Data formats

This section presents the data storage formats used for the products. The official diffusion format is Netcdf.

Netcdf

The official products are stored using the NetCDF format.

NetCDF (network Common Data Form) is an interface for array-oriented data access and a library that provides an implementation of the interface. The netCDF library also defines a machine-independent format for representing scientific data. Together, the interface, library, and format support the creation, access, and sharing of scientific data. The netCDF software was developed at the Unidata Program Center in Boulder, Colorado. Please see Unidata NetCDF pages for more information and to retrieve the NetCDF software package.

NetCDF data is:

  • Self-Describing. A netCDF file includes information about the data it contains

  • Architecture-independent. A netCDF file is represented in a form that can be accessed by computers with different ways of storing integers, characters, and floating-point numbers

  • Direct access. A small subset of a large dataset may be accessed efficiently, without first reading through all the preceding data

  • Appendable. Data can be appended to a netCDF dataset along one dimension without copying the dataset or redefining its structure. The structure of a netCDF dataset can be changed, though this sometimes causes the dataset to be copied

  • Sharable. One writer and multiple readers may simultaneously access the same netCDF file.

The products are stored in NetCDF defined by the Cooperative Ocean/Atmosphere Research Data Service (COARDS) and Climate and Forecast (CF) metadata conventions. The CF convention generalises and extends the COARDS convention but relaxes the COARDS constraints on dimension and order and specifies methods for reducing the size of datasets. A wide range of software is available to write or read NetCDF/CF files.

API are made available by UNIDATA:

  • C/C++/Fortran

  • Java

  • MATLAB, Objective-C, Perl, Python, R, Ruby, Tcl/Tk

File nomenclature

The nomenclature used for the products is:

SWOT_L3_LR_SSH_<FileIdentifier>_<CCC>_<PPP>_<DateBegin>_<DateEnd>_v<Version>.nc

where

  • FileIdentifier is Basic or Expert or Unsmoothed

  • CCC is the number of cycle on 3 digits

  • PPP is the number of pass on 3 digits

  • DateBegin and DateEnd are the begin and end dates in UTC of the measurements in each file.

  • Version is the numerical version x.y.z with three digits refering to one of the releases (ex. 3.0.0)