Optimization of Time Data Codification and Transmission Schemes: Application to Gaia     

J.?PortellEmail author  E.?GarcíA-Berro  X.?Luri 《Experimental Astronomy》2003,16(3):189-212

Gaia is an ambitious space observatory devoted to obtain the largest and most precise astrometric catalogue of astronomical objects from our Galaxy and beyond. On-board processing and transmission of the huge amount of data generated by the instruments is one of its several technological challenges. The measurement time tags are critical for the scientific results of the mission, so they must be measured and transmitted with the highest precision – leading to an important telemetry channel occupation. In this paper we present the optimization of time data, which has resulted in a useful software tool. We also present how time data is adapted to the packet telemetry standard. The several communication layers are illustrated and a method for coding and transmitting the relevant data is described as well. Although our work is focused on Gaia, the timing scheme and the corresponding tools can be applied to any other instrument or mission with similar operational principles.  相似文献   

Stochastic conditional inverse modeling of subsurface mass transport: A brief review and the self-calibrating method   总被引：2，自引：2，他引：0  

J. J.?Gómez-HernándezEmail author  H.-J. W. M. Hendricks?Franssen  A.?Sahuquillo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2003,17(5):319-328

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一个非线性最小二乘混合算法及其在多源多维多类型测量数据联合非线性处理中的应用   总被引：1，自引：0，他引：1  

李述山  陶华学 《测绘科学》2004,29(5):50-52

建立了一个多源、多类型观测量联合处理的数学模型,针对该模型,结合非线性最小二乘的两种常用算法———修正的高斯—牛顿法与阻尼最小二乘法,建立了一个非线性最小二乘的混合算法,该算法不仅具有全局收敛性,而且在一定条件下局部二次收敛。通过算例验证了算法的有效性。  相似文献   

乌鲁木齐气象卫星地面站极轨云图接收质量考核及优化拼图     

张青  孟晋宝 《沙漠与绿洲气象(新疆气象)》2004,27(2):20-22

对乌鲁木齐气象卫星地面站极轨气象卫星接收系统接收的CHRPT、GDPT、HRPT资料进行质量定量考核，对A、B机接收的资料进行优化拼图，并向中心转发；对其设计、实现原理进行描述。  相似文献   

Unravelling the microfacies signatures of parasequences using computer-optimized similarity matrices     

Guy H. Spence  Annie Arnaud-Vanneau†  Hubert Arnaud†  Maurice E. Tucker‡ 《Sedimentology》2004,51(6):1243-1271

The microfacies of a Lower Cretaceous carbonate drillcore from Oman are characterized using optimizing matrices of Jaccard's similarity coefficients of community. Other than systems tract boundaries, there is no obvious evidence of individual parasequences in the core. However, diagnostic patterns in microfossil distribution identify environmental gradients recording changes in water depth. These gradients are used to define individual parasequences, parasequence sets, stacking patterns and key surfaces. The patterns suggest that deposition was controlled by successive fourth‐ to fifth‐order (high‐frequency) relative sea‐level cycles superimposed on an underlying third‐order relative sea‐level rise. Although the correlation of these depositional subunits to systematic changes in water depth and the rate of carbonate accumulation alone is not incontrovertible proof of such a sea‐level control, concurrent multiorder relative sea‐level cyclicity provides by far the most likely explanation. A microfacies deposited when the water depth was shallowing is characterized by a relay of microfossils with affinities that shallow upwards. Conversely, a microfacies that records a gradual increase in water depth has a relay of microfossils with affinities that deepen upwards. Microfacies characterized by an assemblage of microfossils with similar affinities record deposition when the benthic environmental conditions remained stable, either because of an equilibrium between shallow water carbonate deposition and rising sea level, or in deeper water where sediment composition was relatively insensitive to changes of water depth. Microfacies characterized by mixed affinity assemblages record syndepositional reworking. During periods of embedded multiorder sea‐level changes, individual parasequences within systems tracts are shown to record more complex environmental gradients than simply the repetition of successive shallowing‐up units as traditionally represented in carbonate sequence stratigraphic models. The microfacies of an individual parasequence may shallow up, or may record both deepening‐up and shallowing‐up depositional phases, as well as periods of sedimentation when benthic environments remained stable. Individual parasequence boundaries may be submarine or subaerial unconformities, or be conformable, as part of a predictable stratigraphic pattern related to the temporal position of an individual parasequence within the underlying third‐order cycle of relative sea‐level change. The hitherto ubiquitous use of assemblages to describe carbonate microfacies, coupled with the widespread use of the metre‐scale shallowing‐up template to identify parasequences, may have led to such complexities previously being overlooked.  相似文献   

Refinement Indicators for Optimal Selection of Geostatistical Realizations Using the Gradual Deformation Method     

Thomas Schaaf  Guy Chavent  Mokhlès Mezghani 《Mathematical Geology》2004,36(4):425-445

In the analysis of petroleum reservoirs, one of the most challenging problems is to use inverse theory in the search for an optimal parameterization of the reservoir. Generally, scientists approach this problem by computing a sensitivity matrix and then perform a singular value decomposition in order to determine the number of degrees of freedom i.e. the number of independent parameters necessary to specify the configuration of the system. Here we propose a complementary approach: it uses the concept of refinement indicators to select those degrees which have the greatest sensitivity to an objective function quantifying the mismatch between measured and simulated data. We apply this approach to the problem of data integration for petrophysical reservoir charaterization where geoscientists are currently working with multimillion cell geological models. Data integration may be performed by gradually deforming (by a linear combination) a set of these multimillion grid geostatistical realizations during the optimization process. The inversion parameters are then reduced to the number of coefficients of this linear combination. However, there is an infinity of geostatistical realizations to choose from which may not be efficient regarding operational constraints. Following our new approach, we are able through a single objective function evaluation to compute refinement indicators that indicate which realizations might improve the iterative geological model in a significant way. This computation is extremely fast as it implies a single gradient computation through the adjoint state approach and dot products. Using only the most sensitive realizations from a given set, we are able to resolve quicker the optimization problem case. We applied this methodology to the integration of interference test data into 3D geostatistical models.  相似文献   

Determination of regional stress tensors from fault-slip data   总被引：1，自引：0，他引：1  

Peiliang Xu 《Geophysical Journal International》2004,157(3):1316-1330

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岩土工程中一类双重非线性问题的处理方法   总被引：1，自引：0，他引：1  

武亚军  栾茂田  杨敏 《岩土力学》2004,25(Z1):41-46

针对土体和土体与结构接触面上的双重非线性性质,提出了采用理想弹塑性模型来模拟土体和采用非线性弹性-理想塑性模型来模拟土体与结构接触面相结合的方法,详细叙述了该方法的原理和数值实现方法。编制了面向对象的有限元计算程序,通过对地基极限承载力的计算验证了理想塑性模型的正确性,通过对一个受弹性基础梁作用的弹塑性地基分析验证了本文方法的适用性。计算结果表明,该方法简单实用,有一定的推广应用价值。  相似文献   

交互式洪水预报系统及关键技术研究   总被引：5，自引：0，他引：5  

刘金平  张建云 《水文》2004,24(1):4-9

介绍了交互式洪水预报系统的概念和基本结构，分析了实现交互式预报的区域拓扑连接、作业表、模型参数优化、交互修正等关键技术，并以淮河交互式洪水预报系统为例，阐述了系统的组成、实时作业预报的数据流程和应用成果。在分析我国暴雨洪水特性和自然地理条件的基础上，指出了在我国开发交互式洪水预报系统的必要性和应该注意的几个主要问题。  相似文献   

Effects of spatially variable ground motions on the seismic response of a skewed, multi-span, RC highway bridge   总被引：4，自引：0，他引：4  

L. Lou  A. Zerva   《Soil Dynamics and Earthquake Engineering》2005,25(7-10):729-740

This paper presents a study of the influence of spatially variable ground motions on the longitudinal seismic response of a short, three-span, 30-degree skewed, reinforced concrete highway bridge. Linear and nonlinear finite element models are created for the bridge and linear elastic and nonlinear inelastic time history analyses conducted. Three different types of illustrative excitations are considered: The first utilizes spatially variable ground motions incorporating the effects of variable soil conditions, loss of coherency and wave passage as input motions at the structures' supports. The time history with the smallest peak displacement and the one with the largest peak displacement from the spatially variable ones are then used as uniform input motions at all bridge supports. The comparative analysis of the bridge model shows that the uniform ground motion input with the largest peak displacement cannot provide conservative seismic demands for all structural components—in a number of cases it results in lower response than that predicted by spatially variable motions. The present results indicate that there is difficulty in establishing uniform input motions that would have the same effect on the response of bridge models as spatially variable ones. Consequently, spatially variable input motions need to be applied as excitations at the bridge supports.  相似文献