A High Resolution Ultraviolet Spectroradiometer and Its Application in Solar Radiation Measurement

An ultraviolet (UV) spectroradiometer is refurbished and upgraded with a fore-optical module. In addition to measuring total UV irradiance, the UV spectroradiometer can measure solar direct beam and sky radiance at any preset azimuth and elevation angle. This double Czerny-Turner spectroradiometer, with an ion-etched holographic grating operating in the first order with 3600 lines per mm, enables wavelength scanning range from 290 nm to 410 nm, with a nominal bandwidth of 0.1 nm. It can operate with a step-size of 0.0005 nm and a full width at half maximum of 0.01 nm. It has an out-of-band rejection ratio of approximately 10^–10. This high resolution spectroradiometer can be used as a reference instrument for UV radiation measurements and to monitoring atmospheric gases (O3, SO2, NO2). Recently laboratory work suggests that water vapor displays structured absorption features over 290-350 nm region with maximum and minimum cross-sections of 8.4×10-25 and 1.4×10-25 cm2/molecule. We plan to use this high resolution spectroradiometer to detect and analyze water vapor absorption features in UV region in real atmosphere.