Global attributes Clause Samples
Global attributes. To convey some general properties of a file, netCDF format makes available the global attributes feature. Table 5.1: Strings used to identify the species Formula chemical species identifier HNO3 Nitric acid HNO3 H2O Water Vapour H2O Temperature TEMP (PT on extended file) O3 Ozone O3 CH4 Methane CH4 N2O Nitrous oxide N2O NO2 Nitrogen dioxide NO2 CCl3F CFC-11 CCL3F ClONO2 Chlorine nitrate CLONO2 N2O5 Dinitrogen pentaoxide N2O5 CCl2F2 CFC-12 CCL2F2 COF2 Carbonyl fiuoride COF2 CHClF2 HCFC-22 CHCLF2 HCN Hydrogen cyanide HCN CCl4 Carbon tetrachloride CCL4 CF4 CFC-14 CF4 C2H2 Acetylene C2H2 CH3Cl Chloromethane CH3CL COCl2 Phosgene COCL2 C2H6 Ethane C2H6 OCS Carbonyl sulfide OCS HDO Deuterium hydrogen oxide HDO Most of the defined global attributes are self explaining and their contents deal with information about the creation of the file, references, instruments and platform identifiers and some others are needed to comply with the standard conventions. Some attributes provide information about the retrieval process and the structure of the file. Here are more details about some remarkable global attributes: species reports the name of the processed species. If the file is an extended file refering to pT or multi-target retrieval, the attribute contains a comma separated list of the retrieved species; To get information about minor releases of both software and auxiliary data, users have to read dedicated variables inside the file.
Global attributes. The following global attributes are mandatory for SeaDataNet NetCDF. The first two are taken from CF; the remaining two are from OceanSITES: • Conventions – this informs application software of the encoding conventions to which the data conform. If the file conforms to multiple conventions then they are all listed as space-delimited or comma-delimited (if one or more convention labels include embedded spaces) list. The usual value for SeaDataNet will be ‘SeaDataNet_1.0 CF1.6’. Should the file also conform to OceanSITES conventions then this becomes ‘SeaDataNet_1.0, OceanSITES Manual 1.1, CF1.6’ • featureType – this is a description of the spatio-temporal shape of the data held in the NetCDF using a vocabulary specified in CF 1.6. The value to be used is given in the relevant feature-specific profile description • title – this is a plain language label for the file contents, such as ‘CTD data for station CS from North Sea Project cruise RRS Challenger CH33’. It is designed to be used for labelling visualisations of the data held in the file. • date_update – a timestamp (UT to 1-second precision as an ISO8601 string) specifying when the contents (i.e. its attributes and/or values) of the file were last changed. This provides both a publication date and a version label for the dataset contained in the file. It may be earlier (but obviously not later) than the last modification date of the physical file. Other conventions, such as OceanSITES, have specified significant numbers of additional global attributes primarily for the storage of discovery metadata. This hasn’t been done for SeaDataNet, but this doesn’t mean that additional attributes are prohibited. If additional attributes are included it is strongly preferred that their names and usage are taken from an existing convention. Local attributes are allowed if no such suitable attribute can be located. In an ideal world, attributes added by conventions other than CF should be labelled with a namespace to indicate their origin. Unfortunately, this practice hasn’t been universally followed in existing profiles of CF. For SeaDataNet, if local attributes are introduced then labelling them with a namespace is mandatory to ensure identification of their source. The ‘profile’ feature-specific profile includes a large number of example attributes from the OceanSITES convention (data_type, format_version, platform_code, institution, wmo_platform_code, platform_name, history, etc.) for purposes of illustration.
Global attributes. This subsection reports an example of global attributes for Ocean Color family product stored in the NetCDF file.