GGOS: Ensuring a Coherent Earth Observation System

The Global Geodetic Observing System (GGOS) is the response of the international geodetic community, organised under the umbrella of the International Association of Geodesy (IAG), to the need to monitor changes in the Earth system continuously. GGOS is Geodesys contribution to the Global Earth Observation System of Systems (GEOSS) by providing the reference frames needed for all position-dependent observations, thus the foundation for most Earth observations, and measuring changes in the Earth's shape, size, gravity field and rotation over time and space. GGOS is built on the Scientific Services of the IAG (IGS, IVS, ILRS, IDS, IERS, IGFS, ISG, PSMSL, IGETS, IDEMS, ICGEM, BGI) and the products they derive on an operational basis for Earth monitoring using space- and ground-based geodetic techniques. A key objective of GGOS is to realise an integrating framework that moves from the provision of technique-specific products to a level of combined, integrated products as the basis for a consistent modelling and interpretation of Earth system processes and interactions. This is necessary to ensure a coherent Earth monitoring system that contributes significantly to a better understanding of global change and its impacts on the environment and society. This is being achieved through strong international and multidisciplinary cooperation, focusing on (1) bringing together different geodetic observing techniques, services and analysis methods to guarantee that the same standards, conventions, models and parameters are used in all data analysis and modelling of Earth system processes; (2) combining geometric, gravimetric, and Earth rotation observations in data analysis and data assimilation to jointly estimate and model all necessary parameters representing the different elements of the Earth system; (3) identifying science and societal needs that can be addressed by (new) geodetic products and define the requirements for accuracy, time resolution, and consistency of these products; (4) identifying service gaps and developing strategies to fill them; and (5) promoting and enhancing the visibility of Geodesy by improving the accessibility of geodetic observations, information and products to the widest range of users and their attribution. This contribution summarises recent achievements, ongoing activities, and main challenges for the near future.