[Met_help] [rt.rap.ucar.edu #95577] History for Regridding with different projections/coordinate systems and WGS84

[John Halley Gotway via RT]

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  Initial Request
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Hello folks,

we have several current issues with regridding (i.e. not just MET related), but we have been wondering to what extent these issues might go away when we use MET.

A look at the MET user guide provides some insights into the regrid option. The guide isn't specific about the fact that the "from" and "to" grids needs to be from the same projection/coordinate system, but we suspect that this is the case (or we haven't tried it is the other way of putting it!)

We have a lot of head scratching around rotated lat-lon grids as well as observation data sets (mainly) which are in WGS84 which causes no end of headaches... when we need to regrid the model to the observations for example. To what extent are these already supported or will be supported? There is the feeling that preprocessing and storing data in different projections before using MET is inefficient (but for now we have no choice). It would be better done on the fly and more efficient.

Specifically WGS84 is an issue for GPM/TRMM data. It is also an issue for scatterometer data (even though scatterometer data can be treated as point observations).

Regards
Marion

--
Dr Marion Mittermaier     Manager: Model diagnostics and novel verification

Met Office   FitzRoy Road   Exeter   EX1 3PB   United Kingdom
Tel:  +44 (0) 330 135 1604
E-mail: marion.mittermaier at metoffice.gov.uk<mailto:marion.mittermaier at metoffice.gov.uk>  http://www.metoffice.gov.uk<http://www.metoffice.gov.uk/>

http://www.metoffice.gov.uk/research/people/marion-mittermaier

I am co-chair of the WMO WWRP Joint Working Group on Forecast Verification Research (JWGFVR) http://www.wmo.int/pages/prog/arep/wwrp/new/Forecast_Verification.html



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  Complete Ticket History
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Subject: Regridding with different projections/coordinate systems and WGS84
From: John Halley Gotway
Time: Thu Jun 11 08:47:26 2020

Hi Marion,

I see you have some questions about the regridding options in MET. It
does
in fact support regridding data across projection types, meaning that
the
from and to grids do not need to share a common projection.

Randy Bullock is the person who developed the underlying grid code
upon
which the regridding logic is based. Checking the MET website I see
that
while we have some white papers from Randy explaining some parts of
the
code, we do not have one about regridding:

https://dtcenter.org/community-code/model-evaluation-tools-
met/documentation

I do think you could limit the number projections on which data is
stored
and let MET do the regridding. But do realize that regridding incurs
some
computational cost. So I’d recommend testing things out to make sure
the
results are “close enough” numerically and don’t take too long.

The regridding can either be done using the stand-alone
regrid_data_plane
tool or directly in the stats tool using the regrid dictionary. The
former
is more efficient if you’d otherwise need to regrid the same field
multiple
times. But the later is more convenient if you only need to regrid
once.

If you’d like, we could schedule a telecon to discuss regridding
options in
more detail.

Thanks,
John

On Thu, Jun 11, 2020 at 7:05 AM marion.mittermaier at metoffice.gov.uk
via RT <
met_help at ucar.edu> wrote:

>
> Thu Jun 11 07:05:24 2020: Request 95577 was acted upon.
> Transaction: Ticket created by marion.mittermaier at metoffice.gov.uk
>        Queue: met_help
>      Subject: Regridding with different projections/coordinate
systems and
> WGS84
>        Owner: Nobody
>   Requestors: marion.mittermaier at metoffice.gov.uk
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=95577 >
>
>
> Hello folks,
>
> we have several current issues with regridding (i.e. not just MET
> related), but we have been wondering to what extent these issues
might go
> away when we use MET.
>
> A look at the MET user guide provides some insights into the regrid
> option. The guide isn't specific about the fact that the "from" and
"to"
> grids needs to be from the same projection/coordinate system, but we
> suspect that this is the case (or we haven't tried it is the other
way of
> putting it!)
>
> We have a lot of head scratching around rotated lat-lon grids as
well as
> observation data sets (mainly) which are in WGS84 which causes no
end of
> headaches... when we need to regrid the model to the observations
for
> example. To what extent are these already supported or will be
supported?
> There is the feeling that preprocessing and storing data in
different
> projections before using MET is inefficient (but for now we have no
> choice). It would be better done on the fly and more efficient.
>
> Specifically WGS84 is an issue for GPM/TRMM data. It is also an
issue for
> scatterometer data (even though scatterometer data can be treated as
point
> observations).
>
> Regards
> Marion
>
> --
> Dr Marion Mittermaier     Manager: Model diagnostics and novel
verification
>
> Met Office   FitzRoy Road   Exeter   EX1 3PB   United Kingdom
> Tel:  +44 (0) 330 135 1604
> E-mail: marion.mittermaier at metoffice.gov.uk<mailto:
> marion.mittermaier at metoffice.gov.uk>  http://www.metoffice.gov.uk<
> http://www.metoffice.gov.uk/>
>
> http://www.metoffice.gov.uk/research/people/marion-mittermaier
>
> I am co-chair of the WMO WWRP Joint Working Group on Forecast
Verification
> Research (JWGFVR)
>
http://www.wmo.int/pages/prog/arep/wwrp/new/Forecast_Verification.html
>
>
>

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