Sunlight-induced chlorophyll fluorescence observation system and method

Abstract

The invention discloses a sunlight-induced chlorophyll fluorescence observation system and method, and belongs to the technical field of vegetation remote sensing inversion parameter acquisition methods. The observation system comprises a multi-channel optical splitter, a holder, a cosine corrector, an industrial control box and two spectrometers with ultra-high spectral resolution. The two spectrometers with the ultra-high spectral resolution are respectively used for observing sunlight-induced chlorophyll fluorescence and vegetation canopy reflectivity, and light paths of optical fibers entering the spectrometers with the ultra-high spectral resolution comprise a light path for observing the sunlight-induced chlorophyll fluorescence and a light path for observing the vegetation canopy reflectivity; and the optical splitter is used for switching the optical path of the optical fiber entering the ultra-high spectral resolution spectrometer. According to the observation method, every 30 minutes is taken as a whole observation process, and the azimuth angle mode A, the azimuth angle mode B, the main plane mode and the hot spot mode are executed in sequence. According to the method, a plurality of modes are used for observation in the whole observation process, so that the observation efficiency is improved, and a more accurate sunlight-induced chlorophyll fluorescence result is obtained.

Description

Technical Field

[0001] The invention discloses a sunlight-induced chlorophyll fluorescence observation system and method, belonging to the technical field of vegetation remote sensing inversion parameter acquisition methods. Background Art

[0002] Sunlight-induced chlorophyll fluorescence is closely related to vegetation photosynthesis and can be regarded as a direct substitute for describing the mechanism and state of plant photosynthesis. The near-ground ultra-high spectrometer is an emerging scientific research product that has developed with the needs of this scientific research field, with fluorescence observation as the main orientation. The close relationship between fluorescence and vegetation photosynthesis allows technicians to use fluorescence to achieve real-time monitoring of plant diseases and insect pests, water stress or yield estimation, or plant physiologists can use this system for field or laboratory fluorescence to monitor the activity of plant photosynthetic organs and use it for related research. The near-ground multi-angle sunlight-induced chlorophyll fluorescence observation system can continuously obtain hyperspectral data of the vegetation canopy for a long time and accurately invert the sunlight-induced chlorophyll fluorescence of the canopy's yin and yang leaves. In the prior art, the invention patent with the announcement number CN108693154B discloses a method for multi-angle observation and accurate inversion of sunlight-induced chlorophyll fluorescence of vegetation yin and yang leaves, using the following observation method: the gimbal changes the observation azimuth and observation zenith angle through horizontal and vertical rotation, and the observation azimuth angle is fixed as a semicircle rotating from due west through due north to due east, and the azimuth angle changes by 10° at a time. The observation zenith angle is set to the solar zenith angle at that time, but when the solar zenith angle is greater than 40°, the observation zenith angle is set to 40°. Although this method has achieved good observation results, the observation efficiency is low. Summary of the invention

[0003] The object of the present invention is to provide a sunlight-induced chlorophyll fluorescence observation system and method to solve the problem of low efficiency of sunlight-induced chlorophyll fluorescence observation in the prior art.

[0004] A sunlight-induced chlorophyll fluorescence observation system, comprising a multi-channel spectrometer, a pan / tilt, a cosine corrector, an industrial control box and two ultra-high spectral resolution spectrometers;

[0005] The two ultra-high spectral resolution spectrometers are respectively used to observe sunlight-induced chlorophyll fluorescence and observe vegetation canopy reflectance. The optical path of the optical fiber entering the ultra-high spectral resolution spectrometer includes the optical path for observing sunlight-induced chlorophyll fluorescence and the optical path for observing vegetation canopy reflectance. The multi-channel splitter is used to switch the optical path of the optical fiber entering the ultra-high spectral resolution spectrometer. The cosine corrector and the optical fiber of the ultra-high spectral resolution spectrometer are connected together. The industrial control box controls the multi-channel splitter, the pan-tilt head, the cosine corrector and the two ultra-high spectral resolution spectrometers. The multi-channel splitter, the cosine corrector, the industrial control box and the two ultra-high spectral resolution spectrometers are all fixed on the pan-tilt head.

[0006] The ultra-high spectral resolution spectrometer used to observe sunlight-induced chlorophyll fluorescence has a spectral range of 650nm-800nm ​​and a spectral resolution of 0.3nm.

[0007] The ultra-high spectral resolution spectrometer used to observe vegetation canopy reflectance has a spectral range of 350nm-1100nm and a spectral resolution of 1.1nm.

[0008] A sunlight-induced chlorophyll fluorescence observation method uses a sunlight-induced chlorophyll fluorescence observation system. Every 30 minutes is a full observation process, and azimuth mode A, azimuth mode B, main plane mode and hotspot mode are executed in sequence.

[0009] Azimuth mode A was started in the first 10 minutes of an observation. The observation azimuth angle VAA was set at 0° to the south and changed from 60° to 300° in steps of 10°. The observation zenith angle VZA was consistent with the solar zenith angle SZA and was adjusted to 40° when VZA was greater than 40°.

[0010] After ending azimuth mode A, start azimuth mode B, VAA is set to 40° with 0° to the south, VZA is consistent with SZA, and when VZA is greater than 40°, it is adjusted to 40°.

[0011] After the azimuth mode B ends, the main plane mode starts, VAA is consistent with the solar azimuth angle SAA, and the spectra of different VZAs in the back reflection are observed. VZA increases from 10° to 60° in steps of 10°.

[0012] After the main plane mode ends, the hotspot mode begins, and the observations are made until the entire observation process is completed, VAA and SAA are consistent, VZA and SZA are consistent, and the spectrum in the hotspot direction is observed.

[0013] Compared with the prior art, the present invention has the following beneficial effects: the present invention uses multiple modes for observation in the entire observation process, thereby improving the observation efficiency and obtaining more accurate daylight-induced chlorophyll fluorescence results. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of the sunlight-induced chlorophyll fluorescence observation system;

[0015] Figure 2 It is a technical flow chart of the entire observation process;

[0016] Figure 3 This is a graph of wheat far-red sunlight-induced chlorophyll fluorescence observed using existing technology;

[0017] Figure 4 This is a graph of wheat red light sunlight induced chlorophyll fluorescence results observed using existing technology;

[0018] Figure 5 This is a result diagram of wheat far-red sunlight-induced chlorophyll fluorescence observed using the azimuth mode A of the present invention;

[0019] Figure 6 This is a result diagram of wheat red light sunlight induced chlorophyll fluorescence observed using the azimuth mode A of the present invention;

[0020] Figure 7 This is a result diagram of wheat far-red sunlight-induced chlorophyll fluorescence observed using the azimuth mode B of the present invention;

[0021] Figure 8 This is a result diagram of wheat red light sunlight induced chlorophyll fluorescence observed using the azimuth mode B of the present invention;

[0022] Fig. 9 This is a result diagram of wheat far-red sunlight-induced chlorophyll fluorescence observed using the main plane mode of the present invention;

[0023] Fig.10 This is the result of wheat red light sunlight induced chlorophyll fluorescence observed using the main plane mode of the present invention

[0024] Fig.11 This is a result diagram of wheat far-red sunlight-induced chlorophyll fluorescence observed using all modes of the present invention;

[0025] Fig.12 This is a graph of the red light sunlight-induced chlorophyll fluorescence results of wheat observed using all modes of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] A sunlight-induced chlorophyll fluorescence observation system, comprising a multi-channel spectrometer, a pan / tilt, a cosine corrector, an industrial control box and two ultra-high spectral resolution spectrometers;

[0028] The structure of the sunlight-induced chlorophyll fluorescence observation system is as follows: Figure 1As shown, the two ultra-high spectral resolution spectrometers are respectively used to observe sunlight-induced chlorophyll fluorescence and observe vegetation canopy reflectance, the optical path of the optical fiber entering the ultra-high spectral resolution spectrometer includes an optical path for observing sunlight-induced chlorophyll fluorescence and an optical path for observing vegetation canopy reflectance, the multi-channel splitter is used to switch the optical path of the optical fiber entering the ultra-high spectral resolution spectrometer, the cosine corrector and the optical fiber of the ultra-high spectral resolution spectrometer are connected together, the industrial control box controls the multi-channel splitter, the pan-tilt head, the cosine corrector and the two ultra-high spectral resolution spectrometers, and the multi-channel splitter, the cosine corrector, the industrial control box and the two ultra-high spectral resolution spectrometers are all fixed on the pan-tilt head.

[0029] The ultra-high spectral resolution spectrometer used to observe sunlight-induced chlorophyll fluorescence has a spectral range of 650nm-800nm ​​and a spectral resolution of 0.3nm.

[0030] The ultra-high spectral resolution spectrometer used to observe vegetation canopy reflectance has a spectral range of 350nm-1100nm and a spectral resolution of 1.1nm.

[0031] A sunlight-induced chlorophyll fluorescence observation method uses a sunlight-induced chlorophyll fluorescence observation system. Every 30 minutes is a full observation process, and azimuth mode A, azimuth mode B, main plane mode and hotspot mode are executed in sequence.

[0032] A technical flow chart of the entire observation process is as follows: Figure 2 As shown, azimuth mode A is started in the first 10 minutes of a full observation. The observation azimuth angle VAA is 0° to the south and increases from 60° to 300° in steps of 10°. The zenith angle VZA is consistent with the solar zenith angle SZA, and is adjusted to 40° when VZA is greater than 40°. After azimuth mode A is ended, azimuth mode B is started, VAA is 0° to the south and is set to 40°. VZA is consistent with SZA, and is adjusted to 40° when VZA is greater than 40°. After azimuth mode B is ended, the main plane mode is started, VAA is consistent with the solar azimuth angle SAA, and the spectra of different VZAs in the back reflection are observed. VZA increases from 10° to 60° in steps of 10°. After the main plane mode is ended, the hotspot mode is started, and observations are made until the end of a full observation. VAA is consistent with SAA, VZA is consistent with SZA, and the spectrum in the hotspot direction is observed.

[0033] After the pan / tilt platform of the present invention is rotated to a set angle, a multi-channel spectrometer is used to switch the optical path to an optical path for observing sunlight-induced chlorophyll fluorescence, a solar incident spectrum is collected according to an initial integration time, an optimized integration time is calculated, a solar incident spectrum is observed according to the optimized integration time and data is recorded, the multi-channel spectrometer is used to close the optical path, a dark current is recorded according to the optimized integration time, and the dark current is noise data generated by the spectrometer itself when no light enters the spectrometer, the multi-channel spectrometer is used to open the optical path for observing the reflectance of the vegetation canopy, a canopy reflection incident spectrum is collected according to the initial integration time, the optimized integration time is calculated, a canopy reflection incident spectrum is observed according to the optimized integration time and data is recorded, the multi-channel spectrometer is used to close the optical path, and a dark current is recorded according to the optimized integration time. At this point, the observation of the set angle is completed, and the pan / tilt platform is rotated to the next angle.

[0034] The optimized integration time includes:

[0035] T = IT × targetDN / max;

[0036] Where T is the optimized integration time, IT is the customized initial integration time, targetDN is the customized ideal spectrometer recording value, and max is the maximum spectrometer recording value of the spectrum collected within the IT time.

[0037] The present invention uses a sunlight-induced chlorophyll fluorescence observation system, and the detailed information of each component is as follows: the multi-channel spectrometer model is BGS-MPM. Since the spectrometer has only one optical path, and the observation requires continuous switching of the solar incident light and the canopy reflected light, the multi-channel spectrometer can switch the optical fiber entering the spectrometer to observe the optical path of the solar incident light and the canopy reflected light through a mobile component under the control of the observation system software. When measuring the dark current, the optical path is closed to achieve the observation of multiple optical paths. The pan-tilt model is PTU-57 / 42, which rotates in both horizontal and vertical directions to change the observation angle. The ultra-high spectral resolution spectrometer models are QEpro and USB. The spectral range of QEpro is 650-800nm, and the spectral resolution is 0.3nm. It is mainly used for sunlight-induced chlorophyll fluorescence observation. The spectral range of USB is 350-1100nm, and the spectral resolution is 1.1nm. It is mainly used for vegetation canopy reflectance observation. The cosine corrector is a component that captures light signals within a 180-degree field of view by optical scattering. It is used to correct the incident solar radiation so that the observed incident solar radiation is the sum of the radiation in the hemispherical direction. The cosine corrector is usually used in conjunction with an optical fiber, or in certain cases, it is directly connected to the optical fiber of the spectrometer. When measuring radiation on a plane, the cosine corrector is a very necessary accessory. The industrial control box is used to integrate the software system to realize real-time display of chlorophyll fluorescence. The entire observation system is integrated in a 0.6*0.4*0.3m trolley case, which is easy to carry and simple to install.

[0038] The software of the ground-based sunlight-induced chlorophyll fluorescence system is written in C language, and supports computer operating systems including Windows 7, Windows 8 and Windows 10. The main functions are: 1. Optimize the integration time; 2. Control two spectrometers to collect spectra in parallel; 3. Real-time calculation and visualization of irradiance, radiance and reflectance; 4. Real-time calculation and visualization of sunlight-induced chlorophyll fluorescence. The observation cycle is 15 minutes, but the observation mode of the first 15 minutes and the second 15 minutes of every half hour is slightly different, so a complete cycle is completed every half hour.

[0039] After the observation is completed, data processing is performed. During the observation process, a file is generated every 15 minutes in a MATLAB-specific mat file format, which consists of the solar incident spectrum and canopy reflectance spectrum and the corresponding integration time and dark current, solar zenith angle, solar azimuth angle, observation zenith angle, observation azimuth angle, etc. Since the values ​​recorded by the spectrometer do not have physical meaning, it is necessary to calibrate the spectrometer using a standard light source that records radiance values ​​in different bands to obtain a calibration coefficient that can convert the spectrometer record values ​​into radiance. The spectral data obtained by observation is first subtracted from the dark current to eliminate the noise of the instrument itself, then divided by the integration time, normalized to 1 second, and then multiplied by the calibration coefficient to obtain the radiance value, which is used for the subsequent inversion of chlorophyll fluorescence. The radiance of the canopy reflected light divided by the radiance of the solar incident light is the reflectance.

[0040] For fluorescence inversion, there is an oxygen absorption well in solar radiation around 760nm, and the spectrum curve is concave. Fluorescence is emitted outward by plants and can fill this absorption well. By comparing the relative intensity of the radiance of the dark line of the absorption well and its adjacent bands in the solar incident spectrum and the canopy reflection spectrum, the canopy fluorescence can be inverted and extracted. The canopy reflection at the dark line consists of the real reflection ρ of the canopy and the fluorescence F. The fluorescence F is inverted using the spectrum fitting method. ρ and F can be expressed by a polynomial model. The radiance L of the canopy reflection is expressed as:

[0041]

[0042] Where ρ MOD (λ) and F MOD (λ) are the mathematical expressions of reflectance and fluorescence in the corresponding bands, L TOC (λ) represents the observed canopy reflectance radiance, E(λ) is the solar incident radiance, and ε(λ) represents the residual term between the observed value and the fitted value in each band. By solving the linear equations by least squares, we can get ρ MOD (λ) and F MOD (λ), and thus F and ρ are calculated.

[0043] The results of wheat far-red sunlight-induced chlorophyll fluorescence observed using the existing technology (invention patent with announcement number CN108693154B) are shown in the figure below. Figure 3 As shown, the results of red light-induced chlorophyll fluorescence are as follows Figure 4 When the method of the present invention is used, the daily variation of SIF obtained in different modes is obtained, and the red line represents the solar zenith angle (SAA) or the solar azimuth angle (SZA). For a given time point, the SIF value around the red line should be the highest.

[0044] The results of far-red sunlight-induced chlorophyll fluorescence of wheat observed in azimuth mode A are as follows Figure 5The results of sunlight-induced chlorophyll fluorescence in shaded leaves are shown in Figure 6 As shown in Figure 2, the results of far-red sunlight-induced chlorophyll fluorescence of wheat observed in azimuth mode B are as follows: Figure 7 As shown, the results of red light-induced chlorophyll fluorescence are as follows Figure 8 As shown in the figure, the results of far-red sunlight-induced chlorophyll fluorescence of wheat observed in the main plane mode are as follows Fig. 9 As shown, the results of red light-induced chlorophyll fluorescence are as follows Fig.10 shown.

[0045] The results of wheat far-red sunlight-induced chlorophyll fluorescence observed using all modes of the present invention are as follows Fig.11 As shown, the results of red light-induced chlorophyll fluorescence are as follows Fig.12 shown.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features may be replaced by equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sunlight-induced chlorophyll fluorescence observation system, characterized in that: It includes a multi-channel beam splitter, a pan / tilt, a cosine corrector, an industrial control box, and two ultra-high spectral resolution spectrometers; The two ultra-high spectral resolution spectrometers are respectively used to observe sunlight-induced chlorophyll fluorescence and observe vegetation canopy reflectance. The optical path of the optical fiber entering the ultra-high spectral resolution spectrometer includes the optical path for observing sunlight-induced chlorophyll fluorescence and the optical path for observing vegetation canopy reflectance. The multi-channel splitter is used to switch the optical path of the optical fiber entering the ultra-high spectral resolution spectrometer. The cosine corrector and the optical fiber of the ultra-high spectral resolution spectrometer are connected together. The industrial control box controls the multi-channel splitter, the pan-tilt head, the cosine corrector and the two ultra-high spectral resolution spectrometers. The multi-channel splitter, the cosine corrector, the industrial control box and the two ultra-high spectral resolution spectrometers are all fixed on the pan-tilt head.

2. Use of a sunlight-induced chlorophyll fluorescence observation system according to claim 1, characterized in that: The spectral range of the ultra-high spectral resolution spectrometer used to observe sunlight-induced chlorophyll fluorescence is 650nm-800nm.

3. Use of a sunlight-induced chlorophyll fluorescence observation system according to claim 1, characterized in that: The spectral resolution of the ultra-high spectral resolution spectrometer used to observe sunlight-induced chlorophyll fluorescence is 0.3nm.

4. Use of a sunlight-induced chlorophyll fluorescence observation system according to claim 1, characterized in that: The spectral range of the ultra-high spectral resolution spectrometer used to observe vegetation canopy reflectance is 350nm-1100nm.

5. Use of a sunlight-induced chlorophyll fluorescence observation system according to claim 1, characterized in that: The spectral resolution of the ultra-high spectral resolution spectrometer used to observe vegetation canopy reflectance is 1.1nm.

6. A method for observing sunlight-induced chlorophyll fluorescence, characterized in that: Using the sunlight-induced chlorophyll fluorescence observation system according to claim 1, every 30 minutes is a full observation process, and azimuth mode A, azimuth mode B, main plane mode and hotspot mode are executed in sequence.

7. A method for observing sunlight-induced chlorophyll fluorescence according to claim 6, characterized in that: Azimuth mode A was started in the first 10 minutes of an observation. The observation azimuth angle VAA was set at 0° to the south and changed from 60° to 300° in steps of 10°. The observation zenith angle VZA was consistent with the solar zenith angle SZA and was adjusted to 40° when VZA was greater than 40°.

8. The method for observing sunlight-induced chlorophyll fluorescence according to claim 7, characterized in that: After ending azimuth mode A, start azimuth mode B, VAA is set to 40° with 0° to the south, VZA is consistent with SZA, and when VZA is greater than 40°, it is adjusted to 40°.

9. A method for observing sunlight-induced chlorophyll fluorescence according to claim 8, characterized in that: After the azimuth mode B ends, the main plane mode starts, VAA is consistent with the solar azimuth angle SAA, and the spectra of different VZAs in the back reflection are observed. VZA increases from 10° to 60° in steps of 10°.

10. A method for observing sunlight-induced chlorophyll fluorescence according to claim 9, characterized in that: After the main plane mode ends, the hotspot mode begins, and the observations are made until the entire observation process is completed, VAA and SAA are consistent, VZA and SZA are consistent, and the spectrum in the hotspot direction is observed.

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