热红外通道沙尘识别及敏感性分析

沙尘识别是沙尘灾害监测和沙尘气溶胶特性研究的首要工作。利用辐射传输方程进行了沙尘气溶胶的辐射计算，对不同沙尘气溶胶光学厚度下的热红外通道温差ΔT（T_11μm-T_12μm）的变化进行了分析，并针对水汽和陆地表面温度进行了敏感性分析。发现随着沙尘气溶胶光学厚度的增加，ΔT逐渐减小。理论分析表明，利用热红外通道的温度差ΔT进行陆地沙尘识别是可行的。进一步，利用NOAA-AVHRR热红外通道的温度差ΔT < 0进行了3次陆地沙尘识别，经与地面气象站观测的沙尘天气现象相比较，结果基本一致。     

A simple LMS‐based approach to the structural health monitoring benchmark problem

A structure's health or level of damage can be monitored by identifying changes in structural or modal parameters. However, the fundamental modal frequencies can sometimes be less sensitive to (localized) damage in large civil structures, although there are developing algorithms that seek to reduce this difficulty. This research directly identifies changes in structural stiffness due to modeling error or damage using a structural health monitoring method based on adaptive least mean square (LMS) filtering theory. The focus is on computational simplicity to enable real‐time implementation. Several adaptive LMS filtering based approaches are used to analyze the data from the IASC–ASCE Structural Health Monitoring Task Group Benchmark problem. Results are compared with those from the task group and other published results. The proposed methods are shown to be very effective, accurately identifying damage to within 1%, with convergence times of 0.4–13.0 s for the twelve different 4 and 12 degree of freedom benchmark problems. The resulting modal parameters match to within 1% those from the benchmark problem definition. Finally, the methods developed require 1.4–14.0 Mcycles of computation and therefore could easily be implemented in real time. Copyright © 2004 John Wiley & Sons, Ltd.     

Active sensing using impedance‐based ARX models and extreme value statistics for damage detection

In this paper, the applicability of an auto‐regressive model with exogenous inputs (ARX) in the frequency domain to structural health monitoring (SHM) is established. Damage sensitive features that explicitly consider non‐linear system input/output relationships are extracted from the ARX model. Furthermore, because of the non‐Gaussian nature of the extracted features, Extreme Value Statistics (EVS) is employed to develop a robust damage classifier. EVS provides superior performance to standard statistical methods because the data of interest are in the tails (extremes) of the damage sensitive feature distribution. The suitability of the ARX model, combined with EVS, to non‐linear damage detection is demonstrated using vibration data obtained from a laboratory experiment of a three‐story building model. It is found that the vibration‐based method, while able to discern when damage is present in the structure, is unable to localize the damage to a particular joint. An impedance‐based active sensing method using piezoelectric (PZT) material as both an actuator and a sensor is then investigated as an alternative solution to the problem of damage localization. Copyright © 2005 John Wiley & Sons, Ltd.     

Detection of spheriodal free oscillation excited by Peru 8.2 M_s earthquake with five international superconducting gravimeter data

In this paper, authors obtain the spectral peaks of the earth free oscillation and check all normal modes from 0S0 to 0S48 accurately, with the Fourier analysis and the maximum entropy spectrum method dealing jointly with six groups of the observational residual data from five international superconducting gravimeter stations. By comparing the observational results in this paper with three former groups of observations or models, authors notice an extra discrepancy between two observational 0S2 modes excited separately by Peru earthquake and Alaska earthquake, which probably mirrors the anisotropy of the Earth's inner core. The analysis on the splitting 1S2 mode shows that the asymmetric factor of rotationwise spectral splitting is possible to be different from that of anti-rotationwise spectral splitting.     

MNF与MAD变换相结合的城市扩展研究

针对传统变化检测方法存在的缺陷，将最小噪声比率变换(Minimum Noise Fraction, MNF)和多元变化检测(Multivariate Alteration Detection, MAD)方法应用于东营市城市扩展分析。从MNF和MAD变换获得的影像中提取的二值图像可知，检测结果总体精度达到90.1%，Kappa系数为0.802，证明了本文方法在变化区域检测方面的可操作性和有效性。     

局域网络故障检测技术方法

局域网络故障可分为常规故障和非常规故障。对常规故障应采用检查操作对象、分段检测、逐一排除、最终定位故障源的技术方法;非常规故障是一种既复杂又无规则的常见问题,对此种故障应采取屏幕提示、理论分析、经验判断等相结合的技术手段最终定位故障源。     

Identifying environmental impacts of underground construction

Dewatering of the groundwater resource and associated reduced flow of surface water features are potential negative impacts when constructing underground facilities. Little work has been done to develop methods for the early detection of environmental impacts on water resources where major underground construction is being undertaken. Recognizing this, prior to construction of two rock tunnels in the southwestern USA, a 3-year preconstruction program was implemented to monitor over 100 wells, springs, and streams in the project area that might be affected. This preconstruction monitoring phase has established data for a hydrologic reference which indicates a high degree of spatial and temporal variability. This variability must be accounted for when trying to identify construction-related impacts. The project area was subdivided into areas of similar characteristics based on geologic and hydrologic features. Measurements from features within each unit were then normalized and aggregated to derive a single representative flow parameter. This representative flow was then correlated to precipitation and major stream flow records to allow for a method of estimating unimpacted flow and groundwater levels during and after construction. Application of this method proved useful in determining and enabling a quick response to construction-related impacts.     

Spatial distribution of rainfall trends in Sicily (1921-2000)

The feared global climate change could have important effects on various environmental variables including rainfall in many countries around the world. Changes in precipitation regime directly affect water resources management, agriculture, hydrology and ecosystems. For this reason it is important to investigate the changes in the spatial and temporal rainfall pattern in order to improve water management strategies.In this study a non-parametric statistical method (Mann-Kendall rank correlation method) is employed in order to verify the existence of trend in annual, seasonal and monthly rainfall and the distribution of the rainfall during the year. This test is applied to about 250 rain gauge stations in Sicily (Italy) after a series of procedures finalized to the estimation of missing records and to the verification of data consistency.In order to understand the regional pattern of precipitation in Sicily, the detected trends are spatially interpolated using spatial analysis techniques in a GIS environment.The results show the existence of a generalized negative trend for the entire region.     

基于整体变分模型的影像阴影检测算法研究

将影像上普遍存在的阴影视为图像退化的一种特殊形式，以整体变分模型为基础，以影像上阴影区域亮度普遍较暗且较均匀、阴影区域和非阴影区域之间的反差普遍较大的特点为约束，导出了整体变分模型用于影像上阴影检测的基本算法。通过对若干幅实际影像的阴影检测实验表明，本文算法对灰度影像和彩色影像上阴影区域的检测是有效的。     

基于摄动有限元方法对梁结构损伤的识别

结构损伤的定量识别是工程技术中急待解决的问题。利用矩阵摄动和结构有限元动力学理论推出梁结构损伤程度定量识别的公式和方法,该方法仅需要在役结构的固有频率测量值就可识别结构的损伤位置和损伤程度,而且可以识别结构的老化程度,避免了由模态振型识别损伤,因测量自由度不足带来的误差,通过对一钢悬臂梁损伤识别的数值仿真,证明了该方法的有效性。该方法具有较大的工程应用价值。