# Remote Sensing for Irrigation of Horticultural Crops
## 3 Sensors and Platforms
### Remote Sensing Platforms
#### 3.2.3 UAV (Unmanned Aerial Vehicle)  
At present, unmanned airborne vehicles (UAVs) are the most common airborne platforms for civilian and military aircraft remote sensing applications [84].  
Figure 1: (a) Layout of the experimental field: (**a**) a=observation wells; b=pumping well; c=water supply ditch; d= drainage ring. (**b**) Airborne images. (**c**) False color image of Figure 1b.  
Remote sensing with UAVs has very high resolution. It provides fast and low-cost data, and cloud cover does not prevent acquisition, so it is an important instrument for monitoring and managing crops during the growing season [85; 86].  
UAVs come in different sizes related to their total weight. The small systems were defined as an UAV of a maximum weight of 25 kg. [PERSON] et al. [87], [PERSON] et al. [51], [PERSON] et al. [88], [PERSON] et al. [89], and [PERSON] and [PERSON] [34] describe current UAS systems (fixed and rotating wing), solutions and applications. The following description provides only the basics for the UAV remote sensing field; an extended recent review (monograph) on the topic can be found in [PERSON] [90], as well as in [PERSON] and [PERSON] [34].  
Large volumes of UAVs are expected to fly in upcoming years, so safe operation is essential for the user and the public. There are extremely large numbers of UAV applications to remote sensing [34]. [PERSON] and [PERSON] [91] reported the evolution of the use of UAVs in the field of photogrammetry and remote sensing.  
Another state-of-the-art example is available in [PERSON] et al. [92], who studied the use of UAV technology for various crop applications (crop emergence, vigor, characterization of yield potential). The review also reported the potential and future perspectives of using UAV imaging to evaluate the effect of biotic and abiotic stresses for crop breeding and precision crop yield management.  
[PERSON] et al. [88] suggested that UAVs are set to become a crucial factor of a water-resource management toolkit. They can ensure high-resolution data (not available from other platforms such as satellites or aircrafts), in a cost-effective way and in a more sustainable way for water-resource targets. The authors suggest the use of UAVs for data analysis of water resource information (e.g., regular surveys of reservoir resources, soil moisture assessments by thermal imaging, more effective consumption).  
An interesting point of view was reported by [PERSON] [53], who put an emphasis on remote and proximal sensing changes due to a variety of sensors fitted to drones and kites to improve fine-grained understanding of environmental processes. [PERSON] et al. [93] also proposed a grassroots remote sensing and democratic mapping for delivering rapid spatial data (GeoTIFF images) from lightweight drones and kites with open-source geospatial toolkits and android smartphone apps.  
UAVs offer many advantages with respect to other platforms, the main one relying on readiness and repeatability of the measurements. The UAV operator can monitor the procedure and decide to repeat the flight if something went wrong. Conversely, each satellite has a specific revisit time (see Table 1), and it is almost impossible to replicate a survey. The airborne flights try to reduce costs by bringing together several targets and actions (e.g., one strip on different subjects or many strips on the same one). This prevents modification of the flight plan. The operation costs are the lowest for the UAVs, which are flexible and may change sensors/missions/objectives easily. However, satellite sensors cannot be replaced when they are obsolete or out of service.