Irradiance Calibration Research Articles

Evaluation of on-site calibration procedures for SKYNET Prede POM sun–sky photometers

Abstract. To retrieve columnar intensive aerosol properties from sun–sky photometers, both irradiance and radiance calibration factors are needed. For the irradiance the solar calibration constant, V0, which denotes the instrument counts for a direct normal solar flux extrapolated to the top of the atmosphere, must be determined. The solid view angle, SVA, is a measure of the field of view of the instrument, and it is important for obtaining the radiance from sky diffuse irradiance measurements. Each of the three sun-photometer networks considered in the present study (SKYNET, AERONET, WMO GAW) adopts different protocols of calibration, and we evaluate the performance of the on-site calibration procedures, applicable to every kind of sun–sky photometer but tested in this analysis only on SKYNET Prede POM01 instruments, during intercomparison campaigns and laboratory calibrations held in the framework of the Metrology for Aerosol Optical Properties (MAPP) European Metrology Programme for Innovation and Research (EMPIR) project. The on-site calibration, performed as frequently as possible (ideally monthly) to monitor changes in the device conditions, allows operators to track and evaluate the calibration status on a continuous basis, considerably reducing the data gaps incurred by the periodic shipments for performing centralized calibrations. The performance of the on-site calibration procedures for V0 was very good at sites with low turbidity, showing agreement with a reference calibration between 0.5 % and 1.5 % depending on wavelengths. In the urban area, the agreement decreases between 1.7 % and 2.5 %. For the SVA the difference varied from a minimum of 0.03 % to a maximum of 3.46 %.

Advancements in solar spectral irradiance measurements by the TSIS-1 spectral irradiance monitor and its role for long-term data continuity

The first implementation of NASA’s Total and Spectral Solar Irradiance Sensor (TSIS-1) launched on December 15th, 2017, and was integrated into the International Space Station (ISS) to measure both the total solar irradiance (TSI) and the solar spectral irradiance (SSI). The direct measurement of the SSI is made by the LASP Spectral Irradiance Monitor (SIM) and provides data essential to interpreting how the Earth system responds to solar spectral variability. Extensive advances in TSIS-1 SIM instrument design and new SI-traceable spectral irradiance calibration techniques have resulted in improved absolute accuracy with uncertainties of less than 0.5% over the continuous 200–2400 nm spectral range. Furthermore, improvements in the long-term spectral stability corrections provide lower trend uncertainties in SSI variability measurements. Here we present the early results of the TSIS-1 SIM measurements covering the first 5 years of operations. This time period includes the descending phase of solar cycle 24, the last solar minimum, and the ascending phase of solar cycle 25. The TSIS-1 SIM SSI results are compared to previous measurements both in the absolute scale of the solar spectrum and the time dependence of the SSI variability. The TSIS-1 SIM SSI spectrum shows lower IR irradiance (up to 6% at 2400 nm) and small visible increases (~0.5%) from some previous reference solar spectra. Finally, initial comparisons are made to current NRLSSI2 and SATIRE-S SSI model results and offer opportunities to validate model details both for short-term (solar rotation) spectral variability and, for the first time, the longer-term (near half solar cycle) spectral variability across the solar spectrum from the UV to the IR.

Highly-stable solar irradiance calibration light source based on laser galvanometer

Highly-stable solar irradiance calibration light source based on laser galvanometer

Biodosimetry Based on Gamma-H2AX Quantification in Human Peripheral Blood Lymphocytes after Partial-body Irradiation.

Quantification of gamma-H2AX foci can estimate exposure to ionizing radiation. Most nuclear and radiation accidents are partial-body irradiation, and the doses estimated using the total-body irradiation dose estimation formula are often lower than the actual dose. To evaluate the dose-response relation of gamma-H2AX foci in human peripheral blood lymphocytes after partial-body irradiation and establish a simple and high throughput model to estimate partial-body irradiation dose, we collected human peripheral blood and irradiated with 0-, 0.5-, 1-, 2-, 3-, 4-, 5-, 6-, and 8-Gy gamma rays to simulate total-body irradiation in vitro. Gamma-H2AX foci were quantitated by flow cytometry at 1 h after irradiation, and a dose-response curve was established for total-body irradiation dose estimation. Then, a partial-body irradiation dose-response calibration curve was established by adding calibration coefficients based on the Dolphin method. To reflect the data distribution of all doses more realistically, the partial-body irradiation dose-response calibration curve was divided into two sections. In addition, partial-body irradiation was simulated in vitro, and the PBI data were substituted into curves to verify the accuracy of the two partial-body irradiation calibration curves. Results showed that the dose estimation variations were all less than 30% except the 25% partial-body irradiation group at 1 Gy, and the partial-body irradiation calibration dose-response curves were YF 1 = - 3.444 x 2 + 18.532 x + 3.109, R 2 = 0.92 (YF ≤ 27.95); YF 2 = - 2.704 x 2 + 37.97 x - 56.45, R 2 = 0.86 (YF > 27.95). Results also suggested that the partial-body irradiation dose-response calibration curve based on the gamma-H2AX foci quantification in human peripheral blood lymphocytes is a simple and high throughput model to assess partial-body irradiation dose.

Development of an optical method for temperature measurements of the ISAC targets at TRIUMF

The temperatures of isotope separator on-line targets play an important role for the overall target performance, including the yield of the radioactive ion beams and the target lifetime. At TRIUMF an optical technique is being developed to obtain accurate real-time temperature feedback from ISAC and in the future ARIEL targets during beam delivery. The light emitted from within the hot tantalum target container is captured and transmitted into a spectrometer via an ionizer opening. For accurate results an absolute irradiance calibration of the spectrometer is performed to determine the spectral power density. Then, to analyze the light spectra and calculate the maximum temperature, two mathematical methods have been applied. These methods are first evaluated using the spectrum of a light source with a known colour temperature. One method is selected and applied to a tantalum target container heated off-line at nominal temperatures and cross-checked with a thermocouple. The results of the test are in close agreement with the temperatures read by the thermocouple. This paper describes the calibration of the optical system, the methods applied, along with their results and validations. This technique will be applied to the on-line targets and correlate isotope releases with target temperatures for optimizing the delivery of short-lived radioisotopes species.

Organ dose in CT: Comparison between measurements and computational methods

PurposeThis study aims to compare two methods for the organ dose evaluation in computed tomography (CT) in the head- and thorax regions: an experimental method, using radiochromic films, and a computational one, using a commercial software. MethodsGafchromic® XR-QA2 and EBT-3 were characterized in terms of energetic, angular, and irradiation configurations dependence. Two free-in-air irradiation calibration configurations were employed using a CT scanner: with the sensitive surface of the film orthogonal (OC) and parallel (PC) to the beam axis. Different dose–response curves were obtained by varying the irradiation configurations and the beam quality (BQ). Subsequently, films were irradiated within an anthropomorphic phantom using CT-thorax and -head protocols, and the organ dose values obtained were compared with those provided by the commercial software. ResultsAt different configurations, an unchanged dose response was achieved with EBT-3, while a dose response of 15% was obtained with XR-QA2. By varying BQ, XR-QA2 showed a different response below 10%, while EBT-3 showed a variation below 5% for dose values >20 mGy. For films irradiation angle equal to 90°, the normalized to 0° relative response was 41% for the XR-QA2 model and 83% for the EBT-3 one. Organ dose values obtained with EBT-3 for both configurations and with XR-QA2 for OC were in agreement with the DW values, showing percentage discrepancies of less than 25%. ConclusionsThe obtained results showed the potential of EBT-3 in CT patient dosimetry since the lower angular dependence, compared to XR-QA2, compensates for low sensitivity in the diagnostic dose range.

First Results from the Thomson Scattering Diagnostic on the Large Plasma Device

We present the first Thomson scattering measurements of electron density and temperature in the Large Plasma Device (LAPD), a 22 m long magnetized linear plasma device at the University of California Los Angeles (UCLA). The diagnostic spectrally resolves the Doppler shift imparted on light from a frequency-doubled Nd:YAG laser when scattered by plasma electrons. A fiber array coupled to a triple-grating spectrometer is used to obtain high stray light rejection and discriminate the faint scattering signal from a much larger background. In the center of the plasma column, the measured electron density and temperature are about ne≈1.5×1013 cm−3 and Te≈ 3 eV, respectively, depending on the discharge parameters and in good agreement with Langmuir probe data. Optical design considerations to maximize photon count while minimizing alignment sensitivity are discussed in detail and compared to numerical calculations. Raman scattering off of a quartz crystal probe is used for an absolute irradiance calibration of the system.

Pyroelectric detector-based method for low uncertainty spectral irradiance and radiance responsivity calibrations in the infrared using tunable lasers.

The standard uncertainty of detector-based radiance and irradiance responsivity calibrations in the short-wave infrared (SWIR) traditionally has been limited to around 1% or higher by the poor spatial uniformity of detectors used to transfer the scale from radiant power. Pyroelectric detectors offer a solution that avoids the spatial uniformity uncertainty but also introduces additional complications due to alternating current (AC) measurement techniques. Herein, a new, to the best of our knowledge, method for low uncertainty irradiance responsivity calibrations in the SWIR is presented. An absolute spectral irradiance responsivity scale was placed on two pyroelectric detectors (PED) at wavelengths λ from 500 to 3400 nm. The total combined uncertainty (k=1) was ≈0.28% (>1000nm), 0.44% (900 nm), and 0.36% (≈950nm and <900nm) for PED #1 and 0.34% (>1000nm), 0.48% (900 nm), and 0.42% (≈950nm and <900nm) for PED #2. This was done by utilizing a demodulation technique to digitally analyze the time-dependent AC waveforms, which obviates the use of lock-in amplifiers and avoids associated additional uncertainty components.

New traceability chain for spectral irradiance measurement at LNE-Cnam

LNE-Cnam has changed its traceability chain for measuring the spectral irradiance of a light source. This facility allows calibration of spectral irradiance of a standard lamp based on a comparison with a high temperature blackbody (HTBB). The reference spectral irradiance is determined by measuring the temperature of the HTBB with a filter radiometer calibrated against our radiant flux reference. This traceability scheme differs from the one used in our former setup, which was mainly based on the International Temperature Scale, ITS-90. Both principles are used in National Measurement Institutes. Our facility uses well known methods adapted to our best capabilities as well as a particular development in optical arrangement and filter radiometer calibration. Thanks to this new measurement setup, our spectral irradiance reference is now traceable to radiometric reference, i.e. our cryogenic radiometer. We have extended our measurement capability to cover the spectral range from 250 nm to 2500 nm. We have simplified the process by reducing the number of benches (three in one) and the number of operations, and we have designed a compact measuring setup through the use of a rotating integrative sphere. This allows us to reduce by at least a factor two our measurement uncertainties over almost the entire spectral range. With this new measurement facility, France participates in the ongoing CCPR k1.a key comparison. This is a key comparison of the Consultative Committee of Photometry and Radiometry for Spectral irradiance from 250 nm to 2500 nm of tungsten halogen lamps. This communication shows the method used, and its validation.

Raster Thomson scattering in large-scale laser plasmas produced at high repetition rate.

We present optical Thomson scattering measurements of electron density and temperature in a large-scale (∼2 cm) exploding laser plasma produced by irradiating a solid target with a high-energy (5-10J) laser pulse at a high repetition rate (1Hz). The Thomson scattering diagnostic matches this high repetition rate. Unlike previous work performed in single shots at much higher energies, the instrument allows for pointmeasurements anywhere inside the plasma by automatically translating the scattering volume using motorized stages as the experiment is repeated at 1Hz. Measured densities around 4 × 1016cm-3 and temperatures around 7eV result in a scattering parameter near unity, depending on the distance from the target. The measured spectra show the transition from collective scattering close to the target to non-collective scattering at larger distances. Densities obtained by fitting the weakly collective spectra agree to within 10% with an irradiance calibration performed via Raman scattering in nitrogen.

Electrode Erosion of Arc Heater by Emission Spectroscopy

Emission spectroscopy was conducted in a miniature arc heater in China Aerodynamics Research and Development Center to study the erosion of water-cooled copper electrode due to the high-temperature environment. With a 2-mm-diam viewpoint, emission signal of plasma torch at the exit of the nozzle was collected. Three tests were implemented under different conditions with arc currents of 400, 600, and 800 A. Temperature under each condition was determined as , , and . By absolute irradiance calibration, the number density of copper atoms in the flowfield was determined; combined with the estimate of the plasma torch volume and the flow velocity, the erosion rate of copper electrode was given. Apparently, the erosion rate increases with the raise of the current, as shown in the result. Based on experience and the results of previous studies by other researchers, the value of the erosion rate is reliable, which verified a new approach with optical method to investigate the electrode erosion of arc-heated facilities.

A calibration-free two-dimensional spectral soot emission platform for temperature and soot measurements

A simple and cost-effective temperature and soot volume fraction measurement technique that does not rely on spectral or absolute irradiance calibration is developed. The technique is based on a three-sensor CMOS camera, where the broadband sensitivity of RGB sensors were narrowed down to representative wavelengths using a tri-bandpass filter. A telecentric imaging lens was used to improve the accuracy of the tomographic deconvolution of the axisymmetrical ethylene laminar diffusion flames stabilized on a co-flow burner. Temperature and soot concentration measurements have been compared with results previously reported from the same burner. Good agreement for temperature measurements and excellent agreement for soot concentration measurements have been shown. Additionally, to demonstrate the dynamic range of the system, two-dimensional temperature and soot volume fraction fields were measured for four cases of dilution corresponding to various soot loadings. As the dilution rate was increased, the peak soot volume fraction was drastically reduced and temperatures were increased in accordance with the reduced dissipative heat losses from broadband soot radiation.

Silica Raman scattering probe for absolute calibration of Thomson scattering spectrometers

We have developed a solid state probe for an absolute irradiance calibration of the Thomson scattering system on the Large Plasma Device (LAPD), based on Raman scattering off silica.Measurements performed with a triple-grating spectrometer have investigated the intensities of a pulsed laser beam Raman scattered off crystalline and amorphous silica over a range of temperatures of relevance to the LAPD (299–498 K). The data were compared with Rayleigh and Raman scattering intensities in gaseous nitrogen. The measurements show that Raman scattering off quartz allows rapid and accurate alignment and calibration of Thomson scattering systems in plasma physics experiments that cannot be calibrated using conventional methods.

Pre-Launch Radiometric Characterization of EMI-2 on the GaoFen-5 Series of Satellites

The environmental trace gas monitoring instrument (EMI) is a space-borne imaging spectrometer onboard GaoFen-5, which was launched in May 2018, covering wavelengths in the range of 240–710 nm to measure NO2, O3, HCHO, and SO2. An advanced EMI-2 instrument with a higher spatial resolution and sufficient signal-to-noise is currently planned for launch on the GaoFen-5(02) satellite in 2021. The EMI-2 instrument bidirectional scattering distribution function (BSDF) is obtained from the absolute irradiance and radiance calibration on-ground. Based on EMI-2 earth and sun optical paths, the key factors of BSDF parameters are introduced. An NIST-calibrated 1000 W FEL quartz tungsten halogen lamp and a 2D turntable are adopted for the absolute irradiance calibration. A large aperture integrating sphere system is used for the absolute radiance calibration. Based on absolute irradiance and radiance calibration functions, the BSDF parameters are obtained, with accuracy of 4.9% for UV1, 4.3% for UV2, 4.1% for VIS1, and 4.2% for VIS2. The on-ground measurement results show that the reflectance spectrum can be calculated from BSDF parameters. On-orbit application of the EMI-2 instrument BSDF are also discussed.

The linearization of the relationship between scene luminance and digital camera output levels

The linearization of the relationship between scene luminance and digital camera output levels

An in‐depth field validation of “DUSST”: A novel low‐maintenance soiling measurement device

AbstractThis study presents indoor and field validation results for two versions of the “DUSST” optical soiling sensor, intended to be a low‐cost and low‐maintenance device for measuring photovoltaic soiling losses. Indoor testing covers irradiance calibration and temperature dependencies, which are necessary to achieve high accuracy, low uncertainty field measurements. Field testing includes an array of different environments including Saudi Arabia, California, Utah, and Colorado. DUSST versions include a configuration with a 530‐nm light emitting diode (LED) (discussed in previous work) and a unit with seven white LEDs and a polycarbonate collimating optic. The new design increases light intensity fivefold and demonstrates a single linear calibration coefficient is effective to measure soiling losses as high as 75%. Field data from Utah and California demonstrate that daily soiling loss measurements and soiling rate calculations closely match both reference cell and full‐size module measurements of soiling losses and soiling rates. Corrective methods employed on the Utah DUSST sensor suggest that it is possible to achieve measurement errors as low as ±0.1% at two standard deviations. Field data from both Colorado and Saudi Arabia demonstrate that LED lens soiling can occur and that further design optimizations are needed. The lesson learned from all the field deployment locations suggests directions for future design improvements.

Calibration and parameter corrections for the new generation of the TSI monitor on the FY-3E satellite

In order to support the analysis of potential long-term trends in the Sun’s variability and trace the WRR ground calibration ratio to the measurement on the satellite. We established the total solar irradiance (TSI) calibration model in orbit for the new generation of solar radiation monitor on the FY-3E satellite. First, we measured the non-equivalence of the instrument, and the air to vacuum ratio of the SIAR radiometer is 0.9958-0.9973. Then, we established the temperature correction model for the important parameters, such as the aperture area, the standard voltage and the heating wire resistance. Finally, we calibrated the SIAR with the world radiation reference (WRR) and traced the ground calibration result to the measurement on the satellite. The end-to-end calibration ratio is 0.9991-1.0006, and the uncertainties for three channels are all better than 0.08%.

Opto-mechanical design and calibration of a hyperspectral irradiance monitor.

A hyperspectral irradiance monitor (HIM) is designed to measure the direct solar spectral irradiance on the ground, which can be used for research on climate change and vicarious calibration. The spectrometer uses a Féry prism to disperse and converge light, and a linear image sensor (NMOS) measures the spectral irradiance ranging from 400 nm to 1100 nm. The instrument utilizes two flat mirrors to fold the optical path, and optical software is used to optimize the key parameters. The dispersion equation of the prism and two characteristic wavelengths of the laser are utilized for the spectral calibration, for which the uncertainty of the spectral calibration is less than 0.8 nm. A standard lamp is used for the spectral irradiance calibration, for which the uncertainty of the spectral irradiance calibration is less than 2.78% (k=2). The instrument runs stably in the field.

Results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign

We present the results from Verification of Reference Irradiance and Radiance Sources Laboratory Calibration Experiment Campaign. Ten international laboratories took part in the measurements. The spectral irradiance comparison included the measurements of the 1000 W tungsten halogen filament lamps in the spectral range of 350 nm–900 nm in the pilot laboratory. The radiance comparison took a form of round robin where each participant in turn received two transfer radiometers and did the radiance calibration in their own laboratory. The transfer radiometers have seven spectral bands covering the wavelength range from 400 nm–700 nm. The irradiance comparison results showed an agreement between all lamps within ±1.5%. The radiance comparison results presented higher than expected discrepancies at the level of ±4%. Additional investigation to determine the causes for these discrepancies identified them as a combination of the size-of-source effect and instrument effective field of view that affected some of the results.

Research on the irradiance calibration of a VUV dual-grating spectrometer based on synchrotron radiation

A high accuracy instrument calibration is the guarantee of obtaining high precision atmospheric inversion data from a wavelength-dispersive space remote sensing instrument in the orbit. To improve the relative calibration uncertainty of a dual-grating spectrometer in the vacuum-ultraviolet (VUV) band, conventional secondary standard light sources, such as deuterium lamps, used in laboratory calibrating stations are not suited to meet high precision. In this paper we present the calibration of the space instrument based on the Metrology Light Source (MLS) of the Physikalisch-Technische Bundesanstalt (PTB) operated as a primary synchrotron radiation (SR) source with calculable spectral radiant intensity to overcome the limit imposed by secondary transfer standards. For taking into account the difference between the highly linearly polarized SR source and the un-polarized solar radiation, which will be observed by the dual-grating spectrometer in orbit, the calibration was performed at two orientations of the instrument, which are perpendicular to each other with respect to the incident SR. The factors contributing to the uncertainty budget were analyzed. It could be shown that a total relative uncertainty of 2.52% can be achieved, which has greatly improved the calibrating accuracy compared with that obtainable with the conventional standard light source calibrating stations in the VUV spectral range.