For each measurement category listed in this section, a brief discussion is given below of the significance of that measurement (including its relation to the recognised Essential Climate Variables), together with an indication of the present and future measurement capabilities of satellite observations. In each case, specific actions identified by CEOS to better meet the needs of GCOS for the Essential Climate Variables are described. This description is supported by two timeline diagrams spanning the period 2009–2026, indicating the instruments contributing to that measurement and the missions on which they are expected to fly.

The first timeline shows missions that are either:

— current, where the prototype has been launched and financing is approved for the whole series; or

— approved, where financing is available for the whole series, the prototype is fully defined and development is ongoing.

The second timeline shows missions which are notyet approved. They are divided into two categories:

— planned, where financing of the full series is being considered or is available up to the end of detailed definition phase; or

— considered, where conceptual studies and feasibility studies have been completed, and definition of financing is in preparation.

Of course, all missions have a degree of uncertainty. This description of mission status reflects information available from the relevant agencies at the time of compilation. If the launch month of a planned mission has not been specified, the timeline is shown to commence at the beginning of the planned year of launch. Note also that missions currently operating beyond their planned lifetime are shown as operational until the end of 2009 unless an alternative date has been proposed. The timelines in this section represent a qualitative analysis of the provision of data from Earth observation satellites in terms of a number of key geophysical measurements and the requirement for those measurements in different disciplines.