Using InSAR to detect railway deformations
Examensarbete för masterexamen
Wireless, photonics and space engineering (MPWPS), MSc
Railway deformations are issues that can possibly prevent an effective railway network. Serious deformations may lead to decreased speed limits or in worst case the need for closing parts of the railway for traffic until maintenance work has been performed. The idea is that displacement maps from InSAR images can be used to detect problematic areas so that the right actions could be taken before the deformations become so large that they affect the traffic. Displacement images produced by SkyGeo from the TerraSAR-X satellites have been used by Trafikverket in other projects with good result. The issue is that TerraSAR-X data is expensive so the idea is to use the freely available Sentinel-1 data instead. Displacement maps produced by SkyGeo for both Sentinel-1 and TerraSAR-X, and a displacement map produced by processing in the Sentinel Application Platform (SNAP) over an area south of Gothenburg, Sweden are compared. It was found that using persistent scatterer interferometry on a stack of images alone was not enough to remove enough errors and the results were unreliable. However, when looking at the displacement images provided by SkyGeo which has used models for error reduction, it seemed like the results were more reliable. The results from the Sentinel-1 data had more fluctuations and thus a slightly larger RMS error compared to the results from the TerraSAR-X data but the trends were still clearly visible. A comparison of the coherence and RMS errors showed that there is a connection between high coherence values and low RMS errors which means that where there is high coherence there should also be a low RMS error. The conclusion is that the use of Sentinel-1 data to create displacement maps is plausible and seem to work well in the area used in the project. However, further research on error sources and different nature types in other areas is desired before reliable displacement maps can be made over the entire land mass of Sweden.
InSAR, Persistent scatterer, Differential InSAR, Displacement, Sentinel-1, TerraSAR-X.