽  
Vol 369 (1953) ◽  
pp. 4028-4063 ◽  
Author(s):  
Nigel Fox ◽  
Andrea Kaiser-Weiss ◽  
Werner Schmutz ◽  
Kurtis Thome ◽  
Dave Young ◽  
...  
Keyword(s):  
Climate Models ◽  
Causal Attribution ◽  
International System ◽  
Primary Standard ◽  
Sufficient Accuracy ◽  
Time Base ◽  
Satellite Mission ◽  
The Earth ◽  
System Of Units ◽  
Si Traceability

The Earth's climate is undoubtedly changing; however, the time scale, consequences and causal attribution remain the subject of significant debate and uncertainty. Detection of subtle indicators from a background of natural variability requires measurements over a time base of decades. This places severe demands on the instrumentation used, requiring measurements of sufficient accuracy and sensitivity that can allow reliable judgements to be made decades apart. The International System of Units (SI) and the network of National Metrology Institutes were developed to address such requirements. However, ensuring and maintaining SI traceability of sufficient accuracy in instruments orbiting the Earth presents a significant new challenge to the metrology community. This paper highlights some key measurands and applications driving the uncertainty demand of the climate community in the solar reflective domain, e.g. solar irradiances and reflectances/radiances of the Earth. It discusses how meeting these uncertainties facilitate significant improvement in the forecasting abilities of climate models. After discussing the current state of the art, it describes a new satellite mission, called TRUTHS, which enables, for the first time, high-accuracy SI traceability to be established in orbit. The direct use of a ‘primary standard’ and replication of the terrestrial traceability chain extends the SI into space, in effect realizing a ‘metrology laboratory in space’.

scholarly journals Traceable Radiometry Underpinning Terrestrial- and Helio-Studies (TRUTHS): An Element of a Space-Based Climate and Calibration Observatory

2020 ◽  
Vol 12 (15) ◽  
pp. 2400
Author(s):  
Nigel Fox ◽  
Paul Green
Keyword(s):  
Causal Attribution ◽  
International System ◽  
Primary Standard ◽  
Sufficient Accuracy ◽  
Time Base ◽  
Satellite Mission ◽  
Traceability Chain ◽  
The Earth ◽  
System Of Units ◽  
Si Traceability

The Earth’s climate is undoubtedly changing; however, the time scale, consequences, and causal attribution remain the subject of significant debate and uncertainty. Detection of subtle indicators from a background of natural variability requires measurements over a time-base of decades. This places severe demands on the instrumentation used, requiring measurements of sufficient accuracy and sensitivity that can allow reliable judgements to be made decades apart. The International System of Units (SI) was developed to address such requirements, providing a reference framework tied to invariant constants of nature. However, ensuring and maintaining SI traceability of sufficient accuracy in instruments orbiting the Earth presents a significant new challenge to the Earth Observation and metrology communities. This paper describes a new satellite mission, called Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS), which enables, for the first time, high-accuracy SI traceability to be established in orbit. The direct use of a ‘primary standard’ and replication of the terrestrial traceability chain extends the SI into space, in effect realizing a ‘metrology laboratory in space’ providing and enabling SI-traceable measurements of unequivocal accuracy in the solar reflective domain—an enabling element of an international space-based climate observing system. TRUTHS will not only provide a benchmark of the radiation state of the planet (incoming and outgoing) from which to compare change in the shortest time possible, but also facilitate an upgrade in performance of the Earth Observing system as a whole, through ‘in-orbit’ reference calibration.

scholarly journals Establishing SI-Traceability of Nanoparticle Size Values Measured with Line-Start Incremental Centrifugal Liquid Sedimentation

Separations ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 15
Author(s):  
Vikram Kestens ◽  
Victoria A. Coleman ◽  
Jan Herrmann ◽  
Caterina Minelli ◽  
Alex G. Shard ◽  
...  
Keyword(s):  
Particle Size ◽  
Certified Reference Materials ◽  
International System ◽  
Metrological Traceability ◽  
Metrological Reliability ◽  
Limited Information ◽  
System Of Units ◽  
Si Traceability ◽  
Calibration Materials ◽  
Traceability Networks

Line-start incremental centrifugal liquid sedimentation (disc-CLS) is a powerful technique to determine particle size based on the principles of Stokes’ law. As most input quantities of the Stokes equation cannot be easily determined for typical instruments used for this method, an alternative method which depends on calibrating the sedimentation time scale with reference particles has become common practice. Unfortunately, most of these calibration materials (calibrants) come with limited information regarding their metrological reliability (e.g., lack of measurement uncertainties and traceability statements, incomplete measurand definitions). As a consequence, routine particle size results obtained by disc-CLS are mostly only traceable to the calibrant used, and effective comparisons can only be made for those results originating from measurements performed with the same types of calibrants. In this study, we discuss the concept of metrological traceability and demonstrate that particle size results obtained by disc-CLS can be traceable to the ultimate metrological reference, i.e., the unit of length in the International System of Units (SI), the meter. Using the example of two colloidal silica certified reference materials, we describe how laboratories can realize metrological traceability to the SI by simplifying complex traceability networks.

scholarly journals Time scales in the context of general relativity

2011 ◽  
Vol 369 (1953) ◽  
pp. 4131-4142 ◽  
Author(s):  
Bernard Guinot
Keyword(s):  
Relativistic Effect ◽  
International System ◽  
Centre Of Mass ◽  
Frequency Standards ◽  
The Earth ◽  
International Astronomical ◽  
System Of Units ◽  
Definition Of ◽  
Atomic Time

Towards 1967, the accuracy of caesium frequency standards reached such a level that the relativistic effect could not be ignored anymore. Corrections began to be applied for the gravitational frequency shift and for distant time comparisons. However, these corrections were not applied to an explicit theoretical framework. Only in 1991 did the International Astronomical Union provide metrics (then improved in 2000) for a definition of space–time coordinates in reference systems centred at the barycentre of the Solar System and at the centre of mass of the Earth. In these systems, the temporal coordinates (coordinate times) can be realized on the basis of one of them, the International Atomic Time (TAI), which is itself a realized time scale. The definition and the role of TAI in this context will be recalled. There remain controversies regarding the name to be given to the unit of coordinate times and to other quantities appearing in the theory. However, the idea that astrometry and celestial mechanics should adopt the usual metrological rules is progressing, together with the use of the International System of Units, among astronomers.

scholarly journals The fundamental constants of physics and the International System of Units

2021 ◽  
Author(s):  
Diederik Sybolt Wiersma ◽  
Giovanni Mana
Keyword(s):  
New York ◽  
International System ◽  
New York Times ◽  
Fundamental Constants ◽  
Decimal System ◽  
The Earth ◽  
System Of Units ◽  
Unit Of Measurement ◽  
Passenger Aircraft ◽  
Base Units

AbstractAir Canada managed to have a passenger aircraft run out of fuel in mid-air due to confusion about metric units (Stephenson in Mars climate orbiter mishap investigation board phase I report, NASA, 1999), and NASA lost an entire spacecraft due to a misunderstanding amongst engineers about the units used in the propulsion system design (Witkin in Jet’s fuel ran out after metric conversion errors, The New York Times, 1983). Measurements only make sense if the units are correct and well-defined. A unit of measurement is a definite magnitude of a quantity, defined by convention or law. Any other quantity of that kind can then be expressed as a multiple or submultiple of the unit of measurement. The Egyptians used the Farao as definite magnitude, while many years later, the french revolutionists introduced the earth as a reference and laid the foundations for the modern decimal system. Since recently, we have a truly universal and stable system that uses physics’s natural constants and laws to define the base units of measurement. This paper explains how this new concept works and how it is implemented in practice.

scholarly journals SI-Traceability and Measurement Uncertainty of the Atmospheric Infrared Sounder Version 5 Level 1B Radiances

2020 ◽  
Vol 12 (8) ◽  
pp. 1338 ◽  
Author(s):  
Thomas S. Pagano ◽  
Hartmut H. Aumann ◽  
Steven E. Broberg ◽  
Chase Cañas ◽  
Evan M. Manning ◽  
...  
Keyword(s):  
Measurement Uncertainty ◽  
International System ◽  
Atmospheric Temperature ◽  
Recent Analysis ◽  
Spectral Accuracy ◽  
Large Area ◽  
Atmospheric Infrared Sounder ◽  
System Of Units ◽  
Si Traceability ◽  
Better Than

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on 4 May 2002. The AIRS is designed to measure atmospheric temperature and water vapor profiles and has demonstrated exceptional radiometric and spectral accuracy and stability in orbit. The International System of Units (SI)-traceability of the derived radiances is achieved by transferring the calibration from the Large Area Blackbody (LABB) with SI traceable temperature sensors, to the On-Board Calibrator (OBC) blackbody during preflight testing. The AIRS views the OBC blackbody and four full aperture space views every scan. A recent analysis of pre-flight and on-board data has improved our understanding of the measurement uncertainty of the Version 5 AIRS L1B radiance product. For temperatures greater than 260 K, the measurement uncertainty is better than 250 mK 1-sigma for most channels. SI-traceability and quantification of the radiometric measurement uncertainty is critical to reducing biases in reanalysis products and radiative transfer models (RTMs) that use AIRS data, as well as establishing the suitability of AIRS as a benchmark for radiances established in the early 2000s.

scholarly journals Corrections of proper motions in declination by using ILS data

2006 ◽  
pp. 95-99 ◽  
Author(s):  
G. Damljanovic ◽  
N. Pejovic
Keyword(s):  
Earth Rotation ◽  
Sufficient Accuracy ◽  
Proper Motions ◽  
Satellite Mission ◽  
Earth Orientation ◽  
The Earth ◽  
Hipparcos Catalogue ◽  
Order Of Magnitude ◽  
Astronomical Satellite ◽  
Good Agreement

There are nowadays numerous astrometric ground{based observations of some stars referred to Hipparcos Catalogue, made at many observatories during the last century. We used the data on latitude variations, covering the period 1899.7 - 1979.0, of visual Zenith Telescopes (ZT) of International Latitude Service (ILS), to improve the Hipparcos proper motions in declination for stars observed at seven ILS stations: Carloforte, Cincinnati, Gaithersburg Kitab, Mizusawa, Tschardjui and Ukiah. About 15 years elapsed since the HIPPARCOS ESA mission (ESA 1997) observations (1991.25 is the epoch of this catalogue), and with the errors of the Hipparcos proper motions close to 1 mas/yr, the error of apparent places of stars is now more than 15 mas; so that it exceeds the error of the Hipparcos positions by one order of magnitude (which is about 1 mas). Also, for some Hipparcos stars, the errors of proper motions are much larger than the averaged value itself, even not realistic at all (Vondr?k et al. 1998); the Hipparcos astronomical satellite mission lasted less than four years, not enough to get a sufficient accuracy of the proper motions. To improve the accuracy of the proper motions for some Hipparcos stars, the ground-based data were used and some new catalogues were published (such as ARIHIP, EOC-2, etc) during the last decade. Our investigations are in accordance with the Earth Orientation Catalogue - EOC (Vondr?k and Ron 2003) one, based on the Earth rotation programmes ground{based data, but we used different method here. Our results yield better proper motions in declination for stars common to ILS and HIPPARCOS and a good agreement with those from EOC-2.

Dimensions of plane and solid angles and their units in the International System of Units (SI)

2020 ◽  
pp. 26-32
Author(s):  
M. I. Kalinin ◽  
L. K. Isaev ◽  
F. V. Bulygin
Keyword(s):  
Solid Angle ◽  
International System ◽  
International Committee ◽  
Plane Angle ◽  
Arc Length ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
In Series ◽  
Solid Angles

The situation that has developed in the International System of Units (SI) as a result of adopting the recommendation of the International Committee of Weights and Measures (CIPM) in 1980, which proposed to consider plane and solid angles as dimensionless derived quantities, is analyzed. It is shown that the basis for such a solution was a misunderstanding of the mathematical formula relating the arc length of a circle with its radius and corresponding central angle, as well as of the expansions of trigonometric functions in series. From the analysis presented in the article, it follows that a plane angle does not depend on any of the SI quantities and should be assigned to the base quantities, and its unit, the radian, should be added to the base SI units. A solid angle, in this case, turns out to be a derived quantity of a plane angle. Its unit, the steradian, is a coherent derived unit equal to the square radian.

scholarly journals A quantum ampere

2020 ◽  
Vol 87 (4) ◽  
pp. 258-265
Author(s):  
Luca Callegaro
Keyword(s):  
Electric Current ◽  
International System ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
User Friendly

AbstractThe revision of the International System of Units (SI), implemented since 20 May 2019, has redefined the unit of electric current, the ampere ( A), linking it to a fixed value of the elementary charge. This paper discusses the new definition and the realisation of the electrical units by quantum electrical metrology standards, which every year become more and more accessible, reliable and user friendly.

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