SWS

The shortwave spectroradiometer (SWS) measures the absolute visible and near-infrared spectral radiance (units of watts per square meter 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. At the Southern Great Plains site, the SWS is located in a darkroom within the optical trailer to permit calibrations to be conducted without moving the instrument. Calibrations are performed on schedule using the ARM 12″ integrating sphere.

SWS measurements can be used to:

1. Retrieve cloud optical depth, particle size, and water path.
2. Test the cloud optical depth retrieval for overcast and broken cloud fields.
3. Validate/compare with SGP surface remote sensors and future cloud IOP campaigns.
4. Perform multivariate analysis to derive information content in hyper-spectral data sets and improve cloud retrieval algorithm development.
5. Compare with radiative transfer models for testing and validating retrieval procedures.