[ncl-talk] regridding EASE snow data

Dennis Shea shea at ucar.edu
Tue Dec 15 11:10:45 MST 2015 

Sorry about the late response on this.

If this is categorical data, I suggest ESMF regridding using the nearest
neighbor ("neareststod") method.

http://www.ncl.ucar.edu/Applications/ESMF.shtml
See: Example 10 (ESMF_regrid_neareststod_10.ncl
<http://www.ncl.ucar.edu/Applications/Scripts/ESMF_regrid_neareststod_10.ncl>
)

HTH ... Good Luck

D

On Thu, Dec 3, 2015 at 2:03 PM, Mary Haley <haley at ucar.edu> wrote:

> Michael,
>
> I'm not sure what you mean by "it regrids without interpolation". I
> believe ESMF_regrid *is* always interpolating the data, unless I'm
> misunderstanding what you mean by interpolation.
>
> --Mary
>
>
> On Wed, Dec 2, 2015 at 8:50 AM, Michael Notaro <mnotaro at wisc.edu> wrote:
>
>> Thanks, Mary.  I tried using ESMF_regrid (wasn't aware of this function
>> before)
>>
>> and it seemed to work well.  it regrids without interpolation.
>>
>> Michael
>>
>>
>> Michael Notaro
>> Associate Director
>> Nelson Institute Center for Climatic Research
>> University of Wisconsin-Madison
>> Phone: (608) 261-1503
>> Email: mnotaro at wisc.edu
>>
>>
>> ------------------------------
>> *From:* ncl-talk-bounces at ucar.edu <ncl-talk-bounces at ucar.edu> on behalf
>> of Mary Haley <haley at ucar.edu>
>> *Sent:* Wednesday, December 2, 2015 9:39 AM
>> *To:* Michael Notaro
>> *Cc:* ncl-talk at ucar.edu
>> *Subject:* Re: [ncl-talk] regridding EASE snow data
>>
>> Hi Michael,
>>
>> Most of our regridding routines do some sort of interpolation.
>>
>> You could try triple2grid, which *places* values at the nearest locations
>> of a 2D rectilinear grid.
>>
>> You will need to first turn your EASE grid and it's lat/lon values into
>> 1D variables:
>>
>> lat1d    = ndtooned(latitude)
>> lon1d    = ndtooned(longitude)
>> cover1d  = ndtooned(cover)
>> opt      = False  ; if True, then some options are available
>>
>> cover_regrid = triple2grid(lon1d,lat1d,cover1d,lon,lat,opt)
>>
>> I admit I've never tried this, so please let ncl-talk know if this works
>> for you.
>>
>> You can see what "opt" options are available:
>>
>> http://www.ncl.ucar.edu/Document/Functions/Built-in/triple2grid.shtml
>> triple2grid - University Corporation for Atmospheric Research
>> NCL Home > Documentation > Functions > Regridding triple2grid. Places
>> unstructured (randomly-spaced) data onto the nearest locations of a
>> rectilinear grid.
>> Read more...
>> <http://www.ncl.ucar.edu/Document/Functions/Built-in/triple2grid.shtml>
>>
>>
>>
>> --Mary
>>
>>
>> On Tue, Dec 1, 2015 at 12:02 PM, Michael Notaro <mnotaro at wisc.edu> wrote:
>>
>>> Does anyone have a suggestions for quickly regridding
>>>
>>> EASE snow cover data, with the following characteristics,
>>>
>>>
>>> latitude(720 rows, 720 columns)
>>>
>>> longitude(720 rows, 720 columns)
>>>
>>> cover(720 rows, 720 columns)
>>>
>>>
>>> to a new 0.2 degree x 0.2 degree grid, with the following
>>>
>>> characteristics?
>>>
>>>
>>> lat=fspan(0.,90.,451)
>>>
>>> lon=fspan(0.,180.,901)
>>>
>>> grid(451,901)
>>>
>>>
>>> It needs to be regridded, not interpolated, as
>>>
>>> the values are 10 for snow covered land and
>>>
>>> 20 for non-snow covered land.
>>>
>>>
>>> I've tried using getind_latlon2d within dual
>>>
>>> do loops, but it was extremely slow.
>>>
>>>
>>> My latest attempt is below, using mask
>>>
>>> to reduce data to only nearby locations.
>>>
>>> In this case, I am trying to regrid 14 years
>>>
>>> worth of daily snow cover.
>>>
>>>
>>> Thanks, Michael
>>>
>>>
>>>
>>>
>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>>>
>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>>>
>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>>>
>>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
>>>
>>> begin
>>>
>>>
>>> cvr=new((/14,12,31,720,720/),float)
>>>
>>> cvr at _FillValue=1e+35
>>>
>>> cvr=1e+35
>>>
>>>
>>> a=addfile("1999/nhtsd25e2_19990101_v01r01.nc","r")
>>>
>>> latitude=a->latitude ; (rows,cols)
>>>
>>> longitude=a->longitude
>>>
>>>
>>> do iyr=0,13
>>>
>>>   do imn=0,11
>>>
>>>     do id=0,30
>>>
>>>       years=iyr+1999
>>>
>>>       if (imn.le.8) then
>>>
>>>         months="0"+(imn+1)
>>>
>>>       else
>>>
>>>         months=""+(imn+1)
>>>
>>>       end if
>>>
>>>       if (id.le.8) then
>>>
>>>         days="0"+(id+1)
>>>
>>>       else
>>>
>>>         days=""+(id+1)
>>>
>>>       end if
>>>
>>>       filen=""+years+"/nhtsd25e2_"+years+""+months+""+days+"_v01r01.nc"
>>>
>>>       if (isfilepresent(filen)) then
>>>
>>>         a=addfile(filen,"r")
>>>
>>>         cvr(iyr,imn,id,:,:)=byte2flt(a->ims_snow_cover_extent(0,:,:)) ;
>>> byte (time, 720 rows, 720 cols) 10=snow covered land; 20=snow free land
>>>
>>>       end if
>>>
>>>     end do
>>>
>>>   end do
>>>
>>> end do
>>>
>>>
>>> lat=fspan(0.,90.,451)
>>>
>>> lat!0="lat"
>>>
>>> lat at units="degrees_north"
>>>
>>> lat&lat=lat
>>>
>>>
>>> lon=fspan(0.,180.,901)
>>>
>>> lon!0="lon"
>>>
>>> lon at units="degrees_east"
>>>
>>> lon at lon=lon
>>>
>>>
>>> grid=new((/14,12,31,451,901/),float)
>>>
>>> grid at _FillValue=1e+35
>>>
>>> grid=1e+35
>>>
>>>
>>> do i=0,450
>>>
>>>   do j=0,900
>>>
>>>
>>>     cover=mask(cvr,latitude.ge.lat(i)+0.5,False)
>>>
>>>     cover=mask(cover,latitude.le.lat(i)-0.5,False)
>>>
>>>     cover=mask(cover,longitude.ge.lon(j)+0.5,False)
>>>
>>>     cover=mask(cover,longitude.le.lon(j)-0.5,False)
>>>
>>>
>>>     do iyr=0,13
>>>
>>>       do imn=0,11
>>>
>>>         do id=0,30
>>>
>>>
>>>           snow=num(cover(iyr,imn,id,:,:).eq.10)
>>>
>>>           nosnow=num(cover(iyr,imn,id,:,:).eq.20)
>>>
>>>           combined=snow+nosnow
>>>
>>>
>>>           if (combined.gt.0) then
>>>
>>>             if (snow.ge.nosnow) then
>>>
>>>               grid(iyr,imn,id,i,j)=100.
>>>
>>>             else
>>>
>>>               grid(iyr,imn,id,i,j)=0.
>>>
>>>             end if
>>>
>>>           end if
>>>
>>>
>>>         end do
>>>
>>>       end do
>>>
>>>     end do
>>>
>>>
>>>   end do
>>>
>>> end do
>>>
>>> year=ispan(1999,2012,1)
>>>
>>> year!0="year"
>>>
>>> year&year=year
>>>
>>> month=ispan(1,12,1)
>>>
>>> month!0="month"
>>>
>>> month&month=month
>>>
>>> day=ispan(1,31,1)
>>>
>>> day!0="day"
>>>
>>> day&day=day
>>>
>>>
>>> grid!0="year"
>>>
>>> grid!1="month"
>>>
>>> grid!2="day"
>>>
>>> grid!3="lat"
>>>
>>> grid!4="lon"
>>>
>>> grid&year=year
>>>
>>> grid&month=month
>>>
>>> grid&day=day
>>>
>>> grid&lat=lat
>>>
>>> grid&lon=lon
>>>
>>>
>>> system("rm climo_snowcover_asia.nc")
>>>
>>> out=addfile("climo_snowcover_asia.nc","c")
>>>
>>> out->grid=grid
>>>
>>>
>>>
>>> Michael Notaro
>>> Associate Director
>>> Nelson Institute Center for Climatic Research
>>> University of Wisconsin-Madison
>>> Phone: (608) 261-1503
>>> Email: mnotaro at wisc.edu
>>>
>>> _______________________________________________
>>> ncl-talk mailing list
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>>>
>>>
>>
>
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