The positition paper for the session on Network and Data Centre issues will be presented. This session concentrates on the current status and future directions of the IGS network, its data flow and data center activities. We will review progress since the 2004 Bern Workshop "Celebrating a Decade of the International GPS Service IGS" and the goals set there. We will address IGS network documentation, relationships to dense local/regional networks, IGS data flow, standardized naming conventions for data/product file versions designed to allow sensible automatic handling of file replacements, and alternate compression schemes.

The purpose of this multi-year NASA funded project, "GPS DATA PRODUCTS FOR SOLID EARTH SCIENCE" (GDPSES), is to produce and deliver high quality GPS time series and higher-level data products derived from multiple GPS networks along the western US plate boundary, and to use modern IT methodology to make these products easily accessible to the community.

The project processes and posts a daily solution generated by a combination of two independent GPS station position solutions, generated at SIO and JPL using GAMIT and GIPSY respectively. A combination algorithm has been implemented. A combined 10-year long time-series for over 600 western US GPS sites from multiple GPS arrays is available for viewing and download for the scientific community via the project's web portal at http://reason.scign.org.

To achieve the project goals and support current data products, several ongoing IT developments are taking place. In the forefront is an Adaptive Seamless Archive System, which uses web services for GPS data discovery, exchange and storage. GDPSES has unified the station data and metadata inputs into the processing procedures at the independent analysis centers. The project has developed XML schemas for GPS time series, and is developing and implementing an array of data quality tools, to ensure a high-quality combined solution, and to detect anomalies in the time series. Event leveraging will alert users to tectonic, anthropogenic and processing 'events'. In the next few months the project, through its new data portal called GPS Explorer, will enable users to zoom in and access subsets of the data via web services and graphic interfaces. Our presentation will include demonstration of prototype web based data browsing tools under GDPSES development. The community is invited to participate and provide feedback on these tools.

The IGS network has seen a number of enhancements and developments in the past 2 years since the Berne Workshop. This paper will review the relevant areas identified at the previous workshop and progress toward them, as well as other network issues and improvements.

A uniform co-ordinate reference system is fundamental to any project, application, service or product that requires some form of geo-referencing. Most countries in the world have established such reference systems that are used for national surveying, mapping, photogrammetry, remote sensing, Geographical Information Systems (GIS) and the planning and execution of development projects. Many of these national co-ordinate systems are based on reference figures of the Earth which are somewhat outdated and, when based on a local origin or datum, are restricted to a particular country making cross-border or regional mapping and development projects very difficult indeed. When using modern positioning technology such as GNSS, technical understanding and careful mathematical manipulation is required to relate GNSS derived co-ordinates to classical national co-ordinate systems. Many countries are therefore updating these national reference systems to be compatible with the GNSS reference systems.

The African Reference Frame project, AFREF, has the primary objective of defining a continental reference system for Africa to be fully consistent and homogeneous with the global reference frame of the ITRF. One of the core objectives of the project is the establishment of a network of permanent GNSS base stations throughout Africa to be used as a set of fiducial points for the definition of the a unified African refernce frame. These stations will serve not only the fundamental geodetic objectives of AFREF but also the global densification of the IGS stations and the associated benefits to be derived from such a global densification. The network of AFREF base staions will also serve the diverse disciplines for which GNSS data is currently being used and promote an interest in geodesy, geophysics, space physics and atmospheric science among others within African countries.

This paper describes the background, rationale and progress made with AFREF since 2000 and the benefits that the infrastructure of permanent GNSS base stations will have for the diverse range of applications of GNSS data.

China is a country with serious earthquake hazard. To monitor crustal deformation and predict earthquakes using GPS, we established the Crustal Movement Observation Network of China (CMONOC) during 1997-2000. The network has 27 continuous GPS stations to serve as fiducials, and more than 1100 campaign mode stations distributed all over the Chinese continent with a relatively higher density around tectonically active fault zones and the area surrounding Beijing. The continuous stations have been observed since 1998, and seven of them are serving as IGS tracking stations. The campaign mode stations were observed completely 3 times in 1999, 2001, and 2004, respectively. In each campaign, stations were occupied continuously for at least 4 days. Because all the concrete monuments were uniformly designed with forced-centering GPS antenna mount and the campaigns were well organized on a large scale with more than 80 sites occupied simultaneously with the same type of GPS receiver and choke-ring antenna, the data quality was well guaranteed. Using the CMONOC data we derived a crustal movement velocity field of China that clearly demonstrate the characteristics of crustal movement and deformation of various tectonic regions in the Chinese continent, especially the deformation pattern in and around the Tibetan Plateau. The kinematic information from the velocity field provides vital constraints on modeling of continental dynamics. In order to monitor the crustal deformation with a higher resolution both in space and time and provide a nationwide infrastructure for multiple applications such as GPS meteorology, networked RTK, space weather research, and so on, we are now preparing to launch the phase II of CMONOC, and planning to expand the amount of continuous GPS stations to 260 and add another 1000 campaign mode GPS stations to the network. In addition, a nationwide gravimetric network will be added to complement the continuously observed GPS fiducial network. Proposal of the phase II project has been approved by the National Science and Education Council of China, and the project is expected to start in later 2006.

ESA/ESOC has been involved from the start in the provision of GNSS data to the IGS community. Currently a network of 11 worldwide distributed receivers are operated in 10 different locations: Kiruna(Sweden), Kourou(French Guiana), Malindi(Kenya), Maspalomas(Canary Islands), New Norcia(Australia), Perth(Australia), Redu(Belgium), Villafranca(Spain), Cebreros(Spain) and Tahiti(French Polynesia). ESOC makes every effort to continuously update the infrastructure and provide the necessary data to support the generation of all the IGS products. A Hydrogen maser was installed in New Norcia in 2002 and it has been followed by a second one in Cebreros in 2005. There is a planned new redundant Hydrogen Maser for Kourou for 2006/2007. A combined GPS + GLONASS receiver was installed at Kourou in 2002 and recently 2 new units have been acquired and will be deployed soon to improve the worldwide GLONASS network coverage. Additionally with the creation of the ESOC Navigation Facility there is currently a general overhaul of the infrastructure to adapt it to a more operational scenario. Most of the stations contribute data to the network centres in all latency modes: real time 1Hz data, 15 minutes 1 Hz files, hourly and daily 30 seconds files. ESOC is also involved in the deployment of the first experimental Galileo receivers.

The U.S. National Geodetic Survey’s Continuously Operating Reference Station (CORS) network contains approximately 900 GPS sites shared on a voluntary basis by private and public, US and foreign, partner organizations. The CORS network continues to grow in importance as the easiest way for the public to access the US National Spatial Reference System. Although the network was not initially envisaged for use in crustal deformation studies it is now routinely used to estimate Glacial Isostatic Adjustment, measure sea-level rise, and define the motion of the stable part of the North American plate. The network is expected to increase by approximately 200 stations this year and probably more in coming years due to (1) Earthscopes’ plate Boundary Observatory and (2) the large number of real time positioning networks that are being established principally by state Department of Transportation and commercial organizations. This rate of growth of CORS will result in a network with a spacing of ~70 km or greater giving an unprecedented image of crustal deformation within North America. In light of this rapid expansion NGS has updated its guidelines for the establishment and incorporation of sites into CORS. The guidelines focus on minimizing the most common problems that have been identified in current IGS and CORS monuments while allowing flexibility in monument design. The guidelines emphasize the importance of the consistency of computed positional coordinates for a minimum life-time of 15yrs by giving equal importance to the quality of GNSS site's data and the associated metadata. Site operators are required to restrict changes: in the environment around the antenna, to the antenna, avoid using radomes, including a device to permit the antenna to be returned to its same position in 3D-space, etc. To improve the tracking of metadata, we have created a web-based interface to create and update ASCII site logs. To supplement the text based log and to better understand the local site construction a detailed suite of 12 site photographs is required.