Observations of the solar irradiance in the 200-350 nm interval during the ATLAS-1 mission: A comparison among three sets of measurements - SSBUV, SOLSPEC, and SUSIM

The SOLSPEC, SSBUV, and SUSIM spectrometers simultaneously observed the solar spectral irradiance during the ATLAS-I mission flown on board the Space Shuttle Atlantis in March 1992. The three instruments use different methods and means of absolute calibration and were each calibrated preflight and postflight. The three data sets are reported from 200 to 350 nm at 1.1 nm resolution. The method of comparing the three independent data sets is discussed. The importance of a common, precise wavelength scale is shown when comparing the data in wavelength regions of strong Fraunhofer lines. The agreement among the solar irradiance measurements is better than +/-5%. The fact that the calibrations of the three instruments were based on three independent standards provides confidence that the absolute solar spectral irradiance in the range 200-350 nm is now known with an accuracy better than +/-5%. The mean ATLAS-I solar spectrum is compared with simultaneous solar observations from the UARS SOLSTICE and UARS SUSIM instruments. The two mean solar spectra agree to within +/-3%.