All-fiber lidar system for simultaneous measurement of atmospheric co2, ch4 concentrations and wind field

Abstract

The application discloses a kind of simultaneously measuring atmospheric carbon dioxide, methane concentration and wind field all-fiber laser radar system, system includes two carbon dioxide and methane detection light source unit, double-waveband multi-wavelength pulsed laser, circulator, optical transceiver telescope, photoelectric detection module and data acquisition processing module;Each light source unit contains two seed lasers, frequency stabilization module, optical switch, beam splitter and frequency shift module.Two unit outputs are emitted by telescope after frequency shift amplification, echo enters photoelectric detection module by circulator, is detected after being split respectively with local light coherent mixing, finally by data acquisition processing module synchronous inversion carbon dioxide and methane concentration profile and three-dimensional wind field.The application adopts differential absorption and coherent detection cooperation, realizes two kinds of greenhouse gas concentration and wind field synchronous measurement, with distance resolution capability, can be used for carbon emission flux evaluation, and all-fiber structure improves stability.

Description

Technical Field

[0001] This invention belongs to the field of lidar atmospheric remote sensing technology, specifically relating to an all-fiber lidar system that simultaneously measures atmospheric carbon dioxide, methane concentrations and wind fields, and is particularly suitable for high-precision, high spatiotemporal resolution remote sensing monitoring of low-altitude atmospheric carbon emission flux. Technical Background In recent years, the excessive combustion of fossil fuels such as coal, oil, and natural gas has led to massive emissions of greenhouse gases such as CO2 and CH4. Global warming and rising sea levels have made people increasingly aware of the importance of reducing greenhouse gas emissions. Therefore, studying the concentrations of atmospheric carbon dioxide and methane is crucial for researching the global carbon cycle and predicting future global climate change. To estimate carbon emissions, meteorological wind speed data needs to be acquired simultaneously with concentration data. Remote sensing technology, which simultaneously measures carbon dioxide and wind fields in three dimensions, is an important requirement for environmental protection departments and is of great significance for the detection and assessment of carbon emissions.

[0002] Differential absorption lidar (DIAL) and integral path differential absorption lidar (IPDA) are currently the most mature active detection technologies. IPDA technology can only measure the concentration of atmospheric greenhouse gases along the laser transmission path and cannot obtain distance-resolved concentration information. In contrast, DIAL technology has distance-resolved capabilities, enabling it to obtain greenhouse gas concentrations at different locations along the laser transmission path, and is suitable for measuring both methane and carbon dioxide.

[0003] In wind field measurement, coherent Doppler wind lidar (CDWL) uses the optical Doppler frequency shift effect to measure radial wind speed, and has advantages such as high spatiotemporal resolution, high measurement accuracy, high detection sensitivity, and good stability. In recent years, all-fiber coherent wind lidar systems have been widely used in low-altitude three-dimensional wind field detection. The emergence of new technologies such as the dual-pulse differential algorithm has further improved the spatial resolution of wind field detection to the meter level. However, traditional wind lidar systems are typically only used for wind field measurement and have not been integrated with greenhouse gas concentration detection capabilities.

[0004] In terms of system architecture, all-fiber lidar systems use optical fibers to connect various components, offering advantages over traditional space optical systems such as strong anti-interference capabilities, compact structure, high stability, ease of miniaturization, and cost reduction. Current research has explored CO2 profile detection lidars based on an all-fiber integrated architecture, as well as all-fiber multifunctional CO2 lidars integrating single-photon and coherent detection. However, a single all-fiber DIAL lidar system capable of simultaneously detecting CO2 concentration, CH4 concentration, and three-dimensional wind field within a single system is still lacking.

[0005] In summary, the current lidar field faces the following technical challenges: First, there is a lack of single systems capable of simultaneously detecting both CO2 and CH4, two major greenhouse gases, with range resolution; second, greenhouse gas concentration detection and wind field measurement are usually performed by independent systems, making it difficult to achieve synchronous and coordinated monitoring of carbon emission flux; and third, most systems employ spatial optical structures, whose stability and integration need improvement. This invention addresses these problems by proposing an all-fiber lidar system that simultaneously measures atmospheric carbon dioxide and methane concentrations and wind field. Summary of the Invention

[0006] The purpose of this invention is to address the technical shortcomings of existing lidar systems, which typically can only detect a single greenhouse gas, lack distance resolution, cannot simultaneously acquire three-dimensional wind field information, and suffer from insufficient stability due to the use of spatial optical structures. This invention proposes an all-fiber lidar system that simultaneously measures atmospheric carbon dioxide and methane concentrations and wind fields. Based on the synergistic working principle of differential absorption (DIAL) and coherent detection, this system utilizes a single pulsed laser capable of simultaneously outputting two bands (1572 nm and 1645 nm) and four wavelengths. Combined with an all-fiber architecture and high-precision frequency stabilization technology, it achieves synchronous, high-precision, and distance-resolved measurements of CO2 and CH4 concentration profiles and three-dimensional wind fields, thereby supporting the quantitative assessment of atmospheric carbon emission flux and methane emission flux.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows: A full-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind field, the system comprising: a carbon dioxide detection light source unit, a methane detection light source unit, a dual-band multi-wavelength pulsed laser, a circulator, an optical transceiver telescope, a photoelectric detection module, and a data acquisition and processing module.

[0008] The carbon dioxide detection light source unit includes a first seed laser emitting 1572.024 nm seed light, a second seed laser emitting 1572.085 nm seed light, a first laser frequency stabilization module for stabilizing the 1572.024 nm and 1572.085 nm seed light, a first optical switch, a first beam splitter, and a first frequency shifting module. The methane detection light source unit includes a third seed laser emitting 1645.552 nm seed light, a fourth seed laser emitting 1645.807 nm seed light, a second laser frequency stabilization module for stabilizing the 1645.552 nm and 1645.807 nm seed light, a second optical switch, a second beam splitter, and a second frequency shifting module.

[0009] The output terminals of the first seed laser and the second seed laser are respectively connected to the input terminal of the first laser frequency stabilization module. The output terminal of the first laser frequency stabilization module is connected to the two input terminals of the first optical switch. The output terminal of the first optical switch is connected to the input terminal of the first beam splitter. The first output terminal of the first beam splitter is connected to the input terminal of the first frequency shifting module. The second output terminal of the first beam splitter is connected as the local oscillator output terminal to the first local oscillator input terminal of the photodetector module. The output terminal of the first frequency shifting module is connected to the first input terminal of the dual-band multi-wavelength pulsed laser.

[0010] The outputs of the third and fourth seed lasers are respectively connected to the input of the second laser frequency stabilization module. The output of the second laser frequency stabilization module is connected to the two inputs of the second optical switch. The output of the second optical switch is connected to the input of the second beam splitter. The first output of the second beam splitter is connected to the input of the second frequency shifting module. The second output of the second beam splitter is connected as the local oscillator output to the second local oscillator input of the photodetector module. The output of the second frequency shifting module is connected to the second input of the dual-band multi-wavelength pulsed laser.

[0011] The dual-band multi-wavelength pulsed laser is used to amplify the frequency-shifted 1572 nm and 1645 nm seed light into pulses, and simultaneously output pulsed lasers in both 1572 nm and 1645 nm bands. The output of the dual-band multi-wavelength pulsed laser is connected to the first port of the circulator via an optical fiber. The second port of the circulator is connected to the optical transceiver telescope via an optical fiber. The optical transceiver telescope is used to emit the received pulsed laser into the atmosphere and receive the atmospheric backscattered echo signal. The third port of the circulator is connected to the total signal input of the photoelectric detection module via an optical fiber.

[0012] The photoelectric detection module includes a wavelength division multiplexer, a first coupler, a second coupler, a first detector, and a second detector. The input terminal of the wavelength division multiplexer serves as the overall signal input terminal of the photoelectric detection module and is connected to the third port of the circulator. The first output terminal of the wavelength division multiplexer is connected to the first input terminal of the first coupler, the second input terminal of the first coupler is connected to the second output terminal of the first beam splitter, and the output terminal of the first coupler is connected to the input terminal of the first detector. The second output terminal of the wavelength division multiplexer is connected to the first input terminal of the second coupler, the second input terminal of the second coupler is connected to the second output terminal of the second beam splitter, and the output terminal of the second coupler is connected to the input terminal of the second detector.

[0013] The first input terminal of the data acquisition and processing module is electrically connected to the output terminal of the first detector, and the second input terminal of the data acquisition and processing module is electrically connected to the output terminal of the second detector.

[0014] The working process and principle of the system of this invention are as follows: In the carbon dioxide detection channel, the first and second seed lasers emit continuous seed light at 1572.024 nm and 1572.085 nm, respectively. After being frequency-stabilized by the first laser frequency stabilization module, the first optical switch alternately selects the output at a preset frequency, realizing rapid switching between the online wavelength (1572.024 nm) and the offline wavelength (1572.085 nm). The alternately output seed light is split into two beams by the first beam splitter: one beam is directly input to the first coupler of the photoelectric detection module as the 1572 nm local oscillator light; the other beam is input to the first frequency shift module, which modulates the continuous seed light into pulse light and generates a fixed frequency shift, and then sends it to the first input terminal of the dual-band multi-wavelength pulse laser for power amplification.

[0015] In the methane detection channel, the third and fourth seed lasers emit continuous seed light at 1645.552 nm and 1645.807 nm, respectively. After being frequency-stabilized by the second laser frequency stabilization module, the second optical switch alternately selects the output at a preset frequency, achieving rapid switching between the online wavelength (1645.552 nm) and the offline wavelength (1645.807 nm). The alternately output seed light is split into two beams by the second beam splitter: one beam is directly input to the second coupler of the photodetector module as a 1645 nm local oscillator; the other beam is input to the second frequency shift module, which modulates the continuous seed light into pulse light and generates a fixed frequency shift, and then sends it to the second input terminal of the dual-band multi-wavelength pulsed laser for power amplification.

[0016] To ensure that the echo signals of the two bands do not interfere with each other, the switching timing of the first optical switch and the second optical switch is staggered, so that the emission times of the 1572 nm band pulsed laser and the 1645 nm band pulsed laser are staggered, forming a time-division multiplexed emission mode.

[0017] The 1572 nm and 1645 nm dual-band pulsed laser, amplified by the dual-band multi-wavelength pulsed laser, is input from the output end of the pulsed laser through the first port of the circulator, and output from the second port of the circulator to the optical transceiver telescope. After being collimated and expanded by the optical transceiver telescope, it is emitted into the atmosphere.

[0018] During atmospheric transmission, the emitted pulsed laser undergoes selective absorption by CO2 and CH4 molecules, as well as backscattering by atmospheric aerosols and molecules. The dual-band backscattered echo signal, carrying gas absorption information and Doppler frequency shift information, is received by the optical transceiver telescope, input through the second port of the circulator, output through the third port, and sent to the wavelength division multiplexer of the photoelectric detection module.

[0019] The wavelength division multiplexer separates the received echo signal, which includes both 1572 nm and 1645 nm wavelengths, into two paths: a 1572 nm echo signal and a 1645 nm echo signal. The 1572 nm echo signal enters the first coupler and undergoes coherent mixing with the 1572 nm local oscillator light from the first beam splitter, generating a first beat frequency signal carrying Doppler frequency shift information. This first beat frequency signal is detected by the first detector, converted into an electrical signal, and then sent to the data acquisition and processing module. The 1645 nm echo signal enters the second coupler and undergoes coherent mixing with the 1645 nm local oscillator light from the second beam splitter, generating a second beat frequency signal. This second beat frequency signal is detected by the second detector, converted into an electrical signal, and then sent to the data acquisition and processing module.

[0020] The data acquisition and processing module synchronously acquires the first and second beat frequency signals. It obtains the power spectrum by performing a Fourier transform on the beat frequency signals, calculates the Doppler frequency shift based on the peak frequency of the power spectrum, and inverts the radial wind speed. It then inverts the carbon dioxide concentration profile and methane concentration profile based on the peak amplitude of the power spectrum and the differential absorption lidar equation. Finally, it calculates the atmospheric carbon dioxide emission flux and methane emission flux based on the inverted carbon dioxide concentration profile, methane concentration profile, and three-dimensional wind field distribution.

[0021] As a further preferred embodiment of the technical solution of the present invention, the splitting ratio of the first beam splitter and the second beam splitter is 90:10, wherein 90% of the optical energy is used as probe light input to the corresponding frequency shift module, and 10% of the optical energy is used as local oscillator light input to the corresponding coupler, so as to provide sufficient local oscillator power while ensuring the strength of the probe signal.

[0022] As a further preferred embodiment of the technical solution of the present invention, both the first frequency shift module and the second frequency shift module are acousto-optic modulators, used to modulate the input continuous seed light into pulse light and generate a fixed frequency offset, so that a stable intermediate frequency beat frequency signal is formed between the echo signal and the local oscillator light, which facilitates coherent detection.

[0023] As a further preferred embodiment of the technical solution of the present invention, both the first detector and the second detector are InGaAs dual-balanced detectors to improve the common-mode rejection ratio and signal-to-noise ratio of coherent detection.

[0024] As a further preferred embodiment of the technical solution of the present invention, the data acquisition and processing module includes a high-speed acquisition card and a digital signal processor.

[0025] As a further preferred embodiment of the technical solution of the present invention, all optical devices in the system are connected through polarization-maintaining single-mode optical fibers to form an all-fiber integrated system architecture, thereby improving system stability and environmental adaptability.

[0026] As a further preferred embodiment of the technical solution of the present invention, both the first laser frequency stabilization module and the second laser frequency stabilization module adopt wavelength modulation spectroscopy technology to lock the seed laser frequency of the corresponding wavelength to the center frequency of the absorption line of the target gas molecule, with a frequency stabilization accuracy better than ±1 MHz, ensuring the wavelength accuracy requirements of DIAL measurement.

[0027] As a further preferred embodiment of the technical solution of the present invention, the optical transceiver telescope is an off-axis Cassegrain reflecting telescope with an effective aperture of 200 mm, an emitted laser divergence angle of less than 0.1 mrad, and a receiving field of view range of 0.1 mrad to 1 mrad.

[0028] As a further preferred embodiment of the technical solution of the present invention, the optical transceiver telescope has a two-dimensional scanning function, which performs conical scanning in the azimuth and elevation directions and synthesizes a three-dimensional spatial wind field vector by combining multi-angle radial wind speed data.

[0029] Compared with the prior art, the present invention has the following beneficial effects: This invention uses differential absorption lidar technology. The dual-band multi-wavelength pulsed laser can simultaneously and independently output laser light in two bands (1572 nm and 1645 nm) and four wavelengths. It can also achieve rapid switching between online and offline wavelengths of 1572 nm and 1645 nm, and has distance resolution capability, enabling simultaneous measurement of atmospheric carbon dioxide and methane concentrations.

[0030] This invention uses coherent wind lidar technology to achieve real-time detection of atmospheric three-dimensional wind fields with high spatiotemporal resolution and high stability. The system can detect and assess carbon emissions by simultaneously measuring wind fields and atmospheric carbon dioxide concentration.

[0031] The all-fiber lidar system of this invention has strong anti-interference capabilities and is conducive to miniaturization and cost reduction, making it a better choice for civilian and commercial equipment.

[0032] This invention integrates atmospheric carbon dioxide, methane, and wind field detection systems, enabling simultaneous measurement of two major greenhouse gases and wind field information, and possesses distance resolution capability, thus better meeting the needs of greenhouse gas monitoring and carbon emission detection and assessment. Attached Figure Description

[0033] Figure 1 This is a block diagram of the overall structure of the all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind fields according to the present invention.

[0034] Figure 2 This is a structural block diagram of the photoelectric detection module of the all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field, as described in this invention.

[0035] In the diagram: 1—1572.024 nm seed laser, 2—1572.085 nm seed laser, 3—1572 nm laser frequency stabilization module, 4—optical switch, 5—first beam splitter, 6—frequency shifting module, 7—1645.552 nm seed laser, 8—1645.807 nm seed laser, 9—1645 nm laser frequency stabilization module, 10—optical switch, 11—second beam splitter, 12—frequency shifting module, 13—dual-band multi-wavelength pulsed laser, 14—circulator, 15—optical transceiver telescope, 16—photoelectric detection module, 16-1—wavelength division multiplexer, 16-2—first coupler, 16-3—second coupler, 16-4—first detector, 16-5—second detector, 17—data acquisition and processing module. Detailed Implementation

[0036] The following examples and appendices Figure 1 Appendix Figure 2 The specific technical solutions in this invention are described in detail. The technical solutions and parameters described in this invention are only a part of this invention and do not represent all embodiments. All other embodiments based on this invention are within the protection scope of this invention without creative improvements or inventions.

[0037] Please see Figure 1 , Figure 1 This is a block diagram of the overall structure of the all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind field, as described in this invention. Figure 1 As shown, an all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind field includes a 1572.024 nm seed laser 1, a 1572.085 nm seed laser 2, a 1572 nm laser frequency stabilization module 3, an optical switch 4, a first beam splitter 5, a frequency shifting module 6, a 1645.552 nm seed laser 7, a 1645.807 nm seed laser 8, a 1645 nm laser frequency stabilization module 9, an optical switch 10, a second beam splitter 11, a frequency shifting module 12, a dual-band multi-wavelength pulsed laser 13, a circulator 14, an optical transceiver telescope 15, a photoelectric detection module 16, and a data acquisition and processing module 17. The internal structure of the photoelectric detection module 16 is as follows: Figure 2As shown, it specifically includes a wavelength division multiplexer 16-1, a first coupler 16-2, a second coupler 16-3, a first detector 16-4, and a second detector 16-5.

[0038] In this embodiment, all optical devices are connected via polarization-maintaining single-mode optical fibers to form an all-fiber system.

[0039] The 1572.024 nm seed laser 1 emits 1572.024 nm seed light as an online signal for atmospheric carbon dioxide detection, and the 1572.085 nm seed laser 2 emits 1572.085 nm seed light as an offline signal for atmospheric carbon dioxide detection. The 1572 nm laser frequency stabilization module 3 performs frequency stabilization processing on the online and offline lasers. The online and offline seed lights are alternately output through the optical switch 4 and split into two beams after passing through the beam splitter 5. One beam is used as the local oscillator light and enters the photoelectric detection module 16, while the other beam undergoes frequency shifting through the frequency shifting module 6. The frequency shifting module 6 is connected to the dual-band multi-wavelength pulsed laser 13 via optical fiber. The 1572 nm beam emitted by the dual-band multi-wavelength pulsed laser 13 passes sequentially through the circulator 14 and the optical transceiver telescope 15 into the atmosphere. After atmospheric scattering, the 1572 nm light... The nm echo signal is received by the optical transceiver telescope 15, passes through the circulator 14 and enters the photoelectric detection module 16. The output of the photoelectric detection module 16 is connected to the input of the data acquisition and processing module 17.

[0040] The 1645.552 nm seed laser 7 emits 1645.552 nm seed light as an online signal for atmospheric methane detection, and the 1645.807 nm seed laser 8 emits 1645.807 nm seed light as an offline signal for atmospheric methane detection. The 1645 nm laser frequency stabilization module 9 performs frequency stabilization processing on the online and offline lasers. The online and offline seed lights are alternately output through the optical switch 10 and split into two beams after passing through the beam splitter 11. One beam is used as the local oscillator light and enters the photoelectric detection module 16, while the other beam undergoes frequency shifting through the frequency shifting module 12. The frequency shifting module 12 is connected to the dual-band multi-wavelength pulsed laser 13 via optical fiber. The 1645 nm beam emitted by the dual-band multi-wavelength pulsed laser 13 passes sequentially through the circulator 14 and the optical transceiver telescope 15 into the atmosphere. After atmospheric scattering, the 1645 nm light... The nm echo signal is received by the optical transceiver telescope 15, passes through the circulator 14 and enters the photoelectric detection module 16. The output of the photoelectric detection module 16 is connected to the input of the data acquisition and processing module 17.

[0041] In the photoelectric detection module 16, the 1572 nm and 1645 nm echo signals that enter the photoelectric detection module 16 after passing through the circulator 14 are split into two beams of light, 1572 nm and 1645 nm, by the wavelength division multiplexer 16-1. The 1572 nm echo signal and the 1572 nm local oscillator light output from the beam splitter 5 enter the coupler 16-2 to generate a beat frequency signal, which is detected by the detector 16-4. At the same time, the 1645 nm echo signal split by the wavelength division multiplexer 16-1 and the 1645 nm local oscillator light output from the beam splitter 11 enter the coupler 16-3 to generate a beat frequency signal, which is detected by the detector 16-5.

[0042] Below is a specific device used in an example: The frequency shift module 5 and frequency shift module 12 are acousto-optic modulators; the beam splitter 8 and beam splitter 11 are beam splitters with a splitting ratio of 9:1; the digital acquisition and processing module 17 includes an acquisition card and a data preprocessing module; and the detectors 16-4 and 16-5 are InGaAs dual-balanced detectors.

[0043] The specific process of the all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind field in this invention is as follows: Frequency is The 1572 nm seed light is split into two beams with a 9:1 ratio by the beam splitter 5, with 90% of the beam used as a detection signal and then generated by the frequency shift module 6. The frequency shift, after being amplified by the dual-band multi-wavelength pulsed laser 13, passed through the circulator 14 and the optical transceiver telescope 15, enters the atmosphere for detection. The echo signal, after being reflected by the atmosphere, returns to the optical transceiver telescope 15, resulting in a Doppler frequency shift. The light is emitted through the circulator 14 and then into the photodetector module 16. Another 10% of the 1572 nm seed light, acting as the local oscillator signal, enters the photodetector module 16 and generates a beat frequency with the 1572 nm echo signal at coupler 16-2. The digital acquisition and processing module 17 performs a Fourier transform on the measured beat frequency signal to obtain the power spectrum, and then calculates the Doppler frequency shift at the offline wavelength. The wind speed calculated from this is The power spectral amplitudes of different distance gates corresponding to online and offline wavelengths are obtained based on the power spectrum. , , , The distance-resolved carbon dioxide concentration can be calculated as follows: Where R is the detection distance, The distance gate length used in calculating the power spectrum is proportional to the laser pulse width. This represents the difference in absorption cross-section between carbon dioxide molecules and online and offline wavelength light beams.

[0044] The 1645 nm seed light is split into two beams with a 9:1 ratio by the beam splitter 11, with 90% of the beam used as a detection signal and generated by the frequency shift module 12. The frequency shift of the light, after being amplified by the dual-band multi-wavelength pulsed laser 13, passed through the circulator 14 and the optical transceiver telescope 15, enters the atmosphere for detection. The echo signal, after atmospheric reflection, returns to the optical transceiver telescope 15 and the circulator 14 and enters the photoelectric detection module 16. Another 10% of the 1645 nm seed light, as the local oscillator signal, enters the photoelectric detection module 16 and generates a beat frequency with the 1645 nm echo signal at the coupler 16-3. The digital acquisition and processing module 17 performs a Fourier transform on the measured beat frequency signal to obtain the power spectrum, and then obtains the power spectrum amplitude of different distance gates corresponding to the online and offline wavelengths. , , , The distance-resolved methane concentration was calculated to be... Where r is the detection distance, The distance gate length used in calculating the power spectrum is proportional to the laser pulse width. This represents the difference in absorption cross-section of methane molecules for online and offline wavelength light beams.

[0045] Furthermore, the two-band fiber amplification links integrated within the dual-band multi-wavelength pulsed laser 13 can independently control their respective gains and pulse timing. Therefore, the system of the present invention can not only operate in the aforementioned time-division multiplexing mode, but can also switch to a single-band operating mode (i.e., only detecting CO2 or only detecting CH4) in specific application scenarios to simplify system operation and data processing.

[0046] In summary, the specific implementation of the all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind fields provided by this invention achieves high-precision, high-spatial-resolution synchronous measurement of atmospheric CO2 concentration profiles, CH4 concentration profiles, and three-dimensional wind fields through dual-band multi-wavelength seed light sources, all-fiber pulse amplification and transmission, coherent mixing reception, digital signal processing, and combined inversion with differential absorption and Doppler frequency shift. Those skilled in the art can build and operate the system of this invention without creative effort based on the description and drawings in this specification. All equivalent transformations or substitutions based on the concept of this invention fall within the protection scope of this invention.

Claims

1. A full-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentrations, and wind field, characterized in that, include: The carbon dioxide detection light source unit includes a first seed laser (1) that emits 1572.024 nm seed light, a second seed laser (2) that emits 1572.085 nm seed light, a first laser frequency stabilization module (3) that performs frequency stabilization processing on the 1572.024 nm and 1572.085 nm seed light, a first optical switch (4), a first beam splitter (5), and a first frequency shifting module (6). The methane detection light source unit includes a third seed laser (7) that emits 1645.552 nm seed light, a fourth seed laser (8) that emits 1645.807 nm seed light, a second laser frequency stabilization module (9) that performs frequency stabilization processing on the 1645.552 nm and 1645.807 nm seed light, a second optical switch (10), a second beam splitter (11), and a second frequency shifting module (12). A dual-band multi-wavelength pulsed laser (13) has its input end connected to the first frequency shift module (6) and the second frequency shift module (12) respectively via optical fiber. It is used to pulse amplify the frequency-shifted 1572 nm seed light and 1645 nm seed light respectively, and simultaneously output pulsed lasers in two bands of 1572 nm and 1645 nm. The first port of the circulator (14) is connected to the output of the dual-band multi-wavelength pulsed laser (13) via an optical fiber. An optical transceiver telescope (15) is connected to the second port of the circulator (14) via an optical fiber, for transmitting the received pulsed laser to the atmosphere and receiving the atmospheric backscattered echo signal; The photoelectric detection module (16) has its input end connected to the third port of the circulator (14) via optical fiber. The photoelectric detection module (16) includes a wavelength division multiplexer (16-1), a first coupler (16-2), a second coupler (16-3), a first detector (16-4), and a second detector (16-5). The data acquisition and processing module (17) has its input terminals electrically connected to the output terminals of the first detector (16-4) and the second detector (16-5), respectively. The first beam splitter (5) is used to split the 1572 nm seed light alternately output by the first optical switch (4) into two beams, one of which is input as 1572 nm local oscillator light to the first coupler (16-2), and the other beam is input to the first frequency shift module (6); the second beam splitter (11) is used to split the 1645 nm seed light alternately output by the second optical switch (10) into two beams, one of which is input as 1645 nm local oscillator light to the second coupler (16-3), and the other beam is input to the second frequency shift module (12). The wavelength division multiplexer (16-1) is used to separate the echo signal containing 1572 nm and 1645 nm dual bands input to the third port of the circulator (14) into a 1572 nm echo signal and a 1645 nm echo signal. The first coupler (16-2) is used to coherently mix the 1572 nm echo signal with the 1572 nm local oscillator light to generate a first beat frequency signal, and the first detector (16-4) is used to detect the first beat frequency signal. The second coupler (16-3) is used to coherently mix the 1645 nm echo signal with the 1645 nm local oscillator light to generate a second beat frequency signal, and the second detector (16-5) is used to detect the second beat frequency signal. The data acquisition and processing module (17) is used to synchronously acquire the first beat frequency signal and the second beat frequency signal, and invert the atmospheric carbon dioxide concentration profile and radial wind speed according to the first beat frequency signal, and invert the atmospheric methane concentration profile and radial wind speed according to the second beat frequency signal, thereby synthesizing a three-dimensional wind field distribution.

2. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, The dual-band multi-wavelength pulsed laser (13) simultaneously outputs pulsed lasers in two bands: 1572 nm and 1645 nm. The 1572 nm band includes two wavelengths: 1572.024 nm and 1572.085 nm, and the 1645 nm band includes two wavelengths: 1645.552 nm and 1645.807 nm.

3. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, The first optical switch (4) alternately outputs seed light at a preset frequency of 1572.024 nm and 1572.085 nm, and the second optical switch (10) alternately outputs seed light at a preset frequency of 1645.552 nm and 1645.807 nm, thereby realizing rapid switching between online and offline wavelengths.

4. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 3, characterized in that, The switching timing of the first optical switch (4) and the second optical switch (10) is staggered so that the emission times of the 1572 nm band pulsed laser and the 1645 nm band pulsed laser are staggered.

5. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, The splitting ratio of the first beam splitter (5) and the second beam splitter (11) is 90:10, where 90% of the light energy is used as probe light input to the corresponding frequency shift module and 10% of the light energy is used as local oscillator light input to the corresponding coupler.

6. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, Both the first frequency shift module (6) and the second frequency shift module (12) are acousto-optic modulators, used to modulate the input continuous seed light into pulse light and generate a fixed frequency shift.

7. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, Both the first detector (16-4) and the second detector (16-5) are InGaAs dual-balanced detectors.

8. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, The data acquisition and processing module (17) includes a high-speed acquisition card and a digital signal processor. The digital signal processor is used to perform Fourier transform on the acquired beat frequency signal to obtain the power spectrum, calculate the Doppler frequency shift and invert the radial wind speed based on the peak frequency of the power spectrum, and invert the carbon dioxide concentration profile and methane concentration profile based on the peak amplitude of the power spectrum combined with the differential absorption lidar equation.

9. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 8, characterized in that, The data acquisition and processing module (17) is also used to calculate atmospheric carbon dioxide emission flux and methane emission flux based on the carbon dioxide concentration profile, methane concentration profile and three-dimensional wind field distribution obtained by inversion.

10. The all-fiber lidar system for simultaneously measuring atmospheric carbon dioxide, methane concentration, and wind field according to claim 1, characterized in that, Both the first laser frequency stabilization module (3) and the second laser frequency stabilization module (9) adopt wavelength modulation spectroscopy technology to lock the seed laser frequency of the corresponding wavelength to the center frequency of the target gas molecule absorption line, with a frequency stabilization accuracy better than ±1 MHz.

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