Buoy-borne CO2 inversion method, system and equipment based on laser radar detection
By using multiple linear regression to calculate the CO2 absorption cross-section and dual-wavelength lidar system in DIAL technology, the problems of unstable monitoring results and serious specular reflection interference in DIAL technology are solved, real-time, accuracy and stability of CO2 concentration monitoring are achieved, and the system volume and weight are reduced.
Patent Information
- Application Number
- CN202510112068.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-24
- Publication Date
- 2025-05-13
AI Technical Summary
The existing DIAL technology has problems such as complex system, large size, heavy weight, high energy consumption and serious specular reflection interference in carbon dioxide monitoring, resulting in unstable or incorrect monitoring results.
Using a fast calculation of CO2 absorption cross-section method based on multivariate linear regression, two beams of laser pulses with stable frequency and similar wavelengths are alternately emitted by a dual-wavelength laser. Combined with a differential absorption lidar system, the atmospheric backscattered echo signal is analyzed, the CO2 gas concentration is inverted, and the specular reflected signal is actively shielded through the timing control scheme of an integrated acousto-optical modulator.
It improves the real-time, accuracy and stability of CO2 concentration monitoring, reduces the system size and weight, enhances the application capabilities in small or complex environments, and improves measurement accuracy and reliability by effectively shielding the mirror reflected signals.
Smart Images
Figure CN119986688A_ABST
Abstract
Description
Technical Field
[0001] The present application belongs to the field of laser radar detection technology, and specifically relates to a buoy-borne CO2 inversion method and system based on laser radar detection. Background Art
[0002] As one of the main greenhouse gases, carbon dioxide has attracted widespread attention. Changes in carbon dioxide concentration directly affect climate change, air quality, and the greenhouse effect. Since CO2 concentration is unevenly distributed and changes are complex, real-time and accurate monitoring of CO2 concentration profiles is of great significance for global climate monitoring, environmental protection, and policy making.
[0003] Although the existing DIAL technology has achieved certain success in carbon dioxide monitoring, there are still some limitations. For example, the traditional DIAL system design is relatively complex and contains multiple components (such as lasers, detectors, optical systems, data acquisition and processing units, etc.), which makes it large in size and difficult to flexibly deploy in small or complex environments. In addition, the weight and energy consumption of the system are also bottlenecks for its application. For example, in complex environmental conditions, especially in the presence of mirror reflections, the echo signal in the system is easily interfered by strong mirror reflections, which has a great impact on the performance of the detector. Existing technologies often lack effective means to actively shield these reflection signals, resulting in unstable or erroneous measurement results. Summary of the invention
[0004] Based on the above problems, this application adopts a method of rapidly calculating the CO2 absorption cross section based on multivariate linear regression to improve the CO2 inversion speed, ensure the accuracy of real-time monitoring, and improve the real-time, accuracy and stability of CO2 concentration monitoring. Its technical solution is: A method for inverting CO2 carried by a buoy based on laser radar detection comprises the following steps: S1. Two laser pulses with stable frequencies and similar wavelengths are emitted alternately by a dual-wavelength laser, so that the two laser pulses are transmitted along the same path in the atmosphere; one part is scattered by aerosols in the atmosphere, and the other part is absorbed by CO2 gas in the atmosphere; S2. The detection of aerosol scattering echoes can carry the absorption information of CO2 gas to laser pulse energy; S3. In the differential absorption lidar system, the wavelength of one of the laser beams is located near the absorption peak of the CO2 gas absorption spectrum, where the absorption cross section of the CO2 gas is larger, recorded as ; The wavelength of the other laser beam deviates from the absorption peak of CO2 gas and is located at the absorption valley of the CO2 gas absorption spectrum. The absorption cross section of CO2 gas is smaller here, which is recorded as According to the different absorption degree of CO2 gas to the two laser beams, the CO2 gas concentration can be inverted by analyzing the atmospheric backscattered echo signal.
[0005] Preferably, in step S3, the atmospheric echo signal detected by the atmospheric laser radar is expressed as: ; ; yes and The number of detected echo photons, is the receiving efficiency, is the atmospheric echo backscatter coefficient, is the speed of light, is the pulse width, is the receiving area of the receiving telescope, is the detection distance. The extinction coefficient of the laser in the round trip process in the atmosphere includes the scattering attenuation coefficient and the absorption attenuation coefficient. is the scattering attenuation coefficient, is the absorption cross section of CO2, is the extinction coefficient excluding CO2 absorption, is the molecular density of CO2.
[0006] Preferably, in step S3, because and Very close, can be considered and The atmospheric backscattering coefficient of the wavelength is the same, and the extinction coefficient is only related to CO2, that is: ; ; After the two equations are ratioed, logarithmic on both sides, and differentiated, the molecular density of CO2 can be expressed as: ; In the formula and are the starting and ending positions of the distance integration interval calculation, Due to the difference in absorption cross-section, a wavelength with a large difference in absorption cross-section is selected to invert the CO2 concentration.
[0007] Preferably, based on the HITRAN database, the carbon dioxide absorption cross sections under different wavelengths, temperatures and pressures are obtained by molecular simulation, and a model is constructed using a multivariate linear fitting method to achieve rapid calculation of the carbon dioxide absorption cross section from real-time temperature and pressure.
[0008] Preferably, a multivariate regression model between the absorption cross section and wavelength, temperature, and pressure is established, and the specific steps are as follows: Step 1: Data collection and preprocessing: The carbon dioxide absorption cross-section data under different wavelengths λ, temperatures T, and pressures P were collected from the HITRAN simulation system; the data set contained absorption cross-section values under multiple wavelengths, temperatures, and pressures. After data cleaning and normalization, a multi-dimensional feature data matrix was formed; Step 2: According to the relationship between the absorption cross section and wavelength, temperature, and air pressure, a high-order multivariate linear regression model is used for fitting. The constructed regression model is expressed as: ; Among them, σ(λ, T, P) is the absorption cross section of carbon dioxide, λ, T, P are wavelength, temperature and air pressure respectively, β0, β1, β2, β3, β4, β5, β6, β7 are regression coefficients, indicating the degree of influence of each factor on the absorption cross section; Step 3: Use the least square method to optimize the regression coefficients; The objective function is set as: ; in, is the actual value of the i-th sample; is the model prediction value, that is: ; m is the total number of samples; Step 4: Solve the regression coefficient: By simplifying the calculation in matrix form, the solution formula for the regression coefficient β is: ; Where: X is the input feature matrix, each row contains the eigenvalues (λ, T, P) of the sample and its interaction terms; is the column vector of absorption cross section values; β is the regression coefficient vector to be determined.
[0009] A buoy-borne CO2 inversion device based on laser radar detection comprises a box, an integrated box, a dual-wavelength laser and a transceiver telescope group; the integrated box is provided with an acousto-optic regulator, a collection card and a single-photon detector, a flange is connected to the end of the box, the filter and the transceiver telescope are located in the box, the transceiver telescope group is fixed on the inner wall of the box under the flange, a top cover is provided on the end surface of the flange, and a filter is provided on the top cover; the integrated box is located below the transceiver telescope group, on one side of the box; the dual-wavelength laser is located below the transceiver telescope group.
[0010] Preferably, the box is provided with a cooling fan; the integrated box is also provided with a plug and a USB interface; the box is provided with an optical fiber protective shell, and an optical fiber and a filter are arranged inside; the transceiver telescope group includes a transmitting telescope and a receiving telescope.
[0011] Preferably, two load-bearing handles are symmetrically provided on the top cover; a circular filter 1 and a circular filter 2 are provided on the top cover, the diameter of the filter 1 is 10-20 cm, and a wiper is provided on the filter 1; the diameter of the filter 2 is 5-10 cm.
[0012] A buoy-borne CO2 inversion system based on laser radar detection includes a signal transmitting module, a signal recovery unit, a signal control unit, and a data processing unit; Signal transmission module: The dual-band laser emits dual-wavelength pulsed laser, which enters the atmosphere through the transceiver telescope; Signal recovery unit: The echo signal passes through the filter window and then enters the filter through the transmitting and receiving telescope; Signal control unit: The filtered signal enters the acousto-optic modulator, and the optical switch is controlled through the timing control mechanism, so that the signal enters the single-photon detector at the set time; Data processing unit: The detector sends the acquired data to the industrial computer through the acquisition card, and the industrial computer inverts the CO2 concentration in real time and stores it.
[0013] Preferably, the timing control of the acousto-optic modulator is set so that it is turned off in the initial time period after the laser pulse is emitted to prevent the mirror reflection signal from being transmitted to the detector, as follows: Laser emission moment: After the laser pulse trigger signal is sent out, the control signal of the AOM makes the AOM in the closed state, thereby preventing the mirror reflection signal from the laser source from entering the detector; Delay of mirror reflection signal: According to the propagation delay after the laser pulse is emitted, it is determined that the mirror reflection signal will reach the single-photon detector within a specific time. During this time window, the AOM continues to remain closed to avoid receiving strong reflection signals. Reflection signal suppression time period: By adjusting the control timing of the AOM, the time period for suppressing the mirror reflection signal is set. During this time period, the AOM does not transmit any signal, thereby shielding the strong signal reflected back from the laser source; Turn on the AOM: When the mirror reflection signal has been delayed for a predetermined time, the AOM is turned on after a certain period of time, allowing the target's reflection signal to enter the receiving channel normally for subsequent signal acquisition.
[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of rapid calculation of CO2 absorption cross section based on multivariate linear regression is adopted to improve the CO2 inversion speed and ensure the accuracy of real-time monitoring to improve the real-time, accuracy and stability of CO2 concentration monitoring.
[0015] 2. The present invention proposes a timing control scheme for an integrated acousto-optic modulator (AOM). Through precise time modulation, the strong reflection signal in the echo is actively shielded to protect the detector from the impact of excessively strong signals. Compared with the passive suppression method that only relies on signal processing algorithms in the prior art, this scheme achieves effective shielding of mirror reflection interference from the hardware level, greatly improving the measurement accuracy and reliability of the system.
[0016] 3. The present invention integrates the laser, detector, optical system and data acquisition and processing unit into the buoy through a compact structure design based on the buoy, which reduces the volume and weight of the system, facilitates flexible deployment, and has a corrosion-resistant shell design suitable for marine buoy use scenarios and can operate stably for a long time. Compared with the traditional DIAL system, the present invention is more suitable for deployment in small or complex environments, solving the problems of bulky volume and inflexible application in the prior art. At the same time, the optimized energy consumption design makes the system more efficient, prolongs the working time of field applications, and improves portability and applicability. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 This is a top view of the buoy CO2 lidar profiler; Figure 2 This is a front view of the buoy CO2 lidar profiler; Figure 3 It is a stereogram; Figure 4 This is a diagram of some components in the integrated box; Figure 5 It is a workflow diagram.
[0018] In the figure, 1- screw hole, 2- wiper, 3- filter one, 4- filter two, 5- load-bearing handle, 6- top cover, 7- flange, 8- cooling fan, 9- plug, 10- USB interface, 11- single photon detector, 12- transceiver telescope set, 13- optical fiber protective shell, 14- dual-wavelength optical fiber laser, 15- box, 16- integrated box, 17- acoustic and optical regulator, 18- acquisition card, 19- industrial computer, 20- power converter one, 21- power converter two. DETAILED DESCRIPTION
[0019] In order to make the purpose of the present invention: the scheme and advantages of the buoy carbon dioxide lidar profiler more clearly explained, the present invention is further described in detail below in combination with specific implementation methods and with reference to the accompanying drawings.
[0020] A buoy-borne CO2 inversion device based on laser radar detection comprises a frame-type box 15, an integrated box 16, a dual-wavelength laser 14 and a transceiver telescope group 12, wherein the transceiver telescope group 12 comprises a transmitting telescope and a receiving telescope; the integrated box 16 is provided with an acoustic-optical regulator 17, an acquisition card 18, a single-photon detector 11, a plug 9, a USB interface 10 and an industrial computer 19; a flange 7 is connected to the end of the box 15; the filter and the transceiver telescope are located in the box 15; the transceiver telescope group 12 is fixed on the inner wall of the box under the flange 7; a top cover 6 is provided on the end surface of the flange 7; a filter is provided on the top cover 6; the integrated box 16 is located below the transceiver telescope group 12 and on one side of the box 15; the dual-wavelength laser 14 is located below the transceiver telescope group 12, and the system is fixed to the buoy through the screw hole 1 on the flange 7.
[0021] The box body 15 is provided with a cooling fan 8; the box body 1 is provided with an optical fiber protection shell 13, and an optical fiber and a filter are arranged inside.
[0022] The top cover is watertight to ensure good sealing with the buoy hatch and protect the interior. Two load-bearing handles 5 are symmetrically provided on the top cover 6; a circular filter 1 3 and a circular filter 2 4 are provided on the top cover 6. The diameter of the filter 1 is 10-20cm. A wiper is provided on the filter 1 (for regular cleaning of the window to keep the window clear); the diameter of the filter 2 is 5-10cm.
[0023] The power converter 1 20 is a 16-32V to 24V power supply, and the power converter 21 is a 24V to 12V power supply.
[0024] A buoy-borne CO2 inversion system based on laser radar detection includes a signal transmitting module, a signal recovery unit, a signal control unit, and a data processing unit; Signal transmission module: The dual-band laser emits dual-wavelength pulsed laser, which enters the atmosphere through the transceiver telescope; Signal recovery unit: The echo signal passes through the filter window and then enters the filter through the transmitting and receiving telescope; Signal control unit: The filtered signal enters the acousto-optic modulator, and the optical switch is controlled through the timing control mechanism, so that the signal enters the single-photon detector at the set time; Data processing unit: The detector sends the acquired data to the industrial computer through the acquisition card, and the industrial computer inverts the CO2 concentration in real time and stores it.
[0025] After the system is started, the dual-band laser generates dual-wavelength laser (λ on and λ off), the laser is transmitted through the transmitting telescope and enters the atmosphere; after the laser interacts with the CO2 molecules in the atmosphere, the returned scattered signal is collected by the receiving telescope to form a dual-wavelength echo signal P (λ on ) and P(λ off ); The timing mechanism of the signal control unit generates a control signal to drive the acousto-optic modulator (AOM). The AOM shields the strong mirror reflection signal in the initial period of time in terms of timing to ensure that the echo signal received by the detector mainly comes from the target area. The received signal passes through a filter to remove background noise and interference from non-target wavelengths to ensure the purity of the signal. The detector transmits the filtered signal to the data acquisition card, while the buoy sensor obtains environmental parameters such as temperature and pressure. The industrial computer receives and processes the data from the data acquisition card and the buoy sensor. Using the differential absorption formula, the concentration distribution of CO2 in the atmosphere is calculated through the inversion algorithm.
[0026] The technical solution of the present invention is to set the timing control of AOM so that it is closed in the initial time period after the laser pulse is emitted, so as to avoid the transmission of the mirror reflection signal to the detector. The specific implementation steps are as follows: Laser emission moment: After the laser pulse trigger signal is emitted, the control signal of AOM makes AOM in a closed state, thereby preventing the mirror reflection signal from the laser source from entering the detector. Time delay of mirror reflection signal: According to the propagation delay after the laser pulse is emitted, it is determined that the mirror reflection signal will reach the detector within a specific time. In this time window, AOM continues to remain in a closed state to avoid receiving strong reflection signals. Reflection signal suppression time period: By adjusting the control timing of AOM, the time period for suppressing mirror reflection signals is set. In this time period, AOM does not transmit any signal, thereby shielding the strong signal reflected back by the laser source. Turn on AOM: When the mirror reflection signal is delayed by a predetermined time, AOM is turned on after a certain period of time, allowing the reflection signal of the target to enter the receiving channel normally for subsequent signal acquisition.
[0027] The control mechanism mode of AOM is as follows: This solution uses a timing control mechanism (such as FPGA, microcontroller, etc.) to accurately synchronize the emission signal of the laser pulse with the working timing of the AOM. The timing control mechanism generates the control signal of the AOM based on the laser trigger signal, so that the switching operation of the AOM is accurately aligned with the emission time of the laser pulse.
[0028] AOM working status: AOM controls its acousto-optic modulation characteristics to completely shut down or modulate the signal within a specific time. In the closed state, AOM effectively shields the mirror-reflected light from the laser source to prevent it from interfering with the receiving system; in the open state, AOM allows the optical signal reflected by the target to enter the detector normally.
[0029] Precise synchronization: By controlling in sync with the laser emission signal, the timing control module can accurately determine the arrival time of the reflected signal. This control strategy can effectively avoid the saturation of the system due to excessive reflected signals, ensuring that the detector is always in the best sensitivity state.
[0030] Delay compensation: According to the distance between the laser emission and the target object, the propagation time of the reflected signal is calculated, and appropriate delay compensation is added when the AOM is controlled. This compensation ensures that the AOM can be turned on in time before the reflected signal reaches the detector to avoid missing useful reflected signals.
[0031] Modulation mode: In some cases, in addition to simple on / off control, AOM can also suppress reflection signals of different intensities by adjusting its frequency and intensity. In particular, when the mirror reflection signal intensities vary, the influence of interference signals can be flexibly reduced by varying the modulation depth. The technical solution of the present invention can effectively shield the mirror reflection signal generated by the laser source, and prevent it from interfering with the receiving system during the initial period after the laser pulse is emitted, thereby improving the detection sensitivity of the laser radar system to the target reflection signal. At the same time, the present invention can avoid the phenomenon of detector oversaturation caused by strong reflection signals, enhance the reliability and accuracy of the system, and is particularly suitable for laser radar measurement scenarios that require high precision and low interference.
[0032] A method for inverting CO2 carried by a buoy based on laser radar detection comprises the following steps: S1. Differential Absorption Lidar (DIAL) technology uses a laser to alternately emit two laser pulses with stable frequencies and similar wavelengths, so that the two laser pulses are transmitted along the same path in the atmosphere. On the one hand, they are scattered by aerosols in the atmosphere, and on the other hand, they are absorbed by CO2 gas in the atmosphere.
[0033] S2. The detection of aerosol scattering echoes can carry the absorption information of CO2 gas to the laser pulse energy.
[0034] S3. In the differential absorption lidar system, the wavelength of one of the laser beams is located near the absorption peak of the CO2 gas absorption spectrum, where the absorption cross section of the CO2 gas is larger, recorded as ; The wavelength of the other laser beam deviates from the absorption peak of CO2 gas and is located at the absorption valley of the CO2 gas absorption spectrum. The absorption cross section of CO2 gas is smaller here, which is recorded as According to the different absorption degree of CO2 gas to the two laser beams, the CO2 gas concentration can be inverted by analyzing the atmospheric backscattered echo signal. The atmospheric echo signal detected by the atmospheric lidar can generally be expressed as: ; ; In the above formula, yes and The number of detected echo photons, is the receiving efficiency, is the atmospheric echo backscatter coefficient, is the speed of light, is the pulse width, is the receiving area of the receiving telescope, is the detection distance. The extinction coefficient of the laser in the round trip process in the atmosphere includes the scattering attenuation coefficient and the absorption attenuation coefficient. is the scattering attenuation coefficient, is the absorption cross section of CO2, is the extinction coefficient excluding CO2 absorption, is the molecular density of CO2. and Very close, can be considered and The atmospheric backscattering coefficient of the wavelength is the same, and the extinction coefficient is only related to CO2, that is, , Therefore, after the two equations are ratioed, logarithmic on both sides, and differentiated, the molecular density of CO2 can be expressed as: ; In the above formula and are the starting and ending positions of the distance integration interval calculation, It is the absorption cross-section difference. It can be seen that the larger the difference in the absorption cross-section, the better the inversion effect. Therefore, we should try to choose wavelengths with large differences in absorption cross-sections to invert CO2 concentration.
[0035] There are multiple absorption peaks of CO2 molecules in the infrared band. The strong absorption characteristics of carbon dioxide gas in the infrared band can improve the accuracy and stability of the inverted carbon dioxide gas concentration. Based on the HITRAN database, the absorption characteristics of carbon dioxide near 1.5μm are simulated and calculated using the line-by-line integration method. The CO2 absorption cross section is also related to factors such as temperature, pressure, and altitude. During the inversion process, due to the real-time changes in atmospheric temperature and pressure, the efficiency of manually calculating the carbon dioxide absorption cross section is low, which has a great impact on the inversion speed. To solve this problem, based on the HITRAN database, the carbon dioxide absorption cross section under different wavelengths, temperatures and pressures was obtained through molecular simulation, and a model was constructed using a multivariate linear fitting method to achieve rapid calculation of the absorption cross section from real-time temperature and pressure. Traditional CO2 absorption cross section calculation methods often rely on spectral databases or complex physical models. The calculation process is cumbersome and slow, and it is difficult to meet real-time monitoring needs. The present invention proposes a fast inversion method based on a multivariate linear regression fitting model. The method obtains parameters such as ambient temperature, air pressure and laser wavelength, and uses a multivariate linear fitting model to quickly calculate the CO2 absorption cross section. The model is applied to the absorption cross section correction of carbon dioxide concentration inversion, which can improve the CO2 concentration inversion speed and accuracy. Traditional absorption cross section calculation methods usually rely on highly complex physical models or table lookup methods, requiring a large amount of spectral data, environmental parameters (such as temperature, air pressure) and optical path information. This process has a large amount of calculation and a long response time, which cannot meet the needs of high-frequency and large-scale monitoring, limiting the real-time and universality of DIAL technology. The carbon dioxide absorption cross section is a measure of the ability of carbon dioxide molecules to absorb light under specific wavelength, temperature and air pressure conditions. In the DIAL system, the absorption cross section is not only affected by the wavelength, but also significantly affected by environmental factors such as temperature (T) and air pressure (P). In order to accurately invert the carbon dioxide concentration, it is necessary to accurately calculate the absorption cross section under different environmental conditions. By obtaining high-precision spectral data from the HITRAN database and performing simulations, we can simulate the carbon dioxide absorption cross section under different wavelengths, temperatures and air pressures. The traditional method is complex and has poor real-time performance. Therefore, the present invention proposes to quickly calculate the absorption cross section through a multiple linear regression model, thereby accelerating the inversion process. The present invention uses a multiple linear regression method to establish a multiple regression model between the absorption cross section and wavelength, temperature, and pressure based on the carbon dioxide absorption cross section data provided by the HITRAN database. The specific steps are as follows: (1) Data collection and preprocessing: The carbon dioxide absorption cross-section data under different wavelength (λ), temperature (T), and pressure (P) conditions were collected from the HITRAN simulation system. The data set contains the absorption cross-section values under multiple wavelengths, temperatures, and pressure conditions. After data cleaning and normalization, a multi-dimensional feature data matrix is formed.
[0036] (2) Model construction: In order to describe the complex relationship between the absorption cross section and wavelength, temperature, and air pressure, a high-order multivariate linear regression model is used for fitting. The constructed regression model can be expressed as: ; Among them, σ(λ, T, P) is the absorption cross section of carbon dioxide, λ, T, P are wavelength, temperature and air pressure respectively, β0, β1, β2, β3, β4, β5, β6, β7 are regression coefficients, indicating the degree of influence of each factor on the absorption cross section.
[0037] (3) Model training: To ensure high-precision fitting of the regression model, the least squares method is used to optimize the regression coefficients. The basic principle of the least squares method is to minimize the sum of squared errors between the model prediction value and the actual observation value. During the training process, the algorithm minimizes the error between the model prediction value and the actual observation value by optimizing the regression coefficient, thereby improving the fitting accuracy of the model and solving the optimal regression coefficient. The specific training process is as follows: Least squares method objective function: The goal of the least squares method is to minimize the sum of squared errors between the model's prediction results and the actual absorption cross-section data by optimizing the regression coefficients. The objective function is: ; in, is the actual value of the i-th sample; is the model prediction value, that is: ; m is the total number of samples.
[0038] (4) Solving the regression coefficient: By simplifying the calculation in matrix form, the formula for solving the regression coefficient β is: ; Where: X is the input feature matrix, each row contains the eigenvalues (λ, T, P) of the sample and its interaction terms; is the column vector of absorption cross section values; β is the regression coefficient vector to be determined.
[0039] The model fit was evaluated by cross-validation using mean square error (MSE) and coefficient of determination (R 2 ) and other indicators to measure the fitting accuracy and generalization ability of the model.
[0040] Example: The regression model obtained through training can realize the rapid calculation of the carbon dioxide absorption cross section. The calculation process only needs to input the temperature, air pressure and wavelength data obtained in real time, and use the multivariate regression formula to directly obtain the absorption cross section value. Compared with traditional methods, this calculation method has extremely high calculation efficiency and real-time performance.
[0041] 1) Real-time data acquisition: In practical applications, temperature and pressure data are usually acquired in real time through sensors, while the wavelength is determined by the wavelength of the laser in the differential absorption lidar system. By acquiring these environmental parameters in real time and inputting them into the regression model, the carbon dioxide absorption cross section under current environmental conditions can be quickly calculated.
[0042] 2) Calculation steps: Input the acquired environmental data (λ, T, P) into the regression model to quickly obtain the absorption cross-section value σ(λ, T, P). The calculation time is usually in milliseconds, which meets the requirements of real-time inversion.
[0043] 3) Application to differential absorption lidar inversion: In the differential absorption lidar (DIAL) system, the inversion of carbon dioxide concentration depends on the differential absorption signal of two lasers with different wavelengths. The traditional inversion method solves the concentration by calculating the difference of laser echoes and the absorption cross section, while the present invention significantly improves the inversion efficiency by providing a method for quickly calculating the absorption cross section.
[0044] 4) Absorption cross section is used in the inversion process: In the DIAL system, when the laser passes through the atmosphere, part of the energy is absorbed by carbon dioxide. Based on the difference in the laser echo signal and the relationship between the absorption cross section, the carbon dioxide concentration can be calculated using the following formula: in and are the absorption cross sections at two wavelengths respectively.
[0045] In summary, the present invention improves the performance of the differential absorption lidar system in many aspects through structural optimization, hardware innovation and algorithm improvement, expands its application scenarios, and provides a new technical solution for efficient and accurate measurement of carbon dioxide concentration. Inversion efficiency: Through the multivariate linear regression model, the inversion process is made more efficient and faster, especially suitable for application scenarios that require high-frequency real-time monitoring.
Claims
1. A method for inverting CO2 carried by a buoy based on laser radar detection, characterized in that: The following steps are involved: S1. Two laser pulses with stable frequencies and similar wavelengths are emitted alternately by a dual-wavelength laser, so that the two laser pulses are transmitted along the same path in the atmosphere; one part is scattered by aerosols in the atmosphere, and the other part is absorbed by CO2 gas in the atmosphere; S2. The detection of aerosol scattering echoes can carry the absorption information of CO2 gas to the laser pulse energy; S3. In the differential absorption lidar system, the wavelength of one of the laser beams is near the absorption peak of the CO2 gas absorption spectrum, denoted as ; The wavelength of the other laser beam deviates from the absorption peak of CO2 gas and is located at the absorption valley of the CO2 gas absorption spectrum, which is recorded as According to the different absorption degree of CO2 gas to the two laser beams, the CO2 gas concentration can be inverted by analyzing the atmospheric backscattered echo signal.
2. The method for inverting CO2 carried by a buoy based on laser radar detection according to claim 1 is characterized in that: In step S3, the atmospheric echo signal detected by the atmospheric laser radar is expressed as: ； ； yes and The number of detected echo photons, is the receiving efficiency, is the atmospheric echo backscatter coefficient, is the speed of light, is the pulse width, is the receiving area of the receiving telescope, is the detection distance. The extinction coefficient of the laser in the round trip process in the atmosphere includes the scattering attenuation coefficient and the absorption attenuation coefficient. is the scattering attenuation coefficient, is the absorption cross section of CO2, is the extinction coefficient excluding CO2 absorption, is the molecular density of CO2.
3. The method for inverting CO2 carried by a buoy based on laser radar detection according to claim 2 is characterized in that: In step S3, because and Very close, can be considered and The atmospheric backscattering coefficient of the wavelength is the same, and the extinction coefficient is only related to CO2, that is: ； ； After the two equations are ratioed, logarithmic on both sides, and differentiated, the molecular density of CO2 can be expressed as: ； In the formula and are the starting and ending positions of the distance integration interval calculation, Due to the difference in absorption cross-section, a wavelength with a large difference in absorption cross-section is selected to invert the CO2 concentration.
4. The method for inverting CO2 carried by a buoy based on laser radar detection according to claim 1, characterized in that: Based on the HITRAN database, the carbon dioxide absorption cross sections under different wavelengths, temperatures and pressures were obtained through molecular simulation, and a model was constructed using the multivariate linear fitting method to realize the rapid calculation of the carbon dioxide absorption cross section from real-time temperature and pressure.
5. The method for inverting CO2 carried by a buoy based on laser radar detection according to claim 4 is characterized in that: A multivariate regression model between the absorption cross section and wavelength, temperature, and pressure was established. The specific steps are as follows: Step 1: Data collection and preprocessing: The carbon dioxide absorption cross-section data under different wavelengths λ, temperatures T, and pressures P were collected from the HITRAN simulation system; the data set contained absorption cross-section values under multiple wavelengths, temperatures, and pressures. After data cleaning and normalization, a multi-dimensional feature data matrix was formed; Step 2: According to the relationship between the absorption cross section and wavelength, temperature, and air pressure, a high-order multivariate linear regression model is used for fitting. The constructed regression model is expressed as: ； Among them, σ(λ, T, P) is the absorption cross section of carbon dioxide, λ, T, P are wavelength, temperature and air pressure respectively, β0, β1, β2, β3, β4, β5, β6, β7 are regression coefficients, indicating the degree of influence of each factor on the absorption cross section; Step 3: Use the least square method to optimize the regression coefficients; The objective function is set as: ； in, is the actual value of the i-th sample; is the model prediction value, that is: ； m is the total number of samples; Step 4: Solve the regression coefficient: By simplifying the calculation in matrix form, the solution formula for the regression coefficient β is: ； Where: X is the input feature matrix, each row contains the eigenvalues (λ, T, P) of the sample and its interaction terms; is the column vector of absorption cross section values; is the transposed matrix; β is the regression coefficient vector to be determined.
6. A buoy-borne CO2 inversion device based on laser radar detection, using the buoy-borne CO2 inversion method based on laser radar detection as described in any one of claims 1 to 5, characterized in that: It comprises a box, an integrated box, a dual-wavelength laser and a transceiver telescope group; the integrated box is provided with an acousto-optic regulator, a collection card and a single-photon detector; the end of the box is connected with a flange; the filter and the transceiver telescope are located in the box; the transceiver telescope group is fixed on the inner wall of the box under the flange; a top cover is provided on the end surface of the flange; a filter is provided on the top cover; the integrated box is located below the transceiver telescope group, on one side of the box; the dual-wavelength laser is located below the transceiver telescope group.
7. The buoy-borne CO2 inversion device based on laser radar detection according to claim 6 is characterized in that: The box body is provided with a cooling fan; the integrated box is also provided with a plug and a USB interface; the box body is provided with an optical fiber protective shell, and an optical fiber and a filter are arranged inside; the transceiver telescope group includes a transmitting telescope and a receiving telescope.
8. The buoy-borne CO2 inversion device based on laser radar detection according to claim 6 is characterized in that: Two load-bearing handles are symmetrically arranged on the top cover; a circular filter 1 and a circular filter 2 are arranged on the top cover, the diameter of the filter 1 is 10-20 cm, and a wiper is arranged on the filter 1; the diameter of the filter 2 is 5-10 cm.
9. A buoy-borne CO2 inversion system based on laser radar detection, using the buoy-borne CO2 inversion method based on laser radar detection as described in any one of claims 1 to 5, characterized in that: It includes a signal transmitting module, a signal recovery unit, a signal control unit, and a data processing unit; Signal transmission module: The dual-band laser emits dual-wavelength pulsed laser, which enters the atmosphere through the transceiver telescope; Signal recovery unit: The echo signal passes through the filter window and then enters the filter through the transmitting and receiving telescope; Signal control unit: The filtered signal enters the acousto-optic modulator, and the optical switch is controlled by the timing control mechanism, so that the signal enters the single-photon detector at the set time; Data processing unit: The detector sends the acquired data to the industrial computer through the acquisition card, and the industrial computer inverts the CO2 concentration in real time and stores it.
10. The buoy-borne CO2 inversion system based on laser radar detection according to claim 9 is characterized in that: Set the timing control of the AOM so that it is turned off during the initial period after the laser pulse is emitted to prevent the mirror reflection signal from being transmitted to the detector as follows: Laser emission moment: After the laser pulse trigger signal is sent out, the control signal of the AOM makes the AOM in the closed state, thereby preventing the mirror reflection signal from the laser source from entering the detector; Delay of mirror reflection signal: According to the propagation delay after the laser pulse is emitted, it is determined that the mirror reflection signal will reach the single-photon detector within a specific time. During this time window, the AOM continues to remain closed to avoid receiving strong reflection signals. Reflection signal suppression time period: By adjusting the control timing of the AOM, the time period for suppressing the mirror reflection signal is set. During this time period, the AOM does not transmit any signal, thereby shielding the strong signal reflected back from the laser source; Turn on the AOM: When the mirror reflection signal has been delayed for a predetermined time, the AOM is turned on after a certain period of time, allowing the target's reflection signal to enter the receiving channel normally for subsequent signal acquisition.