Aerosol characteristics inversion method based on multi-wavelength Raman-Mie scattering lidar

Abstract

The invention discloses an aerosol characteristic inversion method based on a multi-wavelength Raman-Mie scattering laser radar, comprising the following steps: S1, extracting the Mie scattering wavelength echo signal, and inverting the aerosol extinction coefficient distribution profile; S2, extracting the Raman channel echo signal, and inverting the aerosol extinction coefficient, backscattering coefficient parameters and the ratio of the two; S3, revising the aerosol extinction coefficient in S1 based on the aerosol extinction coefficient, backscattering coefficient parameters and aerosol laser radar ratio constant in S2; obtaining the revised aerosol extinction coefficient distribution profile; S4, based on the revised aerosol extinction coefficient distribution profile in S3, using the gain constant ratio of the horizontal channel and the vertical channel to perform numerical inversion of the aerosol depolarization ratio. The laser radar ratio constant in the Mie scattering inversion method is revised to achieve high-precision inversion of the atmospheric aerosol extinction coefficient. At the same time, the Mie scattering channel is used to invert the aerosol depolarization ratio, and the simultaneous inversion of the atmospheric aerosol microphysical characteristics is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aerosol vertical distribution characteristic inversion, and in particular to an aerosol characteristic inversion method based on a multi-wavelength Raman-Mie scattering laser radar. Background Art

[0002] Atmospheric aerosol is a multi-group system composed of solid or liquid particles and atmospheric media in the atmospheric environment. Its composition phase is complex and has an important impact on many physical changes in the atmosphere. The vertical distribution of aerosol is closely related to the atmospheric environment. The vertical distribution of aerosol will affect solar radiation and reflect PM in the atmosphere. 2.5 The content of aerosols can reflect the degree of atmospheric pollution. In addition, the vertical distribution of aerosols plays an important role in studying the transmission of aerosols such as haze, dust, and smoke. Therefore, studying the vertical distribution changes of aerosol optical properties and microphysical properties is of great significance to studying the structure and formation mechanism of the atmospheric pollution layer. LiDAR is an advanced technical means to study the vertical structure of the atmosphere and the changes in the continuous distribution of aerosols in time and space, and has the advantages of good real-time performance, high spatial resolution, and wide detection range. By measuring echo signals in different bands and inverting optical parameters such as extinction coefficient, backscattering coefficient, lidar ratio, and depolarization ratio, the microphysical characteristics of aerosols can be analyzed, thereby providing a theoretical basis for the spatial distribution and evolution of atmospheric aerosols and atmospheric monitoring research.

[0003] Mie scattering lidar receives Rayleigh scattering signals and Mie scattering signals caused by molecules and aerosols. The Klett and Fernald method is often used to invert the aerosol extinction coefficient. This inversion method requires assuming the lidar ratio constant in advance to complete the closed solution of the lidar equation. However, the assumed parameters will be inaccurate with changes in weather conditions, which will cause inversion errors of optical parameters. Multi-wavelength Raman lidar can detect and obtain Raman scattering radar signals and Mie scattering radar signals. This inversion method does not require assuming the lidar ratio constant, avoids the inversion error introduced by the assumed parameters, and improves the inversion accuracy of the aerosol extinction coefficient. However, it has high requirements for system hardware, and the Raman scattering lidar echo signal is weak. When the solar background radiation is strong during the day, it is difficult to detect the Raman signal, and there is a lot of noise in the detection signal. When the extinction coefficient is inverted, errors and uncertainties are often introduced, which limits the detection time and detection distance of the multi-wavelength Raman lidar. Generally, most lidar equipment products detect partial characteristic information of atmospheric aerosols, while multi-wavelength Raman-Mie scattering lidar equipment can realize the inversion of multiple parameters of atmospheric aerosol microphysical characteristics. The lidar ratio constant is inverted by the Raman channel to analyze the spatial distribution characteristic information of aerosol light scattering. The depolarization ratio constant can be inverted by the parallel and perpendicular channel components of the Mie scattering to analyze the shape characteristics of aerosol particles, thereby realizing the simultaneous measurement of atmospheric aerosol microphysical characteristics. Summary of the invention

[0004] The purpose of the present invention is to provide an aerosol characteristic inversion method based on a multi-wavelength Raman-Mie scattering laser radar to solve the problems raised in the above background technology. The multi-wavelength Raman-Mie scattering laser radar is used to integrate the Raman channel and the Mie scattering channel to invert the aerosol extinction coefficient algorithm, and the laser radar ratio constant in the Mie scattering inversion method is revised to achieve high-precision inversion of the atmospheric aerosol extinction coefficient. At the same time, the Mie scattering channel is used to invert the aerosol depolarization ratio, thereby achieving simultaneous inversion of atmospheric aerosol microphysical characteristics.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for inverting aerosol characteristics based on multi-wavelength Raman-Mie scattering lidar, characterized in that it comprises the following steps:

[0007] S1. Extract the Mie scattering wavelength echo signal and invert the aerosol extinction coefficient distribution profile;

[0008] S2, extracting the Raman channel echo signal, and inverting the aerosol extinction coefficient, the backscattering coefficient parameters and the ratio of the two; the ratio is the aerosol lidar ratio constant;

[0009] S3. Based on the aerosol extinction coefficient, backscattering coefficient parameters and aerosol lidar ratio constant in S2, revise the aerosol extinction coefficient in S1; obtain the revised aerosol extinction coefficient distribution profile;

[0010] S4. Based on the revised aerosol extinction coefficient distribution profile in S3, the echo signals of the horizontal channel component and the vertical channel component of the Mie scattering wavelength are extracted, and the gain constant ratio of the horizontal channel and the vertical channel is used to perform numerical inversion of the aerosol depolarization ratio.

[0011] As a further solution of the present invention: the inversion method in S1 is the Fernald method, specifically:

[0012] When z<z c , the calculation formula of aerosol extinction coefficient at z is:

[0013]

[0014] When z>zc, the calculation formula of the aerosol extinction coefficient at z is:

[0015]

[0016] Where X(z) is the distance correction signal X(z) = P(z)z 2 ,X(z c )=P(zc ) c 2 , z c is the calibration height, z is the actual measured height, α a (z c ) represents the aerosol extinction coefficient at the calibration height, α m (z) represents the boundary value of aerosol extinction coefficient, S a represents the atmospheric aerosol lidar ratio, S m represents the atmospheric molecular lidar ratio.

[0017] As a further solution of the present invention: In S2:

[0018] The Raman method is used to invert the aerosol extinction coefficient, and the formula is:

[0019]

[0020] Among them, λ0 is the incident wavelength of the laser radar, λ R is the wavelength of Raman scattered light, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0, P(λ R ,z) is the received power of the Raman scattered light wavelength at distance z, N N2 (z) is the number density of N2 at a distance z in the atmosphere, α m,λ0 (λ0,z) is the atmospheric extinction coefficient of the atmospheric molecules at a distance z at the laser radar incident wavelength λ0, which can be expressed as α m,λR (λ R , z) is the atmospheric molecule at distance z at the incident wavelength λ of the laser radar R The atmospheric extinction coefficient at can be expressed as k is the Angstrom index of atmospheric aerosol, which takes a value of 1.

[0021] The Raman method is used to invert the aerosol backscattering coefficient, and the formula is:

[0022]

[0023] Among them, z c represents the calibration height, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at a distance z when the lidar wavelength is λ0, β m,λ0 (λ0,z) is the atmospheric molecular backscattering coefficient inverted when the laser radar wavelength is λ0 at distance z.

[0024] As a further solution of the present invention: In S2, the aerosol lidar ratio constant is determined by the Ansmann method, and the formula is:

[0025]

[0026] Among them, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0 and distance z, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at the incident wavelength λ0 and distance z.

[0027] As a further solution of the present invention: in S3, the aerosol extinction coefficient in S1 is revised to be:

[0028] During the period from 0:00 to 1:00 that night, the Raman channel echo signal in the atmospheric environment was selected to invert the aerosol extinction coefficient and backscattering coefficient, and a new lidar ratio constant S was obtained. a ; S m The constant 8π / 3 and the new lidar ratio constant Sa are substituted into the inversion formula of the Fernald method to revise the Mie scattering extinction coefficient and obtain an accurate aerosol extinction coefficient profile.

[0029] The air index is good from 0:00 to 1:00 at night, and the Raman scattering lidar echo signal is weak. When the solar background radiation is strong during the day, it is difficult to detect the Raman signal, and there is a lot of noise in the detection signal. If the received signal during the day is used to invert the extinction coefficient and backscattering coefficient, errors will be introduced. Therefore, the time period with a better air index at night is selected to invert the extinction coefficient and backscattering coefficient, thereby improving the accuracy of the inverted lidar ratio constant.

[0030] As a further solution of the present invention: in S4, the numerical inversion formula of the depolarization ratio is:

[0031]

[0032] Where δ(r) is the aerosol depolarization ratio, K is the gain ratio of the horizontal channel to the vertical channel, and k p and k s are the system gains of the horizontal channel and the vertical channel respectively, P s (z) is the received power of the vertical component of the Mie scattering channel at distance z, P p (z) is the received power of the horizontal component of the Mie scattering channel at distance z.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention is based on a multi-wavelength Raman-Mie scattering lidar, which integrates the Raman channel and the Mie scattering channel to invert the aerosol extinction coefficient algorithm method, thereby improving the detection accuracy of the aerosol extinction coefficient.

[0035] (2) The present invention provides an aerosol extinction coefficient inversion method based on a multi-wavelength Raman-Mie scattering lidar, which uses the Ansmann method to determine the aerosol lidar ratio constant, effectively avoiding the error terms of traditional inversion methods and improving the accuracy of Mie scattering channel inversion of aerosol extinction coefficient.

[0036] (3) Based on the Mie scattering channel signal, the present invention utilizes the echo signals of the horizontal channel component and the vertical channel component of the Mie scattering wavelength to invert the aerosol depolarization ratio, thereby realizing the simultaneous inversion of the shape characteristics of the aerosol particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the method of the present invention; DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] See also Figure 1 In an embodiment of the present invention, a method for inverting aerosol characteristics based on a multi-wavelength Raman-Mie scattering lidar is characterized by comprising the following steps:

[0040] S1. Extract the Mie scattering wavelength echo signal and invert the aerosol extinction coefficient distribution profile;

[0041] S2, extracting the Raman channel echo signal, and inverting the aerosol extinction coefficient, the backscattering coefficient parameters and the ratio of the two; the ratio is the aerosol lidar ratio constant;

[0042] S3. Based on the aerosol extinction coefficient, backscattering coefficient parameters and aerosol lidar ratio constant in S2, revise the aerosol extinction coefficient in S1; obtain the revised aerosol extinction coefficient distribution profile;

[0043] S4. Based on the revised aerosol extinction coefficient distribution profile in S3, the echo signals of the horizontal channel component and the vertical channel component of the Mie scattering wavelength are extracted, and the gain constant ratio of the horizontal channel and the vertical channel is used to perform numerical inversion of the aerosol depolarization ratio.

[0044] As a further solution of the present invention: the inversion method in S1 is the Fernald method, specifically:

[0045] When z<z c , the calculation formula of aerosol extinction coefficient at z is:

[0046]

[0047] When z>z c , the calculation formula of the aerosol extinction coefficient at z is:

[0048]

[0049] Where X(z) is the distance correction signal X(z) = P(z)z 2 ,X(z c )=P(z c ) c 2 , z c is the calibration height, z is the actual measured height, α a (z c ) represents the aerosol extinction coefficient at the calibration height, α m (z) represents the boundary value of aerosol extinction coefficient, S a represents the atmospheric aerosol lidar ratio, S m represents the atmospheric molecular lidar ratio.

[0050] As a further solution of the present invention: In S2:

[0051] The Raman method is used to invert the aerosol extinction coefficient, and the formula is:

[0052]

[0053] Among them, λ0 is the incident wavelength of the laser radar, λ R is the wavelength of Raman scattered light, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0, P(λ R ,z) is the received power of the Raman scattered light wavelength at distance z, N N2 (z) is the number density of N2 at a distance z in the atmosphere, α m,λ0 (λ0,z) is the atmospheric extinction coefficient of the atmospheric molecules at a distance z at the laser radar incident wavelength λ0, which can be expressed as α m,λR (λ R , z) is the atmospheric molecule at distance z at the incident wavelength λ of the laser radar R The atmospheric extinction coefficient at can be expressed as k is the Angstrom index of atmospheric aerosol, which takes a value of 1.

[0054] The Raman method is used to invert the aerosol backscattering coefficient, and the formula is:

[0055]

[0056] Among them, z c represents the calibration height, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at a distance z when the lidar wavelength is λ0, β m,λ0 (λ0,z) is the atmospheric molecular backscattering coefficient inverted when the laser radar wavelength is λ0 at distance z.

[0057] As a further solution of the present invention: In S2, the aerosol lidar ratio constant is determined by the Ansmann method, and the formula is:

[0058]

[0059] Among them, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0 and distance z, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at the incident wavelength λ0 and distance z.

[0060] As a further solution of the present invention: in S3, the aerosol extinction coefficient in S1 is revised to be:

[0061] During the period from 0:00 to 1:00 that night, the Raman channel echo signal in the atmospheric environment was selected to invert the aerosol extinction coefficient and backscattering coefficient, and a new lidar ratio constant S was obtained. a ; S m The constant 8π / 3 and the new lidar ratio constant Sa are substituted into the inversion formula of the Fernald method to revise the Mie scattering extinction coefficient and obtain an accurate aerosol extinction coefficient profile.

[0062] The air index is good from 0:00 to 1:00 at night, and the Raman scattering lidar echo signal is weak. When the solar background radiation is strong during the day, it is difficult to detect the Raman signal, and there is a lot of noise in the detection signal. If the received signal during the day is used to invert the extinction coefficient and backscattering coefficient, errors will be introduced. Therefore, the time period with a better air index at night is selected to invert the extinction coefficient and backscattering coefficient, thereby improving the accuracy of the inverted lidar ratio constant.

[0063] As a further solution of the present invention: in S4, the numerical inversion formula of the depolarization ratio is:

[0064]

[0065] Where δ(r) is the aerosol depolarization ratio, K is the gain ratio of the horizontal channel to the vertical channel, and k p and k s are the system gains of the horizontal channel and the vertical channel respectively, P s (z) is the received power of the vertical component of the Mie scattering channel at distance z, P p (z) is the received power of the horizontal component of the Mie scattering channel at distance z.

[0066] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0067] Therefore, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of implementation of the present application; that is, all equivalent changes made according to the scope of the claims of the present application are within the protection scope of the claims of the present application.

Claims

1. An aerosol characteristics inversion method based on multi-wavelength Raman-Mie scattering lidar, characterized in that: The following steps are involved: S1. Extract the Mie scattering wavelength echo signal and invert the aerosol extinction coefficient distribution profile; S2, extracting the Raman channel echo signal, and inverting the aerosol extinction coefficient, the backscattering coefficient parameters and the ratio of the two; the ratio is the aerosol lidar ratio constant; S3. Based on the aerosol extinction coefficient, backscattering coefficient parameters and aerosol lidar ratio constant in S2, revise the aerosol extinction coefficient in S1; obtain the revised aerosol extinction coefficient distribution profile; S4. Based on the revised aerosol extinction coefficient distribution profile in S3, extract the echo signals of the horizontal channel component and the vertical channel component of the Mie scattering wavelength, and use the gain constant ratio of the horizontal channel and the vertical channel to perform numerical inversion of the aerosol depolarization ratio; In S3, the aerosol extinction coefficient in S1 is revised as follows: During the period from 0:00 to 1:00 that night, the Raman channel echo signal in the atmospheric environment was selected to invert the aerosol extinction coefficient and backscattering coefficient, and a new lidar ratio constant S was obtained. a ; S m The value of the constant 8π / 3 and the new value of the lidar ratio constant Sa are substituted into the inversion formula of the Fernald method to revise the Mie scattering extinction coefficient; In S4, the numerical inversion formula of the depolarization ratio is: Where δ(r) is the aerosol depolarization ratio, K is the gain ratio of the horizontal channel to the vertical channel, and k p and k s are the system gains of the horizontal channel and the vertical channel respectively, P s (z) is the received power of the vertical component of the Mie scattering channel at distance z, P p (z) is the received power of the horizontal component of the Mie scattering channel at distance z.

2. The inversion method according to claim 1, characterized in that: The inversion method in S1 is the Fernald method, specifically: When z<z c， When , the aerosol extinction coefficient at z is calculated as: When z>z c， When , the aerosol extinction coefficient at z is calculated as: Where X(z) is the distance correction signal X(z) = P(z)z 2 ,X(z c )=P(z c ) c 2 , z c is the calibration height, z is the actual measured height, α a (z c ) represents the aerosol extinction coefficient at the calibration height, α m (z) represents the boundary value of aerosol extinction coefficient, S a represents the aerosol lidar ratio constant, S m represents the atmospheric molecular lidar ratio.

3. The inversion method according to claim 1, characterized in that: In S2: The Raman method is used to invert the aerosol extinction coefficient, and the formula is: Among them, λ0 is the incident wavelength of the laser radar, λ R is the wavelength of Raman scattered light, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0, P(λ R ,z) is the received power of the Raman scattered light wavelength at distance z, N N2 (z) is the number density of N2 at a distance z in the atmosphere, α m,λ0 (λ0,z) is the atmospheric extinction coefficient of atmospheric molecules at a distance z at the laser radar incident wavelength λ0, expressed as α m,λR (λ R , z) is the atmospheric molecule at distance z at the incident wavelength λ of the laser radar R The atmospheric extinction coefficient at time , expressed as k is the Angstrom index of atmospheric aerosol, which takes a value of 1; The Raman method is used to invert the aerosol backscattering coefficient, and the formula is: Among them, z c represents the calibration height, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at a distance z when the lidar wavelength is λ0, β m,λ0 (λ0,z) is the atmospheric molecular backscattering coefficient inverted when the laser radar wavelength is λ0 at distance z.

4. The inversion method according to claim 1, characterized in that: In S2, the aerosol lidar ratio constant is determined using the Ansmann method, and the formula is: Among them, α α,λ0 (λ0,z) is the aerosol extinction coefficient inverted by Raman method at incident wavelength λ0 and distance z, β α,λ0 (λ0,z) is the aerosol backscattering coefficient inverted by the Raman method at the incident wavelength λ0 and distance z.

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