Spectral Radiance Measurements Research Articles

A new approach to crystal habit retrieval from far-infrared spectral radiance measurements

Abstract. To generate reliable climate predictions, global models need accurate estimates of all the energy fluxes contributing to the Earth's radiation budget (ERB). Clouds in general, and more specifically ice clouds, play a key role in the determination of the ERB as they may exert either a feedback or a forcing action, depending on their optical and microphysical properties and physical state (solid/liquid). To date, accurate statistics and climatologies of cloud parameters are not available. Specifically, the ice cloud composition in terms of ice crystal shape (or habit) is one of the parameters with the largest uncertainty. The Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) experiment, foreseen to be the ninth Earth Explorer mission of the European Space Agency, will measure, for the first time spectrally resolved from space, the entire upwelling spectrum emitted by the Earth from 100 to 1600 cm−1. The far-infrared portion of the Earth spectrum, especially from 200 to 600 cm−1, is very sensitive to cloud ice crystal shapes; thus, FORUM measurements could also represent an opportunity to study the ice cloud composition in terms of ice crystal habit mixtures. To investigate this possibility, we developed an accurate and advanced scheme allowing us to model ice cloud optical properties – also in cases of clouds composed of mixed ice crystal habits. This feature is in fact necessary because in situ measurements acquired over the years also point out that the shape of ice cloud crystals varies depending on the crystal size range. In our model, the resulting cloud optical properties are also determined by the input habit fractions. Thus, the retrieval of these fractions from spectral radiance measurements can be attempted. Using 375 different cloudy scenarios, we assess the performance of our retrieval scheme in the determination of crystal habit mixtures starting from FORUM-simulated measurements. The most relevant error components affecting the retrieved cloud parameters are not very large and are of random nature; thus, FORUM measurements will allow us to set up an accurate climatology of cloud parameters. To provide an example of the benefit that one could get from the habit mixture retrievals, we also show the improved accuracy of the thermal outgoing fluxes calculations compared to using assumed mixtures.

Pixelwise immersion factor calibration for underwater hyperspectral imaging instruments

In situ spectral reflectance initially captured at high spatial resolution with underwater hyperspectral imaging (UHI) is effective for classification and quantification in oceanic biogeochemical studies; however, the measured spectral radiance is rarely used as an absolute quantity due to challenges in calibration of UHI instruments. In this paper, a commercial UHI instrument was calibrated for radiometric flat field response and pixelwise immersion effect to support in situ measurement of absolute spectral radiance. The radiometric and immersion factor calibrations of the UHI instrument were evaluated quantitatively through comparative experiments with a spectroradiometer and a spectrometer. Results show that the immersion factor of the center pixel of the tested UHI instrument was 1.763 in pure water at 600 nm, and the averaged difference in immersion factor between the center and edge pixel of the UHI instrument in the visible light band was only 1∼3% across its half angle field of view of 35° in air. The new calibration coefficients were further used to calculate the spectral radiance of transmitted sunlight through ice algae clusters in sea ice measured by the UHI instrument during an Arctic under-ice bio-optical survey.

Facility for spectral radiance calibration at low light level

The spectral radiance measurement at daytime level can be realized with high accuracy, while it’s difficult when the spectral radiance is at nighttime level. We design a spectral radiance calibration facility which has the characteristics of completely unchanged spectrum over 3 orders of magnitude and approximately unchanged spectrum for about 6 orders of magnitude. It combines a spectral radiance light source, a precision aperture and a white diffuser together, make it easy to reproduce the spectral radiance at 380 nm from 4 × 10−9 W/(m2·sr·nm) to 4 × 10−3 W/(m2·sr·nm). The facility can be easily used to calibrate a spectroradiometer at nighttime level. When the spectral radiance from 380 nm to 780 nm is around 1 × 10−7W/(m2·sr·nm), the calibration uncertainty of the spectroradiometer is 0.87%∼1.0% (k = 1).

Calibration method of relative spectral response function of indirect imaging spectrometer

In imaging spectrometers, area array detectors are usually used as photoelectric conversion devices, but the inconsistency of the spectral response among pixels can distort the collected target spectra. To improve the spectral radiometric accuracy of imaging spectrometers, calibrating and correcting the inconsistency of the spectral response among pixels is essential. The signal received by each pixel of area array detector of the indirect imaging spectrometer is usually the superposition of the target multi-spectral radiation signals or full-spectral radiation signals. Therefore, its relative spectral radiometric calibration requires measuring the spectral response of each pixel at different wavelengths on the array detector. Under the ideal conditions, the response values of each pixel in the area array detector are different, so the indirect imaging spectrometer cannot simply calibrate the relative spectral response (RSR) function between pixels by using the method of “monochromator + integrating sphere”. In this work, taking the interferometric imaging spectrometer for example, we analyze the influence of the inconsistency of the RSR among pixels on the target spectral radiation measurement accuracy, and propose a system-level RSR function measurement method for the indirect imaging spectrometer based on the Fourier transform modulation calibration source. In addition, we establish a mathematical model for calibrating the RSR function,and provide guidelines for selecting calibration system parameters such as light source, spectral resolution, and OPD sampling interval. The simulation results show that under the ideal noise-free condition, the 1% spectral response inconsistency among pixels results in a relative error of 1.02% to the recovered spectra. After RSR correction, the relative error of the recovered spectra of different rows decreases to 0.08%. Furthermore, in this work we simulate and analyse the influence of spectral signal-to-noise ratio on the calibration accuracy of the RSR function, and point out that increasing the brightness of the calibration light source, extending exposure time, and combining multi-frame interferograms can enhance RSR function calibration accuracy in practical applications. The research result can provide a theoretical basis for realizing the relative spectral radiometric calibration of indirect imaging spectrometer, which is of great significance in promoting quantitative spectral remote sensing.

Influence of field of view angle and positioning error on spectral radiance measurement

为了减小不同光谱辐射计间瞄准区域差异带来的光谱辐射亮度不一致性，讨论了视场角及定位对于测量准确性的影响。通过建立太阳光白板和卤钨灯白板系统光路下的光谱辐射亮度测量模型，分析了不同几何光路视场区域平均辐射亮度与中心辐射亮度的差异。数值模拟表明，太阳光白板光路修正因子仅与视场角大小有关；卤钨灯白板光路修正因子随测量距离增大而减小，距离600 mm时8°和14°视场角的修正因子分别变为0.993 5和0.980 2。最后，实验验证了卤钨灯白板系统下角度误差和位移误差对光谱辐射亮度的影响。结果表明，修正因子对水平方向的角度误差和位移误差呈现非对称性，两侧差异高达2%。因此，依据视场角和几何定位可以对测量结果进行数据修正，有助于提升光谱辐射亮度测量不确定度水平。

Sensitivity of solar-induced fluorescence to spectral stray light in high resolution imaging spectroscopy

Remote sensing of solar-induced chlorophyll fluorescence (SIF) advances our ability to monitor gross primary productivity. Because SIF is usually <5% of recorded canopy radiance, sources of measurement error must be reduced for accurate SIF retrieval. Here we quantify the impact of spectral stray light on SIF retrieval using a high-resolution imaging spectrometer. We first derived the FLD retrieval solution in the presence of stray light under the simplifying assumptions that SIF, reflectance, and stray light are constant across the region of the spectrum used in the retrieval. We show that stray light contributions from the canopy and reference spectra could cancel out if obtained from the same instrument. In practice however, the simplifying assumptions are unlikely to hold because SIF and reflectance vary across regions of the spectrum commonly exploited by the FLD retrieval, and stray light can also vary across the spectrum, as we demonstrate with an empirical example. To quantify the impact of spectral stray light on SIF retrievals in more realistic scenarios, we performed a sensitivity analysis. We used a stray light signal distribution function and measurements of spectral radiance and SIF to generate spectra with known quantities of SIF and stray light over four orders of magnitude of stray light. We then quantified the bias in retrieved SIF using four SIF retrieval approaches—standard FLD, 3FLD, a spectral fitting method (SFM), and a method based on singular value decomposition (SVD)—applied to the red and/or far-red spectral domains. We found that spectral stray light can cause either a positive or negative bias in SIF estimates. In the highest stray light scenario, with spectral stray light one order of magnitude smaller than the radiance signal, the stray light error ranged from < ± 1% of SIF (for O2-A band retrievals with FLD, 3FLD, and SFM methods, and for far-red retrievals in the 748 nm to 756 nm domain with SVD-based and 3FLD methods applied to Fraunhofer lines) to >30% of SIF (O2-B band retrieval with SFM, and 3FLD applied to Fraunhofer lines in the red domain). For context, a bias of 27% of SIF is a comparable magnitude to seasonal variation in SIF observed in the Amazon basin, and to SIF differences among plant functional types. However, when spectral stray light was three orders of magnitude smaller than the radiance signal, mean bias was < ± 2% for all retrieval methods. Our analysis informs when spectral stray light corrections must be performed for SIF remote sensing.

Sensitivity studies toward the retrieval of ice crystal habit distributions inside cirrus clouds from upwelling far infrared spectral radiance observations

In this paper a retrieval procedure of cirrus ice properties, based on the optimal estimation and the Levenberg–Marquardt iterative formula, is extended with a suitable non linear transformation of the cloud state vector parameters to include the crystal habit distribution in addition to the effective diameter and the optical depth. The cloud optical coefficients are linearly combined using different crystal shapes (solid columns, droxtals, hollow columns, bullet rosettes, aggregates and plates) to build up two different mixtures of habits to be used in the retrieval. This approach allows us to retrieve the coefficients of the habit crystals inside cirrus clouds by using upwelling far infrared spectral radiance measurements. The retrieval capability is shown by performing self-consistency tests using the Simultaneous Atmospheric and Cloud Retrieval (SACR) code and a set of 240 synthetic diverse observations in cloudy-sky generated by using realistic atmospheric scenarios (for mid-latitudes, tropics and poles) and the noise anticipated for the new far infrared sensor Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM), which is planned to be launched as the ninth Earth Explorer (EE-9) by the European Space Agency (ESA) in 2026. The sensitivity of the retrieved crystal habit coefficients to parameters that are not retrieved, such as the surface temperature and emissivity, the cloud top and bottom heights, the ice fraction, the water vapour and temperature profiles, together with the biases caused by the cloud vertical and horizontal inhomogeneity, were also assessed and discussed in the paper.

Performance and validation of a radiation model coupled with a transient bubbling fluidized bed combustion model

None of the transient bubbling fluidized bed combustor (BFBC) models couples the solution of radiative transfer equation with the solution of conservation equations of other transport processes although thermal radiation is of considerable importance in such systems, as such an objective requires both accurate and computationally efficient methods for not only the solution of radiative transfer but also the estimation of radiative properties of particle-laden combustion gases. Therefore, in this study, a 1-D transient comprehensive system model for combustion of lignite is coupled with a 3-D radiation model based on method of line solution of discrete ordinates method utilizing one gas spectral line-based weighted sum of gray gases for spectral gas properties, Mie theory for gray particle properties, and gray wall properties. Predictive accuracy of the model is validated against (i) predictions of a computationally inefficient spectral radiation model and (ii) measurements of transient temperature and concentrations of the species O2 and CO obtained from METU 0.3 MWt atmospheric bubbling fluidized bed combustion test rig firing lignite. The outcome of this study provides a comprehensive, accurate, and computationally efficient tool for simulation of transient BFBCs and highlights the significant impact of radiative heat transfer in modeling of industrial boilers.

Erythemal and vitamin D weighted solar UV dose-rates and doses estimated from measurements in mainland France and on Réunion Island.

Solar UV radiation causes beneficial and detrimental changes in human health. International and national Health agencies recommend avoiding sun exposure when the solar rays are strongest (typically 2h before and after solar noon). In this study we detail and refine such recommendations. We estimated biologically-effective radiation (inductive of erythema and pre-vitamin D) using spectral solar UV radiation measurements on a horizontal plane at three French sites equipped with spectroradiometers: Villeneuve d'Ascq (VDA) (North of France); Observatoire de Haute-Provence (OHP) (French Southern Alps); and Saint-Denis de La Réunion (SDR) on Réunion Island, in the Indian Ocean. These sites are very different: VDA is a semi-urban site in a flat region, OHP a rural mountainous site and SDR a coastal urban site on a small mountainous island. Biologically active radiation was analyzed by studying erythema induction and measuring pre-vitamin D synthesis. Dose-rates, doses and times for sunburn induction and vitamin D production were derived. Regarding the level of vitamin D dose considered here (1000IU), we found that at mainland sites time required for vitamin D synthesis was relatively long, even around solar noon, in winter months this could be 2-3h for phototype II individuals exposing their face and hands. In the tropics vitamin D could always be synthesized in a reasonable time (e.g. 20min in winter). By contrast, in summer, the required duration times (exposing face, hands, arms and legs) are very short, approximately 2-4min on the mainland and 1min in the tropics for phototype II individuals. In all skin phototypes the duration of sun exposure required to induce erythema was generally longer than that to produce vitamin D. These quantitative results, obtained using an instrument measuring on a horizontal plane and with an unobstructed view, do not represent realistic values for human exposure. To account for realistic human body exposure, received doses and times of exposure were adjusted. Our study shows that, mostly in summer, the time periods where limited solar exposure is recommended should be extended, especially at low latitude locations.

Comparison of mid-latitude single- and mixed-phase cloud optical depth from co-located infrared spectrometer and backscatter lidar measurements

Abstract. The long-wave downwelling spectral radiance measurements performed by means of the Far-Infrared Radiation Mobile Observation System (FIRMOS) spectrometer at the summit of the Zugspitze (German Alps) in the winter 2018/19 allowed the retrieval of the optical and micro-physical properties of ice and mixed clouds, showing a good agreement of the statistical relationship between the ice water path and the ice optical depth with the ones from previous works. In this paper the optical depths retrieved from FIRMOS are initially compared with selected cases calculated from backscattering light detection and ranging (lidar) data by using a transmittance method. Then, in order to compare the whole FIRMOS dataset, the power-law relationship between backscattering and extinction is used to apply the Klett method and automatize the routine. Minimizing the root mean square differences, the exponent k of the power-law relationship is assessed to be 0.85 with a variability in the range of 0.60–1.10 for ice clouds and 0.50 with a variability within 0.30–0.70 for mixed clouds.

Laboratory calibration for multidirectional spectroradiometers

A method for the calibration of multidirectional spectroradiometers (MUDISs) capable of the simultaneous measurement of spectral radiance at different wavelengths is presented. The calibration of the spectroradiometer is challenging and crucial for high quality measurements of the angular dependence of the radiance. The calibration device consists of an integrating sphere (also known as Ulbrichtkugel), with a diameter of 100 cm, equipped with three 100 W lamps positioned in the lower hemisphere, with the input optics of the MUDIS directed towards the upper hemisphere. The MUDIS detects radiation from 113 different directions simultaneously in a wavelength range from 300 nm to 550 nm. Due to multiple reflections within the sphere, the radiance from the upper hemisphere is nearly homogeneous with deviations of less than 3% on average. Disregarding the 3% variability and assuming a homogeneous radiance inside the upper hemisphere of the integrating sphere, the spectral responsivities of all the MUDIS channels were determined based on the measured zenith radiance, which was detected by a pre-calibrated Network for the Detection of Atmospheric Composition Change reference spectroradiometer containing a scanning double monochromator with a unidirectional input optics. The input optics of the MUDIS contains thin fibers that should not be moved to avoid changes in the instrument’s responsivity. The proposed method is therefore suited to determine the absolute responsivity of the MUDIS for all directions.

Emissivity-compensated radiation thermometry method using a concave mirror.

In this work, a method to simultaneously measure the temperature and emissivity of any specimen, including metals and semiconductor materials, was developed using a concave mirror and a polarized radiometer. The ratio of the enhanced radiance after reflection off the mirror to the original radiance of a specimen allowed for emissivity determination in the range 0.1-0.9, with a variation of 8%. The combined standard uncertainty, uc, of the temperature measurement by the current method is estimated to be 6.0K at a temperature of 800K. This was realized via classification of the parameter α into only three categories that were closely related to the surface roughness. Furthermore, it should be emphasized that the polarized spectral radiance measurements were carried out at a zenith angle of 75°, which contributed significantly to the success of this method.

Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 μm to 20 μm wavelength.

We have constructed, calibrated, and tested a cryogenic low-background infrared radiometer for both spectral radiance and irradiance measurements over the 4 μm to 20 μm wavelength range. The primary purpose of the Missile Defense Transfer Radiometer (MDXR) is to measure absolute irradiance or radiance from cryogenic infrared test chamber sources using a photoconductive Si:As Blocked Impurity Band (BIB) detector and a set of spectral filters. The MDXR also includes an absolute cryogenic radiometer (ACR) and a Fourier transform spectrometer (FTS). For irradiance measurements, the ACR is used to provide the primary power scale for the BIB detector in conjunction with spectral filters, while the FTS/BIB configuration derives its scale from an internal blackbody source. The two measurement scales show agreement for the irradiance of highly collimated (< 1 mrad) infrared beams from 10-13 W/μm/cm2 to 10-8 W/μm/cm2 within the combined relative uncertainties of 2.6 % (coverage factor k = 1.) We have also calibrated the radiometer for radiance measurements by using a large cavity fluid bath blackbody that overfills the spatial and angular extent of the radiometer entrance pupil. The radiometric calibration uncertainty analysis of the radiometer as well as its maintenance and stability are discussed.

Assessment of Equivalence of the Spectral Radiance Scales Following the Results of the Comparison between the National Metrology Institutes of Korea, China, and Russia

The paper presents the assessment of equivalence of the spectral radiance scales in the wavelength range from 250 to 2500 nm, reproduced at the national metrology institutes of Korea (KRISS), China (NIM), and Russia (VNIIOFI), carried out in the framework of international comparisons. The common set of three tungsten strip lamps was used as an artefact. Based on a series of blind measurements of the lamps spectral radiance performed at each laboratory alternately, the reference value of the comparison was determined at each wavelength as a weighted mean of the measured data of three laboratories. The degree of equivalence of each laboratory was then calculated as the deviation of the measurement data of that participant from the reference value. A data analysis method was proposed for calculating the degree of equivalences and their uncertainties. The method is based on processing spectral radiance ratios, rather than differences, which allows eliminating the influence of a result of one particular participant to results of other laboratories. The comparison results confirm the equivalence of spectral radiance scales of all the laboratories within their expanded uncertainties (k = 2) except a few wavelength points.

The Shortwave Spectral Radiometer for Atmospheric Science: Capabilities and Applications from the ARM User Facility

AbstractIndustry advances have greatly reduced the cost and size of ground-based shortwave (SW) sensors for the ultraviolet, visible, and near-infrared spectral ranges that make up the solar spectrum, while simultaneously increasing their ruggedness, reliability, and calibration accuracy needed for outdoor operation. These sensors and collocated meteorological equipment are an important part of the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) User Facility, which has supported parallel integrated measurements of atmospheric and surface properties for more than two decades at fixed and mobile sites around the world. The versatile capability of these ground-based measurements includes 1) rich spectral information required for retrieving cloud and aerosol microphysical properties, such as cloud phase, cloud particle size, and aerosol size distributions, and 2) high temporal resolution needed for capturing fast evolution of cloud microphysical properties in response to rapid changes in meteorological conditions. Here we describe examples of how ARM’s spectral radiation measurements are being used to improve understanding of the complex processes governing microphysical, optical, and radiative properties of clouds and aerosol.

Analysis and improvements of effective emissivities of nonisothermal blackbody cavities.

The emissivity of the blackbody is a very important parameter in spectral radiance measurement systems. In the conventional method, the emissivity is calculated based on the isothermal model. However, the actual temperature distribution in the blackbody cavity is always nonisothermal; the emissivity calculated based on the isothermal model may not accurately present the radiation characteristic of the blackbody. In this study, the actual temperature distributions of two blackbodies (one has an extended cone shape, and the other a 65-mm diameter cylindrical shape) are measured, and the emissivities are calculated accordingly based on the nonisothermal model at a certain temperature (873 K). The results show there are different tendencies of temperature distributions in the two blackbodies. When compared with the isothermal model, the emissivities in the 873 K temperature and 2.0-20.0 µm wavelength condition are about 1.75% and 0.18% lower at the nonisothermal model for the extended cone shape and cylindrical blackbodies, respectively. To improve the emissivity, different types of apertures are customized for the two blackbodies. For the extended cone-shaped blackbody, the emissivity in the 873 K temperature and 2.0-20.0 µm wavelength condition increases by 1.12% when using a ring-shaped graphite aperture in the cavity, whereas for the cylindrical-shaped blackbody, the emissivity in the same condition increases by 0.09% when using a high-reflective aperture in front of the cavity opening. Different from previous studies, this study provides new insight in calculating and improving the effective emissivity of blackbodies by using the measured temperature in the cavity based on the nonisothermal model.

POLUIÇÃO ATMOSFÉRICA ASSOCIADA AO MATERIAL PARTICULADO NO ESTADO DE SÃO PAULO: ANÁLISE BASEADA EM DADOS DE SATÉLITE

A poluição atmosférica gerada pelas atividades antrópicas afeta tanto o equilíbrio climático quanto a qualidade do ar. O Material Particulado (MP) é reconhecidamente o poluente atmosférico com maior impacto na saúde humana. No estado de São Paulo, as principais fontes de MP são as emissões veiculares, nas áreas urbanas, e a queima de biomassa, nas áreas rurais. Com o objetivo de mitigar a poluição nas áreas rurais, em 2007 foi assinado o protocolo agroambiental entre o estado de São Paulo e o setor sucroalcooleiro, o qualtrata da redução e da eliminação gradual do uso da queima como prática de colheita de cana até 2017. A análise da tendência nos níveis dos poluentes atmosféricos no estado é fundamental para a avaliação dos resultados do protocolo. Entretanto, apesar de apresentar a maior rede de monitoramentode qualidade do ar no Brasil, São Paulo não tem monitoramento da poluição atmosférica na maioria dos seus municípios. Nesse contexto, visando avaliar o impacto do protocolo agroambiental, o presente estudo analisou a distribuição espacial e temporal da profundidade óptica do aerossol (AOD) no estado entreos anos de 2007 (quando o protocolo foi assinado) e 2017. AOD é um indicador óptico da abundância do MP na atmosfera, derivado das medidas de radiância espectral do sensor MODIS a bordo do satélite Terra. Os resultados revelaram que, quando a influência do transporte de fumaça das regiões Norte e Centro-Oeste do Brasil é removida, os dados de satélite identificam adequadamente as regiões mais poluídas no estado: as áreas metropolitanas de São Paulo, de Campinas e da Baixada Santista e as porções central e norte, que são dominadas pelas plantações de cana-de-açúcar. Em relação à tendência depoluição, nas áreas a oeste e noroeste do estado, onde ocorreu expansão do cultivo de cana nos últimos anos, apesar das limitações impostas para queima pelo protocolo agroambiental, observou-se tendência significativa de aumento da poluição. Já nas áreas de tradicional cultivo de cana, nas porçõescentro e norte do estado, embora se tenha percebido tendência de redução da poluição associada ao MP, ela não foi significativa.

The SMART‐s Trace Gas and Aerosol Inversions: I. Algorithm Theoretical Basis for Column Property Retrievals

AbstractThe SMART‐s (Spectral Measurements for Atmospheric Radiative Transfer—spectroradiometer) acquires Sun/sky observations for retrieving optimal information on trace gases and aerosols with minimal assumptions. Overall, the algorithm of SMART‐s incorporates a series of retrievals, from fundamental quantities (i.e., column abundance of trace gases and aerosol loading) to higher‐order geophysical parameters (e.g., aerosol physicochemical properties and vertical profiles), utilizing Sun/sky spectral radiance measurements. This paper describes the theoretical basis for column retrievals of trace gases and aerosols. Associated profile retrievals will be presented in follow‐up papers. The current algorithm retrieves the fine/coarse mode of the particle size distribution and spectral complex index of refraction and, thereby, the spectral aerosol single‐scattering albedo ω0. SMART‐s retrieval is unique particularly in its high spectral resolution of the complex index of refraction and ω0 from near‐ultraviolet to near‐infrared wavelengths, which is pivotal information for atmospheric chemistry, climate and other inversions. We theoretically assessed information content and retrieval accuracy of the algorithm and compared different type of measurements including the Aerosol Robotic Network (AERONET) and standard Pandora. For the same levels of radiometric accuracy, SMART‐s measurements provide the most informative aerosol retrievals based on theoretical error analyses. Higher spectral resolution measurements are particularly beneficial for particle size distribution and fine‐mode refractive index retrievals. We applied this algorithm to the AERONET Sun/sky measurements at Kanpur, India, in 2016 to assess algorithm consistency. Even with different assumptions and numerical methods for the inversion, SMART‐s retrieved aerosol parameters agreed well with the AERONET operational products (e.g., absolute mean bias errors less than 0.01 for ω0).

Non-contact temperature measurement at the Physikalisch-Technische Bundesanstalt (PTB)

ABSTRACT At the Physikalisch-Technische Bundesanstalt, the National Metrology Institute of the Federal Republic of Germany, the traceability of non-contact temperature measurement to the International Temperature Scale (ITS-90) is realised without gaps over a temperature range from −170°C to 3000°C. In this paper the main calibration facilities for the calibration of radiation thermometers at temperatures above 1000°C and measurement of spectral radiance, the calibration of radiation thermometers at temperatures below 1000°C, the calibration of infrared thermographic cameras together with a method developed at PTB to correct the non-uniform response of sensor arrays, the calibration of infrared hyperspectral imagers for remote sensing, and emissivity measurement for industry and remote sensing are described. These facilities are tailored for different temperature ranges and different spectral ranges to meet the demand of industry and research for precise, practical non-contact temperature measurement.

Assessment of Equivalence of the Spectral Radiance Scales following the results of the comparison between the National Metrology Institutes of Korea, China, and Russia

The paper presents the assessment of equivalence of the spectral radiance scales in the wavelength range from 250 nm to 2500 nm, reproduced at the national metrology institutes of Korea (KRISS), China (NIM) and Russia (VNIIOFI), carried out in the framework of international comparison. The common set of three tungsten strip lamps was used as an artefact. Based on a series of blind measurements of the lamps spectral radiance performed at each laboratory, the reference value of the comparison was determined at each wavelength as a weighted mean of the measured data of three laboratories. The degree of equivalence of each laboratory was then calculated as the deviation of the measurement data of that participant from the reference value. A data analysis method was proposed for calculating the degree of equivalences and their uncertainties. The method is based on processing spectral radiance ratios, rather than differences, which allows eliminating the influence of a result of one particular participant to results of other laboratories. The comparison results confirm the equivalence of spectral radiance scales of all the laboratories within their expanded uncertainties except a few wavelength points.