The Andes region exhibits high susceptibility to landslides, leading to significant infrastructure, road, and agricultural damage. This study focuses on Ciudad Victoria, a housing program located in a geologically unstable area of Loja, Ecuador. Loja has experienced frequent landslides in recent decades, with Ciudad Victoria initially affected in 2011 and 2015, intensifying during the rainy season in early 2021. However, a comprehensive understanding of this case is currently lacking. Here, we evaluate terrain instability and structural damages through a comprehensive multi-technical approach. In this study, we integrate advanced techniques such as Differential Interferometric Synthetic Aperture Radar (DInSAR), Uncrewed Aerial Vehicles (UAV)-supported field surveys, geomorphological assessments, Electrical Resistivity Tomography (ERT), and a semi-quantitative evaluation of house damages using a Geographic Information System (GIS). The combined analysis of DInSAR, field surveys, and geomorphological observations reveals that soil instability in Ciudad Victoria is primarily influenced by slow-moving translation-type landslides occurring in the SW-NE and S-N directions. These landslides exhibit an average active displacement of 1-4 cm/yr, which increases during the rainy months, reaching velocities of up to 13 cm per month. ERT, supported by the aforementioned observations, indicates a displaced soil volume of approximately 5 Hm3, 3 , with dimensions of roughly 700 m (length), 400 m (width), and 20 m (thickness). A semi- quantitative evaluation reveals that four houses have irreversible structural damages, while 172 houses exhibit severe damage and 553 houses display moderate damages such as cracks and fractures, which also impact water and sewage pipelines. Additionally, we demonstrate how these building damages can be utilized to determine terrain movement, serving as (1) ground-truth information for validating DInSAR data, and (2) facilitating detailed movement characterization. This study exemplifies the effectiveness of coordination among a multidisciplinary team that utilizes diverse techniques and perspectives, ultimately leading to a more precise diagnosis of unstable areas.
Global sea level rise (SLR) has emerged as a pressing concern because of its impacts, especially increased vulnerability of coastal urban areas flooding. This study addresses the pressing concern of SLR and flood vulnerability in the East Coast of North Sumatra (ECNS) and Medan City. We employ a data-driven approach integrating multicriteria analysis, analytical hierarchy process (AHP)-based weighting, and spatial modeling within a geographic information system framework. The analysis considers crucial factors such as slope, land use, soil type, SLR, and land deformation. The study expands the existing framework by incorporating SLR and land subsidence, acknowledging their significant roles in exacerbating flood vulnerability. Future flood-intensity scenarios are simulated based on SLR projections. Data for spatial analysis primarily originated from multisensor satellite imagery, secondary sources from published literature, and field surveys. We validated the consistency of the variable weightings assigned for vulnerability analysis using a consistency ratio threshold (<0.1). Finally, the established flood vulnerability model was validated by comparing its predictions with recorded flood events in the ECNS and Medan City. The ECNS and Medan City areas were classified as very high and highly vulnerable to flooding, respectively.
Investigations into the susceptibility of permafrost landscapes response to thermokarst can be performed using various approaches, depending on the scale of investigation. In many cases, point-based field measurements are extrapolated to larger scales and vice versa. The integration of scales often requires some form of ground control in addition to remote sensing surveys, which are at times exclusively conducted. As upscaling from discrete field measurements can provide spatial coverage and landscape-scale significance, downscaling from remote sensing can offer insight into processes and serve as calibration or verification. Here we present a multiple-scale evaluation of an area initially interpreted as a relict active layer detachment slide (before 1950) on Melville Island in the High Arctic, where differential interferometric synthetic aperture radar (DInSAR) showed subsidence between 2013 and 2015. Ground-based, cryostratigraphy measurements were combined with ground-penetrating radar (GPR) to investigate permafrost ice-content. The results indicate greater subsidence within the relict active layer detachment as detected by DInSAR. GPR surveys and permafrost coring indicated the presence of an ice-rich or massive ice layer near the base of the active layer in this area. In addition, cryostratigraphic evidences of thaw unconformity and of massive ice depth helped validate the interpretations of the geomorphology in the active layer detachment. This combination of methods indicated a localized and inherited landform-subsidence association, which brought further insight into the interpretation of DInSAR subsidence data. The framework presented in this study demonstrates the importance of site-specific investigations of thermokarst signal in order to understand the processes behind the remote sensing results. (C) 2020 Elsevier B.V. All rights reserved.
多年冻土是青藏高原主要的,也是关键的土壤类型。其发生、发展对青藏高原生态、水文等都有重要的影响。自出现合成孔径雷达干涉技术(Interferometric Synthetic Aperture Radar,In SAR)以来,对多年冻土区土壤冻融的研究就出现了一种新的手段,利用该方法可以有效探测近地表土壤的冻融状态。本文首先介绍了多年来各国的星载合成孔径雷达(SAR),然后阐述了该方法的理论基础,最后对差分干涉合成孔径雷达技术(D-In SAR)、小基线子集方法(Small Baseline Subset Approach,SBAS-DIn SAR)和永久散射体技术(Permanent Scatterers,PS)都做出了描述。综上所述,利用适合的SAR数据和有效的In SAR方法研究青藏高原冻土区的冻融状况,可以为今后的科学研究提供范围广、类型多样、精度高的基础数据。
