The range of sensors and resolution of data available from satellites is growing rapidly and we continue to improve how we monitor, map and assess the Earth’s surface. Worldwide changes to our climate have highlighted the importance of monitoring our infrastructure and how we can help predict the failure of critical infrastructure assets remotely from the sky.
The science bit
The Satellite Applications Catapult based at the Harwell Campus in Oxfordshire is using corner reflectors to conduct a six-month monitoring exercise across summer and winter seasons to establish if satellite remote sensing and IoT technology can provide a reliable and sustainable solution for improving and lowering asset management costs.
The primary method of satellite measurement used in this research is Interferometric Synthetic Aperture Radar (InSAR) which has the capability to provide wide-area, high density, remote measurements of movement using radar imagery. The radar waves transmitted from the satellite travel to objects on the Earth’s surface and then are reflected to the satellite to form radar images. The time it takes each radar signal to return is used to calculate the precise position of that point on the Earth’s surface.
When features on the ground move, the distance between the sensor on the satellite and the Earth’s surface changes, thereby producing a corresponding change in measured signal phase. The changes in measured phase that occur between repeat passes of the satellite are used to quantify millimetre scale ground movements.
Why corner reflectors?
It can be difficult to understand exactly what is causing a reflected signal, and in some cases an object may not reflect very well at all. The reflectors used in this project will allow the tracking of movement of very specific points on a structure and compare them with traditional survey movements taken by people on the ground.
This work is part of a scientific study into the technology, and it is hoped that in the future the reflectors themselves won’t be required.
What’s the purpose?
The project team aims to provide collateral to non-expert users to show what the technology is capable of today, and identify any future developments. This will be gathered through the remote monitoring of identified assets in London combined with data collected from in situ instrumentation. That’s one of the more tricky elements of the project – getting the reflectors installed on structures which are not particularly easy to access, are not uniform in shape or surface, and involve many layers of approval to access.
Engineers are not able to constantly monitor bridges and other structures in person, and the ability to remotely monitor assets and detect unexpected movements or sinking to a millimetre level could potentially spot problems before they become disasters. Now that the reflectors are in place, the challenge of this research is to see whether the resolution, accuracy and frequency of satellite measurement is up to the job.
The project team will study and understand how vital structures should and do move under various different loading conditions and environmental scenarios, and constantly monitor these assets.
What’s the benefit?
The project will lead to the creation of an overall roadmap for bridge monitoring services including existing and long term InSAR and IoT service provision. The BIM community will be able to make use of bridge monitoring services and use BIM software to help improve visualisation techniques and develop new asset management solutions.
Progress has been interesting, and some of the challenges faced have been unexpected. It can be difficult for a satellite positioned hundreds of miles above the ground to pick up a relatively small reflector situated in the City of London, sometimes completely surrounded by high rise buildings. However, the Satellite Applications Catapult team of experts has managed to get the reflectors installed in the best available positions and they’re now on their way to collecting some very helpful data!
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