Providing radiometric traceability for the calibration home base of DLR by PTB

Abstract

A dedicated calibration technique was applied for the calibration of the spectral radiance transfer standard (RASTA) of the German Aerospace Center (DLR) at the Physikalisch-Technische Bundesanstalt (PTB), consisting of two independent but complementing calibration procedures to provide redundancy and smallest possible calibration uncertainties. Procedure I included two calibration steps: In a first step the optical radiation source of RASTA, an FEL lamp, was calibrated in terms of its spectral irradiance E λ(λ) in the wavelength range from 350 nm to 2400 nm using the PTB Spectral Irradiance Calibration Equipment (SPICE), while in a second step the spectral radiance factor β 0°:45°(λ) of the RASTA reflection standard was calibrated in a 0°:45°-viewing geometry in the wavelength range from 350 nm to 1700 nm at the robot-based gonioreflectometer facility of PTB. The achieved relative standard uncertainties (k = 1) range from 0.6 % to 3.2 % and 0.1 % to 0.6 % respectively. Procedure II was completely independent from procedure I and allowed to cover the entire spectral range of RASTA from 350 nm to 2500 nm. In the second procedure, the 0°:45°-viewing geometry spectral radiance Lλ,0°:45°(λ) of RASTA was directly calibrated at the Spectral Radiance Comparator Facility (SRCF) of PTB. The relative uncertainties for this calibration procedure range from 0.8 % in the visible up to 7.5 % at 2500 nm (k = 1). In the overlapping spectral range of both calibration procedures the calculated spectral radiance L λ,0°:45°,calc(λ) from procedure I is in good agreement with the direct measurement of procedure II, i.e. well within the combined expanded uncertainties (k = 2) of both procedures. © 2013 AIP Publishing LLC.