# Review of Photogrammetric and Lidar Applications of UAV
## 6 Discussion
### Discussion on Applications of UAVs
#### 6.2.4 Natural Hazards and Geohazards  
UAV technology is also used to track and monitor geohazards. The authors of [58,138] monitored the evolution of erosion, morphological changes in debris cones, and the dynamics of movement of rock blocks and debris cones between stages of measurement in the high mountain environment in the High Tatras. There, the authors used a UAV DJI Phantom 4 equipped with a digital camera with a resolution of 5472 \(\times\) 3648 pixels. The author of [139] monitored seismic faults in the 2021 Maduo earthquake in China based on UAV-lidar technology, InSAR, and field investigation. The study [140] mapped landslides after the 2017 earthquake using high-resolution UAV imagery in the Jiuzhaigou area in Zhangzha City, Jiuzhaigou County, in northwestern Sichuan Province, China. A few days after the earthquake, a Huaao X-UAV flight was conducted, and a high-resolution DEM was derived from the acquired data. The authors of [141] focused on assessing and analyzing rock falls along a national highway in Phitsanulok Province, Thailand. The images collected by UAVs were transformed into digital topographic contours, and a typical cross-section was created using a digital elevation model (DEM). Rockfall boulders were also addressed by the authors of [142], who used a DJI Phantom 4 Pro quadcopter in their study. From a flight altitude of 75 m AGL, they acquired 89 images with a GSD of 3.5 cm, which resulted in the creation of a Digital Surface Model (DSM) and a map of geohazards. When monitoring geohazards, the goal is usually to create a DSM or DTM, for which the SfM method is more suitable. Using the SfM method, we can monitor the development of erosion, morphological changes in objects, and the dynamics of rock movement or landslides. However, an alternative is also the use of LiDAR technology, which can be used to monitor seismic faults during an earthquake. Monitoring of changes in volcano morphology using UAV is involved in the works [143,144]. [PERSON] et al. [143] investigated magnetic field measurements using UAVs in the central part of Chaine des Puys and at the Petit Puy de Dome volcano. [PERSON] et al. [144] monitored the deformation of the summit of Piton de la Fournaise volcano and used ortho-images to fit structural and deformation maps of the study area. The unstable blocks of Sciara del Fuoco volcano on the island of Stromboli, Italy, were investigated using a Saturn UAV and a Canon IXUS 240 camera in [145]. In cooperation with UAVs and ground-based laser scanning, the area of the volcano was monitored by the author [146]. In the Nirano Nature Reserve in Emilia Romagna, Italy, the author acquired more than 350 images using a quadcopter and Canon Power Shot S110 camera. Using images, he produced point clouds and georeferenced ortho-images and DEM, which were used to study volcanic mud complexes. In the work [147], the authors mapped the volcano's crater rim and volcanic dome. In 2012, lidar data were acquired using a LiteMapper 5600 system installed on a Cessna 402B aircraft. Data were obtained at a flight height of 820 m AGL, with 40% lateral and 60% forward overlap, at a density of 5 points/m\({}^{2}\). Two years later, the same area was captured using a fixed-wing UAV with Canon PowerShot S100 camera. As a result, 328 photographs with a resolution of 3000 \(\times\) 4000 pixels were obtained. The authors used the integration of the UAV and satellite imagery at a volcano in East Java, Indonesia [148]. They used a DJI Mavic Pro UAV with a built-in RGB camera equipped with a 1/2.3\" CMOS sensor to generate the DSM and ortho-mosaics. Reference [149] used an RC high-wing UAV equipped with a digital camera for mapping during a volcanic eruption, which produced a DEM that was effectively applied to assess the post-disaster situation. In the field of volcano monitoring, the SfM photogrammetric method led to the representation of high-resolution3D terrain models and allowed the acquisition of high-resolution digital elevation models or accurate deformation maps of the volcano.