Re: [netcdfgroup] spatial "regridding"

• To: netcdfgroup@xxxxxxxxxxxxxxxx, Tom Roche <Tom_Roche@xxxxxxxxx>
• Subject: Re: [netcdfgroup] spatial "regridding"
• From: David William Pierce <dpierce@xxxxxxxx>
• Date: Fri, 6 Jul 2012 14:48:41 -0700

I think your best bet would be to use NCL:

http://www.ncl.ucar.edu/Applications/regrid.shtml

Saves you having to reinvent the wheel.

If NCL seems like too much for just the one task of regridding, you can
also download the ESMF libraries (and a stand alone program) that
implements the NCL regridding:

http://www.earthsystemmodeling.org/

If you go that route, I think It is easier to understand how the ESMF
regridding works if you consult the documentation for an earlier regridding
program, SCRIP:

http://oceans11.lanl.gov/trac/SCRIP/wiki

However I have found SCRIP to be unreliable across seams, and so recommend
against it (although other people seem to find it works for them).

Regards,

--Dave

On Fri, Jul 6, 2012 at 2:43 PM, Tom Roche <Tom_Roche@xxxxxxxxx> wrote:

>
> I'd appreciate advice regarding tools and methods for transforming
> values "contained" in one 2-d netCDF spatial grid in one {projection,
> resolution} to another, or pointers to other resources to consult.
> Apologies if the following is too verbose (I'm guessing this is a
> common usecase) or uses the wrong vocabulary (please correct where
> needed), but here's what I mean:
>
> I want to take N2O emissions from various sources in the contiguous US
> (CONUS) and input them to a particular atmospheric model (CMAQ). My
> group has other inputs (notably, meteorology) for our usecase on a
> 12 km x 12 km Lambert conformal conic (LCC) grid, and the model wants
> everything in one format, so I need to get our N2O emissions on that
> 12x12 LCC. However, most of my N2O emissions will be coming from
> global inventories (EDGAR, GEIA, GFED) which are gridded lat-lon at
> differing resolutions (e.g., 0.1x0.1°). So I need to "regrid" the
> latter emissions. How to do? on linux, preferably programmatically.
> Details:
>
> EDGAR 4.2 gives the mass of N2O emitted from each 0.1x0.1° lat-lon
> gridcell over the globe. From that I can subset the portion that
> intersects the AQMEII North American grid
>
> https://github.com/TomRoche/cornbeltN2O/wiki/AQMEII-North-American-domain
>
> (Pretty sure I can do that with NCO.) I can then use R package=M3
>
> http://cran.r-project.org/web/packages/M3/
>
> to project the nodes of the EDGAR subgrid to LCC. Note that, @ 40° N
> (middle latitude of this subgrid), each EDGAR gridcell's extents are
> ~11 km N-S x ~8.5 km E-W.
>
> Over that "LCC EDGAR" subgrid I would (conceptually) overlay a 12x12
> km LCC CMAQ grid. (Which of course will deviate slightly from those
> exact dimensions--we have the exact grid centers, nodes, and areas.)
> Given
>
> 1 the LCC EDGAR grid's extents are larger than the CMAQ grid's extents
>   (which I can make true)
>
> 2 each CMAQ gridcell is larger than each LCC EDGAR gridcell, over the
>   CMAQ grid's extents (which I believe is true, but should check)
>
> 3 each gridcell in either has no internal structure, so emissions
>   allocated to each gridcell are presumed to be "smeared evenly" by
>   area over the gridcell
>
> each CMAQ gridcell will overlay between 2 and n LCC EDGAR gridcells
> (guessing that n=4 in this case), and I can reallocate emissions
> area-proportionally from each overlaid LCC EDGAR gridcell to the CMAQ
> gridcell. This presumes that I can, programmatically,
>
> 1 identify each underlay (LCC EDGAR) gridcell that an overlay (CMAQ)
>   gridcell intersects
>
> and, for each of the underlay gridcells U_i (with i in 1..n)
> intersected by a given overlay gridcell O,
>
> 2 identify the emissions attributed to U_i e_{U_i} (easy, just lookup)
>
> 3 identify the total area of U_i a_{U_i} (should be an easy
>   computation, given lookup of its corners/gridnodes)
>
> 4 identify the area of intersection I_i between U_i and O (I don't
>   know how to do that)
>
> whereupon I can attribute to O emissions e_O =
>
> \sum_{i=1}^{n} \frac{I_i U_i}{a_{U_i}}
>
> This sounds doable, provided task 4 can be done programmatically, but
> it also sounds error-prone, and I've got a lot of other work to do on
> this project, so I'm more than willing to reuse existing code (esp R,
> since that would fit with my other scripts).
>
> Your coding recommendations are appreciated, as would be pointers to
> helpful resources. Thanks in advance, and feel free to forward,
> Tom Roche <Tom_Roche@xxxxxxxxx>
>
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-- 
David W. Pierce
Division of Climate, Atmospheric Science, and Physical Oceanography
Scripps Institution of Oceanography, La Jolla, California, USA
(858) 534-8276 (voice)  /  (858) 534-8561 (fax)    dpierce@xxxxxxxx

• References:
  • [netcdfgroup] spatial "regridding"
    • From: Tom Roche