GTOS datasets should be harmonised to the extent possible to allow integration of national and regional datasets into a usable global information resource.
Harmonisation seeks to bring together various types, levels and sources of data in such a way that they can be made compatible and comparable, and thus useful for decision making. Harmonisation differs from standardisation in that it does not impose a single methodology or norm, but rather seeks to find ways of integrating or making "an agreeable effect" from information gathered through disparate methodologies.
Harmonisation has been a concern of GTOS since the start - an early meeting of the GTOS Planning Group was hosted by the UNEP Office of Harmonisation of Environmental Measurement in 1994. An excellent summary of the needs and issues in harmonisation was presented at that meeting by E F Roots (1994) and will not be repeated here in detail.
The principal consideration is to find pragmatic ways of making compatible and integrable datasets which have been collected for different purposes under different collection regimes, and using different standards and methodologies. This means avoiding the need to convert all the data to a single standard (impractical), but rather finding ways to make it usable at some higher level of aggregation or generalisation. For some numeric or spatial datasets this could be as simple as applying conversion factors, or a change of map projection. More often in dealing with terrestrial ecosystems data, it is necessary to establish a correspondence between differing classification systems or terminology sets. Common examples are soil, vegetation, land use, and ecological zonation, or descriptive data elements such as threats to habitat, status of species, etc. With biological species data, harmonisation seeks to find a correspondence between similarly described taxa without resolving all taxonomic minutia. Spatial variables which have been collected on different spatial frameworks (e.g. provinces vs. watersheds) may need GIS processing for harmonisation.
A good example at the global level is a handbook of compatible methods of estimating greenhouse gas emissions prepared under the IPCC which defines a number of acceptable methods from which countries may choose depending on pre-established national economic and social statistical frameworks and standards.
Such harmonisation it is often considered more difficult to achieve for terrestrial observations because of natural spatial inhomogeneity and discontinuity of the phenomena. The appropriate role for GTOS will be in co-ordinating and facilitating the development of harmonisation approaches and protocols for identified core datasets.
Develop and maintain an inventory of all of the principal international standards organisations and international scientific bodies active in harmonising environmental data relevant to the GTOS scope (particularly terrestrial ecology classification systems, taxonomy, instrumentation and data collection methodologies).
Identify priority areas where lack of harmonisation is hindering the potential usefulness of GTOS data.
Facilitate and sponsor international expert meetings to develop harmonisation techniques and correspondence tables in key sectors relevant to GTOS.