System and method for determining a plant status

Abstract

The invention relates to a system and method for determining a status of plants. The system includes a light transmitter arranged for providing broad band illumination to one or more plants. The system includes a light receiver including a plurality of receiver channels, the receiver channels arranged for receiving light from said one or more plants in mutually different wavelength bands. The system includes a processing unit arranged for determining a status of said one or more plants on the basis of light received by the plurality of receiver channels. The transmitter may be arranged for transmitting bursts of modulated light.

1 . A method of suppressing effects of at least one of dew and dust when determining a plant status, the method comprising:
 receiving light in mutually different wavelength bands from one or more plants by a light receiver including a plurality of receiver channels;   receiving light at a first wavelength of a known reflection or absorption band of interest;   receiving light at a second wavelength different from the first wavelength;   receiving light at a third wavelength different from the first wavelength and second wavelength; and   subtracting a signal received at the third wavelength from a signal received at the first wavelength to obtain a first value, subtracting the signal received at the third wavelength from a signal received at the second wavelength to obtain a second value, and then determining a ratio of the second value to the first value.   
     
     
         2 . The method according to  claim 1 , further comprising adjusting the signal received at the third wavelength by a correction factor before (i) subtracting the signal received at the third wavelength from the signal received at the first wavelength to obtain the first value and (ii) subtracting the signal received at the third wavelength from the signal received at the second wavelength to obtain the second value. 
     
     
         3 . The method according to  claim 1 , wherein the third wavelength is included in a reference absorption band. 
     
     
         4 . The method according to  claim 3 , wherein the reference absorption band includes a wavelength about 670 nm. 
     
     
         5 . The method according to  claim 1 , wherein the first wavelength is included in a chlorophyll absorption band. 
     
     
         6 . The method according to  claim 5 , wherein the chlorophyll absorption band includes a wavelength about 730 nm, and the second wavelength is about 760-800 nm. 
     
     
         7 . The method according to  claim 1 , wherein the first wavelength is included in a water absorption band. 
     
     
         8 . The method according to  claim 7 , wherein the water absorption band includes a wavelength about 970 nm, and the second wavelength is about 900-930 nm. 
     
     
         9 . The method according to  claim 1 , further comprising determining a status of the one or more plants based on light received by the plurality of receiver channels. 
     
     
         10 . The method according to  claim 9 , further comprising controlling a variable rate applicator system based on the determined status of the one or more plants,
 wherein the variable rate applicator system is one of a fertilizer system, an irrigation system, a fertigation system, and a fertilizer spreader mounted on or pulled by a tractor   
     
     
         11 . A system for suppressing effects of at least one of dew and dust when determining a plant status, the system comprising:
 a light receiver including a plurality of receiver channels, the receiver channels arranged for receiving light from one or more plants in mutually different wavelength bands,   wherein the plurality of receiver channels including:
 a first receiver channel arranged for receiving light at a first wavelength of a known reflection or absorption band of interest; 
 a second receiver channel arranged for receiving light at a second wavelength; and 
 a third receiver channel arranged for receiving light at a third wavelength different from the first wavelength and the second wavelengths, 
   wherein the system further comprises a processing unit configured to subtract a signal received by the third receiver channel from a signal received by the first receiver channel to obtain a first value, subtract the signal received by the third receiver channel from a signal received by the second receiver channel to obtain a second value, and then determine a ratio of the second value to the first value.   
     
     
         12 . The system according to  claim 11 , wherein the processing unit adjusts the signal received by the third receiver channel by a correction factor before (i) subtracting the signal received by the third receiver channel from the signal received by the first receiver channel to obtain the first value and (ii) subtracting the signal received by the third receiver channel from the signal received by the second receiver channel to obtain the second value. 
     
     
         13 . The system according to  claim 11 , wherein the third receiver channel is a reference receiver channel tuned to a reference absorption band. 
     
     
         14 . The system according to  claim 13 , wherein the reference absorption band includes a wavelength about 670 nm. 
     
     
         15 . The system according to  claim 11 , wherein the first receiver channel is tuned to an edge of a chlorophyll absorption band. 
     
     
         16 . The system according to  claim 15 , wherein the chlorophyll absorption band includes a wavelength about 730 nm, and the second receiver channel is tuned to a wavelength about 760-800 nm. 
     
     
         17 . The system according to  claim 11 , wherein the first receiver channel is tuned to a water absorption band. 
     
     
         18 . The system according to  claim 17 , wherein the water absorption band includes a wavelength about 970 nm, and the second receiver channel is tuned to a wavelength about 900-930 nm. 
     
     
         19 . The system according to  claim 11 , wherein each receiver channel includes a light detector, an AC-coupled current to voltage converter, a bandpass-AC-amplifier, a phase rectifier, an integrator, and a hold circuit. 
     
     
         20 . The system according to  claim 19 , wherein the light receiver includes a multiplexer, and an analog to digital converter. 
     
     
         21 . The system according to  claim 19 , wherein each receiver channel includes a light detector and dedicated optics. 
     
     
         22 . The system according to  claim 21 , wherein all receiver channels are mounted in a common receiver frame. 
     
     
         23 . The system according to  claim 11 , wherein the processing unit is configured to determine a status of the one or more plants based on light received by the plurality of receiver channels. 
     
     
         24 . The system according to  claim 23 ,
 wherein the processing unit is configured to control a variable rate applicator system based on the determined status of the one or more plants, and   wherein the variable rate applicator system is one of a fertilizer system, an irrigation system, a fertigation system, and a fertilizer spreader mounted on or pulled by a tractor.