用组合观测法提高γ因子精度的初步研究

水平摆倾斜仪偏离起始平衡面工作时,存在有交互影响,它给观测记录带来误差,从而影响γ因子的精度。本文从理论上论证了交互影响的存在,推导出交互影响的计算公式,总结出消除交互影响的修正方法—组合观测法,并用组合观测法对南昌台倾斜固体潮γ因子的计算进行修正,得到提高γ因子精度的有意义的初步结果。     

双复杂介质条件下频率空间域有限差分法保幅偏移

油气勘探的重点正转向复杂地表条件和复杂地质条件的区域.双复杂条件下的叠前深度偏移是解决复杂地表条件和复杂地质构造成像的有效手段.基于“逐步累加”的“直接下延”法是解决复杂地表成像的有效手段,能够较好地消除地形起伏的影响.波动方程频率空间域有限差分(xwfd)叠前深度偏移对介质速度横向变化有较强的适应性,适宜于复杂构造的偏移成像,同其他常规波动方程深度偏移一样,常规的xwfd偏移方法,主要也是针对相位进行波场延拓,没有对振幅做任何处理.我们基于保幅单程波方程,推导出了基于xwfd的保幅波场延拓算子,针对xwfd求解时引入误差的影响,我们在xwfd保幅波场延拓过程中加入了误差补偿,实现了带误差补偿的xwfd保幅偏移.基于带误差补偿的xwfd保幅算子,应用适合起伏地表的直接下延法,对双复杂介质模型和实际资料进行了试算,改善了双复杂介质的成像效果.其中,误差补偿可以在若干个外推步长上进行,所以相对于保幅傅里叶有限差分(ffd)法偏移来说,该方法在改善成像质量的同时,也具有较高的运算效率.     

误差对大地电磁测深反演的影响

本文讨论了几种不同分布的误差对大地电磁测深反演的影响.首先基于给定的正演模型计算得到相应的理论合成数据,然后在合成数据中分别加入满足不同均值和方差的高斯分布、均匀分布和Gamma分布的误差,最后使用非线性共轭梯度法进行反演.反演结果表明, 较简单的模型在考虑的几种误差分布下可以较好地给出模型的基本信息;但复杂的模型随着误差方差的增大,与已知模型的偏差越明显; 在均值和方差相同时,上述三种不同分布的误差的反演结果相差很小.     

Errors in velocities and displacements deduced from accelerographs: An approach based on the theory of error propagation

Based on the theory of errors, and in particular on the law of error propagation and approximation techniques, we present some simple formulae for random errors of velocities and displacements computed on the basis of numerical integration of accelerometer records. These errors are regarded as function of the characteristic errors of accelerometers and of the duration of the signal for velocities, and of the square of the duration of the signal for displacements. Instabilities in the sampling rate introduce additional noise, which is proportional to the sum of the squares of measurements of acceleration, mostly influenced by high peaks. Because of uneven weighting, however, peaks at early stages of the record are more important than in their later stages.     

东北区夏季月降水数值产品释用预报方法

采用卡尔曼滤波法对国家气候中心的T63动力延伸预报场进行误差订正, 将订正后的预报场用于基于天气系统特征定性判断与相似离度指数定量相似相结合的降水预报模型, 制作东北区51个站点的定量的月降水预报, 并对1996~1998年夏季月降水进行了预报试验, 试验效果较好.     

辽宁一次暴雨过程分析与暴雨落区预报失误原因探讨

从一次高空槽和华北气旋影响的暴雨、局部大暴雨落区预报出发,利用常规地面观测资料、加密自动站资料、高空探测资料和欧洲中心（ECMWF）数值预报产品资料,对2011年7月29-31日辽宁一次暴雨、局部大暴雨过程的天气形势和物理量场进行分析。结果表明：夏季暴雨预报不仅要考虑高层形势、副热带高压强度和位置大尺度环流形势的变化,也要考虑有利的大尺度环流背景下易产生的中小尺度天气系统,此次辽宁暴雨过程中在高空槽和华北气旋的发生发展过程中激发了中尺度气旋,中尺度气旋的强度和移动路径是预报此次暴雨、局部大暴雨落区的关键因素。     

河套地震带的b值时空变化特征分析

本文以b值作为研究对象,在b值由应力状态和介质性质共同决定的理论框架下,开展了河套地震带的b值时空变化特征分析。选取1970年发生在河套地震带的ML≥1.5地震作为考察对象,运用EMR方法定量检测了最小完整性震级Mc的时序非均匀变化,并根据研究区地震活动实况,确定b值的起算震级为ML2.0。运用最小二乘法进行了b值时间扫描计算,结果显示,b值时序变化较好地对应了研究时段内的中强地震活动、台网分布和余震剔除等变化因素。运用极大似然法进行了b值空间扫描计算,结果显示,河套地震带的b值空间差异可能由地壳介质体性质和应力环境共同引起,相对来讲,b值的构造相依特征更为明显。此外,满足各震级档有足够多的地震样本依然是提高b值计算精度的关键环节。     

A general framework for error analysis in measurement-based GIS Part 3: Error analysis in intersections and overlays

This is the third of a four-part series on the development of a general framework for error analysis in measurement-based geographic information systems (MBGIS). In this paper, we study the characteristics of error structures in intersections and polygon overlays. When locations of the endpoints of two line segments are in error, we analyze errors of the intersection point and obtain its error covariance matrix through the propagation of the error covariance matrices of the endpoints. An approximate law of error propagation for the intersection point is formulated within the MBGIS framework. From simulation experiments, it appears that both the relative positioning of two line segments and the error characteristics of the endpoints can affect the error characteristics of the intersection. Nevertheless, the approximate law of error propagation captures nicely the error characteristics under various situations. Based on the derived results, error analysis in polygon-on-polygon overlay operation is also performed. The relationship between the error covariance matrices of the original polygons and the overlaid polygons is approximately established.This project was supported by the earmarked grant CUHK 4362/00H of the Hong Kong Research grants Council.     

在卫星授时中电离层误差实时改正的双极化方法

在卫星定位与授时中，电离层折射误差的影响是十分重要的．目前采用的主要改正方法是双频法，还有电离层模型法．双频法要求卫星发射两个工作频率，而电离层模型法的偏差又较大，这对于使用单频接收机的用户来讲，电离层折射改正就成为一个严重问题，笔者提出的双极化法正好可以解决单频接收机所遇到的问题．双极化法是基于电离层的双折射特性．一个线极化波在电离层中传播时被分裂成两个圆极化波，即左旋圆极化波和右旋圆极化波传播，左旋与右旋圆极化波在电离层中传播的速度不同，则到达接收点的时间也就不同，通过测量两个圆极化波到达接收点的传播时廷差，即可确定电离层折射误差的改正量．     

Error sources of precipitation measurements using electronic weight systems

Liquid precipitation amounts below 0.05 mm in combination with intervals of measurement greater than 3 min and temperature above 15 °C can considerably affect the measured precipitation using electronic weighing gauges. This was shown by tests using different weights put in the gauge in different intervals in order to simulate different precipitation amounts and measuring intervals. These results were confirmed by field intercomparison measurements using pit gauges in two locations in Slovakia. In total, 1571 weight tests consisting of combinations of simulated precipitation amounts of 0.025, 0.05, 0.2 mm and measuring intervals of 1, 2, 3, 5 and 10 min were carried out. Based on these tests and special software, a new gauge was developed. Using this gauge, the abovementioned error sources were minimized. The Slovak Hydrometeorological Institute now uses it at 90 gauge sites. This type of gauge was selected to participate in the current World Meteorological Organization, WMO, Intercomparison measurements of recording precipitation gauges.