scholarly journals Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

2018 ◽  
Vol 11 (7) ◽  
pp. 3871-3882 ◽  
Author(s):  
Anne Kleinert ◽  
Isabell Krisch ◽  
Jörn Ungermann ◽  
Albert Adibekyan ◽  
Berndt Gutschwager ◽  
...  
Keyword(s):  
Water Vapor ◽  
Temperature Distribution ◽  
International System ◽  
Vertical Resolution ◽  
Radiometric Calibration ◽  
Climate Trends ◽  
Trace Species ◽  
Calibration Uncertainty ◽  
System Of Units

Abstract. Limb sounding instruments play an important role in the monitoring of climate trends, as they provide a good vertical resolution. Traceability to the International System of Units (SI) via onboard reference or transfer standards is needed to compare trend estimates from multiple instruments. This study investigates the required uncertainty of these radiation standards to properly resolve decadal trends of climate-relevant trace species like ozone, water vapor, and temperature distribution for the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). Temperature nonuniformities of the onboard reference blackbodies, used for radiometric calibration, have an impact on the calibration uncertainty. The propagation of these nonuniformities through the retrieval is analyzed. A threshold for the maximum tolerable uncertainty of the blackbody temperature is derived, so that climate trends can be significantly identified with GLORIA.

scholarly journals Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

2018 ◽  
Author(s):  
Anne Kleinert ◽  
Isabell Krisch ◽  
Jörn Ungermann ◽  
Albert Adibekyan ◽  
Berndt Gutschwager ◽  
...  
Keyword(s):  
Water Vapor ◽  
Temperature Distribution ◽  
Vertical Resolution ◽  
Radiometric Calibration ◽  
Climate Trends ◽  
Trace Species ◽  
Calibration Uncertainty

Abstract. Limb sounding instruments play an important role for the monitoring of climate trends, as they provide a good vertical resolution. Traceability to the SI via onboard reference or transfer standards is needed to compare trend estimates from multiple instruments. This study investigates the required uncertainty of these radiation standards to properly resolve decadal trends of climate relevant trace species like ozone, water vapor and temperature distribution for the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). Temperature nonuniformities of the onboard reference blackbodies, used for radiometric calibration, have an impact on the calibration uncertainty. The propagation of these nonuniformities through the retrieval is analyzed. A threshold for the maximum tolerable uncertainty of the blackbody temperature is derived, so that climate trends can be significantly identified with GLORIA.

Characterisation Campaign at the Gobabeb RadCalNet Site in Support of Satellite Calibration and Validation Activities

2020 ◽  
Author(s):  
Morven Sinclair ◽  
Chris McLellan ◽  
Agnieszka Bialek ◽  
Emma R Woolliams ◽  
Sarah Taylor ◽  
...  
Keyword(s):  
Working Group ◽  
International System ◽  
Processing System ◽  
Hyperspectral Data ◽  
Sensor Data ◽  
Spectral Information ◽  
Radiometric Calibration ◽  
Atmospheric Conditions ◽  
Calibration And Validation ◽  
System Of Units

<p>With increasing use of satellite-derived data in climate and Earth monitoring, the importance of reliable and traceable radiometric and spectral information is key. Due to the difficulties of maintaining instrument calibration post-launch, vicarious calibration sites play a vital part in ensuring the stability and interoperability of satellite sensor data.</p><p>RadCalNet, the Radiometric Calibration Network established through the Committee on Earth Observation Satellites Working Group on Calibration and Validation (CEOS-WGCV), provides a network of, currently four, instrumented ground reference sites providing users with bottom and top-of-atmosphere (BOA and TOA) reflectance measurements every 30 minutes in 10 nm spectral intervals and for nadir view. (For all sites, more detailed spectral information and off-nadir reflectances can be obtained from site owners). It is a key aspect of RadCalNet that the sites document their traceability to the International System of Units (SI) and that they provide traceable uncertainties associated with individual observations. These documents and uncertainties are peer reviewed by the RadCalNet working group.  Each RadCalNet site provides ground reflectance observations that are propagated to TOA through a centralised processing system. RadCalNet has over 300 active users who value the available information.</p><p>Gobabeb, in Namibia, is one of these four sites, given the reference GONA. GONA was the first site that was established as a new RadCalNet site (the other sites were pre-existing) and the location was determined from a global survey to find suitable sites, primarily due to spatial uniformity and the probability of suitable atmospheric conditions, such as clear skies. With an automatic radiometric station, this site continuously collects atmospheric data and surface radiance measurements. These are then processed to ground spectral reflectance and provided with uncertainties to the RadCalNet processor which propagates values to TOA.</p><p>Due to the limitations of the instrument used for autonomous measurements, recent fieldwork has been carried out in this location to acquire additional hyperspectral data to maintain the quality of the site products. In addition, further site characterisation was conducted to prepare a best location for a new site nearby that is being developed under the HYPERNETS project. This paper presents both the RadCalNet site and the results of the recent fieldwork.</p>

The BIPM Mycotoxin Metrology Capacity Building and Knowledge Transfer Program: Accurate Characterization of a Pure Aflatoxin B1 Material to Avoid Calibration Errors

2019 ◽  
Vol 102 (6) ◽  
pp. 1740-1748
Author(s):  
Ralf D Josephs ◽  
Xiaomin Li ◽  
Xiuqin Li ◽  
Zhen Guo ◽  
Bruno Garrido ◽  
...  
Keyword(s):  
Knowledge Transfer ◽  
Aflatoxin B1 ◽  
Developing Economies ◽  
International System ◽  
Impurity Content ◽  
Transfer Program ◽  
Measurement Capability ◽  
System Of Units ◽  
Food And Feed

Abstract Background: The contamination of food and feed by mycotoxins, Aflatoxin B1 (AfB1) being one of the most prominent examples, is of imminent concern to many countries. Regulatory limits for mycotoxins have been implemented, and these need to be supported by a sound measurement infrastructure for mycotoxin analysis in order to enforce and verify products, protect populations, and avoid technical barriers to trade in food stuffs. Objective: A Capability Building and Knowledge Transfer program on Metrology for Safe Food and Feed in Developing Economies was started at the International Bureau of Weights and Measures to allow National Metrology Institutes or Designated Institutes to work together to strengthen their national mycotoxin metrology infrastructure. Methods: Knowledge transfer to scientists is provided to enable the characterization of selected pure mycotoxin materials and the production of corresponding certified reference material solutions. Results: This higher-order measurement capability can in turn support mycotoxin testing laboratories within their countries through the provision, for example, of standard solutions of critical analytes that are traceable to the International System of Units (SI). Conclusions and Highlights: The purity characterization and value assignment for a high-purity AfB1 material (979.6 ± 2.3 mg/g, k = 2) intended to be used for the gravimetric production of SI traceable calibration solutions for AfB1 is described using an approach combining quantitative NMR and LC–diode array detection–tandem MS for the correction of the mycotoxin-related impurity content.

scholarly journals Spectrally Dependent CLARREO Infrared Spectrometer Calibration Requirement for Climate Change Detection

2017 ◽  
Vol 30 (11) ◽  
pp. 3979-3998 ◽  
Author(s):  
Xu Liu ◽  
Wan Wu ◽  
Bruce A. Wielicki ◽  
Qiguang Yang ◽  
Susan H. Kizer ◽  
...  
Keyword(s):  
Climate Change ◽  
Water Vapor ◽  
Climate Model ◽  
Model Simulation ◽  
Atmospheric Temperature ◽  
Reanalysis Data ◽  
Natural Variability ◽  
Radiometric Calibration ◽  
Climate Trends ◽  
Moisture Profiles

Abstract Detecting climate trends of atmospheric temperature, moisture, cloud, and surface temperature requires accurately calibrated satellite instruments such as the Climate Absolute Radiance and Refractivity Observatory (CLARREO). Previous studies have evaluated the CLARREO measurement requirements for achieving climate change accuracy goals in orbit. The present study further quantifies the spectrally dependent IR instrument calibration requirement for detecting trends of atmospheric temperature and moisture profiles. The temperature, water vapor, and surface skin temperature variability and the associated correlation time are derived using the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. The results are further validated using climate model simulation results. With the derived natural variability as the reference, the calibration requirement is established by carrying out a simulation study for CLARREO observations of various atmospheric states under all-sky conditions. A 0.04-K (k = 2; 95% confidence) radiometric calibration requirement baseline is derived using a spectral fingerprinting method. It is also demonstrated that the requirement is spectrally dependent and that some spectral regions can be relaxed as a result of the hyperspectral nature of the CLARREO instrument. Relaxing the requirement to 0.06 K (k = 2) is discussed further based on the uncertainties associated with the temperature and water vapor natural variability and relatively small delay in the time to detect for trends relative to the baseline case. The methodology used in this study can be extended to other parameters (such as clouds and CO2) and other instrument configurations.

scholarly journals Uncertainty Analysis for RadCalNet Instrumented Test Sites Using the Baotou Sites BTCN and BSCN as Examples

2020 ◽  
Vol 12 (11) ◽  
pp. 1696 ◽  
Author(s):  
Lingling Ma ◽  
Yongguang Zhao ◽  
Emma R. Woolliams ◽  
Caihong Dai ◽  
Ning Wang ◽  
...  
Keyword(s):  
Uncertainty Analysis ◽  
International System ◽  
Uncertainty Budget ◽  
In Situ Monitoring ◽  
Radiometric Calibration ◽  
Atmospheric Conditions ◽  
Vicarious Calibration ◽  
Calibration And Validation ◽  
System Of Units ◽  
Wide Range

Vicarious calibration and validation techniques are important tools to ensure the long-term stability and inter-sensor consistency of satellite sensors making observations in the solar-reflective spectral domain. Automated test sites, which have continuous in situ monitoring of both ground reflectance and atmospheric conditions, can greatly increase the match-up possibilities for a wide range of space agency and commercial sensors. The Baotou calibration and validation test site in China provides operational high-accuracy and high-stability vicarious calibration and validation for high spatial resolution solar-reflective remote-sensing sensors. Two sites, given the abbreviations BTCN (an artificial site) and BSCN (a natural sandy site), have been selected as reference sites for the Committee on Earth Observation Satellites radiometric calibration network (RadCalNet). RadCalNet requires sites to provide data in a consistent format but does not specify the required operational conditions for a RadCalNet site. The two Baotou sites are the only sites to date that make spectral measurements for their continuous operation. One of the core principles of RadCalNet is that each site should have a metrologically rigorous uncertainty budget which also describes the site’s traceability to the international system of units, the SI. This paper shows a formalized metrological approach to determining and documenting the uncertainty budget and traceability of a RadCalNet site. This approach follows the Guide to the Expression of Uncertainty in Measurement. The paper describes the uncertainty analysis for bottom-of-atmosphere and top-of-atmosphere reflectance in the spectral region from 400 to 1000 nm for the Baotou sites and gives preliminary results for the uncertainty propagating this to top-of-atmosphere reflectance.

scholarly journals International System of Units (SI) Traceable Noise-Equivalent Power and Responsivity Characterization of Continuous Wave ErAs:InGaAs Photoconductive Terahertz Detectors

Photonics ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 15 ◽  
Author(s):  
Anuar Fernandez Olvera ◽  
Axel Roggenbuck ◽  
Katja Dutzi ◽  
Nico Vieweg ◽  
Hong Lu ◽  
...  
Keyword(s):  
Continuous Wave ◽  
International System ◽  
Noise Equivalent Power ◽  
National Metrology Institute ◽  
International System Of Units ◽  
System Of Units ◽  
Experimental Values ◽  
Power Measurements ◽  
Thz Power

A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the measured rectified current, the current noise floor in the PCAs, and the incoming THz power for the same conditions. Since the THz power measurements are performed with a pyroelectric detector calibrated by the National Metrology Institute of Germany (PTB), the experimentally obtained values are directly traceable to the International System of Units (SI) for the described conditions. The agreement between the presented model and the experimental results is excellent using only one fitting parameter. A very low NEP of 1.8 fW/Hz at 188.8 GHz is obtained at room temperature.

The BIPM Mycotoxin Metrology Capacity Building and Knowledge Transfer Program: Accurate Characterization of a Pure Aflatoxin B1 Material to Avoid Calibration Errors

2019 ◽  
Vol 102 (6) ◽  
pp. 1740-1748 ◽  
Author(s):  
Ralf D. Josephs ◽  
Xiaomin Li ◽  
Xiuqin Li ◽  
Zhen Guo ◽  
Bruno Garrido ◽  
...  
Keyword(s):  
Knowledge Transfer ◽  
Developing Economies ◽  
International System ◽  
Impurity Content ◽  
Transfer Program ◽  
Measurement Capability ◽  
Weights And Measures ◽  
System Of Units ◽  
Food And Feed

Background: The contamination of food and feed by mycotoxins, Aflatoxin B1 (AfB1) being one of the most prominent examples, is of imminent concern to many countries. Regulatory limits for mycotoxins have been implemented, and these need to be supported by a sound measurement infrastructure for mycotoxin analysis in order to enforce and verify products, protect populations, and avoid technical barriers to trade in food stuffs. Objective: A Capability Building and Knowledge Transfer program on Metrology for Safe Food and Feed in Developing Economies was started at the International Bureau of Weights and Measures to allow National Metrology Institutes or Designated Institutes to work together to strengthen their national mycotoxin metrology infrastructure. Methods: Knowledge transfer to scientists is provided to enable the characterization of selected pure mycotoxin materials and the production of corresponding certified reference material solutions. Results: This higher-order measurement capability can in turn support mycotoxin testing laboratories within their countries through the provision, for example, of standard solutions of critical analytes that are traceable to the International System of Units (SI). Conclusions and Highlights: The purity characterization and value assignment for a high-purity AfB1 material (979.6 ± 2.3 mg/g, k = 2) intended to be used for the gravimetric production of SI traceable calibration solutions for AfB1 is described using an approach combining quantitative NMR and LC–diode array detection–tandem MS for the correction of the mycotoxin-related impurity content.

Calibration of Piezoresistive Cantilever Force Sensors Using the NIST Electrostatic Force Balance

2003 ◽  
Author(s):  
Jon R. Pratt ◽  
David B. Newell ◽  
John A. Kramar ◽  
Eric Whitenton
Keyword(s):  
Mechanical Performance ◽  
Electrostatic Force ◽  
International System ◽  
National Standards ◽  
Force Balance ◽  
Force Sensitivity ◽  
System Of Units ◽  
Load Cells ◽  
Optical Lever

The characterization of material properties and mechanical performance of micro-electromechanical devices often hinges on the accurate measurement of small forces. Calibrated load cells of appropriate size and range are used, but are often not calibrated in a fashion traceable to the International System of Units (SI). Recently, we calibrated a piezoresistive cantilever in terms of SI force sensitivity. Here, we employ this device as a secondary force standard to calibrate another, optical lever based sensor in a force probe instrument, demonstrating an unbroken tracability chain to appropriate national standards.

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.

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