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1
Van De Voort, Frederick R., Abdel Aziz Elkashef e Jean-Simon Blais. "Interlaboratory Assessment of Dry Calibration Milk Powders for Calibrating Infrared Milk Analyzers". Journal of AOAC INTERNATIONAL 74, n. 5 (1 settembre 1991): 772–79. http://dx.doi.org/10.1093/jaoac/74.5.772.
Testo completoAbstract (sommario):
Abstract An interlaboratory study was carried out to assess the performance of preformulated, preanalyzed, dry calibration milk powders designed for calibrating infrared milk analyzers. The calibration powders can be reconstituted to produce consistent calibrations within laboratories. The powders met AOAC specifications In terms of accuracy and repeatability, and provide calibrations with performance characteristics comparable to those produced with conventional calibration milks. The reconstituted solutions were shown to be stable for up to 6 h at 40°C, and can be stored under refrigerated conditions and used for repeated analyses for up to 21 days without apparent deterioration In calibration performance. In general, the calibration powders perform as well as, or better than, the conventional calibrants used by the laboratories participating in the study, and the calibrations could be switched without significantly changing the analytical results. Simulation and cross-calibration analyses indicated that the powdered calibrants produced more consistent results overall than fluid calibration milks. The powdered calibrants, as formulated, are shown to be suitable for any application requiring calibrations that meet AOAC specifications, Including payment applications. The calibration powders have the stability and performance characteristics to serve as a consistent, stable reference standard for monitoring instrument performance, and would be a useful tool for Interlaboratory standardization or accrediting payment and dairy herd analysis laboratories.
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Tsuchida, Satoshi, Hirokazu Yamamoto, Toru Kouyama, Kenta Obata, Fumihiro Sakuma, Tetsushi Tachikawa, Akihide Kamei et al. "Radiometric Degradation Curves for the ASTER VNIR Processing Using Vicarious and Lunar Calibrations". Remote Sensing 12, n. 3 (29 gennaio 2020): 427. http://dx.doi.org/10.3390/rs12030427.
Testo completoAbstract (sommario):
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra platform, which was launched in 1999, has three separate subsystems: a visible and near-infrared (VNIR) radiometer, a shortwave-infrared radiometer, and a thermal-infrared radiometer. The ASTER VNIR bands have been radiometrically corrected for approximately 14 years by the sensor degradation curves estimated from the onboard calibrator according to the original calibration plan. However, this calibration by the onboard calibrator encountered a problem; specifically, it is inconsistent with the results of vicarious calibration and cross calibration. Therefore, the ASTER VNIR processing was applied by the radiometric degradation curves calculated from the results of three calibration approaches, i.e., the onboard calibrator, the vicarious calibration, and the cross calibration since February 2014. Even though the current degradation curves were revised, the inter-band and lunar calibrations show some inconsistencies owing to the different traceability in the bands by different calibration approaches. In this study, the current degradation curves and their problems are explained, and the new curves that are derived from the vicarious calibration with lunar calibration are discussed. The new degradation curves that have the same traceability in the bands will be used for future ASTER VNIR processing.
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Ozdemir, Durmus, Matt Mosley e Ron Williams. "Hybrid Calibration Models: An Alternative to Calibration Transfer". Applied Spectroscopy 52, n. 4 (aprile 1998): 599–603. http://dx.doi.org/10.1366/0003702981943932.
Testo completoAbstract (sommario):
A new procedure for calibrating multiple instruments is presented in which spectra from each are used simultaneously during the construction of multivariate calibration models. The application of partial least-squares (PLS) and genetic regression (GR) to the problem of generating these hybrid calibrations is presented. Spectra of ternary mixtures of methylene chloride, ethyl acetate, and methanol were collected on a dispersive and a Fourier transform spectrometer. Calibration models were generated by using differing numbers of spectra from each instrument simultaneously in the calibration and prediction sets, and then validated by using a set of spectra from each instrument separately. Calibration models were found that perform well on both instruments, even when only a single spectrum from the second instrument was used during the calibration process. As a benchmark, comparison with PLS showed that GR is more effective than PLS in building these hybrid calibration models.
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Chen, Gang, Hua Chen, Yu Bo Guo e Dong Ye. "The Comparison of Two Stereo Vision Sensor Calibration Methods". Advanced Materials Research 317-319 (agosto 2011): 397–400. http://dx.doi.org/10.4028/www.scientific.net/amr.317-319.397.
Testo completoAbstract (sommario):
This paper presents and comparison two stereo vision sensor calibration methods: Volume template based calibration method and the calibration based on virtual stereo pattern. First method use a premade volume template. Second method use a group of random spatial points that are formed by an infrared LED moved with the probe of CMM. Two methods adopt an ideal pin-hole model that ignores the nonlinear distortion of the cameras. Through compare two calibratioin methods, we can draw conclusion that the first method can be applide to stereo sensor calibration in measurement field and the second method could gain higher calibrating precision.
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Harris, Richard W., e Robert C. Chanaud. "A Simplified Method for Calibrating a Sound-Level Meter for Use With a Brüel & Kjær Artificial Mastoid". American Journal of Audiology 7, n. 2 (ottobre 1998): 61–72. http://dx.doi.org/10.1044/1059-0889(1998/011).
Testo completoAbstract (sommario):
The standard method for calibrating a sound-level meter for use with the Brüel & Kjær Artificial Mastoid for bone vibrator tests entails the use of a signal generator, a precision voltmeter, and possibly a frequency counter. This equipment should be certified annually and traceable to the National Institute of Standards and Technology (NIST), and its use generally restricts calibration to a laboratory environment and requires a considerable amount of time. We have developed a simplified method for calibrating the sound-level meter by using a sound-level calibrator and microphone. Using the known sensitivities of the microphone and the artificial mastoid, the sound-level calibrator used for calibration of the microphone may also be used for calibration of the sound-level meter to measure force levels with the artificial mastoid.
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Peiman, Reihaneh, e Keith Clarke. "The Impact of Data Time Span on Forecast Accuracy through Calibrating the SLEUTH Urban Growth Model". International Journal of Applied Geospatial Research 5, n. 3 (luglio 2014): 21–35. http://dx.doi.org/10.4018/ijagr.2014070102.
Testo completoAbstract (sommario):
Does the spacing of time intervals used for model input data have an impact on the model's subsequent calibration and so projections of land use change and urban growth? This study evaluated the performance of the SLEUTH urban growth and land use change model through two independent model calibrations with different temporal extents (1972 to 2006 vs. 2000 to 2006) for the historical Italian cities of Pisa Province and their surroundings. The goal in performing two calibrations was to investigate the sensitivity of SLEUTH forecasts to longer or shorter calibration timelines, that is does calibrating the model over a longer time period produce better model fits and therefore forecasts? The best fit parameters from each calibration were then used in forecasting urban growth in the area up to the year 2027. The authors findings show that the spatial growth estimated by the model was strongly influenced by the physical landscape and road networks. The forecast outputs over 100 Monte Carlo trials reflect the start of newly formed detached settlements towards and along existing roads, i.e., classic urban sprawl. The authors conclude that the short term calibration was a better model fit compared to the long term calibration. Nevertheless, the absolute preference for the short-term calibration over long-term implies that time-sensitivity in calibration remains a challenge for SLEUTH applications.
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Zhang, Bao Long, Shao Jing Zhang, Wei Qi Ding e Hui Shuang Shi. "Fisheye Lens Distortion Calibration Based on the Lens Charactetic Curves". Applied Mechanics and Materials 519-520 (febbraio 2014): 636–39. http://dx.doi.org/10.4028/www.scientific.net/amm.519-520.636.
Testo completoAbstract (sommario):
The fisheye lens is a kind of ultra wide angle lens, which can produce a big super-wide-angle lens distortion. In order to cover a large scope of light, barrel distortion is artificially added to the optical system. However, in some cases this distortion is not allowed, then it requires calibrations of those distortions. Most of the traditional distortion calibration method uses target plane calibration to do it. This paper discusses the way of design fisheye lens, through which we can know the forming process of distortion clearly. Based on this paper, a simple and effective calibration method can be understood. Different from common camera calibration method, the proposed calibration method can avoid the error occurring in the process of calibrating test, that directly use the lens’ characteristic curve. Through multiple sets of experimental verifications, this method is effective and feasible.
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Senn, J. A., J. P. Mills, P. E. Miller, C. Walsh, S. Addy, E. Loerke e M. V. Peppa. "ON-SITE GEOMETRIC CALIBRATION OF THERMAL AND OPTICAL SENSORS FOR UAS PHOTOGRAMMETRY". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B1-2020 (6 agosto 2020): 355–61. http://dx.doi.org/10.5194/isprs-archives-xliii-b1-2020-355-2020.
Testo completoAbstract (sommario):
Abstract. UAS imagery has become a widely used source of information in geomorphic research. When photogrammetric methods are applied to quantify geomorphic change, camera calibration is essential to ensure accuracy of the image measurements. Insufficient self-calibration based on survey data can induce systematic errors that can cause DEM deformations. The typically low geometric stability of consumer grade sensors necessitates in-situ calibration, as the reliability of a lab based calibration can be affected by transport. In this research a robust on-site workflow is proposed that allows the time-efficient and repeatable calibration of thermal and optical sensors at the same time. A stone building was utilised as calibration object with TLS scans for reference. The approach was applied to calculate eight separate camera calibrations using two sensors (DJI Phantom 4 Pro and Workswell WIRIS pro), two software solutions (Vision Measurement System (VMS) and Agisoft Metashape) and two different subsets of images per sensor. The presented results demonstrate that the approach is suitable to determine camera parameters for pre-calibrating photogrammetric surveys.
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Elmore, David F. "Polarization calibration techniques and scheduling for the Daniel K. Inouye Solar Telescope". Proceedings of the International Astronomical Union 10, S305 (dicembre 2014): 102–7. http://dx.doi.org/10.1017/s1743921315004603.
Testo completoAbstract (sommario):
AbstractThe Daniel K. Inouye Solar Telescope (DKIST), formerly Advanced Technology Solar Telescope when it begins operation in 2019 will be by a significant margin Earth's largest solar research telescope. Science priorities dictate an initial suite of instruments that includes four spectro-polarimeters. Accurate polarization calibration of the individual instruments and of the telescope optics shared by those instruments is of critical importance. The telescope and instruments have been examined end-to-end for sources of polarization calibration error, allowable contributions from each of the sources quantified, and techniques identified for calibrating each of the contributors. Efficient use of telescope observing time leads to a requirement of sharing polarization calibrations of common path telescope components among the spectro-polarimeters and for those calibrations to be repeated only as often as dictated by degradation of optical coatings and instrument reconfigurations. As a consequence the polarization calibration of the DKIST is a facility function that requires facility wide techniques.
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Mlcek, Jiri, Lukas Dvorak, Kvetoslava Sustova e Katarzyna Szwedziak. "Accuracy of the FT-NIR Method in Evaluating the Fat Content of Milk Using Calibration Models Developed for the Reference Methods According to Röse-Gottlieb and Gerber". Journal of AOAC INTERNATIONAL 99, n. 5 (1 settembre 2016): 1305–9. http://dx.doi.org/10.5740/jaoacint.16-0107.
Testo completoAbstract (sommario):
Abstract The study examined the effect of the choice of reference method on the functionality and reliability of calibrations in near-IR (NIR) spectroscopy intended for measuring the fat content in raw cow's milk. The fat content in the milk samples was evaluated using methods according to either Röse-Gottlieb or Gerber. The same samples were then subjected to analysis on an Antaris FT-NIR spectrometer. Using a partial least-squares algorithm, calibration models were created for both methods from the values measured. The calibration models show very good values of standard error of calibration: 0.133 for the Gerber method and 0.095 for the Röse-Gottlieb method. These calibrations were subsequently used to analyze 30 new samples of cow's milk of undefined fat content, and the differences in the values were evaluated using statistical paired t-test to a median value at a probability level of α = 0.05. No statistically significant differences were found. It was revealed that the reference method used for calibrating the device evaluating the fat content in raw cow's milk has no effect on the functionality and reliability of the calibration model.
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Haitjema. "Calibration of Displacement Laser Interferometer Systems for Industrial Metrology". Sensors 19, n. 19 (22 settembre 2019): 4100. http://dx.doi.org/10.3390/s19194100.
Testo completoAbstract (sommario):
Displacement laser interferometer systems are widely used for the calibration of machine tools and CMMs (Coordinate Measuring Machines). Additionally, they are often the workhorse in dimensional calibration laboratories, where they act as the basic metrological traceability link for many calibrations. This paper gives a review of the calibration of such systems, where several approaches, such as the calibrations of separate components or the system as a whole, are reviewed. The calibrations discussed are: the laser frequency, the counting system, software evaluation of the environmental conditions, environmental and material temperature sensor calibration and the calibration of optics that is part of the system. For these calibrations considerations are given about the ways these can be carried out and about establishing the re-calibration intervals.
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Birks, John W., Andrew A. Turnipseed, Peter C. Andersen, Craig J. Williford, Stanley Strunk, Brian Carpenter e Christine A. Ennis. "Portable calibrator for NO based on the photolysis of N<sub>2</sub>O and a combined NO<sub>2</sub>∕NO∕O<sub>3</sub> source for field calibrations of air pollution monitors". Atmospheric Measurement Techniques 13, n. 2 (3 marzo 2020): 1001–18. http://dx.doi.org/10.5194/amt-13-1001-2020.
Testo completoAbstract (sommario):
Abstract. A highly portable calibration source of nitric oxide (NO) based on the photolysis of nitrous oxide (N2O) supplied by 8 or 16 g disposable cartridges is demonstrated to serve as an accurate and reliable transfer standard for the calibration of NO monitors in the field. The instrument provides output mixing ratios in the range 0–1000 ppb with a precision and accuracy better than the greater of 3 ppb or 3 % of the target NO mixing ratio over a wide range of environmental conditions of ambient temperature (8.5–35.0 ∘C), pressure (745–1015 mbar corresponding to 2.7–0.0 km of elevation), and relative humidity (0 %–100 % RH). The combination of the NO calibration source with a previously described ozone calibration source based on the photolysis of oxygen in air provides a new instrument capable of outputting calibrated mixing ratios of NO, ozone (O3), and nitrogen dioxide (NO2), where the NO2 is produced by the stoichiometric gas-phase reaction of NO with O3. The portable NO2/NO/O3 calibration source requires no external gas cylinders and can be used for calibrations of NO, NO2, and O3 instruments for mixing ratios up to 1000, 500, and 1000 ppb, respectively. This portable calibrator may serve as a convenient transfer standard for field calibrations of ozone and NOx air pollution monitors.
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Ona, Egil, Valerie Mazauric e Lars Nonboe Andersen. "Calibration methods for two scientific multibeam systems". ICES Journal of Marine Science 66, n. 6 (8 maggio 2009): 1326–34. http://dx.doi.org/10.1093/icesjms/fsp125.
Testo completoAbstract (sommario):
Abstract Ona, E., Mazauric, V., and Andersen, L. N. 2009. Calibration methods for two scientific multibeam systems. – ICES Journal of Marine Science, 66: 1326–1334. The new Simrad scientific multibeam systems, the MS70 sonar and the ME70 echosounder, each transmit over many electronically formed beams with centre frequencies spanning from 70 to 120 kHz. Calibrations of these systems are therefore more complex than for conventional split-beam echosounder systems. Two large tungsten-carbide spheres (75 and 84 mm diameter) were designed and manufactured to facilitate accurate field calibrations over the entire operational bandwidth. These are heavy and therefore stable when suspended beneath a ship, and have target strengths much larger than those of biological targets potentially within the measurement volume. This paper presents procedures for calibrating each system in the field and the results from two such experiments. Detailed inspections of the results for individual beams indicate that minor adjustments in the described procedures might further improve the reported calibration accuracy.
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Sanders, Kate L., e Michael S. Y. Lee. "Evaluating molecular clock calibrations using Bayesian analyses with soft and hard bounds". Biology Letters 3, n. 3 (15 marzo 2007): 275–79. http://dx.doi.org/10.1098/rsbl.2007.0063.
Testo completoAbstract (sommario):
A limiting factor in many molecular dating studies is shortage of reliable calibrations. Current methods for choosing calibrations (e.g. cross-validation) treat them as either correct or incorrect, whereas calibrations probably lie on a continuum from highly accurate to very poor. Bayesian relaxed clock analysis permits inclusion of numerous candidate calibrations as priors: provided most calibrations are reliable, the model appropriate and the data informative, the accuracy of each calibration prior can be evaluated. If a calibration is accurate, then the analysis will support the prior so that the posterior estimate reflects the prior; if a calibration is poor, the posterior will be forced away from the prior. We use this approach to test two fossil dates recently proposed as standard calibrations within vertebrates. The proposed bird–crocodile calibration (approx. 247 Myr ago) appears to be accurate, but the proposed bird–lizard calibration (approx. 255 Myr ago) is substantially too recent.
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Hazen, John, e L. Scorsone. "Infrared Sensor Calibration Facility". Journal of the IEST 35, n. 1 (1 gennaio 1992): 33–40. http://dx.doi.org/10.17764/jiet.2.35.1.d536816582691754.
Testo completoAbstract (sommario):
The Boeing Infrared Sensor (BIRS) Calibration Facility represents a major capital investment by The Boeing Company in optical and infrared technology. The facility was designed and built for calibrating and testing new generation large aperture long wave infrared (LWIR) sensors, seekers, and related technologies. The capability exists to perform both radiometric and goniometric calibrations of large infrared sensors under simulated environmental operating conditions. The system is presently configured for endoatmospheric calibrations with a uniform background field that can be set to simulate the expected mission background levels. During calibration, the sensor under test is also exposed to expected mission temperatures and pressures within the test chamber. The facility could be converted for exoatmospheric testing. The first major test runs in the facility were completed during 1989 with very satisfactory results. This paper will describe system configuration and hardware elements, and will address the modifications made to date. Pitt-Des Moines. Inc. (PDM) of Pittsburgh, Pennsylvania, was the contractor for the turnkey design and construction of the test chambers and thermal vacuum systems. Hughes Danbury Optical Systems (formerly Perkin Elmer Optical Systems) was the hardware supplier for the optical hardware. The Boeing Company performed all optical assembly, integration, testing, and alignment on-site.
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O'Reilly, Joseph E., e Philip C. J. Donoghue. "Tips and nodes are complementary not competing approaches to the calibration of molecular clocks". Biology Letters 12, n. 4 (aprile 2016): 20150975. http://dx.doi.org/10.1098/rsbl.2015.0975.
Testo completoAbstract (sommario):
Molecular clock methodology provides the best means of establishing evolutionary timescales, the accuracy and precision of which remain reliant on calibration, traditionally based on fossil constraints on clade (node) ages. Tip calibration has been developed to obviate undesirable aspects of node calibration, including the need for maximum age constraints that are invariably very difficult to justify. Instead, tip calibration incorporates fossil species as dated tips alongside living relatives, potentially improving the accuracy and precision of divergence time estimates. We demonstrate that tip calibration yields node calibrations that violate fossil evidence, contributing to unjustifiably young and ancient age estimates, less precise and (presumably) accurate than conventional node calibration. However, we go on to show that node and tip calibrations are complementary, producing meaningful age estimates, with node minima enforcing realistic ages and fossil tips interacting with node calibrations to objectively define maximum age constraints on clade ages. Together, tip and node calibrations may yield evolutionary timescales that are better justified, more precise and accurate than either calibration strategy can achieve alone.
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ElNesr, Mohammad N., A. A. Alazba e Mohammad A. El-Farrah. "Correcting Inaccurately Recorded Data due to Faulty Calibration of a Capacitance Water Content Probe". Applied and Environmental Soil Science 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/530732.
Testo completoAbstract (sommario):
Measuring soil water content by capacitance probes requires rigorous calibration to achieve acceptable accuracy. Some of the capacitance probes' users might take several readings using the default device calibrations or other prestored calibrations by mistake. This can lead to logging of faulty readings for periods of up to months or years. This study aimed to (1) study the importance of probe calibration and the level of error that results from using flawed calibrations and (2) to develop a mathematical method to correct the faulty recorded data. This research involved studying eleven scenarios of faulty calibrations including errors in the air/water calibration and in the in-soil calibration. A mathematical method was developed to correct the faulty recorded data and comparisons were made for the data after and before correction. Results indicated that using the manufacturer's default calibration within the software resulted in substantial error values especially for heavy textured soils. It is recommended that users and especially researchers should perform rigorous in-soil calibration wherever the probe is installed, and they should repeat the calibrations whenever the soil structure changed.
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Hegeduš, Hrvoje, Marko Jurcevic e Roman Malaric. "Internet-Enabled Calibration". International Journal of Measurement Technologies and Instrumentation Engineering 1, n. 1 (gennaio 2011): 24–37. http://dx.doi.org/10.4018/ijmtie.2011010103.
Testo completoAbstract (sommario):
Calibration of measuring instruments provides the confidence in measurements. It is the obligation of every laboratory to have its measuring equipment calibrated in regular intervals. This obligation means that the laboratory must send its equipment to the calibration laboratory every year or two depending on the calibration intervals. During this time the equipment is not available and this presents a financial burden to the laboratory of the customer. Since many of the modern instruments include some communication interfaces, it was made possible to create an Internet-enabled calibration system. This term encompasses a wide range of possible applications and services. The Internet-enabled calibrations must address several problems not present in standard calibrations, including security issues, since the equipment is not always under direct control of the calibration laboratory personnel who will sign the calibration certificate. As the traceability and integrity of the calibration process directly depends on the measured data, the reliable and secure remote control and monitoring of instruments must be a crucial aspect of Internet-enabled calibration technologies.
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Foster, Katie, Rudra Pokhrel, Matthew Burkhart e Shane Murphy. "A novel approach to calibrating a photoacoustic absorption spectrometer using polydisperse absorbing aerosol". Atmospheric Measurement Techniques 12, n. 6 (26 giugno 2019): 3351–63. http://dx.doi.org/10.5194/amt-12-3351-2019.
Testo completoAbstract (sommario):
Abstract. A new technique for calibrating photoacoustic aerosol absorption spectrometers with multiple laser passes in the acoustic cavity (multi-pass PAS) has been developed utilizing polydisperse and highly absorbing aerosol. This is the first calibration technique for multi-pass PAS instruments that utilizes particles instead of reactive gases and does not require knowledge of the exact size or refractive index of the absorbing aerosol. In this new method, highly absorbing materials are aerosolized into a polydisperse distribution and measured simultaneously with a multi-pass PAS and a cavity-attenuated phase shift particulate matter single-scattering albedo (CAPS PMSSA, Aerodyne Inc.) instrument. The CAPS PMSSA measures the bulk absorption coefficient through the subtraction of the scattering coefficient from the extinction coefficient. While this approach can have significant errors in ambient aerosol, the accuracy and precision of the CAPS PMSSA are high when the measured aerosol has a low single-scattering albedo (SSA) and particles are less than 300 nm in size, in which case truncation errors are small. To confirm the precision and accuracy of the new calibration approach, a range of aerosol concentrations were sent to the multi-pass PAS and CAPS PMSSA instruments using three different absorbing substances: Aquadag, Regal Black, and Nigrosin. Six repetitions with each of the three substances produced stable calibrations, with the standard deviation of the calibration slopes being less than 2 % at 660 nm and less than 5 % at 405 nm for a given calibration substance. Calibrations were also consistent across the different calibration substances (standard deviation of 2 % at 660 nm and 10 % at 405 nm) except for Nigrosin at 405 nm. The accuracy of the calibration approach is dependent on the SSA of the calibration substance but is roughly 6 % for the calibration substances used here, which all have an SSA near 0.4 at 405 nm. This calibration technique is easily deployed in the field as it involves no toxic or reactive gases and it does not require generation of a monodisperse aerosol. Advantages to this particle-based calibration technique versus techniques based on ozone or nitrogen dioxide absorption include no reactive losses or impact from carrier gases and the broad absorption characteristics of the particles, which eliminate potentially significant errors in calibration that come with small errors in the peak wavelength of the laser light when utilizing gas-phase standards.
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Bhatt, Rajendra, David R. Doelling, Benjamin R. Scarino, Arun Gopalan, Conor O. Haney, Patrick Minnis e Kristopher M. Bedka. "A Consistent AVHRR Visible Calibration Record Based on Multiple Methods Applicable for the NOAA Degrading Orbits. Part I: Methodology". Journal of Atmospheric and Oceanic Technology 33, n. 11 (novembre 2016): 2499–515. http://dx.doi.org/10.1175/jtech-d-16-0044.1.
Testo completoAbstract (sommario):
AbstractThe 35-yr NOAA Advanced Very High Resolution Radiometer (AVHRR) observation record offers an excellent opportunity to study decadal climate variability, provided that all participating AVHRR instruments are calibrated on a consistent radiometric scale. Because of the lack of onboard calibration systems, the solar imaging channels of the AVHRR must be vicariously calibrated using invariant Earth targets as a calibrated reference source. The greatest challenge in calibrating the AVHRR dataset is the orbit degradation of the NOAA satellites, which eventually drift into a terminator orbit several years after launch. Therefore, the invariant targets must be characterized over the full range of solar zenith angles (SZAs) sampled by the satellite instrument.This study outlines a multiple invariant Earth target calibration approach specifically designed to account for the degrading NOAA orbits. The desert, polar ice, and deep convective cloud (DCC) invariant targets are characterized over all observed SZAs using NOAA-16 AVHRR measurements, which are referenced to the Aqua MODIS Collection 6 calibration via direct transfer of the MODIS calibration to the NOAA-16 AVHRR instrument using simultaneous nadir overpass (SNO) observations over the North Pole. The multiple invariant target calibrations are combined using the inverse of their temporal variance to optimize the resulting calibration stability. The NOAA-18 AVHRR gains derived using the desert, polar ice, and DCC targets, as well as from SNO, were found consistent within 1%, thereby validating that the Aqua MODIS calibration is effectively transferred to the reference calibration targets. The companion paper, Part II, applies the methodology across the AVHRR record to derive the sensor-specific calibration coefficients.
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Maurits, L., M. de Heer, T. Honkola, M. Dunn e O. Vesakoski. "Best practices in justifying calibrations for dating language families". Journal of Language Evolution 5, n. 1 (28 dicembre 2019): 17–38. http://dx.doi.org/10.1093/jole/lzz009.
Testo completoAbstract (sommario):
Abstract The use of computational methods to assign absolute datings to language divergence is receiving renewed interest, as modern approaches based on Bayesian statistics offer alternatives to the discredited techniques of glottochronology. The datings provided by these new analyses depend crucially on the use of calibration, but the methodological issues surrounding calibration have received comparatively little attention. Especially, underappreciated is the extent to which traditional historical linguistic scholarship can contribute to the calibration process via loanword analysis. Aiming at a wide audience, we provide a detailed discussion of calibration theory and practice, evaluate previously used calibrations, recommend best practices for justifying calibrations, and provide a concrete example of these practices via a detailed derivation of calibrations for the Uralic language family. This article aims to inspire a higher quality of scholarship surrounding all statistical approaches to language dating, and especially closer engagement between practitioners of statistical methods and traditional historical linguists, with the former thinking more carefully about the arguments underlying their calibrations and the latter more clearly identifying results of their work which are relevant to calibration, or even suggesting calibrations directly.
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De Champlain, Andre F., Andre-Philippe Boulais e Andrew Dallas. "Calibrating the Medical Council of Canada’s Qualifying Examination Part I using an integrated item response theory framework: a comparison of models and designs". Journal of Educational Evaluation for Health Professions 13 (20 gennaio 2016): 6. http://dx.doi.org/10.3352/jeehp.2016.13.6.
Testo completoAbstract (sommario):
Purpose: The aim of this research was to compare different methods of calibrating multiple choice question (MCQ) and clinical decision making (CDM) components for the Medical Council of Canada’s Qualifying Examination Part I (MCCQEI) based on item response theory. Methods: Our data consisted of test results from 8,213 first time applicants to MCCQEI in spring and fall 2010 and 2011 test administrations. The data set contained several thousand multiple choice items and several hundred CDM cases. Four dichotomous calibrations were run using BILOG-MG 3.0. All 3 mixed item format (dichotomous MCQ responses and polytomous CDM case scores) calibrations were conducted using PARSCALE 4. Results: The 2-PL model had identical numbers of items with chi-square values at or below a Type I error rate of 0.01 (83/3,499 or 0.02). In all 3 polytomous models, whether the MCQs were either anchored or concurrently run with the CDM cases, results suggest very poor fit. All IRT abilities estimated from dichotomous calibration designs correlated very highly with each other. IRT-based pass-fail rates were extremely similar, not only across calibration designs and methods, but also with regard to the actual reported decision to candidates. The largest difference noted in pass rates was 4.78%, which occurred between the mixed format concurrent 2-PL graded response model (pass rate= 80.43%) and the dichotomous anchored 1-PL calibrations (pass rate= 85.21%). Conclusion: Simpler calibration designs with dichotomized items should be implemented. The dichotomous calibrations provided better fit of the item response matrix than more complex, polytomous calibrations.
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Gačnik, Jan, Igor Živković, Sergio Ribeiro Guevara, Radojko Jaćimović, Jože Kotnik e Milena Horvat. "Validating an Evaporative Calibrator for Gaseous Oxidized Mercury". Sensors 21, n. 7 (3 aprile 2021): 2501. http://dx.doi.org/10.3390/s21072501.
Testo completoAbstract (sommario):
Understanding atmospheric mercury chemistry is the key for explaining the biogeochemical cycle of mercury and for improving the predictive capability of computational models. Increased efforts are being made to ensure comparable Hg speciation measurements in the air through establishing metrological traceability. While traceability for elemental mercury has been recently set, this is by no means the case for gaseous oxidized mercury (GOM). Since a calibration unit suitable for traceable GOM calibrations based on evaporation of HgCl2 solution was recently developed, the purpose of our work was to extensively evaluate its performance. A highly specific and sensitive 197Hg radiotracer was used for validation over a wide range of concentrations. By comparing experimental and calculated values, we obtained recoveries for the calibration unit. The average recoveries ranged from 88.5% for 1178 ng m−3 HgCl2 gas concentration to 39.4% for 5.90 ng m−3 HgCl2 gas concentration. The losses were due to the adsorption of oxidized Hg on the inner walls of the calibrator and tubing. An adsorption isotherm was applied to estimate adsorption enthalpy (ΔHads); a ΔHads value of −12.33 kJ mol−1 was obtained, suggesting exothermal adsorption. The results of the calibrator performance evaluation suggest that a newly developed calibration unit is only suitable for concentrations of HgCl2 higher than 1 µg m−3. The concentration dependence of recoveries prevents the system from being used for calibration of instruments for ambient GOM measurements. Moreover, the previously assessed uncertainty of this unit at µg m−3 level (2.0%, k = 2) was re-evaluated by including uncertainty related to recovery and was found to be 4.1%, k = 2. Calibrator performance was also evaluated for HgBr2 gas calibration; the recoveries were much lower for HgBr2 gas than for HgCl2 gas even at a high HgBr2 gas concentration (>1 µg m−3). As HgBr2 is often used as a proxy for various atmospheric HgBr species, the suitability of the unit for such calibration must be further developed.
24
Filin, Sagi, e Beáta Csathó. "Improvement of elevation accuracy for mass-balance monitoring using in-flight laser calibration". Annals of Glaciology 34 (2002): 330–34. http://dx.doi.org/10.3189/172756402781817563.
Testo completoAbstract (sommario):
AbstractTo exploit the high accuracy potential of laser ranging, suitable laser-altimeter calibration procedures combining laboratory and in-flight calibration steps are needed. Previous calibration schemes have limited the calibration process to flying over planar surfaces, and systematic errors remained in the system. In this paper we present a laser calibration algorithm that utilizes natural surfaces as calibration sites. This is especially important for calibrating systems in the interior of ice sheets. The proposed approach is demonstrated in calibrating the U.S. National Science Foundation Support Office for Aerogeophysical Research laser altimetry system. The results show a significant improvement in accuracy.
25
Jeske, T., D. McSpadden, N. Kalra, T. Britton, N. Jarvis e D. Lawrence. "AI for Experimental Controls at Jefferson Lab". Journal of Instrumentation 17, n. 03 (1 marzo 2022): C03043. http://dx.doi.org/10.1088/1748-0221/17/03/c03043.
Testo completoAbstract (sommario):
Abstract The AI for Experimental Controls project is developing an AI system to control and calibrate detector systems located at Jefferson Laboratory. Currently, calibrations are performed offline and require significant time and attention from experts. This work would reduce the amount of data and the amount of time spent calibrating in an offline setting. The first use case involves the Central Drift Chamber (CDC) located inside the GlueX spectrometer in Hall D. We use a combination of environmental and experimental data, such as atmospheric pressure, gas temperature, and the flux of incident particles as inputs to a sequential Neural Network (NN) to recommend a high voltage setting and the corresponding calibration constants in order to maintain consistent gain and optimal resolution throughout the experiment. Utilizing AI in this manner represents an initial shift from offline calibration towards near real time calibrations performed at Jefferson Laboratory.
26
Maliuk, A., e I. Zinchenko. "Metallicity calibrations and oxygen abundance evolution in massive galaxies". Advances in Astronomy and Space Physics 8, n. 1 (2018): 24–27. http://dx.doi.org/10.17721/2227-1481.8.24-27.
Testo completoAbstract (sommario):
We determined oxygen abundances for the sample of SDSS galaxies with high masses using R3D, S3D, R2D, S2D, N and O3N2 calibrations. We investigated redshift–metallicity relation for oxygen abundances obtained by each calibration. We found that for galaxies with high stellar masses oxygen abundance obtained using all calibrations is increasing on the time interval from z = 0.5 to z = 0. However, the values of oxygen abundance enrichment rate significantly depend on adopted calibration and ranges from ~0.1 dex per unit redshift for R calibration to ~0.5 dex per unit redshift for O3N2 calibration.
27
Rosenberg, P. D., A. R. Dean, P. I. Williams, J. R. Dorsey, A. Minikin, M. A. Pickering e A. Petzold. "Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign". Atmospheric Measurement Techniques 5, n. 5 (21 maggio 2012): 1147–63. http://dx.doi.org/10.5194/amt-5-1147-2012.
Testo completoAbstract (sommario):
Abstract. Optical particle counters (OPCs) are used regularly for atmospheric research, measuring particle scattering cross sections to generate particle size distribution histograms. This manuscript presents two methods for calibrating OPCs with case studies based on a Passive Cavity Aerosol Spectrometer Probe (PCASP) and a Cloud Droplet Probe (CDP), both of which are operated on the Facility for Airborne Atmospheric Measurements BAe-146 research aircraft. A probability density function based method is provided for modification of the OPC bin boundaries when the scattering properties of measured particles are different to those of the calibration particles due to differences in refractive index or shape. This method provides mean diameters and widths for OPC bins based upon Mie-Lorenz theory or any other particle scattering theory, without the need for smoothing, despite the highly nonlinear and non-monotonic relationship between particle size and scattering cross section. By calibrating an OPC in terms of its scattering cross section the optical properties correction can be applied with minimal information loss, and performing correction in this manner provides traceable and transparent uncertainty propagation throughout the whole process. Analysis of multiple calibrations has shown that for the PCASP the bin centres differ by up to 30% from the manufacturer's nominal values and can change by up to approximately 20% when routine maintenance is performed. The CDP has been found to be less sensitive than the manufacturer's specification with differences in sizing of between 1.6 ± 0.8 μm and 4.7 ± 1.8 μm for one flight. Over the course of the Fennec project in the Sahara the variability of calibration was less than the calibration uncertainty in 6 out of 7 calibrations performed. As would be expected from Mie-Lorenz theory, the impact of the refractive index corrections has been found to be largest for absorbing materials and the impact on Saharan dust measurements made as part of the Fennec project has been found to be up to a factor of 3 for the largest particles measured by CDP with diameters of approximately 120 μm. In an example case, using the calibration and refractive index corrections presented in this work allowed Saharan dust measurement from the PCASP, CDP and a Cloud Imaging Probe to agree within the uncertainty of the calibration. The agreement when using only the manufacturer's specification was poor. Software tools have been developed to perform these calibrations and corrections and are now available as open source resources for the community via the SourceForge repository.
28
Blanco, Marcelo, Jordi Coello, Hortensia Iturriaga, Santiago Maspoch e Esther Rovira. "Wavelength Calibration Transfer between Diode Array UV-Visible Spectrophotometers". Applied Spectroscopy 49, n. 5 (maggio 1995): 593–97. http://dx.doi.org/10.1366/0003702953964084.
Testo completoAbstract (sommario):
The need to obtain expeditious results in control analyses of complex mixtures has turned multivariate calibration procedures into major choices for routine analyses. The inherent complexity of the calibration process and the practical need for analyses to be carried out as near the manufacturing line as possible occasionally entail calibrating with a different instrument from that subsequently employed for the analytical measurements proper. This paper exposes the problems potentially arising in transferring calibrations between diode array UV-Vis spectrophotometers. Basically, such problems originate in wavelength differences between spectrophotometers, even if they meet the manufacturer's specifications and the pharmacopoeia recommendations. We developed a straightforward method for harmonizing instrumental responses on the basis of reference wavelengths corresponding to zero values in the first-derivative spectra for potassium dichromate and benzoic acid standards. The method was applied to the analysis of binary mixtures of theophylline and doxylamine by multiple linear and partial least-squares regression with the use of one spectrophotometer for calibration and four others for analyses.
29
Hu, Xiaoyin, Ye Li, Haoyu Zhang, Yueling Yu e Zhangyi Kang. "Design and Application of Automatic Calibration Device for Multi-Channel Resistance Strain Gauge Indicator". Journal of Physics: Conference Series 2113, n. 1 (1 novembre 2021): 012040. http://dx.doi.org/10.1088/1742-6596/2113/1/012040.
Testo completoAbstract (sommario):
Abstract In this paper, an automatic calibration device for multi-channel resistance strain gauge indicator is designed and its applicability and measurement accuracy are verified at laboratory. The calibration done by original resistance bridge calibrator is time-consuming for its manual operation and complex calibration process. With the intent to increase calibration efficiency, an automatic channel switch device was developed, and the resistance bridge calibrator was automated. The designed calibration device is completely computer controlled enabling a sequence of unmanned measurements. The calibration device was verified at laboratory that the maximum of error is 0.072%. It was applied to calibrate a 60-channel resistance strain gage indicator to approve its practical applicability. The result shows that the designed calibration device can realize automatic calibration and the efficiency is increased by 40%.
30
Kajima, Mariko, Tsukasa Watanabe, Makoto Abe e Toshiyuki Takatsuji. "Calibrator for 2D Grid Plate Using Imaging Coordinate Measuring Machine with Laser Interferometers". International Journal of Automation Technology 9, n. 5 (5 settembre 2015): 541–45. http://dx.doi.org/10.20965/ijat.2015.p0541.
Testo completoAbstract (sommario):
A calibrator for 2D grid plates have been developed. The calibrator was based on a commercial imaging coordinate measuring machine (imaging CMM). A laser interferometer for the calibration of the x-coordinate and two laser interferometers for the calibration of the y-coordinate were attached to the imaging CMM. By applying multistep measurement method for the calibration procedure, the geometrical error in the calibrator was reduced. The calibration of a precision 2D grid plate was demonstrated, and the expanded uncertainty was estimated to be 0.2 μm (k =2).
31
Lynch, Joanna M., David M. Barbano e J. Richard Fleming. "Evaluation of Commercially Available Milk Powders for Calibration of Mid-Infrared Analyzers". Journal of AOAC INTERNATIONAL 78, n. 5 (1 settembre 1995): 1219–24. http://dx.doi.org/10.1093/jaoac/78.5.1219.
Testo completoAbstract (sommario):
Abstract The performance of commercially available shelf-stable milk powders that upon reconstitution can be used as calibration samples for mid-infrared (IR) analyzers was evaluated. Twelve reconstituted powders and 7 raw milk samples were sent to each of 7 laboratories. Each laboratory analyzed the reconstituted powders and milk samples by IR and obtained both corrected and uncorrected data. The corrected data reflected the current calibrations (based on calibration with fresh, raw milk) of each instrument. The uncorrected data from the reconstituted powders were used to derive separate calibration equations for each instrument. Two of the 12 reconstituted powers were discarded from the analysis because of poor quality. The abilities of the powder-based and current calibrations to predict accurately the total protein and fat contents of the 7 raw milk samples were compared. For the current and powder-based calibrations, respectively, the mean differences from chemical analysis for total protein were −0.006 and 0.031%, and the standard deviations of the differences (SDD) were 0.029 and 0.029%. For fat, the mean difference for the current calibration was −0.001%, and the SDD was 0.034%. For the powder-based fat calibration, the mean differences were 0.034% (fat A only), −0.047% (fat B only), and −0.061% (fat A and fat B), and SDDs were 0.046% (fat A only), 0.036% (fat B only), and 0.056% (fat A and fat B). The reconstituted powders did not provide as accurate an IR fat calibration for testing raw milk samples as can be obtained with raw milk calibration samples. This is attributed primarily to differences in the characteristics of the fat in the reconstituted powders and in raw milk. For protein, analytical precisions for both types of calibrations were comparable, and the positive bias for the powder-based calibration is relatively easy to correct by basing calibration on true protein nitrogen instead of total nitrogen.
32
Domínguez-Niño, Jesús María, Heye Reemt Bogena, Johan Alexander Huisman, Bernd Schilling e Jaume Casadesús. "On the Accuracy of Factory-Calibrated Low-Cost Soil Water Content Sensors". Sensors 19, n. 14 (13 luglio 2019): 3101. http://dx.doi.org/10.3390/s19143101.
Testo completoAbstract (sommario):
Soil water content (SWC) monitoring is often used to optimize agricultural irrigation. Commonly, capacitance sensors are used for this task. However, the factory calibrations have been often criticized for their limited accuracy. The aim of this paper is to test the degree of improvement of various sensor- and soil-specific calibration options compared to factory calibrations by taking the 10HS sensor as an example. To this end, a two-step sensor calibration was carried out. In the first step, the sensor response was related to dielectric permittivity using calibration in media with well-defined permittivity. The second step involved the establishment of a site-specific relationship between permittivity and soil water content using undisturbed soil samples and time domain reflectometry (TDR) measurements. Our results showed that a model, which considered the mean porosity and a fitted dielectric permittivity of the solid phase for each soil and depth, provided the best fit between bulk permittivity and SWC. Most importantly, it was found that the two-step calibration approach (RMSE: 1.03 vol.%) provided more accurate SWC estimates compared to the factory calibration (RMSE: 5.33 vol.%). Finally, we used these calibrations on data from drip-irrigated almond and apple orchards and compared the factory calibration with our two-step calibration approach.
33
Choi, Taeyoung, Changyong Cao, Xi Shao e Wenhui Wang. "S-NPP VIIRS Lunar Calibrations over 10 Years in Reflective Solar Bands (RSB)". Remote Sensing 14, n. 14 (13 luglio 2022): 3367. http://dx.doi.org/10.3390/rs14143367.
Testo completoAbstract (sommario):
Since 28 October 2011, the VIIRS Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (S-NPP) has operated over 10 years and successfully generated scientific global images for the Earth’s environment and climate studies. Besides thermal and day night bands, VIIRS has 14 reflective solar bands (RSBs) that cover a spectral range of 0.41 µm to 2.25 µm. The primary and daily source of calibration for the RSBs is the Solar Diffuser (SD) as an onboard calibrator, and its degradations are tracked by the Solar Diffuser Stability Monitor (SDSM). Alternatively, monthly scheduled lunar calibration has provided long-term on-orbit trends that validate the corresponding SD-based calibration results. In this paper, on-orbit lunar calibration and comparison results are focused on, in conjunction with the SD calibrations that are performed by the National Oceanic and Atmospheric Administration (NOAA) VIIRS team. In addition, a recent study showed that there is increasing striping in the VIIRS images in the RSBs caused by the non-uniform SD degradation. The estimation of the SD non-uniformity and a mitigation method is proposed along with the striping reductions.
34
Jessen, W., S. Wilbert, B. Nouri, N. Geuder e H. Fritz. "Calibration methods for rotating shadowband irradiometers and evaluation of calibration duration". Atmospheric Measurement Techniques Discussions 8, n. 10 (6 ottobre 2015): 10249–82. http://dx.doi.org/10.5194/amtd-8-10249-2015.
Testo completoAbstract (sommario):
Abstract. Resource assessment for Concentrated Solar Power (CSP) needs accurate Direct Normal Irradiance (DNI) measurements. An option for such measurement campaigns are Rotating Shadowband Irradiometers (RSIs) with a thorough calibration. Calibration of RSIs and Si-sensors in general is complex because of the inhomogeneous spectral response of such sensors and incorporates the use of several correction functions. A calibration for a given atmospheric condition and air mass might not work well for a different condition. This paper covers procedures and requirements for two calibration methods for the calibration of Rotating Shadowband Irradiometers. The necessary duration of acquisition of test measurements is examined in regard to the site specific conditions at Plataforma Solar de Almeria (PSA) in Spain. Data sets of several long-term calibration periods from PSA are used to evaluate the deviation of results from calibrations with varying duration from the long-term result. The findings show that seasonal changes of environmental conditions are causing small but noticeable fluctuation of calibration results. Certain periods (i.e. November to January and April to May) show a higher likelihood of particularly adverse calibration results. These effects can partially be compensated by increasing the inclusions of measurements from outside these periods. Consequently, the duration of calibrations at PSA can now be selected depending on the time of the year in which measurements are commenced.
35
Mlačnik, Vid, e Igor Pušnik. "Influence of Atmosphere on Calibration of Radiation Thermometers". Sensors 21, n. 16 (16 agosto 2021): 5509. http://dx.doi.org/10.3390/s21165509.
Testo completoAbstract (sommario):
Current process of calibrating radiation thermometers, including thermal imagers, relies on measurement comparison with the temperature of a black body at a set distance. Over time, errors have been detected in calibrations of some radiation thermometers, which were correlated with moisture levels. In this study, effects of atmospheric air on thermal transmission were evaluated by the means of simulations using best available resources of the corresponding datasets. Sources of spectral transmissivity of air were listed, and transmissivity data was obtained from the HITRAN molecular absorption database. Transmissivity data of molecular species was compiled for usual atmospheric composition, including naturally occurring isotopologs. Final influence of spectral transmissivity was evaluated for spectral sensitivities of radiation thermometers in use, and total transmissivity and expected errors were presented for variable humidity and measured temperature. Results reveal that spectral range of measurements greatly influences susceptibility of instruments to atmospheric interference. In particular, great influence on measurements is evident for the high-temperature radiation pyrometer in the spectral range of 2–2.7 µm, which is in use in our laboratory as a traceable reference for high-temperature calibrations. Regarding the calibration process, a requirement arose for matching the humidity parameters during the temperature reference transfer to the lower tiers in the chain of traceability. Narrowing of the permitted range of humidity during the calibration, monitoring, and listing of atmospheric parameters in calibration certificates is necessary, for at least this thermometer and possibly for other thermometers as well.
36
Kim, Daeha, Il Won Jung e Jong Ahn Chun. "A comparative assessment of rainfall–runoff modelling against regional flow duration curves for ungauged catchments". Hydrology and Earth System Sciences 21, n. 11 (15 novembre 2017): 5647–61. http://dx.doi.org/10.5194/hess-21-5647-2017.
Testo completoAbstract (sommario):
Abstract. Rainfall–runoff modelling has long been a special subject in hydrological sciences, but identifying behavioural parameters in ungauged catchments is still challenging. In this study, we comparatively evaluated the performance of the local calibration of a rainfall–runoff model against regional flow duration curves (FDCs), which is a seemingly alternative method of classical parameter regionalisation for ungauged catchments. We used a parsimonious rainfall–runoff model over 45 South Korean catchments under semi-humid climate. The calibration against regional FDCs was compared with the simple proximity-based parameter regionalisation. Results show that transferring behavioural parameters from gauged to ungauged catchments significantly outperformed the local calibration against regional FDCs due to the absence of flow timing information in the regional FDCs. The behavioural parameters gained from observed hydrographs were likely to contain intangible flow timing information affecting predictability in ungauged catchments. Additional constraining with the rising limb density appreciably improved the FDC calibrations, implying that flow signatures in temporal dimensions would supplement the FDCs. As an alternative approach in data-rich regions, we suggest calibrating a rainfall–runoff model against regionalised hydrographs to preserve flow timing information. We also suggest use of flow signatures that can supplement hydrographs for calibrating rainfall–runoff models in gauged and ungauged catchments.
37
Garbacz, Tomasz, e Ľudmila Dulebova. "Calibration Process and Constructions of Extrusion Calibrators". Key Engineering Materials 635 (dicembre 2014): 135–38. http://dx.doi.org/10.4028/www.scientific.net/kem.635.135.
Testo completoAbstract (sommario):
In the cellular extrusion process, the extrusion head gives the extrudate the desired cross-section shape and dimensions, taking into account the Barus effect and the shrinkage effect. However, if strict requirements are imposed with regard to cross-section shape and dimensions, it is necessary to fix the shape and dimensions by calibrating the extrudate obtained. The aim of this study is to present methods and constructional solutions of calibration tooling (calibrators) and to present the new calibrator that constitutes a significant element of the adapted and modernized technological extrusion line.
38
Byrne, Ruby, Miguel F. Morales, Bryna J. Hazelton e Michael Wilensky. "A unified calibration framework for 21 cm cosmology". Monthly Notices of the Royal Astronomical Society 503, n. 2 (8 marzo 2021): 2457–77. http://dx.doi.org/10.1093/mnras/stab647.
Testo completoAbstract (sommario):
ABSTRACT Calibration precision is currently a limiting systematic in 21 cm cosmology experiments. While there are innumerable calibration approaches, most can be categorized as either ‘sky-based,’ relying on an extremely accurate model of astronomical foreground emission, or ‘redundant,’ requiring a precisely regular array with near-identical antenna response patterns. Both of these classes of calibration are inflexible to the realities of interferometric measurement. In practice, errors in the foreground model, antenna position offsets, and beam response inhomogeneities degrade calibration performance and contaminate the cosmological signal. Here, we show that sky-based and redundant calibration can be unified into a highly general and physically motivated calibration framework based on a Bayesian statistical formalism. Our new framework includes sky-based and redundant calibration as special cases but can additionally support relaxing the rigid assumptions implicit in those approaches. We present simulation results demonstrating that, in a simple case, working in an intermediate regime between sky-based and redundant calibration improves calibration performance. Our framework is highly general and encompasses novel calibration approaches including techniques for calibrating compact non-redundant arrays, calibrating to incomplete sky models, and constraining calibration solutions across frequency.
39
Zhao, Chao Feng, Guo Dong Li, Xiang Jin Wang, Zhi Lu Zhang, Cheng Yu Li e Qing Bing Kong. "Design and Realization of the Calibration Equipment for Inertial Navigation System by the Control Computer". Applied Mechanics and Materials 380-384 (agosto 2013): 3354–57. http://dx.doi.org/10.4028/www.scientific.net/amm.380-384.3354.
Testo completoAbstract (sommario):
Aiming at the problem of calibrating the INS in non-laboratory conditions, this thesis proposes the calibration methods by as the core and combined use of double-position directional gyro calibration, four-position horizontal gyro calibration and Schuler circuit accelerometer calibration etc. It builds up the model for scale factor calibrating, controls the inertial platform by the embedded control technique to make it the three-axis turntable state, and uses the Linux OS and C language design control software to design and develop the automatic calibration equipment for the INS. This equipment is simple in operation, easy in use and portable, and therefore can realize automatic calibration in non-laboratory conditions. And the results meet the requirements for guarantee the precision of the system in use.
40
Ren, Jiaxing. "Analysis of the Design and Application of a Novel CT Secondary Cable Line Calibrator". Journal of Electronic Research and Application 8, n. 2 (9 aprile 2024): 7–11. http://dx.doi.org/10.26689/jera.v8i2.6371.
Testo completoAbstract (sommario):
With the rapid development of electrical power systems, ensuring the accuracy and reliability of power transmission has become particularly crucial. The secondary cable line calibrator for current transformers (CT) plays an essential role in calibrating electrical power systems. It is not only related to the safe operation of the system but also directly impacts the accuracy of energy metering. This study aims to design and analyze an efficient CT secondary cable line calibrator to explore its application effects in the power system. By thoroughly analyzing the characteristics of CT secondary cable lines and the design requirements of the calibrator, this paper proposes an innovative design scheme for the calibrator. This device demonstrates significant effects in enhancing the accuracy and stability of power system calibration, providing robust technical support for the optimization and upgrade of the power system. This research not only offers a theoretical basis and practical guidance for the design and application of CT secondary cable line calibrators but also contributes new ideas and methods for the precise calibration and efficient management of the power system.
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Millward, Christopher G., e Gordon A. H. Walker. "An Empirical Hγ - Luminosity Calibration". Symposium - International Astronomical Union 111 (1985): 377–80. http://dx.doi.org/10.1017/s0074180900079006.
Testo completoAbstract (sommario):
High signal-to-noise Reticon spectra for 87 members of 8 open clusters and associations together with 37 stars having reliable parallaxes (early A-type stars with reliable trigonometric parallaxes, eclipsing binaries, and visual binaries) have been used to calibrate the W(Hγ)-Mv relation for spectral types 0 to early A of luminosity classes III-V. The new calibration has a mean probable dispersion of ±0.28 mag. The distance modulus of the Pleiades is 5.54 ± 0.06 mag, which is in excellent agreement with other, recent determinations, as are the distance moduli for all the calibrating clusters. The use of visual-binary parallaxes implies a Hyades distance modulus of about 3.0 which is significantly smaller than the Hanson (1980) value of 3.30 mag. Although no spectral-type corrections are necessary, stellar evolution probably affects the construction of the new calibration and special care should be taken when determining distance moduli from slightly evolved cluster sequences or for individual stars. Systematic departures from the calibration may be present for stars with Vsin i ≥ 220–250 km/sec. Significant residuals are found between our values of W(Hγ) and those of Petrie in the range 1–13 Å equivalent width, which are due in part to systematic errors in Petrie's W(Hγ) measures. Our distance modulus of 11.11 mag for NGC 2244 is in excellent agreement with the photometric distance. The new calibration is compared to other early type star calibrations for main sequence stars. It is 1.2 mag brighter than Petrie's (1965) Hγ calibration at spectral type 06 and 0.7 mag brighter at A3. For types B1 and earlier the new calibration averages 0.4 mag brighter than the Balona and Crampton (1974) Hγ calibration. There is generally good agreement with the Blaauw (1963) MK calibration although the latter is 0.4 mag brighter at spectral type BO. The Crawford (1978) Hβ calibration is up to 0.5 mag brighter for the earlier spectral types and 0.4 mag fainter for later types. More complete discussions of the Hγ-luminosity calibration are available in Millward and Walker (1984, 1985).
42
Schaude, Janik, e Tino Hausotte. "Uncertainty-based determination of recalibration dates". International Journal of Metrology and Quality Engineering 15 (2024): 2. http://dx.doi.org/10.1051/ijmqe/2023017.
Testo completoAbstract (sommario):
Traceability is of vital importance in metrology and is achieved by an unbroken chain of calibrations that relate the measurement result to a reference. Less clear is the temporal aspect of traceability, namely the determination of recalibration dates. Relevant standards require the conduction of recalibrations in a planned manner, and thus in general there is a calibration history consisting of a number of past calibrations for measurands that are part of the traceability chain. Nevertheless, commonly only the results of the last calibration of the standards of the traceability chain are considered when determining a measurement result. Furthermore, recalibration dates are often determined in a rather unscientific manner. Within this paper, a method is proposed to predict the current value of a measurand along with its uncertainty, taking into account all past calibrations. Based on the predetermined target measurement uncertainty of the measurand, it is possible to recognize the need for and thus to date recalibrations. The applicability of the method is investigated by examining the metrological compatibility of the predicted results with the results of subsequent calibrations of the calibration histories of a number of different standards. There is an explainable limitation of the applicability of the method to calibration histories that exhibit a correlation of time and the chosen calibration laboratory. However, the paper leads the way of future research to remedy the currently unsatisfying state regarding the handling of calibration histories and the determination of recalibration dates.
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Reu, Phillip. "Calibration: 2D Calibration". Experimental Techniques 37, n. 5 (settembre 2013): 1–2. http://dx.doi.org/10.1111/ext.12027.
Testo completo
44
Reu, Phillip. "Calibration: Stereo Calibration". Experimental Techniques 38, n. 1 (gennaio 2014): 1–2. http://dx.doi.org/10.1111/ext.12048.
Testo completo
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Ataei, Ali, Jelle Eikhout, Ruud G. H. van Leeuwen, Esther Tanck e Florieke Eggermont. "The effect of variations in CT scan protocol on femoral finite element failure load assessment using phantomless calibration". PLOS ONE 17, n. 3 (18 marzo 2022): e0265524. http://dx.doi.org/10.1371/journal.pone.0265524.
Testo completoAbstract (sommario):
Recently, it was shown that fracture risk assessment in patients with femoral bone metastases using Finite Element (FE) modeling can be performed using a calibration phantom or air-fat-muscle calibration and that non-patient-specific calibration was less favorable. The purpose of this study was to investigate if phantomless calibration can be used instead of phantom calibration when different CT protocols are used. Differences in effect of CT protocols on Hounsfield units (HU), calculated bone mineral density (BMD) and FE failure loads between phantom and two methods of phantomless calibrations were studied. Five human cadaver lower limbs were scanned atop a calibration phantom according to a standard scanning protocol and seven additional commonly deviating protocols including current, peak kilovoltage (kVp), slice thickness, rotation time, field of view, reconstruction kernel, and reconstruction algorithm. The HUs of the scans were calibrated to BMD (in mg/cm3) using the calibration phantom as well as using air-fat-muscle and non-patient-specific calibration, resulting in three models for each scan. FE models were created, and failure loads were calculated by simulating an axial load on the femur. HU, calculated BMD and failure load of all protocols were compared between the three calibration methods. The different protocols showed little variation in HU, BMD and failure load. However, compared to phantom calibration, changing the kVp resulted in a relatively large decrease of approximately 10% in mean HU and BMD of the trabecular and cortical region of interest (ROI), resulting in a 13.8% and 13.4% lower failure load when air-fat-muscle and non-patient-specific calibrations were used, respectively. In conclusion, while we observed significant correlations between air-fat-muscle calibration and phantom calibration as well as between non-patient-specific calibration and phantom calibration, our sample size was too small to prove that either of these calibration approaches was superior. Further studies are necessary to test whether air-fat-muscle or non-patient-specific calibration could replace phantom calibration in case of different scanning protocols.
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Xia, Dan, De Hua Li e Sheng Yong Xu. "Efficient and Accurate Camera Calibration Based on Planar Pattern". Advanced Materials Research 204-210 (febbraio 2011): 1258–61. http://dx.doi.org/10.4028/www.scientific.net/amr.204-210.1258.
Testo completoAbstract (sommario):
We describe an effective method for calibrating cameras by using planar calibration patterns. The calibration pattern control points are localized by Harris detector incorporating the gradient histogram. The accuracy of the calibration control points location consequently improves the accuracy of the camera calibration. Additionally, optimization computation is carried out for increasing the accuracy of camera calibration results. Experiments using real images verified the effectiveness and robustness of the proposed method.
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Hülsen, G., J. Gröbner, A. Bais, M. Blumthaler, P. Disterhoft, B. Johnsen, K. O. Lantz et al. "Intercomparison of erythemal broadband radiometers calibrated by seven UV calibration facilities in Europe and the USA". Atmospheric Chemistry and Physics Discussions 8, n. 1 (6 febbraio 2008): 2249–73. http://dx.doi.org/10.5194/acpd-8-2249-2008.
Testo completoAbstract (sommario):
Abstract. A bi-lateral intercomparison of erythemal broadband radiometers was performed between seven UV calibration facilities. The owners calibrations were compared relative to the characterisation and calibration performed at PMOD/WRC in Davos, Switzerland. The calibration consisted in the determination of the spectral and angular response of the radiometer, followed by an absolute calibration performed outdoors relative to a spectroradiometer which provided the absolute reference. The characterization of the detectors in the respective laboratories are in good agreement: The determination of the angular responses have deviations below ±4% and the spectral responses agree within ±20%. A "blind" intercomparison of the erythemally weighted irradiances derived by the respective institutes and PMOD/WRC showed consistent measurements to within ±2% for the majority of institutes. One institute showed slightly larger deviation of 10%. The differences found between the different instrument calibrations are all within the combined uncertainty of the calibration.
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Hülsen, G., J. Gröbner, A. Bais, M. Blumthaler, P. Disterhoft, B. Johnsen, K. O. Lantz et al. "Intercomparison of erythemal broadband radiometers calibrated by seven UV calibration facilities in Europe and the USA". Atmospheric Chemistry and Physics 8, n. 16 (21 agosto 2008): 4865–75. http://dx.doi.org/10.5194/acp-8-4865-2008.
Testo completoAbstract (sommario):
Abstract. A bi-lateral intercomparison of erythemal broadband radiometers was performed between seven UV calibration facilities. The calibrations provided by the instruments owners were compared relative to the characterisation and calibration performed at PMOD/WRC in Davos, Switzerland. The calibration consisted in the determination of the spectral and angular response of the radiometer, followed by an absolute calibration performed outdoors relative to a spectroradiometer which provided the absolute reference. The characterization of the detectors in the respective laboratories are in good agreement: The determinations of the angular responses have deviations below ±4% and the spectral responses agree within ±20%. A "blind" intercomparison of the erythemally weighted irradiances derived by the respective institutes and PMOD/WRC showed consistent measurements to within ±2% for the majority of institutes. One institute showed slightly larger deviation of 10%. The differences found between the different instrument calibrations are all within the combined uncertainty of the calibration.
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ZHANG Jian, 张健, 张国玉 ZHANG Guo-yu, 孙高飞 SUN Gao-fei, 苏拾 SU Shi e 张建良 ZHANG Jian-liang. "Calibration Method for Standard Scattering Plate Calibration System Used in Calibrating Visibility Meter". ACTA PHOTONICA SINICA 46, n. 3 (2017): 312003. http://dx.doi.org/10.3788/gzxb20174603.0312003.
Testo completo
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Tang, Rui-Yin, Zhou-Mo Zeng, Chang-Ku Sun e Peng Wang. "3-Step-Calibration of 3D Vision Measurement System Based-on Structured Light". International Journal of Automation Technology 8, n. 3 (5 maggio 2014): 484–89. http://dx.doi.org/10.20965/ijat.2014.p0484.
Testo completoAbstract (sommario):
In structured light 3D vision measurement system, calibration tasks are key steps. Aiming at a special application of line structured light measurement, namely computer hard-disk surface planeness measurement at a precision equipment manufacturing company in Singapore, and combining with the structured light measurement model, determined three calibration tasks of the system. The three calibrating tasks concluded: calibrating the camera parameters; calibrating the light plane pose and calibrating the movement pose. At the same time, according to the three calibration results, measured the computer hard disk, and reconstructed the 3D model of the computer hard disk. The experimental results show that, the whole system of three calibration process is simple and reliable, the method does not need any auxiliary adjustment and realize the measurement accuracy about 0.023 mm. The work laid the better foundation for hard disk planeness vision measurement.