add thresholding of parameters with other parameters

[andershenja]

Modern radars can collect many moments/parameters, some of which are related to data quality like SQI and CCOR. These parameters can be used to threshold geophysical parameters. RAVE is particularly well-suited to this kind of operation due to the way data are represented, so an efficient way of processing this can be achieved.
I suggest a method be added to the PolarScanCore? object.
It will be important to keep track of metadata associated with the thresholding, to prevent unnecessary replication.

What to do about traceability and self-documentation? Personally, I don't think thresholding like this necessitates a quality field, but maybe a quality plugin for convenience. I think it's enough with a metadata attribute containing info on:
which moment was thresholded, e.g. DBZH
which moment containing the basis for thresholding, e.g. SQIH
the threshold value
whether the thresholding was upwards or downwards
Such information could easily be represented in an XML block, for example something that is compatible with that which is already used in CfRadial?, called "thresholding_xml".