Solar irradiance measurements in the spectral range 160-400 nm at approximately 0.15-0.20 nm intervals and at 1 nm resolution have been made by Solar Backscatter Ultraviolet (SBUV) series instruments 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 (STS-34) of the Shuttle SBUV (SSBUV) instrument are presented and intercompared. Uncertainties in the instruments' absolute and long-term radiometric calibrations, which vary among the four instruments, are discussed. Comparisons of the initial, or 'day 1', solar spectra from the four instruments shows agreements to within approximately 10%, with spectral biases on the order of +/- 4%. Irradiances measured by the two NOAA instruments and SSBUV agree to within about 5% overall from 270 to 360 nm, with spectral biases on the order of about +/- 2%; the Nimbus-7 SBUV irradiances are an additional 5-10% lower in this region than those measured by the other three instruments.
