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Crop-Spraying System Targets Weeds

Photonics Spectra
Feb 2007
Nadya Anscombe

When farmers want to spray their crops, they can either blanket spray the entire field, or spray spots by hand. Blanket spraying is not only detrimental to the environment, but also leads to yield losses; and spot spraying is time-consuming, labor-intensive and simply not viable for today’s farming methods.

Soon farmers will have another option. Researchers in Australia are developing an automated crop-spraying system that can discriminate among any number of crops, weeds and soils in a field at the traveling speed of a farming vehicle. Using laser technology, the system discriminates among plants and soils by distinguishing wavelengths in the near-infrared. With a series of sensors mounted onto a vehicle spanning the width of the spraying boom, the system sprays herbicides on weeds only and not on the crop. The same system also can scan a field for sought-after plants and can record their locations.


Researchers in Australia are developing a precision crop-spraying system that uses laser technology to distinguish between crops and weeds.

Developed by researchers at Edith Cowan University in Joondalup and at Weed Control Australia in Subiaco, the system differentiates between plants using reflectance data. “Current precision spraying technology lacks selectivity in that it considers everything but soil as a spray target,” said Kamal E. Alameh, director of the Western Australia Centre of Excellence for MicroPhotonic Systems at the university.

Current systems also use tungsten halogen floodlights or LEDs to illuminate the vegetation from above. The divergence of LED illumination causes weak side lobes in the radiation pattern. Because of the weak backscattered light, there is little chance of a fine weed leaf being detected if it does not fall in the most concentrated area of illumination. Instead, the new system uses multiple collimated laser spots to illuminate the vegetation.

The laser spots allow a plant to be detected and spectrally measured, no matter which part of the radiation field hits the plant. “The laser spot array is generated by injecting only one input beam into a unique optical structure based on nano-layered thin films,” Alameh said. “This is a cost-effective approach, and the alignment of the laser spots in an array will not be prone to vibration or shock of the whole sensor unit.”

The precision crop spraying system was made possible by combining this thin-film technology with high-speed detectors and Gigabit Ethernet connectivity to enable sequencing and detection of wavelength-specific laser spots at a very high speed.

According to Alameh, the main challenges in this project were related to processing the reflected data to find significant spectral differences. However, the researchers successfully discriminated between plants and soils using a technique based on extracting the slopes between different wavelengths, he said.

They are testing the system in a controlled environment and using a rotating stage that simulates the speed of a farming vehicle. They also are working on improving a number of points, including fluctuations in sensor-to-plant distance, and are adding more laser sources so that the system can differentiate among a wider variety of plants.

John Rowe, managing director of Weed Control Australia, said that they believe that the system’s initial commercial future lies in producing spot spraying equipment for specialist applications in the broad acre, cotton and sugar cane farming industries. He also noted that the management of skeleton weed in broad acre and guinea grass in sugar cane will save those industries millions of dollars in lost yield.

The company also is examining other applications for the technology, such as protein-level measurements in grain and uses in the sawmill industry. It plans to build three preproduction prototypes targeted at various industries and hopes to be in production within two to three years.

Contact: Kamal E. Alameh, Edith Cowan University; e-mail:

The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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