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

[JETAL SUTARIYA]

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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