GRSG Conference 2022: Orbit to Outcrop
Title: SAR interferometry techniques to measure Earth surface displacements in the Euregio Meuse-Rhine region
Author: Romy Schlögel
In relation with the location for the further Einstein Telescope (ET), we are investigating the ground stability affected by meteorological, seismic and anthropogenic changes in the transborder region between the Netherlands, Belgium & Germany. The Euregio Meuse-Rhine region has been considered for its tranquility, stable ground and cutting-edge scientific institutions and companies while the Interreg project E-TEST (www.etest-emr.eu/) should be a proof of adequate concept (on the prototype side) and geological site.
The purpose of this study is to differentiate local and regional ground uplift, and sub-regional subsidence induced by groundwater level drawdown, possibly enhanced across fault structures, as monitored by various Synthetic Aperture Radar Interferometry (InSAR) processing methods. In fact, a buoyant mantle plume under the Eifel may be responsible for the regional ground uplift including the Weser-Geul region (BE) and the South Limburg region (NL) – which could affect the area selected for the future ET installation.
The current neotectonic activity in the target area is not well known but should be associated with the presence of several active NW-SE trending normal faults where karst also develops as well as along the NE-SW trending thrust faults which are old (Variscan) inactive structures. Identifying deformation hazards (including karst formation) using satellite remote sensing (and connected seismological) techniques is challenging mainly due to the (very) small regional scale deformation, terrain conditions and SAR properties.
Limits of two classes of techniques have been investigated for ground movement monitoring by multi-temporal DInSAR: Persistent Scatterer Interferometry (PSInSAR) and Small Baseline Subset Interferometry (SBAS). Both PSInSAR and SBAS allow to estimate the projection of the displacement rates onto the line-of-sight direction whereas additional measurements (including GNSS data).
Processing is needed to estimate movement components in up-down and east-west directions in a timely manner as available in the Multidimensional SBAS (MSBAS) method. Higher monitoring accuracy should be reached with the presence of scatterers that remain radiometrically stable and maintain a stable (and detectable) phase signature over the time span covering the successive acquisitions.
Different processing techniques considering the Sentinel-1 data are used in this study to evaluate their limits to track such scatterers on a time series of images while detecting and measuring ground motions based on their phase signature. While the lower Rhine graben clearly shows an uplift in Germany, InSAR results confirm the general ground stability over the ET area except for some cropping activities. Nevertheless, displacements of millimetric order are measured along the Gulp and Geul faults, which might be of neotectonic origin.