Laser-Stabilized Real-Time Plant Discrimination Sensor for Precision Agriculture

A novel proximal spectral-reflectance-based plant discrimination sensor for use in selective herbicide spraying systems is developed and its dynamic outdoor performance is experimentally assessed for two plants. For plant illumination, the sensor uses a new stabilized three-wavelength laser diode module that sequentially emits identically polarized laser light beams through a common aperture, along one optical path. Each laser beam enters a multi-spot beam generator, which produces 15 parallel, collimated laser beams spaced over a 230-mm span. The intensity of the reflected light from each beam is detected by a high-speed line scan image sensor. Plant discrimination is based on calculating two different normalised difference vegetation indices, and experimental results show that by improving the stability of the laser diodes, a plant discrimination rate greater than 90% can be achieved with a travelling speed of 7.5 km/h for canola and wild radish, which is a dominant weed in the canola crop field.