For an overview over the full functionality of the CDO package, please refer to the manual that is available at https://code.zmaw.de/projects/cdo/files.
Here we just give a few examples for the use with CM SAF data:
The pure conversion of a CM SAF HDF5 file to netCDF can be done with the “import_cmsaf” operator. The output format is specified with the parameter “-f”:
cdo -f nc import_cmsaf ifile.h5 ofile.nc
Operators can be combined to a command sequence. A typical case for CM SAF data could look like this:
cdo -f nc remapbil,r360x180 -import_cmsaf cmsaf_product.hdf output.nc
(importing CM SAF data, bilinear remapping to a predefined global grid with 1° resolution and conversion to netcdf).
If you work with CM SAF data on original satellite project, an additional file with information on geolocation (latitudes and longitudes of the satellite pixels) is required, to perform such spatial operations:
cdo -f nc remapbil,r720x360 -setgrid,cmsaf_latlon_file.h5 -import_cmsaf cmsaf_instantaneous_product.hdf output.nc
The “setgrid”-operator can also be used to overwrite the grid description, when it was not correctly detected for CM SAF final products or when the proj-library is not available.
If you want to select a specific region, you should define your own grid description file. This could look like this (example for a region in the Atlantic ocean with a spatial resolution of 0.025°):
gridtype = lonlat
xsize = 999
ysize = 479
xfirst = -52
xinc = 0.025
yfirst = 9.0
yinc = 0.025
With this description file, the following sequence of operators would select one parameter (clwp = cloud liquid water path), and remap it to your model grid:
cdo -f nc remapbil,”your_model_grid_description.txt” –selname,”clwp” –setgrid,cmsaf_lat_lon.hdf –import_cmsaf cmsaf_data.hdf outfile.nc
Some CM SAF data are stored as scaled integer values. For some operations, it could be desirable (or necessary) to increase the accuracy of the converted products. This can be done with the parameter “-b”.
cdo -b f32 -f nc fldmean -remapbil,”grid_description.txt” -import_cmsaf cmsaf_product.hdf output.nc