18.01.2022
Figure: Graphic representation of the newly developed HSBB together with a so-called IRIS instrument (a detector that serves as transfer standard for longwave downward radiation measurements).
Within the European series of research projects labelled "Metrology for Earth Observation and Climate" (MetEOC3-4), a new reference blackbody, the so-called "Hemispherical Blackbody" (HSBB), was developed at PTB in cooperation with the Physikalisch-Meteorologisches Observatorium Davos / World Radiation Center (PMOD/WRC).
The infrared radiation that is emitted from the atmosphere and incident on the Earth (the so-called longwave downward radiation) is constantly being measured at many stations around the globe in order to collect important data about climate change and the greenhouse effect. Measurements of this radiation are typically carried out with pyrgeometers, which are spectrally broadband infrared detectors having a hemispherical acceptance angle. To ensure the significance and comparability of the measurement data over the long term, pyrgeometers need to be calibrated regularly. The HSBB was specially designed to meet the specific requirements for the calibration of pyrgeometers. The HSBB is traceable via the Radiation Temperature Scale of PTB [1] to the International Temperature Scale ITS-90 and hence to the SI. The results of the comparison measurements between the measurement standard BB2007 at PMOD/WRC ‒ a well-established reference for longwave downward radiation measurements ‒ and the new HSBB show agreement within the target irradiance uncertainty of 0.5 W/m².
While the traceability of the BB2007 at PMOD/WRC to the SI is based on contact thermometry and optical simulations, a second independent path of traceability has now been established with the help of the HSBB and the performed comparison measurements. The low uncertainties associated with the HSBB raise the prospect of also reducing the uncertainties linked with the measurement of longwave downward radiation.
[1] I. Müller, A. Adibekyan, K. Anhalt, C. Baltruschat, B. Gutschwager, S. König, E. Kononogova, C. Monte, M. Reiniger, S. Schiller, D. R. Taubert, D. Urban, and J. Hollandt. “Non-contact temperature measurement at the Physikalisch-Technische Bundesanstalt (PTB)”. In: Quantitative InfraRed Thermography Journal 18.3 (2020), pp. 187-212.
DOI: https://doi.org/10.1080/17686733.2020.1734392
Contact:
M. Feierabend, 7.32, E-Mail: 
Moritz.Feierabend(at)ptb.de
C. Monte, 7.32, E-Mail: Christian.Monte(at)ptb.de