2. System overview
The real-time Plant Discrimination Unit (PDU) is comprised of two 3-wavelength laser modules, two coated optical cavities, a high-speed linear photodetector array in the form of a line scan camera and an electronic circuit board housing six sub-modules, Fig. 1. These are a laser driver, analogue and digital power supply units, a temperature controller, a central processing unit,
a spray nozzle activator and a line scan camera driver. The PDU is robustly packaged, using a rigid base plate and an accompanying light weight dust cover, to overcome harsh operation conditions such as shocks, vibrations and high temperatures.
The optoelectronic architecture of the PDU, as presented, has the following benefits:
1. The collimated, split laser beams enable spectral reflectancemeasurements to be taken from a small area of leaf of the target plant.
2. The laser module beam combiner/optical cavity design enablesthe laser beams to illuminate the same spot on the leaf, for all wavelengths, making the measured spectral reflectance spatially accurate with regards to different leaf morphologies.
3. The high dynamic range of the line scan sensor, when comparedwith area scan sensors of the type used in multi-spectral imaging, gives a better precision and a higher accuracy of the measured spectral properties.
4. The low complexity of the discrimination algorithm means thatit is not computationally intensive, therefore providing true real-time performance.