## 3 A Comprehensive Monitoring System for Landslides in 'Space-Sky-Ground-Underground'
### Sky-Based Monitoring  
Sky-based monitoring carries out aerial photography and surveying of the test area, mainly by aircraft, UAVs, airships, and other aircraft equipped with high-speed cameras and aerial survey instruments. Among them, the applications of UAVs in landslide monitoring are constantly expanding with the continuous improvement in various types of UAV technologies. This technology primarily utilizes UAVs equipped with high-resolution cameras and Lidar to capture high-definition images of landslides to further compare and analyze the changes in landslides at different times. Based on this, the direction and  
Figure 11: Landslide monitoring based on SBAS-InSAR and PS-InSAR [34]: (**a**) spatial position of landslides; (**b–e**) time-series points of two large landslides; (**f,g**) histogram of deformation rate, the normal density function is fit by red dotted lines. Figure 10: The development history of global satellite navigation systems. rate of landslide sliding are analyzed. Then, the prediction of landslide instability and judgment are carried out combined with other landslide monitoring technologies. With the continuous development of space-based monitoring technology, various types of UAVs suitable for landslide monitoring in different environments have emerged, with measurement accuracy reaching the centimeter level. The commonly used UAV can be divided into fixed-wing UAVs, rotary-wing UAVs, uncrewed airships, and flapping-wing UAVs based on the configuration of the flight platform (Table 2), which provides diversified equipment options for landslide monitoring in different types and geological environments [35; 36]. Currently, with the advancement of artificial intelligence technology, UAV technology can be integrated with techniques such as artificial intelligence and machine learning to analyze and process monitoring data. In actual landslide monitoring, the selection of UAV is often based on the terrain, topography, and meteorological conditions of the landslide area. On this basis, technicians can combine actual monitoring objectives with the situation to achieve the best monitoring effect. [PERSON] et al. [37] collected high-resolution images of landslides by DJI Phantom 3 Advanced UAV and generated the 3D model to realize visual analysis of landslides (Figure 12). The model parameters were compared and verified with the data obtained from the total station. The results show that the difference between uncrewed aerial vehicle monitoring data and total station monitoring values is slight, indicating that this technology has good applicability in estimating the size of landslides. The established three-dimensional model of landslides has excellent application prospects for early warning and prevention of landslide hazards. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Model of UAV**} & **Features** & **Advantage** & **Disadvantage** & **Parameter** \\ \hline \multirow{4}{*}{Fixed-wing UAV} & \multirow{4}{*}{ \begin{tabular}{c} The wings remain fixed and \\ rely on the wind passing \\ through them to provide lift. \\ UAVs need to run up during \\ takeoff and glide down \\ during landing. \\ \end{tabular}  } & Long battery life & High requirements & Range: 30–80 h \\  & & & and high load & \begin{tabular}{c} Scale: \\ conditions \\ \end{tabular}  & \begin{tabular}{c} Scale: \\ light, small, \\ medium \\ \end{tabular}  \\ \hline \multirow{4}{*}{ \begin{tabular}{c} Multirotor \\ UAV \\ \end{tabular}  } & \multirow{4}{*}{ \begin{tabular}{c} A UAV that generates \\ upward lift from its propeller \\ and drives the entire UAV to \\ fly. This type of UAV is \\ divided into multi-rotor \\ UAVs, helicopters, \\ autorotation rotor UAVs, etc. \\ \end{tabular}  } & Easy to operate & Shortest battery life & \begin{tabular}{c} Range: \\ 0.3–1 h \\ scale: \\ scale: \\ light, small, \\ medium \\ \end{tabular}  \\ \hline \multirow{4}{*}{\ \begin{tabular}{c} Airship \\ \end{tabular}  } & \multirow{4}{*}{