VACUUM-ULTRAVIOLET INSTRUMENTATION FOR SOLAR IRRADIANCE AND THERMOSPHERIC AIRGLOW

A NASA sounding rocket experiment was developed to study the solar ext reme-ultraviolet (EUV) spectral irradiance and its effect on the upper atmosphere. Both the solar flux and the terrestrial molecular nitroge n via the Lyman-Birge-Hopfield bands in the far-ultraviolet (FUV) regi on were measured remotely from a sounding rocket on October 27, 1992. The rocket experiment also includes EUV instruments from Boston Univer sity, but only the National Center for Atmospheric Research's (NCAR)/U niversity of Colorado's (CU) four solar instruments and one airglow in strument are discussed. The primary solar EUV instrument is a 0.25-m R owland circle EUV spectrograph that has flown on three rockets since 1 988 measuring the solar spectral irradiance from 30 to 110 nm with 0.2 -nm resolution. Another solar irradiance instrument is an array of six silicon soft x-ray (XUV) photodiodes, each having different metallic filters coated directly on the photodiodes. This photodiode system pro vides a spectral coverage from 0.1 to 80 nm with similar to 15-nm reso lution. The other solar irradiance instrument is a silicon avalanche p hotodiode coupled with pulse height analyzer electronics. This avalanc he photodiode package measures the XUV photon energy, providing a sola r spectrum from 50 to 12,400 eV (25 to 0.1 nm) with an energy resoluti on of about 50 eV. The fourth solar instrument is an XUV imager that i mages the sun at 17.5 nm with a spatial resolution of 20 arc sec. The airglow spectrograph measures the terrestrial FUV airglow emissions al ong the horizon from 125 to 160 nm with 0.2-nm spectral resolution. Th e photon-counting CODACON detectors are used for three of these instru ments and consist of coded arrays of anodes behind microchannel plates .