NetCDF (network Common Data Form) is a file format for storing multidimensional scientific data (variables) such as temperature, humidity, pressure, wind speed, and direction. Usually, there is one n-dimensional (latitude, longitude, level, and/or time or others) record per variable and there can be several different variable in one netCDF file. Dimensions are also treated as variables. And then there are attributes for each variable, for example the name and unit of the variable or a grid or time description, etc. Have a look at the official website if you like:

    Unidata/UCAR

There are several sets of tools to view and manipulate netCDF files - see below. We have several of them installed on our UQAM servers. To get access to them you need to load the following module:

These are the tools you will have access to after executing the above command:

Check content of a netCDF file

ncdump

The ncdump is a command-line utility that converts the content of a netCDF file to ASCII text on standard output. It is a quick tool to look at the content of a netCDF file. Since netCDF files can get fairly large and with the the text output of ncdump I recommend to either just look at the header information (description of variables but not the actual data) with:

or you can redirect the output into, 'less' to view it page by page and to be able to search in the text output with:

However, ncdump will not decode date and time step. To see these you can use 'cdo -sinfo' - see below.

cdo -sinfo

To list all the timesteps in a netCDF file you can use the command:

Generate & manipulate netCDF files

ncgen

ncgen can generate a netCDF file, C program, or Fortran program from a CDL text file.

ncdump and ncgen used together

Used together, ncdump and ncgen can accomplish simple netCDF manipulations with little or no programming:

1) Create a text file with ncdump:

    ncdump  netCDF_file  >  text_file

2) Edit the text file with any editor

3) Generate a netCDF file from the modified text file:

    ncgen  -b  -o  new_netCDF_file  text_file

However, this is not very practical for large netCDF files.

CDO

CDO is a collection of command-line operators to manipulate and analyze climate and numerical weather prediction data; includes support for netCDF-3, netCDF-4 and GRIB1, GRIB2, and other formats. CDO provides more than 350 operators, including

• File information and file operations
• Selection and Comparision
• Modification of meta data
• Arithmetic operations
• Statistical analysis
• Regression and Interpolation
• Vector and spectral Transformations
• Formatted I/O
• Climate indices
• File format conversions

Have a look at the CDO tutorial and full documentation:

     CDO tutorial
     CDO documentation
     CDO reference card

NCO

The NCO toolkit manipulates and analyzes data stored in netCDF-accessible formats, including DAP, HDF4, HDF5, and, most recently, Zarr. The netCDF Operators (NCO) comprise about a dozen standalone, command-line programs that take netCDF, HDF, and/or DAP files as input, then operate (e.g., derive new fields, compute statistics, print, hyperslab, manipulate metadata, regrid) and output the results to screen or files in text, binary, or netCDF formats.

Display data

ncview

Ncview is a visual browser for netCDF format files. Typically you would use ncview to get a quick and easy, push-button look at your netCDF files. You can view simple movies of the data, view along various dimensions, take a look at the actual data values, change color maps, invert the data, etc. To open a netCDF file with ncview you can use the simple command:

panoply

Panoply is a NASA-developed data viewer for netCDF, HDF and GRIB files. It allows users to quickly and easily open a satellite data file, examine the contents, and make a very basic plot of the data. 

To open a netCDF file with ncview you can use the simple command: