Performance of tree canopy diameter measurement based on ultrasonic sensor and DGPS

To carry out precision spray based on fruit tree canopy and to obtain real-time tree canopy diameter in orchard, a measuring system for fruit tree canopy diameter was established on the tractor by using data-collecting facilities such as ultrasonic sensor, DGPS receiver, and electronic compass. Outdoor measurement experiment was conducted on five trees with regular cylinder-shaped canopy. Four calculation methods were introduced for the measurement of tree canopy diameter. Tractor traveling speeds of 0.31 m/s and 0.65 m/s were selected to measure and to examine this measuring system. Error analysis results show that the mean relative errors are 5.54% and 5.80% in computing the canopy diameter between two outer rims using ultrasonic sensor while the tractor is traveling at 0.31 m/s and 0.65 m/s, respectively. After the weighted average fusion of using ultrasonic sensor and DGPS data, the tractor track was corrected and the mean relative error for the two traveling speeds is 14.3% when measured with calculating method using the coordinates obtained by measuring the two outline rim points on tree canopy. The research results provide methods for the control of fruit tree profile spray and collecting information on fruit tree growth.