Infrastructure monitoring using passive remote imagery

Lead Research Organisation: University of Birmingham
Department Name: Electronic, Electrical and Computer Eng

Abstract

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.

Publications

10 25 50
 
Description The key outcome is that within the project it was experimentally proven that passive radar imaging can be used for monitoring surface displacement with a sub-centimetre accuracy.
Exploitation Route All the key research results have been published including open access journal and used in industry
Sectors Aerospace, Defence and Marine,Electronics,Environment,Transport

 
Description ESA EGEP
Amount € 150,000 (EUR)
Funding ID ESA/EGEP/ID.89 
Organisation European Space Agency 
Sector Public
Country France
Start 01/2014 
End 01/2016
 
Description Responsive mode
Amount £450,000 (GBP)
Funding ID ES/N01846X/1 
Organisation Economic and Social Research Council 
Sector Public
Country United Kingdom
Start 08/2016 
End 07/2019
 
Description Space for Rail
Amount £50,000 (GBP)
Organisation European Space Agency 
Sector Public
Country France
Start 05/2016 
End 09/2016
 
Title Signal synchronisation and image formation algorithms 
Description The proposed topology compares consecutive bistatic radar images to measure changes in the observed area during the time interval between measurements. To obtain these images, signal synchronisation as well as image formation algorithms have been built. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact The two developed algorithms enable image formation for GNSS transmissions 
 
Title Surface change measurements under controlled environment 
Description One of the project requirements is to assess the performance of the proposed topology for surface change measurements under ideal conditions. To do this, an experimental test-bed was built on the roof of our department (more information on the test bed can be found at the Physical outputs section). The height of a reference point was manually varied by known amounts, and long-term measurements were conducted over 6 months to investigate the accuracy of the proposed solution compared to the actual height variation 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact This database provides proof of concept for surface change detection using GNSS transmissions 
 
Title Experimental test bed for change detection measurements under ideal conditions 
Description Due to the complexity of the proposed technology, it is essential to assess its performance under a controlled environment. An experimental test-bed has been developed on the roof of our department for this task. The system comprises two antennas, separated by 70m and connected to our already existing receiver. The first antenna is the reference antenna, used for signal synchronisation. The second antenna simulates the performance of a point target. The height of this antenna was varied by known amounts and measurements were taken over 6 months to compare the measured height variation to the actual one. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2012 
Impact The experimental test-bed proved that GNSS-based SAR change detection is possible and feasible 
 
Title Radar change detector imitator 
Description Apart from assessing the performance of the proposed topology for change detection from the radar point of view, it is important to also test its performance from the end product point of view. For this purpose, a device with similar properties to those expected from the proposed system has been built and is now being tested. This device will be used to evaluate the potential in monitoring small-scale ground movements under different practical conditions (different soil types, vegetated or not, under different weather conditions etc). 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2013 
Impact This experimental demonstrator, imitating outputs of a GNSS-based SAR. was used to realise the potential of surface change detection for GNSS from the application point of view