Evaluation of novel ultrasonic sensor actuated nozzle in center pivot irrigation systems

Center pivot irrigation systems are used globally to irrigate large fields. They have higher water application efficiency than other sprinkler or surface irrigation approaches, but this water application efficiency may be further improved by dynamically adjusting the nozzle height in response to plant growth and canopy heterogeneities; this approach is referred to as dynamic elevation spray application (DESA). The key data input required to achieve DESA is the plant canopy height; however, this measurement is challenging to acquire in realtime due to canopy heterogeneity and potential interference from active water spray. An ultrasonic sensor was evaluated for this purpose. Both lab and field evaluations were conducted. Lab evaluations used view angles ranging from 0 degrees to 35 degrees at increments of 5 degrees, and heights ranging from 0.5 m to 1.75 m for corn, clover, and potato. Field evaluations used view angles of 0 degrees and 5 degrees, and heights from 0.5 m to 1.25 m for green beans, green peppers, eggplants, grass, and ground. Regardless of plant type and height, results from the lab suggest that DESA sensor accuracy decreases about 0.5% with one unit increase in angle's degree. When corn was used, the sensor accuracy dropped almost 9%. Results for the field showed that the lowest accuracy (92%) was observed at the green beans with 1.25 height. Field tests with active water spray yielded significantly different measurements from without water spray, but sill had accuracies > 97%. These findings demonstrate the feasibility of using ultrasonic sensors for DESA.