[CF-metadata] COARDS name for a time offset

From: Jonathan Gregory <j.m.gregory>
Date: Sat, 23 Dec 2006 19:23:19 +0000

Dear John

> heres a Grid with 2D lat/lon coordinates:
>
> * short sea_surface_temperature*( nj, ni) ;
> sea_surface_temperature:*coordinates *= "lon lat time" ;
> float *lat*(nj, ni) ;
> float *lon*(nj, ni) ;
> int *time*(nj, ni) ;
>
> we were thinking that this is a Swath:
>
> * short sea_surface_temperature*( nj, ni) ;
> sea_surface_temperature:*coordinates *= "lon lat time" ;
> float *lat*(nj, ni) ;
> float *lon*(nj, ni) ;
> int *time*(nj, ni) ;
>
> the difference being that Grids have an orthogonal time coordinate.

Hmmm ... I can't see any difference between these. What does "orthogonal
time coordinate" mean?

> Now you are proposing
>
> * short sea_surface_temperature*( timeRef, nj, ni) ;
> sea_surface_temperature:*coordinates *= "lon lat time
> timeRef" ;
> float *lat*(nj, ni) ;
> float *lon*(nj, ni) ;
> int *time*(timeRef, nj, ni) ;
> *time*:long_name = "actual time of each pixel" ;
> int *timeRef(*timeRef*) *;
> *timeRef*:long_name = "reference time of sst file" ;

Actually Ed is proposing the time(timeRef,nj,ni) should be a time-offset,
rather than an actual time. I was asking whether it might not be simpler to
make it an absolute time for the SST field, so that the 1D reference time
axis would be just an index rather than having time values.

> I think the general swath situation is that lat,lon doesnt have a
> repeating pattern (i could be wrong)

Apparently GHRSST does have a repeating pattern for every variable relative to
the time of SST, but SST itself doesn't have a repeating pattern.

> So we need some new standard name to be able to distinguish these 2
> kinds of time.

Between absolute time and time-offset - yes, I think so.

Best wishes

Jonathan
Received on Sat Dec 23 2006 - 12:23:19 GMT