Atmospheric stratification iterative inversion method and system based on Fernald method

Abstract

The present application provides an iterative inversion method and system for atmospheric stratification based on the Fernald method, which involves lidar technology. The method includes preprocessing the original echo signal and identifying cloud position information based on the slope method; initializing the aerosol extinction backscattering ratio of the cloud layer, iteratively adjusting the aerosol extinction backscattering ratio of the cloud layer based on the aerosol backscattering coefficient of the cloud base area until the set conditions are met, and recording the final aerosol extinction backscattering ratio of the cloud layer; inverting the aerosol backscattering coefficient sub-profiles of the area below the cloud base and above the cloud top based on the initialized backscattering ratio, inverting the cloud layer aerosol backscattering coefficient sub-profile based on the cloud backscattering ratio, and calculating the vertical profile of the aerosol extinction coefficient at the full height. By dynamically optimizing the aerosol extinction backscattering ratio in the cloud area, negative values ​​and over-suppression at the cloud base are eliminated, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions.

Description

Technical Field

[0001] The present application relates to the field of laser radar technology, and in particular to an atmospheric stratification iterative inversion method and system based on the Fernald method. Background Art

[0002] Among existing lidar atmospheric detection technologies, the Fernald inversion algorithm is a commonly used aerosol extinction coefficient inversion method for single-wavelength Mie scattering lidar. This algorithm treats the aerosol extinction backscatter ratio (lidar ratio) as a constant and calculates the extinction coefficient distribution through back-integration. However, when cirrus clouds or a high-concentration aerosol layer are present in the atmosphere, the actual aerosol extinction backscatter ratio in the cloud or aerosol region often differs significantly from the conventionally assumed value, causing the entire extinction coefficient profile to produce negative values ​​or be distorted at the cloud base or in the cloud layer, affecting the inversion accuracy. For example, if the aerosol extinction backscatter ratio is too low in the cloud base region, the extinction coefficient will be too high; if it is too large, the extinction coefficient will become negative below the cloud base.

[0003] In summary, in the existing technology, the actual aerosol extinction backscattering ratio in cloud areas or aerosol areas is often significantly different from the conventional assumed value. Therefore, the inversion error is large under complex cloud conditions, making it difficult to meet the needs of high-precision, real-time online monitoring. Summary of the Invention

[0004] Based on this, it is necessary to provide an atmospheric stratification iterative inversion method and system based on the Fernald method to address the above technical problems, which can dynamically optimize the aerosol extinction backscattering ratio in the cloud area, eliminate the negative value and over-suppression phenomenon at the cloud base, and help improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions.

[0005] In a first aspect, the present application provides an atmospheric stratification iterative inversion method based on the Fernald method, comprising:

[0006] Preprocessing the original echo signal;

[0007] Based on the pre-processed raw echo signal, cloud position information is identified using the slope method; the cloud position information includes the cloud base height and cloud top height;

[0008] Initialize the aerosol extinction backscatter ratio of the cloud layer, iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area based on the Fernald method until the aerosol backscatter coefficient of the cloud base area meets the set conditions, and record the final backscatter ratio of the cloud layer, including: based on the Fernald method combined with known system constants and calibration points, invert the aerosol backscatter coefficient of the cloud layer according to the value of the aerosol extinction backscatter ratio of the cloud layer; determine whether there are clouds in the current measurement group, and if there are no clouds, directly use the Fernald method to calculate the aerosol backscatter coefficient. If there are clouds, the aerosol backscattering coefficient corresponding to the cloud base area is compared with the reference aerosol backscattering coefficient. If the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, the aerosol extinction backscattering ratio of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer. The aerosol extinction backscattering ratio of the cloud layer is adjusted iteratively for multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold.

[0009] Based on the Fernald method, the aerosol backscattering coefficient sub-profiles of the area below the cloud base and above the cloud top are retrieved according to the initialized aerosol extinction backscattering ratio, and the aerosol backscattering coefficient sub-profile of the cloud layer is retrieved according to the final aerosol extinction backscattering ratio of the cloud layer.

[0010] The vertical profile of the aerosol extinction coefficient at the full height is calculated based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

[0011] In one embodiment, preprocessing the original echo signal includes:

[0012] Select the preset first height range as the background window, perform least square fitting background estimation on the original echo signal, and deduct background noise;

[0013] The signal after background noise deduction is subjected to triangular smoothing to remove high-frequency noise and generate the pre-processed original echo signal.

[0014] In one embodiment, identifying cloud layer position information according to a slope method includes:

[0015] Calculating the linear fitting slope of the pre-processed original echo signal with a fixed spatial resolution within a preset second height range;

[0016] The linear fitting slope of each spatial resolution group is compared with the slope threshold. If the slopes of multiple consecutive spatial resolution groups are greater than the first slope threshold, the corresponding lowest point is determined to be the cloud base. If the linear fitting slope of a spatial resolution group is less than the second slope threshold and the echo signal strength is less than the cloud base signal, the corresponding position is determined to be the cloud top.

[0017] In one embodiment, it is ensured that the cloud base height is greater than a height threshold.

[0018] In one embodiment, initializing the aerosol extinction backscattering ratio of the cloud layer includes initializing the value of the aerosol extinction backscattering ratio of the cloud layer and specifying an upper limit and a lower limit.

[0019] In one embodiment, the aerosol extinction backscattering ratio of the cloud layer is iteratively adjusted according to the aerosol backscattering coefficient of the cloud base region based on the Fernald method until the aerosol backscattering coefficient of the cloud base region meets a set condition, including:

[0020] Based on the Fernald method combined with known system constants and calibration points, the aerosol backscattering coefficient of the cloud layer is inverted according to the value of the aerosol extinction backscattering ratio of the cloud layer;

[0021] Determine whether there are clouds in the current measurement group. If there are no clouds, directly calculate the aerosol backscattering coefficient using the Fernald method. If there are clouds, compare the aerosol backscattering coefficient corresponding to the cloud base area with the reference aerosol backscattering coefficient. If the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, adjust the aerosol extinction backscattering ratio value of the cloud layer according to the initialization value, upper limit and lower limit of the aerosol extinction backscattering ratio of the cloud layer.

[0022] The value of the aerosol extinction backscattering ratio of the cloud layer is adjusted iteratively multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold.

[0023] In one embodiment, adjusting and updating the value of the aerosol extinction backscattering ratio of the cloud layer according to the value, upper limit, and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer includes:

[0024] If the aerosol backscatter coefficient corresponding to the cloud base area is smaller than the aerosol backscatter coefficient of the reference group at the same height, the calculation formula for the aerosol extinction backscatter ratio of the updated cloud layer is as follows:

[0025]

[0026] If the aerosol backscatter coefficient corresponding to the cloud base area is greater than the aerosol backscatter coefficient of the reference group at the same height, the calculation formula for the aerosol extinction backscatter ratio of the updated cloud layer is as follows:

[0027]

[0028] in, is the value of the aerosol extinction backscatter ratio of the updated cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit of the aerosol extinction backscattering ratio of the cloud layer.

[0029] In one embodiment, the calculation process of the aerosol backscatter coefficient of the reference group includes:

[0030] Obtain a continuous cloud-free signal sequence without sudden slope changes within a set time before and after the current cloud profile moment;

[0031] Preprocess the cloud-free signal sequence to generate a cloud-free net signal;

[0032] The aerosol backscattering coefficient profile was calculated based on the cloud-free net signal using the Fernald method, and the value of the aerosol backscattering coefficient profile at the cloud base height was used as the aerosol backscattering coefficient value of the reference group at that height.

[0033] In a second aspect, the present application provides an atmospheric stratification iterative inversion system based on the Fernald method, comprising:

[0034] A signal preprocessing module, used for preprocessing the original echo signal;

[0035] A cloud layer recognition module is used to identify cloud layer position information based on the pre-processed raw echo signal using the slope method; wherein the cloud layer position information includes the cloud base height and cloud top height;

[0036] The backscattering ratio generation module is used to initialize the aerosol extinction backscattering ratio of the cloud layer, iteratively adjust the aerosol extinction backscattering ratio of the cloud layer according to the aerosol backscattering coefficient of the cloud base area based on the Fernald method, until the aerosol backscattering coefficient of the cloud layer meets the set conditions, and record the final aerosol extinction backscattering ratio of the cloud layer, including: based on the Fernald method combined with known system constants and calibration points, invert the aerosol backscattering coefficient of the cloud layer according to the value of the aerosol extinction backscattering ratio of the cloud layer; determine whether there are clouds in the current measurement group, and if there are no clouds, directly use the Fernald method to calculate the aerosol backscattering coefficient. If there are clouds, the aerosol backscattering coefficient corresponding to the cloud base area is compared with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, the aerosol extinction backscattering ratio value of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer; the aerosol extinction backscattering ratio value of the cloud layer is adjusted iteratively multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold;

[0037] The aerosol backscatter coefficient sub-profile inversion module is used to invert the aerosol backscatter coefficient sub-profiles of the area below the cloud base and above the cloud top based on the initialized aerosol backscatter ratio based on the Fernald method, and to invert the aerosol backscatter coefficient sub-profile of the cloud layer based on the final aerosol extinction backscatter ratio of the cloud layer;

[0038] The extinction coefficient vertical profile generation module is used to calculate the vertical profile of the aerosol extinction coefficient at the full height based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

[0039] In a third aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the following steps:

[0040] Preprocessing the original echo signal;

[0041] Based on the pre-processed raw echo signal, cloud position information is identified using the slope method; the cloud position information includes the cloud base height and cloud top height;

[0042] Initialize the aerosol extinction backscatter ratio of the cloud layer, and iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area based on the Fernald method until the aerosol backscatter coefficient of the cloud layer meets the set conditions, and record the final aerosol extinction backscatter ratio of the cloud layer;

[0043] Based on the Fernald method, the aerosol backscattering coefficient sub-profiles of the area below the cloud base and above the cloud top are retrieved according to the initialized aerosol extinction backscattering ratio, and the aerosol backscattering coefficient sub-profile of the cloud layer is retrieved according to the final aerosol extinction backscattering ratio of the cloud layer.

[0044] The vertical profile of the aerosol extinction coefficient at the full height is calculated based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

[0045] This application adopts the above-mentioned atmospheric stratification iterative inversion method based on the Fernald method, which has the following beneficial effects:

[0046] 1. Compare the aerosol extinction backscatter ratio of the cloud layer with the reference aerosol extinction backscatter corresponding to the cloud-free group profile, dynamically optimize the aerosol extinction backscatter ratio in the cloud area, eliminate the negative value and over-suppression phenomenon at the cloud base, and help improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions.

[0047] 2. A segmented backward integral inversion strategy is adopted to determine the aerosol extinction backscattering ratios of the areas below the cloud base, the cloud layer, and the areas above the cloud top, respectively. Then, the aerosol backscattering coefficient sub-profiles of the areas below the cloud base, the cloud layer, and the areas above the cloud top are inverted respectively. Based on the aerosol backscattering coefficient sub-profiles, the vertical profile of the aerosol extinction coefficient at the full height is calculated, thereby effectively suppressing error accumulation and improving the inversion accuracy of the full profile.

[0048] 3. The cloud base and cloud top positions are automatically identified by the slope method and the adaptive threshold method mentioned above to avoid misjudging the aerosol layer as clouds, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic diagram of a pre-processed original echo signal provided in one embodiment;

[0050] Figure 2 Schematic diagram of cloud base and cloud top identification based on the slope method and adaptive threshold method provided in one embodiment; wherein (a) is a schematic diagram of the distribution of radar echo signal slope at different altitude intervals; (b) is a profile of the aerosol extinction coefficient at corresponding altitudes;

[0051] Figure 3 The inversion error comparison curves of the present invention method and the traditional Fernald method in different height intervals provided in one embodiment are shown; wherein (a) is the extinction coefficient comparison curve; (b) is the relative error comparison curve of the extinction coefficient;

[0052] Figure 4Schematic diagram of the vertical profile of the complete atmospheric extinction coefficient obtained by actual measurement using the method of the present application provided in one embodiment; wherein, (a) is the lidar ratio of the cloud calculated using the method of the present application; (b) is the spatiotemporal distribution diagram of the aerosol extinction coefficient inverted by the traditional Fernald method; and (c) is the spatiotemporal distribution diagram of the aerosol extinction coefficient re-inverted using the method of the present application. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0054] First, let's introduce the steps of inverting the aerosol backscattering coefficient and extinction coefficient using the Fernald method:

[0055] Taking Mie scattering lidar as an example, the atmospheric backscatter echo signal it receives can be expressed as:

[0056]

[0057] Where P(z) is the echo power received by the lidar at distance z; C is the system constant; and are the aerosol backscattering coefficient and molecular backscattering coefficient at distance z, respectively; and are the aerosol extinction coefficient and molecular extinction coefficient at distance z, respectively.

[0058] There are five unknowns in the above equation, namely C 、 、 、 and Because the components of molecules in the atmosphere are often relatively stable, It can be calculated using the U.S. Standard Atmosphere Model. Assuming that the molecular extinction backscattering ratio S2 is constant, we have:

[0059]

[0060] Among them, S2 is taken as 8π / 3 according to the atmospheric molecular model.

[0061] for and , we can also assume that the two satisfy the relationship:

[0062]

[0063] Where S1 is the aerosol extinction backscatter ratio, also known as the aerosol lidar ratio. Its value is affected by the aerosol scale spectrum and refractive index and is typically between 10sr and 100sr. The traditional Fernald method assumes this value is constant and does not vary with altitude, assuming S1 = 50sr for the tropospheric and stratospheric background period.

[0064] The constant C needs to be calibrated. The specific method is to find the height z of a low-concentration aerosol near the top of the troposphere. c , and assuming that the aerosol backscatter coefficient at this altitude is known, this value is generally stable at high altitudes and can be taken as 1.01. Therefore, the main error of this method is the aerosol extinction backscatter ratio. Substituting the above relationship into the formula for the atmospheric backscatter echo signal, the atmospheric aerosol backscatter coefficient can be solved:

[0065]

[0066] in, The measured height is at the calibration height z c The atmospheric aerosol backscatter coefficient is in the form of back integration when: X(z)=P(z)z 2 is the distance squared signal.

[0067] In a first aspect, based on the above principles, the present application provides an atmospheric stratification iterative inversion method based on the Fernald method, comprising:

[0068] S100, preprocessing the original echo signal.

[0069] In one embodiment, the original echo signal is preprocessed, including: selecting a preset first height range as a background window, performing least squares fitting background estimation on the original echo signal, and deducting background noise; performing triangular smoothing on the signal after deducting the background noise to remove high-frequency noise and generate a preprocessed original echo signal.

[0070] In one embodiment, referring to Figure 1 , this application gives the pre-processed original laser radar echo signal.

[0071] S200 , based on the pre-processed original echo signal, identifying cloud position information according to a slope method; wherein the cloud position information includes cloud base height and cloud top height.

[0072] In one embodiment, cloud position information is identified according to a slope method, including: calculating the linear fitting slope of the preprocessed original echo signal with a fixed spatial resolution within a preset second altitude range; comparing the linear fitting slope of each spatial resolution group with a slope threshold; if the slopes of multiple consecutive spatial resolution groups are greater than the first slope threshold, the corresponding lowest point is determined to be the cloud base; if the linear fitting slope of a certain spatial resolution group is less than the second slope threshold and the echo signal strength is less than the cloud base signal, the corresponding position is determined to be the cloud top.

[0073] For example, within a preset altitude range of 4-12 km, the linear fit slope of the preprocessed raw echo signal is calculated at a fixed spatial resolution of 150 m. If the slopes of five consecutive spatial resolution groups are all greater than the first slope threshold +0.01, the corresponding lowest point is determined to be cloud base. If the linear fit slope of a spatial resolution group is less than -0.01 and the echo signal strength is less than the cloud base signal, the corresponding location is determined to be cloud top.

[0074] In one embodiment, the cloud base height is ensured to be greater than a height threshold to avoid misidentifying a low-lying aerosol layer as a cloud layer.

[0075] In one embodiment, the altitude threshold comprises 4.5 km.

[0076] The cloud base and cloud top positions are automatically identified by the slope method and the adaptive threshold method mentioned above, avoiding misjudging the aerosol layer as clouds, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions.

[0077] S300: Initialize the aerosol extinction backscatter ratio of the cloud layer. Based on the Fernald method, iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area until the aerosol backscatter coefficient of the cloud base area meets the set conditions. Record the final aerosol extinction backscatter ratio of the cloud layer.

[0078] In one embodiment, initializing the aerosol extinction backscattering ratio of the cloud layer includes initializing the value of the aerosol extinction backscattering ratio of the cloud layer and specifying an upper limit and a lower limit.

[0079] For example, the aerosol extinction backscatter ratio of the initial cloud layer is 80sr, the lower limit of the aerosol extinction backscatter ratio is 50sr, and the upper limit of the aerosol extinction backscatter ratio is 100sr.

[0080] In one embodiment, the aerosol extinction backscattering ratio of the cloud layer is iteratively adjusted according to the aerosol backscattering coefficient of the cloud base region based on the Fernald method until the aerosol backscattering coefficient of the cloud layer meets the set conditions, including: inverting the aerosol backscattering coefficient of the cloud layer according to the value of the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method in combination with known system constants and calibration points; judging whether there are clouds in the current measurement group, and if there are no clouds, directly calculating the aerosol backscattering coefficient using the Fernald method; if there are clouds, adjusting the cloud base region to the The corresponding aerosol backscattering coefficient is compared with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is greater than or equal to the difference threshold, the value of the aerosol extinction backscattering ratio of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer; the value of the aerosol extinction backscattering ratio of the cloud layer is iteratively adjusted multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold.

[0081] In one embodiment, the value of the aerosol extinction backscattering ratio of the updated cloud layer is adjusted according to the value, upper limit, and lower limit of the aerosol extinction backscattering ratio of the initial cloud layer, including: if the aerosol backscattering coefficient corresponding to the cloud base region is less than the reference aerosol backscattering coefficient, that is, the aerosol backscattering coefficient of the reference group at the height, then the calculation formula for the value of the aerosol extinction backscattering ratio of the updated cloud layer is as follows:

[0082]

[0083] If the aerosol backscattering coefficient corresponding to the cloud base area is greater than the reference aerosol backscattering coefficient, that is, the aerosol backscattering coefficient of the reference group in this area, the calculation formula for the aerosol extinction backscattering ratio of the updated cloud layer is as follows:

[0084]

[0085] in, is the value of the aerosol extinction backscatter ratio of the updated cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit of the aerosol extinction backscattering ratio of the cloud layer.

[0086] Compare the value of the aerosol extinction backscattering ratio with the value of the reference aerosol extinction backscattering ratio. Theoretically, if the actual aerosol extinction backscattering ratio of the cloud layer is consistent with the initial value, the aerosol backscattering coefficient corresponding to the cloud base height is equal to the aerosol backscattering coefficient of the reference group at that height. In other words, the initial value does not need to be adjusted and is the actual aerosol extinction backscattering ratio of the cloud layer.

[0087] The actual situation can be divided into two types: if the backscattering coefficient corresponding to the cloud base height is greater than the reference aerosol backscattering coefficient, it means that the aerosol extinction backscattering ratio (80sr) of the assumed initial cloud layer is too large, and this value needs to be reduced to make the aerosol extinction backscattering ratio equal to the reference aerosol extinction backscattering ratio as much as possible, then the aerosol extinction backscattering ratio of the current cloud layer is updated to 65sr, that is, (50+80) / 2=65sr; similarly, if the backscattering coefficient corresponding to the cloud base height is less than the reference aerosol backscattering coefficient, then the aerosol extinction backscattering ratio of the current cloud layer is updated to 90sr, that is, (80sr+100sr) / 2=90sr.

[0088] Repeat the above steps to adjust the aerosol extinction backscattering ratio of the cloud layer until the absolute value of the difference between the backscattering coefficient corresponding to the cloud base height and the reference aerosol backscattering coefficient is less than the difference threshold, and record the final aerosol extinction backscattering ratio of the cloud layer.

[0089] In one embodiment, the reference aerosol backscattering coefficient is the aerosol backscattering coefficient at the altitude when there is no cloud in time closest to the current cloud profile. The calculation process includes: obtaining a continuous cloud-free signal sequence without a sudden change in slope within a set time before and after the current cloud profile moment; preprocessing the cloud-free signal sequence to generate a cloud-free net signal; calculating the aerosol backscattering coefficient profile based on the cloud-free net signal based on the Fernald method, and using the value of the aerosol backscattering coefficient profile at the cloud base height as the reference aerosol backscattering coefficient value.

[0090] In one embodiment, in the case where the cloud layer lasts for a long time, if no cloud-free signal sequence can be found within a set time period, the nearest cloud-free group profile is selected as a reference.

[0091] Through the above process, the aerosol backscattering coefficient corresponding to the cloud base height is compared with the aerosol backscattering coefficient of the reference group at the same height, that is, the reference aerosol backscattering coefficient corresponding to the cloud-free group profile is compared, and the aerosol extinction backscattering ratio in the cloud area is dynamically optimized to eliminate the negative value and over-suppression phenomenon of the cloud base, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud conditions.

[0092] S400, based on the Fernald method, inverts the aerosol backscattering coefficient sub-profiles of the area below the cloud base and above the cloud top according to the initialized aerosol extinction backscattering ratio, and inverts the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer.

[0093] S500 calculates the vertical profile of the aerosol extinction coefficient at the full altitude based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer, and the area above the cloud top.

[0094] A piecewise backward integral inversion strategy is adopted to determine the aerosol extinction backscattering ratios of the area below the cloud base, the cloud layer and the area above the cloud top, respectively. Then, the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top are inverted respectively. Based on the aerosol backscattering coefficient sub-profiles, the vertical profile of the aerosol extinction coefficient at the full height is calculated, thereby effectively suppressing error accumulation and improving the inversion accuracy of the full profile.

[0095] Based on the above method, this application provides a complete inversion process example. This example uses a 532nm wavelength, Mie-scattering lidar system, and the system constants have been obtained through calibration. The sampling resolution is 15m, the data acquisition frequency is 1Hz, and the backscattered echo signal is acquired within the altitude range of 0-10km.

[0096] This application uses the slope method and threshold method to determine whether there are clouds, and calculates the cloud base and cloud top heights. First, the pre-processed original echo signal is taken as a set of data every 150m. Taking the spatial resolution of 15m as an example, there are 10 height points within the range of 150m. The slopes of these 10 points are calculated. If the slope signal can satisfy the positive growth of the slopes of the next 5 consecutive points, then the point is considered to be the location of the cloud base. Secondly, when the signal strength of a certain point is less than the cloud base signal strength and the slope is less than -0.01, the point is considered to be the location of the cloud top. Finally, the calculation of the cloud base height is set to above 4.5km to prevent the aerosol layer from being misjudged as a cloud layer.

[0097] Reference Figure 2 In (a), the black line is the slope distribution of the radar echo signal in the altitude range of 4 to 12 km, and the red line is the fitting slope of the sky background light, with a value of -0.01. The positions of the cloud base and cloud top found by the above method are marked. Figure 2 (b) in Figure 2 (b) is the aerosol extinction coefficient profile at the corresponding height, and Figure 2 The cloud base and cloud height positions in (a) are marked. By comparing the two, we can find that this method can better determine the location of the clouds.

[0098] After locating the cloud layer, the cloud lidar ratio is calculated using a bisection method and linear iteration. Under the assumption of continuous measurements, the cloud-free aerosol extinction coefficient profile closest to the aerosol extinction profile to be inverted is selected. It is assumed that the aerosol layer at cloud base remains stable during this period, meaning that the backscatter ratio remains unchanged. The cloud-free aerosol extinction backscatter ratio at cloud base is used as the reference value for the inversion under cloud conditions. The lidar ratio at the cloud location is set to 100 sr and the Fernald method is used to invert the aerosol extinction coefficient. If the inverted aerosol extinction backscatter ratio at cloud base is smaller than the cloud-free reference value, the cloud lidar ratio is large. The lidar ratio is set to 50 sr and recalculated. If the reference value is too large, the cloud lidar ratio is too small. In this case, the lidar ratio is set to 75 sr and recalculated. If the cloud base backscatter ratio is still too large, the lidar ratio range of 50 to 75 sr is selected. Calculate in sequence and select the set of backscatter ratios closest to the backscatter ratio at the height of the cloud base under cloud-free conditions as the accurate value of the lidar ratio.

[0099] Reference Figure 3 In (a), the aerosol extinction coefficient profile calculated by the above iterative adjustment is more consistent with the simulation input value, which can effectively overcome the problem that traditional methods cannot accurately invert cloud and cloud bottom aerosols. Figure 3 Panel (b) shows the relative errors of the aerosol extinction coefficients retrieved by the two methods. It can be seen that for the high-concentration aerosol layer at 0-5 km, the relative error decreases from a maximum of 50% to 5%; for the low-concentration aerosol region at cloud base at 5-7.5 km, the relative error decreases from a maximum of 60% to 2%; and for the cloud layer at 7.5-9 km, the relative error decreases from a maximum of 90% to 8%. In summary, compared to traditional methods, the Fernald-based atmospheric stratification iterative algorithm can effectively improve the inversion accuracy, especially for the low-concentration aerosol region at cloud base, reducing the overall error by an order of magnitude.

[0100] Figure 4 The actual atmospheric conditions at a certain place are measured using Mie scattering lidar. Figure 4 (a) shows the cloud lidar ratio calculated using the Fernald atmospheric stratification linear iteration method. This method can effectively locate the cloud position and will not mistakenly identify the aerosol layer near the boundary layer as clouds. In addition, at 13:00, tiny clouds around 8km were also accurately identified. Figure 4Panel (b) shows the aerosol extinction coefficient retrieved using the traditional Fernald method. Above 9 km, the inverted extinction coefficient is less than 0 due to insufficient signal-to-noise ratio, resulting in the presence of black scattered points. Because the inversion process fails to account for variations in the cloud lidar ratio, the extinction coefficient below the cloud appears to be less than 0 over a large area, as shown by the black shaded area in the figure. Furthermore, the cloud lidar ratio affects the spatial and temporal distribution of aerosols above and below the cloud, which is not consistent with reality. Figure 4 (c) is the spatiotemporal distribution of aerosol extinction coefficient re-inverted using the method in this paper, which is consistent with Figure 4 Comparison with (b) in Figure 3 shows that the spatial and temporal distribution of clouds and aerosols is more uniform, and the extinction coefficients of clouds and cloud-base aerosols are more accurately inverted.

[0101] The results of the above examples show that the relative inversion errors of the proposed method for processing high-concentration aerosols, low-concentration cloud-base aerosols, and cloud regions are significantly reduced from a maximum of 50%, 60%, and 90% to 5%, 2%, and 8%, respectively. Furthermore, the proposed method exhibits good convergence and adaptability, relying solely on single-wavelength Mie scattering lidar data. It possesses high practical application value and is particularly suitable for real-time, large-scale rapid inversion of atmospheric vertical structure.

[0102] In a second aspect, the present application provides an atmospheric stratification iterative inversion system based on the Fernald method, comprising:

[0103] A signal preprocessing module, used for preprocessing the original echo signal;

[0104] A cloud layer recognition module is used to identify cloud layer position information based on the pre-processed raw echo signal using the slope method; wherein the cloud layer position information includes the cloud base height and cloud top height;

[0105] The backscatter ratio generation module is used to initialize the aerosol extinction backscatter ratio of the cloud layer, iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area based on the Fernald method, until the aerosol backscatter coefficient of the cloud base area meets the set conditions, and record the final aerosol extinction backscatter ratio of the cloud layer, including: based on the Fernald method combined with known system constants and calibration points, invert the aerosol backscatter coefficient of the cloud layer according to the value of the aerosol extinction backscatter ratio of the cloud layer; determine whether there are clouds in the current measurement group, and if there are no clouds, directly use the Fernald method to calculate the aerosol backscatter coefficient of the cloud layer. Sol backscattering coefficient; if there are clouds, the aerosol backscattering coefficient corresponding to the cloud base area is compared with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, the aerosol extinction backscattering ratio value of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer; the aerosol extinction backscattering ratio value of the cloud layer is adjusted iteratively multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold;

[0106] The aerosol backscatter coefficient sub-profile inversion module is used to invert the aerosol backscatter coefficient sub-profiles of the area below the cloud base and above the cloud top based on the initialized aerosol extinction backscatter ratio based on the Fernald method, and to invert the aerosol backscatter coefficient sub-profile of the cloud layer based on the final aerosol extinction backscatter ratio of the cloud layer;

[0107] The extinction coefficient vertical profile generation module is used to calculate the vertical profile of the aerosol extinction coefficient at the full height based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

[0108] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0109] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. In particular, any reference to memory, database, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases.

[0110] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. An atmospheric stratification iterative inversion method based on the Fernald method, characterized in that: include: Preprocessing the original echo signal; Based on the pre-processed raw echo signal, cloud position information is identified using the slope method; the cloud position information includes the cloud base height and cloud top height; Initialize the aerosol extinction backscatter ratio of the cloud layer, iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area based on the Fernald method until the aerosol backscatter coefficient of the cloud base area meets the set conditions, and record the final aerosol extinction backscatter ratio of the cloud layer, including: based on the Fernald method combined with known system constants and calibration points, invert the aerosol backscatter coefficient of the cloud layer according to the value of the aerosol extinction backscatter ratio of the cloud layer; determine whether there are clouds in the current measurement group, and if there are no clouds, directly use the Fernald method to calculate the aerosol backscatter Coefficient; if there are clouds, compare the aerosol backscattering coefficient corresponding to the cloud base area with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, adjust and update the aerosol extinction backscattering ratio value of the cloud layer according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer; iterate the value of the aerosol extinction backscattering ratio of the cloud layer multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold; Based on the Fernald method, the aerosol backscattering coefficient sub-profiles of the area below the cloud base and above the cloud top are retrieved according to the initialized aerosol extinction backscattering ratio, and the aerosol backscattering coefficient sub-profile of the cloud layer is retrieved according to the final aerosol extinction backscattering ratio of the cloud layer. The vertical profile of the aerosol extinction coefficient at the full height is calculated based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

2. The method according to claim 1, characterized in that Preprocess the original echo signal, including: Select the preset first height range as the background window, perform least square fitting background estimation on the original echo signal, and deduct background noise; The signal after background noise deduction is subjected to triangular smoothing to remove high-frequency noise and generate the pre-processed original echo signal.

3. The method according to claim 2, characterized in that Identify cloud position information based on the slope method, including: Calculating the linear fitting slope of the pre-processed original echo signal with a fixed spatial resolution within a preset second height range; The linear fitting slope of each spatial resolution group is compared with the slope threshold. If the slopes of multiple consecutive spatial resolution groups are greater than the first slope threshold, the corresponding lowest point is determined to be the cloud base. If the linear fitting slope of a spatial resolution group is less than the second slope threshold and the echo signal strength is less than the cloud base signal, the corresponding position is determined to be the cloud top.

4. The method according to claim 3, characterized in that Make sure the cloud base height is greater than the height threshold.

5. The method according to any one of claims 1 to 4, characterized in that Initializing the aerosol extinction backscatter ratio of the cloud layer includes: initializing the value of the aerosol extinction backscatter ratio of the cloud layer and specifying an upper limit and a lower limit.

6. The method according to claim 5, characterized in that The value of the aerosol extinction backscattering ratio of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initial cloud layer, including: If the aerosol backscatter coefficient corresponding to the cloud base area is smaller than the aerosol backscatter coefficient of the reference group at the same height, the calculation formula for the aerosol extinction backscatter ratio of the updated cloud layer is as follows: If the aerosol backscatter coefficient corresponding to the cloud base area is greater than the aerosol backscatter coefficient of the reference group at the same height, the calculation formula for the aerosol extinction backscatter ratio of the updated cloud layer is as follows: in, is the value of the aerosol extinction backscatter ratio of the updated cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit of the aerosol extinction backscattering ratio of the cloud layer.

7. The method according to claim 1, characterized in that The reference aerosol backscatter coefficient is the aerosol backscatter coefficient at the closest cloud-free altitude. The calculation process includes: Obtain a continuous cloud-free signal sequence without sudden slope changes within a set time before and after the current cloud profile moment; Preprocess the cloud-free signal sequence to generate a cloud-free net signal; The aerosol backscattering coefficient profile was calculated based on the cloud-free net signal using the Fernald method, and the value of the aerosol backscattering coefficient profile at the cloud base height was used as the aerosol backscattering coefficient value of the reference group.

8. An atmospheric stratification iterative inversion system based on the Fernald method, characterized in that: include: A signal preprocessing module, used for preprocessing the original echo signal; A cloud layer recognition module is used to identify cloud layer position information based on the pre-processed raw echo signal using the slope method; wherein the cloud layer position information includes the cloud base height and cloud top height; The backscatter ratio generation module is used to initialize the aerosol extinction backscatter ratio of the cloud layer, iteratively adjust the aerosol extinction backscatter ratio of the cloud layer according to the aerosol backscatter coefficient of the cloud base area based on the Fernald method, until the aerosol backscatter coefficient of the cloud base area meets the set conditions, and record the final aerosol extinction backscatter ratio of the cloud layer, including: based on the Fernald method combined with known system constants and calibration points, invert the aerosol backscatter coefficient of the cloud layer according to the value of the aerosol extinction backscatter ratio of the cloud layer; determine whether there are clouds in the current measurement group, and if there are no clouds, directly use the Fernald method to calculate the aerosol backscatter coefficient of the cloud layer. Sol backscattering coefficient; if there are clouds, the aerosol backscattering coefficient corresponding to the cloud base area is compared with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, the aerosol extinction backscattering ratio value of the cloud layer is adjusted and updated according to the value, upper limit and lower limit of the aerosol extinction backscattering ratio of the initialized cloud layer; the aerosol extinction backscattering ratio value of the cloud layer is adjusted iteratively multiple times until the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base area and the reference aerosol backscattering coefficient is less than the difference threshold; The aerosol backscatter coefficient sub-profile inversion module is used to invert the aerosol backscatter coefficient sub-profiles of the area below the cloud base and above the cloud top based on the initialized aerosol extinction backscatter ratio based on the Fernald method, and to invert the aerosol backscatter coefficient sub-profile of the cloud layer based on the final aerosol extinction backscatter ratio of the cloud layer; The extinction coefficient vertical profile generation module is used to calculate the vertical profile of the aerosol extinction coefficient at the full height based on the aerosol backscattering coefficient sub-profiles of the area below the cloud base, the cloud layer and the area above the cloud top.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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