XUV Photometer System (XPS): Overview and Calibrations |
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| Authors: | Thomas N Woods Gary Rottman Robert Vest |
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| Institution: | (2) Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, U.S.A.;(3) National Institute of Standards and Technology, Gaithersburg, MD, U.S.A. |
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| Abstract: | The solar soft X-ray (XUV) radiation is highly variable on both short-term time scales of minutes to hours due to flares and
long-term time scales of months to years due to solar cycle variations. Because of the smaller X-ray cross sections, the solar
XUV radiation penetrates deeper than the extreme ultraviolet (EUV) wavelengths and thus influences the photochemistry and
ionization in the mesosphere and lower thermosphere. The XUV Photometer System (XPS) aboard the Solar Radiation and Climate
Experiment (SORCE) is a set of photometers to measure the solar XUV irradiance shortward of 34 nm and the bright hydrogen
emission at 121.6 nm. Each photometer has a spectral bandpass of about 7 nm, and the XPS measurements have an accuracy of
about 20%. The XPS pre-flight calibrations include electronics gain and linearity calibrations in the laboratory over its
operating temperature range, field of view relative maps, and responsivity calibrations using the Synchrotron Ultraviolet
Radiation Facility (SURF) at the National Institute of Standards and Technology (NIST). The XPS in-flight calibrations include
redundant channels used weekly and underflight rocket measurements from the NASA Thermosphere-Ionosphere-Mesosphere-Energetics-Dynamics
(TIMED) program. The SORCE XPS measurements have been validated with the TIMED XPS measurements. The comparisons to solar
EUV models indicate differences by as much as a factor of 4 for some of the models, thus SORCE XPS measurements could be used
to improve these models. |
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