Dear Jonathan,
I don't quite agree with the implication you derive from : "In general, CF
metadata describes what a quantity *is* and not how it was calculated from
other quantities." -- a temperature difference is a temperature, but you don't
want to confuse it with a temperature (pun intended). Suppose you have this
wonderful search engine that finds out that NOAA, UK Met Office, JMA, ECMWF and
many others provide daily fields of sea surface temperatures. Then you load
them all and compute a mean value. What happens if the NOAA values are SST
anomalies rather than actual temperatures? As far as I can tell, the software
would have no way of telling. OK: you can argue this is why we still need
humans, but in my view it defeats the GEOSS concept of interoperability. In
particular, because it should be avoidable. But perhaps a simple solution yould
be to add a standard_name modifier called "derived_quantity" which would mean
that it has similar properties (grid, units, etc.) like the ori
ginal, but values should not be compared with the original.
Best,
Martin
>
> It would probably help if we focussed on some real use-cases
> where it is essential to provide *systematic* metadata i.e.
> which can be processed by programs. It is always possible to
> provide descriptive metadata, useful to humans, in
> non-standardised attributes such as long_name and history,
> and this can explain how the quantity is obtained.
>
> Best wishes
>
> Jonathan
>
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