A parametric study on the impact of satellite attitude errors on GOCE gravity field recovery     

R. Pail 《Journal of Geodesy》2005,79(4-5):231-241

In the recent design of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission, the gravity gradients are defined in the gradiometer reference frame (GRF), which deviates from the actual flight direction (local orbit reference frame, LORF) by up to 3–4°. The main objective of this paper is to investigate the effect of uncertainties in the knowledge of the gradiometer orientation due to attitude reconstitution errors on the gravity field solution. In the framework of several numerical simulations, which are based on a realistic mission configuration, different scenarios are investigated, to provide the accuracy requirements of the orientation information. It turns out that orientation errors have to be seriously considered, because they may represent a significant error component of the gravity field solution. While in a realistic mission scenario (colored gradiometer noise) the gravity field solutions are quite insensitive to small orientation biases, random noise applied to the attitude information can have a considerable impact on the accuracy of the resolved gravity field models.  相似文献   

GGM02 – An improved Earth gravity field model from GRACE     

B. Tapley  J. Ries  S. Bettadpur  D. Chambers  M. Cheng  F. Condi  B. Gunter  Z. Kang  P. Nagel  R. Pastor  T. Pekker  S. Poole  F. Wang 《Journal of Geodesy》2005,79(8):467-478

A new generation of Earth gravity field models called GGM02 are derived using approximately 14 months of data spanning from April 2002 to December 2003 from the Gravity Recovery And Climate Experiment (GRACE). Relative to the preceding generation, GGM01, there have been improvements to the data products, the gravity estimation methods and the background models. Based on the calibrated covariances, GGM02 (both the GRACE-only model GGM02S and the combination model GGM02C) represents an improvement greater than a factor of two over the previous GGM01 models. Error estimates indicate a cumulative error less than 1 cm geoid height to spherical harmonic degree 70, which can be said to have met the GRACE minimum mission goals. Electronic Supplementary Material Supplementary material is available in the online version of this article at  相似文献   

Global height datum unification: a new approach in gravity potential space     

A. A. Ardalan  A. Safari 《Journal of Geodesy》2005,79(9):512-523

The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W ₀=62636855.8 m²/s². According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.  相似文献   

Effects of detailed soil spatial information on watershed modeling across different model scales     

Trevor Quinn  A.-Xing Zhu  James E. Burt   《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):324-338

Hydro-ecological modelers often use spatial variation of soil information derived from conventional soil surveys in simulation of hydro-ecological processes over watersheds at mesoscale (10–100 km²). Conventional soil surveys are not designed to provide the same level of spatial detail as terrain and vegetation inputs derived from digital terrain analysis and remote sensing techniques. Soil property layers derived from conventional soil surveys are often incompatible with detailed terrain and remotely sensed data due to their difference in scales. The objective of this research is to examine the effect of scale incompatibility between soil information and the detailed digital terrain data and remotely sensed information by comparing simulations of watershed processes based on the conventional soil map and those simulations based on detailed soil information across different simulation scales. The detailed soil spatial information was derived using a GIS (geographical information system), expert knowledge, and fuzzy logic based predictive mapping approach (Soil Land Inference Model, SoLIM). The Regional Hydro-Ecological Simulation System (RHESSys) is used to simulate two watershed processes: net photosynthesis and stream flow. The difference between simulation based on the conventional soil map and that based on the detailed predictive soil map at a given simulation scale is perceived to be the effect of scale incompatibility between conventional soil data and the rest of the (more detailed) data layers at that scale. Two modeling approaches were taken in this study: the lumped parameter approach and the distributed parameter approach. The results over two small watersheds indicate that the effect does not necessarily always increase or decrease as the simulation scale becomes finer or coarser. For a given watershed there seems to be a fixed scale at which the effect is consistently low for the simulated processes with both the lumped parameter approach and the distributed parameter approach.  相似文献   

FLAC数值模拟软件及其在地学中的应用   总被引：15，自引：0，他引：15  

龚纪文  崔建军  席先武  林舸 《大地构造与成矿学》2002,26(3):321-325

FLAC是以拉格朗日差分法为基础的一种数值模拟应用软件,主要用于岩土力学工程。近年地质学家将其应用到地质构造和块体运动学、动力学研究中,以证实或证伪地球学家们提出的相关地球动力学模型。本文初步介绍了FLAC应用软件的基本原理、使用方法以及它在国内外地质学上的几个应用实例。  相似文献   

离散裂隙渗流方法与裂隙化渗透介质建模   总被引：4，自引：1，他引：4  

王明玉  陈劲松等 《地球科学》2002,27(1):90-96

流体渗流模拟的连续介质方法通常适用于多孔地质体，并不一定适用于裂隙岩体，由于裂隙分布及其特征与孔隙差异较大。若流体渗流主要受裂隙的控制，对于一定尺寸的裂隙岩体，多孔介质假设则较难刻划裂隙岩体的渗流特征。离散裂隙渗流方法不但可直接用于模拟裂隙岩体非均质性和各向异性等渗流特征，而且可用其确定所研究的裂隙岩体典型单元体及其水力传导（渗透）张量大小。主要讨论了以下问题：（1）饱和裂隙介质中一般的离散流体渗流模拟；（2）裂隙岩体中的REV（典型单元体）及其水力传导（渗透）张量的确定；（3）利用离散裂隙网络流体渗流模型研究裂隙方向几何参数对水力传导系数和REV的影响；（4）在二维和三维离散裂隙流体渗流模型中对区域大裂隙和局部小裂隙的处理方法。调查结果显示离散裂隙流体渗流数学模型可用来评价不同尺度上的裂隙岩体的水力特征，以及裂隙方向对裂隙化岩体的水力特征有着不可忽视的影响。同时，局部小裂隙、区域大裂隙应当区别对待，以便据其所起的作用及水力特征，建立裂隙化岩体相应的流体渗流模型。  相似文献   

Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico   总被引：1，自引：0，他引：1  

Roger González-Herrera  Ismael Sánchez-y-Pinto  José Gamboa-Vargas 《Hydrogeology Journal》2002,10(5):539-552

The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity. Electronic Publication  相似文献   

Thermal and rheological structures of the Xisha Trough, South China Sea   总被引：8，自引：0，他引：8  

Xiaobin Shi  Di Zhou  Xuelin Qiu  Yixiang Zhang 《Tectonophysics》2002,351(4)

The Xisha Trough, located in the northwest of the South China Sea (SCS) mainly rifted 30 Ma ago, has been a failed rift since the cessation of the seafloor spreading of the NW subbasin. Based on the velocity–depth model along Profile OBH-4 across the Xisha Trough, a seven-layer density–depth model is used to estimate density structure for the profile. The relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust. The 2-D temperature field is calculated by applying a 2-D numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus (BDS). The rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power-law steady-state creep in the ductile regime. Rheological model is constructed for a three-layer model involving a granitic upper crust, a quartz diorite lower crust and an olivine upper mantle. Gravity modeling supports basically the velocity–depth model. The Moho along Profile OBH-4 is of relatively high heat flow ranging from 46 to 60 mW/m² and the Moho heat flow is higher in the trough than on the flanks. The depth of the “thermal” lithospheric lower boundary is about 54 km in the center, deepens toward two sides, and is about 75 km at the northern slope area and about 70 km at the southern Xisha–Zhongsha Block. Rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region, showing that the Xisha Trough has been rheologically strengthened, which are mainly due to later thermal relaxation. In addition, the strengthening in rheology during rifting was not the main factor in hampering the breakup of the Xisha Trough.  相似文献   

桩土接触面单元参数分析   总被引：11，自引：0，他引：11       下载免费PDF全文

许宏发  吴华杰  郭少平  廖铁平 《探矿工程》2002,(5):10-12

桩的抗拔特性与接触面的特性密切相关，正确选定接触面的力学参数对于分析桩的抗拔机理有重要意义。根据桩土接触面点面接触模型和库仑摩擦变形原理，在10组土－结构（钢、混凝土）剪切摩擦试验分析的基础上，对桩土接触面摩擦参数的取值问题进行了研究，得到了一些结论，对于桩土接触面力学参数正确取值有一定的参考价值。  相似文献   

Computational modeling of cyclic mobility and post-liquefaction site response   总被引：3，自引：0，他引：3  

Ahmed Elgamal  Zhaohui Yang  Ender Parra 《Soil Dynamics and Earthquake Engineering》2002,22(4)

Under seismic excitation, liquefied clean medium to dense cohesionless soils may regain a high level of shear resistance at large shear strain excursions. This pattern of response, known as a form of cyclic mobility, has been documented by a large body of laboratory sample tests and centrifuge experiments. A plasticity-based constitutive model is developed with emphasis on simulating the cyclic mobility response mechanism and associated pattern of shear strain accumulation. This constitutive model is incorporated into a two-phase (solid–fluid), fully coupled finite element code. Calibration of the constitutive model is described, based on a unique set of laboratory triaxial tests (monotonic and cyclic) and dynamic centrifuge experiments. In this experimental series, Nevada sand at a relative density of about 40% is employed. The calibration effort focused on reproducing the salient characteristics of dynamic site response as dictated by the cyclic mobility mechanism. Finally, using the calibrated model, a numerical simulation is conducted to highlight the effect of excitation frequency content on post-liquefaction ground deformations.  相似文献