The visible Multifilter Rotating Shadowband Radiometer (MFRSR) is a passive instrument that measures global and diffuse components of solar irradiance at six narrowband channels and one open, or broadband, channel. Direct irradiance is not a primary measurement, but is calculated using diffuse and global measurements.
To collect one data record, the MFRSR takes measurements at four different shadowband positions. The first measurement is taken with the shadowband in the nadir (home) position. The next three measurements are, in order, the first side-band, sun-blocked, and second side-band. The side-band measurements are used to correct for the portion of the sky obscured by the shadowband. The nominal wavelengths of the narrowband channels are 415, 500, 615, 673, 870, and 940 nm.
From such measurements, the atmosphere’s aerosol optical depth at each wavelength can be inferred. In turn, these optical depths may be used to derive information about the column abundances of ozone and water vapor, as well as aerosol and other atmospheric constituents.