A high spectral resolution lidar field of view optimization method for water cloud inversion

Abstract

The present invention discloses a method for optimizing the field of view of a high-spectral-resolution laser radar for water cloud inversion, including: establishing a lookup table of the relationship between the water cloud scattering phase matrix and the effective radius; simulating to obtain the atmospheric molecule Rayleigh scattering signals at different field angles; fine-tuning the water cloud parameters, and re-simulating to obtain a set of echo signals at different field angles; calculating the sensitivity of the echo signals at different field angles to the water cloud parameters by fine-tuning the difference between the signals before and after and the water cloud parameters; selecting the two field angle parameters with the highest sensitivity of the echo signals to the effective radius and the extinction coefficient of the water cloud, respectively, as the optimal field of view of the dual-field-of-view high-spectral-resolution laser radar for water cloud inversion; using the optimal field of view setting to observe the water cloud signal, and iteratively inverting the signal to obtain accurate water cloud parameters. By using the present invention, the optimal field angle parameters can be selected for the dual-field-of-view high-spectral-resolution laser radar for water cloud inversion, and accurate inversion of water clouds can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of atmospheric cloud remote sensing laser radar, and in particular relates to a high spectral resolution laser radar field of view optimization method for water cloud inversion. Background Art

[0002] Clouds cover more than 50% of the sky on the earth's surface. They play a vital role in the earth's atmospheric water cycle, climate change, and earth radiation. Cloud-aerosol-radiation interaction is the main source of uncertainty in climate change. On the one hand, it is because the atmospheric interaction itself is a relatively complex system, and on the other hand, it is due to the lack of effective monitoring data on clouds and aerosols. In low-latitude areas, the atmospheric temperature is higher, and there is less chance of ice and water coexisting in the clouds, and water clouds often form. Most of the cumulonimbus and stratocumulus clouds in southern my country in summer belong to this type of cloud. This type of cloud plays a very important role in atmospheric radiation, lightning, precipitation and other atmospheric processes.

[0003] Lidar has the advantages of high temporal and spatial resolution, high detection accuracy, and all-day observation, and has been widely used in the detection of atmospheric clouds and aerosols. However, due to the multiple scattering effect of water clouds, lidar cannot accurately invert the single scattering optical and microphysical properties of water clouds. Therefore, how to accurately simulate the multiple scattering signals of water clouds and obtain high-precision optical and microphysical properties inversion of water clouds is a key problem that needs to be solved in the current lidar water cloud inversion research. The effective radius and extinction coefficient of water clouds are the most important parameters for water cloud inversion. The effective radius describes the size of cloud droplets, and the extinction coefficient describes the scattering characteristics of water clouds to light. The effective radius and extinction coefficient of water clouds can be used to further analyze other key optical and microphysical properties of water clouds such as lidar ratio, number concentration, and liquid water content.

[0004] At present, there are two main methods for water cloud inversion using lidar. One is water cloud inversion based on polarized Mie scattering lidar, which uses the depolarization effect caused by multiple scattering of water clouds to construct a lookup table between the water cloud echo signal detected by polarized Mie scattering lidar and the effective radius and extinction coefficient of water clouds, and based on the optimization inversion theory, it realizes the effective inversion of the effective radius and extinction coefficient of water clouds, but its inversion value is overestimated; the other is to use multi-field Mie scattering or Raman scattering lidar for water cloud inversion, which mainly uses the law of change of multiple scattering intensity of water clouds with field of view angle. However, the former is difficult to accurately invert due to the inhomogeneity of backscattering of cloud particles, and the latter is difficult to observe during the day. Therefore, there are certain problems in the current water cloud inversion methods of lidar, which limits the application of lidar for accurate inversion of water clouds. Summary of the invention

[0005] In view of the shortcomings of existing lidar inversion methods for water clouds, the present invention provides a high-spectral resolution lidar field of view optimization method for water cloud inversion, which can achieve high-precision inversion of the effective radius and extinction coefficient of water clouds throughout the day. Through these two key parameters of water clouds, not only the size of cloud droplet particles, the light scattering characteristics of water clouds, etc. can be analyzed, but also other key optical and microphysical properties of water clouds such as lidar ratio, cloud droplet number concentration and liquid water content can be further analyzed.

[0006] Compared with Mie scattering lidar, high spectral resolution lidar uses a spectral discriminator to separate the Mie scattering signal of atmospheric particles and the Rayleigh scattering signal of molecules. Therefore, it can simulate the forward scattering characteristics of clouds and the uniform backscattering characteristics of atmospheric molecules through a forward calculation model to obtain accurate atmospheric molecular Rayleigh scattering signals for the inversion of water cloud characteristics. Compared with Raman scattering lidar, high spectral resolution lidar can be observed during the day, thereby realizing high-precision inversion of water cloud parameters throughout the day.

[0007] A high spectral resolution lidar field of view optimization method for water cloud inversion uses a dual-field of view high spectral resolution lidar system for water cloud inversion, comprising the following steps:

[0008] (1) Input a series of different water cloud effective radius parameters, calculate the corresponding water cloud scattering phase matrix, and establish a lookup table of the relationship between the water cloud scattering phase matrix and the effective radius parameters;

[0009] (2) Set different high-spectral resolution lidar field of view parameters, input other hardware parameters and water cloud scattering phase matrix, extinction coefficient and spatial height parameters according to the actual system settings, and use the forward calculation model to simulate the atmospheric molecular Rayleigh scattering signals under different receiving field of view angles;

[0010] (3) Based on the perturbation method, the water cloud effective radius and extinction coefficient parameters are adjusted, and a set of atmospheric molecular Rayleigh scattering signals under different receiving field angles are re-simulated to calculate the sensitivity of atmospheric molecular Rayleigh scattering signals under different receiving field angles to the water cloud effective radius and extinction coefficient;

[0011] (4) The two field of view angle parameters with the highest sensitivity to the effective radius and extinction coefficient of atmospheric molecule Rayleigh scattering signals are selected as the optimal field of view of the dual-field of view high spectral resolution lidar for water cloud inversion;

[0012] (5) The water cloud signal is observed using the optimal field of view setting, and the relative error between the measured signal and the simulated signal calculated using the forward calculation model is compared. The water cloud parameters input into the forward calculation model are optimized based on the error iteration. When the relative error is less than the set threshold, the water cloud parameters selected are the accurate water cloud effective radius and extinction coefficient parameters obtained by inversion.

[0013] Furthermore, in step (1), the modified Gamma distribution is used as the water cloud particle size distribution model, the effective radius range of the water cloud is set to 4 to 20 μm, the corresponding water cloud particle size distribution is input, the Mie scattering theory is used to calculate the corresponding water cloud scattering phase matrix, and a corresponding lookup table of the water cloud scattering phase matrix and the effective radius is established.

[0014] In step (2), the forward calculation model is used to calculate the Rayleigh scattering signal of atmospheric molecules. Compared with the single scattering echo signal of water clouds calculated by the general lidar equation, the forward calculation model more comprehensively considers the signal part caused by multiple scattering of water clouds. When other hardware parameters of the high spectral resolution lidar are determined, the Rayleigh scattering signal of atmospheric molecules calculated by the forward calculation model can be written as a function of the receiving field of view angle, effective radius, and extinction coefficient:

[0015] B M,ijk =F(FOV i ,r eff,j ,α k )

[0016] In the formula, B M is the calculated Rayleigh scattering signal of atmospheric molecules; FOV is the receiving field angle of the system; r eff is the effective radius of water cloud; α is the extinction coefficient of water cloud; i=1,...,n; j=1,...,m; k=1,...,p; n, m and p are the numbers of different input field angles, effective radii and extinction coefficients; based on this, n×m×p groups of atmospheric molecular Rayleigh scattering signals with different parameter combinations are obtained.

[0017] In step (3), the water cloud effective radius and extinction coefficient parameters are fine-tuned, and a set of specific formulas for atmospheric molecule Rayleigh scattering signals under different receiving field angles are re-simulated as follows:

[0018] r eff1,j =r eff,j +Δr eff,j

[0019] α 1,k =α k +Δα k

[0020] B M1,ijk =F(FOV i ,r eff1,j ,α 1,k )=B M,ijk +ΔB M,ijk

[0021] In the formula, r eff1 , α1, B M1is the effective radius, extinction coefficient and Rayleigh scattering signal of atmospheric molecules after fine-tuning; Δr eff , Δα, ΔB M is the difference before and after the corresponding fine-tuning.

[0022] Based on the difference before and after fine-tuning, the sensitivity of the atmospheric molecule Rayleigh scattering signal to the effective radius and extinction coefficient of water clouds under different receiving field angles is calculated. The formula is as follows:

[0023]

[0024]

[0025] In the formula, and SC α are the sensitivities of the Rayleigh scattering signal of atmospheric molecules to the effective radius and extinction coefficient of water clouds, respectively.

[0026] The specific process of step (4) is as follows:

[0027] The signal sensitivity obtained in step (3) is plotted as the field of view angle changes. The relationship between the signal sensitivity to the effective radius and the field of view angle and the signal sensitivity to the extinction coefficient and the field of view angle under two conditions of different effective radii and extinction coefficients are obtained, and a total of 4 curves of 2×2 are plotted. Under the conditions of different effective radii and extinction coefficients, the peak position of the signal sensitivity to a single water cloud parameter is consistent, that is, it corresponds to the field of view angle that is most sensitive to the change of effective radius and extinction coefficient, respectively, which is used as the dual field of view angle parameter of the dual-field of view high spectral resolution lidar for water cloud inversion.

[0028] In step (5), the water cloud signal is observed using the optimal field of view setting to obtain the dual-field-of-view measured atmospheric molecule Rayleigh scattering signal; a set of initial values ​​of the water cloud effective radius and extinction coefficient parameters are set, and the high spectral resolution lidar dual-field-of-view simulated atmospheric molecule Rayleigh scattering signal is calculated using the forward calculation model according to the actual system parameters. The simulated signal and the measured signal are compared, and the water cloud parameters are iteratively optimized to gradually reduce the relative error between the simulated signal and the measured signal. When the relative error is less than the set threshold, the selected water cloud parameters are the water cloud effective radius and extinction coefficient parameters obtained by inversion.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention uses a dual-field-of-view high-spectral-resolution lidar system for water cloud inversion. By evaluating the sensitivity of the signal to the effective radius and extinction coefficient parameters of water clouds, a field-of-view angle optimization scheme for water cloud inversion using a high-spectral-resolution lidar system is proposed.

[0031] 2. The present invention overcomes the shortcomings of existing lidar water cloud inversion methods. By selecting the best dual-field-of-view setting and fully considering the multiple scattering information of water clouds, accurate water cloud inversion based on dual-field-of-view high-spectral resolution lidar can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart of a high spectral resolution lidar field of view optimization method for water cloud inversion provided by an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of the structure of a dual-field-of-view high-spectral-resolution laser radar system for water cloud inversion in an embodiment of the present invention;

[0034] Figure 3 The sensitivity of the Rayleigh scattering signal of atmospheric molecules to the effective radius and extinction coefficient of water clouds varies with the field of view in the embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0036] like Figure 1 As shown, a high spectral resolution lidar field of view optimization method for water cloud inversion includes the following steps:

[0037] S1: Use the modified Gamma distribution as the water cloud particle size distribution model, set the effective radius range of water clouds to 4-20 μm, input the corresponding water cloud particle size distribution, use the Mie scattering theory to calculate the corresponding water cloud scattering phase matrix, and establish a corresponding relationship lookup table between the water cloud scattering phase matrix and the effective radius.

[0038] S2: Figure 2As shown, the dual-field-of-view high-spectral-resolution laser radar system for water cloud inversion in the embodiment of the present invention includes several modules including a transmitting system, a receiving system, and a photoelectric detection system, specifically including a narrow-band single-frequency polarized pulse laser 1, a beam expander 2, a first reflector 3, a first telescope 4, a first field-of-view aperture 5, a first collimating eyepiece 6, a second reflector 7, a first iodine molecule absorption cell 8, a first photomultiplier tube channel 9, a second telescope 10, a second field-of-view aperture 11, a second collimating eyepiece 12, a third reflector 13, a polarization beam splitter prism 14, a beam splitter prism 15, a second photomultiplier tube channel 16, a third photomultiplier tube channel 17, a second iodine molecule absorption cell 18, a fourth photomultiplier tube channel 19, and other devices. The polarized laser emitted by the transmitting system is scattered by atmospheric water clouds, and the generated backscattered light is received by two telescope systems with different field-of-view angles, and finally detected by the molecular channel 1 and the molecular channel 2 to obtain echo signals. The laser and detection wavelength of this system is 532nm, the field of view FOV1 and FOV2 are adjustable, and the spatial resolution of signal detection is 7.5m.

[0039] The water cloud height is set to 2000m, the cloud thickness is set to 200m, and the vertical center of the cloud is used as the calculation reference point. The effective radius of the water cloud is set to 6μm, 10μm, 14μm, and 18μm; the extinction coefficient is set to 0.01m -1 、0.02m -1 、0.03m -1 、0.04m -1 The dual field of view angle ranges from 0.2mrad to 6mrad, with a value interval of 0.1mrad. A total of 944 sets of atmospheric molecular Rayleigh scattering signals of high spectral resolution lidar corresponding to different effective radii, extinction coefficients and dual field of view angle combinations were calculated using the forward calculation model.

[0040] S3: Add 0.1μm and 0.001m to the effective radius and extinction coefficient of water clouds respectively -1 The fine-tuning amount is , and other parameters remain unchanged. The forward calculation model is used to calculate again to obtain 944 sets of atmospheric molecular Rayleigh scattering signals of high spectral resolution lidar after fine-tuning.

[0041] S4: Through the fine-tuning of the atmospheric molecule Rayleigh scattering signal, effective radius and extinction coefficient obtained in the above steps S2 and S3, the sensitivity of the atmospheric molecule Rayleigh scattering signal to the effective radius and extinction coefficient of water clouds can be obtained:

[0042]

[0043]

[0044] In the formula, and SC αare the sensitivities of the Rayleigh scattering signal of atmospheric molecules to the effective radius and extinction coefficient of water clouds, respectively.

[0045] S5: Plotting a curve of the signal sensitivity obtained in step S4 as it changes with the field of view angle, and obtaining four curves of signal sensitivity to effective radius-field of view angle and signal sensitivity to extinction coefficient-field of view angle under different effective radius and extinction coefficient conditions, such as Figure 3 shown.

[0046] The horizontal coordinate x in the figure is a parameter proportional to the field of view angle, which can be written as:

[0047]

[0048] Wherein, z is the height of the reference point from the cloud base, which is 100 m in this example; H is the cloud base height, which is 2000 m in this embodiment; λ is the laser wavelength, which is 532 nm in this example.

[0049] Depend on Figure 3 It can be seen from (a) and (b) that under different effective radii and extinction coefficients, the sensitivity of the atmospheric molecule Rayleigh scattering signal to the extinction coefficient decreases monotonically with the increase of the field of view angle. Therefore, in order to obtain the field of view angle with the highest sensitivity to the extinction coefficient, the field of view angle should be as small as possible. At the same time, the influence of the laser radar overlap factor in the actual system needs to be considered. Therefore, the field of view that satisfies the overlap factor of 1 should be selected as the field of view angle for water cloud extinction coefficient inversion. In this embodiment, the field of view angle that meets this condition is 0.2 mrad.

[0050] Depend on Figure 3 From (c) and (d), we can see that under different effective radius and extinction coefficient conditions, the sensitivity of the atmospheric molecule Rayleigh scattering signal to the effective radius increases first and then decreases with the increase of the field of view, and its peak value is around x = 0.8. Therefore, the field of view angle used for the inversion of the effective radius of water clouds can be obtained as:

[0051]

[0052] In this embodiment, the effective radius of water cloud takes a typical value of 9 μm, so the field angle used for inversion of the effective radius of water cloud in this embodiment is 1.4 mrad.

[0053] S6: Set the dual fields of view of the high spectral resolution lidar to 0.2 mrad and 1.4 mrad respectively, observe the water cloud signal, compare the relative error between the measured signal and the simulated signal calculated using the forward calculation model, iteratively optimize the water cloud parameters input into the forward calculation model based on the error, and judge that when the relative error is less than the set threshold, the water cloud parameters selected at this time are the accurate water cloud effective radius and extinction coefficient parameters obtained by inversion.

[0054] In this embodiment, the narrowband single-frequency polarized pulse laser 1 adopts a single longitudinal mode pulse Nd:YAG laser with a spectral width not greater than 15 MHz and a laser divergence angle of not greater than 0.5 mrad, such as a seed-injected single longitudinal mode pulse laser and a single longitudinal mode fiber laser. The single longitudinal mode pulse laser has a wavelength of 532 nm, a single pulse energy of 15 mJ, a repetition frequency of 25 Hz, a bandwidth of 15 MHz, and a laser divergence angle of 0.5 mrad.

[0055] The above-mentioned beam expander 2 can adopt a high-power beam expander, such as the BE05-532 model beam expander of Thorlabs, USA, which has a 5-fold beam expansion, a full-angle divergence angle of the laser emitted after the beam expander of 0.1 mrad, and a laser spot size of 30 mm.

[0056] The first reflector 3, the second reflector 7 and the third reflector 13 can all be ordinary two-inch reflectors, such as GCC-101044 produced by Beijing Daheng Company, with a diameter of 40 mm.

[0057] The first telescope 4 and the second telescope 10 can be general-purpose telescopes such as reflective telescopes and catadioptric telescopes, such as the Schmidt-Cassegrain telescope C11-A XLT with an aperture of 280 mm and a focal length of 2800 mm produced by Celestron Corporation of the United States.

[0058] The apertures of the first field diaphragm 5 and the second field diaphragm 11 are adjustable, and the product model is, for example, SM1D12C from Thorlabs, USA.

[0059] The first collimating eyepiece 6 and the second collimating eyepiece 12 both have a focal length of 100 mm, such as GCL-010111 produced by Beijing Daheng Company.

[0060] The polarization beam splitter prism 14 is a common polarization beam splitter prism, which reflects S polarization and transmits P polarization, such as the PBS252 beam splitter prism produced by Thorlabs, USA.

[0061] The above-mentioned beam splitter prism 15 is a beam splitter with a reflectivity lower than a transmittance, such as a BS025 beam splitter produced by Thorlabs, USA.

[0062] The first photomultiplier tube channel 9, the second photomultiplier tube channel 16, the third photomultiplier tube channel 17 and the fourth photomultiplier tube channel 19 can all use high-speed response and high-sensitivity photodiodes, photomultiplier tubes or charge-coupled devices (CCDs), such as the H10721 photomultiplier tube model of Hamamatsu Corporation of Japan; the narrow-band interference filter has a transmission wavelength range of 532nm-533nm, such as the FL532-1 of Thorlabs Corporation of the United States; the optical lens has a focal length of 100mm, such as the GCL-010111 of Beijing Daheng Company.

[0063] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high spectral resolution lidar field of view optimization method for water cloud inversion, characterized in that: By selecting the optimized field of view angle design of the dual-field-of-view high-spectral resolution lidar system, the lidar signals detected at different field of view angles are made highly sensitive to the water cloud characteristic parameters, and the water cloud characteristic parameters are inverted. The water cloud characteristic parameters include the water cloud effective radius and the extinction coefficient parameters; the following steps are included: (1) Input possible water cloud effective radius parameters in advance, calculate the corresponding water cloud scattering phase matrix, and establish a lookup table of the relationship between the water cloud scattering phase matrix and the effective radius parameters; (2) Setting different high-spectral resolution lidar field of view parameters, and inputting other relevant hardware settings and water cloud scattering phase matrix, extinction coefficient, and spatial height parameters according to the actual lidar system, the forward calculation model is used to simulate the atmospheric molecular Rayleigh scattering signals under different receiving field of view angles; The atmospheric molecule Rayleigh scattering signal obtained by the forward calculation model simulation is written as a function of the receiving field angle, effective radius, and extinction coefficient: B M,ijk =F(FOV i ,r eff，j ,α k ) In the formula, B M is the calculated Rayleigh scattering signal of atmospheric molecules; FOV is the receiving field angle of the system; r eff is the effective radius of water cloud; α is the extinction coefficient of water cloud; i=1,...,n; j=1,...,m; k=1,...,p; n, m and p are the number of different input field angles, effective radii and extinction coefficients; based on this, we can get n×m×p groups of atmospheric molecular Rayleigh scattering signals with different parameter combinations; (3) Based on the perturbation method, the water cloud effective radius and extinction coefficient parameters are adjusted, and a set of atmospheric molecular Rayleigh scattering signals under different receiving field angles are re-simulated to calculate the sensitivity of atmospheric molecular Rayleigh scattering signals under different receiving field angles to the water cloud effective radius and extinction coefficient; The specific formulas for the Rayleigh scattering signals of atmospheric molecules under a set of different receiving field angles are as follows: r eff1，j =r eff，j +Δr eff，j a 1，k =a k +Da k B M1，ijk =F(FOV i ,r eff1，j ,α 1，k )=B M，ijk +ΔB M，ijk In the formula, r eff1 , α1, B M1 is the effective radius, extinction coefficient and Rayleigh scattering signal of atmospheric molecules after fine-tuning; Δr eff , Δα, ΔB M is the difference before and after the corresponding fine-tuning; The sensitivity of the atmospheric molecule Rayleigh scattering signal to the effective radius and extinction coefficient of water clouds under different receiving field angles is calculated as follows: In the formula, and SC α are the sensitivities of the Rayleigh scattering signal of atmospheric molecules to the effective radius and extinction coefficient of water clouds, respectively; (4) The two field of view angle parameters with the highest sensitivity to the effective radius and extinction coefficient of atmospheric molecule Rayleigh scattering signals are selected as the optimal field of view settings of the dual-field of view high spectral resolution lidar for inversion of water cloud characteristic parameters; (5) A dual-field-of-view high-spectral-resolution lidar with an optimal field-of-view setting is used to observe water cloud signals. The relative error between the measured signal and the simulated signal calculated using the forward calculation model is compared. The water cloud characteristic parameters input into the forward calculation model are optimized based on the error iteration. When the relative error is less than the set threshold, the water cloud characteristic parameters selected are the accurate water cloud effective radius and extinction coefficient parameters obtained by inversion.

2. The high spectral resolution lidar field of view optimization method for water cloud inversion according to claim 1 is characterized in that: In step (1), the modified Gamma distribution is used as the water cloud particle size distribution model, the effective radius range of the water cloud is set to 4 to 20 μm, the corresponding water cloud particle size distribution is input, the Mie scattering theory is used to calculate the corresponding water cloud scattering phase matrix, and a corresponding lookup table of the water cloud scattering phase matrix and the effective radius is established.

3. The high spectral resolution lidar field of view optimization method for water cloud inversion according to claim 1 is characterized in that: The specific process of step (4) is as follows: The signal sensitivity obtained in step (3) is plotted as the field of view angle changes. The relationship between the signal sensitivity to the effective radius and the field of view angle and the signal sensitivity to the extinction coefficient and the field of view angle under two conditions of different effective radii and extinction coefficients are obtained, and a total of 4 curves of 2×2 are plotted. Under the conditions of different effective radii and extinction coefficients, the peak position of the signal sensitivity to a single water cloud characteristic parameter is consistent, that is, it corresponds to the field of view angle that is most sensitive to the change of effective radius and extinction coefficient, respectively, which is used as the dual field of view angle parameter of the dual-field of view high spectral resolution lidar for water cloud inversion.

4. The high spectral resolution lidar field of view optimization method for water cloud inversion according to claim 1, characterized in that: The specific process of step (5) is as follows: using the optimal field of view setting to observe the water cloud signal, and obtaining the dual-field-of-view measured atmospheric molecule Rayleigh scattering signal; setting a set of initial values ​​of the water cloud effective radius and extinction coefficient parameters, and using the forward calculation model to calculate the high spectral resolution lidar dual-field-of-view simulated atmospheric molecule Rayleigh scattering signal according to the actual system parameters, comparing the simulated signal with the measured signal, and iteratively optimizing the water cloud characteristic parameters, so that the relative error between the simulated signal and the measured signal gradually decreases. When the relative error is less than the set threshold, the selected water cloud characteristic parameters are the water cloud effective radius and extinction coefficient parameters obtained by inversion.

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