Metadata is the descriptive data necessary to allow us to find, process and use data, information and products. While metadata generally can describe products, services and software as well as data at different stages of manipulation, it can also be a specification. Metadata can be extensive and all-inclusive, or it can be specific to a more limited function. Metadata are used to provide documentation for data sets or services. In essence, metadata answers who, what, when, where, why, and how about every data that are being documented.
More specially, station metadata refers to site/location, instrumentation, observation practices, calibration reports, site layout, site condition, site exposure, changes of location etc.. Climate Metadata have a key role in the process of creating datasets, as the knowledge of the station history provides increased confidence in the statistical techniques employed to ensure that the only variations that remain in a climate time series are due to actual climate variability and change. Meteorological data users other than the climatological community, working in fields like agrometeorology, engineering or aeronautics, also benefit from good metadata. These professionals also need to extract the maximum accuracy from the observations, and often compare data taken in different places or times. A complete knowledge of the measuring conditions will help them to achieve this goal.
Complete metadata describe the history of a station since its establishment to the present and hopefully onwards to the future. Most metadata have to be derived from the station’s documentation, both from current and historical documents, while some others can be obtained from the data themselves. Metadata refers also to information on the units used, the special codes employed, the corrections made to the data, the procedures of quality control applied, the adjustments made to ensure its homogeneity, and the data estimated and filled in, after applying the interpolation procedure selected. In order to provide high quality datasets, it is crucial to maintain comprehensive station documentation and to keep it updated.
A full list of metadata, which ideally should be stored, is described in a technical document (available on CD or via Internet):
Discussion Paper on Stations Metadata and WMO Core Profile: A way forward
Discussion Paper on Climatological needs for minimum Station Metadata in the
frame of the WMO’s Publication 9 Volume A
Report of the CCl Expert Team on WCP Requirements for Metadata