GPS�߳�ת����������С���˷����о�

????????????GPS????????????GPS????????е?????????????????????????????????????????С?????????????????????????????ζ???????桢???ζ???????桢??????ζ???????????????????о?????????С??????????????С?????????????С?????????и???????????????????????????????е???????????????С?????????????и???????????????????     

A new method to determine the tropopause

The tropopause has a complex structure and some interference information may exist in high-resolution global positioning system （GPS）/low earth-orbiting （LEO） radio occultation （RO） data. The position of the tropopause cannot be accurately determined using traditional cold point tropopause （CPT） and lapse rate tropopause （LRT） algorithms. In this paper, an integrative algorithm is developed to determinate tropopause parameters. The algorithm is applied to GPS/COSMIC RO data to obtain a global distribution of the height and temperature of the tropopause. This algorithm improves the utilization rate of GPS/LEO RO data by 30% compared with that from the traditional CPT method. The rationality and reliability of GPS/LEO RO data in probing the Earth＇s atmosphere are verified by our study of the tropopause using COSMIC data.     

通用劈窗算法的NOAA-18(N)AVHRR/3数据地表温度遥感反演与验证

本文以NOAA-18(N)AVHRR/3数据,运用通用劈窗技术获得地表温度。首先,利用MODTRAN 4模拟不同地表和大气状况下热红外通道(Ch4,10.3~11.3μm和Ch5,11.5~12.5μm)的星上亮温,并建立模拟数据库。其次,按照地表温度、大气可降水汽含量、地表比辐射率和观测天顶角,对模拟数据库分组,确定出各分组的通用劈窗算法系数。然后,将构建的地表温度反演模型应用到NOAA-18(N)AVHRR/3数据,模型所需的地表比辐射率由NDVI阈值法确定,大气可降水汽含量是利用Li等(2003)提出的一种劈窗的协方差与方差比的方法来估算。反演结果表明:在观测天顶角小于30°或者大气可降水汽含量小于3.5 g/cm2时,地表温度反演的均方根误差小于1.0K;在观测天顶角小于45°并且大气可降水汽含量小于5.5g/cm2情况下,均方根误差小于1.5K。最后,利用美国通量站的实测数据对地表温度反演结果进行了验证,结果表明均方根误差小于1.8K。     

叠前三参数非高斯反演方法研究

针对地球物理反演中广泛采用的"噪声高斯分布假设",本文研究了叠前地震资料中噪声的非高斯分布特征,提出了针对非高斯噪声的地震叠前非高斯反演概念和思想,构造了能同时压制高斯和非高斯噪声的混合范数作为反演目标函数,采用改进的Powell算法进行求解,有效地抑制了叠前地震资料中的高斯和非高斯混合噪声.模型试算和实际地震数据的反演结果验证了方法的正确性和算法的可靠性.     

煤矿矿震定位中异向波速模型的构建与求解

针对煤矿上覆岩层层状赋存和离层带的特点,构建矿井尺度的微震监测系统异向波速模型,模型中波速向量由地面探头速度与井下探头速度组成.研究了在只有强矿震信号和混有爆破信号两种条件下,以到时残差最小为目标和震源定位误差最小为目标的两种求解模型,模型求解选用具有全局寻优特性的遗传算法与CMEAS算法结合的混合算法.现场实际应用得出,只使用爆破信号的到时残差法最优,混有强矿震信号的到时残差法其次;与爆破信号定位所用的统一简化波速模型相比,震源定位误差大幅度降低.在此基础上进一步减低定位误差,还需从微震台网的优化布设方面解决.     

利用计算机断层成像方法由观测图像重建等离子体层全球密度分布——投影数据不完备问题

在用计算机断层成像方法由EUV观测图像重建等离子体层全球密度分布时,地球的遮挡和有限角度都会导致投影数据不完备,从而无法精确重建出等离子体层的密度分布.本文针对该问题,提出一种基于图像总变差极小化的代数迭代算法.通过重建等离子体层投影数据缺失最为严重的中心子午面,证明该算法能够显著提高重建图像的质量. 并且在IMAGE卫星仅能达到90°的有限投影角度下,此算法重建图像的相关系数可达0.760,而代数迭代算法的相关系数仅为0.696.     

2003年青海德令哈6.7级地震序列的震源机制解及其构造含义

利用8个流动数字地震台和国家数字地震台站的地震波形记录,测量了2003年4月17日青海德令哈6.7级地震及其主要余震的直达P波、SV波、SH波的初动方向和振幅比,应用Snoke(2003)的测定震源机制解的格点尝试法,测定出德令哈地震序列的48个2.4级以上地震的震源机制解.搜集分析了美国哈佛大学测定的德令哈6.7级主震和2004年二期地震活动中的7个地震的震源机制解.基于余震空间分布特征和对震源机制解特征的分析,讨论了德令哈地震序列的可能断层活动方式和地震的构造含义.结果表明,主震和大部分余震都是沿NWW-SEE走向的逆断层错动,北边的上盘可能沿低角度向北倾的断层面向南仰冲;个别正断层余震可能是震源区挤压变形弧顶区附近发生的局部张性破裂;在二期地震活动中,逆断层和走滑断层都有,走滑断层地震主要发生在震源区东侧.德令哈地震活动是青藏高原东北缘NWW-SEE向延伸的挤压带继续处于隆升活动中的表现,这一继承性新构造运动是德令哈地震序列的可能发震原因.     

Frequency‐domain acoustic‐elastic coupled waveform inversion using the Gauss‐Newton conjugate gradient method

We developed a frequency‐domain acoustic‐elastic coupled waveform inversion based on the Gauss‐Newton conjugate gradient method. Despite the use of a high‐performance computer system and a state‐of‐the‐art parallel computation algorithm, it remained computationally prohibitive to calculate the approximate Hessian explicitly for a large‐scale inverse problem. Therefore, we adopted the conjugate gradient least‐squares algorithm, which is frequently used for geophysical inverse problems, to implement the Gauss‐Newton method so that the approximate Hessian is calculated implicitly. Thus, there was no need to store the Hessian matrix. By simultaneously back‐propagating multi‐components consisting of the pressure and displacements, we could efficiently extract information on the subsurface structures. To verify our algorithm, we applied it to synthetic data sets generated from the Marmousi‐2 model and the modified SEG/EAGE salt model. We also extended our algorithm to the ocean‐bottom cable environment and verified it using ocean‐bottom cable data generated from the Marmousi‐2 model. With the assumption of a hard seafloor, we recovered both the P‐wave velocity of complicated subsurface structures as well as the S‐wave velocity. Although the inversion of the S‐wave velocity is not feasible for the high Poisson's ratios used to simulate a soft seafloor, several strategies exist to treat this problem. Our example using multi‐component data showed some promise in mitigating the soft seafloor effect. However, this issue still remains open.     

Analysis of implicit HHT‐α integration algorithm for real‐time hybrid simulation

Real‐time hybrid simulation is a viable experiment technique to evaluate the performance of structures equipped with rate‐dependent seismic devices when subject to dynamic loading. The integration algorithm used to solve the equations of motion has to be stable and accurate to achieve a successful real‐time hybrid simulation. The implicit HHT α‐algorithm is a popular integration algorithm for conducting structural dynamic time history analysis because of its desirable properties of unconditional stability for linear elastic structures and controllable numerical damping for high frequencies. The implicit form of the algorithm, however, requires iterations for nonlinear structures, which is undesirable for real‐time hybrid simulation. Consequently, the HHT α‐algorithm has been implemented for real‐time hybrid simulation using a fixed number of substep iterations. The resulting HHT α‐algorithm with a fixed number of substep iterations is believed to be unconditionally stable for linear elastic structures, but research on its stability and accuracy for nonlinear structures is quite limited. In this paper, a discrete transfer function approach is utilized to analyze the HHT α‐algorithm with a fixed number of substep iterations. The algorithm is shown to be unconditionally stable for linear elastic structures, but only conditionally stable for nonlinear softening or hardening structures. The equivalent damping of the algorithm is shown to be almost the same as that of the original HHT α‐algorithm, while the period elongation varies depending on the structural nonlinearity and the size of the integration time‐step. A modified form of the algorithm is proposed to improve its stability for use in nonlinear structures. The stability of the modified algorithm is demonstrated to be enhanced and have an accuracy that is comparable to that of the existing HHT α‐algorithm with a fixed number of substep iterations. Both numerical and real‐time hybrid simulations are conducted to verify the modified algorithm. The experimental results demonstrate the effectiveness of the modified algorithm for real‐time testing. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient risk assessment of lifeline networks under spatially correlated ground motions using selective recursive decomposition algorithm

For effective hazard mitigation planning and prompt-but-prudent post-disaster responses, it is essential to evaluate the reliability of infrastructure networks accurately and efficiently. A nonsimulation-based algorithm, termed as a recursive decomposition algorithm (RDA), was recently proposed to identify disjoint cut sets and link sets and to compute the network reliability. This paper introduces a ‘selective’ RDA, which preferentially identifies critical disjoint cut sets and link sets to calculate the probabilities of network disconnection events with a significantly reduced number of identified sets. To this end, the original RDA is improved by replacing the shortest path algorithm with an algorithm that identifies the most reliable path, and by using a graph decomposition scheme based on the probabilities associated with the subgraphs. The critical sets identified by the algorithm are also used to compute conditional probability-based importance measures that quantify the relative importance of network components by their contributions to network disconnection events. This paper also introduces a risk assessment framework for lifeline networks based on the use of the selective RDA, which can consider both interevent and intraevent uncertainties of spatially correlated ground motions. The risk assessment framework and the selective RDA are demonstrated by a hypothetical network example, and the gas and water transmission networks of Shelby County in Tennessee, USA. The examples show that the proposed framework and the selective RDA greatly improve efficiency of risk assessment of complex lifeline networks, which are characterized by a large number of components, complex network topology, and statistical dependence between component failures. Copyright © 2012 John Wiley & Sons, Ltd.