A method for lidar quality control

Abstract

The present invention provides a method for quality control of lidar, comprising the following steps: performing Rayleigh scattering fitting correction on the lidar system: fitting the distance-corrected scattering signal and the Rayleigh scattering signal, and adjusting the lidar system according to the fitting result; performing a four-quadrant test on the lidar system, and calibrating the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test result; performing geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system. This method starts from fundamental elements such as the equipment access standard of the aerosol lidar and the quality control of networked observation data, confirms the key factors and key indicators for the quality control of aerosol lidar networking, with the aim of the lidar receiving higher and accurate signals and improving the inversion accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of office equipment, and particularly relates to a method for quality control of lidar. Background Art

[0002] The application of aerosol lidar in the fields of meteorology and environmental protection has been increasingly emphasized. This is because aerosol lidar is unparalleled in monitoring the distribution (spatial distribution, particle size distribution, species distribution, etc.) and spatio-temporal evolution process of particulate matter in the atmosphere, and it can provide spatially and temporally resolved measurements of the above distributions.

[0003] Currently, globally, in the monitoring network formed by aerosol lidar on a continental scale, the EARLINET aerosol lidar network in Europe has been operating for more than 18 years (starting from the LACE98 program in Germany in 1998). Since the application research of lidar in the meteorological and environmental protection departments in China is still in its infancy and most domestic equipment comes from scientific research institutions, there are no unified standards and requirements in aspects such as industrialization and standardization of such equipment. Abroad, a large amount of research has been carried out on clouds, aerosols, etc. using lidar, but it is mainly concentrated on hardware systems, inversion methods and mechanism research, etc. There is less quality control for the lidar data itself. Generally, it is defaulted that the raw data meets the accuracy requirements, and only the inversion results are given, which cannot guarantee the accuracy of the data. Data accuracy is the fundamental guarantee of scientific research, so quality control for lidar is particularly important. Summary of the Invention

[0004] The present invention provides a method for quality control of lidar. Starting from fundamental elements such as the equipment access standard of aerosol lidar and the quality control of network observation data, and based on the general principle of lidar data quality control, the key factors and key indicators for the quality control of aerosol lidar networking are confirmed. The main indicators include Rayleigh scattering fitting correction, four-quadrant (uniformity) test, and geometric overlap factor correction, etc. The purpose is for the lidar to receive higher and accurate signals and improve the inversion accuracy.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for quality control of lidar, comprising the following steps:

[0007] S1. Perform Rayleigh scattering fitting correction on the lidar system: Fit the range-corrected scattered signal with the Rayleigh scattering signal, and adjust the lidar system according to the fitting result;

[0008] S2. Perform a four-quadrant test on the lidar system, and calibrate the position of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test result;

[0009] S3. Correct the geometric overlap factor of the echo signal of the lidar system to obtain the corrected echo signal of the lidar system.

[0010] Preferably, step S1 specifically includes the following steps:

[0011] S11. Fit the received distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) and take the logarithmic coordinates.

[0012] S12. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation:

[0013]

[0014] where r is the distance, RCS(r,λ) is the distance calibration signal, C is the lidar constant, α m (r,λ) is the atmospheric molecular extinction coefficient,

[0015] β m (r,λ) is the backscatter volume coefficient;

[0016] S13. Substitute formula (2) into formula (1) to obtain:

[0017]

[0018] where λ is the laser wavelength (nm), T(r) is the temperature, P a (r) is the pressure;

[0019] S14. Obtain the distance-corrected scattering signal X(r) from the US standard atmospheric molecular model, subtract the background noise N from the measured original signal P(r) B to obtain the effective photon signal Ps(r):

[0020] Ps(r) = P(r) - N B

[0021] N B is obtained by averaging the last M values of the original signal P(r), M is 50, to obtain the distance-corrected scattering signal X(r):

[0022] X(r) = Ps(r) * r * r;

[0023] S15. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r,λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the transmitting optical axis and the receiving optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal.

[0024] Preferably, the step S2 specifically includes the following steps:

[0025] S21. Divide the optical antenna of the lidar into four quadrants to obtain a four-quadrant optical antenna receiving system;

[0026] S22. Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be X 11 、 and the root mean square values be X RMS11 、X RMS4 and X RMS12 . When , save the signal S 1 of the first quadrant and the signal S 4 of the fourth quadrant measured this time;

[0027] S23. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be and the root mean square values be X RMS21 、X RMS3 and X RMS22 . When , save the signal S 2 of the second quadrant and the signal S 3 of the third quadrant measured this time;

[0028] S24. Let the overlap area of the lidar be L O . For a non-coaxial lidar system, assume that in the range of L O +1 to L O +4, the detection signals of the first quadrant are S 11 、S 12 、……S 1n , and the detection signals of the fourth quadrant are S 41 、S 42 、……S 4n . Calculate the systematic difference M 14 between the first quadrant signal and the fourth quadrant echo signal and the standard deviation σ 14 :

[0029]

[0030] S25. In the range of 0 km to 3 km, the detection signals of the second quadrant are S 21 、S 22 、……S 2n, the detection signal in the third quadrant is S 31 and S 32 and so on, S 3n , calculate the systematic difference M 23 between the echo signals in the second and third quadrants and the standard deviation σ 23 of the echo signals in the second and third quadrants:

[0031]

[0032] S26. For a coaxial lidar system, assume that the detection signals in the first quadrant within the range of 0 km to 3 km are S 11 and S 12 and so on, S 1n , the detection signals in the second quadrant are S 21 and S 22 and so on, S 2n , the detection signals in the third quadrant are S 31 and S 32 and so on, S 3n , the detection signals in the fourth quadrant are S 41 and S 42 and so on

[0033] S 4n , calculate the systematic difference between the first and fourth quadrants, the standard deviation between the first and fourth quadrants, as well as the systematic difference between the echo signals in the second and third quadrants and the standard deviation between the echo signals in the second and third quadrants;

[0034] S27. Compare the systematic difference between the first and fourth quadrants with the standard deviation between the first and fourth quadrants, and compare the systematic difference between the echo signals in the second and third quadrants with the standard deviation between the echo signals in the second and third quadrants. Adjust the transmitting optical axis and receiving optical axis according to the comparison results until they meet the standards.

[0035] Preferably, step S3 specifically includes the following steps:

[0036] S31. According to the lidar equation, the effective signal received by the lidar can be expressed as:

[0037]

[0038] where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient;

[0039] Assume that when r = r 0 , the laser emission field of view and the telescope receiving field of view completely coincide. At this time, Y(r) = 1. Taking the natural logarithm of both ends, we get:

[0040] ln[Ps (r)r 2 = ln(Cβ) - 2αr

[0041] Performing linear fitting in the form of y = b + a*r using the least squares method, we can obtain:

[0042] a = -2α

[0043] b = ln(Cβ)

[0044] Then, the geometric overlap factor of the lidar system can be obtained

[0045]

[0046] A specific embodiment of the present invention further provides a lidar quality control method, including the following steps:

[0047] S1. Conduct a four-quadrant test on the lidar system, and calibrate the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test results;

[0048] S2. Conduct Rayleigh scattering fitting correction on the lidar system: Fit the distance-corrected scattering signal and the Rayleigh scattering signal, and adjust the lidar system according to the fitting results;

[0049] S3. Conduct geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system.

[0050] Preferably, the step S1 specifically includes the following steps:

[0051] S11. Divide the optical antenna of the lidar into four quadrants to obtain the four-quadrant of the optical antenna reception system;

[0052] S12. Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be X 11 , and The root mean square values are X RMS11 , X RMS4 and X RMS12 , when , save the signal S 1 of the first quadrant and the signal S 4 of the fourth quadrant of this measurement;

[0053] S13. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be and The root mean square values are X RMS21 , X RMS3 and X RMS22 When , save the detection signals S 2 in the second quadrant and S 3 in the third quadrant of this measurement;

[0054] S14. Let the overlap area of the lidar be L O . For a non-coaxial lidar system, assume that in the range of L O +1 to L O +4, the detection signals in the first quadrant are S 11 , S 12 , …… S 1n , and the detection signals in the fourth quadrant are S 41 , S 42 , …… S 4n . Calculate the systematic difference M 14 between the detection signals in the first quadrant and the echo signals in the fourth quadrant and the standard deviation σ 14 :

[0055] M 14 = ((S 11 - S 41 ) + (S 12 - S 42 ) + L + (S 1n - S 4n )) / n (4)

[0056]

[0057] S15. In the range of 0 km to 3 km, the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , and the detection signals in the third quadrant are S 31 , S 32 , …… S 3n . Calculate the systematic difference M 23 between the detection signals in the second quadrant and the echo signals in the third quadrant and the standard deviation σ 23 :

[0058] M 23 = ((S 21 - S 31 ) + (S 22 - S 32 ) + L + (S 2 n - S3 n)) / n (6)

[0059]

[0060] S16. For a coaxial lidar system, assume that the detection signals in the first quadrant within the distance range of 0 km to 3 km are S 11 、S 12 、……S 1n ; the detection signals in the second quadrant are S 21 、S 22 、……S 2n ; the detection signals in the third quadrant are S 31 、S 32 、……S 3n ; the detection signals in the fourth quadrant are S 41 、S 42 、……S 4n . Calculate the system difference between the first quadrant and the fourth quadrant, the standard deviation between the first quadrant and the fourth quadrant, as well as the system difference between the echo signals of the second quadrant and the third quadrant and the standard deviation between the echo signals of the second quadrant and the third quadrant;

[0061] S17. Compare the system difference between the first quadrant and the fourth quadrant with the standard deviation between the first quadrant and the fourth quadrant, and compare the system difference between the echo signals of the second quadrant and the third quadrant with the standard deviation between the echo signals of the second quadrant and the third quadrant. Adjust the transmitting optical axis and the receiving optical axis according to the comparison results until they meet the standards.

[0062] Preferably, the step S2 specifically includes the following steps:

[0063] S21. Fit the received distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) and take the logarithmic coordinates;

[0064] S22. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation:

[0065]

[0066] where r is the distance, RCS(r,λ) is the distance calibration signal, C is the lidar constant, α m (r,λ) is the atmospheric molecular extinction coefficient,

[0067] β m (r,λ) is the backscattering volume coefficient;

[0068] S23. Substitute formula (2) into formula (1) to obtain:

[0069]

[0070] where λ is the laser wavelength (nm), T(r) is the temperature, and P a (r) is the pressure,

[0071] S24. Obtain the distance-corrected scattering signal X(r) from the American standard atmospheric molecular model, and subtract the background noise N from the measured original signal P(r) B to obtain the effective photon signal Ps(r):

[0072] Ps(r) = P(r) - N B

[0073] N B Take the average of the last M values of the original signal P(r), where M is 50, to obtain the distance-corrected scattering signal X(r):

[0074] X(r) = Ps(r) * r * r;

[0075] S25. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r, λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the transmitting optical axis and the receiving optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal.

[0076] Preferably, step S3 specifically includes the following steps:

[0077] S31. According to the lidar equation, the effective signal received by the lidar can be expressed as:

[0078]

[0079] where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient;

[0080] Let r = r 0 when the laser emission field of view and the telescope receiving field of view are completely coincident, at this time Y(r) = 1. Taking the natural logarithm of both ends, we get:

[0081] ln[P s (r)r 2 = ln(Cβ) - 2αr

[0082] Using the least squares method for linear fitting in the form of y = b + a * r, we can obtain:

[0083] a = -2α

[0084] b = ln(Cβ)

[0085] Thus, the geometric overlap factor of the lidar system can be obtained

[0086]

[0087] By implementing the above technical solutions, the following technical effects are achieved: The lidar quality control method provided by the present invention proposes a complete solution for lidar quality control, clarifies the key factors and key indicators of lidar quality control, provides a reference basis for establishing data quality control standards for the commercial application of domestic lidars, and improves the accuracy of lidar data. Description of the Drawings

[0088] Figure 1 It is a diagram of the division method of the laser position of the non-coaxial system and the four quadrants of the telescope provided by the embodiment of the present invention;

[0089] Figure 2 It is a diagram of the division method of the laser position of the coaxial system and the four quadrants of the telescope provided by the embodiment of the present invention;

[0090] Figure 3 It is a standard table for detecting the signal uniformity of the optical antenna provided by the embodiment of the present invention;

[0091] Figure 4 It is a schematic diagram of the generation principle of the geometric overlap factor of the lidar system provided by the embodiment of the present invention. Detailed Embodiment

[0092] For a better understanding of the technical solutions of the present invention, the following combines the attached Figures 1-4 Describe in detail the embodiments provided by the present invention.

[0093] A lidar quality control method includes the following steps:

[0094] S1. Perform Rayleigh scattering fitting correction on the lidar system: Fit the distance-corrected scattering signal with the Rayleigh scattering signal, and adjust the lidar system according to the fitting result;

[0095] S2. Perform four-quadrant testing on the lidar system, and calibrate the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test results;

[0096] S3. Perform geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system.

[0097] By performing Rayleigh scattering fitting correction on the lidar, it is ensured that there is no overspill in the far field, guaranteeing the signal correctness and stability of the lidar. The quadrant test is used to detect whether the assembly of the receiving system of the system meets the design requirements and can correctly receive the backscattered signals from the near field and the far field. In this embodiment, the receiving system can specifically be a receiving objective lens, a focusing lens, an optical fiber, or a receiving probe. In this embodiment, the order of performing Rayleigh scattering fitting correction or the quadrant test is not restricted. Rayleigh scattering fitting correction can be performed first to detect whether the geometric relationship between the beam emitted by the lidar at the far field location and the receiving system meets the requirements. If it does not meet the requirements, then the transmitting system and the receiving system of the lidar are adjusted. Then, the quadrant test is performed on the radar system to detect whether the laser divergence angle of the radar system and the field of view angle of the telescope match. If they do not match, adjustment is required. Preferably, the position of the transmitting optical axis and the receiving optical axis is adjusted by adjusting the direction of the emitted laser or the direction of the receiving optical axis of the telescope, and then recalibration is performed to meet the calibration requirements. After Rayleigh scattering fitting correction and the quadrant test, an overlap factor test is performed on the lidar system. The overlap factor varies with distance and is defined as the ratio of the beam energy falling into the field of view at a certain distance to the total beam energy at that distance. It is one of the key factors for the lidar to detect the extinction coefficient of near-range aerosols and atmospheric visibility. By using the geometric overlap factor to correct the near-field atmospheric conditions of the signal and performing inversion, relevant atmospheric parameters that conform to the actual situation can be obtained, effectively enabling the lidar system to receive higher and more accurate signals and improving the inversion accuracy.

[0098] In this embodiment, based on the above embodiment, the purpose of Rayleigh fitting is to check whether the geometric relationship between the beam (collimated) emitted by the lidar at the far field location and the receiving system meets the design requirements. If the collimation of the emitted beam is not good, it will cause the laser beam to diverge too much in the far field and "overflow" the coverage range of the receiving field of view angle.

[0099] In this embodiment, preferably, on a clear day after rain (vertical visibility greater than 20 km), the beam is emitted vertically upward. At this time, the number of aerosols in the air is very small, so that the Rayleigh scattering signal at the far end can be measured. The judgment criterion is to fit the distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) in logarithmic coordinates. X(r) should be slightly higher than the Rayleigh scattering signal RCS(r,λ). If it is too low, it means that the geometric relationship between the system transmission and reception is incorrect and needs to be adjusted. Further, the step S1 specifically includes the following steps:

[0100] S11. Fit the received distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) in logarithmic coordinates;

[0101] S12. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation:

[0102]

[0103] where r is the distance, RCS(r,λ) is the distance-calibrated signal, C is the lidar constant, and α m (r,λ) is the atmospheric molecular extinction coefficient,

[0104] β m (r,λ) is the backscattering volume coefficient;

[0105] S13. Substitute formula (2) into formula (1) to obtain:

[0106]

[0107] where λ is the laser wavelength (nm), T(r) is the temperature, and P a (r) is the pressure;

[0108] S14. Obtain the distance-corrected scattering signal X(r) from the US standard atmospheric molecular model, and subtract the background noise N from the measured original signal P(r) B to obtain the effective photon signal Ps(r):

[0109] Ps(r) = P(r) - N B

[0110] N B is obtained by averaging the last M values of the original signal P(r), where M = 50, to obtain the distance-corrected scattering signal X(r):

[0111] X(r) = Ps(r) * r * r;

[0112] S15. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r,λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the transmitting optical axis and the receiving optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal. Specifically, adjust the transmitting optical axis of the lidar system and the receiving optical axis of the lidar by the coincidence degree and the size of the spot centers of the two optical axes.

[0113] Preferably, step S2 specifically includes the following steps:

[0114] S21. Divide the optical antenna of the lidar into four quadrants to obtain the four-quadrant optical antenna receiving system;

[0115] S22. Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be X 11 , and The root mean square values are X RMS11 , X RMS4 and X RMS12 . When , save the signal S 1 in the first quadrant and the signal S 4 in the fourth quadrant of this measurement;

[0116] S23. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves in the distance range of 2 km to 3 km be and The root mean square values are X RMS21 , X RMS3 and X RMS22 . When , save the signal S 2 in the second quadrant and the signal S 3 in the third quadrant of this measurement;

[0117] S24. Let the overlap area of the lidar be L O . For a non - coaxial lidar system, assume that in the range of L O +1 to L O +4, the detection signals in the first quadrant are S 11 , S 12 , …… S 1n , and the detection signals in the fourth quadrant are S 41 , S 42 , …… S 4n . Calculate the systematic difference M 14 between the first - quadrant signal and the fourth - quadrant echo signal and the standard deviation σ 14 of the first - quadrant signal and the fourth - quadrant echo signal:

[0118]

[0119] S25. In the range of 0 km to 3 km, the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , and the detection signals in the third quadrant are S 31 , S 32 , …… S 3n . Calculate the systematic difference M 23 between the second - quadrant and the third - quadrant echo signals and the standard deviation σ of the second - quadrant and the third - quadrant echo signals23 :

[0120] M 23 = ((S 21 - S 31 ) + (S 22 - S 32 ) + L + (S 2 n - S 3 n)) / n (6)

[0121]

[0122] S26. For a coaxial lidar system, assume that the detection signals in the first quadrant within the range of 0 km to 3 km are S 11 , S 12 , …… S 1n , the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , the detection signals in the third quadrant are S 31 , S 32 , …… S 3n , and the detection signals in the fourth quadrant are S 41 , S 42 , ……

[0123] S 4n , calculate the system difference between the first quadrant and the fourth quadrant, the standard deviation between the first quadrant and the fourth quadrant, as well as the system difference between the echo signals of the second quadrant and the third quadrant and the standard deviation between the echo signals of the second quadrant and the third quadrant;

[0124] S27. Compare the system difference between the first quadrant and the fourth quadrant with the standard deviation between the first quadrant and the fourth quadrant, and compare the system difference between the echo signals of the second quadrant and the third quadrant with the standard deviation between the echo signals of the second quadrant and the third quadrant. Adjust the transmitting optical axis and the receiving optical axis according to the comparison results until they meet the standards.

[0125] Preferably, the step S3 specifically includes the following steps:

[0126] S31. According to the lidar equation, the effective signal received by the lidar can be expressed as:

[0127]

[0128] where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient;

[0129] Let r = r 0When the laser emission field of view completely coincides with the telescope receiving field of view, at this time Y(r)=1. Taking the natural logarithm at both ends, we get:

[0130] ln[P s (r)r 2 = ln(Cβ) - 2αr

[0131] Using the least squares method for linear fitting in the form of y = b + a*r, we can obtain:

[0132] a = -2α

[0133] b = ln(Cβ)

[0134] Thus, the geometric overlap factor of the lidar system can be obtained

[0135]

[0136] In this embodiment, by dividing the range-corrected scattered signal X(r) of the radar system echo signal P by the geometric overlap factor, the corrected echo signal of the lidar system is obtained.

[0137] The specific embodiment of the present invention also provides a lidar quality control method, including the following steps:

[0138] S1. Conduct a four-quadrant test on the lidar system, and calibrate the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test results;

[0139] S2. Conduct Rayleigh scattering fitting correction on the lidar system: Fit the range-corrected scattered signal with the Rayleigh scattering signal, and adjust the lidar system according to the fitting results;

[0140] S3. Conduct geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system.

[0141] Based on the above embodiment, in other embodiments, further, in this embodiment, preferably, the optical antenna of the lidar mainly refers to a telescope. As Figures 1-3 shown, there are different division methods for non-coaxial structures and coaxial structures. The following steps are included: S121. Divide the optical antenna of the lidar into four quadrants to obtain the four quadrants of the optical antenna reception system;

[0142] In the non-coaxial mode, the optical axes of the laser emission system and the laser reception system are parallel. As Figure 4As shown in the figure, the emission field of view and the reception field of view of the laser beam gradually transition from complete separation to complete coincidence. Such an optical system structure enables the receiving telescope to only receive partial echo signals within a certain range, resulting in a large error in the inversion result. Therefore, before performing inversion processing on the echo signal, it is necessary to calibrate the system geometric overlap factor Y(r).

[0143] From Figure 4 As shown, within the blind area, the laser beam is not within the reception field of view, and no atmospheric echo signal Y(r)=0 can be received; within the crossover area, the laser beam gradually enters the reception field of view, and the echo signal is partially received by the telescope, gradually increasing to satisfy 0≤Y(r)≤1; within the overlap area, the emitted laser beam completely enters the reception field of view, and the telescope receives all the echo signals, and always Y(r)=1.

[0144] The specific steps of the said step S1 include the following steps:

[0145] S11. Divide the optical antenna of the lidar into four quadrants to obtain the four quadrants of the optical antenna receiving system;

[0146] S12. Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves within the distance range of 2 km to 3 km be X 11 , and The root mean square values are X RMS11 , X RMS4 and X RMS12 . When , save the signal S 1 of the first quadrant and the signal S 4 of the fourth quadrant measured this time;

[0147] S13. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves within the distance range of 2 km to 3 km be and The root mean square values are X RMS21 , X RMS3 and X RMS22 . When , save the signal S 2 of the second quadrant and the signal S 3 of the third quadrant measured this time;

[0148] S14. Let the overlap area of the lidar be L O . For a non-coaxial lidar system, it is assumed that within L O +1 to LO The first quadrant detection signals within the +4 distance range are S 11 、S 12 、……S 1n , and the fourth quadrant detection signals are S 41 、S 42 、……S 4n , calculate the systematic difference M between the first quadrant signals and the fourth quadrant echo signals 14 and the standard deviation σ of the first quadrant signals and the fourth quadrant echo signals 14 :

[0149] M 14 = ((S 11 - S 41 ) + (S 12 - S 42 ) + L + (S 1 n - S 4 n)) / n (4)

[0150]

[0151] S15. Within the range of 0 km to 3 km, the second quadrant detection signals are S 21 、S 22 、……S 2n , and the third quadrant detection signals are S 31 、S 32 、……S 3n , calculate the systematic difference M between the second quadrant and the third quadrant echo signals 23 and the standard deviation σ of the second quadrant and the third quadrant echo signals 23 :

[0152] M 23 = ((S 21 - S 31 ) + (S 22 - S 32 ) + L + (S 2n - S 3n )) / n (6)

[0153]

[0154] S16. For a coaxial lidar system, assume that within the range of 0 km to 3 km, the first quadrant detection signals are S 11 、S 12 、……S 1n , the second quadrant detection signals are S 21 、S 22 、……S 2n , and the third quadrant detection signals are S 31 、S 32, ……S 3n , the detection signal in the fourth quadrant is S 41 , S 42 , ……S 4n , calculate the systematic difference between the first quadrant and the fourth quadrant, the standard deviation between the first quadrant and the fourth quadrant, as well as the systematic difference between the echo signals in the second quadrant and the third quadrant and the standard deviation between the echo signals in the second quadrant and the third quadrant;

[0155] S17. Compare the systematic difference between the first quadrant and the fourth quadrant with the standard deviation between the first quadrant and the fourth quadrant, and compare the systematic difference between the echo signals in the second quadrant and the third quadrant with the standard deviation between the echo signals in the second quadrant and the third quadrant. Adjust the transmitting optical axis and the receiving optical axis according to the comparison results until the standards are met. The calibration method is to check whether the laser divergence angle of the radar system matches the field of view angle of the telescope. If they do not match, adjustment is required; adjust the position of the transmitting optical axis and the receiving optical axis by adjusting the direction of the transmitted laser or the direction of the receiving optical axis of the telescope, and then re - calibrate to meet the calibration requirements.

[0156] On the basis of the above - mentioned embodiments, in other embodiments, further, the step S2 specifically includes the following steps:

[0157] S21. Fit the received distance - corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) and take the logarithmic coordinates;

[0158] S22. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation:

[0159]

[0160] where r is the distance, RCS(r,λ) is the distance - calibrated signal, C is the lidar constant, α m (r,λ) is the atmospheric molecular extinction coefficient,

[0161] β m (r,λ) is the backscattering volume coefficient;

[0162] S23. Substitute formula (2) into formula (1) to obtain:

[0163]

[0164] where λ is the laser wavelength (nm), T(r) is the temperature, P a (r) is the pressure,

[0165] S24. Obtain the distance - corrected scattering signal X(r) from the American standard atmospheric molecular model, and subtract the background noise N from the measured original signal P(r)B Obtain the effective photon signal Ps(r):

[0166] Ps(r) = P(r) - N B

[0167] N B Take the average of the last M values of the original signal P(r), where M is 50, to obtain the distance-corrected scattering signal X(r):

[0168] X(r) = Ps(r) * r * r;

[0169] S25. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r, λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the transmitting optical axis and the receiving optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal. Specifically, adjust the transmitting optical axis of the lidar system and the receiving optical axis of the lidar by the coincidence degree of the spot center points of the two optical axes and the spot size.

[0170] Based on the above embodiments, in other embodiments, further, step S3 specifically includes the following steps:

[0171] S31. According to the lidar equation, the effective signal received by the lidar can be expressed as:

[0172]

[0173] where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient;

[0174] Let r = r 0 When the laser emission field of view and the telescope receiving field of view completely coincide, at this time Y(r) = 1. Take the natural logarithm of both ends to get:

[0175] ln[P s (r)r 2 = ln(Cβ) - 2αr

[0176] Use the least squares method for linear fitting in the form of y = b + a * r, and we can get:

[0177] a = -1α

[0178] b = ln(Cβ)

[0179] Thus, the geometric overlap factor of the lidar system can be obtained

[0180] In this embodiment, the corrected echo signal of the lidar system is obtained by dividing the range-corrected scattered signal X(r) of the radar system echo signal P by the geometric overlap factor.

[0181] The lidar quality control method provided by the embodiments of the present invention performs Rayleigh scattering fitting correction on the lidar to ensure that there is no far-field overflow and to guarantee the signal correctness and stability of the lidar. The four-quadrant (uniformity) test is used to detect whether the assembly of the receiving system (receiving objective lens, focusing lens, optical fiber or receiving probe) of the system meets the design requirements and whether it can correctly receive the backscattered signals from the near field and the far field. This determines the correctness of the overlap factor measurement result and the symmetry of the (biaxial) system. The signal is corrected for the near-field atmospheric conditions using the geometric overlap factor, and the relevant atmospheric parameters that conform to the actual situation are obtained through inversion.

[0182] The above has introduced in detail a lidar quality control method provided by the embodiments of the present invention. For those of ordinary skill in the art, according to the idea of the embodiments of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for lidar quality control, characterized in that, it includes the following steps: S1. Perform Rayleigh scattering fitting correction on the lidar system: Fit the distance-corrected scattering signal with the Rayleigh scattering signal, and adjust the lidar system according to the fitting result; S2. Perform a four-quadrant test on the lidar system, and calibrate the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test result; S3. Perform geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system; The step S2 specifically includes the following steps: S21. Divide the optical antenna of the lidar into four quadrants to obtain the four-quadrant of the optical antenna reception system; Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves within the distance range of 2 km to 3 km be and The root mean square values are X RMS11 , X RMS4 and X RMS12 . When , save the signal S 1 of the first quadrant and the signal S 4 of the fourth quadrant measured this time; S23. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves within the range of 2 km to 3 km be and The root mean square values are X RMS21 、X RMS3 and X RMS22 . When , save the signal S 2 in the second quadrant and the signal S 3 in the third quadrant of this measurement; S24. Let the overlap area of the lidar be L O , for a non-coaxial lidar system, assume that in the range of L O + 1 to L O + 4, the detection signals in the first quadrant are S 11 , S 12 , …… S 1n , and the detection signals in the fourth quadrant are S 41 , S 42 , …… S 4n , where n is the number of detections, calculate the systematic difference M 14 between the signals in the first quadrant and the echo signals in the fourth quadrant and the standard deviation σ 14 : S25. In the range of 0 km to 3 km, the detection signal in the second quadrant is S 21 , S 22 , …… S 2n , the detection signal in the third quadrant is S 31 , S 32 , …… S 3n , calculate the systematic difference M 23 between the echo signals in the second and third quadrants and the standard deviation σ 23 of the echo signals in the second and third quadrants: S26. For a coaxial lidar system, the detection signals in the first quadrant within the range of 0 km to 3 km are S 11 , S 12 , …… S 1n , the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , the detection signals in the third quadrant are S 31 , S 32 , …… S 3n , the detection signals in the fourth quadrant are S 41 , S 42 , …… S 4n . Calculate the systematic difference and standard deviation between the first quadrant and the fourth quadrant, and the systematic difference and standard deviation of the echo signals between the second quadrant and the third quadrant; S27. Compare the system difference between the first quadrant and the fourth quadrant with the standard deviation between the first quadrant and the fourth quadrant, and compare the system difference between the echo signals of the second quadrant and the third quadrant with the standard deviation between the echo signals of the second quadrant and the third quadrant, and adjust the emission optical axis and the reception optical axis according to the comparison result until it meets the standard.

2. The lidar quality control method according to claim 1, characterized in that, the step S1 specifically includes the following steps: S11. Fit the received distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) and take the logarithmic coordinates; S12. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation: where r is the distance, RCS(r, λ) is the distance calibration signal, C is the lidar constant, and α m (r, λ) is the atmospheric molecular extinction coefficient, β m (r, λ) is the backscattering volume coefficient; S13. Substitute formula (2) into formula (1) to get: where λ is the laser wavelength (nm), T(r) is the temperature, and P a (r) is the pressure; S14. Obtain the distance-corrected scattered signal X(r) from the American Standard Atmosphere molecular model, and subtract the background noise N from the measured original signal P(r). B Obtain the effective photon signal Ps(r): Ps(r) = P(r) - N B N B It is obtained by averaging the last M values of the original signal P(r), where M is 50, to obtain the distance-corrected scattered signal X(r): X(r) = Ps(r) * r * r; S15. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r,λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the emission optical axis and the reception optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal.

3. The lidar quality control method according to claim 1, characterized in that, the step S3 specifically includes the following steps: S31. According to the lidar equation, the effective signal received by the lidar can be expressed as: where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient; Let r = r 0 When the laser emission field of view and the telescope receiving field of view completely coincide, at this time Y(r) = 1. Taking the natural logarithm at both ends, we get: ln[P s (r)r 2 = ln(Cβ) - 2αr Using the least squares method for linear fitting in the form of y = b + a * r, we can get: a＝-2α b = ln(Cβ) Thus, the geometric overlap factor of the lidar system can be obtained 4. A method for lidar quality control, characterized in that, it includes the following steps: S1. Perform a four-quadrant test on the lidar system, and calibrate the positions of the emission optical axis of the emission device and the reception optical axis of the reception device of the lidar system according to the test result; S2. Perform Rayleigh scattering fitting correction on the lidar system: Fit the distance-corrected scattering signal with the Rayleigh scattering signal, and adjust the lidar system according to the fitting result; S3. Perform geometric overlap factor correction on the echo signal of the lidar system to obtain the corrected echo signal of the lidar system; The step S1 specifically includes the following steps: S11. Divide the optical antenna of the lidar into four quadrants to obtain the four-quadrant of the optical antenna reception system; S12. Measure in the order of the first quadrant, the fourth quadrant, and the first quadrant. Let the average values of all echo intensity points of the three measured echo curves within the distance range of 2 km to 3 km be and The root mean square values are X RMS11 , X RMS4 and X RMS12 . When , save the signal S 1 of the first quadrant and the signal S 4 of the fourth quadrant measured this time; S13. Measure in the order of the second quadrant, the third quadrant, and the second quadrant. Let the average values of all echo intensity points of the three measured echo curves within the distance range of 2 km to 3 km be and The root mean square values are X RMS21 , X RMS3 and X RMS22 . When , save the signal S 2 in the second quadrant and the signal S 3 in the third quadrant of this measurement; S14. Let the overlap area of the lidar be L O , for a non-coaxial lidar system, assume that in the range of L O + 1 to L O + 4, the detection signals in the first quadrant are S 11 , S 12 , …… S 1n , and the detection signals in the fourth quadrant are S 41 , S 42 , …… S 4n , where n is the number of detections, calculate the systematic difference M 14 between the first quadrant signal and the fourth quadrant echo signal and the standard deviation σ 14 : S15. In the range of 0 km to 3 km, the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , and the detection signals in the third quadrant are S 31 , S 32 , …… S 3n . Calculate the systematic difference M 23 between the echo signals in the second quadrant and the third quadrant and the standard deviation σ 23 of the echo signals in the second quadrant and the third quadrant: S16. For a coaxial lidar system, the detection signals in the first quadrant within the range of 0 km to 3 km are S 11 , S 12 , …… S 1n , the detection signals in the second quadrant are S 21 , S 22 , …… S 2n , The detection signal in the third quadrant is S 31 , S 32 , …… S 3n , and the detection signal in the fourth quadrant is S 41 , S 42 , …… S 4n , calculate the systematic difference between the first and fourth quadrants, the standard deviation between the first and fourth quadrants, as well as the systematic difference of the echo signals between the second and third quadrants and the standard deviation of the echo signals between the second and third quadrants; S17. Compare the systematic difference in the first and fourth quadrants with the standard deviation in the first and fourth quadrants, and compare the systematic difference in the echo signals in the second and third quadrants with the standard deviation in the echo signals in the second and third quadrants. Adjust the transmitting optical axis and the receiving optical axis according to the comparison results until the standards are met.

5. The lidar quality control method according to claim 4, wherein: The step S2 specifically includes the following steps: S21. Fit the received distance-corrected scattering signal X(r) and the Rayleigh scattering signal RCS(r,λ) and take the logarithmic coordinates; S22. The Rayleigh scattering signal RCS(r,λ) is obtained from the lidar equation: where r is the distance, RCS(r, λ) is the distance calibration signal, C is the lidar constant, and α m (r, λ) is the atmospheric molecular extinction coefficient, β m (r, λ) is the backscattering volume coefficient; S23. Substitute formula (2) into formula (1) to obtain: where λ is the laser wavelength (nm), T(r) is the temperature, and P a (r) is the pressure, S24. Obtain the distance-corrected scattered signal X(r) from the United States Standard Atmosphere molecular model, and subtract the background noise N from the measured original signal P(r). B Obtain the effective photon signal Ps(r): Ps(r) = P(r) - N B N B It is obtained by averaging the last M values of the original signal P(r), where M is 50, to obtain the distance-corrected scattered signal X(r): X(r) = Ps(r) * r * r; S25. Compare the distance-corrected scattering signal X(r) with the Rayleigh scattering signal RCS(r,λ). When the value of the distance-corrected scattering signal is lower than the value of the Rayleigh scattering signal, adjust the transmitting optical axis and the receiving optical axis until the value of the distance-corrected scattering signal is higher than the value of the Rayleigh scattering signal.

6. The lidar quality control method according to claim 4, wherein, The step S3 specifically includes the following steps: S31. According to the lidar equation, the effective signal received by the lidar is further expressed as: where C is the lidar system constant, α(r) is the atmospheric extinction coefficient, and β(r) is the backscattering coefficient; Let r = r 0 When the laser emission field of view and the telescope receiving field of view completely coincide, at this time Y(r) = 1. Taking the natural logarithm at both ends, we get: ln[P s (r)r 2 = ln(Cβ) - 2αr Using the least squares method for linear fitting in the form of y = b + a*r, we can obtain: a＝-2α b = ln(Cβ) Thus, the geometric overlap factor of the lidar system can be obtained

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