Evaluation of a laser scanning sensor on detection of complex shaped targets for variable-rate sprayer development

Authors: LIU, HUI - Jiangsu University; Zhu, Heping

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2016
Publication Date: 11/1/2016
Publication URL: https://handle.nal.usda.gov/10113/5801825
Citation: Liu, H., Zhu, H. 2016. Evaluation of a laser scanning sensor on detection of complex shaped targets for variable-rate sprayer development. Transactions of the ASABE. 59(5): 1181-1192.

Interpretive Summary: Simultaneous measurements of plant canopy structure and foliage density are critical for determination of optimal amounts of chemicals in variable-rate spray applications. Unfortunately, the most commonly used radar and ultrasonic sensors have severe limitations under field conditions. In this research, a radial range laser scanning sensor with a specially designed algorithm was evaluated for its accuracy to detect complex targets. Evaluations included regular shaped objects and irregular-shaped ornamental trees of different sizes at different sensor travel speeds and detection distances between the sensor and targets. The dimensions of these targets measured with the laser sensor agreed well with their actual dimensions under indoor and outdoor conditions. Test results demonstrated that the use of the radial range laser sensor and the specifically designed algorithm was able to accurately measure shapes and sizes of complex target surfaces. Subsequently, air-assisted variable-rate prototype sprayers with the integration of the laser sensor and the algorithm were developed to deliver necessary amounts of sprays to target plants based on the plant canopy structures and sprayer travel speeds in real time. The sprayers were successfully tested for precision spray applications and biological control efficacy under commercial field conditions.

Technical Abstract: Sensors that can accurately measure canopy structures are prerequisites for development of advanced variable-rate sprayers. A 270° radial range laser sensor was evaluated for its accuracy to measure dimensions of target surfaces with complex shapes and sizes. An algorithm for data acquisition and 3-dimensional canopy image construction were designed and processed with an embedded computer. Test targets included three beach balls at three heights, a rectangular box, a cylinder, two artificial and three field-grown ornamental trees. Other variables included 2, 3, 4, and 5 m detection distances and sensor travel speeds of 3.2, 4.8, 6.4, and 8.0 km h-1. The laser sensor measurements of test targets were statistically similar with the actual measurements. The mean RMS errors and CVs varied slightly with the detection distance and travel speed. Among all the measurements of dimensions in the ranges of 0.58 to 2.54 m in X direction, 0.58 to 2.54 m in Y direction, and 0.58 to 2.94 m in Z direction, the highest average root mean square error (RMS) was 68 mm occurred in Z direction and the highest average CV was 8.6% occurred in Y direction. Similarity of paired images from the laser sensor and a camera for all targets was greater than 0.85. These tests confirmed the capability of the laser sensor and the algorithm to accurately measure the complex shaped targets, offering potentials for integration of the sensor and algorithm into sprayers that will make real-time adjustment on spray outputs to match plant structures and travel speeds.