Quality Assessment with QC_TND
QC_TND performs quality-control (QC) checks on the major broadband components of Global or Total (T), Direct Normal (N), and Diffuse (D) radiation.
No QC is performed if the solar zenith angle exceeds 75 degrees.
The QC_TND flags are explained in the table below.
Flag | Flag Value |
---|---|
0 |
Untested parameter |
1 |
Parameter took and passed tests for physical limits, model limits for tolerances less than 3%, and reasonable coupling with other parameters for tolerances less than 3%. |
2 |
Parameter inspected by hand and eye; passed inspection (superseded by 1, if 1 is true). |
3 |
Parameter inspected by hand and eye; did not pass inspection (supersedes 1). |
4 |
Parameter was received as missing; was interpolated from neighbors. |
5 |
Parameter was received as missing; was modeled by coupling with the other 2 parameters. Modeled parameter passed all tests for tolerances less than 3%. |
6 |
Parameter was received as missing; was patched by a method other than modeling or interpolation. |
7 |
Parameter lower than 0. |
8 |
Parameter higher than extraterrestrial radiation. |
10–97 |
Parameter exceeded the 3% tolerance in one of 4 ways:
0 – Too low when coupled with other parameters
The particular error is determined by the remainder of MOD (Flag + 2, 4). The percentage error is determined by dividing (Flag + 2) by 4. The error is greater than or equal to the integer result but less than the next highest, except for the 94–97 flags, which signify errors greater than or equal to 24%, no ceiling.
Example:
Flag = 67 becomes 69 when 2 is added. MOD (69, 4) = 1, or a coupled high error was detected first. Percent = 69/4 = 17, so the mismatch was: The mismatch is no less than 17% and less than 18%.
Please note that the highest percentage problem is reported. For radiation values less than 210 W/m2, absolute tolerances are used. In the example above, if the radiation value were 150 W/m2, the error would be between 17% and 18% of 210 W/m2, or about 36 W/m2. |
99 |
Parameter is missing. |
The process by which these flags are determined is shown in the table below.
Group | Test Performed |
---|---|
I |
Parameter within physical limits.
For each parameter:
If the parameter fails ("yes" to any question) any of these tests, it will be flagged according to the results of the Group II tests. |
II |
A clear day was indicated.
Global above clear-day threshold (Bird):
Direct above clear-day threshold (Bird):
Flags are assigned now. If a single parameter failed Group I testing, it is the only one flagged. Otherwise, all parameters that failed ("yes" to a Group II question) are flagged. |
III |
Check coupling among parameters [if a test fails ("yes" to a question) and there was no prior Group I or Group II failure flag all parameters].
At this point, the largest percentage is applied to the questionable parameter(s). |
Note:
- Bird is the Bird Clear Sky Model, Tau500 = 0.85, water vapor = 6.0 cm. These values have been selected to produce a very "dirty," dim sky.
- Rayleigh is the Rayleigh clear sky model, the "cleanest" possible clear sky.
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