机载POS系统中惯性测量单元精度检校方法

本文简要介绍了GPS/INS组合技术的优势和特点,分析了惯性测量单元(IMU)的工作原理及精度影响因素,系统阐述了机载POS系统中IMU的检校方法和精度评定方法,包括初始对准重复性检测、跟踪姿态角精度的标定和静态漂移检测等,并利用双轴数控转台,对3台不同类型的国产POS系统进行了数据采集、处理和对比分析,实验初步表明,...     

等厚薄互层时频特征的正演模拟

本文基于波动理论,利用深度域相移法对不同互层数、不同单层厚度的等厚薄互层进行正演模拟.采用广义S变换分析零偏移距地震道反射复合波的瞬时频谱.研究发现当单层厚度大于3/16波长时,等厚薄互层时域特征为中、高频等幅振荡,瞬时频谱为与单层厚度成反比的单一峰值梳状函数;当单层厚度小于3/16波长时,震源子波的有限带宽对瞬时频谱的高频频率峰有压制作用,导致等厚薄互层中部的时域振幅和频域最大幅度均为低值,薄互层的结构特征不易分辨,说明宽高频的震源子波是提高薄互层分辨能力的关键.此外,理论推导和实验分析均证明:当地层厚度大于1/8波长时,其峰值频率与薄互层单层厚度存在定量解析关系,这为等厚薄互层单层厚度定量预测提供了重要的技术手段.     

VTI介质中非线性对地震波频率和频宽变化的约束

采用改进型FCT有限差分法分别模拟各向同性、具有垂直对称轴的横向各向同性(VTI)以及非线性VTI介质中地震波场,随后采用小波分析探讨VTI介质中非线性对地震波频率和频宽变化的约束.数值模拟及分析结果表明：介质各向异性会引发地震记录中各波型的能量随炮检距的变化,而介质各向异性与非线性的耦合作用则会进一步加剧这种变化.在遵守能量守恒原理的前提下,介质的非线性会引发地震波场中各波型间能量的再分配.同时还会引发地震波速度的波动,且随着入射角的增大,波动幅度变小.这些现象在频率域内的响应表现为主频和频宽的降低或增大、地震记录中与各波型相对应的瞬时主频和频宽峰值出现时刻的偏移以及它们随炮检距变化而表现出的幅值波动.在本文给定的弱非线性介质中（非线性炽较薄且远离震源）,在震源能量较低的情况下,介质的非线性效应会造成地震波瞬时主频和频宽相对于线性介质情况分别为1/10～1/4和1/10～1/3左右的变化量.此外,随着入射波能量的下降,介质非线性所造成的地震波瞬时特征（振幅、主频、频宽）的变化量减小,但随着地震波在穿越非线性介质时路径的加长,非线性作用的累积效应使得波形畸变和频率分布特征的变化（尤其是频宽）等现象得以维持.     

信号的瞬时参数与正交小波基

对于可表成ｕ（ｔ）＝ａ（ｔ）ｃｏｓθ（ｔ）的信号,称ａ（ｔ）为其瞬时振幅,θ（ｔ）为瞬时位相,为瞬时频率．在许多实际问题中,瞬时振幅、位相、频率等瞬时参数的提取有重要意义．但已知的一些瞬时参数计算方法均各有其局限性．本文构造了一种频谱支集紧且有解析表达式的小波,利用它得到一种计算信号瞬时参数的能抗噪声干扰的快速、局部算法．理论分析和数值模拟的结果表明,该方法是实用而有效的,可望能满足许多实际问题的需要．     

基于二维三分量伪谱法模拟数据的EDA介质中横波分裂研究

为了检测定向裂隙介质中横波分裂的方位属性特征,分析地震属性随裂隙密度和方位变化,采用人工吸收边界和反周期扩展边界,用伪谱法获得不同裂隙密度和不同方位地质模型三分量地面记录;应用时频分析和剪切波偏振分析研究由于裂隙方位和密度引起的横波分裂.结果显示,裂隙密度和方位决定着横波分裂的时差和偏振.快慢横波的延迟时间随裂隙密度增大而增加,不同方位相同裂隙密度的横波分裂时差有微小的变化.在45°方位检测时间延迟时间最大.通过时频分析,可以看到不同方位的瞬时主频有显著的变化,在横波分裂处瞬时主频有明显变化.因此,瞬时主频和快横波的偏振以及延迟时间可以作为裂隙方位和密度的指示.     

地震信号瞬时频率的估算

本文比较了四类计算瞬时频率的方法.基于相位差分的方法对噪声敏感;基于零交叉点的方法是针对周期信号提出的,对非周期信号效果不理想,通过插值改善估算结果;基于FIR微分器的方法有三种,基于两点的FIR方法与标准公式较为接近,但会引入半个采样间隔的时移;基于三点的FIR方法可以消除时移,但计算结果会出现负频尖峰;Claerbout方法不仅会引入半个采样间隔的时移,而且估算的频率值可能超过Nyqusit频率.本文在Claerbout公式的基础上导出了一种估算瞬时频率的公式,该公式消除了时移,且负频尖峰也得到抑制;基于时频表示一阶矩的方法的计算结果较为平滑,同时具有一定的抗噪能力.最后用本文导出的公式和时频表示一阶矩两种方法计算了南海东北部一条地震剖面的瞬时频率,并将其结果与Seismic Unix中相关函数的计算结果做了比较,表明本文导出公式的计算结果较为理想.     

Multi-temporal relations between runoff and sediment load based on variable structure cointegration theory

Microscopic and macroscopic multi-temporal correlations between runoff and sediment load were analyzed to reveal the relations between them in the source region of the Yellow River using the complete ensemble empirical mode decomposition with adaptive noise method (CEEMDAN) and cointegration theory. Subsequently, multi-temporal models of runoff and sediment load with structural breaks were developed. The results revealed the following points. (1) The runoff and sediment load relations differed at multi-time scales. Multi-temporal cointegration could reveal the relation between runoff and sediment load at micro scales. (2) A comparison of the original model, composite model 1, and composite model 2 revealed that the multi-temporal cointegration model is better than the original model. (3) The variable structure cointegration model of the runoff and sediment load relation had the highest simulation accuracy, and the smallest average relative error for the simulated runoff was 7.82%. Composite model 2 could more accurately reflect the long-term equilibrium and short-term fluctuating relations between the runoff and sediment load in the source region of the Yellow River.     

一种适用于长弧段的初轨计算方法

根据单位矢量法测轨原理，在人造卫星初轨计算的单位矢量法基础上，给出了一种适用于长弧段的初轨计算方法．该方法既适用于长弧段，也适用于短弧段；适用于各种不同类型的观测资料和任意偏心率、任意轨道倾角的人造地球卫星；有利于提高初轨测定精度；并改善整个计算收敛性．特别需要指出的是，该方法与有摄初轨计算的单位矢量法相结合，为单位矢量法从初轨计算推广到轨道改进打下了坚实的基础．     

Flood hydrograph estimation from arid catchment morphology

Data on performance of a geomorphologic rainfall-runoff model in simulating observed flash flood hydrographs in 32 arid catchments have been analysed. The catchments, which are located in the southwest region of Saudi Arabia, vary in their size, slope of land, and characteristics of soils, and are in zones of different rainstorm characteristics. The sensitivity of the model accuracy with various catchment and rainfall characteristics has been investigated. Size, followed by rate of infiltration and slope of land, are the most effective catchment characteristics affecting the accuracy. In addition, the accuracy varies with spatial and temporal rainfall variation, total rainfall depth, and length of the dry period between two successive rainstorms over catchment. It is sensitive to temporal rainfall variation more than spatial rainfall variation, and to the dry period more than total rainfall depth. Generally, the model did not display an accuracy approaching that of the observations, especially in simulating peak flowrates in large size infiltrating catchments having high temporal rainstorm variation. Guidelines on the best use of the model in arid catchments were proposed.     

A case study in catchment hydrochemistry: Conflicting interpretations from hydrological and chemical observations

Soil water, stream water, groundwater and rain water were sampled through a storm event in a moorland catchment. Samples were analysed for major ions and deuterium. Chloride and deuterium are used as tracers to enable separation of the stream runoff hydrograph into three components: rain, soil and groundwater. The results indicate that rain water arrives in the stream quickly during the event and contributes a significant volume to the runoff peak. The chemical signal in the rain water is, however, significantly damped, apparently due to mixing with soil water held in the catchment before the event. This is further modified before reaching the stream, apparently through mixing with a deeper groundwater component. Interpretation of tracer, chemistry and hydrological data to present an integrated picture of catchment hydrochemical response is difficult due to problems in the chemical and conceptual definition of the flow components.