Software development for real-time ultrasonic mapping of tree canopy size

Ultrasonic transducers have been used for the digital control of agrochemical application rates in sprayers and fertilizer spreaders of tree crops for about 16 years. The early systems were developed before the advent of commercial DGPS receivers and relied on real-time tree canopy sensing and agrochemical rate adjustment according to the size of canopy detected. The widespread availability of fast and accurate DGPS service since 2000 and the rapid evolution of laptop computing power, has offered new opportunities for enhanced processing and spatial mapping of ultrasonically sensed orchard or grove data. The objective of this study was to develop and evaluate a Windows software application for a 10-transducer Durand-Wayland ultrasonic orchard measurement array and Trimble AgGPS132 DGPS that would allow real-time sensing, monitoring, calculation, storage and mapping of citrus tree canopy volume and height. Program code was written in Delphi 5.0 for Windows. Four main program windows displayed (1) real-time instrument status of ground speed, transducer outputs in a bar chart, canopy height, cross-sectional canopy area, and DGPS signal status; (2) database; (3) SQL filter pages to review and sort the acquired spatial data; and (4) canopy volumes and coordinates for individual trees in the citrus grove. The data collected with this automated system were compared with manually measured size data of 30 trees to estimate accuracy, and a grove of 376 citrus trees was surveyed twice with the system to estimate repeatability. Results showed no significant differences between ultrasonically and manually measured tree sizes ranging in height from 2.1 to 4.3 m (R2 = 0.940***; RMSE = 0.157 m) and in volume from 6.3 to 54.0 m3 tree−1 (R2 = 0.944***; RMSE = 3.14 m3 tree−1). The system located tree positions for GIS mapping purposes within 1.37 m, 95% of the time.