Instrument responsivity evolution of SUSIM UARS

Linton E. Floyd; Lynn C. Herring; Dianne K. Prinz; Patrick C. Crane

doi:10.1117/12.328515

27 October 1998 Instrument responsivity evolution of SUSIM UARS

Linton E. Floyd, Lynn C. Herring, Dianne K. Prinz, Patrick C. Crane

Proceedings Volume 3427, Optical Systems Contamination and Degradation; (1998) https://doi.org/10.1117/12.328515
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

The Solar UV Spectral Irradiance Monitor (SUSIM) aboard the Upper Atmosphere Research Satellite (UARS) has been measuring the solar spectral irradiance from 115 nm to 410 nm daily since October 1991. The primary difficulty in maintaining the calibration of these long-term measurements is the correct accounting of degradation in the instrument's responsivity. Accordingly, SUSIM was equipped with redundant optical elements and four stable deuterium lamps, any one of which can replace the sun in the optical path. Periodic calibration of the responsivity of the daily used optical paths is accomplished by comparison of the solar signals from these paths with the solar signals from redundant optical paths containing less-frequently used elements which, in turn, are calibrated using the lamps. Measurements of optical responsivity changes during the first 6.3 years of the SUSIM UARS mission are presented in this paper. The degradation is found to be almost entirely dependent on UV exposure. Consequently, most of the measured degradation takes place in optical elements which precede dispersion. Of these, degradation of transmission elements is strong and has a wavelength dependence similar to that of the lens on the calibration lamps on which contaminant layers apparently also form. The time dependence of the degradation also appears to follow a particular functional form for most wavelengths. Degradation in reflective elements is more moderate and, for some wavelengths, has been observed to reverse, i.e. to increase in responsivity. As an example, the standard channel responsivity at Lyman-(alpha) has increased from its minimum by a factor of more than three.

Citation Download Citation

Linton E. Floyd, Lynn C. Herring, Dianne K. Prinz, and Patrick C. Crane "Instrument responsivity evolution of SUSIM UARS", Proc. SPIE 3427, Optical Systems Contamination and Degradation, (27 October 1998); https://doi.org/10.1117/12.328515

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