UAV-Derived Himalayan Topography: Hazard Assessments and Comparison with Global DEM Products

C Watson,Jeffrey Kargel,Babulal Tiruwa

doi:10.3390/drones3010018

Abstract

Topography derived using human-portable unmanned aerial vehicles (UAVs) and structure from motion photogrammetry offers an order of magnitude improvement in spatial resolution and uncertainty over small survey extents, compared to global digital elevation model (DEM) products, which are often the only available choice of DEMs in the high-mountain Himalaya. Access to fine-resolution topography in the high mountain Himalaya is essential to assess where flood and landslide events present a risk to populations and infrastructure. In this study, we compare the topography of UAV-derived DEMs, three open-access global DEM products, and the 8 m High Mountain Asia (HMA) DEMs (released in December 2017) and assess their suitability for landslide- and flood-related hazard assessments. We observed close similarity between UAV and HMA DEMs when comparing terrain elevation, river channel delineation, landside volume, and landslide-dammed lake area and volume. We demonstrate the use of fine-resolution topography in a flood-modelling scenario relating to landslide-dammed lakes that formed on the Marsyangdi River following the 2015 Gorkha earthquake. We outline a workflow for using UAVs in hazard assessments and disaster situations to generate fine-resolution topography and facilitate real-time decision-making capabilities, such as assessing landslide-dammed lakes, mass movement volumes, and flood risk.

Highlights

The artifacts caused a deviation of the GDEM2 delineated
The GDEM2 was not used in Tal village analysis due to the prevalence of artifacts (Figure 2), which river were channels from the AW3D30 channels by hundreds of metres, in some cases exceeding a kilometre likely caused by persistent cloud cover
We have shown the value of fine-resolution unmanned aerial vehicles (UAVs)-derived digital elevation model (DEM) and orthophotos for topographic representation and hazard assessment in the high mountain Himalaya

Summary

Introduction

Elevation models of Himalayan topography are required for investigating a range of earth surface processes, including quantifying landslide and landslide-dammed lake volumes (e.g., [1,2,3,4,5]); glacial lake outburst flood (GLOF) assessments (e.g., [6,7,8]); hydraulic modelling (e.g., [9,10,11,12]); hydrological modelling (e.g., [13]; and calculating glacier mass balance and ablation processes (e.g., [14,15,16,17]). These DEMs and point clouds are becoming increasingly common for assessing earth system processes and hazards in high mountain environments due to the submetre precision that is achievable [17,24,25]. UAV surveys in the Himalaya are generally limited in spatial extent and by the costs and administration associated with permits, licensing, transportation, and field deployment (Table 1). Flexible flight altitudes and survey times enable tailored data collection to requirements such as achieving a specified spatial resolution or minimising terrain shadows. UAV-derived products, such as DEMs and orthophotos, can be used to map and monitor landslide evolution [26,27] and quantify socioeconomic disruption [28]

Objectives

Results

Discussion

Conclusion