Quality Check Flags
The Quality Check (QC) Philosophy:
Sequential QCs are performed along the processing chain of each OPUS file. The processing of the measured data stops if one QC test fails. If the DC variation of IFG is too high, for example, the FFT and all subsequent steps are omitted. In this case, no output spectrum is generated, just the error flag state in the log file listing the QC status for each measurement. The QC flags are given for both channels separately. FWD and BWD QC flags are resolved, where values of 0, 1, and 2 are possible.
Quality Check Procedure:
In the beginning, a formal test checking whether a submitted OPUS file is compatible with COCCON and the functional extent of the preprocessor is executed. If this test fails, no flag is generated, program execution is stopped altogether. All subsequent tests modify the reported flagging state. The total flagging state of each spectrum is mapped on a single integer number. A spectrum passing all tests has flag content 0 000 000 000 (10 zeroes). Each test modifies a certain position in this integer.
| QC 1 | solar elevation angle too low (less than 1°) |
| QC 2 | IFG DC value too small relative to available ADC range |
| QC 3 | IFG DC variation too high |
| QC 4 | 1000: relative change of IFG centerburst amplitude between FWD and BWD too high 3000: FWD / BWD IFG centerburst positions differ significantly |
| QC 5 | insufficient number of IFG points for specified resolution |
| QC 6 | out-of-band artefacts too high |
| QC 7 | insufficient number of IFG points for phase calculation (in one of single sided IFG recording) |
| QC 8 | spectral calibration significantly differs from reference spectrum |
| QC 9 | compare spectra derived from forward and backward scans; the test is applied after allowing for an overall ordinate scaling factor for adjustment; the summed difference between the spectra should not exceed a predefined threshold |
| QC 10 | in case of analytical phase option: analytical phase fit significantly differs from raw phase |