The in-flight blackbody calibration system for the GLORIA interferometer on board an airborne research platform

[摘要] The Gimballed Limb Observer forRadiance Imaging of the Atmosphere (GLORIA)is a prototype of an imaging Fourier Transform Spectrometer (FTS) forPREMIER, a former candidate mission for ESA's Earth Explorer 7. GLORIA isdeployed on board various research aircraft such as the Russian M55Geophysica or the German HALO. The instrument provides detailedinfrared images of the Upper Troposphere/Lower Stratosphere (UTLS)region, which plays a crucial role in the climate system. GLORIA usesa two-dimensional detector array for infrared limb observations inemission and therefore needs large-area blackbody radiation sources(126 mm × 126 mm) for calibration.

In order to meet the highly demanding uncertainty requirements for thescientific objectives of the GLORIA missions and due to thesophisticated tomographic evaluation scheme, the spatial distributionof the radiance temperature of the blackbody calibration sources hasto be determined with an uncertainty of about 0.1 K. SinceGLORIA is exposed to the hostile environment of the UTLS with mutablelow temperature and pressure, an in-flight calibration system has tobe carefully designed to cope with those adverse circumstances.

The GLORIA in-flight calibration system consists of two identicalweight-optimised high-precision blackbody radiation sources, which areindependently stabilised at two different temperatures. The two pointcalibration is in the range of the observed atmospheric infraredradiance emissions with 10 K below and 30 K aboveambient temperature, respectively. Thermo-Electric Coolers are used tocontrol the temperature of the blackbody radiation sources offeringthe advantage of avoiding cryogens and mechanical coolers. The designand performance of the GLORIA in-flight calibration system ispresented. The blackbody calibration sources have been comprehensivelycharacterised for their spatially (full aperture) and spectrally(7 to 13 μm) resolved radiation properties interms of radiance temperatures traceable to the InternationalTemperature Scale (ITS-90) at the Physikalisch-TechnischeBundesanstalt (PTB), the national metrology institute of Germany.

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