Photonic-based spectral reflectance sensor for ground-based plant detection and weed discrimination

A bench prototype photonic-based spectral reflectance sensor architecture for use in selective herbicide spraying systems performing non-contact spectral reflectance measurements of plants and soil is described and experimental data obtained with simulated farming vehicle traveling speeds of 7 and 22 km/h is presented. The sensor uses a 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 up to 14 parallel laser beams over a 210mm span. The intensity of the reflected light from each spot is detected by a high-speed line scan image sensor. Plant discrimination is based on calculating the slope of the spectral response between the 635nm to 670nm and 670nm to 785nm laser wavelengths. The use of finely spaced and collimated laser beam array, instead of an un-collimated light source, allows detection of narrow leaved plants with a width as small as 12mm.