Quality control coding
Shear-probe quality-control flags
The Q (quality control) flags associated with shear-probe measurements are not compatible with the Ocean Sites Ocean Sites for quality control (QC) coding.
Every dissipation estimate from every probe must have Q flag. The numerical values of the Q flags are as follows:
Q =
0, if all checks pass
1, if FOM > FOM_limit
2, if despike_fraction > despike_fraction_limit
4, if |log(e_max)-log(e_min)|> diss_ratio_limit [math]\displaystyle{ \times \sigma_{\ln\varepsilon} }[/math]
8, if despike_iterations > despike_iterations_limit
The Q flags are combined by their addition. For example a Q value of 3 means that the dissipation estimated failed both FOM_limit test and the despike_fraction test. A value of 15 means that all tests failed. A failure of any one test ([math]\displaystyle{ Q\ne0 }[/math]) means that a dissipation test should not be trusted. The reasons for a failure can be decoded by breaking the value of Q down to its powers of 2.
Another flag that can be used (in addition to the Quality flag) is GOOD PROBE: GOOD_PROBE
0, all probes are good
1, sh1 only
2, sh2 only
3, sh1 and sh2
4, sh3 only
5, sh1 and sh3
6, sh2 and sh3
7, sh1, sh2 and sh3
8, sh4 only
999, all bad
However, this is already provided by the above recommended Q flags.
Ocean Sites Providing quality-control flags according to Ocean Sites is encouraged. These are described at Ocean Sites for quailty control (QC) coding. This flagging scheme is mostly compatible with the primary level flagging recommended by Intergovernmental Oceanographic Commission of UNESCO (2013). However, only the flags of 0, 1, and 4 make sense for dissipation estimates derived from shear-probe data.
| Flag | Meaning | Comment |
|---|---|---|
| 0 | unknown | No QC was performed. |
| 1 | good data | All QC tests passed. |
| 2 | probably good data | Data have failed one or more QC tests but detailed examination after processing (e.g. by visual examination) suggests data is good. |
| 3 | potentially correctable bad data | These data are not to be used without scientific correction or re-calibration (e.g. uncertain shear sensor sensitivity). |
| 4 | bad data | Data have failed one or more tests. |
| 5 | - | Not used |
| 6 | - | Not used |
| 7 | nominal value | Data were not observed but reported (e.g. instrument target depth.). |
| 8 | interpolated value | Missing data may be interpolated from neighboring data in space or time. |
| 9 | missing value | This is a fill value |
[Rolf left the stuff below in place because I do not know what to do with it.]
Climate and Forecast Metadata Convention (CF) requires that QC flags carry attributes. In netCDF (Network Common Data Form) data files, the following information for quality control flagging should be provided for each data variable <PARAM>.
<PARAM>_QC
<PARAM>_QC:long_name = “quality flag of <PARAM>”;
<PARAM>_QC:conventions = “OceanSITES QC Flags”;
<PARAM>_QC:flag_values = 0, 1, 2, 3, 4, 7, 8, 9;
<PARAM>_QC:flag_meanings = “0:unknown 1:good_data 2:probably_good_data 3:potentially_correctable_bad_data 4:bad_data 7:nominal_value 8:interpolated_value 9:missing_value”
