共查询到20条相似文献，搜索用时 578 毫秒
1.
New geoid computations for the Hellenic area are carried out using (a) gravity anomalies for the land area available from old and new data bases, and gravity data for the sea area derived from altimetry and a recent digitization of sea gravity maps, and (b) a 1km × 1km digital terrain model. The EGM96 geopotential model is used as the reference field. In order to assess the quality of the computed geoid heights in the continental area comparisons were carried out with GPS/leveling heights and the recently available European Gravimetric Geoid EGG97. In the sea area the geoid heights were compared with sea surface heights of the recent and more accurate TOPEX/POSEIDON (T/P) altimetry mission. At the end of this article the improvement of the data bases is discussed and some plans for further development in the methodological schedule are pointed out. 相似文献
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This paper looks at the relation between the time-averaged level of the sea surface and a gravimertic geoid, as determined in coastal areas. Measurements in local regions can now be accurate enough to demonstrate that the geoid and mean sea level are not even parallel to each other, let alone identical. The accuracy and pattern structure of surface gravity data in some shelf seas is comparable with those on land, so that a marine geoid can be derived from surface data without using satellite altimetry. The geodetic objective is then to combine the two to determine sea surface topography. In principle, gravimetric studies provide the absolute datum so that local oceanographic models on the shelf can be combined with sea surface topography models related to the global ocean circulation. In contrast, sea surface topography information near deep ocean coasts must come from external sources and satellite altimetry used to give the gravity data needed to offset the less good coverage by ship-borne gravimetry.Marine Bouguer anomalies enable two specific problems of gravity anomaly patterns near the continent ocean transition to be overcome. The necessary extension of Stokes' condensation reduction is developed and illustrated along a north-south profile from the Mediterranean across the Cote d'Azur. The effect on gravity of deep ocean water introduces a geoid correction in the form of a dipolar ridge whose amplitude at the shore is about 11 cm. In addition to geostrophic currents, a semi-quantitative model for the thermohaline effects on sea surface topography is discussed in relation to sea level differences between the Atlantic and Mediterranean.In considering appropriate algorithms for local geoid computation, Kirby's Iterative Fourier Combination routine for combining altimetry and surface gravity is extended to account for global sea surface topography. The impact of very fast spherical harmonic analysis algorithms is discussed and a simple physical model is given which explains the short coherence lengths found for the global gravity field. This necessary assumption for any local geoid computation was hitherto purely empirical.Finally, the use of land data such as tide gauges, ellipsoidal heights from GPS, and orthometric heights from first order levelling are reviewed as ways of corroborating geodetic estimates of sea surface topography and its relation to levelling datums. Successful examples are given from southern England. 相似文献
4.
Ghadi Younis 《Arabian Journal of Geosciences》2015,8(10):8681-8685
In Geodesy, the heights of points are normally orthometric heights measured above the geoid (an equipotential surface created by the earth masses and rotation which approximately coincides with the mean sea level) or the normal heights. It is necessary to transform the GNSS/GPS measured ellipsoidal heights (h) to classical physical heights (orthometric H/Normal H). The total gravity potential of the earth (W) is the summation of two components; gravitational potential (V) by earth masses and the centrifugal potential (Ω). The centrifugal potential is directly calculated, while the gravitational potential (V) needs to be modeled globally or locally using given measurements. The global models of the earth gravitational potential/gravity models (or so-called geoid models) are mostly given using spherical harmonics (SH). A modified approach of SH was defined to fit the use of SH for regional gravity/potential modeling called spherical cap harmonics (SCH). Due to the numerical difficulties of SCH, a simplified approach of SCH is selected to be used for a combined modeling of the earth potential using a variety of observations. This approach is called the Adjusted Spherical Cap harmonics. 相似文献
5.
A local geoid solution for the northern part of Greece is presented based on a recent processing of newly available gravity data in the area 40.25 ≤ /o ≤ 41.00, 22.5 ≤λ ≤ 24.25. The derived gravimetric geoid heights are compared with geoid heights computed at recently measured GPS/ leveling benchmarks. A 4-parameter transformation model is applied to the differences between the two aforementioned geoid height sets, and a discussion is given on the current state of the leveling datum in the test area and the Greek territory. Regional and local transformation parameters are computed and some numerical tests are performed. A common adjustment of gravimetric geoid heights and corresponding GPS/leveling heights will be carried out in another study following an integrated procedure in order to study problems arising from the combination of different height data sets for geoid determination. Finally, some conclusions are drawn on the problems related to the optimization of a local geoid solution. 相似文献
6.
Sandford R. Holdahl 《Tectonophysics》1986,130(1-4):195-212
In tectonically active regions, the geodesist is confronted with the problem of updating heights where the Earth's surface has been vertically deformed by an earthquake. Dislocation theory can be used as a basis for modeling coseismic elevation changes and be incorporated within a general least squares adjustment scheme to correct a network of old leveling measurements and heights that are within the deformed area. Releveling and information obtained from seismologists about the general nature of the earthquake serve as input to the modeling process. Fundamental equations and considerations are presented in this paper to develop dislocation models of vertical coseismic motions. Leveling data sets corresponding to the Fairview Peak, Nevada, Coalinga, California, and Borah Peak, Idaho earthquakes are analyzed. These examples show potential for the method when applied in other areas, even when the physical setting is made complex by ongoing subsidence. The primary benefit of modeling coseismic motion is to avoid the cost of releveling for some lines in a deformed region. Rough modeling prior to any resurveying helps to select the lines to relevel that are most critical to a successful final model. A good model for coseismic motion cannot restore geodetic levelings to their original reliability, but corrected heights can be used in applications not requiring accuracy better than a few centimeters. 相似文献
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Urban earthquake disaster prevention is regarded as an integrated systematic engineering. Urban earthquake disaster prevention system is made up of all the earthquake disaster prevention activities. The concept and composition of urban earthquake disaster prevention system periphery were presented based on system periphery theory. A seismic risk-control mechanism model of system periphery was deduced using exchange rate of periphery as a dependent variable, and an observability–controllability model of system periphery was established and crystallized in its application to the quantitative analysis of practice problem. The input sets of urban earthquake disaster prevention system are determined as the maximum earthquake magnitude happened in or around the city, the measurable earthquake frequency, population density and fixed assets density. The inside state sets of urban earthquake disaster prevention system are determined as disaster resistant ability of buildings, disaster resistant ability of lifelines and investment dynamics in disaster prevention per urban built-up area. The system output is urban seismic risk. The calculative results show the model presented in this study can analyze the influence of system periphery intensity and inside state on seismic risk and can control urban seismic risk by adjusting the parameters of system periphery, the system inside state and human influence intensity. 相似文献
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Application of Dempster-Shafer theory of evidence to GIS-based landslide susceptibility analysis 总被引：9，自引：2，他引：7
No-Wook Park 《Environmental Earth Sciences》2011,62(2):367-376
GIS-based spatial data integration tasks for predictive geological applications, such as landslide susceptibility analysis,
have been regarded as one of the primary geological application issues of GIS. An efficient framework for proper representation
and integration is required for this kind of application. This paper presents a data integration framework based on the Dempster-Shafer
theory of evidence for landslide susceptibility mapping with multiple geospatial data. A data-driven information representation
approach based on spatial association between known landslide occurrences and input geospatial data layers is used to assign
mass functions. After defining mass functions for multiple geospatial data layers, Dempster’s rule of combination is applied
to obtain a series of combined mass functions. Landslide susceptibility mapping using multiple geospatial data sets from Jangheung
in Korea was conducted to illustrate the application of this methodology. The results of the case study indicated that the
proposed methodology efficiently represented and integrated multiple data sets and showed better prediction capability than
that of a traditional logistic regression model. 相似文献
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An attempt is made in this study to develop a model to forecast the cyclonic depressions leading to cyclonic storms over North Indian Ocean (NIO) with 3 days lead time. A multilayer perceptron (MLP) model is developed for the purpose and the forecast quality of the model is compared with other neural network and multiple linear regression models to assess the forecast skill and performances of the MLP model. The input matrix of the model is prepared with the data of cloud coverage, cloud top temperature, cloud top pressure, cloud optical depth, cloud water path collected from remotely sensed moderate resolution imaging spectro-radiometer (MODIS), and sea surface temperature. The input data are collected 3 days before the cyclogenesis over NIO. The target output is the central pressure, pressure drop, wind speed, and sea surface temperature associated with cyclogenesis over NIO. The models are trained with the data and records from 1998 to 2008. The result of the study reveals that the forecast error with MLP model varies between 0 and 7.2 % for target outputs. The errors with MLP are less than radial basis function network, generalized regression neural network, linear neural network where the errors vary between 0 and 8.4 %, 0.3 and 24.8 %, and 0.3 and 32.4 %, respectively. The forecast with conventional statistical multiple linear regression model, on the other hand, generates error values between 15.9 and 32.4 %. The performances of the models are validated for the cyclonic storms of 2009, 2010, and 2011. The forecast errors with MLP model during validation are also observed to be minimum. 相似文献
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On the basis of our analysis of a number of continuous observations made by the monitoring network on Crete, we assume that
electrically active clouds are produced in an atmosphere above the sea on the eve of earthquake. These electrically active
clouds, which occur at heights of 0.1–10 km, create the conditions for electrical discharges in an atmosphere that may be
the source of the very high frequency (VHF) radio-emissions registered on Crete. We further suggest possible mechanisms of
thunder electricity generation. We present the model of convection transport in which the first condition in the generation
of thunder electricity is an atmosphere with a horizontal gradient of temperature. Base on this model, the occurrence of electrical
charges on the surface of the sea and their transportation further upwards to heights of up to 10 km is due to pollution energy
allocated within the bottom of the sea as gases and heat injection. The average flux density and power estimations of the
VHF precursors were made for the Crete net situation to compare with published VHF data and radio star sources. 相似文献
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An improved hybrid gravimetric geoid model for Egypt, EGY-HGM2016, has been recently computed implementing the least-squares collocation (LSC) method through the remove-compute-restore (RCR) procedure. The computation of EGY-HGM2016 involves different datasets in terms of gravity anomalies determined from the GOCE (gravity field and steady-state ocean circulation explorer)-based global geopotential model (SPW-R4) up to d/o 200 and EGM2008 from d/o 201 to 720 combined with terrestrial gravity datasets in terms of 2140 gravity field anomalies and about 121,480 marine surface gravity anomalies. In addition, orthometric heights from 17 GPS/levelling measurements have been considered during the modelling process to improve the determination of the hybrid gravimetric geoid over the Egyptian region. The EGY-HGM2016 model estimated over Egypt provides geoid heights that are ranging from 7.677 to 21.095 m with a standard deviation (st. dev.) of about 2.534 m in the northwest of the country excluding the involvement of the orthometric heights from GPS/levelling measurements. When the later dataset is considered during the implementation of LSC process, hybrid residual height anomalies ranging from ?1.5 to +0.9 m, with a mean of 0.22 m and a st. dev. of 0.17 m, are obtained. Comparison of the predicted hybrid gravimetric geoid with the corresponding ones obtained from EGM2008, GOCE-based SPW R4 model, and GPS/levelling reveals considerable improvements of our EGY-HGM2016 model over Egypt. 相似文献
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对美国目前常用的一些用于流域总量管理的数学模型进行了概括分类,把收集到47个模型划分为流域负荷模型、受纳水体模型和集成化模拟系统三类,并选择其中的19个流域污染负荷模型作为重点进行了比较研究。针对这19个模型,首先对各模型的主要输入数据、模型主要的输出信息、模型所能处理的土地利用类型、模型中水文侵蚀和沉积物的计算机理、污染负荷计算结果的基本形式、所能模拟的污染物类型、模型的时间尺度特征、模型软件的提供者等9个方面作了较为详细的介绍。在此基础上,结合文献调研和对部分模型实际使用的效果,从模型处理不同土地利用类型(包括对流域点源的识别和处理)的适用性、对不同时间尺度的适应性、水文过程的模拟能力、不同类型污染物负荷的计算能力、对污染物运移过程的描述、模型结果输出的友好性、输入数据的需求程度、评估和设计污染总量管理措施的支持能力、以及使用说明文档的完备性等9个方面,对模型性能进行了定性评估,分别用“高”、“中”、“低”来表示模型的优劣程度。 相似文献
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M. Imani R.-J. You C.-Y. Kuo 《International Journal of Environmental Science and Technology》2014,11(4):1035-1042
The demand for accurate predictions of sea level fluctuations in coastal management and ship navigation activities is increasing. To meet such demand, accessible high-quality data and proper modeling process are critically required. This study focuses on developing and validating a neural methodology applicable to the short-term forecast of the Caspian Sea level. The input and output data sets used contain two time series obtained from Topex/Poseidon and Jason-1 satellite altimetry missions from 1993 to 2008. The forecast is performed by multilayer perceptron network, radial basis function, and generalized regression neural networks. Several tests of different artificial neural network (ANN) architectures and learning algorithms are carried out as alternative methods to the conventional models to assess their applicability for estimating Caspian Sea level anomalies. The results derived from the ANN are compared with observed sea level values and with the forecasts calculated by a routine autoregressive moving average (ARMA) model. Different ANNs satisfactorily provide reliable results for the short-term prediction of Caspian Sea level anomalies. The root mean square errors of the differences between observations and predictions from artificial intelligence approaches can be significantly reduced by about 50 % compared with ARMA techniques. 相似文献
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Sid Ahmed Benahmed Daho 《Comptes Rendus Geoscience》2010,342(2):87-94
The main purpose of this article is to discuss the use of GPS positioning together with a gravimetrically determined geoid, for deriving orthometric heights in the North of Algeria, for which a limited number of GPS stations with known orthometric heights are available, and to check, by the same opportunity, the possibility of substituting the classical spirit levelling. For this work, 247 GPS stations which are homogeneously distributed and collected from the international TYRGEONET project, as well as the local GPS/Levelling surveys, have been used. The GPS/Levelling geoidal heights are obtained by connecting the points to the levelling network while gravimetric geoidal heights were interpolated from the geoid model computed by the Geodetic Laboratory of the National Centre of Spatial Techniques from gravity data supplied by BGI. However, and in order to minimise the discordances, systematic errors and datum inconsistencies between the available height data sets, we have tested two parametric models of corrector surface: a four parameter transformation and a third polynomial model are used to find the adequate functional representation of the correction that should be applied to the gravimetric geoid. The comparisons based on these GPS campaigns prove that a good fit between the geoid model and GPS/levelling data has been reached when the third order polynomial was used as corrector surface and that the orthometric heights can be deducted from GPS observations with an accuracy acceptable for the low order levelling network densification. In addition, the adopted methodology has been also applied for the altimetric auscultation of a storage reservoir situated at 40 km from the town of Oran. The comparison between the computed orthometric heights and observed ones allowed us to affirm that the alternative of levelling by GPS is attractive for this auscultation. 相似文献
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Manoj Khandelwal 《Geotechnical and Geological Engineering》2012,30(1):205-217
The purpose of this article is to evaluate and predict the blast induced ground vibration using different conventional vibration
predictors and artificial neural network (ANN) at a surface coal mine of India. Ground Vibration is a seismic wave that spread
out from the blast hole when detonated in a confined manner. 128 blast vibrations were recorded and monitored in and around
the surface coal mine at different strategic and vulnerable locations. Among these, 103 blast vibrations data sets were used
for the training of the ANN network as well as to determine site constants of various conventional vibration predictors, whereas
rest 25 blast vibration data sets were used for the validation and comparison by ANN and empirical formulas. Two types of
ANN model based on two parameters (maximum charge per delay and distance between blast face to monitoring point) and multiple
parameters (burden, spacing, charge length, maximum charge per delay and distance between blast face to monitoring point)
were used in the present study to predict the peak particle velocity. Finally, it is found that the ANN model based on multiple
input parameters have better prediction capability over two input parameters ANN model and conventional vibration predictors. 相似文献
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最佳向上延拓高度的估计 总被引：4，自引：0，他引：4
提出根据两个相邻高度重力异常向上延拓值相关系数与高度的关系 ,以估计应用向上延拓分离区域及剩余重力异常的最佳向上延拓高度的方法。二维模型计算表明 ,不同高度的观测重力异常向上延拓值和观测面上区域重力异常值的互相关系数与高度的关系曲线 ,存在一个明显的极大值 ;这个极大值对应的高度 ,就是从观测异常中分离出这一区域重力异常所需要的最佳向上延拓高度。两个相邻高度重力异常向上延拓值之间的互相关系数与高度的关系曲线 ,存在一个明显的转折点 ,这个转折点对应的高度 ,就是所求的最佳向上延拓高度。应用本方法处理华南北部地区布格重力异常的结果表明 ,由于引起本区区域重力异常的地质因素 ,除了莫霍面及上地壳底面外 ,还受到本区广泛分布甚至出露的花岗岩的影响 ;所以为了从观测异常中分离这一区域异常所需要的最佳向上延拓高度为 2 0 0km ,小于莫霍面及上地壳底界面的平均深度。为了从观测异常中分离出由莫霍面引起的重力异常所需要的向上延拓高度 ,达到 15 0km。因此 ,应用本方法处理实测重力资料 ,必须首先了解引起区域重力异常的场源情况。 相似文献
18.
High precision design wave height is required in extreme marine environments in typhoon-affected sea areas. A new model is built under typhoon effect to calculate the design wave heights. The new model has multiple undetermined parameters, and it is able to fit observed data more flexibly and accurately. In addition, the distribution functions of this new model are based on the maximum entropy principle. Therefore, they can avoid the apriority, which means arbitrarily assigning Poisson distribution to describe the distribution of typhoon occurrence frequency and assigning Gumbel distribution or Pearson-III distribution to describe the distribution of extreme events in the process of applying the compound distribution to deduce the design elevations. The observed data of 18-year (1984–2001) extreme wave heights and the corresponding typhoon events in Maidao are used to test the model. Test results show that the new model is theoretically more stable and more precise when predicting the design wave heights under the typhoon-affected sea areas. 相似文献
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海陆过渡区是海洋与陆地复合与交叉的地理单元,是资源与环境条件最为优越的地区,将航空重力与地面重力有效融合,形成连续的重力场资料,对海陆过渡区资源与环境评价具有重要意义。本文选择日照—连云港海陆过渡区为示范区,开展了航空重力数据与地面重力数据的融合研究。通过数据整理与对比分析,总结了数据间系统差的确定方法,提出了空地重力数据间一致性与差异性的评估方法,并分别采用剖面和平面两种形式对数据间的一致性和差异性进行了量化评估;在数据量化评估的基础上,采用平面均方根误差法分别对混合法与缝合法的数据拼接质量进行了定量评价,为数据融合方法的选择提供了定量依据。研究结果表明,日照—连云港海陆过渡区航空重力与地面重力数据间剖面上的一致系数为0. 81~0. 99,平面上的一致系数为0. 95,数据间一致性较高,具备较好的数据融合基础;对比试验表明,缝合法对于海陆过渡区空地重力数据融合效果更佳,采用缝合法融合后的重力数据与原始空地重力数据间的均方差分别为2. 63×10 -5 m/s 2 、0. 98×10 -5 m/s 2 ,取得了较好的融合效果。日照—连云港海陆过渡区空地重力数据的融合,为同类地区开展多源重力数据的融合提供了借鉴。 相似文献