Validation of the UARS solar ultraviolet irradiances: Comparison with the ATLAS 1 and 2 measurements

Abstract

The measurements of the solar ultraviolet spectral irradiance made by the two Upper Atmosphere Research Satellite (UARS) solar instruments, Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) and SOLar STellar Irradiance Comparison Experiment (SOLSTICE), are compared with same‐day measurements by two solar instruments on the shuttle ATmospheric Laboratory for Applications and Science (ATLAS) missions, ATLAS SUSIM and Shuttle Solar Backscatter UltraViolet (SSBUV) experiment. These measurements from the four instruments agree to within the 2σ uncertainty of any one instrument, which is 5 to 10% for all wavelengths above 160 nm and for strong emission features below 160 nm. Additionally, the long‐term relative accuracy of the two UARS data sets is better than the original 2% goal, especially at wavelengths greater than 160 nm. This level of agreement is credited to accurate preflight calibrations coupled with comprehensive inflight calibrations to track instrument degradation. Two solar irradiance spectra, 119 to 410 nm, are presented; the first combines observations from UARS SUSIM and UARS SOLSTICE taken on March 29, 1992, during the ATLAS 1 mission, and the second combines spectra for April 15, 1993, during the ATLAS 2 mission. The ATLAS 1 mission coincided with the initial decline from the maximum of solar cycle 22 when solar activity was relatively high. The ATLAS 2 mission occurred somewhat later during the declining phase of the solar cycle 22 when solar activity was more moderate.

Improved solar Lyman α irradiance modeling from 1947 through 1999 based on UARS observations

“…The uncertainties for the SME Lyman (x irradiances are -40% [Rottman, 1981;, and the uncertainties for the AE-E Lyman at irradiances are -30% [Hinteregger et al, 1981]. Whereas, the uncertainty for the UARS Lyman cz irradiance is 5% [Woods et al, 1996]. The SME and AE-E measurements could therefore be adjusted within their respective uncertainty levels to agree with the UARS values.…”

The SORCE SIM Solar Spectrum: Comparison with Recent Observations

“…As described by Thuillier et al (2004), in this wavelength region, the ATLAS composite is based on the average of five datasets (SOL-STICE I, UARS SUSIM, SSBUV, ATLAS SUSIM, and SOLSPEC). Woods et al (1996) compared these datasets for 15 April 1993 and found that the two UARS instruments agreed to about 5%. The average uncertainty of the composite rose to about 10% when ATLAS SUSIM and SSBUV were included.…”

“…The overall absolute accuracy of its calibration is valid to about 2% in the 200 to 300 nm range and has a resolution of 0.1 nm with 3 points per resolution element sampling. The UARS SOLSTICE I F-channel instrument (Rottman, Woods, and Sparn, 1993;Woods, Rottman, and Ucker, 1993;Woods et al, 1996) has a SURF II based calibration that is estimated to be accurate to 3% (k = 1). The instrument covers the wavelength range 170 to 315 nm with a resolution of 0.2 nm and a sampling of 3 points per resolution element.…”

Distribution of UV radiation at the Earth's surface from TOMS‐measured UV‐backscattered radiances

“…Cebula et al [1994,1996] estimated the agreement between the UARS SUSIM and the SOLSTICE to be +_5% absolute. The measurements made by the two UARS instruments were compared with the same-day measurements by three other solar instruments (the solar spectrum (SOLSPEC), the shuttle solar backscatter ultraviolet (SSBUV), and the shuttle SUSIM instruments) during the ATLAS-1 and ATLAS-2 space shuttle missions in March 1992 and April 1993, respectively [Cebula et al, 1996;Woods et al, 1996], and ATLAS 3 in November 1994. In the 280-400 nm wavelength region, at 0.5 nm spectral resolution, the difference among the various data sets is less than +_3% and is wavelength dependent.…”