**3. Aerial soil sensing**

#### **3.1 Drone-based remote sensing**

Monitoring soil conditions with remote sensing systems is a new approach that enhances productivity in digital agriculture [90]. Through the development of

unmanned aerial vehicle (UAV) technologies [91, 92], it is now possible to retrieve soil property data with high resolution and low cost for mapping. UAVs reliably transfer soil characteristic data to computers, thereby playing an important role in precision agriculture [93]. When compared to satellites, UAVs have superior control and high spatial resolution [94]. Hu et al. [95] reported that UAVs using 62 hyperspectral bands afforded more reliable data for soil salinity prediction models than satellites, making UAVs a valuable machine for small-scale soil mapping. UAVs are also useful for assessing soil moisture in heterogeneous landscapes [96]. In addition to soil moisture, multispectral images of UAVs can be applied to map the distribution of water stress in crops (**Figure 7**) [98]. Although UAVs play a prominent role in precision agriculture, further attempts should be made to derive from data processing techniques and vegetation calibration in the future [99]. Moreover, UAVs face other challenges, such as limited flight time and stabilization, so future studies should concentrate on addressing these problems [100].
