The IGCP 565 Project

Present state of activities in the field of the Project

• A) The Global Geodetic Observing System: The international cooperation fostered by IAG has led to the establishment of the IAG Services, that provide increasingly valuable observations and products not only to scientist but also for a wide range of non-scientific applications. With the recent developments in geodesy, Earth observations, and societal needs in mind, IAG has established GGOS as the umbrella for all IAG Services. Today, GGOS is a full component of IAG and the permanent observing system of IAG. Three of the IGCP 565 Project Leaders are the Chairs of the GGOS Steering Committee and members of the Executive Committee (Rothacher, Plag, Neilan), one is member of the Executive Committee (Zerbini), one is the Chair of the GGOS Science Panel (Gross), and one is Vice-President of IAG (Rizos).

  GGOS as an organization provides the interface for the IAG Services and Commissions, to the outside world, particularly the main programs in Earth observations and Earth science. GGOS is actively involved in GEO, and GGOS was a partner in the Integrated Global Observing Strategy Partnership (IGOS-P). GGOS constitutes a unique interface for many users to the geodetic Services. GGOS adds to the three main fields of geodesy a new quality and dimension in the context of Earth system research by combining them into one observing system having utmost accuracy and operating in a well-defined and reproducible global terrestrial frame. The observing system, in order to meet its objectives, has to combine the highest measurement precision with spatial and temporal consistency and stability that is maintained over decades. The research needed to achieve these goals influences the agenda of the IAG Commissions and the GGOS Working Groups. The vision for GGOS is to empower Earth science to extend our knowledge and understanding of the Earth system processes, to monitor ongoing changes, and to increase our capability to predict the future behavior of the Earth system. In order to realize this vision, GGOS facilitates networking among the IAG Services and Commissions and other stakeholders in the Earth science and Earth Observation communities, provides scientific advice and coordination that will enable the IAG Services to develop products with higher accuracy and consistency meeting the requirements of particularly global change research, and improves the accessibility of geodetic observations and products for a wide range of users. Ultimately, society benefits from GGOS as a utility supporting Earth science and global Earth observation systems as a basis for informed decisions.

  GGOS as an observing system utilizes the existing and future infrastructure provided by the IAG Services. It aims to provide consistent observations of the Earth's time-variable shape, gravitational field, and rotation. GGOS provides on a global scale and in one coordinate system the spatial and temporal changes of the shape of the solid Earth, oceans, ice covers, and land surfaces. In other words, it delivers a global picture of the surface kinematics of our planet. In addition, it provides estimates of mass anomalies, mass transport, and mass exchange in the Earth system. Surface kinematics and mass transport together are the key to global mass balance determination, and an important contribution to the understanding of the energy and mass budget of our planet (e.g., Rummel et al., 2005; Drewes, 2006). Moreover, the system provides the observations that are needed to determine and maintain a terrestrial reference frame of increasing accuracy and temporal stability (Beutler et al., 2005). For this purpose, GGOS exploits (and tries to extend) the unique constellation of satellite missions relevant to this goal that are in orbit now or planned for the next two decades, by integrating them into one measurement system. The backbone of this integration are the existing global ground networks of tracking stations for the space-geodetic techniques Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR), GNSS and Doppler orbitography and radio positioning integrated by satellite (DORIS). GGOS is integrating these tracking networks with terrestrial gravity networks. GGOS also complements the space segment and global ground networks by airborne and terrestrial campaigns that serve the purpose of calibration and validation, regional densification, and refinement. Furthermore, through the analysis of the dense web of microwave radiation connecting the GNSS satellites with Low Earth Orbiters (LEO) and with the Earth's surface a powerful new technique emerges for probing the atmosphere's composition. Assimilation of these observations into models of weather, climate, oceans, hydrology, ice and solid Earth processes could fundamentally enhance the understanding of the role of surface changes and mass transport in the dynamics of our planet.

  Developing the geodetic observing system into a mass transport and dynamics observing system is a main motivation for the work of GGOS. As pointed out by Plag et al. (2008), in this work, GGOS faces two types of scientific and technological challenges, namely an "internal" and an "external" challenge: The internal challenge to geodesy is to develop GGOS and the geodetic technologies so that they meet the demanding user requirements in terms of reference frame accuracy and availability, as well as in terms of spatial and temporal resolution and accuracy of the geodetic observations. Developing an observing system capable of measuring variations in the Earth's shape, gravity field, and rotation with an accuracy and consistency of 0.1 to 1 ppb, with high spatial and temporal resolution, and increasingly low time latency, is a very demanding task. Accommodating the transition of new technologies as they evolve in parallel to maintaining an operational system is part of this challenge. The external challenge is associated with the integration of the three fields of geodesy into a system providing information on mass transport, surface deformations, and dynamics of the Earth. The Earth system is a complex system with physical, chemical, and biological processes interacting on spatial scales from micrometers to global and temporal scales from seconds to billions of years. Therefore, addressing the external challenge requires a "whole Earth" approach harnessing the expertise of all fields of Earth science.

  While the internal challenge provides a central theme for research and development inside IAG (and is well taken care of in GGOS and the IAG Commissions), the external challenge requires a much broader approach involving cooperation with scientist in other Earth science fields and with Earth observation communities. This is reflected through the membership of the GGOS Science Panel, which includes experts from all relevant fields of Earth Science. It is this challenge that the proposed project aims to address.

  Another challenge for geodesy arises from recent developments in global Earth observation with the establishment of GEO as culmination point. The challenge is to appropriately integrate GGOS as an organization into the international context of Earth observation and society, and to develop GGOS as an observing system in accordance with the strategies and methodologies of the global observing systems for the mutual benefit of all. Earth observation and society at large will benefit from the availability of geodetic observations and products, and GGOS will benefit from an improved visibility and acknowledgment of the valuable service it provides. In order to facilitate the contribution of GGOS to the Global Earth Observing System of Systems (GEOSS), IAG is a Participating Organization in GEO and is represented there by GGOS, which is also a contributing system to the GEOSS. The proposed project will facilitate coordination between GGOS work, related research projects, and activities in the frame of the GEO Work Plan.

• B) Related GEO activities: The observation system for the water cycle is the focus of several Tasks of the GEO Work Plan, addressing with these tasks different aspects of the cycle. Most importantly, Task WA-07-02 focuses on the remote-sensing part of the monitoring system for water quantity, and Task WA-06-05 addresses the in-situ component (for more information, see the Task Sheets available at ftp://ftp.wmo.int/Projects/GEO/TaskSheets/2007-04). For the 2008 Work Plan, it is likely that the Tasks WA-06-05 and WA-07-02 will be merged, and in this case, the proposed project will be included as a direct contribution to this new Task.

  Water-related issues are also covered by the GEO Community of Practice for Water, which is led by Richard Lawford, also co-chair of the IGOS-P Theme on Integrated Global Water Cycle Observations (IGWCO).

• C) Other relevant programs: The IGWCO Theme has provided a description of the basic elements of an integrated observing system for the global water cycle (see Lawford et al., 2004). The geodetic contributions, particularly the one from gravity satellite missions like GRACE, are identified as crucial for regional to global scale variations in the water cycle.

  The Global Energy and Water Cycle Experiment (GEWEX) is a program with the aim to observe, understand, and model the hydrological cycle and energy fluxes in the atmosphere, at land surface and in the upper oceans. GEWEX was initiated by the World Climate Research Programme (WCRP) and is an integrated program of research, observations, and science activities with the ultimate goal to enable the prediction of global and regional climate change. Specifically, GEWEX aims "to reproduce and predict, by means of suitable models, the variations in the global hydrological regime, its impact on atmospheric and surface dynamics, and variations in regional hydrological processes and water resources and their response to changes in the environment, such as the increase in greenhouse gases" (see http://www.gewex.org).

  The Climate Variability and Predictability (CLIVAR) project is a World Climate Research Programme (WCRP) project that has a particular focus on the role of ocean-atmosphere interactions in climate. It works closely with its companion WCRP projects on issues such as the role of the land surface, snow and ice and the role of stratospheric processes in climate (see http://www.clivar.org).

  On the applied side, a number of international programs and organizations are potential partners in the development of products serving improved water resource management. An example is the International Water Management Institute (IWMI, http://www.iwmi.org), which "concentrates on water and related land management challenges faced by poor rural communities." Another example is the Global Water Partnership (GWP, http://www.gwpforum.org/), which is a comprehensive partnership among all those involved in water management and which "actively identifies critical knowledge needs at global, regional and national levels, helps design programs for meeting these needs, and serves as a mechanism for alliance building and information exchange on integrated water resources management." In the frame of the proposed projects, links to these organizations, and particularly their relevant regional bodies will be established in order to gain their support for the applied aspect of the proposed work.

• D) Specific projects: A number of projects addressing the science issues are ongoing, proposed or in preparation. An overview of the projects directly contributing to IGCP 565 is available here.