Differential SAR Interferometry Using Sentinel-1 Imagery-Limitations in Monitoring Fast Moving Landslides: The Case Study of Cyprus

Abstract

Cyprus, being located on the Mediterranean fault zone, exhibits a unique geodynamic regime since its tectonic evolution is driven by the interaction of the Eurasian and African plate. Besides its seismological interest, many active landslides and slope instabilities in areas of steep topography occur in Cyprus, having substantial impact on the built environment, by posing an imminent threat for entire settlements and critical infrastructure. Moreover, extreme meteorological events occur rarely, like severe rainfall and thunderstorms, that combined with the geological properties in some areas and the seismically stressed ground, can lead to landslides, causing severe damages to critical infrastructure. In the present study, the DInSAR methodology is applied for the detection of two individual landslide events that were triggered by heavy rainfall in Limassol and Paphos Districts in February 2019. Six co-event interferometric Synthetic Aperture Radar (SAR) pairs were used to produce displacement maps in vertical and east-west directions to study the resulting slope deformations. The above are carried out using Sentinel-1 imagery that are freely provided under the Copernicus umbrella. The limitations that arise from the speed and complexity of the deformations under study and the adverse residing meteorological conditions that caused these phenomena are investigated, as found in literature. Indeed, the sparse vegetation at the slopes affected by the landslides, the residing meteorological conditions, the heavy rainfall that triggered the two landslides, and the temporal phase aliasing effect due to the speed of the ground deformation were found to be the main limitations for the application of DInSAR methodology, resulting in the underestimation of the ground deformation that occurred.

Destructive M6.2 Petrinja Earthquake (Croatia) in 2020—Preliminary Multidisciplinary Research

“…Interferometry processing was conducted using a well-established procedure from InSAR processing (additional details are provided in [26,27]), and the analysis was performed in the Sentinel Application Platform (SNAP), which is the European Space Agency's (ESA) open toolbox for Sentinel analysis [28]. The most suitable feature of SAR images for earthquake detection is the phase that enables the determination of land displacement.…”

Coseismic Ground Displacement after the Mw6.2 Earthquake in NW Croatia Determined from Sentinel-1 and GNSS CORS Data

“…We created interferograms of unwrapped phase for each subswath in case of Sentinel-1A, merged them after debursting, and continued with a single product in differential SAR processing and unwrapping the phase. We did the unwrapping with the SNAP's plugin snaphu outside of SNAP toolbox, but later on, we computed the displacements separately using well known equations for displacement computation from the unwrapped phase (more details in [12,15]). After the determination of the Line of Sight (LOS) displacement, we corrected the values for the topographic correction and finally computed the estimation of vertical ground displacement after the earthquake.…”

“…It has also been proved by a recent study [13] that InSAR measurements produce noise, but the noise can be reduced without the loss of significant data information by applying the processing techniques. Many recent studies have focused to the usage of SAR technology in the estimation of ground deformation after large earthquakes: Reference [14] estimated the land displacement but without detecting the active major faults; Reference [15] highlighted the need to consider the coherence change analysis and identify the limitations of the SAR applications; others ( [16][17][18][19][20]) estimated earthquake's impact assessment based on the data derived from SAR. Furthermore, the SAR technique is now used for the study of earthquakes and has been applied around the World ( [21][22][23][24][25]) and in Europe ( [26][27][28]).…”

Complex analysis of earthquake deformations using SAR images: Examples from Croatia and Greece

“…The horizontal displacement in N-S direction is more complex and additional assumptions should be taken into account [24,25]. components (modified after [23]).…”