A semiautomated mapping of landslide volume displacements using UAV aerial imagery
Authors: Irimia Radu , Sandric Ionut Cosmin , Ilinca Viorel , Chitu Zenaida , Gheuca Ion 
Published: March 2022

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&lt;p&gt;&lt;span&gt;The&amp;#160;current&amp;#160;study&amp;#160;is&amp;#160;focused&amp;#160;on&amp;#160;assessing&amp;#160;the&amp;#160;spatial&amp;#160;and&amp;#160;temporal&amp;#160;patterns&amp;#160;of&amp;#160;landslide&amp;#160;volume&amp;#160;displacements&amp;#160;using&amp;#160;a&amp;#160;semiautomated&amp;#160;method&amp;#160;and&amp;#160;&lt;/span&gt;&lt;span&gt;Unmanned Aerial Vehicle&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;(&lt;/span&gt;&lt;span&gt;UAV&lt;/span&gt;&lt;span&gt;)&amp;#160;&lt;/span&gt;&lt;span&gt;aerial&amp;#160;imagery.&amp;#160;The case&amp;#160;study&amp;#160;is&amp;#160;located&amp;#160;in&amp;#160;the&amp;#160;Livadea&amp;#160;village&amp;#160;from&amp;#160;Curvature&amp;#160;Subcarpathians,&amp;#160;Romania,&amp;#160;where&amp;#160;a&amp;#160;landslide&amp;#160;was&amp;#160;triggered&amp;#160;on&amp;#160;May 3, 2021.&amp;#160;Three&amp;#160;separate&amp;#160;flights&amp;#160;were&amp;#160;flown&amp;#160;on&amp;#160;May 6, May 25,&amp;#160;and&amp;#160;July&amp;#160;10&amp;#160;using&amp;#160;DJI&amp;#160;Phantom&amp;#160;4&amp;#160;and&amp;#160;Phantom&amp;#160;4 RTK&amp;#160;drones.&amp;#160;Even&amp;#160;though&amp;#160;there&amp;#160;is&amp;#160;a&amp;#160;difference&amp;#160;in camera&amp;#160;resolution,&amp;#160;each&amp;#160;flight&amp;#160;plan&amp;#160;was&amp;#160;created&amp;#160;to&amp;#160;correspond&amp;#160;to&amp;#160;a 4cm/pixel&amp;#160;spatial&amp;#160;resolution,&amp;#160;meaning&amp;#160;that&amp;#160;the&amp;#160;constant&amp;#160;height&amp;#160;above&amp;#160;ground&amp;#160;was&amp;#160;different&amp;#160;between&amp;#160;the&amp;#160;first&amp;#160;flight&amp;#160;and&amp;#160;the&amp;#160;next&amp;#160;two&amp;#160;flights.&amp;#160;For&amp;#160;the&amp;#160;first&amp;#160;flight,&amp;#160;because&amp;#160;the&amp;#160;UAV&amp;#160;equipped&amp;#160;with&amp;#160;the&amp;#160;RTK&amp;#160;receiver&amp;#160;was&amp;#160;not&amp;#160;available, a&amp;#160;graded&amp;#160;consumer&amp;#160;UAV&amp;#160;equipped&amp;#160;with&amp;#160;a Non-RTK&amp;#160;receiver&amp;#160;was&amp;#160;used.&amp;#160;A&amp;#160;maximum&amp;#160;overlap&amp;#160;with&amp;#160;the&amp;#160;smallest&amp;#160;errors&amp;#160;possible&amp;#160;between&amp;#160;all&amp;#160;the&amp;#160;flights&amp;#160;was&amp;#160;obtained&amp;#160;by&amp;#160;orthorectifying&amp;#160;the&amp;#160;first&amp;#160;and&amp;#160;the&amp;#160;third&amp;#160;flights&amp;#160;with&amp;#160;GCPs&amp;#160;collected&amp;#160;from&amp;#160;the&amp;#160;second&amp;#160;flight.&amp;#160;&lt;/span&gt;&lt;span&gt;The&amp;#160;method is based on using aerial imagery collected with UAV and their derived products obtained&amp;#160;by applying the&amp;#160;Structure from Motion&amp;#160;(SfM)&amp;#160;technique.&amp;#160;Because it is an area with dense forest,&amp;#160;the Visible Atmospherically Resistant Index&amp;#160;(VARI) was used to filter out all the pixels&amp;#160;with vegetation from the digital surface models (DSM). The&amp;#160;gaps were filled by using the Empirical Bayesian Kriging interpolation method, implemented in ArcGIS Pro.&amp;#160;The results show&amp;#160;volume displacement&amp;#160;rates of&amp;#160;0.005 cubic meters/meter&amp;#160;for&amp;#160;the&amp;#160;period&amp;#160;between the&amp;#160;first and second flights and 0.05 cubic meters/meter for the period between the second and third flights. The overall displaced volume was&amp;#160;approximately 406000 cubic meters&amp;#160;with&amp;#160;approximately&amp;#160;41000&amp;#160;cubic meters&amp;#160;for&amp;#160;the period between the first and second&amp;#160;flights&amp;#160;and&amp;#160;approximately 365000 cubic meters&amp;#160;between&amp;#160;the&amp;#160;second and&amp;#160;the&amp;#160;third&amp;#160;flight.&amp;#160;This approach proved quick and efficient for&amp;#160;assessing&amp;#160;landslide&amp;#160;volume displacement&amp;#160;when fast response and measures are necessary to reduce landslide consequences.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;strong&gt;&lt;span&gt;Acknowledgement&lt;/span&gt;&lt;/strong&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;This work was supported by a grant of the Romanian Ministry of Education and Research, CCCDI - UEFISCDI,&amp;#160;project number PN-III-P2-2.1-PED-2019-5152, within PNCDI III&amp;#160;(project coordinator Ionu&amp;#539;&amp;#160;&amp;#536;andric,&amp;#160;&lt;/span&gt;&lt;span&gt;https://slidemap.gmrsg.ro&lt;/span&gt;&lt;span&gt;)&amp;#160;and&amp;#160;by the project PN19450103&amp;#160;/&amp;#160;Core Program&amp;#160;(project coordinator Viorel Ilinca).&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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