How to Regrid the netcdf data in order to achieve smaller/greater spatial resolution?

I have a netcdf file with 0.5*0.5 degree (Lat*Lon) grided resolution for precipitation from 1982-2015 in all around the globe. now I want to interpolate (regrid) this file to 0.25*0.25 degree without changing the time. In fact I want to interpolate the precipitation data in 0.25*0.25 lat and lon.

please help me with this issue. If it is possible a sample code can really helpful for me.

Best Regards,

Behzad

Answer 1

[Chad Greene]

Hey Behzad,

This is pretty straightforward: Just use interp2.

When reading the data from the NetCDF file you might need to rotate and flip the grid to get the orientation right, but then let longitude act as the x variable and let latitude act as the y variable.

You can create the quarter-degree grid in one step with cdtgrid like this:

[lati,loni] = cdtgrid(1/4); 

or you can create it manually by

[loni,lati] = meshgrid(min(lon):1/4max(lon),max(lat):-1/4:min(lat)); 

Then use interp2 like

zi = interp2(lon,lat,z,loni,lati); 

Hope that helps.

[Behzad Navidi]

Dear Dr. Chad Greene

Thank you for your answer. I do wath you say and I faced this error. do you have any idea?

my script is:

clc
clear
format compact
close all

filename='precip.mon.total.v2018.nc';
ncdisp(filename)       
lat = ncread(filename,'lat');     
lon = ncread(filename,'lon');  
precip = ncread(filename,'precip');
t = ncread(filename,'time');
lat=double(lat);
lon=double(lon);
precip=double(precip);
t=double(t);
index=find(precip==-9.969209968386869e+36);
precip(index)=nan;

[lati,loni] = cdtgrid(1/4); 
zi = interp2(lon,lat,precip,loni,lati); 

command window show:

Source:
           C:\Users\Behzad\Desktop\precip.mon.total.v2018.nc
Format:
           netcdf4_classic
Global Attributes:
           Original_Source = 'http://www.dwd.de/en/FundE/Klima/KLIS/int/GPCC/GPCC.htm
                              is the webpage and the data is at ftp://ftp.dwd.de/pub/data/gpcc/download.html'
           Reference       = 'Users of the data sets are kindly requested to give feed back and to refer to GPCC publications on this webpage: http://www.dwd.de/bvbw/appmanager/bvbw/dwdwwwDesktop/?_nfpb=true&_pageLabel=_dwdwww_klima_umwelt_datenzentren_wzn&T12404518261141645246564gsbDocumentPath=Content%2FOeffentlichkeit%2FKU%2FKU4%2FKU42%2Fteaser__product__access.html&_state=maximized&_windowLabel=T12404518261141645246564&lastPageLabel=_dwdwww_klima_umwelt_datenzentren_wzn'
           original_source = 'ftp://ftp-anon.dwd.de/pub/data/gpcc/html/fulldata_download.html'
           Conventions     = 'CF 1.0'
           dataset_title   = 'Global Precipitation Climatology Centre (GPCC)'
           References      = 'https://www.esrl.noaa.gov/psd/data/gridded/data.gpcc.html'
           title           = 'GPCC Full Data Reanalysis Version 2018 0.5x0.5 Monthly Total'
           history         = 'Created 09/2018  based on V2018 data obtained via ftp'
           data_modified   = '2019-03-12'
           _NCProperties   = 'version=2,netcdf=4.6.3,hdf5=1.10.5'
Dimensions:
           lat   = 360
           lon   = 720
           nbnds = 2
           time  = 1512  (UNLIMITED)
Variables:
    lat   
           Size:       360x1
           Dimensions: lat
           Datatype:   single
           Attributes:
                       long_name          = 'Latitude'
                       units              = 'degrees_north'
                       standard_name      = 'latitude'
                       axis               = 'Y'
                       coordinate_defines = 'point'
                       actual_range       = [89.75       -89.75]
    lon   
           Size:       720x1
           Dimensions: lon
           Datatype:   single
           Attributes:
                       long_name          = 'Longitude'
                       units              = 'degrees_east'
                       standard_name      = 'longitude'
                       actual_range       = [0.25        359.75]
                       axis               = 'X'
                       coordinate_defines = 'point'
    time  
           Size:       1512x1
           Dimensions: time
           Datatype:   double
           Attributes:
                       long_name          = 'Time'
                       units              = 'days since 1800-1-1 00:00:00'
                       delta_t            = '0000-01-00 00:00:00'
                       avg_period         = '0000-01-00 00:00:00'
                       standard_name      = 'time'
                       axis               = 'T'
                       coordinate_defines = 'start'
                       actual_range       = [33237  79227]
    precip
           Size:       720x360x1512
           Dimensions: lon,lat,time
           Datatype:   single
           Attributes:
                       missing_value = -9.969209968386869e+36
                       units         = 'mm'
                       var_desc      = 'Precipitation'
                       level_desc    = 'Surface'
                       parent_stat   = 'Observations'
                       long_name     = 'GPCC Monthly total of precipitation'
                       valid_range   = [0  8000]
                       statistic     = 'Total'
                       level         = 'Surface'
                       actual_range  = [0      4552.4302]
                       dataset       = 'GPCC Precipitation 0.5degree V2018 Full Reanalysis'
Error using  .' 
Transpose on ND array is not defined. Use PERMUTE instead.
Error in interp2 (line 122)
        V = V.';
Error in test100 (line 23)
zi = interp2(lon,lat,precip,loni,lati); 

Thank you and I looking forward to your answer.

Best Regards