EUV SpectroPhotometer (ESP) in Extreme Ultraviolet Variability Experiment (EVE): Algorithms and Calibrations

摘要

The Extreme ultraviolet SpectroPhotometer (ESP) is one of five channels ofthe Extreme ultraviolet Variability Experiment (EVE) onboard the NASA SolarDynamics Observatory (SDO). The ESP channel design is based on a highly stablediffraction transmission grating and is an advanced version of the SolarExtreme ultraviolet Monitor (SEM), which has been successfully observing solarirradiance onboard the Solar and Heliospheric Observatory (SOHO) since December1995. ESP is designed to measure solar Extreme UltraViolet (EUV) irradiance infour first order bands of the diffraction grating centered around 19 nm, 25 nm,30 nm, and 36 nm, and in a soft X-ray band from 0.1 to 7.0 nm in the zerothorder of the grating. Each band's detector system converts the photo-currentinto a count rate (frequency). The count rates are integrated over 0.25 secincrements and transmitted to the EVE Science and Operations Center for dataprocessing. An algorithm for converting the measured count rates into solarirradiance and the ESP calibration parameters are described. The ESP pre-flightcalibration was performed at the Synchrotron Ultraviolet Radiation Facility ofthe National Institute of Standards and Technology. Calibration parameters wereused to calculate absolute solar irradiance from the Sounding Rocket flightmeasurements on 14 April 2008. These irradiances for the ESP bands closelymatch the irradiance determined for two other EUV channels flownsimultaneously, EVE's Multiple Euv Grating Spectrograph (MEGS) and SOHO'sCharge, Element and Isotope Analysis System / Solar EUV Monitor (CELIAS/SEM).