Active imaging systems for plant growth monitoring
View Patent ↗Active imaging systems for plant growth monitoring acquire images in which each pixel represents an absolute NDVI value obtained with active illumination.
1. An active imaging system for plant growth monitoring comprising:
(a) an unmanned aerial vehicle equipped with:
a light emitter capable of emitting light at two or more wavelengths, the light emitter receiving a modulation signal from a modulator and emitting light modulated by the modulation signal;
a first lens that projects light from the light emitter onto a crop and a second lens that images an area of the crop onto an array of sensor pixels,
a split imaging system such that the area of the crop appears as two images of the same area, at two different wavelengths, on the array of sensor pixels,
each pixel of the array of sensor pixels: detecting light reflected by the crop, generating a detection signal, and mixing the detection signal with the modulation signal from the modulator to obtain a reflectivity measurement of the crop; and,
(b) a processor that computes a vegetative index based on reflectivity measurements obtained at two or more different wavelengths.
2. The system of claim 1 wherein the split imaging system comprises optical bandpass filters for each of the two wavelengths.
3. The system of claim 1 wherein the unmanned aerial vehicle sends reflectivity measurements to a ground station via a radio link.
4. The system of claim 1 , the vegetative index being a normalized difference vegetative index,
N
D
V
I
=
r
NIR
-
r
VIS
r
NIR
+
r
VIS
,
where r NIR and r VIS are crop reflectivity measurements obtained at infrared and visible wavelengths, respectively.
5. The system of claim 1 , the second lens being an anamorphic lens.
6. The system of claim 1 , the processor comprising logic included in the array of sensor pixels.
7. The system of claim 1 , the light emitter comprising a first diode laser that emits light at a visible wavelength and a second diode laser that emits light at an infrared wavelength.
8. A method for plant growth monitoring comprising:
(a) overflying a crop with an unmanned aerial vehicle equipped with:
a light emitter emitting light at two or more wavelengths, the light emitter receiving a modulation signal from a modulator and emitting light modulated by the modulation signal;
a first lens projecting light from the light emitter onto a crop and a second lens imaging an area of the crop onto an array of sensor pixels;
a split imaging system such that the area of the crop appears as two images of the same area, at two different wavelengths, on the array of sensor pixels;
each pixel of the array of sensor pixels: detecting light reflected by the crop, generating a detection signal, and mixing the detection signal with the modulation signal from the modulator to obtain a reflectivity measurement of the crop; and,
(b) a processor computing a vegetative index based on reflectivity measurements obtained at two or more different wavelengths.
9. The method of claim 8 , the vegetative index being a normalized difference vegetative index,
N
D
V
I
=
r
NIR
-
r
VIS
r
NIR
+
r
VIS
,
where r NIR and r VIS are crop reflectivity measurements obtained at infrared and visible wavelengths, respectively.
10. The method of claim 8 , the second lens being an anamorphic lens.
11. The method of claim 10 where the second lens images an area having length and width, and the pixel array obtains alternating visible and infrared reflectivity measurements each time the unmanned aerial vehicle moves by half the length of the imaged area.
12. The method of claim 8 , the processor comprising logic included in the array of sensor pixels.
13. The method of claim 8 , the array of sensor pixels comprising 10,000 or more pixels.
14. The method of claim 8 , the light emitter comprising a first light emitting diode that emits light at a visible wavelength and a second light emitting diode that emits light at an infrared wavelength.
15. The method of claim 8 , the light emitter comprising a first diode laser that emits light at a visible wavelength and a second diode laser that emits light at an infrared wavelength.
16. The method of claim 8 , the crop comprising a plurality of plants and the second lens imaging an area of the crop onto the array of sensor pixels such that each pixel receives light from more than one plant.
17. The method of claim 8 , the crop comprising a plurality of plants and the second lens imaging an area of the crop onto the array of sensor pixels such that each pixel receives light from less than one plant.
18. The method of claim 8 , the crop comprising a plurality of plants and the second lens imaging an area of the crop onto the array of sensor pixels such that there is a one-to-one correspondence between plants and pixels.