ARS | Publication request: Development of variable-rate sprayer with laser scanning sensor to synchronize spray outputs to tree structures

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2012
Publication Date: August 30, 2012
Citation: Chen, Y., Zhu, H., Ozkan, E. 2012. Development of variable-rate sprayer with laser scanning sensor to synchronize spray outputs to tree structures. Transactions of the ASABE. 55(3):773-781.

Interpretive Summary: In nurseries and orchards, foliar pesticide application is the most effective method to protect crops from pest damages and prevent yield losses. However, due to a great diversity in canopy structure and foliage density, conventional spray systems and methodologies are inefficient and often cause excessive pesticide usage. This research developed an experimental air-assisted variable-rate spraying system with integration of high-speed laser scanning technology to characterize the occurrence, height, width and foliage density of tree canopies and then control spray outputs to match targeted tree structures. The integration also included a custom-designed sensor-signal analyzer, automatic variable-rate controller, variable-rate nozzles and a multi-channel air-assisted delivery system. An algorithm was developed to calculate tree canopy volume and foliage density in real time. The accuracy of the variable-rate sprayer to deliver chemicals to targets was validated by examining the uniformity of spray coverage inside different ornamental trees at different travel speeds. Test results demonstrated that the sprayer had capabilities to achieve variable spray rates for different canopy volumes and foliage densities with acceptable variations in spray coverage inside tree canopies. Now, it is feasible to have a new generation of precision sprayers for nursery and orchard growers to prevent excessive pesticide use, and thus reduce production costs, worker exposure to pesticide risks, and adverse environmental contamination.

Technical Abstract: Efficient and effective precision spray equipment and strategies have been constantly demanded to reduce pesticide use in tree crop productions. An experimental variable-rate air-assisted sprayer implemented with a high-speed laser scanning sensor was developed to control the spray output of individual nozzles in real time. The sprayer mainly consisted of a laser scanning sensor control system and an air and liquid delivery system. Each nozzle in the delivery system, coupled with a pulse width modulated (PWM) solenoid valve, achieved variable-rate delivery based on the occurrence, height, width of the target tree and its foliage density. Other components of the sensor control system included a unique algorithm for variable-rate control that instantaneously processed the measurements of the canopy surfaces. To determine the system delay time, a high-speed video camera was used to record the time period between the sensor detection of the canopy and the nozzle activation. Spray deposition uniformity inside canopies were verified by quantifying spray coverage inside four ornamental nursery trees with different sizes and canopy densities at 3.2 and 6.4 km/h travel speeds. Test results demonstrated that the differences in spray coverage inside canopies of these four trees in the spraying direction were not statistically significant even though these trees had different structures, canopy volumes and foliage densities. The canopy volume and foliage density measured with the algorithm developed for the laser sensor-controlled detection system had little variations with the two travel speeds. The design criteria for the sensor controlled system in the experimental sprayer were acceptable for variable-rate applications with a great potential in spray volume and drift reduction thus reducing environmental impact.