The IGS Strategic Plan 2002-2007 will be reviewed and a new plan drafted at a dedicated retreat later this year. As one step in the preparation for this, this session provides an opportunity to solicit the user community for the future needs of scientific and other applications, with a discussion on how IGS might meet those needs. A position paper and a few invited contributions will introduce the session to put it into the context of the strategic planning process, to highlight examples of applications that will need IGS, and to present critical and strategic issues. We especially encourage abstracts from scientific investigators and other users who may not be directly or deeply involved with IGS operations, but who use IGS products or could potentially use future IGS products. We also encourage those more involved in IGS to suggest a strategy for meeting foreseeable needs at any appropriate level (scientific, technical, systems design, operational, political, etc.). Some questions for consideration include: What are the foreseeable needs of science applications, natural hazards, space missions, and other applications and users through 2012? How can those needs be met, and what does this imply for changes and required action within IGS? Are we sufficiently open to innovations, new products, new participants? Are the current plan's strategic directions (LEO's, new GNSS, real time) still the key ones for the coming years? What changes are needed in the IGS in order to be able to play its due role in the Global Geodetic Observing System? How will IGS operations be funded in future? Is there a role for a commercial office in the IGS? (Or should this idea be definitively dropped?) What elements of the Strategic Plan remain valid for the coming years? What can be deleted? What is missing? What needs to be improved? Do we need to change the way we operate and manage our activities (identifying and responding to user requirements; GB, EC, CB, technical elements; reviews, workshops, outreach, elections, appointments, etc.)?

The 26 December 2004 Sumatra earthquake (M_w 9.2-9.3) generated the most deadly tsunami in history. Yet within the first hour, the true danger of a major oceanwide tsunami was not indicated by seismic magnitude estimates, which were far too low (M_w 8.0-8.5). This problem relates to the inherent saturation of early seismic-wave methods. Here we show that the earthquake's true size and tsunami potential can be determined using Global Positioning System (GPS) data up to only 15 minutes after earthquake initiation, by tracking the mean displacement of the Earth's surface associated with the arrival of seismic waves. Within minutes, displacements of >10 mm are detectable as far away as India, consistent with results using weeks of data after the event. These displacements imply M_w 9.0 ± 0.1, indicating a high tsunami potential. This suggests existing GPS infrastructure could be developed into an effective component of tsunami warning systems.

IGS has an opportunity to contribute to future tsunami warning systems around the globe. An important aspect is real-time access to IGS data and precise GPS orbit and clock information, and software to analyze these data in real time. In this study we showed that current 30 second data from the existing IGS network would have been sufficient to identify the extreme tsunami danger. While it is likely that higher rate data would incrementally improve sensitivity, it is clear that densification of the IGS network around subduction zones would be more valuable. However the important message is that using the currently IGS network configuration can be much faster at accurately determining large earthquake magnitudes than using current seismological networks. To assess design requirements we show the effect of adding near-field stations, and the effect of orbit quality by comparing the use of real-time estimated orbits and clocks, ultra-rapid IGS orbits, and the Broadcast Ephemeris.

A 2-hourly data set of atmospheric precipitable water (PW) has been produced from ground-based Global Positioning System (GPS) measurements of zenith tropospheric delay (ZTD) by using the 2-hourly IGS tropospheric product. The PW data are available every two hours at about 80-268 International GNSS Service (IGS) ground stations from 1997 to 2004. An analysis technique is developed to convert ZTD to PW on a global scale. Special efforts are made on deriving surface pressure (Ps) and water-vapor-weighted atmospheric mean temperature (Tm). Ps is derived from global, 3-hourly surface synoptic observations with temporal and vertical adjustments. Tm is calculated from NCEP/NCAR reanalysis with temporal, vertical and horizontal interpolations. The PW dataset is validated by comparing with radiosonde, microwave radiometer (MWR) and satellite data. The comparisons show no significant and systematic bias in the GPS-derived PW data. The scientific applications of the PW dataset include studying the diurnal variations in PW over the globe, quantifying spatial and temporal inhomogeneity and biases in global radiosonde PW data and estimating the diurnal sampling errors in twice-daily radiosonde humidity. The new 5-minute IGS ZTD product available at all IGS stations will be explored in the future work.

Based on our experience with the IGS tropospheric product, we would like to make the following recommendations on improving future IGS products. (1) The long-term stability (consistency in time) is crucial for the application of IGS PW data in climate monitoring studies. Every effort should be made to maintain the consistency of ZTD data in time, including minimizing changes in both instruments and analysis methods. (2) It is very important to investigate various biases in the ZTD product with special emphasis on diurnal biases, such as diurnal mapping function errors. Among the existing water vapor datasets on a global scale, only GPS-estimated PW dataset can provide sufficient temporal resolution to resolve the diurnal cycle of the atmosphere. Diurnal biases in ZTD would result in spurious PW diurnal variations. (3) The surface meteorology sensors with at minimum accurate pressure measurements at all IGS stations would be very useful for calculating the dry delay and removing atmospheric pressure loading of the earth surface. Especially as the 5-min ZTD data become available, the high resolution surface pressure data are required to derive the 5-min PW data. In addition, the IGS surface met sensors need to be regularly maintained and calibrated; the data need to be carefully quality controlled. Current limited IGS surface met data bear various problems. (4) We recommend that some future IGS stations be co-located with the future reference radiosonde network for cross-validation and improving mapping function models. (5) We suggest that in the future the IGS products can be better documented by incorporating details on data characteristics, how they were derived and user-friendly metadata.