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441.
Makoto Uyeshima 《Surveys in Geophysics》2007,28(2-3):199-237
There are several kinds of coupling mechanisms which can convert mechanical, chemical or thermal energies due to seismic or
volcanic activities into electromagnetic energies. As a result of concentrated efforts in laboratory and theoretical research,
the basic relationship between the intensity of electromagnetic sources and changes in mechanical, chemical and thermal state
is becoming established. Also with the progress of the electromagnetic simulation techniques, it has been possible to evaluate
in situ sensitivity. Based on this progress and also due to extensive improvement in measuring techniques, many field experiments
have been performed to elucidate subsurface geophysical processes underlying the preparation stage, onset, and subsequent
healing stage of earthquakes and volcanic eruptions. In volcanic studies, many studies have reported the measurement of electromagnetic
signals which were successfully interpreted in terms of various driving mechanisms. Although there have been numerous reports
about the existence of precursory electromagnetic signals in seismic studies, only a few of them could be successfully explained
by the proposed mechanisms, whereas coseismic phenomena are often consistent with those mechanisms including the absence of
detectable signals. In many cases, one or two orders of higher sensitivity were required, especially for precursory signals.
Generally, electromagnetic methods are more sensitive to near-surface phenomena. It will be necessary to discriminate electromagnetic
signals due to these near-surface sources, which often possess no relationship with the crustal activities. Further efforts
to enhance in situ sensitivity through improvements in observation techniques and in data processing techniques are recommended.
At the same time, multi-disciplinary confirmation against the validity of electromagnetic phenomena will inevitably be necessary.
A Network-MT observation technique has been developed to determine large-scale deep electrical conductivity structure. In
the method, a telephone line network or purpose-built long baseline cables are utilized to measure voltage differences with
long electrode separations. Because of the averaging effect of the electric fields, static shift problems due to small-scale,
near-surface lateral heterogeneities can be alleviated. Several field experiments revealed regional scale deep electrical
conductivity structures related to slab subduction or its stagnation, which enable us to elucidate underlying physical processes
caused by the slab motion. The technique can also be applied to monitor the electric potential field related to crustal activities.
The annual variation of the potential field and electrical conductivity in the French Alps were interpreted to be caused by
the annual variation of lake water level. The method was also used to monitor the regional scale spatio-temporal variation
of the SP field and electrical conductivity before and at the onset of earthquakes and volcanic eruptions. 相似文献
442.
The device described in this paper, known as the traversing erosion beam, is believed to be the first to be designed specifically for measuring rates of downwearing of cohesive foreshores, such as clay shore platforms, under high‐energy wave conditions. It is primarily constructed of Flexlink Aluminium Structural System components and consists of a horizontal beam with a main leg and two further support legs. A sliding ‘dolly’ module is moved along the beam at precise intervals using a longitudinal scale as a reference. The topographic profile of the measurement surface is transferred to the dolly by a vertical sliding steel alloy rod, from which the relative height differences are measured by a separate engineer's digital height gauge placed on the dolly. The main leg of the device fits into a marine grade stainless steel box, which is deeply embedded into the foreshore or shore platform to act a permanent datum. The box is robust and can be expected to have a lifetime of at least a year, and possibly even five years or more. Sample data are provided from a clay shore platform at Warden Point in the Isle of Sheppey, Kent (UK), which demonstrate that the TEB can provide information on seasonal as well as annual rates of downwearing. The device has also been tested successfully on a peat and clay foreshore at Pett Level in Sussex and on a shore platform cut in glacial till at Easington, Yorkshire. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
443.
A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective is to demonstrate the ability of anisotropic unstructured meshes to adequately address the challenge of simulating the hydrodynamics occurring in these three regions within a unique mesh. The refinement criteria blend several hydrodynamic considerations as the tidal wave propagation on the continental shelf and the hydrostatic consistency condition in steep areas. Several meshes illustrate both the validity and the efficiency of the refinement strategy. The selection of the refinement parameters is discussed. Finally, an attempt is made to take into account tidal ellipses, providing another cause for anisotropy in the mesh. 相似文献
445.
446.
本文对GPS短边方位测量中遇到的问题进行了探讨,如仪器的检验,数据剔除率,检核测量误差的方法和方位平差及精度估计等。通过分析推导得出GPS方位边的平差公式和精度估计公式。 相似文献
447.
448.
机载GPS、姿态和激光扫描测距集成定位系统的精确定位方程、误差分析与精度评估 总被引:4,自引:0,他引:4
全球定位系统(GPS),姿态测量(惯性导航系统(INS))和激光扫描测距技术集成的直接空对地定位系统是近年来遥感与测绘领域发展起来的新型定位技术,是定量化三维遥感中获取地面几何信息和生成数字高程模型的主要新技术手段之一。该文给出了该系统的精确定位方程,分析了误差源对定位精度的影响,并给出了数量级评估。结果对实际应用具有重要的参考价值。 相似文献
449.
随着现代小卫星技术的不断发展成熟,利用该技术为地球观测服务将成为一件远景可观,意义深元的事情,文中针对舆型航天遥感立体测绘微小卫星的需求,结合单脉冲测角原理给出了航天遥感测绘小卫星地面站面线系统的整体分析与设计。 相似文献
450.
基于结构光和单CCD相机的物体表面三维测量 总被引:1,自引:0,他引:1
非接触式物体表面三维自动测量是计算机视觉领域的中心任务之一 ,围绕这个问题 ,提出了一种利用结构光 ,单 CCD相机和双定向技术实现物体表面三维自动测量的新方法。采用该方法 ,无需测定相机和结构光光截面之间的相对位置 ,在单目序列影像上就可测量出物体表面的三维坐标。 相似文献