Light sensor with modulated radiant polychromatic source

Abstract

An apparatus is described for assessing plant chlorophyll content remotely sensed by the invention thereby allowing selective monitoring or treatment of individual plants. In one preferred embodiment, a polychromatic emitter provides light beams substantially in the red edge portion of a plant's reflectance spectrum. This light beam illuminates a surface area on the plant, which may be bare ground or plants. The beam of light may be focused, collimated or non-focused. A detector array, usually composed of an array of spectrally sensitive detectors, detects portions of this polychromatic light beam reflected by the surface area and provides a signal indicative of the change in chlorophyll status by determining the wavelength of the red edge inflection point REIP. In another preferred embodiment of the invention, an array of sequentially pulsed monochromatic emitters provides light beams having wavelengths substantially along the red edge portion of a plant's reflectance spectrum. These light beams illuminate a surface area on the plant, which may be bare ground or plants. The beams of light may be focused, collimated or non-focused. A photodetector detects the light reflected by the surface area and provides a signal indicative of the change in chlorophyll status by determining the wavelength of the red edge inflection point REIP. In both embodiments, a controller analyzes the resulting REIP wavelength and 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.

1 . Apparatus for assessing the status of plants in a plant canopy, comprising: 
 (a) a light source having an emission spectrum substantially in the red-edge portion of the plant's reflectance spectrum for illuminating the plant canopy;    (b) a detector for detecting portions of the emission spectrum reflected off of the plant canopy; and    (c) a processor for determining the wavelength of the red edge inflection point of the light collected by the detector.    
   
   
       2 . Apparatus as defined in  claim 1 , further comprising a processor for determining the chlorophyll content of the plant from the red edge inflection point.  
   
   
       3 . Apparatus as defined in  claim 1 , wherein the light source consists of a plurality of monochromatic light sources.  
   
   
       4 . Apparatus as defined in  claim 1 , wherein the light source consists of one or more polychromatic light sources.  
   
   
       5 . Apparatus as defined in  claim 1 , further comprising a mapping system for generating a map of the assessed plant status over a selected area.  
   
   
       6 . Apparatus as defined in  claim 1 , further comprising an applicator responsive to the processor to apply a horticultural material to the plant canopy in response to the assessed plant status.  
   
   
       7 . Apparatus as defined in  claim 6 , wherein the horticultural material is selected from the group consisting of fertilizer, herbicide, insecticide, fungicide, and combinations of such materials.