Application of UAVs in Obtaining the Derivates of the Digital Elevation Model (DEM): A Case Study of Atali Landslide, Uttarakhand

Uttarakhand, a state situated in the foothills of the Himalayas subjected every year to massively destructive landslides owing to the presence of a large number of unstable rock slopes. Geohazards like landslides require real-time monitoring and nowadays the most effective way to model and monitor the landslides is by using UAVs. They offer high time efficiency, cost-effectiveness, and reliable accuracy, which makes them a preferable option for generating high-resolution digital surface models (DSM), which are better than any terrestrial scanners or remotely sensed satellite data. Atali (30° 5′0.67"N 78°26′10.21"E) is one of the extensive cut slopes along NH-7 vulnerable to rock slides frequently during monsoon which makes it necessary to study this area in detail to prevent and mitigate future hazards. The primary objective of this study is the generation of a Digital Elevation Model (DEM) and its derivatives for the above-mentioned site and its further application. The methodology followed in the field is setting up a base station and planning the flight path of an Unmanned Aerial Vehicle (UAV) over the landslide. The drone is equipped with an optical camera and captures raw data, flown at 120 m elevation from the home point. The PPK (Post Processing Kinematics) data post-processing is done and geotagging of images captured by the UAV is performed using Geotag PPK software. This brief survey of landslide using UAV produced a digital surface model (DSM), digital terrain model (DTM), dense 3D point cloud data, and orthomosaic with the resolution of 3.6 cm/pixel GSD (Ground Sampling Distance) after final processing. Various results, such as the slope value of the landslide scarp and toe, general curvature, aspect, and hillshade, are produced, which serves as important information for landslide monitoring. The DSM shows the elevation of the scarp ranging up to 476 m from MSL and the value of maximum slope up to 69°. These parameters help in the detection of certain slopes that are vulnerable to failure in the near future. The application of geoinformatics in landslide studies could help in the calculation of mass and volume change over two epochs by considering the difference between two DSMs that would give us the displacement rate of landslide outflow.