基于图像分割的双能CT不完备数据重建算法优化研究

本文针对基于图像分割的双能CT不完备数据重建算法,提出了图像分割过程和方程组求解环节是优化算法的两个关键点,同时给出了初步优化方法。初步实验结果表明这两方面因素选取的优劣将直接影响重建图像质量。因此,根据实际应用需求,如能改善这两方面因素,基于图像分割的双能CT不完备数据重建算法的重建性能将会进一步提高。     

利用卫星星座对GNSS-R海洋遥感时空特性进行研究

利用仿真方法研究了GNSS-R接收天线俯仰角、卫星轨道长半轴和轨道倾角对镜像反射点数量的影响,对4颗和6颗卫星组成的星座时空分辨率进行了仿真计算,分别获取了星座的时间分辨率。认为由6颗卫星组成的星座,8 h可完成全球5°×5°海洋格点的探测任务。     

基于全球IGS数据的GPS导航星座精密轨道确定

研究GPS导航星座精密轨道确定的基本问题及其处理策略.基于2008年3月29日至4月7日的148个站的IGS站数据,计算了GPS卫星轨道的单天解和3天解,通过与CODE中心的最终轨道进行比较,评价了相应轨道的精度.结果显示,基于该导航星座轨道生成策略,单天轨道解径向精度优于9 cm,3天解轨道径向精度优于5 cm.     

A method to measure enforcement effort in shipping with incomplete information

Current methods in the shipping industry to evaluate performance do not account for differences in fleet profiles of registries such as age, size or ship type and not for bad luck. This can lead to unfair evaluation of enforcement efforts of the international standards. Furthermore, incentives to improve performance are concentrated on decreasing detentions rather than incidents. This article proposes a new method to a longstanding problem to evaluate performance that rectifies shortcomings of the method currently used. The proposed method measures the enforcement effort by means of proxy variables and introduces incentives for improvement that go beyond the currently used 'detention'. The aim is to provide a fair and transparent way. The proposed method is applied and results are compared with methods currently used to demonstrate how the rankings change. The method can be adapted to other areas of the shipping industry such as classification societies or ship management companies.     

Experimental study and mathematical modelling of soluble chemical transfer from unsaturated/saturated soil to surface runoff

A one‐dimensional, two‐layer solute transport model is developed to simulate chemical transport process in an initially unsaturated soil with ponding water on the soil surface before surface runoff starts. The developed mathematical model is tested against a laboratory experiment. The infiltration and diffusion processes are mathematically lumped together and described by incomplete mixing parameters. Based on mass conservation and water balance equations, the model is developed to describe solute transport in a two‐zone layer, a ponding runoff zone and a soil mixing zone. The two‐zone layer is treated as one system to avoid describing the complicated chemical transport processes near the soil surface in the mixing zone. The proposed model was analytically solved, and the solutions agreed well with the experimental data. The developed experimental method and mathematical model were used to study the effect of the soil initial moisture saturation on chemical concentration in surface runoff. The study results indicated that, when the soil was initially saturated, chemical concentration in surface runoff was significantly (two orders of magnitude) higher than that with initially unsaturated soil, while the initial chemical concentrations at the two cases were of the same magnitude. The soil mixing depth for the initially unsaturated soil was much larger than that for the initially saturated soil, and the incomplete runoff mixing parameter was larger for the initially unsaturated soil. The higher the infiltration rate of the soil, the greater the infiltration‐related incomplete mixing parameter. According to the quantitative analysis, the soil mixing depth was found to be sensitive for both initially unsaturated and saturated soils, and the incomplete runoff mixing parameter was sensitive for initially saturated soil but not for the initially unsaturated soil; the incomplete infiltration mixing parameter behaved just the opposite. Some suggestions are made for reducing chemical loss from runoff. Copyright © 2010 John Wiley & Sons, Ltd.     

DMC卫星图像MTF分析及其复原方法研究

复原退化模糊图像是遥感图像处理的研究重点。对成像系统的调制传递函数(MTF)进行了研究,分析了调制传递函数的基本理论。讨论了一种近似测定成像系统调制传递函数的方法,通过有限采样,曲线拟合,傅立叶变换,规格化的一系列处理得到图像获取、传输过程中的点扩展函数(PSF)。提取完整光滑的调制传递函数曲线,在频域中对图像进行去卷积复原,分析和评价了复原结果。将该方法应用于DMC卫星图像,图像质量得到明显提高,收到较好的复原效果。     

不完全LU分解预条件BICGSTAB算法实现感应测井二维FDFD快速正演模拟

在柱坐标系下推导了二维感应测井差分格式,采用频率域有限差分方法求解感应测井正演问题。针对差分近似得到的线性方程组系数矩阵是大型稀疏复系数病态矩阵求解困难等问题,采用不完全LU分解预条件的稳定双共轭梯度(BICGSTAB)算法求解该线性方程组。研究结果表明,本算法具有速度快、精度高和稳定性好等优点,能有效提高感应测井正演模拟的效率和精度。     

北斗卫星广播星历精度评估与单点定位优化模型

利用精密星历产品对BDS-2和BDS-3广播星历的精度进行系统评估,进一步比较分析不同BDS-2和BDS-3卫星星座组合对单点定位的影响,提出一种基于SISRE(signal in space range error)的单点定位加权优化模型.实验结果表明,BDS-2星座中MEO、IGSO和GEO卫星广播星历轨道误差的R...     

用人工神经网络进行空间不完备数据的插补

在地学研究中,特别是区域性资料处理过程中,常常遇到“不完备数据”的问题,即所谓的“数据不全”。在尽量减小估计误差的条件下对缺失数据进行预测或插补,对于充分利用历史资料和已知信息,提高预测质量具有重要意义。利用径向基人工神经网络(RBF)同时具有自组织神经网络和回归网络的优点,可以对缺失数据进行预测。实际区域地球化学数据处理的结果表明,RBF网络对空间不完备数据的建模和预测具有优异的效果。     

Estimation of earthquake hazard parameters for incomplete and uncertain data files

The maximum likelihood estimation of earthquake hazard parameters (maximum regional magnitudem _max, activity rate , and theb parameter in the Gutenberg-Richter distribution) is extended to the cases of incomplete and uncertain data. The method accepts mixed data containing only large (extreme) events and a variable quality of complete data with different threshold magnitude values. Uncertainty of earthquake magnitude is specified by two values, the lower and upper magnitude limits. It is assumed that such an interval contains the real unknown magnitude. The proposed approach allows the combination of different quality catalog parts, e.g. those where the assignment of magnitude is questionable and those with magnitudes precisely determined.As an illustration of the method, the seismic hazard analysis for western Norway and adjacent sea area (4–8°E, 58–64°N) is presented on the basis of the strongest earthquakes felt during the period 1831–1889 and three complete catalog parts, covering the period 1890–1987.Paper presented at the 21st General Assembly of the European Seismological Commission held in Sofia, 1988.On leave from Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland.