In November 2001, by means of a Resolution, the European Union officially launched \u27Global Monitoring for the Environment and Security\u27 (GMES), the second European space programme (after Galileo) essentially driven by the Union. The Resolution inter alia calls for the European Commission to coordinate with the European Space Agency (ESA) the realisation of an operational and autonomous European capability for global monitoring for environment and security by 2008, crucially involving a satellite system. Relevant data which are to form part of such a capability may, in principle, come from a number of different sources: space-based data, airborne data, and in situ-generated data of different terrestrial origin. However, non-space dat...