GLORIA-BB - Two Blackbodies for Infrared Interferometer Calibration

Radiometric Calibation of the GLORIA Infrared Interferometer

For the retrieval of trace gas concentrations, the measured spectra need to be radiometrically calibrated with high accuracy (1%). This will be achieved by a two point calibration using two well-defined blackbody radiance sources (GBB-C and GBB-H) at different temperatures. The Institute for Atmospheric and Environmental Research at the University of Wuppertal designed, built and tested the GLORIA calibration sources.

The optical surface of a GBB (GLORIA BlackBody) (125mm x 125mm) consists of an array of 625 pyramids made of aluminum, which is temperature-controlled by a cooler consisting of 4 times 2 Peltier elements. Temperature is measured at 10 locations using platinum resistors. The pyramid array is varnished with NEXTEL-Velvet Coating 811-21.

The casing surrounding the optical surface is partly thermally decoupled and serves as a straylight baffle. It will also be temperature-controlled by a Peltier cooler. The calibration sources are suspended by GFRP tubes for thermal decoupling.

In order to characterize the properties of the blackbodies an intensive test program at the PTB (Physikalisch-Technische Bundesanstalt) in Berlin has been performed.

Specifications of the Blackbodies

optical surface 125 mm x 125 mm
BB-C temperature = instrument temperature - 10 K
BB-H temperature = instrument temperature +30 K
temperature accuracy < 0.1 K
emissivity > 99.7 %
Design of a GBB
GBB pyramid array
varnished with Nextel Velvet Coating