环境激励下桥梁结构模态频率与波速变化监测研究

基于环境激励的桥梁健康监测方法是未来的发展方向。我们采用宽频带地震计Guralp CMG-6TD,建立了在线桥梁监测系统,对北京市昌平区鲁疃西路大桥进行了连续监测。分别使用随机子空间识别获得桥梁模态参数和尾波干涉法监测桥梁波速变化。结果表明：（1）采用的高灵敏度宽频带速度型地震计,能够连续准确记录宽频带范围内的三分量振动信号,非常适用于长期桥梁动态监测;（2）基于连续记录的环境激励信号,随机子空间法能够稳定可靠地识别桥梁低阶模态参数,尾波干涉法能够连续精确地监测桥梁材料的细微波速变化;（3）温度变化会引起桥梁材料的弹性模量发生显著变化。波速变化呈现振幅为1%的日变化特征,与温度变化呈明显的反相关性,温度敏感系数约为。同时模态频率的变化不太明显,说明波速可能是比模态频率更为敏感的量化损伤指标;（4）模态频率是桥梁整体状态的一种度量,而波速变化可以监测桥梁局部材料弹性性质的变化。将这两者结合起来,利用环境激励信号,连续准确识别桥梁模态频率以及监测波速变化,对于桥梁健康监测具有潜在重要应用价值。     

永久散射体差分干涉测量技术中SAR影像精配准的一种新方法

提出并实现了一种基于加权最小二乘的低相干SAR像对精配准新方法。该方法借助一幅与主、辅影像相干性都较高的第三幅影像来完成低相干SAR影像对的初步配准,利用加权最小二乘法求出二者间的坐标映射函数,从而快速高效地实现低相干SAR影像对的高精度亚像元级配准。采用ERS-1/2实际数据的配准实验,验证了该方法可以提高低相干SAR像对的干涉图质量,提高二者之间的相干性和控制点的配准精度,改善低相干SAR影像对的配准效果,在一定程度上解决了PS InSAR技术中低相干SAR影像对的配准问题。     

相位补偿SAR差分干涉提取山区DEM算法及精度分析

首先,将去平干涉相位和外部DEM模拟的地形相位作差分,以降低干涉图的条纹率。然后,采用模拟的地形相位对差分干涉图的解缠相位进行补偿得到去平干涉图的解缠相位,并用此相位进行基线精化和高程提取。实验结果表明,该算法可得到高程精度更高的山区DEM。与常规干涉算法相比,它不仅可改善解缠精度,还可得到更加真实且相干性明显改善的相干图,减少因相干性低于解缠时设定的相干性阈值而产生的高程空洞区。相比于＂高程补偿＂算法,其可更有效地削弱残余系统相位以及解缠和外部DEM引入的随机相位误差的影响。     

Sentinel-1 TOPS影像干涉处理与形变监测

Sentinel-1A IW模式可获取250 km宽的SAR影像,且噪声小、重访周期短。然而Sentinel-1A的TOPS成像方式造成SAR影像方位向多普勒频率变化较大,干涉数据处理对影像配准要求极高。提出基于DEM和精密轨道的TOPS影像高精度配准和拼接方法,实现TOPS影像干涉变形监测的数据处理,并利用升降轨TOPS影像数据获取门源地震雷达视线向一致的同震变形,证实本文数据处理方法的正确性。     

高分辨率SAR数据在河北省城市形变监测中的应用

针对传统形变监测难以在短时间内进行大面积形变监测的问题,结合基于时间序列的雷达差分干涉测量(PS-InSAR)技术,以TerraSAR-X数据为例,重点研究了高分辨率SAR数据在城市地表形变监测中的应用,并对石家庄市、沧州市城区进行了监测,使用了2013年和2014年间各37景数据,采用了SARPROZ软件进行数据处理。实验结果显示,在石家庄市和沧州市各有三处较大形变区域。根据历史水文地质数据资料对比显示,产生形变的区域主要为地下水漏斗区域和大型建筑施工区域。在对石家庄市的分析结果中还发现,由于建筑施工造成了高铁沿线周边区域的较大沉降。此外,经过与沧州市历史沉降资料对比发现,传统沉降区已得到了有效的控制。总体而言,高分辨率SAR影像差分干涉技术为城市大面积地表形变分析提供了一种行之有效的监测手段,对传统沉降区的持续监测、高铁运行、地铁施工建设等具有重要参考意义。     

Astrometry from Space: New Design of the GAIA Mission

An interferometric astrometric mission, aiming at accuracies at around the10 microarcsec level, was recommended as a high priority concept within thenew ESA Horizon 2000+ scientific programme. The original outline concept forsuch a mission, GAIA, presented its general feasibility but did not addressmany questions of implementation or optimisation. Another concept of aninterferometer for a scanning astrometric satellite is presented. It containsa simpler optical telescope and a more efficient detector system. The designutilizes the full resolution of all light in the dispersed fringes of aFizeau interferometer. A preliminary optimization of the satellite indicatesthat two telescope units with a baseline of 100 cm will achieve a precisionof 3, 8, 22, 68, 302 microarcsec for parallaxes of stars with V = 12, 14, 16, 18, 20 mag, respectively, from a 5 year mission. Simultaneousspectrophotometry of the entire spectrum of each star will be obtained with aresolution corresponding to intermediate band photometry. The expectedprecision of this photometry is about 0.003 mag for V = 16. The performance is good in crowded fields, at least up to one star per 5 arcsec2. A Hipparcos-type beam combiner of 150 cm width is placed in front of atelescope with 4 square apertures of 50 cm. The assumed focal length is f = 60 m and the field 0.5 degree diameter. The detector consists of CCDs used for time delayed integration (drift-scan.)     

Ska and Evla Computing Costs for Wide Field Imaging

I investigate the problem of high dynamic range continuum synthesis imaging in the presence of confusing sources, using scaling arguments and simulations. I derive a quantified cost equation for the computer hardware needed to support such observations for the EVLA and the SKA. This cost has two main components – from the data volume, scaling as D⁻⁶ (where D is the antenna diameter), and from the non-coplanar baselines effect, scaling as D⁻², for a total scaling of D⁻⁸. A factor of two in antenna diameter thus corresponds to 12 years of Moore’s law (18 month doubling time) cost reduction in computing hardware. For a SKA built with 12.5 m antennas observing with 1 arcsecond at 1.4 GHz, I find the computing load to be about 150 Petaflops (costing about $500 million in 2015). For 25 m antennas, the load is about 256 times lower, costing $2 million in 2015. This new cost equation differs from that of Perley and Clark (2003), which has scaling as D⁻⁶. This is because I find that the excellent Fourier plane coverage of the small antenna design does not significantly change the convergence rate of the Clean algorithm, which is already satisfactory in this regime.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.     

雷达差分干涉测量

合成孔径雷达 (SAR)差分干涉测量 (D -InSAR)是利用SAR图像的相位信息提取地表沿雷达视线向的形变信息的一种有效手段。该文阐述D -InSAR的基本原理 ,分析该技术在地震监测、火山研究和细微的地表形变监测等方面的应用研究 ,并分析未来D -InSAR的应用前景。     

基于区域分割和编码的相位解缠方法

分析了相位解缠的原理及干涉条纹数据的特点，提出了一种基于中值自适应滤波，区域分割和编码的解缠方法。实验证明了该方法的可行性。     

Survey and monitoring of landslide displacements by means of L-band satellite SAR interferometry

This paper illustrates the capabilities of L-band satellite SAR interferometry for the investigation of landslide displacements. SAR data acquired by the L-band JERS satellite over the Italian and Swiss Alps have been analyzed together with C-band ERS-1/2 SAR data and in situ information. The use of L-band SAR data with a wavelength larger than the usual C-band, generally considered for ground motion measurements, reduces some of the limitations of differential SAR interferometry, in particular, signal decorrelation induced by vegetation cover and rapid displacements. The sites of the Alta Val Badia region in South Tyrol (Italy), Ruinon in Lombardia (Italy), Saas Grund in Valais (Switzerland) and Campo Vallemaggia in Ticino (Switzerland), representing a comprehensive set of different mass wasting phenomena in various environments, are considered. The landslides in the Alta Val Badia region are good examples for presenting the improved performance of L-band in comparison to C-band for vegetated areas, in particular concerning open forest. The landslides of Ruinon, Saas Grund, and Campo Vallemaggia demonstrate the strength of L-band in observing moderately fast displacements in comparison to C-band. This work, performed with historical SAR data from a satellite which operated until 1998, demonstrates the capabilities of future planned L-band SAR missions, like ALOS and TerraSAR-L, for landslide studies.