Cross-Calibration of TIMED SEE and SOHO EIT Irradiances

Abstract

Absolutely calibrated solar images are necessary for a variety of solar physics problems, such as the identification of solar variability sources and the derivation of differential emission measure (DEM) maps. SOHO EIT is absolutely calibrated by using TIMED SEE spectra to provide a method of determining physical values of irradiance for EIT images. EIT images from 1 April 2002 to 15 March 2005 in the 28.4- and 30.4-nm channels are compared to SEE daily spectra from the same time period. The resulting fitted EIT irradiances are well correlated to SEE irradiance measurements and are within the uncertainties of both instruments. The new cross-calibration results are compared to the currently used calibration based on the UARS SUSIM Mg II index.