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The reduced background calibration facility for detectors and radiators at the Physikalisch-Technische Bundesanstalt

The Physikalisch-Technische Bundesanstalt (PTB) operates a Reduced Background Calibration Facility (RBCF) which provides traceable calibrations of space based infrared remote sensing experiments in terms of radiation temperature and spectral radiance. Traceable measurements from space require the use of calibrated stable detector systems and/or calibration standards on board of the satellites. In any case they should be calibrated under space like conditions to ensure traceability at a minimized uncertainty. This is possible with the RBCF which enables the calibration of radiators and detectors under cryogenic and/or vacuum conditions. The general concept of the RBCF is to connect several sources and detectors under vacuum via a liquid nitrogen cooled beamline. The beamline connects a source- with a detector chamber which also incorporate cooling facilities. Translation units in both chambers enable the RBCF to compare and calibrate different sources and detectors at cryogenic temperatures and under a common vacuum. The radiation of the reference sources and the source under test can additionally be imaged on a vacuum Fourier- Transform Spectrometer (FTIR) to allow spectrally resolved measurements. The FTIR covers the wavelength range from 0.4 μm to 1000 μm. Here several detectors are employed, ranging from an Si-Photodiode to a liquid helium cooled Sicomposite bolometer. Two reference blackbody radiators enable measurements with respect to two reference temperatures, simultaneously. Hereby a compensation of background radiation can be performed and the measurement of very faint sources becomes possible.