Determination of Geopotential Differences between Local Vertical Datums and Realization of a World Height System   总被引：2，自引：0，他引：2  

Burša  Milan  Kouba  Jan  Müller  Achim  Raděj  Karel  True  Scott A.  Vatrt  Viliam  Vojtíšková  Marie 《Studia Geophysica et Geodaetica》2001,45(2):127-132

The methodology developed for connecting Local Vertical Datums (LVD) was applied to the Australian Height Datum (AHD) and the North American Vertical Datum (NAVD88). The geopotential values at AHD and NAVD88 were computed and the corresponding vertical offset of 974 mm with rms 51 mm was obtained between the zero reference surfaces defined by AHD and NAVD88. The solution is based on the four primary geodetic parameters, the GPS/levelling sites and the geopotential model EGM96. The Global Height System (or the Major Vertical Datum) can be defined by a geoidal geopotential value used in the solution as the reference value, or by the geopotential value of the LVD, e.g. NAVD88.  相似文献   

EXPERIMENTS ON FLOW AROUND A CYLINDER IN A SCOURED CHANNEL BED     

I.ISTIARTO  W.H.GRAF 《国际泥沙研究》2001,16(4)

The flow pattern around a cylinder, installed in a scoured channel bed, was experimentally investigated. Detailed measurements of the instantaneous 3D velocities were performed by using an Acoustic Doppler Velocity Profiler (ADVP), from which the profiles of the time-averaged velocities and turbulence stresses were obtained. It is shown that the influence of the cylinder and of the scour hole alters the approach flow; this is essentially confined to the vicinity of the cylinder and to the inside of the scour hole. The horseshoe vortex is measured as a flow reversal inside the scour hole, formed by the downward flow along the cylinder face and the reversed flow at the scour bed.  相似文献   

论对地方地震工作的科学指导与管理     

朱煌武  陈刚正 《华北地震科学》1993,11(4):1-8

根据现代行政管理学及领导管理科学的要求，研究探讨了我国地方地震工作管理的特殊性及其基本要求，提出了科学指导和管理地方地震工作的总体思路和基本模式，即一个指导思想，两个落脚点，三种管理方法和四条保证措施。作者据此总结了我国地方地震工作管理的实践和发展，提出了当前亟待解决的三个问题。  相似文献   

The response of the azimuthal component of the ionospheric electric field to auroral arc brightening     

V. Safargaleev  W. Lyatsky  N. G. Gazey  P. N. Smith  V. Kriviliov 《Annales Geophysicae》1999,18(1):65-73

We have analyzed the response of azimuthal component of the ionospheric electric field to auroral arc activity. We have chosen for analysis three intervals of coordinated EISCAT and TV observations on 18 February, 1993. These intervals include three kinds of arc activity: the appearance of a new auroral arc, the gradual brightening of the existing arc and variations of the arc luminosity. The arcs were mostly east-west aligned. In all cases, the enhancement of arc luminosity is accompanied by a decrease in the westward component of the ionospheric electric field. In contrast, an increase of that component seems to be connected with arc fading. The observed response is assumed to have the same nature as the short circuit of an external electric field by the conductor. The possible consequence of this phenomenon is discussed.  相似文献   

Local configuration measures for categorical spatial data: binary regular lattices     

Barry Boots 《Journal of Geographical Systems》2006,8(1):1-24

This paper examines the utility of a number of pattern measures for local exploratory analysis of binary spatial data. Based on a review of existing pattern measures in cartography, geography, image analysis, and landscape ecology, two fundamental classes of such measures, termed compositional and configurational, are identified. The paper focuses on configurational measures and it is suggested that as many as five such measures (join counts, patch numbers, patch sizes, patch proximity, and distribution of the classes relative to the focal cell of the window) are required to differentiate between all possible local categorical maps. This suggestion is explored by examining aspects of the statistical behaviour (probability distributions and correlations between extreme values of pairs of measures) of a set of 12 configurational measures. Their use is also demonstrated by means of an empirical example.  相似文献   

M L Determination for Local and Regional Events Using a Sparse Network in Southwestern Germany     

Stefan Stange 《Journal of Seismology》2006,10(2):247-257

A method for the determination of consistent local magnitude M _L values (Richter scale, or M _WA) for earthquakes with epicentral distances ranging from 10 km through 1000 km is demonstrated. The raw data consists of nearly 1300 amplitude readings from a network of six digital seismographs in Baden–Württemberg (Southwestern Germany) during 26 months starting in 1995, later extended by another 1000 amplitude readings until 1999. Relying on most of the basics introduced by C.F. Richter a three-parameter attenuation curve (distance correction, magnitude-distance relation) for Baden–Württemberg and adjacent areas is presented. Station corrections are evaluated and the attenuation curve is calibrated with respect to other agencies for distances greater than 650 km. Reasonable parametrisations are discussed and meaningful error bars are attributed. Finally, a seventh station is incorporated by means of its station correction alone, without needing to update the attenuation curve.  相似文献   

A radar-based verification of precipitation forecast for local convective storms     

Daniela Rezacova  Zbynek Sokol  Petr Pesice 《Atmospheric Research》2007,83(2-4):211-224

Local flash flood storms with a rapid hydrological response are a real challenge for quantitative precipitation forecasting (QPF). It is relevant to assess space domains, to which the QPF approaches are applicable. In this paper an attempt is made to evaluate the forecasting capability of a high-resolution numerical weather prediction (NWP) model by means of area-related QPF verification. The results presented concern two local convective events, which occurred in the Czech Republic (CR) on 13 and 15 July 2002 and caused local flash floods. We used the LM COSMO model (Lokall Model of the COSMO consortium) adapted to the horizontal resolution of 2.8 km over a model domain covering the CR. The 18 h forecast of convective precipitation was verified by using radar rainfall totals adjusted to the measured rain gauge data. The grid point-related root mean square error (RMSE) value was calculated over a square around the grid point under the assumption that rainfall values were randomly distributed within the square. The forecast accuracy was characterized by the mean RMSE over the whole verification domain. We attempt to show a dependence of both the RMSE field and the mean RMSE on the square size. The importance of a suitable merger between the radar and rain gauge datasets is demonstrated by a comparison between the verification results obtained with and without the gauge adjustment. The application of verification procedure demonstrates uncertainties in the precipitation forecasts. The model was integrated with initial conditions shifted by 0.5° distances. The four verifications, corresponding to the shifts in the four directions, show differences in the resulting QPF, which depend on the size of verification area and on the direction of the shift.  相似文献   

Neo-liberal ruptures: Local political entities and neighbourhood networks in El Alto, Bolivia     

Juan Manuel Arbona 《Geoforum》2007,38(1):127-137

In October 2003, hundreds of thousands of Bolivians took to the streets demanding the resignation of President Gonzalo Sánchez de Lozada. After 20 years of neo-liberal policies - and the failures to improve the living conditions of the majority - the proposal to export natural gas via Chile was taken by the population as yet another step to sustain an unjust political order. Facing a direct challenge by the population the Sánchez de Lozada administration responded with indiscriminate military force. The result was 63 dead and over 300 wounded, which deepened and extended the social rage and eventually forced the resignation of the President. The neo-liberal project - promoted and defended by Sánchez de Lozada - collapsed. The city of El Alto was the epicentre of the challenges to the legitimacy of this political order. This article focuses on the role of local political entities and neighbourhood networks from El Alto in articulating political spaces that challenged the legitimacy of the institutional infrastructure and led to the October 2003 ruptures in the neo-liberal project. Furthermore, I make the case that the particular histories and memories (of “relocalized” miners and indigenous/peasants) that converged in and defined this city were pivotal in the organization of a “political subsoil” that surged to the surface during the October 2003 events.  相似文献   

A Janus-faced biodiversity change and the partiality of ecological knowledge in a world biodiversity hotspot in Ghana: Implications for biodiversity rehabilitation     

Louis Awanyo 《Geoforum》2007,38(4):739-751

The Gyamfiase-Adenya-Obom cluster of villages in the forest-savanna region of Ghana is located within one of Conservation International’s 34 “World Biodiversity Hotspots” of the most biodiversity-threatened regions of the world. In collaboration with local farmers in this area since 1993, the People, Land Management and Ecological Change Project in Ghana (PLEC-Ghana) has been working on promoting biodiversity rehabilitation to address problems of biodiversity change. This goal is expected to be achieved through agrobiodiversity or biodiversity-friendly agricultural practices. However, farmers’ employment of these practices has been lackluster, even while they acknowledge biodiversity changes, dominated by Chromolaena odorata and other herbaceous species, that are driving the decline in forests and their biodiversity. In interpreting the difficulties of biodiversity rehabilitation in Gyamfiase-Adenya-Obom, this study outlines the diverging ecological knowledge of non-residents/outsiders and local farmers about biodiversity change, which it describes as Janus-like with two diverging faces. One face of biodiversity change shows the detrimental impacts on biodiversity and its observers—non-residents/outsiders—insist on biodiversity rehabilitation that nurtures forests, and the growth and domination of tree species. The other face of biodiversity change shows its agronomic advantages and its observers—the local farmers—are skeptical of current biodiversity rehabilitation practices. Farmers see agronomic benefits in biodiversity change, in particular the benefit of faster soil regeneration within the predominant bush fallow system of farming. And as a result of this observation, farmers continue with practices that sustain a decline in forests and biodiversity. Based on social and ecological research that explores three biodiversity-friendly practices promoted by PLEC-Ghana (fallow management, mulching, and intensive weeding to protect tree seedlings), this article discusses the partiality of ecological perspectives that emphasize either face of biodiversity change but not both, and the implications for biodiversity rehabilitation.  相似文献   

不同标度震级关系和台基影响问题探讨   总被引：2，自引：1，他引：2  

张宏志  刁桂苓  赵明淳  王勤彩  张骁  黄媛 《中国地震》2007,23(2):141-146

利用近年中国数字地震台网观测报告中的中国及邻区地震目录资料,取能够同时计算面波震级MS和近震震级ML的地震,拟合出2种震级之间的关系,发现与过去使用30余年的换算公式存在系统差别。考虑现代化地震数字观测系统有动态范围大、频带宽、台站多、覆盖区域广、测定精度高的特点,由此拟合的关系应当更可靠。考虑不同误差因素统计面波震级MS和近震震级ML的关系表明,2种震级之间换算和不换算的差别并不大,因此建议MS和ML震级之间不换算为宜。分析地震台站的场地响应发现:一些基岩台的放大因子在1附近,场地响应不随频率变化;处于沉积土层的台站,放大因子在低频段大于1,高频段小于1;还有一些台站在某个频段范围大于1,或者小于1。另外,沉积土层台站的单台震级和台网平均震级差也随周期增大,呈现由负到正的增长趋势。看来并不存在固定的台站校正系数,因此不能把台站校正作为提高震级测定精度的方法。  相似文献