CN118112545A - Atmospheric laser radar reference height extraction method and system based on Rayleigh fitting - Google Patents
Atmospheric laser radar reference height extraction method and system based on Rayleigh fitting Download PDFInfo
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Abstract
The invention discloses a method and a system for extracting reference heights of an atmospheric laser radar based on Rayleigh fitting, wherein the method comprises the steps of calculating a scattering signal composed of aerosol and atmospheric molecules based on an original signal of the atmospheric laser radar, carrying out characteristic decomposition on the scattering signal by utilizing a Douglas-Peucker algorithm to obtain a plurality of similar characteristic height sections, testing each height section by utilizing five different Rayleigh Li Nige criteria, and finally extracting an optimal height section from the optimal height section by utilizing an evaluation factor as a reference height. The invention solves the problems of difficult selection of the reference height, poor noise immunity and low calculation efficiency under the condition of complex atmospheric characteristics, and the provided atmospheric laser radar reference height identification method has the characteristics of strong self-adaption, high efficiency and strong noise immunity, and is a key for realizing the calibration and accurate quantitative detection of the atmospheric laser radar.
Description
Technical Field
The invention belongs to the technical field of laser atmosphere remote sensing data inversion, and particularly relates to an atmosphere laser radar reference height extraction method and system based on Rayleigh fitting.
Background
The atmospheric lidar is a remote sensing technology for detecting vertical distribution of aerosol, cloud layer, trace gas and the like in the atmosphere by means of pulse or continuous laser, and has the characteristic of high space-time resolution. With the development of laser and detector technology, the detection capability and system stability of the atmospheric lidar are higher and higher, and the atmospheric lidar is widely applied to atmospheric environment and weather monitoring business.
The atmospheric lidar can quantitatively measure aerosols in the atmosphere. However, for the atmospheric lidar commonly used for aerosol detection, such as elastic lidar, raman lidar, hyperspectral lidar and the like, the radar needs to be calibrated by utilizing a scatterer with known characteristics, and then the accurate quantitative measurement of the aerosol is realized. The optical scattering property of the atmospheric molecules can be calculated by the Rayleigh scattering (RAYLEIGH SCATTERING) theory, and the atmospheric number density can be accurately calculated by utilizing the temperature and pressure profile in the radiosonde or analysis data, so that the scattering signal of the atmospheric molecules can be used as a known quantity for the calibration and quantitative inversion of the atmospheric laser radar.
In actual atmosphere laser radar calibration, a height section with negligible aerosol content is generally selected as a reference height, and an atmosphere laser radar signal and an atmosphere molecule scattering signal are matched, so that radar calibration is realized. The advection layer height, which is generally the aerosol content and its rarity, can be used as an ideal reference height. Most atmospheric lidar systems and raman lidar systems for environmental monitoring, however, have difficulty in efficiently detecting echo signals at the level of the advection due to limitations in detection efficiency. The middle part and the top part of the troposphere have low aerosol content in general and can be used for calibrating an atmospheric laser radar. However, because the entrainment, convection, and remote transmission of aerosols sometimes occur in the middle and top of the troposphere, the reference height needs to be determined in conjunction with the actual situation. The judgment method of the reference height relies on manual intervention, and the reference height is determined by judging the proximity degree of the logarithmic contour of the laser radar signal and the logarithmic contour of the atmospheric molecular scattering signal through naked eyes. This approach relies on manual intervention and is difficult to accommodate for large-scale and real-time data processing requirements. In order to meet the requirement of automatic identification of the reference height, the European laser radar network (EARLINET) proposes to extract the reference height of the atmospheric laser radar by using a segmented Rayleigh fitting method. And matching the signal shape in the comparison window with the atmospheric molecular scattering signal at the corresponding height by selecting the comparison window with a fixed width, calculating a matching factor, and sliding the comparison window from low altitude to high altitude in sequence to obtain a matching factor height sequence, thereby obtaining the optimal reference height. However, this signal reference height extraction algorithm based on a fixed width contrast window makes it difficult to search for a reference height that is less than the contrast window width. In addition, since it is necessary to slide the comparison window sequentially from low to high and calculate the matching factor, the calculation amount is relatively large. And the recognition effect of the algorithm on a far reference height is poor because the background noise and the relatively weak echo signals lead to poor signals of the far signals. How to design an atmospheric laser radar reference height identification method with strong self-adaption, high efficiency and strong noise immunity is a key for realizing atmospheric laser radar calibration and accurate quantitative detection.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an atmospheric laser radar reference height extraction method based on Rayleigh fitting, which is used for efficiently and stably extracting the atmospheric laser radar reference height.
In order to achieve the above purpose, the invention provides an atmospheric lidar reference height extraction method based on Rayleigh fitting, which comprises the following steps:
Step 1, calculating to obtain a scattering signal composed of aerosol and atmospheric molecules based on an original signal of an atmospheric laser radar;
Step 2, decomposing the scattering signal profile by utilizing a Douglas-Peucker algorithm to obtain a plurality of height segments with similar characteristics;
step 3, respectively testing the width, signal attenuation, white noise, signal to noise ratio and signal slope of the signals in the different height sections to find out the height section close to the molecular scattering characteristics;
and 4, performing evaluation factor calculation on the height segments passing the five tests, and finding out the height segment closest to the molecular scattering characteristics as a reference height.
Furthermore, the height is to be determined in step 1The original signal profile of the atmospheric lidar is marked as/> Wherein/>The calculation mode of the background signal of the atmospheric laser radar is as follows:
（1）
wherein BG is background signal of the atmospheric laser radar; 、/> representing minimum and maximum values of range gate indices used to calculate background signals,/> 、/>The numerical value is set according to the actual requirement,/>；/>Represents the/>The height of the distance gate.
Obtaining the height by utilizing the original signal profile of the atmospheric laser radar and the background signal of the atmospheric laser radarEffective detection signal/>, of atmospheric lidarWherein/>The specific formula of the calculation formula is as follows:
（2）
And further obtaining a scattering signal formed by aerosol and atmospheric molecules, namely a distance correction signal of the atmospheric laser radar, wherein the specific calculation formula is as follows:
（3）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Represents the/>Height of individual distance gate,/>，/>Is of height/>The atmospheric lidar effectively detects signals.
Furthermore, the step 2 is based on the heightDistance correction signal/>, of atmospheric lidar atCalculate the scattering ratio signal/>The following formula is shown:
（4）
In the method, in the process of the invention, Represents the/>Height of individual distance gate,/>Is of height/>Theoretical molecular scattering signal at the position is calculated by the following formula:
（5）
In the method, in the process of the invention, And/>Respectively show the height/>Molecular backscattering coefficient and height/>Molecular extinction coefficient of the site, both of which are calculated according to Rayleigh scattering theory,/>；/>Is an exponential function based on a natural constant e; /(I)、/>Represents the/>、/>The height of the distance gate.
According to the Douglas-Peucker algorithm, setting the minimum interval distance asDecomposing the scattering ratio signal profile into a plurality of height segments with similar shape features, and sequentially marking the distance gate subscripts of the height segments as/>Wherein/>Representing the resulting furthest gate index from the decomposition.
In the step 3, the distance correction signals in each height section obtained by decomposition are normalized, and then the width, the signal attenuation, the white noise, the signal to noise ratio and the signal slope test are sequentially carried out on each height section, so that possible reference height sections are judged; assuming that a certain height section is tested, the height section contains a range gate subscript ofNormalizing the distance correction signal within the altitude segment, namely:
（6）
In the method, in the process of the invention, Is of height/>Normalized distance correction signal at,/>Is of height/>Distance correction signal of atmospheric lidar at/，/>The normalization factor is calculated by the following formula:
（7）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Is of height/>The theoretical molecular scattering signal at.
If the width of the current height segment is greater than the set minimum widthThen the width test is passed as shown in the following formula:
（8）
In the method, in the process of the invention, 、/>Respectively represent the/>、/>The height of the distance gate.
For a pair ofNormalized distance correction signal of altitude segment before and at the position, if at/>, is judgedAll height segments/>Normalized distance correction signal means/>Plus one third of the normalized distance correction signal standard deviation/>Greater than the molecular scatter signal, the signal decay test is passed.
Calculating height segmentsInternal normalized distance correction signal/>Scattering signal with theoretical moleculeResidual/>The method comprises the following steps:
（12）
In the method, in the process of the invention, Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Normalized distance correction signal at,/>Is of height/>The theoretical molecular scattering signal at the site,。
For height collectionAnd corresponding residual setsPerforming linear fitting to obtain slope/>And offset/>By means of slope/>And offset/>Removing linear features in the residual sequence, namely:
（13）
carrying out Dubin-Watson test on the residual sequence with the linear characteristics removed, judging whether the residual sequence has an autocorrelation characteristic, if not, considering that the residual sequence meets an important statistical characteristic of white noise characteristics, and passing the white noise test; further computing test statistics if auto-correlation features exist Test statistic/>The calculation is performed by the following formula:
（14）
In the method, in the process of the invention, Is of height/>The residual sequence of the linear feature is removed.
If test statisticsSatisfy/>Then pass the white noise test,/>Is a set threshold.
Calculating height segmentsCumulative signal to noise ratio of signal/>The calculation formula is as follows:
（15）
In the method, in the process of the invention, Is of height/>Effective detection signal of atmospheric lidar at site,/>BG is the background signal of the atmospheric lidar.
If it isGreater than a set minimum cumulative signal-to-noise ratio/>Then the signal to noise ratio test is passed.
Calculating height segmentsSlope/>, of normalized distance correction signal after internal logarithm takingAnd with the height sectionSlope/>, of the internally log molecular scattering signalComparing, if the relative offset of the two meets the requirement, the signal slope test is passed, and the calculation formula is as follows:
（16）
In the method, in the process of the invention, Is the maximum relative deviation allowed.
In step 4, an evaluation factor is calculated for each height section passing the testThe specific calculation formula is as follows:
（17）
wherein,
（18）
（19）
In the method, in the process of the invention,For/>Average value of normalized distance correction signal residual error in altitude segment,/>Is thatStandard deviation of normalized distance correction signal residual in altitude segment,/>Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Residual sequence of linear features is removedThe slope obtained for the linear fit in the white noise test.
Final selection ofThe height segment corresponding to the minimum value is used as the reference height.
The invention also provides an atmospheric laser radar reference height extraction system based on the Rayleigh fitting, which is used for realizing the atmospheric laser radar reference height extraction method based on the Rayleigh fitting.
Further, the system comprises a processor and a memory, wherein the memory is used for storing program instructions, and the processor is used for calling the stored instructions in the memory to execute the atmospheric lidar reference height extraction method based on the Rayleigh fitting.
Or comprises a readable storage medium having stored thereon a computer program which, when executed, implements an atmospheric lidar reference height extraction method based on rayleigh fitting as described above.
Compared with the prior art, the invention has the following advantages:
1) The method utilizes the Douglas-Peucker algorithm to divide the signal into intervals with small gradient difference based on the signal shape, the interval division is dynamic and does not depend on a specific grid, and the division result changes according to the spatial distribution characteristics of an actual observation target, so that the reference height with smaller width can be identified, and the limitation of the fixed window length of the traditional algorithm is eliminated;
2) The invention uses the Douglas-Peucker algorithm to extract the signal segments with similar characteristics, avoids the search of the distance gates from the first distance gate, reduces the search times, reduces the missed judgment times and improves the recognition efficiency of the reference height;
3) The invention enhances the effectiveness of reference height assessment under the condition of low signal-to-noise ratio by judging through the five different dimensionalities of the Rayleigh Li Nige of the width, the signal attenuation, the white noise, the signal-to-noise ratio and the signal slope test;
4) The atmospheric laser radar reference height identification method provided by the invention has the characteristics of strong self-adaption, high efficiency and strong noise immunity, and is a key for realizing the calibration and accurate quantitative detection of the atmospheric laser radar.
Drawings
In order to more clearly illustrate the invention or the technical solutions of the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flow chart of the atmospheric lidar reference height extraction method based on rayleigh fitting of the present invention.
FIG. 2 is a graph of 1064nm lidar signals in the cloudless case: (a) is a lidar raw signal profile; (b) The distance correction signal and the molecular scattering signal profile are used for the atmospheric laser radar; (c) For the scattering ratio profile and boundary points decomposed by the Douglas-Peucker algorithm, the area determined by each two boundary points is a height section of similar features, wherein the area determined by the dotted line is a reference height obtained by recognition.
Fig. 3 shows rayleigh fitting results in the cloud-free case: the upper graph shows the results of five rayleigh fit criteria corresponding to each altitude segment; the lower graph shows the corresponding evaluation factors for each altitude segment after passing the rayleigh fit criterion.
Fig. 4 is a diagram of 1064nm lidar signal in cloudy condition: (a) is a lidar raw signal profile; (b) The distance correction signal and the molecular scattering signal profile are used for the atmospheric laser radar; (c) For the scattering ratio profile and boundary points decomposed by the Douglas-Peucker algorithm, the determined area of each two boundary points is a height section of similar characteristics.
Fig. 5 shows rayleigh fitting results in cloud case: the upper graph shows the results of five rayleigh fit criteria corresponding to each altitude segment; the lower graph shows the corresponding evaluation factors for each altitude segment after passing the rayleigh fit criterion.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and examples of the present invention, and it is apparent that the described examples are some, but not all, examples of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
As shown in fig. 1, the embodiment of the invention provides an atmospheric lidar reference height extraction method based on rayleigh fitting, which comprises the following steps:
and step 1, calculating to obtain a scattering signal composed of aerosol and atmospheric molecules based on an original signal of the atmospheric laser radar.
Will be highThe original signal profile of the atmospheric lidar is marked as/>Wherein/>The background signal of the atmospheric lidar can be calculated by:
（1）
wherein BG is background signal of the atmospheric laser radar; 、/> representing minimum and maximum values of range gate indices used to calculate background signals,/> 、/>The numerical value is set according to the actual requirement,/>；/>Represents the/>The height of the distance gate.
By means of heightAtmospheric lidar original Signal Profile/>And a background signal BG of the atmospheric lidar to obtain a height/>Effective detection signal/>, of atmospheric lidarWherein/>The specific formula of the calculation formula is as follows:
（2）
And further obtaining a scattering signal formed by aerosol and atmospheric molecules, namely a distance correction signal of the atmospheric laser radar, wherein the specific calculation formula is as follows:
（3）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Represents the/>Height of individual distance gate,/>，/>Is of height/>The atmospheric lidar effectively detects signals.
And 2, decomposing the scattering signal profile by utilizing a Douglas-Peucker algorithm to obtain a plurality of height segments with similar characteristics.
Calculating the heightScattering ratio signal at/>The following formula is shown:
（4）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Represents the/>Height of individual distance gate,/>Is of height/>The theoretical molecular scattering signal can be calculated by the following formula:
（5）
In the method, in the process of the invention, And/>Respectively show the height/>Molecular backscattering coefficient and height/>Molecular extinction coefficient of the site, both of which are calculated according to Rayleigh scattering theory,/>；/>Is an exponential function based on a natural constant e; /(I)、/>Represents the/>、/>The height of the distance gate.
According to the Douglas-Peucker algorithm, setting the minimum interval distance asThe scattering ratio signal profile can be decomposed into a plurality of height segments with similarly shaped features, with the distance gate subscripts of the height segments being labeled/>, in sequenceWherein/>Representing the resulting furthest gate index from the decomposition.
And 3, respectively testing the width, the signal attenuation, the white noise, the signal to noise ratio and the signal slope of the signals in the different height sections, and finding out the height section close to the molecular scattering characteristics.
Firstly, normalizing the distance correction signals in each height section obtained by decomposition, and then sequentially testing the width, the signal attenuation, the white noise, the signal to noise ratio and the signal slope of each height section to judge possible reference height sections. Assuming that a certain height section is tested, the height section contains a range gate subscript ofNormalizing the distance correction signal within the altitude segment, namely:
（6）
In the method, in the process of the invention, Is of height/>Normalized distance correction signal at,/>Is of height/>Distance correction signal of atmospheric lidar at/，/>The normalization factor can be calculated by the following formula:
（7）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Is of height/>The theoretical molecular scattering signal at.
Width test:
If the width of the current height segment is greater than the set minimum width Then the test is passed as shown in the following formula:
（8）
In the method, in the process of the invention, 、/>Respectively represent the/>、/>The height of the distance gate.
Signal attenuation test:
For a pair of Normalized distance correction signal of altitude segment before and at the position, if at/>, is judgedAll height segments/>Normalized distance correction signal means/>Plus one third of the normalized distance correction signal standard deviation/>Greater than the molecular scatter signal, the test passed as shown below:
（9）
wherein,
（10）
（11）
In the method, in the process of the invention,Is of height/>Normalized distance correction signal at,/>For/>Average value of normalized distance correction signal in altitude segment,/>For/>Standard deviation of normalized distance correction signal in altitude segment,/>For/>Average value of theoretical molecular scattering signal in high section.
White noise test:
calculating height segments Internal normalized distance correction signal/>Scattering signal with theoretical moleculeResidual/>The method comprises the following steps:
（12）
In the method, in the process of the invention, Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Normalized distance correction signal at,/>Is of height/>The theoretical molecular scattering signal at the site,。
For height collectionAnd corresponding residual setsPerforming linear fitting to obtain slope/>And offset/>By means of slope/>And offset/>Removing linear features in the residual sequence, namely:
（13）
Carrying out Dubin-Watson test on the residual sequence with the linear characteristics removed, judging whether the residual sequence has an autocorrelation characteristic, if not, considering that the residual sequence meets an important statistical characteristic of white noise characteristics, and passing the current test; further computing test statistics if auto-correlation features exist Test statistic/>The calculation is performed by the following formula:
（14）
In the method, in the process of the invention, Is of height/>The residual sequence of the linear feature is removed.
If test statisticsSatisfy/>Then pass this test, this example/>Taking 1.
Signal-to-noise ratio test:
calculating height segments Cumulative signal to noise ratio of signal/>The calculation formula is as follows:
（15）
In the method, in the process of the invention, Is of height/>Effective detection signal of atmospheric lidar at site,/>BG is the background signal of the atmospheric lidar.
If it isGreater than a set minimum cumulative signal-to-noise ratio/>The test is passed.
Signal slope test:
calculating height segments Slope/>, of normalized distance correction signal after internal logarithm takingAnd with the height sectionSlope/>, of the internally log molecular scattering signalIn contrast, if the relative offset of the two meets the requirement, the test is passed, and the calculation formula is as follows:
（16）
In the method, in the process of the invention, Is the maximum relative deviation allowed.
And 4, performing evaluation factor calculation on the height segments passing the five tests, and finding out the height segment closest to the molecular scattering characteristics as a reference height.
Calculating an evaluation factor for each height section passing the testThe specific calculation formula is as follows:
（17）
wherein,
（18）
（19）
In the method, in the process of the invention,For/>Average value of normalized distance correction signal residual error in altitude segment,/>Is thatStandard deviation of normalized distance correction signal residual in altitude segment,/>Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Residual sequence of linear features is removedThe slope obtained for the linear fit in the white noise test.
SelectingThe height segment corresponding to the minimum value is used as the reference height.
In order to verify the effectiveness of the method provided by the invention, a test experiment is carried out on a 1064nm elastic laser radar. Setting the minimum interval distance of the Douglas-Peucker algorithm0.4, A reference height recognition range of 0.8-15 km, minimum width/>0.3 Km, minimum signal to noise threshold/>0.5, Maximum slope relative deviation/>0.1.
The profile of the laser radar detection signal without cloud shielding is shown in fig. 2 (a), the distance correction signal of the laser radar and the atmospheric molecules is shown in fig. 2 (b), and the signal height section after Douglas-Peucker decomposition is shown in fig. 2 (c), so that the signal is decomposed into a height section with approximate linearity after decomposition. The rayleigh fit was performed for each height segment, and the test results are shown in the upper graph of fig. 3, and it can be found that for the low-altitude 0-5 km height segment, no rayleigh test was passed because of the influence of the aerosol signal, and finally three height Duan Tongguo rayleigh fit tests were performed. Calculating an evaluation factorSelecting to obtainThe smallest height section serves as a reference height, i.e. corresponds to 8.5-9.0 km.
The laser radar detection signal profile with the cloud shielding condition is shown in (a) of fig. 4, the distance correction signal of the laser radar and the atmosphere molecule is shown in (b) of fig. 4, and the signal height section after Douglas-Peucker decomposition is shown in (c) of fig. 4. Because of the influence of cloud layer attenuation, all height segments below the cloud layer fail to pass the signal attenuation test, while the height segments above the cloud layer fail to pass the signal attenuation test, the signal to noise ratio is low, the fitting uncertainty is large, the signal to noise ratio test and the signal slope test are difficult to pass, and finally all the height segments pass the Rayleigh fitting test (see figure 5), so that a proper reference height cannot be found, and the result accords with the expectation of identifying the reference height in a cloud scene.
Example 2
Based on the same inventive concept, the invention also provides an atmospheric lidar reference height extraction system based on Rayleigh fitting, which comprises a processor and a memory, wherein the memory is used for storing program instructions, and the processor is used for calling the program instructions in the memory to execute the atmospheric lidar reference height extraction method based on Rayleigh fitting.
Example 3
Based on the same inventive concept, the invention also provides an atmospheric lidar reference height extraction system based on Rayleigh fitting, which comprises a readable storage medium, wherein a computer program is stored on the readable storage medium, and the atmospheric lidar reference height extraction method based on Rayleigh fitting is realized when the computer program is executed.
In particular, the method according to the technical solution of the present invention may be implemented by those skilled in the art using computer software technology to implement an automatic operation flow, and a system apparatus for implementing the method, such as a computer readable storage medium storing a corresponding computer program according to the technical solution of the present invention, and a computer device including the operation of the corresponding computer program, should also fall within the protection scope of the present invention.
The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.
Claims (10)
1. The atmospheric lidar reference height extraction method based on Rayleigh fitting is characterized by comprising the following steps of:
Step 1, calculating to obtain a scattering signal composed of aerosol and atmospheric molecules based on an original signal of an atmospheric laser radar;
Step 2, decomposing the scattering signal profile by utilizing a Douglas-Peucker algorithm to obtain a plurality of height segments with similar characteristics;
step 3, respectively testing the width, signal attenuation, white noise, signal to noise ratio and signal slope of the signals in the different height sections to find out the height section close to the molecular scattering characteristics;
and 4, performing evaluation factor calculation on the height segments passing the five tests, and finding out the height segment closest to the molecular scattering characteristics as a reference height.
2. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 1, wherein the method comprises the following steps: height to be measured in step 1The original signal profile of the atmospheric lidar is marked as/>WhereinThe calculation mode of the background signal of the atmospheric laser radar is as follows:
（1）
wherein BG is background signal of the atmospheric laser radar; 、/> representing minimum and maximum values of range gate indices used to calculate background signals,/> 、/>The numerical value is set according to the actual requirement,/>；/>Represents the/>The height of the distance doors;
obtaining the height by utilizing the original signal profile of the atmospheric laser radar and the background signal of the atmospheric laser radar Effective detection signal/>, of atmospheric lidarWherein/>The specific formula of the calculation formula is as follows:
（2）
And further obtaining a scattering signal formed by aerosol and atmospheric molecules, namely a distance correction signal of the atmospheric laser radar, wherein the specific calculation formula is as follows:
（3）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Represents the/>Height of individual distance gate,/>，/>Is of height/>The atmospheric lidar effectively detects signals.
3. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 2, wherein the method comprises the following steps: height-based in step 2Distance correction signal/>, of atmospheric lidar atCalculate the scattering ratio signal/>The following formula is shown:
（4）
In the method, in the process of the invention, Represents the/>Height of individual distance gate,/>Is of height/>Theoretical molecular scattering signal at the position is calculated by the following formula:
（5）
In the method, in the process of the invention, And/>Respectively show the height/>Molecular backscattering coefficient and height/>Molecular extinction coefficient of the site, both of which are calculated according to Rayleigh scattering theory,/>；/>Is an exponential function based on a natural constant e; /(I)、/>Represents the/>、/>The height of the distance doors;
according to the Douglas-Peucker algorithm, setting the minimum interval distance as Decomposing the scattering ratio signal profile into a plurality of height segments with similar shape features, and sequentially marking the distance gate subscripts of the height segments as/>Wherein/>Representing the resulting furthest gate index from the decomposition.
4. A method for extracting atmospheric lidar reference height based on rayleigh fitting as claimed in claim 3, wherein: in the step 3, firstly normalizing the distance correction signals in each height section obtained by decomposition, and then sequentially testing the width, the signal attenuation, the white noise, the signal to noise ratio and the signal slope of each height section; assuming that a certain height section is tested, the height section contains a range gate subscript ofNormalizing the distance correction signal within the altitude segment, namely:
（6）
In the method, in the process of the invention, Is of height/>Normalized distance correction signal at,/>Is of height/>Distance correction signal of atmospheric lidar at/，/>The normalization factor is calculated by the following formula:
（7）
In the method, in the process of the invention, Is of height/>Distance correction signal of atmospheric lidar at/Is of height/>The theoretical molecular scattering signal at.
5. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 4, wherein the method comprises the following steps: in step 3, if the width of the current height section is greater than the set minimum widthThen the width test is passed as shown in the following formula:
（8）
In the method, in the process of the invention, 、/>Respectively represent the/>、/>The height of the distance doors;
For a pair of Normalized distance correction signal of altitude segment before and at the position, if at/>, is judgedAll the height sections beforeNormalized distance correction signal means/>Plus one third of the standard deviation of the normalized distance correction signalGreater than the molecular scatter signal, the signal decay test is passed.
6. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 4, wherein the method comprises the following steps: calculating the height section in step3Internal normalized distance correction signal/>Scattering signal with theoretical moleculeResidual/>The method comprises the following steps:
（12）
In the method, in the process of the invention, Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Normalized distance correction signal at,/>Is of height/>The theoretical molecular scattering signal at the site,；
For height collectionAnd corresponding residual setsPerforming linear fitting to obtain slope/>And offset/>By means of slope/>And offset/>Removing linear features in the residual sequence, namely:
（13）
Carrying out Dubin-Watson test on the residual sequence with the linear characteristics removed, judging whether the residual sequence has an autocorrelation characteristic, if not, considering that the residual sequence meets an important statistical characteristic of a white noise characteristic, and passing the white noise test; further computing test statistics if auto-correlation features exist Test statistic/>The calculation is performed by the following formula:
（14）
In the method, in the process of the invention, Is of height/>Removing residual sequences of linear features;
If test statistics Satisfy/>Then pass the white noise test,/>Is a set threshold.
7. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 4, wherein the method comprises the following steps: calculating the height section in step3Cumulative signal to noise ratio of signal/>The calculation formula is as follows:
（15）
In the method, in the process of the invention, Is of height/>Effective detection signal of atmospheric lidar at site,/>BG is the background signal of the atmospheric lidar;
If it is Greater than a set minimum cumulative signal-to-noise ratio/>Then the signal to noise ratio test is passed;
calculating height segments Slope/>, of normalized distance correction signal after internal logarithm takingAnd with the height sectionSlope/>, of the internally log molecular scattering signalComparing, if the relative offset of the two meets the requirement, the signal slope test is passed, and the calculation formula is as follows:
（16）
In the method, in the process of the invention, Is the maximum relative deviation allowed.
8. The atmospheric lidar reference height extraction method based on rayleigh fitting of claim 6, wherein the method comprises the following steps: in step 4, the evaluation factors are calculated for each height section passing the testThe specific calculation formula is as follows:
（17）
wherein,
（18）
（19）
In the method, in the process of the invention,For/>Average value of normalized distance correction signal residual error in altitude segment,/>Is thatStandard deviation of normalized distance correction signal residual in altitude segment,/>Is of height/>Residual error of normalized distance correction signal and theoretical molecular scattering signal,/>Is of height/>Residual sequence of linear features is removedLinear fitting of the white noise test results in a slope;
Selecting The height segment corresponding to the minimum value is used as the reference height.
9. An atmospheric lidar reference height extraction system based on rayleigh fitting, comprising a processor and a memory, the memory for storing program instructions, the processor for invoking the program instructions in the memory to perform a method of atmospheric lidar reference height extraction based on rayleigh fitting as claimed in any of claims 1-8.
10. An atmospheric lidar reference height extraction system based on rayleigh fitting, comprising a readable storage medium having stored thereon a computer program which, when executed, implements a rayleigh fitting-based atmospheric lidar reference height extraction method as claimed in any of claims 1-8.
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