Method for selecting calibration height layers of satellite-borne laser radars with different wavelengths

Abstract

The invention provides a method for selecting calibration height layers of satellite-borne laser radars with different wavelengths, and relates to the field of atmospheric remote sensing. On the basis of SAGE III / ISS and reanalysis data, optical parameters of a stratosphere blue light wave band are accurately calculated by combining wavelength conversion and data fusion; comprising the following implementation steps: step 1), selecting SAGE III / ISS data and preprocessing the data; 2) correcting the refractive index of the aerosol, and carrying out stratosphere scattering calculation; 3) establishing a stratosphere aerosol optical parameter wavelength conversion model; step 4), calculating a stratosphere blue light aerosol backscattering coefficient and an atmospheric molecule backscattering coefficient; step 5), data space-time matching fusion; and step 6), calculating an aerosol scattering ratio and selecting a calibration height.

Description

Technical Field

[0001] This application relates to the field of atmospheric remote sensing, and specifically proposes a method for selecting calibration altitude layers at different wavelengths based on spaceborne lidar data. Background Technology

[0002] Spaceborne lidar, a core technology in modern remote sensing, transmits high-precision laser pulses from a satellite platform and receives atmospheric backscattered signals. It has been widely applied in areas such as global cloud-aerosol vertical distribution detection, carbon cycle monitoring, and three-dimensional wind field inversion. By measuring and analyzing the backscattered laser signals, spaceborne lidar satellites provide rich information on atmospheric vertical profiles, including clouds, aerosols, atmospheric wind fields, and carbon dioxide concentrations. For spaceborne lidar measurements, instrument calibration is essential to ensure the accuracy, reliability, and scientific value of the measurement data. Radiometric calibration converts the electrical signals obtained by detectors in different channels into backscattered signals with practical physical meaning, thereby enabling precise measurement of environmental optical parameters.

[0003] In current technologies for radiometric calibration of spaceborne lidar, the calibration area is often selected within a certain altitude region of the stratosphere because the aerosol content in this altitude calibration region is relatively low and stable. However, aerosols in the calibration region are a significant source of radiometric calibration errors for spaceborne lidar. Their optical parameters and variations can affect the accuracy of the calibration results, further impacting the overall reliability of the spaceborne lidar data. Therefore, understanding the optical parameters of stratospheric aerosols is necessary to evaluate the calibration results during calibration.

[0004] Currently, the measurement of aerosol backscattering coefficients in the stratosphere relies on spaceborne and ground-based lidar. However, due to the limitations of lidar's own radiometric calibration, the amount of aerosol optical parameters that can be measured in the stratosphere is limited and the errors are significant. There is currently no reliable source of stratospheric optical parameters. This lack of reliable measurement and acquisition of stratospheric aerosol optical parameters negatively impacts the calibration of spaceborne lidar.

[0005] In view of the above, this patent application is hereby filed. Summary of the Invention

[0006] The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths described in this application aims to solve the problems existing in the prior art by innovatively proposing a multi-wavelength optical parameter inversion model for stratospheric aerosols based on satellite remote sensing data, thus providing a reliable solution for selecting the radiation calibration altitude of spaceborne lidar.

[0007] To achieve the above design objectives, the method for selecting the calibration altitude layer of the spaceborne lidar with different wavelengths is based on SAGE III / ISS and reanalysis data, combined with wavelength conversion and data fusion to accurately calculate the optical parameters of the stratospheric blue light band.

[0008] The implementation steps include the following:

[0009] Step 1) Select SAGE III / ISS data and perform data preprocessing;

[0010] Download the SAGE III / ISS L2 solar aerosol extinction coefficient data and remove low signal-to-noise ratio and outliers from the data;

[0011] Step 2) Aerosol refractive index correction and stratospheric scattering calculation;

[0012] The refractive index of stratospheric aerosols was corrected, and the extinction efficiency factor and backscattering efficiency factor of stratospheric aerosols were calculated based on the Mie scattering theory.

[0013] Step 3) Establish a wavelength conversion model for stratospheric aerosol optical parameters;

[0014] Using Mie scattering theory, an aerosol model and particle size distribution were defined, and a transformation lookup table was established.

[0015] Step 4) Calculate the backscattering coefficient of stratospheric blue light aerosol and the backscattering coefficient of atmospheric molecules;

[0016] Using the stratospheric aerosol optical parameter conversion model, SAGEIII / ISS data were input into a lookup table to obtain the stratospheric blue light band aerosol backscattering coefficient; combined with reanalysis data, the global atmospheric molecular backscattering coefficient was calculated using Rayleigh scattering theory.

[0017] Step 5) Data spatiotemporal matching and fusion;

[0018] The atmospheric molecular backscattering coefficient and the aerosol backscattering coefficient were unified to the same height resolution using the barosphere interpolation method for spatiotemporal matching.

[0019] Step 6) Calculate the aerosol scattering ratio and select the calibration height;

[0020] After spatiotemporal matching, and by dividing the aerosol backscattering coefficient at the same altitude resolution by the molecular backscattering coefficient, the aerosol scattering ratio is obtained. Based on the aerosol scattering ratio, the calibration altitude of the spaceborne lidar with different wavelengths is selected.

[0021] Further, in step 1), the extinction coefficient data of SAGE III / ISS L2 solar aerosols are downloaded and preprocessed, including but not limited to setting a threshold based on the height according to the data uncertainty, excluding data with uncertainty exceeding the threshold, removing outliers in the upper stratosphere, using the MAD (Median Absolute Deviation) method to dynamically select the threshold range of outliers based on the height, removing data with extinction ratio and extinction coefficient exceeding the threshold, and excluding certain large particulate aerosols.

[0022] Further, in step 2), the stratospheric aerosol composition is set, the refractive index is corrected according to the actual temperature of the stratosphere, and the backscattering efficiency and extinction efficiency of different particle sizes under multi-wavelength conditions are calculated according to the Mie scattering theory.

[0023] The stratospheric aerosols were set as sulfate type. The refractive index of the stratospheric aerosols measured in the laboratory was corrected to the actual temperature of the stratospheric zone by Lorentz transformation. The backscattering efficiency and extinction efficiency under multiple wave and different particle sizes were calculated according to Mie scattering theory, and the corresponding data were generated.

[0024] Further, in step 3), using the backscattering efficiency and efficiency obtained in step 2) for multiple wavelengths and different particle sizes, the extinction ratio of 520 / 1020nm, the extinction ratio of 486 / 520nm and the lidar ratio of 486nm are calculated for different particle sizes; a lookup table is established using the 520 / 1020nm extinction ratio as the input parameter to construct an optical parameter wavelength conversion model;

[0025] Based on the following formula: σ(λ)=∫πr 2 n(r)Q ext (λ,r)dr, Calculate the backscattering coefficient and extinction coefficient of an aerosol with particle size r and wavelength λ; where Q ext Q back Here, n(r) represents the extinction efficiency factor and the backscattering efficiency factor, and n(r) is the assumed aerosol particle size spectrum.

[0026] Matching σ(λ) and β(λ) for the same particle size is performed to calculate the extinction ratio of 520 / 1020nm, the extinction ratio of 486 / 520nm and the lidar ratio of 486nm, in order to generate a lookup table.

[0027] Further, in step 4), using the lookup table generated in step 3), based on the SAGEIII / ISS data processed in step 2), the SAGE III / ISS 520 / 1020nm extinction ratio data is calculated and substituted into the lookup table to obtain the optical conversion parameters at the target location.

[0028] Based on the extinction coefficient at 520 nm, the backscattering coefficient of stratospheric aerosols was calculated.

[0029] Atmospheric molecular extinction coefficients were calculated using ERA May average data, and then atmospheric backscattering coefficients were further calculated based on the formula. The molecular extinction coefficient was calculated, where N A is Avogadro's constant, with a value of 6.02214 × 10⁻⁶. 23 (1 / mol); R a Q is the gas constant, with a value of 8.314472 (J / K / mol); s (λ) is the molecular scattering cross section, which is related to the wavelength;

[0030] Using empirical formulas Calculations are performed, and the molecular extinction coefficient is then used based on the formula. The molecular backscattering coefficient was calculated.

[0031] Further, in step 5), based on the atmospheric backscattering coefficient, the height resolution is matched with the SAGEIII / ISS spatial resolution after interpolation and resampling using a cubic spline function on the ERA5 gravitational potential data, and a global three-dimensional mesh is generated. The generated mesh has a horizontal resolution of 0.25°×0.25° and a vertical resolution of 500m.

[0032] Further, in step 6), the molecular backscattering coefficient data and the stratospheric aerosol backscattering coefficient data are spatiotemporally matched and fused to calculate the stratospheric aerosol scattering ratio.

[0033] The formula for calculating the backscatter ratio is: Where R a β is the aerosol scattering ratio. a β is the aerosol backscattering coefficient. m The molecular backscattering coefficient;

[0034] The calibration altitude of spaceborne lidar is selected based on the aerosol scattering ratio.

[0035] In summary, the method for selecting the calibration altitude layer of spaceborne lidar with different wavelengths proposed in this application has the following advantages:

[0036] 1. This application addresses the shortcomings of existing spaceborne lidar in measuring optical parameters of stratospheric aerosols in the blue light band. It can assist in measuring the optical parameters of aerosol blue light wavelength and proposes a novel inversion method, thereby effectively solving the core technical problems of difficulty in obtaining optical parameters of stratospheric aerosols in the blue light band and the small amount of data.

[0037] 2. Based on Mie scattering theory, this application constructs a stratospheric optical parameter conversion lookup table by calculating the optical parameter characteristics of different aerosols under multiple wavelengths and particle sizes, thereby realizing the automatic calculation of stratospheric aerosol optical parameters and the calculation results are more accurate.

[0038] 3. This application effectively supplements the problem of insufficient data on aerosol optical parameters in the stratosphere by calculating the aerosol backscattering ratio to select the calibration height of spaceborne lidar, and provides a better solution for selecting the calibration height of spaceborne lidar at different wavelengths. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the method for selecting the calibration altitude layer of spaceborne lidar with different wavelengths.

[0040] Figure 2 This is a schematic diagram of data preprocessing based on the MAD method; where... Figure 2 (a) is a schematic diagram of the extinction ratio filter value. Figure 2 (b) is a schematic diagram of the extinction coefficient filter value;

[0041] Figure 3 This is a comparison chart showing wavelength conversion of the 486nm stratospheric aerosol profile; among which, Figure 3 (a) is a schematic diagram before wavelength conversion. Figure 3 (b) is a schematic diagram after wavelength conversion;

[0042] Figure 4 This is a comparison chart of aerosol scattering ratio and CALIPSO L3 stratospheric data;

[0043] Figure 5 This is a schematic diagram of the 486nm aerosol scattering ratio calculated using this application. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1, such as Figures 1 to 5As shown, this application proposes a novel method for selecting the calibration altitude layer of a spaceborne lidar with different wavelengths. This method is based on satellite remote sensing data and ERA5 reanalysis data. It constructs a lookup table based on Mie scattering theory to perform wavelength conversion and calculates the optical parameters of different wavelengths of stratospheric aerosols and the aerosol scattering ratio in order to select the calibration altitude of the spaceborne lidar.

[0046] Specifically, Mie scattering is a theory describing the interaction between light waves and particles, first proposed by the German physicist Gustav Mie in 1908. Mie scattering is primarily applicable when the particle size is comparable to or larger than the wavelength of the incident light; it describes the scattering phenomenon of light when interacting with spherical particles (such as water droplets, aerosols, etc.). In Mie scattering, the intensity and distribution of the scattered light depend not only on the wavelength of the incident light and the size of the particles, but also on their shape and refractive index.

[0047] Aerosols are dispersion systems composed of solid or liquid particles suspended in a gaseous medium.

[0048] The backscattering coefficient is a characteristic parameter describing the scattering of electromagnetic waves, sound waves, or other types of waves in the opposite direction to the incident wave during propagation due to inhomogeneities in the medium or the action of a target object. It is usually denoted by β and its unit is km. -1 ·sr -1 The backscattering coefficient measured by lidar consists of two parts: molecular backscattering coefficient and aerosol backscattering coefficient.

[0049] The extinction coefficient represents the degree of light attenuation per unit path length, that is, the proportion of energy lost by light during propagation due to scattering and absorption by media such as aerosols. It is usually represented by α and the unit is km. -1 .

[0050] The extinction ratio represents the ratio of the extinction coefficients between different wavelengths of aerosols, and can characterize the relative size of aerosol particles at the target location to a certain extent.

[0051] Atmospheric pressure refers to the atmospheric pressure acting on a unit area, which is numerically equal to the weight of a vertical column of air extending upwards to the upper boundary of the atmosphere per unit area.

[0052] Temperature refers to the thermal state of a substance and is usually used to describe the level of heat in an object.

[0053] A profile is a curve that shows how a certain parameter of the atmosphere or Earth's surface changes with altitude or distance.

[0054] The implementation steps include the following:

[0055] Step 1) Select SAGE III / ISS data and perform data preprocessing;

[0056] Select and download the 520 and 1020 nm extinction coefficients from the SAGE III / ISS L2 solar v5.3 aerosol extinction coefficient data, and preprocess the data, including removing data with low signal-to-noise ratio and outliers.

[0057] Among them, a threshold is set based on the height of the data uncertainty to exclude data whose uncertainty exceeds the threshold;

[0058] Outliers in the upper stratosphere are removed by using the MAD method (Median Absolute Deviation, a robust metric in statistics, often used to measure the dispersion of data, especially suitable for outlier detection) to dynamically select the outlier threshold range based on altitude.

[0059] Because aerosol concentrations are low above 30 km and an ozone absorption peak exists near 520 nm, the aerosol extinction coefficient exhibits high uncertainty and some negative values. This data uncertainty affects the accuracy of the method, and the negative values ​​do not reflect true physical conditions. Therefore, for data above 30 km, all negative values ​​are discarded, and relative uncertainty is controlled, with data exceeding 100% being removed. For data below 30 km, data with relative uncertainty exceeding 20% ​​are removed.

[0060] Data with extinction ratios and extinction coefficients exceeding the thresholds were discarded to exclude certain large aerosol particles.

[0061] To determine the extinction coefficients at 520 and 1020 nm after removing outliers, firstly, calculate the extinction ratio between 520 and 1020 nm using the following formula: Furthermore, the MAD method is used to remove outliers in the monthly 520 and 1020 nm extinction coefficients and 520 / 1020 nm extinction ratios. For example, the removal interval is 2.5 km as the altitude interval, with the altitude range selected between 20-40 km, and the latitude intervals are -70°S--30°S, -30°S-0°, 0°-30°N, and 30°N-70°N. The threshold within each dynamic interval is determined according to the MAD method, and outliers in the extinction ratio and extinction coefficient exceeding the threshold are filtered out. The metric factor in the MAD method can be selected as 2.5.

[0062] Step 2) Aerosol refractive index correction and stratospheric scattering calculation;

[0063] The refractive index of stratospheric aerosols was corrected, and the extinction efficiency factor and backscattering efficiency factor of stratospheric aerosols at 486, 520, and 1020 nm were calculated based on the Mie scattering theory.

[0064] In the absence of volcanic activity or other unforeseen events, the stratospheric aerosol background field is dominated by sulfate-type aerosols. When performing stratospheric aerosol refractive index correction, the stratospheric aerosols are set as sulfate-type aerosols.

[0065] The refractive index of stratospheric aerosols measured in the laboratory was corrected to the actual temperature of the stratosphere using the Lorentz transformation, and the backscattering efficiency and extinction efficiency under multiple wave and different particle sizes were calculated based on the Mie scattering theory to generate corresponding data.

[0066] Specifically, the sulfate-type aerosol consists of droplets of 75% sulfuric acid and 25% aqueous solution. The aerosol refractive index is measured at 300K, and Lorentz correction is used to adjust the refractive index to 215K. The correction formula is as follows:

[0067]

[0068] Where n(300) is the complex refractive index of the sulfuric acid droplet at 300K, ρ(300) is the density of the sulfuric acid droplet at 300K, and ρ(T) is the density of the sulfuric acid droplet at temperature T.

[0069] According to the table, the density ρ(300) of sulfuric acid droplets at 300K is 1.67 g / cm³. 3 The density ρ(215) of a sulfuric acid droplet at 215 K is 1.75 g / cm³. 3 .

[0070] After refractive index correction, the refractive indices of the sulfuric acid droplet at 215K and wavelengths of 486, 520, and 1020 nm are 1.457, 1.456, 1.445-1.62 × 10⁻⁶, respectively. -5 j.

[0071] Step 3) Establish a stratospheric aerosol optical parameter conversion model;

[0072] Using Mie scattering theory, an aerosol model and particle size distribution were defined, and a transformation lookup table was established.

[0073] The key to establishing a stratospheric aerosol optical parameter conversion model is to establish the correlation between the optical parameters of sulfate aerosols at different wavelengths based on Mie scattering theory, and to establish a link with the extinction coefficient measured by SAGEIII / ISS. For aerosols of the same particle size, the optical parameters at different wavelengths are relatively fixed, and the extinction ratio can characterize the particle size of aerosols to a certain extent.

[0074] Using Mie scattering theory, the aerosol model is set as sulfate aerosol, and the aerosol refractive index is obtained from the calculation results of step 2) above. The particle size distribution is set and a transformation lookup table is established.

[0075] For example, the aerosol particle size distribution is set to a log-normal distribution, as shown in the following formula:

[0076]

[0077] Where, σ g r represents the standard deviation of the particle size distribution. m The geometric mean radius is taken as the spectral standard deviation range of 1.2-2.0, with an interval of 0.1, and the geometric mean radius ranges from 10 to 1500 nm.

[0078] The miepython library in Python is used to calculate and iterate through all results at 486, 520, and 1020 nm, with spectral standard deviations ranging from 1.2 to 2.0 and geometric mean particle sizes between 10 and 1500 nm, and the data is saved.

[0079] Accordingly, the theoretical backscattering coefficients and extinction coefficients that would appear at particle size and spectral standard deviation at 486, 520, and 1020 nm under Mie scattering theory are calculated according to the following formulas.

[0080] σ(λ)=∫πr 2 n(r)Q ext (λ,r)dr,

[0081] Among them, Q ext Q back Here, n(r) represents the extinction efficiency factor and the backscattering efficiency factor, and n(r) is the assumed aerosol particle size spectrum.

[0082] Furthermore, for the same particle size and spectral standard deviation, the extinction ratio at 486 / 520 nm, the lidar ratio at 486 nm, and the lidar ratio at 520 / 1020 nm were calculated and the data were saved under the Mie scattering theory. The calculation formulas are as follows:

[0083]

[0084] In the above formula, The extinction coefficient at 486 nm is given for each case where the spectral standard deviation is between 1.2 and 2.0, and the geometric mean radius is between 10 and 1500 nm. The extinction coefficient at 520 nm is given for each case. The ratio of 486nm lidar in each case.

[0085] Since there is a set of 486 / 520nm extinction ratios for each spectral standard deviation and geometric mean, and the 486 lidar ratio corresponds to the 520 / 1020nm lidar ratio, a stratospheric optical parameter conversion lookup table can be established by using the 520 / 1020nm extinction ratio as input and the 486 / 520nm extinction ratio and the 486 lidar ratio as outputs.

[0086] For the lookup table, the actual calculation can be performed when the spectral standard deviation is 1.5, while the cases corresponding to other spectral standard deviations are used for sensitivity experiments.

[0087] A wavelength conversion model was constructed. The geometric mean radius of the aerosol particle size spectrum parameters was set to a range of 10-1500 nm with a step size interval of 1 nm. The spectral standard deviation parameter was set to 1.2-2.0 with a step size interval of 0.1. The lookup table required for optical parameter conversion was calculated using the case with a spectral standard deviation of 1.5. Other lookup tables were used for spectral standard deviation sensitivity experiments. To make the lookup table results more accurate, the lookup table was interpolated and smoothed using a cubic spline function.

[0088] Step 4) Calculate the backscattering coefficient of stratospheric blue light aerosol and the backscattering coefficient of atmospheric molecules;

[0089] Using the stratospheric aerosol optical parameter conversion model, SAGEIII / ISS data were input into a lookup table to obtain the stratospheric blue light band aerosol backscattering coefficient; combined with reanalysis data, the global atmospheric molecular backscattering coefficient was calculated using Rayleigh scattering theory.

[0090] Specifically, using the lookup table generated in step 3), and based on the SAGE III / ISS data processed in step 2), the SAGE III / ISS 520 / 1020nm extinction ratio data is calculated using the following formula:

[0091]

[0092] For each profile at each height, the 520 / 1020nm extinction ratio data is substituted into the lookup table to obtain the 486 / 520nm extinction ratio and the 486nm lidar ratio at the target location;

[0093] The search results entered into the lookup table are based on the nearest neighbor search result;

[0094] Based on the extinction coefficient at 520 nm, the backscattering coefficient of blue light from stratospheric aerosols was calculated; taking 486 nm as an example, according to the formula... The backscattering coefficient at 486 nm was calculated, where S 486 The 486nm lidar ratio obtained from the lookup table, The extinction ratio is 486 / 520nm, α 520，SAGE The extinction coefficient at 520 nm obtained from step 2);

[0095] The atmospheric molecular extinction coefficient was calculated using ERA May average data, in order to further calculate the atmospheric backscattering coefficient.

[0096] When calculating the backscattering coefficient of atmospheric molecules, Rayleigh scattering is mainly considered, and the calculation process is as follows:

[0097] Based on formula The molecular extinction coefficient was calculated, where N is Avogadro's constant, with a value of 6.02214 × 10⁻⁶. 23 (1 / mol); R a Q is the gas constant, with a value of 8.314472 (J / K / mol); s (λ) is the molecular scattering cross section, which is related to the wavelength;

[0098] Using empirical formulas Calculations are performed, and the molecular extinction coefficient is then used based on the formula. The molecular backscattering coefficient was calculated.

[0099] Step 5) Data spatiotemporal matching and fusion;

[0100] The atmospheric molecular backscattering coefficient and the aerosol backscattering coefficient were unified to the same height resolution using the barosphere interpolation method for spatiotemporal matching.

[0101] Specifically, based on the atmospheric backscattering coefficient calculated in step 4), the height resolution is matched with the SAGEIII / ISS spatial resolution after interpolation and resampling using cubic spline functions based on ERA5 gravity potential data, and a global three-dimensional mesh is generated. The generated mesh has a horizontal resolution of 0.25°×0.25° and a vertical resolution of 500m.

[0102] Step 6) Calculate the aerosol scattering ratio and select the calibration height;

[0103] After spatiotemporal matching, and by dividing the aerosol backscattering coefficient by the molecular backscattering coefficient at the same altitude resolution, the aerosol scattering ratio is obtained. Calibration altitudes for spaceborne lidar of different wavelengths are then selected based on the aerosol scattering ratio.

[0104] Specifically, step 5) is used to perform spatiotemporal matching and fusion of molecular backscattering coefficient data and stratospheric aerosol backscattering coefficient data to calculate the stratospheric aerosol scattering ratio.

[0105] The formula for calculating the backscattering ratio is: Among them, Ra β is the aerosol scattering ratio. a β is the aerosol backscattering coefficient. m is the molecular backscattering coefficient.

[0106] The aerosol can be set as an ideal radiation calibration procedure, i.e., R a，m =1, and the formula for calculating the aerosol error during the calibration process is δR. a =R a -R a，m =R a -1, based on the calculation result δR a <1%, 2%, 3%..., select the acceptable height layer error one by one for radiometric calibration.

[0107] If the above calculation process is used for radiation calibration, that is... To average the profile results at different latitudes and altitudes, with an altitude range of 20-40 km and a step size of 0.5 km, and a latitude range of -70° to 70° and a step size of 5°, the formula for calculating aerosol error during the calibration process is as follows: The result δR can be calculated. a <1%, 2%, 3%..., select acceptable height layer errors one by one for radiometric calibration.

[0108] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for selecting the calibration altitude layer of a spaceborne lidar with different wavelengths, characterized in that: Based on SAGE III / ISS and reanalysis data, wavelength conversion and data fusion were combined to accurately calculate the optical parameters of the stratospheric blue light band. The implementation steps include the following: Step 1) Select SAGE III / ISS data and perform data preprocessing; Download the SAGE III / ISS L2 solar aerosol extinction coefficient data and remove low signal-to-noise ratio and outliers from the data; Step 2) Aerosol refractive index correction and stratospheric scattering calculation; The refractive index of stratospheric aerosols was corrected, and the extinction efficiency factor and backscattering efficiency factor of stratospheric aerosols were calculated based on the Mie scattering theory. Step 3) Establish a wavelength conversion model for stratospheric aerosol optical parameters; Using Mie scattering theory, an aerosol model and particle size distribution were defined, and a transformation lookup table was established. Step 4) Calculate the backscattering coefficient of stratospheric blue light aerosol and the backscattering coefficient of atmospheric molecules; Using the stratospheric aerosol optical parameter conversion model, SAGE III / ISS data were input into a lookup table to obtain the stratospheric blue light band aerosol backscattering coefficient; combined with reanalysis data, the global atmospheric molecular backscattering coefficient was calculated using Rayleigh scattering theory. Step 5) Data spatiotemporal matching and fusion; The atmospheric molecular backscattering coefficient and the aerosol backscattering coefficient were unified to the same height resolution using the barosphere interpolation method for spatiotemporal matching. Step 6) Calculate the aerosol scattering ratio and select the calibration height; After spatiotemporal matching, and by dividing the aerosol backscattering coefficient at the same altitude resolution by the molecular backscattering coefficient, the aerosol scattering ratio is obtained. Based on the aerosol scattering ratio, the calibration altitude of the spaceborne lidar with different wavelengths is selected.

2. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: Step 1) involves downloading and preprocessing the SAGE III / ISS L2 solar aerosol extinction coefficient data, including but not limited to setting a threshold based on the height according to the data uncertainty, excluding data with uncertainty exceeding the threshold, removing outliers in the upper stratosphere, using the MAD (Median Absolute Deviation) method to dynamically select the outlier threshold range based on the height, removing data with extinction ratio and extinction coefficient exceeding the threshold, and excluding certain large particulate aerosols.

3. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: Step 2) Set the stratospheric aerosol composition, correct the refractive index according to the actual temperature of the stratosphere, and calculate the backscattering efficiency and extinction efficiency of different particle sizes under multi-wavelength conditions according to the Mie scattering theory. The stratospheric aerosols were set as sulfate type. The refractive index of the stratospheric aerosols measured in the laboratory was corrected to the actual temperature of the stratospheric zone by Lorentz transformation. The backscattering efficiency and extinction efficiency under multiple wave and different particle sizes were calculated according to Mie scattering theory, and the corresponding data were generated.

4. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: In step 3), using the backscattering efficiency and efficiency obtained in step 2) for multiple wavelengths and different particle sizes, the extinction ratio of 520 / 1020nm, 486 / 520nm and 486nm lidar ratio for different particle sizes are calculated; a lookup table is established using the 520 / 1020nm extinction ratio as the input parameter to construct an optical parameter wavelength conversion model. Based on the following formula: Calculate the backscattering coefficient and extinction coefficient of an aerosol with particle size r and wavelength λ; where Q ext Q back Here, n(r) represents the extinction efficiency factor and the backscattering efficiency factor, and n(r) is the assumed aerosol particle size spectrum. Matching is performed on σ(λ) and β(λ) for the same particle size to calculate the extinction ratio of 520 / 1020nm, the extinction ratio of 486 / 520nm and the lidar ratio of 486nm, in order to generate a lookup table.

5. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: In step 4), using the lookup table generated in step 3), the SAGE III / ISS 520 / 1020nm extinction ratio data is calculated based on the SAGE III / ISS data processed in step 2) and then substituted into the lookup table to obtain the optical conversion parameters at the target location. Based on the extinction coefficient at 520 nm, the backscattering coefficient of stratospheric aerosols was calculated. Atmospheric molecular extinction coefficients were calculated using ERA May average data, and then atmospheric backscattering coefficients were further calculated based on the formula. The molecular extinction coefficient was calculated, where N A is Avogadro's constant, with a value of 6.02214 × 10⁻⁶. 23 (1 / mol); R a Q is the gas constant, with a value of 8.314472 (J / K / mol); s (λ) is the molecular scattering cross section, which is related to the wavelength; Using empirical formulas Calculations are performed, and the molecular extinction coefficient is then used based on the formula. The molecular backscattering coefficient was calculated.

6. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: In step 5), based on the atmospheric backscattering coefficient, the height resolution is matched with the SAGE III / ISS spatial resolution after interpolation and resampling using a cubic spline function on the ERA5 gravitational potential data, and a global three-dimensional mesh is generated. The generated mesh has a horizontal resolution of 0.25°×0.25° and a vertical resolution of 500m.

7. The method for selecting calibration altitude layers for spaceborne lidar of different wavelengths according to claim 1, characterized in that: Step 6) involves spatiotemporal matching and fusion of molecular backscattering coefficient data and stratospheric aerosol backscattering coefficient data to calculate the stratospheric aerosol scattering ratio. The formula for calculating the backscatter ratio is: Where R a β is the aerosol scattering ratio. a β is the aerosol backscattering coefficient. m The molecular backscattering coefficient; The calibration altitude of spaceborne lidar is selected based on the aerosol scattering ratio.

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