Satellite Monitoring of Railways using Interferometric Synthetic Aperture Radar (InSAR)

There is over 15,600 km of track in the Swedish railroad network. This network is vital for the transportation of people and goods across the country. It is important that this network is monitored and maintained to ensure good function and safety. A tool for monitoring and measuring ground deformation over a large area remotely with high frequency and accuracy was developed in recent decades. This tool is known as Interferometric Synthetic Aperture Radar (InSAR), and is used by researchers, geo-technicians, and engineers.
The purpose of this study has been to evaluate the use and feasibility of the InSAR technique for track condition monitoring and compare it to conventional track condition monitoring techniques. Malmbanan, which is primarily used to transport iron-ore from mines in Sweden to the ports of Luleå, Sweden and Narvik, Norway, is used as a case study for this project; specifically, the section between Kiruna and Riksgränsen. Coordinate matching of measurements from the provided Persistent Scatterer Interferometry (PSI) InSAR data and Optram data from survey trains were performed. Then measured changes over different time spans within the two systems were overlapped and classified with different thresholds to see if there is correlation between the two systems. An extensive literature review was also conducted in order to gain an understanding of InSAR technologies and uses.
The literature review showed that there is a large potential and a quickly growing number of applications of InSAR to monitor railways and other types of infrastructure, and that the tools and algorithms for this are being improved. The case study, on the other hand, shows that it can be difficult to directly compare measurement series from different tools, each working on different resolutions in terms of both time and space. InSAR is thus not about to replace techniques such as those behind Optram (using measurement trains). Instead, the approaches offer complementary perspectives, each highlighting different types of issues.
We find that InSAR offers a good way to identify locations with settlements or other types of ground motions. Especially transition zones between settlements and more stable ground can be challenging from a maintenance point of view and can clearly be identified and monitored using InSAR. With the rollout of national InSAR-data, and the large increase in data accessibility, we see a considerable potential for future studies that apply the technique to the railway area.