# UAV-Derived Himalayan Topography: Hazard Assessments and Comparison with Global DEM Products
## 2 Study Sites and Methods  
### Study Sites  
UAV surveys were conducted in two areas of central Nepal with distinct river channel characteristics (Figure 1). Tal village is located at \(\sim\)1680 m a.s.l, with a mean area of interest (AOI) slope  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Consideration** & \multicolumn{2}{c}{**Advantages of UAV Surveying Compared to**} & **Limitations of UAV Surveying Compared to** \\  & **Satellite Imaging** & **Satellite Imaging** \\ \hline Weather & Flying underneath a cloud base & Maximum wind speed restrictions \\  & Flying during optimum lighting conditions & Reduced battery life and risk of equipment loss in adverse weather conditions \\ Altitude & Variable aboveground flight altitude to determine & Maximum aboveground flight altitude may be fixed in commercial UAVs (e.g., \(500\) m) or by \\  & & \multicolumn{2}{c}{} \\  & & \multicolumn{2}{c}{} \\  & Optimise flight time to minimise shadows & local/national regulations \\ Topography & Improved slope coverage from multiazimuthal & Requirement to navigate complex topography or rely \\  & look angles and avoidance of layover & on autonomous navigation \\  & Ability to resolve overhanging topography & Limited survey footprint (several square kilometres \\  & & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\ Spatial and spectral coverage & manual flight control or autonomous route planning software & UAV surveys may need to maintain line of sight to \\  & & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\ Temporal coverage & Investigator-specified repeat interval and season & Fewer repeat times related to high cost of field \\  & or time of day, and coordination with other field & deployments compared to continuously operated \\  & & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\ In situ validation & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\ Permissions, cost, and data & Potential to crowdsource imagery following a disaster or to generate baseline topography for & Transportation costs and limit, licensing, and liability insurance \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\  & \multicolumn{2}{c}{} \\ \end{tabular}
\begin{tabular}{c} \hline \hline
**Transportation costs and import regulations** \\ Permit, licensing, and liability insurance \\ requirements \\ Local permissions or objections to flights \\ Higher costs per square kilomet of survey due to \\ fieldwork deployment \\ \hline \hline \end{tabular}
\end{table}
Table 1: Use of unmanned aerial vehicles (UAVs) in the Himalaya.  
of 37\({}^{\circ}\). The village is situated on the infill of a former landslide-dammed lake [30] and is located on the Marsyangdi River. The Pisang Landslides occurred following the 2015 Gorkha earthquake upstream of Lower Pisang village (\(\sim\)3200 m a.s.l), which is situated on a terrace above the Marsyangdi River [5]. The village is within the Annapurna Conservation Area (ACA), which is the largest protected area in Nepal (7629 km\({}^{2}\)). The Pisang Landslides AOI had a mean slope of 26\({}^{\circ}\).