[ncl-talk] [EXT]Re: Error in regridding SMAP Freeze Thaw binary data

[Kunal Bali]

Hi,
Did you try

cdo remapbil,NLDS.file yourfile.nc output.nc
(NLDS) = you can use any file (NLDS.file) with 0.125 resolution


---
Kunal Bali






On Tue, 1 Feb 2022 at 18:40, JETAL SUTARIYA via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hi Dave,
>
> Thank you very much for your helpful comment.
> I tried your first suggestion and it worked out well.
>
> I have searched in NCL, CDO and NCO manuals and websites for binary data
> regridding, but was unable to find something resonating.
> If anybody finds it, please let me know for future reference.
>
> Thanks,
> Jetal
>
>
>
> On Tue, Feb 1, 2022 at 6:33 PM Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> *External Email*
>> Jetal, you are using linint2 regridding.  This and most other regridders
>> will naturally compute fractional averages from the surrounding ones and
>> zeros.  I can think of several strategies to reduce down to your desired
>> ones and zeros.
>>
>> 1.  This is the simplest and quickest.  Trust that the numerical
>> averaging is an accurate representation of the desired outcome.  Apply a
>> simple numeric threshold to convert to ones and zeros.  Do this right after
>> linint2 and the print statements.  The first line is necessary to handle
>> the missing values that you showed, and you might want to adjust this for
>> the desired missing value outcome.
>>
>>      flh   = where ( ismissing (flh), 0, flh )
>>      flh2 = where ( (flh .ge. 0.5), 1, 0 )
>>
>> 2.  Write your own regridding algorithm that decides ones and zeros based
>> on nearby input grid points, and your choice of decision criteria.  For
>> example, weighted or unweighted averages or counts, of input grid points
>> within a given radius of each output grid point.
>>
>> This could also be as simple as "copy the nearest input grid point value
>> to the output grid point".
>>
>> 3.  Search NCL docs for a regridding method specifically designed for
>> ones and zeros.  I doubt that there is one, but maybe.  ESMF could possibly
>> have something like this, for the same reason as yours.
>>
>> 4.  Look at NCO operators and CDO for the same thing.
>>
>>
>> On Tue, Feb 1, 2022 at 5:52 PM JETAL SUTARIYA via ncl-talk <
>> ncl-talk at mailman.ucar.edu> wrote:
>>
>>> Hi NCL Community,
>>>
>>> I am trying to regrid the SMAP L3 Freeze thaw 36 km data to NLDAS grid
>>> (1/8th degree). I have already converted data from EASE grid to regular
>>> lat/lon grids separately.
>>> But SMAP freeze thaw contains binary data i.e. 0 if grid is non-frozen
>>> and 1 if grid is frozen so when I regrid the file; I get different values
>>> between 0 and 1,
>>> for eg., 0.05755893, 0.3908837, 0.7242084,
>>>     0.8300187, 0.496694, 0.1633693, 0, 0, 0, 0, 0, 0, _, _, _, _, _, 0,
>>> 0, 0,
>>>     0.007007165, 0.02686451, 0.04672185, 0.045869, 0.02601166,
>>> 0.006154316,
>>>     0.01370303, 0.03356037, 0.05341771, 0.03917314, 0.0193158, 0, 0, 0,
>>> 0, 0,
>>>     0, 0.007237409, 0.02709475, 0.04695209, 0.04563876, 0.02578142.
>>> This is incorrect since the data should be binary in the regridded
>>> freeze thaw variable.
>>> Does anybody have an idea how to reflect that while regridding?
>>>
>>> I have attached a few files here: 1) ncl script that I used to complete
>>> this task, 2) Screenshots of the PrintVarSummary error of input and gridded
>>> variable 3) Screenshot of output variable which is not binary.
>>>
>>> Any suggestions are very helpful.
>>> Thanks,
>>> Jetal
>>>
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