Intercomparisons of the solar irradiance measurements from the Nimbus-7 SBUV, the NOAA-9 and NOAA-11 SBUV/2, and the STS-34 SSBUV instruments - A preliminary study

Results are presented of solar irradiance measurements in the spectral range 160-400 nm at approximately 0.15-0.20-nm intervals and at 1-nm resolution performed continually since November 1978. Solar irradiance data from the Nimbus-7 SBUV satellite instrument, the SBUV/2 instruments on the NOAA-9 and NOAA-11 satellites, and the October 1989 flight of the Shuttle SBUV instrument are presented and compared. Uncertainties in the instruments' absolute and long-term radiometric calibrations, which vary among the four instruments, are discussed. Comparisons of the initial solar spectra from the four instruments show agreement to within approximately 10 percent, with spectral biases on the order of +/-4 percent. Irradiances measured by the two NOAA instruments and SSBUV agree to within about 5 percent overall from 270 to 360 nm, with spectral biases on the order of about +/-2 percent. The Nimbus-7 SBUV irradiances are an additional 5-10 percent lower in this region than those measured by the other three instruments.