A real-time ultrasonic system to measure wild blueberry plant height during harvesting

Spatial variations in wild blueberry plant height pose a serious challenge for the operator to maintain the optimum harvester picking head height. Harvester head adjustment based on plant height increases harvestable fruit yield and quality while preventing plant pulling. An advanced Ultrasonic Plant Height Measurement System II (UPHMS II) was developed and incorporated into a commercial mechanical harvester. The developed system consisted of three ultrasonic sensors covering the width of the harvester head, a real-time kinematics global positioning system (RTK-GPS), custom built software, and a rugged computer. The custom software acquired and processed the ultrasonic sensing data in real-time during mechanical harvesting. Four wild blueberry fields were selected in central Nova Scotia to evaluate the performance of the developed system. Forty eight experimental plots were randomly constructed within four fields and wild blueberry plant heights were recorded manually prior to harvest. The UPHMS II was tested and evaluated to estimate plant height. The manual plant height measurements were compared with ultrasonically sensed data to ensure the accuracy of the developed system. A previous system (UPHMS I) comprising of one ultrasonic sensor was also tested and evaluated. Results of regression and scatter plots revealed that the UPHMS II was able to sense plant height in real-time more accurately with root mean square error (RMSE) of 1.7 cm when compared with the UPHMS I (RMSE = 5.7 cm). The UPHMS II equipped with three sensors covered the complete width of the harvester (0.91 m), which showed higher accuracy compared to the UPHMS I.