Can Drones Map Earth Cracks? Landslide Measurements in North Greece Using UAV Photogrammetry for Nature-Based Solutions
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sustainability Article Can Drones Map Earth Cracks? Landslide Measurements in North Greece Using UAV Photogrammetry for Nature-Based Solutions Paschalis D. Koutalakis 1 , Ourania A. Tzoraki 1 , Georgios I. Prazioutis 2, Georgios T. Gkiatas 3 and George N. Zaimes 3,* 1 Department of Marine Sciences, University of the Aegean, University Hill, 81100 Mytilene, Greece; [email protected] (P.D.K.); [email protected] (O.A.T.) 2 Department of Surveying and Geoinformatics Engineering, International Hellenic University, University Campus Magnisias, 62124 Serres, Greece; [email protected] 3 UNESCO Chair Con-E-Ect, Department of Forest and Natural Environment Sciences, International Hellenic University, University Campus Drama, 1st km Drama-Mikrohoriou, 66100 Drama, Greece; [email protected] * Correspondence: [email protected]; Tel.: +30-2521-060-411 Abstract: The accuracy of photogrammetry for geohazards monitoring has improved within the last years because of the “drone revolution”. This study is an attempt to perform morphometric measure- ments in a landslide event that took place near the village Nea Zichni in Northern Greece. The DJI Mavic 2 Pro was selected to capture orthoimages of the entire area including the landslide event but also other adjusted disaster phenomena. The images were loaded in the commercial software Pix4D in order to produce orthomosaics and digital surface models of the area. The georeferenced results Citation: Koutalakis, P.D.; Tzoraki, were further analyzed in ArcGIS in order to digitize and estimate the morphometric parameters of O.A.; Prazioutis, G.I.; Gkiatas, G.T.; Zaimes, G.N. Can Drones Map Earth the landslide, such as its area and volume, but also to detect cracks and plot the tensile cracking Cracks? Landslide Measurements in directions. We conclude that the methodology and produced outputs are crucial for the responsible North Greece Using UAV authorities to detect, monitor and mitigate natural disasters such as landslide events and other mass Photogrammetry for Nature-Based movements. The best practices to control mass movements are nature-based solutions such as soil Solutions. Sustainability 2021, 13, 4697. bioengineering and proper vegetation cover assisted by engineering measures. Finally, our goal is to https://doi.org/10.3390/su13094697 frequently monitor the landslide phenomenon in order to determine its evolution. Academic Editor: Alejandro Keywords: drone; DSM; fissures; geohazard; GIS; mapping; natural disaster; nature-based solutions; Gonzalez-Ollauri orthomosaic; UAS Received: 15 March 2021 Accepted: 19 April 2021 Published: 22 April 2021 1. Introduction The definition of the landslide hazard is difficult because it is a very complex nat- Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in ural (or even man-triggered) phenomenon [1]. A landslide is “a process of changes in published maps and institutional affil- the stress–strain state of a slope groundmass leading to a mass separation and ground iations. movement downslope, while maintaining a continuous contact between sliding mass and underlying undisturbed ground” [2]. This specific definition of “landslide” excludes other related types of slope failures such as subsidence, toppling and rockfall [3,4]. In general, a landslide develops in time through several stages (prefailure deformations, failure itself and postfailure displacements) but it can also be a sudden event. Additionally, there are Copyright: © 2021 by the authors. landslides with many movement episodes, separated by long or short periods of relative Licensee MDPI, Basel, Switzerland. This article is an open access article inactivity [5]. Landslides are complicated phenomena and may exhibit many different slope distributed under the terms and failures apart from the main soil slump, e.g., topples, rockfall, subsidence, creep, etc. while conditions of the Creative Commons typical and profound types of fractures are the tensile cracks or fissures (Figure1)[6,7]. Attribution (CC BY) license (https:// Geohazards such as landslides, mass movements, subsidence and sinkholes have been creativecommons.org/licenses/by/ recorded in many areas of Greece (Florina, Thessaloniki, Thessaly, etc.) [8–10] as well as in 4.0/). other parts of the world (Ebro River in Spain, Mexico City, Venice in Italy, etc.) [11–13]. Most Sustainability 2021, 13, 4697. https://doi.org/10.3390/su13094697 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, x FOR PEER REVIEW 2 of 21 while typical and profound types of fractures are the tensile cracks or fissures (Figure 1) [6,7]. Geohazards such as landslides, mass movements, subsidence and sinkholes have been recorded in many areas of Greece (Florina, Thessaloniki, Thessaly, etc.) [8–10] as well Sustainability 2021, 13, 4697 as in other parts of the world (Ebro River in Spain, Mexico City, Venice in Italy, etc.)2 of 20[11– 13]. Most of these cases are characterized by the presence of loose sedimentary deposits with confined or semiconfined aquifers, as well as artesian aquifers [14,15]. Slope satura- oftion these by cases water are is characterized a primary cause by the of presence landslid ofes. loose This sedimentary can occur by deposits extreme with precipitation confined orevents semiconfined [16], by aquifers, active faults as well and as earthquakes artesian aquifers [17], [14by, 15intense]. Slope human saturation activities, by water construc- is a primarytions and cause urbanization of landslides. causes This [18,19], can occur by by climate extreme change precipitation in permafrost events regions [16], by [20] active and faultsby sea and level earthquakes rise in coastal [17], byareas intense (including human tsunamis) activities, [21,22]. constructions and urbanization causes [Landslides18,19], by climate and other change catastrophic in permafrost events regions have [significant20] and by impacts sea level on rise human in coastal com- areasmunities (including and can tsunamis) result in [21 several,22]. kinds of damage, such as economic losses and, in the worstLandslides cases, casualties and other [23,24]. catastrophic Monitoring events is have mandatory significant in order impacts to investigate on human commu-such phe- nitiesnomena, and can to resultassess in the several possible kinds triggering of damage, factors such asand economic to measure losses the and, evolution in the worst of the cases,postemergency casualties [23 phase.,24]. Monitoring There are isvarious mandatory meth inods, order tools to investigateand approaches such phenomena, for landslide tomonitoring assess the possible that include triggering geophones factors andand to incl measureinometers, the evolution topographical of the postemergencysurvey measure- phase.ments There with are total various stations methods, or Global tools Navigati and approacheson Satellite for Systems landslide (GNSS) monitoring receivers, that in-Air- cludeborne geophones Light Detection and inclinometers, and Ranging topographical (LiDAR) systems, survey measurementsTerrestrial Laser with Scanners total stations (TLSs), orphotogrammetric Global Navigation techniques Satellite Systemsusing aerial (GNSS) photos receivers, or high Airborne resolution Light satellite Detection images, and Dif- Rangingferential (LiDAR) Interferometry systems, using Terrestrial radar Laser images Scanners (DInSAR) (TLSs), and photogrammetric photogrammetric techniques techniques usingusing aerial data photos from Unmanned or high resolution Aerial Vehicles satellite (U images,AVs) [25–28]. Differential A successful Interferometry innovative using ex- radarample images is the (DInSAR)LITMUS landslide and photogrammetric detection system, techniques which provides using data a web from portal Unmanned and a live Aerialdemonstration Vehicles (UAVs) map of [25 the–28 events.]. A successful The LITMUS innovative combines example multiple is the physical LITMUS sensors landslide such detectionas near system,real-time which data providesfrom the aUnited web portal States and Geological a live demonstration Survey (USGS) map seismic of the network, events. Thethe LITMUS Tropical combines Rainfall Measuring multiple physical Mission sensorsby National such Aeronautics as near real-time and Space data Administra- from the Unitedtion (NASA), States Geological but also Surveyreports (USGS)from social seismic media, network, e.g., Twitter, the Tropical YouTube, Rainfall and Measuring Instagram Mission[29]. by National Aeronautics and Space Administration (NASA), but also reports from social media, e.g., Twitter, YouTube, and Instagram [29]. Figure 1. An idealized illustration of a landslide that has evolved to a slump-earth flow. The image also contains the main parts of the landslide with labels (image based on Varnes classification 1978). Figure 1. An idealized illustration of a landslide that has evolved to a slump-earth flow. The image also contains the main parts of the landslide with labels (image based on Varnes classification 1978). The Unmanned Aerial Vehicles (UAVs), or the Remotely Piloted Aircraft Systems (RPAS), or as they are most well-known “drones”, are tools that can provide spatial resolution datasets on local or wider scale areas [30,31]. The UAV is a component of an unmanned aircraft/aerial system (UAS), which includes the tool, the pilot and the communication system [32]. During the last decade, the combination of: (a) the rapid development of low cost UAV with improved battery life and (b) the reduction in the dimensions and costs of the optical