*1.2.2 Unmanned aerial vehicles (UAVs)*

Unmanned aerial vehicles (UAVs, or drones), are being used by researchers to monitor catchments. Structure from Motion (SfM) three-dimensional point clouds can be derived from digital images collected on board UAVs, similar to the type of data produced by Light Detection and Ranging (LiDAR) technology [6]. The technological development of UAVs and their ability to derive high-resolution 3D information has made UAV image acquisition appealing in several applications. The UAV systems are mounted with red, green, blue (RGB), colour-infrared (CIR) and multispectral (MS) cameras [7]. They allow for near real-time monitoring of an area and comparably low operational costs, with the RGB cameras being the most economical [8]. Images from airborne sensors can provide a unique method of monitoring [9]. Drone systems are used to get a better visual representation of the area being studied. These images are generally taken from a height between 500 and 1,000 meters. The drawback to this method of monitoring is that the payload for most of these systems is relatively low, therefore the instruments choice is important.
