[CF-metadata] New standard names for satellite obs data

From: Mike Grant <mggr>
Date: Thu, 21 Oct 2010 19:10:27 +0100

Hi Jon,

Thanks for the helpful summary :) We have had similar issues with
handling data that represents time periods, and it'd certainly be good
to find some way to address that.

On 21/10/10 15:28, Jon Blower wrote:
> 1. Steve and Roy both asked (I think) why we can't have a more general
> notion of precision that applies to all coordinate axes, not just time.
> I argue that precision in time *can be* (but is not always) different
> semantically. When I say "these data are representative of June 2009" I
> don't mean "these data were collected on the 15th of June 2009, plus or
> minus 15 days". The concept of "data representative of a time period"
> is very different from "data collected at an uncertain time".
> "Representative" data is commonly found in high-level analysed products,
> not so much in instrument records I guess.

That raises an interesting point - perhaps accuracy and
representativeness are getting bundled together into precision in this
discussion, and should instead be considered separately?

For example, a satellite might pass over an area once a day, taking
about 10mins to cover it. The accuracy of a seconds-since-epoch
timestamp at the center point might then be +/- 5mins (with a precision
of 1 second) but the data for that timestamp might be considered to be
representative of the whole day as there is no more coverage.

This accuracy / representativeness split would apply equally to other
coordinate types as well as time - for example, a satellite pixel
coordinate has a accuracy based on the quality of the geolocation (e.g.
100m) but represents a much larger area (e.g. 1km square).

One could encode both accuracy and representativeness in one field by
making the precision of a timestamp imply representativeness, but that
loses some of the semantics above.

Without wishing to get into too much of a tangle on the issue, perhaps
there's a case for improving CF's description of both accuracy and
representativeness [of coordinates]?

Cheers,

Mike.

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Received on Thu Oct 21 2010 - 12:10:27 BST