Effect of single arrival time on the hypocentral focal depth determination     

Nitzan Rabinowitz  David M. Steinberg 《Geophysical Journal International》1988,94(3):567-570

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SHORT COMMUNICATION APPLICATION OF THE POWELL METHOD TO THE OPTIMIZATION OF FLOW INJECTION SYSTEMS     

M.DELVALLE  J.ALONSO  M.POCH  J.BARTROLí 《地理学报(英文版)》1988,(Z1)

This paper describes the application of the Powell algorithm to the optimization of a flow injectionsystem configuration.The performance of this algorithm has been compared with the modified simplexmethod.The system studied is the determination of ammonia,based on the indophenol blue reaction.Alinear combination of sensitivity and sample throughput is used as the objective function because of itssimultaneous optimization capability.Results obtained show that the proposed method may reach theoptimal conditions with a lower number of experimental evaluations.  相似文献   

Inverse problem in hydrogeology   总被引：14，自引：6，他引：8  

Jesús Carrera  Andrés Alcolea  Agustín Medina  Juan Hidalgo  Luit J. Slooten 《Hydrogeology Journal》2005,13(1):206-222

The state of the groundwater inverse problem is synthesized. Emphasis is placed on aquifer characterization, where modelers have to deal with conceptual model uncertainty (notably spatial and temporal variability), scale dependence, many types of unknown parameters (transmissivity, recharge, boundary conditions, etc.), nonlinearity, and often low sensitivity of state variables (typically heads and concentrations) to aquifer properties. Because of these difficulties, calibration cannot be separated from the modeling process, as it is sometimes done in other fields. Instead, it should be viewed as one step in the process of understanding aquifer behavior. In fact, it is shown that actual parameter estimation methods do not differ from each other in the essence, though they may differ in the computational details. It is argued that there is ample room for improvement in groundwater inversion: development of user-friendly codes, accommodation of variability through geostatistics, incorporation of geological information and different types of data (temperature, occurrence and concentration of isotopes, age, etc.), proper accounting of uncertainty, etc. Despite this, even with existing codes, automatic calibration facilitates enormously the task of modeling. Therefore, it is contended that its use should become standard practice.

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Resumen Se sintetiza el estado del problema inverso en aguas subterráneas. El énfasis se ubica en la caracterización de acuíferos, donde los modeladores tienen que enfrentar la incertidumbre del modelo conceptual (principalmente variabilidad temporal y espacial), dependencia de escala, muchos tipos de parámetros desconocidos (transmisividad, recarga, condiciones limitantes, etc), no linealidad, y frecuentemente baja sensibilidad de variables de estado (típicamente presiones y concentraciones) a las propiedades del acuífero. Debido a estas dificultades, no puede separarse la calibración de los procesos de modelado, como frecuentemente se hace en otros campos. En su lugar, debe de visualizarse como un paso en el proceso de entendimiento del comportamiento del acuífero. En realidad, se muestra que los métodos reales de estimación de parámetros no difieren uno del otro en lo esencial, aunque sí pueden diferir en los detalles computacionales. Se discute que existe amplio espacio para la mejora del problema inverso en aguas subterráneas: desarrollo de códigos amigables al usuario, acomodamiento de variabilidad a través de geoestadística, incorporación de información geológica y diferentes tipos de datos (temperatura, presencia y concentración de isótopos, edad, etc), explicación apropiada de incertidumbre, etc. A pesar de esto, aún con los códigos existentes, la calibración automática facilita enormemente la tarea de modelado. Por lo tanto, se sostiene que su uso debería de convertirse en práctica standard.

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Résumé Létat du problème inverse des eaux souterraines est synthétisé. Laccent est placé sur la caractérisation de laquifère, où les modélisateurs doivent jouer avec lincertitude des modèles conceptuels (notamment la variabilité spatiale et temporelle), les facteurs déchelle, plusieurs inconnues sur différents paramètres (transmissivité, recharge, conditions aux limites, etc.), la non linéarité, et souvent la sensibilité de plusieurs variables détat (charges hydrauliques, concentrations) des propriétés de laquifère. A cause de ces difficultés, le calibrage ne peut être séparé du processus de modélisation, comme cest le cas dans dautres cas de figure. Par ailleurs, il peut être vu comme une des étapes dans le processus de détermination du comportement de laquifère. Il est montré que les méthodes dévaluation des paramètres actuels ne diffèrent pas si ce nest dans les détails des calculs informatiques. Il est montré quil existe une large panoplie de techniques d ‹inversion : codes de calcul utilisables par tout-un-chacun, accommodation de la variabilité via la géostatistique, incorporation dinformations géologiques et de différents types de données (température, occurrence, concentration en isotopes, âge, etc.), détermination de lincertitude. Vu ces développements, la calibration automatique facilite énormément la modélisation. Par ailleurs, il est souhaitable que son utilisation devienne une pratique standardisée.

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Synthetically adaptive robust filtering for satellite orbit determination   总被引：7，自引：0，他引：7  

YANG Yuanxi & WEN Yuanlan . Xi''''an Research Institute of Surveying  Mapping  Xi抋''''an  China  . College of Aerospace  Material Engineering  National University of Defense Technology  Changsha  China 《中国科学D辑(英文版)》2004,47(7):585-592

The precise orbit information is the premise of the application of satellite, and the precise orbit deter- mination includes dynamic and geometric methods. The dynamic method estimates the position and veloc-ity of a satellite at one epoch by extending the obser-vational arc in order to include more observations of different epochs in it. It is realized by integrating the dynamic equation of the satellite so that the observa-tions at different epochs are related to the particular state. The dy…  相似文献   

Atmospheric densities derived from CHAMP/STAR accelerometer observations   总被引：3，自引：0，他引：3  

S. Bruinsma  D. Tamagnan  R. Biancale 《Planetary and Space Science》2004,52(4):297-312

The satellite CHAMP carries the accelerometer STAR in its payload and thanks to the GPS and SLR tracking systems accurate orbit positions can be computed. Total atmospheric density values can be retrieved from the STAR measurements, with an absolute uncertainty of 10-15%, under the condition that an accurate radiative force model, satellite macro-model, and STAR instrumental calibration parameters are applied, and that the upper-atmosphere winds are less than . The STAR calibration parameters (i.e. a bias and a scale factor) of the tangential acceleration were accurately determined using an iterative method, which required the estimation of the gravity field coefficients in several iterations, the first result of which was the EIGEN-1S (Geophys. Res. Lett. 29 (14) (2002) 10.1029) gravity field solution. The procedure to derive atmospheric density values is as follows: (1) a reduced-dynamic CHAMP orbit is computed, the positions of which are used as pseudo-observations, for reference purposes; (2) a dynamic CHAMP orbit is fitted to the pseudo-observations using calibrated STAR measurements, which are saved in a data file containing all necessary information to derive density values; (3) the data file is used to compute density values at each orbit integration step, for which accurate terrestrial coordinates are available. This procedure was applied to 415 days of data over a total period of 21 months, yielding 1.2 million useful observations. The model predictions of DTM-2000 (EGS XXV General Assembly, Nice, France), DTM-94 (J. Geod. 72 (1998) 161) and MSIS-86 (J. Geophys. Res. 92 (1987) 4649) were evaluated by analysing the density ratios (i.e. “observed” to “computed” ratio) globally, and as functions of solar activity, geographical position and season. The global mean of the density ratios showed that the models underestimate density by 10-20%, with an rms of 16-20%. The binning as a function of local time revealed that the diurnal and semi-diurnal components are too strong in the DTM models, while all three models model the latitudinal gradient inaccurately. Using DTM-2000 as a priori, certain model coefficients were re-estimated using the STAR-derived densities, yielding the DTM-STAR test model. The mean and rms of the global density ratios of this preliminary model are 1.00 and 15%, respectively, while the tidal and latitudinal modelling errors become small. This test model is only representative of high solar activity conditions, while the seasonal effect is probably not estimated accurately due to correlation with the solar activity effect. At least one more year of data is required to separate the seasonal effect from the solar activity effect, and data taken under low solar activity conditions must also be assimilated to construct a model representative under all circumstances.  相似文献   

利用中心差分法进行GPS定速时最佳点数的选取     

王潜心  徐天河  龚佑兴 《武汉大学学报(信息科学版)》2012,37(3):265-268,353

分析了利用中心差分法进行GPS定速时的主要误差来源,证明了当数据采样率一定时,增加中心差分法的点数可减少微分过程中的截断误差,但同时会放大导出相位率的观测误差,得出中心差分法的最佳点数应使这两种误差之和最小的结论。实验结果表明,当数据采样间隔为1s、载体平均速度和加速度为20m.s-1和0.2m.s-2时,9个点的中心差分法定速精度最高。  相似文献   

利用C波段转发数据实现GEO卫星轨道确定     

毛悦  宋晓勇  贾小林  吴显兵  冯来平 《测绘科学技术学报》2012,29(3):175-178

为了提高我国卫星导航系统GEO卫星定轨能力,针对我国卫星导航系统所特有的新数据和新方法,利用CAPS系统的C波段转发式测距数据进行了单GEO卫星定轨实验.在分析该方法技术特点的基础上,从定轨残差和轨道重叠弧段比较等方面,对定轨结果进行了分析.由于设备转发时延是影响该方法定轨精度的重要因素,因此同时还分析了系统偏差对定轨精度的影响,得出了一些有益的结论.  相似文献   

利用GPS伪距导出的多普勒频移测速     

夏敬潮  叶世榕 《测绘信息与工程》2012,37(6):83-84

推导了利用伪距观测值获取多普勒频移的公式,并利用导出的多普勒频移来确定载体的速度。实测数据表明,利用伪距导出的多普勒频移测速,可以达到dm/s级的水平。在没有原始多普勒观测值或者相位观测出现了频繁周跳的情况下,可以利用伪距导出的多普勒频移获得载体概略的速度信息。  相似文献   

云的立体观测研究进展   总被引：1，自引：0，他引：1  

李艳兵  黄思训  翟景秋 《热带气象学报》2008,24(6):743-747

对云的立体观测的研究历史做了回顾,按照具有代表性的观测平台的变化划分了4个发展阶段,分别予以介绍,内容包括典型平台、技术途径和特点、同步精度、云高指定精度等。重点介绍了双星联合观测的云高指定技术,分析了关键技术和可能存在的问题,为技术实现做了较好的准备。  相似文献   

The Data Depth-weight-kernel Estimation of the Model Error of Satellite Orbit Determination     

Xiao-Gang Pan  Hai-Yin Zhou 《Chinese Astronomy and Astrophysics》2009,33(3):293-304

It is an objective fact that there exists error in the satellite dynamic model and it will be transferred to satellite orbit determination algorithm, forming a part of the connotative model error. Mixed with the systematic error and random error of the measurements, they form the unitive model error and badly restrict the precision of the orbit determination. We deduce in detail the equations of orbit improvement for a system with dynamic model error, construct the parametric model for the explicit part of the model and nonparametric model for the error that can not be explicitly described. We also construct the partially linear orbit determination model, estimate and fit the model error using a two-stage estimation and a kernel function estimation, and finally make the corresponding compensation in the orbit determination. Beginning from the data depth theory, a data depth weight kernel estimator for model error is proposed for the sake of promoting the steadiness of model error estimation. Simulation experiments of SBSS are performed. The results show clearly that the model error is one of the most important effects that will influence the precision of the orbit determination. The kernel function method can effectively estimate the model error, with the window width as a major restrict parameter. A data depth-weight-kernel estimation, however, can improve largely the robustness of the kernel function and therefore improve the precision of orbit determination.  相似文献