## 4 Real-Time Control and Optimisation  
Due to factors such as differences in soil composition and weather, the infiltration characteristics at the field scale will vary both spatially and temporally. For most conventional irrigation systems that seek to apply water uniformly, this will mean that the on-farm WUE will be equally variable across  
Figure 2: An example of a device with multiple sensors (**a**), with the ability to measure soil properties (**b**) (moisture, conductivity and temperature), air temperature and relative humidity. The device has a 2G/3G connectivity, and its web platform has an open Application Programming Interface (API) for ease of integration with other systems.  
the field [21]. The variability in WUE is more pronounced in surface irrigation systems (e.g., furrow) whereby irrigation water is conveyed over the soil surface. Hence, in the recent times, the concept of real-time control and optimisation, which was traditionally used in other branches of engineering, has gained prominence in irrigation water management.  
In the context of irrigation, real-time control implies measurements taken during an irrigation event (e.g., advance of water in a furrow system) are processed for the modification of the same irrigation event. This is at variance with conventional management systems which typically rely on previous or historical measurements, which are affected by the temporal nature of infiltration characteristics. Real-time control is feasible when the control process is automated so that the feedback can be implemented rapidly. On the other hand, optimisation is the process of manipulating various variables of an irrigation system with the aim of achieving the best possible outcome. This has traditionally been achieved through trial and error or irrigator experience; however, owing to the advancement in computing technology in the recent past, the use of simulation models has been on the increase [22].  
Surface irrigation systems that can be controlled and optimised in real time are sometimes referred to as smart irrigation systems (Figure 3). They are regarded as improvements from purely automated systems, which are mostly designed to reduce irrigation labour requirement through automation of some tasks. The traditional or conventional irrigation systems are associated with high labour requirement and low WUE (Figure 3).  
In surface irrigation systems in particular, adaptive real-time control has been proposed for the management of temporal infiltration variability [23; 24; 25]. A real-time optimisation system for furrow irrigation was tested in a field of commercially grown cotton in Queensland, Australia, demonstrated potential for an improvement in WUE and a reduction in labour requirement [26]. The system involved measurement of the inflow rate, sensing of the advance of water along the furrow, a computing system with a simulation model, and a telemetry system to facilitate communications between different components. A commercial prototype of this system was produced, and trials in a commercially irrigated field showed that it is able to control irrigation events by cut-off time to achieve the maximum application efficiency [27].  
Hence, it is clear that real-time control and optimisation in the Australian irrigation industry is still at its infancy, particularly in surface irrigation. However, based on the amount of research and the progress made so far (for instance the commissioning of prototype systems), it is conceivable that, in the future, it will play a bigger role in irrigation water management and improvement of WUE.  
Figure 3: Advances in irrigation technologies.