Sentinel-1 DInSAR for Monitoring Active Landslide “Fish-Fish” Northeast Bulgaria

At the Northern Black Sea coast of Bulgaria, large numbers of active landslides are located. The situation has changed in the last 30 years since large technogenic load was put on it caused by construction activities in that area. For this reason, tracking activation of the landslides and surface movements in them is a critical task that must be carried out. This is the reason to perform a pilot investigation for a single landslide using synthetic aperture radar (SAR) from ESAs’ Sentinel-1 mission. As main advantages of said data pointed out should be the uninterrupted time series, the unrestricted access, and the compatibility with other data operating in the radar C-band. In the recent years, the landslide found in the residential area “Fish-fish” has been the subject of our research by making terrain observations, geodetic and geologic investigations. In the last years, two surveys by unmanned aerial system (UAS) were done spanned in one and half year period focused at studying the deformations that took place in its area. The first one has the task to create precise digital elevation model of the zone, while with the second the surface motions were registered. For this research, SAR data were used to establish the magnitude of the geodynamic processes in the area of the landslide for the period 2015–2022. To complete this task, seven uninterrupted time series covering the time span from late autumn to early spring were created using the small baseline approach (SBAS). The period was limited to the said one, because in the researched area large parts are vegetated, which causes spatial decorrelation in the interferograms. As a result of our research produced were 42 interferometric images using SAR data in SLC format allowing creation of deformation maps for the zone of “Fish-fish” landslide. The analysis of the obtained results confirmed that the applied technique provides sound information and is solid basis for systematic monitoring of the area.