Atmosphere layering iteration inversion method and system based on Fernald method

Abstract

The invention provides an atmosphere layering iteration inversion method and system based on a Fernald method, and relates to a laser radar technology. The method comprises the following steps: preprocessing an original echo signal, and identifying cloud layer position information according to a slope method; initializing the aerosol extinction backscattering ratio of the cloud layer, carrying out iterative adjustment on the aerosol extinction backscattering ratio of the cloud layer according to the aerosol backscattering coefficient of the cloud base region until a set condition is met, and recording the final aerosol extinction backscattering ratio of the cloud layer; and according to the initialized backscattering ratio, inverting aerosol backscattering coefficient sub-profiles of a region below the cloud bottom and a region above the cloud top, according to the backscattering ratio of the cloud, inverting a cloud layer aerosol backscattering coefficient sub-profile, and calculating an aerosol extinction coefficient vertical profile of a complete height. By dynamically optimizing the extinction backscattering ratio of the aerosol in the cloud region, the cloud bottom negative value and the excessive inhibition phenomenon are eliminated, and the inversion precision of the vertical profile of the extinction coefficient of the aerosol under the complex cloud gas condition can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of lidar, and particularly to an atmospheric stratification iterative inversion method and system based on the Fernald method. Background Art

[0002] In the existing lidar atmospheric detection technology, the Fernald inversion algorithm is a commonly used method for inverting the aerosol extinction coefficient of single-wavelength Mie scattering lidar. It regards the aerosol extinction backscattering ratio (lidar ratio) as a fixed value and calculates the extinction coefficient distribution through backscattering integration. However, when there are cirrus clouds or high-concentration aerosol layers in the atmosphere, the true aerosol extinction backscattering ratio in the cloud area or aerosol area often differs greatly from the conventional assumed value, resulting in negative values or distortion of the entire extinction coefficient profile in the cloud base or cloud layer area, affecting the inversion accuracy. For example, in the cloud base area, if the aerosol extinction backscattering ratio is too small, the extinction coefficient will be too high; if it is too large, negative values of the extinction coefficient will appear below the cloud base.

[0003] In summary, in the prior art, the true aerosol extinction backscattering ratio in the cloud area or aerosol area often differs greatly from the conventional assumed value, so the inversion error is large under complex cloud and gas conditions, and it is difficult to meet the requirements of high-precision and real-time online monitoring. Summary of the Invention

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

[0005] In the first aspect, the present application provides an atmospheric stratification iterative inversion method based on the Fernald method, including: Preprocess the original echo signal; Based on the preprocessed original echo signal, identify the cloud layer position information according to the slope method; wherein, the cloud layer position information includes the cloud base height and the cloud top height; Initialize the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base area until the aerosol backscattering coefficient in the cloud base area meets the set conditions, and record the final backscattering ratio of the cloud layer; Based on the Fernald method, invert the sub-profile of the aerosol backscattering coefficient in the area below the cloud base and above the cloud top according to the initialized aerosol extinction backscattering ratio, and invert the sub-profile of the aerosol backscattering coefficient of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; Calculate the vertical profile of aerosol extinction coefficient at full height according to the aerosol backscattering coefficient sub-profiles in the region below the cloud base, the cloud layer, and the region above the cloud top.

[0006] In one embodiment, preprocess the original echo signal, including: Select a preset first height range as the background window, perform least squares fitting background estimation on the original echo signal, and subtract the background noise; Perform triangular smoothing on the signal after subtracting the background noise to remove high-frequency noise and generate the preprocessed original echo signal.

[0007] In one embodiment, identify the cloud layer position information according to the slope method, including: Within a preset second height range, calculate the linear fitting slope of the preprocessed original echo signal with a fixed spatial resolution; Compare the linear fitting slope of each spatial resolution group 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 as 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 intensity is less than the cloud base signal, the corresponding position is determined as the cloud top.

[0008] In one embodiment, ensure that the cloud base height is greater than the height threshold.

[0009] In one embodiment, initialize the aerosol extinction backscattering ratio of the cloud layer, including: initializing the value of the aerosol extinction backscattering ratio of the cloud layer and specifying the upper limit value and the lower limit value.

[0010] In one embodiment, iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base region until the aerosol backscattering coefficient in the cloud base region meets the set conditions, 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; Judge whether there is a cloud in the current measurement group. If there is no cloud, directly calculate the aerosol backscattering coefficient using the Fernald method; if there is a cloud, compare the aerosol backscattering coefficient corresponding to the cloud base region with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base region and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, adjust and update the value of the aerosol extinction backscattering ratio of the cloud layer according to the initialized value, the upper limit value, and the lower limit value of the aerosol extinction backscattering ratio of the cloud layer; Iteratively adjust 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 bottom region and the reference aerosol backscattering coefficient is less than the difference threshold.

[0011] In one embodiment, adjusting and updating the value of the aerosol extinction backscattering ratio of the cloud layer according to the initialized value, upper limit value, and lower limit value of the aerosol extinction backscattering ratio of the cloud layer includes: If the aerosol backscattering coefficient corresponding to the cloud bottom region is less than the aerosol backscattering coefficient of the reference group at this height, the calculation formula for the updated value of the aerosol extinction backscattering ratio of the cloud layer is as follows:

[0012] If the aerosol backscattering coefficient corresponding to the cloud bottom region is greater than the aerosol backscattering coefficient of the reference group at this height, the calculation formula for the updated value of the aerosol extinction backscattering ratio of the cloud layer is as follows:

[0013] Wherein, is the updated value of the aerosol extinction backscattering ratio of the cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit value of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit value of the aerosol extinction backscattering ratio of the cloud layer.

[0014] In one embodiment, the calculation process of the aerosol backscattering coefficient of the reference group includes: Obtain a continuous cloud-free signal sequence without slope mutation 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; Based on the Fernald method, calculate the aerosol backscattering coefficient profile according to the cloud-free net signal, and use the value of the aerosol backscattering coefficient profile at the cloud bottom height as the aerosol backscattering coefficient value of the reference group at this height.

[0015] In a second aspect, the present application provides an atmospheric layer iterative inversion system based on the Fernald method, including: A signal preprocessing module for preprocessing the original echo signal; A cloud layer identification module for identifying the cloud layer position information based on the preprocessed original echo signal according to the slope method; wherein, the cloud layer position information includes the cloud bottom height and the cloud top height; A backscattering ratio generation module is used to initialize the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base region 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; An aerosol backscattering coefficient sub-profile inversion module is used to invert the aerosol backscattering coefficient sub-profiles in the region below the cloud base and above the cloud top based on the Fernald method according to the initialized aerosol backscattering ratio, and invert the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; An extinction coefficient vertical profile generation module is used to calculate the vertical profile of the aerosol extinction coefficient at the full height according to the aerosol backscattering coefficient sub-profiles in the region below the cloud base, the cloud layer, and above the cloud top.

[0016] In a third aspect, the present application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program thereon, and when the computer program is executed by a processor, the following steps are implemented: Preprocess the original echo signal; Based on the preprocessed original echo signal, identify the cloud layer position information according to the slope method; wherein, the cloud layer position information includes the cloud base height and the cloud top height; Initialize the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base region 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; Based on the Fernald method, invert the aerosol backscattering coefficient sub-profiles in the region below the cloud base and above the cloud top according to the initialized aerosol backscattering ratio, and invert the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; Calculate the vertical profile of the aerosol extinction coefficient at the full height according to the aerosol backscattering coefficient sub-profiles in the region below the cloud base, the cloud layer, and above the cloud top.

[0017] The present application adopts the above-mentioned atmospheric layer iterative inversion method based on the Fernald method, and has the following beneficial effects: 1. Compare the aerosol extinction backscattering ratio of the cloud layer with the reference aerosol extinction backscattering corresponding to the cloud-free group profile, dynamically optimize the aerosol extinction backscattering ratio in the cloud region, eliminate the negative value at the cloud base and the over-suppression phenomenon, and help improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud and gas conditions.

[0018] 2. Adopt a segmented backward integration inversion strategy to determine the aerosol extinction backscattering ratio in the region below the cloud base, within the cloud layer, and above the cloud top respectively, and then invert the aerosol backscattering coefficient sub-profiles in the region below the cloud base, within the cloud layer, and above the cloud top respectively. Calculate the vertical profile of the aerosol extinction coefficient at the full height based on the aerosol backscattering coefficient sub-profiles, thereby effectively suppressing error accumulation and improving the inversion accuracy of the full profile.

[0019] 3. Automatically identify the cloud base and cloud top positions through the slope method and the above-mentioned adaptive threshold method to avoid misjudging the aerosol layer as a cloud, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud and aerosol conditions. Brief Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the preprocessed original echo signal provided in an embodiment; Figure 2 It is a schematic diagram of the cloud base and cloud top identified based on the slope method and the adaptive threshold method provided in an embodiment; among them, (a) is a schematic diagram of the distribution of the slope of the radar echo signal in different height intervals; (b) is a profile diagram of the aerosol extinction coefficient at the corresponding height; Figure 3 It is a comparison curve of the inversion errors of the method of the present application and the traditional Fernald method in different height intervals provided in an embodiment; among them, (a) is a comparison curve of the extinction coefficient; (b) is a comparison curve of the relative error of the extinction coefficient; Figure 4 It is a schematic diagram of the vertical profile of the complete atmospheric extinction coefficient obtained through actual measurement using the method of the present application in an embodiment; among them, (a) is the lidar ratio of the cloud calculated using the method of the present application; (b) is the spatio-temporal distribution diagram of the aerosol extinction coefficient inverted by the traditional Fernald method; (c) is the spatio-temporal distribution diagram of the aerosol extinction coefficient re-inverted using the method of the present application. Detailed Embodiment

[0021] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0022] First, introduce the steps of inverting the aerosol backscattering coefficient and extinction coefficient by the Fernald method: Taking the Mie scattering lidar as an example, the atmospheric backscattering echo signal received by it can be expressed as:

[0023] Where, P(z) is the echo power received by the lidar at a distance z; C is the system constant; and are the aerosol backscattering coefficient and the molecular backscattering coefficient at a distance z, respectively; and are the aerosol extinction coefficient and the molecular extinction coefficient at a distance z, respectively.

[0024] There are five unknowns in the above equation, which are C , , , and . Since the composition of molecules in the atmosphere is often relatively stable, the of air molecules can be calculated through the US Standard Atmosphere Model. Assuming that the molecular extinction backscattering ratio S2 is constant, we have:

[0025] Where, S2 takes the value of 8π / 3 according to the atmospheric molecular model.

[0026] For and , it can also be assumed that the two satisfy the relationship:

[0027] Where, S1 is the aerosol extinction backscattering ratio, that is, the aerosol lidar ratio, and its value is affected by the aerosol size spectrum and refractive index, usually between 10 sr and 100 sr. In the traditional Fernald method, it is considered a constant value that does not change with height, and S1 = 50 sr is taken for the troposphere and stratosphere background periods.

[0028] For the constant C, calibration is required. The specific method is to find the height z c of a certain low-concentration aerosol near the tropopause, and assume that the aerosol backscattering coefficient at this height 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 backscattering ratio. Substituting the above relationship into the formula for the atmospheric backscattering echo signal, the atmospheric aerosol backscattering coefficient can be solved:

[0029] Where, is the atmospheric aerosol backscattering coefficient when the measurement height is below the calibration height z c , and it takes the form of backward integration; X(z) = P(z)z 2 is the distance squared signal.

[0030] In a first aspect, based on the above principle, the present application provides an iterative inversion method for atmospheric stratification based on the Fernald method, including: S100, preprocess the original echo signal.

[0031] In one embodiment, preprocessing the original echo signal includes: selecting a preset first height range as a background window, performing least squares fitting background estimation on the original echo signal, and subtracting background noise; performing triangular smoothing on the signal after subtracting background noise to remove high-frequency noise, and generating a preprocessed original echo signal.

[0032] In one embodiment, referring to Figure 1 , the present application gives the original lidar echo signal after preprocessing.

[0033] S200, based on the preprocessed original echo signal, identify cloud layer position information according to the slope method; wherein, the cloud layer position information includes cloud base height and cloud top height.

[0034] In one embodiment, identifying cloud layer position information according to the slope method includes: within a preset second height range, calculating the linear fitting slope of the preprocessed original echo signal at a fixed spatial resolution; 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 a first slope threshold, the corresponding lowest point is determined as the cloud base; if the linear fitting slope of a certain spatial resolution group is less than a second slope threshold and the echo signal intensity is less than the cloud base signal, the corresponding position is determined as the cloud top.

[0035] For example, within a preset height range of 4 - 12 km, calculate the linear fitting slope of the preprocessed original echo signal at a fixed spatial resolution of every 150 m. When the slopes of 5 consecutive spatial resolution groups are all greater than the first slope threshold + 0.01, the corresponding lowest point is determined as the cloud base; if the linear fitting slope of a certain spatial resolution group is less than -0.01 and the echo signal intensity is less than the cloud base signal, the corresponding position is determined as the cloud top.

[0036] In one embodiment, ensure that the cloud base height is greater than a height threshold to avoid misjudging the low-altitude aerosol layer as a cloud layer.

[0037] In one embodiment, the height threshold includes 4.5 km.

[0038] Automatically identify the cloud base and cloud top positions through the slope method and the above-mentioned adaptive threshold method, avoiding misjudging the aerosol layer as a cloud, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud and gas conditions.

[0039] S300, initialize the aerosol extinction backscatter ratio of the cloud layer, and iteratively adjust the aerosol extinction backscatter ratio of the cloud layer based on the Fernald method according to the aerosol backscatter coefficient in the cloud base region until the aerosol backscatter coefficient in the cloud base region meets the set conditions, and record the final aerosol extinction backscatter ratio of the cloud layer.

[0040] In one embodiment, 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 the upper limit value and the lower limit value.

[0041] For example, initialize the value of the aerosol extinction backscatter ratio of the cloud layer to 80 sr, the lower limit value of the aerosol extinction backscatter ratio to 50 sr, and the upper limit value of the aerosol extinction backscatter ratio to 100 sr.

[0042] In one embodiment, iteratively adjusting the aerosol extinction backscatter ratio of the cloud layer based on the Fernald method according to the aerosol backscatter coefficient in the cloud base region until the aerosol backscatter coefficient of the cloud layer meets the set conditions includes: based on the Fernald method combined with known system constants and calibration points, inversely calculate 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 is a cloud in the current measurement group, if there is no cloud, directly calculate the aerosol backscatter coefficient using the Fernald method; if there is a cloud, compare the aerosol backscatter coefficient corresponding to the cloud base region with the reference aerosol backscatter coefficient; if the absolute value of the difference between the aerosol backscatter coefficient corresponding to the cloud base region and the reference aerosol backscatter coefficient is greater than or equal to the difference threshold, adjust and update the value of the aerosol extinction backscatter ratio of the cloud layer according to the value, upper limit value, and lower limit value of the initialized aerosol extinction backscatter ratio of the cloud layer; iteratively adjust the value of the aerosol extinction backscatter ratio of the cloud layer multiple times until the absolute value of the difference between the aerosol backscatter coefficient corresponding to the cloud base region and the reference aerosol backscatter coefficient is less than the difference threshold.

[0043] In one embodiment, adjusting and updating the value of the aerosol extinction backscatter ratio of the cloud layer according to the value, upper limit value, and lower limit value of the initialized aerosol extinction backscatter ratio of the cloud layer includes: if the aerosol backscatter coefficient corresponding to the cloud base region is less than the reference aerosol backscatter coefficient, that is, the aerosol backscatter coefficient of the reference group at this height, the calculation formula for the updated value of the aerosol extinction backscatter ratio of the cloud layer is as follows:

[0044] If the aerosol backscatter coefficient corresponding to the cloud base region is greater than the reference aerosol backscatter coefficient, that is, the aerosol backscatter coefficient of the reference group in this region, the calculation formula for the updated value of the aerosol extinction backscatter ratio of the cloud layer is as follows:

[0045] Among them, is the value of the aerosol extinction backscattering ratio of the updated cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit value of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit value of the aerosol extinction backscattering ratio of the cloud layer.

[0046] Compare the value of the aerosol extinction backscattering ratio with the value of the reference aerosol extinction backscattering ratio. Theoretically, if the true 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 this height. That is to say, the initial value does not need to be adjusted, and it is the true aerosol extinction backscattering ratio of the cloud layer.

[0047] The actual situation can be divided into two cases: If the backscattering coefficient corresponding to the cloud base height is greater than the reference aerosol backscattering coefficient, it means that the assumed initial aerosol extinction backscattering ratio of the cloud layer (80 sr) is too large, and then this value needs to be reduced. Try to make the value of the aerosol extinction backscattering ratio equal to the value of the reference aerosol extinction backscattering ratio, and update the aerosol extinction backscattering ratio of the current cloud layer to 65 sr, that is, (50 + 80) / 2 = 65 sr; Similarly, if the backscattering coefficient corresponding to the cloud base height is less than the reference aerosol backscattering coefficient, update the aerosol extinction backscattering ratio of the current cloud layer to 90 sr, that is, (80 sr + 100 sr) / 2 = 90 sr.

[0048] Repeat the above adjustment steps for 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 aerosol extinction backscattering ratio of the final cloud layer.

[0049] In one embodiment, the reference aerosol backscattering coefficient is the aerosol backscattering coefficient at this height when there is no cloud closest in time. The calculation process includes: obtaining a continuous cloud-free signal sequence without slope mutation within a set time before and after the current cloud profile time; preprocessing the cloud-free signal sequence to generate a cloud-free net signal; calculating the aerosol backscattering coefficient profile based on the Fernald method according to the cloud-free net signal, and taking the value of the aerosol backscattering coefficient profile at the cloud base height as the reference aerosol backscattering coefficient value.

[0050] In one embodiment, for the case where the cloud layer has a long duration, if no cloud-free signal sequence can be searched within the set time before and after, select the closest cloud-free group profile as the reference.

[0051] 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 this height, that is, the reference aerosol backscattering coefficient corresponding to the profile of the cloud-free group is compared, and the aerosol extinction backscattering ratio in the cloud area is dynamically optimized to eliminate the negative value at the cloud base and the over-suppression phenomenon, which helps to improve the inversion accuracy of the vertical profile of the aerosol extinction coefficient under complex cloud and aerosol conditions.

[0052] S400, based on the Fernald method, the sub-profile of the aerosol backscattering coefficient in the area below the cloud base and above the cloud top is inverted according to the initialized aerosol extinction backscattering ratio, and the sub-profile of the aerosol backscattering coefficient in the cloud layer is inverted according to the final aerosol extinction backscattering ratio of the cloud layer.

[0053] S500, calculate the vertical profile of the aerosol extinction coefficient at the full height according to the sub-profiles of the aerosol backscattering coefficient in the area below the cloud base, the cloud layer, and above the cloud top.

[0054] Adopt a segmented backward integration inversion strategy to determine the aerosol extinction backscattering ratios in the area below the cloud base, the cloud layer, and above the cloud top respectively, and then invert the sub-profiles of the aerosol backscattering coefficient in the area below the cloud base, the cloud layer, and above the cloud top respectively. Calculate the vertical profile of the aerosol extinction coefficient at the full height based on the sub-profiles of the aerosol backscattering coefficient, so as to effectively suppress the error accumulation and improve the inversion accuracy of the full profile.

[0055] Based on the above method, this application gives an example of a complete inversion process. This example uses a 532nm wavelength, Mie scattering lidar system, and the system constant has been obtained by calibration. The sampling resolution is 15m, the data acquisition frequency is 1Hz, and the backscattering echo signal in the height range of 0 - 10km is obtained.

[0056] This application uses the slope method and the threshold method to determine whether there is a cloud and calculate the cloud base and cloud top heights. First, take the preprocessed original echo signal every 150m as a group of data. Taking the spatial resolution of 15m as an example, there are 10 height points within 150m. Calculate the slopes of these 10 points. If the slope signal can satisfy that the slopes of the subsequent 5 consecutive points are all positively increasing, then this point is considered the location of the cloud base. Secondly, when the signal intensity of a certain point is less than the signal intensity of the cloud base and the slope is less than -0.01, this point is considered the location of the cloud top. Finally, set the calculation of the cloud base height above 4.5km to prevent misjudging the aerosol layer as a cloud layer.

[0057] Refer to Figure 2 In (a) of, the black line is the slope distribution of the radar echo signal in the height range of 4 - 12km, the red line is the fitted slope of the sky background light, with a value of -0.01, and the positions of the cloud base and cloud top found according to the above method are marked; Refer to Figure 2in (b), Figure 2 in (b) is the aerosol extinction coefficient profile at the corresponding height, and the cloud base height position in Figure 2 (a) is marked. By comparing the two, it can be found that this method can better determine the position of the cloud.

[0058] After finding the cloud layer position, the lidar ratio of the cloud is calculated by the bisection method and the linear iteration method. On the premise of continuous measurement, select the aerosol extinction coefficient profile of the cloud-free area closest to the aerosol extinction profile to be retrieved. Assume that the aerosol layer at the cloud base height remains stable during this period, that is, the backscatter ratio remains unchanged. Take the aerosol extinction backscatter ratio at the cloud base height under cloud-free conditions as the reference value for the inversion under cloudy conditions. Set the lidar ratio at the position of the cloud to 100 sr and substitute it into the Fernald method for the inversion of the aerosol extinction coefficient. If the aerosol extinction backscatter ratio at the retrieved cloud base is smaller than the reference value under cloud-free conditions, it means that the lidar ratio of the cloud is relatively large; set the lidar ratio to 50 sr and recalculate. If the reference value is too large, it means that the lidar ratio of the cloud is relatively small. At this time, set the lidar ratio to 75 sr and recalculate. If the backscatter ratio at the cloud base is still too large, then select the lidar ratio range of 50 - 75 sr. Calculate in turn, and select the group with the backscatter ratio closest to the backscatter ratio at the cloud base height under cloud-free conditions as the accurate value of the lidar ratio.

[0059] Refer to Figure 3 (a), the aerosol extinction coefficient profile calculated by the above iterative adjustment is more consistent with the simulated input value, and can effectively overcome the inability of the traditional method to accurately retrieve clouds and aerosols under the cloud. Refer to Figure 3 (b) gives the relative errors of the aerosol extinction coefficients retrieved by the two methods. It can be found that for the high-concentration aerosol layer at 0 - 5 km, the inversion relative error decreases from a maximum of 50% to 5%; for the low-concentration aerosol area at the cloud base of 5 - 7.5 km, the inversion relative error decreases from a maximum of 60% to 2%; for the cloud layer area of 7.5 - 9 km, the inversion relative error decreases from a maximum of 90% to 8%. In summary, compared with the traditional method, the atmospheric stratification iterative algorithm based on Fernald can effectively improve the inversion accuracy, especially for the inversion accuracy of the low-concentration aerosol area at the cloud base, and the overall error is reduced by an order of magnitude.

[0060] Figure 4 is the actual atmospheric condition measured by a Mie scattering lidar at a certain place. Figure 4(a) in it shows the lidar ratio of clouds calculated using the Fernald atmospheric stratification linear iteration method. Using this method, the cloud layer position can be effectively found, and the aerosol layer near the boundary layer will not be misidentified as clouds; in addition, at 13:00, the tiny cloud layer near 8 km was also accurately identified. Figure 4 (b) in it shows the aerosol extinction coefficient retrieved by the traditional Fernald method. In the area above 9 km, due to insufficient signal-to-noise ratio, the retrieved extinction coefficient is less than 0, so there are black scatter points; since the change in the lidar ratio of clouds is not considered during the retrieval process, the extinction coefficient in the area below the clouds shows a large area less than 0, that is, the black shaded area in the figure; in addition, affected by the lidar ratio of clouds, the spatio-temporal distribution of aerosols between the clouds and below the clouds is uneven and does not conform to the actual situation. Figure 4 (c) in it is the spatio-temporal distribution map of the aerosol extinction coefficient retrieved again using the method of this article. Comparing with Figure 4 (b) in it, it is found that the spatio-temporal distribution of clouds and aerosols is more uniform, and the extinction coefficients of aerosols between the clouds and below the clouds are also retrieved more accurately.

[0061] The results of the above embodiments show that when the method of this application is used to process high-concentration aerosols, low-concentration aerosols below the clouds, and cloud layer regions, the relative retrieval errors are reduced from a maximum of 50%, 60%, and 90% to 5%, 2%, and 8% respectively, and the errors are significantly reduced. At the same time, the method of this application has good convergence and adaptability, only depends on single-wavelength Mie scattering lidar data, has high practical application value, and is especially suitable for real-time and large-scale rapid retrieval scenarios of the atmospheric vertical structure.

[0062] In a second aspect, this application provides an atmospheric stratification iterative retrieval system based on the Fernald method, including: A signal preprocessing module, used for preprocessing the original echo signal; A cloud layer identification module, used for identifying the cloud layer position information based on the preprocessed original echo signal according to the slope method; wherein, the cloud layer position information includes the cloud base height and the cloud top height; A backscattering ratio generation module, used for initializing the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjusting the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base area until the aerosol backscattering coefficient in the cloud base area meets the set conditions, and recording the final aerosol extinction backscattering ratio of the cloud layer; An aerosol backscattering coefficient sub-profile retrieval module, used for retrieving the aerosol backscattering coefficient sub-profiles in the area below the cloud base and above the cloud top based on the Fernald method according to the initialized aerosol extinction backscattering ratio, and retrieving the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; The extinction coefficient vertical profile generation module is used to calculate the aerosol extinction coefficient vertical profile at the full height according to the aerosol backscattering coefficient sub-profiles in the area below the cloud base, the cloud layer, and the area above the cloud top.

[0063] 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 method embodiments are implemented.

[0064] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing 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 method embodiments. Among them, any reference to a memory, a database, or other media used in the various embodiments provided in the present application can include at least one of non-volatile and volatile memories. 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), magnetoresistive 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), etc. The databases involved in the various embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., and are not limited thereto.

[0065] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, 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, it should be considered to be within the scope described in this specification.

[0066] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. An atmospheric stratification iterative inversion method based on the Fernald method, characterized in that, Including: Preprocess the original echo signal; Based on the preprocessed original echo signal, identify the cloud layer position information according to the slope method; wherein, the cloud layer position information includes the cloud base height and the cloud top height; Initialize the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base region until the aerosol backscattering coefficient in the cloud base region meets the set conditions, and record the final aerosol extinction backscattering ratio of the cloud layer; Based on the Fernald method, invert the aerosol backscattering coefficient sub-profiles in the region below the cloud base and above the cloud top according to the initialized aerosol extinction backscattering ratio, and invert the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; Calculate the vertical profile of the aerosol extinction coefficient at the full height according to the aerosol backscattering coefficient sub-profiles in the region below the cloud base, the cloud layer, and above the cloud top.

2. The method according to claim 1, characterized in that Preprocess the original echo signal, including: Select a preset first height range as the background window, perform least squares fitting background estimation on the original echo signal, and subtract the background noise; Perform triangular smoothing on the signal after subtracting the background noise to remove high-frequency noise and generate the preprocessed original echo signal.

3. The method according to claim 2, wherein Identify the cloud layer position information according to the slope method, including: Within a preset second height range, calculate the linear fitting slope of the preprocessed original echo signal with a fixed spatial resolution; Compare the linear fitting slope of each spatial resolution group 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 as 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 intensity is less than the cloud base signal, the corresponding position is determined as the cloud top.

4. The method according to claim 3, characterized in that, Ensure that 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, Initialize the aerosol extinction backscattering ratio of the cloud layer, including: initialize the value of the aerosol extinction backscattering ratio of the cloud layer and specify the upper limit value and the lower limit value.

6. The method according to claim 5, characterized in that Iteratively adjust the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient in the cloud base region until the aerosol backscattering coefficient in the cloud base region meets the set conditions, 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; Judge whether there is cloud in the current measurement group. If there is no cloud, directly calculate the aerosol backscattering coefficient using the Fernald method; if there is cloud, compare the aerosol backscattering coefficient corresponding to the cloud base region with the reference aerosol backscattering coefficient; if the absolute value of the difference between the aerosol backscattering coefficient corresponding to the cloud base region and the aerosol backscattering coefficient at the reference height is greater than or equal to the difference threshold, adjust and update the value of the aerosol extinction backscattering ratio of the cloud layer according to the value, upper limit value, and lower limit value of the initialized aerosol extinction backscattering ratio of the cloud layer; Iteratively adjust 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 region and the reference aerosol backscattering coefficient is less than the difference threshold.

7. The method according to claim 6, wherein Adjust and update the value of the aerosol extinction backscattering ratio of the cloud layer according to the value, upper limit value, and lower limit value of the aerosol extinction backscattering ratio of the initialized cloud layer, including: If the aerosol backscattering coefficient corresponding to the cloud base region is less than the aerosol backscattering coefficient of the reference group at this height, the calculation formula for the updated value of the aerosol extinction backscattering ratio of the cloud layer is as follows: If the aerosol backscattering coefficient corresponding to the cloud base region is greater than the aerosol backscattering coefficient of the reference group at this height, the calculation formula for the updated value of the aerosol extinction backscattering ratio of the cloud layer is as follows: Among them, is the value of the aerosol extinction backscattering ratio of the updated cloud layer; is the value of the aerosol extinction backscattering ratio of the current cloud layer; is the upper limit value of the aerosol extinction backscattering ratio of the cloud layer; is the lower limit value of the aerosol extinction backscattering ratio of the cloud layer.

8. The method according to claim 6, wherein The reference aerosol backscattering coefficient is the aerosol backscattering coefficient at this height when it is cloudless and closest in time. The calculation process includes: Obtain a continuous cloudless signal sequence without slope mutations within a set time before and after the current cloud profile time; Preprocess the cloudless signal sequence to generate a cloudless net signal; Based on the Fernald method, calculate the aerosol backscattering coefficient profile according to the cloudless net signal, and use the value of the aerosol backscattering coefficient profile at the cloud base height as the reference group aerosol backscattering coefficient value.

9. An atmospheric layer iterative inversion system based on the Fernald method, characterized in that, Including: A signal preprocessing module for preprocessing the original echo signal; A cloud layer identification module for identifying the cloud layer position information based on the preprocessed original echo signal according to the slope method; wherein, the cloud layer position information includes the cloud base height and the cloud top height; A backscattering ratio generation module for initializing the aerosol extinction backscattering ratio of the cloud layer, and iteratively adjusting the aerosol extinction backscattering ratio of the cloud layer based on the Fernald method according to the aerosol backscattering coefficient of the cloud base region until the aerosol backscattering coefficient of the cloud base region meets the set conditions, and recording the final aerosol extinction backscattering ratio of the cloud layer; An aerosol backscattering coefficient sub-profile inversion module for inverting the aerosol backscattering coefficient sub-profiles of the region below the cloud base and the region above the cloud top based on the Fernald method according to the initialized aerosol extinction backscattering ratio, and inverting the aerosol backscattering coefficient sub-profile of the cloud layer according to the final aerosol extinction backscattering ratio of the cloud layer; An extinction coefficient vertical profile generation module for calculating the aerosol extinction coefficient vertical profile of the complete height according to the aerosol backscattering coefficient sub-profiles of the region below the cloud base, the cloud layer, and the region above the cloud top.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method described in any one of claims 1 to 8.

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