Visible Multifilter Rotating Shadowband Radiometer
Visible Multifilter Rotating Shadowband Radiometer

Vis-MFRSR interior

The Visible Multifilter Rotating Shadowband Radiometer (vis-MFRSR) measures solar irradiance at six narrowband wavelengths (nominal 415, 500, 615, 673, 870, and 940 nm; each 10 nm FWHM) plus one unfiltered (open) silicon photodiode of 300-1040 nm. These wavelengths (except the 940 nm water-vapor band) were selected to permit a Langley analysis (Slusser, et al., 2000) for the direct determination of optical depth. The shadowband enables the instrument to measure the three components of solar irradiance, total horizontal, diffuse, and direct normal, simultaneously across all seven channels through a single Lambertian diffuser made of Spectralon®. The vis-MFRSR is environmentally sealed and thermally stabilized at ~40°C, and uses state-of-the-art interference filter photodiode detectors. All channels use silicon (Si) photodiodes, which for the six discrete wavelengths are each hermetically encapsulated with the appropriate filter.

Originally these instruments were lamp calibrated at the CUCF facility in Boulder, Colorado. Now the calibration of this instrument is done by cycling the instruments through NOAA’s calibration facility at Mauna Loa obtaining an MLO calibration factor, although when significant instrument refurbishing is performed they are sent through CUCF to receive full calibration. We also use the data at the deployment site to provide an In-Situ Langley calibration factor as well. The calibration information for this instrument can be found under the Location Information, Deployment History. Detailed information about our Langley Analysis can be found under our Data Processing Procedures.

Measurements are made every 15 seconds and integrated into 3-minute averages and stored by an on-board computer, which is part of the datalogger for the vis-MFRSR.