Optical spectral reflectance sensor and controller

• US 6,596,996 B1
• Filed: 07/24/2001
• Issued: 07/22/2003
• Est. Priority Date: 07/24/2001
• Status: Expired due to Term

• Current Assignee: Board of Regents of Oklahoma State University
• Original Assignee: Board of Regents of Oklahoma State University
• Inventors: Needham, Duane, Johnson, Gordon V., Raun, William R., Solie, John B., Stone, Marvin L.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): MORAN, TIMOTHY J
• Application Number:
  US09/912,077
• Time in Patent Office: 728 Days
• Field of Search: 250/340, 250/341.1, 250/341.8, 250/339.01, 250/339.05, 250/339.11, 250/358.1, 47/17
• US Class Current: 250/341.8
• CPC Class Codes: A01C 21/007 Determining fertilization requirements
• CPC Class Codes: G01J 3/427 Dual wavelengths spectrometry
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01N 2021/3155 Measuring in two spectral ranges, e.g. UV and visible
• CPC Class Codes: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/4738 Diffuse reflection precedence is given to G01N21/55 - G01N21/57 if specular component is taken into consideration, e.g. also for testing fluids, fibrous materials
• CPC Class Codes: G01N 2201/0627 Use of several LED's for spectral resolution
• CPC Class Codes: G01N 2201/0691 Modulated (not pulsed supply)
• CPC Class Codes: G01N 2201/0694 Microprocessor controlled supply

Abstract

A spectral reflectance sensor including: a light source for emitting a modulated beam of red light; a light source for emitting a modulated beam of near infrared light; a receiver for receiving reflected light produced by either the red source or the near infrared source; a receiver for receiving incident light from either the red source or the infrared source; a signal conditioner responsive to the modulation such that the signals produced by the receivers in response to reflected and incident light from the source can be discriminated from signals produced by ambient light; and a microprocessor having an input such that the microprocessor can determine the intensities of incident red light, reflected red light; incident near infrared light; and reflected near infrared light. From these intensities, and by knowing the growing days since emergence or planting, the sensor can calculate the mid-growing season nitrogen fertilizer requirements of a plant.

Claims

1. A spectral reflectance sensor for determining the reflectance of a plant comprising:

a housing;

a light source housed in said housing, said light source projecting light of a predetermined wavelength;

a reflected light receiver including;

a first photodetector positioned to receive reflected light originating from said light source

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

a first output;

a direct light receiver including;

a second photodetector positioned to receive incident light from said light source; and

a second output;

a discriminator for distinguishing the light originating from said light source and reflected by a plant from ambient light; and

a microprocessor having an input for reading said first output and an input for reading said second output,

wherein the reflectance at said predetermined wavelength is proportional to the quotient of the value of said first output divided by the value of said second output.

2. The spectral reflectance sensor of claim 1 wherein said light source is a first light source and said predetermined wavelength of light is a first predetermined wavelength of light and the reflectance sensor further comprises:

a second light source housed in said housing, said second light source projecting light of a second predetermined wavelength.

3. The spectral reflectance sensor of claim 2 further comprising:

a selector in communication with said microprocessor wherein said microprocessor can select either said first light source to emit light or said second light source to emit light,

wherein said microprocessor can measure the reflectance at said first predetermined wavelength independently of the reflectance at said second predetermined wavelength of light.

4. The spectral reflectance sensor of claim 3 wherein said first light source produces red light of a predetermined wavelength and said second light source produces near infrared light of a predetermined wavelength and wherein said microprocessor calculates NDVI based on the reflectance computed while red light is emitted and the reflectance computed while near infrared light is emitted.

5. The spectral reflectance sensor of claim 1 wherein said light source is a first light source of a plurality of light sources and each light source of said plurality of light sources produces light at a predetermined wavelength different from the wavelength of each of the other light sources of said plurality of light sources.

6. The spectral reflectance sensor of claim 5 wherein each light source of said plurality of light sources comprises a plurality of light emitting diodes.

7. A normalized difference vegetation index sensor comprising:

a first light source which emits a modulated beam of red light;

a second light source which emits a modulated beam of near infrared light;

a first receiver for receiving reflected light produced by said first light source and said second light source, said receiver having a first output;

a second receiver for receiving incident light from said first light source and said second light source, said second receiver having a second output;

a signal conditioner responsive to the modulation of said modulated beam such that said signal conditioner can discriminate between said first or second light sources and ambient light, said signal conditioner having a first input for receiving said first output or said second output and said signal conditioner having a third output;

a microprocessor having a second input for receiving the output of said signal conditioner such that said microprocessor can determine the intensity of said first light source, the intensity of said second light source, the intensity of the reflected light received from said first light source; and

the intensity of the reflected light received from said second light source,

wherein said microprocessor provides an output indicative of the normalized difference vegetation index calculated from the intensities determined from the signal at said second input.