Light sensor with modulated radiant polychromatic source

• US 20050098713A1
• Filed: 11/07/2003
• Published: 05/12/2005
• Est. Priority Date: 09/23/2003
• Status: Active Grant

• Current Assignee: Kyle H. Holland Trustee Of The Maranatha Trust
• Original Assignee: Kyle Holland
• Inventors: Holland, Kyle
• Granted Patent: US 7,408,145 B2
• Time in Patent Office: Days
• US Class Current: 250/221
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/36 Investigating two or more bands of a spectrum by separate detectors
• CPC Class Codes: G01N 2021/635 Photosynthetic material analysis, e.g. chrorophyll
• CPC Class Codes: G01N 2021/8466 Investigation of vegetal material, e.g. leaves, plants, fruits
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence

Abstract

An apparatus is described for assessing plant status using biophysical and biochemical properties of the plant remotely sensed by the invention thereby allowing selective monitoring, elimination or treatment of individual plants. In a preferred embodiment, a single polychromatic emitter provides coincident light beams; one beam substantially in the visible portion of the spectrum (400 nm to 700 nm) and the other in the near infrared (NIR) portion of the spectrum (700 nm to 1100 nm). This light beam illuminates a small surface area on the ground, which may be bare ground, desired plants or undesired weeds. The beam of light may be focused, collimated or non-focused. A detector array, usually composed of a visible detector and a NIR detector, detects portions of this polychromatic light beam reflected by the surface area and provides a signal indicative of whether the detected light was reflected by a plant or by some non-plant object such as soil. A controller analyzes this signal and, assuming a plant is detected, responds by activating a device to take some action with respect to the plant or stores the analyzed signal with corresponding DGPS position in the controller'"'"'s memory for later analysis. A number of actions may be taken by the controller. For instance, if the plant is a weed, the desired action might be to spray herbicide on the weed. Or, if the plant is a crop that is determined to be lacking in nutrient, the desired action may be to apply fertilizer. Additionally, if the plant under test is a turf landscape, such as found on golf courses and sporting fields, plant biomass may be mapped and geo-located using GPS for later, comparative analysis.

Claims

1. A light sensor for measuring the reflectance of an object, comprising:

(a) a light source with a means of modulating the light source, and a means to set and monitor optical power of the light source;

(b) a reflected light receiver comprised of a plurality of photodetectors comprised of at least one photodetector sensitive to visible light positioned to receive reflected light originating from the light source and including ambient light compensation means for reducing the effects of ambient light on the photodetector and a first output, and at least one photodetector sensitive to nonvisible light positioned to receive reflected light originating from said light source and including ambient light compensation means for reducing the effects of ambient light on said second photodetector and a second output;

(c) a detector for distinguishing the light originating from the light source and light reflected by the object from ambient light; and

(d) a computational device for performing calculations based on reading the first output, reading the second output and the light source power.

2. A light sensor as defined in claim 1, wherein the light source is comprised of two or more light sources selected from the group comprising quasi-monochromatic light sources, polychromatic light sources, monochromatic light sources, and combinations thereof.

3. A light sensor as defined in claim 1, wherein each light source is modulated at the same frequency in synchrony with the other light source or sources.

4. A light sensor as defined in claim 1, wherein the light source a polychromatic light source simultaneously emitting visible light and infrared light.

5. A light sensor as defined in claim 1, wherein the light source is comprised of at least one polychromatic light source simultaneously emitting visible light and infrared light and at least one quasi-monochromatic or monochromatic light source.

6. A light sensor as defined in claim 1, further comprising apparatus for improving ambient light compensation comprising a diffraction grating and wherein said reflected light receiver receives light from the diffraction grating.

7. A light sensor as defined in claim 1, further comprising apparatus for improving ambient light compensation comprising a linear variable filter and wherein said reflected light receiver receives light through the linear variable filter.

8. A light sensor as defined in claim 1, wherein the photodetector array is a linear photodiode array or linear CCD array.

9. A light sensor as defined in claim 1, wherein the photodetector array is comprised of imaging detectors.

10. A light sensor as defined in claim 1, further comprising optics associated with said light source for producing a beam of light having a substantially constant flux density between about 12 inches and about 6 feet from the light source.

11. A light sensor as defined in claim 1, wherein the light source simultaneously illuminates a substantially identical area with both visible and nonvisible light.

12. A light sensor as defined in claim 1, wherein the object comprises a plant.

13. A light sensor as defined in claim 12, further comprising an applicator responsive to the computational device for applying a product to the plant.

14. A light sensor as defined in claim 13, wherein the applicator is separated from the light receiver by 3 feet or more.

15. A light sensor for measuring the fluorescence of a plant, comprising:

(a) a light source with a means of modulating the light source, and a means to set and monitor optical power of the light source;

(b) a reflected light receiver comprising a first photodetector sensitive to light between about 690 nm and about 720 nm light and positioned to receive emitted light originating from the plant due to the excitation by the light source;

ambient light compensation means for reducing the effects of ambient light on the first photodetector; and

a first output;

a second photodetector sensitive to between about 720nm and about 780nm light positioned to receive emitted light originating from the plant due to excitation by the light source;

ambient light compensation means for reducing the effects of ambient light on the second photodetector; and

a second output;

(c) a detection means for distinguishing the light originating from the light source and emitted by the plant from ambient light; and

(d) a computational device to calculate a measurement based on reading the first output and reading the second output and light source power.

16. A sensor as defined in claim 15, wherein the sensor measures reflectance and fluorescence.

17. A light sensor for measuring the reflectance of an object, comprising:

(a) a light source comprising a first light source projecting light of a first wavelength, a second light source projecting light of a second wavelength, a means of modulation of the first and second light sources, and a means to set and monitor optical power of the first and second light sources;

(b) a reflected light receiver comprising a first photodetector sensitive to visible light positioned to receive reflected light originating from the first light source, ambient light compensation means for reducing the effects of ambient light on the first photodetector; and

a first output;

a second photodetector sensitive to nonvisible light positioned to receive reflected light originating from said light source, and ambient light compensation means for reducing the effects of ambient light on said second photodetector; and

a second output;

(c) a detection means for distinguishing the light originating from said light source and reflected by an object from ambient light; and

(d) a computational device to perform a calculation based on reading said first output and input for reading said second output and light source power.

18. A method for measuring the reflectance of a plant, comprising the steps of:

(a) projecting light of a first wavelength from a first light source, light of a second wavelength from a second light source, modulating the first and second light sources, and setting and monitoring optical power of the first and second light sources;

(b) receiving reflected light originating from the first light source in a reflected light receiver comprising a first photodetector sensitive to visible light, and reducing the effects of ambient light on the first photodetector in an ambient light compensation means; and

a first output;

(c) positioning a second photodetector sensitive to nonvisible light to receive reflected light originating from the light source, and reducing the effects of ambient light on said second photodetector in an ambient light compensation means; and

a second output;

(c) a detection means for distinguishing the light originating from said light source and reflected by the object from ambient light; and

(d) calculating in a computational device a vegetative index based on reading said first output and said second output and light source power.

19. A method as defined in claim 18, wherein the first light source is comprised of a plurality of light sources emitting light of wavelengths between about 450 nm and about 645 nm and the second light source emits light of wavelengths in the near infrared, and wherein the calculation of the vegetative index correlates to plant biomass, plant chlorophyll content, plant pigment content or combinations thereof.

20. A method as defined in claim 18, wherein the first light source is comprised of a plurality of light sources emitting light of wavelengths between about 450 nm and about 645 nm and the second light source emits light of wavelengths in the near infrared, and wherein the calculation of the vegetative index correlates to plant biomass, plant chlorophyll content, plant pigment content or combinations thereof.

21. A method as defined in claim 18, wherein the first light source is comprised of a plurality of light sources emitting light of red, blue and green wavelengths and the second light source emits light of wavelengths in the near infrared, and wherein the calculation of the vegetative index corresponds to plant color, plant biomass or combinations thereof.