Abstract

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.

© 2008 Optical Society of America

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References

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  1. R. B. Brown and S. D. Noble, "Site-specific weed management: sensing requirements - what do we need to see," Weed Sci. 53, 252-258, (2005).
    [CrossRef]
  2. J. Sinden, R. Jones, R. Hester, D. Odom, C. Kalisch, R. James and O. Cacho, "The economic impact of weeds in Australia," Technical Series # 8, (CRC for Australian Weed Management, 2004).
    [PubMed]
  3. NTech Industries, http://www.ntechindustries.com/concept.html
  4. P. S. Thenkabail, E. A. Enclona, M. S. Ashton, and B. Van der Meer, "Accuracy assessments of hyperspectral waveband performance for vegetation analysis applications," Remote. Sens. Environ. 91, 354-376, (2004).
    [CrossRef]
  5. K. Sahba, S. Askraba and K. E. Alameh, "Non-contact laser spectroscopy for plant discrimination in terrestrial crop spraying," Opt. Express 14, 12485-12493, (2006).
    [CrossRef] [PubMed]

2006 (1)

2005 (1)

R. B. Brown and S. D. Noble, "Site-specific weed management: sensing requirements - what do we need to see," Weed Sci. 53, 252-258, (2005).
[CrossRef]

2004 (1)

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

Alameh, K. E.

Ashton, M. S.

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

Askraba, S.

Brown, R. B.

R. B. Brown and S. D. Noble, "Site-specific weed management: sensing requirements - what do we need to see," Weed Sci. 53, 252-258, (2005).
[CrossRef]

Enclona, E. A.

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

Noble, S. D.

R. B. Brown and S. D. Noble, "Site-specific weed management: sensing requirements - what do we need to see," Weed Sci. 53, 252-258, (2005).
[CrossRef]

Sahba, K.

Thenkabail, P. S.

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

Opt. Express (1)

Remote. Sens. Environ. (1)

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

Weed Sci. (1)

R. B. Brown and S. D. Noble, "Site-specific weed management: sensing requirements - what do we need to see," Weed Sci. 53, 252-258, (2005).
[CrossRef]

Other (2)

J. Sinden, R. Jones, R. Hester, D. Odom, C. Kalisch, R. James and O. Cacho, "The economic impact of weeds in Australia," Technical Series # 8, (CRC for Australian Weed Management, 2004).
[PubMed]

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

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Figures (5)

Fig. 1.
Fig. 1.

Typical measured reflectance spectrum of leaves of skeleton weed. In general the variations in the reflectance between 550nm and 800nm can be used to discriminate between different plants.

Fig. 2.
Fig. 2.

Concept of laser based real-time weed monitoring and spraying sensor. Plants are illuminated with laser beams at varying wavelengths along one optical path, striking the same spot on the leaf, stem or soil. Processing of the reflected light signal for each wavelength determines plant or soil identification. When required, the control unit generates a signal to open the valve on the spray unit.

Fig. 3.
Fig. 3.

Laser combination module with three wavelengths and optical structure projecting multiple laser beams onto an experimental screen holding a leaf over background soil

Fig. 4.
Fig. 4.

Intensity profile of 14 spots illuminating a background screen recorded by image sensor. Inset shows quadratic fitting of measured intensity profile for three peaks.

Fig. 5.
Fig. 5.

Average values of S1, S2 and NDVI for static, 7km/h and 22km/h measurements of Spathiphyllum leaf at different distances. S1 and S2 are plotted against the left axis and NDVI against the right axis. circle – 58cm, filled triangle – 69cm and square – 80cm.

Equations (2)

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

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