The Vipava River Valley is well known as a landslide-prone area in Slovenia. Since the area is very large, the application of in situ monitoring systems is limited. An efficient method that can monitor the whole area of the Vipava River Valley is highly required. In this study, the SBAS DInSAR method is applied to monitor the displacement behavior of landslides in this area. Using four images of ALOS2-PALSAR2 data, captured from March 2016 to December 2018, clear LOS displacement distribution maps are obtained. The temporal transition of the displacement behavior is also obtained using 273 images of Sentinel-1A/B for both ascending and descending passes taken from September 2016 to January 2019. The monitoring results for the Slano blato landslide are demonstrated in this paper. LOS displacements of several cm are detected despite the countermeasure works that were performed. The SBAS DInSAR gives a better understanding of the spatio-temporal landslide displacements in the area.

1. Introduction

The Vipava River Valley, located in the southwest part of Slovenia, is well known as a landslideprone area (Bizjak and Zupančič, 2009; Jemec Auflič et al., 2017; Verbovšek et al., 2018). There are four remarkable landslides in this area, namely, Rebrnice, Stogovce, Slano blato, and Selo. The area extends 40 km in length and several km in width. The landslides are characterized by various volumes and velocities in their movement. The occurrence of debris flows and landslides sometimes causes damage to houses, infrastructures, farmland, etc. Moreover, the lives of people in the surrounding villages are also endangered due to slope failures, rock falls, and debris flows. Several mitigation plans have been conducted to minimize the risk of landslides, such as constructing piles, retaining walls, check dams, drainage wells, etc. Nevertheless, some landslides are still active and potentially hazardous.

It is vital that the current situation of the landslides be known and that better mitigation plans be designed by monitoring the landslide behavior along with conducting geological and geotechnical studies. An effective method that is capable of covering extensive areas and realizing spatio-temporal continuous monitoring is needed. The Small Baseline Differential Interferometry SAR (SBAS DInSAR) is known as a useful method for ground surface deformation monitoring (Berardino et al. 2002; Ferretti, 2014). The first and second authors succeeded in applying this method to the long-term monitoring of land-subsidence (Yastika et al., 2019). The same method is applied for monitoring landslide displacements in this study. The data observed by ALOS2-PALSAR2 and Sentinel-1A/B are used for the analyses. This study presents the preliminary results in order to gain a better understanding of the landslide behavior over the whole area of the Vipava River Valley.

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