Radar imagery taken by satellites (InSAR) can be used to monitor millimetre-scale movements of built environment assets over time. Because satellite data is collected and stored consistently, and—in the case of the European Space Agency’s Sentinel—freely available for retrospective analysis, it can inform forensic investigations after a major incident. Data collection and interpretation can be carried out remotely, and historic data can be compared with other forms of monitoring to better understand how significant changes manifest. Learning about patterns of change in the data can then be applied to interpreting current satellite data. The range of possible applications is considerable and includes the possibility of predicting (and pre-empting) major infrastructural failures.
From better, more flexible targets (new reflector designs) to more efficient interpretation with the assistance of simulations, 3D-modelling techniques, and machine-learning, CDBB researchers collaborated to advance the state-of-the-art in satellite monitoring for asset management. As a result of this research, we can better understand the performance of existing structures, creating robust and reliable data that can leverage whole-life value of an asset or portfolio of assets by informing more efficient asset management.
Process
Directed by Dr Sakthy Selvakumaran (Cambridge) and Professor Tim Wright (University of Leeds), a cross-institutional research team pursued four parallel enquiries to enhance the cutting-edge applications of satellite monitoring for the built environment:
Dr Krisztina Kelevitz (Leeds) designed a new array of reflectors suitable for infrastructure monitoring. The goal was to enhance existing and freely available Sentinel-1 InSAR measurements. Traditionally, large meter-scale corner reflectors have been used for ground motion measurement. That scale is not suited for deployment on structures such as bridges. Could several small reflectors provide a meaningful alternative? The design, manufacturing, and deployment of these reflectors was completed in January 2018, allowing researchers to collect InSAR and Global Navigation Satellite System (GNSS) data. The underlying principle of this technology is comparable to bicycle safety equipment: a sequence of tiny reflectors at different angles may combine to reflect more light in more directions compared with a similarly-sized single-faced reflector. The results demonstrate that this strategy is successful for asset monitoring, with suitable applications including railway embankments. The team have also designed vertical reflectors, now in prototype, continuing the research into alternative installations.
The second strand of intended research had to be set aside when pandemic movement restrictions prevented the necessary fieldwork. Adapting to circumstance, Dr Zahra Sadeghi (Leeds) refocused on data interpretation and the potential of 3D modelling. Could we better understand and predict reflectivity in satellite SAR images prior to construction? Sadeghi simulated SAR reflectivity maps of three bridges with different scattering characteristics in London at X band, comparing the simulations with the real TerraSAR-X images. The team also linked the strong point signatures in the simulated images, which can be selected as coherent pixels by InSAR, to 3D scattering centres in 3D models of the bridges. The comparisons demonstrated which surfaces of a bridge interact with radar signal to generate the signals seen in InSAR data. Sadeghi’s vision is to be able to use this information in design, to design and build structures that would be well suited to regular remote monitoring by InSAR over their operational lifetime.
The third strand of research is crucial in the adoption of such measurement technologies by industry: furthering work on validating InSAR results using existing ground-based measurements. A key limitation of InSAR measurements is that they provide line-of-sight (one-dimensional) measurement. This work included using multiple satellite viewing geometries to understand how well actual three-dimensional movement could be captured. Case studies include measurements of ground settlement after major tunnelling activity in central London, using data captured by TfL during tunnelling work at Bank Underground Station. Minute-by-minute monitoring is essential during tunnelling operations; yet land continues to settle over subsequent years and satellite monitoring offers an effective solution to measuring subtle movement and detecting anomalies over days, months and years. The comparison of data collected in situ with contemporaneous satellite data helps analysts understand the most relevant signals of movement in the InSAR data.
The fourth line of research tackled the scale of data. A satellite image of the Greater London area includes tens of thousands of measurement points, yielding more data than the human mind can process. Monitoring a single built asset over time can mean handling terabytes of data. To harness the predictive capacity of satellite monitoring across a network of assets, machine-assistance is essential. To what extent can we already create AI-driven systems to reveal changes at scale? Dr Gabriel Martin (Cambridge) investigated the possibilities for automation, focussing on InSAR data for Greater London. His methods identified key signatures in time series data, so that specific behaviours and patterns could be automatically identified. These were validated by association with specific structural behaviours and key construction events during the period of time studied.
Findings from the research have been presented to the European Geosciences Union (Austria, May 2022), the European Space Agency’s Living Planet Symposium (Germany, May 2022) and the IEEE International Geoscience and Remote Sensing Symposium (Online, July 2021 and 2022).
Publications include an account of the corner-reflector array work (Kelevitz et al, 2022), a comparative study of monitoring methods (Selvakumaran et al, 2022), and results from the application of algorithms for large area monitoring (Martin et al, 2022). A further journal article is anticipated, documenting InSAR monitoring of tunnelling works (with London Underground and the University of Oxford).
So what?
InSAR data has the potential to revolutionise how asset networks are monitored, enhancing maintenance and reducing incidence of catastrophic failure, and providing a safe and cost-effective alternative to scheduled site visits. CDBB research has developed and trialled new tools to improve the quality and availability of relevant InSAR data, advanced our understanding of what InSAR data reflects and how, and taken steps to enable monitoring of movement at scale.
Industry impact
Early adopters of InSAR-based monitoring for investigatory purposes include tier one construction companies and strategic asset owners. For example, the researchers worked closely with Transport for London, where InSAR techniques look set to play a key role the monitoring of future tunnelling projects. Meanwhile, the developers constructing the UK’s second high-speed railway line (HS2) are piloting the use of new reflector designs to monitor embankments, inspired by (and in consultation with) CDBB advances.
Pre-existing relationships with these asset owners meant that user requirements could be taken into account during the design phase. Outcomes were easily steered towards deliverables that could be implemented in practice, securing value for industry.
The scope for large-scale, nationwide monitoring of the structural health of bridges, rail networks, tunnels and other infrastructure means that InSAR should become key in forecasting (and preventing) potential failures.
"Satellite derived data can mitigate the risk of failure and provide significant cost savings as it facilitates non-intrusive structural health assessments of different types of assets. This approach provides significant value to industry by reducing human effort, minimising construction and O&M costs as well as providing useful structural health information to ensure rapid and effective operational decision making.”
Tariq Darwood, R&D Expert, EDF R&D UK Centre
"We are grateful for the development work carried out by CDBB researchers in Cambridge and Leeds, which has led to the development of a prototype next-generation radar multi-reflector. We have developed these ideas further into a product that we are now taking to market. We are now able to offer more flexibility when customers require high precision ground and structure movement data at specific locations on their land, infrastructure or building."
Matthew Bray, SatSense Ltd
Wider benefits
Combining a range of monitoring technologies enables assessment of new generation techniques such as satellite monitoring and comparison with more traditional monitoring. Satellite radar imagery is becoming more accessible and available at increasing spatial and time resolutions. Its capability to monitor structures, cover large areas, and monitor remote locations will provide valuable insights to asset owners and managers.
With the effects of climate change around the world resulting in extreme weather events, such as flooding, the use of satellite monitoring can track changes in a geographical area as well as individual structures providing potentially important indicators of change.
This project’s case studies have enhanced industry understanding of satellite monitoring technology in the context of infrastructure and construction, as well as advancing the state-of-the-art. Bespoke trials are costly exercises for suppliers, who are often small enterprises with limited financial means. By assessing the technology and sharing results as open access publications and through presentations where invited, this project has enabled SMEs to have access to cutting-edge monitoring techniques.
Collaborators
- Transport for London
- University of Leeds & COMET (https://comet.nerc.ac.uk/)
- SatSense
- BKwai
- Ramboll
- Satellite Applications Catapult
- SAR data provided by European Space Agency (ESA), Italian Space Agency (ASI) and Airbus
Find out more
The Research profile provides more information about the origins of this research and introduces the research team.
A video introduction to the work is available as part of the CDBB Digital Twin Journeys series: Digital Twins from Space:
Lead investigator Dr Selvakumaran also offers a clear account of the value of monitoring in a TEDx talk recorded at Newnham College (drawing on earlier related research): How satellites can help predict infrastructure collapse:
A CDBB blogpost from Sakthy Selvakumaran outlines early progress with corner reflectors and how this research intersects with other projects including the wider Digital Twin programme (written following a CDBB and Catapult Knowledge Exchange event held in November 2020).
