Coherence-differential absorption laser radar capable of eliminating turbulence influence

Abstract

The invention discloses a coherent-differential absorption laser radar capable of eliminating turbulence influence. Comprising a first seed laser, a first optical fiber amplifier, a first acousto-optic modulator, a second seed laser, a second optical fiber amplifier, a second acousto-optic modulator, a first optical fiber beam combiner, an optical fiber circulator, a telescope, a second optical fiber beam combiner, a heterodyne detector, a first radio frequency filter, a first power detector, a second radio frequency filter and a second power detector. A data acquisition card and a signal generator. The coherent-differential absorption laser radar capable of eliminating the turbulence influence has the advantages that a gas absorption signal and an atmospheric background scattering signal can be synchronously measured, the influence of the atmospheric turbulence differential absorption laser radar is reduced or even eliminated, and then the gas molecule concentration measurement precision is improved.

Description

Technical Field

[0001] This invention relates to lidar technology, and more particularly to a coherent-differential absorption lidar that eliminates the effects of turbulence. Background Technology

[0002] A lidar (Light Detection and Ranging) system is a radar system that uses laser beams to detect the position, velocity, and other characteristics of a target. Lidar emits a laser beam towards the target, then compares the received signal (target echo) with the emitted signal. After appropriate processing, it can obtain relevant information about the target, such as its distance, azimuth, altitude, velocity, attitude, and even shape. This allows for the detection, tracking, and identification of targets such as aircraft and missiles. A lidar system consists of a laser transmitter, an optical receiver, a turntable, and an information processing system. The laser converts electrical pulses into light pulses and emits them. The optical receiver then converts the light pulses reflected from the target back into electrical pulses, which are then displayed on a monitor.

[0003] Laser differential absorption spectrometry (DAS) is primarily used to measure the concentration distribution of specific gases in the atmosphere. Based on the different absorption characteristics of different substances for specific wavelengths of light, DAS emits two laser pulses of different wavelengths and measures the difference between the returned signals from these two wavelengths to infer the concentration of the target gas. The two different wavelengths of laser pulses are: one wavelength that is strongly absorbed by the target gas (called the "online" wavelength), and the other wavelength that is almost not absorbed (called the "offline" wavelength).

[0004] In existing technologies, differential absorption lidar measures greenhouse gas concentrations by using two lasers with wavelengths located at the absorption peak and absorption wing region of gas molecules, respectively. The lasers are time-division multiplexed to emit absorption probe light and background probe light separately, and to measure the gas molecule absorption signal and atmospheric scattering background signal separately.

[0005] In recent years, to improve measurement sensitivity, differential absorption lidar has incorporated laser heterodyne technology, utilizing backscattered echoes and seed lasers coupled together—a process known as coherent-differential absorption lidar. By detecting the difference frequency signal intensity between the backscattered light and the seed laser, the accuracy of gas concentration detection can be further improved. Differential absorption lidar and coherent-differential absorption lidar offer advantages such as minimal environmental influence and good directivity.

[0006] Coherent-differential absorption lidar (CEL) determines the concentration of atmospheric absorbers by alternately measuring the absorption intensity of gas molecules and the atmospheric scattering background signal. However, during the measurement process, atmospheric turbulence causes random fluctuations and phase changes in the backscattered light intensity of the lidar, resulting in varying effects of atmospheric turbulence on the lidar echo signal at different times. Because CEL employs a time-division multiplexing method, the impact of atmospheric turbulence on the backscattered echo signal differs at different times. Therefore, the time-division measured echo signal cannot eliminate the influence of turbulence, limiting the measurement accuracy of CEL. Although the influence of atmospheric turbulence can be reduced through multiple averaging operations, it cannot be completely eliminated, further limiting the accuracy of gas concentration detection. Summary of the Invention

[0007] To overcome the shortcomings of the existing technologies, this invention provides a coherent-differential absorption lidar that eliminates the influence of turbulence, so as to simultaneously measure gas absorption signals and atmospheric background scattering signals, reduce or even eliminate the influence of atmospheric turbulence differential absorption lidar, and thus improve the accuracy of gas molecule concentration measurement.

[0008] The present invention adopts the following technical solution to solve the technical problem.

[0009] A coherent-differential absorption lidar for eliminating the effects of turbulence includes a first seed laser 1, a first fiber amplifier 2, a first acousto-optic modulator 3, a second seed laser 4, a second fiber amplifier 5, a second acousto-optic modulator 6, a first fiber combiner 7, a fiber optic circulator 8, a telescope 9, a second fiber combiner 10, a heterodyne detector 11, a first radio frequency filter 12, a first power detector 13, a second radio frequency filter 14, a second power detector 15, a data acquisition card 16, and a signal generator 17.

[0010] The laser beam emitted by the first seed laser 1 is divided into two paths. The first laser beam a1 is sent to the first fiber optic combiner 7 through the first fiber amplifier 2 and the first acousto-optic modulator 3 in sequence; the second laser beam b1 is input to the second fiber optic combiner 10.

[0011] The laser beam emitted by the second seed laser 4 is divided into two paths. The first laser beam a2 is sent to the first fiber optic combiner 7 through the second fiber amplifier 5 and the second acousto-optic modulator 6 in sequence; the second laser beam b2 is input to the second fiber optic combiner 10.

[0012] The first fiber optic combiner 7 receives the first laser beam a1 and the first laser beam a2, and sends the combined beam h1 to the fiber optic circulator 8; the combined beam h1 is then sent to the telescope 9 after passing through the fiber optic circulator 8; the telescope 9 receives the combined beam h1 sent by the fiber optic circulator 8 and returns the echo signal to the fiber optic circulator 8; the fiber optic circulator 8 receives the echo signal from the telescope 9 and sends it to the second fiber optic combiner 10.

[0013] The second fiber optic combiner 10 receives the echo signal from the telescope 9 sent by the fiber optic circulator 8, the second laser beam b1 sent by the first seed laser 1, and the second laser beam b2 sent by the second seed laser 4. After obtaining the second combined beam h2, it sends it to the heterodyne detector 11.

[0014] The output signal of the heterodyne detector 11 is divided into two outputs. The first output signal passes through the first radio frequency filter 12 and the first power detector 13 in sequence and is then input to the data acquisition card 16. The second output signal passes through the second radio frequency filter 14 and the second power detector 15 in sequence and is then input to the data acquisition card 16.

[0015] The data acquisition card 16 is also connected to the signal generator 17 and receives the trigger signal sent by the signal generator 17.

[0016] The structural features of the coherent-differential absorption lidar for eliminating turbulence effects of the present invention also lie in:

[0017] Furthermore, the first acousto-optic modulator 3 is also connected to the signal generator 17 and receives the trigger signal sent by the signal generator 17.

[0018] Furthermore, the second acousto-optic modulator 6 is also connected to the signal generator 17 and receives trigger signals sent by the signal generator 17.

[0019] Furthermore, the first fiber amplifier 2 and the second fiber amplifier 5 have the same output power.

[0020] Furthermore, the combining ratio of the first fiber combiner 7 is 50%:50%.

[0021] Furthermore, the frequency shift Δf1 of the first acousto-optic modulator 3 is less than the frequency shift Δf2 of the second acousto-optic modulator 6.

[0022] Furthermore, the center of the filtering bandwidth of the first RF filter 12 is the frequency shift amount Δf1 of the first acousto-optic modulator 3, and the upper sideband cutoff frequency of the first RF filter 12 is less than the frequency shift amount Δf2 of the second acousto-optic modulator 6.

[0023] Furthermore, the center of the filtering bandwidth of the second RF filter 14 is Δf2, and the lower sideband cutoff frequency of the second RF filter 14 is greater than the frequency shift amount Δf1 of the first acousto-optic modulator 3.

[0024] Furthermore, the performance specifications of the first power detector 13 and the second power detector 15 are the same.

[0025] Furthermore, the first acoustic-optic modulator 3, the second acoustic-optic modulator 6, and the data acquisition card 16 are synchronously controlled by the signal generator 17.

[0026] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0027] This invention discloses a coherent-differential absorption lidar for eliminating the effects of turbulence, comprising a first seed laser, a first fiber amplifier, a first acousto-optic modulator, a second seed laser, a second fiber amplifier, a second acousto-optic modulator, a first fiber combiner, a fiber circulator, a telescope, a second fiber combiner, a heterodyne detector, a first radio frequency filter, a first power detector, a second radio frequency filter, a second power detector, a data acquisition card, and a signal generator.

[0028] The coherent-differential absorption lidar of the present invention, which eliminates the influence of turbulence, can simultaneously measure gas absorption signals and atmospheric background scattering signals, thereby reducing or even eliminating the influence of atmospheric turbulence differential absorption lidar and improving the accuracy of gas molecule concentration measurement. Attached Figure Description

[0029] Figure 1 This is a structural block diagram of a coherent-differential absorption lidar for eliminating the effects of turbulence according to the present invention.

[0030] Figure 2 This is a schematic diagram of the echo signal of a coherent-differential absorption lidar for eliminating the effects of turbulence according to the present invention.

[0031] Figure 3 This is a schematic diagram of the heterodyne signal spectrum of a coherent-differential absorption lidar for eliminating the effects of turbulence according to the present invention.

[0032] Appendix Figure 1-3 The reference numerals in the attached figures are explained as follows: 1. First seed laser; 2. First fiber amplifier; 3. First acousto-optic modulator; 4. Second seed laser; 5. Second fiber amplifier; 6. Second acousto-optic modulator; 7. First fiber combiner; 8. Fiber circulator; 9. Transmitting and receiving telescope; 10. Second fiber combiner; 11. Heterodyne detector; 12. First radio frequency filter; 13. First power detector; 14. Second radio frequency filter; 15. Second power detector; 16. Data acquisition card.

[0033] The present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings. Detailed Implementation

[0034] See Figures 1-3 The present invention provides a coherent-differential absorption lidar for eliminating the effects of turbulence, comprising a first seed laser 1, a first fiber amplifier 2, a first acousto-optic modulator 3, a second seed laser 4, a second fiber amplifier 5, a second acousto-optic modulator 6, a first fiber combiner 7, a fiber optic circulator 8, a telescope 9, a second fiber combiner 10, a heterodyne detector 11, a first radio frequency filter 12, a first power detector 13, a second radio frequency filter 14, a second power detector 15, a data acquisition card 16, and a signal generator 17.

[0035] The laser beam emitted by the first seed laser 1 is divided into two paths. The first laser beam a1 is sent to the first fiber optic combiner 7 through the first fiber amplifier 2 and the first acousto-optic modulator 3 in sequence; the second laser beam b1 is input to the second fiber optic combiner 10.

[0036] The laser beam emitted by the second seed laser 4 is divided into two paths. The first laser beam a2 is sent to the first fiber optic combiner 7 through the second fiber amplifier 5 and the second acousto-optic modulator 6 in sequence; the second laser beam b2 is input to the second fiber optic combiner 10.

[0037] The first fiber optic combiner 7 receives the first laser beam a1 and the first laser beam a2, and sends the combined beam h1 to the fiber optic circulator 8; the combined beam h1 is then sent to the telescope 9 after passing through the fiber optic circulator 8; the telescope 9 receives the combined beam h1 sent by the fiber optic circulator 8 and returns the echo signal to the fiber optic circulator 8; the fiber optic circulator 8 receives the echo signal from the telescope 9 and sends it to the second fiber optic combiner 10.

[0038] The second fiber optic combiner 10 receives the echo signal from the telescope 9 sent by the fiber optic circulator 8, the first combined beam h1, the second laser beam b1 sent by the first seed laser 1, and the second laser beam b2 emitted by the second seed laser 4, and sends the second combined beam h2 to the heterodyne detector 11.

[0039] The output signal of the heterodyne detector 11 is divided into two outputs. The first output signal passes through the first radio frequency filter 12 and the first power detector 13 in sequence and is then input to the data acquisition card 16. The second output signal passes through the second radio frequency filter 14 and the second power detector 15 in sequence and is then input to the data acquisition card 16.

[0040] The data acquisition card 16 is also connected to the signal generator 17 and receives the trigger signal sent by the signal generator 17.

[0041] like Figure 1 This is a framework diagram of the verification process of a coherent-differential absorption lidar for eliminating the effects of turbulence according to the present invention. The laser beam output by the first seed laser 1 is split into two beams. The first laser beam a1 is input to the input end of the first fiber amplifier 2. The output end of the first fiber amplifier 2 is connected to the input end of the first acousto-optic modulator 3. The output end of the first acousto-optic modulator is connected to the first input port of the first fiber combiner 7.

[0042] The second laser beam b1 of the first seed laser 1 is input to the first input port of the second fiber combiner 10.

[0043] The laser beam output by the second seed laser 4 is divided into two beams. The first laser beam a2 of the second seed laser 4 is input to the input end of the second fiber amplifier 5. The first output port of the second seed laser 4 is connected to the second fiber amplifier 5. The output end of the second fiber amplifier is connected to the second acousto-optic modulator 6. The output end of the second acousto-optic modulator is connected to the second input port of the first fiber combiner 7.

[0044] The second laser beam b2 of the second seed laser 4 is input to the second input port of the second fiber combiner 10.

[0045] In specific implementation, the wavelength λ of the output laser beam of the first seed laser 1 on Located at the molecular absorption peak of the gas being measured. The wavelength λ of the laser beam output by the second seed laser 4. off Located in the molecular absorption wings region of the gas to be measured, such as Figure 2 As shown.

[0046] The output port of the first fiber optic combiner 7 is connected to the first port of the fiber optic circulator 8, and the second port of the fiber optic circulator is connected to the telescope 9, which is used to emit laser light and receive echo signals. The third port of the fiber optic circulator 8 is connected to the third input port of the second fiber optic combiner 10, and the output port of the optical combiner 10 is connected to the input port of the heterodyne detector 11.

[0047] The output port of the heterodyne detector 11 is connected to the input port of the first radio frequency filter 12, the output port of the first radio frequency filter 12 is connected to the input port of the first power detector 13, and the output port of the first power detector 13 is connected to the high-speed acquisition card 16.

[0048] The output port of the heterodyne detector 11 is also connected to the input port of the second radio frequency filter 14, the output port of the second radio frequency filter 14 is connected to the input port of the second power detector 15, and the output port of the second power detector 15 is connected to the high-speed acquisition card 16.

[0049] The first acousto-optic modulator 3, the second acousto-optic modulator 6, and the high-speed acquisition card 16 are synchronously controlled by the signal generator 17. When the signal generator 17 outputs a high level, the first acousto-optic modulator 3 and the second acousto-optic modulator 6 simultaneously output lasers, and the signal generator 17 outputs a trigger signal to the high-speed acquisition card 16, which then begins to acquire signals.

[0050] In specific implementation, the first acousto-optic modulator 3 is also connected to the signal generator 17 and receives the trigger signal sent by the signal generator 17.

[0051] In a specific implementation, the second acousto-optic modulator 6 is also connected to the signal generator 17 and receives the trigger signal sent by the signal generator 17.

[0052] The trigger signal generated by the signal generator 17 is sent to the first acoustic-optic modulator 3 and the second acoustic-optic modulator 6.

[0053] In practice, the first fiber amplifier 2 and the second fiber amplifier 5 have the same output power.

[0054] In specific implementation, the combining ratio of the first fiber optic combiner 7 is 50%:50%.

[0055] In specific implementation, the frequency shift Δf1 of the first acousto-optic modulator 3 is less than the frequency shift Δf2 of the second acousto-optic modulator 6.

[0056] In specific implementation, the difference between the frequency shift Δf1 of the first acousto-optic modulator 3 and the frequency shift Δf2 of the second acousto-optic modulator 6 is greater than 30MHz, so as to avoid mutual interference between the gas molecule absorption signal and the heterodyne signal generated by the first seed laser 1 and the atmospheric background scattering signal and the heterodyne signal generated by the second seed laser 4, that is, Δf2-Δf1>30MHz.

[0057] In specific implementation, the center of the filtering bandwidth of the first radio frequency filter 12 is the frequency shift amount Δf1 of the first acousto-optic modulator 3, and the upper sideband cutoff frequency of the first radio frequency filter 12 is less than the frequency shift amount Δf2 of the second acousto-optic modulator 6.

[0058] In specific implementation, the center of the filtering bandwidth of the second RF filter 14 is Δf2, and the lower sideband cutoff frequency of the second RF filter 14 is greater than the frequency shift amount Δf1 of the first acousto-optic modulator 3.

[0059] like Figure 3 In the middle, the first radio frequency filter is Figure 1 The first RF filter 12 and the second RF filter are... Figure 1 The second radio frequency filter 14 in the middle.

[0060] This invention provides a coherent-differential absorption lidar that eliminates the effects of turbulence, measuring gas concentration N by measuring molecular absorption signal power P. Son With atmospheric background scattering signal power P Soff The ratio is obtained as shown in the following formula (1);

[0061]

[0062] The difference frequency signal amplitude V output by the heterodyne detector 11 in the coherent differential absorption lidar on or V off Proportional to seed laser power P LO The power P of the echo signal received by the telescope Son or P Soff The coherence efficiency η between the seed laser and the echo signal:

[0063]

[0064] In formula (2), V on V represents the amplitude of the difference frequency signal between the molecular absorption signal and the laser beam emitted by the first seed laser 1. off η(t1) is the difference frequency signal amplitude between the atmospheric background scattering signal and the laser beam emitted by the second seed laser 4; the absorption signal is measured at time t1, and the atmospheric background scattering signal is measured at time t2; η(t1) is the coherence efficiency of the laser beam emitted by the first seed laser 1 and the echo signal of that laser beam measured at time t1, and η(t2) is the coherence efficiency of the laser beam emitted by the second seed laser 4 and the echo signal of that laser beam measured at time t1.

[0065] By V on With V off The ratio of the concentration of the gas to be measured in the atmosphere N can be obtained from the following formula (3);

[0066]

[0067] The echo signal received by the telescope is affected by atmospheric turbulence, and the polarization state and phase will change randomly. In the traditional coherent-differential absorption lidar measurement, time division multiplexing is used to measure molecular absorption signal and atmospheric background scattering signal. The absorption signal is measured at time t1 and the atmospheric background scattering signal is measured at time t2. The coherence efficiency is different at different times, that is, η(t1)≠η(t2), which leads to errors in the measured gas concentration N, as shown in the following formula (4);

[0068]

[0069] When using synchronous transmission λ on Laser and λ offLaser, simultaneously measuring the echo signals of two laser beams, i.e. t1=t2, η(t1)=η(t2), the gas concentration N measured in this way is shown in the following formula (5);

[0070]

[0071] In summary, synchronous measurement of the absorption signal and the atmospheric background scattering signal eliminates the gas concentration measurement error caused by the random variation in the heterodyne signal amplitude due to the random decoherence of the echo signal caused by atmospheric turbulence in the time-division multiplexing method.

[0072] In practice, the performance indicators of the first power detector 13 and the second power detector 15 are the same.

[0073] In practice, the first acoustic-optic modulator 3, the second acoustic-optic modulator 6, and the data acquisition card 16 are synchronously controlled by the signal generator 17.

[0074] The data acquisition card 16 used in this invention is a high-speed acquisition card with a sampling rate higher than 10MHz.

[0075] like Figure 1 The coherent-differential absorption lidar of this invention splits the laser beams output from two seed lasers into two beams. The first laser beam a1 is amplified and modulated using acousto-optic modulation, and the first laser beam a2 is frequency-shifted, amplified, and modulated using acousto-optic modulation. Both beams are then input to a first fiber combiner 7 to combine into a first combined beam h1. This combined beam h1 then passes through a fiber circulator 8, receives the echo signal from a telescope 9, and is input by the fiber circulator 8 to a second fiber combiner 10. There, it is combined again with the second laser beams b1 and b2 via the second fiber combiner 10 before being sent to a heterodyne detector 11. This invention simultaneously measures molecular absorption signals (…). Figure 1 The echo signal received by the telescope 9 and the atmospheric background scattering signal ( Figure 1 The method of eliminating the influence of atmospheric turbulence on the echo signal (received by the telescope 9) can solve the problems of asynchronous detection of absorption signal and background signal in existing differential absorption lidar, and inconsistent influence of atmospheric turbulence on molecular absorption signal and atmospheric background scattering signal.

[0076] The coherent-differential absorption lidar of the present invention can simultaneously measure gas absorption signals and atmospheric background scattering signals, which can reduce the influence of atmospheric turbulence differential absorption lidar and thus improve the accuracy of gas molecule concentration measurement.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A coherent-differential absorption lidar for eliminating the effects of turbulence, characterized in that, It includes a first seed laser (1), a first fiber amplifier (2), a first acousto-optic modulator (3), a second seed laser (4), a second fiber amplifier (5), a second acousto-optic modulator (6), a first fiber combiner (7), a fiber circulator (8), a telescope (9), a second fiber combiner (10), a heterodyne detector (11), a first radio frequency filter (12), a first power detector (13), a second radio frequency filter (14), a second power detector (15), a data acquisition card (16), and a signal generator (17); The laser beam emitted by the first seed laser (1) is divided into two paths. The first laser beam a1 is sent to the first fiber combiner (7) through the first fiber amplifier (2) and the first acousto-optic modulator (3) in sequence; the second laser beam b1 is input to the second fiber combiner (10). The laser beam emitted by the second seed laser (4) is divided into two paths. The first laser beam a2 is sent to the first fiber combiner (7) through the second fiber amplifier (5) and the second acousto-optic modulator (6) in sequence; the second laser beam b2 is input to the second fiber combiner (10). The first fiber combiner (7) receives the first laser beam a1 and the first laser beam a2 and sends the combined beam h1 to the fiber circulator (8); the combined beam h1 is sent to the telescope (9) after passing through the fiber circulator (8); the telescope (9) receives the combined beam h1 sent by the fiber circulator (8) and returns the echo signal to the fiber circulator (8); the fiber circulator (8) receives the echo signal from the telescope (9) and sends it to the second fiber combiner (10). The second fiber combiner (10) receives the echo signal from the telescope (9) sent by the fiber circulator (8), the second laser beam b1 sent by the first seed laser (1) and the second laser beam b2 sent by the second seed laser (4), and sends the second combined beam h2 to the heterodyne detector (11). The output signal of the heterodyne detector (11) is divided into two outputs. The first output signal passes through the first radio frequency filter (12) and the first power detector (13) in sequence and is then input to the data acquisition card (16). The second output signal passes through the second radio frequency filter (14) and the second power detector (15) in sequence and is then input to the data acquisition card (16). The data acquisition card (16) is also connected to the signal generator (17) and receives the trigger signal sent by the signal generator (17).

2. The coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The first acousto-optic modulator (3) is also connected to the signal generator (17) and receives the trigger signal sent by the signal generator (17).

3. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The second acousto-optic modulator (6) is also connected to the signal generator (17) and receives the trigger signal sent by the signal generator (17).

4. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The first fiber amplifier (2) and the second fiber amplifier (5) have the same output power.

5. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The first fiber combiner (7) has a combining ratio of 50%:50%.

6. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The frequency shift Δf1 of the first acousto-optic modulator (3) is less than the frequency shift Δf2 of the second acousto-optic modulator (6).

7. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The center of the filtering bandwidth of the first radio frequency filter (12) is the frequency shift Δf1 of the first acousto-optic modulator (3), and the upper sideband cutoff frequency of the first radio frequency filter (12) is less than the frequency shift Δf2 of the second acousto-optic modulator (6).

8. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The center of the filtering bandwidth of the second radio frequency filter (14) is Δf2, and the lower sideband cutoff frequency of the second radio frequency filter (14) is greater than the frequency shift amount Δf1 of the first acousto-optic modulator (3).

9. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The performance indicators of the first power detector (13) and the second power detector (15) are the same.

10. A coherent-differential absorption lidar for eliminating turbulence effects according to claim 1, characterized in that, The first acoustic-optic modulator (3), the second acoustic-optic modulator (6), and the data acquisition card (16) are synchronously controlled by the signal generator (17).

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