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Looking Above for Help Below

Mark Bowersox

I was in central London last weekend and you can't help but notice all of the work that is going on above ground to support Crossrail, a railway link that passes directly through central London and that will join Maidenhead and Heathrow in the west of London to Shenfield and Abbey Wood in the east of London. The project is the largest construction project in Europe. At the heart of the project is approximately 25 miles of new tunnels that are going to be constructed beneath the streets of London. Channeling beneath a city is a huge task, due to varying geology, an array of sewers, tunnels, pipes, and the foundations of buildings, which must surely make it a delicate and complicated of engineering projects. I would have thought that one of the biggest challenges posed by any tunneling project would be to mitigate any effects on the surface structures and reduce land movement and subsidence.

Whilst thinking about the depths of the earth below me in London, I looked to the sky above me to consider the possibilities that remote sensing applications could give in monitoring land movement and subsidence.  Indeed in a city like London plagued by clouds Satellite Interferometric Synthetic Aperture Radar (InSAR) can be used to measure and map changes on the Earth's surface as small as a few millimeters. Bouncing radar signals off the ground from the same point in space but at varying times, the radar satellite can measure changes in distance between the satellite and the ground as the land surface subsides.  Mapping the ground surface changes through these interferograms from the InSAR data can surely help construction and engineering companies understand any effects of subsidence that may have been caused by tunneling.

I wonder if techniques of change detection like InSAR are used to manage the impact of large scale construction project.

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