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1. WO2000025114 - FLUORESCENCE DETECTION ASSEMBLY FOR DETERMINATION OF SIGNIFICANT VEGETATION PARAMETERS

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[ EN ]

WHAT IS CLAIMED IS:

1. Fluorescence detection assembly for determination of relevant vegetation parameters comprising:
- an excitation source (1) consisting in a high repetitive pulsed low power laser device with several nanosecond pulse length and an excitation wavelength in the red spectral region of preferable 670 nm;
a beam forming optical device (2) ;
- a dichroic beam splitter (5) coupling the formed excitation beam co-axial to the optical axis (9) of a receiver optic and directing this beam to a vegetation target subject to be investigated;
a basic fluorescence detector system (3) including an entrance optical device (4) receiving fluorescence emission via said dichroic beam splitter (5) and forming an image of the excitation spot at the sensitive detector area, and an interference filter (10) blocking out the elastic back scatter signal;
- an electronic detection device (7) operating at the doubled pulse repetition rate of said excitation laser (1) and sampling the active signal synchronously with the laser emission on the one hand and the passive background signal with a fixed delay in the microsecond range before or after the active signal on the other hand, recording those signals by means of a fast sample and hold circuit coupled to an analog to digital converter which enables a digital signal processing, said electronic detection device further comprising means for determining the pure fluorescence signal by subtracting the background signal from the active signal electronically or in a post processing procedure; and
a trigger and timing electronic device (6) synchronizing the laser pulses with the sample intervals of said detection electronic device.

2. Fluorescence detection assembly according to claim 1 wherein said laser device (1) is a laser diode operating in the red spectral region.

3. Fluorescence detection assembly according to claim 1 or claim 2 wherein the power of said laser device (1) is chosen > 0,5 W peak power.

4. Fluorescence detection assembly according to claim 1-wherein said beam forming device (2) comprises an astigmatism correction lens, i.e. a cylinder lens, and a beam expander/reducer to a point spot.

5. Fluorescence detection assembly according to claim 1 wherein said fluorescence detector (3) is a photo multiplier tube operating in continuous mode.

6. Fluorescence detection assembly according to claim 1 wherein said fluorescence detector (3) is an avalanche diode.

7. Fluorescence detection assembly according to claim 1 wherein said fluorescence detector (3) is a standard photo diode.

8. Fluorescence detection assembly according to claim 1 wherein said entrance optical device (4) comprises in its aperture a spheric lens, which forms an image of the excitation spot at the masked sensitive area of said fluorescence detector (3) .

9. Fluorescence detection assembly according to claim 1 wherein the center wavelength and bandwidth of said interference filter (10) is chosen appropriately in the range from 680-740 nm, the blocking quality beside the transmission
-3
being more than 10

10. Fluorescence detection assembly according to claim 1 wherein said sample and hold circuit has an analog bandwidth chosen appropriately between 40 and 200 MHz.

11. Fluorescence detection assembly according to claim 1 wherein said basic fluorescence detector system (3) is supplemented by additional detector elements (13) , and additional dichroic beam splitters (11) are provided to the-optical axis (12) at the detection side to form specific fluorescence detection bands, the number, center wavelength and bandwidth thereof depending on the scope of investigation.

12. Fluorescence detection assembly according to one of the claims 1 to 3 wherein a second laser is added for monitoring blue and/or green fluorescence, the excitation wavelength of said second laser being fixed in the range from 350 to 400 nm, with similar power and timing specifications as the red laser excitation source.

13. Fluorescence detection assembly according to claim 1 further comprising two additional detectors recording the elastic back scatter signal at the emission wavelengths of the laser sources.

14. Fluorescence detection assembly according to any preceding claim comprising an additional photodiode, installed in the optical path at the excitation system monitoring the laser pulse energy.

15. Fluorescence detection assembly according to any preceding claim comprising a PAR (photosynthetic active radiation) -sensor located above the measurement position monitoring the environmental light conditions.

16. Fluorescence detection assembly according to any preceding claim comprising a vertical movable, horizontally oriented light bar determining the canopy top level and thus plant height, the vertical position of the detector package being coupled with said light bar and being fixed or moving relative to it.

17. Fluorescence detection assembly according to claim 15 and-claim 16 comprising hydraulic, pneumatic or mechanical elements realizing the movement of said light bar sensor as well as said detector package.

18. Fluorescence detection assembly according to one of the claims 1 to 10 utilized for detection of chlorophyll containing plants or plant organs (plant recognition) wherein said assembly for the detection of green vegetation consists of one excitation laser diode operating at 670 nm and one detector module with an interference filter transmitting at a wavelength in the range from 680 to 740 nm with a spectral bandwidth between 5 and 25 nm, and wherein a suitable threshold is used to recognize vegetation, wherein the contrast between vegetated and non vegetated targets is as high that a recognition is done without any further signal processing.

19. Fluorescence detection assembly according to claim 18 wherein the plant position is defined relative to the position of the detector head and the distribution of plant material is determined by assuming a controlled two or three dimensional movement of the carrier platform.

20. Fluorescence detection assembly according to claim 18 or claim 19 applied to steering systems for greenhouse or horticulture robots.

21. Fluorescence detection assembly according to claim 18 or claim 19 applied to plant (weed) detection systems with subsequent plant destruction.

22. Fluorescence detection assembly according to claim 11 utilized for determination of chlorophyll concentrations wherein said assembly comprises two detection devices the detection channels being located at 680 - 690 ± 5 nm and-720 - 740 ± 5 or 10 nm, wherein the background corrected signals are divided and determine changes of the relative chlorophyll content per leaf area, and wherein the multiplication of the ratio with a predetermined calibration factor determines the absolute chlorophyll concentrations.

23. Fluorescence detection assembly according to claim 22 applied to greenhouse robots determining the chlorophyll status of plants and thus describing the growth state or long term stress conditions of plants.

24. Fluorescence detection assembly according to claim 22 applied to any chlorophyll containing material determining the state of maturity when specific fruits lose their typical green color (e.g. cherry, banana, apple, nuts, etc.).

25. Fluorescence detection assembly according to claim 22 applied to any chlorophyll containing material observing changes in the chlorophyll concentration what allows decay monitoring of fresh fruits (if they contain chlorophyll in their skin) and vegetation (e.g. cucumber, some apple types or salad leaves) .

26. Fluorescence detection assembly according to claim 22 however utilized for controlling site specific fertilization based on the fact that chlorophyll concentration of leaves is dependent and thus correlated on the nitrogen and sulfur supply of the whole plant so that fertilizer deficiencies are visible by characteristic reduction and distributions of the chlorophyll concentration which effect is accompanied by reduced growth speed and characteristic changes in the plant (leaf) density, said detection assembly comprising a detector head regarding the spatial structure and therefore located at a movable "robot" arm (X-Y actor) which is mounted at a moving platform (e.g. vehicle) which provides the . third-movement component (Z-component) .

27. Fluorescence detection assembly according to claim 26 wherein the vertical position of said "robot" arm is regulated by said light bar which determines the actual upper canopy level and wherein the detector head is adjusted relative to the upper canopy level, or moves between soil and this level.

28. Fluorescence detection assembly according to claim 26 and claim 27 wherein the three dimensional profile of the relevant plant parameters is monitored taking into account the horizontal movement of said carrier platform (tractor) .

29. Fluorescence detection assembly according to claim 26 however utilized for differentiation between monocotyledon and dicotyledon plants based on the characteristic that monocotyledon (MC) and dicotyledon (DC) plant types are distinguishable by their characteristic feature of the fluorescence emission spectra from 400 to 750 nm, this characteristic being observable by measuring the blue fluorescence relative to the red chlorophyll emission, said assembly being equipped with an additional excitation source exciting efficiently the blue fluorescence and performing an inter-calibration of the two excitation sources to normalize the fluorescence intensities to the excitation pulse power, and said assembly being provided with one additional detector module with a center wavelength in the range between 430 and 460 nm (Δλ = 10 - 50 nm) .

30. Fluorescence detection assembly according to claim 29 wherein said additional source is a triplet Nd:YAG laser 355 nm.

31. Fluorescence detection assembly according to claim- 29 or-claim 30 comprising additional detector modules monitoring e.g. the green fluorescence (500 - 550 nm; Δλ = 10 - 50 nm) to improve the knowledge about the spectral emission feature of the occurring plant types.

32. Fluorescence detection assembly according to claim 29 comprising only one detection channel as implemented in accordance with claim 18 to assess the red chlorophyll fluorescence .

33. Fluorescence detection assembly according to claim 29 comprising a PAR sensor monitoring the illumination environment and thus interpreting the band ratios with regard to the environmental light conditions.

34. Fluorescence detection assembly according to claim 29 wherein a predetermined ratio threshold is provided defining whether a signal belongs to a MC or DC plant.

35. Fluorescence detection assembly according to claim 29 wherein a classification algorithm in the case of programmable post processing is provided defining whether a signal belongs to a MC or DC plant.

36. Fluorescence detection assembly according to one of the claims 29 to 35 applied to site specific herbicide treatment in terms weed position and type.

37. Fluorescence detection assembly according to claim 29 extended by the second detection band in the red fluorescence region and one detector package to monitor the elastic back scatter signal and utilized for detection of various fungal infections .

38. Fluorescence detection assembly according to claim 37 wherein effects on the photosynthetic system will be recognized by changes in the fluorescence intensity.

39. Fluorescence detection assembly according to claim 37 wherein changes in the leaf morphological structure, total cell destruction or variations in the composition of the plant pigment constituents will be determined by the channel ratio of the red detection bands and wherein inhomogeneous infections (e.g. rust), and their characteristic distribution over the total leaf area or canopy provides an additional (quantitative) identification criteria.

40. Fluorescence detection assembly according to claim 37 wherein changes in the composition of blue and/or green fluorescence emitting pigments as result of the infection are recognized by the detection channels in this range and wherein some fungi are characteristic sources of blue and/or green fluorescence themselves (e.g. mildew) and can thus be discovered.

41. Fluorescence detection assembly according to claim 37 wherein leaf surfaces are possibly covered with an additional tissue layer (e.g. mildew mycel) causing a significantly increased surface reflectance which effect is recognized by the elastic back scatter signal at the red as well as at the UV excitation wavelength.

42. Fluorescence detection assembly according to one of the claims 37 to 41 applied to site specific fungicide treatment in terms fungi position and type.

43. Fluorescence detection assembly according to claim 18 however utilized for monitoring the photosynthetic activity-of vegetation by time series wherein the investigated target is fixed and thus the variation is only time dependent.

44. Fluorescence detection assembly according to claim 22 however utilized for monitoring the photosynthetic activity of vegetation by time series wherein the investigated target is variable (normalization to relative chlorophyll content) .

45. Fluorescence detection assembly according to claim 43 or claim 44 comprising a PAR sensor determining the environmental light condition.

46. Fluorescence detection assembly according to claim 43 or claim 44 wherein the digitized fluorescence values are interpreted with respect to the according illumination situation and history while post processing.

47. Fluorescence detection assembly according to one of the claims 43 to 46 applied to scientific investigation of long term processes, where the interaction of plants and variable environmental conditions is investigated.

48. Fluorescence detection assembly according to one of the claims 43 to 46 applied to the scientific investigation of the Kautzky kinetic and all related parameter which can only be measured at dark adapted plant, at a fixed position.

49. Fluorescence detection assembly according to claim 48 wherein the source of actinic light is the excitation source itself if the repetition rate is increased to induce an actinic reaction.

50. Fluorescence detection assembly according to claim 48 wherein the source of actinic light is a triggering extra white light source which illuminates the plant . at a_ determined time.

51. Fluorescence detection assembly according to one of the claims 43 to 46 applied to the scientific investigation of the Genty-Parameter which can be obtained by measuring the steady state fluorescence as well as the steady state fluorescence superimposed by a saturating light pulse.

52. Fluorescence detection assembly according to claim 51 wherein the steady state fluorescence (Fs) will be excited remotely by the laser diode while an additional white lamp or the sun act as actinic light and the saturating light (Fm1) will be generated by an additional light source, e.g. a flash lamp such that due to the detection of the passive background signal this system will be able to monitor Fs and Fm' and the intensity of the saturating light.