Cooperative sunlight-induced chlorophyll fluorescence measurement method

Abstract

The invention discloses a cooperative sunlight-induced chlorophyll fluorescence measurement method, and relates to the technical field of crop growth monitoring, the method is realized based on a cooperative sunlight-induced chlorophyll fluorescence measurement system, and the cooperative sunlight-induced chlorophyll fluorescence measurement system adopts a combination mode of combining a single spectrometer with a single optical fiber. The optical fiber is driven by the rotating mechanism to rotate to two different detection positions to cooperatively measure the solar incident radiation illuminance irrad and the canopy reflection radiation illuminance rad, so that the fixed deviation between instruments can be effectively eliminated, and meanwhile, the integrity of an optical path is ensured to a certain extent; the cosine corrector and the optical fiber adopt a split structure, the optical fiber faces upwards and is matched with the cosine corrector to measure the solar incident radiation illuminance irrad so as to obtain a larger view field range, and the optical fiber faces downwards to directly measure the canopy reflection radiation illuminance rad so as to focus a target plant canopy in a concentrated manner, so that the influence of too many ground interferents due to the too large view field range is avoided; and the measurement accuracy can be improved.

Description

Technical Field

[0001] This application relates to the field of crop growth monitoring technology, and in particular to a synergistic sunlight-induced chlorophyll fluorescence measurement method. Background Technology

[0002] Gross Primary Productivity (GPP) is the total amount of carbon absorbed by plants through photosynthesis. Accurately and in real-time understanding of the spatiotemporal distribution characteristics of GPP is of great significance for carbon cycle assessment. The light energy absorbed by plant chlorophyll ultimately exists in three main forms: photosynthesis, heat dissipation, and chlorophyll fluorescence, with a certain balance existing among these three forms. Therefore, the intensity of solar-induced chlorophyll fluorescence (SIF) is related to photosynthetic capacity and is also known as a probe of photosynthesis. It is more sensitive to photosynthesis than traditional vegetation indices and has become a new opportunity for estimating GPP at regional and larger spatial scales in the past decade.

[0003] Unlike large-scale SIF observations by satellites, ground-based SIF observations help to reduce SIF-related research to the canopy scale, so as to better study its coupling mechanism with photosynthesis. Ground-based SIF measurements require obtaining solar incident irradiance and canopy reflected irradiance to retrieve SIF results. Currently, there are two main measurement methods: (1) using two spectrometers to measure together, with each spectrometer connected to an optical fiber. One spectrometer measures canopy reflected irradiance through the connected optical fiber, and the other spectrometer measures solar incident irradiance through the connected optical fiber. However, this dual-spectrum measurement has fixed deviations between instruments, such as optical path grating spectral deviation and detector quantum efficiency deviation, which affect the accuracy of the measurement results. (2) A spectrometer is connected to two optical fibers via an optical path switching switch. The spectrometer measures the solar incident irradiance through one of the optical fibers, and then the optical path switching switch is used to switch to measure the canopy reflected irradiance through the other optical fiber. Compared with the dual spectrometer measurement method, this measurement method can effectively eliminate the influence of fixed deviations between spectrometers. However, the optical path switching switch destroys the integrity of the optical path to a certain extent, resulting in a difference between the radiation value calculated by the calibration coefficient and the actual radiation value. The accuracy of the measurement results is also not ideal. Summary of the Invention

[0004] This application addresses the aforementioned problems and technical needs by proposing a synergistic sunlight-induced chlorophyll fluorescence measurement method. The technical solution of this application is as follows: A synergistic sunlight-induced chlorophyll fluorescence measurement method, comprising: A collaborative solar-induced chlorophyll fluorescence measurement system was constructed in the crop planting area. The collaborative solar-induced chlorophyll fluorescence measurement system includes a base frame, a spectrometer, optical fiber, a rotating mechanism, a cosine corrector, and a data acquisition and control host. The base frame includes a vertical frame and a horizontal bar. The output port of the optical fiber is connected to the spectrometer, and the spectrometer is connected to the data acquisition and control host. The data acquisition and control host is also connected to and controls the rotating mechanism to drive the input port of the optical fiber to rotate. The cosine corrector is fixed on the horizontal bar of the base frame with the light-receiving surface vertically upward. The size of the optical path connection port of the cosine corrector matches the size of the optical fiber, and the optical path connection port of the cosine corrector is located on the rotation path of the input port of the optical fiber. During the daytime, the data acquisition and control host controls the rotating mechanism to rotate the optical fiber's inlet to the first detection position, so that the optical fiber's inlet is connected to the optical path connector of the cosine corrector, and the solar incident radiation irrad is measured; and, the rotating mechanism controls the rotating mechanism to rotate the optical fiber's inlet to the second detection position, so that the optical fiber's inlet faces the crop canopy below the crossbar, and the canopy reflected radiation radiance rad is measured. The solar-induced chlorophyll fluorescence value was obtained by inverting the solar incident irrad and the canopy reflected irrad.

[0005] A further technical solution is that the light-receiving surface of the cosine corrector adopts a glass hemispherical dome structure, and the optical path connection port of the cosine corrector also includes a light-shielding structure. The light-shielding structure includes a protrusion and a base plate. The protrusion is continuously arranged around the circumferential edge of the optical path connection port, and the base plate is fixed on the end face of the protrusion. A guide groove is opened on the base plate from the optical fiber through port to the optical path connection port. The opening size of the guide groove decreases sequentially from the optical fiber through port to the optical path connection port. The guide groove is located on the rotation path of the optical fiber's light inlet.

[0006] A further technical solution is that the rotating mechanism includes a rotary motor, an optical fiber mounting base, and a rigid optical fiber sleeve. The surface of the optical fiber mounting base is a semi-circular disk structure with a predetermined thickness. The rotary motor is fixed on a crossbar with its shaft running horizontally. The motor shaft is connected to the center of the optical fiber mounting base. The outer periphery of the optical fiber mounting base is provided with an optical fiber slot that matches the optical fiber. The rigid optical fiber sleeve is fixed at one end of the optical fiber mounting base in the diameter direction. The length extension direction of the rigid optical fiber sleeve is perpendicular to the diameter direction of the optical fiber mounting base on its surface. The inner diameter of the rigid optical fiber sleeve matches the circumferential dimension of the optical fiber and is open at both ends. The optical fiber's inlet starts from the other end of the optical fiber mounting base relative to the rigid optical fiber sleeve in the diameter direction, and is wound around the optical fiber slot fixed on the outer periphery of the optical fiber mounting base. When it reaches the end where the rigid optical fiber sleeve is located, it passes through the opening at one end of the rigid optical fiber sleeve and protrudes from the opening at the other end of the rigid optical fiber sleeve and is fixed to the rigid optical fiber sleeve. When the rotary motor is activated, the optical fiber mounting base drives the rigid optical fiber sleeve to rotate under the drive of the motor shaft, thereby driving the optical fiber's inlet to rotate.

[0007] A further technical solution involves using a spectrometer with a built-in shutter to measure solar incident irradiance (irrad) and canopy reflected irradiance (rad), including: The acquisition control host controls the rotating mechanism to rotate the optical fiber's inlet to the first detection position, and controls the spectrometer to adaptively adjust the integration time T_int1; it acquires the solar incident radiation DN_s, keeps the integration time T_int1 constant, closes the spectrometer's internal shutter, and measures the dark noise DC_s; it calculates the solar incident irrad = cof1 * (DN_s - DC_s) / T_int1, where cof1 is the first calibration coefficient; The acquisition control host controls the rotating mechanism to rotate the optical fiber's inlet to the second detection position, and controls the spectrometer to adaptively adjust the integration time T_int2; acquires the canopy reflected radiation DN_r, and keeps the integration time T_int2 unchanged, closes the spectrometer's internal shutter and measures the dark noise DC_r; calculates the canopy reflected radiation brightness rad=cof2*(DN_r-DC_r) / T_int2, where cof2 is the second calibration coefficient.

[0008] A further technical solution is that the collaborative sunlight-induced chlorophyll fluorescence measurement system also includes a calibration detection light source, which is fixed on the base frame and located above the crossbar. The acquisition and control host is connected to and controls the calibration detection light source. The collaborative sunlight-induced chlorophyll fluorescence measurement method also includes: When the acquisition and control host detects an abnormal measurement result, it stops the measurement and waits until nighttime to turn on the calibration detection light source to perform a calibration operation to update the first calibration coefficient cof1 and the second calibration coefficient cof2. After the calibration operation is completed, the calibration detection light source is turned off.

[0009] A further technical solution involves the acquisition and control host detecting whether the measurement results are abnormal, including: When the correlation coefficient between the calculated solar incident irradiance and the reference incident irradiance is less than the coefficient threshold, the measurement result is determined to be abnormal.

[0010] A further technical solution is that the synergistic sunlight-induced chlorophyll fluorescence measurement method also includes: After the initial setup of the collaborative sunlight-induced chlorophyll fluorescence measurement system, the acquisition and control host turns on the calibration detection light source during the nighttime period and controls the rotating mechanism to rotate the optical fiber's light inlet to the first detection position, so that the optical fiber's light inlet is connected to the optical path connection port of the cosine corrector, and the incident irradiance of the calibration detection light source is measured as the reference incident irradiance.

[0011] A further technical solution involves performing a calibration operation to update the first calibration coefficient cof1 and the second calibration coefficient cof2, including: The acquisition control host controls the rotating mechanism to rotate the optical fiber's inlet to the first detection position, so that the optical fiber's inlet is connected to the optical path connection port of the cosine corrector. The host controls the spectrometer to adaptively adjust the integration time T_int1, acquire the incident radiation DN_1, and keep the integration time T_int1 unchanged. The internal shutter of the spectrometer is closed and the dark noise DC_1 is measured. The first calibration coefficient cof1 is updated according to cof1=Irrad / ((DN_l-DC_l) / T_intl, and the second calibration coefficient cof2 is updated using the updated first calibration coefficient cof1; where Irrad is the reference incident irradiance.

[0012] A further technical solution is that the filament axis of the calibration test light source is oriented towards the light-receiving surface of the cosine corrector, and the angle θ1 between the filament axis of the calibration test light source and the optical axis of the cosine corrector is equal to the angle θ2 between the filament axis of the calibration test light source and the support frame.

[0013] A further technical solution is that the synergistic sunlight-induced chlorophyll fluorescence measurement method also includes: After the collaborative sunlight-induced chlorophyll fluorescence measurement system is set up in the crop planting area, the height of the crossbar in the base frame above the ground and the orientation of the light inlet of the calibration fiber when it is rotated to the second detection position are adjusted so that the coverage of the target crop in the field of view reaches the coverage threshold when the fiber is rotated to the second detection position.

[0014] The beneficial technical effects of this application are: This application discloses a collaborative solar-induced chlorophyll fluorescence measurement method. This method is based on a collaborative solar-induced chlorophyll fluorescence measurement system. The collaborative solar-induced chlorophyll fluorescence measurement system adopts a combination of a single spectrometer and a single optical fiber. A rotating mechanism drives the optical fiber to rotate to two different detection positions to collaboratively measure the solar incident irradiance (irrad) and canopy reflected radiance (rad). This can effectively eliminate fixed deviations between instruments and, to a certain extent, ensure the integrity of the optical path. Furthermore, the cosine corrector and the optical fiber adopt a split structure. The optical fiber faces upward and works with the cosine corrector to measure the solar incident irradiance (irrad) to obtain a larger field of view. The optical fiber faces downward and directly measures the canopy reflected radiance (rad) to focus on the target plant canopy. This avoids the influence of too many ground interferences due to the large field of view and helps to improve measurement accuracy.

[0015] The light-receiving surface of the cosine corrector adopts a glass hemispherical structure, which can effectively reduce the impact of rainwater and dust on the measurement. In addition, the cosine corrector is equipped with a light-shielding structure with a guide groove at the optical path connection port, which improves the alignment accuracy of the optical fiber and the optical path connection port and reduces optical interference at the interface.

[0016] To adapt to field measurement scenarios, this collaborative sunlight-induced chlorophyll fluorescence measurement system is also equipped with a calibration detection light source, and can automatically detect and calibrate on-site to update the calibration coefficients, ensuring the reliability of long-term SIF measurements in the field. Attached Figure Description

[0017] Figure 1 This is a flowchart of a synergistic sunlight-induced chlorophyll fluorescence measurement method according to an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of a collaborative sunlight-induced chlorophyll fluorescence measurement system built in one embodiment.

[0019] Figure 3 yes Figure 2 A magnified view of the local structure of the co-operational solar-induced chlorophyll fluorescence measurement system in the crossbar region.

[0020] Figure 4 yes Figure 2 A magnified view of the local structure when the optical fiber inlet is rotated to the first detection position by the rotating mechanism in the collaborative solar-induced chlorophyll fluorescence measurement system.

[0021] Figure 5 Yes, yes Figure 2 A magnified view of the local structure when the optical fiber inlet is rotated to the second detection position by the rotating mechanism in the collaborative solar-induced chlorophyll fluorescence measurement system.

[0022] Figure 6This is a schematic diagram of the rotating mechanism in one embodiment.

[0023] Figure 7 This is a schematic diagram of the cosine corrector in one embodiment.

[0024] Figure 8 yes Figure 2 An application scenario diagram of the co-operational sunlight-induced chlorophyll fluorescence measurement system. Detailed Implementation

[0025] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0026] This application discloses a synergistic sunlight-induced chlorophyll fluorescence measurement method, which includes the following steps, please refer to... Figure 1 The flowchart shown below: Step 110: Establish a collaborative sunlight-induced chlorophyll fluorescence measurement system in the crop planting area.

[0027] Please refer to Figure 2 The system structure diagram shown, and Figure 3 and Figure 4 The enlarged view of the partial structure shown illustrates that the collaborative sunlight-induced chlorophyll fluorescence measurement system includes a base frame, a spectrometer 210, an optical fiber 220, a rotation mechanism 230, a cosine corrector 240, and a data acquisition and control host 250. The base frame includes a vertical frame 201 and a horizontal bar 202. The vertical frame 201 is arranged vertically, and the horizontal bar 202 is erected and fixed to the vertical frame 201 horizontally.

[0028] The data acquisition and control host 250 and the spectrometer 210 are fixed on the base frame, usually on the stand 201. The spectrometer 210 is connected to the data acquisition and control host 250. In addition, the spectrometer 210 is usually built in a box with temperature control function to ensure that the operating temperature of the spectrometer 210 is within a certain range.

[0029] The cosine corrector 240 is fixed to the crossbar 202 of the base frame with its light-receiving surface vertically upward. The output port of the optical fiber 220 is connected to the spectrometer 210, and the input port of the optical fiber 220 extends to the fixed position of the cosine corrector 240 and is assembled with the rotating mechanism 230. The acquisition control host 250 is also connected to and controls the rotating mechanism 230 to drive the optical fiber 220 to rotate.

[0030] In one embodiment, to protect the optical fiber 220, the base frame is constructed using a hollow tube, and the optical fiber 220 is internally routed within the base frame to extend to the cosine corrector 240, such as... Figure 4 As shown, the optical fiber 220 runs inside the hollow crossbar 202 and exits at the cosine corrector 240.

[0031] The cosine corrector 240 and the optical fiber 220 adopt a split structure, that is, the optical path connection port of the cosine corrector 240 and the optical inlet port of the optical fiber 220 are not directly fixed together, but the size of the optical path connection port of the cosine corrector 240 matches the size of the optical fiber 220, and the optical path connection port of the cosine corrector 240 is located on the rotation path of the optical inlet port of the optical fiber 220.

[0032] The rotating mechanism 230 can rotate the optical inlet of the optical fiber 220 between a first detection position and a second detection position. The first detection position is where the optical path connection port of the cosine corrector 240 is located, and the second detection position is the position facing the crop planting area 100. A schematic diagram of the optical inlet of the optical fiber 220 at the first detection position is shown below. Figure 4 As shown, a schematic diagram of the optical inlet of fiber optic 220 at the second detection position is as follows. Figure 5 As shown.

[0033] In one embodiment, to ensure the stability and reliability of the fiber rotation, please refer to the specific structure of the rotation mechanism 230. Figures 4-6 The rotating mechanism 230 includes a rotating motor 231, an optical fiber mounting base 232, and a rigid optical fiber sheath 233. The surface of the optical fiber mounting base 232 has a semi-circular structure and a predetermined thickness. The rotating motor 231 is fixed on the crossbar 202 and the motor shaft is along the horizontal direction. The motor shaft of the rotating motor 231 is connected to the center position of the optical fiber mounting base 232. In one embodiment, the motor shaft of the rotating motor 231 is connected to the center position of the optical fiber mounting base 232 through a coaxial rotating tool 234.

[0034] The outer periphery of the fiber optic mounting base 232 is provided with a fiber optic slot 232a that matches the fiber optic cable 220. A rigid fiber optic sleeve 233 is fixed to one end of the fiber optic mounting base 232 in the diameter direction, and the length extension direction of the rigid fiber optic sleeve 233 is perpendicular to the diameter direction of the fiber optic mounting base 232 on its surface. The inner diameter of the rigid fiber optic sleeve 233 matches the circumferential dimension of the fiber optic cable 220, and both ends of the rigid fiber optic sleeve 233 are open. The fiber optic mounting base 232 and the rigid fiber optic sleeve 233 can be a separate structure or an integrated structure.

[0035] The optical fiber 220's inlet begins at the other end of the optical fiber mounting base 232 along its diameter, wraps around the optical fiber slot 232a fixed to the outer periphery of the optical fiber mounting base 232, and passes through the opening at one end of the rigid optical fiber sleeve 233 when it reaches that end. It then protrudes from the other end of the rigid optical fiber sleeve 233 and is fixed thereto. When the rotary motor 231 operates, the optical fiber mounting base 232, driven by the motor shaft, rotates the rigid optical fiber sleeve 233, thereby rotating the inlet of the optical fiber 220.

[0036] When the optical inlet of fiber optic cable 220 is rotated to the first detection position, the optical inlet of fiber optic cable 220 aligns with the optical path connection port of cosine corrector 240. At this time, fiber optic cable 220 and cosine corrector 240 cooperate in measurement, providing a large field of view. To prevent water accumulation after rain and dust on the surface of the cosine corrector from affecting the measurement of solar incident radiation, the light-receiving surface of cosine corrector 240 adopts a glass hemispherical structure. Cosine corrector 240 provides an external optical path connection port. The internal optical path structure design of cosine corrector 240 can refer to existing cosine correctors and will not be elaborated here.

[0037] In traditional methods, the optical path connector of the cosine corrector 240 is directly fixed to the optical input port of the optical fiber 220. However, since this application adopts a split structure, to ensure the accurate connection between the optical input port of the optical fiber 220 and the optical path connector of the cosine corrector 240, please refer to... Figure 7 The schematic diagram of the cosine corrector 240 shown illustrates that the cosine corrector 240 also includes a light-shielding structure at the optical path connection port 241. The light-shielding structure includes a protrusion 242 and a base plate 243. The protrusion 242 is continuously arranged around the circumferential edge of the optical path connection port 241. One end face of the protrusion 242 is fixed to the bottom surface of the cosine corrector 240, and the other end face is connected to the base plate 243. This light-shielding structure covers the outside of the optical path connection port 241. A guide groove 243a is formed on the base plate 243, extending from the fiber optic port to the optical path connection port 241. The opening size of the guide groove 243a decreases sequentially from the fiber optic port to the optical path connection port 241. The guide groove 243a is located on the rotation path of the optical fiber 220's inlet. In this way, when the light inlet of the optical fiber 220 rotates from the second detection position to the first detection position, it is guided to the position of the optical path connection port 241 via the guide groove 243a, ensuring the alignment accuracy. Moreover, the docking position of the optical path connection port 241 and the light inlet of the optical fiber 220 is inside the light-shielding structure, reducing light leakage interference.

[0038] When the light inlet of the fiber optic cable 220 is rotated to the second detection position, the light inlet of the fiber optic cable 220 is directly facing the crop planting area 100. The field of view of the fiber optic cable 220 itself is relatively small, about 25°, which can ensure that the field of view of the fiber optic cable 220 is focused on the canopy area of ​​the target crop, avoiding the influence of non-target crops on the measurement. Common non-target crops include field ridges, weeds and base frames. This can better adapt to the situation of low or relatively uniform canopy. In practical applications, multiple synergistic sunlight-induced chlorophyll fluorescence measurement systems may be set up, which can also avoid mutual interference between different synergistic sunlight-induced chlorophyll fluorescence measurement systems.

[0039] When the optical fiber 220's inlet is rotated to the second detection position, its optical axis is vertically downward, focusing on the canopy area of ​​the target crop. This method is suitable for situations where the target crop's canopy height is low, as the canopy is lower than the inlet of the optical fiber 220. Alternatively, when the optical fiber 220's inlet is rotated to the second detection position, its optical axis forms a predetermined angle with the vertical direction, tilting downward to focus on the target crop's canopy area. This method is suitable for situations where the target crop's canopy height is high. When the target crop's canopy is high within the crop planting area 100 (e.g., in a forest), vertical downward detection requires the horizontal bar 202 to be higher than the target crop's canopy height. This results in a higher base frame, increasing construction difficulty. Furthermore, when the optical fiber installation height exceeds 10 meters, the fluorescence inversion results are subject to strong atmospheric interference. This method of focusing on the target crop's canopy area at an tilted angle reduces the height requirement for the base frame. The orientation of the optical axis of the optical fiber 220 when the optical inlet is rotated to the second detection position can be conveniently and quickly controlled by the rotation mechanism 230.

[0040] In another embodiment, to better ensure that the optical fiber 220 is focused on the target crop, the crossbar 202 is detachably assembled with the support frame 201. The crossbar 202 adopts a telescopic adjustment structure. After the collaborative sunlight-induced chlorophyll fluorescence measurement system is set up in the crop planting area, the height of the crossbar 202 above the ground and the distance of the end of the crossbar 202 extending into the crop planting area 100 can be adjusted to adjust the height of the optical fiber's inlet above the ground and the lateral extension distance. The orientation of the optical fiber's inlet when rotated to the second detection position can also be calibrated, thereby ensuring that the field of view is covered by the crop. This ensures that the coverage rate of the target crop within the field of view reaches the coverage threshold when the optical fiber 220 is rotated to the second detection position, thus guaranteeing the proportion of the target crop within the field of view.

[0041] In step 120, during the daytime, the data acquisition control host controls the rotating mechanism 230 to rotate the light inlet of the optical fiber 220 to the first detection position, so that the light inlet of the optical fiber 220 is connected to the optical path connection port of the cosine corrector 240, and the solar incident irradiance (irrad) is measured. Then, the rotating mechanism 230 is controlled to rotate the light inlet of the optical fiber 220 to the second detection position, so that the light inlet of the optical fiber 220 faces the crop canopy below the crossbar 202, and the canopy reflected irradiance (rad) is measured.

[0042] In one embodiment, the spectrometer 210 has a built-in shutter, and the measurements of solar incident irradiance (irrad) and canopy reflected irradiance (rad) specifically include: The acquisition control host 250 controls the rotating mechanism 230 to rotate the optical fiber 220's inlet to the first detection position, and controls the spectrometer to adaptively adjust the integration time T_int1. Solar incident radiation DN_s is acquired, and while keeping the integration time T_int1 constant, the spectrometer's internal shutter is closed, and the dark noise DC_s is measured. Thus, the solar incident irrad = cof1 * (DN_s - DC_s) / T_int1 is calculated. Here, cof1 is a pre-determined first calibration coefficient.

[0043] The acquisition control host 250 controls the rotating mechanism 230 to rotate the optical fiber 220's inlet to the second detection position, and controls the spectrometer to adaptively adjust the integration time T_int2. Canopy reflected radiation DN_r is acquired, and while keeping the integration time T_int2 constant, the spectrometer's internal shutter is closed, and the dark noise DC_r is measured. Thus, the canopy reflected radiation radiance rad = cof2 * (DN_r - DC_r) / T_int2 is calculated. Here, cof2 is a pre-determined second calibration coefficient.

[0044] The daytime period can be customized. For example, in one instance, 10:00-16:00 can be defined as the daytime period. In practical applications, measurements are taken periodically and continuously during the daytime period.

[0045] Step 130: The solar-induced chlorophyll fluorescence value (SIF) is obtained by inverting the solar incident irrad and canopy reflected irrad. The specific inversion method can refer to existing methods and will not be elaborated here.

[0046] Because this collaborative solar-induced chlorophyll fluorescence measurement system is set up for field measurements, the surface of the glass hemispherical dome of the cosine corrector is prone to erosion or scratches, affecting the transmittance of the glass dome. Additionally, the rotating mechanism may not rotate completely. These problems can lead to decreased measurement accuracy. Therefore, to ensure continuous and effective measurements over a long period, this collaborative solar-induced chlorophyll fluorescence measurement system also includes a calibration detection light source 260. This calibration detection light source 260 is fixed on the base frame and located above the crossbar 202. The acquisition and control host 250 is connected to and controls the calibration detection light source 260. In one example, the calibration detection light source 260 uses a halogen tungsten lamp, which has a high similarity to the solar spectrum and a wide spectral range of 300nm-1200nm. Halogen tungsten lamps are thermal radiation light sources, and their spectral energy distribution is similar to sunlight, exhibiting a continuous and smooth transition characteristic. In practical applications, after adjusting the height of the crossbar 202 relative to the ground, the calibration detection light source 260 can be fixed at a predetermined position on the stand 201 according to the position of the cosine corrector, so that the calibration detection light source 260 and the stand 201 have the required relative position. For better lighting effects, please refer to... Figure 8The filament axis of the calibration detection light source 260 is oriented toward the light-receiving surface of the cosine corrector 240, and the angle θ1 between the filament axis of the calibration detection light source 260 and the optical axis of the cosine corrector is equal to the angle θ2 between the filament axis of the calibration detection light source 260 and the support frame 201. Figure 8 Take the case where the optical axis of the optical fiber 220 is vertically downward when the optical inlet is rotated to the second detection position.

[0047] During the operation of this collaborative daylight-induced chlorophyll fluorescence measurement system, when the acquisition and control host detects an abnormal measurement result, it stops the measurement and waits until the nighttime period. Then, it turns on the calibration detection light source 260 to perform a calibration operation to update the first calibration coefficient cof1 and the second calibration coefficient cof2. After the calibration operation is completed, the calibration detection light source 260 is turned off. Similarly, the nighttime period can be customized. When the acquisition and control host detects a normal measurement result, it executes step 130 to perform inversion and conduct the next measurement.

[0048] The data acquisition and control host can determine whether the measurement result is abnormal by comparing the calculated solar incident irradiance irrad with the reference incident irradiance irrad_ref. Specifically, after measuring the solar incident irradiance irrad, the correlation coefficient between the solar incident irradiance irrad and the reference incident irradiance irrad_ref is calculated. When the correlation coefficient is less than the coefficient threshold, the measurement result is determined to be abnormal; otherwise, the measurement result is determined to be normal.

[0049] The reference incident irrad_ref is determined after the initial setup of the collaborative solar-induced chlorophyll fluorescence measurement system. After the initial setup and debugging of the collaborative solar-induced chlorophyll fluorescence measurement system, the acquisition control host turns on the calibration detection light source during the nighttime period and controls the rotating mechanism to rotate the light inlet of fiber optic 220 to the first detection position, so that the light inlet of fiber optic 220 is connected to the optical path connection port of the cosine corrector, and the solar incident irrad_ref is measured at this time.

[0050] During calibration, after the acquisition control host 250 turns on the calibration detection light source 260, it controls the rotating mechanism to rotate the optical fiber 220's inlet to the first detection position, so that the optical fiber 220's inlet is connected to the optical path connection port of the cosine corrector. The spectrometer adaptively adjusts the integration time T_int1, acquires the incident radiation DN_1, and keeps the integration time T_int1 constant. The spectrometer's internal shutter is closed, and the dark noise DC_1 is measured. The first calibration coefficient cof1 is updated according to cof1 = Irrad / ((DN_l-DC_l) / T_intl, where Irrad is the reference incident irradiance. Then, based on the two calibration parameters... The relationship between the calibration coefficients is updated by updating the second calibration coefficient cof2 using the updated first calibration coefficient cof1. Specifically, there is a defined proportional relationship between the first calibration coefficient cof1 and the second calibration coefficient cof2. This proportional relationship is determined during factory calibration. The specific method is as follows: the cosine corrector is placed at a certain distance, and the cosine corrector is irradiated with a light source that has been verified by the metrology institute. A photometer is used to measure the irradiance and radiance at the front and rear ends of the cosine corrector, respectively. The ratio of the irradiance to the radiance is used as the fixed proportional relationship between the first calibration coefficient cof1 and the second calibration coefficient cof2 when updating the coefficients thereafter.

[0051] The above are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.

Claims

1. A synergistic method of measuring chlorophyll fluorescence induced by sunlight, characterized by, The method comprises the following steps: A cooperative sunlight-induced chlorophyll fluorescence measurement system is built in a crop planting area, which comprises a base frame, a spectrometer, an optical fiber, a rotating mechanism, a cosine corrector, and a collection control host. The base frame comprises a stand and a crossbar. The light outlet of the optical fiber is connected to the spectrometer, and the spectrometer is connected to the collection control host. The collection control host is also connected to and controls the rotating mechanism to drive the light inlet of the optical fiber to rotate. The cosine corrector is fixed on the crossbar of the base frame with the light receiving surface vertically upward. The size of the light path connection port of the cosine corrector matches the size of the optical fiber, and the light path connection port of the cosine corrector is located on the rotation path of the light inlet of the optical fiber. The collection control host controls the rotating mechanism to drive the light inlet of the optical fiber to rotate to a first detection position during the daytime, so that the light inlet of the optical fiber is connected to the light path connection port of the cosine corrector, and the solar incident radiation irradiance irrad is measured. The rotating mechanism is controlled to drive the light inlet of the optical fiber to rotate to a second detection position, so that the light inlet of the optical fiber is directed towards the crop canopy below the crossbar, and the canopy reflected radiation brightness rad is measured. The sunlight-induced chlorophyll fluorescence value is obtained by inversion according to the solar incident radiation irradiance irrad and the canopy reflected radiation brightness rad.

2. The method of synergistic, diurnal, chlorophyll fluorescence measurements according to claim 1, characterized in that, The light receiving surface of the cosine corrector adopts a glass hemisphere cover structure. The light path connection port of the cosine corrector further comprises a light shielding structure, which comprises a protruding part and a bottom plate. The protruding part is continuously arranged around the circumferential edge of the light path connection port, and the bottom plate is fixed on the end face of the protruding part. A guide groove is formed in the bottom plate from the optical fiber passing port to the light path connection port. The opening size of the guide groove decreases from the optical fiber passing port to the light path connection port. The guide groove is located on the rotation path of the light inlet of the optical fiber.

3. The method of synergistic, diurnal, chlorophyll fluorescence measurements according to claim 1, characterized in that, The rotating mechanism comprises a rotating motor, an optical fiber fixed mounting seat, and a hard optical fiber sleeve. The surface of the optical fiber fixed mounting seat is in a semicircular disc structure and has a predetermined thickness. The rotating motor is fixed on the crossbar with the motor shaft in the horizontal direction. The motor shaft of the rotating motor is connected to the center of the optical fiber fixed mounting seat. The outer periphery of the optical fiber fixed mounting seat is provided with an optical fiber clamping groove matched with the optical fiber. The hard optical fiber sleeve is fixed at one end of the diameter direction of the optical fiber fixed mounting seat. The length extension direction of the hard optical fiber sleeve is perpendicular to the diameter direction of the optical fiber fixed mounting seat on the surface of the optical fiber fixed mounting seat. The inner diameter of the hard optical fiber sleeve matches the circumferential size of the optical fiber and the two ends are open. The light inlet of the optical fiber is arranged in the optical fiber clamping groove fixed on the outer periphery of the optical fiber fixed mounting seat from the other end of the hard optical fiber sleeve in the diameter direction. When reaching the end where the hard optical fiber sleeve is located, the light inlet penetrates into the one end opening of the hard optical fiber sleeve, and the other end opening of the hard optical fiber sleeve is exposed and fixed with the hard optical fiber sleeve. When the rotating motor operates, the optical fiber fixed mounting seat drives the hard optical fiber sleeve to rotate under the drive of the motor shaft, thereby driving the light inlet of the optical fiber to rotate.

4. The method of synergistic diurnal chlorophyll fluorescence measurements according to claim 1, characterized in that, The spectrometer is provided with a built-in shutter. The measurement of the solar incident radiation irradiance irrad and the canopy reflected radiation brightness rad comprises the following steps: The acquisition control host controls the rotating mechanism to rotate the light inlet of the optical fiber to a first detection position, and controls the spectrometer to adaptively adjust the integration time T_int1; the solar incident radiation DN_s is collected, and the integration time T_int1 is kept unchanged, the internal shutter of the spectrometer is closed and the dark noise DC_s is measured; the solar incident radiation irradiance irrad=cof1*(DN_s-DC_s) / T_int1 is calculated, wherein cof1 is the first calibration coefficient; The acquisition control host controls the rotating mechanism to rotate the light inlet of the optical fiber to a second detection position, and controls the spectrometer to adaptively adjust the integration time T_int2; the canopy reflected radiation DN_r is collected, and the integration time T_int2 is kept unchanged, the internal shutter of the spectrometer is closed and the dark noise DC_r is measured; the canopy reflected radiation brightness rad=cof2*(DN_r-DC_r) / T_int2 is calculated, wherein cof2 is the second calibration coefficient.

5. The method of synergistic solar-induced chlorophyll fluorescence measurement according to claim 4, characterized in that, The cooperative sunlight-induced chlorophyll fluorescence measurement system also includes a calibration detection light source fixed on the base frame and located above the crossbar, and the acquisition control host is connected to and controls the calibration detection light source; the cooperative sunlight-induced chlorophyll fluorescence measurement method also includes: When the acquisition control host detects that the measurement result is abnormal, it stops measuring and waits until the night period to turn on the calibration detection light source to perform calibration operation, so as to update the first calibration coefficient cof1 and the second calibration coefficient cof2, and turn off the calibration detection light source after completing the calibration operation.

6. The method of synergistic solar-induced chlorophyll fluorescence measurement according to claim 5, characterized in that, The acquisition control host detects whether the measurement result is abnormal, including: When it is detected that the correlation coefficient of the calculated solar incident radiation irradiance and the reference incident radiation irradiance is less than the coefficient threshold, it is determined that the measurement result is abnormal.

7. The method of synergistic diurnal chlorophyll fluorescence measurements according to claim 6, characterized in that, The cooperative sunlight-induced chlorophyll fluorescence measurement method also includes: After the cooperative sunlight-induced chlorophyll fluorescence measurement system is initially built, the acquisition control host turns on the calibration detection light source in the night period, controls the rotating mechanism to rotate the light inlet of the optical fiber to the first detection position, so that the light inlet of the optical fiber is connected to the light path connection port of the cosine corrector, and measures the incident radiation irradiance of the calibration detection light source as the reference incident radiation irradiance.

8. The method of synergistic solar-induced chlorophyll fluorescence measurement according to claim 5, characterized in that, Performing calibration operation to update the first calibration coefficient cof1 and the second calibration coefficient cof2 includes: The acquisition control host controls the rotating mechanism to rotate the light inlet of the optical fiber to the first detection position, so that the light inlet of the optical fiber is connected to the light path connection port of the cosine corrector, controls the spectrometer to adaptively adjust the integration time T_int1, collects the incident radiation DN_1, keeps the integration time T_int1 unchanged, closes the internal shutter of the spectrometer and measures the dark noise DC_1, updates the first calibration coefficient cof1 according to cof1=Irrad / ((DN_l-DC_l) / T_intl, and updates the second calibration coefficient cof2 using the updated first calibration coefficient cof1; wherein Irrad is the reference incident radiation irradiance.

9. The method of synergistic solar-induced chlorophyll fluorescence measurement according to claim 5, characterized in that, The filament axial direction of the calibration detection light source is directed towards the light receiving surface of the cosine corrector, and the included angle θ1 between the filament axial direction of the calibration detection light source and the optical axis of the cosine corrector is equal to the included angle θ2 between the filament axial direction of the calibration detection light source and the stand.

10. The method of synergistic solar-induced chlorophyll fluorescence measurement according to claim 5, characterized in that, The cooperative sunlight-induced chlorophyll fluorescence measurement method further comprises: After the cooperative sunlight-induced chlorophyll fluorescence measurement system is built in the crop planting area, the height of the horizontal rod in the base stand relative to the ground is adjusted, and the orientation of the light inlet of the calibration optical fiber when rotating to the second detection position is adjusted, so that the target crop coverage in the field of view range of the optical fiber when rotating to the second detection position reaches the coverage threshold.

Images