SGP/BRS/C1 - Downwelling SW below empirical limit

Downwelling shortwave values appear to drop below the empirical limit (-10 W/m^2) at 
night, and during the day the values are less than the calculated downwelling shortwave by 
about 20-30 W/m^2 (at times close to 50 W/m^2 difference). Field techs performed maintenance 
but could not find obvious instrument problems.

The data exhibit the three component failure with global being flagged too low. The 
difference is likely due to the artifact of the cosine response of the particular installed PSP 
coupled with typical uncertainties of this set of installed radiometers. Also the unique 
variation of pyranometer responsivity (calibration factor) as a function of solar zenith 
angle could play a factor in the discrepancy.

Users should use a derived value for the downwelling shortwave hemispheric irradiance 

(DS). Where DS = diffuse component + direct normal * cos(SZA) component described in 
the SIRS handbook (Section 7.2).

• inst_global

• down_short_hemisp_min
• down_short_hemisp_max
• down_short_hemisp_std
• down_short_hemisp