cmsaf (version 1.9.5)

cmsaf.sub: Subtract the fields of two input NetCDF files.

Description

The function subtracts the fields of infile2 from the fields of infile1. Infiles have to have the same spatial and temporal dimension or one infile can contain only one timestep. The outfile uses the meta data of infile1.

Usage

cmsaf.sub(vari1, vari2, infile1, infile2, outfile, nc34)

Arguments

vari1

Name of variable in infile1 (character).

vari2

Name of variable in infile2 (character).

infile1

Filename of first input NetCDF file. This may include the directory (character).

infile2

Filename of second input NetCDF file. This may include the directory (character).

outfile

Filename of output NetCDF file. This may include the directory (character).

nc34

NetCDF version of output file. If nc34=4 the output file will be in NetCDFv4 format (numeric). Default output is NetCDFv3.

Value

A NetCDF file including the subtracted fields of infile1 and infile2 is written.

Examples

# NOT RUN {
## Create an example NetCDF file with a similar structure
## as used by CM SAF. The file is created with the ncdf4 package.
## Alternatively example data can be freely downloaded here: 
## <https://wui.cmsaf.eu/>

library(ncdf4)

## create some (non-realistic) example data

  lon <- seq(5,15,0.5)
  lat <- seq(45,55,0.5)
  time <- c(as.Date('2000-01-01'), as.Date('2001-02-01'))
  origin <- as.Date('1983-01-01 00:00:00')
  time <- as.numeric(difftime(time,origin,units='hour'))
  data1 <- array(250:350,dim=c(21,21,1))
  data2 <- array(230:320,dim=c(21,21,1))

## create two example NetCDF files

   x <- ncdim_def(name='lon',units='degrees_east',vals=lon)
   y <- ncdim_def(name='lat',units='degrees_north',vals=lat)
   t <- ncdim_def(name='time',units='hours since 1983-01-01 00:00:00',
   vals=time[1],unlim=TRUE)
   var1 <- ncvar_def('SIS','W m-2',list(x,y,t),-1,prec='short')
   vars <- list(var1)
   ncnew <- nc_create('CMSAF_example_file_1.nc',vars)
   ncvar_put(ncnew,var1,data1)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   nc_close(ncnew)

   t <- ncdim_def(name='time',units='hours since 1983-01-01 00:00:00',
   vals=time[2],unlim=TRUE)
   ncnew <- nc_create('CMSAF_example_file_2.nc',vars)
   ncvar_put(ncnew,var1,data2)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   nc_close(ncnew)

## Subtract the fields of both example CM SAF NetCDF files and write the 
## result into one output file.
   cmsaf.sub('SIS','SIS','CMSAF_example_file_1.nc', 'CMSAF_example_file_2.nc', 
   'CMSAF_example_file_sub.nc')
# }