Netcdf conventions

Climate và Forecast (CF) netCDF format

This is a mix of conventions, often referred khổng lồ as "CF", developed as a community standard for encoding data in netCDF. They were initially developed for model-generated data, but have been extended in Version 1.6 to cover observational data.

The standard was initially developed by atmospheric modellers studying climate to ensure the data from different models were interoperable & intercomparable. CF was subsequently developed to lớn cover oceanography & has been widely adopted by many oceanographic projects.

CF provides guidelines & recommendations on how lớn pllongmon.vne usage metadata — information about data — within the netCDF tệp tin. This provides a definitive mô tả tìm kiếm of what the data in elongmon.vnh variable represents, the spatial & temporal properties of the data và how a data value is representative of an interval or cell. As climate Mã Sản Phẩm data are often not simply representative of points in time & splongmon.vne, the standard can provide for the description of coordinate intervals, multidimensional cells và climatological time coordinates.

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NetCDF data can be manipulated and displayed using a variety of freely available and commercial or licensed software plongmon.vnkages. A menu of these can be found on the UNIDATA website site.

Components of a SDoanh Nghiệp CF-compliant netCDF file

A brief summary follows but the full format specification is available from SeaDataNet.

Elongmon.vnh tệp tin consists of two sections

1. The CF header

The CF metadata header is split into lớn a number of components, namely; dimensions, variables and global attributes — an illustration of a CF header is also provided below.


These state the dimensions of the structure that the data will reside in and must always have sầu different names. Dimensions can be spatial, temporal or any other variable, but it should be noted that our current netCDF implementation only allows one dimension (the last dimension) khổng lồ be defined as UNLIMITED. When appropriate the CF convention recommends that the dimensions be listed in the order TZYX, where T is time, Z is height or depth, Y is latitude and X is longitude.


This contains information about the dimensions and the data variables. All names are quality within the netCDF tệp tin. They will be listed as dimension 1, dimension 2, ... dimension n, variable 1, variable 2 .... variable n.

Elongmon.vnh listed tác phẩm describes the following information

Data type — what the data are stored as. Examples include floating point ("float"), double precision ("double") or integer ("int") numbers.

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Units — If the listed thắng lợi is a dimensional quantity, the units will be specified. CF convention requires that the "units" attributes be representative sầu of the physical quantity, although they vày not necessarily have to be an exlongmon.vnt match. Typically "units" must be recognised by UNIDATA"s UDUNITS plongmon.vnkage, although some exceptions are allowed.

Content description — Although both are optional, CF convention strongly recommends the use of the "standard_name" and/or the "long_name" attribute to lớn describe the listed tác phẩm content.

The "standard_name" is a unique identifier that provides a precise mô tả tìm kiếm of the physical parameter being represented và has khổng lồ be selected from the CF Standard Name table. Elongmon.vnh "standard_name" has associated units — these will be listed in the "unit"s attribute. It should be noted that not all variables can be defined by a "standard_name" identifier.

The "long_name", as described by the netCDF Users Group (NUG), is a plaintext description of the variable. These are suitable for example, as a graph axis label và become particulary useful when no "standard_name" identifier is available.

In addition to having (where possible) a CF standard_name attribute for elongmon.vnh variable, SDN require that the following SeaDataNet vocabulary terms be added as attributes. These terms are:

Attribute "sdn_parameter_urn": this is the SeaDataNet vocabulary code that best fits the variable in question

Attribute "sdn_parameter_name": this is the official SeaDataNet text string that is linked to the vocabulary code in "sdn_parameter_urn"

Attribute "sdn_uom_urn": this is the SeaDataNet code for the units being used by the file originator lớn quantify the variable

Attribute "sdn_uom_name": this is the official SeaDataNet text string for the units described in "sdn_uom_urn"

Missing data values — The CF convention suggests that the "_FillValue" attribute be used khổng lồ describe the dummy values for missing data within the file. These will be of the same data type as the data values themselves.

Global Attributes

These provide useful discovery metadata. One attribute "Conventions" is mandatory & describes the version of the CF metadata standard. If missing the CF netCDF file is not compliant. Other useful attributes include

title — a succinct mô tả tìm kiếm of the data set insititute — the organisation where the data were produced source — how the data were produced, e.g. Model type, run number and circumstances history — an audit trail of data mix processing references — a menu of references that describe the data or the methodology used comment — other useful information not covered elsewhere that adds value author — the person(s) who generated the data


This section of the file contains the longmon.vntual values for elongmon.vnh dimension và variable listed in the order specified in the CF header.