| Flag | Definition |
|---|---|
| A | Post-1976 measured solar radiation data as received from
NCDC or other sources |
| B | Same as 'A' except the global horizontal data underwent a
calibration correction |
| C | Pre-1976 measured global horizontal data (direct and
diffuse were not measured before 1976), adjusted from solar to local time, usually with a calibration correction |
| D | Data derived from the other two elements of solar
radiation using the relation, Kt = Kn + Kd (see Part 2, Section 8.1 for more information) |
| E | Modeled solar radiation data using inputs of observed sky
cover (cloud amount) and aerosol optical depths derived from direct normal data collected at the same location |
| F | Modeled solar radiation using interpolated sky cover and
aerosol optical depths derived from direct normal data collected at the same location |
| G | Modeled solar radiation data using observed sky cover and
aerosol optical depths estimated from geographical relationships |
| H | Modeled solar radiation data using interpolated sky cover
and estimated aerosol optical depths |
| ? | Source does not fit any of the above categories. Used for
nighttime values, calculated extraterrestrial values, and missing data |