# Review of Photogrammetric and Lidar Applications of UAV
## 6 Discussion
### Discussion on Applications of UAVs
#### 6.2.4 Natural Hazards and Geohazards
Thanks to the flight at low altitudes, magnetic anomalies and changes in the volcanic context were displayed well, and morphological information could also be derived. LiDAR technology is equally effective in this area of monitoring, but the cost of equipment and the risk of damage to expensive devices is significantly greater. The authors of [150] used GEO 2 UAV equipped with a SONY A6000 camera to monitor landslides. The landslide area was observed from a flight height of 100 m, with 80% longitudinal and 60% lateral overlap, resulting in 291 images. [PERSON] et al. [151] monitored, using UAV technology, an active landslide located in western Greece and generated highly detailed ortho-mosaics and digital surface models (DSM) using the SfM photogrammetric method. Their study used a DJI UAV Matrice 600 equipped with an X5 camera that captures photos with a resolution of 4608 \(\times\) 3456 pixels and a DJI UAV Phantom 4 with a camera set to with an image resolution of 4000 \(\times\) 3000 pixels. The data were collected from a flight height of 110 m AGL, with 90% longitudinal and 75% lateral overlap. The authors of [152] used an UAV to document a steep landslide triggered by rainfall and flooding on both sides of the Rjecina River valley near Rijeka, Croatia. The authors of [153] attempted to perform landslide detection and prediction using a SibGIS UAS hexacopter equipped with two cameras. [PERSON] et al. [154] used a Quest 300 mini fixed-wing UAV with a Panasonic Lumix DMC-LX5 camera at a flight height of 90 m AGL to create a digital elevation model (DEM) to demonstrate the movement and changes in the landslide. [PERSON] et al. [155] monitored geohazards and landslides in Tuscany using a multicopter UAV named Saturn, which was developed at the University of Florence. In their publication, [PERSON] et al. [156] used a fixed-wing UAV with a Canon EOS 450D digital camera to map landslides caused by rainfall. A UAV can provide observations with high spatio-temporal resolution and enable operational monitoring of landslides and provide analyses of surface deformation. The SfM method is very often used to monitor and map landslides. This method is suitable for creating ortho-mosaic, DSM and DEM, which are most often generated during landslides. Using this method, it is also possible to detect and predict landslides. UAVs are also used to check the stability of slopes. The authors of [157] addressed the instability of the Elva valley road in northern Italy. They performed 19 flights in this area using a DJI Phantom 4 with an FC6310 camera. They acquired approximately 1700 images, from which they produced digital surface models (DSM) at three different scales: a large-scale DSM of the entire road, a medium-scale DSM to assess parts of the slope, and a small-scale DSM to assess individual discontinuities. The publication [158] used an AS350 helicopter with a Leica ALS80-HP airborne lidar system and a DJI Phantom 4 RTK UAV with an FC6310 camera (1\({}^{\prime\prime}\) CMOS) to monitor slope disturbance in the Juzhaigou area. Point clouds using lidar were acquired from a flight height of 1500-3000 m AGL, and 377 high-resolution images were acquired using the DJI UAV Phantom 4 RTK, where a dense point cloud was made. [PERSON] et al. [159] monitored a landslide that occurred on the R201 railway line Zapresic-Cakovec using a DJI Phantom 2 Vison+ and produced a digital terrain model. The article [160] used the UAV to acquire 3D orthographic images of the slopes and used them to assess slope stability and quantitative hazard assessment at sites in Croatia. [PERSON] et al. in [161] monitored the stability of a rocky slope along a highway in Pengerang, Johor, Malaysia. A survey using UAV technology was carried out with a DJI Phantom 4 PRO + V2.0 from a flight height of 5-30 m with an image overlap of more than 60%. From 246 acquired images, 3D point clouds and an accurate 3D surface model (DSM) were made. The authors of [162] analyzed the stability of a slope with a block rock massif using the lidar Leica ALS80-HP and UAV Phantom 4.