Infrastructure monitoring using passive remote imagery

大型工程结构，如铁路和公路土方工程、桥梁、管道和水坝，可能出于多种原因需要进行监测。这些措施包括监察工程的一般表现，以及在出现初步或实际故障（例如山泥倾泻）时发出警告。新的基础设施建设项目，特别是城市地区的大型地下室和隧道，可能需要广泛的监测系统，以便能够测量由此产生的地面位移，并在必要时进行补偿。这种监测的费用很高，特别是在可能偏远或无法到达的大地理区域进行监测的费用。更有效的监测和预警系统有可能节省大量资金，甚至人的生命。评估基础设施性能的最有效方法之一是测量表面变化（位移），并将不稳定或性能损失与这种变化的变化率联系起来。许多技术目前用于表面变化测量；这些包括扩展计、D-GPS系统、棱镜监测、无反射激光系统、摄影测量和干涉测量线性地面合成孔径雷达。所有这些系统都有其优点和局限性。许多都很昂贵，有些只能在有限的距离内运行，有些需要安装监控特定位置（如反射器），有些不能在黑暗或恶劣天气下运行。使用卫星图像有可能具有成本效益地测量地表变化。星载干涉合成孔径雷达（InSAR）利用轨道卫星对给定区域进行成像。卫星连续通过的图像可以用来计算地面位移。星载InSAR表面变化探测器的主要缺点是它们是为全球而不是局部区域监测目的而开发的，并且卫星重访时间很长。另一个潜在的问题是，仅使用一颗或两颗卫星，感兴趣的区域可能处于电磁阴影中（即，由于障碍物阻挡卫星信号，卫星无法照亮该区域）。这种情况尤其可能发生在城市地区或丘陵地带。最近的进展使得使用地面安装接收器的InSAR子类得以发展，即无源干涉空间-表面双基地合成孔径雷达（PInSS-BSAR）。PInSS-BSAR拓扑结构有一个固定在地面上的固定接收器，成像天线指向感兴趣的区域。相对于地表移动的卫星产生一个电磁测距信号，照亮观测区域。信号被地球表面反射，然后被雷达天线接收。通过使用两个天线，一个固定在另一个上面，就可以计算垂直方向上的位移变化。PInSS-BSAR最好使用非合作发射机，即用于其他目的的卫星。全球导航卫星系统，如GPS和伽利略提供大量的非地球同步卫星，同时在地平线上运行，以不同的角度照亮特定地区。在任何时候，卫星都应该覆盖整个地球表面，没有任何一点在电磁阴影中。这种系统的范围预计可达数公里，其持续监测的能力将提供对过度位移的有效预警。拟议的研究旨在利用PInSS-BSAR开发一种具有成本效益的监测系统来测量地表变化，具体应用于公路和铁路等线性基础设施及其相关的路堤和切割斜坡。原型设备将与现有的常规地面位移仪器进行验证，该仪器已安装用于监测两个大型失效基础设施斜坡。

Large engineering structures such as railway and highway earthworks, bridges, pipelines and dams may need to be monitored for a number of reasons. These include general performance monitoring and providing a warning of incipient or actual failure (e.g. a landslip). New infrastructure construction projects, particularly large basements and tunnels in urban areas, may require extensive monitoring systems to enable the resulting ground displacements to be measured and compensated for where necessary. The cost of such monitoring, especially over large geographical areas which may be remote or inaccessible, is significant. More efficient monitoring and early warning systems have the potential to save large sums of money, and even human life. One of the most effective ways of assessing the performance of infrastructure is to measure surface variation (displacement) and relate instability or loss of performance to the rate of change of this variation. A number of technologies are currently used for surface variation measurement; these include extensometers, D-GPS systems, prism monitoring, reflectorless laser systems, photogrammetry, and interferometric linear ground based synthetic aperture radar. All of these systems have advantages and limitations. Many are expensive, some only operate over limited distances, others require installations to monitor particular locations (such as reflectors), and some will not operate in the dark or in poor weather.The use of satellite imagery offers the potential for cost-effective measurement of surface variations. Spaceborne Interferometric Synthetic Aperture Radars (InSAR) make use of orbiting satellites to image a given area. Images from successive passes of the satellite can be used to calculate ground displacements. The primary drawback with spaceborne InSAR surface change detectors is that they were developed for global, rather than local, area monitoring purposes and have a long satellite revisit time. Another potential problem is that using only one or two satellites, an area of interest could be in an electromagnetic shadow (i.e., the satellite cannot illuminate the area due to an obstacle blocking the satellite signal). This can occur especially in urban areas or hilly terrain.Recent advances have enabled the development of a subclass of InSAR using ground surface mounted receivers, the Passive Interferometric Space-Surface Bistatic Synthetic Aperture Radar (PInSS-BSAR). The PInSS-BSAR topology has a stationary receiver fixed on the ground, with the imaging antennae pointed towards the area of interest. A satellite moving relative to the surface generates an electromagnetic ranging signal illuminating the observation area. The signal is reflected by the earth's surface, and received by the radar antennae. By using two antennae, one fixed above the other, it will be possible to calculate the change in displacement in the vertical direction. PInSS-BSAR is best utilised using non-cooperative transmitters, i.e. satellites being used for other purposes. Global Navigation Satellite Systems, such as GPS and Galileo provide large numbers of non-geostationary, simultaneously operating satellites above the horizon, which illuminate a particular region at different angles. At any time, the satellites should cover the entire surface of the planet without any points in electromagnetic shadow. The range of such as system is expected to be kilometres, and its ability to monitor continuously will provide effective early warning of excessive displacements.The proposed research seeks to develop a cost-effective monitoring system using PInSS-BSAR to measure surface variations, with specific application to linear infrastructure such as roads and railways, and their associated embankment and cutting slopes. The prototype device will be verified against existing conventional surface displacement instrumentation already installed to monitor two large failing infrastructure slopes.