Laser radar system and method for detecting lower troposphere temperature profile based on echo coherence degree

Abstract

The invention relates to the technical field of laser atmosphere detection, and discloses a laser radar system for detecting a lower troposphere temperature profile based on echo coherence degree, which comprises a laser device and a telescope shared by receiving and transmitting, and is characterized in that the laser device at least comprises a multimode optical fiber coupler and a narrow-band optical filter; two interferometers with an optical path difference are arranged at the receiving optical rear end of the laser, and atmosphere back scattering echoes received by the telescope are transmitted to the narrow-band optical filter through the multimode optical fiber coupler and then enter the interferometers to obtain emitted laser pulses; the multimode optical fiber coupler sends laser pulses to the interferometer, and collected backscattered and emitted laser samples are coherent through four channels of the interferometer and then are detected as electric signals through the multiplication photodiode.

Description

Technical Field

[0001] The present invention relates to the technical field of laser atmospheric detection, and more specifically to a laser radar system and method for detecting the temperature profile of the lower troposphere based on echo coherence. Background Art

[0002] The renewal of the ground-based meteorological observation network has become an urgent and necessary task. In the new generation of ground-based observation networks, lidar has become an indispensable core device with its high-precision and high-resolution detection capabilities, especially in the high-density detection of thermodynamic profiles in the lower troposphere. Among the existing lidar solutions for detecting tropospheric temperature, pure rotational Raman lidar is favored by experts in the field. Its advantages are mainly reflected in two aspects: first, its inversion method is mature and the detection accuracy is moderate; second, its principle is simple and the system structure is clear.

[0003] However, pure rotational Raman lidar has significant limitations in practical applications. The pure rotational Raman inelastic scattering cross section of the atmosphere is much smaller than the Mie-Rayleigh-Brillouin elastic scattering cross section, resulting in weak echo signal strength. This weakness is particularly prominent during daytime operation, and due to the low signal-to-noise ratio, serious random errors will be introduced. In order to improve the signal-to-noise ratio, the power of the pure rotational Raman lidar transmitter must be greatly increased, but this is contrary to the requirements of the ground meteorological observation network for lidar to cover a large area, be unmanned, and be networked. Summary of the invention

[0004] The technical problem to be solved by the present invention is that, in order to improve the signal-to-noise ratio in the prior art, the power of the pure rotational Raman lidar transmitter must be greatly increased, but this is contrary to the requirements of the ground meteorological observation network for large-area coverage, unmanned intervention and networked layout of the lidar. A lidar system and method based on echo coherence detection of the tropospheric temperature profile is provided.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a laser radar system based on echo coherence detection of the temperature profile of the lower troposphere, which has:

[0006] Lasers that are ultraviolet, single-frequency, narrow linewidth, small pulse energy, and high repetition rate, and

[0007] A telescope for sending and receiving.

[0008] Wherein, the laser comprises at least a multimode fiber coupler and a narrow-band filter.

[0009] The laser receiving optical back end is provided with two interferometers with optical path difference.

[0010] The atmospheric backscattered echo received by the telescope is transmitted to the narrowband filter through the multimode fiber coupler and then enters the interferometer to obtain the transmitted laser pulse;

[0011] The multimode fiber coupler transmits the laser pulse to the interferometer, and the collected backscattered and emitted laser samples are coherently transmitted through the four channels of the interferometer and then detected as electrical signals by the multiplication photodiode.

[0012] In some embodiments, after the atmospheric backscattering passes through the interferometer with high spectral resolution, the signals of the four channels of the interferometer exhibit different characteristics due to interference.

[0013] In some embodiments, the amplified optical coherent signal is integrated over time pulses and normalized by the emitted light sample signal.

[0014] In some embodiments, the coherence of the atmosphere scattered echo light is composed of the linear superposition of aerosol scattered radiation and molecular scattered radiation.

[0015] In some embodiments, the coherence of the backscattered light radiation is a linear superposition of the coherence of the aerosol scattered radiation and the coherence of the molecular scattered radiation.

[0016] In some embodiments, the backscattered radiation received by the telescope is alternately input into at least one of the interferometers.

[0017] In some embodiments, the optical path difference of one interferometer is 30-90 cm, and the optical path difference of the other interferometer is 3 cm-4 cm.

[0018] In some embodiments, the temperature profile of the atmosphere is obtained by analyzing the coherence of pure gas molecule backscattering and establishing a quantitative relationship between the spectrum width of the gas molecule backscattering radiation and the temperature of the atmosphere.

[0019] In a second aspect, a method for detecting a temperature profile of the lower troposphere based on echo coherence comprises:

[0020] Step 1, disconnecting the seed source of the laser, sampling the multi-mode emission laser output by the laser, and directly injecting it into the interferometer;

[0021] Step 2, measuring the interference contrast of large backscattering as a function of height;

[0022] Step 3, obtaining the profile measurement value of the coherence varying with the height and the profile measurement value of the coherence varying with the height;

[0023] Step 4, calculating the profile measurement value of the scattered backscatter interference contrast;

[0024] Step 5, obtaining the temperature profile of the atmosphere according to the profile of height change;

[0025] Step 6: Starting from the standard atmosphere model, cross-iterate the step 6 and the step 5 to optimize the calculation result of the temperature profile.

[0026] In the laser radar system for detecting the tropospheric temperature profile based on echo coherence described in the present invention, high-precision inversion of the tropospheric temperature profile is achieved by accurately measuring the coherence of atmospheric backscattering, which can effectively solve the problem of low signal-to-noise ratio and serious random errors caused by weak echo signals during daytime operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0028] Figure 1 This is a schematic diagram of the power spectrum distribution of the laser backscattered by the atmosphere;

[0029] Figure 2 There are two Michelson interferometers with optical path differences of 30 cm and 3 cm;

[0030] Figure 3a is the Rayleigh-Brillouin scattering spectrum at different heights;

[0031] Figure 3b Simulate the Rayleigh-Brillouin scattering spectrum for the superposition of three Gaussian line shapes;

[0032] Figure 4 This is the step of temperature profile inversion. DETAILED DESCRIPTION

[0033] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0034] like Figure 1 As shown, in the first embodiment of the laser radar system for detecting the lower tropospheric temperature profile based on echo coherence of the present invention, the laser radar system for detecting the lower tropospheric temperature profile based on echo coherence at least includes a laser and a telescope for transmitting and receiving.

[0035] Among them, the laser has the characteristics of ultraviolet, single frequency, narrow line width, small pulse energy and high repetition rate.

[0036] Specifically, the laser includes at least a multimode fiber coupler and a narrowband filter.

[0037] The laser receiving optical back end is equipped with two interferometers with optical path difference.

[0038] Among them, single longitudinal mode, narrow linewidth laser pulses are emitted through continuous wave, single frequency, narrow linewidth seed laser injection;

[0039] The atmospheric backscattered echo received by the telescope is sent to a narrowband filter through a multimode fiber coupler and then enters an interferometer to obtain the transmitted laser pulse;

[0040] Specifically, the interferometer is arranged in the receiver of the laser radar, and includes two four-channel orthogonal polarization Mach-Zehnder interferometers, wherein the optical path differences thereof are 30 cm and 3 cm respectively;

[0041] Interferometer calibration: calibrate the four-channel efficiency parameters and self-interference influence factors of the two interferometers respectively;

[0042] Interference contrast measurement: Calculate the atmospheric backscattering interference contrast at different altitudes through the four-channel signal of the interferometer;

[0043] Rayleigh-Brillouin backscattering interference contrast calculation: Substitute the equation to calculate the Rayleigh-Brillouin backscattering interference contrast;

[0044] The multimode fiber coupler sends the laser pulse to the interferometer, and the collected backscattered and transmitted laser samples are coherently transmitted through the four channels of the interferometer and then detected as electrical signals by the multiplication photodiode.

[0045] By injecting a continuous wave, single frequency, narrow line width (within 5MHz) seed laser and resonating the seed laser with the oscillator cavity of the pulsed fundamental laser, the transmitter can emit laser pulses with a single longitudinal mode and narrow line width (50MHz). Subsequently, the fundamental laser pulse is converted into a violet or ultraviolet laser pulse with an efficiency of more than 25%. The energy of a single pulse is relatively small (within 1mJ), and the pulse repetition frequency is relatively high (above 1kHz); such as the triple frequency of the Nd:YAG laser 354.7-354.9nm, or the double frequency of the alexandrite sapphire laser 360nm-380nm.

[0046] In the technical solution, the lidar receives and detects the elastic scattering with a larger scattering cross section of the atmosphere, rather than the inelastic scattering (Raman scattering) with a smaller scattering cross section. Two interferometers with a very different optical path difference are used, and the coherence of the elastic scattering is calculated through the channel signal of the interferometer. The coherence of aerosol scattering is eliminated through a set of simultaneous equations to obtain the coherence of pure molecular scattering, and then the vertical profile of atmospheric temperature is inverted from the coherence of molecular scattering at different heights. Under the same transmission power, the elastic scattering signal of molecules is stronger than the inelastic scattering signal. The former has a relatively high signal-to-noise ratio and a relatively small random error. By accurately measuring the coherence of atmospheric backscattering, the high-precision inversion of the tropospheric temperature profile is achieved, providing a new technical means for the ground meteorological observation network.

[0047] In some embodiments, after the atmospheric backscatter passes through the high spectral resolution interferometer, the signals of the four channels of the interferometer exhibit different characteristics due to interference;

[0048] The amplified optical coherent signal is accumulated through time pulses and normalized by the emitted light sample signal. Then, based on the signals of each channel and after specific calculation steps, the coherence (interference contrast) of the atmospheric scattered echo light can be obtained.

[0049] In some embodiments, the coherence of the atmospheric scattered echo light is the linear superposition of the aerosol scattered radiation and the molecular scattered radiation; the coherence of the backscattered light radiation is the linear superposition of the aerosol scattered coherence and the molecular scattered coherence.

[0050] That is, the backscattered light radiation of the atmosphere can be regarded as the linear superposition of aerosol Mie scattered radiation and molecular scattered radiation. Similarly, the coherence of the backscattered light radiation can also be regarded as the linear superposition of the coherence of the two scattered radiations.

[0051] In some embodiments, the backscattered radiation received by the telescope is alternately input into at least one interferometer; one interferometer has an optical path difference of 30-90 cm and the other interferometer has an optical path difference of 3 cm-4 cm.

[0052] The backscattered radiation received by the telescope is sent alternately to two interferometers with very different optical path differences, one of which has an optical path difference of 30-90cm and the other of which has an optical path difference of 3cm-4cm. Two different sets of equations about the backscattering coherence are obtained from the interferometers. From these equations, the coherence of the Rayleigh-Brillouin backscattering of pure gas molecules can be solved.

[0053] In some embodiments, the coherence of pure gas molecule backscattering is analyzed by solving equations to obtain gas molecule backscattering radiation, and the temperature profile of the atmosphere is obtained based on the quantitative relationship between the spectrum width of the gas molecule backscattering radiation and the temperature of the atmosphere.

[0054] In some embodiments, the laser radar of the present invention, in addition to the above-mentioned transmitter, the transmitting and receiving shared telescope, the narrow-band filter, and the single-photon detection module, has a core unit, namely, a high spectral resolution frequency discriminator, including a long optical path Mach-Zehnder interferometer (optical path difference of 30cm-90cm), and another short optical path Mach-Zehnder interferometer (optical path difference of 3cm-4cm);

[0055] Specifically: a large number of gas molecules backscatter the incident laser, and the Doppler frequency shift caused by the irregular thermal motion of the molecules causes the backscattering spectrum to broaden;

[0056] The average speed of molecular motion is related to the macroscopic temperature, so the width of the backscattered spectrum is directly related to the atmospheric temperature;

[0057] The Brownian motion speed of aerosols in the atmosphere is low, so the Mie backscattering spectrum of aerosols is very small;

[0058] After the atmospheric backscattering passes through the high spectral resolution interferometer, the signals of the four channels of the interferometer show different characteristics due to interference. Based on the signals of each channel, the coherence of the atmospheric backscattering spectrum can be obtained. This coherence is directly related to the optical path difference of the interferometer and the bandwidth of the scattering spectrum.

[0059] The atmospheric backscattered echo received by the telescope is sent to the narrowband filter through a multimode fiber coupler and then enters the interferometer. At the same time, a small portion of the transmitted laser pulse energy is sampled and sent to the interferometer by the same multimode fiber coupler. The collected backscattered laser and the transmitted laser samples are coherent through the four channels of the interferometer and then detected as electrical signals by a photomultiplier diode (or other photodetector). The amplified optical coherent signal is accumulated over time (pulses) and normalized by the transmitted light sample signal.

[0060] Among them, the four-channel signal of the interferometer can obtain the coherence of the atmospheric scattered echo light after a certain step of calculation; the atmospheric backscattered light radiation can be regarded as the linear superposition of the aerosol Mie backscattered radiation and the molecular backscattered radiation;

[0061] Similarly, the coherence of the backscattered radiation can be considered as the linear superposition of the coherence of the two scattered radiations;

[0062] By sending the backscattered radiation received by the telescope alternately to two interferometers with very different optical path lengths, two different sets of equations for the coherence of the echo scattering can be obtained, from which the coherence of the backscattering of pure gas molecules can be solved;

[0063] The coherence of pure gas molecule scattering can be Fourier transformed to obtain the Rayleigh-Brillouin spectrum of the gas molecule scattered radiation;

[0064] There is a definite quantitative relationship between the spectral width of the backscattered radiation from gas molecules and the temperature of the atmosphere;

[0065] The model of the Rayleigh-Brillouin spectrum can be approximated by the algebraic formula (3) with dimensionless parameters x and y; x represents the optical frequency shift,

[0066] y represents the molecular collision frequency,

[0067] y can be viewed as the ratio of the acoustic wavelength to the mean free path of molecular collisions,

[0068] x and y are relative to Normalization of

[0069]

[0070] ω is the angular frequency shift of scattered light relative to the incident light, n is the number density of atmospheric molecules, p and T are the atmospheric pressure and atmospheric temperature, and the atmospheric shear viscosity η = 1.846×10 -5 Pam -1 s -1 , λ is the wavelength of the incident light, k = 4π / λ, v0 = (k B T / m) 1 / 2 is the Maxwell distribution average value of the random thermal motion speed of atmospheric molecules, k B is the Boltzmann constant, and the average molecular mass of the atmosphere is m = 4.789×10 -26 kg.

[0071] The model uses the standard deviation σ R , integral intensity The central Gaussian line shape is used to represent the Rayleigh spectrum peak, and the superposition integrated intensity is The standard deviation is σ B , in ±x B The two Gaussian lines offset at represent the double peaks of the Brillouin spectrum, thus describing the spontaneous Rayleigh-Brillouin spectrum S(x, y) in the form of a hydrodynamic state, as Figure 3b .

[0072] when When , the Rayleigh-Brillouin spectrum S(x, y) can be normalized and written as:

[0073]

[0074] y can be used to represent the spectrum model σ R , σ B and x B A set of parameter values.

[0075]

[0076] σ R (y) = 0.70813 - 0.16366y 2 +0.19132y 3 -0.07217y 4 ---(5)

[0077] σ B (y)=0.07845·exp[-4.8863y]+0.80400·exp[-0.15003y]-0.45142---(6)

[0078] x B (y) = 0.80893 - 0.30208 × 0.1089 y ---(7)

[0079] Substituting equations (4)-(7) into equation (3), we can obtain the analytical expression approximated by the Rayleigh-Brillouin line shape;

[0080] According to the theory of partially coherent light, the interference contrast of the interferometer coherent signal and the spectral density function S(x, y) of the input light are Fourier transforms of each other. The complex coherence of atmospheric backscatter detected by the interferometer is M BR (τ)exp(-j2πL / λ). τ is the magnified times the dimensionless time difference, corresponding to the normalized frequency shift x, satisfies t is the coherence time difference between the two arms of the interferometer, and L is the optical path difference between the two arms of the interferometer;

[0081] Here c is the speed of light;

[0082] The Fourier transform of the Rayleigh-Brillouin scattering spectrum (3) is as follows:

[0083]

[0084] The complex coherence of Rayleigh-Brillouin backscattering should be M BR (τ)exp(-j2πL / c),M BR (τ) is the modulus of the complex coherence, also called M BR (τ) is the interference contrast. and Bundle Substitute into (9)

[0085]

[0086] The left side of equation (9-1) can be measured using the 8-channel interference signal of two interferometers, and the right side of the equation is an algebraic expression about y. When the measured value on the left side is obtained, equation (9-1) becomes an equation about y.

[0087] The interference contrast of atmospheric backscattering can be approximated by a linear combination of the Rayleigh-Brillouin backscattering spectrum interference contrast and the Mie backscattering spectrum interference contrast.

[0088]

[0089] M atm , M BR and M par They represent the coherence modulus of atmospheric backscattering, Rayleigh-Brillouin backscattering and Mie backscattering, i.e., interference contrast. RB is the Rayleigh-Brillouin backscattering coefficient of atmospheric molecules, which has a relatively wide spectrum; β par is the Mie backscattering coefficient of atmospheric aerosol. The Brownian motion speed of aerosol is small. par The value of M laser Almost, both belong to narrow spectrum; R β (R) = [β RB (R)+M par (R)] / β RB (R) is called the backscattering ratio at the atmospheric height R, such as Figure 1 As shown. atm , M RB and M par They are also related to the height R, so I will not explain them one by one below;

[0090]

[0091] Two four-channel orthogonal polarization Mach-Zehnder interferometers are placed in the laser radar receiver, such as Figure 2 As shown in Figure 1, their optical path differences are 30 cm and 3 cm respectively. When the optical path difference L1 of the interferometer is 30 cm, the Rayleigh-Brillouin backscattering interference contrast M of the atmospheric molecules is BR (30)≈0.0. The spectral width of the emitted laser itself does not exceed 50 MHz, which is comparable to the coherence of the aerosol Mie backscattering;

[0092]

[0093] (14) After deformation, we get as well as Substitute into formula (15);

[0094]

[0095] After plastic surgery, we get (16)

[0096] The left side of equation (16) is related to the Fourier transform of the Rayleigh-Brillouin spectrum of the atmosphere, and the right side is composed of two sets of measurable parameters of the lidar. atm (30) and M atm (03), the Rayleigh-Brillouin backscattering interference contrast M can be calculated BR (03) measured value.

[0097] The photoelectric efficiency parameter a of the four channels (i = 1 to 4) of the Mach-Zehnder interferometer with an optical path difference of 30 cm 30,i In addition, there is also the influence factor M of the interferometer itself on the interference contrast of the four-channel signal 30,i ,These quantities can be obtained through experimental calibration. The backscattered signal detected by the four channels of the interferometer is expressed as:

[0098]

[0099] The four-channel signal S 30，i and structural parameters M 30,i , we can get M atm (30):

[0100]

[0101] Similarly, for a Mach-Zehnder interferometer with an optical path difference of 3 cm, the channel efficiency parameter a 03，i The interferometer structure parameters can be 03，i , we can get M atm (03):

[0102]

[0103] The M obtained by combining equation (19) and equation (20) is at m(30) and M atm (03) Substituting into equation (16), we can obtain M BR Substituting the measured value of (03) into formula (9-1), we can get:

[0104]

[0105] Solve equation (21) to obtain the value of y(R); and v0=(k B T / m) 1 / 2 Combining them, we get formula (22);

[0106] p(R) still uses the US standard atmospheric model, and the y(R) value changes with the height R, so each y(R) value can get a corresponding temperature value, thus obtaining the temperature profile;

[0107]

[0108] According to the above analysis, it is feasible to use two Mach-Zehnder interferometers with a large optical path difference to process the atmospheric scattered echo signal for temperature measurement.

[0109] Second, a method for detecting the temperature profile of the lower troposphere based on echo coherence, such as Figure 4 As shown in Figure 2, the basic steps (reverse inversion) for inverting the tropospheric atmospheric temperature profile are summarized as follows:

[0110] Step 1, disconnect the seed source of the laser, sample the multi-mode emission laser output by the laser, and directly inject it into the interferometer;

[0111] The seed source of the laser is disconnected. At this time, the laser emits multi-mode laser. A small part of the multi-mode emission laser is sampled and directly injected into the interferometer. The four-channel signal is used to calibrate the first group of Mach-Zehnder interferometer four-channel efficiency parameters a 30，1 , a 30，2 , a 30，3 ,a 30 , 4;

[0112] When the seed laser is injected, the laser outputs a single longitudinal mode laser pulse, and the four parameters M of the interference influencing factors of the first group of Mach-Zehnder interferometers are calibrated. 30，1 , M 30，2 , M 30，3 , M 30，4 ; The echo signals S of different heights R of the four channels of the first group of Mach-Zehnder interferometers 30，1 , S 30，2 , S 30，3 , S 30，4 , the interference contrast M of the large backscattering with an optical path difference of 30 cm is obtained from equation (19): atm (30) Measurement value varying with height R;

[0113] Step 2, measuring the variation of interference contrast of large backscattering with height;

[0114] Calibrate the photoelectric efficiency parameter a of the four channels of the second group of Mach-Zehnder interferometers 03，1 , a 03，2 , a 03，3 , a 03，4 ; Calibrate the four parameters M that affect the interference factor of the second group of Mach-Zehnder interferometers themselves 03，1 , M 03，2 , M 03，3 , M 03，4 ; The interference contrast M of the large backscattering with an optical path difference of 30 cm is obtained from equation (20): atm (03) Measurement value varying with height R;

[0115] Step 3, obtaining the profile measurement value of the coherence varying with the height and the profile measurement value of the coherence varying with the height;

[0116] Coherence M atm (30) Profile measurements and coherence M as a function of height R atm (03) The measured value of the profile changing with height R is substituted into equation (16) to obtain the Rayleigh-Brillouin backscattering interference contrast M with an optical path difference of 3 cm: BR (03);

[0117] Step 4, calculating the profile measurement value of the backscattering interference contrast of the scattered light;

[0118] The Rayleigh-Brillouin backscattering interference contrast profile M BR (03) The measured value in step 3 is substituted into the right side of equation (21). The atmospheric pressure p adopts the value of the standard atmospheric model. The right side of equation (21) is an algebraic expression about y. For any height R, a transcendental equation about y is obtained by the right side of equation (21). This equation is solved iteratively to solve the profile of y changing with the height R.

[0119] Step 5, obtaining the temperature profile of the atmosphere according to the profile of height change;

[0120] Substitute the profile of y(R) changing with height R into Obtain the atmospheric temperature profile T(R);

[0121] Step 6, starting from the standard atmosphere model, cross-iterate step 6 and step 5 to optimize the calculation result of the temperature profile;

[0122] According to the ideal gas state equation and the atmospheric quasi-static equation p surrepresents the atmospheric pressure on the ground, g gravity acceleration; the first cycle starts from the p(R) standard atmosphere mode, and then steps 6 and 5 are cross-iterated;

[0123] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A laser radar system for detecting the temperature profile of the lower troposphere based on echo coherence, characterized in that: have: Lasers that are ultraviolet, single-frequency, narrow linewidth, small pulse energy, and high repetition rate, and A telescope for sending and receiving. Wherein, the laser at least includes a multimode fiber coupler and a narrow-band filter. The laser receiving optical back end is provided with two interferometers with optical path difference. The atmospheric backscattered echo received by the telescope is transmitted to the narrowband filter through the multimode fiber coupler and then enters the interferometer to obtain the transmitted laser pulse; The multimode fiber coupler transmits the laser pulse to the interferometer, and the collected backscattered and emitted laser samples are coherently processed by the four channels of the interferometer and then detected as electrical signals by the multiplication photodiode.

2. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 1, characterized in that: After the atmospheric backscattering passes through the interferometer with high spectral resolution, the signals of the four channels of the interferometer present different characteristics due to the interference effect.

3. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 2, characterized in that: The amplified optical coherent signal is accumulated through time pulses and normalized by the emitted optical sample signal.

4. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 3 is characterized in that: The coherence of the atmospheric scattered echo light is composed of the linear superposition of aerosol scattered radiation and molecular scattered radiation.

5. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 4, characterized in that: The coherence of the backscattered light radiation is the linear superposition of the coherence of the aerosol scattered radiation and the coherence of the molecular scattered radiation.

6. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 5, characterized in that: The backscattered radiation received by the telescope is alternately input into at least one of the interferometers.

7. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 6, characterized in that: The optical path difference of one interferometer is 30-90cm, and the optical path difference of the other interferometer is 3cm-4cm.

8. The laser radar system based on echo coherence detection of lower tropospheric temperature profile according to claim 7, characterized in that: By analyzing the coherence of pure gas molecule backscattering, the quantitative relationship between the spectrum width of gas molecule backscattering radiation and the temperature of the atmosphere is established, thereby obtaining the temperature profile of the atmosphere.

9. A method for detecting the temperature profile of the lower troposphere based on echo coherence, characterized in that: include: Step 1, disconnecting the seed source of the laser, sampling the multi-mode emission laser output by the laser, and directly injecting it into the interferometer; Step 2, measuring the change of interference contrast of large backscattering with height change; Step 3, obtaining the profile measurement value of the coherence varying with the height and the profile measurement value of the coherence varying with the height; Step 4, calculating the profile measurement value of the scattered backscatter interference contrast; Step 5, obtaining the temperature profile of the atmosphere according to the profile of height change; Step 6: Starting from the standard atmosphere model, cross-iterate the step 6 and the step 5 to optimize the calculation result of the temperature profile.

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