2020年2月3日四川青白江5.1级地震总结     

韩颜颜  马亚伟  解孟雨  臧阳  苑争一  于晨  田雷  王月  张小涛  姚琪  薛艳  韦进 《地震地磁观测与研究》2020,41(5):141-152

针对2020年2月3日四川青白江5.1级地震发生前的地震活动和地球物理观测异常、构造背景、震源物理参数，以及地震序列特征等进行系统总结。结果表明，青白江5.1级地震发生前存在小震调制比高值、地磁低点位移、重力固体潮高噪声等中短期异常；地震序列活动特征显示，此次地震为一次孤立型地震序列，序列参数计算结果与当前余震活动水平基本相符。另外，青白江地震发生在龙泉山断裂带上，震源机制计算结果显示为一次逆冲型破裂事件，与龙泉山断裂构造性质一致。同时，此次地震发生在四川盆地的少震弱震区，对于川滇及川滇藏交界地区后续7级以上地震的发生具有一定预测意义。  相似文献   

Assessment of a new solution for tracking pebbles in rivers based on active RFID          下载免费PDF全文

Mathieu Cassel  Thomas Dépret  Hervé Piégay 《地球表面变化过程与地形》2017,42(13):1938-1951

Low‐frequency passive integrated transponders (PIT tags), are commonly used for monitoring pebble mobility in gravel‐bed rivers. Although early studies reported high recovery rates for PIT tags used in small streams, recovery rates in larger systems remain low, substantially limiting the possibilities for their use in such rivers. These low recovery rates are potentially due to missed detections caused by tag signal collision, burial in the sediment layer deeper than the maximum detection range and insufficient (but still exhausting) field effort to cover the concerned areas. A potential solution for addressing these problems is to use active ultra‐high frequency (a‐UHF) transponders as these have a greater detection range and anti‐collision protocols. In order to assess the potential of such transponders for pebble tracking in rivers, we used 433.92 MHz COIN‐ID and COIN‐HC models (ELA Innovation Company, Montpellier, France). We completed several tests to (i) characterize transponder detection ranges in the water and in saturated sediment and (ii) develop field protocols for locating tags by combining global positioning systems (GPS) sites and transponder received signal strength indication (RSSI) levels. The results showed that (i) the maximum detection ranges are about 2.4 m in the water column and more than 2.6 m in a column of saturated gravelly‐sandy sediment, (ii) RSSI spatial interpolation can be used to determine transponder position with good accuracy (< 1 m), (iii) the desired minimal level of accuracy can be adjusted depending on in‐field effort and signal impulse interval, (iv) the RSSI maximal value observed cannot yet be used to determine transponder burial depth because of the multipath propagation of radio frequencies and the semi‐directional emission of the tag signal. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Characteristics of eigen-system for flexural gravity wave problems     

S. Mandal  A. Chakrabarti 《地球物理与天体物理流体动力学》2017,111(4):249-281

For a class of boundary value problems associated with flexural gravity waves, characteristics of the eigen-system are analysed which are used to study the convergence of the expansion formulae in both cases of single and two layer fluids in water of finite and infinite depths. Using Green’s function technique, the spectral representations of the vertical eigenfunctions are obtained which are used along with the orthogonal mode-coupling relations to prove the convergence of the expansion formulae. Using the expansion formulae flexural gravity wave scattering due to multiple articulations in the presence of compression are investigated. The problem is studied in both the cases of single-layer and two-layer fluids in finite water depth. Effects of compressive force, stiffness of the connectors, length of the elastic plates and water depth, position of interface on wave scattering by articulated plates are studied by analysing the reflection and transmission coefficients. This procedure of proving the convergence of expansion formulae is independent of water depth. The concept and methodology for dealing with wave-structure interaction problems discussed here can be generalised to deal with problems of similar nature arising in the broad area of mathematical physics and engineering.  相似文献   

缺少控制点的星载SAR遥感影像对地目标定位   总被引：4，自引：2，他引：2  

袁修孝  吴颖丹 《武汉大学学报(信息科学版)》2010,(1)

从距离和多普勒方程出发,构建了无需地面控制点的直接对地目标定位模型,推导了缺少控制点时的精化轨道参数及成像几何参数等的数学模型。经过对北京某地区一景ENVISAT ASAR影像进行直接对地目标定位,获得了实地上±170.966 m(约±8.7像素)的平面精度;利用单个地面控制点对星载SAR影像的定向参数实施调整后,对地目标定位平面精度提高到±54.665 m(约±2.8像素),控制点数目增加到4个时,对地目标定位平面精度接近±2像素。结果显示,对困难地区采用星载SAR遥感影像对地目标定位具有很好的应用前景。  相似文献   

GPS在机载雷达测速精度鉴定中的应用     

王云河  王存良 《全球定位系统》2010,35(2):5-8

论述了利用GPS来鉴定机载雷达的测速精度，推导了雷达对目标径向的速度基准值计算公式及其精度计算公式，并计算了该速度基准值及其精度，结果表明：能够满足速度基准值精度要求。强调了在做测速精度鉴定方案时，需要计算在被鉴定速度方向上的速度基准值精度是否满足要求。  相似文献   

岩石加速破裂行为的物理自相似律   总被引：4，自引：0，他引：4       下载免费PDF全文

杨百存  秦四清  薛雷  陈竑然  吴晓娲  张珂 《地球物理学报》2017,60(5):1746-1760

掌握岩石变形破坏过程中体积膨胀点至峰值强度点之间加速破裂行为的演化规律,是实现地质灾害物理预测的关键.本文考虑裂纹张开和闭合两种情况,基于断裂力学建立了三轴应力作用下裂纹扩展临界尺度与等效应力的关系.对微元体破坏概率,分别采用以等效应力表达的Weibull分布函数和裂纹尺度分形函数,通过对比导出了形状参数m与裂纹分布分维D_f关系的表达式.一个有趣的发现是,岩石峰值强度点与体积膨胀点应变比仅与m或D_f有关.对岩石蠕变或准蠕变破坏,合理的m值范围为[1.0,4.0],在此范围内应变比近似为常数1.48,该常数是描述不同尺度岩石加速破裂规律的物理自相似常数.实例分析表明,基于岩石加速破裂规律构建的多锁固段脆性破裂理论,其适用性广,尤其在崩滑和大地震预测领域,具有良好应用前景.此外,本文给出了b值与m值定量关系,以解释b值的物理意义,并探讨将其用于地震预测的可行性.  相似文献   

Nonlinear adaptive control of an underwater towed vehicle     

Francisco Curado Teixeira  António Pedro Aguiar 《Ocean Engineering》2010,37(13):1193-1220

This paper addresses the problem of simultaneous depth tracking and attitude control of an underwater towed vehicle. The system proposed uses a two-stage towing arrangement that includes a long primary cable, a gravitic depressor, and a secondary cable. The towfish motion induced by wave driven disturbances in both the vertical and horizontal planes is described using an empirical model of the depressor motion and a spring-damper model of the secondary cable. A nonlinear, Lyapunov-based, adaptive output feedback control law is designed and shown to regulate pitch, yaw, and depth tracking errors to zero. The controller is designed to operate in the presence of plant parameter uncertainty. When subjected to bounded external disturbances, the tracking errors converge to a neighbourhood of the origin that can be made arbitrarily small. In the implementation proposed, a nonlinear observer is used to estimate the linear velocities used by the controller thus dispensing with the need for costly sensor suites. The results obtained with computer simulations show that the controlled system exhibits good performance about different operating conditions when subjected to sea-wave driven disturbances and in the presence of sensor noise. The system holds promise for application in oceanographic missions that require depth tracking or bottom-following combined with precise vehicle attitude control.  相似文献   

3维重构精度估计的矩阵分析方法     

夏科蕊  孙敏 《测绘软科学研究》2010,(3):54-58

3维重构可以由影像序列快捷方便地提取目标的3维几何信息。但3维重构的基础是多视几何理论,其计算是基于矩阵推导的非线性过程,故传统摄影测量理论难以用于评估其误差,本文提出一种3维重构精度的估计方法,采用矩阵分析方法,给出了评定重构精度的推导过程,并结合实验数据验证了精度估计的正确性。  相似文献   

一种新的BOC调制无模糊跟踪鉴别器设计     

唐斌  郭盛桃  刘富 《全球定位系统》2010,35(5):16-20

建立了导航接收机码跟踪延迟锁定环的数学模型，讨论了DP和EMLP鉴别器在不同信号、不同前端滤波器带宽的鉴别曲线特性，阐述了BOC调制模糊跟踪产生的原因。针对BOC调制信号的模糊跟踪问题，从BOC调制的机理出发，将BOC调制分成伪码和副栽波两部分分析，阐述了一种新的鉴别器设计。实验表明：新鉴别器设计，鉴别曲线线性跟踪区域斜率最高为9，可实现BOC调制的无模糊跟踪。  相似文献   

GPS软件接收机跟踪通道信号统计分析     

李作虎  史俊文  刘雪瑞  贾赞杰 《测绘学院学报》2010,(2)

传统的基于硬件的接收机由于芯片的封装性很难用来进行通道信号的分析研究,而基于软件无线电技术的软件接收机则很容易做到。软件接收机的跟踪通道信号统计分析可用于接收机算法的测试与比对以及卫星信号性能的分析与评估。这里搭建了GPS软件接收机L1中频数字信号处理平台,对跟踪通道输出的I、Q支路信号进行了均值、标准方差以及均方根(RMS)统计。分析了各统计值与通道对应卫星的高度角、信号强度以及噪声之间的关系。基于统计结果提出了一种估计信道信噪比的方法。最后比较了不同信号采样频率对相关三角形和导航定位解算精度的影响。  相似文献