Radiometric Standards Research Articles

Method for Monitoring of Neutron Fields near High-Energy Accelerators

The monitoring of neutron radiation from high-energy accelerators cannot fully rely on the standard dosimeters and radiometers manufactured in Russia, since these are sensitive only to neutrons with energies below some 10 MeV. This is because neutrons of higher energies can significantly contribute to the personnel doses both close to the accelerator shield and in the neutron multiscattered field around the shield. In this paper, we propose to measure the ambient neutron dose in energy range 10–2 MeV to 1 GeV with a device consisting of two polyethylene balls with diameters of 3 and 10 in. housing slow-neutron detectors. The larger ball also comprises a lead converter (10'' + Pb). This device can be implemented in zonal radiation monitoring in the near-accelerator area.

Realization of spectral irradiance responsivity at NIS-Egypt

Realization of the absolute spectral irradiance responsivity of photodetectors in A/W/cm2 is a fundamental requirement for many photometric, radiometric and colorimetric applications. This work aimed to develop a standardized radiometric setup for realizing the absolute spectral irradiance responsivity in the range of 500 nm–950 nm at the National Institute of Standards (NIS), Egypt. A silicon trap detector, calibrated against the primary standard cryogenic radiometer, is used as a transfer standard for the calibration of S2281 Hamamatsu silicon photodiode, as a working standard, using a lamp-double monochromator based system. The accompanied uncertainty components affecting the measurements were investigated.

Traceability of the Network for Detection of the Mesospheric Change (NDMC) to radiometric standards via a Near Infrared Filter Radiometer

We discuss a route to provide traceability to spectroradiometers that are operated within the network for detection of the mesospheric change. The spectrometers measure spectral radiance at low light levels (350 W m-2 sr-1 m-1) at 1.55 μm. The traceability chain is based on a travelling reference source that is calibrated against a black body via a near infrared filter radiometer. In this paper the requirements, design and performance of the filter radiometer are discussed. It is demonstrated that the filter radiometer is suitable for transferring the scale at very low radiance levels, providing SI traceability to the traveling reference radiance source within the required measurement uncertainty of 1 %.

The development of the advanced cryogenic radiometer facility at NRC

The National Research Council (NRC) of Canada has established a next generation facility for the primary realization of optical radiant power. The main feature of this facility is a new cryogenic electrical substitution radiometer with a closed-cycle helium cryocooler. A monochromator-based approach allows for detector calibrations at any desired wavelength. A custom-designed motion apparatus includes two transfer standard radiometer mounting ports which has increased our measurement capability by allowing the calibration of two photodetectors in one measurement cycle. Measurement uncertainties have been improved through several upgrades, including newly designed and constructed transimpedance amplifiers for the transfer standard radiometers, and a higher power broadband light source. The most significant improvements in uncertainty arise from the enhanced characteristics of the new cryogenic radiometer including its higher cavity absorptance and reduced non-equivalence effects.

Real-Time Determination of Earth Radiation Budget Spectral Signatures for Nonlinear Unfiltering of Results from MERBE

AbstractAmong the best ways to gain more certainty in climate model prediction is to compare and constrain simulations with worldwide satellite measurements of the Earth radiation budget (ERB) short- and longwave radiant fluxes (SW and LW), which drive climate processes. Recent calls to ensure orbital ERB measurements track true climate, rather than instrument changes, led to the creation of the Moon and Earth Radiation Budget Experiment (MERBE). This independent project is recalibrating multiple existing ERB devices from different international space agencies so they adhere to common SI-traceable radiometric standards, by regularly sampling the unaltering constants of lunar reflectivity/emissivity, thus ensuring no artificial trends exist. This work details the use of MODTRAN to give an instantaneous SW and LW Earth spectrum for all scenes viewed by devices in the project, to then be used with instrument spectral responses for unfiltering radiances. In the majority of cases when data from a collocated imager are available, a dual-layer unfiltering is also performed separately on cloudy and cloud-free areas, yielding clear and overcast ERB spectral results. Additionally, use is made of improved in-flight methods to derive spectral responses from a previous American Meteorological Society study, and comparisons between Earth MERBE radiances from two identical devices operating on Terra/Aqua are shown along with results from the CERES project. These demonstrate an order of magnitude improvement in relative accuracy for edition 1 MERBE results over CERES and show that the latest CERES data are less accurate and stable than claimed.

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

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 Espanol de Metrologia (CEM), in collaboration with the Instituto de Optica of Consejo Superior de Investigaciones Cientificas (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.

《第7回》測光量(cd)および測光・放射標準についての基礎解説と最近の話題

《第7回》測光量(cd)および測光・放射標準についての基礎解説と最近の話題

Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13–14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368–862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found < 0.01 at all the 306–320 nm Brewer wavelengths.

EUV data processing methods of the Solar Auto-Calibrating EUV Spectrometers (SolACES) aboard the International Space Station

ContextSince 2008, the Solar Auto-Calibrating EUV Spectrometer (SolACES) experiment monitors the solar EUV radiation. SolACES is part of the SOLAR mission, a device mounted on the COLUMBUS module on the International Space Station (ISS). The SolACES device is capable of measuring the EUV radiation of the full solar disk, with three grazing incidence spectrometers, covering the spectral range from 17 to 135nm. IssueDegradation and ageing effects of hardware components are a major issue in the field of EUV measurements. In addition, propellant pollution from ISS logistic vehicles strongly complicate the instrumental operation as well as the data evaluation. To correct these effects, two double ionization chambers have been mounted onto the device frame. These are considered as a primary radiometric detector standard. By refilling the ionization chambers, the absolute EUV flux can be measured. Efficiency changes, being a severe issue in the field of measurements of EUV radiation, can corrected via an in-situ auto-calibration. The use of this method requires a thorough understanding of electron multiplier degradation and processes inside an ionization chamber. AimsThe main focus of this paper lies on the correction of hardware ageing effects in the spectrometer readout, as well as on the usage of ionization chamber measurements for absolute calibration. Additionally, we intend to demonstrate the long term stability of the in-orbit calibration principle of EUV spectrometers with double ionization chambers. MethodsIn this paper, we first briefly present the instrument and its components. Second, we list, explain, and correct various degradation effects within the spectrometer units. The core part are the adjustments between spectrometer and ionization chamber data, for calibration purposes. Results and perspectivesThe proof of concept of the in-orbit calibration, via ionization chambers, is given, by intercomparison of EUV data from SolACES with other experiments, over almost one decade. The presented data can be used for further investigations in climate modelling, as well as contribute to a SSI composite.

Thermodynamic temperature by primary radiometry.

Above the freezing temperature of silver (1234.93 K), the International Temperature Scale of 1990 (ITS-90) gives a temperature, T90, in terms of a defining fixed-point blackbody and Planck's law of thermal radiation in ratio form. Alternatively, by using Planck's law directly, thermodynamic temperature can be determined by applying radiation detectors calibrated in absolute terms for their spectral responsivity. With the advent of high-quality semiconductor photodiodes and the development of high-accuracy cryogenic radiometers during the last two decades radiometric detector standards with very small uncertainties in the range of 0.01-0.02% have been developed for direct, absolute radiation thermometry with uncertainties comparable to those for the realization of the ITS-90. This article gives an overview of a number of design variants of different types of radiometer used for primary radiometry and describes their calibration. Furthermore, details and requirements regarding the experimental procedure for obtaining low uncertainty thermodynamic temperatures with these radiometers are presented, noting that such radiometers can also be used at temperatures well below the silver point. Finally, typical results obtained by these methods are reviewed.

Shrunken Locally Linear Embedding for Passive Microwave Retrieval of Precipitation

This paper introduces a new Bayesian approach to the inverse problem of passive microwave rainfall retrieval. The proposed methodology relies on a regularization technique and makes use of two joint dictionaries of coincidental rainfall profiles and their corresponding upwelling spectral radiative fluxes. A sequential detection-estimation strategy is adopted, which basically assumes that similar rainfall intensity values and their spectral radiances live close to some sufficiently smooth manifolds with analogous local geometry. The detection step employs a nearest neighborhood classification rule, while the estimation scheme is equipped with a constrained shrinkage estimator to ensure stability of retrieval and some physical consistency. The algorithm is examined using coincidental observations of the active precipitation radar (PR) and passive microwave imager (TMI) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. We present promising results of instantaneous rainfall retrieval for some tropical storms and mesoscale convective systems over ocean, land, and coastal zones. We provide evidence that the algorithm is capable of properly capturing different storm morphologies including high intensity rain-cells and trailing light rainfall, especially over land and coastal areas. The algorithm is also validated at an annual scale for calendar year 2013 versus the standard (version 7) radar (2A25) and radiometer (2A12) rainfall products of the TRMM satellite.

SAURAN: A new resource for solar radiometric data in Southern Africa

A new resource for sun strength data in Southern Africa has been established with the commissioning of a regional network of solar monitoring stations. The Southern African Universities Radiometric Network (SAURAN) is an initiative of Stellenbosch University and the University of KwaZulu-Natal (UKZN), and consists of an initial set of ten ground stations equipped with secondary standard thermopile radiometers. SAURAN’s aim is to provide a long-term record of sun strength in a region that shows excellent potential for the deployment of solar energy technologies. Instruments measuring direct normal irradiance (DNI), diffuse horizontal irradiance (DHI) and global horizontal irradiance (GHI) feed time-averaged data over 1-minute, hourly and daily intervals to a central archive from where they are accessible to the public via a website interface. Meteorological data is also provided by most of the stations. This paper gives a brief background to the SAURAN project and describes the network’s operation, coverage and future expansion. Examples of solar energy irradiance plots are also provided to illustrate the information available from the SAURAN database.

可在轨溯源的太阳反射波段光学遥感仪器辐射定标基准传递链路

The weakness of current radiometric calibration methods for optical remote sensing instruments was analyzed to satisfy the precision needs of quantitative remote sensing and the data fusion coming from multi satellites.A standard transfer chain for radiometric calibration of optical sensing instruments with traceability was designed by taking a space cryogenic radiometer as a primary system for radiometric reference and the sun as the light source,which includes a solar monochromator,a transfer radiometer,a solar spectral irradiance monitor and a solar diffuser,etc.In radiometric calibra-tion,the transfer radiometer and the solar spectral irradiance monitor were calibrated firstly by using spectral radiometric standards provided by the solar monochromator.And then the solar diffuser was calibrated by using the transfer radiometer.The radiometric standard was transferred to an imaging spectrometer for an earth observing standard,so that the radiometric standard could be used for inter calibration of other remote sensing instruments on other satellites.The analysis on the radiometric calibration for the standard transfer chain shows that the uncertainty of optical sensing instruments is0.75%.It demonstrates that the proposed method is helpful for constructing calibration networks of remote sensing covering China in space and air and provides a technology foundation for developing space data quality assurance system parallel to the ground system of primary radiometric standards.

Calibration of a Photodiode Array Spectrometer Against the Copper Point

This paper describes a method to calibrate photodiode array spectrometers in the spectral radiance mode using a fixed-point blackbody as a reference source. Fixed-point blackbodies are characterized by their excellent emissivity, uniformity, and stability, which make them superior to both conventional standard lamps and variable temperature blackbodies. The temperature of these fixed points is accurately determined being traceable to either the International Temperature Scale (ITS-90) or thermodynamically through radiometric standards. The potential advantage of the fixed-point traceability chain is that it can be universally reproduced without recourse to any hierarchical calibrations or standards. The paper presents the calibration system and discusses the limitations of such an approach. The method used obtained an uncertainty of around 1.4 % (\(k = 2\)) associated with radiance responsivity across the spectral region from 550 nm to 1050 nm, which is comparable to what is readily achieved with a lamp-tile or lamp-illuminated spherical source.

1m口径红外测量系统的辐射定标

To measure infrared radiation characteristics of air targets, the calibration system for a 1 m aperture infrared measurement system was designed. A mathematic model of calibration for the infrared measurement system was given and a radiometric calibration system was established by combinations of a cavity blackbody and a collimator as the standard radiation source. Because the spectral response of the infrared measuring system is selective, the calibration principle based on conventional radiometric calibration method has theoretical errors and reduces the precision of radiometric calibration. To solve the problem, a relative spectral calibration method based on a monochromator and a standard radiometer was proposed. The mathematical model was given and a relative spectral calibration was performed. Finally, the experiments on radiation characteristic measurement were performed in the field by using the blackbody as a simulated target. The results show that the measurement max error from the 1 m aperture infrared radiation characteristic measurement system is 9.5% and improves by an average of 8.7% as compared with that of the conventional method. These show that the proposed method meets the requirements of practical applications and is suitable for the radiometric calibration in the out-fields.

Solar EUV Irradiance Measurements by the Auto-Calibrating EUV Spectrometers (SolACES) Aboard the International Space Station (ISS)

SolACES is part of the ESA SOLAR ISS mission that started aboard the shuttle mission STS-122 on 7 February 2008. The instrument has recorded solar extreme ultraviolet (EUV) irradiance from 16 to 150 nm during the extended solar activity minimum and the beginning solar cycle 24 with rising solar activity and increasingly changing spectral composition. The SOLAR mission has been extended from a period of 18 months to > 8 years until the end of 2016. SolACES is operating three grazing incidence planar grating spectrometers and two three-current ionization chambers. The latter ones are considered as primary radiometric detector standards. Re-filling the ionization chambers with three different gases repeatedly and using overlapping band-pass filters, the absolute EUV fluxes are derived in these spectral intervals. This way the serious problem of continuing efficiency changes in space-borne instrumentation is overcome during the mission. Evaluating the three currents of the ionization chambers, the overlapping spectral ranges of the spectrometers and of the filters plus inter-comparing the results from the EUV photon absorption in the gases with different absorption cross sections, there are manifold instrumental possibilities to cross-check the results providing a high degree of reliability to the spectral irradiance derived. During the mission a very strong up-and-down variability of the spectrometric efficiency by orders of magnitude is observed. One of the effects involved is channeltron degradation. However, there are still open questions on other effects contributing to these changes. A survey of the measurements carried out and first results of the solar spectral irradiance (SSI) data are presented. Inter-comparison with EUV data from other space missions shows good agreement such that the international effort has started to elaborate a complete set of EUV-SSI data taking into account all data available from 2008 to 2013.

Quantum Efficiency Measurement of Lamp Phosphors in Accordance with Radiometric Standards

To measure the quantum efficiencies of lamp phosphors, a JCSS (Japan Calibration Service System) traceable measurement method that uses a polychromator, with improved optical design to reduce stray light, and an integrating sphere has been developed. To verify the measurement accuracy of this method, a monochromator, which has a 0 - 45°incident optical system, was used. The BRDF (Bidirectional Reflectance Distribution Function) of the phosphor was measured by a goniophotometer. A comparison was made between these JCSS traceable measuring devices on the 260-400 nm wavelength characteristics of the internal quantum efficiency of the blue phosphor BAM (BaMgAl10O17:Eu2+) , which has excitation characteristics up to 400 nm. The results agreed within 4 % of the difference of the measured values. This is a good agreement considering that it was a composite measure and that the uncertainty of the spectral irradiance standard in the spectral region is lower than 3 %. It has also been established that the proposed method using a polychromator and an integrating sphere shows sufficient measurement accuracy.

AN ASSESSMENT OF ULTRAVIOLET RADIATION COMPONENTS OF LIGHT EMITTED FROM ELECTRIC ARC AND THEIR POSSIBLE EXPOSURE RISKS

The study of Ultraviolet Radiation has of recent become interesting because of the health hazards it poses to human. Apart from its intensity reaching the earth from the sun, other man-made sources have been identified. We have undertaken the measurement of UV radiation from electric arc welding light generated by 240 TURBO Clarke weld arc operated at a voltage of 120 V using the National Institute of Standard and Technology UVX radiometer and sensors of UVP Company, Upland, USA. Three sensors UVX-25, UVX-31 and UVX-36 were used to measure the three components of UV radiation namely UV-C, UV-B and UV-A respectively. Each of these sensors or probes was set at the same varying distances in turn from the emitted arc light. The result showed that the UVX-25 probe (for UV-C) recorded the highest intensities going from 3.4 to 0.2 mW/cm 2 ; the UVX-31 probe (for UV-B) recorded intensities ranging from 3.2 to 0.8 mW/cm 2 while UVX-36 probe (for UV-A) recorded intensities from 1.60 to 0.96 mW/cm 2 , all measured at distances from 25.0 cm to 350.0 cm respectively from the UV light. Converting mW/cm2 to mJ/cm 2 , our recorded values clearly showed that for 1.0 second the UVX-25 recorded UV radiation 3.4 to 0.2 mJ/cm 2 , UVX-31 recorded 3.2 to 0.8 mJ/cm 2 and UVX-36 recorded 1.60 to 0.96 mJ/cm 2 from a distance of 25 to 350 cm respectively. According to American Conference of Governmental Hygienist (ACGH), the Threshold Limit Value (TVL) of exposure for UV-C and UV-B radiations ranges from 3.0 mJ/cm 2 to 1000 mJ/cm 2 , for exposure to the eye not exceeding 8 hours period, while for UV-A, the TLV should not exceed 1.0 mW/cm 2 for period greater than 16 seconds. These values are therefore high for exposure limits of 8 hours for UV-B and UV-C and the 16 minutes for UV-A. The investigation showed that UV-radiation emitted from arc welding machine of the type used in this work could indeed pose harmful health risk to the occupational electric arc worker if no serious precaution is undertaken in the course of performing his work. KEYWORDS : Ultra-violet radiation, Intensity, Exposure, Health, Distance.

Performance and Long-Term Stability of the Prelaunch Radiometric Calibration Facility for the Clouds and the Earth's Radiant Energy System Instruments

The Radiometric Calibration Facility (RCF) at Northrop Grumman Aerospace Systems was used between 1995 and 2008 to establish the prelaunch calibration of the first six Clouds and the Earth's Radiant Energy System (CERES) instruments, with the seventh CERES instrument scheduled to be tested in the RCF in 2012. This paper reviews the performance of the RCF radiometric standards, which are the narrow-field blackbody (NFBB) and the short-wave reference source, as well as the RCF transfer active-cavity radiometer, in the context of the CERES prelaunch calibration process. A detailed investigation of the long-term stability of these standards over the 1999-2008 time span of CERES FM5 testing is reported, showing that the RCF calibrations in the long and short waves have remained stable relative to the NFBB absolute reference at levels of 0.06% and 0.5%, respectively, over the eight-year span.

Extending single-photon optimized superconducting transition edge sensors beyond the single-photon counting regime

Typically, transition edge sensors resolve photon number of up to 10 or 20 photons, depending on the wavelength and TES design. We extend that dynamic range up to 1000 photons, while maintaining sub-shot noise detection process uncertainty of the number of detected photons and beyond that show a monotonic response up to ≈ 6 · 10(6) photons in a single light pulse. This mode of operation, which heats the sensor far beyond its transition edge into the normal conductive regime, offers a technique for connecting single-photon-counting measurements to radiant-power measurements at picowatt levels. Connecting these two usually incompatible operating regimes in a single detector offers significant potential for directly tying photon counting measurements to conventional cryogenic radiometric standards. In addition, our measurements highlight the advantages of a photon-number state source over a coherent pulse source as a tool for characterizing such a detector.