3.1. GHOST Strategy
Dr Scholes presented the GHOST that has been developed by the GCOS/GTOS TOPC and the GTOS Scientific and Technical Planning Group. The strategy is based on the principle that it is not possible to measure everything, everywhere, all the time. It is therefore necessary to design an optimal sampling strategy that retains adequate spatial and temporal resolution, but is also affordable and practical. A hierarchical strategy in which at one extreme a few variables are measured regularly in a large number of places, and at the other extreme a large number of variables are measured in a few locations for a limited period, meets these requirements. The hierarchy divides fairly naturally into five tiers, each with more-or-less unique characteristics and roles although existing facilities often straddle more than one tier. The concept is applicable to the three main areas which GHOST is concerned with -- the land surface, freshwater ecosystems and cryospheric surfaces -- each of which would have their own hierarchy, but sharing tier 5. The observing system could be built largely out of existing national and international observation systems, research centres and stations, with modest additions of stations and sites where representation is inadequate.
The proposed hierarchy is incompletely nested. In other words, not all research stations (tier 3) have associated research centres (tier 2) and vice versa, sites with stations, and so on; but in most cases there are strong linkages between the tiers. Within the hierarchies for the land, freshwater and cryosphere, there needs to be a balance between different types of systems: for example between natural, agricultural and urban ecosystems on the land; between rivers, lakes, and estuaries in freshwater systems; and between ice sheets, ice caps, glaciers and permafrost in the cryosphere. There is also a geographical balance, which ranges from broad representation at tiers 1 and 2, detailed representation at tier 3, unbiased sampling at tier 4 and complete coverage at tier 5.
3.2. GHOST Summary
In summary GHOST is:
A conceptual framework with 5 nominal levels (tiers);
Highly integrated, vertically and horizontally;
Currently climate oriented;
Statistically efficient.
But should not be considered:
A rigid blueprint;
A fully nested hierarchy.
