DOE Office of Scientific and Technical Information (OSTI.GOV)

Güver, Tolga; Özel, Feryal; Psaltis, Dimitrios

Many techniques for measuring neutron star radii rely on absolute flux measurements in the X-rays. As a result, one of the fundamental uncertainties in these spectroscopic measurements arises from the absolute flux calibrations of the detectors being used. Using the stable X-ray burster, GS 1826–238, and its simultaneous observations by Chandra HETG/ACIS-S and RXTE /PCA as well as by XMM-Newton EPIC-pn and RXTE /PCA, we quantify the degree of uncertainty in the flux calibration by assessing the differences between the measured fluxes during bursts. We find that the RXTE /PCA and the Chandra gratings measurements agree with each other withinmore » their formal uncertainties, increasing our confidence in these flux measurements. In contrast, XMM-Newton EPIC-pn measures 14.0 ± 0.3% less flux than the RXTE /PCA. This is consistent with the previously reported discrepancy with the flux measurements of EPIC-pn, compared with EPIC MOS1, MOS2, and ACIS-S detectors. We also show that any intrinsic time-dependent systematic uncertainty that may exist in the calibration of the satellites has already been implicity taken into account in the neutron star radius measurements.« less

Normalization and calibration of geostationary satellite radiances for the International Satellite Cloud Climatology Project

NASA Technical Reports Server (NTRS)

Desormeaux, Yves; Rossow, William B.; Brest, Christopher L.; Campbell, G. G.

1993-01-01

Procedures are described for normalizing the radiometric calibration of image radiances obtained from geostationary weather satellites that contributed data to the International Satellite Cloud Climatology Project. The key step is comparison of coincident and collocated measurements made by each satellite and the concurrent AVHRR on the 'afternoon' NOAA polar-orbiting weather satellite at the same viewing geometry. The results of this comparison allow transfer of the AVHRR absolute calibration, which has been established over the whole series, to the radiometers on the geostationary satellites. Results are given for Meteosat-2, 3, and 4, for GOES-5, 6, and 7, for GMS-2, 3, and 4 and for Insat-1B. The relative stability of the calibrations of these radiance data is estimated to be within +/- 3 percent; the uncertainty of the absolute calibrations is estimated to be less than 10 percent. The remaining uncertainties are at least two times smaller than for the original radiance data.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) on-board blackbody calibration system

NASA Astrophysics Data System (ADS)

Best, Fred A.; Revercomb, Henry E.; Knuteson, Robert O.; Tobin, David C.; Ellington, Scott D.; Werner, Mark W.; Adler, Douglas P.; Garcia, Raymond K.; Taylor, Joseph K.; Ciganovich, Nick N.; Smith, William L., Sr.; Bingham, Gail E.; Elwell, John D.; Scott, Deron K.

2005-01-01

The NASA New Millennium Program's Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) instrument provides enormous advances in water vapor, wind, temperature, and trace gas profiling from geostationary orbit. The top-level instrument calibration requirement is to measure brightness temperature to better than 1 K (3 sigma) over a broad range of atmospheric brightness temperatures, with a reproducibility of +/-0.2 K. For in-flight radiometric calibration, GIFTS uses views of two on-board blackbody sources (290 K and 255 K) along with cold space, sequenced at regular programmable intervals. The blackbody references are cavities that follow the UW Atmospheric Emitted Radiance Interferometer (AERI) design, scaled to the GIFTS beam size. The cavity spectral emissivity is better than 0.998 with an absolute uncertainty of less than 0.001. Absolute blackbody temperature uncertainties are estimated at 0.07 K. This paper describes the detailed design of the GIFTS on-board calibration system that recently underwent its Critical Design Review. The blackbody cavities use ultra-stable thermistors to measure temperature, and are coated with high emissivity black paint. Monte Carlo modeling has been performed to calculate the cavity emissivity. Both absolute temperature and emissivity measurements are traceable to NIST, and detailed uncertainty budgets have been developed and used to show the overall system meets accuracy requirements. The blackbody controller is housed on a single electronics board and provides precise selectable set point temperature control, thermistor resistance measurement, and the digital interface to the GIFTS instrument. Plans for the NIST traceable ground calibration of the on-board blackbody system have also been developed and are presented in this paper.

The Dependence of Cloud Property Trend Detection on Absolute Calibration Accuracy of Passive Satellite Sensors

NASA Astrophysics Data System (ADS)

Shea, Y.; Wielicki, B. A.; Sun-Mack, S.; Minnis, P.; Zelinka, M. D.

2016-12-01

Detecting trends in climate variables on global, decadal scales requires highly accurate, stable measurements and retrieval algorithms. Trend uncertainty depends on its magnitude, natural variability, and instrument and retrieval algorithm accuracy and stability. We applied a climate accuracy framework to quantify the impact of absolute calibration on cloud property trend uncertainty. The cloud properties studied were cloud fraction, effective temperature, optical thickness, and effective radius retrieved using the Clouds and the Earth's Radiant Energy System (CERES) Cloud Property Retrieval System, which uses Moderate-resolution Imaging Spectroradiometer measurements (MODIS). Modeling experiments from the fifth phase of the Climate Model Intercomparison Project (CMIP5) agree that net cloud feedback is likely positive but disagree regarding its magnitude, mainly due to uncertainty in shortwave cloud feedback. With the climate accuracy framework we determined the time to detect trends for instruments with various calibration accuracies. We estimated a relationship between cloud property trend uncertainty, cloud feedback, and Equilibrium Climate Sensitivity and also between effective radius trend uncertainty and aerosol indirect effect trends. The direct relationship between instrument accuracy requirements and climate model output provides the level of instrument absolute accuracy needed to reduce climate model projection uncertainty. Different cloud types have varied radiative impacts on the climate system depending on several attributes, such as their thermodynamic phase, altitude, and optical thickness. Therefore, we also conducted these studies by cloud types for a clearer understanding of instrument accuracy requirements needed to detect changes in their cloud properties. Combining this information with the radiative impact of different cloud types helps to prioritize among requirements for future satellite sensors and understanding the climate detection capabilities of existing sensors.

The Absolute Magnitude of the Sun in Several Filters

NASA Astrophysics Data System (ADS)

Willmer, Christopher N. A.

2018-06-01

This paper presents a table with estimates of the absolute magnitude of the Sun and the conversions from vegamag to the AB and ST systems for several wide-band filters used in ground-based and space-based observatories. These estimates use the dustless spectral energy distribution (SED) of Vega, calibrated absolutely using the SED of Sirius, to set the vegamag zero-points and a composite spectrum of the Sun that coadds space-based observations from the ultraviolet to the near-infrared with models of the Solar atmosphere. The uncertainty of the absolute magnitudes is estimated by comparing the synthetic colors with photometric measurements of solar analogs and is found to be ∼0.02 mag. Combined with the uncertainty of ∼2% in the calibration of the Vega SED, the errors of these absolute magnitudes are ∼3%–4%. Using these SEDs, for three of the most utilized filters in extragalactic work the estimated absolute magnitudes of the Sun are M B = 5.44, M V = 4.81, and M K = 3.27 mag in the vegamag system and M B = 5.31, M V = 4.80, and M K = 5.08 mag in AB.

Uncertainty analysis technique for OMEGA Dante measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, M. J.; Widmann, K.; Sorce, C.

2010-10-15

The Dante is an 18 channel x-ray filtered diode array which records the spectrally and temporally resolved radiation flux from various targets (e.g., hohlraums, etc.) at x-ray energies between 50 eV and 10 keV. It is a main diagnostic installed on the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The absolute flux is determined from the photometric calibration of the x-ray diodes, filters and mirrors, and an unfold algorithm. Understanding the errors on this absolute measurement is critical for understanding hohlraum energetic physics. We present a new method for quantifying the uncertainties on the determinedmore » flux using a Monte Carlo parameter variation technique. This technique combines the uncertainties in both the unfold algorithm and the error from the absolute calibration of each channel into a one sigma Gaussian error function. One thousand test voltage sets are created using these error functions and processed by the unfold algorithm to produce individual spectra and fluxes. Statistical methods are applied to the resultant set of fluxes to estimate error bars on the measurements.« less

Uncertainty Analysis Technique for OMEGA Dante Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

May, M J; Widmann, K; Sorce, C

2010-05-07

The Dante is an 18 channel X-ray filtered diode array which records the spectrally and temporally resolved radiation flux from various targets (e.g. hohlraums, etc.) at X-ray energies between 50 eV to 10 keV. It is a main diagnostics installed on the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The absolute flux is determined from the photometric calibration of the X-ray diodes, filters and mirrors and an unfold algorithm. Understanding the errors on this absolute measurement is critical for understanding hohlraum energetic physics. We present a new method for quantifying the uncertainties on the determinedmore » flux using a Monte-Carlo parameter variation technique. This technique combines the uncertainties in both the unfold algorithm and the error from the absolute calibration of each channel into a one sigma Gaussian error function. One thousand test voltage sets are created using these error functions and processed by the unfold algorithm to produce individual spectra and fluxes. Statistical methods are applied to the resultant set of fluxes to estimate error bars on the measurements.« less

Experimental power density distribution benchmark in the TRIGA Mark II reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snoj, L.; Stancar, Z.; Radulovic, V.

2012-07-01

In order to improve the power calibration process and to benchmark the existing computational model of the TRIGA Mark II reactor at the Josef Stefan Inst. (JSI), a bilateral project was started as part of the agreement between the French Commissariat a l'energie atomique et aux energies alternatives (CEA) and the Ministry of higher education, science and technology of Slovenia. One of the objectives of the project was to analyze and improve the power calibration process of the JSI TRIGA reactor (procedural improvement and uncertainty reduction) by using absolutely calibrated CEA fission chambers (FCs). This is one of the fewmore » available power density distribution benchmarks for testing not only the fission rate distribution but also the absolute values of the fission rates. Our preliminary calculations indicate that the total experimental uncertainty of the measured reaction rate is sufficiently low that the experiments could be considered as benchmark experiments. (authors)« less

A calculation and uncertainty evaluation method for the effective area of a piston rod used in quasi-static pressure calibration

NASA Astrophysics Data System (ADS)

Gu, Tingwei; Kong, Deren; Shang, Fei; Chen, Jing

2018-04-01

This paper describes the merits and demerits of different sensors for measuring propellant gas pressure, the applicable range of the frequently used dynamic pressure calibration methods, and the working principle of absolute quasi-static pressure calibration based on the drop-weight device. The main factors affecting the accuracy of pressure calibration are analyzed from two aspects of the force sensor and the piston area. To calculate the effective area of the piston rod and evaluate the uncertainty between the force sensor and the corresponding peak pressure in the absolute quasi-static pressure calibration process, a method for solving these problems based on the least squares principle is proposed. According to the relevant quasi-static pressure calibration experimental data, the least squares fitting model between the peak force and the peak pressure, and the effective area of the piston rod and its measurement uncertainty, are obtained. The fitting model is tested by an additional group of experiments, and the peak pressure obtained by the existing high-precision comparison calibration method is taken as the reference value. The test results show that the peak pressure obtained by the least squares fitting model is closer to the reference value than the one directly calculated by the cross-sectional area of the piston rod. When the peak pressure is higher than 150 MPa, the percentage difference is less than 0.71%, which can meet the requirements of practical application.

Planck 2013 results. VIII. HFI photometric calibration and mapmaking

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bertincourt, B.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bridges, M.; Bucher, M.; Burigana, C.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chen, X.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Filliard, C.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Le Jeune, M.; Lellouch, E.; Leonardi, R.; Leroy, C.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Maurin, L.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Moreno, R.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rusholme, B.; Santos, D.; Savini, G.; Scott, D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Techene, S.; Terenzi, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

This paper describes the methods used to produce photometrically calibrated maps from the Planck High Frequency Instrument (HFI) cleaned, time-ordered information. HFI observes the sky over a broad range of frequencies, from 100 to 857 GHz. To obtain the best calibration accuracy over such a large range, two different photometric calibration schemes have to be used. The 545 and 857 GHz data are calibrated by comparing flux-density measurements of Uranus and Neptune with models of their atmospheric emission. The lower frequencies (below 353 GHz) are calibrated using the solar dipole. A component of this anisotropy is time-variable, owing to the orbital motion of the satellite in the solar system. Photometric calibration is thus tightly linked to mapmaking, which also addresses low-frequency noise removal. By comparing observations taken more than one year apart in the same configuration, we have identified apparent gain variations with time. These variations are induced by non-linearities in the read-out electronics chain. We have developed an effective correction to limit their effect on calibration. We present several methods to estimate the precision of the photometric calibration. We distinguish relative uncertainties (between detectors, or between frequencies) and absolute uncertainties. Absolute uncertainties lie in the range from 0.54% to 10% from 100 to 857 GHz. We describe the pipeline used to produce the maps from the HFI timelines, based on the photometric calibration parameters, and the scheme used to set the zero level of the maps a posteriori. We also discuss the cross-calibration between HFI and the SPIRE instrument on board Herschel. Finally we summarize the basic characteristics of the set of HFI maps included in the 2013 Planck data release.

Improved Absolute Radiometric Calibration of a UHF Airborne Radar

NASA Technical Reports Server (NTRS)

Chapin, Elaine; Hawkins, Brian P.; Harcke, Leif; Hensley, Scott; Lou, Yunling; Michel, Thierry R.; Moreira, Laila; Muellerschoen, Ronald J.; Shimada, Joanne G.; Tham, Kean W.;

Comparison of IPSM 1990 photon dosimetry code of practice with IAEA TRS‐398 and AAPM TG‐51.

PubMed Central

Henríquez, Francisco Cutanda

2009-01-01

Several codes of practice for photon dosimetry are currently used around the world, supported by different organizations. A comparison of IPSM 1990 with both IAEA TRS‐398 and AAPM TG‐51 has been performed. All three protocols are based on the calibration of ionization chambers in terms of standards of absorbed dose to water, as it is the case with other modern codes of practice. This comparison has been carried out for photon beams of nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV. An NE 2571 graphite ionization chamber was used in this study, cross‐calibrated against an NE 2611A Secondary Standard, calibrated in the National Physical Laboratory (NPL). Absolute dose in reference conditions was obtained using each of these three protocols including: beam quality indices, beam quality conversion factors both theoretical and NPL experimental ones, correction factors for influence quantities and absolute dose measurements. Each protocol recommendations have been strictly followed. Uncertainties have been obtained according to the ISO Guide to the Expression of Uncertainty in Measurement. Absorbed dose obtained according to all three protocols agree within experimental uncertainty. The largest difference between absolute dose results for two protocols is obtained for the highest energy: 0.7% between IPSM 1990 and IAEA TRS‐398 using theoretical beam quality conversion factors. PACS number: 87.55.tm

Calibration of the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

NASA Technical Reports Server (NTRS)

Thome, Kurtis; Barnes, Robert; Baize, Rosemary; O'Connell, Joseph; Hair, Jason

2010-01-01

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) plans to observe climate change trends over decadal time scales to determine the accuracy of climate projections. The project relies on spaceborne earth observations of SI-traceable variables sensitive to key decadal change parameters. The mission includes a reflected solar instrument retrieving at-sensor reflectance over the 320 to 2300 nm spectral range with 500-m spatial resolution and 100-km swath. Reflectance is obtained from the ratio of measurements of the earth s surface to those while viewing the sun relying on a calibration approach that retrieves reflectance with uncertainties less than 0.3%. The calibration is predicated on heritage hardware, reduction of sensor complexity, adherence to detector-based calibration standards, and an ability to simulate in the laboratory on-orbit sources in both size and brightness to provide the basis of a transfer to orbit of the laboratory calibration including a link to absolute solar irradiance measurements.

Measurement of optical to electrical and electrical to optical delays with ps-level uncertainty.

PubMed

Peek, H Z; Pinkert, T J; Jansweijer, P P M; Koelemeij, J C J

2018-05-28

We present a new measurement principle to determine the absolute time delay of a waveform from an optical reference plane to an electrical reference plane and vice versa. We demonstrate a method based on this principle with 2 ps uncertainty. This method can be used to perform accurate time delay determinations of optical transceivers used in fiber-optic time-dissemination equipment. As a result the time scales in optical and electrical domain can be related to each other with the same uncertainty. We expect this method will be a new breakthrough in high-accuracy time transfer and absolute calibration of time-transfer equipment.

Uncertainty Evaluations of the CRCS In-orbit Field Radiometric Calibration Methods for Thermal Infrared Channels of FENGYUN Meteorological Satellites

NASA Astrophysics Data System (ADS)

Zhang, Y.; Rong, Z.; Min, M.; Hao, X.; Yang, H.

2017-12-01

Meteorological satellites have become an irreplaceable weather and ocean-observing tool in China. These satellites are used to monitor natural disasters and improve the efficiency of many sectors of Chinese national economy. It is impossible to ignore the space-derived data in the fields of meteorology, hydrology, and agriculture, as well as disaster monitoring in China, a large agricultural country. For this reason, China is making a sustained effort to build and enhance its meteorological observing system and application system. The first Chinese polar-orbiting weather satellite was launched in 1988. Since then China has launched 14 meteorological satellites, 7 of which are sun synchronous and 7 of which are geostationary satellites; China will continue its two types of meteorological satellite programs. In order to achieve the in-orbit absolute radiometric calibration of the operational meteorological satellites' thermal infrared channels, China radiometric calibration sites (CRCS) established a set of in-orbit field absolute radiometric calibration methods (FCM) for thermal infrared channels (TIR) and the uncertainty of this method was evaluated and analyzed based on TERRA/AQUA MODIS observations. Comparisons between the MODIS at pupil brightness temperatures (BTs) and the simulated BTs at the top of atmosphere using radiative transfer model (RTM) based on field measurements showed that the accuracy of the current in-orbit field absolute radiometric calibration methods was better than 1.00K (@300K, K=1) in thermal infrared channels. Therefore, the current CRCS field calibration method for TIR channels applied to Chinese metrological satellites was with favorable calibration accuracy: for 10.5-11.5µm channel was better than 0.75K (@300K, K=1) and for 11.5-12.5µm channel was better than 0.85K (@300K, K=1).

Assessment of uncertainty in ROLO lunar irradiance for on-orbit calibration

USGS Publications Warehouse

Stone, T.C.; Kieffer, H.H.; Barnes, W.L.; Butler, J.J.

2004-01-01

A system to provide radiometric calibration of remote sensing imaging instruments on-orbit using the Moon has been developed by the US Geological Survey RObotic Lunar Observatory (ROLO) project. ROLO has developed a model for lunar irradiance which treats the primary geometric variables of phase and libration explicitly. The model fits hundreds of data points in each of 23 VNIR and 9 SWIR bands; input data are derived from lunar radiance images acquired by the project's on-site telescopes, calibrated to exoatmospheric radiance and converted to disk-equivalent reflectance. Experimental uncertainties are tracked through all stages of the data processing and modeling. Model fit residuals are ???1% in each band over the full range of observed phase and libration angles. Application of ROLO lunar calibration to SeaWiFS has demonstrated the capability for long-term instrument response trending with precision approaching 0.1% per year. Current work involves assessing the error in absolute responsivity and relative spectral response of the ROLO imaging systems, and propagation of error through the data reduction and modeling software systems with the goal of reducing the uncertainty in the absolute scale, now estimated at 5-10%. This level is similar to the scatter seen in ROLO lunar irradiance comparisons of multiple spacecraft instruments that have viewed the Moon. A field calibration campaign involving NASA and NIST has been initiated that ties the ROLO lunar measurements to the NIST (SI) radiometric scale.

SNPP VIIRS RSB Earth View Reflectance Uncertainty

NASA Technical Reports Server (NTRS)

Lei, Ning; Twedt, Kevin; McIntire, Jeff; Xiong, Xiaoxiong

2017-01-01

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite uses its 14 reflective solar bands to passively collect solar radiant energy reflected off the Earth. The Level 1 product is the geolocated and radiometrically calibrated top-of- the-atmosphere solar reflectance. The absolute radiometric uncertainty associated with this product includes contributions from the noise associated with measured detector digital counts and the radiometric calibration bias. Here, we provide a detailed algorithm for calculating the estimated standard deviation of the retrieved top-of-the-atmosphere spectral solar radiation reflectance.

Uncertainty in cloud optical depth estimates made from satellite radiance measurements

NASA Technical Reports Server (NTRS)

Pincus, Robert; Szczodrak, Malgorzata; Gu, Jiujing; Austin, Philip

1995-01-01

The uncertainty in optical depths retrieved from satellite measurements of visible wavelength radiance at the top of the atmosphere is quantified. Techniques are briefly reviewed for the estimation of optical depth from measurements of radiance, and it is noted that these estimates are always more uncertain at greater optical depths and larger solar zenith angles. The lack of radiometric calibration for visible wavelength imagers on operational satellites dominates the uncertainty retrievals of optical depth. This is true for both single-pixel retrievals and for statistics calculated from a population of individual retrievals. For individual estimates or small samples, sensor discretization can also be significant, but the sensitivity of the retrieval to the specification of the model atmosphere is less important. The relative uncertainty in calibration affects the accuracy with which optical depth distributions measured by different sensors may be quantitatively compared, while the absolute calibration uncertainty, acting through the nonlinear mapping of radiance to optical depth, limits the degree to which distributions measured by the same sensor may be distinguished.

SU-G-BRB-14: Uncertainty of Radiochromic Film Based Relative Dose Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devic, S; Tomic, N; DeBlois, F

2016-06-15

Purpose: Due to inherently non-linear dose response, measurement of relative dose distribution with radiochromic film requires measurement of absolute dose using a calibration curve following previously established reference dosimetry protocol. On the other hand, a functional form that converts the inherently non-linear dose response curve of the radiochromic film dosimetry system into linear one has been proposed recently [Devic et al, Med. Phys. 39 4850–4857 (2012)]. However, there is a question what would be the uncertainty of such measured relative dose. Methods: If the relative dose distribution is determined going through the reference dosimetry system (conversion of the response bymore » using calibration curve into absolute dose) the total uncertainty of such determined relative dose will be calculated by summing in quadrature total uncertainties of doses measured at a given and at the reference point. On the other hand, if the relative dose is determined using linearization method, the new response variable is calculated as ζ=a(netOD)n/ln(netOD). In this case, the total uncertainty in relative dose will be calculated by summing in quadrature uncertainties for a new response function (σζ) for a given and the reference point. Results: Except at very low doses, where the measurement uncertainty dominates, the total relative dose uncertainty is less than 1% for the linear response method as compared to almost 2% uncertainty level for the reference dosimetry method. The result is not surprising having in mind that the total uncertainty of the reference dose method is dominated by the fitting uncertainty, which is mitigated in the case of linearization method. Conclusion: Linearization of the radiochromic film dose response provides a convenient and a more precise method for relative dose measurements as it does not require reference dosimetry and creation of calibration curve. However, the linearity of the newly introduced function must be verified. Dave Lewis is inventor and runs a consulting company for radiochromic films.« less

The Atacama Cosmology Telescope: Calibration with the Wilkinson Microwave Anisotropy Probe Using Cross-Correlations

NASA Technical Reports Server (NTRS)

Hajian, Amir; Acquaviva, Viviana; Ade, Peter A. R.; Aguirre, Paula; Amiri, Mandana; Appel, John William; Barrientos, L. Felipe; Battistelli, Elia S.; Bond, John R.; Brown, Ben;

Absolute detector-based spectrally tunable radiant source using digital micromirror device and supercontinuum fiber laser.

PubMed

Li, Zhigang; Wang, Xiaoxu; Zheng, Yuquan; Li, Futian

2017-06-10

High-accuracy absolute detector-based spectroradiometric calibration techniques traceable to cryogenic absolute radiometers have made progress rapidly in recent decades under the impetus of atmospheric quantitative spectral remote sensing. A high brightness spectrally tunable radiant source using a supercontinuum fiber laser and a digital micromirror device (DMD) has been developed to meet demands of spectroradiometric calibrations for ground-based, aeronautics-based, and aerospace-based remote sensing instruments and spectral simulations of natural scenes such as the sun and atmosphere. Using a supercontinuum fiber laser as a radiant source, the spectral radiance of the spectrally tunable radiant source is 20 times higher than the spectrally tunable radiant source using conventional radiant sources such as tungsten halogen lamps, xenon lamps, or LED lamps, and the stability is better than ±0.3%/h. Using a DMD, the spectrally tunable radiant source possesses two working modes. In narrow-band modes, it is calibrated by an absolute detector, and in broad-band modes, it can calibrate for remote sensing instrument. The uncertainty of the spectral radiance of the spectrally tunable radiant source is estimated at less than 1.87% at 350 nm to 0.85% at 750 nm, and compared to only standard lamp-based calibration, a greater improvement is gained.

A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors.

PubMed

Waugh, C J; Rosenberg, M J; Zylstra, A B; Frenje, J A; Séguin, F H; Petrasso, R D; Glebov, V Yu; Sangster, T C; Stoeckl, C

2015-05-01

Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition, comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.

A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

DOE PAGES

Waugh, C. J.; Rosenberg, M. J.; Zylstra, A. B.; ...

2015-05-27

Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition,more » comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.« less

A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waugh, C. J.; Rosenberg, M. J.; Zylstra, A. B.

Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition,more » comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.« less

A method for in situ absolute DD yield calibration of neutron time-of-flight detectors on OMEGA using CR-39-based proton detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waugh, C. J., E-mail: cjwaugh@mit.edu; Zylstra, A. B.; Frenje, J. A.

2015-05-15

Neutron time of flight (nTOF) detectors are used routinely to measure the absolute DD neutron yield at OMEGA. To check the DD yield calibration of these detectors, originally calibrated using indium activation systems, which in turn were cross-calibrated to NOVA nTOF detectors in the early 1990s, a direct in situ calibration method using CR-39 range filter proton detectors has been successfully developed. By measuring DD neutron and proton yields from a series of exploding pusher implosions at OMEGA, a yield calibration coefficient of 1.09 ± 0.02 (relative to the previous coefficient) was determined for the 3m nTOF detector. In addition,more » comparison of these and other shots indicates that significant reduction in charged particle flux anisotropies is achieved when bang time occurs significantly (on the order of 500 ps) after the trailing edge of the laser pulse. This is an important observation as the main source of the yield calibration error is due to particle anisotropies caused by field effects. The results indicate that the CR-39-nTOF in situ calibration method can serve as a valuable technique for calibrating and reducing the uncertainty in the DD absolute yield calibration of nTOF detector systems on OMEGA, the National Ignition Facility, and laser megajoule.« less

Absolute Ages and Distances of 22 GCs Using Monte Carlo Main-sequence Fitting

NASA Astrophysics Data System (ADS)

O'Malley, Erin M.; Gilligan, Christina; Chaboyer, Brian

2017-04-01

The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than σ π /π ≤ 0.10 and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the distance to Galactic globular clusters (GCs). A Monte Carlo analysis was used, taking into account uncertainties in the model construction parameters, to generate stellar models and isochrones to fit to the calibration stars. The isochrones that fit the calibration stars best were then used to determine the distances and ages of 22 GCs with metallicities ranging from -2.4 dex to -0.7 dex. We find distances with an average uncertainty of 0.15 mag and absolute ages ranging from 10.8 to 13.6 Gyr with an average uncertainty of 1.6 Gyr. Using literature proper motion data, we calculate orbits for the clusters, finding six that reside within the Galactic disk/bulge, while the rest are considered halo clusters. We find no strong evidence for a relationship between age and Galactocentric distance, but we do find a decreasing age-[Fe/H] relation.

Approaches on calibration of bolometer and establishment of bolometer calibration device

NASA Astrophysics Data System (ADS)

Xia, Ming; Gao, Jianqiang; Ye, Jun'an; Xia, Junwen; Yin, Dejin; Li, Tiecheng; Zhang, Dong

2015-10-01

Bolometer is mainly used for measuring thermal radiation in the field of public places, labor hygiene, heating and ventilation and building energy conservation. The working principle of bolometer is under the exposure of thermal radiation, temperature of black absorbing layer of detector rise after absorption of thermal radiation, which makes the electromotive force produced by thermoelectric. The white light reflective layer of detector does not absorb thermal radiation, so the electromotive force produced by thermoelectric is almost zero. A comparison of electromotive force produced by thermoelectric of black absorbing layer and white reflective layer can eliminate the influence of electric potential produced by the basal background temperature change. After the electromotive force which produced by thermal radiation is processed by the signal processing unit, the indication displays through the indication display unit. The measurement unit of thermal radiation intensity is usually W/m2 or kW/m2. Its accurate and reliable value has important significance for high temperature operation, labor safety and hygiene grading management. Bolometer calibration device is mainly composed of absolute radiometer, the reference light source, electric measuring instrument. Absolute radiometer is a self-calibration type radiometer. Its working principle is using the electric power which can be accurately measured replaces radiation power to absolutely measure the radiation power. Absolute radiometer is the standard apparatus of laser low power standard device, the measurement traceability is guaranteed. Using the calibration method of comparison, the absolute radiometer and bolometer measure the reference light source in the same position alternately which can get correction factor of irradiance indication. This paper is mainly about the design and calibration method of the bolometer calibration device. The uncertainty of the calibration result is also evaluated.

In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Barbielini, G; Bastieri, D.; Bechtol, K.; Bellazzini, R.;

In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; /Stanford U., HEPL /SLAC /KIPAC, Menlo Park; Ajello, M.

The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in themore » Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between {approx}6 and {approx}13 GeV with an estimated uncertainty of {approx}2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.« less

Error Budget for a Calibration Demonstration System for the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

NASA Technical Reports Server (NTRS)

Thome, Kurtis; McCorkel, Joel; McAndrew, Brendan

2013-01-01

A goal of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is to observe highaccuracy, long-term climate change trends over decadal time scales. The key to such a goal is to improving the accuracy of SI traceable absolute calibration across infrared and reflected solar wavelengths allowing climate change to be separated from the limit of natural variability. The advances required to reach on-orbit absolute accuracy to allow climate change observations to survive data gaps exist at NIST in the laboratory, but still need demonstration that the advances can move successfully from to NASA and/or instrument vendor capabilities for spaceborne instruments. The current work describes the radiometric calibration error budget for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The resulting SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climatequality data collections is given. Key components in the error budget are geometry differences between the solar and earth views, knowledge of attenuator behavior when viewing the sun, and sensor behavior such as detector linearity and noise behavior. Methods for demonstrating this error budget are also presented.

Development of an experimental variable temperature set-up for a temperature range from 2.2 K to 325 K for cost-effective temperature sensor calibration

NASA Astrophysics Data System (ADS)

Pal, Sandip; Kar, Ranjan; Mandal, Anupam; Das, Ananda; Saha, Subrata

2017-05-01

A prototype of a variable temperature insert has been developed in-house as a cryogenic thermometer calibration facility. It was commissioned in fulfilment of the very stringent requirements of the temperature control of the cryogenic system. The calibration facility is designed for calibrating industrial cryogenic thermometers that include a temperature sensor and the wires heat-intercept in the 2.2 K-325 K temperature range. The isothermal section of the calibration block onto which the thermometers are mounted is weakly linked with the temperature control zone mounted with cooling capillary coil and cryogenic heater. The connecting wires of the thermometer are thermally anchored with the support of the temperature insert. The calibration procedure begins once the temperature of the support is stabilized. Homogeneity of the calibration block’s temperature is established both by simulation and by cross-comparison of two calibrated sensors. The absolute uncertainty present in temperature measurement is calculated and found comparable with the measured uncertainty at different temperature points. Measured data is presented in comparison to the standard thermometers at fixed points and it is possible to infer that the absolute accuracy achieved is better than  ±0.5% of the reading in comparison to the fixed point temperature. The design and development of simpler, low cost equipment, and approach to analysis of the calibration results are discussed further in this paper, so that it can be easily devised by other researchers.

Use of the Moon for spacecraft calibration over 350-2500 nm

USGS Publications Warehouse

Kieffer, H.H.; Anderson, J.M.

1998-01-01

The Moon is the only natural object outside the Earth's atmosphere that is within the dynamic range of most imaging instruments on Earth-orbiting spacecraft. The excellent photometric stability of the Lunar surface will allow its use as a long-term instrument calibration source once the dependence of Lunar spectral radiance on phase and libration angles are well characterized. A program to provide this characterization is underway. Observations are being made in 23 bands within 350-950 nm, 7 of which correspond closely with spacecraft instrument bands. Observations in nine bands within 950-2500 nm began recently. Although at this time the absolute Lunar radiance model is preliminary and uncertainties are larger than most instrument calibration goals, changes in spacecraft instrument sensitivity can be precisely monitored and absolute calibration can be applied retroactively as the accuracy of the Lunar spectral radiance model improves. Several space-based imaging systems have already begun using the Moon for calibration and the EOS AM-1 platform will make periodic attitude maneuvers for Lunar and space calibration.

Demonstrating the Error Budget for the Climate Absolute Radiance and Refractivity Observatory Through Solar Irradiance Measurements

NASA Technical Reports Server (NTRS)

Thome, Kurtis; McCorkel, Joel; McAndrew, Brendan

2016-01-01

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe highaccuracy, long-term climate change trends and to use decadal change observations as a method to determine the accuracy of climate change. A CLARREO objective is to improve the accuracy of SI-traceable, absolute calibration at infrared and reflected solar wavelengths to reach on-orbit accuracies required to allow climate change observations to survive data gaps and observe climate change at the limit of natural variability. Such an effort will also demonstrate National Institute of Standards and Technology (NIST) approaches for use in future spaceborne instruments. The current work describes the results of laboratory and field measurements with the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. SOLARIS allows testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. Results of laboratory calibration measurements are provided to demonstrate key assumptions about instrument behavior that are needed to achieve CLARREO's climate measurement requirements. Absolute radiometric response is determined using laser-based calibration sources and applied to direct solar views for comparison with accepted solar irradiance models to demonstrate accuracy values giving confidence in the error budget for the CLARREO reflectance retrieval.

Electro-optical equivalent calibration technology for high-energy laser energy meters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Ji Feng, E-mail: wjfcom2000@163.com; Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900; Graduate School of China Academy of Engineering Physics, Beijing 100088

Electro-optical equivalent calibration with high calibration power and high equivalence is particularly well-suited to the calibration of high-energy laser energy meters. A large amount of energy is reserved during this process, however, which continues to radiate after power-off. This study measured the radiation efficiency of a halogen tungsten lamp during power-on and after power-off in order to calculate the total energy irradiated by a lamp until the high-energy laser energy meter reaches thermal equilibrium. A calibration system was designed based on the measurement results, and the calibration equivalence of the system was analyzed in detail. Results show that measurement precisionmore » is significantly affected by the absorption factor of the absorption chamber and by heat loss in the energy meter. Calibration precision is successfully improved by enhancing the equivalent power and reducing power-on time. The electro-optical equivalent calibration system, measurement uncertainty of which was evaluated as 2.4% (k = 2), was used to calibrate a graphite-cone-absorption-cavity absolute energy meter, yielding a calibration coefficient of 1.009 and measurement uncertainty of 3.5% (k = 2). A water-absorption-type high-energy laser energy meter with measurement uncertainty of 4.8% (k = 2) was considered the reference standard, and compared to the energy meter calibrated in this study, yielded a correction factor of 0.995 (standard deviation of 1.4%).« less

Improving Photometric Calibration of Meteor Video Camera Systems

NASA Technical Reports Server (NTRS)

Ehlert, Steven; Kingery, Aaron; Cooke, William

2016-01-01

Current optical observations of meteors are commonly limited by systematic uncertainties in photometric calibration at the level of approximately 0.5 mag or higher. Future improvements to meteor ablation models, luminous efficiency models, or emission spectra will hinge on new camera systems and techniques that significantly reduce calibration uncertainties and can reliably perform absolute photometric measurements of meteors. In this talk we discuss the algorithms and tests that NASA's Meteoroid Environment Office (MEO) has developed to better calibrate photometric measurements for the existing All-Sky and Wide-Field video camera networks as well as for a newly deployed four-camera system for measuring meteor colors in Johnson-Cousins BV RI filters. In particular we will emphasize how the MEO has been able to address two long-standing concerns with the traditional procedure, discussed in more detail below.

Absolute photometric calibration of IRAC: lessons learned using nine years of flight data

NASA Astrophysics Data System (ADS)

Carey, S.; Ingalls, J.; Hora, J.; Surace, J.; Glaccum, W.; Lowrance, P.; Krick, J.; Cole, D.; Laine, S.; Engelke, C.; Price, S.; Bohlin, R.; Gordon, K.

2012-09-01

Significant improvements in our understanding of various photometric effects have occurred in the more than nine years of flight operations of the Infrared Array Camera aboard the Spitzer Space Telescope. With the accumulation of calibration data, photometric variations that are intrinsic to the instrument can now be mapped with high fidelity. Using all existing data on calibration stars, the array location-dependent photometric correction (the variation of flux with position on the array) and the correction for intra-pixel sensitivity variation (pixel-phase) have been modeled simultaneously. Examination of the warm mission data enabled the characterization of the underlying form of the pixelphase variation in cryogenic data. In addition to the accumulation of calibration data, significant improvements in the calibration of the truth spectra of the calibrators has taken place. Using the work of Engelke et al. (2006), the KIII calibrators have no offset as compared to the AV calibrators, providing a second pillar of the calibration scheme. The current cryogenic calibration is better than 3% in an absolute sense, with most of the uncertainty still in the knowledge of the true flux densities of the primary calibrators. We present the final state of the cryogenic IRAC calibration and a comparison of the IRAC calibration to an independent calibration methodology using the HST primary calibrators.

Calibration of the COBE FIRAS instrument

NASA Technical Reports Server (NTRS)

Fixsen, D. J.; Cheng, E. S.; Cottingham, D. A.; Eplee, R. E., Jr.; Hewagama, T.; Isaacman, R. B.; Jensen, K. A.; Mather, J. C.; Massa, D. L.; Meyer, S. S.

1994-01-01

The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the Cosmic Background Explorer (COBE) satellite was designed to accurately measure the spectrum of the cosmic microwave background radiation (CMBR) in the frequency range 1-95/cm with an angular resolution of 7 deg. We describe the calibration of this instrument, including the method of obtaining calibration data, reduction of data, the instrument model, fitting the model to the calibration data, and application of the resulting model solution to sky observations. The instrument model fits well for calibration data that resemble sky condition. The method of propagating detector noise through the calibration process to yield a covariance matrix of the calibrated sky data is described. The final uncertainties are variable both in frequency and position, but for a typical calibrated sky 2.6 deg square pixel and 0.7/cm spectral element the random detector noise limit is of order of a few times 10(exp -7) ergs/sq cm/s/sr cm for 2-20/cm, and the difference between the sky and the best-fit cosmic blackbody can be measured with a gain uncertainty of less than 3%.

Characterization of the Exradin W1 scintillator for use in radiotherapy.

PubMed

Carrasco, P; Jornet, N; Jordi, O; Lizondo, M; Latorre-Musoll, A; Eudaldo, T; Ruiz, A; Ribas, M

2015-01-01

To evaluate the main characteristics of the Exradin W1 scintillator as a dosimeter and to estimate measurement uncertainties when used in radiotherapy. We studied the calibration procedure, energy and modality dependence, short-term repeatability, dose-response linearity, angular dependence, temperature dependence, time to reach thermal equilibrium, dose-rate dependence, water-equivalent depth of the effective measurement point, and long-term stability. An uncertainty budget was derived for relative and absolute dose measurements in photon and electron beams. Exradin W1 showed a temperature dependence of -0.225% °C(-1). The loss of sensitivity with accumulated dose decreased with use. The sensitivity of Exradin W1 was energy independent for high-energy photon and electron beams. All remaining dependencies of Exradin W1 were around or below 0.5%, leading to an uncertainty budget of about 1%. When a dual channel electrometer with automatic trigger was not used, timing effects became significant, increasing uncertainties by one order of magnitude. The Exradin W1 response is energy independent for high energy x-rays and electron beams, and only one calibration coefficient is needed. A temperature correction factor should be applied to keep uncertainties around 2% for absolute dose measurements and around 1% for relative measurements in high-energy photon and electron beams. The Exradin W1 scintillator is an excellent alternative to detectors such as diodes for relative dose measurements.

On the prospects of cross-calibrating the Cherenkov Telescope Array with an airborne calibration platform

NASA Astrophysics Data System (ADS)

Brown, Anthony M.

2018-01-01

Recent advances in unmanned aerial vehicle (UAV) technology have made UAVs an attractive possibility as an airborne calibration platform for astronomical facilities. This is especially true for arrays of telescopes spread over a large area such as the Cherenkov Telescope Array (CTA). In this paper, the feasibility of using UAVs to calibrate CTA is investigated. Assuming a UAV at 1km altitude above CTA, operating on astronomically clear nights with stratified, low atmospheric dust content, appropriate thermal protection for the calibration light source and an onboard photodiode to monitor its absolute light intensity, inter-calibration of CTA's telescopes of the same size class is found to be achievable with a 6 - 8 % uncertainty. For cross-calibration of different telescope size classes, a systematic uncertainty of 8 - 10 % is found to be achievable. Importantly, equipping the UAV with a multi-wavelength calibration light source affords us the ability to monitor the wavelength-dependent degradation of CTA telescopes' optical system, allowing us to not only maintain this 6 - 10 % uncertainty after the first few years of telescope deployment, but also to accurately account for the effect of multi-wavelength degradation on the cross-calibration of CTA by other techniques, namely with images of air showers and local muons. A UAV-based system thus provides CTA with several independent and complementary methods of cross-calibrating the optical throughput of individual telescopes. Furthermore, housing environmental sensors on the UAV system allows us to not only minimise the systematic uncertainty associated with the atmospheric transmission of the calibration signal, it also allows us to map the dust content above CTA as well as monitor the temperature, humidity and pressure profiles of the first kilometre of atmosphere above CTA with each UAV flight.

Progress in obtaining an absolute calibration of a total deuterium-tritium neutron yield diagnostic based on copper activationa)

NASA Astrophysics Data System (ADS)

Ruiz, C. L.; Chandler, G. A.; Cooper, G. W.; Fehl, D. L.; Hahn, K. D.; Leeper, R. J.; McWatters, B. R.; Nelson, A. J.; Smelser, R. M.; Snow, C. S.; Torres, J. A.

2012-10-01

The 350-keV Cockroft-Walton accelerator at Sandia National laboratory's Ion Beam facility is being used to calibrate absolutely a total DT neutron yield diagnostic based on the 63Cu(n,2n)62Cu(β+) reaction. These investigations have led to first-order uncertainties approaching 5% or better. The experiments employ the associated-particle technique. Deuterons at 175 keV impinge a 2.6 μm thick erbium tritide target producing 14.1 MeV neutrons from the T(d,n)4He reaction. The alpha particles emitted are measured at two angles relative to the beam direction and used to infer the neutron flux on a copper sample. The induced 62Cu activity is then measured and related to the neutron flux. This method is known as the F-factor technique. Description of the associated-particle method, copper sample geometries employed, and the present estimates of the uncertainties to the F-factor obtained are given.

Progress in obtaining an absolute calibration of a total deuterium-tritium neutron yield diagnostic based on copper activation.

PubMed

Ruiz, C L; Chandler, G A; Cooper, G W; Fehl, D L; Hahn, K D; Leeper, R J; McWatters, B R; Nelson, A J; Smelser, R M; Snow, C S; Torres, J A

2012-10-01

The 350-keV Cockroft-Walton accelerator at Sandia National laboratory's Ion Beam facility is being used to calibrate absolutely a total DT neutron yield diagnostic based on the (63)Cu(n,2n)(62)Cu(β+) reaction. These investigations have led to first-order uncertainties approaching 5% or better. The experiments employ the associated-particle technique. Deuterons at 175 keV impinge a 2.6 μm thick erbium tritide target producing 14.1 MeV neutrons from the T(d,n)(4)He reaction. The alpha particles emitted are measured at two angles relative to the beam direction and used to infer the neutron flux on a copper sample. The induced (62)Cu activity is then measured and related to the neutron flux. This method is known as the F-factor technique. Description of the associated-particle method, copper sample geometries employed, and the present estimates of the uncertainties to the F-factor obtained are given.

Absolute Calibration of Optical Satellite Sensors Using Libya 4 Pseudo Invariant Calibration Site

NASA Technical Reports Server (NTRS)

Mishra, Nischal; Helder, Dennis; Angal, Amit; Choi, Jason; Xiong, Xiaoxiong

2014-01-01

The objective of this paper is to report the improvements in an empirical absolute calibration model developed at South Dakota State University using Libya 4 (+28.55 deg, +23.39 deg) pseudo invariant calibration site (PICS). The approach was based on use of the Terra MODIS as the radiometer to develop an absolute calibration model for the spectral channels covered by this instrument from visible to shortwave infrared. Earth Observing One (EO-1) Hyperion, with a spectral resolution of 10 nm, was used to extend the model to cover visible and near-infrared regions. A simple Bidirectional Reflectance Distribution function (BRDF) model was generated using Terra Moderate Resolution Imaging Spectroradiometer (MODIS) observations over Libya 4 and the resulting model was validated with nadir data acquired from satellite sensors such as Aqua MODIS and Landsat 7 (L7) Enhanced Thematic Mapper (ETM+). The improvements in the absolute calibration model to account for the BRDF due to off-nadir measurements and annual variations in the atmosphere are summarized. BRDF models due to off-nadir viewing angles have been derived using the measurements from EO-1 Hyperion. In addition to L7 ETM+, measurements from other sensors such as Aqua MODIS, UK-2 Disaster Monitoring Constellation (DMC), ENVISAT Medium Resolution Imaging Spectrometer (MERIS) and Operational Land Imager (OLI) onboard Landsat 8 (L8), which was launched in February 2013, were employed to validate the model. These satellite sensors differ in terms of the width of their spectral bandpasses, overpass time, off-nadir-viewing capabilities, spatial resolution and temporal revisit time, etc. The results demonstrate that the proposed empirical calibration model has accuracy of the order of 3% with an uncertainty of about 2% for the sensors used in the study.

The absolute amplitude calibration of the SEASAT synthetic aperture radar - An intercomparison with other L-band radar systems

NASA Technical Reports Server (NTRS)

Held, D.; Werner, C.; Wall, S.

1983-01-01

The absolute amplitude calibration of the spaceborne Seasat SAR data set is presented based on previous relative calibration studies. A scale factor making it possible to express the perceived radar brightness of a scene in units of sigma-zero is established. The system components are analyzed for error contribution, and the calibration techniques are introduced for each stage. These include: A/D converter saturation tests; prevention of clipping in the processing step; and converting the digital image into the units of received power. Experimental verification was performed by screening and processing the data of the lava flow surrounding the Pisgah Crater in Southern California, for which previous C-130 airborne scatterometer data were available. The average backscatter difference between the two data sets is estimated to be 2 dB in the brighter, and 4 dB in the dimmer regions. For the SAR a calculated uncertainty of 3 dB is expected.

Synthetic isotope mixtures for the calibration of isotope amount ratio measurements of carbon

NASA Astrophysics Data System (ADS)

Russe, K.; Valkiers, S.; Taylor, P. D. P.

2004-07-01

Synthetic isotope mixtures for the calibration of carbon isotope amount ratio measurements have been prepared by mixing carbon tetrafluoride highly enriched in 13C with carbon tetrafluoride depleted in 13C. Mixing procedures based on volumetry and gravimetry are described. The mixtures served as primary measurement standards for the calibration of isotope amount ratio measurements of the Isotopic Reference Materials PEF1, NBS22 and USGS24. Thus SI-traceable measurements of absolute carbon isotope amount ratios have been performed for the first time without any hypothesis needed for a correction of oxygen isotope abundances, such as is the case for measurements on carbon dioxide. As a result, "absolute" carbon isotope amount ratios determined via carbon tetrafluoride have smaller uncertainties than those published for carbon dioxide. From the measurements of the Reference Materials concerned, the absolute carbon isotope amount ratio of Vienna Pee Dee Belemnite (VPDB)--the hypothetical material upon which the scale for relative carbon isotope ratio measurements is based--was calculated to be R13(VPDB) = (11 101 +/- 16) × 10-6.

The NIST Detector-Based Luminous Intensity Scale

PubMed Central

Cromer, C. L.; Eppeldauer, G.; Hardis, J. E.; Larason, T. C.; Ohno, Y.; Parr, A. C.

1996-01-01

The Système International des Unités (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factor k = 2, and thus a 2 standard deviation estimate) of 0.46 %, almost a factor-of-two improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the spectral luminous efficiency function for photopic vision. The wide dynamic range of the photometers aid in their calibration. The components of the photometers were carefully measured and selected to reduce the sources of error and to provide baseline data for aging studies. Periodic remeasurement of the photometers indicate that a yearly recalibration is required. The design, characterization, calibration, evaluation, and application of the photometers are discussed. PMID:27805119

Calibrated work function mapping by Kelvin probe force microscopy

NASA Astrophysics Data System (ADS)

Fernández Garrillo, Pablo A.; Grévin, Benjamin; Chevalier, Nicolas; Borowik, Łukasz

2018-04-01

We propose and demonstrate the implementation of an alternative work function tip calibration procedure for Kelvin probe force microscopy under ultrahigh vacuum, using monocrystalline metallic materials with known crystallographic orientation as reference samples, instead of the often used highly oriented pyrolytic graphite calibration sample. The implementation of this protocol allows the acquisition of absolute and reproducible work function values, with an improved uncertainty with respect to unprepared highly oriented pyrolytic graphite-based protocols. The developed protocol allows the local investigation of absolute work function values over nanostructured samples and can be implemented in electronic structures and devices characterization as demonstrated over a nanostructured semiconductor sample presenting Al0.7Ga0.3As and GaAs layers with variable thickness. Additionally, using our protocol we find that the work function of annealed highly oriented pyrolytic graphite is equal to 4.6 ± 0.03 eV.

Absolute Radiometric Calibration of Narrow-Swath Imaging Sensors with Reference to Non-Coincident Wide-Swath Sensors

NASA Technical Reports Server (NTRS)

McCorkel, Joel; Thome, Kurtis; Lockwood, Ronald

2012-01-01

An inter-calibration method is developed to provide absolute radiometric calibration of narrow-swath imaging sensors with reference to non-coincident wide-swath sensors. The method predicts at-sensor radiance using non-coincident imagery from the reference sensor and knowledge of spectral reflectance of the test site. The imagery of the reference sensor is restricted to acquisitions that provide similar view and solar illumination geometry to reduce uncertainties due to directional reflectance effects. Spectral reflectance of the test site is found with a simple iterative radiative transfer method using radiance values of a well-understood wide-swath sensor and spectral shape information based on historical ground-based measurements. At-sensor radiance is calculated for the narrow-swath sensor using this spectral reflectance and atmospheric parameters that are also based on historical in situ measurements. Results of the inter-calibration method show agreement on the 2 5 percent level in most spectral regions with the vicarious calibration technique relying on coincident ground-based measurements referred to as the reflectance-based approach. While the variability of the inter-calibration method based on non-coincident image pairs is significantly larger, results are consistent with techniques relying on in situ measurements. The method is also insensitive to spectral differences between the sensors by transferring to surface spectral reflectance prior to prediction of at-sensor radiance. The utility of this inter-calibration method is made clear by its flexibility to utilize image pairings with acquisition dates differing in excess of 30 days allowing frequent absolute calibration comparisons between wide- and narrow-swath sensors.

Uncertainty Assessment of the SeaWiFS On-Orbit Calibration

NASA Technical Reports Server (NTRS)

Eplee, Robert E., Jr.; Meister, Gerhard; Patt, Frederick S.; Franz, Bryan A.; McClain, Charles R.

2011-01-01

Ocean color climate data records require water-leaving radiances with 5% absolute and 1% relative accuracies as input. Because of the amplification of any sensor calibration errors by the atmospheric correction, the 1% relative accuracy requirement translates into a 0.1% long-term radiometric stability requirement for top-of-the atmosphere radiances. The rigorous on-orbit calibration program developed and implemented for SeaWiFS by the NASA Ocean Biology Processing Group (OBPG) Calibration and Validation Team (CVT) has allowed the CVT to maintain the stability of the radiometric calibration of SeaWiFS at 0.13% or better over the mission. The uncertainties in the resulting calibrated top-of-the-atmosphere (TOA) radiances can be addressed in terms of accuracy (biases in the measurements), precision (scatter in the measurements), and stability (repeatability of the measurements). The calibration biases of lunar observations relative to the USGS RObotic Lunar Observatory (ROLO) photometric model of the Moon are 2-3%. The biases from the vicarious calibration against the Marine Optical Buoy (MOBY) are 1-2%. The precision of the calibration derived from the solar calibration signal-tonoise ratios are 0.16%, from the lunar residuals are 0.13%, and from the vicarious gains are 0.10%. The long-term stability of the TOA radiances, derived from the lunar time series, is 0.13%. The stability of the vicariouslycalibrated TOA radiances, incorporating the uncertainties in the MOBY measurements and the atmospheric correction, is 0.30%. These results allow the OBPG to produce climate data records from the SeaWiFS ocean color data.

Calibration of IR test chambers with the missile defense transfer radiometer

NASA Astrophysics Data System (ADS)

Kaplan, Simon G.; Woods, Solomon I.; Carter, Adriaan C.; Jung, Timothy M.

2013-05-01

The Missile Defense Transfer Radiometer (MDXR) is designed to calibrate infrared collimated and flood sources over the fW/cm2 to W/cm2 power range from 3 μm to 28μ m in wavelength. The MDXR operates in three different modes: as a filter radiometer, a Fourier-transform spectrometer (FTS)-based spectroradiometer, and as an absolute cryogenic radiometer (ACR). Since 2010, the MDXR has made measurements of the collimated infrared irradiance at the output port of seven different infrared test chambers at several facilities. We present a selection of results from these calibration efforts compared to signal predictions from the respective chamber models for the three different MDXR calibration modes. We also compare the results to previous measurements made of the same chambers with a legacy transfer radiometer, the NIST BXR. In general, the results are found to agree within their combined uncertainties, with the MDXR having 30 % lower uncertainty and greater spectral coverage.

Absolute Calibration of Si iRMs used for Si Paleo-nutrient proxies

NASA Astrophysics Data System (ADS)

Vocke, Robert; Rabb, Savelas

2016-04-01

The Avogadro Project is an ongoing international effort, coordinated by the International Bureau of Weights and Measures (BIPM) and the International Avogadro Coordination (IAC) to redefine the SI unit mole in terms of the Avogadro constant and the SI unit kg in terms of the Planck constant. One of the outgrowths of this effort has been the development of a novel, precise and highly accurate method to measure calibrated (absolute) isotopic ratios that are traceable to the SI (Vocke et al., 2014 Metrologia 51, 361, Azuma et al., 2015 Metrologia 52 360). This approach has also been able to produce absolute Si isotope ratio data with lower levels of uncertainty when compared to the traditional "Atomic Weights" method of absolute isotope ratio measurement. Silicon isotope variations (reported as delta(Si30)and delta(Si29)) in silicic acid dissolved in ocean waters, in biogenic silica and in diatoms are extremely informative paleo-nutrient proxies. The utility and comparability of such measurements however depends on calibration with artifact isotopic Reference Materials (iRMs). We will be reporting new measurements on the iRMs NBS-28 (RM 8546 - Silica Sand), Diatomite, Big Batch and SRM 990 using the Avogadro measurement approach, comparing them with prior assessments of these iRMs.

An interlaboratory comparison study on the measurement of elements in PM10

NASA Astrophysics Data System (ADS)

Yatkin, Sinan; Belis, Claudio A.; Gerboles, Michel; Calzolai, Giulia; Lucarelli, Franco; Cavalli, Fabrizia; Trzepla, Krystyna

2016-01-01

An inter-laboratory comparison study was conducted to measure elemental loadings on PM10 samples, collected in Ispra, a regional background/rural site in Italy, using three different XRF (X-ray Fluorescence) methods, namely Epsilon 5 by linear calibration, Quant'X by the standardless analysis, and PIXE (Particle Induced X-ray Emission) with linear calibration. A subset of samples was also analyzed by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Several metrics including method detection limits (MDLs), precision, bias from a NIST standard reference material (SRM 2783) quoted values, relative absolute difference, orthogonal regression and the ratio of the absolute difference between the methods to claimed uncertainty were used to compare the laboratories. The MDLs were found to be comparable for many elements. Precision estimates were less than 10% for the majority of the elements. Absolute biases from SRM 2783 remained less than 20% for the majority of certified elements. The regression results of PM10 samples showed that the three XRF laboratories measured very similar mass loadings for S, K, Ti, Mn, Fe, Cu, Br, Sr and Pb with slopes within 20% of unity. The ICP-MS results confirmed the agreement and discrepancies between XRF laboratories for Al, K, Ca, Ti, V, Cu, Sr and Pb. The ICP-MS results are inconsistent with the XRF laboratories for Fe and Zn. The absolute differences between the XRF laboratories generally remained within their claimed uncertainties, showing a pattern generally consistent with the orthogonal regression results.

A reference tristimulus colorimeter

NASA Astrophysics Data System (ADS)

Eppeldauer, George P.

2002-06-01

A reference tristimulus colorimeter has been developed at NIST with a transmission-type silicon trap detector (1) and four temperature-controlled filter packages to realize the Commission Internationale de l'Eclairage (CIE) x(λ), y(λ) and z(λ) color matching functions (2). Instead of lamp standards, high accuracy detector standards are used for the colorimeter calibration. A detector-based calibration procedure is being suggested for tristimulus colorimeters wehre the absolute spectral responsivity of the tristimulus channels is determined. Then, color (spectral) correct and peak (amplitude) normalization are applied to minimize uncertainties caused by the imperfect realizations of the CIE functions. As a result of the corrections, the chromaticity coordinates of stable light sources with different spectral power distributions can be measured with uncertainties less than 0.0005 (k=1).

Influence of three common calibration metrics on the diagnosis of climate change impacts on water resources

NASA Astrophysics Data System (ADS)

Seiller, G.; Roy, R.; Anctil, F.

2017-04-01

Uncertainties associated to the evaluation of the impacts of climate change on water resources are broad, from multiple sources, and lead to diagnoses sometimes difficult to interpret. Quantification of these uncertainties is a key element to yield confidence in the analyses and to provide water managers with valuable information. This work specifically evaluates the influence of hydrological modeling calibration metrics on future water resources projections, on thirty-seven watersheds in the Province of Québec, Canada. Twelve lumped hydrologic models, representing a wide range of operational options, are calibrated with three common objective functions derived from the Nash-Sutcliffe efficiency. The hydrologic models are forced with climate simulations corresponding to two RCP, twenty-nine GCM from CMIP5 (Coupled Model Intercomparison Project phase 5) and two post-treatment techniques, leading to future projections in the 2041-2070 period. Results show that the diagnosis of the impacts of climate change on water resources are quite affected by the hydrologic models selection and calibration metrics. Indeed, for the four selected hydrological indicators, dedicated to water management, parameters from the three objective functions can provide different interpretations in terms of absolute and relative changes, as well as projected changes direction and climatic ensemble consensus. The GR4J model and a multimodel approach offer the best modeling options, based on calibration performance and robustness. Overall, these results illustrate the need to provide water managers with detailed information on relative changes analysis, but also absolute change values, especially for hydrological indicators acting as security policy thresholds.

SATELLITE-MOUNTED LIGHT SOURCES AS PHOTOMETRIC CALIBRATION STANDARDS FOR GROUND-BASED TELESCOPES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albert, J., E-mail: jalbert@uvic.ca

2012-01-15

A significant and growing portion of systematic error on a number of fundamental parameters in astrophysics and cosmology is due to uncertainties from absolute photometric and flux standards. A path toward achieving major reduction in such uncertainties may be provided by satellite-mounted light sources, resulting in improvement in the ability to precisely characterize atmospheric extinction, and thus helping to usher in the coming generation of precision results in astronomy. Using a campaign of observations of the 532 nm pulsed laser aboard the CALIPSO satellite, collected using a portable network of cameras and photodiodes, we obtain initial measurements of atmospheric extinction,more » which can apparently be greatly improved by further data of this type. For a future satellite-mounted precision light source, a high-altitude balloon platform under development (together with colleagues) can provide testing as well as observational data for calibration of atmospheric uncertainties.« less

Traceable X,Y self-calibration at single nm level of an optical microscope used for coherence scanning interferometry

NASA Astrophysics Data System (ADS)

Ekberg, Peter; Mattsson, Lars

2018-03-01

Coherence scanning interferometry used in optical profilers are typically good for Z-calibration at nm-levels, but the X,Y accuracy is often left without further notice than typical resolution limits of the optics, i.e. of the order of ~1 µm. For the calibration of metrology tools we rely on traceable artefacts, e.g. gauge blocks for traditional coordinate measurement machines, and lithographically mask made artefacts for microscope calibrations. In situations where the repeatability and accuracy of the measurement tool is much better than the uncertainty of the traceable artefact, we are bound to specify the uncertainty based on the calibration artefact rather than on the measurement tool. This is a big drawback as the specified uncertainty of a calibrated measurement may shrink the available manufacturing tolerance. To improve the uncertainty in X,Y we can use self-calibration. Then, we do not need to know anything more than that the artefact contains a pattern with some nominal grid. This also gives the opportunity to manufacture the artefact in-house, rather than buying a calibrated and expensive artefact. The self-calibration approach we present here is based on an iteration algorithm, rather than the traditional mathematical inversion, and it leads to much more relaxed constrains on the input measurements. In this paper we show how the X,Y errors, primarily optical distortions, within the field of view (FOV) of an optical coherence scanning interferometry microscope, can be reduced with a large factor. By self-calibration we achieve an X,Y consistency in the 175  ×  175 µm2 FOV of ~2.3 nm (1σ) using the 50×  objective. Besides the calibrated coordinate X,Y system of the microscope we also receive, as a bonus, the absolute positions of the pattern in the artefact with a combined uncertainty of 6 nm (1σ) by relying on a traceable 1D linear measurement of a twin artefact at NIST.

Use of Inverse-Modeling Methods to Improve Ground-Water-Model Calibration and Evaluate Model-Prediction Uncertainty, Camp Edwards, Cape Cod, Massachusetts

USGS Publications Warehouse

Walter, Donald A.; LeBlanc, Denis R.

2008-01-01

Historical weapons testing and disposal activities at Camp Edwards, which is located on the Massachusetts Military Reservation, western Cape Cod, have resulted in the release of contaminants into an underlying sand and gravel aquifer that is the sole source of potable water to surrounding communities. Ground-water models have been used at the site to simulate advective transport in the aquifer in support of field investigations. Reasonable models developed by different groups and calibrated by trial and error often yield different predictions of advective transport, and the predictions lack quantitative measures of uncertainty. A recently (2004) developed regional model of western Cape Cod, modified to include the sensitivity and parameter-estimation capabilities of MODFLOW-2000, was used in this report to evaluate the utility of inverse (statistical) methods to (1) improve model calibration and (2) assess model-prediction uncertainty. Simulated heads and flows were most sensitive to recharge and to the horizontal hydraulic conductivity of the Buzzards Bay and Sandwich Moraines and the Buzzards Bay and northern parts of the Mashpee outwash plains. Conversely, simulated heads and flows were much less sensitive to vertical hydraulic conductivity. Parameter estimation (inverse calibration) improved the match to observed heads and flows; the absolute mean residual for heads improved by 0.32 feet and the absolute mean residual for streamflows improved by about 0.2 cubic feet per second. Advective-transport predictions in Camp Edwards generally were most sensitive to the parameters with the highest precision (lowest coefficients of variation), indicating that the numerical model is adequate for evaluating prediction uncertainties in and around Camp Edwards. The incorporation of an advective-transport observation, representing the leading edge of a contaminant plume that had been difficult to match by using trial-and-error calibration, improved the match between an observed and simulated plume path; however, a modified representation of local geology was needed to simultaneously maintain a reasonable calibration to heads and flows and to the plume path. Advective-transport uncertainties were expressed as about 68-, 95-, and 99-percent confidence intervals on three dimensional simulated particle positions. The confidence intervals can be graphically represented as ellipses around individual particle positions in the X-Y (geographic) plane and in the X-Z or Y-Z (vertical) planes. The merging of individual ellipses allows uncertainties on forward particle tracks to be displayed in map or cross-sectional view as a cone of uncertainty around a simulated particle path; uncertainties on reverse particle-track endpoints - representing simulated recharge locations - can be geographically displayed as areas at the water table around the discrete particle endpoints. This information gives decisionmakers insight into the level of confidence they can have in particle-tracking results and can assist them in the efficient use of available field resources.

Radiometric calibration of the Landsat MSS sensor series

USGS Publications Warehouse

Helder, Dennis L.; Karki, Sadhana; Bhatt, Rajendra; Micijevik, Esad; Aaron, David; Jasinski, Benjamin

2012-01-01

Multispectral remote sensing of the Earth using Landsat sensors was ushered on July 23, 1972, with the launch of Landsat-1. Following that success, four more Landsat satellites were launched, and each of these carried the Multispectral Scanner System (MSS). These five sensors provided the only consistent multispectral space-based imagery of the Earth's surface from 1972 to 1982. This work focuses on developing both a consistent and absolute radiometric calibration of this sensor system. Cross-calibration of the MSS was performed through the use of pseudoinvariant calibration sites (PICSs). Since these sites have been shown to be stable for long periods of time, changes in MSS observations of these sites were attributed to changes in the sensors themselves. In addition, simultaneous data collections were available for some MSS sensor pairs, and these were also used for cross-calibration. Results indicated substantial differences existed between instruments, up to 16%, and these were reduced to 5% or less across all MSS sensors and bands. Lastly, this paper takes the calibration through the final step and places the MSS sensors on an absolute radiometric scale. The methodology used to achieve this was based on simultaneous data collections by the Landsat-5 MSS and Thematic Mapper (TM) instruments. Through analysis of image data from a PICS location and through compensating for the spectral differences between the two instruments, the Landsat-5 MSS sensor was placed on an absolute radiometric scale based on the Landsat-5 TM sensor. Uncertainties associated with this calibration are considered to be less than 5%.

Accounting for sensor calibration, data validation, measurement and sampling uncertainties in monitoring urban drainage systems.

PubMed

Bertrand-Krajewski, J L; Bardin, J P; Mourad, M; Béranger, Y

2003-01-01

Assessing the functioning and the performance of urban drainage systems on both rainfall event and yearly time scales is usually based on online measurements of flow rates and on samples of influent effluent for some rainfall events per year. In order to draw pertinent scientific and operational conclusions from the measurement results, it is absolutely necessary to use appropriate methods and techniques in order to i) calibrate sensors and analytical methods, ii) validate raw data, iii) evaluate measurement uncertainties, iv) evaluate the number of rainfall events to sample per year in order to determine performance indicator with a given uncertainty. Based an previous work, the paper gives a synthetic review of required and techniques, and illustrates their application to storage and settling tanks. Experiments show that, controlled and careful experimental conditions, relative uncertainties are about 20% for flow rates in sewer pipes, 6-10% for volumes, 25-35% for TSS concentrations and loads, and 18-276% for TSS removal rates. In order to evaluate the annual pollutant interception efficiency of storage and settling tanks with a given uncertainty, efforts should first be devoted to decrease the sampling uncertainty by increasing the number of sampled events.

Frequency comb calibrated frequency-sweeping interferometry for absolute group refractive index measurement of air.

PubMed

Yang, Lijun; Wu, Xuejian; Wei, Haoyun; Li, Yan

2017-04-10

The absolute group refractive index of air at 194061.02 GHz is measured in real time using frequency-sweeping interferometry calibrated by an optical frequency comb. The group refractive index of air is calculated from the calibration peaks of the laser frequency variation and the interference signal of the two beams passing through the inner and outer regions of a vacuum cell when the frequency of a tunable external cavity diode laser is scanned. We continuously measure the refractive index of air for 2 h, which shows that the difference between measured results and Ciddor's equation is less than 9.6×10^-8, and the standard deviation of that difference is 5.9×10^-8. The relative uncertainty of the measured refractive index of air is estimated to be 8.6×10^-8. The data update rate is 0.2 Hz, making it applicable under conditions in which air refractive index fluctuates fast.

Development of high power UV irradiance meter calibration device

NASA Astrophysics Data System (ADS)

Xia, Ming; Gao, Jianqiang; Yin, Dejin; Li, Tiecheng

2016-09-01

With the rapid development of China's economy, many industries have more requirements for UV light applications, such as machinery manufacturing, aircraft manufacturing using high power UV light for detection, IT industry using high power UV light for curing component assembly, building materials, ink, paint and other industries using high power UV light for material aging test etc. In these industries, there are many measuring instruments for high power UV irradiance which are need to traceability. But these instruments are mostly imported instruments, these imported UV radiation meter are large range, wide wavelength range and high accuracy. They have exceeded our existing calibration capability. Expand the measuring range and improve the measurement accuracy of UV irradiance calibration device is a pressing matter of the moment. The newly developed high power UV irradiance calibration device is mainly composed of high power UV light, UV filter, condenser, UV light guide, optical alignment system, standard cavity absolute radiometer. The calibration device is using optical alignment system to form uniform light radiation field. The standard is standard cavity absolute radiometer, which can through the electrical substitution method, by means of adjusting and measuring the applied DC electric power at the receiver on a heating wire, which is equivalent to the thermo-electromotive force generated by the light radiation power, to achieve absolute optical radiation measurement. This method is the commonly used effective method for accurate measurement of light irradiation. The measuring range of calibration device is (0.2 200) mW/cm2, and the uncertainty of measurement results can reached 2.5% (k=2).

In-Situ Transfer Standard and Coincident-View Intercomparisons for Sensor Cross-Calibration

NASA Technical Reports Server (NTRS)

Thome, Kurt; McCorkel, Joel; Czapla-Myers, Jeff

2013-01-01

There exist numerous methods for accomplishing on-orbit calibration. Methods include the reflectance-based approach relying on measurements of surface and atmospheric properties at the time of a sensor overpass as well as invariant scene approaches relying on knowledge of the temporal characteristics of the site. The current work examines typical cross-calibration methods and discusses the expected uncertainties of the methods. Data from the Advanced Land Imager (ALI), Advanced Spaceborne Thermal Emission and Reflection and Radiometer (ASTER), Enhanced Thematic Mapper Plus (ETM+), Moderate Resolution Imaging Spectroradiometer (MODIS), and Thematic Mapper (TM) are used to demonstrate the limits of relative sensor-to-sensor calibration as applied to current sensors while Landsat-5 TM and Landsat-7 ETM+ are used to evaluate the limits of in situ site characterizations for SI-traceable cross calibration. The current work examines the difficulties in trending of results from cross-calibration approaches taking into account sampling issues, site-to-site variability, and accuracy of the method. Special attention is given to the differences caused in the cross-comparison of sensors in radiance space as opposed to reflectance space. The results show that cross calibrations with absolute uncertainties lesser than 1.5 percent (1 sigma) are currently achievable even for sensors without coincident views.

Instrumentation and First Results of the Reflected Solar Demonstration System for the Climate Absolute Radiance and Refractivity Observatory

NASA Technical Reports Server (NTRS)

McCorkel, Joel; Thome, Kurtis; Hair, Jason; McAndrew, Brendan; Jennings, Don; Rabin, Douglas; Daw, Adrian; Lundsford, Allen

2012-01-01

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission key goals include enabling observation of high accuracy long-term climate change trends, use of these observations to test and improve climate forecasts, and calibration of operational and research sensors. The spaceborne instrument suites include a reflected solar spectroradiometer, emitted infrared spectroradiometer, and radio occultation receivers. The requirement for the RS instrument is that derived reflectance must be traceable to Sl standards with an absolute uncertainty of <0.3% and the error budget that achieves this requirement is described in previo1L5 work. This work describes the Solar/Lunar Absolute Reflectance Imaging Spectroradiometer (SOLARIS), a calibration demonstration system for RS instrument, and presents initial calibration and characterization methods and results. SOLARIS is an Offner spectrometer with two separate focal planes each with its own entrance aperture and grating covering spectral ranges of 320-640, 600-2300 nm over a full field-of-view of 10 degrees with 0.27 milliradian sampling. Results from laboratory measurements including use of integrating spheres, transfer radiometers and spectral standards combined with field-based solar and lunar acquisitions are presented. These results will be used to assess the accuracy and repeatability of the radiometric and spectral characteristics of SOLARIS, which will be presented against the sensor-level requirements addressed in the CLARREO RS instrument error budget.

Inflight Calibration of the Lunar Reconnaissance Orbiter Camera Wide Angle Camera

NASA Astrophysics Data System (ADS)

Mahanti, P.; Humm, D. C.; Robinson, M. S.; Boyd, A. K.; Stelling, R.; Sato, H.; Denevi, B. W.; Braden, S. E.; Bowman-Cisneros, E.; Brylow, S. M.; Tschimmel, M.

2016-04-01

The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) has acquired more than 250,000 images of the illuminated lunar surface and over 190,000 observations of space and non-illuminated Moon since 1 January 2010. These images, along with images from the Narrow Angle Camera (NAC) and other Lunar Reconnaissance Orbiter instrument datasets are enabling new discoveries about the morphology, composition, and geologic/geochemical evolution of the Moon. Characterizing the inflight WAC system performance is crucial to scientific and exploration results. Pre-launch calibration of the WAC provided a baseline characterization that was critical for early targeting and analysis. Here we present an analysis of WAC performance from the inflight data. In the course of our analysis we compare and contrast with the pre-launch performance wherever possible and quantify the uncertainty related to various components of the calibration process. We document the absolute and relative radiometric calibration, point spread function, and scattered light sources and provide estimates of sources of uncertainty for spectral reflectance measurements of the Moon across a range of imaging conditions.

The fossilized birth–death process for coherent calibration of divergence-time estimates

PubMed Central

Heath, Tracy A.; Huelsenbeck, John P.; Stadler, Tanja

2014-01-01

Time-calibrated species phylogenies are critical for addressing a wide range of questions in evolutionary biology, such as those that elucidate historical biogeography or uncover patterns of coevolution and diversification. Because molecular sequence data are not informative on absolute time, external data—most commonly, fossil age estimates—are required to calibrate estimates of species divergence dates. For Bayesian divergence time methods, the common practice for calibration using fossil information involves placing arbitrarily chosen parametric distributions on internal nodes, often disregarding most of the information in the fossil record. We introduce the “fossilized birth–death” (FBD) process—a model for calibrating divergence time estimates in a Bayesian framework, explicitly acknowledging that extant species and fossils are part of the same macroevolutionary process. Under this model, absolute node age estimates are calibrated by a single diversification model and arbitrary calibration densities are not necessary. Moreover, the FBD model allows for inclusion of all available fossils. We performed analyses of simulated data and show that node age estimation under the FBD model results in robust and accurate estimates of species divergence times with realistic measures of statistical uncertainty, overcoming major limitations of standard divergence time estimation methods. We used this model to estimate the speciation times for a dataset composed of all living bears, indicating that the genus Ursus diversified in the Late Miocene to Middle Pliocene. PMID:25009181

Calibration strategies for the Cherenkov Telescope Array

NASA Astrophysics Data System (ADS)

Gaug, Markus; Berge, David; Daniel, Michael; Doro, Michele; Förster, Andreas; Hofmann, Werner; Maccarone, Maria C.; Parsons, Dan; de los Reyes Lopez, Raquel; van Eldik, Christopher

2014-08-01

The Central Calibration Facilities workpackage of the Cherenkov Telescope Array (CTA) observatory for very high energy gamma ray astronomy defines the overall calibration strategy of the array, develops dedicated hardware and software for the overall array calibration and coordinates the calibration efforts of the different telescopes. The latter include LED-based light pulsers, and various methods and instruments to achieve a calibration of the overall optical throughput. On the array level, methods for the inter-telescope calibration and the absolute calibration of the entire observatory are being developed. Additionally, the atmosphere above the telescopes, used as a calorimeter, will be monitored constantly with state-of-the-art instruments to obtain a full molecular and aerosol profile up to the stratosphere. The aim is to provide a maximal uncertainty of 10% on the reconstructed energy-scale, obtained through various independent methods. Different types of LIDAR in combination with all-sky-cameras will provide the observatory with an online, intelligent scheduling system, which, if the sky is partially covered by clouds, gives preference to sources observable under good atmospheric conditions. Wide-field optical telescopes and Raman Lidars will provide online information about the height-resolved atmospheric extinction, throughout the field-of-view of the cameras, allowing for the correction of the reconstructed energy of each gamma-ray event. The aim is to maximize the duty cycle of the observatory, in terms of usable data, while reducing the dead time introduced by calibration activities to an absolute minimum.

Empirical photometric calibration of the Gaia red clump: Colours, effective temperature, and absolute magnitude

NASA Astrophysics Data System (ADS)

Ruiz-Dern, L.; Babusiaux, C.; Arenou, F.; Turon, C.; Lallement, R.

2018-01-01

Context. Gaia Data Release 1 allows the recalibration of standard candles such as the red clump stars. To use those stars, they first need to be accurately characterised. In particular, colours are needed to derive interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. Aims: The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia red clump stars of the solar neighbourhood through colour-colour, effective temperature-colour, and absolute magnitude-colour relations from the Gaia, Johnson, 2MASS, HIPPARCOS, Tycho-2, APASS-SLOAN, and WISE photometric systems, and the APOGEE DR13 spectroscopic temperatures. Methods: We used a 3D extinction map to select low reddening red giants. To calibrate the colour-colour and the effective temperature-colour relations, we developed a MCMC method that accounts for all variable uncertainties and selects the best model for each photometric relation. We estimated the red clump absolute magnitude through the mode of a kernel-based distribution function. Results: We provide 20 colour versus G-Ks relations and the first Teff versus G-Ks calibration. We obtained the red clump absolute magnitudes for 15 photometric bands with, in particular, MKs = (-1.606 ± 0.009) and MG = (0.495 ± 0.009) + (1.121 ± 0.128)(G-Ks-2.1). We present a dereddened Gaia-TGAS HR diagram and use the calibrations to compare its red clump and its red giant branch bump with Padova isochrones. Full Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A116

Offsets in fiber-coupled diode laser hygrometers caused by parasitic absorption effects and their prevention

NASA Astrophysics Data System (ADS)

Buchholz, B.; Ebert, V.

2014-07-01

Large systematic errors in absorption spectrometers (AS) can be caused by ‘parasitic’ optical absorption (parA) outside the measurement region. In particular, calibration-free direct tunable diode laser AS (dTDLAS) can take advantage of an effective parA-compensation to provide correct absolute values. However, parA also negatively affects calibrated AS in calibration frequency and stability. A common strategy to suppress parA in TDLAS systems is to fiber-couple the light source and even the detector. However, this can be a critical approach if the TDL spectrometer is validated/calibrated under laboratory conditions in ambient humidity and used afterwards in much drier and variable conditions, for example in aircrafts. This paper shows that, e.g., ‘hermetically sealed’ butterfly packages, despite fiber coupling, can possess fixed as well as variable parA sections. Two new methods for absolute parA-quantification in dTDLAS were developed, including a novel, fiber-coupled, parA-free I0-detector for permanent parA-monitoring. Their dependences on ambient humidity/pressure and temporal behavior were studied. For the example of a 1.4 µm dTDLAS hygrometer SEALDH-II with a commercial DFB-laser module and an extractive 1.5 m path cell, we quantified the parA-induced signal offsets and their dependence on cell pressure. The conversion of parA-uncertainty into H2O signal uncertainty was studied and an updated uncertainty budget including parA-uncertainty was derived. The studies showed that parA in commercial laser modules can cause substantial, systematic concentration offsets of ≈25 ppmv fixed and ≈100 ppmv variable offsets for one meter absorption path. Applying our parA-quantification techniques these offsets could be compensated by a factor of 20 to an overall offset uncertainty of 4.5 ppmv m-1. Finally, we developed an innovative, integrated, µ-pumped closed-loop air drying unit for the parA minimization and temporal stabilization in airborne laser hygrometers. This compact and light weight dryer eliminates the variable parA by ambient humidity in less than 120 min and is well suited for airborne applications as it fulfils all airborne operation and safety restrictions.

Development of a low-level 39Ar calibration standard – Analysis by absolute gas counting measurements augmented with simulation

DOE PAGES

Williams, Richard M.; Aalseth, C. E.; Brandenberger, J. M.; ...

2017-02-17

Here, this paper describes the generation of 39Ar, via reactor irradiation of potassium carbonate, followed by quantitative analysis (length-compensated proportional counting) to yield two calibration standards that are respectively 50 and 3 times atmospheric background levels. Measurements were performed in Pacific Northwest National Laboratory's shallow underground counting laboratory studying the effect of gas density on beta-transport; these results are compared with simulation. The total expanded uncertainty of the specific activity for the ~50 × 39Ar in P10 standard is 3.6% (k=2).

Development of a low-level 39Ar calibration standard – Analysis by absolute gas counting measurements augmented with simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Richard M.; Aalseth, C. E.; Brandenberger, J. M.

Here, this paper describes the generation of 39Ar, via reactor irradiation of potassium carbonate, followed by quantitative analysis (length-compensated proportional counting) to yield two calibration standards that are respectively 50 and 3 times atmospheric background levels. Measurements were performed in Pacific Northwest National Laboratory's shallow underground counting laboratory studying the effect of gas density on beta-transport; these results are compared with simulation. The total expanded uncertainty of the specific activity for the ~50 × 39Ar in P10 standard is 3.6% (k=2).

Characterization of air-coupled ultrasound transducers in the frequency range 40 kHz-2 mHz using light diffraction tomography.

PubMed

Almqvist, M; Holm, A; Persson, H W; Lindström, K

2000-01-01

The aim of this work was to show the applicability of light diffraction tomography on airborne ultrasound in the frequency range 40 kHz-2 MHz. Seven different air-coupled transducers were measured to show the method's performance regarding linearity, absolute pressure measurements, phase measurements, frequency response, S/N ratio and spatial resolution. A calibrated microphone and the pulse-echo method were used to evaluate the results. The absolute measurements agreed within the calibrated microphone's uncertainty range. Pulse waveforms and corresponding FFT diagrams show the method's higher bandwidth compared with the microphone. Further, the method offers non-perturbing measurements with high spatial resolution, which was especially advantageous for measurements close to the transducer surfaces. The S/N ratio was higher than or in the same range as that of the two comparison methods.

On the absolute calibration of SO2 cameras

USGS Publications Warehouse

Lübcke, Peter; Bobrowski, Nicole; Illing, Sebastian; Kern, Christoph; Alvarez Nieves, Jose Manuel; Vogel, Leif; Zielcke, Johannes; Delgados Granados, Hugo; Platt, Ulrich

2013-01-01

This work investigates the uncertainty of results gained through the two commonly used, but quite different, calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO2 camera, a NFOVDOAS system and an Imaging DOAS (I-DOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective results are compared with measurements from an I-DOAS to verify the calibration curve over the spatial extent of the image. The results show that calibration cells, while working fine in some cases, can lead to an overestimation of the SO2 CD by up to 60% compared with CDs from the DOAS measurements. Besides these errors of calibration, radiative transfer effects (e.g. light dilution, multiple scattering) can significantly influence the results of both instrument types. The measurements presented in this work were taken at Popocatepetl, Mexico, between 1 March 2011 and 4 March 2011. Average SO2 emission rates between 4.00 and 14.34 kg s−1 were observed.

ASTER preflight and inflight calibration and the validation of level 2 products

USGS Publications Warehouse

Thome, K.; Aral, K.; Hook, S.; Kieffer, H.; Lang, H.; Matsunaga, T.; Ono, A.; Palluconi, F. D.; Sakuma, H.; Slater, P.; Takashima, T.; Tonooka, H.; Tsuchida, S.; Welch, R.M.; Zalewski, E.

1998-01-01

This paper describes the preflight and inflight calibration approaches used for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The system is a multispectral, high-spatial resolution sensor on the Earth Observing System's (EOS)-AMl platform. Preflight calibration of ASTER uses well-characterized sources to provide calibration and preflight round-robin exercises to understand biases between the calibration sources of ASTER and other EOS sensors. These round-robins rely on well-characterized, ultra-stable radiometers. An experiment held in Yokohama, Japan, showed that the output from the source used for the visible and near-infrared (VNIR) subsystem of ASTER may be underestimated by 1.5%, but this is still within the 4% specification for the absolute, radiometric calibration of these bands. Inflight calibration will rely on vicarious techniques and onboard blackbodies and lamps. Vicarious techniques include ground-reference methods using desert and water sites. A recent joint field campaign gives confidence that these methods currently provide absolute calibration to better than 5%, and indications are that uncertainties less than the required 4% should be achievable at launch. The EOS-AMI platform will also provide a spacecraft maneuver that will allow ASTER to see the moon, allowing further characterization of the sensor. A method for combining the results of these independent calibration results is presented. The paper also describes the plans for validating the Level 2 data products from ASTER. These plans rely heavily upon field campaigns using methods similar to those used for the ground-reference, vicarious calibration methods. ?? 1998 IEEE.

The Next Generation Heated Halo for Blackbody Emissivity Measurement

NASA Astrophysics Data System (ADS)

Gero, P.; Taylor, J. K.; Best, F. A.; Revercomb, H. E.; Knuteson, R. O.; Tobin, D. C.; Adler, D. P.; Ciganovich, N. N.; Dutcher, S. T.; Garcia, R. K.

2011-12-01

The accuracy of radiance measurements from space-based infrared spectrometers is contingent on the quality of the calibration subsystem, as well as knowledge of its uncertainty. Future climate benchmarking missions call for measurement uncertainties better than 0.1 K (k=3) in radiance temperature for the detection of spectral climate signatures. Blackbody cavities impart the most accurate calibration for spaceborne infrared sensors, provided that their temperature and emissivity is traceably determined on-orbit. The On-Orbit Absolute Radiance Standard (OARS) has been developed at the University of Wisconsin to meet the stringent requirements of the next generation of infrared remote sensing instruments. It provides on-orbit determination of both traceable temperature and emissivity for calibration blackbodies. The Heated Halo is the component of the OARS that provides a robust and compact method to measure the spectral emissivity of a blackbody in situ. A carefully baffled thermal source is placed in front of a blackbody in an infrared spectrometer system, and the combined radiance of the blackbody and Heated Halo reflection is observed. Knowledge of key temperatures and the viewing geometry allow the blackbody cavity spectral emissivity to be calculated. We present the results from the Heated Halo methodology implemented with a new Absolute Radiance Interferometer (ARI), which is a prototype space-based infrared spectrometer designed for climate benchmarking that was developed under the NASA Instrument Incubator Program (IIP). We compare our findings to models and other experimental methods of emissivity determination.

Performance of Different Light Sources for the Absolute Calibration of Radiation Thermometers

NASA Astrophysics Data System (ADS)

Martín, M. J.; Mantilla, J. M.; del Campo, D.; Hernanz, M. L.; Pons, A.; Campos, J.

2017-09-01

The evolving mise en pratique for the definition of the kelvin (MeP-K) [1, 2] will, in its forthcoming edition, encourage the realization and dissemination of the thermodynamic temperature either directly (primary thermometry) or indirectly (relative primary thermometry) via fixed points with assigned reference thermodynamic temperatures. In the last years, the Centro Español de Metrología (CEM), in collaboration with the Instituto de Óptica of Consejo Superior de Investigaciones Científicas (IO-CSIC), has developed several setups for absolute calibration of standard radiation thermometers using the radiance method to allow CEM the direct dissemination of the thermodynamic temperature and the assignment of the thermodynamic temperatures to several fixed points. Different calibration facilities based on a monochromator and/or a laser and an integrating sphere have been developed to calibrate CEM's standard radiation thermometers (KE-LP2 and KE-LP4) and filter radiometer (FIRA2). This system is based on the one described in [3] placed in IO-CSIC. Different light sources have been tried and tested for measuring absolute spectral radiance responsivity: a Xe-Hg 500 W lamp, a supercontinuum laser NKT SuperK-EXR20 and a diode laser emitting at 6473 nm with a typical maximum power of 120 mW. Their advantages and disadvantages have been studied such as sensitivity to interferences generated by the laser inside the filter, flux stability generated by the radiant sources and so forth. This paper describes the setups used, the uncertainty budgets and the results obtained for the absolute temperatures of Cu, Co-C, Pt-C and Re-C fixed points, measured with the three thermometers with central wavelengths around 650 nm.

Absolute Calibration of Si iRMs used for Measurements of Si Paleo-nutrient proxies

NASA Astrophysics Data System (ADS)

Vocke, R. D., Jr.; Rabb, S. A.

2016-12-01

Silicon isotope variations (reported as δ30Si and δ29Si, relative to NBS28) in silicic acid dissolved in ocean waters, in biogenic silica and in diatoms are extremely informative paleo-nutrient proxies. The resolution and comparability of such measurements depend on the quality of the isotopic Reference Materials (iRMs) defining the delta scale. We report new absolute Si isotopic measurements on the iRMs NBS28 (RM 8546 - Silica Sand), Diatomite, and Big Batch using the Avogadro measurement approach and comparing them with prior assessments of these iRMs. The Avogadro Si measurement technique was developed by the German Physikalish-Technische Bundesanstalt (PTB) to provide a precise and highly accurate method to measure absolute isotopic ratios in highly enriched 28Si (99.996%) material. These measurements are part of an international effort to redefine the kg and mole based on the Planck constant h and the Avogadro constant NA, respectively (Vocke et al., 2014 Metrologia 51, 361, Azuma et al., 2015 Metrologia 52 360). This approach produces absolute Si isotope ratio data with lower levels of uncertainty when compared to the traditional "Atomic Weights" method of absolute isotope ratio measurement calibration. This is illustrated in Fig. 1 where absolute Si isotopic measurements on SRM 990, separated by 40+ years of advances in instrumentation, are compared. The availability of this new technique does not say that absolute Si isotopic ratios are or ever will be better for normal Si isotopic measurements when seeking isotopic variations in nature, because they are not. However, by determining the absolute isotopic ratios of all the Si iRM scale artifacts, such iRMs become traceable to the metric system (SI); thereby automatically conferring on all the artifact-based δ30Si and δ29Si measurements traceability to the base SI unit, the mole. Such traceability should help reduce the potential of bias between different iRMs and facilitate the replacement of delta-scale artefacts when they run out. Fig. 1 Comparison of absolute isotopic measurements of SRM 990 using two radically different approaches to absolute calibration and mass bias corrections.

Optical calibration of the Auger fluorescence telescopes

NASA Astrophysics Data System (ADS)

Matthews, John A. J.

2003-02-01

The Pierre Auger Observatory is optimized to study the cosmic ray spectrum in the region of the Greisen-Zatsepin-Kuz'min (GZK) cutoff, i.e.cosmic rays with energies of ~1020eV. Cosmic rays are detected as extensive air showers. To measure these showers each Auger site combines a 3000sq-km ground array with air fluorescence telescopes into a hybrid detector. Our design choice is motivated by the heightened importance of the energy scale, and related systematic uncertainties in shower energies, for experiments investigating the GZK cutoff. This paper focuses on the optical calibration of the Auger fluorescence telescopes. The optical calibration is done three independent ways: an absolute end-to-end calibration using a uniform, calibrated intensity, light-source at the telescope entrance aperture, a component by component calibration using both laboratory and in-situ measurements, and Rayleigh scattered light from external laser beams. The calibration concepts and related instrumentation are summarized. Results from the 5-month engineering array test are presented.

Radiometric cross-calibration of the Terra MODIS and Landsat 7 ETM+ using an invariant desert site

USGS Publications Warehouse

Choi, T.; Angal, A.; Chander, G.; Xiong, X.

2008-01-01

A methodology for long-term radiometric cross-calibration between the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) sensors was developed. The approach involves calibration of near-simultaneous surface observations between 2000 and 2007. Fifty-seven cloud-free image pairs were carefully selected over the Libyan desert for this study. The Libyan desert site (+28.55??, +23.39??), located in northern Africa, is a high reflectance site with high spatial, spectral, and temporal uniformity. Because the test site covers about 12 kmx13 km, accurate geometric preprocessing is required to match the footprint size between the two sensors to avoid uncertainties due to residual image misregistration. MODIS Level IB radiometrically corrected products were reprojected to the corresponding ETM+ image's Universal Transverse Mercator (UTM) grid projection. The 30 m pixels from the ETM+ images were aggregated to match the MODIS spatial resolution (250 m in Bands 1 and 2, or 500 m in Bands 3 to 7). The image data from both sensors were converted to absolute units of at-sensor radiance and top-ofatmosphere (TOA) reflectance for the spectrally matching band pairs. For each band pair, a set of fitted coefficients (slope and offset) is provided to quantify the relationships between the testing sensors. This work focuses on long-term stability and correlation of the Terra MODIS and L7 ETM+ sensors using absolute calibration results over the entire mission of the two sensors. Possible uncertainties are also discussed such as spectral differences in matching band pairs, solar zenith angle change during a collection, and differences in solar irradiance models.

Absolute near-infrared refractometry with a calibrated tilted fiber Bragg grating.

PubMed

Zhou, Wenjun; Mandia, David J; Barry, Seán T; Albert, Jacques

2015-04-15

The absolute refractive indices (RIs) of water and other liquids are determined with an uncertainty of ±0.001 at near-infrared wavelengths by using the tilted fiber Bragg grating (TFBG) cladding mode resonances of a standard single-mode fiber to measure the critical angle for total internal reflection at the interface between the fiber and its surroundings. The necessary condition to obtain absolute RIs (instead of measuring RI changes) is a thorough characterization of the dispersion of the core mode effective index of the TFBG across the full range of its cladding mode resonance spectrum. This technique is shown to be competitive with the best available measurements of the RIs of water and NaCl solutions at wavelengths in the vicinity of 1550 nm.

Analysis of the sources of uncertainty for EDR2 film‐based IMRT quality assurance

PubMed Central

Shi, Chengyu; Papanikolaou, Nikos; Yan, Yulong; Weng, Xuejun; Jiang, gyu

2006-01-01

In our institution, patient‐specific quality assurance (QA) for intensity‐modulated radiation therapy (IMRT) is usually performed by measuring the dose to a point using an ion chamber and by measuring the dose to a plane using film. In order to perform absolute dose comparison measurements using film, an accurate calibration curve should be used. In this paper, we investigate the film response curve uncertainty factors, including film batch differences, film processor temperature effect, film digitization, and treatment unit. In addition, we reviewed 50 patient‐specific IMRT QA procedures performed in our institution in order to quantify the sources of error in film‐based dosimetry. Our study showed that the EDR2 film dosimetry can be done with less than 3% uncertainty. The EDR2 film response was not affected by the choice of treatment unit provided the nominal energy was the same. This investigation of the different sources of uncertainties in the film calibration procedure can provide a better understanding of the film‐based dosimetry and can improve quality control for IMRT QA. PACS numbers: 87.86.Cd, 87.53.Xd, 87.57.Nk PMID:17533329

134Cs emission probabilities determination by gamma spectrometry

NASA Astrophysics Data System (ADS)

de Almeida, M. C. M.; Poledna, R.; Delgado, J. U.; Silva, R. L.; Araujo, M. T. F.; da Silva, C. J.

2018-03-01

The National Laboratory for Ionizing Radiation Metrology (LNMRI/IRD/CNEN) of Rio de Janeiro performed primary and secondary standardization of different radionuclides reaching satisfactory uncertainties. A solution of 134Cs radionuclide was purchased from commercial supplier to emission probabilities determination of some of its energies. 134Cs is a beta gamma emitter with 754 days of half-life. This radionuclide is used as standard in environmental, water and food control. It is also important to germanium detector calibration. The gamma emission probabilities (Pγ) were determined mainly for some energies of the 134Cs by efficiency curve method and the Pγ absolute uncertainties obtained were below 1% (k=1).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, N; Lu, S; Qin, Y

Purpose: To evaluate the dosimetric uncertainty associated with Gafchromic (EBT3) films and establish an absolute dosimetry protocol for Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiotherapy (SBRT). Methods: EBT3 films were irradiated at each of seven different dose levels between 1 and 15 Gy with open fields, and standard deviations of dose maps were calculated at each color channel for evaluation. A scanner non-uniform response correction map was built by registering and comparing film doses to the reference diode array-based dose map delivered with the same doses. To determine the temporal dependence of EBT3 films, the average correction factors of differentmore » dose levels as a function of time were evaluated up to four days after irradiation. An integrated film dosimetry protocol was developed for dose calibration, calibration curve fitting, dose mapping, and profile/gamma analysis. Patient specific quality assurance (PSQA) was performed for 93 SRS/SBRT treatment plans. Results: The scanner response varied within 1% for the field sizes less than 5 × 5 cm{sup 2}, and up to 5% for the field sizes of 10 × 10 cm{sup 2}. The scanner correction method was able to remove visually evident, irregular detector responses found for larger field sizes. The dose response of the film changed rapidly (∼10%) in the first two hours and plateaued afterwards, ∼3% change between 2 and 24 hours. The mean uncertainties (mean of the standard deviations) were <0.5% over the dose range 1∼15Gy for all color channels for the OD response curves. The percentage of points passing the 3%/1mm gamma criteria based on absolute dose analysis, averaged over all tests, was 95.0 ± 4.2. Conclusion: We have developed an absolute film dose dosimetry protocol using EBT3 films. The overall uncertainty has been established to be approximately 1% for SRS and SBRT PSQA. The work was supported by a Research Scholar Grant, RSG-15-137-01-CCE from the American Cancer Society.« less

The Heated Halo for Space-Based Blackbody Emissivity Measurement

NASA Astrophysics Data System (ADS)

Gero, P.; Taylor, J. K.; Best, F. A.; Revercomb, H. E.; Garcia, R. K.; Adler, D. P.; Ciganovich, N. N.; Knuteson, R. O.; Tobin, D. C.

2012-12-01

The accuracy of radiance measurements with space-based infrared spectrometers is contingent on the quality of the calibration subsystem, as well as knowledge of its uncertainty. Upcoming climate benchmark missions call for measurement uncertainties better than 0.1 K (k=3) in radiance temperature for the detection of spectral climate signatures. Blackbody cavities impart the most accurate calibration for spaceborne infrared sensors, provided that their temperature and emissivity is traceably determined on-orbit. The On-Orbit Absolute Radiance Standard (OARS) has been developed at the University of Wisconsin and has undergone further refinement under the NASA Instrument Incubator Program (IIP) to meet the stringent requirements of the next generation of infrared remote sensing instruments. It provides on-orbit determination of both traceable temperature and emissivity for calibration blackbodies. The Heated Halo is the component of the OARS that provides a robust and compact method to measure the spectral emissivity of a blackbody in situ. A carefully baffled thermal source is placed in front of a blackbody in an infrared spectrometer system, and the combined radiance of the blackbody and Heated Halo reflection is observed. Knowledge of key temperatures and the viewing geometry allow the blackbody cavity spectral emissivity to be calculated. We present the results from the Heated Halo methodology implemented with a new Absolute Radiance Interferometer (ARI), which is a prototype space-based infrared spectrometer designed for climate benchmarking. We show the evolution of the technical readiness level of this technology and we compare our findings to models and other experimental methods of emissivity determination.

Absolute reactivity calibration of accelerator-driven systems after RACE-T experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jammes, C. C.; Imel, G. R.; Geslot, B.

2006-07-01

The RACE-T experiments that were held in november 2005 in the ENEA-Casaccia research center near Rome allowed us to improve our knowledge of the experimental techniques for absolute reactivity calibration at either startup or shutdown phases of accelerator-driven systems. Various experimental techniques for assessing a subcritical level were inter-compared through three different subcritical configurations SC0, SC2 and SC3, about -0.5, -3 and -6 dollars, respectively. The area-ratio method based of the use of a pulsed neutron source appears as the most performing. When the reactivity estimate is expressed in dollar unit, the uncertainties obtained with the area-ratio method were lessmore » than 1% for any subcritical configuration. The sensitivity to measurement location was about slightly more than 1% and always less than 4%. Finally, it is noteworthy that the source jerk technique using a transient caused by the pulsed neutron source shutdown provides results in good agreement with those obtained from the area-ratio technique. (authors)« less

Absolute measurements of fast neutrons using yttrium.

PubMed

Roshan, M V; Springham, S V; Rawat, R S; Lee, P; Krishnan, M

2010-08-01

Yttrium is presented as an absolute neutron detector for pulsed neutron sources. It has high sensitivity for detecting fast neutrons. Yttrium has the property of generating a monoenergetic secondary radiation in the form of a 909 keV gamma-ray caused by inelastic neutron interaction. It was calibrated numerically using MCNPX and does not need periodic recalibration. The total yttrium efficiency for detecting 2.45 MeV neutrons was determined to be f(n) approximately 4.1x10(-4) with an uncertainty of about 0.27%. The yttrium detector was employed in the NX2 plasma focus experiments and showed the neutron yield of the order of 10(8) neutrons per discharge.

A game-theoretic approach for calibration of low-cost magnetometers under noise uncertainty

NASA Astrophysics Data System (ADS)

Siddharth, S.; Ali, A. S.; El-Sheimy, N.; Goodall, C. L.; Syed, Z. F.

2012-02-01

Pedestrian heading estimation is a fundamental challenge in Global Navigation Satellite System (GNSS)-denied environments. Additionally, the heading observability considerably degrades in low-speed mode of operation (e.g. walking), making this problem even more challenging. The goal of this work is to improve the heading solution when hand-held personal/portable devices, such as cell phones, are used for positioning and to improve the heading estimation in GNSS-denied signal environments. Most smart phones are now equipped with self-contained, low cost, small size and power-efficient sensors, such as magnetometers, gyroscopes and accelerometers. A magnetometer needs calibration before it can be properly employed for navigation purposes. Magnetometers play an important role in absolute heading estimation and are embedded in many smart phones. Before the users navigate with the phone, a calibration is invoked to ensure an improved signal quality. This signal is used later in the heading estimation. In most of the magnetometer-calibration approaches, the motion modes are seldom described to achieve a robust calibration. Also, suitable calibration approaches fail to discuss the stopping criteria for calibration. In this paper, the following three topics are discussed in detail that are important to achieve proper magnetometer-calibration results and in turn the most robust heading solution for the user while taking care of the device misalignment with respect to the user: (a) game-theoretic concepts to attain better filter parameter tuning and robustness in noise uncertainty, (b) best maneuvers with focus on 3D and 2D motion modes and related challenges and (c) investigation of the calibration termination criteria leveraging the calibration robustness and efficiency.

Performance analysis of a film dosimetric quality assurance procedure for IMRT with regard to the employment of quantitative evaluation methods.

PubMed

Winkler, Peter; Zurl, Brigitte; Guss, Helmuth; Kindl, Peter; Stuecklschweiger, Georg

2005-02-21

A system for dosimetric verification of intensity-modulated radiotherapy (IMRT) treatment plans using absolute calibrated radiographic films is presented. At our institution this verification procedure is performed for all IMRT treatment plans prior to patient irradiation. Therefore clinical treatment plans are transferred to a phantom and recalculated. Composite treatment plans are irradiated to a single film. Film density to absolute dose conversion is performed automatically based on a single calibration film. A software application encompassing film calibration, 2D registration of measurement and calculated distributions, image fusion, and a number of visual and quantitative evaluation utilities was developed. The main topic of this paper is a performance analysis for this quality assurance procedure, with regard to the specification of tolerance levels for quantitative evaluations. Spatial and dosimetric precision and accuracy were determined for the entire procedure, comprising all possible sources of error. The overall dosimetric and spatial measurement uncertainties obtained thereby were 1.9% and 0.8 mm respectively. Based on these results, we specified 5% dose difference and 3 mm distance-to-agreement as our tolerance levels for patient-specific quality assurance for IMRT treatments.

Deformation Monitoring of the Submillimetric UPV Calibration Baseline

NASA Astrophysics Data System (ADS)

García-Asenjo, Luis; Baselga, Sergio; Garrigues, Pascual

2017-06-01

A 330 m calibration baseline was established at the Universitat Politècnica de València (UPV) in 2007. Absolute scale was subsequently transferred in 2012 from the Nummela Standard Baseline in Finland and distances between pillars were determined with uncertainties ranging from 0.1 mm to 0.3 mm. In order to assess the long-term stability of the baseline three field campaigns were carried out from 2013 to 2015 in a co-operative effort with the Universidad Complutense de Madrid (UCM), which provided the only Mekometer ME5000 distance meter available in Spain. Since the application of the ISO17123-4 full procedure did not suffice to come to a definite conclusion about possible displacements of the pillars, we opted for the traditional geodetic network approach. This approach had to be adapted to the case at hand in order to deal with problems such as the geometric weakness inherent to calibration baselines and scale uncertainty derived from both the use of different instruments and the high correlation between the meteorological correction and scale determination. Additionally, the so-called the maximum number of stable points method was also tested. In this contribution it is described the process followed to assess the stability of the UPV submillimetric calibration baseline during the period of time from 2012 to 2015.

Development, characterization, and validation of an optical transfer standard for ammonia in air

NASA Astrophysics Data System (ADS)

Lüttschwager, Nils; Balslev-Harder, David; Leuenberger, Daiana; Pogány, Andrea; Werhahn, Olav; Ebert, Volker

2017-04-01

Ammonia is an atmospheric trace gas that is predominantly emitted from anthropogenic agricultural activities. Since elevated levels of ammonia can have negative effects to human health as well as ecosystems, it is imperative to monitor and control ammonia emissions. This requires SI-traceable standards to calibrate ammonia monitoring instrumentation and to make measurements comparable. The lack of such standards became a pressing issue in recent years and the MetNH3 project (www.metnh3.eu) was initiated to fill the gap, pursuing different strategies. The work that we present was part of these endeavours and focusses on the development and application of an optical transfer standard for amount fraction measurements of ammonia in ambient air. An optical transfer standard (OTS) offers an alternative to calibrations of air monitoring instrumentation by means of reference gas mixtures. With an OTS, absolute amount fraction results are derived by evaluating absorption spectra using a spectral model and pre-measured spectral properties of the analyte. In that way, the instrument can measure calibration gas-independent ("calibration-free") and, moreover, can itself serve as standard to calibrate air monitoring analyzers. Molecular spectral properties are the excellent, non-drifting point of reference of the OTS and form, together with traceable measurements of temperature and pressure, the basis for SI-traceable amount fraction measurements. We developed an OTS based on a commercial cavity-ring-down spectrometer with a detection limit below 1 ppb (1 nmol/mol). A custom spectral data evaluation routine for absolute, calibration-free measurements, as well as measurements of spectral properties of ammonia with the focus on measurement uncertainty and traceability [1] are the fundaments of our OTS. Validation measurements were conducted using a SI-traceable ammonia reference gas generator over a period of several months. Here, we present an evaluation of the performance of our OTS from 1 ppb to 200 ppb. We found the results obtained with the OTS to be concordant to reference gas mixtures yielding amount fraction results with standard uncertainties of less than 3 %, for which an uncertainty budget is provided. Acknowledgement: This work was supported by the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. References 1. A. Pogány, O. Werhahn, and V. Ebert, High-Accuracy Ammonia Line Intensity Measurements at 1.5 µm, in Imaging and Applied Optics 2016, OSA Technical Digest (online) (Optical Society of America, 2016), paper JT3A.15, DOI: 10.1364/3D.2016.JT3A.15

Exploring a Black Body Source as an Absolute Radiometric Calibration Standard and Comparison with a NIST Traced Lamp Standard

NASA Technical Reports Server (NTRS)

Green, Robert O.; Chrien, Thomas; Sarture, Chuck

2001-01-01

Radiometric calibration of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) is required for the scientific research and application objectives pursued with the spectroscopic measurements. Specifically calibration is required for: inter-comparison of AVIRIS data measured at different locations and at different times; analysis of AVIRIS data with data measured by other instruments; and analysis of AVIRIS data in conjunction with computer models. The primary effect of radiometric calibration is conversion of AVIRIS instrument response values (digitized numbers, or DN) to units of absolute radiance. For example, a figure shows the instrument response spectrum measured by AVIRIS over a portion of Rogers Dry Lake, California, and another figure shows the same spectrum calibrated to radiance. Only the calibrated spectrum may be quantitatively analyzed for science research and application objectives. Since the initial development of the AVIRIS instrument-radiometric calibration has been based upon a 1000-W irradiance lamp with a calibration traced to the National Institute of Standards and Technology (NIST). There are several advantages to this irradiance-lamp calibration approach. First, the considerable effort of NIST backs up the calibration. Second, by changing the distance to the lamp, the output can closely span the radiance levels measured by AVIRIS. Third, this type of standard is widely used. Fourth, these calibrated lamps are comparatively inexpensive. Conversely, there are several disadvantages to this approach as well. First, the lamp is not a primary standard. Second, the lamp output characteristics may change in an unknown manner through time. Third, it is difficult to assess, constrain, or improve the calibration uncertainty delivered with the lamp. In an attempt to explore the effect and potentially address some of these disadvantages a set of analyses and measurements comparing an irradiance lamp with a black-body source have been completed. This research is ongoing, and the current set of measurements, analyses, and results are presented in this paper.

Absolute frequency atlas from 915 nm to 985 nm based on laser absorption spectroscopy of iodine

NASA Astrophysics Data System (ADS)

Nölleke, Christian; Raab, Christoph; Neuhaus, Rudolf; Falke, Stephan

2018-04-01

This article reports on laser absorption spectroscopy of iodine gas between 915 nm and 985 nm. This wavelength range is scanned utilizing a narrow linewidth and mode-hop-free tunable diode-laser whose frequency is actively controlled using a calibrated wavelength meter. This allows us to provide an iodine atlas that contains almost 10,000 experimentally observed reference lines with an uncertainty of 50 MHz. For common lines, good agreement is found with a publication by Gerstenkorn and Luc (1978). The new rich dataset allows existing models of the iodine molecule to be refined and can serve as a reference for laser frequency calibration and stabilization.

Advancing Absolute Calibration for JWST and Other Applications

NASA Astrophysics Data System (ADS)

Rieke, George; Bohlin, Ralph; Boyajian, Tabetha; Carey, Sean; Casagrande, Luca; Deustua, Susana; Gordon, Karl; Kraemer, Kathleen; Marengo, Massimo; Schlawin, Everett; Su, Kate; Sloan, Greg; Volk, Kevin

2017-10-01

We propose to exploit the unique optical stability of the Spitzer telescope, along with that of IRAC, to (1) transfer the accurate absolute calibration obtained with MSX on very bright stars directly to two reference stars within the dynamic range of the JWST imagers (and of other modern instrumentation); (2) establish a second accurate absolute calibration based on the absolutely calibrated spectrum of the sun, transferred onto the astronomical system via alpha Cen A; and (3) provide accurate infrared measurements for the 11 (of 15) highest priority stars with no such data but with accurate interferometrically measured diameters, allowing us to optimize determinations of effective temperatures using the infrared flux method and thus to extend the accurate absolute calibration spectrally. This program is integral to plans for an accurate absolute calibration of JWST and will also provide a valuable Spitzer legacy.

Absolute radiometric calibration of advanced remote sensing systems

NASA Technical Reports Server (NTRS)

Slater, P. N.

1982-01-01

The distinction between the uses of relative and absolute spectroradiometric calibration of remote sensing systems is discussed. The advantages of detector-based absolute calibration are described, and the categories of relative and absolute system calibrations are listed. The limitations and problems associated with three common methods used for the absolute calibration of remote sensing systems are addressed. Two methods are proposed for the in-flight absolute calibration of advanced multispectral linear array systems. One makes use of a sun-illuminated panel in front of the sensor, the radiance of which is monitored by a spectrally flat pyroelectric radiometer. The other uses a large, uniform, high-radiance reference ground surface. The ground and atmospheric measurements required as input to a radiative transfer program to predict the radiance level at the entrance pupil of the orbital sensor are discussed, and the ground instrumentation is described.

Absolute surface reconstruction by slope metrology and photogrammetry

NASA Astrophysics Data System (ADS)

Dong, Yue

Developing the manufacture of aspheric and freeform optical elements requires an advanced metrology method which is capable of inspecting these elements with arbitrary freeform surfaces. In this dissertation, a new surface measurement scheme is investigated for such a purpose, which is to measure the absolute surface shape of an object under test through its surface slope information obtained by photogrammetric measurement. A laser beam propagating toward the object reflects on its surface while the vectors of the incident and reflected beams are evaluated from the four spots they leave on the two parallel transparent windows in front of the object. The spots' spatial coordinates are determined by photogrammetry. With the knowledge of the incident and reflected beam vectors, the local slope information of the object surface is obtained through vector calculus and finally yields the absolute object surface profile by a reconstruction algorithm. An experimental setup is designed and the proposed measuring principle is experimentally demonstrated by measuring the absolute surface shape of a spherical mirror. The measurement uncertainty is analyzed, and efforts for improvement are made accordingly. In particular, structured windows are designed and fabricated to generate uniform scattering spots left by the transmitted laser beams. Calibration of the fringe reflection instrument, another typical surface slope measurement method, is also reported in the dissertation. Finally, a method for uncertainty analysis of a photogrammetry measurement system by optical simulation is investigated.

Luminosity determination in pp collisions at $$\\sqrt{s} = 7$$ TeV using the ATLAS detector at the LHC

DOE PAGES

Aad, G.; Abbott, B.; Abdallah, J.; ...

2011-04-27

Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0 < μ < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have amore » common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, H; Menon, G; Sloboda, R

The purpose of this study was to investigate the accuracy of radiochromic film calibration procedures used in external beam radiotherapy when applied to I-125 brachytherapy sources delivering higher doses, and to determine any necessary modifications to achieve similar accuracy in absolute dose measurements. GafChromic EBT3 film was used to measure radiation doses upwards of 35 Gy from 6 MV, 75 kVp and (∼28 keV) I-125 photon sources. A custom phantom was used for the I-125 irradiations to obtain a larger film area with nearly constant dose to reduce the effects of film heterogeneities on the optical density (OD) measurements. RGBmore » transmission images were obtained with an Epson 10000XL flatbed scanner, and calibration curves relating OD and dose using a rational function were determined for each colour channel and at each energy using a non-linear least square minimization method. Differences found between the 6 MV calibration curve and those for the lower energy sources are large enough that 6 MV beams should not be used to calibrate film for low-energy sources. However, differences between the 75 kVp and I-125 calibration curves were quite small; indicating that 75 kVp is a good choice. Compared with I-125 irradiation, this gives the advantages of lower type B uncertainties and markedly reduced irradiation time. To obtain high accuracy calibration for the dose range up to 35 Gy, two-segment piece-wise fitting was required. This yielded absolute dose measurement accuracy above 1 Gy of ∼2% for 75 kVp and ∼5% for I-125 seed exposures.« less

Absolute calibration of sniffer probes on Wendelstein 7-X

NASA Astrophysics Data System (ADS)

Moseev, D.; Laqua, H. P.; Marsen, S.; Stange, T.; Braune, H.; Erckmann, V.; Gellert, F.; Oosterbeek, J. W.

2016-08-01

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m2 per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m2 per MW injected beam power is measured.

Absolute calibration of sniffer probes on Wendelstein 7-X.

PubMed

Moseev, D; Laqua, H P; Marsen, S; Stange, T; Braune, H; Erckmann, V; Gellert, F; Oosterbeek, J W

2016-08-01

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up to 340 kW/m(2) per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m(2) per MW injected beam power is measured.

D-D Neutron Generator Calibrations and Hardware in the LUX-ZEPLIN Dark Matter Search Experiment

NASA Astrophysics Data System (ADS)

Taylor, Will; Lux-Zeplin Collaboration

2016-03-01

The LUX-ZEPLIN (LZ) dark matter search experiment will be a two-phase liquid/gas xenon time projection chamber with 7 tonnes of active liquid xenon (LXe) located at the 4850 ft level of the Sanford Underground Research Facility in Lead, SD. LZ will utilize an in-situ, absolute calibration of nuclear recoils (NR) in LXe using mono-energetic 2.45 MeV neutrons produced by a D-D neutron generator. This technique was used in the LUX detector to measured the NR charge yield in LXe (Qy) to 0.7 keV recoil energy and the NR light yield in LXe (Ly) to recoil energies of 1.1 keV - both of which were the lowest energy measurements achieved in the field. These absolute, ultra-low energy calibrations of the NR signal yields in LXe provide clear measurements of the detector response used for the WIMP search analysis. The improvements made for LZ will include shorter neutron pulse times, multiple neutron conduit configurations, and lower energy neutrons. The upgrades allow for even lower energy measurements of the nuclear recoil response in LXe and an independent measurement of Ly, as well as providing less uncertainty in energy reconstruction. In addition to discussing the physics of the neutron calibrations, I will describe the hardware systems used to implement them.

Parameter Optimisation and Uncertainty Analysis in Visual MODFLOW based Flow Model for predicting the groundwater head in an Eastern Indian Aquifer

NASA Astrophysics Data System (ADS)

Mohanty, B.; Jena, S.; Panda, R. K.

2016-12-01

The overexploitation of groundwater elicited in abandoning several shallow tube wells in the study Basin in Eastern India. For the sustainability of groundwater resources, basin-scale modelling of groundwater flow is indispensable for the effective planning and management of the water resources. The basic intent of this study is to develop a 3-D groundwater flow model of the study basin using the Visual MODFLOW Flex 2014.2 package and successfully calibrate and validate the model using 17 years of observed data. The sensitivity analysis was carried out to quantify the susceptibility of aquifer system to the river bank seepage, recharge from rainfall and agriculture practices, horizontal and vertical hydraulic conductivities, and specific yield. To quantify the impact of parameter uncertainties, Sequential Uncertainty Fitting Algorithm (SUFI-2) and Markov chain Monte Carlo (McMC) techniques were implemented. Results from the two techniques were compared and the advantages and disadvantages were analysed. Nash-Sutcliffe coefficient (NSE), Coefficient of Determination (R2), Mean Absolute Error (MAE), Mean Percent Deviation (Dv) and Root Mean Squared Error (RMSE) were adopted as criteria of model evaluation during calibration and validation of the developed model. NSE, R2, MAE, Dv and RMSE values for groundwater flow model during calibration and validation were in acceptable range. Also, the McMC technique was able to provide more reasonable results than SUFI-2. The calibrated and validated model will be useful to identify the aquifer properties, analyse the groundwater flow dynamics and the change in groundwater levels in future forecasts.

Flood loss modelling with FLF-IT: a new flood loss function for Italian residential structures

NASA Astrophysics Data System (ADS)

Hasanzadeh Nafari, Roozbeh; Amadio, Mattia; Ngo, Tuan; Mysiak, Jaroslav

2017-07-01

The damage triggered by different flood events costs the Italian economy millions of euros each year. This cost is likely to increase in the future due to climate variability and economic development. In order to avoid or reduce such significant financial losses, risk management requires tools which can provide a reliable estimate of potential flood impacts across the country. Flood loss functions are an internationally accepted method for estimating physical flood damage in urban areas. In this study, we derived a new flood loss function for Italian residential structures (FLF-IT), on the basis of empirical damage data collected from a recent flood event in the region of Emilia-Romagna. The function was developed based on a new Australian approach (FLFA), which represents the confidence limits that exist around the parameterized functional depth-damage relationship. After model calibration, the performance of the model was validated for the prediction of loss ratios and absolute damage values. It was also contrasted with an uncalibrated relative model with frequent usage in Europe. In this regard, a three-fold cross-validation procedure was carried out over the empirical sample to measure the range of uncertainty from the actual damage data. The predictive capability has also been studied for some sub-classes of water depth. The validation procedure shows that the newly derived function performs well (no bias and only 10 % mean absolute error), especially when the water depth is high. Results of these validation tests illustrate the importance of model calibration. The advantages of the FLF-IT model over other Italian models include calibration with empirical data, consideration of the epistemic uncertainty of data, and the ability to change parameters based on building practices across Italy.

Calibration of ground-based microwave radiometers - Accuracy assessment and recommendations for network users

NASA Astrophysics Data System (ADS)

Pospichal, Bernhard; Küchler, Nils; Löhnert, Ulrich; Crewell, Susanne; Czekala, Harald; Güldner, Jürgen

2016-04-01

Ground-based microwave radiometers (MWR) are becoming widely used in atmospheric remote sensing and start to be routinely operated by national weather services and other institutions. However, common standards for calibration of these radiometers and a detailed knowledge about the error characteristics is needed, in order to assimilate the data into models. Intercomparisons of calibrations by different MWRs have rarely been done. Therefore, two calibration experiments in Lindenberg (2014) and Meckenheim (2015) were performed in the frame of TOPROF (Cost action ES1303) in order to assess uncertainties and differences between various instruments. In addition, a series of experiments were taken in Oklahoma in autumn 2014. The focus lay on the performance of the two main instrument types, which are currently used operationally. These are the MP-Profiler series by Radiometrics Corporation as well as the HATPRO series by Radiometer Physics GmbH (RPG). Both instrument types are operating in two frequency bands, one along the 22 GHz water vapour line, the other one at the lower wing of the 60 GHz oxygen absorption complex. The goal was to establish protocols for providing quality controlled (QC) MWR data and their uncertainties. To this end, standardized calibration procedures for MWR were developed and recommendations for radiometer users were compiled. We focus here mainly on data types, integration times and optimal settings for calibration intervals, both for absolute (liquid nitrogen, tipping curve) as well as relative (hot load, noise diode) calibrations. Besides the recommendations for ground-based MWR operators, we will present methods to determine the accuracy of the calibration as well as means for automatic data quality control. In addition, some results from the intercomparison of different radiometers will be discussed.

Absolute empirical rate coefficient for the excitation of the 117.6 nm line in C III

NASA Astrophysics Data System (ADS)

Gardner, L. D.; Daw, A. N.; Janzen, P. H.; Atkins, N.; Kohl, J. L.

2005-05-01

We have measured the absolute cross sections for electron impact excitation (EIE) of C2+ (2s2p 3P° - 2p2 3P) for energies from below threshold to 17 eV above and derived EIE rate coefficients required for astrophysical applications. The uncertainty in the rate coefficient at a typical solar temperature of formation of C2+ is less than ± 6 %. Ions are produced in a 5 GHz Electron Cyclotron Resonance (ECR) ion source, extracted, formed into a beam, and transported to a collision chamber where they collide with electrons from an electron beam inclined at 45 degrees. The beams are modulated and the radiation from the decay of the excited ions at λ 117.6 nm is detected synchronously using an absolutely calibrated optical system that subtends slightly over π steradians. The fractional population of the C2+ metastable state in the incident ion beam has been determined experimentally to be 0.42 ± 0.03 (1.65 σ). At the reported ± 15 % total experimental uncertainty level (1.65 σ), the measured structure and absolute scale of the cross section are in fairly good agreement with 6-term close-coupling R-matrix calculations and 90-term R-matrix with pseudo-states calculations, although some minor differences are seen just above threshold. As density-sensitive line intensity ratios vary by only about a factor of 5 as the density changes by nearly a factor of 100, even a 30 % uncertainty in the excitation rate can lead to a factor of 3 error in density. This work is supported by NASA Supporting Research and Technology grants NAG5- 9516 and NAG5-12863 in Solar and Heliospheric Physics and by the Smithsonian Astrophysical Observatory.

Z-correction, a method for achieving ultraprecise self-calibration on large area coordinate measurement machines for photomasks

NASA Astrophysics Data System (ADS)

Ekberg, Peter; Stiblert, Lars; Mattsson, Lars

2014-05-01

High-quality photomasks are a prerequisite for the production of flat panel TVs, tablets and other kinds of high-resolution displays. During the past years, the resolution demand has become more and more accelerated, and today, the high-definition standard HD, 1920 × 1080 pixels2, is well established, and already the next-generation so-called ultra-high-definition UHD or 4K display is entering the market. Highly advanced mask writers are used to produce the photomasks needed for the production of such displays. The dimensional tolerance in X and Y on absolute pattern placement on these photomasks, with sizes of square meters, has been in the range of 200-300 nm (3σ), but is now on the way to be <150 nm (3σ). To verify these photomasks, 2D ultra-precision coordinate measurement machines are used with even tighter tolerance requirements. The metrology tool MMS15000 is today the world standard tool used for the verification of large area photomasks. This paper will present a method called Z-correction that has been developed for the purpose of improving the absolute X, Y placement accuracy of features on the photomask in the writing process. However, Z-correction is also a prerequisite for achieving X and Y uncertainty levels <90 nm (3σ) in the self-calibration process of the MMS15000 stage area of 1.4 × 1.5 m2. When talking of uncertainty specifications below 200 nm (3σ) of such a large area, the calibration object used, here an 8-16 mm thick quartz plate of size approximately a square meter, cannot be treated as a rigid body. The reason for this is that the absolute shape of the plate will be affected by gravity and will therefore not be the same at different places on the measurement machine stage when it is used in the self-calibration process. This mechanical deformation will stretch or compress the top surface (i.e. the image side) of the plate where the pattern resides, and therefore spatially deform the mask pattern in the X- and Y-directions. Errors due to this deformation can easily be several hundred nanometers. When Z-correction is used in the writer, it is also possible to relax the flatness demand of the photomask backside, leading to reduced manufacturing costs of the plates.

Improvement of Gaofen-3 Absolute Positioning Accuracy Based on Cross-Calibration

PubMed Central

Deng, Mingjun; Li, Jiansong

2017-01-01

The Chinese Gaofen-3 (GF-3) mission was launched in August 2016, equipped with a full polarimetric synthetic aperture radar (SAR) sensor in the C-band, with a resolution of up to 1 m. The absolute positioning accuracy of GF-3 is of great importance, and in-orbit geometric calibration is a key technology for improving absolute positioning accuracy. Conventional geometric calibration is used to accurately calibrate the geometric calibration parameters of the image (internal delay and azimuth shifts) using high-precision ground control data, which are highly dependent on the control data of the calibration field, but it remains costly and labor-intensive to monitor changes in GF-3’s geometric calibration parameters. Based on the positioning consistency constraint of the conjugate points, this study presents a geometric cross-calibration method for the rapid and accurate calibration of GF-3. The proposed method can accurately calibrate geometric calibration parameters without using corner reflectors and high-precision digital elevation models, thus improving absolute positioning accuracy of the GF-3 image. GF-3 images from multiple regions were collected to verify the absolute positioning accuracy after cross-calibration. The results show that this method can achieve a calibration accuracy as high as that achieved by the conventional field calibration method. PMID:29240675

The recalibration of the IUE scientific instrument

NASA Technical Reports Server (NTRS)

Imhoff, Catherine L.; Oliversen, Nancy A.; Nichols-Bohlin, Joy; Casatella, Angelo; Lloyd, Christopher

1988-01-01

The IUE instrument was recalibrated because of long time-scale changes in the scientific instrument, a better understanding of the performance of the instrument, improved sets of calibration data, and improved analysis techniques. Calibrations completed or planned include intensity transfer functions (ITF), low-dispersion absolute calibrations, high-dispersion ripple corrections and absolute calibrations, improved geometric mapping of the ITFs to spectral images, studies to improve the signal-to-noise, enhanced absolute calibrations employing corrections for time, temperature, and aperture dependence, and photometric and geometric calibrations for the FES.

NIST TXR Validation of S-HIS radiances and a UW-SSEC Blackbody

NASA Astrophysics Data System (ADS)

Taylor, J. K.; O'Connell, J.; Rice, J. P.; Revercomb, H. E.; Best, F. A.; Tobin, D. C.; Knuteson, R. O.; Adler, D. P.; Ciganovich, N. C.; Dutcher, S. T.; Laporte, D. D.; Ellington, S. D.; Werner, M. W.; Garcia, R. K.

2007-12-01

The ability to accurately validate infrared spectral radiances measured from space by direct comparison with airborne spectrometer radiances was first demonstrated using the Scanning High-resolution Interferometer Sounder (S-HIS) aircraft instrument flown under the AIRS on the NASA Aqua spacecraft in 2002 with subsequent successful comparisons in 2004 and 2006. The comparisons span a range of conditions, including arctic and tropical atmospheres, daytime and nighttime, and ocean and land surfaces. Similar comprehensive and successful comparisons have also been conducted with S-HIS for the MODIS sensors, the Tropospheric Emission Spectrometer (TES), and most recently the MetOp Infrared Atmospheric Sounding Interferometer (IASI). These comparisons are part of a larger picture that already shows great progress toward transforming our ability to make, and verify, highly accurate spectral radiance observations from space. A key challenge, especially for climate, is to carefully define the absolute accuracy of satellite radiances. Our vision of the near-term future of spectrally resolved infrared radiance observation includes a new space-borne mission that provides benchmark observations of the emission spectrum for climate. This concept, referred to as the CLimate Absolute Radiance and REfractivity Observatory (CLARREO) in the recent NRC Decadal Survey provides more complete spectral and time-of-day coverage and would fly basic physical standards to eliminate the need to assume on-board reference stability. Therefore, the spectral radiances from this mission will also serve as benchmarks to propagate a highly accurate calibration to other space-borne IR instruments. For the current approach of calibrating infrared flight sensors, in which thermal vacuum tests are conducted before launch and stability is assumed after launch, in-flight calibration validation is essential for highly accurate applications. At present, airborne observations provide the only source of direct radiance validation with resulting traceable uncertainties approaching the level required for remote sensing and climate applications (0.1 K 3- sigma). For the calibration validation process to be accurate, repeatable, and meaningful, the reference instrument must be extremely well characterized and understood, carefully maintained, and accurately calibrated, with the calibration accuracy of the reference instrument tied to absolute standards. Tests of the S-HIS absolute calibration have been conducted using the NIST transfer radiometer (TXR). The TXR provides a more direct connection to the Blackbody reference sources maintained by NIST than the normal traceability of blackbody temperature scales and paint emissivity measurements. Two basic tests were conducted: (1) comparison of radiances measured by the S-HIS to those from the TXR, and (2) measuring the reflectivity of a UW-SSEC blackbody by using the TXR as a stable detector. Preliminary results from both tests are very promising for confirming and refining the expected absolute accuracy of the S-HIS.

UV scale calibration transfer from an improved pyroelectric detector standard to field UV-A meters and 365 nm excitation sources

NASA Astrophysics Data System (ADS)

Eppeldauer, G. P.; Podobedov, V. B.; Cooksey, C. C.

2017-05-01

Calibration of the emitted radiation from UV sources peaking at 365 nm, is necessary to perform the ASTM required 1 mW/cm2 minimum irradiance in certain military material (ships, airplanes etc) tests. These UV "black lights" are applied for crack-recognition using fluorescent liquid penetrant inspection. At present, these nondestructive tests are performed using Hg-lamps. Lack of a proper standard and the different spectral responsivities of the available UV meters cause significant measurement errors even if the same UV-365 source is measured. A pyroelectric radiometer standard with spectrally flat (constant) response in the UV-VIS range has been developed to solve the problem. The response curve of this standard determined from spectral reflectance measurement, is converted into spectral irradiance responsivity with <0.5% (k=2) uncertainty as a result of using an absolute tie point from a Si-trap detector traceable to the primary standard cryogenic radiometer. The flat pyroelectric radiometer standard can be used to perform uniform integrated irradiance measurements from all kinds of UV sources (with different peaks and distributions) without using any source standard. Using this broadband calibration method, yearly spectral calibrations for the reference UV (LED) sources and irradiance meters is not needed. Field UV sources and meters can be calibrated against the pyroelectric radiometer standard for broadband (integrated) irradiance and integrated responsivity. Using the broadband measurement procedure, the UV measurements give uniform results with significantly decreased uncertainties.

Landsat Data Continuity Mission Calibration and Validation

NASA Technical Reports Server (NTRS)

Markham, Brian L.; Dabney, Philip W.; Storey, James C.; Morfitt, Ron; Knight, Ed; Kvaran, Geir; Lee, Kenton

2008-01-01

The primary payload for the Landsat Data Continuity Mission (LDCM) is the Operational Land Imager (OLI), being built by Ball Aerospace and Technologies, under contract to NASA. The OLI has spectral bands similar to the Landsat-7 ETM+, minus the thermal band and with two new bands, a 443 nm band and 1375 nm cirrus detection band. On-board calibration systems include two solar diffusers (routine and pristine), a shutter and three sets of internal lamps (routine, backup and pristine). Being a pushbroom opposed to a whiskbroom design of ETM+, the system poses new challenges for characterization and calibration, chief among them being the large focal plane with 75000+ detectors. A comprehensive characterization and calibration plan is in place for the instrument and the data throughout the mission including Ball, NASA and the United States Geological Survey, which will take over operations of LDCM after on-orbit commissioning. Driving radiometric calibration requirements for OLI data include radiance calibration to 5% uncertainty (1 q); reflectance calibration to 3% uncertainty (1 q) and relative (detector-to-detector) calibration to 0.5% (J (r). Driving geometric calibration requirements for OLI include bandto- band registration of 4.5 meters (90% confidence), absolute geodetic accuracy of 65 meters (90% CE) and relative geodetic accuracy of 25 meters (90% CE). Key spectral, spatial and radiometric characterization of the OLI will occur in thermal vacuum at Ball Aerospace. During commissioning the OLI will be characterized and calibrated using celestial (sun, moon, stars) sources and terrestrial sources. The USGS EROS ground processing system will incorporate an image assessment system similar to Landsat-7 for characterization and calibration. This system will have the added benefit that characterization data will be extracted as part of the normal image data processing, so that the characterization data available will be significantly larger than for Landsat-7 ETM+.

Fabrication, characterization, and modeling of comixed films for NXS calibration targets [Fabrication and metrology of the NXS calibration targets

DOE PAGES

Jaquez, Javier; Farrell, Mike; Huang, Haibo; ...

2016-08-01

In 2014/2015 at the Omega laser facility, several experiments took place to calibrate the National Ignition Facility (NIF) X-ray spectrometer (NXS), which is used for high-resolution time-resolved spectroscopic experiments at NIF. The spectrometer allows experimentalists to measure the X-ray energy emitted from high-energy targets, which is used to understand key data such as mixing of materials in highly compressed fuel. The purpose of the experiments at Omega was to obtain information on the instrument performance and to deliver an absolute photometric calibration of the NXS before it was deployed at NIF. The X-ray emission sources fabricated for instrument calibration weremore » 1-mm fused silica spheres with precisely known alloy composition coatings of Si/Ag/Mo, Ti/Cr/Ag, Cr/Ni/Zn, and Zn/Zr, which have emission in the 2- to 18-keV range. Critical to the spectrometer calibration is a known atomic composition of elements with low uncertainty for each calibration sphere. This study discusses the setup, fabrication, and precision metrology of these spheres as well as some interesting findings on the ternary magnetron-sputtered alloy structure.« less

Landsat-7 ETM+ On-Orbit Reflective-Band Radiometric Stability and Absolute Calibration

NASA Technical Reports Server (NTRS)

Markham, Brian L.; Thome, Kurtis J.; Barsi, Julia A.; Kaita, Ed; Helder, Dennis L.; Barker, John L.

2003-01-01

The Landsat-7 spacecraft carries the Enhanced Thematic Mapper Plus (ETM+) instrument. This instrument images the Earth land surface in eight parts of the electromagnetic spectrum, termed spectral bands. These spectral images are used to monitor changes in the land surface, so a consistent relationship, i.e., calibration, between the image data and the Earth surface brightness, is required. The ETM+ has several on- board calibration devices that are used to monitor this calibration. The best on-board calibration source employs a flat white painted reference panel and has indicated changes of between 0.5% to 2% per year in the ETM+ response, depending on the spectral band. However, most of these changes are believed to be caused by changes in the reference panel, as opposed to changes in the instrument's sensitivity. This belief is based partially on on-orbit calibrations using instrumented ground sites and observations of "invariant sites", hyper-arid sites of the Sahara and Arabia. Changes determined from these data sets indicate are 0.1% - 0.6% per year. Tests and comparisons to other sensors also indicate that the uncertainty of the calibration is at the 5% level.

Fabrication, characterization, and modeling of comixed films for NXS calibration targets [Fabrication and metrology of the NXS calibration targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaquez, Javier; Farrell, Mike; Huang, Haibo

In 2014/2015 at the Omega laser facility, several experiments took place to calibrate the National Ignition Facility (NIF) X-ray spectrometer (NXS), which is used for high-resolution time-resolved spectroscopic experiments at NIF. The spectrometer allows experimentalists to measure the X-ray energy emitted from high-energy targets, which is used to understand key data such as mixing of materials in highly compressed fuel. The purpose of the experiments at Omega was to obtain information on the instrument performance and to deliver an absolute photometric calibration of the NXS before it was deployed at NIF. The X-ray emission sources fabricated for instrument calibration weremore » 1-mm fused silica spheres with precisely known alloy composition coatings of Si/Ag/Mo, Ti/Cr/Ag, Cr/Ni/Zn, and Zn/Zr, which have emission in the 2- to 18-keV range. Critical to the spectrometer calibration is a known atomic composition of elements with low uncertainty for each calibration sphere. This study discusses the setup, fabrication, and precision metrology of these spheres as well as some interesting findings on the ternary magnetron-sputtered alloy structure.« less

π0 mass reconstruction in NOvA Far Detector.

NASA Astrophysics Data System (ADS)

Edayath, Sijith

2017-01-01

NOvA is a long-baseline neutrino oscillation experiment with functionally identical, segmented, tracking calorimeter Near and Far detectors. The detectors lie 14.6 mrad off-axis from the Fermilab NuMI beam, with a well-defined peak in neutrino energy at 2 GeV. The absolute calibration of the energy scale of the detectors is a major systematic uncertainty in long-baseline oscillation search in NOvA. Neutrino detectors make use of some standard candles for absolute energy calibration. Stopping muon energy distributions, Michel electron energy distributions, and invariant π0 mass are among them. In this talk, we cover NOvA's use of a new method to identify π0 with cosmic origins in the NOvA Far Detector. We employ a computer vision based particle identifier using convolutional neural networks (CVN) to identify π0s, complementing an existing strategy to identify π0 from the neutrino beam using more traditional methods in the Near Detector. Registered for PhD at Cochin University of Science and Technology, India and doing research in NOvA experiment at Fermilab.

High speed reflectometer for EUV mask-blanks

NASA Astrophysics Data System (ADS)

Wies, Christian; Lebert, Rainer; Jagle, Bernhard; Juschkin, L.; Sobel, F.; Seitz, H.; Walter, Ronny; Laubis, C.; Scholze, F.; Biel, W.; Steffens, O.

2005-06-01

AIXUV GmbH and partners have developed a high speed Reflectometer for EUV mask-blanks which is fully compliant with the SEMI-standard P38 for EUV-mask-blank metrology. The system has been installed in June 2004 at SCHOTT Lithotec AG. It features high throughput, high lateral and spectral resolution, high reproducibility and low absolute uncertainty. Using AIXUV's EUV-LAMP and debris mitigation, low cost-of-ownership and high availability is expected. The spectral reflectance of up to 3 mask-blanks per hour can be measured with at least 20 spots each. The system is push button-controlled. Results are stored in CSV file format. For a spot size of 0.1x1 mm2, 2000 spectral channels of 1.6 pm bandwidth are recorded from 11.6 nm to 14.8 nm. The reflectance measurement is based on the comparison of the sample under test to two reference mirrors calibrated at the PTB radiometry laboratory at BESSY II. The three reflection spectra are recorded simultaneously. For each spot more than 107 photons are accumulated in about 20 s, providing statistical reproducibility below 0.2% RMS. The total uncertainty is below 0.5% absolute. Wavelength calibration better than 1 pm RMS over the whole spectral range is achieved by reference to NIST published wavelengths of about 100 xenon emission lines. It is consistent with the wavelength of the krypton 3d-5p absorption resonance at 13.5947 nm to better than 2 pm.

High speed reflectometer for EUV mask-blanks

NASA Astrophysics Data System (ADS)

Wies, C.; Lebert, R.; Jaegle, B.; Juschkin, L.; Sobel, F.; Seitz, H.; Walter, R.; Laubis, C.; Scholze, F.; Biel, W.; Steffens, O.

2005-05-01

AIXUV GmbH and partners have developed a high speed Reflectometer for EUV mask-blanks which is fully compliant with the SEMI-standard P38 for EUV-mask-blank metrology. The system has been installed in June 2004 at SCHOTT Lithotec AG. It features high throughput, high lateral and spectral resolution, high reproduci-bility and low absolute uncertainty. Using AIXUV's EUV-LAMP and debris mitigation, low cost-of-ownership and high availability is expected. The spectral reflectance of up to 3 mask-blanks per hour can be measured with at least 20 spots each. The system is push button-controlled. Results are stored in CSV file format. For a spot size of 0.1×1 mm2, 2000 spectral chan-nels of 1.6 pm bandwidth are recorded from 11.6 nm to 14.8 nm. The reflectance measurement is based on the comparison of the sample under test to two reference mirrors calibrated at the PTB radiometry laboratory at BESSY II. The three reflection spectra are recorded simultaneously. For each spot more than 107 photons are ac-cumulated in about 20 s, providing statistical reproducibility below 0.2 % RMS. The total uncertainty is below 0.5 % absolute. Wavelength calibration better than 1 pm RMS over the whole spectral range is achieved by refe-rence to NIST published wavelengths of about 100 xenon emission lines. It is consistent with the wavelength of the krypton 3d-5p absorption resonance at 13.5947 nm to better than 2 pm.

Uncertainty Analysis of Instrument Calibration and Application

NASA Technical Reports Server (NTRS)

Tripp, John S.; Tcheng, Ping

1999-01-01

Experimental aerodynamic researchers require estimated precision and bias uncertainties of measured physical quantities, typically at 95 percent confidence levels. Uncertainties of final computed aerodynamic parameters are obtained by propagation of individual measurement uncertainties through the defining functional expressions. In this paper, rigorous mathematical techniques are extended to determine precision and bias uncertainties of any instrument-sensor system. Through this analysis, instrument uncertainties determined through calibration are now expressed as functions of the corresponding measurement for linear and nonlinear univariate and multivariate processes. Treatment of correlated measurement precision error is developed. During laboratory calibration, calibration standard uncertainties are assumed to be an order of magnitude less than those of the instrument being calibrated. Often calibration standards do not satisfy this assumption. This paper applies rigorous statistical methods for inclusion of calibration standard uncertainty and covariance due to the order of their application. The effects of mathematical modeling error on calibration bias uncertainty are quantified. The effects of experimental design on uncertainty are analyzed. The importance of replication is emphasized, techniques for estimation of both bias and precision uncertainties using replication are developed. Statistical tests for stationarity of calibration parameters over time are obtained.

Towards a standard for the dynamic measurement of pressure based on laser absorption spectroscopy

PubMed Central

Douglass, K O; Olson, D A

2016-01-01

We describe an approach for creating a standard for the dynamic measurement of pressure based on the measurement of fundamental quantum properties of molecular systems. From the linewidth and intensities of ro-vibrational transitions we plan on making an accurate determination of pressure and temperature. The goal is to achieve an absolute uncertainty for time-varying pressure of 5 % with a measurement rate of 100 kHz, which will in the future serve as a method for the traceable calibration of pressure sensors used in transient processes. To illustrate this concept we have used wavelength modulation spectroscopy (WMS), due to inherent advantages over direct absorption spectroscopy, to perform rapid measurements of carbon dioxide in order to determine the pressure. The system records the full lineshape profile of a single ro-vibrational transition of CO2 at a repetition rate of 4 kHz and with a systematic measurement uncertainty of 12 % for the linewidth measurement. A series of pressures were measured at a rate of 400 Hz (10 averages) and from these measurements the linewidth was determined with a relative uncertainty of about 0.5 % on average. The pressures measured using WMS have an average difference of 0.6 % from the absolute pressure measured with a capacitance diaphragm sensor. PMID:27881884

A Liquid Density Standard Over Wide Ranges of Temperature and Pressure Based on Toluene

PubMed Central

McLinden, Mark O.; Splett, Jolene D.

2008-01-01

The density of liquid toluene has been measured over the temperature range −60 °C to 200 °C with pressures up to 35 MPa. A two-sinker hydrostatic-balance densimeter utilizing a magnetic suspension coupling provided an absolute determination of the density with low uncertainties. These data are the basis of NIST Standard Reference Material® 211d for liquid density over the temperature range −50 °C to 150 °C and pressure range 0.1 MPa to 30 MPa. A thorough uncertainty analysis is presented; this includes effects resulting from the experimental density determination, possible degradation of the sample due to time and exposure to high temperatures, dissolved air, uncertainties in the empirical density model, and the sample-to-sample variations in the SRM vials. Also considered is the effect of uncertainty in the temperature and pressure measurements. This SRM is intended for the calibration of industrial densimeters. PMID:27096111

Uncertainty propagation in the calibration equations for NTC thermistors

NASA Astrophysics Data System (ADS)

Liu, Guang; Guo, Liang; Liu, Chunlong; Wu, Qingwen

2018-06-01

The uncertainty propagation problem is quite important for temperature measurements, since we rely so much on the sensors and calibration equations. Although uncertainty propagation for platinum resistance or radiation thermometers is well known, there have been few publications concerning negative temperature coefficient (NTC) thermistors. Insight into the propagation characteristics of uncertainty that develop when equations are determined using the Lagrange interpolation or least-squares fitting method is presented here with respect to several of the most common equations used in NTC thermistor calibration. Within this work, analytical expressions of the propagated uncertainties for both fitting methods are derived for the uncertainties in the measured temperature and resistance at each calibration point. High-precision calibration of an NTC thermistor in a precision water bath was performed by means of the comparison method. Results show that, for both fitting methods, the propagated uncertainty is flat in the interpolation region but rises rapidly beyond the calibration range. Also, for temperatures interpolated between calibration points, the propagated uncertainty is generally no greater than that associated with the calibration points. For least-squares fitting, the propagated uncertainty is significantly reduced by increasing the number of calibration points and can be well kept below the uncertainty of the calibration points.

New calibrators for the Cepheid period-luminosity relation

NASA Technical Reports Server (NTRS)

Evans, Nancy R.

1992-01-01

IUE spectra of six Cepheids have been used to determine their absolute magnitudes from the spectral types of their binary companions. The stars observed are U Aql, V659 Cen, Y Lac, S Nor, V350 Sgr, and V636 Sco. The absolute magnitude for V659 Cen is more uncertain than for the others because its reddening is poorly determined and the spectral type is hotter than those of the others. In addition, a reddening law with extra absorption in the 2200 A region is necessary, although this has a negligible effect on the absolute magnitude. For the other Cepheids, and also Eta Aql and W Sgr, the standard deviation from the Feast and Walker period-luminosity-color (PLC) relation is 0.37 mag, confirming the previously estimated internal uncertainty. The absolute magnitudes for S Nor from the binary companion and from cluster membership are very similar. The preliminary PLC zero point is less than 2 sigma (+0.21 mag) different from that of Feast and Walker. The same narrowing of the instability strip at low luminosities found by Fernie is seen.

Experimental and Metrological Basis for SI-Traceable Infrared Radiance Measurements From Space

NASA Astrophysics Data System (ADS)

Gero, P. J.; Dykema, J. A.; Anderson, J. G.; Leroy, S. S.

2007-12-01

In order to establish a climate benchmark record and to be useful in interdecadal climate forecast testing, satellite measurements of high spectral resolution infrared radiance must have uncertainty estimates that can be proven beyond a doubt. An uncertainty in radiance of about 1 part in 1000 is required for climate applications. This can be accomplished by appealing to the best measurement practices of the metrology community. The International System of Units (SI) are linked to fundamental physical properties of matter, and can be realized anywhere in the world without bias. By doing so, one can make an accurate observation to within a specified uncertainty. Achieving SI-traceable radiance measurements from space is a novel requirement, and requires specialized sensor design and a disciplined experimental approach. Infrared remote sensing satellite instruments typically employ blackbody calibration targets, which are tied to the SI through Planck's law and the definition of the Kelvin. The blackbody temperature and emissivity, however, must be determined accurately on- orbit, in order for the blackbody emission scale to be SI-traceable. We outline a methodology of instrument design, pre-flight calibration and on-orbit diagnostics for realizing SI- traceable infrared radiance measurements. This instrument is intended as a component of the Climate Absolute Radiance and Refractivity Earth Observatory (CLARREO), a high priority recommendation of the National Research Council decadal survey. Calibration blackbodies for remote sensing differ from a perfect Planckian blackbody; thus the component uncertainties must be evaluated in order to confer traceability. We have performed traceability experiments in the laboratory to verify blackbody temperature, emissivity and the end-to-end radiance scale. We discuss the design of the Harvard standard blackbody and an intercomparison campaign that will be conducted with the GIFTS blackbody (University of Wisconsin, Madison) and radiometric calibration facilities at NIST. The GIFTS blackbody is a high-performance space-qualified design with a new generation of on-orbit thermometer calibration via miniaturized fixed point cells. NIST facilities allow the step-by-step measurement of blackbody surface properties, thermal properties, on-axis emissivity, and end-to-end radiometric performance. These activities will lay the experimental groundwork for achieving SI-traceable infrared radiance measurements on a satellite instrument.

System and method for calibrating a rotary absolute position sensor

NASA Technical Reports Server (NTRS)

Davis, Donald R. (Inventor); Permenter, Frank Noble (Inventor); Radford, Nicolaus A (Inventor)

2012-01-01

A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.

A statistical method for estimating rates of soil development and ages of geologic deposits: A design for soil-chronosequence studies

USGS Publications Warehouse

Switzer, P.; Harden, J.W.; Mark, R.K.

1988-01-01

A statistical method for estimating rates of soil development in a given region based on calibration from a series of dated soils is used to estimate ages of soils in the same region that are not dated directly. The method is designed specifically to account for sampling procedures and uncertainties that are inherent in soil studies. Soil variation and measurement error, uncertainties in calibration dates and their relation to the age of the soil, and the limited number of dated soils are all considered. Maximum likelihood (ML) is employed to estimate a parametric linear calibration curve, relating soil development to time or age on suitably transformed scales. Soil variation on a geomorphic surface of a certain age is characterized by replicate sampling of soils on each surface; such variation is assumed to have a Gaussian distribution. The age of a geomorphic surface is described by older and younger bounds. This technique allows age uncertainty to be characterized by either a Gaussian distribution or by a triangular distribution using minimum, best-estimate, and maximum ages. The calibration curve is taken to be linear after suitable (in certain cases logarithmic) transformations, if required, of the soil parameter and age variables. Soil variability, measurement error, and departures from linearity are described in a combined fashion using Gaussian distributions with variances particular to each sampled geomorphic surface and the number of sample replicates. Uncertainty in age of a geomorphic surface used for calibration is described using three parameters by one of two methods. In the first method, upper and lower ages are specified together with a coverage probability; this specification is converted to a Gaussian distribution with the appropriate mean and variance. In the second method, "absolute" older and younger ages are specified together with a most probable age; this specification is converted to an asymmetric triangular distribution with mode at the most probable age. The statistical variability of the ML-estimated calibration curve is assessed by a Monte Carlo method in which simulated data sets repeatedly are drawn from the distributional specification; calibration parameters are reestimated for each such simulation in order to assess their statistical variability. Several examples are used for illustration. The age of undated soils in a related setting may be estimated from the soil data using the fitted calibration curve. A second simulation to assess age estimate variability is described and applied to the examples. ?? 1988 International Association for Mathematical Geology.

Planar imaging of OH density distributions in a supersonic combustion tunnel

NASA Technical Reports Server (NTRS)

Quagliaroli, T. M.; Laufer, G.; Krauss, R. H.; Mcdaniel, J. C., Jr.

1993-01-01

Images of absolute OH number density were obtained using planar laser-induced fluorescence (PLIF) in a supersonic H2-air combustion tunnel. A tunable KrF excimer laser was used to excite the Q2(11) ro-vibronic line. Calibration of the PLIF images was obtained by referencing the signal measured in the flame to that obtained by the excitation of OH produced by thermal dissociation of H2O in an atmospheric furnace. Measurement errors due to uncertainty in internal furnace atmospheric conditions and image temperature correction are estimated.

Goddard Laser for Absolute Measurement of Radiance for Instrument Calibration in the Ultraviolet to Short Wave Infrared

NASA Technical Reports Server (NTRS)

McAndrew, Brendan; McCorkel, Joel; Shuman, Timothy; Zukowski, Barbara; Traore, Aboubakar; Rodriguez, Michael; Brown, Steven; Woodward, John

2018-01-01

A description of the Goddard Laser for Absolute Calibration of Radiance, a tunable, narrow linewidth spectroradiometric calibration tool, and results from calibration of an earth science satellite instrument from ultraviolet to short wave infrared wavelengths.

A highly accurate absolute gravimetric network for Albania, Kosovo and Montenegro

NASA Astrophysics Data System (ADS)

Ullrich, Christian; Ruess, Diethard; Butta, Hubert; Qirko, Kristaq; Pavicevic, Bozidar; Murat, Meha

2016-04-01

The objective of this project is to establish a basic gravity network in Albania, Kosovo and Montenegro to enable further investigations in geodetic and geophysical issues. Therefore the first time in history absolute gravity measurements were performed in these countries. The Norwegian mapping authority Kartverket is assisting the national mapping authorities in Kosovo (KCA) (Kosovo Cadastral Agency - Agjencia Kadastrale e Kosovës), Albania (ASIG) (Autoriteti Shtetëror i Informacionit Gjeohapësinor) and in Montenegro (REA) (Real Estate Administration of Montenegro - Uprava za nekretnine Crne Gore) in improving the geodetic frameworks. The gravity measurements are funded by Kartverket. The absolute gravimetric measurements were performed from BEV (Federal Office of Metrology and Surveying) with the absolute gravimeter FG5-242. As a national metrology institute (NMI) the Metrology Service of the BEV maintains the national standards for the realisation of the legal units of measurement and ensures their international equivalence and recognition. Laser and clock of the absolute gravimeter were calibrated before and after the measurements. The absolute gravimetric survey was carried out from September to October 2015. Finally all 8 scheduled stations were successfully measured: there are three stations located in Montenegro, two stations in Kosovo and three stations in Albania. The stations are distributed over the countries to establish a gravity network for each country. The vertical gradients were measured at all 8 stations with the relative gravimeter Scintrex CG5. The high class quality of some absolute gravity stations can be used for gravity monitoring activities in future. The measurement uncertainties of the absolute gravity measurements range around 2.5 micro Gal at all stations (1 microgal = 10-8 m/s2). In Montenegro the large gravity difference of 200 MilliGal between station Zabljak and Podgorica can be even used for calibration of relative gravimeters. The complete basic gravimetric network of these countries will be tied to these absolute stations. In this presentation all the stations and results will be presented in detail and some special results analysed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moseev, D., E-mail: dmitry.moseev@ipp.mpg.de; Laqua, H. P.; Marsen, S.

Here we report the first measurements of the power levels of stray radiation in the vacuum vessel of Wendelstein 7-X using absolutely calibrated sniffer probes. The absolute calibration is achieved by using calibrated sources of stray radiation and the implicit measurement of the quality factor of the Wendelstein 7-X empty vacuum vessel. Normalized absolute calibration coefficients agree with the cross-calibration coefficients that are obtained by the direct measurements, indicating that the measured absolute calibration coefficients and stray radiation levels in the vessel are valid. Close to the launcher, the stray radiation in the empty vessel reaches power levels up tomore » 340 kW/m{sup 2} per MW injected beam power. Furthest away from the launcher, i.e., half a toroidal turn, still 90 kW/m{sup 2} per MW injected beam power is measured.« less

Comparison of the uncertainties of several European low-dose calibration facilities

NASA Astrophysics Data System (ADS)

Dombrowski, H.; Cornejo Díaz, N. A.; Toni, M. P.; Mihelic, M.; Röttger, A.

2018-04-01

The typical uncertainty of a low-dose rate calibration of a detector, which is calibrated in a dedicated secondary national calibration laboratory, is investigated, including measurements in the photon field of metrology institutes. Calibrations at low ambient dose equivalent rates (at the level of the natural ambient radiation) are needed when environmental radiation monitors are to be characterised. The uncertainties of calibration measurements in conventional irradiation facilities above ground are compared with those obtained in a low-dose rate irradiation facility located deep underground. Four laboratories quantitatively evaluated the uncertainties of their calibration facilities, in particular for calibrations at low dose rates (250 nSv/h and 1 μSv/h). For the first time, typical uncertainties of European calibration facilities are documented in a comparison and the main sources of uncertainty are revealed. All sources of uncertainties are analysed, including the irradiation geometry, scattering, deviations of real spectra from standardised spectra, etc. As a fundamental metrological consequence, no instrument calibrated in such a facility can have a lower total uncertainty in subsequent measurements. For the first time, the need to perform calibrations at very low dose rates (< 100 nSv/h) deep underground is underpinned on the basis of quantitative data.

Spectroradiometric considerations for advanced land observing systems

NASA Technical Reports Server (NTRS)

Slater, P. N.

1986-01-01

Research aimed at improving the inflight absolute radiometric calibration of advanced land observing systems was initiated. Emphasis was on the satellite sensor calibration program at White Sands. Topics addressed include: absolute radiometric calibration of advanced remote sensing; atmospheric effects on reflected radiation; inflight radiometric calibration; field radiometric methods for reflectance and atmospheric measurement; and calibration of field relectance radiometers.

Novel calibration for LA-ICP-MS-based fission-track thermochronology

NASA Astrophysics Data System (ADS)

Soares, C. J.; Guedes, S.; Hadler, J. C.; Mertz-Kraus, R.; Zack, T.; Iunes, P. J.

2014-01-01

We present a novel age-equation calibration for fission-track age determinations by laser ablation inductively coupled plasma mass spectrometry. This new calibration incorporates the efficiency factor of an internal surface, [ ηq]is, which is obtained by measuring the projected fission-track length, allowing the determination of FT ages directly using the recommended spontaneous fission decay constant. Also, the uranium concentrations in apatite samples are determined using a Durango (Dur-2, 7.44 μg/g U) crystal and a Mud Tank (MT-7, 6.88 μg/g U) crystal as uranium reference materials. The use of matrix-matched reference materials allows a reduction in the uncertainty of the uranium measurements to those related to counting statistics, which are ca. 1 % taking into account that no extra source of uncertainty has to be considered. The equations as well as the matrix-matched reference materials are evaluated using well-dated samples from Durango, Fish Canyon Tuff, and Limberg as unknown samples. The results compare well with their respective published ages determined through other dating methods. Additionally, the results agree with traditional fission-track ages using both the zeta approach and the absolute approach, suggesting that the calibration presented in this work can be robustly applied in geological context. Furthermore, considering that fission-track ages can be determined without an age standard sample, the fission-track thermochronology approach presented here is assumed to be a valuable dating tool.

Uncertainty analysis of a groundwater flow model in east-central Florida

USGS Publications Warehouse

Sepúlveda, Nicasio; Doherty, John E.

2014-01-01

A groundwater flow model for east-central Florida has been developed to help water-resource managers assess the impact of increased groundwater withdrawals from the Floridan aquifer system on heads and spring flows originating from the Upper Floridan aquifer. The model provides a probabilistic description of predictions of interest to water-resource managers, given the uncertainty associated with system heterogeneity, the large number of input parameters, and a nonunique groundwater flow solution. The uncertainty associated with these predictions can then be considered in decisions with which the model has been designed to assist. The “Null Space Monte Carlo” method is a stochastic probabilistic approach used to generate a suite of several hundred parameter field realizations, each maintaining the model in a calibrated state, and each considered to be hydrogeologically plausible. The results presented herein indicate that the model’s capacity to predict changes in heads or spring flows that originate from increased groundwater withdrawals is considerably greater than its capacity to predict the absolute magnitudes of heads or spring flows. Furthermore, the capacity of the model to make predictions that are similar in location and in type to those in the calibration dataset exceeds its capacity to make predictions of different types at different locations. The quantification of these outcomes allows defensible use of the modeling process in support of future water-resources decisions. The model allows the decision-making process to recognize the uncertainties, and the spatial/temporal variability of uncertainties that are associated with predictions of future system behavior in a complex hydrogeological context.

Uncertainty analysis of a groundwater flow model in East-central Florida.

PubMed

Sepúlveda, Nicasio; Doherty, John

2015-01-01

A groundwater flow model for east-central Florida has been developed to help water-resource managers assess the impact of increased groundwater withdrawals from the Floridan aquifer system on heads and spring flows originating from the Upper Floridan Aquifer. The model provides a probabilistic description of predictions of interest to water-resource managers, given the uncertainty associated with system heterogeneity, the large number of input parameters, and a nonunique groundwater flow solution. The uncertainty associated with these predictions can then be considered in decisions with which the model has been designed to assist. The "Null Space Monte Carlo" method is a stochastic probabilistic approach used to generate a suite of several hundred parameter field realizations, each maintaining the model in a calibrated state, and each considered to be hydrogeologically plausible. The results presented herein indicate that the model's capacity to predict changes in heads or spring flows that originate from increased groundwater withdrawals is considerably greater than its capacity to predict the absolute magnitudes of heads or spring flows. Furthermore, the capacity of the model to make predictions that are similar in location and in type to those in the calibration dataset exceeds its capacity to make predictions of different types at different locations. The quantification of these outcomes allows defensible use of the modeling process in support of future water-resources decisions. The model allows the decision-making process to recognize the uncertainties, and the spatial or temporal variability of uncertainties that are associated with predictions of future system behavior in a complex hydrogeological context. © 2014, National Ground Water Association.

Results of Absolute Cavity Pyrgeometer and Infrared Integrating Sphere Comparisons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, Ibrahim M; Sengupta, Manajit; Dooraghi, Michael R

Accurate and traceable atmospheric longwave irradiance measurements are required for understanding radiative impacts on the Earth's energy budget. The standard to which pyrgeometers are traceable is the interim World Infrared Standard Group (WISG), maintained in the Physikalisch-Meteorologisches Observatorium Davos (PMOD). The WISG consists of four pyrgeometers that were calibrated using Rolf Philipona's Absolute Sky-scanning Radiometer [1]. The Atmospheric Radiation Measurement (ARM) facility has recently adopted the WISG to maintain the traceability of the calibrations of all Eppley precision infrared radiometer (PIR) pyrgeometers. Subsequently, Julian Grobner [2] developed the infrared interferometer spectrometer and radiometer (IRIS) radiometer, and Ibrahim Reda [3] developedmore » the absolute cavity pyrgeometer (ACP). The ACP and IRIS were developed to establish a world reference for calibrating pyrgeometers with traceability to the International System of Units (SI). The two radiometers are unwindowed with negligible spectral dependence, and they are traceable to SI units through the temperature scale (ITS-90). The two instruments were compared directly to the WISG three times at PMOD and twice at the Southern Great Plains (SGP) facility to WISG-traceable pyrgeometers. The ACP and IRIS agreed within +/- 1 W/m2 to +/- 3 W/m2 in all comparisons, whereas the WISG references exhibit a 2-5 Wm2 low bias compared to the ACP/IRIS average, depending on the water vapor column, as noted in Grobner et al. [4]. Consequently, a case for changing the current WISG has been made by Grobner and Reda. However, during the five comparisons the column water vapor exceeded 8 mm. Therefore, it is recommended that more ACP and IRIS comparisons should be held under different environmental conditions and water vapor column content to better establish the traceability of these instruments to SI with established uncertainty.« less

Nist Microwave Blackbody: The Design, Testing, and Verification of a Conical Brightness Temperature Source

NASA Astrophysics Data System (ADS)

Houtz, Derek Anderson

Microwave radiometers allow remote sensing of earth and atmospheric temperatures from space, anytime, anywhere, through clouds, and in the dark. Data from microwave radiometers are high-impact operational inputs to weather forecasts, and are used to provide a vast array of climate data products including land and sea surface temperatures, soil moisture, ocean salinity, cloud precipitation and moisture height profiles, and even wind speed and direction, to name a few. Space-borne microwave radiometers have a major weakness when it comes to long-term climate trends due to their lack of traceability. Because there is no standard, or absolute reference, for microwave brightness temperature, nationally or internationally, individual instruments must each rely on their own internal calibration source to set an absolute reference to the fundamental unit of Kelvin. This causes each subsequent instrument to have a calibration offset and there is no 'true' reference. The work introduced in this thesis addresses this vacancy by proposing and introducing a NIST microwave brightness temperature source that may act as the primary reference. The NIST standard will allow pre-launch calibration of radiometers across a broad range of remote sensing pertinent frequencies between 18 GHz and 220 GHz. The blackbody will be capable of reaching temperatures ranging between liquid nitrogen boiling at approximately 77 K and warm-target temperature of 350 K. The brightness temperature of the source has associated standard uncertainty ranging as a function of frequency between 0.084 K and 0.111 K. The standard can be transferred to the calibration source in the instrument, providing traceability of all subsequent measurements back to the primary standard. The development of the NIST standard source involved predicting and measuring its brightness temperature, and minimizing the associated uncertainty of this quantity. Uniform and constant physical temperature along with well characterized and maximized emissivity are fundamental to a well characterized blackbody. The chosen geometry is a microwave absorber coated copper cone. Electromagnetic and thermal simulations are introduced to optimize the design. Experimental verifications of the simulated quantities confirm the predicted performance of the blackbody.

An absolute photometric system at 10 and 20 microns

NASA Technical Reports Server (NTRS)

Rieke, G. H.; Lebofsky, M. J.; Low, F. J.

1985-01-01

Two new direct calibrations at 10 and 20 microns are presented in which terrestrial flux standards are referred to infrared standard stars. These measurements give both good agreement and higher accuracy when compared with previous direct calibrations. As a result, the absolute calibrations at 10 and 20 microns have now been determined with accuracies of 3 and 8 percent, respectively. A variety of absolute calibrations based on extrapolation of stellar spectra from the visible to 10 microns are reviewed. Current atmospheric models of A-type stars underestimate their fluxes by about 10 percent at 10 microns, whereas models of solar-type stars agree well with the direct calibrations. The calibration at 20 microns can probably be determined to about 5 percent by extrapolation from the more accurate result at 10 microns. The photometric system at 10 and 20 microns is updated to reflect the new absolute calibration, to base its zero point directly on the colors of A0 stars, and to improve the accuracy in the comparison of the standard stars.

Quantifying the Climate-Scale Accuracy of Satellite Cloud Retrievals

NASA Astrophysics Data System (ADS)

Roberts, Y.; Wielicki, B. A.; Sun-Mack, S.; Minnis, P.; Liang, L.; Di Girolamo, L.

2014-12-01

Instrument calibration and cloud retrieval algorithms have been developed to minimize retrieval errors on small scales. However, measurement uncertainties and assumptions within retrieval algorithms at the pixel level may alias into decadal-scale trends of cloud properties. We first, therefore, quantify how instrument calibration changes could alias into cloud property trends. For a perfect observing system the climate trend accuracy is limited only by the natural variability of the climate variable. Alternatively, for an actual observing system, the climate trend accuracy is additionally limited by the measurement uncertainty. Drifts in calibration over time may therefore be disguised as a true climate trend. We impose absolute calibration changes to MODIS spectral reflectance used as input to the CERES Cloud Property Retrieval System (CPRS) and run the modified MODIS reflectance through the CPRS to determine the sensitivity of cloud properties to calibration changes. We then use these changes to determine the impact of instrument calibration changes on trend uncertainty in reflected solar cloud properties. Secondly, we quantify how much cloud retrieval algorithm assumptions alias into cloud optical retrieval trends by starting with the largest of these biases: the plane-parallel assumption in cloud optical thickness (τC) retrievals. First, we collect liquid water cloud fields obtained from Multi-angle Imaging Spectroradiometer (MISR) measurements to construct realistic probability distribution functions (PDFs) of 3D cloud anisotropy (a measure of the degree to which clouds depart from plane-parallel) for different ISCCP cloud types. Next, we will conduct a theoretical study with dynamically simulated cloud fields and a 3D radiative transfer model to determine the relationship between 3D cloud anisotropy and 3D τC bias for each cloud type. Combining these results provides distributions of 3D τC bias by cloud type. Finally, we will estimate the change in frequency of occurrence of cloud types between two decades and will have the information needed to calculate the total change in 3D optical thickness bias between two decades. If we uncover aliases in this study, the results will motivate the development and rigorous testing of climate specific cloud retrieval algorithms.

Evaluation of assigned-value uncertainty for complex calibrator value assignment processes: a prealbumin example.

PubMed

Middleton, John; Vaks, Jeffrey E

2007-04-01

Errors of calibrator-assigned values lead to errors in the testing of patient samples. The ability to estimate the uncertainties of calibrator-assigned values and other variables minimizes errors in testing processes. International Organization of Standardization guidelines provide simple equations for the estimation of calibrator uncertainty with simple value-assignment processes, but other methods are needed to estimate uncertainty in complex processes. We estimated the assigned-value uncertainty with a Monte Carlo computer simulation of a complex value-assignment process, based on a formalized description of the process, with measurement parameters estimated experimentally. This method was applied to study uncertainty of a multilevel calibrator value assignment for a prealbumin immunoassay. The simulation results showed that the component of the uncertainty added by the process of value transfer from the reference material CRM470 to the calibrator is smaller than that of the reference material itself (<0.8% vs 3.7%). Varying the process parameters in the simulation model allowed for optimizing the process, while keeping the added uncertainty small. The patient result uncertainty caused by the calibrator uncertainty was also found to be small. This method of estimating uncertainty is a powerful tool that allows for estimation of calibrator uncertainty for optimization of various value assignment processes, with a reduced number of measurements and reagent costs, while satisfying the requirements to uncertainty. The new method expands and augments existing methods to allow estimation of uncertainty in complex processes.

Validation of modelled imaging plates sensitivity to 1-100 keV x-rays and spatial resolution characterisation for diagnostics for the "PETawatt Aquitaine Laser".

PubMed

Boutoux, G; Batani, D; Burgy, F; Ducret, J-E; Forestier-Colleoni, P; Hulin, S; Rabhi, N; Duval, A; Lecherbourg, L; Reverdin, C; Jakubowska, K; Szabo, C I; Bastiani-Ceccotti, S; Consoli, F; Curcio, A; De Angelis, R; Ingenito, F; Baggio, J; Raffestin, D

2016-04-01

Thanks to their high dynamic range and ability to withstand electromagnetic pulse, imaging plates (IPs) are commonly used as passive detectors in laser-plasma experiments. In the framework of the development of the diagnostics for the Petawatt Aquitaine Laser facility, we present an absolute calibration and spatial resolution study of five different available types of IP (namely, MS-SR-TR-MP-ND) performed by using laser-induced K-shell X-rays emitted by a solid silver target irradiated by the laser ECLIPSE at CEntre Lasers Intenses et Applications. In addition, IP sensitivity measurements were performed with a 160 kV X-ray generator at CEA DAM DIF, where the absolute response of IP SR and TR has been calibrated to X-rays in the energy range 8-75 keV with uncertainties of about 15%. Finally, the response functions have been modeled in Monte Carlo GEANT4 simulations in order to reproduce experimental data. Simulations enable extrapolation of the IP response functions to photon energies from 1 keV to 1 GeV, of interest, e.g., for laser-driven radiography.

Validation of modelled imaging plates sensitivity to 1-100 keV x-rays and spatial resolution characterisation for diagnostics for the "PETawatt Aquitaine Laser"

NASA Astrophysics Data System (ADS)

Boutoux, G.; Batani, D.; Burgy, F.; Ducret, J.-E.; Forestier-Colleoni, P.; Hulin, S.; Rabhi, N.; Duval, A.; Lecherbourg, L.; Reverdin, C.; Jakubowska, K.; Szabo, C. I.; Bastiani-Ceccotti, S.; Consoli, F.; Curcio, A.; De Angelis, R.; Ingenito, F.; Baggio, J.; Raffestin, D.

2016-04-01

Thanks to their high dynamic range and ability to withstand electromagnetic pulse, imaging plates (IPs) are commonly used as passive detectors in laser-plasma experiments. In the framework of the development of the diagnostics for the Petawatt Aquitaine Laser facility, we present an absolute calibration and spatial resolution study of five different available types of IP (namely, MS-SR-TR-MP-ND) performed by using laser-induced K-shell X-rays emitted by a solid silver target irradiated by the laser ECLIPSE at CEntre Lasers Intenses et Applications. In addition, IP sensitivity measurements were performed with a 160 kV X-ray generator at CEA DAM DIF, where the absolute response of IP SR and TR has been calibrated to X-rays in the energy range 8-75 keV with uncertainties of about 15%. Finally, the response functions have been modeled in Monte Carlo GEANT4 simulations in order to reproduce experimental data. Simulations enable extrapolation of the IP response functions to photon energies from 1 keV to 1 GeV, of interest, e.g., for laser-driven radiography.

Four Years of Absolutely Calibrated Hyperspectral Data from the Atmospheric Infrared Sounder (AIRS) on the Eos Aqua

NASA Technical Reports Server (NTRS)

Aumann, Hartmut H.; Broberg, Steve; Elliott, Denis; Gregorich, Dave

2006-01-01

This viewgraph presentation reviews four years of absolute calibration of hyperspectral data from the AIRS instrument located on the EOS AQUA spacecraft. The following topics are discussed: 1) A quick overview of AIRS; 2) What absolute calibration accuracy and stability are required for climate applications?; 3) Validating of radiance accuracy and stability: Results from four years of AIRS data; and 4) Conclusions.

Improvements in absolute seismometer sensitivity calibration using local earth gravity measurements

USGS Publications Warehouse

Anthony, Robert E.; Ringler, Adam; Wilson, David

2018-01-01

The ability to determine both absolute and relative seismic amplitudes is fundamentally limited by the accuracy and precision with which scientists are able to calibrate seismometer sensitivities and characterize their response. Currently, across the Global Seismic Network (GSN), errors in midband sensitivity exceed 3% at the 95% confidence interval and are the least‐constrained response parameter in seismic recording systems. We explore a new methodology utilizing precise absolute Earth gravity measurements to determine the midband sensitivity of seismic instruments. We first determine the absolute sensitivity of Kinemetrics EpiSensor accelerometers to 0.06% at the 99% confidence interval by inverting them in a known gravity field at the Albuquerque Seismological Laboratory (ASL). After the accelerometer is calibrated, we install it in its normal configuration next to broadband seismometers and subject the sensors to identical ground motions to perform relative calibrations of the broadband sensors. Using this technique, we are able to determine the absolute midband sensitivity of the vertical components of Nanometrics Trillium Compact seismometers to within 0.11% and Streckeisen STS‐2 seismometers to within 0.14% at the 99% confidence interval. The technique enables absolute calibrations from first principles that are traceable to National Institute of Standards and Technology (NIST) measurements while providing nearly an order of magnitude more precision than step‐table calibrations.

A reassessment of absolute energies of the x-ray L lines of lanthanide metals

NASA Astrophysics Data System (ADS)

Fowler, J. W.; Alpert, B. K.; Bennett, D. A.; Doriese, W. B.; Gard, J. D.; Hilton, G. C.; Hudson, L. T.; Joe, Y.-I.; Morgan, K. M.; O'Neil, G. C.; Reintsema, C. D.; Schmidt, D. R.; Swetz, D. S.; Szabo, C. I.; Ullom, J. N.

2017-08-01

We introduce a new technique for determining x-ray fluorescence line energies and widths, and we present measurements made with this technique of 22 x-ray L lines from lanthanide-series elements. The technique uses arrays of transition-edge sensors, microcalorimeters with high energy-resolving power that simultaneously observe both calibrated x-ray standards and the x-ray emission lines under study. The uncertainty in absolute line energies is generally less than 0.4 eV in the energy range of 4.5 keV to 7.5 keV. Of the seventeen line energies of neodymium, samarium, and holmium, thirteen are found to be consistent with the available x-ray reference data measured after 1990; only two of the four lines for which reference data predate 1980, however, are consistent with our results. Five lines of terbium are measured with uncertainties that improve on those of existing data by factors of two or more. These results eliminate a significant discrepancy between measured and calculated x-ray line energies for the terbium L l line (5.551 keV). The line widths are also measured, with uncertainties of 0.6 eV or less on the full-width at half-maximum in most cases. These measurements were made with an array of approximately one hundred superconducting x-ray microcalorimeters, each sensitive to an energy band from 1 keV to 8 keV. No energy-dispersive spectrometer has previously been used for absolute-energy estimation at this level of accuracy. Future spectrometers, with superior linearity and energy resolution, will allow us to improve on these results and expand the measurements to more elements and a wider range of line energies.

Uncertainties in Coastal Ocean Color Products: Impacts of Spatial Sampling

NASA Technical Reports Server (NTRS)

Pahlevan, Nima; Sarkar, Sudipta; Franz, Bryan A.

2016-01-01

With increasing demands for ocean color (OC) products with improved accuracy and well characterized, per-retrieval uncertainty budgets, it is vital to decompose overall estimated errors into their primary components. Amongst various contributing elements (e.g., instrument calibration, atmospheric correction, inversion algorithms) in the uncertainty of an OC observation, less attention has been paid to uncertainties associated with spatial sampling. In this paper, we simulate MODIS (aboard both Aqua and Terra) and VIIRS OC products using 30 m resolution OC products derived from the Operational Land Imager (OLI) aboard Landsat-8, to examine impacts of spatial sampling on both cross-sensor product intercomparisons and in-situ validations of R(sub rs) products in coastal waters. Various OLI OC products representing different productivity levels and in-water spatial features were scanned for one full orbital-repeat cycle of each ocean color satellite. While some view-angle dependent differences in simulated Aqua-MODIS and VIIRS were observed, the average uncertainties (absolute) in product intercomparisons (due to differences in spatial sampling) at regional scales are found to be 1.8%, 1.9%, 2.4%, 4.3%, 2.7%, 1.8%, and 4% for the R(sub rs)(443), R(sub rs)(482), R(sub rs)(561), R(sub rs)(655), Chla, K(sub d)(482), and b(sub bp)(655) products, respectively. It is also found that, depending on in-water spatial variability and the sensor's footprint size, the errors for an in-situ validation station in coastal areas can reach as high as +/- 18%. We conclude that a) expected biases induced by the spatial sampling in product intercomparisons are mitigated when products are averaged over at least 7 km × 7 km areas, b) VIIRS observations, with improved consistency in cross-track spatial sampling, yield more precise calibration/validation statistics than that of MODIS, and c) use of a single pixel centered on in-situ coastal stations provides an optimal sampling size for validation efforts. These findings will have implications for enhancing our understanding of uncertainties in ocean color retrievals and for planning of future ocean color missions and the associated calibration/validation exercises.

Iterative Boltzmann plot method for temperature and pressure determination in a xenon high pressure discharge lamp

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zalach, J.; Franke, St.

2013-01-28

The Boltzmann plot method allows to calculate plasma temperatures and pressures if absolutely calibrated emission coefficients of spectral lines are available. However, xenon arcs are not very well suited to be analyzed this way, as there are only a limited number of lines with atomic data available. These lines have high excitation energies in a small interval between 9.8 and 11.5 eV. Uncertainties in the experimental method and in the atomic data further limit the accuracy of the evaluation procedure. This may result in implausible values of temperature and pressure with inadmissible uncertainty. To omit these shortcomings, an iterative schememore » is proposed that is making use of additional information about the xenon fill pressure. This method is proved to be robust against noisy data and significantly reduces the uncertainties. Intentionally distorted synthetic data are used to illustrate the performance of the method, and measurements performed on a laboratory xenon high pressure discharge lamp are analyzed resulting in reasonable temperatures and pressures with significantly reduced uncertainties.« less

Creation and Validation of Sintered PTFE BRDF Targets & Standards

PubMed Central

Durell, Christopher; Scharpf, Dan; McKee, Greg; L’Heureux, Michelle; Georgiev, Georgi; Obein, Gael; Cooksey, Catherine

2016-01-01

Sintered polytetrafluoroethylene (PTFE) is an extremely stable, near-perfect Lambertian reflecting diffuser and calibration standard material that has been used by national labs, space, aerospace and commercial sectors for over two decades. New uncertainty targets of 2 % on-orbit absolute validation in the Earth Observing Systems community have challenged the industry to improve is characterization and knowledge of almost every aspect of radiometric performance (space and ground). Assuming “near perfect” reflectance for angular dependent measurements is no longer going to suffice for many program needs. The total hemispherical spectral reflectance provides a good mark of general performance; but, without the angular characterization of bidirectional reflectance distribution function (BRDF) measurements, critical data is missing from many applications and uncertainty budgets. Therefore, traceable BRDF measurement capability is needed to characterize sintered PTFE’s angular response and provide a full uncertainty profile to users. This paper presents preliminary comparison measurements of the BRDF of sintered PTFE from several laboratories to better quantify the BRDF of sintered PTFE, assess the BRDF measurement comparability between laboratories, and improve estimates of measurement uncertainties under laboratory conditions. PMID:26900206

Creation and Validation of Sintered PTFE BRDF Targets & Standards.

PubMed

Durell, Christopher; Scharpf, Dan; McKee, Greg; L'Heureux, Michelle; Georgiev, Georgi; Obein, Gael; Cooksey, Catherine

2015-09-21

Sintered polytetrafluoroethylene (PTFE) is an extremely stable, near-perfect Lambertian reflecting diffuser and calibration standard material that has been used by national labs, space, aerospace and commercial sectors for over two decades. New uncertainty targets of 2 % on-orbit absolute validation in the Earth Observing Systems community have challenged the industry to improve is characterization and knowledge of almost every aspect of radiometric performance (space and ground). Assuming "near perfect" reflectance for angular dependent measurements is no longer going to suffice for many program needs. The total hemispherical spectral reflectance provides a good mark of general performance; but, without the angular characterization of bidirectional reflectance distribution function (BRDF) measurements, critical data is missing from many applications and uncertainty budgets. Therefore, traceable BRDF measurement capability is needed to characterize sintered PTFE's angular response and provide a full uncertainty profile to users. This paper presents preliminary comparison measurements of the BRDF of sintered PTFE from several laboratories to better quantify the BRDF of sintered PTFE, assess the BRDF measurement comparability between laboratories, and improve estimates of measurement uncertainties under laboratory conditions.

Absolute Magnitude Calibration for Dwarfs Based on the Colour-Magnitude Diagrams of Galactic Clusters

NASA Astrophysics Data System (ADS)

Karaali, S.; Gökçe, E. Yaz; Bilir, S.; Güçtekin, S. Tunçel

2014-07-01

We present two absolute magnitude calibrations for dwarfs based on colour-magnitude diagrams of Galactic clusters. The combination of the Mg absolute magnitudes of the dwarf fiducial sequences of the clusters M92, M13, M5, NGC 2420, M67, and NGC 6791 with the corresponding metallicities provides absolute magnitude calibration for a given (g - r)0 colour. The calibration is defined in the colour interval 0.25 ≤ (g - r)0 ≤ 1.25 mag and it covers the metallicity interval - 2.15 ≤ [Fe/H] ≤ +0.37 dex. The absolute magnitude residuals obtained by the application of the procedure to another set of Galactic clusters lie in the interval - 0.15 ≤ ΔMg ≤ +0.12 mag. The mean and standard deviation of the residuals are < ΔMg > = - 0.002 and σ = 0.065 mag, respectively. The calibration of the MJ absolute magnitude in terms of metallicity is carried out by using the fiducial sequences of the clusters M92, M13, 47 Tuc, NGC 2158, and NGC 6791. It is defined in the colour interval 0.90 ≤ (V - J)0 ≤ 1.75 mag and it covers the same metallicity interval of the Mg calibration. The absolute magnitude residuals obtained by the application of the procedure to the cluster M5 ([Fe/H] = -1.40 dex) and 46 solar metallicity, - 0.45 ≤ [Fe/H] ≤ +0.35 dex, field stars lie in the interval - 0.29 and + 0.35 mag. However, the range of 87% of them is rather shorter, - 0.20 ≤ ΔMJ ≤ +0.20 mag. The mean and standard deviation of all residuals are < ΔMJ > =0.05 and σ = 0.13 mag, respectively. The derived relations are applicable to stars older than 4 Gyr for the Mg calibration, and older than 2 Gyr for the MJ calibration. The cited limits are the ages of the youngest calibration clusters in the two systems.

Uncertainty Analysis of Inertial Model Attitude Sensor Calibration and Application with a Recommended New Calibration Method

NASA Technical Reports Server (NTRS)

Tripp, John S.; Tcheng, Ping

1999-01-01

Statistical tools, previously developed for nonlinear least-squares estimation of multivariate sensor calibration parameters and the associated calibration uncertainty analysis, have been applied to single- and multiple-axis inertial model attitude sensors used in wind tunnel testing to measure angle of attack and roll angle. The analysis provides confidence and prediction intervals of calibrated sensor measurement uncertainty as functions of applied input pitch and roll angles. A comparative performance study of various experimental designs for inertial sensor calibration is presented along with corroborating experimental data. The importance of replicated calibrations over extended time periods has been emphasized; replication provides independent estimates of calibration precision and bias uncertainties, statistical tests for calibration or modeling bias uncertainty, and statistical tests for sensor parameter drift over time. A set of recommendations for a new standardized model attitude sensor calibration method and usage procedures is included. The statistical information provided by these procedures is necessary for the uncertainty analysis of aerospace test results now required by users of industrial wind tunnel test facilities.

First Absolutely Calibrated Localized Measurements of Ion Velocity in the MST in Locked and Rotating Plasmas

NASA Astrophysics Data System (ADS)

Baltzer, M.; Craig, D.; den Hartog, D. J.; Nornberg, M. D.; Munaretto, S.

2015-11-01

An Ion Doppler Spectrometer (IDS) is used on MST for high time-resolution passive and active measurements of impurity ion emission. Absolutely calibrated measurements of flow are difficult because the spectrometer records data within 0.3 nm of the C+5 line of interest, and commercial calibration lamps do not produce lines in this narrow range . A novel optical system was designed to absolutely calibrate the IDS. The device uses an UV LED to produce a broad emission curve in the desired region. A Fabry-Perot etalon filters this light, cutting transmittance peaks into the pattern of the LED emission. An optical train of fused silica lenses focuses the light into the IDS with f/4. A holographic diffuser blurs the light cone to increase homogeneity. Using this light source, the absolute Doppler shift of ion emissions can be measured in MST plasmas. In combination with charge exchange recombination spectroscopy, localized ion velocities can now be measured. Previously, a time-averaged measurement along the chord bisecting the poloidal plane was used to calibrate the IDS; the quality of these central chord calibrations can be characterized with our absolute calibration. Calibration errors may also be quantified and minimized by optimizing the curve-fitting process. Preliminary measurements of toroidal velocity in locked and rotating plasmas will be shown. This work has been supported by the US DOE.

Measurement of Far-Infrared Paint Emissivity for Reference Blackbody Modeling and Design

NASA Astrophysics Data System (ADS)

Kaplan, S. G.; Hanssen, L. M.; Mekhontsev, S. N.

2008-12-01

Blackbody sources are typically used for both ground-based and on-orbit calibration of infrared radiometers for atmospheric sounding. Accurate knowledge of the emissivity (or reflectivity) of the painted cavity surfaces is important for the design and modeling of the blackbody performance. Devices designed for the mid- to long-wave infrared (2 μm to 100 μm) generally use specular black paint and multiple (4 to 6) bounces to achieve high emissivity and uniform radiance over the required optical extent. To meet the CLARREO goal of long-term climate monitoring with an absolute uncertainty of < 0.1 K (3 σ), it will be necessary to calibrate radiance measurements to < 0.1 % uncertainty, which could require knowledge of paint emissivity with < 0.005 uncertainty at long wavelength. Critical material parameters include the dependence of emissivity on wavelength, angle of incidence, polarization, and temperature (200 K to 350 K), as well as contributions of scattered light. We present measurement methods and results in support of the CORSAIR SI-traceable far-infrared blackbody design, including temperature-dependent specular reflectance measurements out to 100 μm and angle-dependent data out to 25 μm. In addition, we describe the design for a proposed new facility at NIST (CBS3) that will enable hemispherical-directional emittance and reflectance measurements versus temperature and angle out to 100 μm.

Absolute radiometric calibration of Landsat using a pseudo invariant calibration site

USGS Publications Warehouse

Helder, D.; Thome, K.J.; Mishra, N.; Chander, G.; Xiong, Xiaoxiong; Angal, A.; Choi, Tae-young

2013-01-01

Pseudo invariant calibration sites (PICS) have been used for on-orbit radiometric trending of optical satellite systems for more than 15 years. This approach to vicarious calibration has demonstrated a high degree of reliability and repeatability at the level of 1-3% depending on the site, spectral channel, and imaging geometries. A variety of sensors have used this approach for trending because it is broadly applicable and easy to implement. Models to describe the surface reflectance properties, as well as the intervening atmosphere have also been developed to improve the precision of the method. However, one limiting factor of using PICS is that an absolute calibration capability has not yet been fully developed. Because of this, PICS are primarily limited to providing only long term trending information for individual sensors or cross-calibration opportunities between two sensors. This paper builds an argument that PICS can be used more extensively for absolute calibration. To illustrate this, a simple empirical model is developed for the well-known Libya 4 PICS based on observations by Terra MODIS and EO-1 Hyperion. The model is validated by comparing model predicted top-of-atmosphere reflectance values to actual measurements made by the Landsat ETM+ sensor reflective bands. Following this, an outline is presented to develop a more comprehensive and accurate PICS absolute calibration model that can be Système international d'unités (SI) traceable. These initial concepts suggest that absolute calibration using PICS is possible on a broad scale and can lead to improved on-orbit calibration capabilities for optical satellite sensors.

Challenges in modeling the X-29 flight test performance

NASA Technical Reports Server (NTRS)

Hicks, John W.; Kania, Jan; Pearce, Robert; Mills, Glen

1987-01-01

Presented are methods, instrumentation, and difficulties associated with drag measurement of the X-29A aircraft. The initial performance objective of the X-29A program emphasized drag polar shapes rather than absolute drag levels. Priorities during the flight envelope expansion restricted the evaluation of aircraft performance. Changes in aircraft configuration, uncertainties in angle-of-attack calibration, and limitations in instrumentation complicated the analysis. Limited engine instrumentation with uncertainties in overall in-flight thrust accuracy made it difficult to obtain reliable values of coefficient of parasite drag. The aircraft was incapable of tracking the automatic camber control trim schedule for optimum wing flaperon deflection during typical dynamic performance maneuvers; this has also complicated the drag polar shape modeling. The X-29A was far enough off the schedule that the developed trim drag correction procedure has proven inadequate. However, good drag polar shapes have been developed throughout the flight envelope. Preliminary flight results have compared well with wind tunnel predictions. A more comprehensive analysis must be done to complete performance models. The detailed flight performance program with a calibrated engine will benefit from the experience gained during this preliminary performance phase.

Challenges in modeling the X-29A flight test performance

NASA Technical Reports Server (NTRS)

Hicks, John W.; Kania, Jan; Pearce, Robert; Mills, Glen

1987-01-01

The paper presents the methods, instrumentation, and difficulties associated with drag measurement of the X-29A aircraft. The initial performance objective of the X-29A program emphasized drag polar shapes rather than absolute drag levels. Priorities during the flight envelope expansion restricted the evaluation of aircraft performance. Changes in aircraft configuration, uncertainties in angle-of-attack calibration, and limitations in instrumentation complicated the analysis. Limited engine instrumentation with uncertainties in overall in-flight thrust accuracy made it difficult to obtain reliable values of coefficient of parasite drag. The aircraft was incapable of tracking the automatic camber control trim schedule for optimum wing flaperon deflection during typical dynamic performance maneuvers; this has also complicated the drag polar shape modeling. The X-29A was far enough off the schedule that the developed trim drag correction procedure has proven inadequate. Despite these obstacles, good drag polar shapes have been developed throughout the flight envelope. Preliminary flight results have compared well with wind tunnel predictions. A more comprehensive analysis must be done to complete the performance models. The detailed flight performance program with a calibrated engine will benefit from the experience gained during this preliminary performance phase.

Confidence-Accuracy Calibration in Absolute and Relative Face Recognition Judgments

ERIC Educational Resources Information Center

Weber, Nathan; Brewer, Neil

2004-01-01

Confidence-accuracy (CA) calibration was examined for absolute and relative face recognition judgments as well as for recognition judgments from groups of stimuli presented simultaneously or sequentially (i.e., simultaneous or sequential mini-lineups). When the effect of difficulty was controlled, absolute and relative judgments produced…

Seven-year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources

NASA Astrophysics Data System (ADS)

Weiland, J. L.; Odegard, N.; Hill, R. S.; Wollack, E.; Hinshaw, G.; Greason, M. R.; Jarosik, N.; Page, L.; Bennett, C. L.; Dunkley, J.; Gold, B.; Halpern, M.; Kogut, A.; Komatsu, E.; Larson, D.; Limon, M.; Meyer, S. S.; Nolta, M. R.; Smith, K. M.; Spergel, D. N.; Tucker, G. S.; Wright, E. L.

2011-02-01

We present WMAP seven-year observations of bright sources which are often used as calibrators at microwave frequencies. Ten objects are studied in five frequency bands (23-94 GHz): the outer planets (Mars, Jupiter, Saturn, Uranus, and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg A, 3C274, and 3C58). The seven-year analysis of Jupiter provides temperatures which are within 1σ of the previously published WMAP five-year values, with slightly tighter constraints on variability with orbital phase (0.2% ± 0.4%), and limits (but no detections) on linear polarization. Observed temperatures for both Mars and Saturn vary significantly with viewing geometry. Scaling factors are provided which, when multiplied by the Wright Mars thermal model predictions at 350 μm, reproduce WMAP seasonally averaged observations of Mars within ~2%. An empirical model is described which fits brightness variations of Saturn due to geometrical effects and can be used to predict the WMAP observations to within 3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated. Uncertainties in Uranus temperatures are 3%-4% in the 41, 61, and 94 GHz bands; the smallest uncertainty for Neptune is 8% for the 94 GHz band. Intriguingly, the spectrum of Uranus appears to show a dip at ~30 GHz of unidentified origin, although the feature is not of high statistical significance. Flux densities for the five selected fixed celestial sources are derived from the seven-year WMAP sky maps and are tabulated for Stokes I, Q, and U, along with polarization fraction and position angle. Fractional uncertainties for the Stokes I fluxes are typically 1% to 3%. Source variability over the seven-year baseline is also estimated. Significant secular decrease is seen for Cas A and Tau A: our results are consistent with a frequency-independent decrease of about 0.53% per year for Cas A and 0.22% per year for Tau A. We present WMAP polarization data with uncertainties of a few percent for Tau A. Where appropriate, WMAP results are compared against previous findings in the literature. With an absolute calibration uncertainty of 0.2%, WMAP data are a valuable asset for calibration work. WMAP is the result of a partnership between Princeton University and NASA's Goddard Space Flight Center. Scientific guidance is provided by the WMAP Science Team.

SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: PLANETS AND CELESTIAL CALIBRATION SOURCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiland, J. L.; Odegard, N.; Hill, R. S.

2011-02-01

We present WMAP seven-year observations of bright sources which are often used as calibrators at microwave frequencies. Ten objects are studied in five frequency bands (23-94 GHz): the outer planets (Mars, Jupiter, Saturn, Uranus, and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg A, 3C274, and 3C58). The seven-year analysis of Jupiter provides temperatures which are within 1{sigma} of the previously published WMAP five-year values, with slightly tighter constraints on variability with orbital phase (0.2% {+-} 0.4%), and limits (but no detections) on linear polarization. Observed temperatures for both Mars and Saturn vary significantly with viewing geometry.more » Scaling factors are provided which, when multiplied by the Wright Mars thermal model predictions at 350 {mu}m, reproduce WMAP seasonally averaged observations of Mars within {approx}2%. An empirical model is described which fits brightness variations of Saturn due to geometrical effects and can be used to predict the WMAP observations to within 3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated. Uncertainties in Uranus temperatures are 3%-4% in the 41, 61, and 94 GHz bands; the smallest uncertainty for Neptune is 8% for the 94 GHz band. Intriguingly, the spectrum of Uranus appears to show a dip at {approx}30 GHz of unidentified origin, although the feature is not of high statistical significance. Flux densities for the five selected fixed celestial sources are derived from the seven-year WMAP sky maps and are tabulated for Stokes I, Q, and U, along with polarization fraction and position angle. Fractional uncertainties for the Stokes I fluxes are typically 1% to 3%. Source variability over the seven-year baseline is also estimated. Significant secular decrease is seen for Cas A and Tau A: our results are consistent with a frequency-independent decrease of about 0.53% per year for Cas A and 0.22% per year for Tau A. We present WMAP polarization data with uncertainties of a few percent for Tau A. Where appropriate, WMAP results are compared against previous findings in the literature. With an absolute calibration uncertainty of 0.2%, WMAP data are a valuable asset for calibration work.« less

The stars: an absolute radiometric reference for the on-orbit calibration of PLEIADES-HR satellites

NASA Astrophysics Data System (ADS)

Meygret, Aimé; Blanchet, Gwendoline; Mounier, Flore; Buil, Christian

2017-09-01

The accurate on-orbit radiometric calibration of optical sensors has become a challenge for space agencies who gather their effort through international working groups such as CEOS/WGCV or GSICS with the objective to insure the consistency of space measurements and to reach an absolute accuracy compatible with more and more demanding scientific needs. Different targets are traditionally used for calibration depending on the sensor or spacecraft specificities: from on-board calibration systems to ground targets, they all take advantage of our capacity to characterize and model them. But achieving the in-flight stability of a diffuser panel is always a challenge while the calibration over ground targets is often limited by their BDRF characterization and the atmosphere variability. Thanks to their agility, some satellites have the capability to view extra-terrestrial targets such as the moon or stars. The moon is widely used for calibration and its albedo is known through ROLO (RObotic Lunar Observatory) USGS model but with a poor absolute accuracy limiting its use to sensor drift monitoring or cross-calibration. Although the spectral irradiance of some stars is known with a very high accuracy, it was not really shown that they could provide an absolute reference for remote sensors calibration. This paper shows that high resolution optical sensors can be calibrated with a high absolute accuracy using stars. The agile-body PLEIADES 1A satellite is used for this demonstration. The star based calibration principle is described and the results are provided for different stars, each one being acquired several times. These results are compared to the official calibration provided by ground targets and the main error contributors are discussed.

Temporal and spatial variations of the absolute reflectivity of Jupiter and Saturn from 0.38 to 1.7 μm with PlanetCam-UPV/EHU

NASA Astrophysics Data System (ADS)

Mendikoa, I.; Sánchez-Lavega, A.; Pérez-Hoyos, S.; Hueso, R.; Rojas, J. F.; López-Santiago, J.

2017-11-01

Aims: We provide measurements of the absolute reflectivity of Jupiter and Saturn along their central meridians in filters covering a wide range of visible and near-infrared wavelengths (from 0.38 to 1.7 μm) that are not often presented in the literature. We also give measurements of the geometric albedo of both planets and discuss the limb-darkening behavior and temporal variability of their reflectivity values for a period of four years (2012-2016). Methods: This work is based on observations with the PlanetCam-UPV/EHU instrument at the 1.23 m and 2.2 m telescopes in Calar Alto Observatory (Spain). The instrument simultaneously observes in two channels: visible (VIS; 0.38-1.0 μm) and short-wave infrared (SWIR; 1.0-1.7 μm). We obtained high-resolution observations via the lucky-imaging method. Results: We show that our calibration is consistent with previous independent determinations of reflectivity values of these planets and, for future reference, provide new data extended in the wavelength range and in the time. Our results have an uncertainty in absolute calibration of 10-20%. We show that under the hypothesis of constant geometric albedo, we are able to detect absolute reflectivity changes related to planetary temporal evolution of about 5-10%. Tables A.1-A.4 and B.1-B.8 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A72

Uncertainty Analysis for Angle Calibrations Using Circle Closure

PubMed Central

Estler, W. Tyler

1998-01-01

We analyze two types of full-circle angle calibrations: a simple closure in which a single set of unknown angular segments is sequentially compared with an unknown reference angle, and a dual closure in which two divided circles are simultaneously calibrated by intercomparison. In each case, the constraint of circle closure provides auxiliary information that (1) enables a complete calibration process without reference to separately calibrated reference artifacts, and (2) serves to reduce measurement uncertainty. We derive closed-form expressions for the combined standard uncertainties of angle calibrations, following guidelines published by the International Organization for Standardization (ISO) and NIST. The analysis includes methods for the quantitative evaluation of the standard uncertainty of small angle measurement using electronic autocollimators, including the effects of calibration uncertainty and air turbulence. PMID:28009359

Absolute flux density calibrations of radio sources: 2.3 GHz

NASA Technical Reports Server (NTRS)

Freiley, A. J.; Batelaan, P. D.; Bathker, D. A.

1977-01-01

A detailed description of a NASA/JPL Deep Space Network program to improve S-band gain calibrations of large aperture antennas is reported. The program is considered unique in at least three ways; first, absolute gain calibrations of high quality suppressed-sidelobe dual mode horns first provide a high accuracy foundation to the foundation to the program. Second, a very careful transfer calibration technique using an artificial far-field coherent-wave source was used to accurately obtain the gain of one large (26 m) aperture. Third, using the calibrated large aperture directly, the absolute flux density of five selected galactic and extragalactic natural radio sources was determined with an absolute accuracy better than 2 percent, now quoted at the familiar 1 sigma confidence level. The follow-on considerations to apply these results to an operational network of ground antennas are discussed. It is concluded that absolute gain accuracies within + or - 0.30 to 0.40 db are possible, depending primarily on the repeatability (scatter) in the field data from Deep Space Network user stations.

UNDERFLIGHT CALIBRATION OF SOHO/CDS AND HINODE/EIS WITH EUNIS-07

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Tongjiang; Brosius, Jeffrey W.; Thomas, Roger J.

2011-12-01

Flights of Goddard Space Flight Center's Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket in 2006 and 2007 provided updated radiometric calibrations for Solar and Heliospheric Observatory/Coronal Diagnostic Spectrometer (SOHO/CDS) and Hinode/Extreme Ultraviolet Imaging Spectrometer (Hinode/EIS). EUNIS carried two independent imaging spectrographs covering wavebands of 300-370 A in first order and 170-205 A in second order. After each flight, end-to-end radiometric calibrations of the rocket payload were carried out in the same facility used for pre-launch calibrations of CDS and EIS. During the 2007 flight, EUNIS, SOHO/CDS, and Hinode/EIS observed the same solar locations, allowing the EUNIS calibrations to bemore » directly applied to both CDS and EIS. The measured CDS NIS 1 line intensities calibrated with the standard (version 4) responsivities with the standard long-term corrections are found to be too low by a factor of 1.5 due to the decrease in responsivity. The EIS calibration update is performed in two ways. One uses the direct calibration transfer of the calibrated EUNIS-07 short wavelength (SW) channel. The other uses the insensitive line pairs, in which one member was observed by the EUNIS-07 long wavelength (LW) channel and the other by EIS in either the LW or SW waveband. Measurements from both methods are in good agreement, and confirm (within the measurement uncertainties) the EIS responsivity measured directly before the instrument's launch. The measurements also suggest that the EIS responsivity decreased by a factor of about 1.2 after the first year of operation (although the size of the measurement uncertainties is comparable to this decrease). The shape of the EIS SW response curve obtained by EUNIS-07 is consistent with the one measured in laboratory prior to launch. The absolute value of the quiet-Sun He II 304 A intensity measured by EUNIS-07 is consistent with the radiance measured by CDS NIS in quiet regions near the disk center and the solar minimum irradiance recently obtained by CDS NIS and the Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment.« less

Planck 2013 results. V. LFI calibration

NASA Astrophysics Data System (ADS)

Planck Collaboration; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Cappellini, B.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chen, X.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Colombi, S.; Colombo, L. P. L.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Kangaslahti, P.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Naselsky, P.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Paci, F.; Pagano, L.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, D.; Peel, M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Ricciardi, S.; Riller, T.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Watson, R.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

2014-11-01

We discuss the methods employed to photometrically calibrate the data acquired by the Low Frequency Instrument on Planck. Our calibration is based on a combination of the orbital dipole plus the solar dipole, caused respectively by the motion of the Planck spacecraft with respect to the Sun and by motion of the solar system with respect to the cosmic microwave background (CMB) rest frame. The latter provides a signal of a few mK with the same spectrum as the CMB anisotropies and is visible throughout the mission. In this data releasewe rely on the characterization of the solar dipole as measured by WMAP. We also present preliminary results (at 44 GHz only) on the study of the Orbital Dipole, which agree with the WMAP value of the solar system speed within our uncertainties. We compute the calibration constant for each radiometer roughly once per hour, in order to keep track of changes in the detectors' gain. Since non-idealities in the optical response of the beams proved to be important, we implemented a fast convolution algorithm which considers the full beam response in estimating the signal generated by the dipole. Moreover, in order to further reduce the impact of residual systematics due to sidelobes, we estimated time variations in the calibration constant of the 30 GHz radiometers (the ones with the largest sidelobes) using the signal of an internal reference load at 4 K instead of the CMB dipole. We have estimated the accuracy of the LFI calibration following two strategies: (1) we have run a set of simulations to assess the impact of statistical errors and systematic effects in the instrument and in the calibration procedure; and (2) we have performed a number of internal consistency checks on the data and on the brightness temperature of Jupiter. Errors in the calibration of this Planck/LFI data release are expected to be about 0.6% at 44 and 70 GHz, and 0.8% at 30 GHz. Both these preliminary results at low and high ℓ are consistent with WMAP results within uncertainties and comparison of power spectra indicates good consistency in the absolute calibration with HFI (0.3%) and a 1.4σ discrepancy with WMAP (0.9%).

Confidence-accuracy calibration in absolute and relative face recognition judgments.

PubMed

Weber, Nathan; Brewer, Neil

2004-09-01

Confidence-accuracy (CA) calibration was examined for absolute and relative face recognition judgments as well as for recognition judgments from groups of stimuli presented simultaneously or sequentially (i.e., simultaneous or sequential mini-lineups). When the effect of difficulty was controlled, absolute and relative judgments produced negligibly different CA calibration, whereas no significant difference was observed for simultaneous and sequential mini-lineups. Further, the effect of difficulty on CA calibration was equivalent across judgment and mini-lineup types. It is interesting to note that positive (i.e., old) recognition judgments demonstrated strong CA calibration whereas negative (i.e., new) judgments evidenced little or no CA association. Implications for eyewitness identification are discussed. (c) 2004 APA, all rights reserved.

ACCOUNTING FOR CALIBRATION UNCERTAINTIES IN X-RAY ANALYSIS: EFFECTIVE AREAS IN SPECTRAL FITTING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyunsook; Kashyap, Vinay L.; Drake, Jeremy J.

2011-04-20

While considerable advance has been made to account for statistical uncertainties in astronomical analyses, systematic instrumental uncertainties have been generally ignored. This can be crucial to a proper interpretation of analysis results because instrumental calibration uncertainty is a form of systematic uncertainty. Ignoring it can underestimate error bars and introduce bias into the fitted values of model parameters. Accounting for such uncertainties currently requires extensive case-specific simulations if using existing analysis packages. Here, we present general statistical methods that incorporate calibration uncertainties into spectral analysis of high-energy data. We first present a method based on multiple imputation that can bemore » applied with any fitting method, but is necessarily approximate. We then describe a more exact Bayesian approach that works in conjunction with a Markov chain Monte Carlo based fitting. We explore methods for improving computational efficiency, and in particular detail a method of summarizing calibration uncertainties with a principal component analysis of samples of plausible calibration files. This method is implemented using recently codified Chandra effective area uncertainties for low-resolution spectral analysis and is verified using both simulated and actual Chandra data. Our procedure for incorporating effective area uncertainty is easily generalized to other types of calibration uncertainties.« less

Interferometric thickness calibration of 300 mm silicon wafers

NASA Astrophysics Data System (ADS)

Wang, Quandou; Griesmann, Ulf; Polvani, Robert

2005-12-01

The "Improved Infrared Interferometer" (IR 3) at the National Institute of Standards and Technology (NIST) is a phase-measuring interferometer, operating at a wavelength of 1550 nm, which is being developed for measuring the thickness and thickness variation of low-doped silicon wafers with diameters up to 300 mm. The purpose of the interferometer is to produce calibrated silicon wafers, with a certified measurement uncertainty, which can be used as reference wafers by wafer manufacturers and metrology tool manufacturers. We give an overview of the design of the interferometer and discuss its application to wafer thickness measurements. The conversion of optical thickness, as measured by the interferometer, to the wafer thickness requires knowledge of the refractive index of the material of the wafer. We describe a method for measuring the refractive index which is then used to establish absolute thickness and thickness variation maps for the wafer.

Techniques for improving the accuracy of cyrogenic temperature measurement in ground test programs

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.; Fabik, Richard H.

1993-01-01

The performance of a sensor is often evaluated by determining to what degree of accuracy a measurement can be made using this sensor. The absolute accuracy of a sensor is an important parameter considered when choosing the type of sensor to use in research experiments. Tests were performed to improve the accuracy of cryogenic temperature measurements by calibration of the temperature sensors when installed in their experimental operating environment. The calibration information was then used to correct for temperature sensor measurement errors by adjusting the data acquisition system software. This paper describes a method to improve the accuracy of cryogenic temperature measurements using corrections in the data acquisition system software such that the uncertainty of an individual temperature sensor is improved from plus or minus 0.90 deg R to plus or minus 0.20 deg R over a specified range.

A new method to calibrate the absolute sensitivity of a soft X-ray streak camera

NASA Astrophysics Data System (ADS)

Yu, Jian; Liu, Shenye; Li, Jin; Yang, Zhiwen; Chen, Ming; Guo, Luting; Yao, Li; Xiao, Shali

2016-12-01

In this paper, we introduce a new method to calibrate the absolute sensitivity of a soft X-ray streak camera (SXRSC). The calibrations are done in the static mode by using a small laser-produced X-ray source. A calibrated X-ray CCD is used as a secondary standard detector to monitor the X-ray source intensity. In addition, two sets of holographic flat-field grating spectrometers are chosen as the spectral discrimination systems of the SXRSC and the X-ray CCD. The absolute sensitivity of the SXRSC is obtained by comparing the signal counts of the SXRSC to the output counts of the X-ray CCD. Results show that the calibrated spectrum covers the range from 200 eV to 1040 eV. The change of the absolute sensitivity in the vicinity of the K-edge of the carbon can also be clearly seen. The experimental values agree with the calculated values to within 29% error. Compared with previous calibration methods, the proposed method has several advantages: a wide spectral range, high accuracy, and simple data processing. Our calibration results can be used to make quantitative X-ray flux measurements in laser fusion research.

Solid laboratory calibration of a nonimaging spectroradiometer.

PubMed

Schaepman, M E; Dangel, S

2000-07-20

Field-based nonimaging spectroradiometers are often used in vicarious calibration experiments for airborne or spaceborne imaging spectrometers. The calibration uncertainties associated with these ground measurements contribute substantially to the overall modeling error in radiance- or reflectance-based vicarious calibration experiments. Because of limitations in the radiometric stability of compact field spectroradiometers, vicarious calibration experiments are based primarily on reflectance measurements rather than on radiance measurements. To characterize the overall uncertainty of radiance-based approaches and assess the sources of uncertainty, we carried out a full laboratory calibration. This laboratory calibration of a nonimaging spectroradiometer is based on a measurement plan targeted at achieving a

AIRS Science Accomplishments Version 4.0/Plans for Version 5

NASA Technical Reports Server (NTRS)

Pagano, Thomas S.; Aumann, Hartmut; Elliott, Denis; Granger, Stephanie; Kahn, Brain; Eldering, Annmarie; Irion, Bill; Fetzer, Eric; Olsen, Ed; Lee, Sung-Yung;

Intramural Comparison of NIST Laser and Optical Fiber Power Calibrations.

PubMed

Lehman, John H; Vayshenker, Igor; Livigni, David J; Hadler, Joshua

2004-01-01

The responsivity of two optical detectors was determined by the method of direct substitution in four different NIST measurement facilities. The measurements were intended to demonstrate the determination of absolute responsivity as provided by NIST calibration services at laser and optical-communication wavelengths; nominally 633 nm, 850 nm, 1060 nm, 1310 nm, and 1550 nm. The optical detectors have been designated as checks standards for the purpose of routine intramural comparison of our calibration services and to meet requirements of the NIST quality system, based on ISO 17025. The check standards are two optical-trap detectors, one based on silicon and the other on indium gallium arsenide photodiodes. The four measurement services are based on: (1) the laser optimized cryogenic radiometer (LOCR) and free field collimated laser light; (2) the C-series isoperibol calorimeter and free-field collimated laser light; (3) the electrically calibrated pyroelectric radiometer and fiber-coupled laser light; (4) the pyroelectric wedge trap detector, which measures light from a lamp source and monochromator. The results indicate that the responsivity of the check standards, as determined independently using the four services, agree to within the published expanded uncertainty ranging from approximately 0.02 % to 1.24 %.

Characterization of the uncertainty of divergence time estimation under relaxed molecular clock models using multiple loci.

PubMed

Zhu, Tianqi; Dos Reis, Mario; Yang, Ziheng

2015-03-01

Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time estimates will not approach point values even if an infinite amount of sequence data are used in the analysis. In a previous study we developed a finite-sites theory to characterize the uncertainty in Bayesian divergence time estimation in analysis of large but finite sequence data sets under a strict molecular clock. As most modern clock dating analyses use more than one locus and are conducted under relaxed clock models, here we extend the theory to the case of relaxed clock analysis of data from multiple loci (site partitions). Uncertainty in posterior time estimates is partitioned into three sources: Sampling errors in the estimates of branch lengths in the tree for each locus due to limited sequence length, variation of substitution rates among lineages and among loci, and uncertainty in fossil calibrations. Using a simple but analogous estimation problem involving the multivariate normal distribution, we predict that as the number of loci ([Formula: see text]) goes to infinity, the variance in posterior time estimates decreases and approaches the infinite-data limit at the rate of 1/[Formula: see text], and the limit is independent of the number of sites in the sequence alignment. We then confirmed the predictions by using computer simulation on phylogenies of two or three species, and by analyzing a real genomic data set for six primate species. Our results suggest that with the fossil calibrations fixed, analyzing multiple loci or site partitions is the most effective way for improving the precision of posterior time estimation. However, even if a huge amount of sequence data is analyzed, considerable uncertainty will persist in time estimates. © The Author(s) 2014. Published by Oxford University Press on behalf of the Society of Systematic Biologists.

Balance Calibration – A Method for Assigning a Direct-Reading Uncertainty to an Electronic Balance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mike Stears

2010-07-01

Paper Title: Balance Calibration – A method for assigning a direct-reading uncertainty to an electronic balance. Intended Audience: Those who calibrate or use electronic balances. Abstract: As a calibration facility, we provide on-site (at the customer’s location) calibrations of electronic balances for customers within our company. In our experience, most of our customers are not using their balance as a comparator, but simply putting an unknown quantity on the balance and reading the displayed mass value. Manufacturer’s specifications for balances typically include specifications such as readability, repeatability, linearity, and sensitivity temperature drift, but what does this all mean when themore » balance user simply reads the displayed mass value and accepts the reading as the true value? This paper discusses a method for assigning a direct-reading uncertainty to a balance based upon the observed calibration data and the environment where the balance is being used. The method requires input from the customer regarding the environment where the balance is used and encourages discussion with the customer regarding sources of uncertainty and possible means for improvement; the calibration process becomes an educational opportunity for the balance user as well as calibration personnel. This paper will cover the uncertainty analysis applied to the calibration weights used for the field calibration of balances; the uncertainty is calculated over the range of environmental conditions typically encountered in the field and the resulting range of air density. The temperature stability in the area of the balance is discussed with the customer and the temperature range over which the balance calibration is valid is decided upon; the decision is based upon the uncertainty needs of the customer and the desired rigor in monitoring by the customer. Once the environmental limitations are decided, the calibration is performed and the measurement data is entered into a custom spreadsheet. The spreadsheet uses measurement results, along with the manufacturer’s specifications, to assign a direct-read measurement uncertainty to the balance. The fact that the assigned uncertainty is a best-case uncertainty is discussed with the customer; the assigned uncertainty contains no allowance for contributions associated with the unknown weighing sample, such as density, static charges, magnetism, etc. The attendee will learn uncertainty considerations associated with balance calibrations along with one method for assigning an uncertainty to a balance used for non-comparison measurements.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobs, Daniel C.; Bowman, Judd; Parsons, Aaron R.

We present a catalog of spectral measurements covering a 100-200 MHz band for 32 sources, derived from observations with a 64 antenna deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. For transit telescopes such as PAPER, calibration of the primary beam is a difficult endeavor and errors in this calibration are a major source of error in the determination of source spectra. In order to decrease our reliance on an accurate beam calibration, we focus on calibrating sources in a narrow declination range from –46° to –40°. Since sources atmore » similar declinations follow nearly identical paths through the primary beam, this restriction greatly reduces errors associated with beam calibration, yielding a dramatic improvement in the accuracy of derived source spectra. Extrapolating from higher frequency catalogs, we derive the flux scale using a Monte Carlo fit across multiple sources that includes uncertainty from both catalog and measurement errors. Fitting spectral models to catalog data and these new PAPER measurements, we derive new flux models for Pictor A and 31 other sources at nearby declinations; 90% are found to confirm and refine a power-law model for flux density. Of particular importance is the new Pictor A flux model, which is accurate to 1.4% and shows that between 100 MHz and 2 GHz, in contrast with previous models, the spectrum of Pictor A is consistent with a single power law given by a flux at 150 MHz of 382 ± 5.4 Jy and a spectral index of –0.76 ± 0.01. This accuracy represents an order of magnitude improvement over previous measurements in this band and is limited by the uncertainty in the catalog measurements used to estimate the absolute flux scale. The simplicity and improved accuracy of Pictor A's spectrum make it an excellent calibrator in a band important for experiments seeking to measure 21 cm emission from the epoch of reionization.« less

Preliminary Evaluation of the Radiometric Calibration of LANDSAT-4 Thematic Mapper Data by the Canada Centre for Remote Sensing

NASA Technical Reports Server (NTRS)

Murphy, J.; Park, W.; Fitzgerald, A.

1985-01-01

The radiometric characteristics of the LANDSAT-4 TM sensor are being studied with a view to developing absolute and relative radiometric calibration procedures. Preliminary results from several different approaches to the relative correction of all detectors within each band are reported. Topics covered include: the radiometric correction method; absolute calibration; the relative radiometric calibration algorithm; relative gain and offset calibration; relative gain and offset observations; and residual radiometric stripping.

Comparison of Calibration Methods for Tristimulus Colorimeters.

PubMed

Gardner, James L

2007-01-01

Uncertainties in source color measurements with a tristimulus colorimeter are estimated for calibration factors determined, based on a known source spectral distribution or on accurate measurements of the spectral responsivities of the colorimeter channels. Application is to the National Institute of Standards and Technology (NIST) colorimeter and an International Commission on Illumination (CIE) Illuminant A calibration. Detector-based calibration factors generally have lower uncertainties than source-based calibration factors. Uncertainties are also estimated for calculations of spectral mismatch factors. Where both spectral responsivities of the colorimeter channels and the spectral power distributions of the calibration and test sources are known, uncertainties are lowest if the colorimeter calibration factors are recalculated for the test source; this process also avoids correlations between the CIE Source A calibration factors and the spectral mismatch factors.

Comparison of Calibration Methods for Tristimulus Colorimeters

PubMed Central

Gardner, James L.

2007-01-01

Uncertainties in source color measurements with a tristimulus colorimeter are estimated for calibration factors determined, based on a known source spectral distribution or on accurate measurements of the spectral responsivities of the colorimeter channels. Application is to the National Institute of Standards and Technology (NIST) colorimeter and an International Commission on Illumination (CIE) Illuminant A calibration. Detector-based calibration factors generally have lower uncertainties than source-based calibration factors. Uncertainties are also estimated for calculations of spectral mismatch factors. Where both spectral responsivities of the colorimeter channels and the spectral power distributions of the calibration and test sources are known, uncertainties are lowest if the colorimeter calibration factors are recalculated for the test source; this process also avoids correlations between the CIE Source A calibration factors and the spectral mismatch factors. PMID:27110460

Absolute calibration of optical streak cameras on picosecond time scales using supercontinuum generation

DOE PAGES

Patankar, S.; Gumbrell, E. T.; Robinson, T. S.; ...

2017-08-17

Here we report a new method using high stability, laser-driven supercontinuum generation in a liquid cell to calibrate the absolute photon response of fast optical streak cameras as a function of wavelength when operating at fastest sweep speeds. A stable, pulsed white light source based around the use of self-phase modulation in a salt solution was developed to provide the required brightness on picosecond timescales, enabling streak camera calibration in fully dynamic operation. The measured spectral brightness allowed for absolute photon response calibration over a broad spectral range (425-650nm). Calibrations performed with two Axis Photonique streak cameras using the Photonismore » P820PSU streak tube demonstrated responses which qualitatively follow the photocathode response. Peak sensitivities were 1 photon/count above background. The absolute dynamic sensitivity is less than the static by up to an order of magnitude. We attribute this to the dynamic response of the phosphor being lower.« less

Rayleigh scattering cross-section measurements of nitrogen, argon, oxygen and air

NASA Astrophysics Data System (ADS)

Thalman, Ryan; Zarzana, Kyle J.; Tolbert, Margaret A.; Volkamer, Rainer

2014-11-01

Knowledge about Rayleigh scattering cross sections is relevant to predictions about radiative transfer in the atmosphere, and needed to calibrate the reflectivity of mirrors that are used in high-finesse optical cavities to measure atmospheric trace gases and aerosols. In this work we have measured the absolute Rayleigh scattering cross-section of nitrogen at 405.8 and 532.2 nm using cavity ring-down spectroscopy (CRDS). Further, multi-spectral measurements of the scattering cross-sections of argon, oxygen and air are presented relative to that of nitrogen from 350 to 660 nm using Broadband Cavity Enhanced Spectroscopy (BBCES). The reported measurements agree with refractive index based theory within 0.2±0.4%, and have an absolute accuracy of better than 1.3%. Our measurements expand the spectral range over which Rayleigh scattering cross section measurements of argon, oxygen and air are available at near-ultraviolet wavelengths. The expressions used to represent the Rayleigh scattering cross-section in the literature are evaluated to assess how uncertainties affect quantities measured by cavity enhanced absorption spectroscopic (CEAS) techniques. We conclude that Rayleigh scattering cross sections calculated from theory provide accurate data within very low error bounds, and are suited well to calibrate CEAS measurements of atmospheric trace gases and aerosols.

Absolute, pressure-dependent validation of a calibration-free, airborne laser hygrometer transfer standard (SEALDH-II) from 5 to 1200 ppmv using a metrological humidity generator

NASA Astrophysics Data System (ADS)

Buchholz, Bernhard; Ebert, Volker

2018-01-01

Highly accurate water vapor measurements are indispensable for understanding a variety of scientific questions as well as industrial processes. While in metrology water vapor concentrations can be defined, generated, and measured with relative uncertainties in the single percentage range, field-deployable airborne instruments deviate even under quasistatic laboratory conditions up to 10-20 %. The novel SEALDH-II hygrometer, a calibration-free, tuneable diode laser spectrometer, bridges this gap by implementing a new holistic concept to achieve higher accuracy levels in the field. We present in this paper the absolute validation of SEALDH-II at a traceable humidity generator during 23 days of permanent operation at 15 different H2O mole fraction levels between 5 and 1200 ppmv. At each mole fraction level, we studied the pressure dependence at six different gas pressures between 65 and 950 hPa. Further, we describe the setup for this metrological validation, the challenges to overcome when assessing water vapor measurements on a high accuracy level, and the comparison results. With this validation, SEALDH-II is the first airborne, metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale.

Calibration Against the Moon. I: A Disk-Resolved Lunar Model for Absolute Reflectance Calibration

DTIC Science & Technology

2010-01-01

average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Calibration against the Moon I: A disk- resolved lunar model for absolute reflectance...of the disk- resolved Moon at visible to near infrared wavelengths. It has been developed in order to use the Moon as a calibration reference

Uncertainty Estimate for the Outdoor Calibration of Solar Pyranometers: A Metrologist Perspective

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, I.; Myers, D.; Stoffel, T.

2008-12-01

Pyranometers are used outdoors to measure solar irradiance. By design, this type of radiometer can measure the; total hemispheric (global) or diffuse (sky) irradiance when the detector is unshaded or shaded from the sun disk, respectively. These measurements are used in a variety of applications including solar energy conversion, atmospheric studies, agriculture, and materials science. Proper calibration of pyranometers is essential to ensure measurement quality. This paper describes a step-by-step method for calculating and reporting the uncertainty of the calibration, using the guidelines of the ISO 'Guide to the Expression of Uncertainty in Measurement' or GUM, that is applied tomore » the pyranometer; calibration procedures used at the National Renewable Energy Laboratory (NREL). The NREL technique; characterizes a responsivity function of a pyranometer as a function of the zenith angle, as well as reporting a single; calibration responsivity value for a zenith angle of 45 ..deg... The uncertainty analysis shows that a lower uncertainty can be achieved by using the response function of a pyranometer determined as a function of zenith angle, in lieu of just using; the average value at 45..deg... By presenting the contribution of each uncertainty source to the total uncertainty; users will be able to troubleshoot and improve their calibration process. The uncertainty analysis method can also be used to determine the uncertainty of different calibration techniques and applications, such as deriving the uncertainty of field measurements.« less

Absolute x-ray energy calibration and monitoring using a diffraction-based method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Xinguo, E-mail: xhong@bnl.gov; Weidner, Donald J.; Duffy, Thomas S.

2016-07-27

In this paper, we report some recent developments of the diffraction-based absolute X-ray energy calibration method. In this calibration method, high spatial resolution of the measured detector offset is essential. To this end, a remotely controlled long-translation motorized stage was employed instead of the less convenient gauge blocks. It is found that the precision of absolute X-ray energy calibration (ΔE/E) is readily achieved down to the level of 10{sup −4} for high-energy monochromatic X-rays (e.g. 80 keV). Examples of applications to pair distribution function (PDF) measurements and energy monitoring for high-energy X-rays are presented.

Calibration Uncertainties in the Droplet Measurement Technologies Cloud Condensation Nuclei Counter

NASA Astrophysics Data System (ADS)

Hibert, Kurt James

Cloud condensation nuclei (CCN) serve as the nucleation sites for the condensation of water vapor in Earth's atmosphere and are important for their effect on climate and weather. The influence of CCN on cloud radiative properties (aerosol indirect effect) is the most uncertain of quantified radiative forcing changes that have occurred since pre-industrial times. CCN influence the weather because intrinsic and extrinsic aerosol properties affect cloud formation and precipitation development. To quantify these effects, it is necessary to accurately measure CCN, which requires accurate calibrations using a consistent methodology. Furthermore, the calibration uncertainties are required to compare measurements from different field projects. CCN uncertainties also aid the integration of CCN measurements with atmospheric models. The commercially available Droplet Measurement Technologies (DMT) CCN Counter is used by many research groups, so it is important to quantify its calibration uncertainty. Uncertainties in the calibration of the DMT CCN counter exist in the flow rate and supersaturation values. The concentration depends on the accuracy of the flow rate calibration, which does not have a large (4.3 %) uncertainty. The supersaturation depends on chamber pressure, temperature, and flow rate. The supersaturation calibration is a complex process since the chamber's supersaturation must be inferred from a temperature difference measurement. Additionally, calibration errors can result from the Kohler theory assumptions, fitting methods utilized, the influence of multiply-charged particles, and calibration points used. In order to determine the calibration uncertainties and the pressure dependence of the supersaturation calibration, three calibrations are done at each pressure level: 700, 840, and 980 hPa. Typically 700 hPa is the pressure used for aircraft measurements in the boundary layer, 840 hPa is the calibration pressure at DMT in Boulder, CO, and 980 hPa is the average surface pressure at Grand Forks, ND. The supersaturation calibration uncertainty is 2.3, 3.1, and 4.4 % for calibrations done at 700, 840, and 980 hPa respectively. The supersaturation calibration change with pressure is on average 0.047 % supersaturation per 100 hPa. The supersaturation calibrations done at UND are 42-45 % lower than supersaturation calibrations done at DMT approximately 1 year previously. Performance checks confirmed that all major leaks developed during shipping were fixed before conducting the supersaturation calibrations. Multiply-charged particles passing through the Electrostatic Classifier may have influenced DMT's activation curves, which is likely part of the supersaturation calibration difference. Furthermore, the fitting method used to calculate the activation size and the limited calibration points are likely significant sources of error in DMT's supersaturation calibration. While the DMT CCN counter's calibration uncertainties are relatively small, and the pressure dependence is easily accounted for, the calibration methodology used by different groups can be very important. The insights gained from the careful calibration of the DMT CCN counter indicate that calibration of scientific instruments using complex methodology is not trivial.

Preliminary Error Budget for the Reflected Solar Instrument for the Climate Absolute Radiance and Refractivity Observatory

NASA Technical Reports Server (NTRS)

Thome, Kurtis; Gubbels, Timothy; Barnes, Robert

2011-01-01

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) plans to observe climate change trends over decadal time scales to determine the accuracy of climate projections. The project relies on spaceborne earth observations of SI-traceable variables sensitive to key decadal change parameters. The mission includes a reflected solar instrument retrieving at-sensor reflectance over the 320 to 2300 nm spectral range with 500-m spatial resolution and 100-km swath. Reflectance is obtained from the ratio of measurements of the earth s surface to those while viewing the sun relying on a calibration approach that retrieves reflectance with uncertainties less than 0.3%. The calibration is predicated on heritage hardware, reduction of sensor complexity, adherence to detector-based calibration standards, and an ability to simulate in the laboratory on-orbit sources in both size and brightness to provide the basis of a transfer to orbit of the laboratory calibration including a link to absolute solar irradiance measurements. The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe high-accuracy, long-term climate change trends and to use decadal change observations as the most critical method to determine the accuracy of climate change projections such as those in the IPCC Report. A rigorously known accuracy of both decadal change observations as well as climate projections is critical in order to enable sound policy decisions. The CLARREO Project will implement a spaceborne earth observation mission designed to provide rigorous SI traceable observations (i.e., radiance, reflectance, and refractivity) that are sensitive to a wide range of key decadal change variables, including: 1) Surface temperature and atmospheric temperature profile 2) Atmospheric water vapor profile 3) Far infrared water vapor greenhouse 4) Aerosol properties and anthropogenic aerosol direct radiative forcing 5) Total and spectral solar irradiance 6) Broadband reflected and emitted radiative fluxes 7) Cloud properties 8) Surface albedo There are two methods the CLARREO mission will rely on to achieve these critical decadal change benchmarks: direct and reference inter-calibration. A quantitative analysis of the strengths and weaknesses of the two methods has led to the recommended CLARREO mission approach. The project consists of two satellites launched into 90-degree, precessing orbits separated by 90 degrees. The instrument suite receiver on each spacecraft includes one emitted infrared spectrometer, two reflected solar spectrometers: dividing the spectrum from ultraviolet through near infrared, and one global navigation receiver for radio occultation. The measurements will be acquired for a period of three years minimum, with a five-year lifetime goal, enabling follow-on missions to extend the climate record over the decades needed to understand climate change. The current work concentrates on the reflected solar instrument giving an overview of its design and calibration approach. The calibration description includes the approach to achieving an SI-traceable system on orbit. The calibration overview is followed by a preliminary error budget based on techniques currently in place at the National Institute of Standards and Technology (NIST).

A revised design for microarray experiments to account for experimental noise and uncertainty of probe response.

PubMed

Pozhitkov, Alex E; Noble, Peter A; Bryk, Jarosław; Tautz, Diethard

2014-01-01

Although microarrays are analysis tools in biomedical research, they are known to yield noisy output that usually requires experimental confirmation. To tackle this problem, many studies have developed rules for optimizing probe design and devised complex statistical tools to analyze the output. However, less emphasis has been placed on systematically identifying the noise component as part of the experimental procedure. One source of noise is the variance in probe binding, which can be assessed by replicating array probes. The second source is poor probe performance, which can be assessed by calibrating the array based on a dilution series of target molecules. Using model experiments for copy number variation and gene expression measurements, we investigate here a revised design for microarray experiments that addresses both of these sources of variance. Two custom arrays were used to evaluate the revised design: one based on 25 mer probes from an Affymetrix design and the other based on 60 mer probes from an Agilent design. To assess experimental variance in probe binding, all probes were replicated ten times. To assess probe performance, the probes were calibrated using a dilution series of target molecules and the signal response was fitted to an adsorption model. We found that significant variance of the signal could be controlled by averaging across probes and removing probes that are nonresponsive or poorly responsive in the calibration experiment. Taking this into account, one can obtain a more reliable signal with the added option of obtaining absolute rather than relative measurements. The assessment of technical variance within the experiments, combined with the calibration of probes allows to remove poorly responding probes and yields more reliable signals for the remaining ones. Once an array is properly calibrated, absolute quantification of signals becomes straight forward, alleviating the need for normalization and reference hybridizations.

Testing Astronomical and 40Ar/39Ar Timescales for the K/Pg Boundary Interval Using High-Resolution Magnetostratigraphy and U-Pb Geochronology in the Denver Basin of Colorado

NASA Astrophysics Data System (ADS)

Clyde, W.; Bowring, S. A.; Johnson, K. R.; Ramezani, J.; Jones, M. M.

2015-12-01

Accurate and precise calibration of the Geomagnetic Polarity Timescale (GPTS) in absolute time is critical for resolving rates of geological and biological processes which in turn help constrain the underlying causes of those processes. Numerical calibration of the GPTS was traditionally carried out by interpolation between a limited number of 40Ar/39Ar dated volcanic ash deposits from superpositional sequences with well-defined magnetostratigraphies. More recently, the Neogene part of the GPTS has been calibrated using high-resolution astrochronological methods, however the application of these approaches to pre-Neogene parts of the timescale is controversial given the uncertainties in relevant orbital parameters this far back in time and differing interpretations of local cyclostratigraphic records. The Cretaceous-Paleogene (K/Pg) boundary interval is a good example, where various astronomical and 40Ar/39Ar calibrations have been proposed with varying degrees of agreement. The Denver Basin (Colorado, USA) contains one of the most complete stratigraphic sequences across the K/Pg boundary in the world, preserving evidence of bolide impact as well as biotic extinction and recovery in a thick stratigraphic package that is accessible by both core and outcrop. We present a series of high-precision U-Pb age determinations from interbedded volcanic ash deposits within a tightly constrained magnetobiostratigraphic framework across the K/Pg boundary in the Denver Basin. This new timeline provides a precise absolute age for the K/Pg boundary, constrains the ages of magnetic polarity Chrons C28 to C30, and provides a direct and independent test of early Paleogene astronomical and 40Ar/39Ar based timescales. Temporal calibration of fossil pollen evidence of the "fern spike" in the Denver Basin shows that plant extinctions peaked within ~50-500 years of the bolide impact and primary productivity recovered ~500-5000 years after the impact.

First TSI observations of the new Compact Lightweight Absolute Radiometer (CLARA)

NASA Astrophysics Data System (ADS)

Walter, B.; Finsterle, W.; Koller, S.; Levesque, P. L.; Pfiffner, D.; Schmutz, W. K.

2017-12-01

Continuous and precise Total Solar Irradiance (TSI) measurements are indispensable to evaluate the influence of short- and long-term solar radiative emission variations on the Earth's energy budget. The existence of a potentially long-term trend in the suns activity and whether or not such a trend could be climate effective is still a matter of debate. The Compact Lightweight Absolute Radiometer (CLARA) is one of PMOD/WRC's future contributions to the almost seamless series of space borne TSI measurements since 1978. CLARA is one of three payloads of the Norwegian micro satellite NORSAT-1, along with Langmuir probes for space plasma research and an Automatic Identification System (AIS) receiver to monitor maritime traffic in Norwegian waters. NORSAT-1 was launched July 14th 2017 and the nominal operation of CLARA will start after the instrument commissioning beginning August 21st2017. We present the design, calibration and first TSI observations of CLARA, a new generation of active cavity Electrical Substitution Radiometers (ESR) comprising the latest radiometer developments of PMOD/WRC: i) A three-cavity design for degradation tracking and redundancy, ii) a digital control loop with feed forward system allowing for measurement cadences of 30s, iii) an aperture arrangement to reduce internal scattered light and iv) a new cavity and heatsink design to minimize non-equivalence, size and weight of the instrument. CLARA was end-to-end calibrated against the SI traceable cryogenic radiometer of the TSI Radiometer Facility (TRF) in Boulder (Colorado). The absolute measurement uncertainties for the three SI-traceable TSI detectors of CLARA are 567, 576 and 912 ppm (k = 1).

Fundamental principles of absolute radiometry and the philosophy of this NBS program (1968 to 1971)

NASA Technical Reports Server (NTRS)

Geist, J.

1972-01-01

A description is given work performed on a program to develop an electrically calibrated detector (also called absolute radiometer, absolute detector, and electrically calibrated radiometer) that could be used to realize, maintain, and transfer a scale of total irradiance. The program includes a comprehensive investigation of the theoretical basis of absolute detector radiometry, as well as the design and construction of a number of detectors. A theoretical analysis of the sources of error is also included.

Spectral Irradiance Calibration in the Infrared. Part 6; 3-35 microns Spectra of Three Southern Standard Stars

NASA Technical Reports Server (NTRS)

Cohen, Martin; Witteborn, Fred C.; Bregman, Jesse D.; Wooden, Diane H.; Salama, Alberto; Metcalfe, Leo

1996-01-01

We present three new absolutely calibrated continuous stellar spectra from 3 to 35 microns, constructed as far as possible from actual observed spectral fragments taken from the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars- alpha(sup 1) Cen, alpha TrA, and epsilon Car-augment our previous archive of complete absolutely calibrated spectra for northern K and M giants. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors. KAO and IRAS data in the 15-30 micron range suggest that the spectra of cool giants are close to Rayleigh-Jeans slopes. Our observations of alpha(sup 1) Cen, absolutely calibrated via our adopted Sirius model, indicate an angular diameter in very good agreement with values in the literature, demonstrating 'closure' of the set of spectra within our absolute framework. We compare our observed alpha(sup 1) Cen spectrum with a published grid of theoretical models from Kurucz, and adopt a plausible theoretical shape, that fits our spectrum, as a secondary reference spectrum in the southern sky.

SPRT Calibration Uncertainties and Internal Quality Control at a Commercial SPRT Calibration Facility

NASA Astrophysics Data System (ADS)

Wiandt, T. J.

2008-06-01

The Hart Scientific Division of the Fluke Corporation operates two accredited standard platinum resistance thermometer (SPRT) calibration facilities, one at the Hart Scientific factory in Utah, USA, and the other at a service facility in Norwich, UK. The US facility is accredited through National Voluntary Laboratory Accreditation Program (NVLAP), and the UK facility is accredited through UKAS. Both provide SPRT calibrations using similar equipment and procedures, and at similar levels of uncertainty. These uncertainties are among the lowest available commercially. To achieve and maintain low uncertainties, it is required that the calibration procedures be thorough and optimized. However, to minimize customer downtime, it is also important that the instruments be calibrated in a timely manner and returned to the customer. Consequently, subjecting the instrument to repeated calibrations or extensive repeated measurements is not a viable approach. Additionally, these laboratories provide SPRT calibration services involving a wide variety of SPRT designs. These designs behave differently, yet predictably, when subjected to calibration measurements. To this end, an evaluation strategy involving both statistical process control and internal consistency measures is utilized to provide confidence in both the instrument calibration and the calibration process. This article describes the calibration facilities, procedure, uncertainty analysis, and internal quality assurance measures employed in the calibration of SPRTs. Data will be reviewed and generalities will be presented. Finally, challenges and considerations for future improvements will be discussed.

Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC

NASA Astrophysics Data System (ADS)

Beuermann, K.; Burwitz, V.; Rauch, T.

2006-11-01

Context: .The absolute calibration of space-borne instruments in the soft X-ray regime rests strongly on model spectra of hot white dwarfs. Aims: .We analyze the Chandra LETG+HRC observations of the white dwarfs HZ43 A and Sirius B and of the neutron star RX J185635-3754 with the aim of resolving current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We apply the derived photon spectra to a cross-calibration of the LETG+HRC-S with the short-wavelength EUVE spectrometer and the ROSAT PSPC. Methods: .We tie HZ43 A to the flux of RX J1856 in the 44-48 Å range and perform a simultaneous least squares fit to the LETG+HRC spectra of the three stars. This allows us to determine an internally consistent set of spectral energy distributions and an empirically derived wavelength-dependent correction to the LETG+HRC-S effective area. We employ NLTE model atmospheres calculated with TMAP for the white dwarfs and a two-blackbody model for RX J1856, tied to the respective optical fluxes. Results: .The two-blackbody model for RX J1856 features a hot spot on a cooler star and yields kT_spot=62.8±0.4 eV and kT_star=32.3±0.7 eV with a stellar angular radius as seen from infinity of 0.1371±0.0010 km pc-1. For HZ43 A, our fit yields T_eff = 51 126± 660 K and log g=7.90±0.080 (cgs) with anti-correlated errors (1-σ) which include not only the statistical but also the systematic uncertainties of the fit. HZ43AB displays a previously detected bremsstrahlung component with a temperature kT≃ 0.6 keV. For Sirius B, we find T_eff = 24 923± 115 K for fixed log g = 8.6. The calibration of the short-wavelength EUVE spectrometer differs from that of the LETG+HRC-S by 15± 7%. The ROSAT PSPC is found to be correctly calibrated within a few percent and reports of a major miscalibration are unfounded. Conclusions: .We have obtained improved parameters for RX J185635-3754, HZ43 A, and Sirius B which fit the observations from the optical to the soft X-ray regime. Our approach allows us to quote their absolute spectral fluxes at selected wavelengths which may aid the calibration of other space-borne instruments.

Concentration Independent Calibration of β-γ Coincidence Detector Using 131mXe and 133Xe

DOE Office of Scientific and Technical Information (OSTI.GOV)

McIntyre, Justin I.; Cooper, Matthew W.; Carman, April J.

Absolute efficiency calibration of radiometric detectors is frequently difficult and requires careful detector modeling and accurate knowledge of the radioactive source used. In the past we have calibrated the b-g coincidence detector of the Automated Radioxenon Sampler/Analyzer (ARSA) using a variety of sources and techniques which have proven to be less than desirable.[1] A superior technique has been developed that uses the conversion-electron (CE) and x-ray coincidence of 131mXe to provide a more accurate absolute gamma efficiency of the detector. The 131mXe is injected directly into the beta cell of the coincident counting system and no knowledge of absolute sourcemore » strength is required. In addition, 133Xe is used to provide a second independent means to obtain the absolute efficiency calibration. These two data points provide the necessary information for calculating the detector efficiency and can be used in conjunction with other noble gas isotopes to completely characterize and calibrate the ARSA nuclear detector. In this paper we discuss the techniques and results that we have obtained.« less

Ultraviolet photometry from the Orbiting Astronomical Observatory. XXI - Absolute energy distribution of stars in the ultraviolet

NASA Technical Reports Server (NTRS)

Bless, R. C.; Code, A. D.; Fairchild, E. T.

1976-01-01

The absolute energy distribution in the ultraviolet is given for the stars alpha Vir, eta UMa, and alpha Leo. The calibration is based on absolute heterochromatic photometry between 2920 and 1370 A carried out with an Aerobee sounding rocket. The fundamental radiation standard is the synchrotron radiation from 240-MeV electrons in a certain synchrotron storage ring. On the basis of the sounding-rocket calibration, the preliminary OAO-2 spectrometer calibration has been revised; the fluxes for the three program stars are tabulated in energy per second per square centimeter per unit wavelength interval.

Recent Surface Reflectance Measurement Campaigns with Emphasis on Best Practices, SI Traceability and Uncertainty Estimation

NASA Technical Reports Server (NTRS)

Helder, Dennis; Thome, Kurtis John; Aaron, Dave; Leigh, Larry; Czapla-Myers, Jeff; Leisso, Nathan; Biggar, Stuart; Anderson, Nik

2012-01-01

A significant problem facing the optical satellite calibration community is limited knowledge of the uncertainties associated with fundamental measurements, such as surface reflectance, used to derive satellite radiometric calibration estimates. In addition, it is difficult to compare the capabilities of calibration teams around the globe, which leads to differences in the estimated calibration of optical satellite sensors. This paper reports on two recent field campaigns that were designed to isolate common uncertainties within and across calibration groups, particularly with respect to ground-based surface reflectance measurements. Initial results from these efforts suggest the uncertainties can be as low as 1.5% to 2.5%. In addition, methods for improving the cross-comparison of calibration teams are suggested that can potentially reduce the differences in the calibration estimates of optical satellite sensors.

Spectral irradiance calibration in the infrared. I - Ground-based and IRAS broadband calibrations

NASA Technical Reports Server (NTRS)

Cohen, Martin; Walker, Russell G.; Barlow, Michael J.; Deacon, John R.

1992-01-01

Absolutely calibrated versions of realistic model atmosphere calculations for Sirius and Vega by Kurucz (1991) are presented and used as a basis to offer a new absolute calibration of infrared broad and narrow filters. In-band fluxes for Vega are obtained and defined to be zero magnitude at all wavelengths shortward of 20 microns. Existing infrared photometry is used differentially to establish an absolute scale of the new Sirius model, yielding an angular diameter within 1 sigma of the mean determined interferometrically by Hanbury Brown et al. (1974). The use of Sirius as a primary infrared stellar standard beyond the 20 micron region is suggested. Isophotal wavelengths and monochromatic flux densities for both Vega and Sirius are tabulated.

Linked Sensitivity Analysis, Calibration, and Uncertainty Analysis Using a System Dynamics Model for Stroke Comparative Effectiveness Research.

PubMed

Tian, Yuan; Hassmiller Lich, Kristen; Osgood, Nathaniel D; Eom, Kirsten; Matchar, David B

2016-11-01

As health services researchers and decision makers tackle more difficult problems using simulation models, the number of parameters and the corresponding degree of uncertainty have increased. This often results in reduced confidence in such complex models to guide decision making. To demonstrate a systematic approach of linked sensitivity analysis, calibration, and uncertainty analysis to improve confidence in complex models. Four techniques were integrated and applied to a System Dynamics stroke model of US veterans, which was developed to inform systemwide intervention and research planning: Morris method (sensitivity analysis), multistart Powell hill-climbing algorithm and generalized likelihood uncertainty estimation (calibration), and Monte Carlo simulation (uncertainty analysis). Of 60 uncertain parameters, sensitivity analysis identified 29 needing calibration, 7 that did not need calibration but significantly influenced key stroke outcomes, and 24 not influential to calibration or stroke outcomes that were fixed at their best guess values. One thousand alternative well-calibrated baselines were obtained to reflect calibration uncertainty and brought into uncertainty analysis. The initial stroke incidence rate among veterans was identified as the most influential uncertain parameter, for which further data should be collected. That said, accounting for current uncertainty, the analysis of 15 distinct prevention and treatment interventions provided a robust conclusion that hypertension control for all veterans would yield the largest gain in quality-adjusted life years. For complex health care models, a mixed approach was applied to examine the uncertainty surrounding key stroke outcomes and the robustness of conclusions. We demonstrate that this rigorous approach can be practical and advocate for such analysis to promote understanding of the limits of certainty in applying models to current decisions and to guide future data collection. © The Author(s) 2016.

Cruise Summary of WHP P6, A10, I3 and I4 Revisits in 2003

NASA Astrophysics Data System (ADS)

Kawano, T.; Uchida, H.; Schneider, W.; Kumamoto, Y.; Nishina, A.; Aoyama, M.; Murata, A.; Sasaki, K.; Yoshikawa, Y.; Watanabe, S.; Fukasawa, M.

2004-12-01

Japan Agency for Marin-Earth Science and Technology (JAMSTEC) conducted a research cruise to round in the southern hemisphere by R/V Mirai. In this presentation, we introduce an outline of the cruise and data quality obtained during the cruise. The cruise started on Aug. 3, 2003 in Brisbane, Australia and sailed eastward until it reached Fremantle, Australia on Feb. 19, 2004. It contained six legs and legs 1, 2, 4 and 5 were revisits of WOCE Hydrographic Program (WHP) sections P6W, P6E, A10 and I3/I4, respectively. The sections consisted of about 500 hydrographic stations in total. On each station, CTD profiles and up to 36 water samples by 12L Niskin-X bottles were taken from the surface to within 10 m of the bottom. Water samples were analyzed at every station for salinity, dissolved oxygen (DO), and nutrients and at alternate stations for concentration of freons, dissolved inorganic carbon (CT), total alkalinity (AT), pH, and so on. Approximately 17,000 samples were obtained for salinity. The standard seawater was measured repeatedly to estimate the uncertainty caused by the setting and stability of the salinometer. The standard deviation of 699 repeated runs of standard seawater was 0.0002 in salinity. Replicate samples, which are a pair of samples drawn from the same Niskin bottle to different sample bottles, were taken to evaluate the overall uncertainty. The standard deviation of absolute differences of 2,769 replicates was also 0.0002 in salinity. For DO, about 13,400 samples were obtained. The analysis was made by a photometric titration technique. The reproducibility estimated from the absolute standard deviation of 1,625 replicates was about 0.09 umol/kg. CTD temperature was calibrated against a deep ocean standards thermometer (SBE35) which was attached to the CTD using a polynomial expression Tcal = T - (a +b*P + c*t), where Tcal is calibrated temperature, T is CTD temperature, P is CTD pressure and t is time. Calibration coefficients, a, b and c, were determined for each station by minimizing the sum of absolute deviation from SBE35 temperature below 2,000dbar. CTD salinity and DO were fitted to values obtained by sampled water analysis using similar polynomials. These corrections yielded deviations of about 0.0002 K in temperature, 0.0003 in salinity and 0.6 umol/kg in DO. Nutrients analyses were accomplished on 16,000 samples using the reference material of nutrients in seawater (RMNS). To establish the traceability and to get higher quality data, 500 bottles of RMNS from the same lot and 150 sets of RMNSs were used. The precisions of phosphate, nitrate and silicate measurements were 0.18 %, 0.17 % and 0.16 % in terms of median of those at 493 stations, respectively. The nutrients concentrations could be expressed with uncertainties explicitly because of the repeated runs of RMNSs. All the analyses for the CO{2}-system parameters in water columns were finished onboard. Analytical precisions of CT, AT and pH were estimated to be \\sim1.0 umol/kg, \\sim2.0 umol/kg, and \\sim7*10-4 pH unit, respectively. Approximately 6,300 samples were obtained for CFC-11 and CFC-12. The concentrations were determined with an electron capture detector - gas chromatograph (ECD-GC) attached the purge and trapping system. The reproducibility estimated from the absolute standard deviation of 365 replicates was less than 1% with respect to the surface concentrations.

Lyman alpha SMM/UVSP absolute calibration and geocoronal correction

NASA Technical Reports Server (NTRS)

Fontenla, Juan M.; Reichmann, Edwin J.

1987-01-01

Lyman alpha observations from the Ultraviolet Spectrometer Polarimeter (UVSP) instrument of the Solar Maximum Mission (SMM) spacecraft were analyzed and provide instrumental calibration details. Specific values of the instrument quantum efficiency, Lyman alpha absolute intensity, and correction for geocoronal absorption are presented.

Absolute sensitivity calibration of an extreme ultraviolet spectrometer for tokamak measurements

NASA Astrophysics Data System (ADS)

Guirlet, R.; Schwob, J. L.; Meyer, O.; Vartanian, S.

2017-01-01

An extreme ultraviolet spectrometer installed on the Tore Supra tokamak has been calibrated in absolute units of brightness in the range 10-340 Å. This has been performed by means of a combination of techniques. The range 10-113 Å was absolutely calibrated by using an ultrasoft-X ray source emitting six spectral lines in this range. The calibration transfer to the range 113-182 Å was performed using the spectral line intensity branching ratio method. The range 182-340 Å was calibrated thanks to radiative-collisional modelling of spectral line intensity ratios. The maximum sensitivity of the spectrometer was found to lie around 100 Å. Around this wavelength, the sensitivity is fairly flat in a 80 Å wide interval. The spatial variations of sensitivity along the detector assembly were also measured. The observed trend is related to the quantum efficiency decrease as the angle of the incoming photon trajectories becomes more grazing.

Effects of temporal and spatial resolution of calibration data on integrated hydrologic water quality model identification

NASA Astrophysics Data System (ADS)

Jiang, Sanyuan; Jomaa, Seifeddine; Büttner, Olaf; Rode, Michael

2014-05-01

Hydrological water quality modeling is increasingly used for investigating runoff and nutrient transport processes as well as watershed management but it is mostly unclear how data availablity determins model identification. In this study, the HYPE (HYdrological Predictions for the Environment) model, which is a process-based, semi-distributed hydrological water quality model, was applied in two different mesoscale catchments (Selke (463 km2) and Weida (99 km2)) located in central Germany to simulate discharge and inorganic nitrogen (IN) transport. PEST and DREAM(ZS) were combined with the HYPE model to conduct parameter calibration and uncertainty analysis. Split-sample test was used for model calibration (1994-1999) and validation (1999-2004). IN concentration and daily IN load were found to be highly correlated with discharge, indicating that IN leaching is mainly controlled by runoff. Both dynamics and balances of water and IN load were well captured with NSE greater than 0.83 during validation period. Multi-objective calibration (calibrating hydrological and water quality parameters simultaneously) was found to outperform step-wise calibration in terms of model robustness. Multi-site calibration was able to improve model performance at internal sites, decrease parameter posterior uncertainty and prediction uncertainty. Nitrogen-process parameters calibrated using continuous daily averages of nitrate-N concentration observations produced better and more robust simulations of IN concentration and load, lower posterior parameter uncertainty and IN concentration prediction uncertainty compared to the calibration against uncontinuous biweekly nitrate-N concentration measurements. Both PEST and DREAM(ZS) are efficient in parameter calibration. However, DREAM(ZS) is more sound in terms of parameter identification and uncertainty analysis than PEST because of its capability to evolve parameter posterior distributions and estimate prediction uncertainty based on global search and Bayesian inference schemes.

Spectral Irradiance Calibration in the Infrared. 4; 1.2-35um Spectra of Six Standard Stars

NASA Technical Reports Server (NTRS)

Cohen, Martin; Witteborn, Fred C.; Walker, Russell G.; Bregman, Jesse D.; Wooden, Diane H.

1995-01-01

We present five new absolutely calibrated continuous stellar spectra from 1.2 to 35 microns, constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars, Beta Peg, Delta Boo, Beta And, Beta Gem, and Delta Hya, augment our already created complete absolutely calibrated spectrum for a Tau. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors.

Spectral Irradiance Calibration in the Infrared. Part 4; 1.2 - 35 microns Spectra of Six Standard Stars

NASA Technical Reports Server (NTRS)

Cohen, Martin; Witteborn, Fred C.; Walker, Russell G.; Bregman, Jesse D.; Wooden, Diane H.

1995-01-01

We present five new absolutely calibrated continuous stellar spectra from 1.2 to 35 microns, constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars- beta Peg, alpha Boo, beta And, beta Gem, and alpha Hya-augment our already created complete absolutely calibrated spectrum for alpha Tau. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors.

Estimating Divergence Dates and Substitution Rates in the Drosophila Phylogeny

PubMed Central

Obbard, Darren J.; Maclennan, John; Kim, Kang-Wook; Rambaut, Andrew; O’Grady, Patrick M.; Jiggins, Francis M.

2012-01-01

An absolute timescale for evolution is essential if we are to associate evolutionary phenomena, such as adaptation or speciation, with potential causes, such as geological activity or climatic change. Timescales in most phylogenetic studies use geologically dated fossils or phylogeographic events as calibration points, but more recently, it has also become possible to use experimentally derived estimates of the mutation rate as a proxy for substitution rates. The large radiation of drosophilid taxa endemic to the Hawaiian islands has provided multiple calibration points for the Drosophila phylogeny, thanks to the "conveyor belt" process by which this archipelago forms and is colonized by species. However, published date estimates for key nodes in the Drosophila phylogeny vary widely, and many are based on simplistic models of colonization and coalescence or on estimates of island age that are not current. In this study, we use new sequence data from seven species of Hawaiian Drosophila to examine a range of explicit coalescent models and estimate substitution rates. We use these rates, along with a published experimentally determined mutation rate, to date key events in drosophilid evolution. Surprisingly, our estimate for the date for the most recent common ancestor of the genus Drosophila based on mutation rate (25–40 Ma) is closer to being compatible with independent fossil-derived dates (20–50 Ma) than are most of the Hawaiian-calibration models and also has smaller uncertainty. We find that Hawaiian-calibrated dates are extremely sensitive to model choice and give rise to point estimates that range between 26 and 192 Ma, depending on the details of the model. Potential problems with the Hawaiian calibration may arise from systematic variation in the molecular clock due to the long generation time of Hawaiian Drosophila compared with other Drosophila and/or uncertainty in linking island formation dates with colonization dates. As either source of error will bias estimates of divergence time, we suggest mutation rate estimates be used until better models are available. PMID:22683811

The Kelvin and Temperature Measurements

PubMed Central

Mangum, B. W.; Furukawa, G. T.; Kreider, K. G.; Meyer, C. W.; Ripple, D. C.; Strouse, G. F.; Tew, W. L.; Moldover, M. R.; Johnson, B. Carol; Yoon, H. W.; Gibson, C. E.; Saunders, R. D.

2001-01-01

The International Temperature Scale of 1990 (ITS-90) is defined from 0.65 K upwards to the highest temperature measurable by spectral radiation thermometry, the radiation thermometry being based on the Planck radiation law. When it was developed, the ITS-90 represented thermodynamic temperatures as closely as possible. Part I of this paper describes the realization of contact thermometry up to 1234.93 K, the temperature range in which the ITS-90 is defined in terms of calibration of thermometers at 15 fixed points and vapor pressure/temperature relations which are phase equilibrium states of pure substances. The realization is accomplished by using fixed-point devices, containing samples of the highest available purity, and suitable temperature-controlled environments. All components are constructed to achieve the defining equilibrium states of the samples for the calibration of thermometers. The high quality of the temperature realization and measurements is well documented. Various research efforts are described, including research to improve the uncertainty in thermodynamic temperatures by measuring the velocity of sound in gas up to 800 K, research in applying noise thermometry techniques, and research on thermocouples. Thermometer calibration services and high-purity samples and devices suitable for “on-site” thermometer calibration that are available to the thermometry community are described. Part II of the paper describes the realization of temperature above 1234.93 K for which the ITS-90 is defined in terms of the calibration of spectroradiometers using reference blackbody sources that are at the temperature of the equilibrium liquid-solid phase transition of pure silver, gold, or copper. The realization of temperature from absolute spectral or total radiometry over the temperature range from about 60 K to 3000 K is also described. The dissemination of the temperature scale using radiation thermometry from NIST to the customer is achieved by calibration of blackbody sources, tungsten-strip lamps, and pyrometers. As an example of the research efforts in absolute radiometry, which impacts the NIST spectral irradiance and radiance scales, results with filter radiometers and a high-temperature blackbody are summarized. PMID:27500019

Calibration of Speed Enforcement Down-The-Road Radars

PubMed Central

Jendzurski, John; Paulter, Nicholas G.

2009-01-01

We examine the measurement uncertainty associated with different methods of calibrating the ubiquitous down-the-road (DTR) radar used in speed enforcement. These calibration methods include the use of audio frequency sources, tuning forks, a fifth wheel attached to the rear of the vehicle with the radar unit, and the speedometer of the vehicle. We also provide an analysis showing the effect of calibration uncertainty on DTR-radar speed measurement uncertainty. PMID:27504217

Absolute Wavelength Calibration of the IDSII Spectrometer for Impurity Ion Velocity Measurements in the MST

NASA Astrophysics Data System (ADS)

Baltzer, M.; Craig, D.; den Hartog, D. J.; Nornberg, M. D.; MST Team

2014-10-01

The MST operates two Ion Doppler Spectrometers (IDS) for high time-resolution passive and active measurements of impurity ion emission. Absolutely calibrated measurements of flow are difficult because the spectrometers record data within 0.3 nm of the line of interest, and commercial calibration lamps do not produce lines in this narrow range . Four calibration methods were investigated. First, emission along the chord bisecting the poloidal plane was measured as it should have no time-averaged Doppler shift. Second, a calibrated CCD spectrometer and the IDSII were used to observe the same plasma from opposing sides so as to measure opposite Doppler shifts. The unshifted line is located halfway between the two opposing measurements. Third, the two fibers of the IDSI were positioned to take absolute flow measurements using opposing views. Substituting the IDSII for one of the IDSI fibers, absolute measurements of flow from the IDSI were used to calibrate the IDSII. Finally, an optical system was designed to filter an ultraviolet LED, providing a known wavelength source within the spectral range covered by the IDSII. The optical train is composed of an air-gapped etalon and fused silica lenses. The quality of calibration for each of these methods is analyzed and their results compared. Preliminary impurity ion velocity measurements are shown. This work has been supported by the US DOE and the NSF.

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and ρR are determined in thin-shell inertial-confinement-fusion implosions.

PubMed

Rosenberg, M J; Zylstra, A B; Frenje, J A; Rinderknecht, H G; Johnson, M Gatu; Waugh, C J; Séguin, F H; Sio, H; Sinenian, N; Li, C K; Petrasso, R D; Glebov, V Yu; Hohenberger, M; Stoeckl, C; Sangster, T C; Yeamans, C B; LePape, S; Mackinnon, A J; Bionta, R M; Talison, B; Casey, D T; Landen, O L; Moran, M J; Zacharias, R A; Kilkenny, J D; Nikroo, A

2014-10-01

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ∼1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in the filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF.

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and pR are determined in thin-shell inertial-confinement-fusion implosions

DOE PAGES

Rosenberg, M. J.; Zylstra, A. B.; Frenje, J. A.; ...

2014-10-10

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ~1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in themore » filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF« less

A compact proton spectrometer for measurement of the absolute DD proton spectrum from which yield and ρR are determined in thin-shell inertial-confinement-fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenberg, M. J., E-mail: mrosenbe@mit.edu; Zylstra, A. B.; Frenje, J. A.

2014-10-01

A compact, step range filter proton spectrometer has been developed for the measurement of the absolute DD proton spectrum, from which yield and areal density (ρR) are inferred for deuterium-filled thin-shell inertial confinement fusion implosions. This spectrometer, which is based on tantalum step-range filters, is sensitive to protons in the energy range 1-9 MeV and can be used to measure proton spectra at mean energies of ~1-3 MeV. It has been developed and implemented using a linear accelerator and applied to experiments at the OMEGA laser facility and the National Ignition Facility (NIF). Modeling of the proton slowing in themore » filters is necessary to construct the spectrum, and the yield and energy uncertainties are ±<10% in yield and ±120 keV, respectively. This spectrometer can be used for in situ calibration of DD-neutron yield diagnostics at the NIF.« less

Management of groundwater in-situ bioremediation system using reactive transport modelling under parametric uncertainty: field scale application

NASA Astrophysics Data System (ADS)

Verardo, E.; Atteia, O.; Rouvreau, L.

2015-12-01

In-situ bioremediation is a commonly used remediation technology to clean up the subsurface of petroleum-contaminated sites. Forecasting remedial performance (in terms of flux and mass reduction) is a challenge due to uncertainties associated with source properties and the uncertainties associated with contribution and efficiency of concentration reducing mechanisms. In this study, predictive uncertainty analysis of bio-remediation system efficiency is carried out with the null-space Monte Carlo (NSMC) method which combines the calibration solution-space parameters with the ensemble of null-space parameters, creating sets of calibration-constrained parameters for input to follow-on remedial efficiency. The first step in the NSMC methodology for uncertainty analysis is model calibration. The model calibration was conducted by matching simulated BTEX concentration to a total of 48 observations from historical data before implementation of treatment. Two different bio-remediation designs were then implemented in the calibrated model. The first consists in pumping/injection wells and the second in permeable barrier coupled with infiltration across slotted piping. The NSMC method was used to calculate 1000 calibration-constrained parameter sets for the two different models. Several variants of the method were implemented to investigate their effect on the efficiency of the NSMC method. The first variant implementation of the NSMC is based on a single calibrated model. In the second variant, models were calibrated from different initial parameter sets. NSMC calibration-constrained parameter sets were sampled from these different calibrated models. We demonstrate that in context of nonlinear model, second variant avoids to underestimate parameter uncertainty which may lead to a poor quantification of predictive uncertainty. Application of the proposed approach to manage bioremediation of groundwater in a real site shows that it is effective to provide support in management of the in-situ bioremediation systems. Moreover, this study demonstrates that the NSMC method provides a computationally efficient and practical methodology of utilizing model predictive uncertainty methods in environmental management.

Comparison of Two Methodologies for Calibrating Satellite Instruments in the Visible and Near-Infrared

NASA Technical Reports Server (NTRS)

Barnes, Robert A.; Brown, Steven W.; Lykke, Keith R.; Guenther, Bruce; Butler, James J.; Schwarting, Thomas; Turpie, Kevin; Moyer, David; DeLuccia, Frank; Moeller, Christopher

2015-01-01

Traditionally, satellite instruments that measure Earth-reflected solar radiation in the visible and near infrared wavelength regions have been calibrated for radiance responsivity in a two-step method. In the first step, the relative spectral response (RSR) of the instrument is determined using a nearly monochromatic light source such as a lamp-illuminated monochromator. These sources do not typically fill the field-of-view of the instrument nor act as calibrated sources of light. Consequently, they only provide a relative (not absolute) spectral response for the instrument. In the second step, the instrument views a calibrated source of broadband light, such as a lamp-illuminated integrating sphere. The RSR and the sphere absolute spectral radiance are combined to determine the absolute spectral radiance responsivity (ASR) of the instrument. More recently, a full-aperture absolute calibration approach using widely tunable monochromatic lasers has been developed. Using these sources, the ASR of an instrument can be determined in a single step on a wavelength-by-wavelength basis. From these monochromatic ASRs, the responses of the instrument bands to broadband radiance sources can be calculated directly, eliminating the need for calibrated broadband light sources such as lamp-illuminated integrating spheres. In this work, the traditional broadband source-based calibration of the Suomi National Preparatory Project (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) sensor is compared with the laser-based calibration of the sensor. Finally, the impact of the new full-aperture laser-based calibration approach on the on-orbit performance of the sensor is considered.

Comparison of two methodologies for calibrating satellite instruments in the visible and near infrared

PubMed Central

Barnes, Robert A.; Brown, Steven W.; Lykke, Keith R.; Guenther, Bruce; Butler, James J.; Schwarting, Thomas; Moyer, David; Turpie, Kevin; DeLuccia, Frank; Moeller, Christopher

2016-01-01

Traditionally, satellite instruments that measure Earth-reflected solar radiation in the visible and near infrared wavelength regions have been calibrated for radiance responsivity in a two-step method. In the first step, the relative spectral response (RSR) of the instrument is determined using a nearly monochromatic light source such as a lamp-illuminated monochromator. These sources do not typically fill the field-of-view of the instrument nor act as calibrated sources of light. Consequently, they only provide a relative (not absolute) spectral response for the instrument. In the second step, the instrument views a calibrated source of broadband light, such as a lamp-illuminated integrating sphere. The RSR and the sphere absolute spectral radiance are combined to determine the absolute spectral radiance responsivity (ASR) of the instrument. More recently, a full-aperture absolute calibration approach using widely tunable monochromatic lasers has been developed. Using these sources, the ASR of an instrument can be determined in a single step on a wavelength-by-wavelength basis. From these monochromatic ASRs, the responses of the instrument bands to broadband radiance sources can be calculated directly, eliminating the need for calibrated broadband light sources such as integrating spheres. In this work, the traditional broadband source-based calibration of the Suomi National Preparatory Project (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) sensor is compared with the laser-based calibration of the sensor. Finally, the impact of the new full-aperture laser-based calibration approach on the on-orbit performance of the sensor is considered. PMID:26836861

Optical Region Spectrophotometry: Past and Present

NASA Astrophysics Data System (ADS)

Adelman, Saul J.

In the 1960s and 1970s optical region spectrophotometry achieved the status of a major tool in stellar research. New instrumentation, rotating grating scanners using photomultiplier tubes as detectors, and improved absolute calibrations of Vega made this possible. After this period the use of this technique declined to its near demise at present. The use of Vega as the primary standard has been both a blessing as it is so bright and a curse especially as modeling it correctly requires treating it as a fast rotating star seen nearly pole-on. It may be better to use several stars to define any future absolute calibration. With absolutely calibrated fluxes and Balmer profiles, often Hγ, investigators used the predictions of model atmospheres to find both the effective temperatures and the surface gravities of stars. The fluxes were photometrically calibrated low dispersion spectra with a typical resolution of order 25 Å. A typical data set consisted of 10-15 values covering most of the optical spectral region. At present two instrumental projects ACCESS and the ASTRA Spectrophotometer promise, respectively, a new substantially improved absolute calibration of the optical fluxes of several targets and the availability of a considerable amount of well-calibrated optical flux data for use in studies concerned with stellar properties. They jointly promise to revive optical region spectrophotometric studies.

Absolute calorimetric calibration of low energy brachytherapy sources

NASA Astrophysics Data System (ADS)

Stump, Kurt E.

In the past decade there has been a dramatic increase in the use of permanent radioactive source implants in the treatment of prostate cancer. A small radioactive source encapsulated in a titanium shell is used in this type of treatment. The radioisotopes used are generally 125I or 103Pd. Both of these isotopes have relatively short half-lives, 59.4 days and 16.99 days, respectively, and have low-energy emissions and a low dose rate. These factors make these sources well suited for this application, but the calibration of these sources poses significant metrological challenges. The current standard calibration technique involves the measurement of ionization in air to determine the source air-kerma strength. While this has proved to be an improvement over previous techniques, the method has been shown to be metrologically impure and may not be the ideal means of calbrating these sources. Calorimetric methods have long been viewed to be the most fundamental means of determining source strength for a radiation source. This is because calorimetry provides a direct measurement of source energy. However, due to the low energy and low power of the sources described above, current calorimetric methods are inadequate. This thesis presents work oriented toward developing novel methods to provide direct and absolute measurements of source power for low-energy low dose rate brachytherapy sources. The method is the first use of an actively temperature-controlled radiation absorber using the electrical substitution method to determine total contained source power of these sources. The instrument described operates at cryogenic temperatures. The method employed provides a direct measurement of source power. The work presented here is focused upon building a metrological foundation upon which to establish power-based calibrations of clinical-strength sources. To that end instrument performance has been assessed for these source strengths. The intent is to establish the limits of the current instrument to direct further work in this field. It has been found that for sources with powers above approximately 2 muW the instrument is able to determine the source power in agreement to within less than 7% of what is expected based upon the current source strength standard. For lower power sources, the agreement is still within the uncertainty of the power measurement, but the calorimeter noise dominates. Thus, to provide absolute calibration of lower power sources additional measures must be taken. The conclusion of this thesis describes these measures and how they will improve the factors that limit the current instrument. The results of the work presented in this thesis establish the methodology of active radiometric calorimetey for the absolute calibration of radioactive sources. The method is an improvement over previous techniques in that there is no reliance upon the thermal properties of the materials used or the heat flow pathways on the source measurements. The initial work presented here will help to shape future refinements of this technique to allow lower power sources to be calibrated with high precision and high accuracy.

Application of quantitative 1H NMR for the calibration of protoberberine alkaloid reference standards.

PubMed

Wu, Yan; He, Yi; He, Wenyi; Zhang, Yumei; Lu, Jing; Dai, Zhong; Ma, Shuangcheng; Lin, Ruichao

2014-03-01

Quantitative nuclear magnetic resonance spectroscopy (qNMR) has been developed into an important tool in the drug analysis, biomacromolecule detection, and metabolism study. Compared with mass balance method, qNMR method bears some advantages in the calibration of reference standard (RS): it determines the absolute amount of a sample; other chemical compound and its certified reference material (CRM) can be used as internal standard (IS) to obtain the purity of the sample. Protoberberine alkaloids have many biological activities and have been used as reference standards for the control of many herbal drugs. In present study, the qNMR methods were developed for the calibration of berberine hydrochloride, palmatine hydrochloride, tetrahydropalmatine, and phellodendrine hydrochloride with potassium hydrogen phthalate as IS. Method validation was carried out according to the guidelines for the method validation of Chinese Pharmacopoeia. The results of qNMR were compared with those of mass balance method and the differences between the results of two methods were acceptable based on the analysis of estimated measurement uncertainties. Therefore, qNMR is an effective and reliable analysis method for the calibration of RS and can be used as a good complementarity to the mass balance method. Copyright © 2013 Elsevier B.V. All rights reserved.

Absolute charge calibration of scintillating screens for relativistic electron detection

NASA Astrophysics Data System (ADS)

Buck, A.; Zeil, K.; Popp, A.; Schmid, K.; Jochmann, A.; Kraft, S. D.; Hidding, B.; Kudyakov, T.; Sears, C. M. S.; Veisz, L.; Karsch, S.; Pawelke, J.; Sauerbrey, R.; Cowan, T.; Krausz, F.; Schramm, U.

2010-03-01

We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC/mm2. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10-100 pC/mm2 was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference to simplify the transfer of a one-time absolute calibration to different experimental setups.

Calibration of High Heat Flux Sensors at NIST

PubMed Central

Murthy, A. V.; Tsai, B. K.; Gibson, C. E.

1997-01-01

An ongoing program at the National Institute of Standards and Technology (NIST) is aimed at improving and standardizing heat-flux sensor calibration methods. The current calibration needs of U.S. science and industry exceed the current NIST capability of 40 kW/m2 irradiance. In achieving this goal, as well as meeting lower-level non-radiative heat flux calibration needs of science and industry, three different types of calibration facilities currently are under development at NIST: convection, conduction, and radiation. This paper describes the research activities associated with the NIST Radiation Calibration Facility. Two different techniques, transfer and absolute, are presented. The transfer calibration technique employs a transfer standard calibrated with reference to a radiometric standard for calibrating the sensors using a graphite tube blackbody. Plans for an absolute calibration facility include the use of a spherical blackbody and a cooled aperture and sensor-housing assembly to calibrate the sensors in a low convective environment. PMID:27805156

Artifact correction and absolute radiometric calibration techniques employed in the Landsat 7 image assessment system

USGS Publications Warehouse

Boncyk, Wayne C.; Markham, Brian L.; Barker, John L.; Helder, Dennis

1996-01-01

The Landsat-7 Image Assessment System (IAS), part of the Landsat-7 Ground System, will calibrate and evaluate the radiometric and geometric performance of the Enhanced Thematic Mapper Plus (ETM +) instrument. The IAS incorporates new instrument radiometric artifact correction and absolute radiometric calibration techniques which overcome some limitations to calibration accuracy inherent in historical calibration methods. Knowledge of ETM + instrument characteristics gleaned from analysis of archival Thematic Mapper in-flight data and from ETM + prelaunch tests allow the determination and quantification of the sources of instrument artifacts. This a priori knowledge will be utilized in IAS algorithms designed to minimize the effects of the noise sources before calibration, in both ETM + image and calibration data.

First pure frequency measurement of an optical transition in helium: Lamb shift on the 23S1 metastable level

NASA Astrophysics Data System (ADS)

Pavone, F. S.; Marin, F.; de Natale, P.; Inguscio, M.; Biraben, F.

1994-07-01

The 23S1-33P40He transition at λ0=389 nm is measured with respect to a previously frequency calibrated 87Rb two-photon transition at 2λ0=778 nm. The 4He absolute frequency is 770 732 839 058 (190) kHz, with an accuracy of 2.4 parts in 1010. A Lamb shift value of +4057.61 (79) MHz, with 600 kHz uncertainty arising from the theoretical position of the 33P0 energy level, is extracted for the 23S1 level. This value is more than 2 orders of magnitude more accurate than the current best theoretical predictions.

Calibrated intercepts for solar radiometers used in remote sensor calibration

NASA Technical Reports Server (NTRS)

Gellman, David I.; Biggar, Stuart F.; Slater, Philip N.; Bruegge, Carol J.

1991-01-01

Calibrated solar radiometer intercepts allow spectral optical depths to be determined for days with intermittently clear skies. This is of particular importance on satellite sensor calibration days that are cloudy except at the time of image acquisition. This paper describes the calibration of four solar radiometers using the Langley-Bouguer technique for data collected on days with a clear, stable atmosphere. Intercepts are determined with an uncertainty of less than six percent, corresponding to a maximum uncertainty of 0.06 in optical depth. The spread of voltage intercepts calculated in this process is carried through three methods of radiometric calibration of satellite sensors to yield an uncertainty in radiance at the top of the atmosphere of less than one percent associated with the uncertainty in solar radiometer intercepts for a range of ground reflectances.

Recent Infrasound Calibration Activity at Los Alamos

NASA Astrophysics Data System (ADS)

Whitaker, R. W.; Marcillo, O. E.

2014-12-01

Absolute infrasound sensor calibration is necessary for estimating source sizes from measured waveforms. This can be an important function in treaty monitoring. The Los Alamos infrasound calibration chamber is capable of absolute calibration. Early in 2014 the Los Alamos infrasound calibration chamber resumed operations in its new location after an unplanned move two years earlier. The chamber has two sources of calibration signals. The first is the original mechanical piston, and the second is a CLD Dynamics Model 316 electro-mechanical unit that can be digitally controlled and provide a richer set of calibration options. During 2008-2010 a number of upgrades were incorporated for improved operation and recording. In this poster we give an overview of recent chamber work on sensor calibrations, calibration with the CLD unit, some measurements with different porous hoses and work with impulse sources.

A spectroscopic transfer standard for accurate atmospheric CO measurements

NASA Astrophysics Data System (ADS)

Nwaboh, Javis A.; Li, Gang; Serdyukov, Anton; Werhahn, Olav; Ebert, Volker

2016-04-01

Atmospheric carbon monoxide (CO) is a precursor of essential climate variables and has an indirect effect for enhancing global warming. Accurate and reliable measurements of atmospheric CO concentration are becoming indispensable. WMO-GAW reports states a compatibility goal of ±2 ppb for atmospheric CO concentration measurements. Therefore, the EMRP-HIGHGAS (European metrology research program - high-impact greenhouse gases) project aims at developing spectroscopic transfer standards for CO concentration measurements to meet this goal. A spectroscopic transfer standard would provide results that are directly traceable to the SI, can be very useful for calibration of devices operating in the field, and could complement classical gas standards in the field where calibration gas mixtures in bottles often are not accurate, available or stable enough [1][2]. Here, we present our new direct tunable diode laser absorption spectroscopy (dTDLAS) sensor capable of performing absolute ("calibration free") CO concentration measurements, and being operated as a spectroscopic transfer standard. To achieve the compatibility goal stated by WMO for CO concentration measurements and ensure the traceability of the final concentration results, traceable spectral line data especially line intensities with appropriate uncertainties are needed. Therefore, we utilize our new high-resolution Fourier-transform infrared (FTIR) spectroscopy CO line data for the 2-0 band, with significantly reduced uncertainties, for the dTDLAS data evaluation. Further, we demonstrate the capability of our sensor for atmospheric CO measurements, discuss uncertainty calculation following the guide to the expression of uncertainty in measurement (GUM) principles and show that CO concentrations derived using the sensor, based on the TILSAM (traceable infrared laser spectroscopic amount fraction measurement) method, are in excellent agreement with gravimetric values. Acknowledgement Parts of this work have been carried out within the European Metrology Research Programme (EMRP) ENV52 project-HIGHGAS (Metrology for high-impact greenhouse gases). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. References [1] EMRP project ENV52-HIGHGAS (Metrology for high-impact greenhouse gases), available at: http://www.euramet.org/. [2] J. Nwaboh, A. Manninen, J. Mohn, J. C. Petersen, O. Werhahn, and V.Ebert, European Geosciences Union General Assembly 2015, EGU2015-13542, 2015, Vienna Austria

Strategy for the absolute neutron emission measurement on ITER.

PubMed

Sasao, M; Bertalot, L; Ishikawa, M; Popovichev, S

2010-10-01

Accuracy of 10% is demanded to the absolute fusion measurement on ITER. To achieve this accuracy, a functional combination of several types of neutron measurement subsystem, cross calibration among them, and in situ calibration are needed. Neutron transport calculation shows the suitable calibration source is a DT/DD neutron generator of source strength higher than 10(10) n/s (neutron/second) for DT and 10(8) n/s for DD. It will take eight weeks at the minimum with this source to calibrate flux monitors, profile monitors, and the activation system.

Optimal test selection for prediction uncertainty reduction

DOE PAGES

Mullins, Joshua; Mahadevan, Sankaran; Urbina, Angel

2016-12-02

Economic factors and experimental limitations often lead to sparse and/or imprecise data used for the calibration and validation of computational models. This paper addresses resource allocation for calibration and validation experiments, in order to maximize their effectiveness within given resource constraints. When observation data are used for model calibration, the quality of the inferred parameter descriptions is directly affected by the quality and quantity of the data. This paper characterizes parameter uncertainty within a probabilistic framework, which enables the uncertainty to be systematically reduced with additional data. The validation assessment is also uncertain in the presence of sparse and imprecisemore » data; therefore, this paper proposes an approach for quantifying the resulting validation uncertainty. Since calibration and validation uncertainty affect the prediction of interest, the proposed framework explores the decision of cost versus importance of data in terms of the impact on the prediction uncertainty. Often, calibration and validation tests may be performed for different input scenarios, and this paper shows how the calibration and validation results from different conditions may be integrated into the prediction. Then, a constrained discrete optimization formulation that selects the number of tests of each type (calibration or validation at given input conditions) is proposed. Furthermore, the proposed test selection methodology is demonstrated on a microelectromechanical system (MEMS) example.« less

EUNIS Underflight Calibrations of CDS, EIT, TRACE, EIS, and EUVI

NASA Technical Reports Server (NTRS)

Thomas, Roger J.; Rabin, Douglas M.; Jess, David B.; Wang, Tongjiang

2008-01-01

The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a sounding rocket instrument that obtains imaged high-resolution solar spectra. It has now had two successful flights, on 2006 April 12 and 2007 November 16, providing data to support underflight calibrations for a number of orbiting solar experiments on both occasions. A regular part of each campaign is the end-to-end radiometric calibration of the rocket payload carried out at RAL in the UK, using the same facility that provided pre-flight CDS and EIS calibrations. The measurements, traceable to primary radiometric standards, can establish the absolute EUNIS response within a relative uncertainty of 10% over its full longwave bandpass of 300-370A. During each EUNIS flight, coordinated observations are made of overlapping solar locations by all participating space experiments, and identified by subsequent image co-registrations, allowing the EUNIS calibrations to be applied to these other instruments as well. The calibration transfer is straightforward for wavelengths within the EUNIS LW bandpass, and is extended to other wavelengths by means of a series of 'insensitive' line-ratios, with one line of each pair in the calibrated band and the other in the transfer band. In this way, the EUNIS-06 flight is able to update the radiometric calibrations of CDS NISl (plus 2nd order NIS2 near 2x304A), all four channels of EIT, and the three EUV channels of TRACE. The EUNIS-07 flight will further update those missions, as well as both channels of Hinode/EIT and all four channels of STEREO/SECCHI/EUVI. Future EUNIS flights have been proposed that will continue this underflight calibration service. EUNIS is supported by the NASA Heliophysics Division through its Low Cost Access to Space Program in Solar and Heliospheric Physics.

EUNIS Underflight Calibrations of CDS, EIT, TRACE, EIS, and EUVI

NASA Technical Reports Server (NTRS)

Thomas, Roger J.; Wang, Tongjiang; Rabin, Douglas M.; Jess, David B.

2008-01-01

The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a sounding rocket instrument that obtains imaged high-resolution solar spectra. It has now had two successful flights, on 2006 April 12 and 2007 November 16, providing data to support underflight calibrations for a number of orbiting solar experiments on both occasions. A regular part of each campaign is the end-to-end radiometric calibration of the rocket payload carried out at RAL in the UK, using the same facility that provided pre-flight CDS and EIS calibrations. The measurements, traceable to primary radiometric standards, can establish the absolute EUNIS response within a total uncertainty of 10% over its full longwave bandpass of 300-370A. During each EUNIS flight, coordinated observations are made of overlapping solar locations by all participating space experiments, and identified by subsequent image co-registrations, allowing the EUNIS calibrations to be applied to these other instruments as well. The calibration transfer is straightforward for wavelengths within the EUNIS LW bandpass, and is extended to other wavelengths by means of a series of temperature- and density-insensitive line-ratios, with one line of each pair in the calibrated band and the other in the transfer band. In this way, the EUNIS-06 flight is able to update the radiometric calibrations of CDS NISl (and 2nd-order NIS2 near 2x304A), all four channels of EIT, and the three EUV channels of TRACE. The EUNIS-07 flight will further update those missions, as well as both channels of Hinode/EIS and all four channels of STEREO/SECCHI/EUVI. Future EUNIS flights have been proposed that will continue this underflight calibration service. EUNIS is supported by the NASA Heliophysics Division through its Low Cost Access to Space Program in Solar and Heliospheric Physics.

Temporal dynamics of sand dune bidirectional reflectance characteristics for absolute radiometric calibration of optical remote sensing data

NASA Astrophysics Data System (ADS)

Coburn, Craig A.; Logie, Gordon S. J.

2018-01-01

Attempts to use pseudoinvariant calibration sites (PICS) for establishing absolute radiometric calibration of Earth observation (EO) satellites requires high-quality information about the nature of the bidirectional reflectance distribution function (BRDF) of the surfaces used for these calibrations. Past studies have shown that the PICS method is useful for evaluating the trend of sensors over time or for the intercalibration of sensors. The PICS method was not considered until recently for deriving absolute radiometric calibration. This paper presents BRDF data collected by a high-performance portable goniometer system to develop a temporal BRDF model for the Algodones Dunes in California. By sampling the BRDF of the sand surface at similar solar zenith angles to those normally encountered by EO satellites, additional information on the changing nature of the surface can improve models used to provide absolute radiometric correction. The results demonstrated that the BRDF of a reasonably simple sand surface was complex with changes in anisotropy taking place in response to changing solar zenith angles. For the majority of observation and illumination angles, the spectral reflectance anisotropy observed varied between 1% and 5% in patterns that repeat around solar noon.

A BAYESIAN METHOD FOR CALCULATING REAL-TIME QUANTITATIVE PCR CALIBRATION CURVES USING ABSOLUTE PLASMID DNA STANDARDS

EPA Science Inventory

In real-time quantitative PCR studies using absolute plasmid DNA standards, a calibration curve is developed to estimate an unknown DNA concentration. However, potential differences in the amplification performance of plasmid DNA compared to genomic DNA standards are often ignore...

Radiance calibration of the High Altitude Observatory white-light coronagraph on Skylab

NASA Technical Reports Server (NTRS)

Poland, A. I.; Macqueen, R. M.; Munro, R. H.; Gosling, J. T.

1977-01-01

The processing of over 35,000 photographs of the solar corona obtained by the white-light coronograph on Skylab is described. Calibration of the vast amount of data was complicated by temporal effects of radiation fog and latent image loss. These effects were compensated by imaging a calibration step wedge on each data frame. Absolute calibration of the wedge was accomplished through comparison with a set of previously calibrated glass opal filters. Analysis employed average characteristic curves derived from measurements of step wedges from many frames within a given camera half-load. The net absolute accuracy of a given radiance measurement is estimated to be 20%.

Spectral Irradiance Calibration in the Infrared. Part 4; 1.2-35 micrometer Spectra of Six Standard Stars

NASA Technical Reports Server (NTRS)

Cohen, Martin; Witteborn, Fred C.; Walker, Russell, G.; Bregman, Jesse D.; Wooden, Diane H.

1995-01-01

Five new absolutely calibrated continuous stellar spectra from 1.2 to 35 microns are presented. The spectra were constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars (beta Peg, alpha Boo, beta And, beta Gem, and alpha Hya) augment the author's already created complete absolutely calibrated spectrum for alpha Tau. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors.

Measuring the Hubble constant with Type Ia supernovae as near-infrared standard candles

NASA Astrophysics Data System (ADS)

Dhawan, Suhail; Jha, Saurabh W.; Leibundgut, Bruno

2018-01-01

The most precise local measurements of H0 rely on observations of Type Ia supernovae (SNe Ia) coupled with Cepheid distances to SN Ia host galaxies. Recent results have shown tension comparing H0 to the value inferred from CMB observations assuming ΛCDM, making it important to check for potential systematic uncertainties in either approach. To date, precise local H0 measurements have used SN Ia distances based on optical photometry, with corrections for light curve shape and colour. Here, we analyse SNe Ia as standard candles in the near-infrared (NIR), where luminosity variations in the supernovae and extinction by dust are both reduced relative to the optical. From a combined fit to 9 nearby calibrator SNe with host Cepheid distances from Riess et al. (2016) and 27 SNe in the Hubble flow, we estimate the absolute peak J magnitude MJ = -18.524 ± 0.041 mag and H0 = 72.8 ± 1.6 (statistical) ±2.7 (systematic) km s-1 Mpc-1. The 2.2% statistical uncertainty demonstrates that the NIR provides a compelling avenue to measuring SN Ia distances, and for our sample the intrinsic (unmodeled) peak J magnitude scatter is just 0.10 mag, even without light curve shape or colour corrections. Our results do not vary significantly with different sample selection criteria, though photometric calibration in the NIR may be a dominant systematic uncertainty. Our findings suggest that tension in the competing H0 distance ladders is likely not a result of supernova systematics that could be expected to vary between optical and NIR wavelengths, like dust extinction. We anticipate further improvements in H0 with a larger calibrator sample of SNe Ia with Cepheid distances, more Hubble flow SNe Ia with NIR light curves, and better use of the full NIR photometric data set beyond simply the peak J-band magnitude.

Pulsating stars and the distance scale

NASA Astrophysics Data System (ADS)

Macri, Lucas

2017-09-01

I present an overview of the latest results from the SH0ES project, which obtained homogeneous Hubble Space Telescope (HST) photometry in the optical and near-infrared for ˜ 3500 and ˜ 2300 Cepheids, respectively, across 19 supernova hosts and 4 calibrators to determine the value of H0 with a total uncertainty of 2.4%. I discuss the current 3.4σ "tension" between this local measurement and predictions of H0 based on observations of the CMB and the assumption of "standard" ΛCDM. I review ongoing efforts to reach σ(H0) = 1%, including recent advances on the absolute calibration of Milky Way Cepheid period-luminosity relations (PLRs) using a novel astrometric technique with HST. Lastly, I highlight recent results from another collaboration on the development of new statistical techniques to detect, classify and phase extragalactic Miras using noisy and sparsely-sampled observations. I present preliminary Mira PLRs at various wavelengths based on the application of these techniques to a survey of M33.

Atmospheric correction for JPSS-2 VIIRS response versus scan angle measurements

NASA Astrophysics Data System (ADS)

McIntire, Jeffrey; Moeller, Chris; Oudrari, Hassan; Xiong, Xiaoxiong

2017-09-01

The Joint Polar Satellite System 2 (JPSS-2) Visible Infrared Imaging Radiometer Suite (VIIRS) includes one spectral band centered in a strong atmospheric absorption region. As much of the pre-launch calibration is performed under laboratory ambient conditions, accurately accounting for the absorption, and thereby ensuring the transfer of the sensor calibration to on-orbit operations, is necessary to generate science quality data products. This work is focused on the response versus scan angle (RVS) measurements, which characterize the relative scan angle dependent reflectance of the JPSS-2 VIIRS instrument optics. The spectral band of interest, centered around 1378 nm, is within a spectral region strongly effected by water vapor absorption. The methodology used to model the absolute humidity and the atmospheric transmittance under the laboratory conditions is detailed. The application of this transmittance to the RVS determination is then described including an uncertainty estimate; a comparison to the pre-launch measurements from earlier sensor builds is also performed.

Evaluation of calibration efficacy under different levels of uncertainty

DOE PAGES

Heo, Yeonsook; Graziano, Diane J.; Guzowski, Leah; ...

2014-06-10

This study examines how calibration performs under different levels of uncertainty in model input data. It specifically assesses the efficacy of Bayesian calibration to enhance the reliability of EnergyPlus model predictions. A Bayesian approach can be used to update uncertain values of parameters, given measured energy-use data, and to quantify the associated uncertainty.We assess the efficacy of Bayesian calibration under a controlled virtual-reality setup, which enables rigorous validation of the accuracy of calibration results in terms of both calibrated parameter values and model predictions. Case studies demonstrate the performance of Bayesian calibration of base models developed from audit data withmore » differing levels of detail in building design, usage, and operation.« less

Radio measurements of the energy and the depth of the shower maximum of cosmic-ray air showers by Tunka-Rex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bezyazeekov, P.A.; Budnev, N.M.; Gress, O.A.

2016-01-01

We reconstructed the energy and the position of the shower maximum of air showers with energies E ∼> 100 PeV applying a method using radio measurements performed with Tunka-Rex. An event-to-event comparison to air-Cherenkov measurements of the same air showers with the Tunka-133 photomultiplier array confirms that the radio reconstruction works reliably. The Tunka-Rex reconstruction methods and absolute scales have been tuned on CoREAS simulations and yield energy and X{sub max} values consistent with the Tunka-133 measurements. The results of two independent measurement seasons agree within statistical uncertainties, which gives additional confidence in the radio reconstruction. The energy precision of Tunka-Rex is comparablemore » to the Tunka-133 precision of 15%, and exhibits a 20% uncertainty on the absolute scale dominated by the amplitude calibration of the antennas. For X{sub max}, this is the first direct experimental correlation of radio measurements with a different, established method. At the moment, the X{sub max} resolution of Tunka-Rex is approximately 40 g/cm{sup 2}. This resolution can probably be improved by deploying additional antennas and by further development of the reconstruction methods, since the present analysis does not yet reveal any principle limitations.« less

Experimental verification of stopping-power prediction from single- and dual-energy computed tomography in biological tissues

NASA Astrophysics Data System (ADS)

Möhler, Christian; Russ, Tom; Wohlfahrt, Patrick; Elter, Alina; Runz, Armin; Richter, Christian; Greilich, Steffen

2018-01-01

An experimental setup for consecutive measurement of ion and x-ray absorption in tissue or other materials is introduced. With this setup using a 3D-printed sample container, the reference stopping-power ratio (SPR) of materials can be measured with an uncertainty of below 0.1%. A total of 65 porcine and bovine tissue samples were prepared for measurement, comprising five samples each of 13 tissue types representing about 80% of the total body mass (three different muscle and fatty tissues, liver, kidney, brain, heart, blood, lung and bone). Using a standard stoichiometric calibration for single-energy CT (SECT) as well as a state-of-the-art dual-energy CT (DECT) approach, SPR was predicted for all tissues and then compared to the measured reference. With the SECT approach, the SPRs of all tissues were predicted with a mean error of (-0.84  ±  0.12)% and a mean absolute error of (1.27  ±  0.12)%. In contrast, the DECT-based SPR predictions were overall consistent with the measured reference with a mean error of (-0.02  ±  0.15)% and a mean absolute error of (0.10  ±  0.15)%. Thus, in this study, the potential of DECT to decrease range uncertainty could be confirmed in biological tissue.

The Extreme Spin of the Black Hole in Cygnus X-1

NASA Technical Reports Server (NTRS)

Gou, Lijun; McClintock, Jeffre E.; Reid, Mark J.; Orosz, Jerome A.; Steiner, James F.; Narayan, Ramesh; Xiang, Jingen; Remillard, Ronald A.; Arnaud, Keith A.; Davis, Shane W.

2005-01-01

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observatIOns. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these.results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum.spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-I contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamIcal model, we find a* > 0.92 (3(sigma)). In our analysis, we include the uncertainties in black hole mass orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity.

The Extreme Spin of the Black Hole in Cygnus X-1

NASA Technical Reports Server (NTRS)

Gou, Lijun; McClintock, Jeffrey E.; Reid, Mark J.; Orosz, Jerome A.; Steiner, James F.; Narayan, Ramesh; Xiang, Jingen; Remillard, Ronald A.; Arnaud, Keith A.; Davis, Shane W.

2011-01-01

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole s accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamical model, we find a. > 0.92 (3 ). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle, and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk s low luminosity.

Absolute Radiometric Calibration of EUNIS-06

NASA Technical Reports Server (NTRS)

Thomas, R. J.; Rabin, D. M.; Kent, B. J.; Paustian, W.

2007-01-01

The Extreme-Ultraviolet Normal-Incidence Spectrometer (EUNIS) is a soundingrocket payload that obtains imaged high-resolution spectra of individual solar features, providing information about the Sun's corona and upper transition region. Shortly after its successful initial flight last year, a complete end-to-end calibration was carried out to determine the instrument's absolute radiometric response over its Longwave bandpass of 300 - 370A. The measurements were done at the Rutherford-Appleton Laboratory (RAL) in England, using the same vacuum facility and EUV radiation source used in the pre-flight calibrations of both SOHO/CDS and Hinode/EIS, as well as in three post-flight calibrations of our SERTS sounding rocket payload, the precursor to EUNIS. The unique radiation source provided by the Physikalisch-Technische Bundesanstalt (PTB) had been calibrated to an absolute accuracy of 7% (l-sigma) at 12 wavelengths covering our bandpass directly against the Berlin electron storage ring BESSY, which is itself a primary radiometric source standard. Scans of the EUNIS aperture were made to determine the instrument's absolute spectral sensitivity to +- 25%, considering all sources of error, and demonstrate that EUNIS-06 was the most sensitive solar E W spectrometer yet flown. The results will be matched against prior calibrations which relied on combining measurements of individual optical components, and on comparisons with theoretically predicted 'insensitive' line ratios. Coordinated observations were made during the EUNIS-06 flight by SOHO/CDS and EIT that will allow re-calibrations of those instruments as well. In addition, future EUNIS flights will provide similar calibration updates for TRACE, Hinode/EIS, and STEREO/SECCHI/EUVI.

Absolute high spectral resolution measurements of surface solar radiation for detection of water vapour continuum absorption.

PubMed

Gardiner, T D; Coleman, M; Browning, H; Tallis, L; Ptashnik, I V; Shine, K P

2012-06-13

Solar-pointing Fourier transform infrared (FTIR) spectroscopy offers the capability to measure both the fine scale and broadband spectral structure of atmospheric transmission simultaneously across wide spectral regions. It is therefore suited to the study of both water vapour monomer and continuum absorption behaviours. However, in order to properly address this issue, it is necessary to radiatively calibrate the FTIR instrument response. A solar-pointing high-resolution FTIR spectrometer was deployed as part of the 'Continuum Absorption by Visible and Infrared radiation and its Atmospheric Relevance' (CAVIAR) consortium project. This paper describes the radiative calibration process using an ultra-high-temperature blackbody and the consideration of the related influence factors. The result is a radiatively calibrated measurement of the solar irradiation at the ground across the IR region from 2000 to 10 000 cm(-1) with an uncertainty of between 3.3 and 5.9 per cent. This measurement is shown to be in good general agreement with a radiative-transfer model. The results from the CAVIAR field measurements are being used in ongoing studies of atmospheric absorbers, in particular the water vapour continuum.

Radiometric calibration of optical microscopy and microspectroscopy apparata over a broad spectral range using a special thin-film luminescence standard

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valenta, J., E-mail: jan.valenta@mff.cuni.cz; Greben, M.

2015-04-15

Application capabilities of optical microscopes and microspectroscopes can be considerably enhanced by a proper calibration of their spectral sensitivity. We propose and demonstrate a method of relative and absolute calibration of a microspectroscope over an extraordinary broad spectral range covered by two (parallel) detection branches in visible and near-infrared spectral regions. The key point of the absolute calibration of a relative spectral sensitivity is application of the standard sample formed by a thin layer of Si nanocrystals with stable and efficient photoluminescence. The spectral PL quantum yield and the PL spatial distribution of the standard sample must be characterized bymore » separate experiments. The absolutely calibrated microspectroscope enables to characterize spectral photon emittance of a studied object or even its luminescence quantum yield (QY) if additional knowledge about spatial distribution of emission and about excitance is available. Capabilities of the calibrated microspectroscope are demonstrated by measuring external QY of electroluminescence from a standard poly-Si solar-cell and of photoluminescence of Er-doped Si nanocrystals.« less

The Absolute Abundance of Iron in the Solar Corona.

PubMed

White; Thomas; Brosius; Kundu

2000-05-10

We present a measurement of the abundance of Fe relative to H in the solar corona using a technique that differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory with thermal bremsstrahlung radio data from the VLA. The coronal Fe abundance is derived by equating the thermal bremsstrahlung radio emission calculated from the EUV Fe line data to that observed with the VLA, treating the Fe/H abundance as the sole unknown. We apply this technique to a compact cool active region and find Fe&solm0;H=1.56x10-4, or about 4 times its value in the solar photosphere. Uncertainties in the CDS radiometric calibration, the VLA intensity measurements, the atomic parameters, and the assumptions made in the spectral analysis yield net uncertainties of approximately 20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values.

Absolute calibration of a hydrogen discharge lamp in the vacuum ultraviolet

NASA Technical Reports Server (NTRS)

Nealy, J. E.

1975-01-01

A low-pressure hydrogen discharge lamp was calibrated for radiant intensity in the vacuum ultraviolet spectral region on an absolute basis and was employed as a laboratory standard source in spectrograph calibrations. This calibration was accomplished through the use of a standard photodiode detector obtained from the National Bureau of Standards together with onsite measurements of spectral properties of optical components used. The stability of the light source for use in the calibration of vacuum ultraviolet spectrographs and optical systems was investigated and found to be amenable to laboratory applications. The lamp was studied for a range of operating parameters; the results indicate that with appropriate peripheral instrumentation, the light source can be used as a secondary laboratory standard source when operated under preset controlled conditions. Absolute intensity measurements were recorded for the wavelengths 127.7, 158.0, 177.5, and 195.0 nm for a time period of over 1 month, and the measurements were found to be repeatable to within 11 percent.

How Do Various Maize Crop Models Vary in Their Responses to Climate Change Factors?

NASA Technical Reports Server (NTRS)

Bassu, Simona; Brisson, Nadine; Grassini, Patricio; Durand, Jean-Louis; Boote, Kenneth; Lizaso, Jon; Jones, James W.; Rosenzweig, Cynthia; Ruane, Alex C.; Adam, Myriam;

How do various maize crop models vary in their responses to climate change factors?

PubMed

Bassu, Simona; Brisson, Nadine; Durand, Jean-Louis; Boote, Kenneth; Lizaso, Jon; Jones, James W; Rosenzweig, Cynthia; Ruane, Alex C; Adam, Myriam; Baron, Christian; Basso, Bruno; Biernath, Christian; Boogaard, Hendrik; Conijn, Sjaak; Corbeels, Marc; Deryng, Delphine; De Sanctis, Giacomo; Gayler, Sebastian; Grassini, Patricio; Hatfield, Jerry; Hoek, Steven; Izaurralde, Cesar; Jongschaap, Raymond; Kemanian, Armen R; Kersebaum, K Christian; Kim, Soo-Hyung; Kumar, Naresh S; Makowski, David; Müller, Christoph; Nendel, Claas; Priesack, Eckart; Pravia, Maria Virginia; Sau, Federico; Shcherbak, Iurii; Tao, Fulu; Teixeira, Edmar; Timlin, Dennis; Waha, Katharina

2014-07-01

Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models diverge on grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth, and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [CO2 ], we present the largest maize crop model intercomparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania). While individual models differed considerably in absolute yield simulation at the four sites, an ensemble of a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. Temperature increase had strong negative influence on modeled yield response of roughly -0.5 Mg ha(-1) per °C. Doubling [CO2 ] from 360 to 720 μmol mol(-1) increased grain yield by 7.5% on average across models and the sites. That would therefore make temperature the main factor altering maize yields at the end of this century. Furthermore, there was a large uncertainty in the yield response to [CO2 ] among models. Model responses to temperature and [CO2 ] did not differ whether models were simulated with low calibration information or, simulated with high level of calibration information. © 2014 John Wiley & Sons Ltd.

Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping

NASA Astrophysics Data System (ADS)

White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota, A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales, A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki, W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.; Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.; Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann, G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.

2017-07-01

The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at λ = 3 mm and 5900 K at λ = 1.3 mm. These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of about 25'', the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range. Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool. Prominences above the solar limb are a common feature of the single-dish images.

A stoichiometric calibration method for dual energy computed tomography

NASA Astrophysics Data System (ADS)

Bourque, Alexandra E.; Carrier, Jean-François; Bouchard, Hugo

2014-04-01

The accuracy of radiotherapy dose calculation relies crucially on patient composition data. The computed tomography (CT) calibration methods based on the stoichiometric calibration of Schneider et al (1996 Phys. Med. Biol. 41 111-24) are the most reliable to determine electron density (ED) with commercial single energy CT scanners. Along with the recent developments in dual energy CT (DECT) commercial scanners, several methods were published to determine ED and the effective atomic number (EAN) for polyenergetic beams without the need for CT calibration curves. This paper intends to show that with a rigorous definition of the EAN, the stoichiometric calibration method can be successfully adapted to DECT with significant accuracy improvements with respect to the literature without the need for spectrum measurements or empirical beam hardening corrections. Using a theoretical framework of ICRP human tissue compositions and the XCOM photon cross sections database, the revised stoichiometric calibration method yields Hounsfield unit (HU) predictions within less than ±1.3 HU of the theoretical HU calculated from XCOM data averaged over the spectra used (e.g., 80 kVp, 100 kVp, 140 kVp and 140/Sn kVp). A fit of mean excitation energy (I-value) data as a function of EAN is provided in order to determine the ion stopping power of human tissues from ED-EAN measurements. Analysis of the calibration phantom measurements with the Siemens SOMATOM Definition Flash dual source CT scanner shows that the present formalism yields mean absolute errors of (0.3 ± 0.4)% and (1.6 ± 2.0)% on ED and EAN, respectively. For ion therapy, the mean absolute errors for calibrated I-values and proton stopping powers (216 MeV) are (4.1 ± 2.7)% and (0.5 ± 0.4)%, respectively. In all clinical situations studied, the uncertainties in ion ranges in water for therapeutic energies are found to be less than 1.3 mm, 0.7 mm and 0.5 mm for protons, helium and carbon ions respectively, using a generic reconstruction algorithm (filtered back projection). With a more advanced method (sinogram affirmed iterative technique), the values become 1.0 mm, 0.5 mm and 0.4 mm for protons, helium and carbon ions, respectively. These results allow one to conclude that the present adaptation of the stoichiometric calibration yields a highly accurate method for characterizing tissue with DECT for ion beam therapy and potentially for photon beam therapy.

Visible Infrared Imaging Radiometer Suite (VIIRS) and uncertainty in the ocean color calibration methodology

NASA Astrophysics Data System (ADS)

Turpie, Kevin R.; Eplee, Robert E.; Meister, Gerhard

2015-09-01

During the first few years of the Suomi National Polar-orbiting Partnership (NPP) mission, the NASA Ocean Color calibration team continued to improve on their approach to the on-orbit calibration of the Visible Infrared Imaging Radiometer Suite (VIIRS). As the calibration was adjusted for changes in ocean band responsitivity, the team also estimated a theoretic residual error in the calibration trends well within a few tenths of a percent, which could be translated into trend uncertainties in regional time series of surface reflectance and derived products, where biases as low as a few tenths of a percent in certain bands can lead to significant effects. This study looks at effects from spurious trends inherent to the calibration and biases that arise between reprocessing efforts because of extrapolation of the timedependent calibration table. With the addition of new models for instrument and calibration system trend artifacts, new calibration trends led to improved estimates of ocean time series uncertainty. Table extrapolation biases are presented for the first time. The results further the understanding of uncertainty in measuring regional and global biospheric trends in the ocean using VIIRS, which better define the roles of such records in climate research.

A distance-independent calibration of the luminosity of type Ia supernovae and the Hubble constant

NASA Technical Reports Server (NTRS)

Leibundgut, Bruno; Pinto, Philip A.

1992-01-01

The absolute magnitude of SNe Ia at maximum is calibrated here using radioactive decay models for the light curve and a minimum of assumptions. The absolute magnitude parameter space is studied using explosion models and a range of rise times, and absolute B magnitudes at maximum are used to derive a range of the H0 and the distance to the Virgo Cluster from SNe Ia. Rigorous limits for H0 of 45 and 105 km/s/Mpc are derived.

Imager for Mars Pathfinder (IMP) image calibration

USGS Publications Warehouse

Reid, R.J.; Smith, P.H.; Lemmon, M.; Tanner, R.; Burkland, M.; Wegryn, E.; Weinberg, J.; Marcialis, R.; Britt, D.T.; Thomas, N.; Kramm, R.; Dummel, A.; Crowe, D.; Bos, B.J.; Bell, J.F.; Rueffer, P.; Gliem, F.; Johnson, J. R.; Maki, J.N.; Herkenhoff, K. E.; Singer, Robert B.

1999-01-01

The Imager for Mars Pathfinder returned over 16,000 high-quality images from the surface of Mars. The camera was well-calibrated in the laboratory, with <5% radiometric uncertainty. The photometric properties of two radiometric targets were also measured with 3% uncertainty. Several data sets acquired during the cruise and on Mars confirm that the system operated nominally throughout the course of the mission. Image calibration algorithms were developed for landed operations to correct instrumental sources of noise and to calibrate images relative to observations of the radiometric targets. The uncertainties associated with these algorithms as well as current improvements to image calibration are discussed. Copyright 1999 by the American Geophysical Union.

Monte-Carlo-based uncertainty propagation with hierarchical models—a case study in dynamic torque

NASA Astrophysics Data System (ADS)

Klaus, Leonard; Eichstädt, Sascha

2018-04-01

For a dynamic calibration, a torque transducer is described by a mechanical model, and the corresponding model parameters are to be identified from measurement data. A measuring device for the primary calibration of dynamic torque, and a corresponding model-based calibration approach, have recently been developed at PTB. The complete mechanical model of the calibration set-up is very complex, and involves several calibration steps—making a straightforward implementation of a Monte Carlo uncertainty evaluation tedious. With this in mind, we here propose to separate the complete model into sub-models, with each sub-model being treated with individual experiments and analysis. The uncertainty evaluation for the overall model then has to combine the information from the sub-models in line with Supplement 2 of the Guide to the Expression of Uncertainty in Measurement. In this contribution, we demonstrate how to carry this out using the Monte Carlo method. The uncertainty evaluation involves various input quantities of different origin and the solution of a numerical optimisation problem.

A variable acceleration calibration system

NASA Astrophysics Data System (ADS)

Johnson, Thomas H.

2011-12-01

A variable acceleration calibration system that applies loads using gravitational and centripetal acceleration serves as an alternative, efficient and cost effective method for calibrating internal wind tunnel force balances. Two proof-of-concept variable acceleration calibration systems are designed, fabricated and tested. The NASA UT-36 force balance served as the test balance for the calibration experiments. The variable acceleration calibration systems are shown to be capable of performing three component calibration experiments with an approximate applied load error on the order of 1% of the full scale calibration loads. Sources of error are indentified using experimental design methods and a propagation of uncertainty analysis. Three types of uncertainty are indentified for the systems and are attributed to prediction error, calibration error and pure error. Angular velocity uncertainty is shown to be the largest indentified source of prediction error. The calibration uncertainties using a production variable acceleration based system are shown to be potentially equivalent to current methods. The production quality system can be realized using lighter materials and a more precise instrumentation. Further research is needed to account for balance deflection, forcing effects due to vibration, and large tare loads. A gyroscope measurement technique is shown to be capable of resolving the balance deflection angle calculation. Long term research objectives include a demonstration of a six degree of freedom calibration, and a large capacity balance calibration.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patankar, S.; Gumbrell, E. T.; Robinson, T. S.

Here we report a new method using high stability, laser-driven supercontinuum generation in a liquid cell to calibrate the absolute photon response of fast optical streak cameras as a function of wavelength when operating at fastest sweep speeds. A stable, pulsed white light source based around the use of self-phase modulation in a salt solution was developed to provide the required brightness on picosecond timescales, enabling streak camera calibration in fully dynamic operation. The measured spectral brightness allowed for absolute photon response calibration over a broad spectral range (425-650nm). Calibrations performed with two Axis Photonique streak cameras using the Photonismore » P820PSU streak tube demonstrated responses which qualitatively follow the photocathode response. Peak sensitivities were 1 photon/count above background. The absolute dynamic sensitivity is less than the static by up to an order of magnitude. We attribute this to the dynamic response of the phosphor being lower.« less

On the Photometric Calibration of FORS2 and the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Bramich, D.; Moehler, S.; Coccato, L.; Freudling, W.; Garcia-Dabó, C. E.; Müller, P.; Saviane, I.

2012-09-01

An accurate absolute calibration of photometric data to place them on a standard magnitude scale is very important for many science goals. Absolute calibration requires the observation of photometric standard stars and analysis of the observations with an appropriate photometric model including all relevant effects. In the FORS Absolute Photometry (FAP) project, we have developed a standard star observing strategy and modelling procedure that enables calibration of science target photometry to better than 3% accuracy on photometrically stable nights given sufficient signal-to-noise. In the application of this photometric modelling to large photometric databases, we have investigated the Sloan Digital Sky Survey (SDSS) and found systematic trends in the published photometric data. The amplitudes of these trends are similar to the reported typical precision (˜1% and ˜2%) of the SDSS photometry in the griz- and u-bands, respectively.

Improved absolute calibration of LOPES measurements and its impact on the comparison with REAS 3.11 and CoREAS simulations

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hiller, R.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Nehls, S.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schoo, S.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2016-02-01

LOPES was a digital antenna array detecting the radio emission of cosmic-ray air showers. The calibration of the absolute amplitude scale of the measurements was done using an external, commercial reference source, which emits a frequency comb with defined amplitudes. Recently, we obtained improved reference values by the manufacturer of the reference source, which significantly changed the absolute calibration of LOPES. We reanalyzed previously published LOPES measurements, studying the impact of the changed calibration. The main effect is an overall decrease of the LOPES amplitude scale by a factor of 2.6 ± 0.2, affecting all previously published values for measurements of the electric-field strength. This results in a major change in the conclusion of the paper 'Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations' published by Apel et al. (2013) : With the revised calibration, LOPES measurements now are compatible with CoREAS simulations, but in tension with REAS 3.11 simulations. Since CoREAS is the latest version of the simulation code incorporating the current state of knowledge on the radio emission of air showers, this new result indicates that the absolute amplitude prediction of current simulations now is in agreement with experimental data.

CALIBRATION, OPTIMIZATION, AND SENSITIVITY AND UNCERTAINTY ALGORITHMS APPLICATION PROGRAMMING INTERFACE (COSU-API)

EPA Science Inventory

The Application Programming Interface (API) for Uncertainty Analysis, Sensitivity Analysis, and Parameter Estimation (UA/SA/PE API) tool development, here fore referred to as the Calibration, Optimization, and Sensitivity and Uncertainty Algorithms API (COSU-API), was initially d...

First-principles calibration of 40Ar/39Ar mineral standards and complete extraction of 40Ar* from sanidine

NASA Astrophysics Data System (ADS)

Morgan, L. E.; Kuiper, K.; Mark, D.; Postma, O.; Villa, I. M.; Wijbrans, J. R.

2010-12-01

40Ar/39Ar geochronology relies on comparing argon isotopic data for unknowns to those for knowns. Mineral standards used as neutron fluence monitors must be dated by the K-Ar method (or at least referenced to a mineral of known K-Ar age). The commonly used age of 28.02 ± 0.28 Ma for the Fish Canyon sanidine (FCs) (Renne et al., 1998) is based upon measurements of radiogenic 40Ar in GA1550 biotite (McDougall and Roksandic, 1974), but underlying full data were not published (these measurements were never intended for use as an international standard), so uncertainties are difficult to assess. Recent developments by Kuiper et al. (2008) and Renne et al. (2010) are limited by their reliance on the accuracy of other systems. Modern technology should allow for more precise and accurate calibration of primary K-Ar and 40Ar/39Ar standards. From the ideal gas law, the number of moles of 40Ar in a system can be calculated from measurements of pressure, volume, and temperature. Thus we have designed and are proceeding to build a pipette system to introduce well-determined amounts of 40Ar into noble gas extraction lines and mass spectrometers. This system relies on components with calibrations traceable to SI unit prototypes, including a diaphragm pressure gauge (MKS Instruments), thermocouples, and a “slug” of an accurately determined volume to be inserted into the reservoir for volume determinations of the reservoir and pipette. The system will be renewable, with a lifetime of ca. 1 month for gas in the reservoir, and portable, to permit interlaboratory calibrations. The quantitative extraction of 40Ar* from the mineral standard is of highest importance; for sanidine standards this is complicated by high melt viscosity during heating. Experiments adding basaltic “zero age glass” (ZAG) to decrease melt viscosity are underway. This has previously been explored by McDowell (1983) with a resistance furnace, but has not been quantitatively addressed with laser heating. The sensitivity of each participating mass spectrometer will be calibrated by the bracketing standards approach, alternating measurements of pipette gas and mineral standards. This will convert relative abundances into absolute molar quantities and allow for quantification of interlaboratory systematic bias. Uncertainty propagation indicates uncertainties of the molar quantity of 40Ar in mineral standards will be < 0.25% (2σ), a considerable improvement of one component of the uncertainties involved in 40Ar/39Ar geochronology. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° [215458].

Exploring the Chemical Link Between Local Ellipticals and Their High-Redshift Progenitors

NASA Technical Reports Server (NTRS)

Leja, Joel; Van Dokkum, Pieter G.; Momcheva, Ivelina; Brammer, Gabriel; Skelton, Rosalind E.; Whitaker, Katherine E.; Andrews, Brett H.; Franx, Marijn; Kriek, Mariska; Van Der Wel, Arjen;

Importance of Calibration/Validation Traceability for Multi-Sensor Imaging Spectrometry Applications

NASA Technical Reports Server (NTRS)

Thome, K.

2017-01-01

Knowledge of calibration traceability is essential for ensuring the quality of data products relying on multiple sensors and especially true for imaging spectrometers. The current work discusses the expected impact that imaging spectrometers have in ensuring radiometric traceability for both multispectral and hyperspectral products. The Climate Absolute Radiance and Refractivity Observatory Pathfinder mission is used to show the role that high-accuracy imaging spectrometers can play in understanding test sites used for vicarious calibration of sensors. The associated Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer calibration demonstration system is used to illustrate recent advances in laboratory radiometric calibration approaches that will allow both the use of imaging spectrometers as calibration standards as well as to ensure the consistency of the multiple imaging spectrometers expected to be on orbit in the next decade.

Calibrating the stress-time curve of a combined finite-discrete element method to a Split Hopkinson Pressure Bar experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osthus, Dave; Godinez, Humberto C.; Rougier, Esteban

We presenmore » t a generic method for automatically calibrating a computer code to an experiment, with uncertainty, for a given “training” set of computer code runs. The calibration technique is general and probabilistic, meaning the calibration uncertainty is represented in the form of a probability distribution. We demonstrate the calibration method by calibrating a combined Finite-Discrete Element Method (FDEM) to a Split Hopkinson Pressure Bar (SHPB) experiment with a granite sample. The probabilistic calibration method combines runs of a FDEM computer simulation for a range of “training” settings and experimental uncertainty to develop a statistical emulator. The process allows for calibration of input parameters and produces output quantities with uncertainty estimates for settings where simulation results are desired. Input calibration and FDEM fitted results are presented. We find that the maximum shear strength σ t max and to a lesser extent maximum tensile strength σ n max govern the behavior of the stress-time curve before and around the peak, while the specific energy in Mode II (shear) E t largely governs the post-peak behavior of the stress-time curve. Good agreement is found between the calibrated FDEM and the SHPB experiment. Interestingly, we find the SHPB experiment to be rather uninformative for calibrating the softening-curve shape parameters (a, b, and c). This work stands as a successful demonstration of how a general probabilistic calibration framework can automatically calibrate FDEM parameters to an experiment.« less

Calibrating the stress-time curve of a combined finite-discrete element method to a Split Hopkinson Pressure Bar experiment

DOE PAGES

Osthus, Dave; Godinez, Humberto C.; Rougier, Esteban; ...

2018-05-01

We presenmore » t a generic method for automatically calibrating a computer code to an experiment, with uncertainty, for a given “training” set of computer code runs. The calibration technique is general and probabilistic, meaning the calibration uncertainty is represented in the form of a probability distribution. We demonstrate the calibration method by calibrating a combined Finite-Discrete Element Method (FDEM) to a Split Hopkinson Pressure Bar (SHPB) experiment with a granite sample. The probabilistic calibration method combines runs of a FDEM computer simulation for a range of “training” settings and experimental uncertainty to develop a statistical emulator. The process allows for calibration of input parameters and produces output quantities with uncertainty estimates for settings where simulation results are desired. Input calibration and FDEM fitted results are presented. We find that the maximum shear strength σ t max and to a lesser extent maximum tensile strength σ n max govern the behavior of the stress-time curve before and around the peak, while the specific energy in Mode II (shear) E t largely governs the post-peak behavior of the stress-time curve. Good agreement is found between the calibrated FDEM and the SHPB experiment. Interestingly, we find the SHPB experiment to be rather uninformative for calibrating the softening-curve shape parameters (a, b, and c). This work stands as a successful demonstration of how a general probabilistic calibration framework can automatically calibrate FDEM parameters to an experiment.« less

Using inductively coupled plasma-mass spectrometry for calibration transfer between environmental CRMs.

PubMed

Turk, G C; Yu, L L; Salit, M L; Guthrie, W F

2001-06-01

Multielement analyses of environmental reference materials have been performed using existing certified reference materials (CRMs) as calibration standards for inductively coupled plasma-mass spectrometry. The analyses have been performed using a high-performance methodology that results in comparison measurement uncertainties that are significantly less than the uncertainties of the certified values of the calibration CRM. Consequently, the determined values have uncertainties that are very nearly equivalent to the uncertainties of the calibration CRM. Several uses of this calibration transfer are proposed, including, re-certification measurements of replacement CRMs, establishing traceability of one CRM to another, and demonstrating the equivalence of two CRMs. RM 8704, a river sediment, was analyzed using SRM 2704, Buffalo River Sediment, as the calibration standard. SRM 1632c, Trace Elements in Bituminous Coal, which is a replacement for SRM 1632b, was analyzed using SRM 1632b as the standard. SRM 1635, Trace Elements in Subbituminous Coal, was also analyzed using SRM 1632b as the standard.

Comparison of Two Methodologies for Calibrating Satellite Instruments in the Visible and Near Infrared

NASA Technical Reports Server (NTRS)

Barnes, Robert A.; Brown, Steven W.; Lykke, Keith R.; Guenther, Bruce; Xiong, Xiaoxiong (Jack); Butler, James J.

2010-01-01

Traditionally, satellite instruments that measure Earth-reflected solar radiation in the visible and near infrared wavelength regions have been calibrated for radiance response in a two-step method. In the first step, the spectral response of the instrument is determined using a nearly monochromatic light source, such a lamp-illuminated monochromator. Such sources only provide a relative spectral response (RSR) for the instrument, since they do not act as calibrated sources of light nor do they typically fill the field-of-view of the instrument. In the second step, the instrument views a calibrated source of broadband light, such as lamp-illuminated integrating sphere. In the traditional method, the RSR and the sphere spectral radiance are combined and, with the instrument's response, determine the absolute spectral radiance responsivity of the instrument. More recently, an absolute calibration system using widely tunable monochromatic laser systems has been developed, Using these sources, the absolute spectral responsivity (ASR) of an instrument can be determined on a wavelength-hy-wavelength basis. From these monochromatic ASRs. the responses of the instrument bands to broadband radiance sources can be calculated directly, eliminating the need for calibrated broadband light sources such as integrating spheres. Here we describe the laser-based calibration and the traditional broad-band source-based calibration of the NPP VIIRS sensor, and compare the derived calibration coefficients for the instrument. Finally, we evaluate the impact of the new calibration approach on the on-orbit performance of the sensor.

A new algorithm for five-hole probe calibration, data reduction, and uncertainty analysis

NASA Technical Reports Server (NTRS)

Reichert, Bruce A.; Wendt, Bruce J.

1994-01-01

A new algorithm for five-hole probe calibration and data reduction using a non-nulling method is developed. The significant features of the algorithm are: (1) two components of the unit vector in the flow direction replace pitch and yaw angles as flow direction variables; and (2) symmetry rules are developed that greatly simplify Taylor's series representations of the calibration data. In data reduction, four pressure coefficients allow total pressure, static pressure, and flow direction to be calculated directly. The new algorithm's simplicity permits an analytical treatment of the propagation of uncertainty in five-hole probe measurement. The objectives of the uncertainty analysis are to quantify uncertainty of five-hole results (e.g., total pressure, static pressure, and flow direction) and determine the dependence of the result uncertainty on the uncertainty of all underlying experimental and calibration measurands. This study outlines a general procedure that other researchers may use to determine five-hole probe result uncertainty and provides guidance to improve measurement technique. The new algorithm is applied to calibrate and reduce data from a rake of five-hole probes. Here, ten individual probes are mounted on a single probe shaft and used simultaneously. Use of this probe is made practical by the simplicity afforded by this algorithm.

Quantum correlations from a room-temperature optomechanical cavity

NASA Astrophysics Data System (ADS)

Purdy, T. P.; Grutter, K. E.; Srinivasan, K.; Taylor, J. M.

2017-06-01

The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam’s thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks.

Autonomous sensor particle for parameter tracking in large vessels

NASA Astrophysics Data System (ADS)

Thiele, Sebastian; Da Silva, Marco Jose; Hampel, Uwe

2010-08-01

A self-powered and neutrally buoyant sensor particle has been developed for the long-term measurement of spatially distributed process parameters in the chemically harsh environments of large vessels. One intended application is the measurement of flow parameters in stirred fermentation biogas reactors. The prototype sensor particle is a robust and neutrally buoyant capsule, which allows free movement with the flow. It contains measurement devices that log the temperature, absolute pressure (immersion depth) and 3D-acceleration data. A careful calibration including an uncertainty analysis has been performed. Furthermore, autonomous operation of the developed prototype was successfully proven in a flow experiment in a stirred reactor model. It showed that the sensor particle is feasible for future application in fermentation reactors and other industrial processes.

Rocket calibration of the Nimbus 6 solar constant measurements.

PubMed

Duncan, C H; Harrison, R G; Hickey, J R; Kendall, J M; Thekaekara, M P; Willson, R C

1977-10-01

Total solar irradiance was observed simultaneously outside the earth's atmosphere by three types of absolute cavity radiometers and duplicates of four of the Nimbus 6 Earth Radiation Budget (ERB) solar channels in a June 1976 Sounding Rocket Experiment. The preliminary average solar constant result from the cavity radiometers is 1367 W m(-2) with an uncertainty of less than +/-0.5% in SI units. The duplicate ERB channel 3 on the rocket gave a value of 1389 W mm(-2) which agreed exactly with the Nimbus 6 ERB channel 3 measurement made simultaneously with the rocket flight. Therefore, Nimbus 6 ERB solar constant values should be reduced approximately 1.6% in order to convert the values to SI units.

Characterization and Uncertainty Analysis of a Reference Pressure Measurement System for Wind Tunnels

NASA Technical Reports Server (NTRS)

Amer, Tahani; Tripp, John; Tcheng, Ping; Burkett, Cecil; Sealey, Bradley

2004-01-01

This paper presents the calibration results and uncertainty analysis of a high-precision reference pressure measurement system currently used in wind tunnels at the NASA Langley Research Center (LaRC). Sensors, calibration standards, and measurement instruments are subject to errors due to aging, drift with time, environment effects, transportation, the mathematical model, the calibration experimental design, and other factors. Errors occur at every link in the chain of measurements and data reduction from the sensor to the final computed results. At each link of the chain, bias and precision uncertainties must be separately estimated for facility use, and are combined to produce overall calibration and prediction confidence intervals for the instrument, typically at a 95% confidence level. The uncertainty analysis and calibration experimental designs used herein, based on techniques developed at LaRC, employ replicated experimental designs for efficiency, separate estimation of bias and precision uncertainties, and detection of significant parameter drift with time. Final results, including calibration confidence intervals and prediction intervals given as functions of the applied inputs, not as a fixed percentage of the full-scale value are presented. System uncertainties are propagated beginning with the initial reference pressure standard, to the calibrated instrument as a working standard in the facility. Among the several parameters that can affect the overall results are operating temperature, atmospheric pressure, humidity, and facility vibration. Effects of factors such as initial zeroing and temperature are investigated. The effects of the identified parameters on system performance and accuracy are discussed.

Time scale controversy: Accurate orbital calibration of the early Paleogene

NASA Astrophysics Data System (ADS)

Roehl, U.; Westerhold, T.; Laskar, J.

2012-12-01

Timing is crucial to understanding the causes and consequences of events in Earth history. The calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating. Uncertainties in the computations of Earth's orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 Ma. Attempts to construct a robust astronomically tuned time scale for the early Paleogene by integrating radioisotopic and astronomical dating are only partially consistent. Here, using the new La2010 and La2011 orbital solutions, we present the first accurate astronomically calibrated time scale for the early Paleogene (47-65 Ma) uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the Fish Canyon standard. Comparison with geological data confirms the stability of the new La2011 solution back to 54 Ma. Subsequent anchoring of floating chronologies to the La2011 solution using the very long eccentricity nodes provides an absolute age of 55.530 ± 0.05 Ma for the onset of the Paleocene/Eocene Thermal Maximum (PETM), 54.850 ± 0.05 Ma for the early Eocene ash -17, and 65.250 ± 0.06 Ma for the K/Pg boundary. The new astrochronology presented here indicates that the intercalibration and synchronization of U/Pb and 40Ar/39Ar radioisotopic geochronology is much more challenging than previously thought.

Time scale controversy: Accurate orbital calibration of the early Paleogene

NASA Astrophysics Data System (ADS)

Westerhold, Thomas; RöHl, Ursula; Laskar, Jacques

2012-06-01

Timing is crucial to understanding the causes and consequences of events in Earth history. The calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating. Uncertainties in the computations of Earth's orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 Ma. Attempts to construct a robust astronomically tuned time scale for the early Paleogene by integrating radioisotopic and astronomical dating are only partially consistent. Here, using the new La2010 and La2011 orbital solutions, we present the first accurate astronomically calibrated time scale for the early Paleogene (47-65 Ma) uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the Fish Canyon standard. Comparison with geological data confirms the stability of the new La2011 solution back to ˜54 Ma. Subsequent anchoring of floating chronologies to the La2011 solution using the very long eccentricity nodes provides an absolute age of 55.530 ± 0.05 Ma for the onset of the Paleocene/Eocene Thermal Maximum (PETM), 54.850 ± 0.05 Ma for the early Eocene ash -17, and 65.250 ± 0.06 Ma for the K/Pg boundary. The new astrochronology presented here indicates that the intercalibration and synchronization of U/Pb and 40Ar/39Ar radioisotopic geochronology is much more challenging than previously thought.

Signal inference with unknown response: calibration-uncertainty renormalized estimator.

PubMed

Dorn, Sebastian; Enßlin, Torsten A; Greiner, Maksim; Selig, Marco; Boehm, Vanessa

2015-01-01

The calibration of a measurement device is crucial for every scientific experiment, where a signal has to be inferred from data. We present CURE, the calibration-uncertainty renormalized estimator, to reconstruct a signal and simultaneously the instrument's calibration from the same data without knowing the exact calibration, but its covariance structure. The idea of the CURE method, developed in the framework of information field theory, is to start with an assumed calibration to successively include more and more portions of calibration uncertainty into the signal inference equations and to absorb the resulting corrections into renormalized signal (and calibration) solutions. Thereby, the signal inference and calibration problem turns into a problem of solving a single system of ordinary differential equations and can be identified with common resummation techniques used in field theories. We verify the CURE method by applying it to a simplistic toy example and compare it against existent self-calibration schemes, Wiener filter solutions, and Markov chain Monte Carlo sampling. We conclude that the method is able to keep up in accuracy with the best self-calibration methods and serves as a noniterative alternative to them.

Assessment of spectral, misregistration, and spatial uncertainties inherent in the cross-calibration study

USGS Publications Warehouse

Chander, G.; Helder, D.L.; Aaron, David; Mishra, N.; Shrestha, A.K.

2013-01-01

Cross-calibration of satellite sensors permits the quantitative comparison of measurements obtained from different Earth Observing (EO) systems. Cross-calibration studies usually use simultaneous or near-simultaneous observations from several spaceborne sensors to develop band-by-band relationships through regression analysis. The investigation described in this paper focuses on evaluation of the uncertainties inherent in the cross-calibration process, including contributions due to different spectral responses, spectral resolution, spectral filter shift, geometric misregistrations, and spatial resolutions. The hyperspectral data from the Environmental Satellite SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY and the EO-1 Hyperion, along with the relative spectral responses (RSRs) from the Landsat 7 Enhanced Thematic Mapper (TM) Plus and the Terra Moderate Resolution Imaging Spectroradiometer sensors, were used for the spectral uncertainty study. The data from Landsat 5 TM over five representative land cover types (desert, rangeland, grassland, deciduous forest, and coniferous forest) were used for the geometric misregistrations and spatial-resolution study. The spectral resolution uncertainty was found to be within 0.25%, spectral filter shift within 2.5%, geometric misregistrations within 0.35%, and spatial-resolution effects within 0.1% for the Libya 4 site. The one-sigma uncertainties presented in this paper are uncorrelated, and therefore, the uncertainties can be summed orthogonally. Furthermore, an overall total uncertainty was developed. In general, the results suggested that the spectral uncertainty is more dominant compared to other uncertainties presented in this paper. Therefore, the effect of the sensor RSR differences needs to be quantified and compensated to avoid large uncertainties in cross-calibration results.

Rapid, absolute calibration of x-ray filters employed by laser-produced plasma diagnostics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, G. V.; Beiersdorfer, P.; Emig, J.

2008-10-15

The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are detected using the high resolution EBIT Calorimeter Spectrometer (ECS), developed for LLNL at the NASA/Goddard Space Flight Center. X-ray filter transmission efficiency is determined by dividing the x-ray counts detected when the filter is in the line of sight by those detected when out of the line of sight. Verification ofmore » filter thickness can be completed in only a few hours, and absolute efficiencies can be calibrated in a single day over a broad range from about 0.1 to 15 keV. The EBIT calibration lab has been used to field diagnostics (e.g., the OZSPEC instrument) with fully calibrated x-ray filters at the OMEGA laser. Extensions to use the capability for calibrating filter transmission for the DANTE instrument on the National Ignition Facility are discussed.« less

Limits to lichenometry

NASA Astrophysics Data System (ADS)

Rosenwinkel, Swenja; Korup, Oliver; Landgraf, Angela; Dzhumabaeva, Atyrgul

2015-12-01

Lichenometry is a straightforward and inexpensive method for dating Holocene rock surfaces. The rationale is that the diameter of the largest lichen scales with the age of the originally fresh rock surface that it colonised. The success of the method depends on finding the largest lichen diameters, a suitable lichen-growth model, and a robust calibration curve. Recent critique of the method motivates us to revisit the accuracy and uncertainties of lichenometry. Specifically, we test how well lichenometry is capable of resolving the ages of different lobes of large active rock glaciers in the Kyrgyz Tien Shan. We use a bootstrapped quantile regression to calibrate local growth curves of Xanthoria elegans, Aspicilia tianshanica, and Rhizocarpon geographicum, and report a nonlinear decrease in dating accuracy with increasing lichen diameter. A Bayesian type of an analysis of variance demonstrates that our calibration allows discriminating credibly between rock-glacier lobes of different ages despite the uncertainties tied to sample size and correctly identifying the largest lichen thalli. Our results also show that calibration error grows with lichen size, so that the separability of rock-glacier lobes of different ages decreases, while the tendency to assign coeval ages increases. The abundant young (<200 yr) specimen of fast-growing X. elegans are in contrast with the fewer, slow-growing, but older (200-1500 yr) R. geographicum and A. tianshanica, and record either a regional reactivation of lobes in the past 200 years, or simply a censoring effect of lichen mortality during early phases of colonisation. The high variance of lichen sizes captures the activity of rock-glacier lobes, which is difficult to explain by regional climatic cooling or earthquake triggers alone. Therefore, we caution against inferring palaeoclimatic conditions from the topographic position of rock-glacier lobes. We conclude that lichenometry works better as a tool for establishing a relative, rather than an absolute, chronology of rock-glacier lobes in the northern Tien Shan.

Computational modeling of colorimetric primary transducer for metrological assurance in additive manufacturing

NASA Astrophysics Data System (ADS)

Skliarov, Volodymyr

2018-03-01

Many additive manufacturing (AM) systems are based on laser technology. The advantage of laser technology is that it provides a high-intensity and high-collimation energy beam that can be controlled. Since AM requires that the material on each layer has to be solid or connected to the previous one, the energy of laser radiation is exactly the needed technical tool for the processing of the material. AM uses two types of laser processing: cutting and heating. One of the most popular (common) types of measurements in the field of laser metrology is the control of the energy parameters of the sources of laser radiation. At present, calorimeters provide the highest accuracy of absolute measurements of laser radiation in the power range from several watts to tens of kilowatts. The main elements that determine the accuracy of reproduction, maintenance and transfer of the unit of laser power are the primary measuring converters (PMCs), which are the part of the equipment of the national primary measurement standards of Ukraine. A significant contribution to the uncertainty budget of the primary measuring calorimetric converter is the unbalanced replacement of laser radiation by the heat flux that calibrates this converter. The heterogeneous internal structure of the calorimetric primary converter, the nonlinearity of processes occurring in it, and the multifactorial process of its calibration substantially complicate the development of primary measuring converters. The purpose of this paper is to simulate the thermal field of the primary converter for maximum reduction of the uncertainty of calibration. The presented research is a part of the scientific work that NSC "Institute of Metrology" carries out under COOMET and EMPIRE projects. The modeling was performed in the academic version of ANSYS.

Calibration and energy measurement of optically levitated nanoparticle sensors

NASA Astrophysics Data System (ADS)

Hebestreit, Erik; Frimmer, Martin; Reimann, René; Dellago, Christoph; Ricci, Francesco; Novotny, Lukas

2018-03-01

Optically levitated nanoparticles offer enormous potential for precision sensing. However, as for any other metrology device, the absolute measurement performance of a levitated-particle sensor is limited by the accuracy of the calibration relating the measured signal to an absolute displacement of the particle. Here, we suggest and demonstrate calibration protocols for levitated-nanoparticle sensors. Our calibration procedures include the treatment of anharmonicities in the trapping potential, as well as a protocol using a harmonic driving force, which is applicable if the sensor is coupled to a heat bath of unknown temperature. Finally, using the calibration, we determine the center-of-mass temperature of an optically levitated particle in thermal equilibrium from its motion and discuss the optimal measurement time required to determine the said temperature.

Uncertainty of climate change impact on groundwater reserves - Application to a chalk aquifer

NASA Astrophysics Data System (ADS)

Goderniaux, Pascal; Brouyère, Serge; Wildemeersch, Samuel; Therrien, René; Dassargues, Alain

2015-09-01

Recent studies have evaluated the impact of climate change on groundwater resources for different geographical and climatic contexts. However, most studies have either not estimated the uncertainty around projected impacts or have limited the analysis to the uncertainty related to climate models. In this study, the uncertainties around impact projections from several sources (climate models, natural variability of the weather, hydrological model calibration) are calculated and compared for the Geer catchment (465 km2) in Belgium. We use a surface-subsurface integrated model implemented using the finite element code HydroGeoSphere, coupled with climate change scenarios (2010-2085) and the UCODE_2005 inverse model, to assess the uncertainty related to the calibration of the hydrological model. This integrated model provides a more realistic representation of the water exchanges between surface and subsurface domains and constrains more the calibration with the use of both surface and subsurface observed data. Sensitivity and uncertainty analyses were performed on predictions. The linear uncertainty analysis is approximate for this nonlinear system, but it provides some measure of uncertainty for computationally demanding models. Results show that, for the Geer catchment, the most important uncertainty is related to calibration of the hydrological model. The total uncertainty associated with the prediction of groundwater levels remains large. By the end of the century, however, the uncertainty becomes smaller than the predicted decline in groundwater levels.

Sensitivity and Uncertainty Analysis for Streamflow Prediction Using Different Objective Functions and Optimization Algorithms: San Joaquin California

NASA Astrophysics Data System (ADS)

Paul, M.; Negahban-Azar, M.

2017-12-01

The hydrologic models usually need to be calibrated against observed streamflow at the outlet of a particular drainage area through a careful model calibration. However, a large number of parameters are required to fit in the model due to their unavailability of the field measurement. Therefore, it is difficult to calibrate the model for a large number of potential uncertain model parameters. This even becomes more challenging if the model is for a large watershed with multiple land uses and various geophysical characteristics. Sensitivity analysis (SA) can be used as a tool to identify most sensitive model parameters which affect the calibrated model performance. There are many different calibration and uncertainty analysis algorithms which can be performed with different objective functions. By incorporating sensitive parameters in streamflow simulation, effects of the suitable algorithm in improving model performance can be demonstrated by the Soil and Water Assessment Tool (SWAT) modeling. In this study, the SWAT was applied in the San Joaquin Watershed in California covering 19704 km2 to calibrate the daily streamflow. Recently, sever water stress escalating due to intensified climate variability, prolonged drought and depleting groundwater for agricultural irrigation in this watershed. Therefore it is important to perform a proper uncertainty analysis given the uncertainties inherent in hydrologic modeling to predict the spatial and temporal variation of the hydrologic process to evaluate the impacts of different hydrologic variables. The purpose of this study was to evaluate the sensitivity and uncertainty of the calibrated parameters for predicting streamflow. To evaluate the sensitivity of the calibrated parameters three different optimization algorithms (Sequential Uncertainty Fitting- SUFI-2, Generalized Likelihood Uncertainty Estimation- GLUE and Parameter Solution- ParaSol) were used with four different objective functions (coefficient of determination- r2, Nash-Sutcliffe efficiency- NSE, percent bias- PBIAS, and Kling-Gupta efficiency- KGE). The preliminary results showed that using the SUFI-2 algorithm with the objective function NSE and KGE has improved significantly the calibration (e.g. R2 and NSE is found 0.52 and 0.47 respectively for daily streamflow calibration).

Approaches to highly parameterized inversion: A guide to using PEST for model-parameter and predictive-uncertainty analysis

USGS Publications Warehouse

Doherty, John E.; Hunt, Randall J.; Tonkin, Matthew J.

2010-01-01

Analysis of the uncertainty associated with parameters used by a numerical model, and with predictions that depend on those parameters, is fundamental to the use of modeling in support of decisionmaking. Unfortunately, predictive uncertainty analysis with regard to models can be very computationally demanding, due in part to complex constraints on parameters that arise from expert knowledge of system properties on the one hand (knowledge constraints) and from the necessity for the model parameters to assume values that allow the model to reproduce historical system behavior on the other hand (calibration constraints). Enforcement of knowledge and calibration constraints on parameters used by a model does not eliminate the uncertainty in those parameters. In fact, in many cases, enforcement of calibration constraints simply reduces the uncertainties associated with a number of broad-scale combinations of model parameters that collectively describe spatially averaged system properties. The uncertainties associated with other combinations of parameters, especially those that pertain to small-scale parameter heterogeneity, may not be reduced through the calibration process. To the extent that a prediction depends on system-property detail, its postcalibration variability may be reduced very little, if at all, by applying calibration constraints; knowledge constraints remain the only limits on the variability of predictions that depend on such detail. Regrettably, in many common modeling applications, these constraints are weak. Though the PEST software suite was initially developed as a tool for model calibration, recent developments have focused on the evaluation of model-parameter and predictive uncertainty. As a complement to functionality that it provides for highly parameterized inversion (calibration) by means of formal mathematical regularization techniques, the PEST suite provides utilities for linear and nonlinear error-variance and uncertainty analysis in these highly parameterized modeling contexts. Availability of these utilities is particularly important because, in many cases, a significant proportion of the uncertainty associated with model parameters-and the predictions that depend on them-arises from differences between the complex properties of the real world and the simplified representation of those properties that is expressed by the calibrated model. This report is intended to guide intermediate to advanced modelers in the use of capabilities available with the PEST suite of programs for evaluating model predictive error and uncertainty. A brief theoretical background is presented on sources of parameter and predictive uncertainty and on the means for evaluating this uncertainty. Applications of PEST tools are then discussed for overdetermined and underdetermined problems, both linear and nonlinear. PEST tools for calculating contributions to model predictive uncertainty, as well as optimization of data acquisition for reducing parameter and predictive uncertainty, are presented. The appendixes list the relevant PEST variables, files, and utilities required for the analyses described in the document.

Landsat-5 TM reflective-band absolute radiometric calibration

USGS Publications Warehouse

Chander, G.; Helder, D.L.; Markham, B.L.; Dewald, J.D.; Kaita, E.; Thome, K.J.; Micijevic, E.; Ruggles, T.A.

2004-01-01

The Landsat-5 Thematic Mapper (TM) sensor provides the longest running continuous dataset of moderate spatial resolution remote sensing imagery, dating back to its launch in March 1984. Historically, the radiometric calibration procedure for this imagery used the instrument's response to the Internal Calibrator (IC) on a scene-by-scene basis to determine the gain and offset of each detector. Due to observed degradations in the IC, a new procedure was implemented for U.S.-processed data in May 2003. This new calibration procedure is based on a lifetime radiometric calibration model for the instrument's reflective bands (1-5 and 7) and is derived, in part, from the IC response without the related degradation effects and is tied to the cross calibration with the Landsat-7 Enhanced Thematic Mapper Plus. Reflective-band absolute radiometric accuracy of the instrument tends to be on the order of 7% to 10%, based on a variety of calibration methods.

An atlas of selected calibrated stellar spectra

NASA Technical Reports Server (NTRS)

Walker, Russell G.; Cohen, Martin

1992-01-01

Five hundred and fifty six stars in the IRAS PSC-2 that are suitable for stellar radiometric standards and are brighter than 1 Jy at 25 microns were identified. In addition, 123 stars that meet all of our criteria for calibration standards, but which lack a luminosity class were identified. An approach to absolute stellar calibration of broadband infrared filters based upon new models of Vega and Sirius due to Kurucz (1992) is presented. A general technique used to assemble continuous wide-band calibrated infrared spectra is described and an absolutely calibrated 1-35 micron spectrum of alpha(Tau) is constructed and the method using new and carefully designed observations is independently validated. The absolute calibration of the IRAS Low Resolution Spectrometer (LRS) database is investigated by comparing the observed spectrum of alpha(Tau) with that assumed in the original LRS calibration scheme. Neglect of the SiO fundamental band in alpha(Tau) has led to the presence of a specious 'emission' feature in all LRS spectra near 8.5 microns, and to an incorrect spectral slope between 8 and 12 microns. Finally, some of the properties of asteroids that effect their utility as calibration objects for the middle and far infrared region are examined. A technique to determine, from IRAS multiwaveband observations, the basic physical parameters needed by various asteroid thermal models that minimize the number of assumptions required is developed.

Status of use of lunar irradiance for on-orbit calibration

USGS Publications Warehouse

Stone, T.C.; Kieffer, H.H.; Anderson, J.M.; ,

2002-01-01

Routine observations of the Moon have been acquired by the Robotic Lunar Observatory (ROLO) for over four years. The ROLO instruments measure lunar radiance in 23 VNIR (Moon diameter ???500 pixels) and 9 SWIR (???250 pixels) passbands every month when the Moon is at phase angle less than 90 degrees. These are converted to exoatmospheric values at standard distances using an atmospheric extinction model based on observations of standard stars and a NIST-traceable absolute calibration source. Reduction of the stellar images also provides an independent pathway for absolute calibration. Comparison of stellar-based and lamp-based absolute calibrations of the lunar images currently shows unacceptably large differences. An analytic model of lunar irradiance as a function of phase angle and viewing geometry is derived from the calibrated lunar images. Residuals from models which fit hundreds of observations at each wavelength average less than 2%. Comparison with SeaWiFS observations over three years reveals a small quasi-periodic change in SeaWiFS responsivity that correlates with distance from the Sun for the first two years, then departs from this correlation.

Calculating Measurement Uncertainty of the “Conventional Value of the Result of Weighing in Air”

DOE PAGES

Flicker, Celia J.; Tran, Hy D.

2016-04-02

The conventional value of the result of weighing in air is frequently used in commercial calibrations of balances. The guidance in OIML D-028 for reporting uncertainty of the conventional value is too terse. When calibrating mass standards at low measurement uncertainties, it is necessary to perform a buoyancy correction before reporting the result. When calculating the conventional result after calibrating true mass, the uncertainty due to calculating the conventional result is correlated with the buoyancy correction. We show through Monte Carlo simulations that the measurement uncertainty of the conventional result is less than the measurement uncertainty when reporting true mass.more » The Monte Carlo simulation tool is available in the online version of this article.« less

Hydrometer calibration by hydrostatic weighing with automated liquid surface positioning

NASA Astrophysics Data System (ADS)

Aguilera, Jesus; Wright, John D.; Bean, Vern E.

2008-01-01

We describe an automated apparatus for calibrating hydrometers by hydrostatic weighing (Cuckow's method) in tridecane, a liquid of known, stable density, and with a relatively low surface tension and contact angle against glass. The apparatus uses a laser light sheet and a laser power meter to position the tridecane surface at the hydrometer scale mark to be calibrated with an uncertainty of 0.08 mm. The calibration results have an expanded uncertainty (with a coverage factor of 2) of 100 parts in 106 or less of the liquid density. We validated the apparatus by comparisons using water, toluene, tridecane and trichloroethylene, and found agreement within 40 parts in 106 or less. The new calibration method is consistent with earlier, manual calibrations performed by NIST. When customers use calibrated hydrometers, they may encounter uncertainties of 370 parts in 106 or larger due to surface tension, contact angle and temperature effects.

Calibration of the Microwave Limb Sounder on the Upper Atmosphere Research Satellite

NASA Technical Reports Server (NTRS)

Jarnot, R. F.; Cofield, R. E.; Waters, J. W.; Flower, D. A.; Peckham, G. E.

1996-01-01

The Microwave Limb Sounder (MLS) is a three-radiometer, passive, limb emission instrument onboard the Upper Atmosphere Research Satellite (UARS). Radiometric, spectral and field-of-view calibrations of the MLS instrument are described in this paper. In-orbit noise performance, gain stability, spectral baseline and dynamic range are described, as well as use of in-flight data for validation and refinement of prelaunch calibrations. Estimated systematic scaling uncertainties (3 sigma) on calibrated limb radiances from prelaunch calibrations are 2.6% in bands 1 through 3, 3.4% in band 4, and 6% in band 5. The observed systematic errors in band 6 are about 15%, consistent with prelaunch calibration uncertainties. Random uncertainties on individual limb radiance measurements are very close to the levels predicted from measured radiometer noise temperature, with negligible contribution from noise and drifts on the regular in-flight gain calibration measurements.

Determining the importance of model calibration for forecasting absolute/relative changes in streamflow from LULC and climate changes

USGS Publications Warehouse

Niraula, Rewati; Meixner, Thomas; Norman, Laura M.

2015-01-01

Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Assessing the impact of LULC and climate changes on streamflow is typically done with a calibrated and validated watershed model. However, there is a debate on the degree of calibration required. The objective of this study was to quantify the variation in estimated relative and absolute changes in streamflow associated with LULC and climate changes with different calibration approaches. The Soil and Water Assessment Tool (SWAT) was applied in an uncalibrated (UC), single outlet calibrated (OC), and spatially-calibrated (SC) mode to compare the relative and absolute changes in streamflow at 14 gaging stations within the Santa Cruz River Watershed in southern Arizona, USA. For this purpose, the effect of 3 LULC, 3 precipitation (P), and 3 temperature (T) scenarios were tested individually. For the validation period, Percent Bias (PBIAS) values were >100% with the UC model for all gages, the values were between 0% and 100% with the OC model and within 20% with the SC model. Changes in streamflow predicted with the UC and OC models were compared with those of the SC model. This approach implicitly assumes that the SC model is “ideal”. Results indicated that the magnitude of both absolute and relative changes in streamflow due to LULC predicted with the UC and OC results were different than those of the SC model. The magnitude of absolute changes predicted with the UC and SC models due to climate change (both P and T) were also significantly different, but were not different for OC and SC models. Results clearly indicated that relative changes due to climate change predicted with the UC and OC were not significantly different than that predicted with the SC models. This result suggests that it is important to calibrate the model spatially to analyze the effect of LULC change but not as important for analyzing the relative change in streamflow due to climate change. This study also indicated that model calibration in not necessary to determine the direction of change in streamflow due to LULC and climate change.

Absolute Radiometric Calibration of the GÖKTÜRK-2 Satellite Sensor Using Tuz GÖLÜ (landnet Site) from Ndvi Perspective

NASA Astrophysics Data System (ADS)

Sakarya, Ufuk; Hakkı Demirhan, İsmail; Seda Deveci, Hüsne; Teke, Mustafa; Demirkesen, Can; Küpçü, Ramazan; Feray Öztoprak, A.; Efendioğlu, Mehmet; Fehmi Şimşek, F.; Berke, Erdinç; Zübeyde Gürbüz, Sevgi

2016-06-01

TÜBİTAK UZAY has conducted a research study on the use of space-based satellite resources for several aspects of agriculture. Especially, there are two precision agriculture related projects: HASSAS (Widespread application of sustainable precision agriculture practices in Southeastern Anatolia Project Region (GAP) Project) and AKTAR (Smart Agriculture Feasibility Project). The HASSAS project aims to study development of precision agriculture practice in GAP region. Multi-spectral satellite imagery and aerial hyperspectral data along with ground measurements was collected to analyze data in an information system. AKTAR aims to develop models for irrigation, fertilization and spectral signatures of crops in Inner Anatolia. By the end of the project precision agriculture practices to control irrigation, fertilization, pesticide and estimation of crop yield will be developed. Analyzing the phenology of crops using NDVI is critical for the projects. For this reason, absolute radiometric calibration of the Red and NIR bands in space-based satellite sensors is an important issue. The Göktürk-2 satellite is an earth observation satellite which was designed and built in Turkey and was launched in 2012. The Göktürk-2 satellite sensor has a resolution 2.5 meters in panchromatic and 5 meters in R/G/B/NIR bands. The absolute radiometric calibration of the Göktürk-2 satellite sensor was performed via the ground-based measurements - spectra-radiometer, sun photometer, and meteorological station- in Tuz Gölü cal/val site in 2015. In this paper, the first ground-based absolute radiometric calibration results of the Göktürk-2 satellite sensor using Tuz Gölü is demonstrated. The absolute radiometric calibration results of this paper are compared with the published cross-calibration results of the Göktürk-2 satellite sensor utilizing Landsat 8 imagery. According to the experimental comparison results, the Göktürk-2 satellite sensor coefficients for red and NIR bands estimated in this work sustained to agree within 2% of calibration coefficients estimated in the cross-calibration results.

SU-E-T-491: Importance of Energy Dependent Protons Per MU Calibration Factors in IMPT Dose Calculations Using Monte Carlo Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Randeniya, S; Mirkovic, D; Titt, U

2014-06-01

Purpose: In intensity modulated proton therapy (IMPT), energy dependent, protons per monitor unit (MU) calibration factors are important parameters that determine absolute dose values from energy deposition data obtained from Monte Carlo (MC) simulations. Purpose of this study was to assess the sensitivity of MC-computed absolute dose distributions to the protons/MU calibration factors in IMPT. Methods: A “verification plan” (i.e., treatment beams applied individually to water phantom) of a head and neck patient plan was calculated using MC technique. The patient plan had three beams; one posterior-anterior (PA); two anterior oblique. Dose prescription was 66 Gy in 30 fractions. Ofmore » the total MUs, 58% was delivered in PA beam, 25% and 17% in other two. Energy deposition data obtained from the MC simulation were converted to Gy using energy dependent protons/MU calibrations factors obtained from two methods. First method is based on experimental measurements and MC simulations. Second is based on hand calculations, based on how many ion pairs were produced per proton in the dose monitor and how many ion pairs is equal to 1 MU (vendor recommended method). Dose distributions obtained from method one was compared with those from method two. Results: Average difference of 8% in protons/MU calibration factors between method one and two converted into 27 % difference in absolute dose values for PA beam; although dose distributions preserved the shape of 3D dose distribution qualitatively, they were different quantitatively. For two oblique beams, significant difference in absolute dose was not observed. Conclusion: Results demonstrate that protons/MU calibration factors can have a significant impact on absolute dose values in IMPT depending on the fraction of MUs delivered. When number of MUs increases the effect due to the calibration factors amplify. In determining protons/MU calibration factors, experimental method should be preferred in MC dose calculations. Research supported by National Cancer Institute grant P01CA021239.« less

Intercomparison Between in situ and AVHRR Polar Pathfinder-Derived Surface Albedo over Greenland

NASA Technical Reports Server (NTRS)

Stroeve, Julienne C.; Box, Jason E.; Fowler, Charles; Haran, Terence; Key, Jeffery

2001-01-01

The Advanced Very High Resolution (AVHRR) Polar Pathfinder Data (APP) provides the first long time series of consistent, calibrated surface albedo and surface temperature data for the polar regions. Validations of these products have consisted of individual studies that analyzed algorithm performance for limited regions and or time periods. This paper reports on comparisons made between the APP-derived surface albedo and that measured at fourteen automatic weather stations (AWS) around the Greenland ice sheet from January 1997 to August 1998. Results show that satellite-derived surface albedo values are on average 10% less than those measured by the AWS stations. However, the station measurements tend to be biased high by about 4% and thus the differences in absolute albedo may be less (e.g. 6%). In regions of the ice sheet where the albedo variability is small, such as the dry snow facies, the APP albedo uncertainty exceeds the natural variability. Further work is needed to improve the absolute accuracy of the APP-derived surface albedo. Even so, the data provide temporally and spatially consistent estimates of the Greenland ice sheet albedo.

An Introduction to the Global Space-based Inter-Calibration System from a EUMETSAT Perspective

NASA Astrophysics Data System (ADS)

Wagner, S. C.; Hewison, T.; Roebeling, R. A.; Koenig, M.; Schulz, J.; Miu, P.

2012-04-01

The Global Space-based Inter-Calibration System (GSICS) (Goldberg and al. 2011) is an international collaborative effort which aims to monitor, improve and harmonize the quality of observations from operational weather and environmental satellites of the Global Observing System (GOS). GSICS aims at ensuring consistent accuracy among space-based observations worldwide for climate monitoring, weather forecasting, and environmental applications. This is achieved through a comprehensive calibration strategy, which involves monitoring instrument performances, operational inter-calibration of satellite instruments, tying the measurements to absolute references and standards, and recalibration of archived data. A major part of this strategy involves direct comparison of collocated observations from pairs of satellite instruments, which are used to systematically generate calibration functions to compare and correct the calibration of monitored instruments to references. These GSICS Corrections are needed for accurately integrating data from multiple observing systems into both near real-time and re-analysis products, applications and services. This paper gives more insight into the activities carried out by EUMETSAT as a GSICS Processing and Research Centre. Currently these are closely bound to the in-house development and operational implementation of calibration methods for solar and thermal band channels of geostationary and polar-orbiting satellites. They include inter-calibration corrections for Meteosat imagers using reference instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite for solar band channels, the Infrared Atmospheric Sounding Interferometer (IASI) on-board Metop-A and, for historic archive data, the High-resolution InfraRed Sounder (HIRS). Additionally, bias monitoring is routinely performed, allowing users to visualise the calibration accuracy of the instruments in near real-time. These activities are based on principles and protocols defined by the GSICS Research Working Group and Data Management Working Group, which require assessment of the calibration uncertainties to ensure the traceability to community references.

Uncertainty analysis of thermocouple measurements used in normal and abnormal thermal environment experiments at Sandia's Radiant Heat Facility and Lurance Canyon Burn Site.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakos, James Thomas

2004-04-01

It would not be possible to confidently qualify weapon systems performance or validate computer codes without knowing the uncertainty of the experimental data used. This report provides uncertainty estimates associated with thermocouple data for temperature measurements from two of Sandia's large-scale thermal facilities. These two facilities (the Radiant Heat Facility (RHF) and the Lurance Canyon Burn Site (LCBS)) routinely gather data from normal and abnormal thermal environment experiments. They are managed by Fire Science & Technology Department 09132. Uncertainty analyses were performed for several thermocouple (TC) data acquisition systems (DASs) used at the RHF and LCBS. These analyses apply tomore » Type K, chromel-alumel thermocouples of various types: fiberglass sheathed TC wire, mineral-insulated, metal-sheathed (MIMS) TC assemblies, and are easily extended to other TC materials (e.g., copper-constantan). Several DASs were analyzed: (1) A Hewlett-Packard (HP) 3852A system, and (2) several National Instrument (NI) systems. The uncertainty analyses were performed on the entire system from the TC to the DAS output file. Uncertainty sources include TC mounting errors, ANSI standard calibration uncertainty for Type K TC wire, potential errors due to temperature gradients inside connectors, extension wire uncertainty, DAS hardware uncertainties including noise, common mode rejection ratio, digital voltmeter accuracy, mV to temperature conversion, analog to digital conversion, and other possible sources. Typical results for 'normal' environments (e.g., maximum of 300-400 K) showed the total uncertainty to be about {+-}1% of the reading in absolute temperature. In high temperature or high heat flux ('abnormal') thermal environments, total uncertainties range up to {+-}2-3% of the reading (maximum of 1300 K). The higher uncertainties in abnormal thermal environments are caused by increased errors due to the effects of imperfect TC attachment to the test item. 'Best practices' are provided in Section 9 to help the user to obtain the best measurements possible.« less

Modeling the relationship between photosynthetically active radiation and global horizontal irradiance using singular spectrum analysis

NASA Astrophysics Data System (ADS)

Zempila, Melina-Maria; Taylor, Michael; Bais, Alkiviadis; Kazadzis, Stelios

2016-10-01

We report on the construction of generic models to calculate photosynthetically active radiation (PAR) from global horizontal irradiance (GHI), and vice versa. Our study took place at stations of the Greek UV network (UVNET) and the Hellenic solar energy network (HNSE) with measurements from NILU-UV multi-filter radiometers and CM pyranometers, chosen due to their long (≈1 M record/site) high temporal resolution (≈1 min) record that captures a broad range of atmospheric environments and cloudiness conditions. The uncertainty of the PAR measurements is quantified to be ±6.5% while the uncertainty involved in GHI measurements is up to ≈±7% according to the manufacturer. We show how multi-linear regression and nonlinear neural network (NN) models, trained at a calibration site (Thessaloniki) can be made generic provided that the input-output time series are processed with multi-channel singular spectrum analysis (M-SSA). Without M-SSA, both linear and nonlinear models perform well only locally. M-SSA with 50 time-lags is found to be sufficient for identification of trend, periodic and noise components in aerosol, cloud parameters and irradiance, and to construct regularized noise models of PAR from GHI irradiances. Reconstructed PAR and GHI time series capture ≈95% of the variance of the cross-validated target measurements and have median absolute percentage errors <2%. The intra-site median absolute error of M-SSA processed models were ≈8.2±1.7 W/m2 for PAR and ≈9.2±4.2 W/m2 for GHI. When applying the models trained at Thessaloniki to other stations, the average absolute mean bias between the model estimates and measured values was found to be ≈1.2 W/m2 for PAR and ≈0.8 W/m2 for GHI. For the models, percentage errors are well within the uncertainty of the measurements at all sites. Generic NN models were found to perform marginally better than their linear counterparts.

A Framework for Propagation of Uncertainties in the Kepler Data Analysis Pipeline

NASA Technical Reports Server (NTRS)

Clarke, Bruce D.; Allen, Christopher; Bryson, Stephen T.; Caldwell, Douglas A.; Chandrasekaran, Hema; Cote, Miles T.; Girouard, Forrest; Jenkins, Jon M.; Klaus, Todd C.; Li, Jie;

Absolute calibration of the mass scale in the inverse problem of the physical theory of fireballs

NASA Astrophysics Data System (ADS)

Kalenichenko, V. V.

1992-08-01

A method of the absolute calibration of the mass scale is proposed for solving the inverse problem of the physical theory of fireballs. The method is based on data on the masses of fallen meteorites whose fireballs have been photographed in flight. The method can be applied to fireballs whose bodies have not experienced significant fragmentation during their flight in the atmosphere and have kept their shape relatively well. Data on the Lost City and Innisfree meteorites are used to calculate the calibration coefficients.

Absolute Calibration of Image Plate for electrons at energy between 100 keV and 4 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, H; Back, N L; Eder, D C

2007-12-10

The authors measured the absolute response of image plate (Fuji BAS SR2040) for electrons at energies between 100 keV to 4 MeV using an electron spectrometer. The electron source was produced from a short pulse laser irradiated on the solid density targets. This paper presents the calibration results of image plate Photon Stimulated Luminescence PSL per electrons at this energy range. The Monte Carlo radiation transport code MCNPX results are also presented for three representative incident angles onto the image plates and corresponding electron energies depositions at these angles. These provide a complete set of tools that allows extraction ofmore » the absolute calibration to other spectrometer setting at this electron energy range.« less

Calibration-free absolute frequency response measurement of directly modulated lasers based on additional modulation.

PubMed

Zhang, Shangjian; Zou, Xinhai; Wang, Heng; Zhang, Yali; Lu, Rongguo; Liu, Yong

2015-10-15

A calibration-free electrical method is proposed for measuring the absolute frequency response of directly modulated semiconductor lasers based on additional modulation. The method achieves the electrical domain measurement of the modulation index of directly modulated lasers without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it doubles measuring frequency range by setting a specific frequency relationship between the direct and additional modulation. Both the absolute and relative frequency response of semiconductor lasers are experimentally measured from the electrical spectrum of the twice-modulated optical signal, and the measured results are compared to those obtained with conventional methods to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed semiconductor lasers with high-resolution electrical spectrum analysis.

A Calibration Method for Nanowire Biosensors to Suppress Device-to-device Variation

PubMed Central

Ishikawa, Fumiaki N.; Curreli, Marco; Chang, Hsiao-Kang; Chen, Po-Chiang; Zhang, Rui; Cote, Richard J.; Thompson, Mark E.; Zhou, Chongwu

2009-01-01

Nanowire/nanotube biosensors have stimulated significant interest; however the inevitable device-to-device variation in the biosensor performance remains a great challenge. We have developed an analytical method to calibrate nanowire biosensor responses that can suppress the device-to-device variation in sensing response significantly. The method is based on our discovery of a strong correlation between the biosensor gate dependence (dIds/dVg) and the absolute response (absolute change in current, ΔI). In2O3 nanowire based biosensors for streptavidin detection were used as the model system. Studying the liquid gate effect and ionic concentration dependence of strepavidin sensing indicates that electrostatic interaction is the dominant mechanism for sensing response. Based on this sensing mechanism and transistor physics, a linear correlation between the absolute sensor response (ΔI) and the gate dependence (dIds/dVg) is predicted and confirmed experimentally. Using this correlation, a calibration method was developed where the absolute response is divided by dIds/dVg for each device, and the calibrated responses from different devices behaved almost identically. Compared to the common normalization method (normalization of the conductance/resistance/current by the initial value), this calibration method was proved advantageous using a conventional transistor model. The method presented here substantially suppresses device-to-device variation, allowing the use of nanosensors in large arrays. PMID:19921812

Evaluation of factors affecting CGMS calibration.

PubMed

Buckingham, Bruce A; Kollman, Craig; Beck, Roy; Kalajian, Andrea; Fiallo-Scharer, Rosanna; Tansey, Michael J; Fox, Larry A; Wilson, Darrell M; Weinzimer, Stuart A; Ruedy, Katrina J; Tamborlane, William V

2006-06-01

The optimal number/timing of calibrations entered into the CGMS (Medtronic MiniMed, Northridge, CA) continuous glucose monitoring system have not been previously described. Fifty subjects with Type 1 diabetes mellitus (10-18 years old) were hospitalized in a clinical research center for approximately 24 h on two separate days. CGMS and OneTouch Ultra meter (LifeScan, Milpitas, CA) data were obtained. The CGMS was retrospectively recalibrated using the Ultra data varying the number and timing of calibrations. Resulting CGMS values were compared against laboratory reference values. There was a modest improvement in accuracy with increasing number of calibrations. The median relative absolute deviation (RAD) was 14%, 15%, 13%, and 13% when using three, four, five, and seven calibration values, respectively (P < 0.001). Corresponding percentages of CGMS-reference pairs meeting the International Organisation for Standardisation criteria were 66%, 67%, 71%, and 72% (P < 0.001). Nighttime accuracy improved when daytime calibrations (pre-lunch and pre-dinner) were removed leaving only two calibrations at 9 p.m. and 6 a.m. (median difference, -2 vs. -9 mg/dL, P < 0.001; median RAD, 12% vs. 15%, P = 0.001). Accuracy was better on visits where the average absolute rate of glucose change at the times of calibration was lower. On visits with average absolute rates <0.5, 0.5 to <1.0, 1.0 to <1.5, and >or=1.5 mg/dL/min, median RAD values were 13% versus 14% versus 17% versus 19%, respectively (P = 0.05). Although accuracy is slightly improved with more calibrations, the timing of the calibrations appears more important. Modifying the algorithm to put less weight on daytime calibrations for nighttime values and calibrating during times of relative glucose stability may have greater impact on accuracy.

Evaluation of Factors Affecting CGMS Calibration

PubMed Central

2006-01-01

Background The optimal number/timing of calibrations entered into the Continuous Glucose Monitoring System (“CGMS”; Medtronic MiniMed, Northridge, CA) have not been previously described. Methods Fifty subjects with T1DM (10–18y) were hospitalized in a clinical research center for ~24h on two separate days. CGMS and OneTouch® Ultra® Meter (“Ultra”; LifeScan, Milpitas, CA) data were obtained. The CGMS was retrospectively recalibrated using the Ultra data varying the number and timing of calibrations. Resulting CGMS values were compared against laboratory reference values. Results There was a modest improvement in accuracy with increasing number of calibrations. The median relative absolute deviation (RAD) was 14%, 15%, 13% and 13% when using 3, 4, 5 and 7 calibration values, respectively (p<0.001). Corresponding percentages of CGMS-reference pairs meeting the ISO criteria were 66%, 67%, 71% and 72% (p<0.001). Nighttime accuracy improved when daytime calibrations (pre-lunch and pre-dinner) were removed leaving only two calibrations at 9p.m. and 6a.m. (median difference: −2 vs. −9mg/dL, p<0.001; median RAD: 12% vs. 15%, p=0.001). Accuracy was better on visits where the average absolute rate of glucose change at the times of calibration was lower. On visits with average absolute rates <0.5, 0.5-<1.0, 1.0-<1.5 and ≥1.5mg/dL/min, median RAD values were 13% vs. 14% vs. 17% vs. 19%, respectively (p=0.05). Conclusions Although accuracy is slightly improved with more calibrations, the timing of the calibrations appears more important. Modifying the algorithm to put less weight on daytime calibrations for nighttime values and calibrating during times of relative glucose stability may have greater impact on accuracy. PMID:16800753

How Reliable is Bayesian Model Averaging Under Noisy Data? Statistical Assessment and Implications for Robust Model Selection

NASA Astrophysics Data System (ADS)

Schöniger, Anneli; Wöhling, Thomas; Nowak, Wolfgang

2014-05-01

Bayesian model averaging ranks the predictive capabilities of alternative conceptual models based on Bayes' theorem. The individual models are weighted with their posterior probability to be the best one in the considered set of models. Finally, their predictions are combined into a robust weighted average and the predictive uncertainty can be quantified. This rigorous procedure does, however, not yet account for possible instabilities due to measurement noise in the calibration data set. This is a major drawback, since posterior model weights may suffer a lack of robustness related to the uncertainty in noisy data, which may compromise the reliability of model ranking. We present a new statistical concept to account for measurement noise as source of uncertainty for the weights in Bayesian model averaging. Our suggested upgrade reflects the limited information content of data for the purpose of model selection. It allows us to assess the significance of the determined posterior model weights, the confidence in model selection, and the accuracy of the quantified predictive uncertainty. Our approach rests on a brute-force Monte Carlo framework. We determine the robustness of model weights against measurement noise by repeatedly perturbing the observed data with random realizations of measurement error. Then, we analyze the induced variability in posterior model weights and introduce this "weighting variance" as an additional term into the overall prediction uncertainty analysis scheme. We further determine the theoretical upper limit in performance of the model set which is imposed by measurement noise. As an extension to the merely relative model ranking, this analysis provides a measure of absolute model performance. To finally decide, whether better data or longer time series are needed to ensure a robust basis for model selection, we resample the measurement time series and assess the convergence of model weights for increasing time series length. We illustrate our suggested approach with an application to model selection between different soil-plant models following up on a study by Wöhling et al. (2013). Results show that measurement noise compromises the reliability of model ranking and causes a significant amount of weighting uncertainty, if the calibration data time series is not long enough to compensate for its noisiness. This additional contribution to the overall predictive uncertainty is neglected without our approach. Thus, we strongly advertise to include our suggested upgrade in the Bayesian model averaging routine.

Simulations of VLBI observations of a geodetic satellite providing co-location in space

NASA Astrophysics Data System (ADS)

Anderson, James M.; Beyerle, Georg; Glaser, Susanne; Liu, Li; Männel, Benjamin; Nilsson, Tobias; Heinkelmann, Robert; Schuh, Harald

2018-02-01

We performed Monte Carlo simulations of very-long-baseline interferometry (VLBI) observations of Earth-orbiting satellites incorporating co-located space-geodetic instruments in order to study how well the VLBI frame and the spacecraft frame can be tied using such measurements. We simulated observations of spacecraft by VLBI observations, time-of-flight (TOF) measurements using a time-encoded signal in the spacecraft transmission, similar in concept to precise point positioning, and differential VLBI (D-VLBI) observations using angularly nearby quasar calibrators to compare their relative performance. We used the proposed European Geodetic Reference Antenna in Space (E-GRASP) mission as an initial test case for our software. We found that the standard VLBI technique is limited, in part, by the present lack of knowledge of the absolute offset of VLBI time to Coordinated Universal Time at the level of microseconds. TOF measurements are better able to overcome this problem and provide frame ties with uncertainties in translation and scale nearly a factor of three smaller than those yielded from VLBI measurements. If the absolute time offset issue can be resolved by external means, the VLBI results can be significantly improved and can come close to providing 1 mm accuracy in the frame tie parameters. D-VLBI observations with optimum performance assumptions provide roughly a factor of two higher uncertainties for the E-GRASP orbit. We additionally simulated how station and spacecraft position offsets affect the frame tie performance.

Calibration-induced uncertainty of the EPIC model to estimate climate change impact on global maize yield

NASA Astrophysics Data System (ADS)

Xiong, Wei; Skalský, Rastislav; Porter, Cheryl H.; Balkovič, Juraj; Jones, James W.; Yang, Di

2016-09-01

Understanding the interactions between agricultural production and climate is necessary for sound decision-making in climate policy. Gridded and high-resolution crop simulation has emerged as a useful tool for building this understanding. Large uncertainty exists in this utilization, obstructing its capacity as a tool to devise adaptation strategies. Increasing focus has been given to sources of uncertainties for climate scenarios, input-data, and model, but uncertainties due to model parameter or calibration are still unknown. Here, we use publicly available geographical data sets as input to the Environmental Policy Integrated Climate model (EPIC) for simulating global-gridded maize yield. Impacts of climate change are assessed up to the year 2099 under a climate scenario generated by HadEM2-ES under RCP 8.5. We apply five strategies by shifting one specific parameter in each simulation to calibrate the model and understand the effects of calibration. Regionalizing crop phenology or harvest index appears effective to calibrate the model for the globe, but using various values of phenology generates pronounced difference in estimated climate impact. However, projected impacts of climate change on global maize production are consistently negative regardless of the parameter being adjusted. Different values of model parameter result in a modest uncertainty at global level, with difference of the global yield change less than 30% by the 2080s. The uncertainty subjects to decrease if applying model calibration or input data quality control. Calibration has a larger effect at local scales, implying the possible types and locations for adaptation.

Calibration aspects of the JEM-EUSO mission

NASA Astrophysics Data System (ADS)

Adams, J. H.; Ahmad, S.; Albert, J.-N.; Allard, D.; Anchordoqui, L.; Andreev, V.; Anzalone, A.; Arai, Y.; Asano, K.; Ave Pernas, M.; Baragatti, P.; Barrillon, P.; Batsch, T.; Bayer, J.; Bechini, R.; Belenguer, T.; Bellotti, R.; Belov, K.; Berlind, A. A.; Bertaina, M.; Biermann, P. L.; Biktemerova, S.; Blaksley, C.; Blanc, N.; Błȩcki, J.; Blin-Bondil, S.; Blümer, J.; Bobik, P.; Bogomilov, M.; Bonamente, M.; Briggs, M. S.; Briz, S.; Bruno, A.; Cafagna, F.; Campana, D.; Capdevielle, J.-N.; Caruso, R.; Casolino, M.; Cassardo, C.; Castellinic, G.; Catalano, C.; Catalano, G.; Cellino, A.; Chikawa, M.; Christl, M. J.; Cline, D.; Connaughton, V.; Conti, L.; Cordero, G.; Crawford, H. J.; Cremonini, R.; Csorna, S.; Dagoret-Campagne, S.; de Castro, A. J.; De Donato, C.; de la Taille, C.; De Santis, C.; del Peral, L.; Dell'Oro, A.; De Simone, N.; Di Martino, M.; Distratis, G.; Dulucq, F.; Dupieux, M.; Ebersoldt, A.; Ebisuzaki, T.; Engel, R.; Falk, S.; Fang, K.; Fenu, F.; Fernández-Gómez, I.; Ferrarese, S.; Finco, D.; Flamini, M.; Fornaro, C.; Franceschi, A.; Fujimoto, J.; Fukushima, M.; Galeotti, P.; Garipov, G.; Geary, J.; Gelmini, G.; Giraudo, G.; Gonchar, M.; González Alvarado, C.; Gorodetzky, P.; Guarino, F.; Guzmán, A.; Hachisu, Y.; Harlov, B.; Haungs, A.; Hernández Carretero, J.; Higashide, K.; Ikeda, D.; Ikeda, H.; Inoue, N.; Inoue, S.; Insolia, A.; Isgrò, F.; Itow, Y.; Joven, E.; Judd, E. G.; Jung, A.; Kajino, F.; Kajino, T.; Kaneko, I.; Karadzhov, Y.; Karczmarczyk, J.; Karus, M.; Katahira, K.; Kawai, K.; Kawasaki, Y.; Keilhauer, B.; Khrenov, B. A.; Kim, J.-S.; Kim, S.-W.; Kim, S.-W.; Kleifges, M.; Klimov, P. A.; Kolev, D.; Kreykenbohm, I.; Kudela, K.; Kurihara, Y.; Kusenko, A.; Kuznetsov, E.; Lacombe, M.; Lachaud, C.; Lee, J.; Licandro, J.; Lim, H.; López, F.; Maccarone, M. C.; Mannheim, K.; Maravilla, D.; Marcelli, L.; Marini, A.; Martinez, O.; Masciantonio, G.; Mase, K.; Matev, R.; Medina-Tanco, G.; Mernik, T.; Miyamoto, H.; Miyazaki, Y.; Mizumoto, Y.; Modestino, G.; Monaco, A.; Monnier-Ragaigne, D.; Morales de los Ríos, J. A.; Moretto, C.; Morozenko, V. S.; Mot, B.; Murakami, T.; Murakami, M. Nagano; Nagata, M.; Nagataki, S.; Nakamura, T.; Napolitano, T.; Naumov, D.; Nava, R.; Neronov, A.; Nomoto, K.; Nonaka, T.; Ogawa, T.; Ogio, S.; Ohmori, H.; Olinto, A. V.; Orleański, P.; Osteria, G.; Panasyuk, M. I.; Parizot, E.; Park, I. H.; Park, H. W.; Pastircak, B.; Patzak, T.; Paul, T.; Pennypacker, C.; Perez Cano, S.; Peter, T.; Picozza, P.; Pierog, T.; Piotrowski, L. W.; Piraino, S.; Plebaniak, Z.; Pollini, A.; Prat, P.; Prévôt, G.; Prieto, H.; Putis, M.; Reardon, P.; Reyes, M.; Ricci, M.; Rodríguez, I.; Rodríguez Frías, M. D.; Ronga, F.; Roth, M.; Rothkaehl, H.; Roudil, G.; Rusinov, I.; Rybczyński, M.; Sabau, M. D.; Sáez-Cano, G.; Sagawa, H.; Saito, A.; Sakaki, N.; Sakata, M.; Salazar, H.; Sánchez, S.; Santangelo, A.; Santiago Crúz, L.; Sanz Palomino, M.; Saprykin, O.; Sarazin, F.; Sato, H.; Sato, M.; Schanz, T.; Schieler, H.; Scotti, V.; Segreto, A.; Selmane, S.; Semikoz, D.; Serra, M.; Sharakin, S.; Shibata, T.; Shimizu, H. M.; Shinozaki, K.; Shirahama, T.; Siemieniec-Oziȩbło, G.; Silva López, H. H.; Sledd, J.; Słomińska, K.; Sobey, A.; Sugiyama, T.; Supanitsky, D.; Suzuki, M.; Szabelska, B.; Szabelski, J.; Tajima, F.; Tajima, N.; Tajima, T.; Takahashi, Y.; Takami, H.; Takeda, M.; Takizawa, Y.; Tenzer, C.; Tibolla, O.; Tkachev, L.; Tokuno, H.; Tomida, T.; Tone, N.; Toscano, S.; Trillaud, F.; Tsenov, R.; Tsunesada, Y.; Tsuno, K.; Tymieniecka, T.; Uchihori, Y.; Unger, M.; Vaduvescu, O.; Valdés-Galicia, J. F.; Vallania, P.; Valore, L.; Vankova, G.; Vigorito, C.; Villaseñor, L.; von Ballmoos, P.; Wada, S.; Watanabe, J.; Watanabe, S.; Watts, J.; Weber, M.; Weiler, T. J.; Wibig, T.; Wiencke, L.; Wille, M.; Wilms, J.; Włodarczyk, Z.; Yamamoto, T.; Yamamoto, Y.; Yang, J.; Yano, H.; Yashin, I. V.; Yonetoku, D.; Yoshida, K.; Yoshida, S.; Young, R.; Zotov, M. Yu.; Zuccaro Marchi, A.

2015-11-01

The JEM-EUSO telescope will be, after calibration, a very accurate instrument which yields the number of received photons from the number of measured photo-electrons. The project is in phase A (demonstration of the concept) including already operating prototype instruments, i.e. many parts of the instrument have been constructed and tested. Calibration is a crucial part of the instrument and its use. The focal surface (FS) of the JEM-EUSO telescope will consist of about 5000 photo-multiplier tubes (PMTs), which have to be well calibrated to reach the required accuracy in reconstructing the air-shower parameters. The optics system consists of 3 plastic Fresnel (double-sided) lenses of 2.5 m diameter. The aim of the calibration system is to measure the efficiencies (transmittances) of the optics and absolute efficiencies of the entire focal surface detector. The system consists of 3 main components: (i) Pre-flight calibration devices on ground, where the efficiency and gain of the PMTs will be measured absolutely and also the transmittance of the optics will be. (ii) On-board relative calibration system applying two methods: a) operating during the day when the JEM-EUSO lid will be closed with small light sources on board. b) operating during the night, together with data taking: the monitoring of the background rate over identical sites. (iii) Absolute in-flight calibration, again, applying two methods: a) measurement of the moon light, reflected on high altitude, high albedo clouds. b) measurements of calibrated flashes and tracks produced by the Global Light System (GLS). Some details of each calibration method will be described in this paper.

Gradient-based model calibration with proxy-model assistance

NASA Astrophysics Data System (ADS)

Burrows, Wesley; Doherty, John

2016-02-01

Use of a proxy model in gradient-based calibration and uncertainty analysis of a complex groundwater model with large run times and problematic numerical behaviour is described. The methodology is general, and can be used with models of all types. The proxy model is based on a series of analytical functions that link all model outputs used in the calibration process to all parameters requiring estimation. In enforcing history-matching constraints during the calibration and post-calibration uncertainty analysis processes, the proxy model is run for the purposes of populating the Jacobian matrix, while the original model is run when testing parameter upgrades; the latter process is readily parallelized. Use of a proxy model in this fashion dramatically reduces the computational burden of complex model calibration and uncertainty analysis. At the same time, the effect of model numerical misbehaviour on calculation of local gradients is mitigated, this allowing access to the benefits of gradient-based analysis where lack of integrity in finite-difference derivatives calculation would otherwise have impeded such access. Construction of a proxy model, and its subsequent use in calibration of a complex model, and in analysing the uncertainties of predictions made by that model, is implemented in the PEST suite.

Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images

NASA Astrophysics Data System (ADS)

von der Linden, Anja; Allen, Mark T.; Applegate, Douglas E.; Kelly, Patrick L.; Allen, Steven W.; Ebeling, Harald; Burchat, Patricia R.; Burke, David L.; Donovan, David; Morris, R. Glenn; Blandford, Roger; Erben, Thomas; Mantz, Adam

2014-03-01

This is the first in a series of papers in which we measure accurate weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at redshifts 0.15 ≲ zCl ≲ 0.7, in order to calibrate X-ray and other mass proxies for cosmological cluster experiments. The primary aim is to improve the absolute mass calibration of cluster observables, currently the dominant systematic uncertainty for cluster count experiments. Key elements of this work are the rigorous quantification of systematic uncertainties, high-quality data reduction and photometric calibration, and the `blind' nature of the analysis to avoid confirmation bias. Our target clusters are drawn from X-ray catalogues based on the ROSAT All-Sky Survey, and provide a versatile calibration sample for many aspects of cluster cosmology. We have acquired wide-field, high-quality imaging using the Subaru Telescope and Canada-France-Hawaii Telescope for all 51 clusters, in at least three bands per cluster. For a subset of 27 clusters, we have data in at least five bands, allowing accurate photometric redshift estimates of lensed galaxies. In this paper, we describe the cluster sample and observations, and detail the processing of the SuprimeCam data to yield high-quality images suitable for robust weak-lensing shape measurements and precision photometry. For each cluster, we present wide-field three-colour optical images and maps of the weak-lensing mass distribution, the optical light distribution and the X-ray emission. These provide insights into the large-scale structure in which the clusters are embedded. We measure the offsets between X-ray flux centroids and the brightest cluster galaxies in the clusters, finding these to be small in general, with a median of 20 kpc. For offsets ≲100 kpc, weak-lensing mass measurements centred on the brightest cluster galaxies agree well with values determined relative to the X-ray centroids; miscentring is therefore not a significant source of systematic uncertainty for our weak-lensing mass measurements. In accompanying papers, we discuss the key aspects of our photometric calibration and photometric redshift measurements (Kelly et al.), and measure cluster masses using two methods, including a novel Bayesian weak-lensing approach that makes full use of the photometric redshift probability distributions for individual background galaxies (Applegate et al.). In subsequent papers, we will incorporate these weak-lensing mass measurements into a self-consistent framework to simultaneously determine cluster scaling relations and cosmological parameters.

New NREL Method Reduces Uncertainty in Photovoltaic Module Calibrations |

Science.gov Websites

calibration traceability to certified test laboratories. This reliable calibration, in turn, determines the of a spire flash simulator, SOMS outdoor test bed, and LACSS continuous simulator. In NREL's Cell and % (k=2 coverage factor). This value is the lowest reported Pmax uncertainty of any accredited test

Estimation of the quantification uncertainty from flow injection and liquid chromatography transient signals in inductively coupled plasma mass spectrometry

NASA Astrophysics Data System (ADS)

Laborda, Francisco; Medrano, Jesús; Castillo, Juan R.

2004-06-01

The quality of the quantitative results obtained from transient signals in high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS) and flow injection-inductively coupled plasma mass spectrometry (FI-ICPMS) was investigated under multielement conditions. Quantification methods were based on multiple-point calibration by simple and weighted linear regression, and double-point calibration (measurement of the baseline and one standard). An uncertainty model, which includes the main sources of uncertainty from FI-ICPMS and HPLC-ICPMS (signal measurement, sample flow rate and injection volume), was developed to estimate peak area uncertainties and statistical weights used in weighted linear regression. The behaviour of the ICPMS instrument was characterized in order to be considered in the model, concluding that the instrument works as a concentration detector when it is used to monitorize transient signals from flow injection or chromatographic separations. Proper quantification by the three calibration methods was achieved when compared to reference materials, although the double-point calibration allowed to obtain results of the same quality as the multiple-point calibration, shortening the calibration time. Relative expanded uncertainties ranged from 10-20% for concentrations around the LOQ to 5% for concentrations higher than 100 times the LOQ.

Uncertainty representation of grey numbers and grey sets.

PubMed

Yang, Yingjie; Liu, Sifeng; John, Robert

2014-09-01

In the literature, there is a presumption that a grey set and an interval-valued fuzzy set are equivalent. This presumption ignores the existence of discrete components in a grey number. In this paper, new measurements of uncertainties of grey numbers and grey sets, consisting of both absolute and relative uncertainties, are defined to give a comprehensive representation of uncertainties in a grey number and a grey set. Some simple examples are provided to illustrate that the proposed uncertainty measurement can give an effective representation of both absolute and relative uncertainties in a grey number and a grey set. The relationships between grey sets and interval-valued fuzzy sets are also analyzed from the point of view of the proposed uncertainty representation. The analysis demonstrates that grey sets and interval-valued fuzzy sets provide different but overlapping models for uncertainty representation in sets.

Galileo FOC Satellite Group Delay Estimation based on Raw Method and published IOV Metadata

NASA Astrophysics Data System (ADS)

Reckeweg, Florian; Schönemann, Erik; Springer, Tim; Enderle, Werner

2017-04-01

In December 2016, the European GNSS Agency (GSA) published the Galileo In-Orbit Validation (IOV) satellite metadata. These metadata include among others the so-called Galileo satellite group delays, which were measured in an absolute sense by the satellite manufacturer on-ground for all three Galileo frequency bands E1, E5 and E6. Therewith Galileo is the first Global Navigation Satellite System (GNSS) for which absolute calibration values for satellite on-board group delays have been published. The different satellite group delays for the three frequency bands lead to the fact that the signals will not be transmitted at exactly the same epoch. Up to now, due to the lack of absolute group delays, it is common practice in GNSS analyses to estimate and apply the differences of these satellite group delays, commonly known as differential code biases (DCBs). However, this has the drawback that the determination of the "raw" clock and the absolute ionosphere is not possible. The use of absolute bias calibrations for satellites and receivers is a major step into the direction of more realistic (in a physical sense) clock and atmosphere estimates. The Navigation Support Office at the European Space Operation Centre (ESOC) was from the beginning involved in the validation process of the Galileo metadata. For the work presented in this presentation we will use the absolute bias calibrations of the Galileo IOV satellites to estimate and validate the absolute receiver group delays of the ESOC GNSS network and vice versa. The receiver group delays have exemplarily been calibrated in a calibration campaign with an IFEN GNSS Signal-Simulator at ESOC. Based on the calibrated network, making use of the ionosphere constraints given by the IOV satellites, GNSS raw observations are processed to estimate satellite group delays for the operational Galileo (Full Operational Capability) FOC satellites. In addition, "raw" satellite clock offsets are estimated, which are free of the ionosphere-free bias, which is inherent to all common satellite clock products, generated with the standard ionosphere-free linear combination processing approach. In the raw observation processing method, developed by the Navigation Support Office at ESOC, no differences or linear combinations of GNSS observations are formed and ionosphere parameters and multi-signal group delay parameters can be jointly estimated by making use of all available code and phase observations on multiple frequencies.

Evaluation of absolute measurement using a 4π plastic scintillator for the 4πβ-γ coincidence counting method.

PubMed

Unno, Y; Sanami, T; Sasaki, S; Hagiwara, M; Yunoki, A

2018-04-01

Absolute measurement by the 4πβ-γ coincidence counting method was conducted by two photomultipliers facing across a plastic scintillator to be focused on β ray counting efficiency. The detector was held with a through-hole-type NaI(Tl) detector. The results include absolutely determined activity and its uncertainty especially about extrapolation. A comparison between the obtained and known activities showed agreement within their uncertainties. Copyright © 2017 Elsevier Ltd. All rights reserved.

Solar-diffuser panel and ratioing radiometer approach to satellite sensor on-board calibration

NASA Technical Reports Server (NTRS)

Slater, Philip N.; Palmer, James M.

1991-01-01

The use of a solar-diffuser panel is a desirable approach to the on-board absolute radiometric calibration of satellite multispectral sensors used for earth observation in the solar reflective spectral range. It provides a full aperture, full field, end-to-end calibration near the top of the sensor's dynamic range and across its entire spectral response range. A serious drawback is that the panel's reflectance, and the response of any simple detector used to monitor its reflectance may change with time. This paper briefly reviews some preflight and on-board methods for absolute calibration and introduces the ratioing-radiometer concept in which the radiance of the panel is ratioed with respect to the solar irradiance at the time the multispectral sensor is viewing the panel in its calibration mode.

Absolute calibration of Doppler coherence imaging velocity images

NASA Astrophysics Data System (ADS)

Samuell, C. M.; Allen, S. L.; Meyer, W. H.; Howard, J.

2017-08-01

A new technique has been developed for absolutely calibrating a Doppler Coherence Imaging Spectroscopy interferometer for measuring plasma ion and neutral velocities. An optical model of the interferometer is used to generate zero-velocity reference images for the plasma spectral line of interest from a calibration source some spectral distance away. Validation of this technique using a tunable diode laser demonstrated an accuracy better than 0.2 km/s over an extrapolation range of 3.5 nm; a two order of magnitude improvement over linear approaches. While a well-characterized and very stable interferometer is required, this technique opens up the possibility of calibrated velocity measurements in difficult viewing geometries and for complex spectral line-shapes.

SU-G-BRB-15: Verifications of Absolute and Relative Dosimetry of a Novel Stereotactic Breast Device: GammaPodTM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Becker, S; Mossahebi, S; Yi, B

Purpose: A dedicated stereotactic breast radiotherapy device, GammaPod, was developed to treat early stage breast cancer. The first clinical unit was installed and commissioned at University of Maryland. We report our methodology of absolute dosimetry in multiple calibration conditions and dosimetric verifications of treatment plans produced by the system. Methods: GammaPod unit is comprised of a rotating hemi-spherical source carrier containing 36 Co-60 sources and a concentric tungsten collimator providing beams of 15 and 25 mm. Absolute dose calibration formalism was developed with modifications to AAPM protocols for unique geometry and different calibration medium (acrylic, polyethylene or liquid water). Breastmore » cup-size specific and collimator output factors were measured and verified with respect to Monte-Carlo simulations for single isocenter plans. Multiple isocenter plans were generated for various target size, location and cup-sizes in phantoms and 20 breast cancer patients images. Stereotactic mini-farmer chamber, OSL and TLD detectors as well as radio-chromic films were used for dosimetric measurements. Results: At the time of calibration (1/14/2016), absolute dose rate of the GammaPod was established to be 2.10 Gy/min in acrylic for 25 mm for sources installed in March 2011. Output factor for 15 mm collimator was measured to be 0.950. Absolute dose calibration was independently verified by IROC-Houston with a TLD/Institution ratio of 0.99. Cup size specific output measurements in liquid water for single isocenter were found to be within 3.0% of MC simulations. Point-dose measurements of multiple isocenter treatment plans were found to be within −1.0 ± 1.2 % of treatment planning system while 2-dimensional gamma analysis yielded a pass rate of 97.9 ± 2.2 % using gamma criteria of 3% and 2mm. Conclusion: The first GammaPod treatment unit for breast stereotactic radiotherapy was successfully installed, calibrated and commissioned for patient treatments. An absolute dosimetry and dosimetric verification protocols were successfully created.« less

Evaluating Statistical Process Control (SPC) techniques and computing the uncertainty of force calibrations

NASA Technical Reports Server (NTRS)

Navard, Sharon E.

1989-01-01

In recent years there has been a push within NASA to use statistical techniques to improve the quality of production. Two areas where statistics are used are in establishing product and process quality control of flight hardware and in evaluating the uncertainty of calibration of instruments. The Flight Systems Quality Engineering branch is responsible for developing and assuring the quality of all flight hardware; the statistical process control methods employed are reviewed and evaluated. The Measurement Standards and Calibration Laboratory performs the calibration of all instruments used on-site at JSC as well as those used by all off-site contractors. These calibrations must be performed in such a way as to be traceable to national standards maintained by the National Institute of Standards and Technology, and they must meet a four-to-one ratio of the instrument specifications to calibrating standard uncertainty. In some instances this ratio is not met, and in these cases it is desirable to compute the exact uncertainty of the calibration and determine ways of reducing it. A particular example where this problem is encountered is with a machine which does automatic calibrations of force. The process of force calibration using the United Force Machine is described in detail. The sources of error are identified and quantified when possible. Suggestions for improvement are made.

Sand dune ridge alignment effects on surface BRF over the Libya-4 CEOS calibration site.

PubMed

Govaerts, Yves M

2015-02-03

The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm.

Improved dewpoint-probe calibration

NASA Technical Reports Server (NTRS)

Stephenson, J. G.; Theodore, E. A.

1978-01-01

Relatively-simple pressure-control apparatus calibrates dewpoint probes considerably faster than conventional methods, with no loss of accuracy. Technique requires only pressure measurement at each calibration point and single absolute-humidity measurement at beginning of run. Several probes can be calibrated simultaneously and points can be checked above room temperature.

Calibration of X-Ray Observatories

NASA Technical Reports Server (NTRS)

Weisskopf, Martin C.; L'Dell, Stephen L.

2011-01-01

Accurate calibration of x-ray observatories has proved an elusive goal. Inaccuracies and inconsistencies amongst on-ground measurements, differences between on-ground and in-space performance, in-space performance changes, and the absence of cosmic calibration standards whose physics we truly understand have precluded absolute calibration better than several percent and relative spectral calibration better than a few percent. The philosophy "the model is the calibration" relies upon a complete high-fidelity model of performance and an accurate verification and calibration of this model. As high-resolution x-ray spectroscopy begins to play a more important role in astrophysics, additional issues in accurately calibrating at high spectral resolution become more evident. Here we review the challenges of accurately calibrating the absolute and relative response of x-ray observatories. On-ground x-ray testing by itself is unlikely to achieve a high-accuracy calibration of in-space performance, especially when the performance changes with time. Nonetheless, it remains an essential tool in verifying functionality and in characterizing and verifying the performance model. In the absence of verified cosmic calibration sources, we also discuss the notion of an artificial, in-space x-ray calibration standard. 6th

The spectral energy distribution of Zeta Puppis and HD 50896

NASA Technical Reports Server (NTRS)

Holm, A. V.; Cassinelli, J. P.

1977-01-01

The ultraviolet spectral energy distribution of the O5f star Zeta Pup and the WN5 star HD 50896 are derived from OAO-2 observations with the calibration of Bless, Code, and Fairchild (1976). An estimate of the interstellar reddening (0.12 magnitude) of the Wolf-Rayet star is determined from the size of the characteristic interstellar extinction bump at 4.6 inverse microns. After correction for extinction, both stars show a flat energy distribution in the ultraviolet. The distribution of HD 50896 from 1100 A to 2 microns is in good agreement with results of extended model atmospheres, but some uncertainty remains because of the interstellar-extinction correction. The absolute energy distribution of Zeta Pup is fitted by a 42,000-K plane-parallel model if the model's flux is adjusted for the effects of electron scattering in the stellar wind and for UV line blanketing that was determined empirically from high-resolution Copernicus satellite observations. To achieve this fit, it is necessary to push both the spectroscopically determined temperature and the ultraviolet calibration to the limits of their probable errors.

[On-orbit response variation analysis of FY-3 MERSI reflective solar bands based on Dunhuang site calibration].

PubMed

Sun, Ling; Guo, Mao-Hua; Xu, Na; Zhang, Li-Jun; Liu, Jing-Jing; Hu, Xiu-Qing; Li, Yuan; Rong, Zhi-Guo; Zhao, Ze-Hui

2012-07-01

MERSI is the keystone payload of FengYun-3 and there have been two sensors operating on-orbit since 2008. The on-orbit response changes obviously at reflective solar bands (RSBs) and must be effectively monitored and corrected. However MERSI can not realize the RSBs onboard absolute radiometric calibration. This paper presents a new vicarious calibration (VC) method for RSBs based on in-situ BRDF model, and vector radiometric transfer model 6SV with gaseous absorption correction using MOTRAN. The results of synchronous VC experiments in 4 years show that the calibration uncertainties are within 5% except for band at the center of water vapor absorption, and 3% for most bands. Aqua MODIS was taken as the radiometric reference to evaluate the accuracy of this VC method. By comparison of the simulated radiation at top of atmosphere (TOA) with MODIS measurement, it was revealed that the average relative differences are within 3% for window bands with wavelengths less than 1 microm, and 5% for bands with wavelengths larger than 1 microm (except for band 7 at 2.1 microm). Besides, the synchronous nadir observation cross analysis shows the excellent agreement between re-calibrated MERSI TOA apparent reflectance and MODIS measurements. Based on the multi-year site calibration results, it was found that the calibration coefficients could be fitted with two-order polynomials, thus the daily calibration updates could be realized and the response variation between two calibration experiments could be corrected timely; there are large response changes at bands with wavelengths less than 0.6 microm, the degradation rate of the first year at band 8 (0.41 microm) is about 14%; the on-orbit response degradation is maximum at the beginning, the degradation rates slow down after one year in operation, and after two years the responses even increase at some band with wavelengths larger than 0.6 microm.

Continuous glucose monitoring system: dawn period calibration does not change accuracy of the method.

PubMed

Augusto, Gustavo A; Sousa, André G P; Perazo, Marcela N A; Correa-Giannella, Maria L C; Nery, Marcia; Melo, Karla F S de

2009-06-01

Continuous glucose monitoring system is a valuable instrument to measure glycemic control, which uses a retrospective calibration based upon 3 to 4 capillary glucose meter values inserted by the patient each day. We evaluated the interference of calibration during the dawn period in the system accuracy. The monitoring data were retrospectively divided into two groups: with (Group A) or without (Group B) the dawn period calibration (between 1:00 and 5:00 AM). Accuracy of the method was expressed by relative absolute difference. Thirty-four continuous glucose monitoring data were evaluated comprising a total of 112 nights. A total of 289 paired readings were analyzed - 195 in Group A and 94 in Group B. We did not find a difference in relative absolute difference (RAD%) in any analyzed period of day by adding dawn calibration. These data suggest that dawn calibration does not alter accuracy of method.

Campaign-Style Measurements of Vertical Seafloor Deformation in the Cascadia Subduction Zone Using an Absolute Self-Calibrating Pressure Recorder

NASA Astrophysics Data System (ADS)

Cook, M. J.; Sasagawa, G. S.; Roland, E. C.; Schmidt, D. A.; Wilcock, W. S. D.; Zumberge, M. A.

2017-12-01

Seawater pressure can be used to measure vertical seafloor deformation since small seafloor height changes produce measurable pressure changes. However, resolving secular vertical deformation near subduction zones can be difficult due to pressure gauge drift. A typical gauge drift rate of about 10 cm/year exceeds the expected secular rate of 1 cm/year or less in Cascadia. The absolute self-calibrating pressure recorder (ASCPR) was developed to solve the issue of gauge drift by using a deadweight calibrator to make campaign-style measurements of the absolute seawater pressure. Pressure gauges alternate between observing the ambient seawater pressure and the deadweight calibrator pressure, which is an accurately known reference value, every 10-20 minutes for several hours. The difference between the known reference pressure and the observed seafloor pressure allows offsets and transients to be corrected to determine the true, absolute seafloor pressure. Absolute seafloor pressure measurements provide a great utility for geodetic deformation studies. The measurements provide instrument-independent, benchmark values that can be used far into the future as epoch points in long-term time series or as important calibration points for other continuous pressure records. The ASCPR was first deployed in Cascadia in 2014 and 2015, when seven concrete seafloor benchmarks were placed along a trench-perpendicular profile extending from 20 km to 105 km off the central Oregon coast. Two benchmarks have ASCPR measurements that span three years, one benchmark spans two years, and four benchmarks span one year. Measurement repeatability is currently 3 to 4 cm, but we anticipate accuracy on the order of 1 cm with improvements to the instrument metrology and processing tidal and non-tidal oceanographic signals.

Traceable Dynamic Calibration of Force Transducers by Primary Means

PubMed Central

Vlajic, Nicholas; Chijioke, Ako

2018-01-01

We describe an apparatus for traceable, dynamic calibration of force transducers using harmonic excitation, and report calibration measurements of force transducers using this apparatus. In this system, the force applied to the transducer is produced by the acceleration of an attached mass, and is determined according to Newton’s second law, F = ma. The acceleration is measured by primary means, using laser interferometry. The capabilities of this system are demonstrated by performing dynamic calibrations of two shear-web-type force transducers up to a frequency of 2 kHz, with an expanded uncertainty below 1.2 %. We give an accounting of all significant sources of uncertainty, including a detailed consideration of the effects of dynamic tilting (rocking), which is a leading source of uncertainty in such harmonic force calibration systems. PMID:29887643

q-bosons and the q-analogue quantized field

NASA Technical Reports Server (NTRS)

Nelson, Charles A.

1995-01-01

The q-analogue coherent states are used to identify physical signatures for the presence of a 1-analogue quantized radiation field in the q-CS classical limits where the absolute value of z is large. In this quantum-optics-like limit, the fractional uncertainties of most physical quantities (momentum, position, amplitude, phase) which characterize the quantum field are O(1). They only vanish as O(1/absolute value of z) when q = 1. However, for the number operator, N, and the N-Hamiltonian for a free q-boson gas, H(sub N) = h(omega)(N + 1/2), the fractional uncertainties do still approach zero. A signature for q-boson counting statistics is that (Delta N)(exp 2)/ (N) approaches 0 as the absolute value of z approaches infinity. Except for its O(1) fractional uncertainty, the q-generalization of the Hermitian phase operator of Pegg and Barnett, phi(sub q), still exhibits normal classical behavior. The standard number-phase uncertainty-relation, Delta(N) Delta phi(sub q) = 1/2, and the approximate commutation relation, (N, phi(sub q)) = i, still hold for the single-mode q-analogue quantized field. So, N and phi(sub q) are almost canonically conjugate operators in the q-CS classical limit. The q-analogue CS's minimize this uncertainty relation for moderate (absolute value of z)(exp 2).

Landsat-7 ETM+ radiometric stability and absolute calibration

USGS Publications Warehouse

Markham, B.L.; Barker, J.L.; Barsi, J.A.; Kaita, E.; Thome, K.J.; Helder, D.L.; Palluconi, Frank Don; Schott, J.R.; Scaramuzza, Pat; ,

2002-01-01

Launched in April 1999, the Landsat-7 ETM+ instrument is in its fourth year of operation. The quality of the acquired calibrated imagery continues to be high, especially with respect to its three most important radiometric performance parameters: reflective band instrument stability to better than ??1%, reflective band absolute calibration to better than ??5%, and thermal band absolute calibration to better than ??0.6 K. The ETM+ instrument has been the most stable of any of the Landsat instruments, in both the reflective and thermal channels. To date, the best on-board calibration source for the reflective bands has been the Full Aperture Solar Calibrator, which has indicated changes of at most -1.8% to -2.0% (95% C.I.) change per year in the ETM+ gain (band 4). However, this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on ground observations, which bound the changes in gain in band 4 at -0.7% to +1.5%. Also, ETM+ stability is indicated by the monitoring of desert targets. These image-based results for four Saharan and Arabian sites, for a collection of 35 scenes over the three years since launch, bound the gain change at -0.7% to +0.5% in band 4. Thermal calibration from ground observations revealed an offset error of +0.31 W/m 2 sr um soon after launch. This offset was corrected within the U. S. ground processing system at EROS Data Center on 21-Dec-00, and since then, the band 6 on-board calibration has indicated changes of at most +0.02% to +0.04% (95% C.I.) per year. The latest ground observations have detected no remaining offset error with an RMS error of ??0.6 K. The stability and absolute calibration of the Landsat-7 ETM+ sensor make it an ideal candidate to be used as a reference source for radiometric cross-calibrating to other land remote sensing satellite systems.

Determination of the reference air kerma rate for 192Ir brachytherapy sources and the related uncertainty.

PubMed

van Dijk, Eduard; Kolkman-Deurloo, Inger-Karine K; Damen, Patricia M G

2004-10-01

Different methods exist to determine the air kerma calibration factor of an ionization chamber for the spectrum of a 192Ir high-dose-rate (HDR) or pulsed-dose-rate (PDR) source. An analysis of two methods to obtain such a calibration factor was performed: (i) the method recommended by [Goetsch et al., Med. Phys. 18, 462-467 (1991)] and (ii) the method employed by the Dutch national standards institute NMi [Petersen et al., Report S-EI-94.01 (NMi, Delft, The Netherlands, 1994)]. This analysis showed a systematic difference on the order of 1% in the determination of the strength of 192Ir HDR and PDR sources depending on the method used for determining the air kerma calibration factor. The definitive significance of the difference between these methods can only be addressed after performing an accurate analysis of the associated uncertainties. For an NE 2561 (or equivalent) ionization chamber and an in-air jig, a typical uncertainty budget of 0.94% was found with the NMi method. The largest contribution in the type-B uncertainty is the uncertainty in the air kerma calibration factor for isotope i, N(i)k, as determined by the primary or secondary standards laboratories. This uncertainty is dominated by the uncertainties in the physical constants for the average mass-energy absorption coefficient ratio and the stopping power ratios. This means that it is not foreseeable that the standards laboratories can decrease the uncertainty in the air kerma calibration factors for ionization chambers in the short term. When the results of the determination of the 192Ir reference air kerma rates in, e.g., different institutes are compared, the uncertainties in the physical constants are the same. To compare the applied techniques, the ratio of the results can be judged by leaving out the uncertainties due to these physical constants. In that case an uncertainty budget of 0.40% (coverage factor=2) should be taken into account. Due to the differences in approach between the method used by NMi and the method recommended by Goetsch et al., an extra type-B uncertainty of 0.9% (k= 1) has to be taken into account when the method of Goetsch et al. is applied. Compared to the uncertainty of 1% (k= 2) found for the air calibration of 192Ir, the difference of 0.9% found is significant.

Dosimetric accuracy of Kodak EDR2 film for IMRT verifications.

PubMed

Childress, Nathan L; Salehpour, Mohammad; Dong, Lei; Bloch, Charles; White, R Allen; Rosen, Isaac I

2005-02-01

Patient-specific intensity-modulated radiotherapy (IMRT) verifications require an accurate two-dimensional dosimeter that is not labor-intensive. We assessed the precision and reproducibility of film calibrations over time, measured the elemental composition of the film, measured the intermittency effect, and measured the dosimetric accuracy and reproducibility of calibrated Kodak EDR2 film for single-beam verifications in a solid water phantom and for full-plan verifications in a Rexolite phantom. Repeated measurements of the film sensitometric curve in a single experiment yielded overall uncertainties in dose of 2.1% local and 0.8% relative to 300 cGy. 547 film calibrations over an 18-month period, exposed to a range of doses from 0 to a maximum of 240 MU or 360 MU and using 6 MV or 18 MV energies, had optical density (OD) standard deviations that were 7%-15% of their average values. This indicates that daily film calibrations are essential when EDR2 film is used to obtain absolute dose results. An elemental analysis of EDR2 film revealed that it contains 60% as much silver and 20% as much bromine as Kodak XV2 film. EDR2 film also has an unusual 1.69:1 silver:halide molar ratio, compared with the XV2 film's 1.02:1 ratio, which may affect its chemical reactions. To test EDR2's intermittency effect, the OD generated by a single 300 MU exposure was compared to the ODs generated by exposing the film 1 MU, 2 MU, and 4 MU at a time to a total of 300 MU. An ion chamber recorded the relative dose of all intermittency measurements to account for machine output variations. Using small MU bursts to expose the film resulted in delivery times of 4 to 14 minutes and lowered the film's OD by approximately 2% for both 6 and 18 MV beams. This effect may result in EDR2 film underestimating absolute doses for patient verifications that require long delivery times. After using a calibration to convert EDR2 film's OD to dose values, film measurements agreed within 2% relative difference and 2 mm criteria to ion chamber measurements for both sliding window and step-and-shoot fluence map verifications. Calibrated film results agreed with ion chamber measurements to within 5 % /2 mm criteria for transverse-plane full-plan verifications, but were consistently low. When properly calibrated, EDR2 film can be an adequate two-dimensional dosimeter for IMRT verifications, although it may underestimate doses in regions with long exposure times.

ScaRaB: first results of absolute and cross calibration

NASA Astrophysics Data System (ADS)

Trémas, Thierry L.; Aznay, Ouahid; Chomette, Olivier

2015-10-01

ScaRaB (SCAnner for RAdiation Budget) is the name of three radiometers whose two first flight models have been launched in 1994 and 1997. The instruments were mounted on-board Russian satellites, METEOR and RESURS. On October 12th 2011, a last model has been launched from the Indian site of Sriharikota. ScaRaB is a passenger of MEGHA-TROPIQUES, an Indo-French joint Satellite Mission for studying the water cycle and energy exchanges in the tropics. ScaRaB is composed of four parallel and independent channels. Channel-2 and channel-3 are considered as the main ones. Channel-1 is dedicated to measure solar radiance (0.5 to 0.7 μm) while channel-4 (10 to 13 μm) is an infrared window. The absolute calibration of ScaRab is assured by internal calibration sources (black bodies and a lamp for channel-1). However, during the commissioning phase, the lamp used for the absolute calibration of channel-1 revealed to be inaccurate. We propose here an alternative calibration method based on terrestrial targets. Due to the spectral range of channel-1, only calibration over desert sites (temporal monitoring) and clouds (cross band) is suitable. Desert sites have been widely used for sensor calibration since they have a stable spectral response over time. Because of their high reflectances, the atmospheric effect on the upward radiance is relatively minimal. In addition, they are spatially uniform. Their temporal instability without atmospheric correction has been determined to be less than 1-2% over a year. Very-high-altitude (10 km) bright clouds are good validation targets in the visible and near-infrared spectra because of their high spectrally consistent reflectance. If the clouds are very high, there is no need to correct aerosol scattering and water vapor absorption as both aerosol and water vapor are distributed near the surface. Only Rayleigh scattering and ozone absorption need to be considered. This method has been found to give a 4% uncertainty. Radiometric cross calibration of Earth observation sensors is a crucial need to guarantee or quantify the consistency of measurements from different sensors. ScaRaB is compatible with CERES mission. Two main spectral bands are measured by the radiometer: A short-wave channel (0.2 to 4 μm) dedicated to solar fluxes and a Total channel (0.2 to 200 μm) for fluxes combining the infrared earth radiance and the albedo. The earth long-wave radiance is isolated by subtracting the short-wave channel to the Total channel. Both Earth Radiation Budget missions (CERES and ScaRaB) have the same specification: to provide an accuracy of ~1% in the measurement of short-wave and long-wave radiances and an estimation of the short-wave and long-wave fluxes less than 10 W/m2. We use the CERES PAPS and Cross-Track SSF datasets for direct radiances and fluxes comparisons during two validation phases. The first one occurred during April 17th to June 8th (51 days) in 2012 and the second one occurred between March 22th and May 31st 2015. The first validation campaign has been held with the CERES team using the Terra FM2 data. The CERES PAPS mode was used to align the swath scan, in order to increase the collocated pixels between the two instruments. This campaign allowed us to validate the ScaRaB radiances and to refine the error budget. The second validation campaign aims to provide a temporal monitoring of ScaRab calibration.

Multi-objective calibration and uncertainty analysis of hydrologic models; A comparative study between formal and informal methods

NASA Astrophysics Data System (ADS)

Shafii, M.; Tolson, B.; Matott, L. S.

2012-04-01

Hydrologic modeling has benefited from significant developments over the past two decades. This has resulted in building of higher levels of complexity into hydrologic models, which eventually makes the model evaluation process (parameter estimation via calibration and uncertainty analysis) more challenging. In order to avoid unreasonable parameter estimates, many researchers have suggested implementation of multi-criteria calibration schemes. Furthermore, for predictive hydrologic models to be useful, proper consideration of uncertainty is essential. Consequently, recent research has emphasized comprehensive model assessment procedures in which multi-criteria parameter estimation is combined with statistically-based uncertainty analysis routines such as Bayesian inference using Markov Chain Monte Carlo (MCMC) sampling. Such a procedure relies on the use of formal likelihood functions based on statistical assumptions, and moreover, the Bayesian inference structured on MCMC samplers requires a considerably large number of simulations. Due to these issues, especially in complex non-linear hydrological models, a variety of alternative informal approaches have been proposed for uncertainty analysis in the multi-criteria context. This study aims at exploring a number of such informal uncertainty analysis techniques in multi-criteria calibration of hydrological models. The informal methods addressed in this study are (i) Pareto optimality which quantifies the parameter uncertainty using the Pareto solutions, (ii) DDS-AU which uses the weighted sum of objective functions to derive the prediction limits, and (iii) GLUE which describes the total uncertainty through identification of behavioral solutions. The main objective is to compare such methods with MCMC-based Bayesian inference with respect to factors such as computational burden, and predictive capacity, which are evaluated based on multiple comparative measures. The measures for comparison are calculated both for calibration and evaluation periods. The uncertainty analysis methodologies are applied to a simple 5-parameter rainfall-runoff model, called HYMOD.

Ultra-portable field transfer radiometer for vicarious calibration of earth imaging sensors

NASA Astrophysics Data System (ADS)

Thome, Kurtis; Wenny, Brian; Anderson, Nikolaus; McCorkel, Joel; Czapla-Myers, Jeffrey; Biggar, Stuart

2018-06-01

A small portable transfer radiometer has been developed as part of an effort to ensure the quality of upwelling radiance from test sites used for vicarious calibration in the solar reflective. The test sites are used to predict top-of-atmosphere reflectance relying on ground-based measurements of the atmosphere and surface. The portable transfer radiometer is designed for one-person operation for on-site field calibration of instrumentation used to determine ground-leaving radiance. The current work describes the detector- and source-based radiometric calibration of the transfer radiometer highlighting the expected accuracy and SI-traceability. The results indicate differences between the detector-based and source-based results greater than the combined uncertainties of the approaches. Results from recent field deployments of the transfer radiometer using a solar radiation based calibration agree with the source-based laboratory calibration within the combined uncertainties of the methods. The detector-based results show a significant difference to the solar-based calibration. The source-based calibration is used as the basis for a radiance-based calibration of the Landsat-8 Operational Land Imager that agrees with the OLI calibration to within the uncertainties of the methods.

Development of a 300 L Calibration Bath for Oceanographic Thermometers

NASA Astrophysics Data System (ADS)

Baba, S.; Yamazawa, K.; Nakano, T.; Saito, I.; Tamba, J.; Wakimoto, T.; Katoh, K.

2017-11-01

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has been developing a 300 L calibration bath to calibrate 24 oceanographic thermometers (OT) simultaneously and thereby reduce the calibration work load necessary to service more than 180 OT every year. This study investigated characteristics of the developed 300 L calibration bath using a SBE 3plus thermometer produced by an OT manufacturer. We also used 11 thermistor thermometers that were calibrated to be traceable to the international temperature scale of 1990 (ITS-90) within 1 mK of standard uncertainty through collaboration of JAMSTEC and NMIJ/AIST. Results show that the time stability of temperature of the developed bath was within ± 1 mK. Furthermore, the temperature uniformity was ± 1.3 mK. The expanded uncertainty (k=2) components for the characteristics of the developed 300 L calibration bath were estimated as 2.9 mK, which is much less than the value of 10 mK: the required specification for uncertainty of calibration for the OT. These results demonstrated the utility of this 300 L calibration bath as a device for use with a new calibration system.

Analysis of the calibration methods and error propagation for the sensitivity S and the cooling time constant τc of the gold metal foil bolometers

NASA Astrophysics Data System (ADS)

Murari, A.; Cecconello, M.; Marrelli, L.; Mast, K. F.

2004-08-01

Bolometers are radiation sensors designed to have a spectral response as constant as possible in the region of interest. In high-temperature plasmas, the main radiation output is in the ultraviolet and SXR part of the spectrum and the metal foil bolometers are special detectors developed for this interval. For such sensors, as in general for all bolometers, the absolute calibration is a crucial issue. This problem becomes particularly severe when, like in nuclear fusion, the sensors are not easily accessible. In this article, a detailed description of the in situ calibration methods for the bolometer sensitivity S and the cooling time τc, the two essential parameters characterizing the behavior of the sensor, is provided and an estimate of the uncertainties for both constants is presented. The sensitivity S is determined via an electrical calibration, in which the effect of the cables connecting the bolometers to the powering circuitry is taken into account leading to an effective estimate for S. Experimental measurements confirming the quality of the adopted coaxial cable modelling are reported. The cooling time constant τc is calculated via an optical calibration, in which the bolometer is stimulated by a light-emitting diode. The behavior of τc in a broad pressure range is investigated, showing that it does not depend upon this quantity up until 10-2 mbar, well above the standard operating conditions of many applications. The described methods were tested on 36 bolometric channels of RFX tomography, providing a significant statistical basis for present applications and future developments of both the calibration procedures and the detectors.

Measuring Broadband IR Irradiance in the Direct Solar Beam (Poster)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, I.; Konings, J.; Xie, Y.

Solar and atmospheric science radiometers, e.g. pyranometers, pyrheliometers, and photovoltaic cells are calibrated with traceability to a consensus reference, which is maintained by Absolute Cavity Radiometers (ACRs). The ACR is an open cavity with no window, developed to measure extended broadband direct solar irradiance beyond the ultraviolet and infrared bands below and above 0.2 micrometers and 50 micrometers, respectively. On the other hand, pyranometers and pyrheliometers are developed to measure broadband shortwave irradiance from approximately 0.3 micrometers to 3 micrcometers, while the present photovoltaic cells are limited to approximately 0.3 micrometers to 1 micrometers. The broadband mismatch of ACR versusmore » such radiometers causes discrepancy in radiometers' calibration methods that has not been discussed or addressed in the solar and atmospheric science literature. Pyrgeometers are also used for solar and atmospheric science applications and calibrated with traceability to consensus reference, yet calibrated during nighttime only, because no consensus reference has yet been established for the daytime longwave irradiance. This poster shows a method to measure the broadband IR irradiance in the direct solar beam from 3 micrometers to 50 micrometers, as first step that might be used to help develop calibration methods to address the mismatch between broadband ACR and shortwave radiometers, and the lack of a daytime reference for pyrgeometers. The irradiance was measured from sunrise to sunset for 5 days when the sun disk was cloudless; the irradiance varied from approximately 1 Wm-2 to 16 Wm-2 for solar zenith angle from 80 degres to 16 degrees respectively; estimated uncertainty is 1.5 Wm-2.« less

Response of hydrology to climate change in the southern Appalachian mountains using Bayesian inference

Treesearch

Wei Wu; James S. Clark; James M. Vose

2012-01-01

Predicting long-term consequences of climate change on hydrologic processes has been limited due to the needs to accommodate the uncertainties in hydrological measurements for calibration, and to account for the uncertainties in the models that would ingest those calibrations and uncertainties in climate predictions as basis for hydrological predictions. We implemented...

The visible absorption spectrum of NO3 measured by high-resolution Fourier transform spectroscopy

NASA Astrophysics Data System (ADS)

Orphal, J.; Fellows, C. E.; Flaud, P.-M.

2003-02-01

The visible absorption spectrum of the nitrate radical NO3 has been measured using high-resolution Fourier transform spectroscopy. The spectrum was recorded at 294 K using a resolution of 0.6 cm-1 (corresponding to 0.026 nm at 662 nm) and covers the 12600-21500 cm-1 region (465-794 nm). Compared to absorption spectra of NO3 recorded previously, the new data show improvements concerning absolute wavelength calibration (uncertainty 0.02 cm-1), and spectral resolution. A new interpretation and model of the temperature dependence of the strong (0-0) band around 662 nm are proposed. The results are important for long-path tropospheric absorption measurements of NO3 and optical remote sensing of the Earth's atmosphere from space.

The performance of the CASTOR calorimeter during LHC Run 2

NASA Astrophysics Data System (ADS)

van de Klundert, Merijn H. F.; CMS Collaboration

2017-11-01

CASTOR is an electromagnetic and hadronic tungsten-quartz sampling Cerenkov calorimeter located at the Compact Muon Solenoid experiment at the Large Hadron Collider. The detector has pseudorapidity borders at -5.2 and -6.6. An overview is presented on the various aspects of CASTOR’s performance and their relations during LHC Run 2. The equalisation of CASTOR’s channels is performed using beam-halo muons. Thereafter, CASTOR’s pedestal spectrum is studied. It is shown that noise estimates which are extracted using a fit, give on average a 10% lower threshold than statistical estimates. Gain correction factors, which are needed for the intercalibration, are obtained using a statistical, in-situ applicable method. The results of this method are shown to be reasonably consistent with laboratory measurements. Penultimately the absolute calibration is discussed, with emphasis on the relation between the scale uncertainty and CASTOR’s alignment. It is shown that the alignment’s contribution to the systematic uncertainty is decreased by over 50% in LHC Run 2 w.r.t. LHC Run 1. Finally generalisations of the conclusions to other subsystems and future improvements are discussed.

Consistency between real and synthetic fast-ion measurements at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Rasmussen, J.; Nielsen, S. K.; Stejner, M.; Geiger, B.; Salewski, M.; Jacobsen, A. S.; Korsholm, S. B.; Leipold, F.; Michelsen, P. K.; Moseev, D.; Schubert, M.; Stober, J.; Tardini, G.; Wagner, D.; The ASDEX Upgrade Team

2015-07-01

Internally consistent characterization of the properties of the fast-ion distribution from multiple diagnostics is a prerequisite for obtaining a full understanding of fast-ion behavior in tokamak plasmas. Here we benchmark several absolutely-calibrated core fast-ion diagnostics at ASDEX Upgrade by comparing fast-ion measurements from collective Thomson scattering, fast-ion {{\\text{D}}α} spectroscopy, and neutron rate detectors with numerical predictions from the TRANSP/NUBEAM transport code. We also study the sensitivity of the theoretical predictions to uncertainties in the plasma kinetic profiles. We find that theory and measurements generally agree within these uncertainties for all three diagnostics during heating phases with either one or two neutral beam injection sources. This suggests that the measurements can be described by the same model assuming classical slowing down of fast ions. Since the three diagnostics in the adopted configurations probe partially overlapping regions in fast-ion velocity space, this is also consistent with good internal agreement among the measurements themselves. Hence, our results support the feasibility of combining multiple diagnostics at ASDEX Upgrade to reconstruct the fast-ion distribution function in 2D velocity space.

A suggestion for computing objective function in model calibration

USGS Publications Warehouse

Wu, Yiping; Liu, Shuguang

2014-01-01

A parameter-optimization process (model calibration) is usually required for numerical model applications, which involves the use of an objective function to determine the model cost (model-data errors). The sum of square errors (SSR) has been widely adopted as the objective function in various optimization procedures. However, ‘square error’ calculation was found to be more sensitive to extreme or high values. Thus, we proposed that the sum of absolute errors (SAR) may be a better option than SSR for model calibration. To test this hypothesis, we used two case studies—a hydrological model calibration and a biogeochemical model calibration—to investigate the behavior of a group of potential objective functions: SSR, SAR, sum of squared relative deviation (SSRD), and sum of absolute relative deviation (SARD). Mathematical evaluation of model performance demonstrates that ‘absolute error’ (SAR and SARD) are superior to ‘square error’ (SSR and SSRD) in calculating objective function for model calibration, and SAR behaved the best (with the least error and highest efficiency). This study suggests that SSR might be overly used in real applications, and SAR may be a reasonable choice in common optimization implementations without emphasizing either high or low values (e.g., modeling for supporting resources management).

Spectral Irradiance Calibration in the Infrared. 7. 5-14 microns Spectroscopy of the Asteroids Ceres, Vesta, and Pallas

NASA Technical Reports Server (NTRS)

Cohen, Martin; Witteborn, Fred C.; Roush, Ted; Bregman, Jesse; Wooden, Diane

1996-01-01

We describe our efforts to seek "closure" in our infrared absolute calibration scheme by comparing spectra of asteroids, absolutely calibrated through reference stars, with "Standard Thermal Models" and "Thermophysical Models" for these bodies. Our use of continuous 5-14 microns airborne spectra provides complete sampling of the rise to, and peak, of the infrared spectral energy distribution and constrains these models. Such models currently support the absolute calibration of ISO-PHOT at far-infrared wave- lengths (as far as 300 microns), and contribute to that of the Mid-Infrared Spectrometer on the "Infrared Telescope in Space" in the 6-12 microns region. The best match to our observed spectra of Ceres and Vesta is a, standard thermal model using a beaming factor of unity. We also report the presence of three emissivity features in Ceres which may complicate the traditional model extrapolation to the far-infrared from contemporaneous ground-based N-band photometry that is used to support calibration of, for example, ISO-PHOT. While identification of specific materials that cause these features is not made, we discuss families of minerals that may be responsible.

Absolute laser-intensity measurement and online monitor calibration using a calorimeter at a soft X-ray free-electron laser beamline in SACLA

NASA Astrophysics Data System (ADS)

Tanaka, Takahiro; Kato, Masahiro; Saito, Norio; Owada, Shigeki; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya

2018-06-01

This paper reports measurement of the absolute intensity of free-electron laser (FEL) and calibration of online intensity monitors for a brand-new FEL beamline BL1 at SPring-8 Angstrom Compact free-electron LAser (SACLA) in Japan. To measure the absolute intensity of FEL, we used a room-temperature calorimeter originally developed for FELs in the hard X-ray range. By using the calorimeter, we calibrated online intensity monitors of BL1, gas monitors (GMs), based on the photoionization of argon gas, in the photon energy range from 25 eV to 150 eV. A good correlation between signals obtained from the calorimeter and GMs was observed in the pulse energy range from 1 μJ to 100 μJ, where the upper limit is nearly equal to the maximum pulse energy at BL1. Moreover, the calibration result of the GMs, measured in terms of the spectral responsivity, demonstrates a characteristic photon-energy dependence owing to the occurrence of the Cooper minimum in the total ionization cross-section of argon gas. These results validate the feasibility of employing the room-temperature calorimeter in the measurement of absolute intensity of FELs over the specified photon energy range.

Stormwater quality modelling in combined sewers: calibration and uncertainty analysis.

PubMed

Kanso, A; Chebbo, G; Tassin, B

2005-01-01

Estimating the level of uncertainty in urban stormwater quality models is vital for their utilization. This paper presents the results of application of a Monte Carlo Markov Chain method based on the Bayesian theory for the calibration and uncertainty analysis of a storm water quality model commonly used in available software. The tested model uses a hydrologic/hydrodynamic scheme to estimate the accumulation, the erosion and the transport of pollutants on surfaces and in sewers. It was calibrated for four different initial conditions of in-sewer deposits. Calibration results showed large variability in the model's responses in function of the initial conditions. They demonstrated that the model's predictive capacity is very low.

Calibration of hydrometers

NASA Astrophysics Data System (ADS)

Lorefice, Salvatore; Malengo, Andrea

2006-10-01

After a brief description of the different methods employed in periodic calibration of hydrometers used in most cases to measure the density of liquids in the range between 500 kg m-3 and 2000 kg m-3, particular emphasis is given to the multipoint procedure based on hydrostatic weighing, known as well as Cuckow's method. The features of the calibration apparatus and the procedure used at the INRiM (formerly IMGC-CNR) density laboratory have been considered to assess all relevant contributions involved in the calibration of different kinds of hydrometers. The uncertainty is strongly dependent on the kind of hydrometer; in particular, the results highlight the importance of the density of the reference buoyant liquid, the temperature of calibration and the skill of operator in the reading of the scale in the whole assessment of the uncertainty. It is also interesting to realize that for high-resolution hydrometers (division of 0.1 kg m-3), the uncertainty contribution of the density of the reference liquid is the main source of the total uncertainty, but its importance falls under about 50% for hydrometers with a division of 0.5 kg m-3 and becomes somewhat negligible for hydrometers with a division of 1 kg m-3, for which the reading uncertainty is the predominant part of the total uncertainty. At present the best INRiM result is obtained with commercially available hydrometers having a scale division of 0.1 kg m-3, for which the relative uncertainty is about 12 × 10-6.

HST/WFC3 flux calibration ladder: Vega

NASA Astrophysics Data System (ADS)

Deustua, Susana E.; Bohlin, Ralph; Pirzkal, Nor; MacKenty, John

2014-08-01

Vega is one of only a few stars calibrated against an SI-traceable blackbody, and is the historical flux standard. Photometric zeropoints of the Hubble Space Telescope's instruments rely on Vega, through the transfer of its calibration via stellar atmosphere models to the suite of standard stars. HST's recently implemented scan mode has enabled us to develop a path to an absolute SI traceable calibration for HST IR observations. To fill in the crucial gap between 0.9 and 1.7 micron in the absolute calibration, we acquired -1st order spectra of Vega with the two WFC3 infrared grisms. At the same time, we have improved the calibration of the -1st orders of both WFC3 IR grisms, as well as extended the dynamic range of WFC3 science observations by a factor of 10000. We describe our progress to date on the WFC3 `flux calibration ladder' project to provide currently needed accurate zeropoint measurements in the IR

Tunable Diode Laser Absorption Spectroscopy Sensor for Calibration Free Humidity Measurements in Pure Methane and Low CO2 Natural Gas.

PubMed

Nwaboh, Javis Anyangwe; Pratzler, Sonja; Werhahn, Olav; Ebert, Volker

2017-05-01

We report a new direct tunable diode laser absorption spectroscopy (dTDLAS) sensor for absolute measurements of H 2 O in methane, ethane, propane, and low CO 2 natural gas. The sensor is operated with a 2.7 µm DFB laser, equipped with a high pressure single pass gas cell, and used to measure H 2 O amount of substance fractions in the range of 0.31-25 000 µmol/mol. Operating total gas pressures are up to 5000 hPa. The sensor has been characterized, addressing the traceability of the spectrometric results to the SI and the evaluation of the combined uncertainty, following the guide to the expression of uncertainty in measurement (GUM). The relative reproducibility of H 2 O amount of substance fraction measurements at 87 µmol/mol is 0.26% (0.23 µmol/mol). The maximum precision of the sensor was determined using a H 2 O in methane mixture, and found to be 40 nmol/mol for a time resolution of 100 s. This corresponds to a normalized detection limit of 330 nmol mol -1 ·m Hz -1/2 . The relative combined uncertainty of H 2 O amount fraction measurements delivered by the sensor is 1.2%.

Sentinel-2: State of the Image Quality Calibration at the End of the Commissioning

NASA Astrophysics Data System (ADS)

Tremas, Thierry; Lonjou, Vincent; Lacherade, Sophie; Gaudel-Vacaresse, Angelique; Languille, Florie

2016-08-01

This article summarizes the activity of CNES during the In Orbit Calibration Phase of Sentinel 2A as well as the transfer of production of GIPP (Ground Image Processing Parameters) from CNES to ESRIN. The state of the main calibration parameters and performances, few months before PDGS is declared fully operational, are listed and explained.In radiometry a special attention is paid to the absolute calibration using the on-board diffuser, and the vicarious calibration methods using instrumented or statistically well characterized sites and inter- comparisons with other sensors. Regarding geometry, the presentation focuses on the performances of absolute location with and without reference points. The requirements of multi-band and multi-temporal registration are exposed. Finally, the construction and the rule of the GRI (Ground Reference Images) in the future are explained.

Impact of Pitot tube calibration on the uncertainty of water flow rate measurement

NASA Astrophysics Data System (ADS)

de Oliveira Buscarini, Icaro; Costa Barsaglini, Andre; Saiz Jabardo, Paulo Jose; Massami Taira, Nilson; Nader, Gilder

2015-10-01

Water utility companies often use Cole type Pitot tubes to map velocity profiles and thus measure flow rate. Frequent monitoring and measurement of flow rate is an important step in identifying leaks and other types of losses. In Brazil losses as high as 42% are common and in some places even higher values are found. When using Cole type Pitot tubes to measure the flow rate, the uncertainty of the calibration coefficient (Cd) is a major component of the overall flow rate measurement uncertainty. A common practice is to employ the usual value Cd = 0.869, in use since Cole proposed his Pitot tube in 1896. Analysis of 414 calibrations of Cole type Pitot tubes show that Cd varies considerably and values as high 0.020 for the expanded uncertainty are common. Combined with other uncertainty sources, the overall velocity measurement uncertainty is 0.02, increasing flowrate measurement uncertainty by 1.5% which, for the Sao Paulo metropolitan area (Brazil) corresponds to 3.5 × 107 m3/year.

Improved Strategies and Optimization of Calibration Models for Real-time PCR Absolute Quantification

EPA Science Inventory

Real-time PCR absolute quantification applications rely on the use of standard curves to make estimates of DNA target concentrations in unknown samples. Traditional absolute quantification approaches dictate that a standard curve must accompany each experimental run. However, t...

Cantilever spring constant calibration using laser Doppler vibrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohler, Benjamin

2007-06-15

Uncertainty in cantilever spring constants is a critical issue in atomic force microscopy (AFM) force measurements. Though numerous methods exist for calibrating cantilever spring constants, the accuracy of these methods can be limited by both the physical models themselves as well as uncertainties in their experimental implementation. Here we report the results from two of the most common calibration methods, the thermal tune method and the Sader method. These were implemented on a standard AFM system as well as using laser Doppler vibrometry (LDV). Using LDV eliminates some uncertainties associated with optical lever detection on an AFM. It also offersmore » considerably higher signal to noise deflection measurements. We find that AFM and LDV result in similar uncertainty in the calibrated spring constants, about 5%, using either the thermal tune or Sader methods provided that certain limitations of the methods and instrumentation are observed.« less

Evaluation of the Long-Term Stability and Temperature Coefficient of Dew-Point Hygrometers

NASA Astrophysics Data System (ADS)

Benyon, R.; Vicente, T.; Hernández, P.; De Rivas, L.; Conde, F.

2012-09-01

The continuous quest for improved specifications of optical dew-point hygrometers has raised customer expectations on the performance of these devices. In the absence of a long calibration history, users with a limited prior experience in the measurement of humidity, place reliance on manufacturer specifications to estimate long-term stability. While this might be reasonable in the case of measurement of electrical quantities, in humidity it can lead to optimistic estimations of uncertainty. This article reports a study of the long-term stability of some hygrometers and the analysis of their performance as monitored through regular calibration. The results of the investigations provide some typical, realistic uncertainties associated with the long-term stability of instruments used in calibration and testing laboratories. Together, these uncertainties can help in establishing initial contributions in uncertainty budgets, as well as in setting the minimum calibration requirements, based on the evaluation of dominant influence quantities.

Link calibration against receiver calibration: an assessment of GPS time transfer uncertainties

NASA Astrophysics Data System (ADS)

Rovera, G. D.; Torre, J.-M.; Sherwood, R.; Abgrall, M.; Courde, C.; Laas-Bourez, M.; Uhrich, P.

2014-10-01

We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). Relative calibration estimates the delay of equipment or the delay of a time transfer link with respect to reference equipment. It is based on the circulation of some travelling GPS equipment between the stations in the network, against which the local equipment is measured. Two techniques can be considered: first a station calibration by the computation of the hardware delays of the local GPS equipment; second the computation of a global hardware delay offset for the time transfer between the reference points of two remote time scales. This last technique is called a ‘link’ calibration, with respect to the other one, which is a ‘receiver’ calibration. The two techniques require different measurements on site, which change the uncertainty budgets, and we discuss this and related issues. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. The travelling equipment comprised two GPS receivers of different types, along with the required signal generator and distribution amplifier, and one time interval counter. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.

Red clump stars and Gaia: calibration of the standard candle using a hierarchical probabilistic model

NASA Astrophysics Data System (ADS)

Hawkins, Keith; Leistedt, Boris; Bovy, Jo; Hogg, David W.

2017-10-01

Distances to individual stars in our own Galaxy are critical in order to piece together the nature of its velocity and spatial structure. Core helium burning red clump (RC) stars have similar luminosities, are abundant throughout the Galaxy and thus constitute good standard candles. We build a hierarchical probabilistic model to quantify the quality of RC stars as standard candles using parallax measurements from the first Gaia data release. A unique aspect of our methodology is to fully account for (and marginalize over) parallax, photometry and dust correction uncertainties, which lead to more robust results than standard approaches. We determine the absolute magnitude and intrinsic dispersion of the RC in 2MASS bands J, H, Ks, Gaia G band and WISE bands W1, W2, W3 and W4. We find that the absolute magnitude of the RC is -1.61 ± 0.01 (in Ks), +0.44 ± 0.01 (in G), -0.93 ± 0.01 (in J), -1.46 ± 0.01 (in H), -1.68 ± 0.02 (in W1), -1.69 ± 0.02 (in W2), -1.67 ± 0.02 (in W3) and -1.76 ± 0.01 mag (in W4). The mean intrinsic dispersion is ˜0.17 ± 0.03 mag across all bands (yielding a typical distance precision of ˜8 per cent). Thus RC stars are reliable and precise standard candles. In addition, we have also re-calibrated the zero-point of the absolute magnitude of the RC in each band, which provides a benchmark for future studies to estimate distances to RC stars. Finally, the parallax error shrinkage in the hierarchical model outlined in this work can be used to obtain more precise parallaxes than Gaia for the most distant RC stars across the Galaxy.

A novel validation and calibration method for motion capture systems based on micro-triangulation.

PubMed

Nagymáté, Gergely; Tuchband, Tamás; Kiss, Rita M

2018-06-06

Motion capture systems are widely used to measure human kinematics. Nevertheless, users must consider system errors when evaluating their results. Most validation techniques for these systems are based on relative distance and displacement measurements. In contrast, our study aimed to analyse the absolute volume accuracy of optical motion capture systems by means of engineering surveying reference measurement of the marker coordinates (uncertainty: 0.75 mm). The method is exemplified on an 18 camera OptiTrack Flex13 motion capture system. The absolute accuracy was defined by the root mean square error (RMSE) between the coordinates measured by the camera system and by engineering surveying (micro-triangulation). The original RMSE of 1.82 mm due to scaling error was managed to be reduced to 0.77 mm while the correlation of errors to their distance from the origin reduced from 0.855 to 0.209. A simply feasible but less accurate absolute accuracy compensation method using tape measure on large distances was also tested, which resulted in similar scaling compensation compared to the surveying method or direct wand size compensation by a high precision 3D scanner. The presented validation methods can be less precise in some respects as compared to previous techniques, but they address an error type, which has not been and cannot be studied with the previous validation methods. Copyright © 2018 Elsevier Ltd. All rights reserved.

Absolute detector calibration using twin beams.

PubMed

Peřina, Jan; Haderka, Ondřej; Michálek, Václav; Hamar, Martin

2012-07-01

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.

An evaluation of the accuracy of geomagnetic data obtained from an unattended, automated, quasi-absolute station

USGS Publications Warehouse

Herzog, D.C.

1990-01-01

A comparison is made of geomagnetic calibration data obtained from a high-sensitivity proton magnetometer enclosed within an orthogonal bias coil system, with data obtained from standard procedures at a mid-latitude U.S. Geological Survey magnetic observatory using a quartz horizontal magnetometer, a Ruska magnetometer, and a total field magnetometer. The orthogonal coil arrangement is used with the proton magnetometer to provide Deflected-Inclination-Deflected-Declination (DIDD) data from which quasi-absolute values of declination, horizontal intensity, and vertical intensity can be derived. Vector magnetometers provide the ordinate values to yield baseline calibrations for both the DIDD and standard observatory processes. Results obtained from a prototype system over a period of several months indicate that the DIDD unit can furnish adequate absolute field values for maintaining observatory calibration data, thus providing baseline control for unattended, remote stations. ?? 1990.

Absolute brightness temperature measurements at 3.5-mm wavelength. [of sun, Venus, Jupiter and Saturn

NASA Technical Reports Server (NTRS)

Ulich, B. L.; Rhodes, P. J.; Davis, J. H.; Hollis, J. M.

1980-01-01

Careful observations have been made at 86.1 GHz to derive the absolute brightness temperatures of the sun (7914 + or - 192 K), Venus (357.5 + or - 13.1 K), Jupiter (179.4 + or - 4.7 K), and Saturn (153.4 + or - 4.8 K) with a standard error of about three percent. This is a significant improvement in accuracy over previous results at millimeter wavelengths. A stable transmitter and novel superheterodyne receiver were constructed and used to determine the effective collecting area of the Millimeter Wave Observatory (MWO) 4.9-m antenna relative to a previously calibrated standard gain horn. The thermal scale was set by calibrating the radiometer with carefully constructed and tested hot and cold loads. The brightness temperatures may be used to establish an absolute calibration scale and to determine the antenna aperture and beam efficiencies of other radio telescopes at 3.5-mm wavelength.

Absolute Calibration of the AXAF Telescope Effective Area

NASA Technical Reports Server (NTRS)

Kellogg, E.; Cohen, L.; Edgar, R.; Evans, I.; Freeman, M.; Gaetz, T.; Jerius, D.; McDermott, W. C.; McKinnon, P.; Murray, S.;

Radiometer Calibration and Characterization (RCC) User's Manual: Windows Version 4.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreas, Afshin M.; Wilcox, Stephen M.

2016-02-29

The Radiometer Calibration and Characterization (RCC) software is a data acquisition and data archival system for performing Broadband Outdoor Radiometer Calibrations (BORCAL). RCC provides a unique method of calibrating broadband atmospheric longwave and solar shortwave radiometers using techniques that reduce measurement uncertainty and better characterize a radiometer's response profile. The RCC software automatically monitors and controls many of the components that contribute to uncertainty in an instrument's responsivity. This is a user's manual and guide to the RCC software.

Refinement of Protocols for Measuring the Apparent Optical Properties of Seawater. Chapter 8

NASA Technical Reports Server (NTRS)

Hooker, Stanford B.; Zibordi, Giuseppe; Berthon, Jean-Francois; Nirek, Andre; Antoine, David

2003-01-01

Ocean color satellite missions, like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) or the Moderate Resolution Imaging Spectroradiometer (MODIS) projects, are tasked with acquiring a global ocean color data set, validating and monitoring the accuracy and quality of the data, processing the radiometric data into geophysical units using a set of atmospheric and bio-optical algorithms, and distributing the final products to the scientific community. The long-standing requirement of the SeaWiFS Project, for example, is to produce spectral water-leaving radiances, LW(lambda), to within 5% absolute (lambda denotes wavelength) and chlorophyll a concentrations to within 35% (Hooker and Esaias 1993), and most ocean color sensors have the same or similar requirements. Although a diverse set of activities are required to ensure the accuracy requirements are met (Hooker and McClain 2000), the perspective here is with field observations. The accurate determination of upper ocean apparent optical properties (AOPs) is essential for the vicarious calibration of ocean color data and the validation of the derived data products, because the sea-truth measurements are used to evaluate the satellite observations (Hooker and McClain 2000). The uncertainties with in situ AOP measurements have various sources: a) the sampling procedures used in the field, including the environmental conditions encountered; b) the absolute characterization of the radiometers in the laboratory; c) the conversion of the light signals to geophysical units in a processing scheme, and d) the stability of the radiometers in the harsh environment they are subjected to during transport and use. Assuming ideal environmental conditions, so this aspect can be neglected, the SeaWiFS ground-truth uncertainty budget can only be satisfied if each uncertainty is on the order of 1-2%, or what is generally referred to as 1% radiometry. In recent years, progress has been made in estimating the magnitude of some of these uncertainties and in defining procedures for minimizing them. For the SeaWiFS Project, the first step was to convene a workshop to draft the SeaWiFS Ocean Optics Protocols (hereafter referred to as the Protocols). The Protocols initially adhered to the Joint Global Ocean Flux Study (JGOFS) sampling procedures (JGOFS 1991) and defined the standards for optical measurements to be used in SeaWiFS calibration and validation activities (Mueller and Austin 1992). Over time, the Protocols were revised (Mueller and Austin 1995), and then recurringly updated on essentially an annual basis (Mueller 2000, 2002, and 2003) as part of the Sensor Inter-comparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) project. 98

Calibration procedure for a laser triangulation scanner with uncertainty evaluation

NASA Astrophysics Data System (ADS)

Genta, Gianfranco; Minetola, Paolo; Barbato, Giulio

2016-11-01

Most of low cost 3D scanning devices that are nowadays available on the market are sold without a user calibration procedure to correct measurement errors related to changes in environmental conditions. In addition, there is no specific international standard defining a procedure to check the performance of a 3D scanner along time. This paper aims at detailing a thorough methodology to calibrate a 3D scanner and assess its measurement uncertainty. The proposed procedure is based on the use of a reference ball plate and applied to a triangulation laser scanner. Experimental results show that the metrological performance of the instrument can be greatly improved by the application of the calibration procedure that corrects systematic errors and reduces the device's measurement uncertainty.

A Novel Non-Intrusive Method to Resolve the Thermal-Dome-Effect of Pyranometers: Radiometric Calibration and Implications

NASA Technical Reports Server (NTRS)

Ji, Qiang; Tsay, Si-Chee; Lau, K. M.; Hansell, R. A.; Butler, J. J.; Cooper, J. W.

2011-01-01

Traditionally the calibration equation for pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile's output voltage; therefore only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer's thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a-few-percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST-traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and non-linearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol's direct-radiative effect using field measurements with and without considering the pyranometer's thermal effect. The results of radiative transfer model simulation show that a pyranometer's thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere.

A Novel Nonintrusive Method to Resolve the Thermal Dome Effect of Pyranometers: Radiometric Calibration and Implications

NASA Technical Reports Server (NTRS)

Ji. Q.; Tsay, S.-C.; Lau, K. M.; Hansell, R. A.; Butler, J. J.; Cooper, J. W.

2011-01-01

Traditionally the calibration equation for pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile s output voltage; therefore, only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer s thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a few percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and nonlinearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol s direct radiative effect using field measurements with and without considering the pyranometer s thermal effect. The results of radiative transfer model simulation show that a pyranometer s thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere.

Integrating river incision rates over timescales in the Ecuadorian Andes: from uplift history to current erosion rates

NASA Astrophysics Data System (ADS)

Campforts, Benjamin; Govers, Gerard; Vanacker, Veerle; Tenorio, Gustavo

2013-04-01

River profile development is studied at different timescales, from the response to uplift over millions of years over steady state erosion rates over millennia to the response to a single event, such as a major landslide. At present, few attempts have been made to compare data obtained over various timescales. Therefore we do not know to what extent data and model results are compatible: do long-term river profile development models yield erosion rates that are compatible with information obtained over shorter time spans, both in terms of absolute rates and spatial patterns or not? Such comparisons could provide crucial insights into the nature of river development and allow us to assess the confidence we may have when predicting river response at different timescales (e.g. Kirchner et al., 2001). A major issue hampering such comparison is the uncertainty involved in the calibration of long-term river profile development models. Furthermore, calibration data on different timescales are rarely available for a specific region. In this research, we set up a river profile development model similar to the one used by Roberts & White (2010) and successfully calibrated it for the northern Ecuadorian Andes using detailed uplift and sedimentological data. Subsequently we used the calibrated model to simulate river profile development in the southern Ecuadorian Andes. The calibrated model allows to reconstruct the Andean uplift history in southern Ecuador, which is characterized by a very strong uplift phase during the last 5 My. Erosion rates derived from the modeled river incision rates were then compared with 10Be derived basin-wide erosion rates for a series of basins within the study area. We found that the model-inferred erosion rates for the last millennia are broadly compatible with the cosmogenic derived denudation rates, both in terms of absolute erosion rates as well as in terms of their spatial distribution. Hence, a relatively simple river profile development model captures the essential controls on long-term landscape development in the studied landscapes. Kirchner, J., Finkel, R., and Riebe, C., 2001, Mountain erosion over 10 yr, 10 ky, and 10 my time scales: Geology, v. 29, no. 7, p. 591-594. Roberts, G., and White, N., 2010, Estimating uplift rate histories from river profiles using African examples: Journal of Geophysical Research, v. 115, p. 1-24.

Achieving Climate Change Absolute Accuracy in Orbit

NASA Technical Reports Server (NTRS)

Wielicki, Bruce A.; Young, D. F.; Mlynczak, M. G.; Thome, K. J; Leroy, S.; Corliss, J.; Anderson, J. G.; Ao, C. O.; Bantges, R.; Best, F.;

Landsat-8 Thermal Infrared Sensor (TIRS) Vicarious Radiometric Calibration

NASA Technical Reports Server (NTRS)

Barsi, Julia A.; Shott, John R.; Raqueno, Nina G.; Markham, Brian L.; Radocinski, Robert G.

2014-01-01

Launched in February 2013, the Landsat-8 carries on-board the Thermal Infrared Sensor (TIRS), a two-band thermal pushbroom imager, to maintain the thermal imaging capability of the Landsat program. The TIRS bands are centered at roughly 10.9 and 12 micrometers (Bands 10 and 11 respectively). They have 100 m spatial resolution and image coincidently with the Operational Land Imager (OLI), also on-board Landsat-8. The TIRS instrument has an internal calibration system consisting of a variable temperature blackbody and a special viewport with which it can see deep space; a two point calibration can be performed twice an orbit. Immediately after launch, a rigorous vicarious calibration program was started to validate the absolute calibration of the system. The two vicarious calibration teams, NASA/Jet Propulsion Laboratory (JPL) and the Rochester Institute of Technology (RIT), both make use of buoys deployed on large water bodies as the primary monitoring technique. RIT took advantage of cross-calibration opportunity soon after launch when Landsat-8 and Landsat-7 were imaging the same targets within a few minutes of each other to perform a validation of the absolute calibration. Terra MODIS is also being used for regular monitoring of the TIRS absolute calibration. The buoy initial results showed a large error in both bands, 0.29 and 0.51 W/sq m·sr·micrometers or -2.1 K and -4.4 K at 300 K in Band 10 and 11 respectively, where TIRS data was too hot. A calibration update was recommended for both bands to correct for a bias error and was implemented on 3 February 2014 in the USGS/EROS processing system, but the residual variability is still larger than desired for both bands (0.12 and 0.2 W/sq m·sr·micrometers or 0.87 and 1.67 K at 300 K). Additional work has uncovered the source of the calibration error: out-of-field stray light. While analysis continues to characterize the stray light contribution, the vicarious calibration work proceeds. The additional data have not changed the statistical assessment but indicate that the correction (particularly in band 11) is probably only valid for a subset of data. While the stray light effect is small enough in Band 10 to make the data useful across a wide array of applications, the effect in Band 11 is larger and the vicarious results suggest that Band 11 data should not be used where absolute calibration is required.

Quality assurance and quality control methodologies used within the Austrian UV monitoring network.

PubMed

Mario, Blumthaler

2004-01-01

The Austrian UVB monitoring network is operational since 1997. Nine detectors for measuring erythemally weighted solar UV irradiance are distributed over Austria in order to cover the main populated areas as well as different levels of altitude. The detectors are calibrated to indicate the UV-Index, the internationally agreed unit for erythemally weighted solar UV irradiance. Calibration is carried out in the laboratory for determination of spectral sensitivity of each detector, and under the sun for absolute comparison with a well-calibrated, double-monochromator spectroradiometer. For the conversion from detector-weighted units to erythemally weighted units a lookup table is used, which is calculated using a radiative transfer model and which reflects the dependence of the conversion on the solar zenith angle and total ozone content of the atmosphere. The uncertainty of the calibration is about +/-7%, dominated by the uncertainty of the calibration lamp for the spectroradiometer (+/-4%). The long-term stability of this type of detectors has been found to be not satisfactory. Therefore, routinely every year all detectors are completely recalibrated. Variations of the calibration factors up to +/-10% are found. Thus, during routine operation, several measures take place for quality control. The measured data are compared to results of model calculations with a radiative transfer model, where clear sky and an aerosol-free atmosphere are assumed. At each site, the UV data are also compared with data from a co-located pyranometer measuring total solar irradiance. These two radiation quantities are well correlated, especially on clear days and when the ozone content is taken into account. If suspicious measurements are found for one detector in the network, a well-calibrated travelling reference detector of the same type is set up side-by-side, allowing the identification of relative differences of approximately 3%. If necessary, a recalibration is carried out. As the main aim for the Austrian UV monitoring network is the information of the public about the actual levels of UVB irradiance, the measurement results are published on-line in the Internet (http://www.uibk.ac.at/projects/uv-index). For the previous day and backwards approximately 2 years, the distribution of maximal UVB levels over Austria is shown on a regional map. Additionally, near real-time data of most of the measurement stations are presented with a delay of usually less than half-an-hour. Together with these actually measured data there is also shown the diurnal variation of the maximal expected value of the UV-Index under ideal clear conditions.

Lunar Cratering Chronology: Calibrating Degree of Freshness of Craters to Absolute Ages

NASA Astrophysics Data System (ADS)

Trang, D.; Gillis-Davis, J.; Boyce, J. M.

2013-12-01

The use of impact craters to age-date surfaces of and/or geomorphological features on planetary bodies is a decades old practice. Various dating techniques use different aspects of impact craters in order to determine ages. One approach is based on the degree of freshness of primary-impact craters. This method examines the degradation state of craters through visual inspection of seven criteria: polygonality, crater ray, continuous ejecta, rim crest sharpness, satellite craters, radial channels, and terraces. These criteria are used to rank craters in order of age from 0.0 (oldest) to 7.0 (youngest). However, the relative decimal scale used in this technique has not been tied to a classification of absolute ages. In this work, we calibrate the degree of freshness to absolute ages through crater counting. We link the degree of freshness to absolute ages through crater counting of fifteen craters with diameters ranging from 5-22 km and degree of freshness from 6.3 to 2.5. We use the Terrain Camera data set on Kaguya to count craters on the continuous ejecta of each crater in our sample suite. Specifically, we divide the crater's ejecta blanket into quarters and count craters between the rim of the main crater out to one crater radii from the rim for two of the four sections. From these crater counts, we are able to estimate the absolute model age of each main crater using the Craterstats2 tool in ArcGIS. Next, we compare the degree of freshness for the crater count-derived age of our main craters to obtain a linear inverse relation that links these two metrics. So far, for craters with degree of freshness from 6.3 to 5.0, the linear regression has an R2 value of 0.7, which corresponds to a relative uncertainty of ×230 million years. At this point, this tool that links degree of freshness to absolute ages cannot be used with craters <8km because this class of crater degrades quicker than larger craters. A graphical solution exists for correcting the degree of freshness for craters <8 km in diameter. We convert this graphical solution to a single function of two independent variables, observed degree of freshness and crater diameter. This function, which results in a corrected degree of freshness is found through a curve-fitting routine and corrects the degree of freshness for craters <8 km in diameter. As a result, we are able to derive absolute ages from the degree of freshness of craters with diameters from about ≤20 km down to a 1 km in diameter with a precision of ×230 million years.

A robust approach to using of the redundant information in the temperature calibration

NASA Astrophysics Data System (ADS)

Strnad, R.; Kňazovická, L.; Šindelář, M.; Kukal, J.

2013-09-01

In the calibration laboratories are used standard procedures for calculating of the calibration model coefficients based on well described standards (EN 60751, ITS-90, EN 60584, etc.). In practice, sensors are mostly calibrated in more points and redundant information is used as a validation of the model. This paper will present the influence of including all measured points with respect to their uncertainties to the measured models using standard weighted least square methods. A special case with regards of the different level of the uncertainty of the measured points in case of the robust approach will be discussed. This will go to the different minimization criteria and different uncertainty propagation methodology. This approach also will eliminate of the influence of the outline measurements in the calibration. In practical part will be three cases of this approach presented, namely industrial calibration according to the standard EN 60751, SPRT according to the ITS-90 and thermocouple according to the standard EN 60584.

Improved GPS-based time link calibration involving ROA and PTB.

PubMed

Esteban, Héctor; Palacio, Juan; Galindo, Francisco Javier; Feldmann, Thorsten; Bauch, Andreas; Piester, Dirk

2010-03-01

The calibration of time transfer links is mandatory in the context of international collaboration for the realization of International Atomic Time. In this paper, we present the results of the calibration of the GPS time transfer link between the Real Instituto y Observatorio de la Armada (ROA) and the Physikalisch-Technische Bundesanstalt (PTB) by means of a traveling geodetic-type GPS receiver and an evaluation of the achieved type A and B uncertainty. The time transfer results were achieved by using CA, P3, and also carrier phase PPP comparison techniques. We finally use these results to re-calibrate the two-way satellite time and frequency transfer (TWSTFT) link between ROA and PTB, using one month of data. We show that a TWSTFT link can be calibrated by means of GPS time comparisons with an uncertainty below 2 ns, and that potentially even sub-nanosecond uncertainty can be achieved. This is a novel and cost-effective approach compared with the more common calibration using a traveling TWSTFT station.

Calibration of a time-resolved hard-x-ray detector using radioactive sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoeckl, C., E-mail: csto@lle.rochester.edu; Theobald, W.; Regan, S. P.

A four-channel, time-resolved, hard x-ray detector (HXRD) has been operating at the Laboratory for Laser Energetics for more than a decade. The slope temperature of the hot-electron population in direct-drive inertial confinement fusion experiments is inferred by recording the hard x-ray radiation generated in the interaction of the electrons with the target. Measuring the energy deposited by hot electrons requires an absolute calibration of the hard x-ray detector. A novel method to obtain an absolute calibration of the HXRD using single photons from radioactive sources was developed, which uses a thermoelectrically cooled, low-noise, charge-sensitive amplifier.

ITER-relevant calibration technique for soft x-ray spectrometer.

PubMed

Rzadkiewicz, J; Książek, I; Zastrow, K-D; Coffey, I H; Jakubowska, K; Lawson, K D

2010-10-01

The ITER-oriented JET research program brings new requirements for the low-Z impurity monitoring, in particular for the Be—the future main wall component of JET and ITER. Monitoring based on Bragg spectroscopy requires an absolute sensitivity calibration, which is challenging for large tokamaks. This paper describes both “component-by-component” and “continua” calibration methods used for the Be IV channel (75.9 Å) of the Bragg rotor spectrometer deployed on JET. The calibration techniques presented here rely on multiorder reflectivity calculations and measurements of continuum radiation emitted from helium plasmas. These offer excellent conditions for the absolute photon flux calibration due to their low level of impurities. It was found that the component-by-component method gives results that are four times higher than those obtained by means of the continua method. A better understanding of this discrepancy requires further investigations.

Absolute wavelength calibration of a Doppler spectrometer with a custom Fabry-Perot optical system

NASA Astrophysics Data System (ADS)

Baltzer, M. M.; Craig, D.; Den Hartog, D. J.; Nishizawa, T.; Nornberg, M. D.

2016-11-01

An Ion Doppler Spectrometer (IDS) is used for fast measurements of C VI line emission (343.4 nm) in the Madison Symmetric Torus. Absolutely calibrated flow measurements are difficult because the IDS records data within 0.25 nm of the line. Commercial calibration lamps do not produce lines in this narrow range. A light source using an ultraviolet LED and etalon was designed to provide a fiducial marker 0.08 nm wide. The light is coupled into the IDS at f/4, and a holographic diffuser increases homogeneity of the final image. Random and systematic errors in data analysis were assessed. The calibration is accurate to 0.003 nm, allowing for flow measurements accurate to 3 km/s. This calibration is superior to the previous method which used a time-averaged measurement along a chord believed to have zero net Doppler shift.

Earth Radiation Budget Experiment scanner radiometric calibration results

NASA Technical Reports Server (NTRS)

Lee, Robert B., III; Gibson, M. A.; Thomas, Susan; Meekins, Jeffrey L.; Mahan, J. R.

1990-01-01

The Earth Radiation Budget Experiment (ERBE) scanning radiometers are producing measurements of the incoming solar, earth/atmosphere-reflected solar, and earth/atmosphere-emitted radiation fields with measurement precisions and absolute accuracies, approaching 1 percent. ERBE uses thermistor bolometers as the detection elements in the narrow-field-of-view scanning radiometers. The scanning radiometers can sense radiation in the shortwave, longwave, and total broadband spectral regions of 0.2 to 5.0, 5.0 to 50.0, and 0.2 to 50.0 micrometers, respectively. Detailed models of the radiometers' response functions were developed in order to design the most suitable calibration techniques. These models guided the design of in-flight calibration procedures as well as the development and characterization of a vacuum-calibration chamber and the blackbody source which provided the absolute basis upon which the total and longwave radiometers were characterized. The flight calibration instrumentation for the narror-field-of-view scanning radiometers is presented and evaluated.

Absolute calibration of neutron detectors on the C-2U advanced beam-driven FRC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magee, R. M., E-mail: rmagee@trialphaenergy.com; Clary, R.; Korepanov, S.

2016-11-15

In the C-2U fusion energy experiment, high power neutral beam injection creates a large fast ion population that sustains a field-reversed configuration (FRC) plasma. The diagnosis of the fast ion pressure in these high-performance plasmas is therefore critical, and the measurement of the flux of neutrons from the deuterium-deuterium (D-D) fusion reaction is well suited to the task. Here we describe the absolute, in situ calibration of scintillation neutron detectors via two independent methods: firing deuterium beams into a high density gas target and calibration with a 2 × 10{sup 7} n/s AmBe source. The practical issues of each methodmore » are discussed and the resulting calibration factors are shown to be in good agreement. Finally, the calibration factor is applied to C-2U experimental data where the measured neutron rate is found to exceed the classical expectation.« less

Absolute wavelength calibration of a Doppler spectrometer with a custom Fabry-Perot optical system.

PubMed

Baltzer, M M; Craig, D; Den Hartog, D J; Nishizawa, T; Nornberg, M D

2016-11-01

An Ion Doppler Spectrometer (IDS) is used for fast measurements of C VI line emission (343.4 nm) in the Madison Symmetric Torus. Absolutely calibrated flow measurements are difficult because the IDS records data within 0.25 nm of the line. Commercial calibration lamps do not produce lines in this narrow range. A light source using an ultraviolet LED and etalon was designed to provide a fiducial marker 0.08 nm wide. The light is coupled into the IDS at f/4, and a holographic diffuser increases homogeneity of the final image. Random and systematic errors in data analysis were assessed. The calibration is accurate to 0.003 nm, allowing for flow measurements accurate to 3 km/s. This calibration is superior to the previous method which used a time-averaged measurement along a chord believed to have zero net Doppler shift.

Absolute calibration of neutron detectors on the C-2U advanced beam-driven FRC.

PubMed

Magee, R M; Clary, R; Korepanov, S; Jauregui, F; Allfrey, I; Garate, E; Valentine, T; Smirnov, A

2016-11-01

In the C-2U fusion energy experiment, high power neutral beam injection creates a large fast ion population that sustains a field-reversed configuration (FRC) plasma. The diagnosis of the fast ion pressure in these high-performance plasmas is therefore critical, and the measurement of the flux of neutrons from the deuterium-deuterium (D-D) fusion reaction is well suited to the task. Here we describe the absolute, in situ calibration of scintillation neutron detectors via two independent methods: firing deuterium beams into a high density gas target and calibration with a 2 × 10 7 n/s AmBe source. The practical issues of each method are discussed and the resulting calibration factors are shown to be in good agreement. Finally, the calibration factor is applied to C-2U experimental data where the measured neutron rate is found to exceed the classical expectation.

Calibrating Wide Field Surveys

NASA Astrophysics Data System (ADS)

González Fernández, Carlos; Irwin, M.; Lewis, J.; González Solares, E.

2017-09-01

"In this talk I will review the strategies in CASU to calibrate wide field surveys, in particular applied to data taken with the VISTA telescope. These include traditional night-by-night calibrations along with the search for a global, coherent calibration of all the data once observations are finished. The difficulties of obtaining photometric accuracy of a few percent and a good absolute calibration will also be discussed."

Inertial Sensor Error Reduction through Calibration and Sensor Fusion.

PubMed

Lambrecht, Stefan; Nogueira, Samuel L; Bortole, Magdo; Siqueira, Adriano A G; Terra, Marco H; Rocon, Eduardo; Pons, José L

2016-02-17

This paper presents the comparison between cooperative and local Kalman Filters (KF) for estimating the absolute segment angle, under two calibration conditions. A simplified calibration, that can be replicated in most laboratories; and a complex calibration, similar to that applied by commercial vendors. The cooperative filters use information from either all inertial sensors attached to the body, Matricial KF; or use information from the inertial sensors and the potentiometers of an exoskeleton, Markovian KF. A one minute walking trial of a subject walking with a 6-DoF exoskeleton was used to assess the absolute segment angle of the trunk, thigh, shank, and foot. The results indicate that regardless of the segment and filter applied, the more complex calibration always results in a significantly better performance compared to the simplified calibration. The interaction between filter and calibration suggests that when the quality of the calibration is unknown the Markovian KF is recommended. Applying the complex calibration, the Matricial and Markovian KF perform similarly, with average RMSE below 1.22 degrees. Cooperative KFs perform better or at least equally good as Local KF, we therefore recommend to use cooperative KFs instead of local KFs for control or analysis of walking.

NIST Standard Reference Material 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering

DOE PAGES

Allen, Andrew J.; Zhang, Fan; Kline, R. Joseph; ...

2017-03-07

The certification of a new standard reference material for small-angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra-small-angle X-ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008–0.25 Å –1, together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments thatmore » employ a transmission measurement geometry, working with a wide range of X-ray energies or wavelengths. As a result, the validation of the SRM SAXS intensity calibration using small-angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.« less

NIST Standard Reference Material 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Andrew J.; Zhang, Fan; Kline, R. Joseph

The certification of a new standard reference material for small-angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra-small-angle X-ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008–0.25 Å –1, together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments thatmore » employ a transmission measurement geometry, working with a wide range of X-ray energies or wavelengths. As a result, the validation of the SRM SAXS intensity calibration using small-angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.« less

NIST Standard Reference Material 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering.

PubMed

Allen, Andrew J; Zhang, Fan; Kline, R Joseph; Guthrie, William F; Ilavsky, Jan

2017-04-01

The certification of a new standard reference material for small-angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra-small-angle X-ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008-0.25 Å -1 , together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments that employ a transmission measurement geometry, working with a wide range of X-ray energies or wavelengths. The validation of the SRM SAXS intensity calibration using small-angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.

Evaluation of hydrocarbon flow standard facility equipped with double-wing diverter using four types of working liquids

NASA Astrophysics Data System (ADS)

Doihara, R.; Shimada, T.; Cheong, K. H.; Terao, Y.

2017-06-01

A flow calibration facility based on the gravimetric method using a double-wing diverter for hydrocarbon flows from 0.1 m3 h-1 to 15 m3 h-1 was constructed as a national measurement standard in Japan. The original working liquids were kerosene and light oil. The calibration facility was modified to calibrate flowmeters with two additional working liquids, industrial gasoline (flash point  >  40 °C) and spindle oil, to achieve calibration over a wide viscosity range at the same calibration test rig. The kinematic viscosity range is 1.2 mm2 s-1 to 24 mm2 s-1. The contributions to the measurement uncertainty due to different types of working liquids were evaluated experimentally in this study. The evaporation error was reduced by using a seal system at the weighing tank inlet. The uncertainty due to droplets from the diverter wings was reduced by a modified diverter operation. The diverter timing errors for all types of working liquids were estimated. The expanded uncertainties for the calibration facility were estimated to be 0.020% for mass flow and 0.030% for volumetric flow for all considered types of liquids. Internal comparisons with other calibration facilities were also conducted, and the agreement was confirmed to be within the claimed expanded uncertainties.

Probabilistic models and uncertainty quantification for the ionization reaction rate of atomic Nitrogen

NASA Astrophysics Data System (ADS)

Miki, K.; Panesi, M.; Prudencio, E. E.; Prudhomme, S.

2012-05-01

The objective in this paper is to analyze some stochastic models for estimating the ionization reaction rate constant of atomic Nitrogen (N + e- → N+ + 2e-). Parameters of the models are identified by means of Bayesian inference using spatially resolved absolute radiance data obtained from the Electric Arc Shock Tube (EAST) wind-tunnel. The proposed methodology accounts for uncertainties in the model parameters as well as physical model inadequacies, providing estimates of the rate constant that reflect both types of uncertainties. We present four different probabilistic models by varying the error structure (either additive or multiplicative) and by choosing different descriptions of the statistical correlation among data points. In order to assess the validity of our methodology, we first present some calibration results obtained with manufactured data and then proceed by using experimental data collected at EAST experimental facility. In order to simulate the radiative signature emitted in the shock-heated air plasma, we use a one-dimensional flow solver with Park's two-temperature model that simulates non-equilibrium effects. We also discuss the implications of the choice of the stochastic model on the estimation of the reaction rate and its uncertainties. Our analysis shows that the stochastic models based on correlated multiplicative errors are the most plausible models among the four models proposed in this study. The rate of the atomic Nitrogen ionization is found to be (6.2 ± 3.3) × 1011 cm3 mol-1 s-1 at 10,000 K.

Parameter estimation for groundwater models under uncertain irrigation data

USGS Publications Warehouse

Demissie, Yonas; Valocchi, Albert J.; Cai, Ximing; Brozovic, Nicholas; Senay, Gabriel; Gebremichael, Mekonnen

2015-01-01

The success of modeling groundwater is strongly influenced by the accuracy of the model parameters that are used to characterize the subsurface system. However, the presence of uncertainty and possibly bias in groundwater model source/sink terms may lead to biased estimates of model parameters and model predictions when the standard regression-based inverse modeling techniques are used. This study first quantifies the levels of bias in groundwater model parameters and predictions due to the presence of errors in irrigation data. Then, a new inverse modeling technique called input uncertainty weighted least-squares (IUWLS) is presented for unbiased estimation of the parameters when pumping and other source/sink data are uncertain. The approach uses the concept of generalized least-squares method with the weight of the objective function depending on the level of pumping uncertainty and iteratively adjusted during the parameter optimization process. We have conducted both analytical and numerical experiments, using irrigation pumping data from the Republican River Basin in Nebraska, to evaluate the performance of ordinary least-squares (OLS) and IUWLS calibration methods under different levels of uncertainty of irrigation data and calibration conditions. The result from the OLS method shows the presence of statistically significant (p < 0.05) bias in estimated parameters and model predictions that persist despite calibrating the models to different calibration data and sample sizes. However, by directly accounting for the irrigation pumping uncertainties during the calibration procedures, the proposed IUWLS is able to minimize the bias effectively without adding significant computational burden to the calibration processes.

A Calibration to Predict the Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis Revision 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narlesky, Joshua Edward; Kelly, Elizabeth J.

2015-09-10

This report documents the new PG calibration regression equation. These calibration equations incorporate new data that have become available since revision 1 of “A Calibration to Predict the Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis” was issued [3] The calibration equations are based on a weighted least squares (WLS) approach for the regression. The WLS method gives each data point its proper amount of influence over the parameter estimates. This gives two big advantages, more precise parameter estimates and better and more defensible estimates of uncertainties. The WLS approach makes sense both statistically and experimentally because themore » variances increase with concentration, and there are physical reasons that the higher measurements are less reliable and should be less influential. The new magnesium calibration includes a correction for sodium and separate calibration equation for items with and without chlorine. These additional calibration equations allow for better predictions and smaller uncertainties for sodium in materials with and without chlorine. Chlorine and sodium have separate equations for RICH materials. Again, these equations give better predictions and smaller uncertainties chlorine and sodium for RICH materials.« less

Full-Field Calibration of Color Camera Chromatic Aberration using Absolute Phase Maps.

PubMed

Liu, Xiaohong; Huang, Shujun; Zhang, Zonghua; Gao, Feng; Jiang, Xiangqian

2017-05-06

The refractive index of a lens varies for different wavelengths of light, and thus the same incident light with different wavelengths has different outgoing light. This characteristic of lenses causes images captured by a color camera to display chromatic aberration (CA), which seriously reduces image quality. Based on an analysis of the distribution of CA, a full-field calibration method based on absolute phase maps is proposed in this paper. Red, green, and blue closed sinusoidal fringe patterns are generated, consecutively displayed on an LCD (liquid crystal display), and captured by a color camera from the front viewpoint. The phase information of each color fringe is obtained using a four-step phase-shifting algorithm and optimum fringe number selection method. CA causes the unwrapped phase of the three channels to differ. These pixel deviations can be computed by comparing the unwrapped phase data of the red, blue, and green channels in polar coordinates. CA calibration is accomplished in Cartesian coordinates. The systematic errors introduced by the LCD are analyzed and corrected. Simulated results show the validity of the proposed method and experimental results demonstrate that the proposed full-field calibration method based on absolute phase maps will be useful for practical software-based CA calibration.

Calibration of diffuse correlation spectroscopy blood flow index with venous-occlusion diffuse optical spectroscopy in skeletal muscle

PubMed Central

Li, Zhe; Baker, Wesley B.; Parthasarathy, Ashwin B.; Ko, Tiffany S.; Wang, Detian; Schenkel, Steven; Durduran, Turgut; Li, Gang; Yodh, Arjun G.

2015-01-01

Abstract. We investigate and assess the utility of a simple scheme for continuous absolute blood flow monitoring based on diffuse correlation spectroscopy (DCS). The scheme calibrates DCS using venous-occlusion diffuse optical spectroscopy (VO-DOS) measurements of arm muscle tissue at a single time-point. A calibration coefficient (γ) for the arm is determined, permitting conversion of DCS blood flow indices to absolute blood flow units, and a study of healthy adults (N=10) is carried out to ascertain the variability of γ. The average DCS calibration coefficient for the right (i.e., dominant) arm was γ=(1.24±0.15)×108 (mL·100  mL−1·min−1)/(cm2/s). However, variability can be significant and is apparent in our site-to-site and day-to-day repeated measurements. The peak hyperemic blood flow overshoot relative to baseline resting flow was also studied following arm-cuff ischemia; excellent agreement between VO-DOS and DCS was found (R2=0.95, slope=0.94±0.07, mean difference=−0.10±0.45). Finally, we show that incorporation of subject-specific absolute optical properties significantly improves blood flow calibration accuracy. PMID:26720870

Positioning sensor by combining optical projection and photogrammetry

NASA Astrophysics Data System (ADS)

Zheng, Benrui

Six spatial parameters, (x, y, z) for translation, and pitch, roll, and yaw for rotation, are used to describe the 3-dimensional position and orientation of a rigid body---the 6 degrees of freedom (DOF). The ability to measure these parameters is required in a diverse range of applications including machine tool metrology, robot calibration, motion control, motion analysis, and reconstructive surgery. However, there are limitations associated with the currently available measurement systems. Shortcomings include some of the following: short dynamic range, limited accuracy, line of sight restrictions, and capital cost. The objective of this dissertation was to develop a new metrology system that overcomes line of sight restrictions, reduces system costs, allows large dynamic range and has the potential to provide high measurement accuracy. The new metrology system proposed in this dissertation is based on a combination of photogrammetry and optical pattern projection. This system has the potential to enable real-time measurement of a small lightweight module's location. The module generates an optical pattern that is observable on the surrounding walls, and photogrammetry is used to measure the absolute coordinates of features in the projected optical pattern with respect to a defined global coordinate system. By combining these absolute coordinates with the known angular information of the optical projection beams, a minimization algorithm can be used to extract the absolute coordinates and angular orientation of the module itself. The feasibility of the proposed metrology system was first proved through preliminary experimental tests. By using a module with a 7x7 dot matrix pattern, experimental agreement of 1 to 5 parts in 103 was obtained by translating the module over 0.9 m and by rotating it through 60°. The proposed metrology system was modeled through numerical simulations and factors affecting the uncertainty of the measurement were investigated. The simulation results demonstrate that optimum design of the projected pattern gives a lower associated measurement uncertainty than is possible by direct photogrammetric measurement with traditional tie points alone. Based on the simulation results, a few improvements have been made to the proposed metrology systems. These improvements include using a module with larger full view angle and larger number of dots, performing angle calibration for the module, using a virtual camera approach to determine the module location and employing multiple coordinates system for large range rotation measurement. With the new proposed virtual camera approach, experimental agreement at the level of 3 parts in 104 was observed for the one dimension translation test. The virtual camera approach is faster than the algorithm and an additional minimization analysis is no longer needed. In addition, the virtual camera approach offers an additional benefit that it is no longer necessary to identify all dots in the pattern and so is more amenable to use in realistic and usually complicated environments. A preliminary rotation test over 120° was conducted by tying three coordinate systems together. It was observed that the absolute values of the angle differences between the measured angle and the encoder reading are smaller than 0.23° for all measurements. It is found that this proposed metrology system has the ability to measure larger angle range (up to 360°) by using multiple coordinate systems. The uncertainty analysis of the proposed system was performed through Monte Carlo simulation and it was demonstrated that the experimental results are consistent with the analysis.

Uncertainty in Calibration, Detection and Estimation of Metal Concentrations in Engine Plumes Using OPAD

NASA Technical Reports Server (NTRS)

Hopkins, Randall C.; Benzing, Daniel A.

1998-01-01

Improvements in uncertainties in the values of radiant intensity (I) can be accomplished mainly by improvements in the calibration process and in minimizing the difference between the background and engine plume radiance. For engine tests in which the plume is extremely bright, the difference in luminance between the calibration lamp and the engine plume radiance can be so large as to cause relatively large uncertainties in the values of R. This is due to the small aperture necessary on the receiving optics to avoid saturating the instrument. However, this is not a problem with the SSME engine since the liquid oxygen/hydrogen combustion is not as bright as some other fuels. Applying the instrumentation to other type engine tests may require a much brighter calibration lamp.

Changes in deviation of absorbed dose to water among users by chamber calibration shift.

PubMed

Katayose, Tetsurou; Saitoh, Hidetoshi; Igari, Mitsunobu; Chang, Weishan; Hashimoto, Shimpei; Morioka, Mie

2017-07-01

The JSMP01 dosimetry protocol had adopted the provisional 60 Co calibration coefficient [Formula: see text], namely, the product of exposure calibration coefficient N C and conversion coefficient k D,X . After that, the absorbed dose to water D w  standard was established, and the JSMP12 protocol adopted the [Formula: see text] calibration. In this study, the influence of the calibration shift on the measurement of D w among users was analyzed. The intercomparison of the D w using an ionization chamber was annually performed by visiting related hospitals. Intercomparison results before and after the calibration shift were analyzed, the deviation of D w among users was re-evaluated, and the cause of deviation was estimated. As a result, the stability of LINAC, calibration of the thermometer and barometer, and collection method of ion recombination were confirmed. The statistical significance of standard deviation of D w was not observed, but that of difference of D w among users was observed between N C and [Formula: see text] calibration. Uncertainty due to chamber-to-chamber variation was reduced by the calibration shift, consequently reducing the uncertainty among users regarding D w . The result also pointed out uncertainty might be reduced by accurate and detailed instructions on the setup of an ionization chamber.

Absolute magnitude calibration using trigonometric parallax - Incomplete, spectroscopic samples

NASA Technical Reports Server (NTRS)

Ratnatunga, Kavan U.; Casertano, Stefano

1991-01-01

A new numerical algorithm is used to calibrate the absolute magnitude of spectroscopically selected stars from their observed trigonometric parallax. This procedure, based on maximum-likelihood estimation, can retrieve unbiased estimates of the intrinsic absolute magnitude and its dispersion even from incomplete samples suffering from selection biases in apparent magnitude and color. It can also make full use of low accuracy and negative parallaxes and incorporate censorship on reported parallax values. Accurate error estimates are derived for each of the fitted parameters. The algorithm allows an a posteriori check of whether the fitted model gives a good representation of the observations. The procedure is described in general and applied to both real and simulated data.

Incorporating Land-Use Mapping Uncertainty in Remote Sensing Based Calibration of Land-Use Change Models

NASA Astrophysics Data System (ADS)

Cockx, K.; Van de Voorde, T.; Canters, F.; Poelmans, L.; Uljee, I.; Engelen, G.; de Jong, K.; Karssenberg, D.; van der Kwast, J.

2013-05-01

Building urban growth models typically involves a process of historic calibration based on historic time series of land-use maps, usually obtained from satellite imagery. Both the remote sensing data analysis to infer land use and the subsequent modelling of land-use change are subject to uncertainties, which may have an impact on the accuracy of future land-use predictions. Our research aims to quantify and reduce these uncertainties by means of a particle filter data assimilation approach that incorporates uncertainty in land-use mapping and land-use model parameter assessment into the calibration process. This paper focuses on part of this work, more in particular the modelling of uncertainties associated with the impervious surface cover estimation and urban land-use classification adopted in the land-use mapping approach. Both stages are submitted to a Monte Carlo simulation to assess their relative contribution to and their combined impact on the uncertainty in the derived land-use maps. The approach was applied on the central part of the Flanders region (Belgium), using a time-series of Landsat/SPOT-HRV data covering the years 1987, 1996, 2005 and 2012. Although the most likely land-use map obtained from the simulation is very similar to the original classification, it is shown that the errors related to the impervious surface sub-pixel fraction estimation have a strong impact on the land-use map's uncertainty. Hence, incorporating uncertainty in the land-use change model calibration through particle filter data assimilation is proposed to address the uncertainty observed in the derived land-use maps and to reduce uncertainty in future land-use predictions.

SU-E-T-118: Dose Verification for Accuboost Applicators Using TLD, Ion Chamber and Gafchromic Film Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chisela, W; Yao, R; Dorbu, G

Purpose: To verify dose delivered with HDR Accuboost applicators using TLD, ion chamber and Gafchromic film measurements and to examine applicator leakage. Methods: A microSelectron HDR unit was used to deliver a dose of 50cGy to the mid-plane of a 62mm thick solid water phantom using dwell times from Monte Carlo pre-calculated nomograms for a 60mm, 70mm Round and 60mm Skin-Dose Optimized (SDO) applicators respectively. GafChromic EBT3+ film was embedded in the phantom midplane horizontally to measure dose distribution. Absolute dose was also measured with TLDs and an ADCL calibrated parallel-plate ion chamber placed in the film plane at fieldmore » center for each applicator. The film was calibrated using 6MV x-ray beam. TLDs were calibrated in a Cs-137 source at UW-Madison calibration laboratory. Radiation leakage through the tungsten alloy shell was measured with a film wrapped around outside surface of a 60mm Round applicator. Results: Measured maximum doses at field center are consistently lower than predicated by 5.8% for TLD, 8.8% for ion chamber, and 2.6% for EBT3+ film on average, with measurement uncertainties of 2.2%, 0.3%, and 2.9% for TLD, chamber, film respectively. The total standard uncertainties for ion chamber and Gafchromic film measurement are 4.9% and 4.6% respectively[1]. The area defined by the applicator aperture was covered by 80% of maximum dose for 62mm compression thickness. When 100cGy is delivered to mid-plane with a 60mm Round applicator, surface dose ranges from 60cGy to a maximum of 145cGy, which occurs at source entrance to the applicator. Conclusion: Measured doses by all three techniques are consistently lower than predicted in our measurements. For a compression thickness of 62 mm, the field size defined by the applicator is only covered by 80% of prescribed dose. Radiation leakage of up to 145cGy was found at the source entrance of applicators.« less

A dosimetry study comparing NCS report-5, IAEA TRS-381, AAPM TG-51 and IAEA TRS-398 in three clinical electron beam energies

NASA Astrophysics Data System (ADS)

Palmans, Hugo; Nafaa, Laila; de Patoul, Nathalie; Denis, Jean-Marc; Tomsej, Milan; Vynckier, Stefaan

2003-05-01

New codes of practice for reference dosimetry in clinical high-energy photon and electron beams have been published recently, to replace the air kerma based codes of practice that have determined the dosimetry of these beams for the past twenty years. In the present work, we compared dosimetry based on the two most widespread absorbed dose based recommendations (AAPM TG-51 and IAEA TRS-398) with two air kerma based recommendations (NCS report-5 and IAEA TRS-381). Measurements were performed in three clinical electron beam energies using two NE2571-type cylindrical chambers, two Markus-type plane-parallel chambers and two NACP-02-type plane-parallel chambers. Dosimetry based on direct calibrations of all chambers in 60Co was investigated, as well as dosimetry based on cross-calibrations of plane-parallel chambers against a cylindrical chamber in a high-energy electron beam. Furthermore, 60Co perturbation factors for plane-parallel chambers were derived. It is shown that the use of 60Co calibration factors could result in deviations of more than 2% for plane-parallel chambers between the old and new codes of practice, whereas the use of cross-calibration factors, which is the first recommendation in the new codes, reduces the differences to less than 0.8% for all situations investigated here. The results thus show that neither the chamber-to-chamber variations, nor the obtained absolute dose values are significantly altered by changing from air kerma based dosimetry to absorbed dose based dosimetry when using calibration factors obtained from the Laboratory for Standard Dosimetry, Ghent, Belgium. The values of the 60Co perturbation factor for plane-parallel chambers (katt . km for the air kerma based and pwall for the absorbed dose based codes of practice) that are obtained from comparing the results based on 60Co calibrations and cross-calibrations are within the experimental uncertainties in agreement with the results from other investigators.

Calibration of the JET neutron activation system for DT operation

NASA Astrophysics Data System (ADS)

Bertalot, L.; Roquemore, A. L.; Loughlin, M.; Esposito, B.

1999-01-01

The neutron activation system at JET is a pneumatic transfer system capable of positioning activation samples close to the plasma. Its primary purpose is to provide a calibration for the time-dependent neutron yield monitors (fission chambers and solid state detectors). Various activation reactions with different high energy thresholds were used including 56Fe(n,p) 56Mn, 27Al(n,α) 24Na, 93Nb(n,2n) 92mNb, and 28Si(n,p) 28Al reactions. The silicon reaction, with its short half life (2.25 min), provides a prompt determination of the 14 MeV DT yield. The neutron induced γ-ray activity of the Si samples was measured using three sodium iodide scintillators, while two high purity germanium detectors were used for other foils. It was necessary to use a range of sample masses and different counting geometries in order to cover the wide range of neutron yields (1015-1019 neutrons) while avoiding excessive count rates in the detectors. The absolute full energy peak efficiency calibration of the detectors was measured taking into account the source-detector geometry, the self-attenuation of the samples and cross-talk effects. An error analysis of the neutron yield measurement was performed including uncertainties in efficiency calibration, neutron transport calculations, cross sections, and counting statistics. Cross calibrations between the different irradiation ends were carried out in DD and DT (with 1% and 10% tritium content) discharges. The effect of the plasma vertical displacement was also experimentally studied. An agreement within 10% was found between the 14 MeV neutron yields measured from Si, Fe, Al, Nb samples in DT discharges.

Measuring Broadband IR Irradiance in the Direct Solar Beam and Recent Development

NASA Astrophysics Data System (ADS)

Reda, I.; Andreas, A.; Dooraghi, M.; Habte, A.; Sengupta, M.; Kutchenreiter, M.

2016-12-01

Solar and atmospheric science radiometers such as pyranometers, pyrheliometers, and photovoltaic cells are calibrated with traceability to consensus Reference, which is maintained by Absolute Cavity Radiometers (ACRs). An ACR is an open cavity with no window, and developed to measure extended broadband spectrum of the terrestrial direct solar beam irradiance, extends beyond the ultraviolet and infrared bands; i.e. below 0.2 µm and above 50 µm, respectively. On the other hand, the pyranometers and pyrheliometers were developed to measure broadband shortwave irradiance from approximately 0.3 µm to 3 µm, while the present photovoltaic cells are limited to the spectral range of approximately 0.3 µm to 1 µm. The broadband mismatch of ACR versus such radiometers causes discrepancy in radiometers' calibration methods that has not been discussed or addressed in the solar and atmospheric science literature. Pyrgeometers are also used for solar and atmospheric science applications and calibrated with traceability to consensus Reference, yet they are calibrated during nighttime only, because no consensus reference has yet been established for the daytime longwave irradiance. This poster describes a method to measure the broadband longwave irradiance in the terrestrial direct solar beam from 3 µm to 50 µm, as a first step that might be used to help develop calibration methods to address the mismatch between broadband ACR and shortwave radiometers, and the lack of a daytime reference for pyrgeometers. The described method is used to measure the irradiance from sunrise to sunset; the irradiance varied from approximately 1 Wm-2 to 16 Wm-2 with an estimated uncertainty of 1.5 Wm-2, for a solar zenith angle range from 80° to 16°, respectively.

Calibration of the Late Cretaceous to Paleocene geomagnetic polarity and astrochronological time scales: new results from high-precision U-Pb geochronology

NASA Astrophysics Data System (ADS)

Ramezani, Jahandar; Clyde, William; Wang, Tiantian; Johnson, Kirk; Bowring, Samuel

2016-04-01

Reversals in the Earth's magnetic polarity are geologically abrupt events of global magnitude that makes them ideal timelines for stratigraphic correlation across a variety of depositional environments, especially where diagnostic marine fossils are absent. Accurate and precise calibration of the Geomagnetic Polarity Timescale (GPTS) is thus essential to the reconstruction of Earth history and to resolving the mode and tempo of biotic and environmental change in deep time. The Late Cretaceous - Paleocene GPTS is of particular interest as it encompasses a critical period of Earth history marked by the Cretaceous greenhouse climate, the peak of dinosaur diversity, the end-Cretaceous mass extinction and its paleoecological aftermaths. Absolute calibration of the GPTS has been traditionally based on sea-floor spreading magnetic anomaly profiles combined with local magnetostratigraphic sequences for which a numerical age model could be established by interpolation between an often limited number of 40Ar/39Ar dates from intercalated volcanic ash deposits. Although the Neogene part of the GPTS has been adequately calibrated using cyclostratigraphy-based, astrochronological schemes, the application of these approaches to pre-Neogene parts of the timescale has been complicated given the uncertainties of the orbital models and the chaotic behavior of the solar system this far back in time. Here we present refined chronostratigraphic frameworks based on high-precision U-Pb geochronology of ash beds from the Western Interior Basin of North America and the Songliao Basin of Northeast China that places tight temporal constraints on the Late Cretaceous to Paleocene GPTS, either directly or by testing their astrochronological underpinnings. Further application of high-precision radioisotope geochronology and calibrated astrochronology promises a complete and robust Cretaceous-Paleogene GPTS, entirely independent of sea-floor magnetic anomaly profiles.

Improving the Traceability of Meteorological Measurements at Automatic Weather Stations in Thailand

NASA Astrophysics Data System (ADS)

Keawprasert, T.; Sinhaneti, T.; Phuuntharo, P.; Phanakulwijit, S.; Nimsamer, A.

2017-08-01

A joint project between the National Institute of Metrology Thailand (NIMT) and the Thai Meteorology Department (TMD) was established for improving the traceability of meteorology measurements at automatic weather stations (AWSs) in Thailand. The project aimed to improve traceability of air temperature, relative humidity and atmospheric pressure by implementing on-site calibration facilities and developing of new calibration procedures. First, new portable calibration facilities for air temperature, humidity and pressure were set up as working standard of the TMD. A portable humidity calibrator was applied as a uniform and stable source for calibration of thermo-hygrometers. A dew-point hygrometer was employed as reference hygrometer and a platinum resistance thermometer (PRT) traceable to NIMT was used as reference thermometer. The uniformity and stability in both temperature and relative humidity were characterized at NIMT. A transportable pressure calibrator was used for calibration of air pressure sensor. The estimate overall uncertainty of the calibration setup is 0.2 K for air temperature, 1.0 % for relative humidity and 0.2 hPa for atmospheric pressure, respectively. Second, on-site calibration procedures were developed and four AWSs in the central part and the northern of Thailand were chosen as pilot stations for on-site calibration using the new calibration setups and developed calibration procedures. At each station, the calibration was done at the minimum temperature, average temperature and maximum temperature of the year, for air temperature, 20 %, 55 % and 90 % for relative humidity at the average air temperature of that station and at a one-year statistics pressure range for atmospheric pressure at ambient temperature. Additional in-field uncertainty contributions such as the temperature dependence on relative humidity measurement were evaluated and included in the overall uncertainty budget. Preliminary calibration results showed that using a separate PRT probe at these AWSs would be recommended for improving the accuracy of air temperature measurement. In case of relative humidity measurement, the data logger software is needed to be upgraded for achieving higher accuracy of less than 3 %. For atmospheric pressure measurement, a higher accuracy barometer traceable to NIMT could be used to reduce the calibration uncertainty to below 0.2 hPa.

Radiometric calibration updates to the Landsat collection

USGS Publications Warehouse

Micijevic, Esad; Haque, Md. Obaidul; Mishra, Nischal

2016-01-01

The Landsat Project is planning to implement a new collection management strategy for Landsat products generated at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center. The goal of the initiative is to identify a collection of consistently geolocated and radiometrically calibrated images across the entire Landsat archive that is readily suitable for time-series analyses. In order to perform an accurate land change analysis, the data from all Landsat sensors must be on the same radiometric scale. Landsat 7 Enhanced Thematic Mapper Plus (ETM+) is calibrated to a radiance standard and all previous sensors are cross-calibrated to its radiometric scale. Landsat 8 Operational Land Imager (OLI) is calibrated to both radiance and reflectance standards independently. The Landsat 8 OLI reflectance calibration is considered to be most accurate. To improve radiometric calibration accuracy of historical data, Landsat 1-7 sensors also need to be cross-calibrated to the OLI reflectance scale. Results of that effort, as well as other calibration updates including the absolute and relative radiometric calibration and saturated pixel replacement for Landsat 8 OLI and absolute calibration for Landsat 4 and 5 Thematic Mappers (TM), will be implemented into Landsat products during the archive reprocessing campaign planned within the new collection management strategy. This paper reports on the planned radiometric calibration updates to the solar reflective bands of the new Landsat collection.

Quantifying the uncertainty of nonpoint source attribution in distributed water quality models: A Bayesian assessment of SWAT's sediment export predictions

NASA Astrophysics Data System (ADS)

Wellen, Christopher; Arhonditsis, George B.; Long, Tanya; Boyd, Duncan

2014-11-01

Spatially distributed nonpoint source watershed models are essential tools to estimate the magnitude and sources of diffuse pollution. However, little work has been undertaken to understand the sources and ramifications of the uncertainty involved in their use. In this study we conduct the first Bayesian uncertainty analysis of the water quality components of the SWAT model, one of the most commonly used distributed nonpoint source models. Working in Southern Ontario, we apply three Bayesian configurations for calibrating SWAT to Redhill Creek, an urban catchment, and Grindstone Creek, an agricultural one. We answer four interrelated questions: can SWAT determine suspended sediment sources with confidence when end of basin data is used for calibration? How does uncertainty propagate from the discharge submodel to the suspended sediment submodels? Do the estimated sediment sources vary when different calibration approaches are used? Can we combine the knowledge gained from different calibration approaches? We show that: (i) despite reasonable fit at the basin outlet, the simulated sediment sources are subject to uncertainty sufficient to undermine the typical approach of reliance on a single, best fit simulation; (ii) more than a third of the uncertainty of sediment load predictions may stem from the discharge submodel; (iii) estimated sediment sources do vary significantly across the three statistical configurations of model calibration despite end-of-basin predictions being virtually identical; and (iv) Bayesian model averaging is an approach that can synthesize predictions when a number of adequate distributed models make divergent source apportionments. We conclude with recommendations for future research to reduce the uncertainty encountered when using distributed nonpoint source models for source apportionment.

Calibration and Measurement Uncertainty Estimation of Radiometric Data: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habte, A.; Sengupta, M.; Reda, I.

2014-11-01

Evaluating the performance of photovoltaic cells, modules, and arrays that form large solar deployments relies on accurate measurements of the available solar resource. Therefore, determining the accuracy of these solar radiation measurements provides a better understanding of investment risks. This paper provides guidelines and recommended procedures for estimating the uncertainty in calibrations and measurements by radiometers using methods that follow the International Bureau of Weights and Measures Guide to the Expression of Uncertainty (GUM). Standardized analysis based on these procedures ensures that the uncertainty quoted is well documented.

MOESHA: A genetic algorithm for automatic calibration and estimation of parameter uncertainty and sensitivity of hydrologic models

EPA Science Inventory

Characterization of uncertainty and sensitivity of model parameters is an essential and often overlooked facet of hydrological modeling. This paper introduces an algorithm called MOESHA that combines input parameter sensitivity analyses with a genetic algorithm calibration routin...

Multiple Use One-Sided Hypotheses Testing in Univariate Linear Calibration

NASA Technical Reports Server (NTRS)

Krishnamoorthy, K.; Kulkarni, Pandurang M.; Mathew, Thomas

1996-01-01

Consider a normally distributed response variable, related to an explanatory variable through the simple linear regression model. Data obtained on the response variable, corresponding to known values of the explanatory variable (i.e., calibration data), are to be used for testing hypotheses concerning unknown values of the explanatory variable. We consider the problem of testing an unlimited sequence of one sided hypotheses concerning the explanatory variable, using the corresponding sequence of values of the response variable and the same set of calibration data. This is the situation of multiple use of the calibration data. The tests derived in this context are characterized by two types of uncertainties: one uncertainty associated with the sequence of values of the response variable, and a second uncertainty associated with the calibration data. We derive tests based on a condition that incorporates both of these uncertainties. The solution has practical applications in the decision limit problem. We illustrate our results using an example dealing with the estimation of blood alcohol concentration based on breath estimates of the alcohol concentration. In the example, the problem is to test if the unknown blood alcohol concentration of an individual exceeds a threshold that is safe for driving.

Potential improvements aimed at high precision δ13C isotopic ratio determinations in CO2 mixtures using optical absorption spectrometry.

PubMed

Koulikov, Serguei; Assonov, Sergey; Fajgelj, Ales; Tans, Pieter

2018-07-01

The manuscript explores some advantages and limitations of laser based optical spectroscopy, aimed at achieving robust, high-reproducibility 13 C 16 O 2 and 12 C 16 O 2 ratio determinations on the VPDB-CO 2 δ 13 C scale by measuring the absorbance of line pairs of 13 C 16 O 2 and 12 C 16 O 2 . In particular, the sensitivities of spectroscopic lines to both pressure (P) and temperature (T) are discussed. Based on the considerations and estimations presented, a level of reproducibility of the 13 C 16 O 2 / 12 C 16 O 2 ratio determinations may be achieved of about 10 -6 . Thus one may establish an optical spectroscopic measurement technique for robust, high-precision 13 C 16 O 2 and 12 C 16 O 2 ratio measurements aimed at very low uncertainty. (Notably, creating such an optical instrument and developing technical solutions is beyond the scope of this paper.) The total combined uncertainty will also include the uncertainty component(s) related to the accuracy of calibration on the VPDB-CO 2 δ 13 C scale. Addressing high-accuracy calibrations is presently not straightforward - absolute numerical values of 13 C/ 12 C for the VPDB-CO 2 scale are not well known. Traditional stable isotope mass-spectrometry uses calibrations vs CO 2 evolved from the primary carbonate reference materials; which can hardly be used for calibrating commercial optical stable isotope analysers. In contrast to mass-spectrometry, the major advantage of the laser-based spectrometric technique detailed in this paper is its high robustness. Therefore one can introduce a new spectrometric δ 13 C characterisation method which, being once well-calibrated on the VPDB-CO 2 scale, may not require any further (re-)calibrations. This can be used for characterisation of δ 13 C in CO 2 -in-air mixtures with high precision and also with high accuracy. If this technique can be realised with the estimated long-term reproducibility (order of 10 -6 ), it could potentially serve as a more convenient Optical Transfer Standard (OTS), characterising large amounts of CO 2 gas mixtures on the VPDB-CO 2 δ 13 C scale without having to compare to carbonate-evolved CO 2 . Furthermore, if the OTS method proves to be successful, it might be considered for re-defining the VPDB-CO 2 δ 13 C-scale as the ratio of selected CO 2 spectroscopic absorbance lines measured at pre-defined T & P conditions. The approach can also be expanded to δ 18 O characterisation (using 16 O 12 C 18 O and 16 O 12 C 16 O absorbance lines) of CO 2 gas mixtures and potentially to other isotope ratios of other gases. Copyright © 2018 Elsevier B.V. All rights reserved.

Calibrating airborne measurements of airspeed, pressure and temperature using a Doppler laser air-motion sensor

NASA Astrophysics Data System (ADS)

Cooper, W. A.; Spuler, S. M.; Spowart, M.; Lenschow, D. H.; Friesen, R. B.

2014-09-01

A new laser air-motion sensor measures the true airspeed with a standard uncertainty of less than 0.1 m s-1 and so reduces uncertainty in the measured component of the relative wind along the longitudinal axis of the aircraft to about the same level. The calculated pressure expected from that airspeed at the inlet of a pitot tube then provides a basis for calibrating the measurements of dynamic and static pressure, reducing standard uncertainty in those measurements to less than 0.3 hPa and the precision applicable to steady flight conditions to about 0.1 hPa. These improved measurements of pressure, combined with high-resolution measurements of geometric altitude from the global positioning system, then indicate (via integrations of the hydrostatic equation during climbs and descents) that the offset and uncertainty in temperature measurement for one research aircraft are +0.3 ± 0.3 °C. For airspeed, pressure and temperature, these are significant reductions in uncertainty vs. those obtained from calibrations using standard techniques. Finally, it is shown that although the initial calibration of the measured static and dynamic pressures requires a measured temperature, once calibrated these measured pressures and the measurement of airspeed from the new laser air-motion sensor provide a measurement of temperature that does not depend on any other temperature sensor.

Absolute mass scale calibration in the inverse problem of the physical theory of fireballs.

NASA Astrophysics Data System (ADS)

Kalenichenko, V. V.

A method of the absolute mass scale calibration is suggested for solving the inverse problem of the physical theory of fireballs. The method is based on the data on the masses of the fallen meteorites whose fireballs have been photographed in their flight. The method may be applied to those fireballs whose bodies have not experienced considerable fragmentation during their destruction in the atmosphere and have kept their form well enough. Statistical analysis of the inverse problem solution for a sufficiently representative sample makes it possible to separate a subsample of such fireballs. The data on the Lost City and Innisfree meteorites are used to obtain calibration coefficients.

Orientation of three-component geophones in the San Andreas Fault observatory at depth Pilot Hole, Parkfield, California

USGS Publications Warehouse

Oye, V.; Ellsworth, W.L.

2005-01-01

To identify and constrain the target zone for the planned SAFOD Main Hole through the San Andreas Fault (SAF) near Parkfield, California, a 32-level three-component (3C) geophone string was installed in the Pilot Hole (PH) to monitor and improve the locations of nearby earthquakes. The orientation of the 3C geophones is essential for this purpose, because ray directions from sources may be determined directly from the 3D particle motion for both P and S waves. Due to the complex local velocity structure, rays traced from explosions and earthquakes to the PH show strong ray bending. Observed azimuths are obtained from P-wave polarization analysis, and ray tracing provides theoretical estimates of the incoming wave field. The differences between the theoretical and the observed angles define the calibration azimuths. To investigate the process of orientation with respect to the assumed velocity model, we compare calibration azimuths derived from both a homogeneous and 3D velocity model. Uncertainties in the relative orientation between the geophone levels were also estimated for a cluster of 36 earthquakes that was not used in the orientation process. The comparison between the homogeneous and the 3D velocity model shows that there are only minor changes in these relative orientations. In contrast, the absolute orientations, with respect to global North, were significantly improved by application of the 3D model. The average data residual decreased from 13?? to 7??, supporting the importance of an accurate velocity model. We explain the remaining residuals by methodological uncertainties and noise and with errors in the velocity model.

SU-F-T-76: Total Skin Electron Therapy: An-End-To-End Examination of the Absolute Dosimetry with a Rando Phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, G; Ha, J; Zhou, S

Purpose: To examine and validate the absolute dose for total skin electron therapy (TSET) through an end-to-end test with a Rando phantom using optically stimulated luminescent dosimeters (OSLDs) and EBT3 radiochromic films. Methods: A Varian Trilogy linear accelerator equipped with the special procedure 6 MeV HDTSe- was used to perform TSET irradiations using a modified Stanford 6-dual-field technique. The absolute dose was calibrated using a Markus ion chamber at a reference depth of 1.3cm at 100 cm SSD with a field size of 36 × 36 cm at the isocenter in solid water slabs. The absolute dose was cross validatedmore » by a farmer ion chamber. Then the dose rate in the unit of cGy/Mu was calibrated using the Markus chamber at the treatment position. OSLDs were used to independently verify the dose using the calibrated dose rate. Finally, a patient treatment plan (200 cGy/cycle) was delivered in the QA mode to a Rando phantom, which had 16 pairs of OSLDs and EBT3 films taped onto its surface at different anatomical positions. The doses recorded were read out to validate the absolute dosimetry for TSET. Results: The OSLD measurements were within 7% agreement with the planned dose except the shoulder areas, where the doses recorded were 23% lower on average than those of the planned. The EBT3 film measurements were within 10% agreement with the planned dose except the shoulder and the scalp vertex areas, where the respective doses recorded were 18% and 14% lower on average than those of the planned. The OSLDs gave more consistent dose measurements than those of the EBT3 films. Conclusion: The absolute dosimetry for TSET was validated by an end-to-end test with a Rando phantom using the OSLDs and EBT3 films. The beam calibration and monitor unit calculations were confirmed.« less

Effect of soil property uncertainties on permafrost thaw projections: a calibration-constrained analysis

NASA Astrophysics Data System (ADS)

Harp, D. R.; Atchley, A. L.; Painter, S. L.; Coon, E. T.; Wilson, C. J.; Romanovsky, V. E.; Rowland, J. C.

2016-02-01

The effects of soil property uncertainties on permafrost thaw projections are studied using a three-phase subsurface thermal hydrology model and calibration-constrained uncertainty analysis. The null-space Monte Carlo method is used to identify soil hydrothermal parameter combinations that are consistent with borehole temperature measurements at the study site, the Barrow Environmental Observatory. Each parameter combination is then used in a forward projection of permafrost conditions for the 21st century (from calendar year 2006 to 2100) using atmospheric forcings from the Community Earth System Model (CESM) in the Representative Concentration Pathway (RCP) 8.5 greenhouse gas concentration trajectory. A 100-year projection allows for the evaluation of predictive uncertainty (due to soil property (parametric) uncertainty) and the inter-annual climate variability due to year to year differences in CESM climate forcings. After calibrating to measured borehole temperature data at this well-characterized site, soil property uncertainties are still significant and result in significant predictive uncertainties in projected active layer thickness and annual thaw depth-duration even with a specified future climate. Inter-annual climate variability in projected soil moisture content and Stefan number are small. A volume- and time-integrated Stefan number decreases significantly, indicating a shift in subsurface energy utilization in the future climate (latent heat of phase change becomes more important than heat conduction). Out of 10 soil parameters, ALT, annual thaw depth-duration, and Stefan number are highly dependent on mineral soil porosity, while annual mean liquid saturation of the active layer is highly dependent on the mineral soil residual saturation and moderately dependent on peat residual saturation. By comparing the ensemble statistics to the spread of projected permafrost metrics using different climate models, we quantify the relative magnitude of soil property uncertainty to another source of permafrost uncertainty, structural climate model uncertainty. We show that the effect of calibration-constrained uncertainty in soil properties, although significant, is less than that produced by structural climate model uncertainty for this location.

A parallel calibration utility for WRF-Hydro on high performance computers

NASA Astrophysics Data System (ADS)

Wang, J.; Wang, C.; Kotamarthi, V. R.

2017-12-01

A successful modeling of complex hydrological processes comprises establishing an integrated hydrological model which simulates the hydrological processes in each water regime, calibrates and validates the model performance based on observation data, and estimates the uncertainties from different sources especially those associated with parameters. Such a model system requires large computing resources and often have to be run on High Performance Computers (HPC). The recently developed WRF-Hydro modeling system provides a significant advancement in the capability to simulate regional water cycles more completely. The WRF-Hydro model has a large range of parameters such as those in the input table files — GENPARM.TBL, SOILPARM.TBL and CHANPARM.TBL — and several distributed scaling factors such as OVROUGHRTFAC. These parameters affect the behavior and outputs of the model and thus may need to be calibrated against the observations in order to obtain a good modeling performance. Having a parameter calibration tool specifically for automate calibration and uncertainty estimates of WRF-Hydro model can provide significant convenience for the modeling community. In this study, we developed a customized tool using the parallel version of the model-independent parameter estimation and uncertainty analysis tool, PEST, to enabled it to run on HPC with PBS and SLURM workload manager and job scheduler. We also developed a series of PEST input file templates that are specifically for WRF-Hydro model calibration and uncertainty analysis. Here we will present a flood case study occurred in April 2013 over Midwest. The sensitivity and uncertainties are analyzed using the customized PEST tool we developed.

Radiometric stability of the Multi-angle Imaging SpectroRadiometer (MISR) following 15 years on-orbit

NASA Astrophysics Data System (ADS)

Bruegge, Carol J.; Val, Sebastian; Diner, David J.; Jovanovic, Veljko; Gray, Ellyn; Di Girolamo, Larry; Zhao, Guangyu

2014-09-01

The Multi-angle Imaging SpectroRadiometer (MISR) has successfully operated on the EOS/ Terra spacecraft since 1999. It consists of nine cameras pointing from nadir to 70.5° view angle with four spectral channels per camera. Specifications call for a radiometric uncertainty of 3% absolute and 1% relative to the other cameras. To accomplish this, MISR utilizes an on-board calibrator (OBC) to measure camera response changes. Once every two months the two Spectralon panels are deployed to direct solar-light into the cameras. Six photodiode sets measure the illumination level that are compared to MISR raw digital numbers, thus determining the radiometric gain coefficients used in Level 1 data processing. Although panel stability is not required, there has been little detectable change in panel reflectance, attributed to careful preflight handling techniques. The cameras themselves have degraded in radiometric response by 10% since launch, but calibration updates using the detector-based scheme has compensated for these drifts and allowed the radiance products to meet accuracy requirements. Validation using Sahara desert observations show that there has been a drift of ~1% in the reported nadir-view radiance over a decade, common to all spectral bands.

Validation of modelled imaging plates sensitivity to 1-100 keV x-rays and spatial resolution characterisation for diagnostics for the “PETawatt Aquitaine Laser”

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boutoux, G., E-mail: boutoux@celia.u-bordeaux1.fr; Batani, D.; Burgy, F.

2016-04-15

Thanks to their high dynamic range and ability to withstand electromagnetic pulse, imaging plates (IPs) are commonly used as passive detectors in laser-plasma experiments. In the framework of the development of the diagnostics for the Petawatt Aquitaine Laser facility, we present an absolute calibration and spatial resolution study of five different available types of IP (namely, MS-SR-TR-MP-ND) performed by using laser-induced K-shell X-rays emitted by a solid silver target irradiated by the laser ECLIPSE at CEntre Lasers Intenses et Applications. In addition, IP sensitivity measurements were performed with a 160 kV X-ray generator at CEA DAM DIF, where the absolutemore » response of IP SR and TR has been calibrated to X-rays in the energy range 8-75 keV with uncertainties of about 15%. Finally, the response functions have been modeled in Monte Carlo GEANT4 simulations in order to reproduce experimental data. Simulations enable extrapolation of the IP response functions to photon energies from 1 keV to 1 GeV, of interest, e.g., for laser-driven radiography.« less

A novel Bayesian approach to accounting for uncertainty in fMRI-derived estimates of cerebral oxygen metabolism fluctuations

PubMed Central

Simon, Aaron B.; Dubowitz, David J.; Blockley, Nicholas P.; Buxton, Richard B.

2016-01-01

Calibrated blood oxygenation level dependent (BOLD) imaging is a multimodal functional MRI technique designed to estimate changes in cerebral oxygen metabolism from measured changes in cerebral blood flow and the BOLD signal. This technique addresses fundamental ambiguities associated with quantitative BOLD signal analysis; however, its dependence on biophysical modeling creates uncertainty in the resulting oxygen metabolism estimates. In this work, we developed a Bayesian approach to estimating the oxygen metabolism response to a neural stimulus and used it to examine the uncertainty that arises in calibrated BOLD estimation due to the presence of unmeasured model parameters. We applied our approach to estimate the CMRO2 response to a visual task using the traditional hypercapnia calibration experiment as well as to estimate the metabolic response to both a visual task and hypercapnia using the measurement of baseline apparent R2′ as a calibration technique. Further, in order to examine the effects of cerebral spinal fluid (CSF) signal contamination on the measurement of apparent R2′, we examined the effects of measuring this parameter with and without CSF-nulling. We found that the two calibration techniques provided consistent estimates of the metabolic response on average, with a median R2′-based estimate of the metabolic response to CO2 of 1.4%, and R2′- and hypercapnia-calibrated estimates of the visual response of 27% and 24%, respectively. However, these estimates were sensitive to different sources of estimation uncertainty. The R2′-calibrated estimate was highly sensitive to CSF contamination and to uncertainty in unmeasured model parameters describing flow-volume coupling, capillary bed characteristics, and the iso-susceptibility saturation of blood. The hypercapnia-calibrated estimate was relatively insensitive to these parameters but highly sensitive to the assumed metabolic response to CO2. PMID:26790354

A novel Bayesian approach to accounting for uncertainty in fMRI-derived estimates of cerebral oxygen metabolism fluctuations.

PubMed

Simon, Aaron B; Dubowitz, David J; Blockley, Nicholas P; Buxton, Richard B

2016-04-01

Calibrated blood oxygenation level dependent (BOLD) imaging is a multimodal functional MRI technique designed to estimate changes in cerebral oxygen metabolism from measured changes in cerebral blood flow and the BOLD signal. This technique addresses fundamental ambiguities associated with quantitative BOLD signal analysis; however, its dependence on biophysical modeling creates uncertainty in the resulting oxygen metabolism estimates. In this work, we developed a Bayesian approach to estimating the oxygen metabolism response to a neural stimulus and used it to examine the uncertainty that arises in calibrated BOLD estimation due to the presence of unmeasured model parameters. We applied our approach to estimate the CMRO2 response to a visual task using the traditional hypercapnia calibration experiment as well as to estimate the metabolic response to both a visual task and hypercapnia using the measurement of baseline apparent R2' as a calibration technique. Further, in order to examine the effects of cerebral spinal fluid (CSF) signal contamination on the measurement of apparent R2', we examined the effects of measuring this parameter with and without CSF-nulling. We found that the two calibration techniques provided consistent estimates of the metabolic response on average, with a median R2'-based estimate of the metabolic response to CO2 of 1.4%, and R2'- and hypercapnia-calibrated estimates of the visual response of 27% and 24%, respectively. However, these estimates were sensitive to different sources of estimation uncertainty. The R2'-calibrated estimate was highly sensitive to CSF contamination and to uncertainty in unmeasured model parameters describing flow-volume coupling, capillary bed characteristics, and the iso-susceptibility saturation of blood. The hypercapnia-calibrated estimate was relatively insensitive to these parameters but highly sensitive to the assumed metabolic response to CO2. Copyright © 2016 Elsevier Inc. All rights reserved.

A fully Bayesian method for jointly fitting instrumental calibration and X-ray spectral models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Jin; Yu, Yaming; Van Dyk, David A.

2014-10-20

Owing to a lack of robust principled methods, systematic instrumental uncertainties have generally been ignored in astrophysical data analysis despite wide recognition of the importance of including them. Ignoring calibration uncertainty can cause bias in the estimation of source model parameters and can lead to underestimation of the variance of these estimates. We previously introduced a pragmatic Bayesian method to address this problem. The method is 'pragmatic' in that it introduced an ad hoc technique that simplified computation by neglecting the potential information in the data for narrowing the uncertainty for the calibration product. Following that work, we use amore » principal component analysis to efficiently represent the uncertainty of the effective area of an X-ray (or γ-ray) telescope. Here, however, we leverage this representation to enable a principled, fully Bayesian method that coherently accounts for the calibration uncertainty in high-energy spectral analysis. In this setting, the method is compared with standard analysis techniques and the pragmatic Bayesian method. The advantage of the fully Bayesian method is that it allows the data to provide information not only for estimation of the source parameters but also for the calibration product—here the effective area, conditional on the adopted spectral model. In this way, it can yield more accurate and efficient estimates of the source parameters along with valid estimates of their uncertainty. Provided that the source spectrum can be accurately described by a parameterized model, this method allows rigorous inference about the effective area by quantifying which possible curves are most consistent with the data.« less

The Near-infrared Tip of the Red Giant Branch. II. An Absolute Calibration in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Hoyt, Taylor J.; Freedman, Wendy L.; Madore, Barry F.; Seibert, Mark; Beaton, Rachael L.; Hatt, Dylan; Jang, In Sung; Lee, Myung Gyoon; Monson, Andrew J.; Rich, Jeffrey A.

2018-05-01

We present a new empirical JHK absolute calibration of the tip of the red giant branch (TRGB) in the Large Magellanic Cloud (LMC). We use published data from the extensive Near-Infrared Synoptic Survey containing 3.5 million stars, 65,000 of which are red giants that fall within one magnitude of the TRGB. Adopting the TRGB slopes from a companion study of the isolated dwarf galaxy IC 1613, as well as an LMC distance modulus of μ 0 = 18.49 mag from (geometric) detached eclipsing binaries, we derive absolute JHK zero points for the near-infrared TRGB. For a comparison with measurements in the bar alone, we apply the calibrated JHK TRGB to a 500 deg2 area of the 2MASS survey. The TRGB reveals the 3D structure of the LMC with a tilt in the direction perpendicular to the major axis of the bar, which is in agreement with previous studies.

Analysis of uncertainties in turbine metal temperature predictions

NASA Technical Reports Server (NTRS)

Stepka, F. S.

1980-01-01

An analysis was conducted to examine the extent to which various factors influence the accuracy of analytically predicting turbine blade metal temperatures and to determine the uncertainties in these predictions for several accuracies of the influence factors. The advanced turbofan engine gas conditions of 1700 K and 40 atmospheres were considered along with those of a highly instrumented high temperature turbine test rig and a low temperature turbine rig that simulated the engine conditions. The analysis showed that the uncertainty in analytically predicting local blade temperature was as much as 98 K, or 7.6 percent of the metal absolute temperature, with current knowledge of the influence factors. The expected reductions in uncertainties in the influence factors with additional knowledge and tests should reduce the uncertainty in predicting blade metal temperature to 28 K, or 2.1 percent of the metal absolute temperature.

A photometric study of the Orion OB 1 association. 2: Photometric analysis

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.; Hesser, J. E.

1976-01-01

The procedures adopted for analysis of photometric data in terms of color excesses, intrinsic color indexes, absolute visual magnitudes, and rotational-velocity effects are discussed in detail for Orion association B-, intermediate (I)-, and AF-type stars. The effects of the nebular environment and a comparison of various calibrations of Balmer-line and four-color indexes are considered for the determination of individual absolute magnitudes for B-type stars. When absolute magnitudes of stars in the region of the Orion Nebula are determined from the beta index, emission mechanisms appear to spuriously brighten them. A detailed comparison of absolute magnitudes derived from Balmer-line indexes and MK spectral-type calibrations is presented. The data are also examined with regard to the effects of polarization and infrared excesses. The results suggest a complex combination of intracluster and circumstellar origins for these processes.

Detection of Unexpected High Correlations between Balance Calibration Loads and Load Residuals

NASA Technical Reports Server (NTRS)

Ulbrich, N.; Volden, T.

2014-01-01

An algorithm was developed for the assessment of strain-gage balance calibration data that makes it possible to systematically investigate potential sources of unexpected high correlations between calibration load residuals and applied calibration loads. The algorithm investigates correlations on a load series by load series basis. The linear correlation coefficient is used to quantify the correlations. It is computed for all possible pairs of calibration load residuals and applied calibration loads that can be constructed for the given balance calibration data set. An unexpected high correlation between a load residual and a load is detected if three conditions are met: (i) the absolute value of the correlation coefficient of a residual/load pair exceeds 0.95; (ii) the maximum of the absolute values of the residuals of a load series exceeds 0.25 % of the load capacity; (iii) the load component of the load series is intentionally applied. Data from a baseline calibration of a six-component force balance is used to illustrate the application of the detection algorithm to a real-world data set. This analysis also showed that the detection algorithm can identify load alignment errors as long as repeat load series are contained in the balance calibration data set that do not suffer from load alignment problems.

Probabilistic flood inundation mapping at ungauged streams due to roughness coefficient uncertainty in hydraulic modelling

NASA Astrophysics Data System (ADS)

Papaioannou, George; Vasiliades, Lampros; Loukas, Athanasios; Aronica, Giuseppe T.

2017-04-01

Probabilistic flood inundation mapping is performed and analysed at the ungauged Xerias stream reach, Volos, Greece. The study evaluates the uncertainty introduced by the roughness coefficient values on hydraulic models in flood inundation modelling and mapping. The well-established one-dimensional (1-D) hydraulic model, HEC-RAS is selected and linked to Monte-Carlo simulations of hydraulic roughness. Terrestrial Laser Scanner data have been used to produce a high quality DEM for input data uncertainty minimisation and to improve determination accuracy on stream channel topography required by the hydraulic model. Initial Manning's n roughness coefficient values are based on pebble count field surveys and empirical formulas. Various theoretical probability distributions are fitted and evaluated on their accuracy to represent the estimated roughness values. Finally, Latin Hypercube Sampling has been used for generation of different sets of Manning roughness values and flood inundation probability maps have been created with the use of Monte Carlo simulations. Historical flood extent data, from an extreme historical flash flood event, are used for validation of the method. The calibration process is based on a binary wet-dry reasoning with the use of Median Absolute Percentage Error evaluation metric. The results show that the proposed procedure supports probabilistic flood hazard mapping at ungauged rivers and provides water resources managers with valuable information for planning and implementing flood risk mitigation strategies.

Software For Calibration Of Polarimetric SAR Data

NASA Technical Reports Server (NTRS)

Van Zyl, Jakob; Zebker, Howard; Freeman, Anthony; Holt, John; Dubois, Pascale; Chapman, Bruce

1994-01-01

POLCAL (Polarimetric Radar Calibration) software tool intended to assist in calibration of synthetic-aperture radar (SAR) systems. In particular, calibrates Stokes-matrix-format data produced as standard product by NASA/Jet Propulsion Laboratory (JPL) airborne imaging synthetic aperture radar (AIRSAR). Version 4.0 of POLCAL is upgrade of version 2.0. New options include automatic absolute calibration of 89/90 data, distributed-target analysis, calibration of nearby scenes with corner reflectors, altitude or roll-angle corrections, and calibration of errors introduced by known topography. Reduces crosstalk and corrects phase calibration without use of ground calibration equipment. Written in FORTRAN 77.

Absolute Single Photoionization Cross Sections of Se^3+ For the Determination of Elemental Abundances in Planetary Nebulae

NASA Astrophysics Data System (ADS)

Esteves, David; Sterling, Nicholas; Aguilar, Alex; Kilcoyne, A. L. David; Phaneuf, Ronald; Bilodeau, Rene; Red, Eddie; McLaughlin, Brendan; Norrington, Patrick; Balance, Connor

2009-05-01

Numerical simulations show that derived elemental abundances in astrophysical nebulae can be uncertain by factors of two or more due to atomic data uncertainties alone, and of these uncertainties, absolute photoionization cross sections are the most important. Absolute single photoionization cross sections for Se^3+ ions have been measured from 42 eV to 56 eV at the ALS using the merged beams photo-ion technique. Theoretical photoionization cross section calculations were also performed for these ions using the state-of-the-art fully relativistic Dirac R-matrix code (DARC). The calculations show encouraging agreement with the experimental measurements.

COMMENT: Comment on 'Evaluation of the local value of the Earth gravity field in the context of the new definition of the kilogram'

NASA Astrophysics Data System (ADS)

Svitlov, S. M.

2010-06-01

A recent paper (Baumann et al 2009 Metrologia 46 178-86) presents a method to evaluate the free-fall acceleration at a desired point in space, as required for the watt balance experiment. The claimed uncertainty of their absolute gravity measurements is supported by two bilateral comparisons using two absolute gravimeters of the same type. This comment discusses the case where absolute gravity measurements are traceable to a key comparison reference value. Such an approach produces a more complete uncertainty budget and reduces the risk of the results of different watt balance experiments not being compatible.

Vacuum Radiance-Temperature Standard Facility for Infrared Remote Sensing at NIM

NASA Astrophysics Data System (ADS)

Hao, X. P.; Song, J.; Xu, M.; Sun, J. P.; Gong, L. Y.; Yuan, Z. D.; Lu, X. F.

2018-06-01

As infrared remote sensors are very important parts of Earth observation satellites, they must be calibrated based on the radiance temperature of a blackbody in a vacuum chamber prior to launch. The uncertainty of such temperature is thus an essential component of the sensors' uncertainty. This paper describes the vacuum radiance-temperature standard facility (VRTSF) at the National Institute of Metrology of China, which will serve to calibrate infrared remote sensors on Chinese meteorological satellites. The VRTSF can be used to calibrate vacuum blackbody radiance temperature, including those used to calibrate infrared remote sensors. The components of the VRTSF are described in this paper, including the VMTBB, the LNBB, the FTIR spectrometer, the reduced-background optical system, the vacuum chamber used to calibrate customers' blackbody, the vacuum-pumping system and the liquid-nitrogen-support system. The experimental methods and results are expounded. The uncertainty of the radiance temperature of VMTBB is 0.026 °C at 30 °C over 10 μm.

Precise dielectric property measurements and E-field probe calibration for specific absorption rate measurements using a rectangular waveguide

PubMed Central

Hakim, B M; Beard, B B; Davis, C C

2018-01-01

Specific absorption rate (SAR) measurements require accurate calculations of the dielectric properties of tissue-equivalent liquids and associated calibration of E-field probes. We developed a precise tissue-equivalent dielectric measurement and E-field probe calibration system. The system consists of a rectangular waveguide, electric field probe, and data control and acquisition system. Dielectric properties are calculated using the field attenuation factor inside the tissue-equivalent liquid and power reflectance inside the waveguide at the air/dielectric-slab interface. Calibration factors were calculated using isotropicity measurements of the E-field probe. The frequencies used are 900 MHz and 1800 MHz. The uncertainties of the measured values are within ±3%, at the 95% confidence level. Using the same waveguide for dielectric measurements as well as calibrating E-field probes used in SAR assessments eliminates a source of uncertainty. Moreover, we clearly identified the system parameters that affect the overall uncertainty of the measurement system. PMID:29520129

Calibration Method of an Ultrasonic System for Temperature Measurement

PubMed Central

Zhou, Chao; Wang, Yueke; Qiao, Chunjie; Dai, Weihua

2016-01-01

System calibration is fundamental to the overall accuracy of the ultrasonic temperature measurement, and it is basically involved in accurately measuring the path length and the system latency of the ultrasonic system. This paper proposes a method of high accuracy system calibration. By estimating the time delay between the transmitted signal and the received signal at several different temperatures, the calibration equations are constructed, and the calibrated results are determined with the use of the least squares algorithm. The formulas are deduced for calculating the calibration uncertainties, and the possible influential factors are analyzed. The experimental results in distilled water show that the calibrated path length and system latency can achieve uncertainties of 0.058 mm and 0.038 μs, respectively, and the temperature accuracy is significantly improved by using the calibrated results. The temperature error remains within ±0.04°C consistently, and the percentage error is less than 0.15%. PMID:27788252

Development and Characterization of a Low-Pressure Calibration System for Hypersonic Wind Tunnels

NASA Technical Reports Server (NTRS)

Green, Del L.; Everhart, Joel L.; Rhode, Matthew N.

2004-01-01

Minimization of uncertainty is essential for accurate ESP measurements at very low free-stream static pressures found in hypersonic wind tunnels. Statistical characterization of environmental error sources requires a well defined and controlled calibration method. A calibration system has been constructed and environmental control software developed to control experimentation to eliminate human induced error sources. The initial stability study of the calibration system shows a high degree of measurement accuracy and precision in temperature and pressure control. Control manometer drift and reference pressure instabilities induce uncertainty into the repeatability of voltage responses measured from the PSI System 8400 between calibrations. Methods of improving repeatability are possible through software programming and further experimentation.

Investigation of mass dependence effects for the accurate determination of molybdenum isotope amount ratios by MC-ICP-MS using synthetic isotope mixtures.

PubMed

Malinovsky, Dmitry; Dunn, Philip J H; Petrov, Panayot; Goenaga-Infante, Heidi

2015-01-01

Methodology for absolute Mo isotope amount ratio measurements by multicollector inductively coupled plasma-mass spectrometry (MC-ICP-MS) using calibration with synthetic isotope mixtures (SIMs) is presented. For the first time, synthetic isotope mixtures prepared from seven commercially available isotopically enriched molybdenum metal powders ((92)Mo, (94)Mo, (95)Mo, (96)Mo, (97)Mo, (98)Mo, and (100)Mo) are used to investigate whether instrumental mass discrimination of Mo isotopes in MC-ICP-MS is consistent with mass-dependent isotope distribution. The parent materials were dissolved and mixed as solutions to obtain mixtures with accurately known isotope amount ratios. The level of elemental impurities in the isotopically enriched molybdenum metal powders was quantified by ICP-MS by using both high-resolution and reaction cell instruments to completely resolve spectral interferences. The Mo isotope amount ratio values with expanded uncertainty (k = 2), determined by MC-ICP-MS for a high-purity Mo rod from Johnson Matthey, were as follows: (92)Mo/(95)Mo = 0.9235(9), (94)Mo/(95)Mo = 0.5785(8), (96)Mo/(95)Mo = 1.0503(9), (97)Mo/(95)Mo = 0.6033(6), (98)Mo/(95)Mo = 1.5291(20), and (100)Mo/(95)Mo = 0.6130(7). A full uncertainty budget for the measurements is presented which shows that the largest contribution to the uncertainty budget comes from correction for elemental impurities (∼51%), followed by the contribution from weighing operations (∼26 %). The atomic weight of molybdenum was calculated to be 95.947(2); the uncertainty in parentheses is expanded uncertainty with the coverage factor of 2. A particular advantage of the developed method is that calibration factors for all six Mo isotope amount ratios, involving the (95)Mo isotope, were experimentally determined. This allows avoiding any assumption on mass-dependent isotope fractions in MC-ICP-MS, inherent to the method of double spike previously used for Mo isotope amount ratio measurements. However, data obtained in this study show that instrumental mass discrimination in MC-ICP-MS is consistent with mass-dependent Mo isotope fractionation. This was demonstrated by a good agreement between experimentally obtained and theoretically expected values of the exponent of isotope fractionation, β, for each triad of Mo isotopes.

First Results of Field Absolute Calibration of the GPS Receiver Antenna at Wuhan University.

PubMed

Hu, Zhigang; Zhao, Qile; Chen, Guo; Wang, Guangxing; Dai, Zhiqiang; Li, Tao

2015-11-13

GNSS receiver antenna phase center variations (PCVs), which arise from the non-spherical phase response of GNSS signals have to be well corrected for high-precision GNSS applications. Without using a precise antenna phase center correction (PCC) model, the estimated position of a station monument will lead to a bias of up to several centimeters. The Chinese large-scale research project "Crustal Movement Observation Network of China" (CMONOC), which requires high-precision positions in a comprehensive GPS observational network motived establishment of a set of absolute field calibrations of the GPS receiver antenna located at Wuhan University. In this paper the calibration facilities are firstly introduced and then the multipath elimination and PCV estimation strategies currently used are elaborated. The validation of estimated PCV values of test antenna are finally conducted, compared with the International GNSS Service (IGS) type values. Examples of TRM57971.00 NONE antenna calibrations from our calibration facility demonstrate that the derived PCVs and IGS type mean values agree at the 1 mm level.

Seafloor multibeam backscatter calibration experiment: comparing 45°-tilted 38-kHz split-beam echosounder and 30-kHz multibeam data

NASA Astrophysics Data System (ADS)

Ladroit, Yoann; Lamarche, Geoffroy; Pallentin, Arne

2018-06-01

Obtaining absolute seafloor backscatter measurements from hydrographic multibeam echosounders is yet to be achieved. We propose a low-cost experiment to calibrate the various acquisition modes of a 30-kHz Kongsberg EM 302 multibeam echosounder in a range of water depths. We use a 38-kHz Simrad EK60 calibrated fisheries split-beam echosounder mounted at 45° angle on the vessel's hull as a reference for the calibration. The processing to extract seafloor backscatter from the EK60 requires bottom detection, ray tracing and motion compensation to obtain acceptable geo-referenced backscatter measurements from this non-hydrographic system. Our experiment was run in Cook Strait, New Zealand, on well-known seafloor patches in shallow, mid, and deep-water depths. Despite acquisition issues due to weather, our results demonstrate the strong potential of such an approach to obtain system's absolute calibration which is required for quantitative use of backscatter strength data.

Corsica: A Multi-Mission Absolute Calibration Site

NASA Astrophysics Data System (ADS)

Bonnefond, P.; Exertier, P.; Laurain, O.; Guinle, T.; Femenias, P.

2013-09-01

In collaboration with the CNES and NASA oceanographic projects (TOPEX/Poseidon and Jason), the OCA (Observatoire de la Côte d'Azur) developed a verification site in Corsica since 1996, operational since 1998. CALibration/VALidation embraces a wide variety of activities, ranging from the interpretation of information from internal-calibration modes of the sensors to validation of the fully corrected estimates of the reflector heights using in situ data. Now, Corsica is, like the Harvest platform (NASA side) [14], an operating calibration site able to support a continuous monitoring with a high level of accuracy: a 'point calibration' which yields instantaneous bias estimates with a 10-day repeatability of 30 mm (standard deviation) and mean errors of 4 mm (standard error). For a 35-day repeatability (ERS, Envisat), due to a smaller time series, the standard error is about the double ( 7 mm).In this paper, we will present updated results of the absolute Sea Surface Height (SSH) biases for TOPEX/Poseidon (T/P), Jason-1, Jason-2, ERS-2 and Envisat.

Cross-calibration of the Terra MODIS, Landsat 7 ETM+ and EO-1 ALI sensors using near-simultaneous surface observation over the Railroad Valley Playa, Nevada, test site

USGS Publications Warehouse

Chander, G.; Angal, A.; Choi, T.; Meyer, D.J.; Xiong, X.; Teillet, P.M.

2007-01-01

A cross-calibration methodology has been developed using coincident image pairs from the Terra Moderate Resolution Imaging Spectroradiometer (MODIS), the Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and the Earth Observing EO-1 Advanced Land Imager (ALI) to verify the absolute radiometric calibration accuracy of these sensors with respect to each other. To quantify the effects due to different spectral responses, the Relative Spectral Responses (RSR) of these sensors were studied and compared by developing a set of "figures-of-merit." Seven cloud-free scenes collected over the Railroad Valley Playa, Nevada (RVPN), test site were used to conduct the cross-calibration study. This cross-calibration approach was based on image statistics from near-simultaneous observations made by different satellite sensors. Homogeneous regions of interest (ROI) were selected in the image pairs, and the mean target statistics were converted to absolute units of at-sensor reflectance. Using these reflectances, a set of cross-calibration equations were developed giving a relative gain and bias between the sensor pair.

Absolute Flux Calibration of the IRAC Instrument on the Spitzer Space Telescope Using Hubble Space Telescope Flux Standards

NASA Astrophysics Data System (ADS)

Bohlin, R. C.; Gordon, K. D.; Rieke, G. H.; Ardila, D.; Carey, S.; Deustua, S.; Engelbracht, C.; Ferguson, H. C.; Flanagan, K.; Kalirai, J.; Meixner, M.; Noriega-Crespo, A.; Su, K. Y. L.; Tremblay, P.-E.

2011-05-01

The absolute flux calibration of the James Webb Space Telescope (JWST) will be based on a set of stars observed by the Hubble and Spitzer Space Telescopes. In order to cross-calibrate the two facilities, several A, G, and white dwarf stars are observed with both Spitzer and Hubble and are the prototypes for a set of JWST calibration standards. The flux calibration constants for the four Spitzer IRAC bands 1-4 are derived from these stars and are 2.3%, 1.9%, 2.0%, and 0.5% lower than the official cold-mission IRAC calibration of Reach et al., i.e., in agreement within their estimated errors of ~2%. The causes of these differences lie primarily in the IRAC data reduction and secondarily in the spectral energy distributions of our standard stars. The independent IRAC 8 μm band-4 fluxes of Rieke et al. are about 1.5% ± 2% higher than those of Reach et al. and are also in agreement with our 8 μm result.

Radiation calibration for LWIR Hyperspectral Imager Spectrometer

NASA Astrophysics Data System (ADS)

Yang, Zhixiong; Yu, Chunchao; Zheng, Wei-jian; Lei, Zhenggang; Yan, Min; Yuan, Xiaochun; Zhang, Peizhong

2014-11-01

The radiometric calibration of LWIR Hyperspectral imager Spectrometer is presented. The lab has been developed to LWIR Interferometric Hyperspectral imager Spectrometer Prototype(CHIPED-I) to study Lab Radiation Calibration, Two-point linear calibration is carried out for the spectrometer by using blackbody respectively. Firstly, calibration measured relative intensity is converted to the absolute radiation lightness of the object. Then, radiation lightness of the object is is converted the brightness temperature spectrum by the method of brightness temperature. The result indicated †that this method of Radiation Calibration calibration was very good.

How well do we know the incoming solar infrared radiation?

NASA Astrophysics Data System (ADS)

Elsey, Jonathan; Coleman, Marc; Gardiner, Tom; Shine, Keith

2017-04-01

The solar spectral irradiance (SSI) has been identified as a key climate variable by the Global Climate Observing System (Bojinski et al. 2014, Bull. Amer. Meteor. Soc.). It is of importance in the modelling of atmospheric radiative transfer, and the quantification of the global energy budget. However, in the near-infrared spectral region (between 2000-10000 cm-1) there exists a discrepancy of 7% between spectra measured from the space-based SOLSPEC instrument (Thuillier et al. 2015, Solar Physics) and those from a ground-based Langley technique (Bolseé et al. 2014, Solar Physics). This same difference is also present between different analyses of the SOLSPEC data. This work aims to reconcile some of these differences by presenting an estimate of the near-infrared SSI obtained from ground-based measurements taken using an absolutely calibrated Fourier transform spectrometer. Spectra are obtained both using the Langley technique and by direct comparison with a radiative transfer model, with appropriate handling of both aerosol scattering and molecular continuum absorption. Particular focus is dedicated to the quantification of uncertainty in these spectra, from both the inherent uncertainty in the measurement setup and that from the use of the radiative transfer code and its inputs.

Comparison of model estimated and measured direct-normal solar irradiance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halthore, R.N.; Schwartz, S.E.; Michalsky, J.J.

1997-12-01

Direct-normal solar irradiance (DNSI), the energy in the solar spectrum incident in unit time at the Earth{close_quote}s surface on a unit area perpendicular to the direction to the Sun, depends only on atmospheric extinction of solar energy without regard to the details of the extinction, whether absorption or scattering. Here we report a set of closure experiments performed in north central Oklahoma in April 1996 under cloud-free conditions, wherein measured atmospheric composition and aerosol optical thickness are input to a radiative transfer model, MODTRAN 3, to estimate DNSI, which is then compared with measured values obtained with normal incidence pyrheliometersmore » and absolute cavity radiometers. Uncertainty in aerosol optical thickness (AOT) dominates the uncertainty in DNSI calculation. AOT measured by an independently calibrated Sun photometer and a rotating shadow-band radiometer agree to within the uncertainties of each measurement. For 36 independent comparisons the agreement between measured and model-estimated values of DNSI falls within the combined uncertainties in the measurement (0.3{endash}0.7{percent}) and model calculation (1.8{percent}), albeit with a slight average model underestimate ({minus}0.18{plus_minus}0.94){percent}; for a DNSI of 839Wm{sup {minus}2} this corresponds to {minus}1.5{plus_minus}7.9Wm{sup {minus}2}. The agreement is nearly independent of air mass and water-vapor path abundance. These results thus establish the accuracy of the current knowledge of the solar spectrum, its integrated power, and the atmospheric extinction as a function of wavelength as represented in MODTRAN 3. An important consequence is that atmospheric absorption of short-wave energy is accurately parametrized in the model to within the above uncertainties. {copyright} 1997 American Geophysical Union« less

14 MeV calibration of JET neutron detectors—phase 1: calibration and characterization of the neutron source

NASA Astrophysics Data System (ADS)

Batistoni, P.; Popovichev, S.; Cufar, A.; Ghani, Z.; Giacomelli, L.; Jednorog, S.; Klix, A.; Lilley, S.; Laszynska, E.; Loreti, S.; Packer, L.; Peacock, A.; Pillon, M.; Price, R.; Rebai, M.; Rigamonti, D.; Roberts, N.; Tardocchi, M.; Thomas, D.; Contributors, JET

2018-02-01

In view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is  ±10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e. the neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within  ±5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances.

Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers

NASA Astrophysics Data System (ADS)

Lye, J. E.; Harty, P. D.; Butler, D. J.; Crosbie, J. C.; Livingstone, J.; Poole, C. M.; Ramanathan, G.; Wright, T.; Stevenson, A. W.

2016-06-01

The absolute dose delivered to a dynamically scanned sample in the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter anticipated to be established as a primary standard for synchrotron dosimetry. The calorimetry was compared to measurements using a free-air chamber (FAC), a PTW 31 014 Pinpoint ionization chamber, and a PTW 34 001 Roos ionization chamber. The IMBL beam height is limited to approximately 2 mm. To produce clinically useful beams of a few centimetres the beam must be scanned in the vertical direction. In practice it is the patient/detector that is scanned and the scanning velocity defines the dose that is delivered. The calorimeter, FAC, and Roos chamber measure the dose area product which is then converted to central axis dose with the scanned beam area derived from Monte Carlo (MC) simulations and film measurements. The Pinpoint chamber measures the central axis dose directly and does not require beam area measurements. The calorimeter and FAC measure dose from first principles. The calorimetry requires conversion of the measured absorbed dose to graphite to absorbed dose to water using MC calculations with the EGSnrc code. Air kerma measurements from the free air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. The two ionization chambers are secondary standards requiring calibration with kilovoltage x-ray tubes. The Roos and Pinpoint chambers were calibrated against the Australian primary standard for air kerma at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Agreement of order 2% or better was obtained between the calorimetry and ionization chambers. The FAC measured a dose 3-5% higher than the calorimetry, within the stated uncertainties.

SU-F-T-569: Implementation of a Patient Specific QA Method Using EBT-XD for CyberKnife SRS/SBRT Plans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zerouali, K; Aubry, J; Doucet, R

2016-06-15

Purpose: To implement the new EBT-XD Gafchromic films for accurate dosimetric and geometric validation of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) CyberKnife (CK) patient specific QA. Methods: Film calibration was performed using a triplechannel film analysis on an Epson 10000XL scanner. Calibration films were irradiated using a Varian Clinac 21EX flattened beam (0 to 20 Gy), to ensure sufficient dose homogeneity. Films were scanned to a resolution of 0.3 mm, 24 hours post irradiation following a well-defined protocol. A set of 12 QA was performed for several types of CK plans: trigeminal neuralgia, brain metastasis, prostate andmore » lung tumors. A custom made insert for the CK head phantom has been manufactured to yield an accurate measured to calculated dose registration. When the high dose region was large enough, absolute dose was also measured with an ionization chamber. Dose calculation is performed using MultiPlan Ray-tracing algorithm for all cases since the phantom is mostly made from near water-equivalent plastic. Results: Good agreement (<2%) was found between the dose to the chamber and the film, when a chamber measurement was possible The average dose difference and standard deviations between film measurements and TPS calculations were respectively 1.75% and 3%. The geometric accuracy has been estimated to be <1 mm, combining robot positioning uncertainty and film registration to calculated dose. Conclusion: Patient specific QA measurements using EBT-XD films yielded a full 2D dose plane with high spatial resolution and acceptable dose accuracy. This method is particularly promising for trigeminal neuralgia plan QA, where the positioning of the spatial dose distribution is equally or more important than the absolute delivered dose to achieve clinical goals.« less

An Integrated Understanding of Confidence and User Calibration in Information Systems Use

ERIC Educational Resources Information Center

Tang, Fengchun

2012-01-01

Dealing with uncertainty is a critical part of human decision-making and confidence reflects one's belief about the relative likelihood that various outcomes occur when making decision under uncertainty. Unfortunately, confidence often deviates from the actual quality of the decision, leading to under- or over-confidence. Calibration, the…

Experimental validation of a self-calibrating cryogenic mass flowmeter

NASA Astrophysics Data System (ADS)

Janzen, A.; Boersch, M.; Burger, B.; Drache, J.; Ebersoldt, A.; Erni, P.; Feldbusch, F.; Oertig, D.; Grohmann, S.

2017-12-01

The Karlsruhe Institute of Technology (KIT) and the WEKA AG jointly develop a commercial flowmeter for application in helium cryostats. The flowmeter functions according to a new thermal measurement principle that eliminates all systematic uncertainties and enables self-calibration during real operation. Ideally, the resulting uncertainty of the measured flow rate is only dependent on signal noises, which are typically very small with regard to the measured value. Under real operating conditions, cryoplant-dependent flow rate fluctuations induce an additional uncertainty, which follows from the sensitivity of the method. This paper presents experimental results with helium at temperatures between 30 and 70 K and flow rates in the range of 4 to 12 g/s. The experiments were carried out in a control cryostat of the 2 kW helium refrigerator of the TOSKA test facility at KIT. Inside the cryostat, the new flowmeter was installed in series with a Venturi tube that was used for reference measurements. The measurement results demonstrate the self-calibration capability during real cryoplant operation. The influences of temperature and flow rate fluctuations on the self-calibration uncertainty are discussed.

40 CFR 1066.310 - Coastdown procedures for vehicles above 14,000 pounds GVWR.

Code of Federal Regulations, 2014 CFR

2014-07-01

...) Calibrate the equipment by running the zero-wind and zero-angle calibrations within 24 hours before... = mean ambient absolute temperature during testing, in K. p act = average ambient pressuring during the...

The Zugspitze radiative closure experiment for quantifying water vapor absorption over the terrestrial and solar infrared - Part 2: Accurate calibration of high spectral-resolution infrared measurements of surface solar radiation

NASA Astrophysics Data System (ADS)

Reichert, Andreas; Rettinger, Markus; Sussmann, Ralf

2016-09-01

Quantitative knowledge of water vapor absorption is crucial for accurate climate simulations. An open science question in this context concerns the strength of the water vapor continuum in the near infrared (NIR) at atmospheric temperatures, which is still to be quantified by measurements. This issue can be addressed with radiative closure experiments using solar absorption spectra. However, the spectra used for water vapor continuum quantification have to be radiometrically calibrated. We present for the first time a method that yields sufficient calibration accuracy for NIR water vapor continuum quantification in an atmospheric closure experiment. Our method combines the Langley method with spectral radiance measurements of a high-temperature blackbody calibration source (< 2000 K). The calibration scheme is demonstrated in the spectral range 2500 to 7800 cm-1, but minor modifications to the method enable calibration also throughout the remainder of the NIR spectral range. The resulting uncertainty (2σ) excluding the contribution due to inaccuracies in the extra-atmospheric solar spectrum (ESS) is below 1 % in window regions and up to 1.7 % within absorption bands. The overall radiometric accuracy of the calibration depends on the ESS uncertainty, on which at present no firm consensus has been reached in the NIR. However, as is shown in the companion publication Reichert and Sussmann (2016), ESS uncertainty is only of minor importance for the specific aim of this study, i.e., the quantification of the water vapor continuum in a closure experiment. The calibration uncertainty estimate is substantiated by the investigation of calibration self-consistency, which yields compatible results within the estimated errors for 91.1 % of the 2500 to 7800 cm-1 range. Additionally, a comparison of a set of calibrated spectra to radiative transfer model calculations yields consistent results within the estimated errors for 97.7 % of the spectral range.

Photometry with FORS

NASA Astrophysics Data System (ADS)

Freudling, W.; Møller, P.; Patat, F.; Moehler, S.; Romaniello, M.; Jehin, E.; O'Brien, K.; Izzo, C.; Pompei, E.

Photometric calibration observations are routinely carried out with all ESO imaging cameras in every clear night. The nightly zeropoints derived from these observations are accurate to about 10%. Recently, we have started the FORS Absolute Photometry Project (FAP) to investigate, if and how percent-level absolute photometric accuracy can be achieved with FORS1, and how such photometric calibration can be offered to observers. We found that there are significant differences between the sky-flats and the true photometric response of the instrument which partially depend on the rotator angle. A second order correction to the sky-flat significantly improves the relative photometry within the field. We demonstrate the feasibility of percent level photometry and describe the calibrations necessary to achieve that level of accuracy.

Dating Tips for Divergence-Time Estimation.

PubMed

O'Reilly, Joseph E; Dos Reis, Mario; Donoghue, Philip C J

2015-11-01

The molecular clock is the only viable means of establishing an accurate timescale for Life on Earth, but it remains reliant on a capricious fossil record for calibration. 'Tip-dating' promises a conceptual advance, integrating fossil species among their living relatives using molecular/morphological datasets and evolutionary models. Fossil species of known age establish calibration directly, and their phylogenetic uncertainty is accommodated through the co-estimation of time and topology. However, challenges remain, including a dearth of effective models of morphological evolution, rate correlation, the non-random nature of missing characters in fossil data, and, most importantly, accommodating uncertainty in fossil age. We show uncertainty in fossil-dating propagates to divergence-time estimates, yielding estimates that are older and less precise than those based on traditional node calibration. Ultimately, node and tip calibrations are not mutually incompatible and may be integrated to achieve more accurate and precise evolutionary timescales. Copyright © 2015 Elsevier Ltd. All rights reserved.

Long Term Uncertainty Investigations of 1 MN Force Calibration Machine at NPL, India (NPLI)

NASA Astrophysics Data System (ADS)

Kumar, Rajesh; Kumar, Harish; Kumar, Anil; Vikram

2012-01-01

The present paper is an attempt to study the long term uncertainty of 1 MN hydraulic multiplication system (HMS) force calibration machine (FCM) at the National Physical Laboratory, India (NPLI), which is used for calibration of the force measuring instruments in the range of 100 kN - 1 MN. The 1 MN HMS FCM was installed at NPLI in 1993 and was built on the principle of hydraulic amplifications of dead weights. The best measurement capability (BMC) of the machine is ± 0.025% (k = 2) and it is traceable to national standards by means of precision force transfer standards (FTS). The present study discusses the uncertainty variations of the 1 MN HMS FCM over the years and describes the other parameters in detail, too. The 1 MN HMS FCM was calibrated in the years 2004, 2006, 2007, 2008, 2009 and 2010 and the results have been reported.

40 CFR 1065.790 - Mass standards.

Code of Federal Regulations, 2013 CFR

2013-07-01

... are certified as NIST-traceable within 0.1% uncertainty. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your highest calibration weight has no greater...

40 CFR 1065.790 - Mass standards.

Code of Federal Regulations, 2014 CFR

2014-07-01

... are certified as NIST-traceable within 0.1% uncertainty. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your highest calibration weight has no greater...

40 CFR 1065.790 - Mass standards.

Code of Federal Regulations, 2012 CFR

2012-07-01

... are certified as NIST-traceable within 0.1% uncertainty. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your highest calibration weight has no greater...

Relationship between LIBS Ablation and Pit Volume for Geologic Samples: Applications for in situ Absolute Geochronology

NASA Technical Reports Server (NTRS)

Devismes, D.; Cohen, Barbara A.

2014-01-01

In planetary sciences, in situ absolute geochronology is a scientific and engineering challenge. Currently, the age of the Martian surface can only be determined by crater density counting. However this method has significant uncertainties and needs to be calibrated with absolute ages. We are developing an instrument to acquire in situ absolute geochronology based on the K-Ar method. The protocol is based on the laser ablation of a rock by hundreds of laser pulses. Laser Induced Breakdown Spectroscopy (LIBS) gives the potassium content of the ablated material and a mass spectrometer (quadrupole or ion trap) measures the quantity of 40Ar released. In order to accurately measure the quantity of released 40Ar in cases where Ar is an atmospheric constituent (e.g., Mars), the sample is first put into a chamber under high vacuum. The 40Arquantity, the concentration of K and the estimation of the ablated mass are the parameters needed to give the age of the rocks. The main uncertainties with this method are directly linked to the measures of the mass (typically some µg) and of the concentration of K by LIBS (up to 10%). Because the ablated mass is small compared to the mass of the sample, and because material is redeposited onto the sample after ablation, it is not possible to directly measure the ablated mass. Our current protocol measures the ablated volume and estimates the sample density to calculate ablated mass. The precision and accuracy of this method may be improved by using knowledge of the sample's geologic properties to predict its response to laser ablation, i.e., understanding whether natural samples have a predictable relationship between laser energy deposited and resultant ablation volume. In contrast to most previous studies of laser ablation, theoretical equations are not highly applicable. The reasons are numerous, but the most important are: a) geologic rocks are complex, polymineralic materials; b) the conditions of ablation are unusual (for example, variable vacuum pressure), and c) the ablation is made with hundreds of successive laser pulses. In this work, we aim to understand the effects that occur on LIBS spectra when a homogeneous rock or a mineral is ablated under high vacuum. Understanding these effects is important to define best practices for LIBS measurements and may lead to improved measurement (or possibly prediction) of the ablated volume. We will describe our laboratory approach and first results, and discuss its utility for situ absolute geochronology campaigns.

ACCESS: Design and Sub-System Performance

NASA Technical Reports Server (NTRS)

Kaiser, Mary Elizabeth; Morris, Matthew J.; McCandliss, Stephan R.; Rasucher, Bernard J.; Kimble, Randy A.; Kruk, Jeffrey W.; Pelton, Russell; Mott, D. Brent; Wen, Hiting; Foltz, Roger;

A Summary of Lightpipe Radiation Thermometry Research at NIST

PubMed Central

Tsai, Benjamin K.

2006-01-01

During the last 10 years, research in light-pipe radiation thermometry has significantly reduced the uncertainties for temperature measurements in semiconductor processing. The National Institute of Standards and Technology (NIST) has improved the calibration of lightpipe radiation thermometers (LPRTs), the characterization procedures for LPRTs, the in situ calibration of LPRTs using thin-film thermocouple (TFTC) test wafers, and the application of model-based corrections to improve LPRT spectral radiance temperatures. Collaboration with industry on implementing techniques and ideas established at NIST has led to improvements in temperature measurements in semiconductor processing. LPRTs have been successfully calibrated at NIST for rapid thermal processing (RTP) applications using a sodium heat-pipe blackbody between 700 °C and 900 °C with an uncertainty of about 0.3 °C (k = 1) traceable to the International Temperature Scale of 1990. Employing appropriate effective emissivity models, LPRTs have been used to determine the wafer temperature in the NIST RTP Test Bed with an uncertainty of 3.5 °C. Using a TFTC wafer for calibration, the LPRT can measure the wafer temperature in the NIST RTP Test Bed with an uncertainty of 2.3 °C. Collaborations with industry in characterizing and calibrating LPRTs will be summarized, and future directions for LPRT research will be discussed. PMID:27274914

A Summary of Lightpipe Radiation Thermometry Research at NIST.

PubMed

Tsai, Benjamin K

2006-01-01

During the last 10 years, research in light-pipe radiation thermometry has significantly reduced the uncertainties for temperature measurements in semiconductor processing. The National Institute of Standards and Technology (NIST) has improved the calibration of lightpipe radiation thermometers (LPRTs), the characterization procedures for LPRTs, the in situ calibration of LPRTs using thin-film thermocouple (TFTC) test wafers, and the application of model-based corrections to improve LPRT spectral radiance temperatures. Collaboration with industry on implementing techniques and ideas established at NIST has led to improvements in temperature measurements in semiconductor processing. LPRTs have been successfully calibrated at NIST for rapid thermal processing (RTP) applications using a sodium heat-pipe blackbody between 700 °C and 900 °C with an uncertainty of about 0.3 °C (k = 1) traceable to the International Temperature Scale of 1990. Employing appropriate effective emissivity models, LPRTs have been used to determine the wafer temperature in the NIST RTP Test Bed with an uncertainty of 3.5 °C. Using a TFTC wafer for calibration, the LPRT can measure the wafer temperature in the NIST RTP Test Bed with an uncertainty of 2.3 °C. Collaborations with industry in characterizing and calibrating LPRTs will be summarized, and future directions for LPRT research will be discussed.

A methodology for obtaining on-orbit SI-traceable spectral radiance measurements in the thermal infrared

NASA Astrophysics Data System (ADS)

Dykema, John A.; Anderson, James G.

2006-06-01

A methodology to achieve spectral thermal radiance measurements from space with demonstrable on-orbit traceability to the International System of Units (SI) is described. This technique results in measurements of infrared spectral radiance R(\\tilde {\\upsilon }) , with spectral index \\tilde {\\upsilon } in cm-1, with a relative combined uncertainty u_c[R(\\tilde {\\upsilon })] of 0.0015 (k = 1) for the average mid-infrared radiance emitted by the Earth. This combined uncertainty, expressed in brightness temperature units, is equivalent to ±0.1 K at 250 K at 750 cm-1. This measurement goal is achieved by utilizing a new method for infrared scale realization combined with an instrument design optimized to minimize component uncertainties and admit tests of radiometric performance. The SI traceability of the instrument scale is established by evaluation against source-based and detector-based infrared scales in defined laboratory protocols before launch. A novel strategy is executed to ensure fidelity of on-orbit calibration to the pre-launch scale. This strategy for on-orbit validation relies on the overdetermination of instrument calibration. The pre-launch calibration against scales derived from physically independent paths to the base SI units provides the foundation for a critical analysis of the overdetermined on-orbit calibration to establish an SI-traceable estimate of the combined measurement uncertainty. Redundant calibration sources and built-in diagnostic tests to assess component measurement uncertainties verify the SI traceability of the instrument calibration over the mission lifetime. This measurement strategy can be realized by a practical instrument, a prototype Fourier-transform spectrometer under development for deployment on a small satellite. The measurement record resulting from the methodology described here meets the observational requirements for climate monitoring and climate model testing and improvement.

Effect of Correlated Precision Errors on Uncertainty of a Subsonic Venturi Calibration

NASA Technical Reports Server (NTRS)

Hudson, S. T.; Bordelon, W. J., Jr.; Coleman, H. W.

1996-01-01

An uncertainty analysis performed in conjunction with the calibration of a subsonic venturi for use in a turbine test facility produced some unanticipated results that may have a significant impact in a variety of test situations. Precision uncertainty estimates using the preferred propagation techniques in the applicable American National Standards Institute/American Society of Mechanical Engineers standards were an order of magnitude larger than precision uncertainty estimates calculated directly from a sample of results (discharge coefficient) obtained at the same experimental set point. The differences were attributable to the effect of correlated precision errors, which previously have been considered negligible. An analysis explaining this phenomenon is presented. The article is not meant to document the venturi calibration, but rather to give a real example of results where correlated precision terms are important. The significance of the correlated precision terms could apply to many test situations.

Mathematical modeling of a survey-meter used to measure radioactivity in human thyroids: Monte Carlo calculations of the device response and uncertainties

PubMed Central

Khrutchinsky, Arkady; Drozdovitch, Vladimir; Kutsen, Semion; Minenko, Victor; Khrouch, Valeri; Luckyanov, Nickolas; Voillequé, Paul; Bouville, André

2012-01-01

This paper presents results of Monte Carlo modeling of the SRP-68-01 survey meter used to measure exposure rates near the thyroid glands of persons exposed to radioactivity following the Chernobyl accident. This device was not designed to measure radioactivity in humans. To estimate the uncertainty associated with the measurement results, a mathematical model of the SRP-68-01 survey meter was developed and verified. A Monte Carlo method of numerical simulation of radiation transport has been used to calculate the calibration factor for the device and evaluate its uncertainty. The SRP-68-01 survey meter scale coefficient, an important characteristic of the device, was also estimated in this study. The calibration factors of the survey meter were calculated for 131I, 132I, 133I, and 135I content in the thyroid gland for six age groups of population: newborns; children aged 1 yr, 5 yr, 10 yr, 15 yr; and adults. A realistic scenario of direct thyroid measurements with an “extended” neck was used to calculate the calibration factors for newborns and one-year-olds. Uncertainties in the device calibration factors due to variability of the device scale coefficient, variability in thyroid mass and statistical uncertainty of Monte Carlo method were evaluated. Relative uncertainties in the calibration factor estimates were found to be from 0.06 for children aged 1 yr to 0.1 for 10-yr and 15-yr children. The positioning errors of the detector during measurements deviate mainly in one direction from the estimated calibration factors. Deviations of the device position from the proper geometry of measurements were found to lead to overestimation of the calibration factor by up to 24 percent for adults and up to 60 percent for 1-yr children. The results of this study improve the estimates of 131I thyroidal content and, consequently, thyroid dose estimates that are derived from direct thyroid measurements performed in Belarus shortly after the Chernobyl accident. PMID:22245289

A Hierarchical Multi-Model Approach for Uncertainty Segregation, Prioritization and Comparative Evaluation of Competing Modeling Propositions

NASA Astrophysics Data System (ADS)

Tsai, F. T.; Elshall, A. S.; Hanor, J. S.

2012-12-01

Subsurface modeling is challenging because of many possible competing propositions for each uncertain model component. How can we judge that we are selecting the correct proposition for an uncertain model component out of numerous competing propositions? How can we bridge the gap between synthetic mental principles such as mathematical expressions on one hand, and empirical observation such as observation data on the other hand when uncertainty exists on both sides? In this study, we introduce hierarchical Bayesian model averaging (HBMA) as a multi-model (multi-proposition) framework to represent our current state of knowledge and decision for hydrogeological structure modeling. The HBMA framework allows for segregating and prioritizing different sources of uncertainty, and for comparative evaluation of competing propositions for each source of uncertainty. We applied the HBMA to a study of hydrostratigraphy and uncertainty propagation of the Southern Hills aquifer system in the Baton Rouge area, Louisiana. We used geophysical data for hydrogeological structure construction through indictor hydrostratigraphy method and used lithologic data from drillers' logs for model structure calibration. However, due to uncertainty in model data, structure and parameters, multiple possible hydrostratigraphic models were produced and calibrated. The study considered four sources of uncertainties. To evaluate mathematical structure uncertainty, the study considered three different variogram models and two geological stationarity assumptions. With respect to geological structure uncertainty, the study considered two geological structures with respect to the Denham Springs-Scotlandville fault. With respect to data uncertainty, the study considered two calibration data sets. These four sources of uncertainty with their corresponding competing modeling propositions resulted in 24 calibrated models. The results showed that by segregating different sources of uncertainty, HBMA analysis provided insights on uncertainty priorities and propagation. In addition, it assisted in evaluating the relative importance of competing modeling propositions for each uncertain model component. By being able to dissect the uncertain model components and provide weighted representation of the competing propositions for each uncertain model component based on the background knowledge, the HBMA functions as an epistemic framework for advancing knowledge about the system under study.

Spreadsheet for designing valid least-squares calibrations: A tutorial.

PubMed

Bettencourt da Silva, Ricardo J N

2016-02-01

Instrumental methods of analysis are used to define the price of goods, the compliance of products with a regulation, or the outcome of fundamental or applied research. These methods can only play their role properly if reported information is objective and their quality is fit for the intended use. If measurement results are reported with an adequately small measurement uncertainty both of these goals are achieved. The evaluation of the measurement uncertainty can be performed by the bottom-up approach, that involves a detailed description of the measurement process, or using a pragmatic top-down approach that quantify major uncertainty components from global performance data. The bottom-up approach is not so frequently used due to the need to master the quantification of individual components responsible for random and systematic effects that affect measurement results. This work presents a tutorial that can be easily used by non-experts in the accurate evaluation of the measurement uncertainty of instrumental methods of analysis calibrated using least-squares regressions. The tutorial includes the definition of the calibration interval, the assessments of instrumental response homoscedasticity, the definition of calibrators preparation procedure required for least-squares regression model application, the assessment of instrumental response linearity and the evaluation of measurement uncertainty. The developed measurement model is only applicable in calibration ranges where signal precision is constant. A MS-Excel file is made available to allow the easy application of the tutorial. This tool can be useful for cases where top-down approaches cannot produce results with adequately low measurement uncertainty. An example of the application of this tool to the determination of nitrate in water by ion chromatography is presented. Copyright © 2015 Elsevier B.V. All rights reserved.

40 CFR 1065.790 - Mass standards.

Code of Federal Regulations, 2010 CFR

2010-07-01

... are certified as NIST-traceable within 0.1 % uncertainty. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your lowest calibration weight has no greater than...

40 CFR 1065.790 - Mass standards.

Code of Federal Regulations, 2011 CFR

2011-07-01

... are certified as NIST-traceable within 0.1 % uncertainty. Calibration weights may be certified by any calibration lab that maintains NIST-traceability. Make sure your lowest calibration weight has no greater than...

The Absolute Reflectance and New Calibration Site of the Moon

NASA Astrophysics Data System (ADS)

Wu, Yunzhao; Wang, Zhenchao; Cai, Wei; Lu, Yu

2018-05-01

How bright the Moon is forms a simple but fundamental and important question. Although numerous efforts have been made to answer this question such as use of sophisticated electro-optical measurements and suggestions for calibration sites, the answer is still debated. An in situ measurement with a calibration panel on the surface of the Moon is crucial for obtaining the accurate absolute reflectance and resolving the debate. China’s Chang’E-3 (CE-3) “Yutu” rover accomplished this type of measurement using the Visible-Near Infrared Spectrometer (VNIS). The measurements of the VNIS, which were at large emission and phase angles, complement existing measurements for the range of photometric geometry. The in situ reflectance shows that the CE-3 landing site is very dark with an average reflectance of 3.86% in the visible bands. The results are compared with recent mission instruments: the Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC), the Spectral Profiler (SP) on board the SELENE, the Moon Mineralogy Mapper (M3) on board the Chandrayaan-1, and the Chang’E-1 Interference Imaging Spectrometer (IIM). The differences in the measurements of these instruments are very large and indicate inherent differences in their absolute calibration. The M3 and IIM measurements are smaller than LROC WAC and SP, and the VNIS measurement falls between these two pairs. When using the Moon as a radiance source for the on-orbit calibration of spacecraft instruments, one should be cautious about the data. We propose that the CE-3 landing site, a young and homogeneous surface, should serve as the new calibration site.

Novalis' Poetic Uncertainty: A "Bildung" with the Absolute

ERIC Educational Resources Information Center

Mika, Carl

2016-01-01

Novalis, the Early German Romantic poet and philosopher, had at the core of his work a mysterious depiction of the "absolute." The absolute is Novalis' name for a substance that defies precise knowledge yet calls for a tentative and sensitive speculation. How one asserts a truth, represents an object, and sets about encountering things…

Characterizing absolute piezoelectric microelectromechanical system displacement using an atomic force microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evans, J., E-mail: radiant@ferrodevices.com; Chapman, S., E-mail: radiant@ferrodevices.com

Piezoresponse Force Microscopy (PFM) is a popular tool for the study of ferroelectric and piezoelectric materials at the nanometer level. Progress in the development of piezoelectric MEMS fabrication is highlighting the need to characterize absolute displacement at the nanometer and Ångstrom scales, something Atomic Force Microscopy (AFM) might do but PFM cannot. Absolute displacement is measured by executing a polarization measurement of the ferroelectric or piezoelectric capacitor in question while monitoring the absolute vertical position of the sample surface with a stationary AFM cantilever. Two issues dominate the execution and precision of such a measurement: (1) the small amplitude ofmore » the electrical signal from the AFM at the Ångstrom level and (2) calibration of the AFM. The authors have developed a calibration routine and test technique for mitigating the two issues, making it possible to use an atomic force microscope to measure both the movement of a capacitor surface as well as the motion of a micro-machine structure actuated by that capacitor. The theory, procedures, pitfalls, and results of using an AFM for absolute piezoelectric measurement are provided.« less

Photovoltaic Calibrations at the National Renewable Energy Laboratory and Uncertainty Analysis Following the ISO 17025 Guidelines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emery, Keith

The measurement of photovoltaic (PV) performance with respect to reference conditions requires measuring current versus voltage for a given tabular reference spectrum, junction temperature, and total irradiance. This report presents the procedures implemented by the PV Cell and Module Performance Characterization Group at the National Renewable Energy Laboratory (NREL) to achieve the lowest practical uncertainty. A rigorous uncertainty analysis of these procedures is presented, which follows the International Organization for Standardization (ISO) Guide to the Expression of Uncertainty in Measurement. This uncertainty analysis is required for the team’s laboratory accreditation under ISO standard 17025, “General Requirements for the Competence ofmore » Testing and Calibration Laboratories.” The report also discusses additional areas where the uncertainty can be reduced.« less

Telescope Scientist on the Advanced X-ray Astrophysics Observatory

NASA Technical Reports Server (NTRS)

VanSpeybroeck, L.; Smith, Carl M. (Technical Monitor)

2002-01-01

This period included many scientific observations made with the Chandra Observatory. The results, as is well known, are spectacular. Fortunately, the High Resolution Mirror Assembly (HRMA) performance continues to be essentially identical to that predicted from ground calibration data. The Telescope Scientist Team has improved the mirror model to provide a more accurate description to the Chandra observers and enable them to reduce the systematic errors and uncertainties in their data reduction. We also have made considerable progress in improving the scattering model. There also has been progress in the scientific program. At this time 58 distant clusters of galaxies have been observed. We are performing a systematic analysis of this rather large data set for the purpose of determining absolute distances utilizing the Sunyaev Zel'dovich effect. These observations also have been used to study the evolution of the cluster baryon mass function and the cosmological constraints which result from this evolution.

Quantum correlations from a room-temperature optomechanical cavity.

PubMed

Purdy, T P; Grutter, K E; Srinivasan, K; Taylor, J M

2017-06-23

The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam's thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

40 CFR 60.5220 - What are the performance testing, monitoring, and calibration requirements for compliance with...

Code of Federal Regulations, 2011 CFR

2011-07-01

... per million dry volume absolute value of the mean difference between the method and the continuous... activities (including, as applicable, calibration checks and required zero and span adjustments). Any such...

The OLI Radiometric Scale Realization Round Robin Measurement Campaign

NASA Technical Reports Server (NTRS)

Cutlip, Hansford; Cole,Jerold; Johnson, B. Carol; Maxwell, Stephen; Markham, Brian; Ong, Lawrence; Hom, Milton; Biggar, Stuart

2011-01-01

A round robin radiometric scale realization was performed at the Ball Aerospace Radiometric Calibration Laboratory in January/February 2011 in support of the Operational Land Imager (OLI) Program. Participants included Ball Aerospace, NIST, NASA Goddard Space Flight Center, and the University of Arizona. The eight day campaign included multiple observations of three integrating sphere sources by nine radiometers. The objective of the campaign was to validate the radiance calibration uncertainty ascribed to the integrating sphere used to calibrate the OLI instrument. The instrument level calibration source uncertainty was validated by quatnifying: (1) the long term stability of the NIST calibrated radiance artifact, (2) the responsivity scale of the Ball Aerospace transfer radiometer and (3) the operational characteristics of the large integrating sphere.

Absolute frequency measurement of the ? optical clock transition in ? with an uncertainty of ? using a frequency link to international atomic time

NASA Astrophysics Data System (ADS)

Baynham, Charles F. A.; Godun, Rachel M.; Jones, Jonathan M.; King, Steven A.; Nisbet-Jones, Peter B. R.; Baynes, Fred; Rolland, Antoine; Baird, Patrick E. G.; Bongs, Kai; Gill, Patrick; Margolis, Helen S.

2018-03-01

The highly forbidden ? electric octupole transition in ? is a potential candidate for a redefinition of the SI second. We present a measurement of the absolute frequency of this optical transition, performed using a frequency link to International Atomic Time to provide traceability to the SI second. The ? optical frequency standard was operated for 76% of a 25-day period, with the absolute frequency measured to be 642 121 496 772 645.14(26) Hz. The fractional uncertainty of ? is comparable to that of the best previously reported measurement, which was made by a direct comparison to local caesium primary frequency standards.

From Hubble's NGSL to Absolute Fluxes

NASA Technical Reports Server (NTRS)

Heap, Sara R.; Lindler, Don

2012-01-01

Hubble's Next Generation Spectral Library (NGSL) consists of R-l000 spectra of 374 stars of assorted temperature, gravity, and metallicity. Each spectrum covers the wavelength range, 0.18-1.00 microns. The library can be viewed and/or downloaded from the website, http://archive.stsci.edu/prepds/stisngsll. Stars in the NGSL are now being used as absolute flux standards at ground-based observatories. However, the uncertainty in the absolute flux is about 2%, which does not meet the requirements of dark-energy surveys. We are therefore developing an observing procedure that should yield fluxes with uncertainties less than 1 % and will take part in an HST proposal to observe up to 15 stars using this new procedure.

Research yields precise uncertainty equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, E.H.; Ferguson, K.R.

1987-08-03

Results of a study of orifice-meter accuracy by Chevron Oil Field Research Co. at its Venice, La., calibration facility have important implications for natural gas custody-transfer measurement. The calibration facility, data collection, and equipment calibration were described elsewhere. This article explains the derivation of uncertainty factors and details the study's findings. The results were based on calibration of two 16-in. orifice-meter runs. The experimental data cover a beta-ratio range of from 0.27 to 0.71 and a Reynolds number range of from 4,000,000 to 35,000,000. Discharge coefficients were determined by comparing the orifice flow to the flow from critical-flow nozzles.

Calibration uncertainty for Advanced LIGO's first and second observing runs

NASA Astrophysics Data System (ADS)

Cahillane, Craig; Betzwieser, Joe; Brown, Duncan A.; Goetz, Evan; Hall, Evan D.; Izumi, Kiwamu; Kandhasamy, Shivaraj; Karki, Sudarshan; Kissel, Jeff S.; Mendell, Greg; Savage, Richard L.; Tuyenbayev, Darkhan; Urban, Alex; Viets, Aaron; Wade, Madeline; Weinstein, Alan J.

2017-11-01

Calibration of the Advanced LIGO detectors is the quantification of the detectors' response to gravitational waves. Gravitational waves incident on the detectors cause phase shifts in the interferometer laser light which are read out as intensity fluctuations at the detector output. Understanding this detector response to gravitational waves is crucial to producing accurate and precise gravitational wave strain data. Estimates of binary black hole and neutron star parameters and tests of general relativity require well-calibrated data, as miscalibrations will lead to biased results. We describe the method of producing calibration uncertainty estimates for both LIGO detectors in the first and second observing runs.

Impact of influent data frequency and model structure on the quality of WWTP model calibration and uncertainty.

PubMed

Cierkens, Katrijn; Plano, Salvatore; Benedetti, Lorenzo; Weijers, Stefan; de Jonge, Jarno; Nopens, Ingmar

2012-01-01

Application of activated sludge models (ASMs) to full-scale wastewater treatment plants (WWTPs) is still hampered by the problem of model calibration of these over-parameterised models. This either requires expert knowledge or global methods that explore a large parameter space. However, a better balance in structure between the submodels (ASM, hydraulic, aeration, etc.) and improved quality of influent data result in much smaller calibration efforts. In this contribution, a methodology is proposed that links data frequency and model structure to calibration quality and output uncertainty. It is composed of defining the model structure, the input data, an automated calibration, confidence interval computation and uncertainty propagation to the model output. Apart from the last step, the methodology is applied to an existing WWTP using three models differing only in the aeration submodel. A sensitivity analysis was performed on all models, allowing the ranking of the most important parameters to select in the subsequent calibration step. The aeration submodel proved very important to get good NH(4) predictions. Finally, the impact of data frequency was explored. Lowering the frequency resulted in larger deviations of parameter estimates from their default values and larger confidence intervals. Autocorrelation due to high frequency calibration data has an opposite effect on the confidence intervals. The proposed methodology opens doors to facilitate and improve calibration efforts and to design measurement campaigns.

Accuracy, reproducibility, and uncertainty analysis of thyroid-probe-based activity measurements for determination of dose calibrator settings.

PubMed

Esquinas, Pedro L; Tanguay, Jesse; Gonzalez, Marjorie; Vuckovic, Milan; Rodríguez-Rodríguez, Cristina; Häfeli, Urs O; Celler, Anna

2016-12-01

In the nuclear medicine department, the activity of radiopharmaceuticals is measured using dose calibrators (DCs) prior to patient injection. The DC consists of an ionization chamber that measures current generated by ionizing radiation (emitted from the radiotracer). In order to obtain an activity reading, the current is converted into units of activity by applying an appropriate calibration factor (also referred to as DC dial setting). Accurate determination of DC dial settings is crucial to ensure that patients receive the appropriate dose in diagnostic scans or radionuclide therapies. The goals of this study were (1) to describe a practical method to experimentally determine dose calibrator settings using a thyroid-probe (TP) and (2) to investigate the accuracy, reproducibility, and uncertainties of the method. As an illustration, the TP method was applied to determine 188 Re dial settings for two dose calibrator models: Atomlab 100plus and Capintec CRC-55tR. Using the TP to determine dose calibrator settings involved three measurements. First, the energy-dependent efficiency of the TP was determined from energy spectra measurements of two calibration sources ( 152 Eu and 22 Na). Second, the gamma emissions from the investigated isotope ( 188 Re) were measured using the TP and its activity was determined using γ-ray spectroscopy methods. Ambient background, scatter, and source-geometry corrections were applied during the efficiency and activity determination steps. Third, the TP-based 188 Re activity was used to determine the dose calibrator settings following the calibration curve method [B. E. Zimmerman et al., J. Nucl. Med. 40, 1508-1516 (1999)]. The interobserver reproducibility of TP measurements was determined by the coefficient of variation (COV) and uncertainties associated to each step of the measuring process were estimated. The accuracy of activity measurements using the proposed method was evaluated by comparing the TP activity estimates of 99m Tc, 188 Re, 131 I, and 57 Co samples to high purity Ge (HPGe) γ-ray spectroscopy measurements. The experimental 188 Re dial settings determined with the TP were 76.5 ± 4.8 and 646 ± 43 for Atomlab 100plus and Capintec CRC-55tR, respectively. In the case of Atomlab 100plus, the TP-based dial settings improved the accuracy of 188 Re activity measurements (confirmed by HPGe measurements) as compared to manufacturer-recommended settings. For Capintec CRC-55tR, the TP-based settings were in agreement with previous results [B. E. Zimmerman et al., J. Nucl. Med. 40, 1508-1516 (1999)] which demonstrated that manufacturer-recommended settings overestimate 188 Re activity by more than 20%. The largest source of uncertainty in the experimentally determined dial settings was due to the application of a geometry correction factor, followed by the uncertainty of the scatter-corrected photopeak counts and the uncertainty of the TP efficiency calibration experiment. When using the most intense photopeak of the sample's emissions, the TP method yielded accurate (within 5% errors) and reproducible (COV = 2%) measurements of sample's activity. The relative uncertainties associated with such measurements ranged from 6% to 8% (expanded uncertainty at 95% confidence interval, k = 2). Accurate determination/verification of dose calibrator dial settings can be performed using a thyroid-probe in the nuclear medicine department.

Experimental Investigations of Non-Stationary Properties In Radiometer Receivers Using Measurements of Multiple Calibration References

NASA Technical Reports Server (NTRS)

Racette, Paul; Lang, Roger; Zhang, Zhao-Nan; Zacharias, David; Krebs, Carolyn A. (Technical Monitor)

2002-01-01

Radiometers must be periodically calibrated because the receiver response fluctuates. Many techniques exist to correct for the time varying response of a radiometer receiver. An analytical technique has been developed that uses generalized least squares regression (LSR) to predict the performance of a wide variety of calibration algorithms. The total measurement uncertainty including the uncertainty of the calibration can be computed using LSR. The uncertainties of the calibration samples used in the regression are based upon treating the receiver fluctuations as non-stationary processes. Signals originating from the different sources of emission are treated as simultaneously existing random processes. Thus, the radiometer output is a series of samples obtained from these random processes. The samples are treated as random variables but because the underlying processes are non-stationary the statistics of the samples are treated as non-stationary. The statistics of the calibration samples depend upon the time for which the samples are to be applied. The statistics of the random variables are equated to the mean statistics of the non-stationary processes over the interval defined by the time of calibration sample and when it is applied. This analysis opens the opportunity for experimental investigation into the underlying properties of receiver non stationarity through the use of multiple calibration references. In this presentation we will discuss the application of LSR to the analysis of various calibration algorithms, requirements for experimental verification of the theory, and preliminary results from analyzing experiment measurements.

A procedure for accurate calibration of the orientation of the three sensors in a vector magnetometer. [at the Goddard Space Flight Center

NASA Technical Reports Server (NTRS)

Mcpherron, R. L.

1977-01-01

Procedures are described for the calibration of a vector magnetometer of high absolute accuracy. It is assumed that the calibration will be performed in the magnetic test facility of Goddard Space Flight Center (GSFC). The first main section of the report describes the test equipment and facility calibrations required. The second presents procedures for calibrating individual sensors. The third discusses the calibration of the sensor assembly. In a final section recommendations are made to GSFC for modification of the test facility required to carry out the calibration procedures.

Consistency of L4 TM absolute calibration with respect to the L5 TM sensor based on near-simultaneous image acquisition

NASA Astrophysics Data System (ADS)

Chander, Gyanesh; Helder, Dennis L.; Malla, Rimy; Micijevic, Esad; Mettler, Cory J.

2007-09-01

The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the backbone of an extensive archive. Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic ranges, as previously defined. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria. The cross-calibration approach involved comparing image statistics derived from large common areas observed eight days apart by the two sensors. This paper summarizes the average percent differences in reflectance estimates obtained between the two sensors. The work presented in this paper is a first step in understanding the current performance of L4 TM absolute calibration and potentially serves as a platform to revise and improve the radiometric calibration procedures implemented for the processing of L4 TM data.

Consistency of L4 TM absolute calibration with respect to the L5 TM sensor based on near-simultaneous image acquisition

USGS Publications Warehouse

Chander, G.; Helder, D.L.; Malla, R.; Micijevic, E.; Mettler, C.J.

2007-01-01

The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the backbone of an extensive archive. Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic ranges, as previously defined. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria. The cross-calibration approach involved comparing image statistics derived from large common areas observed eight days apart by the two sensors. This paper summarizes the average percent differences in reflectance estimates obtained between the two sensors. The work presented in this paper is a first step in understanding the current performance of L4 TM absolute calibration and potentially serves as a platform to revise and improve the radiometric calibration procedures implemented for the processing of L4 TM data.

Uncertainty quantification in volumetric Particle Image Velocimetry

NASA Astrophysics Data System (ADS)

Bhattacharya, Sayantan; Charonko, John; Vlachos, Pavlos

2016-11-01

Particle Image Velocimetry (PIV) uncertainty quantification is challenging due to coupled sources of elemental uncertainty and complex data reduction procedures in the measurement chain. Recent developments in this field have led to uncertainty estimation methods for planar PIV. However, no framework exists for three-dimensional volumetric PIV. In volumetric PIV the measurement uncertainty is a function of reconstructed three-dimensional particle location that in turn is very sensitive to the accuracy of the calibration mapping function. Furthermore, the iterative correction to the camera mapping function using triangulated particle locations in space (volumetric self-calibration) has its own associated uncertainty due to image noise and ghost particle reconstructions. Here we first quantify the uncertainty in the triangulated particle position which is a function of particle detection and mapping function uncertainty. The location uncertainty is then combined with the three-dimensional cross-correlation uncertainty that is estimated as an extension of the 2D PIV uncertainty framework. Finally the overall measurement uncertainty is quantified using an uncertainty propagation equation. The framework is tested with both simulated and experimental cases. For the simulated cases the variation of estimated uncertainty with the elemental volumetric PIV error sources are also evaluated. The results show reasonable prediction of standard uncertainty with good coverage.

[Evaluation of uncertainty for determination of tin and its compounds in air of workplace by flame atomic absorption spectrometry].

PubMed

Wei, Qiuning; Wei, Yuan; Liu, Fangfang; Ding, Yalei

2015-10-01

To investigate the method for uncertainty evaluation of determination of tin and its compounds in the air of workplace by flame atomic absorption spectrometry. The national occupational health standards, GBZ/T160.28-2004 and JJF1059-1999, were used to build a mathematical model of determination of tin and its compounds in the air of workplace and to calculate the components of uncertainty. In determination of tin and its compounds in the air of workplace using flame atomic absorption spectrometry, the uncertainty for the concentration of the standard solution, atomic absorption spectrophotometer, sample digestion, parallel determination, least square fitting of the calibration curve, and sample collection was 0.436%, 0.13%, 1.07%, 1.65%, 3.05%, and 2.89%, respectively. The combined uncertainty was 9.3%.The concentration of tin in the test sample was 0.132 mg/m³, and the expanded uncertainty for the measurement was 0.012 mg/m³ (K=2). The dominant uncertainty for determination of tin and its compounds in the air of workplace comes from least squares fitting of the calibration curve and sample collection. Quality control should be improved in the process of calibration curve fitting and sample collection.

Comparison of the temperature accuracy between smart phone based and high-end thermal cameras using a temperature gradient phantom

NASA Astrophysics Data System (ADS)

Klaessens, John H.; van der Veen, Albert; Verdaasdonk, Rudolf M.

2017-03-01

Recently, low cost smart phone based thermal cameras are being considered to be used in a clinical setting for monitoring physiological temperature responses such as: body temperature change, local inflammations, perfusion changes or (burn) wound healing. These thermal cameras contain uncooled micro-bolometers with an internal calibration check and have a temperature resolution of 0.1 degree. For clinical applications a fast quality measurement before use is required (absolute temperature check) and quality control (stability, repeatability, absolute temperature, absolute temperature differences) should be performed regularly. Therefore, a calibrated temperature phantom has been developed based on thermistor heating on both ends of a black coated metal strip to create a controllable temperature gradient from room temperature 26 °C up to 100 °C. The absolute temperatures on the strip are determined with software controlled 5 PT-1000 sensors using lookup tables. In this study 3 FLIR-ONE cameras and one high end camera were checked with this temperature phantom. The results show a relative good agreement between both low-cost and high-end camera's and the phantom temperature gradient, with temperature differences of 1 degree up to 6 degrees between the camera's and the phantom. The measurements were repeated as to absolute temperature and temperature stability over the sensor area. Both low-cost and high-end thermal cameras measured relative temperature changes with high accuracy and absolute temperatures with constant deviations. Low-cost smart phone based thermal cameras can be a good alternative to high-end thermal cameras for routine clinical measurements, appropriate to the research question, providing regular calibration checks for quality control.

Determination of the carbon, hydrogen and nitrogen contents of alanine and their uncertainties using the certified reference material L-alanine (NMIJ CRM 6011-a).

PubMed

Itoh, Nobuyasu; Sato, Ayako; Yamazaki, Taichi; Numata, Masahiko; Takatsu, Akiko

2013-01-01

The carbon, hydrogen, and nitrogen (CHN) contents of alanine and their uncertainties were estimated using a CHN analyzer and the certified reference material (CRM) L-alanine. The CHN contents and their uncertainties, as measured using the single-point calibration method, were 40.36 ± 0.20% for C, 7.86 ± 0.13% for H, and 15.66 ± 0.09% for N; the results obtained using the bracket calibration method were also comparable. The method described in this study is reasonable, convenient, and meets the general requirement of having uncertainties ≤ 0.4%.

Radiometer calibration methods and resulting irradiance differences: Radiometer calibration methods and resulting irradiance differences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habte, Aron; Sengupta, Manajit; Andreas, Afshin

Accurate solar radiation measured by radiometers depends on instrument performance specifications, installation method, calibration procedure, measurement conditions, maintenance practices, location, and environmental conditions. This study addresses the effect of different calibration methodologies and resulting differences provided by radiometric calibration service providers such as the National Renewable Energy Laboratory (NREL) and manufacturers of radiometers. Some of these methods calibrate radiometers indoors and some outdoors. To establish or understand the differences in calibration methodologies, we processed and analyzed field-measured data from radiometers deployed for 10 months at NREL's Solar Radiation Research Laboratory. These different methods of calibration resulted in a difference ofmore » +/-1% to +/-2% in solar irradiance measurements. Analyzing these differences will ultimately assist in determining the uncertainties of the field radiometer data and will help develop a consensus on a standard for calibration. Further advancing procedures for precisely calibrating radiometers to world reference standards that reduce measurement uncertainties will help the accurate prediction of the output of planned solar conversion projects and improve the bankability of financing solar projects.« less