PREMOS is a space experiment scheduled to fly on the French solar mission PICARD. The experiment comprises filter radiometers and absolute radiometers to measure the spectral and total solar irradiance. The aim of PREMOS is
to contribute to the long term monitoring of the total solar irradiance,
to use irradiance observations for ‘nowcasting’ the state of the terrestrial middle atmosphere and
to provide long term sensitivity calibration for the solar imaging instrument SODISM on PICARD.
In this paper we describe the calibration of the instruments. The filter radiometer channels in the visible and near IR were characterized at PMOD/WRC and the UV channels were calibrated at PTB Berlin. The absolute radiometers were compared with the World Radiometric Reference at PMOD/WRC and a power calibration relative to a primary cryogenic radiometer standard was performed in vacuum and air at NPL.
PTB and DLR join their expertise and experience in optical radiometry and in THz techniques to perform what is to our knowledge the first traceable measurement of radiant power of a THz quantum cascade laser and the first absolute calibration of a THz radiation detector against a cryogenic radiometer (CR). A total standard uncertainty of 7.3% was achieved at a frequency of 2.5 THz corresponding to a wavelength of 120 µm. This uncertainty is dominated by the limited knowledge of the absorptance of the CR cavity. All other uncertainty contributions including those arising from diffraction are only 2%.
A cryogenic-radiometer-based calibration facility utilizing monochromatized radiation of an argon arc plasma has been put into operation at the PTB. The high radiance of the plasma source allows us to improve the accuracy of the UV spectral responsivity scale between 200 nm and 410 nm and to achieve relative standard uncertainties of about 0.1% to 0.2%. Comparison with the PTB laser-based cryogenic radiometer at five laser lines in the UV indicated excellent agreement.
At the Physikalisch-Technische Bundesanstalt (PTB), absolutelycalibrated filter radiometers based on silicon photodiodes are routinely used for thermodynamic temperature determinations of blackbodies in the range from the zinc fixed point (FP) (419 • C) up to 3,000 • C. To extend the temperature range down to the tin FP (232 • C), we have designed two new filter radiometers based on indium gallium arsenide (InGaAs) photodiodes with center wavelengths at 1,300 nm and 1,550 nm. For the absolute calibration of the spectral irradiance responsivity of the new InGaAs filter radiometers, the spectral responsivity measurement in the near-infrared (NIR) spectral range has been significantly improved. With a newly developed tuneable laser and monochromator-based cryogenic radiometer facility, the relative standard uncertainty of the NIR spectral responsivity has been reduced from 0.17 % to about 0.03 %. By using the calibrated InGaAs filter radiometer in conjunction with the large-area double sodium heat pipe of the PTB, the first results for the difference between the thermodynamic temperature T and the ITS-90 temperature T 90 in the temperature range from the zinc FP up to the aluminum FP (660 • C) are presented. The values for T -T 90 determined with the new InGaAs filter radiometers are consistent within their relative standard uncertainty of about 30 mK at 419 • C to about 60 mK at 660 • C.
Abstract. The Physikalisch-Technische Bundesanstalt (PTB) expanded its capabilities of
the absolute measurement of radiant power to the spectral range of the
mid-infrared (MIR) by implementing additional MIR laser radiation sources at
one of the PTB's cryogenic electrical substitution radiometer facilities.
This extension enables absolute calibrations of the spectral responsivity of
detectors in the MIR traceable to the International System of Units (SI). The thermopile detector TS-76 was characterized and calibrated in view of its
spectral responsivity s(λ) in the wavelength range between 1.5 and
10.6 µm at the expanded cryogenic electrical substitution
radiometer facility. The relative standard measurement uncertainty was
significantly reduced to 1.4 % by developing an optimized and thermally
stabilized detector housing
design. The TS-76 was established as a mid-infrared transfer detector for the
SI traceable measurement of radiant power and the dissemination of the
spectral responsivity s(λ) in the MIR.
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