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Atmospheric measurements for climate research

Especially interesting for
  • meteorology
  • climate research

Quantitative spectroscopic measurements in the infrared spectral range are essential for the determination of the density distribution of trace gases and of temperature curves in the Earth's atmosphere. Hereby, the traceability of such radiometric measurements to the International Temperature Scale via Planck's radiation law is an indispensible basis to achieve the smallest measurement uncertainties and to render reliable proof of long-term tendencies. For this purpose, PTB has – in cooperation with the University of Wuppertal (Bergische Universität Wuppertal, BUW), Forschungszentrum Jülich (FZJ) and the Institute of Technology, Karlsruhe (KIT) – traced the calibration radiators of the instrument for atmospheric research GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) back to the radiation temperature scale of PTB with measurement uncertainties of smaller than 100 mK.

The infrared Fourier spectrometer GLORIA which performs – mounted on the body of a research aircraft – measurements of particle densities and temperatures in the Earth's atmosphere
(source: ZAT ; F Z Jülich)

GLORIA is an airborne infrared Fourier spectrometer combined with a spatially resolving infrared detector which can perform more than 16,000 spatially and spectrally resolved atmospheric observations at the same time. By means of limb sounding, the instrument generates 3-dimensional images of the atmosphere in the spectral range from 7 μm to 13 μm with a resolution unachieved so far. Of particular interest is the dynamic transition region between the Upper Troposphere and the Lower Stratosphere (UTLS region) at a height of approx. 10 km to 15 km which is highly relevant to the climate on Earth.

For the regularly repeated in-flight calibration sequences of GLORIA, the BUW has developed large-area black-body radiators which – due to an innovative surface structure – exhibit an extreme blackness and a very good isothermy and, thus, provide, during the flight, black-body radiation of defined temperature in very good approximation. To meet the very high requirements for the knowledge of the radiation temperature of these reference radiators, these were extensively characterized and calibrated by radiometry at the Reduced Background Calibration Facility (RBCF) of PTB. The RBCF is a measuring facility which is unique in Europe and which has been developed especially for the calibration of instruments for remote sensing of the Earth in the infrared spectral range under conditions which come close to the conditions during application.

GLORIA has already carried out first measurement flights on the Russian high-altitude research aircraft Geophysica during the ESA measurement campaign ESSenCe and on the German research aircraft HALO during the TACS/ESMVal campaign in which the instrument could demonstrate its function and calibration. Further flights, in particular on HALO, for which GLORIA has been developed, will follow. To observe possible changes in the radiation temperatures of the reference radiators, the radiators were calibrated at the RBCF each time before and after the respective aircraft campaigns.

It is planned to continue the successful cooperation to obtain – for this important region of the atmosphere – highprecision data which are relevant to the climate and which have been traced back permanently to the International Temperature Scale. The experience gained by the BUW and by PTB on the aircraft-borne reference radiators is intended, among other things, to be taken into account also for the development of calibration radiators for a balloon-borne GLORIA instrument and, thus, also serves as a test for a subsequent satelliteborne version of the Fourier spectrometer.


Jörg Hollandt
Department 7.3 Detector Radiometry and Radiation Thermometry
Phone: +49 (0)30 3481-7369
Opens window for sending emailjoerg.hollandt(at)ptb.de

Scientific publication

C. Monte, B. Gutschwager, A. Adibekyan, M. Kehrt, A. Ebersoldt, F. Olschewski, J. Hollandt: Radiometric calibration of the in-flight blackbody calibration system of the GLORIA interferometer. Atmos. Meas. Tech. Discuss., 6, 1–45 (2013)