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Laboratory for Atmospheric and Space Physics

Ground Calibration

The XUV Photometers (XPs) are silicon XUV photodiodes with thin film filters to measure the integrated solar UV irradiance from 0.1 to 35 nm with a typical bandpass of 7 nm. These silicon XUV photodiodes are reference detectors for NIST in the XUV spectral region because they are extremely stable. The XPs are not expected to degrade by more than a couple of percent over the SORCE mission based on the stability tests that NIST and others have performed on these photodiodes as a function of exposure level to photons and high energy particles. Because the solar variability below 35 nm is expected to be a factor of 2 to 1000 (wavelength-dependent), the XPs can serve as an on-board reference detector. The estimated uncertainty for this assumption of detector stability is about 2%, as proven for the SNOE XPS and TIMED SEE XPS.