Argo QC codes

[kerfoot]

There was some discussion (and general consensus, I think), that we should use the QC flag values from the Argo manual. Currently, we're using the IMOS flags, which appear to be a slight variant of these.

Unless there are any objections, I'm going to replace the IMOS flag values and meanings with the Argo ones to bring us in line with that project.

[kerfoot]

I'm wondering if we should/can add a global (or variable) attribute specifying the origin of the flag values and meanings? If so, is there a standard attribute?

[dpsnowden]

I think Argo flags are a good default set. But, I think we should use the IMOS convention for referencing an external table to allow for flexibility in the future. See the IMOS manual page 12 for an example. They include a variable attribute called VARIABLE.quality_control_set which takes values from a table that is managed externally. So quality_control_set=1 may point to the first entry in the table which may be the Argo flag set, or the IMOS flag set or whatever. I suggest we follow their convention for consistency. BUT, I don't think referencing an external table is sufficient documentation. I think we should also include the flag definitions as a flag_meanings attribute so that the file is truly self describing.

Eventually we will register whatever flag sets we need at MMI. See the CO-OPS flag definitions there as an example.