DLR's New Traceable Radiance Standard “RASTA”

The German Aerospace Center (DLR) operates the Calibation Home Base (CHB) as a facility for the calibration of airborne imaging spectrometers such as APEX, HySpex and ROSIS, and for field spectrometers. Absolute radiometric calibration is performed so far using an integrating sphere that is traceable to SI units through calibration at the German Metrology Institute PTB. However, the stability of the radiance output is not monitored regularily and reliably since the small size (diameter 50 cm, exit port 20 cm x 4 cm) and the design make it difficult to install a device at a reproducible position which is suited to measure accurately changes of the spectral radiance. This drawback was the motivation to develop a new radiance standard (RASTA) which allows monitoring of small changes in the wavelength range from 380 to 2500 nm. The realisation is presented here.