| 20 Aug 2026
Evaluating European Ground Motion Service against Local InSAR Analysis along Key Swedish Corridors
Abstract. Ground motion poses a significant threat to the safety and functionality of transport infrastructure, particularly in regions affected by landslides, subsidence, freeze–thaw processes, and large-scale tunnelling. Interferometric Synthetic Aperture Radar (InSAR) enables millimeter-level displacement monitoring over large areas and is used to support infrastructure risk assessment. Here, we evaluate the usability of two InSAR approaches, (i) Persistent Scatterer Interferometry (PSI) using displacement products from the European Ground Motion Service (EGMS), and (ii) a combined Persistent- and Distributed-Scatterer (PS+DS) phase-linking workflow across key Swedish transport corridors. Rather than a strictly controlled methodological comparison, we evaluate how differences between operational InSAR solutions translate into practical performance for infrastructure monitoring. Results show that PS+DS consistently yields five times as many measurement points while maintaining RMSE values within a similar range to EGMS (mostly below 6 mm in the Line Of Sight direction). The EGMS exhibits narrower RMSE distributions, but PS+DS achieves comparable median RMSE of the measurement points across most land-cover types and corridor environments. Both datasets capture similar displacement patterns along all corridors, with measurement points from both approaches concentrating within the linear corridor geometry. Overall, the five-fold increase in PS+DS point density offers infrastructure operators a practical pathway to finer-scale ground motion monitoring for railway maintenance and risk assessment, while demonstrating how the choice of operational InSAR processing strategy shapes the information available for Earth-observation-based infrastructure applications.
This is a very important and timely study evaluating the usability of publicly available EGMS data versus more advanced and adapted InSAR processing approaches for linear infrastructure monitoring. The authors have selected five case studies in Sweden and investigate how differences in the assumptions and processing strategies adopted by different InSAR approaches affect the resulting deformation estimates and their suitability for an operational railway-monitoring application.
I consider this to be a valuable and critical assessment that deserves publication. In my view, however, the manuscript still needs a revision as it does not fully communicate the importance and richness of the results the authors have obtained.
Major Comments
For example, in Fig. 2c, uplift/stability appears to be detected at the northern end of the railway, whereas the PS+DS results in Fig. 2d indicate subsidence at approximately the same location. A similar inconsistency appears in the southern part of the study area. This raises an important question: which of these deformation estimates is more reliable, and what is the possible reason for the discrepancy?
When examining the results presented in the Supplementary Material, I find several other locations where similarly interesting discrepancies occur. Since one of the main objectives of the study is to objectively assess and compare the different processing approaches, I strongly recommend that the authors make better use of these differences. Rather than focusing primarily on the consistency of the results, the manuscript would be considerably more valuable if it explicitly highlighted where the approaches disagree, investigated the possible causes of these discrepancies, and discussed their implications for operational infrastructure monitoring.
Since the paper aims to evaluate the applicability of the different InSAR products for operational railway monitoring, the results from all five cases are important for demonstrating the robustness and generality of the conclusions. I therefore recommend moving at least the key results from Cases 3–5 into the main text, while retaining additional details in the Supplementary Material if necessary.
Minor Comment
-Line 100: The authors state:
“The interferometric phase also contains contributions from topography, atmospheric delays, and noise, which different InSAR methods model and separate to isolate the ground-motion signal.”
Given that InSAR is a mature technique with a history of approximately three decades, I suggest citing some of the foundational/original publications on interferometric SAR at this point, rather than relying primarily on recent literature in 2024.
Piter, A., et al. (2026). SARvey-survey with SAR: A new Open-Source InSAR Research Software. Environmental Modelling & Software, 107004, https://doi.org/10.1016/j.envsoft.2026.107004
I hope the authors find my comments useful in improving the quality of the manuscript