Calibration of the solar EUV spectral irradiance instruments aboard the TIMED and SDO satellites

Understanding both the absolute value and time variability of the solar extreme ultraviolet (EUV) spectral irradiance is necessary for understanding the structure and variability of the Earth's thermosphere and ionosphere. Long-term measurement of the solar EUV irradiance requires a calibration scheme that addresses the following issues: (1) The calibration must be referenced to repeatable radiometric standards; (2) Changes in calibration throughout the duration of the measurements must be tracked; and (3) The measurements must be validated with independent instruments and models. The calibration and performance of the TIMED Solar EUV Experiment (SEE), which has been measuring the solar EUV irradiance since early 2002, will be discussed. In addition, the calibration plans for the upcoming EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO) will be outlined.