Satellite technology is giving scientists a new source of information to help us measure movements in the Earth’s surface – and that could help us protect the infrastructure of Wales.
The European Space Agency’s Sentinel-1 mission is now providing a wealth of open access SAR (Synthetic Aperture Radar) data for both academic and commercial purposes.
The geo-engineering and geo-environmental sectors are just starting to explore the use of this data to monitor ground movement at man-made structures.
To make the most of this new source of information, it’s now essential that research is carried out into the best methods for combining it with ‘conventional’ ground-based geophysics.
That’s why TerraDat and the University of South Wales have joined forced after successfully acquiring funding from the EU for their PhD project: ‘’Next Generation Monitoring of Critical Welsh Infrastructure: Integrating InSAR Satellite Data with Conventional Geophysics”.
The PhD aims to develop a system which will bring together both the satellite and ground data.
Why would this be useful?
It would help identify major infrastructure items such as buildings, roads, bridges, or dams, which are at risk of landslides or ground movements and help the authorities to take action to protect them.
It could also help engineers and architects when they are planning major infrastructure projects.
What is InSAR?
Interferometric Synthetic Aperture Radar (InSAR) is a technique for measuring ground deformation from orbiting satellites.
The SAR instrument onboard emits a pulse of radar waves and measures the phase (a defined position of a point in time on a waveform cycle) and amplitude of signal reflected (returned) from the Earth’s surface.
Radar was chosen because, unlike visible or infrared light, its waves can penetrate most weather clouds. They are also equally effective in darkness.
The phase recorded is compared with another satellite measure to get an accurate and precise measurement of ground deformation. Measurements can be made to a few centimetres or less.
Surface deformation maps can be made from results. They are called interferograms.
This geophysical technique has been used extensively over the past 20 years to make huge progress in the understanding of volcanoes and plate tectonics.
It has been used to measure the effects of volcanic eruptions, earthquakes, the movement of glaciers, landslides, and subsidence.
Now, it is increasingly being used to measure and monitor man-made structures and activities in rural and man-made environments.
How is TerraDat involved?
TerraDat is using InSAR data to monitor the temporal variation of ground movement at dam structures and other areas prone to landslides and subsidence.
The aim is to establish a baseline of acceptable movement, so it is then possible to identify anomalous or significant creep and advise authorities when remedial works are necessary.
To understand what triggers and controls this movement, conventional geophysical investigation and monitoring methods are then be integrated. That gives us an overall, holistic understanding.
TerraDat will be developing electrical monitoring methods to create time domain geophysical surveys.
These can then be interpreted alongside InSAR-derived ground deformation data.
The company is working alongside Knowledge Economy Skills Scholarship (KESS) PhD partner Nick Farnham.
Joanna Hamlyn, TerraDat’s Senior Project Geophysicist on the project, said: “The project will also asses how InSAR performs between urban and rural environments, how it can be integrated with GPS, and it will outline strategies to combine InSAR with conventional geophysical monitoring methods to provide a commercial product.
“Within the first six months of the project three case study sites have been identified across Wales. Successful multidisciplinary geophysical surveys have already been acquired and provided important information for the maintenance of critical infrastructure.
“The available InSAR data is being processed by our project partner company SatSense and will further provide those responsible for such assets with a holistic understanding of their structures.”
One of the sites the team will be monitoring is the Llyn Barlwyd dam near Ffestiniog.
It’s a post-medieval, 75m long dam in a steep-sided gully which is 10m wide at its base and stands to a height of 10m.
The dam is constructed from outer stone and an inner filling of tipped slate.
What are the electrical monitoring methods TerraDat uses?
Electrical Resistivity Tomography (ERT) looks at the electrical characteristics of materials under the ground’s surface.
Different levels of resistivity, or conductivity, correspond with different materials such as water, ice, rock, or soil, so ERT builds a picture of groundwater, geological structures, sinkholes, and fractures, and this helps geophysicists assess whether there is a risk of movement or landslips.
Regularly-spaced electrodes are used to inject current into the ground. They are connected to a central control unit which records the data.
The separation of the electrodes and the geometry determine the depth of the investigation.
Greater electrode separation leads to data from greater depths.
You can read more about this technique here.
If you’re monitoring the ground under infrastructure such as dams, roads, or bridges, our geophysical surveys will help warn you about any potential for movement. Call us on +44 (0) 2920 700127 for more information.