1 STRUCTURAL DEFORMATION OF THE HIGH-SPEED LINE (HSL) INFRASTRUCTURE IN THE NETHERLANDS; OBSERVATIONS USING SATELLITE RADAR INTERFEROMETRY Mahmut ARIKAN and Ramon F. HANSSEN Delft Institute of Earth Observation and Space Systems, Delft University of Technology, The Netherlands Abstract: The Southern High-Speed Line (HSL), in Dutch known as ‘HSL-Zuid,’ is a dedicated 125 km high-speed rail line, forming part of a new route between Antwerp, Belgium and Amsterdam. Construction began in 2000, and major engineering projects include the 7.2 km tunnel Leiderdorp-Hazerswoude under the ‘Green Heart,’ an agricultural area between the country's four largest cities, Amsterdam, Rotterdam, The Hague and Utrecht. North of this tunnel, a section of the line near the city of Rijpwetering, containing the sharpest curve on the entire route, experienced significant structural deformation during the construction stage due to ground instability, and 800 m of the line had to be rebuilt. Local in- situ surveys show that up to 19 mm of horizontal deformation occurred after the reconstruction stage in 2006. Here we investigate whether local deformation of this kind can be observed by satellite radar interferometry, using a fine-tuned processing approach dedicated for this application. We report on the procedure followed, on the constraints in the parameter estimation and the obtained level of precision and reliability. The combination of a forward model to simulate radar observations from in situ measured displacements and an inverse model using the satellite data to estimate the displacements will be presented. 1. INTRODUCTION The Southern High-Speed Line (HSL) is a dedicated 125 km high speed rail line connecting the Netherlands, especially an urban agglomerate of cities known as the Randstad, to numerous European economical centres, see Figure 1. People are increasingly willing to travel more but spend less time while travelling for business or for pleasure. Annually, about 14 million people are expected to travel by the HSL railway. In this aspect, the project is expected to accommodate most of the international heavy traffic to the Netherlands. The transportation along the HSL line is planned at a speed of 250 kilometres per hour on the domestic routes and at a top speed of 300 kilometres per hour on the route of Amsterdam to Paris. Between the both centres, the travel time is expected to decrease to three hours. Additionally, the project is competitive in medium-range travel, such as with cars and