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Experiences with a three-current ionization chamber as primary detector standard for absolute calibration in space

: Schäfer, Robert; Schmidtke, Gerhard; Brunner, Raimund


Applied optics 57 (2018), Nr.24, S.6851-6859
ISSN: 0003-6935
ISSN: 1539-4522
ISSN: 1559-128X
Fraunhofer IPM ()
space instrumentation; calibration; Extreme Ultraviolet Radiation; photoionization; Soft X-Rays

Context: With ISS-SOLAR-SolACES, a new approach in terms of calibrating solar spectral irradiance (SSI) data was validated during the mission period from 2008 to 2017: an ionization chamber (IC) as primary detector standard, operated in space, allowed daily calibration measurements. Issue: Though primary photo-ionization efficiencies and higher-order ionization effects from photoelectrons are constant with time, filter transmissions and signal contributions from solar x-rays are to be determined for the SSI data evaluation, requiring a deeper investigation. Aims and Methods: The experiences made with ionization chambers in the laboratory and aboard the ISS-SOLAR-SolACES mission are presented. They include the determination of higher-order ionization effects, the measured transmission of the filters with time, and the treatment of the solar soft x-ray background. Recommended combinations of IC filling gases and filter materials as well as laboratory and in-space measurements will provide correction procedures for different levels of solar activity to achieve further improvement of SSI data accuracy in the spectral range from 1 nm to 133 nm. Results and Perspectives: The usage of the IC technology aims for establishing absolute SolACES-type calibration equipment in space, providing reference SSI data sets in solar and solar-terrestrial science, as well as in related applications such as global navigation satellite system signal evaluation.