The UGA Smart Sensor Array (UGA SSA) consists of smart sensor nodes and a Gateway. A “smart sensor node” is defined as the combination of electronics and sensors installed at each location in the field. A UGA SSA node consists of a circuit board, a radio frequency (RF) transmitter, soil moisture sensors and temperature sensors. Each sensor node accommodates up to 3 Watermark® soil moisture sensors and 2 thermocouples for measuring temperature.
In the future, other sensor types (nutrient, pH) can be added to the node. The RF transmitter is a postage stamp-sized intelligent low-cost, low-power radio module capable of acquiring, analyzing, and transmitting sensor data.
Data from all the nodes are routed to a centrally located node known as the Gateway at 5 minute intervals. At the Gateway, data are stored on net-book computer and transmitted via cellular modem to an FTP server hourly. The net-book computer is powered by a solar panel.
One unique characteristic of the UGA SSA is that it uses wireless mesh networks to communicate between irrigation sensor nodes. As the name implies, mesh networks create a wireless network between the nodes. The RF transmitters act as a repeater to pass along data from other nodes to form a meshed network of nodes. If any of the nodes in the network stop transmitting or receiving or if signal pathways become blocked, the operating software re-configures signal routes in order to maintain data acquisition from the network. To overcome the attenuating effect of the plant canopy on radio transmissions, the RF transmitter antenna is mounted on spring-loaded, hollow, flexible fiberglass rods approximately 8ft above ground level. This design allows field equipment such as tractors and sprayers to pass over the sensors – something which no other truly wireless system offers. The effective range of the RF transmitter is about 2500 ft.
An important characteristic of our system is its affordable cost – a 20-node system can be installed for a onetime cost of $3500. Installing irrigation sensors throughout an irrigated field is key to understanding and managing the soil moisture variability which exists in all fields. With extensive testing, we have proven that our system is robust, reliable, easy to use, and affordable.
We have been developing the UGA SSA for the past several years. We have tested the system in its current configuration under field conditions for two entire cropping seasons including the 2011 season and the system has proved to be extremely robust. Each sensor node is powered by two AA batteries which under field conditions have an effective life which exceeds 140 days.
The strength of the UGA SSA is that its low cost allows for the installation of many sensor nodes which clearly show the variability of soil water tension in the field. Sensors installed at 4, 12, and 20 inches provide excellent information on the effect of irrigation and precipitation events on soil water tension.
During 2012, the UGA SSA was deployed in eight peanut and cotton fields. A minimum of 10 sensor nodes were installed in each field and soil moisture was recorded for the entire growing season. Please see the Flint Irrigation Scheduling Tool project for more information.