Interpreting QCFIT Plots
Three scatter plots are presented for each site-month of data based on daily solar position:
|Ranges||Air Mass||Zenith Angle|
|Low||1.00 - 1.25||0 - 36.96°|
|Medium||1.25 - 2.50||36.96 - 66.57°|
|High||2.50 - 5.76||66.57 - 80.00°|
The irradiance data are presented as paired-data in K-space. The abscissa represents the Kt (global) and the ordinate is the corresponding value of Kn (direct normal). The boundaries for each case have been determined by the analyst using QCFIT results for historical data. The boundaries are shown in the plots as a solid line. No data should appear above the diagonal as this is physically impossible. The quality flags are assigned according to the normal K-distance from the QCFIT boundary:
d = [INT(flag + 2)/4]/100
(for flags 10 - 93*)
These flags indicate the test that was performed, the manner of the failure (high or low), and the distance from the boundary to the data point (magnitude of the failure). See the accompanying table for details.
Clear-sky data congregate in the upper right-hand portion of the plots. Irradiance data collected under overcast conditions should fall at the bottom of the boundary, nearer the left-hand side.
*The first 3 flags (01 through 03) indicate the data passed 1-, 2-, or 3-component tests. The next 3 flags (04 through 06) are not used by SERI_QC. Flags 07 and 08 indicate data below or above empirical limits, respectively. Flag 09 is assigned to data that are considered "Strange, but true." Data that are physically impossible (DNI > 0 and DS = 0) are flagged 94 through 98. Missing data are flagged "99."