The Shortwave Spectroradiometer (SWS), measures the absolute visible and near infrared spectral radiance (units of watts per meter square per nanometer per steradian) of the zenith directly above the instrument. The SWS is a moderate resolution sensor comprised of two Zeiss spectroradiometers (MMS 1 NIR enhanced and NIR-PGS 2.2) for visible and near-infrared detection in the wavelength range 350 - 2170 nm. The sampling frequency is 1 Hz. The spectral resolution is 8 nm for the MMS 1 NIR and 12 nm for the NIR-PGS 2.2. The light collector has a narrow field of view (1.4°) collimator at the front end of a high-grade custom-made fiber optic bundle. The SWS does daily daytime measurements. The SWS is located in a darkroom, constructed by SGP site personnel within the optical trailer, to permit calibrations to be conducted without the necessity of moving the instrument to a different location. Calibrations are performed at regularly scheduled times using the ARM 12" integrating sphere.
The SWS measurements can be used to retrieve cloud optical depth, particle size and cloud water path, test the cloud optical depth retrieval for overcast and broken cloud fields, validation/comparison with SGP surface remote sensors and future cloud IOP campaigns, multivariate analysis to derive information content in hyper spectral data sets and to improve cloud retrieval algorithm development, compare with radiative transfer models for testing and validating retrieval procedures.