Supplementary material to “Geodetic Observations Help to Understand Geohazards and Mitigate Disasters”
Hans-Peter Plag, Nevada Bureau of Mines and Technology, University of Nevada, Reno
Susanna Zerbini, University of Bologna, Bologna, Italy
Citation:
Plag, H.-P., and S. Zerbini (2008), Geodetic observations help to understand geohazards and mitigate disasters, Eos Trans. AGU, 89(17), 163.
[Full Article (pdf)]
GEO/GGOS Workshop demonstrated contribution of geodetic observations to the understanding of geohazards, planning of mitigation, and prevention of disasters
GEO/GGOS Workshop “The GGOS Contribution to GEOSS and an Observing System for Geohazards and Disaster Prevention”, October 5-6, 2007, International Geohazards Week, ESA Facility ESRIN, Frascati, Italy
The Workshop “The GGOS Contribution to GEOSS and an Observing System for Geohazards and Disaster Prevention” took place on October 5-6, 2007, at the ESA Facility ESRIN in Frascati, Italy, as part of the International Geohazards Week (see http://earth.esa.int/workshops/2007Geohazards/). About 50 scientists from both the geodetic and geohazards communities attended more than 20 presentations, many of them invited, and took part in lively discussions. The Workshop is documented at http://geodesy.unr.edu/ggos/ggosws_2007/ and most of the presentations are available there. The main objective of the workshop was to reach out from the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) to the space agencies and the geohazards communities, which were present in Frascati during that week. The Workshop was organized into an opening session and three topical sessions.
The opening session included presentations from highest-level representatives of three space agencies (ESA, NASA, and ASI) and from the Secretariat of the Group on Earth Observations (GEO). The representatives of the space agencies emphasized the fundamental importance of the geodetic reference frames for satellite missions and Earth observation, and stated that their work virtually would be impossible without continuous access to the International Celestial Reference Frame (ICRF), the International Terrestrial Reference Frame (ITRF), and Earth rotation parameters. They highlighted their past support to the geodetic community and confirmed their commitment to further developments of the infrastructure necessary for, at least, the evolutionary maintenance of the ITRF and ICRF. The representative of the GEO Secretariat identified the infrastructure integrated under the umbrella of GGOS as a core element in the Global Earth Observation System of Systems (GEOSS). He also considered GGOS, which builds upon the IAG Services, as an example of successful international cooperation and coordination on the basis of best efforts, which can be used as a template for GEO.
The first topical session of the workshop introduced GGOS and addressed the main contributions of GGOS to Earth observations. GGOS is a complex organization and an observing system with many active contributors relying on infrastructure maintained to a large extent by others (including the space agencies and national authorities). Thus, in order to serve many, GGOS depends on contributions from many, including the space agencies. The terrestrial reference frame is of monumental importance for understanding the Earth system and global change, as well as for planning of mitigation and adaptation with the aim to reduce the impact of global change and geohazards on society. Although being already very high, the accuracy of the reference frame still is a key limitation in quantifying global change processes such as changes in sea level and in the large ice sheets. Therefore, improvements of the terrestrial reference frame are a key step towards a better quantitative understanding of these processes and of the potential impacts on society. GGOS strives to improve the reference frames at various levels including technological developments, improvements of the infrastructure, better data analysis, and extended support from contributors. A key scientific and technological challenge for GGOS is consistency across the three areas of geodesy (Earth's shape, gravity field, and rotation) and between observations and models. This requires consistency of techniques, infrastructure, conventions, data processing, modeling, and interpretation. Network simulations indicate that there seems to be a limit for accuracy improvements through improved networks. In order to ensure that GGOS reaches its accuracy goals, improvements in data processing and modeling are also required.
The second topical session illustrated the contribution of geodetic observations to the understanding of Earth system processes, in particular, those related to mass transport and geohazards. Geodetic observations, such as the satellite gravity missions, have provided new insight into mass transport in the global water cycle on sub-continental to global spatial scales. At seasonal time scales, mass redistribution in the fluid envelop of the Earth is well constrained by geodetic observations, but understanding the driving processes requires a combination of different parameters (surface displacements, gravity changes, Earth rotation perturbations). The satellite gravity mission Gravity Recovery And Climate Experiment (GRACE) brought huge progress in monitoring time-variable gravity and facilitated significantly improved understanding of the underlying mass redistribution (mainly in the water cycle). However, the different contributing processes cannot be separated without additional inputs from models or independent observations. Global change and geohazards phenomena are inherently linked with the terrestrial reference frame, and the traditional approach of separating processes may have to be augmented by an integrated way of determining the reference frame. Thus, a proper combination of physical models and geodetic observations may be required in order to facilitate a better understanding of these phenomena.
The third topical session focused on the contribution of GGOS to the understanding of the processes causing geohazards and the potential contribution to prediction and early warning. It was pointed out that systems aiming at prediction of geohazards and early warning systems work best if they are mutually informed and consistent. GGOS has the necessary bandwidth to cover both roles and, for scientific, efficiency, and practical reasons should play both roles. InSAR was shown to be very versatile for the early detection of hazardous areas, and, therefore, it could enable informed decisions on where to invest in dedicated monitoring systems. However, this will require a comprehensive coverage of the land surfaces by InSAR, improvements of the reference frame, and analysis of the images for all potentially instable areas. GPS studies in tectonically active regions revealed the existence of nearly periodic slow seismic events accounting for significant energy release, thus revolutionizing our understanding of the underlying processes. GPS studies also discovered upward traveling seismic waves in the atmosphere. Therefore the Earth's surface is no longer the frontier of seismology: remote sensing of seismic waves and tsunamis from space appears possible and could be a component in early warning systems for tsunamis. GRACE was shown to sense gravity signals associated with large seismic events, and it was proposed that gravity from space might help to mitigate the lack of geodetic infrastructure on the ocean floor. Geodesy and GGOS already contribute to tsunami early warning system in several ways, and there is still a significant additional potential to be exploited. For monitoring of very hazardous areas on volcanoes, a combination of terrestrial and space-geodetic techniques can facilitate comprehensive observations of surface displacements without putting too much infrastructure at risk. Although geodetic techniques provide excellent observations of surface displacements, in many cases the understanding of the link between the geodetic parameters and subsurface dynamics, such as the dynamics of magma, is not at the same level, and better models need to be developed, in particular, for early warning applications at volcanoes.
In summary, the workshop demonstrated the importance of space-geodetic techniques for Earth sciences and particularly the monitoring and understanding of the processes driving global change and geohazards. Many of the presentations underlined the fundamental contribution of GGOS for Earth observation systems, which depend on a high-accuracy reference frame. Geodesy and GGOS are also pivotal for many practical applications in the field of geohazards, including early warning. However, the link between the providers (GGOS and the geodetic community) and the users in geohazards assessments, adaptation, mitigation, early warning, and disaster prevention and recovery needs strengthening in order to better exploit the full potential of GGOS for societal benefits.
References
Hans-Peter Plag, Nevada Bureau of Mines and Geology, University of Nevada, Reno, hpplag@unr.edu, and Susanna Zerbini, Dept. of Physics, University of Bologna, Italy. For International Geohazards Week, see http://earth.esa.int/workshops/2007Geohazards/, for the GEO/GGOS Workshop, see http://geodesy.unr.edu/ggos/ggosws_2007/.
