Reconstruction of 3D Deformation from GNSS and InSAR Data: A Case Study in Groningen Using EGMS Data.

Accurate 3D surface deformation analysis is essential for understanding geodynamic processes and mitigating related hazards. We present a methodology that fuses GNSS and InSAR time series to achieve robust deformation estimates. Our case study focuses on the Groningen region in the Netherlands, an area undergoing significant subsidence and seismicity due to decades of gas extraction. In addition, Groningen benefits from a dense GNSS network spanning approximately 50 × 50 km, offering an ideal testbed for integrated deformation analyses.
The proposed workflow involves preparing GNSS time series from Nevada Geodetic Laboratory by removing common-mode errors and detrending for plate motion, then referencing all stations to a central GNSS antenna. A moving average filter further refines the GNSS time-series. In parallel, we refine the “Basic” EGMS InSAR products by applying smoothed calibration trends derived from the “Calibrated” products. Subsequently, the daily average deformation of InSAR Line-of-Sight (LOS) points near the reference GNSS station is subtracted from all persistent scatterers, ensuring consistent reference frames across both datasets.
To combine InSAR LOS deformation with GNSS 3D data, we identify persistent scatterers within a 100-meter radius of each GNSS antenna and synchronize the reference epochs between both datasets. We then rotate the GNSS East-North-Up coordinates so that one axis aligns with the InSAR LOS, apply an error-weighted least-squares solution to fuse the measurements, and finally reintroduce the out-of-LOS components derived from the pre-processed GNSS data. The resulting full 3D deformation field is then converted back to the ENU coordinate system.
Preliminary analyses suggest that integrating GNSS and InSAR improves reliability in all three components, with particularly notable benefits in the north component. Moving forward, this fusion strategy can be extended to smaller-scale monitoring projects (e.g., dams or bridges), offering a versatile approach to detecting and characterizing localized deformation anomalies.