Abstract

The early development of a novel micro-photonic based sensing architecture for use in selective herbicide spraying systems performing non-contact spectral reflectance measurements of plants and soil in real time has been described. A combination module allows three laser diodes of different wavelengths to sequentially emit identically polarized light beams through a common aperture, along one optical path. Each exiting beam enters an optical structure which generates up to 14 parallel laser beams. A pair of combination modules and optical structures generates 28 beams over a 420mm span which illuminates the plants from above. The intensity of the reflected light from each spot is detected by a high speed line scan image sensor. Plant discrimination is based on analyzing the Gaussian profile of reflected laser light at distinguishing wavelengths. Two slopes in the spectral response curves from 635nm to 670nm and 670nm to 785nm are used to discriminate different plants. Furthermore, by using a finely spaced and collimated laser beam array, instead of an un-collimated light source, detection of narrow leaved plants with a width greater than 20mm is achievable.

© 2006 Optical Society of America

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References

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  1. N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).
  2. J. Sinden, et. al., "The economic impact of weeds in Australia," Technical Series # 8, Cooperate Research Centre for Australian Weed Management, February 2004.
  3. NTech Industries, "WeedSeeker: Concept," http://www.ntechindustries.com/concept.html.
  4. N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).
  5. N. Zhang Wang, F. E. Dowell, Y. Sun, and D. E. Peterson, "Testing of a Spectral-based Weed Sensor," American Society of Agricultural Engineers (2000).
  6. J. Beck and T. Vyse, "Structure and method for differentiating one object from another object," U.S. Patent 5 296 702, March 22, 1994.
  7. J. Beck and T. Vyse, "Structure and method usable for differentiating a plant from soil in a field," U.S. Patent 5 389 781, February 14, 1995.
  8. W. L. Felton, "Commercial progress in spot spraying weeds," in Brighton Crop Protection Conference - Weeds, British Crop Protection Council (1995), 3, 1087-1096.
  9. P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
    [CrossRef]
  10. H. D Young, Statistical treatment of experimental data, (McGraw-Hill Book Company, Inc., 1962).

2004

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

2002

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

2001

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

Ashton, M. S.

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

Dowell, F. E.

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

Enclona, E. A.

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

Peterson, D. E.

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

Sun, Y.

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

Thankabail, P. S

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

Van Der Meer, B.

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

Wang, N. Z.

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

ASAE Trans.

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Design of an Optical Weed Sensor Using Plant Spectral Characteristics," ASAE Trans.,  44, 409-419 (2001).

Computers and Electronics in Agriculture

N. Z. Wang, F. E. Dowell, Y. Sun, D. E. Peterson, "Precision agriculture - a worldwide overview," Computers and Electronics in Agriculture,  36, 354-376 (2002).

Remote Sens. Environ.

P. S Thankabail, E. A. Enclona, M. S. Ashton, B. Van Der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote Sens. Environ.,  91, 354-376 (2004).
[CrossRef]

Other

H. D Young, Statistical treatment of experimental data, (McGraw-Hill Book Company, Inc., 1962).

J. Sinden, et. al., "The economic impact of weeds in Australia," Technical Series # 8, Cooperate Research Centre for Australian Weed Management, February 2004.

NTech Industries, "WeedSeeker: Concept," http://www.ntechindustries.com/concept.html.

N. Zhang Wang, F. E. Dowell, Y. Sun, and D. E. Peterson, "Testing of a Spectral-based Weed Sensor," American Society of Agricultural Engineers (2000).

J. Beck and T. Vyse, "Structure and method for differentiating one object from another object," U.S. Patent 5 296 702, March 22, 1994.

J. Beck and T. Vyse, "Structure and method usable for differentiating a plant from soil in a field," U.S. Patent 5 389 781, February 14, 1995.

W. L. Felton, "Commercial progress in spot spraying weeds," in Brighton Crop Protection Conference - Weeds, British Crop Protection Council (1995), 3, 1087-1096.

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Figures (11)

Fig. 1.
Fig. 1.

Typical reflectance spectrum of a green leaf. Variations in the reflectance of the ‘red edge’ between 650nm and 800nm can be used to discriminate between different plants.

Fig. 2.
Fig. 2.

The sensor will emit light at varying wavelengths along one optical path, striking the same spot on the leaf, stem or soil. Processing of the digitally recorded reflected light signal for each wavelength will determine plant or soil identification and hence a strike signal is sent to the spray valve accordingly.

Fig. 3.
Fig. 3.

Laser beam combination.

Fig. 4.
Fig. 4.

(a) Multiple beam projection. (b) Resulting spot array projected onto an experimental screen holding a leaf over background soil.

Fig. 5.
Fig. 5.

Measured optical power for each spot projected from two adjacent cavities at each wavelength.

Fig. 6.
Fig. 6.

Gaussian intensity profile of three spots striking a green leaf recorded by a line scan imager.

Fig. 7.
Fig. 7.

Flow chart for a single acquisition cycle. This cycle must be completed before the farming vehicle has traveled 4mm – the spot diameter of the projected beam. This is to ensure each of the three frames grabbed is from the same spatial points on the plant or soil.

Fig. 8.
Fig. 8.

Spectral response of plants and soil used for experimentation.

Fig. 9.
Fig. 9.

Determined average slope values for the four sample plants.

Fig. 10.
Fig. 10.

Standard deviation of the mean for slopes S 1 and S 2 for the four sample plants.

Fig. 11.
Fig. 11.

Average NDVI values for the four samples plants, soil and colored paper.

Equations (4)

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S 1 = R 635 R 670 λ 670 λ 635
S 2 = R 785 R 670 λ 785 λ 635 ,
R λ = I λ P λ .
NDVI = R 785 R 670 R 785 + R 670 .

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