Aerosol lidar inversion method based on dual-wavelength Mie scattering lidar

Abstract

The present invention discloses an aerosol lidar inversion method based on a dual-wavelength Mie scattering lidar, which belongs to the field of lidar technology and includes the following steps: SA1, forward modeling the first effective radius R eff A relationship table of the first extinction coefficient ratio, first backscattering coefficient ratio, and first lidar ratio of the dual wavelengths within the range; SB1, assuming the second lidar ratio of the dual wavelength, to obtain the second extinction coefficient ratio and the second backscattering coefficient ratio; S2, assigning the second extinction coefficient ratio to the first extinction coefficient ratio of SA1, substituting it into the relationship in step SA1 to invert and obtain the second effective radius; S3, obtaining a new dual-wavelength lidar ratio; S4, comparing the new dual-wavelength lidar ratio obtained in step S3 with the second lidar ratio assumed in step SB1. When it exceeds the expected error, replace the assumed second lidar ratio in step SB1, and repeat steps SB1, S2, S3, and S4; otherwise, the dual-wavelength lidar ratio obtained in step S3 is considered to be the most accurate value.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to an aerosol laser radar inversion method based on a dual-wavelength Mie scattering laser radar. Background Art

[0002] LiDAR has high spatial and temporal resolution, allowing atmospheric observations under various conditions, and can be used to observe the optical properties of atmospheric aerosols. The LiDAR ratio, also known as the extinction backscattering ratio, is an important optical parameter related to the aerosol type, and is also one of the key error sources in the inversion of Mie scattering LiDAR data. In 1984, when Fernald proposed the inversion method of aerosol backscattering coefficient and extinction coefficient, he assumed that there was a relationship between the extinction coefficient and the backscattering coefficient, and believed that the extinction coefficient ratio to the backscattering coefficient was a constant, and used the LiDAR ratio to represent this constant. Some researchers have found that the LiDAR ratio is only related to the composition and relative scale spectrum distribution of particulate matter. Therefore, the study of the LiDAR ratio is helpful in analyzing the composition of aerosols, distinguishing aerosol types, and improving the accuracy of aerosol optical parameter inversion, which is of great significance to atmospheric science research;

[0003] With the rapid development of lidar technology, lidars suitable for various application scenarios have emerged. Currently, the main lidars used for aerosol detection include Mie-scattering lidar, Raman lidar, and high-spectral-resolution lidar (HSRL). Accordingly, numerous methods for inverting lidar ratios have been proposed, such as the constrained inversion method for Mie-scattering lidar, the Raman lidar inversion method, and the HSRL inversion method. In 1989, SASANO used a dual-wavelength method, assuming that the aerosol backscattering coefficient (or extinction coefficient) profiles at different wavelengths in the aerosol layer are similar, and used this as a constraint to invert the lidar ratio. Currently, various aerosol lidar ratio inversion methods have their own advantages and disadvantages, and there is no optimal solution. Joint inversion can leverage the strengths of multiple methods. To this end, an aerosol lidar inversion method based on dual-wavelength Mie-scattering lidar is proposed. Summary of the Invention

[0004] In order to reduce the error in the lidar inversion process, a new inversion algorithm is provided. To this end, the present invention proposes an aerosol lidar inversion method based on a dual-wavelength Mie scattering lidar. The specific scheme is as follows:

[0005] The aerosol lidar inversion method based on dual-wavelength Mie scattering lidar includes the following steps:

[0006] S1, SA11: Select the aerosol type and calculate the extinction efficiency factor Q of the aerosol ext and the backscattering efficiency factor Q back , determine the first effective radius R of the study eff scope;

[0007] SA12: Forward first effective radius R eff A table showing the relationship between the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first lidar ratio of the dual wavelengths within the range;

[0008] SB1: Assuming a dual-wavelength second lidar ratio, the processed lidar raw data is then inverted using the Fernald method to calculate the dual-wavelength second extinction coefficient and second backscattering coefficient, and the second extinction coefficient ratio and second backscattering coefficient ratio are obtained;

[0009] S2, assign the second extinction coefficient ratio calculated in step SB1 to the first extinction coefficient ratio of SA12 in S1, substitute the first extinction coefficient ratio of the dual wavelengths and the first backscattering ratio and the first effective radius R in step SA12. eff In the relationship between , the second effective radius of the particle is obtained by inversion;

[0010] S3, after inversion, the second effective radius is obtained, and the value of the second effective radius is assigned to the first effective radius R in SA12 eff , according to the laser radar ratio of step SA12 - the first effective radius R eff The relationship between the two is obtained, and the new dual-wavelength lidar ratio is obtained;

[0011] S4. Compare the new dual-wavelength lidar ratio obtained in step S3 with the second lidar ratio assumed in step SB1. If it exceeds the expected error, replace the assumed second lidar ratio in step SB1 with the average value of the new dual-wavelength lidar ratio obtained in step S3 and the assumed second lidar ratio in step SB1, and repeat steps SB1, S2, S3, and S4; otherwise, the dual-wavelength lidar ratio obtained in step S3 is considered to be the most accurate value.

[0012] As a further preferred embodiment of the present invention: in step SA11, the first effective radius R of the study is determined eff The range uses Gamma distribution, the specific steps are as follows:

[0013] SA111. Calculate the relationship between the aerosol equivalent volume radius and the spectral distribution parameters. The form of the Gamma spectral distribution n(r) is:

[0014] n(r)=n0r u e -vr (1)

[0015] Where n0 is the number concentration parameter, which indicates the number of aerosol particles per unit volume; r is the aerosol equivalent volume radius; u is the distribution shape factor, and v is the slope factor;

[0016] SA112: Limit the effective radius of aerosol particles to [0.01, 100] μm, as the first effective radius R of the particles. eff scope;

[0017] SA113, the ratio of the third-order moment to the second-order moment of the Gamma spectrum distribution is used as the first effective radius R of the particle eff :

[0018]

[0019] As a further preferred embodiment of this technical solution, step SA12 is specifically as follows:

[0020] SA12, forward first effective radius R eff The relationship table of the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first laser radar within the range is as follows:

[0021] SA121, using the light scattering model method, and based on the Gamma spectrum distribution n(r), extinction efficiency factor Q ext , backscattering efficiency factor Q back and the aerosol equivalent volume radius r, and obtain each first effective radius R eff The corresponding first extinction coefficient α and first backscattering coefficient β are as follows:

[0022]

[0023]

[0024] SA122, each first effective radius R eff The first extinction coefficient α and the first backscattering coefficient β of the two selected wavelengths are respectively ratioed Get the first extinction coefficient ratio of the dual wavelengths, the first backscattering ratio and the first effective radius R eff The relationship between the first extinction coefficient of the two wavelengths and the first backscattering coefficient The first extinction backscattering ratio of the dual wavelength is obtained, that is, the first laser radar ratio and the first effective radius R eff The relationship between the first effective radius R eff A relationship table of the first extinction coefficient ratio, first backscattering coefficient ratio, and first lidar ratio of dual wavelengths within the range.

[0025] As a further preferred embodiment of this technical solution, step SB1 is specifically as follows:

[0026] SB11. According to Fernald's hypothesis, the second lidar with aerosols is S a =α a / βa and the second LiDAR ratio of the molecule S m =α m / β m , the integral format of the second backscattering coefficient of aerosol can be calculated from the lidar equation:

[0027]

[0028] Where z is the altitude, P(z) is the atmospheric backscatter echo power at altitude z received by the lidar, C is the lidar constant, E is the lidar output energy, subscript a represents aerosol, and subscript m represents molecule.

[0029] SB12. Let X(z)=P(z)z 2 , assuming the elevation z c The second backscattering coefficient of atmospheric aerosol at β a (z c ) or the second extinction coefficient α a (z c ) is known, the above formula can be transformed into:

[0030]

[0031] SB13, again

[0032] A(I, I+1)=(S a -S m )[β m (I)+β m (I+1)]Δz (5-3)

[0033] The forward integration iterative format for obtaining the atmospheric aerosol backscattering coefficient is:

[0034]

[0035] SB14. The back-integration iteration format of the atmospheric aerosol backscattering coefficient is:

[0036]

[0037] The atmospheric aerosol extinction coefficient is obtained by multiplying the backscatter coefficient by the lidar ratio.

[0038] As a further preferred embodiment of the present invention: in step S2, for the multi-value interval, the first extinction backscattering ratio - the first effective radius R eff The auxiliary setting step is: judging the value of the first extinction backscattering ratio, which is close to an effective radius in the multiple values, that is, the corresponding effective radius is the second effective radius.

[0039] The beneficial effects of the present invention are:

[0040] (1) The present invention is a new lidar ratio inversion algorithm that combines the light scattering model method and the dual-wavelength method, and ultimately obtains a relatively reasonable aerosol lidar ratio through iteration;

[0041] (2) The method of the present invention only requires two wavelengths. First, the extinction coefficient and backscattering coefficient of the dual wavelengths are forward-modeled. The ratio is used to obtain the corresponding relationship between the extinction coefficient ratio, the backscattering coefficient ratio, and the lidar ratio and the effective radius. First, the lidar ratio is assumed based on experience. The aerosol extinction coefficient and backscattering coefficient are inverted using the Fernald method. The extinction coefficient ratio is substituted into the forward extinction coefficient-effective radius lookup table. For multi-value intervals, the backscattering coefficient ratio and the backscattering coefficient-effective radius lookup table are used to assist in determining the value, thereby inverting the particle effective radius. Then, the corresponding lidar ratio is obtained according to the forward lidar ratio-effective radius lookup table. By substituting the lidar ratio back into the Fernald method for inversion, a loop iteration is formed until the lidar ratio used by the Fernald method and the found lidar ratio are within the allowable error range. It is considered that the iteration has converged and a relatively accurate lidar ratio has been obtained. The algorithm has high operating efficiency and can be automatically executed. It can meet the requirements of massive lidar data processing and can be further applied to the study of cloud lidar ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of the aerosol lidar inversion method based on dual-wavelength Mie scattering lidar proposed in the present invention.

[0043] Figure 2 This is a relationship diagram of the extinction coefficient ratio, backscattering ratio and effective radius obtained in step SA12 of the present invention.

[0044] Figure 3 This is a relationship diagram of the laser radar and effective radius obtained in step SA12 of the present invention.

[0045] Figure 4 This is an example diagram of the inversion results of the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0047] Example

[0048] like Figure 1As shown in FIG, the aerosol lidar inversion method based on the dual-wavelength Mie scattering lidar includes the following steps:

[0049] S1, SA11: Select the aerosol type and calculate the extinction efficiency factor Q of the aerosol using the miepython function based on the Mie scattering theory ext and the backscattering efficiency factor Q back ;

[0050] At the same time, the spectral distribution model is selected. Common spectral distribution models include Junge distribution, lognormal distribution and Gamma distribution. Gamma distribution is selected to determine the first effective radius R of the study. eff scope;

[0051] Determine the first effective radius R of the study eff The specific steps of the scope are:

[0052] SA111. Calculate the relationship between the aerosol equivalent volume radius and the spectral distribution parameters. The form of the Gamma spectral distribution n(r) is:

[0053] n(r)=n0r u e -vr (1)

[0054] Where n0 is the number concentration parameter, which indicates the number of aerosol particles per unit volume; r is the aerosol equivalent volume radius; u is the distribution shape factor, and v is the slope factor;

[0055] SA112: Limit the effective radius of aerosol particles to [0.01, 100] μm, as the first effective radius R of the particles. eff scope;

[0056] SA113, the ratio of the third-order moment to the second-order moment of the Gamma spectrum distribution is used as the first effective radius R of the particle eff :

[0057]

[0058] Determine the first effective radius R within the range according to formula (2) eff The corresponding Gamma spectral distribution parameter v.

[0059] SA12: Forward first effective radius R eff The relationship table of the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first laser radar within the range is as follows:

[0060] SA121, since aerosols in the real atmosphere are aggregates with a certain scale spectrum and shape distribution, their overall optical properties are determined by the optical properties of individual particles weighted by the distribution of particle scale spectrum. The light scattering model method is used, and according to the Gamma spectrum distribution n(r), the extinction efficiency factor Q ext , backscattering efficiency factor Q back and the aerosol equivalent volume radius r, and obtain each first effective radius R eff The corresponding first extinction coefficient α and first backscattering coefficient β are as follows:

[0061]

[0062]

[0063] SA122, each first effective radius R eff The first extinction coefficient α and the first backscattering coefficient β of the two selected wavelengths are respectively ratioed The first extinction coefficient ratio of the dual wavelengths, the first backscattering ratio and the first effective radius R can be obtained. eff relationship, such as Figure 2 As shown, in the first effective radius interval [0.15, 0.5] um, the first extinction coefficient ratio changes with the first effective radius R eff Increasing monotonically decreases, and a lookup table can be constructed accordingly; outside this interval, a first extinction coefficient ratio corresponds to two first effective radii, and there is a multi-value phenomenon, but the first backscattering coefficient ratio and the first effective radius are a single-value relationship; then the first extinction coefficient ratio of the two wavelengths is respectively increased by the first backscattering coefficient The first extinction backscattering ratio (first laser radar ratio) of the dual wavelength and the first effective radius R can be obtained. eff relationship, such as Figure 3 As shown, in the first effective radius interval [0.01, 1.1]um, the ratio of the first laser radar of 355nm wavelength to that of 1064nm wavelength is between 15-100, and there is a fluctuation phenomenon as the first effective radius increases. Thus, the first effective radius R is established. eff A relationship table of the first extinction coefficient ratio, first backscattering coefficient ratio, and first lidar ratio of dual wavelengths within the range.

[0064] SB1: Based on empirical assumptions, the second lidar ratio of the dual wavelength is then assumed. The processed lidar raw data is then inverted using the Fernald method to calculate the second extinction coefficient and second backscattering coefficient of the dual wavelength, resulting in the second extinction coefficient ratio and second backscattering coefficient ratio. The specific steps are as follows:

[0065] SB11. According to Fernald's hypothesis, the second lidar with aerosols is S a =αa / β a and the second LiDAR ratio of the molecule S m =α m / β m , the integral format of the second backscattering coefficient of aerosol can be calculated from the lidar equation:

[0066]

[0067] Where z is the altitude, P(z) is the atmospheric backscatter echo power at altitude z received by the lidar, C is the lidar constant, E is the lidar output energy, subscript a represents aerosol, and subscript m represents molecule;

[0068] SB12. Let X(z)=P(z)z 2 , assuming the elevation z c The second backscattering coefficient of atmospheric aerosol at β a (z c ) or the second extinction coefficient α a (z c ) is known, the above formula can be transformed into:

[0069]

[0070] SB13, again

[0071] A(I, I+1)=(S a -S m )[β m (I)+β m (I+1)]Δz (5-3)

[0072] The forward integration iterative format for obtaining the atmospheric aerosol backscattering coefficient is:

[0073]

[0074] SB14. The back-integration iteration format of the atmospheric aerosol backscattering coefficient is:

[0075]

[0076] The atmospheric aerosol extinction coefficient can be obtained by multiplying the backscatter coefficient by the lidar ratio;

[0077] S2, assign the second extinction coefficient ratio calculated in step SB1 to the first extinction coefficient ratio of SA12 in S1, substitute the first extinction coefficient ratio of the dual wavelengths and the first backscattering ratio and the first effective radius R in step SA12. eff In the relationship between the two, the second effective radius of the particle is obtained by inversion. For the multi-value interval, the extinction backscattering ratio - the first effective radius Reff The auxiliary setting step is: judging the value of the first extinction backscattering ratio to be close to an effective radius among the multiple values, that is, the corresponding effective radius is the second effective radius;

[0078] S3, after inversion, the second effective radius is obtained, and the value of the second effective radius is assigned to the first effective radius R in SA12 eff , according to the laser radar ratio of step SA12 - the first effective radius R eff The relationship between the two is obtained, and the new dual-wavelength lidar ratio is obtained;

[0079] S4. Compare the new dual-wavelength lidar ratio obtained in step S3 with the second lidar ratio assumed in step SB1. If it exceeds the expected error, replace the assumed second lidar ratio in step SB1 with the average value of the new dual-wavelength lidar ratio obtained in step S3 and the assumed second lidar ratio in step SB1, and repeat steps SB1, S2, S3, and S4; otherwise, the dual-wavelength lidar ratio obtained in step S3 is considered to be the most accurate value.

[0080] The inversion effect is as follows Figure 4 As shown, the initial assumption of inversion is Sa_355=80,Sa_1064=50. After the lidar ratio iteration, it finally converges. The boundary layer is about 2km. The second extinction coefficient ratio in the boundary layer is about 1.8-2.8, showing an increasing trend. Figure 2 The second effective radius found is about 0.05-0.09um. Figure 3 The corresponding laser radar ratio of 355nm wavelength is about 20-40, and the laser radar ratio of 1064nm wavelength is about 37-61, both of which are within a reasonable range.

[0081] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. Aerosol lidar inversion method based on dual-wavelength Mie scattering lidar, characterized by: The following steps are involved: S1, SA11: Select the aerosol type and calculate the extinction efficiency factor of the aerosol and backscattering efficiency factor , determine the first effective radius of the study scope; SA12: Forward first effective radius A table showing the relationship between the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first lidar ratio of the dual wavelengths within the range; SB1: Assuming a dual-wavelength second lidar ratio, the processed lidar raw data is then inverted using the Fernald method to calculate the dual-wavelength second extinction coefficient and second backscattering coefficient, and the second extinction coefficient ratio and second backscattering coefficient ratio are obtained; S2, assign the second extinction coefficient ratio calculated in step SB1 to the first extinction coefficient ratio of SA12 in S1, and substitute the first extinction coefficient ratio of the dual wavelengths and the first backscattering ratio and the first effective radius in step SA12. In the relationship between , the second effective radius of the particle is obtained by inversion; S3, after inversion to obtain the second effective radius, assign the value of the second effective radius to the first effective radius in SA12 , according to the laser radar ratio of step SA12-first effective radius The relationship between the two is obtained, and the new dual-wavelength lidar ratio is obtained; S4. Compare the new dual-wavelength lidar ratio obtained in step S3 with the second lidar ratio assumed in step SB1. If the expected error is exceeded, replace the assumed second lidar ratio in step SB1 with the average of the new dual-wavelength lidar ratio obtained in step S3 and the assumed second lidar ratio in step SB1, and repeat steps SB1, S2, S3, and S4. Otherwise, the dual-wavelength lidar ratio obtained in step S3 is considered to be the most accurate value. In step SA11, the first effective radius of the study is determined The range uses Gamma distribution, the specific steps are as follows: SA111, Calculate the relationship between aerosol equivalent volume radius and spectral distribution parameters, Gamma spectral distribution The form is: ； in is the number concentration parameter, which indicates how many aerosol particles there are per unit volume; is the aerosol equivalent volume radius; u is the distribution shape factor, and v is the slope factor; SA112: Limit the effective radius of aerosol particles to [0.01, 100] μm as the first effective radius of the particles. scope; SA113, the ratio of the third-order moment to the second-order moment of the Gamma spectrum distribution is used as the first effective radius of the particle : ； Step SA12 is specifically as follows: SA12, forward first effective radius The relationship table of the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first laser radar within the range is as follows: SA121, using the light scattering model method, and based on the Gamma spectrum distribution , extinction efficiency factor , backscattering efficiency factor and aerosol equivalent volume radius , get each first effective radius The corresponding first extinction coefficient and the first backscatter coefficient , the formula is as follows: ； SA122, each first effective radius The first extinction coefficient at two selected wavelengths and the first backscatter coefficient Ratio , , get the first extinction coefficient ratio of the dual wavelengths and the first backscattering ratio and the first effective radius The relationship between the first extinction coefficient of the two wavelengths and the first backscattering coefficient , , get the first extinction backscattering ratio of the dual wavelength, that is, the first laser radar ratio and the first effective radius The relationship between the first effective radius A table showing the relationship between the first extinction coefficient ratio, the first backscattering coefficient ratio, and the first lidar ratio of the dual wavelengths within the range; Step SB1 is specifically as follows: SB11. According to Fernald hypothesis, the second lidar with aerosols and the second LiDAR ratio of molecules , the integral format of the second backscattering coefficient of aerosol can be calculated from the lidar equation: ； Where z is the altitude, P(z) is the atmospheric backscatter echo power at altitude z received by the lidar, C is the lidar constant, E is the lidar output energy, subscript a represents aerosol, and subscript m represents molecule; SB12, Order , assuming elevation The second backscattering coefficient of atmospheric aerosol at or the second extinction coefficient If is known, the above formula can be transformed into: ； SB13, again ； The forward integration iterative format for obtaining the atmospheric aerosol backscattering coefficient is: ； SB14. The back-integration iteration format of the atmospheric aerosol backscattering coefficient is: ； The atmospheric aerosol extinction coefficient is obtained by multiplying the backscatter coefficient by the lidar ratio.

2. The aerosol lidar inversion method based on dual-wavelength Mie scattering lidar according to claim 1 is characterized in that: In step S2, for the multi-value interval, the first extinction backscattering ratio-first effective radius The auxiliary setting step is: judging the value of the first extinction backscattering ratio, which is close to an effective radius in the multiple values, that is, the corresponding effective radius is the second effective radius.

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