Master´s Thesis Defense by Mark Peter Owen Falkenberg – Niels Bohr Institutet - Københavns Universitet

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Master´s Thesis Defense by Mark Peter Owen Falkenberg

Land Deformation in Danish Coastal Cities measured by Satellite

Measuring topographic changes has been done using the Global Positioning System for years. New techniques have made it possible to measure these changes without the use of GPS, but by radar. This technique is called Interferometric Synthetic Aperture Radar (InSAR) and works by detecting surface deformation, using differences in the phase of returning radar signals. Using InSAR for measurements in deformation can yield mm scale changes in deformation over spans of day or years. One of the strongest sides of InSAR monitoring is the number of data points it produces. As a GPS measurement is only a single measurement and a InSAR sweep can produce tens of thousands or even hundreds of thousands depending of the size of the area of interest. InSAR has applications in several geophysical monitoring projects, such as volcano and earthquake monitoring, or in monitoring subsidence and structural stability. In this study radar images from three coastal areas in Denmark were used in conjunction with the open source software packages Doris and StaMPS to create deformation maps. The areas in question are Copenhagen, Esbjerg and Skagen. For the Copenhagen area, where there is constant urban development, it would be expected that there would be subsidence. This is, however, not the case as most of the central area seems to be at equilibrium. Sweden and northern Copenhagen experience upheaval.

The Esbjerg area is built on a landfill and dredging area. This, in combination with urban development, makes subsidence in Esbjerg very likely. However the area generally experiences uplift, with some extreme cases out on blåvands hug. Skagen and the Skagen peninsula experience a lot of pressure from ocean forces of Kattegat and the North sea. The peninsula area has been monitored for some time and it has been found out that the shore of the peninsula moves each year due to sediment deposits transported from the shores of northern Jutland. With large amounts of sediment deposited each year on the peninsula, the Skagen area is also an ideal candidate for subsidence. This is confirmed by the InSAR deformation map showing that the Skagen peninsula is experiencing subsidence at a fairly alarming level. 

The final deformation maps along with their standard deviations provided a good idea of what topographic changes are occurring at the monitored areas. In comparison with GPS data it can be seen that the InSAR measurements got the gradient right, however the precision of isolated points on the maps could be improved with more data.