Implications of measured differences in the spectroradiometric sensitivity of SBUV/2 instruments in air and vacuum on long-term measurements of stratospheric ozone and solar irradiance variations

William K. Fowler; Kevin W. Kelly; Donald F. Heath

doi:10.1117/12.257143

8 November 1996 Implications of measured differences in the spectroradiometric sensitivity of SBUV/2 instruments in air and vacuum on long-term measurements of stratospheric ozone and solar irradiance variations

William K. Fowler, Kevin W. Kelly, Donald F. Heath

Author Affiliations +

Proceedings Volume 2815, Optical Radiation Measurements III; (1996) https://doi.org/10.1117/12.257143
Event: SPIE's 1996 International Symposium on Optical Science, Engineering, and Instrumentation, 1996, Denver, CO, United States

Abstract

In recent years, the consistency of ultraviolet solar spectral irradiance measurements has improved to the extent that broad band averages of solar irradiances agree to within a few percent over ranges of a few hundred nanometers. Over spectral ranges from tens to tenths of nanometers significantly larger disagreements in spectral irradiances are observed. Some well known factors which contribute to measurement uncertainties over smaller wavelength intervals are wavelength calibration errors, uncertainties in radiometric standards especially in the transition region from one standard to another, and differences and uncertainties in slit scattering function between instruments. Extensive pre-launch radiometric calibration of SBUV-2 ozone monitoring instruments in air and vacuum have indicated new sources of radiometric calibration uncertainties. These are effects of Woods anomalies in grating efficiency and wavelength dependent changes (sometimes with significant structure) in the reflectance of MgF₂ overcoated aluminum surfaces which seems to be associated with the absorption and desorption of water vapor by the MgF₂ thin film. These effects combine to produce wavelength dependent radiometric calibration differences between air and vacuum conditions of as much as 10 percent or more. These results indicate that one should not assume that an accurate radiometric calibration in air is valid in space for the wavelength region of 200 - 400 nm.

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William K. Fowler, Kevin W. Kelly, and Donald F. Heath "Implications of measured differences in the spectroradiometric sensitivity of SBUV/2 instruments in air and vacuum on long-term measurements of stratospheric ozone and solar irradiance variations", Proc. SPIE 2815, Optical Radiation Measurements III, (8 November 1996); https://doi.org/10.1117/12.257143

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