*5.2. Sensor and Communication Networks*

Sensors are equipment used to collect a range of data such as soil moisture and weather in order to improve agricultural management. Typical examples of sensors used in irrigation water managemen<sup>t</sup> include soil moisture probes and weather stations. Traditionally, equipment for monitoring crop or soil water status were connected using cables and often required manual reading and the data used to schedule future irrigations. Apart from the inaccuracies that come with using historical data for future water management, such manual processes are time-consuming and often expensive. The use of wireless sensor technologies to improve WUE in irrigated agriculture is on the increase.

More often, a series of wireless sensors are used to monitor various parameters in the field, for example soil moisture and weather data. This is especially driven by the fact that the recent advancement in technology and competition has led to the availability of cheap sensors. A wireless sensor network consists of a number of individual sensors (sensor nodes), a sink node or hub to receive and process data from the sensor nodes, and a communication technology [32]. The sensor networks may also have actuators that can be used to automate the irrigation system.

The wireless communication technologies that are used for agricultural purposes including water managemen<sup>t</sup> are discussed in many texts, for instance Rehman et al. [32]. The current communication technologies used in agriculture are ZigBee, Bluetooth, WiFi, GPRS/3G/4G, Long Range Radio (LoRa) and SigFox [33]. The ZigBee technology is commonly preferred in irrigation water managemen<sup>t</sup> because of the range, low cost, energy efficiency and reliability [32,34].

The use of wireless sensors that measure soil moisture, temperature and humidity and relay the data over the 3G internet network is described in Reference [35]. The automation of such crucial data collection means that the irrigation system can be controlled in real time, thereby achieving higher WUE.

It appears from the literature reviewed that research into water loss through leakage has concentrated on urban water supply distribution networks. The techniques used to detect leakages in urban water distribution networks can be applied in irrigation settings. Pressure sensors connected to a wireless sensor network can play a vital role in in detecting leakages, and thus facilitate faster repair and prevention of further losses [36]. There is also a potential for using smart water technology to detect losses in water pipelines [37].

There are substantial ongoing research activities involving sensors and communication networks which are likely to lead to improved products and services in the future. It is also likely that communication networks will be used in a more integrated manner to achieve multiple objectives, for example irrigation and urban water supply using smart water meters.
