Science03/03/2008 |
| Externe auteur |
| Decadal Sea Level Trends in the Bay of Biscay from Tide Gauges, GPS and TOPEX Marcos, M., Wöppelmann, G., Bosch, W. and Savcenko, R. 2007. Journal of Marine Systems , 68: pp. 529-536. The aim of the first continuous sea level observations was to measure tides, and some of these are still in operation, having provided coastal sea level records for more than a century. The knowledge of long-term changes in coastlines at local scales is important for practical purposes, such as coastal planning and hazards prevention. This paper addresses two main issues: 1) sea level trends at the Bay of Biscay derived from TOPEX observations and from coastal tide gauges are analysed; and 2) coastal and altimetric sea level trends are compared using instantaneous altimetry measurements. In order to account for vertical land movements in coastal tide gauges, GPS data were used to correct sea level trends. This paper presents results of these comparisons and shows that we are at the stage of achieving the challenge of an accuracy in sea level trends of 1mm/year expressed in a well-defined global reference frame. Detecting Bridge Dynamics with GPS and Triaxial Accelerometers Meng, X., Dodson, A.H. and Roberts, G.W. 2007. Engineering Structures, 29: pp. 3178-3184. Efforts have been made in recent years to use an integrated monitoring system consisting of dual-frequency GPS receivers and triaxial accelerometers for the detection of the dynamics of structures such as high-rise buildings and short-to-medium-span bridges. The focus of this paper is on the algorithm aspects for the detection of structural dynamics of a test bridge and the development of analytical methods. For the identification of structural dynamics, GPS and triaxial accelerometers have been used in field tests to record the response of the Wilford Bridge, a suspension footbridge over the River Trent in Nottingham.??This paper concludes that GPS is a viable tool for both structural deflection monitoring and natural frequency detection, and the measurements from a triaxial accelerometer can be used to validate the estimated dynamics from the GPS measurements and improve the overall monitoring system performance. Defining the Source Region of the Indian Ocean Tsunami from GPS, Altimeters, Tide Gauges and Tsunami Models Pietrzak, J., Socquet, A., Ham, D., Simons, W., Vigny, C., Labeur, R.J., Schrama, E., Stelling, G. and Vatvani, D. 2007. Earth and Planetary Science Letters, 261: pp. 49-64. The accurate determination of the spatial distribution of earthquake rupture mechanisms is of importance for tsunami warning and will ultimately lead to a better understanding of seismic hazards. This paper demonstrates how tsunami model results, validated against independent altimetry data and tide gauge arrival time data, can be used to select between the results of five co-seismic slip inversions. This is the first time GPS data have been used together with tsunami models to improve the estimates of the slip along a thrust-fault earthquake. The paper concludes that the incorporation of permanent real-time GPS stations would represent a valuable component of future tsunami warning systems. Monitoring and Modelling Particle and Reach-scale Morphological Change in Gravel-bed Rivers: Applications and Challenges Rumsby, B.T., Brasington, J., Langham, J.A., McLelland, S.J., Middleton, R. and Rollinson, G. 2008. Geomorphology: Challenges in Geomorphological Methods and Techniques, 93: pp. 40-54. This paper focuses on developments in topographic data acquisition, including airborne remote sensing, digital photogrammetry, differential GPS and laser profiling (for example, LIDAR) technologies that allow rapid acquisition of high-resolution and high-precision topographic data sets over a range of spatial scales. ?These developments have offered new opportunities for investigating spatial and temporal patterns of morphological change in gravel-bed rivers and have contributed to revitalisation in three key areas: 1) morphometric estimates of sediment transport and sediment budgeting; 2) boundary conditions for numerical models, including computational fluid dynamics and cellular modelling; and 3) three-dimensional characterisation of morphology that is independent of flow stage. The potential is clear but there remain a number of significant challenges, including quality control and the effects of error on specific applications and morphologies. This paper presents results from two investigations, representing field and laboratory analyses of gravel-bed river morphology at different spatial scales and for different applications. ? These case studies highlight the strengths and weaknesses of specific technologies and approaches to the analysis of channel and floodplain morphology and change, and suggest key areas that remain to be fully resolved. GPS and Space-Based Geodetic Methods Blewitt, G. 2007. Treatise on Geophysics(Ed G. Schubert), pp. 351-390. Space-based geodetic methods such as Global Positioning System (GPS) have revolutionised our view of the Earth, enabling us to observe plate tectonics in progress, right when it happens. The relative positions between any pair of geodetic stations in the world can be determined with a precision measured in millimetre; thus, the long-term movement of the Earth’s surface can be monitored to within 1 mm yr1. Dense networks of GPS stations are now being used to map various properties of the Earth’s crust and surface. This chapter of the book “Treatise on Geophysics” provides a summary of the developments that led to this (geophysical) tool, and also introduces the fundamentals of space geodesy and how it is being applied to geophysical research. |
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| Archive |
| Archive > March 2008, Volume 12, number 2 > Science |
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