Chlorophyll fluorescence continuous monitoring system and method based on miniature laser radar

Abstract

The invention discloses a chlorophyll fluorescence continuous monitoring system and method based on a miniature laser radar. According to the method, non-invasive detection and analysis are carried out on plants by utilizing a sensing technology, a spectrum technology and an imaging technology through a non-destructive detection technology under the condition that the tissue structure and chemical components of the plants are not damaged. The system comprises a transmitting circuit, a detection circuit, a double-layer optical filter and a core processor. According to the method, photosynthetically active radiation can be calculated by acquiring leaf fluorescence constant signals, ambient light information and ambient temperature information; and the chlorophyll fluorescence quantum productivity is calculated by combining a chlorophyll fluorescence measurement method, so that the detection method for quantifying chlorophyll fluorescence on the leaf canopy level is realized. The modulated fluorescence technology disclosed by the invention has the characteristics of rapid, simple, sensitive and reliable measurement, no interference on a sample, capability of measuring under the condition of ambient light and the like, and plays an effective role in promoting solving of a plurality of ecological key problems.

Description

Technical Field

[0001] The present invention relates to the field of laser radar detection, and in particular to a chlorophyll fluorescence continuous monitoring system and method based on a micro laser radar. Background Art

[0002] Photosynthesis is the only way for green plants to obtain energy and is also the basis for all life activities of green plants. The distribution pathways of light irradiated on the leaves are divided into reflection, transmission and absorption. After chlorophyll in the leaves of plants absorbs light energy, it first converts it into electrical energy and then into chemical energy. The non-destructive detection technology of plant photosynthetic information refers to the non-invasive detection and analysis of plants by means of spectroscopy, imaging sensing, etc. without destroying the tissue structure and chemical composition of the plants.

[0003] Existing chlorophyll content analysis technologies include electrical signal analysis technology, image analysis technology, and thermal detection technology. However, compared with other non-destructive technologies, chlorophyll fluorescence detection technology can fully and dynamically reflect the photosynthetic state of plants, and has the characteristics of high sensitivity and high time resolution, so it has a higher performance in measurement accuracy, and can monitor and analyze plants in real time. It has a very broad application prospect in fields such as plant ecology. It can not only monitor plants non-invasively, but also provide more accurate and detailed photosynthetic information data, so as to comprehensively evaluate the growth, development and disease status of plants.

[0004] Micro-LiDAR is an active remote sensing technology that uses laser diodes to obtain measurement data, making it a promising candidate for portable measurement and handheld instruments. Chlorophyll fluorescence is stimulated by emitting light that meets the absorption peak of leaf photosynthetic pigments, ensuring that the energy of the excitation light interacts with chlorophyll molecules to the maximum extent, thereby generating a fluorescence signal. This solution has a fast response and low cost, and is also capable of measuring chlorophyll fluorescence at the canopy level of vegetation for a long time under full illumination conditions.

[0005] It is of great practical value to study a low-cost, fast, real-time, and environmentally resistant micro-lidar chlorophyll fluorescence continuous monitoring system. This will help achieve precise irrigation and fertilization in the agricultural field, because by monitoring the photosynthesis capacity of plants, the water and nutrient content in the soil can be adjusted in time to improve the yield and quality of crops. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a chlorophyll fluorescence continuous monitoring system and method based on a micro-lidar, which can reduce the system cost and facilitate miniaturization integration, thereby realizing long-term measurement of chlorophyll fluorescence at the vegetation canopy level under full illumination conditions.

[0007] Technical solution:

[0008] A chlorophyll fluorescence continuous monitoring system based on a micro laser radar includes a transmitting circuit, a detecting circuit, a double-layer optical filter, a core processor, data acquisition and data processing. The transmitting circuit mainly uses pulse modulation technology to achieve effective excitation of chlorophyll fluorescence signals. The chlorophyll fluorescence signal is reflected by the leaves and collected by the detecting circuit. The fluorescence signal is focused on the photosensitive surface of the PIN photodiode through the double-layer optical filter and converted into an electrical signal, which is then collected by a high-speed analog-to-digital converter (ADC) controlled by the core processor for subsequent chlorophyll fluorescence quantum yield analysis.

[0009] Furthermore, the transmitting circuit adopts a laser diode with a wavelength of 450nm, and the emission wavelength and frequency are precisely controlled by pulse modulation technology.

[0010] Furthermore, the detection circuit is a dual quadratic active RC filter circuit based on a feedback structure combined with a photodiode design, which is used to convert the weak current signal generated by the photodiode into a stable voltage signal and provide filtering and amplification functions; it is composed of an operational amplifier U1, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, a resistor R3 and a photodiode VD, the cathode of the photodiode VD is connected to the resistor R1 and the capacitor C1, and the anode is connected to the dual quadratic active RC filter circuit composed of the operational amplifier U1.

[0011] Furthermore, the detection circuit can output an ambient light signal, and is composed of a subtraction circuit composed of an operational amplifier, which includes an operational amplifier U2 and resistors R4 and R5; the input end 1 of the operational amplifier U2 is a weak current signal generated by a photodiode converted into a stable voltage signal, the input end 2 is a fluorescence output signal output by the detection circuit, and the output end is the difference between the two signals, namely the ambient light signal Rc, where R4=R5, and the value is between 10K-100KΩ.

[0012] Furthermore, the detection circuit can output a fluorescence output signal, and is composed of a feedback network consisting of a fluorescence amplification circuit and an integration circuit formed by a T-type feedback network, including an operational amplifier U3, an operational amplifier U4, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a resistor R10 and a capacitor C3; the non-inverting input terminal of the T-type feedback network is connected to the positive electrode of the photodiode VD, wherein the output of the operational amplifier U3 is connected to the inverting input terminal of the operational amplifier U4, and the output of the operational amplifier U4 is connected to the non-inverting input terminal of the operational amplifier U3.

[0013] Furthermore, the double-layer optical filter is used to extract the fluorescence signal and filter out the interference light in the optical path system.

[0014] Furthermore, the core processor adopts an STM32 single-chip microcomputer or FPGA to realize the control of the wavelength and frequency of the transmitting circuit and the control of the synchronous detection timing of the detection circuit.

[0015] A method for continuous monitoring of chlorophyll fluorescence based on a micro laser radar comprises the following steps:

[0016] Data collection phase:

[0017] (1) By setting a specific transmission frequency, the timing of laser emission and reception is synchronized with the clock signal of the acquisition system; the 200kHz signal emitted by the transmitting circuit is used as a reference signal based on the principle of synchronous detection to ensure the accuracy and reliability of data acquisition.

[0018] (2) The weak current signal generated by the photodiode is converted into a stable voltage signal through the detection circuit; the current generated by the photodiode is usually very weak (microampere level), and the improved biquadratic active RC filter circuit based on the feedback structure can not only convert the photocurrent into a voltage signal, but also provide filtering and amplification functions, thereby greatly improving the sensitivity;

[0019] (3) In order to separate the fluorescence yield signal from the ambient light signal, the signal of the photoelectric amplifier circuit and the fluorescence yield signal are respectively sent to the two input ends of the subtraction circuit by setting an appropriate subtraction circuit ratio, thereby outputting the ambient light signal; to achieve accurate measurement of the fluorescence yield, the T-type feedback network (U3) and the integration circuit (U4) need to be reasonably adjusted to ensure the accuracy and stability of signal processing;

[0020] (4) Since the ADC has a limited voltage range, first obtain the actual measurement value, and then compare the collected voltage value with the preset voltage value through the comparison module to obtain the comparison result. If the comparison result exceeds the ADC measurement range, it needs to be reduced in voltage before being sent to the ADC for collection; if the comparison result is within the ADC range, it can be directly analyzed.

[0021] (5) The information after data collection is encoded by the core processor and transmitted to the PC or host computer using the USB2.0 communication protocol for real-time processing;

[0022] Data processing stage:

[0023] (6) Data storage and transmission: To ensure the reliability and integrity of the data transmission process, a data frame structure including data header, data length, data content and checksum is designed. After the data receiving end performs preliminary verification, the data that meets the requirements will be stored in the database for subsequent analysis and processing.

[0024] (7) Preprocessing: The main task is to filter out irrelevant noise and interference signals and retain useful fluorescence signals. A second-order bandpass filter is designed, and its center frequency is set in the main frequency band of chlorophyll fluorescence signal 650-800nm. After filtering, the signal enters the next step of feature extraction process.

[0025] (8) Feature extraction: The fast Fourier transform (FFT) algorithm is mainly used to perform spectrum analysis on the filtered fluorescence signal to extract the characteristic frequency and amplitude of the signal. The FFT algorithm can convert the time domain signal into a frequency domain signal and reveal the spectral characteristics of the signal. By analyzing the spectrum graph, the characteristic frequency of chlorophyll fluorescence can be determined and its amplitude can be calculated, thereby evaluating the photosynthesis capacity of the plant.

[0026] Furthermore, in the step (1), the LED emission frequency is not less than 200kHz, and the emission wavelength corresponds to the specific absorption peak of the photosynthetic pigment of the plant to be tested. Since the light emitting area of ​​a single LED light source is relatively small, it is regarded as a point light source. Since the light field of the point light source will gradually decay with distance, a uniformly arranged LED array is used to ensure that the light field irradiated on the vegetation is uniform. In the step (2), by improving the position of the input signal of the biquadratic active RC filter circuit based on the feedback structure, it is ensured that the amplification factor of the operational amplifier is not less than 50 and the frequency response is not less than 1.6kHz, thereby ensuring that the circuit can filter, smooth, amplify and isolate the collected weak signal, and ensure that the signal can be better collected and restored by the ADC. In the step (3), the T-type feedback network (U3) and the integration circuit (U4), the gain of the T-type feedback network and the gain of the integration circuit, the device response speed and the frequency response need to be matched to avoid the operational amplifier from generating self-oscillation at high frequency.

[0027] Chlorophyll fluorescence measurement requires a special fluorescence excitation light source to excite chlorophyll fluorescence. In theory, chlorophyll fluorescence can be excited by light from ultraviolet light to red light, but photosynthetic pigments have specific absorption peaks, so chlorophyll fluorescence instruments usually use red light and blue light for excitation. In terms of the transmitting circuit, the present invention selects a blue light LED with a wavelength of about 450nm as the excitation light source. At the same time, the luminous area of ​​a single LED light source is relatively small and can be approximately regarded as a point light source. Since the light field of a point light source will gradually attenuate with distance, when designing the PCB of the transmitting circuit, an evenly arranged LED array is used to superimpose the light field of the point light source array to ensure that the light field irradiated on the vegetation is uniform.

[0028] Since the chlorophyll fluorescence signal is very weak (no more than 1% of the absorbed radiation), in order to meet the requirements of performance indicators, the system of the present application adopts a dual quadratic active RC filter receiving and transmitting circuit based on a feedback structure. This circuit can filter, smooth, amplify and isolate the collected weak signal to ensure that the signal can be better collected and restored by the ADC.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0030] 1. The system of the present invention only uses a double-layer optical filter and a dual-quadratic active RC filter circuit with a feedback structure, which can effectively separate the fluorescence output signal from the ambient light signal.

[0031] 2. The system of the present invention has a compact structure and high stability. The present invention can be fixed on a tripod to better adapt to the fluorescence signal measurement of leaf canopies in different regions, and has great value for promotion and application;

[0032] 3. The method of the present invention combines the matched filter algorithm, directly detects the fluorescence signal of chlorophyll in the plant canopy, and realizes the detection method of quantitative chlorophyll fluorescence at the leaf canopy level; constructs a non-destructive detection system with fast response speed, high sensitivity and convenient carrying. In addition, the proposed principle of synchronous detection of receiving and transmitting signals has simple control logic and is easy to implement through a single-chip microcomputer or FPGA, which is conducive to the development of low-cost and miniaturized systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the packaging structure of the system of the present invention.

[0034] Figure 2 It is the overall framework diagram of the system of the present invention.

[0035] Figure 3 The figure is a flow chart of detection and transmission in the system of the present invention.

[0036] Figure 4 The figure is a flow chart of data collection and processing in the system of the present invention.

[0037] Figure 5 The schematic diagram of the photoelectric amplification circuit of the detection circuit in the system of the present invention.

[0038] Figure 6 It is a circuit for separating and subtracting ambient light signals and fluorescence yield information in the system of the present invention.

[0039] Figure 7 The schematic diagram is a T-type feedback network (U3) and an integration circuit (U4) of the detection circuit in the system of the present invention.

[0040] List of reference numerals:

[0041] 1-PCB fixing hole, 2-data transmission interface, 3-fixing hole, 4-switch reserved hole, 5-detection circuit, 6-transmitting circuit, 7-ball head. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0043] like Figure 1 As shown, the appearance package of the present invention adopts 3D printing technology that is easy to customize. The transmitting circuit 6 and the detection circuit 5 are placed in a circular barrel of a suitable size and fixed by screws. According to the layout design of the PCB, the present application also provides a data transmission interface 2 so that the collected data can be transmitted to the host computer in real time. The entire model is fixed on the tripod through the fixing hole 3 to ensure stability. In order to better adapt to the fluorescent signals of the leaf canopy in different regions, the present application is equipped with a spherical pan head 7 on the tripod, which can be adjusted at multiple angles to quickly change the detection range and angle to achieve all-round collection and detection. This can better adapt to the measurement needs of different crops.

[0044] like Figure 2 As shown, the transmitting circuit of the present invention includes a modulated high-frequency carrier, a power driving circuit and an LED light source for exciting chlorophyll fluorescence. In order to realize chlorophyll fluorescence measurement, a special fluorescence excitation light source is required. In the present invention, a blue light LED with a wavelength of about 450nm is selected as the excitation light source. The excitation process is as follows: First, the light source is controlled to enter a weak excitation state through the transmitting circuit to measure the initial fluorescence (F0) of the leaf. Then, the saturated pulse light is turned on to instantly close the PSII reaction center that is fully opened under dark adaptation conditions, thereby measuring the maximum fluorescence (F m ). Subsequently, the fluorescence intensity of the leaves tends to stabilize, and the measured value is (Fs). When the fluorescence intensity stabilizes, the PSII reaction center gradually closes. At this time, the light source is controlled to turn on the saturated pulse light again to measure the maximum fluorescence (Fm') under the pulse light.

[0045] Maximum variable fluorescence in the dark: F V =F m -F0

[0046] The maximum or potential quantum yield of PSII in fully dark-adapted leaves: F V / F m

[0047] Maximum variable fluorescence under light adaptation: F′ V =F′ m -F′0

[0048] Actual photochemical efficiency of PSII under light adaptation:

[0049] Linear electron transfer rate: ETR = Φ PSII ×PFD×α×β

[0050] Among them, PFD is light flux density, α represents the absorption rate of light by the blade, and the common value is around 0.85, and β represents the proportion of absorbed photons absorbed by PSII, which is usually set to 0.5 by default.

[0051] The detection circuit includes an optical system, a photodetector, and a receiving system. The core processor includes a circuit drive system, a data acquisition system, and a data transmission system. The data preprocessing stage covers data acquisition, denoising, and storage. On the visual interface, this application sets various filtering operations and data saving options.

[0052] like Figure 3 As shown, when the chlorophyll fluorescence signal reaches the photodiode, it needs to pass through an achromatic lens and a 650-800nm ​​bandpass filter. The function of the achromatic lens is to improve the detection efficiency of the fluorescence signal, while the bandpass filter is mainly used to eliminate useless spectral components in the received signal. After being processed by a double-layer optical filter, these fluorescence signals are focused on the photosensitive surface of the PIN photodiode. Among them, the low-pass filter (λ<800nm) is used to narrow the spectral range to the maximum absorption peak area of ​​chlorophyll fluorescence (650-800nm). Through the photoelectric effect of the PIN photodiode, the fluorescence signal is converted into an electrical signal. Since the chlorophyll fluorescence signal is very weak (no more than 1% of the absorbed radiation), in order to meet the requirements of performance indicators, the system of this application adopts a dual-quadratic active RC filter receiving and transmitting circuit based on a feedback structure. This circuit can filter, smooth, amplify and isolate the collected weak signals to ensure that the signal can be better collected and restored by the ADC. Chlorophyll fluorescence measurement requires a special fluorescence excitation light source to excite chlorophyll fluorescence. In terms of the emission circuit, the present invention selects a blue light LED with a wavelength of about 450nm as the excitation light source, which corresponds to the specific absorption peak of most leaf photosynthetic pigments.

[0053] like Figure 4As shown, in the process of data acquisition and transmission, the present invention ensures that the timing of laser emission and reception is synchronized with the clock signal of the acquisition system through the principle of synchronous detection of emission and reception. The present application uses the 200kHz signal emitted by the transmitting circuit as a reference signal to achieve precise synchronization. This synchronization performance can ensure the accurate acquisition of chlorophyll fluorescence signals, and synchronize them with other measurement parameters for analysis and processing, so as to obtain accurate and reliable measurement results. This method helps to eliminate timing deviations, ensure the accuracy and reliability of data acquisition, and provide a stable and accurate data basis for research. The main functions include real-time acquisition interface and data observation interface. Users can save the collected data in the form of files through this interface, which is convenient for further analysis of fluorescence signal data, query of historical data, and analysis and processing of data. Such a user interface design makes data acquisition and analysis more convenient and efficient, and provides users with a convenient operating experience.

[0054] like Figure 5 As shown, in the detection circuit photodiode data acquisition part of the present invention, by improving the dual quadratic active RC filter circuit based on the feedback structure, the photodiode generates a current proportional to the light intensity when it is illuminated. The output signal is processed by R1 and C1, and the capacitor C1 and the resistor R1 form an input filter to remove the noise signal or high-frequency component generated by the photodiode. The low-frequency signal will pass through, while the high-frequency signal is filtered out by C1. After filtering, it is input to the operational amplifier. Due to the virtual short-circuit effect of the operational amplifier, the positive input terminal is grounded, so the circuit works in the inverting mode, and the input signal is amplified and output inverted. R2, R3 and C2 form the feedback network of the operational amplifier. The gain and frequency response of the feedback network control circuit are specifically determined by the combination of R2, R3 and C2. The function of the operational amplifier is to convert the photocurrent signal into a voltage signal and amplify it. The input photocurrent is converted into a voltage signal by the resistor R1, then amplified by the operational amplifier, and finally output as an amplified voltage signal.

[0055] like Figure 6 As shown, the detection circuit of the present invention can output an ambient light signal, and is composed of a subtraction circuit composed of an operational amplifier, including an operational amplifier U2 and resistors R4 and R5; the input end 1 of the operational amplifier U2 is a weak current signal generated by a photodiode converted into a stable voltage signal, the input end 2 is a fluorescent output signal output by the detection circuit, and the output end is the difference between the two signals, namely the ambient light signal Rc, wherein R4=R5, and the value is between 10K-100KΩ.

[0056] like Figure 7As shown, in the ambient light signal and fluorescence yield information separation circuit of the present invention, the gain of the T-type feedback network (U3) is mainly determined by resistors R6, R7 and R8. The gain formula of the T-type network is: The signal input from the VD terminal first passes through R6, then enters the T-type feedback network, and finally outputs to V through the operational amplifier. O When the integration circuit (U4) is added as feedback, the output of the entire circuit is no longer just the amplification of the input signal, but the integration of the input signal over time. The integration circuit (U4) can accumulate low-frequency signals, thereby enhancing the amplification of low-frequency signals. Since the integration process will cause the gain of high-frequency signals to decrease, high-frequency signals will be suppressed. The formula derivation process is as follows:

[0057]

[0058]

[0059] From equations (1), (2) and (3), we can derive the relationship between input and output:

[0060]

[0061] Due to the introduction of the integration circuit, the feedback effect formed enables the output voltage of the operational amplifier to accumulate the changes of the input signal over time and adjust the overall output according to this change. At the same time, the integration circuit also acts as a filter to effectively filter out high-frequency noise in the input signal. In the interaction with the T-type network, the feedback circuit of the T-type network has an important influence on the gain characteristics of the operational amplifier. The size of the feedback determines the gain characteristics of the operational amplifier, which further affects the frequency response of the circuit.

Claims

1. A chlorophyll fluorescence continuous monitoring system based on micro laser radar, characterized in that: It includes an emission circuit, a detection circuit, a double-layer optical filter and a core processor; the emission circuit uses pulse modulation technology to achieve effective excitation of chlorophyll fluorescence signals, wherein the chlorophyll fluorescence signals are reflected by the leaves and collected by the detection circuit, and the fluorescence signals are focused onto the photosensitive surface of the PIN photodiode through the double-layer optical filter and converted into electrical signals, which are then collected by the high-speed analog-to-digital converter ADC controlled by the core processor for subsequent chlorophyll fluorescence quantum yield analysis.

2. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 1 is characterized in that: The transmitting circuit adopts a laser diode with a wavelength of 450nm, and accurately controls the emission wavelength and frequency through pulse modulation technology.

3. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 1 is characterized in that: The detection circuit is a dual quadratic active RC filter circuit based on a feedback structure combined with a photodiode design, which is used to convert the weak current signal generated by the photodiode into a stable voltage signal and provide filtering and amplification functions; it is composed of an operational amplifier U1, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, a resistor R3 and a photodiode VD, the cathode of the photodiode VD is connected to the resistor R1 and the capacitor C1, and the anode is connected to the dual quadratic active RC filter circuit composed of the operational amplifier U1.

4. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 1 is characterized in that: The detection circuit can output an ambient light signal and is composed of a subtraction circuit composed of an operational amplifier, including an operational amplifier U2 and resistors R4 and R5; the input end 1 of the operational amplifier U2 is a weak current signal generated by a photodiode converted into a stable voltage signal, the input end 2 is a fluorescent output signal output by the detection circuit, and the output end is the difference between the two signals, namely the ambient light signal Rc, where R4=R5, and the value is between 10K-100KΩ.

5. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 4 is characterized in that: The detection circuit can output a fluorescence output signal, and is composed of a fluorescence amplification circuit composed of a T-type feedback network and a feedback network composed of an integration circuit, including an operational amplifier U3, an operational amplifier U4, a resistor R6, a resistor R7, a resistor R8, a resistor R9, a resistor R10 and a capacitor C3; the non-inverting input terminal of the T-type feedback network is connected to the positive electrode of the photodiode VD, wherein the output of the operational amplifier U3 is connected to the inverting input terminal of the operational amplifier U4, and the output of the operational amplifier U4 is connected to the non-inverting input terminal of the operational amplifier U3.

6. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 1 is characterized in that: The double-layer optical filter is used to extract fluorescence signals and filter out interfering light in the optical path system.

7. The chlorophyll fluorescence continuous monitoring system based on micro laser radar according to claim 1 is characterized in that: The core processor adopts an STM32 single-chip microcomputer or FPGA, has data acquisition and data processing functions, and is used to realize the control of the wavelength and frequency of the transmitting circuit, and the control of the synchronous detection timing of the detection circuit.

8. A method for continuous monitoring of chlorophyll fluorescence based on micro laser radar, characterized in that: The system according to any one of claims 1 to 7 comprises the following steps: Data collection phase: (1) By setting a specific transmission frequency, the timing of laser emission and reception is synchronized with the clock signal of the acquisition system; the 200kHz signal emitted by the transmitting circuit is used as a reference signal based on the principle of synchronous detection to ensure the accuracy and reliability of data acquisition; (2) The weak current signal generated by the photodiode is converted into a stable voltage signal through the detection circuit; the current generated by the photodiode is usually very weak, and the improved biquadratic active RC filter circuit based on the feedback structure can not only convert the photocurrent into a voltage signal, but also provide filtering and amplification functions, thereby greatly improving the sensitivity; (3) In order to separate the fluorescence yield signal from the ambient light signal, the signal of the photoelectric amplifier circuit and the fluorescence yield signal are respectively sent to the two input ends of the subtraction circuit by setting an appropriate subtraction circuit ratio, thereby outputting the ambient light signal; to achieve accurate measurement of the fluorescence yield, the T-type feedback network and the integration circuit need to be reasonably adjusted to ensure the accuracy and stability of signal processing; (4) Since the ADC has a limited voltage collection range, the actual measurement value is first obtained, and the collected voltage value is compared with the preset voltage value through the comparison module to obtain a comparison result; if the comparison result exceeds the ADC measurement range, it needs to be reduced in voltage before being sent to the ADC for collection; if the comparison result is within the ADC range, it is directly analyzed; (5) The information after data collection is encoded by the core processor and transmitted to the PC or host computer using the USB2.0 communication protocol for real-time processing; Data processing stage: (6) Data storage and transmission: To ensure the reliability and integrity of the data transmission process, a data frame structure including a data header, data length, data content, and a checksum is designed; after a preliminary check is performed at the data receiving end, data that meets the requirements will be stored in the database for subsequent analysis and processing; (7) Preprocessing: The main task is to filter out irrelevant noise and interference signals and retain useful fluorescence signals. A second-order bandpass filter is designed, and its center frequency is set in the main frequency band of chlorophyll fluorescence signal 650-800nm. After filtering, the signal enters the next step of feature extraction process. (8) Feature extraction: The fast Fourier transform (FFT) algorithm is mainly used to perform spectrum analysis on the filtered fluorescence signal and extract the characteristic frequency and amplitude of the signal. The FFT algorithm can convert the time domain signal into a frequency domain signal and reveal the spectral characteristics of the signal. By analyzing the spectrum diagram, the characteristic frequency of chlorophyll fluorescence is determined and its amplitude is calculated, thereby evaluating the photosynthesis capacity of the plant.

9. The method for continuous monitoring of chlorophyll fluorescence based on micro laser radar according to claim 8, characterized in that: In the step (1), the LED emission frequency is not less than 200kHz, and the emission wavelength corresponds to the specific absorption peak of the photosynthetic pigment of the plant to be tested. Since the light emitting area of ​​a single LED light source is relatively small, it is regarded as a point light source. Since the light field of the point light source will gradually decay with distance, an evenly arranged LED array is used to ensure that the light field irradiated on the vegetation is uniform. In the step (2), by improving the position of the input signal of the biquadratic active RC filter circuit based on the feedback structure, the amplification factor of the operational amplifier is ensured to be not less than 50 and the frequency response is not less than 1.6kHz, thereby ensuring that the circuit can filter, smooth, amplify and isolate the collected weak signal, and ensure that the signal can be better collected and restored by the ADC. In the step (3), the T-type feedback network and the integration circuit, the gain of the T-type feedback network and the gain of the integration circuit, the device response speed and the frequency response need to be matched to avoid the operational amplifier from generating self-oscillation at high frequency.

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