基于共轭梯度搜索的病态问题处理方法

在最小二乘平差准则基础上,把病态平差问题转化为无约束的二次规划问题,并利用优化理论分析病态对平差解的影响。通过共轭梯度搜索算法在可行域中寻找最优步长因子,自动寻找最速下降方向,并给出迭代初值的设置方法。分析近似计算中病态问题与局部最优解的关系,讨论局部最优解的快速迭代方法,并通过实例验证算法的有效性,计算迭代的速度。由于整个过程没有对法方程系数矩阵进行求逆计算,该算法可用于处理大规模系数矩阵高病态的平差问题。     

Algorithm Studies on How to Obtain a Conditional Nonlinear Optimal Perturbation (CNOP)

The conditional nonlinear optimal perturbation (CNOP), which is a nonlinear generalization of the linear singular vector (LSV), is applied in important problems of atmospheric and oceanic sciences, including ENSO predictability, targeted observations, and ensemble forecast. In this study, we investigate the computational cost of obtaining the CNOP by several methods. Differences and similarities, in terms of the computational error and cost in obtaining the CNOP, are compared among the sequential quadratic programming (SQP) algorithm, the limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm, and the spectral projected gradients (SPG2) algorithm. A theoretical grassland ecosystem model and the classical Lorenz model are used as examples. Numerical results demonstrate that the computational error is acceptable with all three algorithms. The computational cost to obtain the CNOP is reduced by using the SQP algorithm. The experimental results also reveal that the L-BFGS algorithm is the most effective algorithm among the three optimization algorithms for obtaining the CNOP. The numerical results suggest a new approach and algorithm for obtaining the CNOP for a large-scale optimization problem.     

GPS静态相对定位技术在城市区域控制测量中的应用

以泰安市泰山区为例,介绍了GPS静态相对定位技术在新建控制网测量中的应用,讨论了用GPS静态相对定位技术建立城市区域控制网的方法,指出了在GPS测量中应注意的问题。基线解算和网平差方面,进行了三维无约束平差计算和二维约束平差,分析了城市GPS区域控制网所能达到的精度。在GPS网三维无约束平差的基础上,结合人工干预的方法剔除误差,使之可以达到更高等级GPS网的测量精度要求,能够满足城市建设和城市规划的测量成果的需求。     

Estimation of hypocentral parameters of local earthquakes when crustal layers have constantP-velocities and dipping interfaces

The paper describes an algorithm for estimating the hypocentral coordinates and origin time of local earthquakes when the wave speed model to be employed is a layered one with dipping interfaces. A constrained least-squared error problem has been solved using the penalty function approach, in conjunction with the sequential unconstrained optimization technique of Fiacco and McCormick. Joint confidence intervals for the computed parameters are estimated using the approach of Bard for nonlinear problems. These results show that when a hypocentre lies outside the array of recording stations and head waves from a dipping interface are involved, then its inclination must be taken into account for dip angles exceeding 5°.     

一种基于无约束总变分模型的阴影检测方法

阴影检测是进行阴影处理前的重要步骤,总变分模型可以用于影像阴影检测.通过对总变分模型进行改进,提出了一种基于无约束总变分模型的阴影检测方法.经实验及统计分析证明,在合适的迭代条件下,该方法对于单一阴影影像的处理效果理想.     

A statistical approach to disentangle environmental forcings in a lacustrine record: the Lago Chungará case (Chilean Altiplano)

A high resolution multiproxy study (magnetic susceptibility, X-ray diffraction, XRF scanner, gray-colour values, Total Organic Carbon, Total Inorganic Carbon, Total Carbon and Total Biogenic Silica) of the sedimentary infill of Lago Chungará (northern Chilean Altiplano) was undertaken to unravel the environmental forcings controlling its evolution using a number of different multivariate statistical techniques. Redundancy analyses enabled us to identify the main provenance of the studied proxies whereas stratigraphically unconstrained cluster analyses allowed us to distinguish the “outsiders” as result of anomalous XRF scanner acquisitions. Principal Component Analysis (PCA) was employed to identify and isolate the main underlying environmental gradients that characterize the sedimentary infill of Lago Chungará. The first eigenvector of the PCA could be interpreted as an indicator of changes in the input of volcaniclastic material, whereas the second one would indicate changes in water availability. The chronological model of this sedimentary sequence was constructed using 17 AMS ¹⁴C and 1 ²³⁸U/²³⁰Th dates in order to characterize the volcaniclastic input and the changes in water availability in the last 12,300 cal years BP. Comparison of the reconstructed volcaniclastic input of Lago Chungará with the dust particle record from the Nevado Sajama ice core suggested that the Parinacota volcano eruptions were the main source of dust during the mid and Late Holocene rather than the dry out lakes as has previously been pointed out. The comparison of the water availability reconstruction of Lago Chungará with three of the most detailed paleoenvironmental records of the region (Paco Cocha, Lake Titicaca and Salar Uyuni) showed an heterogeneous (and sometimes contradictory) temporal and spatial pattern distribution of moisture. Although the four reconstructions showed a good correlation, each lacustrine ecosystem responded differently to the moisture oscillations that affected this region. The variations in the paleoenvironmental records could be attributed to the dating uncertainities, lake size, lake morphology, catchment size and lacustrine ecosystem responses to the abrupt arid events.     

MATLAB软件支持下的GPS基线向量网的三维无约束平差

在采用GPS后处理软件进行基线解算且经过各项检核合格之后,需要进行基线向量网的三维无约束平差、三维约束平差、二维约束平差等处理过程。而目前相关的文献中对采用秩亏自由网平差进行GPS基线向量的无约束平差涉及较少,且往往是一笔带过[1]。本论文在对GPS基线向量网三维无约束平差及秩亏自由网平差数学模型进行引述的基础上,结合某工程案例,利用MATLAB强大的矩阵计算功能进行了基线向量网的三维无约束平差。以期为GPS数据后处理人员以及相关专业的大中专在校学生对该内容的理解与掌握提供一定的借鉴和帮助。     

GPS网形与GPS网质量的关系分析

基于GPS静态相对测量,基线数据处理采用双差观测值单基线解算的一般模式,讨论GPS网基线解算和3维无约束平差的公式,得出GPS网的质量与基线向量质量和GPS网结构有关,而与网形和点位无关,并通过实验数据,分析验证了这一观点,提出了一些有益的结论。     

Estimation of water cloud model vegetation parameters using a genetic algorithm

Abstract

The water cloud model is used to account for the effect of vegetation water content on radar backscatter data. The model generally comprises two parameters that characterize the vegetated terrain, A and B, and two bare soil parameters, C and D. In the present study, parameters A and B were estimated using a genetic algorithm (GA) optimization technique and compared with estimates obtained by the sequential unconstrained minimization technique (SUMT) from measured backscatter data. The parameter estimation was formulated as a least squares optimization problem by minimizing the deviations between the backscatter coefficients retrieved from the ENVISAT ASAR image and those predicted by the water cloud model. The bias induced by three different objective functions was statistically analysed by generating synthetic backscatter data. It was observed that, when the backscatter coefficient data contain no errors, the objective functions do not induce any bias in the parameter estimation and the true parameters are uniquely identified. However, in the presence of noise, these objective functions induce bias in the parameter estimates. For the cases considered, the objective function based on the sum of squares of normalized deviations with respect to the computed backscatter coefficient resulted in the best possible estimates. A comparison of the GA technique with the SUMT was undertaken in estimating the water cloud model parameters. For the case considered, the GA technique performed better than the SUMT in parameter estimation, where the root mean squared error obtained from the GA was about half of that obtained by the SUMT.

Editor D. Koutsoyiannis; Associate editor L. See

Citation Kumar, K., Hari Prasad, K.S. and Arora, M.K., 2012. Estimation of water cloud model vegetation parameters using a genetic algorithm. Hydrological Sciences Journal, 57 (4), 776–789.     

一种基于GPS—RTK的超快速静态控制测量新方法

讨论利用GPS-RTK的作业模式,采用超快速静态建立GPS控制网的新方法。将常规的RTK方法中参考站固定不动改变为参考站和流动站交替流动,每时段至少获得一条独立的基线向量,所有的基线按设计的网形组成多边形GPS网,网的各项指标执行城市GPS规范,数据按静态网的数据处理方法进行。实践结果表明,该方法获得的结果可靠,具有速度快、效率高、操作简便等特点,能达到城市GPS规范各等级的精度要求。