The last four decades have seen an initially slow but recently increasingly rapid programmatic development in Earth observations on global scale, with the acceleration mainly being due to a growing awareness of the political and societal leaders of the need for comprehensive Earth observations in support of their quest for sustainable development. As a starting point for this development, the first World Summit in Stockholm in 1972 can be identified. Subsequent milestones preparing the ground for the current development were in 1987 the publication of the so-called Brundtland report 'Our Common Future', which revitalized the concept of sustainable development, and in 1988 the establishment of the Intergovernmental Panel on Climate Change (IPCC) by several United Nations' agencies. The World Summit in Rio de Janeiro, Brazil, in 1992 emphasized again the need for comprehensive Earth observations both in its Agenda 21 and the United Nations' Framework Convention on Climate Change. Important steps following this Summit were in the early 1990ies the initiation of the Global Climate, Ocean, and Terrestrial Observing Systems (GCOS, GOOS, and GTOS, respectively), and the development towards an Integrated Global Observing Strategy (IGOS), with the latter emphasizing stable, homogeneous, long-term observations and the necessity of a transition from research to operational monitoring. It was followed in 1998 by the establishment of the IGOS Partnership (IGOS-P), which brought together most major global providers, users, and funding agencies in Earth observation.

The last five years have seen a very rapid progress: Following up the recommendations of the recent World Summit on Sustainable Development in Johannesburg, South Africa, in 2002, the first Earth Observation Summit (EOS-I) was held in Washington, DC, in July 2003. EOS-I initiated an unprecedented effort towards coordination of global Earth observation. Through its declaration, EOS-I established the ad hoc Group of Earth Observation (ad hoc GEO) with the task to draft within 18 months a 10-year Implementation Plan for the Global Earth Observation System of Systems (GEOSS). Over the next 18 months, the ad hoc GEO met six times, and the requested plan was drafted together with a reference document containing many details of the envisaged GEOSS. The work of the ad hoc GEO was guided by the Framework document adopted by EOS-II, held in Tokyo in April 2004, which identifies nine major societal benefit areas of Earth observations, including climate, water, and disasters, which heavily depend on geodetic observations. This Implementation Plan was adopted by EOS-III in February 2005 in Brussels, which also established GEO permanently. The presence is dominated by the first steps towards an implementation of GEOSS, which is to a large extent built around the nine societal benefit areas identified by EOS-II.

In parallel to this global development, IAG has developed the concept of a Global Geodetic Observing System (GGOS). As a Participating Organization in GEO, IAG was involved in designing GEOSS and contributes to the implementation of GEOSS with the goal to develop GGOS consistently with the needs and progress of GEOSS for a maximum mutual benefit. Moreover, steps are undertaken to establish GGOS as a partner in IGOS-P and to associate GGOS to an appropriate United Nations' agency. These steps will ensure that GGOS as the umbrella for the IAG services is appropriately integrated into a rapidly developing Earth observation framework for the benefit of the global society.

At the IAG General Assembly 2003 in Budapest the IAG formally established the Global Geodetic Observing System (GGOS) as its major and, at present, its only project. In view of the natural hazards that occurred in recent years and the ever increasing influence of human society on the Earth system, the monitoring of this complex system with its components (solid Earth, oceans, atmosphere, hydrosphere, and biosphere etc.) is of utmost importance for mankind. GGOS is the contribution of geodesy (and IAG) to the monitoring of the Earth System and, thus, to the international activities like the Group on Earth Observation (GEO) with the Global Earth Observing System of Systems (GEOSS), the Integrated Global Observing Strategy Partnership (IGOS-P) and other initiatives. GGOS itself should not be considered a service generating products of its own. It is heavily relying on the operational and scientific work of the IAG Services and IAG Commissions. Therefore, GGOS represents an umbrella for the products derived by the IAG Services (IVS, ILRS, IGS, IDS, IGFS, ...) using the space geodetic techniques (VLBI, SLR/LLR, GNSS, DORIS), altimetry, InSAR, gravity missions, and in-situ measurements etc. that allow the observation of the Earth system with an unprecedented accuracy of less than one part in one billion. To the outside world, the IAG Services should appear as the components of a unique large integrated observing system that spans the activities from the collection of the raw data (of stations and satellites), the determination of the geometry, Earth rotation and gravity field of the Earth and the temporal variations thereof, to the combination, modeling and interpretation of the space geodetic results. This setup will allow GGOS to make major contributions to the monitoring and observation of the Earth system and, thus eventually, to a saver future of society. In this contribution we will give an overview of the present status of GGOS and the future developments foreseen.

The Global Geodetic Observing System (GGOS) is a major step forward for the evolution of the International Association of Geodesy (IAG). As stated in the GGOS Terms of Reference, GGOS will be “…considering the Earth system as a whole (including the geosphere, hydrosphere, atmosphere and biosphere), monitoring Earth system components and their interaction by geodetic techniques and studying them from the geodetic point of view...”.

The data, products, working groups and projects of the IGS can significantly contribute to these goals. The GNSS geodetic technique is unique in being utilized in a broad range of multi-disciplinary studies and applications relevant to the Earth system. IGS, through its classic suite of products (orbits, station position and velocity and time) is a key to densifying the global reference frame ITRF, and enables users to access it as well. Further, other products of the IGS coming from projects or under development within the working groups, are useful for improving understanding of the Earth process include:

The Ground Networks and Communication Working Group is working toward the implementation of properly designed and structured ground-based geodetic networks to materialize the reference systems to support sub-mm global change measurements over space, time and evolving technologies. The WG is working with the IAG measurement services (the IGS, ILRS, IVS, IDS, IGFS, and IERS) to develop a strategy for building, integrating, and maintaining the fundamental network of instruments and supporting infrastructure in a sustainable way to satisfy the long-term (10-20 year) requirements in the terrestrial reference frame, Earth orientation and gravity field monitoring, precision orbit determination, local deformation monitoring, and other geodetic and gravimetric applications required for the long-term observation of global change. As a starting point, the Working Group is examining options for 1 mm and 0.1 mm/yr stabilities of the reference frame, since its influences all of the other geodetic products.

Early steps in the process are: definition of the critical contributions that each technique provides to the TRF, POD, EOP, etc; characterize the improvements that could be anticipated over the next ten years with each technique; understand the present error sources for each technique (instrument and modeling) and how these errors sources propagate into the analysis products; and using simulation techniques, quantify the improvement in the reference frame as stations are added and station capabilities (co-location, data quantity and quality) are improved.

The Working Group assumes that the GNSS and the DORIS Networks will be at least as robust as they are presently and that planned upgrades in the ground systems and the satellites will come to fruition. Some augmentation is also assumed where the present networks would be significantly enhanced with additional stations.

We will review the progress to date in organizing the Working Group and the studies currently underway.