## 6 Conclusions
The expected impact of our suggested approaches for monitoring and identifying instability in railway infrastructure is to improve the early identification of rail fatigue for rail asset management. This development is anticipated to result in the augmentation of the sustainable safety of rail transport. Based on information evaluated and reported by the Turkish State of Railways Maintenance Department, it has been determined that 73% of the regional railway lines and engineering structures in Turkiye are more than 70 years old. Hence, employing an InSAR remote sensing approach for assessing such old structures will be highly advantageous for the purpose of monitoring their condition and implementing precautionary measures as needed. In conclusion, the Copernicus Programme's Sentinel-1 missions are highly valuable and practical for obtaining cost-effective data to monitor railways and their related facilities. These missions offer free and open-access data, further emphasizing their significance. Conceptualization, G.K. and Z.C. ; methodology, G.K. and Z.C. ; software, G.K.; validation, G.K. and Z.C. ; formal analysis, G.K.; investigation, G.K.; resources, G.K.; data curation, G.K.; writing--original draft preparation, G.K.; writing--review and editing, G.K. and Z.C. ; visualization, G.K.; supervision, Z.C. ; project administration, Z.C. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Sentinel-1 satellite data were obtained from The Copernicus Open Access Hub. CSK satellite data and diagnostic train raw data are private sources and not publicly available data, as they are only used by the relevant departments of the Turkish State of Railways. Conflicts of Interest: The authors declare no conflicts of interest. * [PERSON] et al. (2014) [PERSON]; [PERSON]; [PERSON] Railway Infrastructure Monitoring using Satellite Radar Data. _Int. J. Railway. Tech._**2014**, \(3\), 79-91. [CrossRef]
* [PERSON] et al. (2017) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Seasonal deformation features on Qinghai-Tibet railway observed using time-series InSAR technique with high-resolution TerraSAR-X images. _Remote Sens. Lett._**2017**, \(8\), 1-10. [CrossRef]
* [PERSON] et al. (2018) [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON], [PERSON] Railway Bridge Monitoring with Sar: A Case Study. In Proceedings of the IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain, 22-27 July 2018. * [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON]; [PERSON] _Railways' Stability Observation by Satellite Radar Images_; IntechOpen: London, UK, 2018. [CrossRef]
* [PERSON] et al. (2019) [PERSON]; [PERSON]; [PERSON]; [PERSON] InSAR technique applied to the monitoring of the Qinghai-Tibet Railway. _Nat. Hazards Earth Syst. Sci._**2019**, _19_, 2229-2240. [CrossRef]
* [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Monitoring surface deformation of high-speed railway using time-series InSAR method in northeast China. In Proceedings of the IOP Conference Series: Earth Environmental Science, Changchun, China, 11-14 October 2020. * [PERSON] et al. (2021) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Using TerraSAR X-Band and Sentinel-1 C-Band SAR Interferometry for Deformation along Beijing-Tianjin Inrector Railway Analysis. _IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens._**2021**, _14_, 4832-4841. [CrossRef]
* [PERSON] et al. (2022) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] InSAR analysis of C-band data for transport infrastructure monitoring. In _Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields_; Taylor & Francis: London, UK, 2022; Volume 2. * [PERSON] et al.