A dual-wavelength particle spectrum inversion method

Abstract

The invention relates to particle spectrum inversion, and in particular to a dual-wavelength particle spectrum inversion method, which reads raw data of a dual-wavelength laser radar, pre-processes the wavelength data, and checks whether the wavelength data is valid. If the wavelength data is invalid, the invalid wavelength data is discarded and S1 is returned. Otherwise, extinction coefficient inversion is performed on the wavelength data, the extinction coefficient ratio is calculated, and the aerosol effective diameter of the extinction coefficient ratio within the corresponding wavelength is searched in a database. If the extinction coefficient ratio within the wavelength cannot be found in the database, it is discarded and S1 is returned. Otherwise, the corresponding aerosol effective diameter is output, corrected by an aerosol model, and the particle spectrum is output after correction to complete the inversion. The technical solution provided by the invention can effectively overcome the defects of complex hardware equipment structure and large calculation amount in the prior art.

Description

Technical Field

[0001] The invention relates to particle spectrum inversion, and in particular to a dual-wavelength particle spectrum inversion method. Background Art

[0002] The spectral distribution of aerosol particles refers to the distribution of aerosol particle concentrations corresponding to different radii. Studying the aerosol particle spectrum can better reveal particulate matter concentrations, causes of haze, particle size spectrum distribution, etc., and plays an important role in scientific research on air pollution control and climate change. At present, the main method of detection is to use an aerosol particle size spectrometer, but this type of equipment can only detect single-point values. If you want to detect the distribution of aerosol particle spectrum within a regional range, you need to use multiple devices for detection. As an active remote sensing device, lidar can detect aerosols within a spatial range, but the inversion of aerosol particle spectrum is a major problem.

[0003] In the prior art, three wavelengths (355nm, 532nm, 1064nm) are used to invert particle spectrum distribution. The hardware equipment has a complex structure and high cost. In addition, the inversion is calculated through GCV regularization, which is complex and requires a large amount of calculation. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a dual-wavelength particle spectrum inversion method, which can effectively overcome the defects of the prior art such as complex hardware equipment structure and large amount of calculation.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] A dual-wavelength particle spectrum inversion method comprises the following steps:

[0009] S1. Read the raw data of the dual-wavelength laser radar, pre-process the wavelength data, and check whether the wavelength data is valid;

[0010] S2. If the wavelength data is invalid, the invalid wavelength data is discarded and the process returns to S1. Otherwise, the extinction coefficient of the wavelength data is inverted.

[0011] S3, calculating the extinction coefficient ratio, and searching the database for the aerosol effective diameter of the extinction coefficient ratio within the corresponding wavelength;

[0012] S4. If the extinction coefficient ratio within the wavelength cannot be found in the database, it is discarded and returned to S1, otherwise the corresponding aerosol effective diameter is output;

[0013] S5. Correction is performed through the aerosol model, and the particle spectrum is output after correction to complete the inversion.

[0014] Preferably, the preprocessing of the wavelength data in S1 includes:

[0015] The average value of the last segment of the original data is taken as the background value, and the wavelength data is deducted from the background value by subtracting the background value from the data sequence;

[0016] The wavelength data is corrected by manually correcting the near-ground segment data in the original data and performing geometric factor correction.

[0017] Preferably, the step of performing extinction coefficient inversion on the wavelength data in S2 includes:

[0018] The Mie scattering lidar equation is solved and the extinction coefficient is calculated using the Fernald method by assuming the lidar ratio.

[0019] Preferably, the Mie scattering laser radar equation is as follows:

[0020]

[0021] Where P(r) is the atmospheric backscatter echo power at the height r received by the lidar, P t is the laser power emitted by the laser radar, k is the laser radar system constant, β m (r) is the backscattering coefficient of air molecules, β a (r) is the backscattering coefficient of atmospheric aerosol, α m (r') is the extinction coefficient of air molecules, α a (r') is the extinction coefficient of atmospheric aerosol;

[0022] The atmospheric aerosol extinction coefficient is calculated by the following formula:

[0023]

[0024] In the formula, S a is the extinction backscatter ratio of atmospheric aerosol, or lidar ratio, S m is the extinction backscattering ratio of air molecules.

[0025] Preferably, the calculation of the extinction coefficient ratio in S3 includes:

[0026] The calculated extinction coefficients corresponding to the two wavelengths are divided to obtain a set of ratio sequences.

[0027] Preferably, the corresponding relationship between the extinction coefficient ratio and the aerosol effective diameter in the database is obtained by simulation calculation.

[0028] Preferably, the aerosol model is the true value range of effective particle diameters under different weather conditions and different aerosol types obtained through statistics of historical detection data.

[0029] (III) Beneficial effects

[0030] Compared with the prior art, the dual-wavelength particle spectrum inversion method provided by the present invention performs extinction coefficient inversion by dual wavelengths, which not only reduces the complexity of the hardware equipment structure, but also reduces the amount of calculation; the corresponding relationship between the extinction coefficient ratio of different wavelengths and the effective diameter of the aerosol is calculated by simulation, and a database is established, so that the effective diameter of the aerosol can be accurately found; different aerosol models are established through historical detection data, and the inversion results are corrected, thereby improving the precision and accuracy of the inversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 It is a schematic diagram of the process of the present invention;

[0033] Figure 2 This is the relationship curve between the extinction coefficient ratio and the aerosol effective diameter at dual wavelengths of 337nm and 1060nm. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0035] A dual-wavelength particle spectrum inversion method, such as Figure 1 As shown, S1, read the original data of the dual-wavelength laser radar, pre-process the wavelength data, and check whether the wavelength data is valid.

[0036] The wavelength data is preprocessed, including:

[0037] The average value of the last segment of the original data is taken as the background value, and the wavelength data is deducted from the background value by subtracting the background value from the data sequence;

[0038] The wavelength data is corrected by manually correcting the near-ground segment data in the original data and performing geometric factor correction.

[0039] When equipment is abnormal or extreme weather occurs during detection, the wavelength data may become invalid. In this case, the invalid wavelength data should be discarded.

[0040] S2. If the wavelength data is invalid, the invalid wavelength data is discarded and the process returns to S1. Otherwise, the extinction coefficient of the wavelength data is inverted.

[0041] Among them, the extinction coefficient inversion of wavelength data includes:

[0042] The Mie scattering lidar equation is solved and the extinction coefficient is calculated using the Fernald method by assuming the lidar ratio.

[0043] The Mie scattering lidar equation is as follows:

[0044]

[0045] Where P(r) is the atmospheric backscatter echo power at the height r received by the lidar, P t is the laser power emitted by the laser radar, k is the laser radar system constant, β m (r) is the backscattering coefficient of air molecules, β a (r) is the backscattering coefficient of atmospheric aerosol, α m (r') is the extinction coefficient of air molecules, α a (r') is the extinction coefficient of atmospheric aerosol.

[0046] The atmospheric aerosol extinction coefficient is calculated by the following formula:

[0047]

[0048] In the formula, S a is the extinction backscatter ratio of atmospheric aerosol, or lidar ratio, S m is the extinction backscattering ratio of air molecules.

[0049] S3. Calculate the extinction coefficient ratio and search the database for the aerosol effective diameter of the extinction coefficient ratio within the corresponding wavelength.

[0050] S4. If the extinction coefficient ratio within the wavelength cannot be found in the database, it is discarded and returned to S1, otherwise the corresponding aerosol effective diameter is output.

[0051] Among them, the calculation of the extinction coefficient ratio includes:

[0052] The calculated extinction coefficients corresponding to the two wavelengths are divided to obtain a set of ratio sequences.

[0053] The corresponding relationship between the extinction coefficient ratio and the aerosol effective diameter in the database was obtained through simulation calculation.

[0054] S5. Correction is performed through the aerosol model, and the particle spectrum is output after correction to complete the inversion.

[0055] The aerosol model is the true value range of the effective diameter of particles under different weather conditions and different aerosol types obtained through statistics of historical detection data.

[0056] The inversion process of the technical solution of the present application is described below using dual wavelengths of 335nm and 1064nm and dual wavelengths of 532nm and 1064nm.

[0057] 1) The dual-wavelength laser radar has an emission wavelength of 355nm and 1064nm, and the laser radar raw data includes 355nm wavelength channel detection data and 1064nm wavelength channel detection data. First, read the raw data of the dual-wavelength laser radar, subtract the background and correct the geometric factors for the data of wavelength 355nm and wavelength 1064nm, then check whether the corrected data is valid, discard the invalid data, and invert the extinction coefficient for the valid data. The extinction coefficient inversion uses the Fernald method to calculate the extinction coefficients corresponding to the wavelengths of 355nm and 1064nm and then divide them to obtain a set of ratio sequences. The aerosol effective diameter of the 355nm / 1064nm extinction coefficient ratio is searched in the database; if the wavelength and extinction coefficient ratio cannot be found in the database, it is discarded. If it can be found, the search value is output and corrected through the aerosol model. After correction, the particle spectrum value is output and the inversion is completed.

[0058] 2) The dual-wavelength laser radar has an emission wavelength of 532nm and 1064nm, and the laser radar raw data includes 532nm wavelength channel detection data and 1064nm wavelength channel detection data. First, read the raw data of the dual-wavelength laser radar, and subtract the background and geometric factor correction for the data of wavelength 532nm and wavelength 1064nm; then check whether the corrected data is valid, discard invalid data, and invert the extinction coefficient for valid data. The extinction coefficient inversion uses the Fernald method to calculate the extinction coefficient corresponding to the wavelength of 532nm and the wavelength of 1064nm, and then divide them to obtain a set of ratio sequences. Look up the aerosol effective diameter of the 532nm / 1064nm extinction coefficient ratio in the database; if the wavelength and extinction coefficient ratio cannot be found in the database, it will be discarded. If it can be found, the search value is output and corrected through the aerosol model. After correction, the particle spectrum value is output and the inversion ends.

[0059] like Figure 2As shown, through simulation calculation, the relationship between the extinction coefficient ratio of 337nm wavelength and 1060nm wavelength, the relationship between the backscattering coefficient ratio and the effective diameter of the particle, and the relationship between the extinction coefficient ratio of 550nm wavelength and 1060nm wavelength and the effective diameter of the particle are obtained respectively (Note: the intersection of each curve with the y-axis in the figure represents from top to bottom the relationship between the extinction coefficient ratio of 337nm wavelength and 1060nm wavelength and the effective diameter of the particle, the relationship between the extinction coefficient ratio of 550nm wavelength and 1060nm wavelength and the effective diameter of the particle, the relationship between the backscattering coefficient ratio of 337nm wavelength and 1060nm wavelength and the effective diameter of the particle, and the relationship between the backscattering coefficient ratio of 550nm wavelength and 1060nm wavelength and the effective diameter of the particle).

[0060] In the effective particle diameter range of 0.1-1um, the extinction coefficient ratio of 337nm wavelength and 1060nm wavelength is linearly related to the effective particle diameter, so the effective particle diameter can be inverted using dual wavelengths of 355nm and 1064nm. In the technical solution of this application, in order to improve the accuracy of inversion, a wavelength combination whose extinction coefficient ratio is linearly related to the effective diameter of aerosol particles should be selected when selecting dual wavelengths.

[0061] At the same time, more aerosol models are needed to establish a database to improve the accuracy of the inversion, and to compare and verify the detection results through horizontal detection and aerosol particle size spectrometer.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-wavelength particle spectrum inversion method, characterized in that: The following steps are involved: S1. Read the raw data of the dual-wavelength laser radar, pre-process the wavelength data, and check whether the wavelength data is valid, wherein the emission wavelength of the dual-wavelength laser radar is 355nm, 1064nm or 532nm, 1064nm; S2. If the wavelength data is invalid, the invalid wavelength data is discarded and the process returns to S1. Otherwise, the extinction coefficient of the wavelength data is inverted. S3, calculating the extinction coefficient ratio, and searching the database for the aerosol effective diameter of the extinction coefficient ratio within the corresponding wavelength; S4. If the extinction coefficient ratio within the wavelength cannot be found in the database, it is discarded and returned to S1, otherwise the corresponding aerosol effective diameter is output; S5. Correction is performed through the aerosol model, and the particle spectrum is output after correction to complete the inversion; The wavelength data is preprocessed as described in S1, including: The average value of the last segment of the original data is taken as the background value, and the wavelength data is deducted from the background value by subtracting the background value from the data sequence; By manually correcting the near-ground segment data in the original data, the wavelength data is corrected by geometric factors; The extinction coefficient inversion of the wavelength data described in S2 includes: Solve the Mie scattering lidar equation and calculate the extinction coefficient using the Fernald method by assuming the lidar ratio; The Mie scattering lidar equation is as follows: Where P(r) is the atmospheric backscatter echo power at the height r received by the lidar, P t is the laser power emitted by the laser radar, k is the laser radar system constant, β m (r) is the backscattering coefficient of air molecules at height r, β a (r) is the backscattering coefficient of atmospheric aerosol at height r, α m (r') is the extinction coefficient of air molecules, α a (r') is the extinction coefficient of atmospheric aerosol; The atmospheric aerosol extinction coefficient is calculated by the following formula: In the formula, α a (r) is the extinction coefficient of atmospheric aerosol at height r, S a is the extinction backscatter ratio of atmospheric aerosol, or lidar ratio, S m is the extinction backscattering ratio of air molecules, α m (r) is the extinction coefficient of air molecules at height r; The aerosol model is the true value range of effective particle diameters under different weather conditions and different aerosol types obtained through statistics of historical detection data.

2. The dual-wavelength particle spectrum inversion method according to claim 1, characterized in that: Calculating the extinction coefficient ratio as described in S3 includes: The calculated extinction coefficients corresponding to the two wavelengths are divided to obtain a set of ratio sequences.

3. The dual-wavelength particle spectrum inversion method according to claim 2, characterized in that: The corresponding relationship between the extinction coefficient ratio and the aerosol effective diameter in the database is obtained through simulation calculation.

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