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.
The main components are the head that houses the filter detectors and amplification circuitry, the stepper motor with shadowband and the mounting frame. The instrument is set up with the motor aligned toward the Equator. The stepper motor and shadowband alternately cover and uncover the diffuser, allowing measurements of global and diffuse irradiance at six narrowband channels and one open channel to be made. Direct irradiance is calculated from the global and diffuse measurements.
To collect one data record, the MFRSR takes measurements at four different shadowband positions:
<li>The initial measurement taken while the shadowband is in the home position out of the 180° field of view. Sometimes called the nadir, or unblocked, measurement.</li>
<li>Next, the first of two side-band measurements is taken. The two side-band measurements are used to correct for the signal lost due to the portion of the sky obscured by the shadowband during the following measurement.</li>
<li>Then, the sun-blocked measurement is taken. This is the measurement taken while the shadowband’s shadow is cast over the diffuser.</li>
<li>Finally, the second side-band measurement is taken. When this last measurement is completed, the shadowband then returns to the home position.</li>
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, one may infer the atmosphere’s aerosol optical depth at each wavelength, the column abundances of ozone and water vapor.
Harrison, L, J Michalsky, and J Berndt. 1994. “Automated multifilter rotating shadow-band radiometer: An instrument for optical depth and radiation measurements.” Applied Optics 33(22):5118-5125, doi:10.1364/AO.33.005118.
Harrison, L, and J Michalsky. 1994. “Objective algorithms for the retrieval of optical depths from groundbased measurements.” Applied Optics 33(22):5126-5132, doi:10.1364/AO.33.005126.
Michalsky, JJ, JC Liljegren, and LC Harrison. 1995. “A comparison of sun photometer derivations of total column water vapor and ozone to standard measures of same at the Southern Great Plains Atmospheric Radiation Measurement site.” Journal of Geophysical Research 100(D12):25,995-26,003, doi:10.1029/95JD02706
PI: Marco Cacciani, <a href=”mailto:firstname.lastname@example.org” target=”_blank” rel=”noopener noreferrer”>email@example.com</a>