Validating ocean tide loading models using GPS

Ocean tides cause periodic deformations of the Earths surface, also referred to as ocean tide loading (OTL). Tide-induced displacements of the Earths crust relying on OTL models are usually taken into account in GPS (Global Positioning System) data analyses. On the other hand, it is also possible to validate OTL models using GPS analyses. The following simple approach is used to validate OTL models. Based on a particular model, instantaneous corrections of the site coordinates due to OTL are computed. Site-specific scale factors, f, for these corrections are estimated in a standard least-squares adjustment process of GPS observations together with other relevant parameters. A resulting value of f close to unity indicates a good agreement of the model with the actual site displacements. Such scale factors are computed for about 140 globally distributed IGS (International GPS Service) tracking sites. Three OTL models derived from the ocean tide models FES95.2.1, FES99, and GOT00.2 are analyzed. As expected, the most reliable factors are estimated for sites with a large loading effect. In general, the scaling factors have a value close to unity and no significant differences between the three ocean tide models could be observed. It is found that the validation approach is easy to apply. Without requiring much additional effort for a global and self-consistent GPS data analysis, it allows detection of general model misfits on the basis of a large number of globally distributed sites. For detailed validation studies on OTL models, the simultaneous estimation of amplitudes and phases for the main contributing partial tides within a GPS parameter adjustment process would provide more detailed answers.     

数字震害评估的发展与应用

随着网络化地理信息系统的应用、全球定位系统的普及应用和卫星遥感影像分辨率的不断提高,“数字地球”技术在地震工程领域的应用逐渐成熟,数字化震害评估符合现代地震工程的发展趋势。本文综述了数字化技术在地震工程领域的研究现状及其发展前景,提出了利用“3S”技术进行数字震害评估的设想。     

NOAA Weather Radio (NWR) – A Coastal Solution to Tsunami Alert and Notification

The Washington State/Local Tsunami Work Group adopted the NOAA Weather Radio All-Hazards Warning System to warn citizens quickly and effectively of not only tsunami hazards but also other natural or man-made hazards. In concert with an array of deep ocean tsunami detectors, land-based seismic sensors, and warning messages issued by the tsunami warning centers, NWR provides a means to expeditiously get critical decision-making information to emergency managers, elected officials, and first responders. To implement the NWR strategy effectively, a partnership was developed to add a repeater to the NWR system to provide complete coverage to the coast of Washington and to shipping lanes off the coast. The Work Group also recognized the need to disseminate time critical hazard information on tsunamis to the public on beaches and in high traffic areas, so it developed a new notification system, with the first prototype installed on 2 July 2003 in Ocean Shores, Washington. A public education program also was developed to improve the impacted communities understanding of the tsunami hazard, the warning system, and actions they should take if a tsunami occurs.     

A shock-wave heating model for chondrule formation II. Minimum size of chondrule precursors

Chondrule formation due to the shock wave heating of dust particles with a wide variety of shock properties are examined. We numerically simulate the steady postshock region in a framework of one-dimensional hydrodynamics, taking into account many of the physical and chemical processes that determine the properties of the region, especially nonequilibrium chemical reactions of gas species. We mainly focus on the dust particle shrinkage due to the evaporation in the postshock hot gas and the precursor size conditions for chondrule formation. We find that the small precursors whose radii are smaller than a critical value, , cannot form chondrules because they evaporate away completely in the postshock region. The minimum value of is about 10 μm, though it depends on the shock speed and the preshock gas density. Furthermore, we demonstrate the chondrule size distributions which are formed through the shock-wave heating. These results indicate that the shock-wave heating model can be regarded as a strong candidate for the mechanism of chondrule formation.     

The role of the Pernicana Fault System in the spreading of Mt. Etna (Italy) during the 2002–2003 eruption

Flank instability and collapse are observed at many volcanoes. Among these, Mt. Etna is characterized by the spreading of its eastern and southern flanks. The eastern spreading area is bordered to the north by the E–W-trending Pernicana Fault System (PFS). During the 2002–2003 Etna eruption, ground fracturing along the PFS migrated eastward from the NE Rift, to as far as the 18 km distant coastline. The deformation consisted of dextral en-echelon segments, with sinistral and normal kinematics. Both of these components of displacement were one order of magnitude larger (~1 m) in the western, previously known, portion of the PFS with respect to the newly surveyed (~9 km long) eastern section (~0.1 m). This eastern section is located along a pre-existing, but previously unknown, fault, where displaced man-made structures give overall slip rates (1–1.9 cm/year), only slightly lower than those calculated for the western portion (1.4–2.3 cm/year). After an initial rapid motion during the first days of the 2002–2003 eruption, movement of the western portion of the PFS decreased dramatically, while parts of the eastern portion continued to move. These data suggest a model of spreading of the eastern flank of Etna along the PFS, characterized by eruptions along the NE Rift, instantaneous, short-lived, meter-scale displacements along the western PFS and more long-lived centimeter-scale displacements along the eastern PFS. The surface deformation then migrated southwards, reactivating, one after the other, the NNW–SSE-trending Timpe and Trecastagni faults, with displacements of ~0.1 and ~0.04 m, respectively. These structures, along with the PFS, mark the boundaries of two adjacent blocks, moving at different times and rates. The new extent of the PFS and previous activity over its full length indicate that the sliding eastern flank extends well below the Ionian Sea. The clustering of seismic activity above 4 km b.s.l. during the eruption suggests a deep décollement for the moving mass. The collected data thus suggests a significant movement (volume >1,100 km³) of the eastern flank of Etna, both on-shore and off-shore.Editorial responsibility: R. Cioni     

Numerical investigation of the effects of upwelling on harmful algal blooms off the west Florida coast

The initiation of the toxic harmful algal bloom (HAB), Karenia brevis, along the west Florida coast has been associated with upwelling events. Upwelling processes may be responsible for the transport of nutrients or algae from deep offshore locations across the Florida shelf to the coast. The influence of coastal wind-driven upwelling on the onset and occurrences of K. brevis in this region was numerically investigated using Rutgers University's Regional Ocean Modeling System. Computations were carried out in an idealized model domain, a two-dimensional slice in the cross-shore and vertical directions. The surface forcing data used was from several offshore meteorological buoys. The motion of the algae was simulated using Lagrangian particles and a passive tracer. The numerical simulations of three K. brevis events in 2000–2002 showed that the particles respond (with upwelling/downwelling) to the along-shore wind stresses as expected and some upwelling was present during the events. Comparison of the passive tracer fields with measured fluorescence data exposed the model's sensitivity to the particular surface forcing data employed and the relatively more significant role played by surface forcing over initial conditions. The present model set-up constitutes a useful predictive tool for conditions conducive to the onset of HABs. It is planned to be used in a real-time mode to aid the NOAA HAB monitoring and forecasting system.     

Development in Precision Seafloor Survey and Mapping in China

This article presents a general introduction to the development in China since 1980s in precision seafloor survey and mapping. Emphasis is given to the processing and integration of data from the acquisition system centered on the multibeam bathymetric survey equipment, and to the interactive map generation systems, MBChart, SeaMap, and SeaGIIS. Application of these systems will also be described.     

多波束测深系统的精度评估方法研究

在分析了多波束测深系统测量误差来源的基础上，讨论了多波柬测深系统静态精度、相对精度和绝对精度的系统精度评估方法。采用的静态精度评估方法就是在多波柬测深系统静止的条件下考核其对同一位置测量深度的误差；相对精度评估方法就是布设多条交叉重叠的测线，考核交叉重叠点的测深误差；绝对精度评估方法是在多波束测深的同时利用高精度的测深仪测量同一区域，用此参考地理模型来检验多波束测深的精度。根据误差理论，三种精度评估的方法分别从系统稳定性、自符合性和系统误差方面确定各误差源的综合误差，它们是检验多波束测深系统精度是否符合海道测量标准的有效方法。文中给出了系统试验数据的重要结果及设备验收的方法。     

地理信息系统(GIS)在海洋地质中的应用

地理信息系统是一门空间数据管理科学和智能化高新技术，它是由地理学、地图学、计算机科学、遥感技术、数学等相互作用相互交叉而形成的，有向数据自动化处理研究、数据结构研究、空间关系理论研究、人工智能和专家系统研究发展的趋势。在海洋地质中，地理信息系统目前主要应用于海底地形地貌模拟、海洋地质资料科学管理与共享、海洋地质资料处理等。随着全球尺度海洋学研究的进一步开展及海洋地理信息系统的产生，地理信息系统在海洋地质中的应用前景良好。     

一种基于平面不等式约束法的北斗三频数据组合选取方法

GNSS现代化的标志之一是三频或多频数据的广泛使用,文中在研究北斗三频数据组合原理、优化选取准则的基础上,推导出一种基于平面不等式约束法的三频数据组合选取方法。该方法将长波长条件转化为组合系数的线性关系,将弱电离层条件转化为平面域,将低噪声条件转化为椭圆域,依此建立模型并给出模型的几何解释,最后应用该方法选取特性较优的北斗三频数据组合,并总结了一些组合系数的特点。结果证明,该方法组合系数选取效率大于枚举法等常规方法,从而为多频数据组合理论的研究提供参考。