A method and system for CO2 detection based on lidar

Abstract

This invention relates to the field of CO2 detection technology, and discloses a CO2 detection method and system based on lidar. The CO2 detection method includes sequentially outputting a first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width into the detection space. The absorption rate of the laser light with the first, second, and third wavelengths decreases sequentially; the narrow pulse width is smaller than the long pulse width. The laser echo signal is received and coherently detected. Differential absorption inversion is performed on the obtained differential intermediate frequency electrical signal to determine the first CO2 concentration within a preset near-range range and the second CO2 concentration within a preset far-range range, and the total CO2 concentration along the entire path of the detection space is determined. The technical solution of this invention provides comprehensive and reliable data for the accurate monitoring of atmospheric carbon dioxide.

Description

Technical Field

[0001] This invention relates to the field of CO2 detection technology, and in particular to a CO2 detection method and system based on lidar. Background Technology

[0002] In the current global context of addressing climate change, accurate monitoring of greenhouse gases, especially carbon dioxide (CO2), has become a core technological requirement for achieving scientific accounting and effective regulation of carbon emissions. Atmospheric CO2 is not only a major driver of climate change, but its spatiotemporal distribution characteristics also directly reflect the dynamic processes of human activities, vegetation respiration, and ocean exchange.

[0003] Differential absorption lidar technology utilizes lasers as an active light source, independent of external illumination, and possesses all-weather, high spatiotemporal resolution profile detection capabilities, making it the most effective means of achieving three-dimensional atmospheric CO2 detection. However, in CO2 lidar technology, the pulse width of the laser pulse is a key parameter affecting spatial resolution. For example, narrow laser pulses can achieve higher spatial resolution, but they are difficult to achieve high energy output, resulting in limited detection range. Conversely, wide laser pulses can achieve greater detection range, but they suffer from a larger detection blind zone.

[0004] Therefore, it is evident that one of the core challenges in the current development of CO2 lidar technology is how to take into account various detection needs while using lidar to detect CO2, and achieve more comprehensive detection of CO2 in the atmosphere. Summary of the Invention

[0005] The purpose of this invention is to provide a CO2 detection method and system based on lidar, which can achieve more comprehensive and reliable detection of CO2 in the atmospheric environment without significantly increasing equipment costs.

[0006] To address the aforementioned technical problems, this invention provides a CO2 detection method based on lidar, comprising: A first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width are sequentially output into the detection space; wherein, the absorption rate of the laser light with the first wavelength, the second wavelength, and the third wavelength decreases sequentially; and the narrow pulse width is smaller than the long pulse width; Receive laser echo signals and perform coherent detection on each of the laser echo signals to obtain the differential intermediate frequency electrical signal corresponding to each of the laser echo signals; Differential absorption inversion operation is performed on the differential intermediate frequency electrical signals corresponding to the first laser signal and the second laser signal respectively to obtain the first CO2 concentration within a preset short distance range; Differential absorption inversion operation is performed on the differential intermediate frequency electrical signals corresponding to the third laser signal and the fourth laser signal respectively to obtain the second CO2 concentration within a preset long distance range; The total CO2 concentration along the detection path is determined based on the first CO2 concentration and the second CO2 concentration.

[0007] In an optional embodiment of the present invention, the first wavelength is located within the wavelength range corresponding to the absorption peak of the CO2 gas absorption spectrum; the second wavelength is located within the wavelength range corresponding to the wing of the absorption peak of the CO2 gas absorption spectrum; and the third wavelength is located within the wavelength range corresponding to the absorption valley of the CO2 gas absorption spectrum.

[0008] In an optional embodiment of the present invention, the first wavelength is 2050.92 nm to 2050.97 nm, the second wavelength is 2050.97 nm to 2051.00 nm, and the third wavelength is 2051.00 nm to 2051.10 nm.

[0009] In an optional embodiment of the present invention, the narrow pulse width is 10ns~30ns, the long pulse width is 600ns~800ns; and the pulse interval of the first laser signal, the second laser signal, the third laser signal and the fourth laser signal is 25μs~100μs; The duration of the output signals of the first laser signal, the second laser signal, the third laser signal, and the fourth laser signal is not less than 1ms.

[0010] In an optional embodiment of the present invention, after obtaining the first CO2 concentration and the second CO2 concentration, the method further includes: A fast Fourier transform is performed on the differential intermediate frequency electrical signal corresponding to the second laser signal to obtain the first power spectrum peak frequency corresponding to the second laser signal within the preset short-range range; A fast Fourier transform is performed on the differential intermediate frequency electrical signal corresponding to the fourth laser signal to obtain the second power spectrum peak frequency corresponding to the fourth laser signal within the preset long distance range; Based on the first power spectrum peak frequency, the second power spectrum peak frequency, and the radial wind field inversion formula Radial wind speed inversion calculations are performed to obtain the near-field radial wind speed within the preset near-distance range and the far-field radial wind speed within the preset far-distance range; wherein, Location point radial wind speed, The third wavelength, The peak frequency of the power spectrum. This refers to the intrinsic intermediate frequency; The near-field radial wind speed and the first CO2 concentration are multiplied respectively, and the far-field radial wind speed and the second CO2 concentration are multiplied to obtain the total path CO2 flux in the detection space.

[0011] A CO2 detection system based on lidar includes: A multi-wavelength light source and modulation module are used to generate a first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width; wherein the absorption rate of the laser light with CO2 decreases sequentially from the first wavelength, the second wavelength, and the third wavelength; and the narrow pulse width is smaller than the long pulse width; An optical transceiver antenna module is used to output the first laser signal, the second laser signal, the third laser signal and the fourth laser signal to the detection space, and to receive laser echo signals; The signal detection module is used to coherently detect each of the laser echo signals to obtain a differential intermediate frequency electrical signal; The data acquisition and control module is used to perform differential absorption inversion operation on the differential intermediate frequency electrical signal to obtain a first CO2 concentration within a preset near range and a second CO2 concentration within a preset far range, and to determine the CO2 concentration along the entire path of the detection space based on the first CO2 concentration and the second CO2 concentration.

[0012] In an optional embodiment of the present invention, the multi-wavelength light source and modulation module includes a multi-wavelength light source module and a pulse width modulation module; The multi-wavelength light source module includes a first seed laser for outputting a laser signal of a first wavelength, a second seed laser for outputting a laser signal of a second wavelength, a third seed laser for outputting a laser signal of a third wavelength, and a switching optical switch. The first, second, and third input terminals of the switching optical switch are respectively connected to the output terminals of the first seed laser, the second seed laser, and the third seed laser; the output terminal of the switching optical switch is connected to the input terminal of the pulse width modulation module. The pulse width modulation module includes a first-stage preamplifier, an acousto-optic modulator, a second-stage preamplifier, and a main amplifier connected in sequence. The acousto-optic modulator is used to modulate the laser signal of the first wavelength into a laser pulse with a narrow pulse width, modulate the laser signal of the second wavelength into a laser pulse with a long pulse width, and modulate the laser signal of the third wavelength into two different laser pulses with narrow and long pulse widths.

[0013] In an optional embodiment of the present invention, the multi-wavelength light source and modulation module includes a seed laser, an IQ modulator, a high-speed signal generator, and a signal amplification module; The seed laser is used to output a laser signal of a second wavelength; The high-speed signal generator is used to drive the IQ modulator to modulate the second wavelength laser signal into a first wavelength or a third wavelength laser signal. The signal amplification module includes a first-stage preamplifier, a second-stage preamplifier, and a main amplifier connected in sequence.

[0014] In an optional embodiment of the present invention, the IQ modulator is a lithium niobate crystal modulator; the high-speed signal generator is an AWG sequence generator.

[0015] In an optional embodiment of the present invention, a beam splitter is provided between the first-stage preamplifier and the second-stage preamplifier; the input terminal of the beam splitter is connected to the output terminal of the first-stage preamplifier; and the first output terminal of the beam splitter is connected to the input terminal of the second-stage preamplifier. The optical transceiver antenna module includes an optical circulator and a combined transceiver telescope; The signal detection module includes an optical fiber coupler and a balanced detector; the first input end of the optical fiber coupler is connected to the second output end of the optical splitter coupler; the second input end of the optical fiber coupler is connected to the optical circulator; and the output end of the optical fiber coupler is connected to the balanced detector.

[0016] The present invention provides a CO2 detection method and system based on lidar. The lidar CO2 detection method includes sequentially outputting a first laser signal with a first wavelength and narrow pulse width, a second laser signal with a third wavelength and narrow pulse width, a third laser signal with a second wavelength and long pulse width, and a fourth laser signal with a third wavelength and long pulse width into a detection space. The absorption rate of the laser light with the first, second, and third wavelengths decreases sequentially, and the narrow pulse width is smaller than the long pulse width. The method involves receiving laser echo signals and performing coherent detection on each laser echo signal to obtain the differential intermediate frequency (IF) electrical signal corresponding to each laser echo signal. Differential absorption inversion operations are performed on the differential IF electrical signals corresponding to the first and second laser signals to obtain a first CO2 concentration within a preset near-range. Differential absorption inversion operations are performed on the differential IF electrical signals corresponding to the third and fourth laser signals to obtain a second CO2 concentration within a preset long-range. Based on the first and second CO2 concentrations, the total CO2 concentration along the entire path of the detection space is determined.

[0017] This invention employs three laser signals with different wavelengths and varying CO2 absorption rates to form four different laser pulses with two pulse widths. Coherent detection and differential absorption inversion are performed on the laser echo signals corresponding to the first and second laser signals, which have narrower pulses, to obtain high-resolution detection of CO2 concentration in the near-range. Meanwhile, coherent detection and differential absorption inversion are performed on the laser echo signals corresponding to the third and fourth laser signals, which have wider pulses, to obtain CO2 concentration detection in the far-range range. This achieves complementary detection of CO2 concentration in both the near-range and far-range ranges within the detection space, ultimately obtaining the full-path CO2 concentration within the detection space that can meet various detection requirements, providing comprehensive and reliable data for the accurate monitoring of carbon dioxide in the atmosphere. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the laser signal sequence for CO2 detection using a conventional lidar system. Figure 2 A schematic diagram showing the wavelength and absorptivity of the laser signal used by a conventional lidar for detecting CO2: Figure 3A schematic flowchart of a CO2 detection method based on lidar provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the output timing of each laser signal provided in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the variation of the absorption cross section of a laser beam for CO2 with wavelength, provided in an embodiment of the present invention. Figure 6 This is a schematic diagram illustrating the variation of the absorption cross-section of laser light in water with wavelength, as provided in an embodiment of the present invention. Figure 7 A schematic diagram of a frame structure for a CO2 detection system based on lidar provided in an embodiment of the present invention; Figure 8 A schematic diagram of another framework structure of the CO2 detection system based on lidar provided in an embodiment of the present invention; In the attached diagram: 10 is a multi-wavelength light source and modulation module, 101 is a seed laser, 102 is an IQ modulator, 103 is a high-speed signal generator, 11 is a multi-wavelength light source module, 111 is a first seed laser, 112 is a second seed laser, 113 is a third seed laser, 114 is a switching optical switch, 12 is a pulse width modulation module, 120 is an acousto-optic modulator, 121 is a first-stage preamplifier, 122 is a second-stage preamplifier, 123 is a main amplifier, 124 is a beam splitter coupler, 20 is an optical transceiver antenna module, 21 is an optical circulator, 22 is a transceiver telescope, 30 is a signal detection module, 31 is a balanced detector, 32 is an optical fiber coupler, and 40 is a data acquisition and control module. Detailed Implementation

[0020] The core of this invention is to provide a CO2 detection method and system based on lidar, which can achieve more comprehensive detection of CO2 in space and provide comprehensive and reliable data for accurate monitoring of carbon dioxide in the atmospheric environment.

[0021] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To facilitate understanding of the technical solutions in this invention, the principle of lidar detection of CO2 concentration in the atmosphere will be briefly explained first.

[0023] like Figure 1As shown, in the process of using lidar to detect CO2 concentration, it is necessary to use lidar to alternately output online and offline laser pulse signals to the atmosphere. The online and offline laser pulse signals are laser pulses with the same pulse width and frequency, but their wavelengths are different.

[0024] The absorption rate of laser light for CO2 fluctuates with wavelength, meaning that the absorption rate of laser light for CO2 has multiple local maxima and minima, also known as absorption peaks and troughs. Therefore... Figure 2 As shown, when selecting the laser wavelength for the Online and Offline laser pulse signals, the wavelength corresponding to the absorption peak can be selected as the Online laser pulse signal within a local wavelength range that contains at least one absorption peak and one absorption valley. The wavelength is selected, and the wavelength corresponding to the absorption valley is chosen as the offline laser pulse signal. wavelength.

[0025] When detecting CO2 in the atmosphere, online and offline laser pulse signals are sequentially output into the atmosphere. Both laser pulse signals are partially absorbed by CO2 and partially reflected back, which are the echo signals corresponding to the laser pulse signals. The online and offline laser echo signals reflected back from the atmosphere can be used to retrieve the concentration of CO2 in the atmosphere.

[0026] In practical applications, if both the online and offline laser pulse signals are narrow pulses, the detected CO2 concentration, while possessing high spatial resolution, can only detect CO2 concentrations within a few hundred meters of the lidar, thus limiting the spatial range at which CO2 can be detected. Conversely, if both the online and offline laser pulse signals are wide pulses, although they can detect CO2 concentrations at greater distances in the atmosphere, a detection blind zone exists within the close-range detection area.

[0027] Based on the above discussion, such as Figures 3 to 5 As shown, Figure 3 This is a schematic flowchart of a CO2 detection method based on lidar provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the output timing of each laser signal provided in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the variation of CO2 absorption rate by laser light with wavelength, as provided in an embodiment of the present invention.

[0028] In one specific embodiment of the present invention, the CO2 detection method based on lidar can be as follows.

[0029] S1: The detection space outputs a first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width in sequence; wherein, the absorption rate of the laser light with the first wavelength, the second wavelength, and the third wavelength decreases in sequence; and the narrow pulse width is smaller than the long pulse width.

[0030] It is understood that the lidar system in this embodiment primarily detects the concentration of CO2 in the atmospheric environment, and the detection space in this step is the atmospheric environment. During the actual detection of CO2 concentration in the ambient atmosphere, the lidar system can periodically output a first laser signal, a second laser signal, a third laser signal, and a fourth laser signal sequentially. These four laser signals are formed based on three different laser beams and two different pulse widths.

[0031] The first, second, third, and fourth laser signals correspond to wavelengths of the first, third, second, and third wavelengths, respectively, and their corresponding pulse widths are narrow pulse width, narrow pulse width, long pulse width, and long pulse width, respectively. Furthermore, the absorption rates of the first and second wavelength laser signals for CO2 concentration are greater than that of the third wavelength laser signal, while the narrow pulse width is less than the long pulse width. Therefore, during CO2 concentration detection, the first and second laser signals together form one set of online and offline laser signals; the third and fourth laser signals form another set of online and offline laser signals.

[0032] Reference Figure 4 ,exist Figure 4 In the illustrated embodiment, the Online1 laser signal and the Offline1 laser signal are equivalent to the first and second laser signals in this embodiment, while the Online2 laser signal and the Offline2 laser signal are equivalent to the third and fourth laser signals in this embodiment.

[0033] Of course, in Figure 4 The illustrated embodiment only shows the laser signal output by the lidar detection system within one cycle. However, in practical applications, the lidar detection system can continuously and repeatedly output signals such as... Figure 4 The multiple laser signals shown enable the detection of the temporal variation of CO2 concentration in the atmospheric environment.

[0034] In addition, the first and third wavelengths corresponding to the first and third laser signals should be different; and in order to reduce the difficulty of modulating and forming the first and third laser signals, the first and second wavelengths can be selected as two wavelengths that have certain differences in magnitude and also have certain differences in CO2 absorption rate.

[0035] In an optional embodiment of the present invention, the first wavelength may be within the wavelength range corresponding to the absorption peak of the CO2 gas absorption spectrum; the second wavelength may be within the wavelength range corresponding to the wing of the absorption peak of the CO2 gas absorption spectrum; and the third wavelength may be within the wavelength range corresponding to the absorption valley of the CO2 gas absorption spectrum.

[0036] Reference Figure 5 , Figure 5 The absorption cross-section of CO2 by different laser signals varying with wavelength was characterized; it can be understood that the absorption cross-section of CO2 is a parameter proportional to the CO2 absorptivity, therefore... Figure 5 The absorption cross section of CO2 is used to characterize the absorption rate of CO2 by lasers of different wavelengths.

[0037] Figure 5 Taking a wavelength range where the first, second, and third wavelengths are all approximately 2550 nm as an example, the absorption peak (maximum absorptivity) of the CO2 absorption spectrum corresponds to a wavelength of 2050.952 nm, while the absorption trough (minimum absorptivity) corresponds to a position after 2051 nm. Therefore, within this wavelength range, the first wavelength can be selected as 2050.92 nm to 2050.97 nm, the second wavelength as 2050.97 nm to 2051 nm, and the third wavelength as 2051 nm to 2051.10 nm.

[0038] In addition, refer to Figure 6 , in and Figure 5 Within the same wavelength range shown, the laser beams of the first, second, and third wavelengths have relatively small absorption cross-sections for water vapor. Therefore, in this embodiment, according to... Figure 5 By selecting the first, second, and third wavelengths within the wavelength ranges corresponding to the absorption peaks, absorption peak wings, and absorption valleys shown, the interference of water vapor in the environment on CO2 concentration measurement can be avoided to a certain extent.

[0039] Further optionally, for the narrow pulse widths corresponding to the first and second laser signals in this embodiment (such as...) Figure 5The t1 in the figure can be 10ns~30ns, for example, 10ns, 15ns, 20ns, 25ns, or 30ns; in short, it can be determined based on the spatial resolution requirements for CO2 concentration detection in close space during actual measurement.

[0040] Secondly, the pulse widths corresponding to the third and fourth laser signals (such as...) Figure 5 The value of t2 can be 600ns to 800ns; for example, it can be 600ns, 650ns, 680ns, 700ns, 750ns, 780ns, 800ns, etc.

[0041] In addition, to avoid mutual interference between two adjacent pulse signals, the pulse interval of the first, second, third and fourth laser signals is 25μs~100μs.

[0042] Furthermore, within the same cycle, the duration of the first and second laser signals can be the same, while the duration of the third and fourth laser signals can be the same. For example, within the same cycle, the duration of each laser signal should not be less than 1ms. Of course, the duration of the first and third laser signals can be the same or different. However, it should be ensured that within the same cycle time period, the number of pulses output by the first, second, third, and fourth laser signals should not be less than 10, specifically including 40 pulses.

[0043] S2: Receive laser echo signals and perform coherent detection on each laser echo signal to obtain the differential intermediate frequency electrical signal corresponding to each laser echo signal.

[0044] It is understandable that during the process of sequentially outputting the first, second, third, and fourth laser signals into the detection space, while each laser signal is absorbed by CO2 in the atmospheric detection space, a portion of the signal is also reflected back. In other words, for each laser signal, a corresponding laser echo signal can be collected and received.

[0045] Therefore, coherent detection can be performed on the first laser echo signal corresponding to the first laser signal, the second laser echo signal corresponding to the second laser signal, the third laser echo signal corresponding to the third laser signal, and the fourth laser echo signal corresponding to the fourth laser signal. Specifically, each laser echo signal can be mixed with its corresponding intrinsic light and then the mixed signal can be detected to obtain the differential intermediate frequency electrical signal corresponding to each laser echo signal.

[0046] S3: Perform differential absorption inversion operation on the differential intermediate frequency electrical signals corresponding to the first laser signal and the second laser signal respectively to obtain the first CO2 concentration within a preset short distance range.

[0047] S4: Perform differential absorption inversion operation on the differential intermediate frequency electrical signals corresponding to the third and fourth laser signals respectively to obtain the second CO2 concentration within a preset long-distance range.

[0048] S5: Determine the CO2 concentration along the entire path of the detection space based on the first CO2 concentration and the second CO2 concentration.

[0049] In coherent differential absorption-hyperspectral resolution lidar technology, when the wavelengths of two laser signals are similar and the emission interval between the two wavelengths is small, it can be assumed that the influence of atmospheric temperature, pressure, and atmospheric turbulence on the two signals is the same; therefore, the average number density of carbon dioxide molecules per unit volume in the atmosphere under the range-resolved observation mode satisfies the following molecular number density expression: ; in, , These represent the carbon dioxide number density within a preset near-distance range and a preset far-distance range, respectively. These are the absorption cross sections of carbon dioxide for laser signals of the first, second, and third wavelengths, respectively. This represents the range resolution of the lidar. The backscattered powers corresponding to the first, second, third, and fourth laser echo signals, respectively, can be obtained through square-law detection or power spectrum analysis of the differential intermediate frequency electrical signals corresponding to each laser echo signal. Therefore, based on the four sets of differential intermediate frequency electrical signals corresponding to the four laser echo signals obtained by coherent detection, and the aforementioned molecular number expression, the carbon dioxide molecular number density within a preset near-range and preset far-range range can be determined by inversion.

[0050] Based on the molecular number density obtained above, in the distance resolution observation mode, the formula for the volume concentration ratio of atmospheric carbon dioxide is further applied. Therefore, the final expression for the total carbon dioxide concentration along the entire pathway can be determined as follows: ; in, Let be the total number density of atmospheric molecules at location r. This can be calculated by determining the atmospheric pressure and temperature at location r based on atmospheric models or meteorological analysis data, and then combining this with the ideal gas equation. This refers to the distance threshold used to divide the preset near-distance range and the preset far-distance range. Its value can be determined based on the measurement distance and accuracy achievable using the carbon dioxide concentration determined by the first and second laser signals, as well as the measurement distance and accuracy achievable using the carbon dioxide concentration determined by the third and fourth laser signals. For example, this... The preset range can be 200m, which means the spatial range between 0 and 200 meters from the lidar, while the preset long range means the spatial range between the lidar system and more than 200 meters.

[0051] Based on the above embodiments, simple CO2 concentration measurement can only reflect the static distribution characteristics of greenhouse gases in space. To accurately quantify the emission rate of carbon sources and the absorption capacity of carbon sinks, it is necessary to further obtain CO2 flux data, that is, the mass of CO2 passing through a unit area per unit time. This depends on the simultaneous high-precision joint observation of CO2 concentration and atmospheric radial wind field.

[0052] Based on this, in another optional embodiment of the present invention, after obtaining the first CO2 concentration and the second CO2 concentration, the method may further include: S51: Perform a fast Fourier transform on the differential intermediate frequency electrical signal corresponding to the second laser signal to obtain the first power spectrum peak frequency corresponding to the second laser signal within a preset short distance range; S52: Perform a fast Fourier transform on the differential intermediate frequency electrical signal corresponding to the fourth laser signal to obtain the second power spectrum peak frequency corresponding to the fourth laser signal within a preset long distance range; S53: Based on the peak frequency of the first power spectrum, the peak frequency of the second power spectrum, and the radial wind field inversion formula Radial wind speed inversion calculations are performed to obtain the near-field radial wind speed within a preset near-range range and the far-field radial wind speed within a preset far-range range; wherein, Location point radial wind speed, The third wavelength, The peak frequency of the power spectrum. This refers to the intrinsic intermediate frequency; S54: Multiply the near-field radial wind speed and the first CO2 concentration respectively, and multiply the far-field radial wind speed and the second CO2 concentration to obtain the total path CO2 flux in the detection space.

[0053] In this embodiment, the mid-frequency beat signal based on the laser echo signal not only contains intensity information for concentration inversion but also carries the Doppler frequency shift generated by the wind-driven movement of atmospheric aerosols, further enabling wind measurement in space. To avoid signal attenuation caused by strong absorption, laser wavelengths at the offline1 and offline2 wavelengths located in the CO2 absorption valley can be selected for wind measurement, matching the concentration segmentation logic. The wind field extraction also adopts a segmented collaborative strategy; the specific process is as follows: (1) Near-field wind speed extraction: Perform fast Fourier transform on the differential intermediate frequency electrical signal corresponding to the short-pulse offline1 echo signal (i.e., the second laser loop signal corresponding to the second laser signal) to obtain the near-field wind speed. The first power spectrum peak frequency at Therefore, the near-field radial wind speed is ;in The third wavelength, For the local oscillator intermediate frequency, 80MHz can be chosen; (2) Far-field wind speed extraction: Perform a fast Fourier transform on the differential intermediate frequency electrical signal corresponding to the wide-pulse offline2 echo signal (i.e., the fourth laser loop signal corresponding to the fourth laser signal) to obtain the far-field wind speed. The second power spectrum peak frequency at that location Similarly, the far-field radial wind speed is ; (3) Accurate calculation of dynamic CO2 flux throughout the entire path; Since the lidar system alternately emits pulses at a high time-division multiplexing frequency of 1 kHz within a single optical path, it ensures that the wind field and gas concentration distribution along the detection path have absolute spatial coaxiality and temporal synchronization within the integration time, and the radial flux of CO2 at a distance r is calculated. The exact product of the carbon dioxide concentration and wind speed along the entire path is obtained as follows: ; This refers to the carbon dioxide concentration.

[0054] This embodiment eliminates the need for a physical combination of a "concentration radar + wind-measuring radar" dual-system detection. Instead, it utilizes a coherent heterodyne detection architecture to extract the Doppler frequency shift and deeply reuses the offline wavelengths in differential absorption for collaborative wind measurement. Specifically, it extracts near-field wind speed using the short-pulse offline1 echo and far-field wind speed using the long-pulse offline2 echo. Because the concentration and wind field data share the same receiver and receiver circuit, the same local oscillator, the same detector, and the same nanosecond-level pulse timing sequence, it achieves perfect spatial coaxiality and temporal synchronization of concentration and wind field data detection. This completely eliminates the cross-system errors between the two splicing systems for concentration and wind field data from a physical perspective, enabling accurate calculation of the dynamic CO2 flux along the entire path from near-surface to the top of the boundary layer.

[0055] In summary, this invention employs three laser signals with different wavelengths and varying CO2 absorption rates to form four different laser pulses with two pulse widths. Coherent detection and differential absorption inversion are performed on the laser echo signals corresponding to the first and second laser signals, which have narrower pulses, to obtain high-resolution detection of CO2 concentration in the near-range. Meanwhile, coherent detection and differential absorption inversion are performed on the laser echo signals corresponding to the third and fourth laser signals, which have wider pulses, to obtain CO2 concentration detection in the far-range. This achieves complementary detection of CO2 concentration in both the near-range and far-range ranges within the detection space, ultimately obtaining a more comprehensive full-path CO2 concentration that can meet various detection needs, providing comprehensive and reliable data for accurate monitoring of carbon dioxide in the atmosphere.

[0056] Based on the above embodiments, such as Figure 7 As shown, Figure 7 This is a schematic diagram of the framework structure of a lidar-based CO2 detection system provided in an embodiment of the present invention. It is understood that this lidar-based CO2 detection system is also used to implement the lidar-based CO2 detection method described above.

[0057] In one specific embodiment of the present invention, the lidar-based CO2 detection system may include: The multi-wavelength light source and modulation module 10 are used to generate a first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width; wherein the absorption rate of the laser light with CO2 decreases sequentially from the first wavelength to the second wavelength and the third wavelength; and the narrow pulse width is smaller than the long pulse width; The optical transceiver antenna module 20 is used to output a first laser signal, a second laser signal, a third laser signal and a fourth laser signal to the detection space, and to receive laser echo signals; Signal detection module 30 is used to coherently detect each of the laser echo signals to obtain differential intermediate frequency electrical signals; The data acquisition and control module 40 is used to perform differential absorption inversion operation on the differential intermediate frequency electrical signal to obtain the first CO2 concentration within a preset near distance range and the second CO2 concentration within a preset far distance range, and to determine the CO2 concentration of the entire path in the detection space based on the first CO2 concentration and the second CO2 concentration.

[0058] In this embodiment, the multi-wavelength light source and modulation module 10 can output three different wavelength laser signals, namely the first wavelength, the second wavelength, and the third wavelength. It can further modulate the first wavelength laser signal into a laser pulse signal with a narrow pulse width, that is, form the first laser signal. The second wavelength laser signal is modulated into a laser pulse signal with a long pulse width, thereby forming the third laser signal. The third wavelength laser signal can be modulated into two laser pulse signals with narrow pulse width and long pulse width, which are then output as the second laser signal and the fourth laser signal, respectively.

[0059] Furthermore, the relationship between the first wavelength, the second wavelength, and the third wavelength, the narrow pulse width and the wide pulse width, the first laser signal, the second laser signal, the third laser signal and the fourth laser signal formed, and the output order and method of the four laser signals in this embodiment are the same as in the embodiment of the above-mentioned CO2 detection method based on lidar, and will not be repeated in this embodiment.

[0060] like Figure 7 As shown, in one optional embodiment, the multi-wavelength light source and modulation module 10 may specifically include: The multi-wavelength light source and modulation module 10 includes a multi-wavelength light source module 11 and a pulse width modulation module 12; The multi-wavelength light source module 11 includes a first seed laser 111 for outputting a laser signal of a first wavelength, a second seed laser 112 for outputting a laser signal of a second wavelength, a third seed laser 113 for outputting a laser signal of a third wavelength, and a switching optical switch 114. The first, second, and third input terminals of the switching optical switch 114 are connected to the output terminals of the first seed laser 111, the second seed laser 112, and the third seed laser 113, respectively; the output terminal of the switching optical switch 114 is connected to the input terminal of the pulse width modulation module 12. The pulse width modulation module 12 includes a first-stage preamplifier 121, an acousto-optic modulator 120, a second-stage preamplifier 122, and a main amplifier 123 connected in sequence. The acousto-optic modulator 120 is used to modulate a laser signal of a first wavelength into a laser pulse with a narrow pulse width, to modulate a laser signal of a second wavelength into a laser pulse with a long pulse width, and to modulate a laser signal of a third wavelength into two different laser pulses with narrow and long pulse widths.

[0061] This embodiment is equipped with three lasers, each capable of outputting laser signals of three different wavelengths. These lasers, along with a switching optical switch 114, enable switchable output of the three different wavelengths. All three lasers can be narrow-linewidth continuous-wave (CW) semiconductor lasers, meaning that all three lasers output continuous-wave laser signals after passing through the switching switch 114. The output terminals of the three lasers are connected to the three input terminals of the switching optical switch 114. This switching optical switch 114 is connected to a timing controller, which, when triggered by the timing controller, cycles through the inputs according to a preset time-division multiplexing sequence (online1-offline-online2-offline-online1...).

[0062] Furthermore, the pulse modulation module 12 in this embodiment includes a multi-stage amplifier and an acousto-optic modulator 120, wherein the acousto-optic modulator 120 is used to modulate the three different wavelengths of continuous wave laser signals into two different pulse widths of pulsed laser. Specifically, when a laser signal of the first wavelength is output through the switching switch 114, the acousto-optic modulator 120 modulates it into a first laser signal with a narrow pulse width; when a laser signal of the second wavelength is output through the switching switch 114, the acousto-optic modulator 120 modulates it into a third laser signal with a long pulse width; and when a laser signal of the third wavelength is output through the switching switch 114, if a second laser signal is currently needed, the acousto-optic modulator 120 modulates the pulse width of the laser signal into a narrow pulse, and if a fourth laser signal is currently needed, the acousto-optic modulator 120 modulates the pulse width of the laser signal into a long pulse.

[0063] In addition, the primary preamplifier 121, the secondary preamplifier 122, and the main amplifier 123 are mainly used to amplify and modulate the pulsed laser.

[0064] Optionally, an optical splitter coupler 124 may be provided between the primary preamplifier 121 and the secondary preamplifier 122; the input terminal of the optical splitter coupler 124 is connected to the output terminal of the primary preamplifier 121; the first output terminal of the optical splitter coupler 124 is connected to the input terminal of the secondary preamplifier 122. The optical transceiver antenna module 20 includes an optical circulator 21 and a transceiver combined telescope 22; The signal detection module 30 includes an optical fiber coupler 32 and a balanced detector 31; the first input end of the optical fiber coupler 32 is connected to the second output end of the optical splitter coupler 124; the second input end of the optical fiber coupler 32 is connected to the optical circulator 21; and the output end of the optical fiber coupler 32 is connected to the balanced detector 31.

[0065] like Figure 7As shown, the continuous seed laser output from the switching optical switch 114 enters the first-stage preamplifier 121 for initial power boosting and then enters the beam splitter coupler 124, specifically a 1×2 beam splitter, which splits the laser signal output from the first-stage preamplifier 121 into two laser signals according to a set splitting ratio (e.g., 99:1). About 1% of the laser is split off as the local oscillator light, which is transmitted directly to the signal detection module 30 through the second output terminal of the beam splitter coupler 124 without modulation and subsequent amplification, serving as the reference light field for heterodyne detection. The remaining 99% of the laser is output to the AOM (acousto-optic modulator 120) through the first output terminal of the beam splitter coupler 124, and modulated into a pulsed laser sequence by the AOM. The sequence then enters the second-stage preamplifier 122 and the main amplifier 123 (using a thulium-doped fiber amplifier TDFA) for multi-stage power amplification, ultimately outputting a high-beam-quality pulsed laser (e.g., amplifying short pulsed lasers to an energy of 10 μJ and long pulsed lasers to an energy of 200 μJ).

[0066] Furthermore, in this embodiment, the splitting ratio of the laser signal into two signals by the beam splitter 124 is not necessarily 99:1, but can be other ratios; however, it should be ensured that the signal strength output to the signal detection module 30 through the second end of the beam splitter 124 is much smaller than the signal strength output to the acousto-optic modulator 12 through the first output end of the beam splitter 124. This will not be discussed in detail in this embodiment.

[0067] Based on this, the first port of the optical circulator 21 is connected to the output of the main amplifier 123, the second port is connected to the transceiver telescope 22, and the third port is connected to the second input of the fiber optic coupler 32. Thus, the high-energy pulsed laser output from the main amplifier 123 is input to the first port of the optical circulator 21 and output to the transceiver telescope 22 via the second port. After beam expansion and collimation by the transceiver telescope 22, the laser signal is emitted towards the atmospheric target area. Simultaneously, the backscattered echo signal generated by aerosols and molecules in the atmosphere is received by the same transceiver telescope 22 and transmitted to the second port of the optical circulator 21, finally outputting from the third port. The weak echo signal light output from the third port of the optical circulator 21, together with the reserved local oscillator light output from the second output of the beam splitter 124, is input to a fiber optic coupler 32, where interference mixing occurs. The mixed laser signal is split into two groups at a 1:1 ratio and incident on the balanced detector 31. The balanced detector 31 suppresses the common-mode noise of the local oscillator light through a differential amplifier circuit and outputs an intermediate frequency (IF) beat signal containing Doppler frequency shift and intensity information.

[0068] The analog electrical signal (i.e., differential intermediate frequency electrical signal) output by the balanced detector 31 is connected to the data acquisition and control module 40. The data acquisition and control module 40 may specifically include an acquisition module, a signal processing unit (such as an FPGA or host computer), and a DSP module. The acquisition module has a built-in high-speed analog-to-digital converter (such as an ADC with a sampling rate of 1 GSPS) to convert the analog signal into a digital signal. The signal processing unit performs a Fast Fourier Transform (FFT) on the digital signal and performs dual-path parallel processing to invert the carbon dioxide concentration at different distance segments. It can also further invert the radial wind field of the entire path. The DSP module finally multiplies the concentration data with wind speed data that are strictly time-aligned within the same distance gate to output a high-precision, spatiotemporally mismatch-free three-dimensional CO2 flux profile.

[0069] In an optional embodiment of the present invention, the lidar-based CO2 detection system can employ an all-fiber optical path design (except for the space transceiver section), and achieve dynamic modulation of the pulse width through an acousto-optic modulator 120 (AOM). Combined with differential absorption detection technology, it can achieve all-weather, high-precision, and low-blind-zone detection of atmospheric carbon dioxide flux. The lidar-based CO2 detection system mainly consists of five parts: a multi-wavelength seed light source module (i.e., multi-wavelength light source module 11), a MOPA (master oscillator power amplifier) ​​transmission module (i.e., pulse width modulation module 12), an optical transceiver antenna module 20, a signal detection module 30, and a data acquisition and control module 40. The parameters of each key component can be configured according to Table 1 below.

[0070] Table 1 Parameters of Key Components in the System

[0071] Based on Table 2 above, the connection relationships and configurations between the various components in a specific embodiment of a lidar CO2 detection system can be as follows.

[0072] (1) Multi-wavelength seed source module; equipped with three narrow linewidth continuous wave (CW) semiconductor lasers as seed sources, as detailed below: The first seed laser 111, as an online laser, can have its output wavelength locked at 2050.952 nm (the center wavelength of the strong absorption peak of carbon dioxide, used for close-range detection). The second seed laser 112, as an online2 laser, can have its output wavelength locked at 2050.996 nm (the wavelength of the carbon dioxide absorption peak wing, used for long-distance detection). The third seed laser 113 is an offline laser with its output wavelength locked at 2051.0063 nm (the wavelength of the carbon dioxide absorption valley). The outputs of the three lasers are connected to the input of an optical switch (optical switch 114); the optical switch is cyclically selected according to the preset time-division multiplexing sequence (online1-offline-online2-offline-online1…) triggered by the timing controller.

[0073] (2) MOPA transmission and modulation module; the continuous seed light output from the optical switch first enters the first-stage preamplifier 121 for preliminary power boost; the amplified beam is transmitted to the polarization-maintaining fiber coupler and split into two paths according to the splitting ratio (e.g., 99:1); as follows: ①Local oscillator optical path: About 1% of the optical power is separated as local oscillator light, which is transmitted directly to the coherent detection module through optical fiber without modulation and subsequent amplification, and serves as the reference optical field for heterodyne detection; ② Modulation optical path: The remaining approximately 99% of the optical power is used as signal light and enters the acousto-optic modulator 120 (AOM). The AOM (Analog Optical Module) is the core modulation device that, under the influence of an electrical drive signal, chops continuous laser light into pulsed laser light. The AOM's driving logic is strictly synchronized with the front-end optical switch, and the system timing can be configured as follows: a1. When the optical switch selects the online1 wavelength, the AOM is driven to generate a short pulse of 20 ns to achieve low blind zone detection; a2. When the optical switch first selects the offline wavelength, the AOM is driven to generate a short pulse of 20 ns, which generates differential absorption detection with the online wavelength; b1. When the optical switch selects the online2 wavelength, the AOM is driven to generate a long pulse of 800 ns to obtain narrow linewidth and high energy, which is suitable for long-distance detection; b2. When the optical switch selects the offline wavelength for the second time, the AOM is driven to generate a short pulse of 800 ns, which generates differential absorption detection with the online wavelength; The pulsed light sequence modulated by AOM is then sequentially amplified by a second-stage preamplifier 122 and a main amplifier 123 (using a thulium-doped fiber amplifier TDFA) for multi-stage power amplification, ultimately outputting a high-beam-quality pulsed laser (short pulse energy 10μJ, long pulse energy 200μJ).

[0074] (3) Optical transceiver antenna module 20; The high-energy pulsed laser output from the main amplifier 123 is connected to port one of the optical circulator 21 through an optical fiber, and output from port two to the transceiver telescope 22. After the laser beam is expanded and collimated by the transceiver telescope 22, it is emitted towards the atmospheric target area. Meanwhile, the backscattered echo signals generated by aerosols and molecules in the atmosphere are received by the same telescope, coupled into the optical fiber, and transmitted to port two of the optical circulator 21, and finally output from port three into the detection optical path.

[0075] (4) Signal detection module 30: The weak echo signal light output from port 3 of the optical circulator 21, together with the local oscillator light reserved in step (2) above, is input to a 2×2 and 50:50 fiber coupler 32, which interferes and mixes, and then splits into two output lights that are respectively incident on the balanced detector 31. The balanced detector 31 effectively suppresses the common mode noise of the local oscillator light through the differential amplifier circuit, and outputs a differential intermediate frequency electrical signal containing Doppler frequency shift and intensity information.

[0076] (5) Data acquisition and control module 40; The analog electrical signal output by the balanced detector 31 is connected to the acquisition module. The acquisition module has a built-in high-speed analog-to-digital converter (ADC, sampling rate 1 GSPS) to convert the analog signal into a digital signal; the subsequent signal processing unit (FPGA or host computer) performs a fast Fourier transform (FFT) on the digital signal and performs dual-channel parallel processing; as follows: a. Extract power spectrum data and, based on the wavelength (online1 / online2 / offline) and pulse width mode of the currently emitted laser pulse signal, invert the carbon dioxide concentration at different distance segments; b. Frequency shift extraction path (wind speed measurement): Extract the peak frequency shift (Doppler shift) of the FFT spectrum of the short pulse offline1 and the long pulse offline2, and invert the radial wind field of the entire path; c. Flux synthesis: The DSP module multiplies the concentration data with wind speed data that are strictly time-aligned within the same distance to output a high-precision, spatiotemporally mismatch-free three-dimensional CO2 flux profile.

[0077] Based on the above discussion, such as Figure 8 As shown, Figure 8 This is a schematic diagram of another framework structure of the CO2 detection system based on lidar provided in an embodiment of the present invention.

[0078] In one specific embodiment of the present invention, the lidar-based CO2 detection system may include: The multi-wavelength light source and modulation module 10 includes a seed laser 101, an IQ modulator 102, a high-speed signal generator 103, and a signal amplification module. The seed laser 101 is used to output a laser signal of a second wavelength; The high-speed signal generator 103 is used to drive the IQ modulator 102 to modulate the second wavelength laser signal into a first wavelength or a third wavelength laser signal. The signal amplification module includes a first-stage preamplifier 121, a second-stage preamplifier 122, and a main amplifier 123 connected in sequence; The optical transceiver antenna module 20 is used to output a first laser signal, a second laser signal, a third laser signal and a fourth laser signal to the detection space, and to receive laser echo signals; Signal detection module 30 is used to perform coherent heterodyne detection on each laser echo signal to obtain differential intermediate frequency electrical signal; The data acquisition and control module 40 is used to invert the differential intermediate frequency electrical signal to determine the first CO2 concentration within a preset near range and the second CO2 concentration within a preset far range, and to determine the CO2 concentration along the entire path of the detection space based on the first CO2 concentration and the second CO2 concentration.

[0079] Optionally, the IQ modulator can be a lithium niobate crystal modulator; the high-speed signal generator can be an AWG sequence generator.

[0080] and the above Figure 7 Unlike the embodiments shown, the multi-wavelength light source and modulation module 10 in this embodiment contains only one seed laser 101. By utilizing the electro-optic effect of lithium niobate (LiNbO3) crystal and high-speed radio frequency driving technology, the frequency of the single continuous wave laser output by the seed laser 101 is directly modulated, thereby realizing time-division multiplexing output of three wavelengths. Compared with the above scheme, using lithium niobate crystal for laser frequency modulation and pulse fast modulation eliminates the need for optical switching and AOM as well as two sets of lasers, reducing the complexity of the system.

[0081] Specifically, the sequence generator function of the AWG can be used to arrange the above basic laser pulses into a loop. A key parameter N (number of grouped pulses) needs to be set, which determines the wavelength switching rate of the switching optical switch 114. The target switching rate can be set to a 1kHz switching rate (switching rate of the switching optical switch), and the number of loops is calculated to be 10. The output laser signal sequence can then be as shown in Table 2.

[0082] Table 2

[0083] and the above Figure 7 Similar to the embodiments shown, in an optional implementation of this embodiment, a beam splitter 114 may be provided between the first-stage preamplifier 121 and the second-stage preamplifier 122; the input terminal of the beam splitter 114 is connected to the output terminal of the first-stage preamplifier 121; and the first output terminal of the beam splitter 114 is connected to the input terminal of the second-stage preamplifier 122. In addition, the optical transceiver antenna module 20 includes an optical circulator 21 and a transceiver combined telescope 22; The signal detection module 30 includes an optical fiber coupler 32 and a balanced detector 31; the first input end of the optical fiber coupler 32 is connected to the second output end of the optical splitter coupler 114; the second input end of the optical fiber coupler 32 is connected to the optical circulator 21; and the output end of the optical fiber coupler 32 is connected to the balanced detector 31.

[0084] In conjunction with the above embodiments, the working methods and principles of the primary preamplifier 121, secondary preamplifier 122, main amplifier 123, optical transceiver antenna module 20, data acquisition and control module 40, and other device modules in this embodiment are all the same as those described above. Figure 7 The embodiments shown are the same, and will not be described again in this embodiment.

[0085] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that the elements inherent in a process, method, article, or apparatus that includes a list of elements are included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Additionally, portions of the technical solutions provided in the embodiments of the present invention that are consistent with the implementation principles of corresponding technical solutions in the prior art have not been described in detail to avoid excessive elaboration.

[0086] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A method for CO2 detection based on a laser radar, characterized in that, include: A first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width are sequentially output into the detection space; wherein, the absorption rate of the laser light with the first wavelength, the second wavelength, and the third wavelength decreases sequentially; and the narrow pulse width is smaller than the long pulse width; Receive laser echo signals and perform coherent detection on each of the laser echo signals to obtain the differential intermediate frequency electrical signal corresponding to each of the laser echo signals; Differential absorption inversion operation is performed on the differential intermediate frequency electrical signals corresponding to the first laser signal and the second laser signal respectively to obtain the first CO2 concentration within a preset short distance range; Differential absorption inversion operation is performed on the differential intermediate frequency electrical signals corresponding to the third laser signal and the fourth laser signal respectively to obtain the second CO2 concentration within a preset long distance range; Based on the first CO2 concentration and the second CO2 concentration, determine the CO2 concentration along the entire path of the detection space; The first wavelength is located within the wavelength range corresponding to the absorption peak of the CO2 gas absorption line; the second wavelength is located within the wavelength range corresponding to the wing of the absorption peak of the CO2 gas absorption line; and the third wavelength is located within the wavelength range corresponding to the absorption valley of the CO2 gas absorption line. The narrow pulse width is 10ns~30ns, and the long pulse width is 600ns~800ns; and the pulse interval of the first laser signal, the second laser signal, the third laser signal and the fourth laser signal is 25μs~100μs; The duration of the output signals of the first laser signal, the second laser signal, the third laser signal, and the fourth laser signal is not less than 1ms.

2. The lidar-based CO2 detection method of claim 1, wherein, The first wavelength is from 2050.92nm to 2050.97nm, the second wavelength is from 2050.97nm to 2051.00nm, and the third wavelength is from 2051.00nm to 2051.10nm.

3. The CO2 detection method based on lidar as described in claim 1 or 2, characterized in that, After obtaining the first CO2 concentration and the second CO2 concentration, the process further includes: A fast Fourier transform is performed on the differential intermediate frequency electrical signal corresponding to the second laser signal to obtain the first power spectrum peak frequency corresponding to the second laser signal within the preset short-range range; A fast Fourier transform is performed on the differential intermediate frequency electrical signal corresponding to the fourth laser signal to obtain the second power spectrum peak frequency corresponding to the fourth laser signal within the preset long distance range; Based on the first power spectrum peak frequency, the second power spectrum peak frequency, and the radial wind field inversion formula Radial wind speed inversion calculations are performed to obtain the near-field radial wind speed within the preset near-distance range and the far-field radial wind speed within the preset far-distance range; wherein, Location point radial wind speed, The third wavelength, The peak frequency of the power spectrum. This refers to the intrinsic intermediate frequency; The near-field radial wind speed and the first CO2 concentration are multiplied respectively, and the far-field radial wind speed and the second CO2 concentration are multiplied to obtain the total path CO2 flux in the detection space.

4. A CO2 detection system based on lidar, characterized in that, include: A multi-wavelength light source and modulation module are used to generate a first laser signal with a first wavelength and a narrow pulse width, a second laser signal with a third wavelength and a narrow pulse width, a third laser signal with a second wavelength and a long pulse width, and a fourth laser signal with a third wavelength and a long pulse width. The absorption rate of the laser light with CO2 decreases sequentially from the first wavelength to the second wavelength and the third wavelength. The narrow pulse width is smaller than the long pulse width. The first wavelength is located within the wavelength range corresponding to the absorption peak of the CO2 gas absorption spectrum. The second wavelength is located within the wavelength range corresponding to the wing of the absorption peak of the CO2 gas absorption spectrum. The third wavelength is located within the wavelength range corresponding to the absorption valley of the CO2 gas absorption spectrum. The narrow pulse width is 10ns to 30ns, and the long pulse width is 600ns to 800ns. The pulse interval of the first, second, third, and fourth laser signals is 25μs to 100μs. The duration of the output signals of the first, second, third, and fourth laser signals is not less than 1ms. An optical transceiver antenna module is used to output the first laser signal, the second laser signal, the third laser signal and the fourth laser signal to the detection space, and to receive laser echo signals; The signal detection module is used to coherently detect each of the laser echo signals to obtain a differential intermediate frequency electrical signal; The data acquisition and control module is used to perform differential absorption inversion operation on the differential intermediate frequency electrical signal to obtain a first CO2 concentration within a preset near range and a second CO2 concentration within a preset far range, and to determine the CO2 concentration along the entire path of the detection space based on the first CO2 concentration and the second CO2 concentration.

5. The CO2 detection system based on lidar as described in claim 4, characterized in that, The multi-wavelength light source and modulation module include a multi-wavelength light source module and a pulse width modulation module; The multi-wavelength light source module includes a first seed laser for outputting a laser signal of a first wavelength, a second seed laser for outputting a laser signal of a second wavelength, a third seed laser for outputting a laser signal of a third wavelength, and a switching optical switch. The first, second, and third input terminals of the switching optical switch are respectively connected to the output terminals of the first seed laser, the second seed laser, and the third seed laser; the output terminal of the switching optical switch is connected to the input terminal of the pulse width modulation module. The pulse width modulation module includes a first-stage preamplifier, an acousto-optic modulator, a second-stage preamplifier, and a main amplifier connected in sequence. The acousto-optic modulator is used to modulate the laser signal of the first wavelength into a laser pulse with a narrow pulse width, modulate the laser signal of the second wavelength into a laser pulse with a long pulse width, and modulate the laser signal of the third wavelength into two different laser pulses with narrow and long pulse widths.

6. The CO2 detection system based on lidar as described in claim 4, characterized in that, The multi-wavelength light source and modulation module includes a seed laser, an IQ modulator, a high-speed signal generator, and a signal amplification module; The seed laser is used to output a laser signal of a second wavelength; The high-speed signal generator is used to drive the IQ modulator to modulate the second wavelength laser signal into a first wavelength or a third wavelength laser signal. The signal amplification module includes a first-stage preamplifier, a second-stage preamplifier, and a main amplifier connected in sequence.

7. The CO2 detection system based on lidar as described in claim 6, characterized in that, The IQ modulator is a lithium niobate crystal modulator; the high-speed signal generator is an AWG sequence generator.

8. The CO2 detection system based on lidar as described in claim 5 or 6, characterized in that, A beam splitter is provided between the first-stage preamplifier and the second-stage preamplifier; the input terminal of the beam splitter is connected to the output terminal of the first-stage preamplifier; the first output terminal of the beam splitter is connected to the input terminal of the second-stage preamplifier. The optical transceiver antenna module includes an optical circulator and a combined transceiver telescope; The signal detection module includes an optical fiber coupler and a balanced detector; the first input end of the optical fiber coupler is connected to the second output end of the optical splitter coupler; the second input end of the optical fiber coupler is connected to the optical circulator; and the output end of the optical fiber coupler is connected to the balanced detector.

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