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oe1(光电查) - 科学论文

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出版时间
  • 2018
研究主题
  • spectral irradiance
  • correlated color temperature
  • double monochromator
  • color rendering index
  • Uncertainty of measurement
应用领域
  • Measurement and Control Technology and Instruments
机构单位
  • Brno University of Technology
149 条数据
?? 中文（中国） ▾

  • [IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Calibration of Current Shunt Standards in the Megahertz Region

    摘要： Beyond 1 A (from 2 A to 100 A typically) standard current shunts are currently calibrated in magnitude up to 100 kHz and in phase angle up to 200 kHz. For such high current levels and above these frequencies the existing traceable measurement methods are not able to characterize current shunts and cannot provide the phase and magnitude of impedance simultaneously. This paper briefly describes a new broadband method for measuring current shunt standards beyond 1 A in the megahertz region and presents experimental results demonstrating the efficiency of this approach.

    关键词： Calibration method,current measurement,VNA,uncertainty,current shunt,phase angle,wideband measurements,ac-dc difference

    更新于2025-09-10 09:29:36

  • [IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Harmonic Power Standard of VTT MIKES

    摘要： This paper describes the new single-phase harmonic power standard of VTT MIKES. The standard is based on a custom digitizer, which is developed for AC metrology in the laboratory, and for field measurement campaigns. Test signal generation uses a dual channel arbitrary function generator, a voltage amplifier, and a transconductance amplifier. Reference voltage and current measurements are respectively based on a capacitive-resistive voltage divider and two different types of resistive shunt designs.

    关键词： power measurement,measurement uncertainty,measurement standards,Measurement

    更新于2025-09-10 09:29:36

  • AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Optimisation of aiming strategies in solar tower power plants

    摘要： Inclement weather effects have a direct impact on the efficiency of a Solar Power Tower plant and have the potential to damage the receiver by flash heating. An optimised aiming strategy for the heliostat field mitigates the risk of receiver damage and maximises plant efficiency. A stochastic integer programming approach is applied to optimise the aiming strategy of the heliostat field, with uncertainty in the cloud location, size and density. The optimisation technique is demonstrated with a test case and results are presented for near real-time simulation of the optimal aiming strategy.

    关键词： Solar Power Tower,stochastic integer programming,cloud uncertainty,heliostat field,aiming strategy

    更新于2025-09-10 09:29:36

  • Calibrated optical time transfer of UTC(k) for supervision of telecom networks

    摘要： We report on the evaluation of the performance of optical time transfer links connecting a facility of Deutsche Telekom in Bremen with the Physikalisch-Technische Bundesanstalt in Braunschweig. In the current configuration three links have been established, two via a hub in Hannover and one using an independent alternate route. They are equipped with electronically stabilized fiber optic time and frequency transfer systems and parallel operation is maintained since December 2016. A novel method of link calibration, composed of two steps (one performed in the laboratory and the second one in the field), to accurately determine the influence of fiber chromatic dispersion is discussed in detail, and a thorough analysis of the uncertainty budget is given. We show that the time transfer performance achieved is difficult to characterize based on measurements with time interval counters that are the standard equipment in timing laboratories and in the telecommunications sector. In our experiments, values of TDEV at the low ps-level at averaging times between 104 to 106 seconds have been achieved. The uncertainty of time transfer (including all kinds of delays) is of the order of 50 ps in a cascade of links. The results obtained show that such a kind of link is capable to deliver signals to a remote end with an instability being at least two orders of magnitude below the current requirements included in relevant Recommendations of the International Telecommunication Union – Telecommunication Sector (ITU-T). Moreover, the current implementation would allow primary Cs fountain clocks to be compared at the level of their performance, that is characterized by an uncertainty at the low 10-16 level and a frequency instability of the same order of magnitude at one day averaging.

    关键词： propagation delay calibration,frequency transfer,telecom network supervision,time transfer,uncertainty budget,fiber optic

    更新于2025-09-10 09:29:36

  • Wave-optics uncertainty propagation and regression-based bias model in GNSS radio occultation bending angle retrievals

    摘要： A new reference occultation processing system (rOPS) will include a Global Navigation Satellite System (GNSS) radio occultation (RO) retrieval chain with integrated uncertainty propagation. In this paper, we focus on wave-optics bending angle (BA) retrieval in the lower troposphere and introduce (1) an empirically estimated boundary layer bias (BLB) model then employed to reduce the systematic uncertainty of excess phases and bending angles in about the lowest 2 km of the troposphere and (2) the estimation of (residual) systematic uncertainties and their propagation together with random uncertainties from excess phase to bending angle profiles. Our BLB model describes the estimated bias of the excess phase transferred from the estimated bias of the bending angle, for which the model is built, informed by analyzing refractivity fluctuation statistics shown to induce such biases. The model is derived from regression analysis using a large ensemble of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO observations and concurrent European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields. It is formulated in terms of predictors and adaptive functions (powers and cross products of predictors), where we use six main predictors derived from observations: impact altitude, latitude, bending angle and its standard deviation, canonical transform (CT) amplitude, and its fluctuation index. Based on an ensemble of test days, independent of the days of data used for the regression analysis to establish the BLB model, we find the model very effective for bias reduction and capable of reducing bending angle and corresponding refractivity biases by about a factor of 5. The estimated residual systematic uncertainty, after the BLB profile subtraction, is lower bounded by the uncertainty from the (indirect) use of ECMWF analysis fields but is significantly lower than the systematic uncertainty without BLB correction. The systematic and random uncertainties are propagated from excess phase to bending angle profiles, using a perturbation approach and the wave-optical method recently introduced by Gorbunov and Kirchengast (2015), starting with estimated excess phase uncertainties. The results are encouraging and this uncertainty propagation approach combined with BLB correction enables a robust reduction and quantification of the uncertainties of excess phases and bending angles in the lower troposphere.

    关键词： wave-optics uncertainty propagation,bending angle retrievals,refractivity fluctuation statistics,GNSS radio occultation,boundary layer bias model

    更新于2025-09-10 09:29:36

  • Fast Active Learning for Hyperspectral Image Classification using Extreme Learning Machine

    摘要： Due to undulating and complexity of the earth’s surface, obtaining the training samples for remote sensing data is time consuming and expensive. Therefore, it is highly desirable to design a model that uses as few labelled samples as possible and reducing the computational time. Several active learning (AL) algorithms have been proposed in the literature for the classification of hyperspectral images (HSI).However, its performance in term of computational time has not been focused yet. In this paper, we have proposed AL approach based on Extreme Learning Machine (ELM) that effectively decreases the computational time while maintaining the classification accuracy. Further, the effectiveness of the proposed approach has been depicted by comparing its performance with state-of-the-art AL algorithms in terms of classification accuracy and computational time as well. The ELM based active learning (ELM-AL) with different query strategies were conducted on two HSI data sets. The proposed approach achieves the classification accuracy up to 90% which is comparable to support vector machine (SVM) based AL (SVM-AL) approach but effectively reduces the computational time significantly by 1000 times. Thus proposed system shows the encouraging results with adequate classification accuracy while reducing the computation time drastically.

    关键词： Uncertainty sampling,Remote Sensing Image,Extreme learning machine,Classification,Active learning,Uncertainty measure,Hyperspectral Image

    更新于2025-09-09 09:28:46

  • Initial entanglement between detectors allows violating Heisenberg's uncertainty relations

    摘要： Physics textbooks introduce an inequality derived by Kennard that concerns the impossibility of preparing a quantum state with well defined momentum and position. However, Heisenberg had formulated two different inequalities: one stating the impossibility of a simultaneous detection of position and momentum with arbitrary precision, and another one imposing a tradeoff between the precision on the measurement of a variable and the backaction on a subsequent measurement of a conjugated variable. Here, we explore the connections among these three inequalities, and we show that the latter can be violated, if the detectors are initially entangled. The results, besides being of fundamental interest, can be useful for building up an ideal momentum, or position, detector (i.e. one that introduces no noise in the measurement, besides the intrinsic statistical noise of the input state).

    关键词： quantum mechanics,Heisenberg's uncertainty relations,entanglement,detectors

    更新于2025-09-09 09:28:46

  • Improving accuracy of interatomic potentials: more physics or more data? A case study of silica

    摘要： In this paper we test two strategies to improving the accuracy of machine-learning potentials, namely adding more fitting parameters thus making use of large volumes of available quantum-mechanical data, and adding a charge-equilibration model to account for ionic nature of the SiO2 bonding. To that end, we compare Moment Tensor Potentials (MTPs) and MTPs combined with the charge-equilibration (QEq) model (MTP+QEq) fitted to a density functional theory dataset of α-quartz SiO2-based structures. In order to make a meaningful comparison, in addition to the accuracy, we assess the uncertainty of predictions of each potential. It is shown that adding the QEq model to MTP does not make any improvement over the MTP potential alone, while adding more parameters does improve the accuracy and uncertainty of its predictions.

    关键词： machine-learning interatomic potentials,Moment Tensor Potential,charge-equilibration model,uncertainty quantification

    更新于2025-09-09 09:28:46

  • [IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Preliminary Evaluation of Sentinel-2 Bottom of Atmosphere Reflectance Using the 6Sv Code in Beijing Area

    摘要： In this study, the Sentinel-2A Bottom Of Atmosphere (BOA) reflectance imageries over Beijing area from Dec 2016 to Nov 2017 were generated by the Sen2Cor processor and evaluated using the AERONET measurements and the 6SV code. The result shows a poor correlation between the Sen2Cor retrieved AOT and the ground data with R = 0.289 possibly because of the limitation of the AOT algorithm. The errors of Sen2Cor retrieved AOT and water vapor pressure have a great effect on the BOA reflectance and spectral indices such as NDVI. The highest relative uncertainty of the Sen2Cor BOA reflectance is 37.76% for B01 and the lowest correlation is 0.859 for B09. The result also shows that a high-accuracy atmospheric correction is still crucial and urgent for the Sentinel-2A data.

    关键词： 6SV code,atmospheric correction,AERONET,Sentinel-2,uncertainty

    更新于2025-09-09 09:28:46

  • Aerosol optical depth in the European Brewer Network

    摘要： The high spatial and temporal variability of aerosols makes networks capable of measuring their properties in near real time of high scientific interest. In this work we present and discuss results of an aerosol optical depth algorithm to be used in the European Brewer Network, which provides data in near real time of more than 30 spectrophotometers located from Tamanrasset (Algeria) to Kangerlussuaq (Greenland). Using data from the Brewer Intercomparison Campaigns in the years 2013 and 2015, and the period in between, plus comparisons with Cimel sunphotometers and UVPFR instruments, we check the precision, stability, and uncertainty of the Brewer AOD in the ultraviolet range from 300 to 320 nm. Our results show a precision better than 0.01, an uncertainty of less than 0.05, and a stability similar to that of the ozone measurements for well-maintained instruments. We also discuss future improvements to our algorithm with respect to the input data, their processing, and the characterization of the Brewer instruments for the measurement of aerosols.

    关键词： European Brewer Network,uncertainty,ultraviolet range,precision,aerosol optical depth,stability,Brewer spectrophotometer

    更新于2025-09-09 09:28:46