This research is focused on registering the movements along the slope of the several slopes located on south-west of the mountain Stara Planina and establishing their average annual values. Currently at national level there are a low number of studies targeted at operational monitoring of the investigated slopes. These objects are quite specific for research since those kind of natural phenomena are inaccessible by other means or are quite dangerous to be investigated. On the other hand, the moving slopes are causing damages to infrastructural objects such as roads, bridges or power lines. Their behavior is difficult to forecast and for this reason they can be considered as natural hazards. Obtaining precise data for the single slope movements is done by in-situ investigations such as geodetic acquisitions, terrestrial laser scanning, and geological observations, which all require financial resources and human effort. For this reason, we used remotely sensed data from satellite based SAR instruments processed using the DInSAR method in order to analyze the motions of single slope and to establish a technique for the investigation of mountain slopes. An advantage of the selected method is the possibility to register the vertical movements of the whole slope with centimeter accuracy. This approach is based on the free access to the SAR data and tools for their thematic processing provided by ESA. In this study an emphasis is put on the manner how the obstacles encountered during the interferometric processing (e.g. presence of vegetation or topography) have been overcome. From the downloaded set of SAR images covering the region created were two multitemporal InSAR data series from ascending and descending orbits of the satellite. The results from the autumn-winter pairs exhibited good correlation with the expected displacements along the studied slope having a magnitude of 0.8 m.
The main objective of this research is monitoring of landslide areas by integrating results from interferometric images, and GNSS data from permanent and local geodetic networks. This study is providing reliable information with regard to the hazard geo-processes taking place in the region of the landslide area Thracian Rocks. To accomplish the aforesaid the first step was to create a local archive of about 400 SLC images from ESA operated mission Sentinel-1 starting from the beginning of 2015. In this archive data from ascending and descending satellite orbits were included in order to increase the reliability of the information derived from SAR data. Due to considerable occurrence of vegetation in the studied area, which is recognized as one of the factors increasing the decorrelation during DInSAR processing, the authors processed mainly scenes with minimum availability of leaves on the trees and shrubs – autumn and spring. The geological setting of the landslide region reveals a narrow strip formed by old landslides that have an average width of 400–500 m and steep slopes of 40–50 m at certain locations. From this setting it was established that the landslide bodies have been formed by 3–4 visible linearly oriented steps and landslide packages with different heights creating negative ground forms with permanent or temporary swamps. Besides the ancient landslides a recent active local landslide processes occur forming recent landslides. In the framework of this study a control geodynamic network covering the landslide area located in the surroundings of Thracian Cliffs golf club was established. In it included are 10 points stabilized with metal pipes which are used to monitor deformations in this area. An advantage of the approach should be pointed out the possibility to map areas that are inaccessible by other means.
The territorial distribution of landslides along the Northern Bulgarian Black Sea coast has been evaluated by analyzing the results of field surveys for 2018 and 2019 based on geological surveys and processing of interferometric images from synthesized aperture radars (SAR). A local image archive of Sentinel-1A / B was created for the period 2015 - 2019 for this region and interferograms were produced every 4 months, 8 months, 1 year and in case of registering an event, led to the activation of landslide processes. A raster map of the concentration of deformations of the Earth's crust was created based on data from the obtained interferograms. Areas with active landslide movements along the Northern Bulgarian Black Sea coast have been identified for monitoring with the Global Navigation Satellite Systems (GNSS). A geodynamic network of 30 points covering the landslide circus ”Dalgiya Yar” and landslide “Thracian Cliffs“ was established and the first measurement cycle was carried out.
Satellite radar instruments deliver SAR data that are able to provide information on the magnitude of ground motions in range of centimeters. Such information is of extreme importance is assessing the consequences of natural or man-made disasters. Since earthquakes are occurring constantly and are not possible to predict it is recognized that any information on the size of this events is important for the local and national authorities responsible for mitigation of the post-event damages. In this research presented are the results obtained after processing two sets of SAR data along with other supplementary data in order to produce two interferometric images that provide information on the deformation processes after several earthquakes that took place on the Ionian shore of Albania in the second half of November 2019. The resulting deformation maps from ascending and descending orbits of the Sentinel1 satellite mission were compared to increase the reliability of the conclusions made upon them. The outcomes reported suggest that it would be possible to deliver to the national authorities details on deformation in regions that are problematical to inspect directly.
The landslides are one of the well-known natural hazards occurring on the North East Black Sea coast of Bulgaria. The previous researches that take into account the geological and meteorological peculiarities of this region confirmed that the geomorphological conditions in this region are extremely favorable for landslide formation. Two are the main drivers that are being responsible for activation of the landslide processes in the area investigated. The first one is the sea erosion and the other is the increasing groundwater level. The influence of those is highly aggravated by the construction activities that took place in the last decades and the lack of sewerage networks. Those findings are based on information provided by the national authority responsible for monitoring and filing the landslides in Bulgaria. This was the motivation for developing and implementing reliable and accurate method for operational monitoring of the landslide processes in the said area. For development of such method data from SAR instruments were used. In this specific study data from Sentinel-1 SAR mission were processed by the freely provided by ESA SNAP software. Final results are interferometric images (IFIs) providing information about the ground movements. In this paper we present results reflecting the subsidence in the area of a landslide located some 20km north of the Albena resort. In the last decade two events have caused damages to the infrastructure in the area - one occurred in January 2015 which was attributed to the heavy rains the previous summer and the other took place in mid of August 2018. Both have been studied by processing SAR data for the periods mentioned. The results obtained are considered reliable since they have been reaffirmed by geodetic surveys and other terrain measurements. The outcomes of this research will contribute to better understanding the ongoing slow movements of the Earth’s crust, and for forecasting and early warning of geological hazards.
One of the key input parameters in obtaining end products from SAR data is the DEM used during their processing. This holds true especially when persistent scatterers InSAR method should be applied for example to study slow moving landslides or subsidence. Since nowadays most of the raw SAR data are of space borne origin for their correct processing to high precision products for relatively small areas with centimeter accuracy a DEM taking into account the particularities of the local topography is needed. Most of the DEMs used by the SAR processing software such as SRTM or ASTER are obtained by the same type of instrument and present some disagreements with height information acquired by leveling measurements or other geodetic means. This was the motivation for initiating this research – to prove the need of creating and using local DEM in SAR data processing at small scale and to check what the magnitude of the discrepancy between final InSAR products is in both cases where SRTM/ASTER and local DEM has been used. In addition investigated were two scenarios for SAR data processing – one with small baseline between image pairs and one having large baseline image pairs – in order to find out in which case local DEM has bigger impact. In course of this study two reference areas were considered – Bankya village near Sofia (SW region of Bulgaria) and Mirovo salt extraction site (NE region of Bulgaria). The reason those areas were selected lies in the high number of landslides registered and monitored by the competent authorities in the mentioned locations. The significance of the results obtained is witnessed by the fact that both sites we used have been included as reference sites for Bulgaria in the PanGeo EU funded project dealing with delivering information regarding ground instability geohazard as areas prone to subsidence of natural and manmade origin. In the said project largest part of the information has been extracted from Envisat SAR data, but now this information could be supplemented by adding such from Sentinel-1 derived by us. During this research two local DEMs have been extracted from the tiles including the areas of investigation, one using SRTM data and one from ASTER, and after this procedure both were compared to the DEM gathered by leveling measurements. Finally conclusions are drawn and a direction for future research steps is provided.