Method, device and storage medium for calibrating focal length of doppler lidar

Abstract

The application discloses a method and device for calibrating the focal length of a Doppler laser radar and a storage medium, and the method comprises the following steps: acquiring echo signals of horizontal detection of a coherent Doppler laser radar; performing distance and focusing function correction on the carrier-to-noise ratio of the echo signals to obtain a corrected signal; performing linear fitting on the corrected signal after logarithmic transformation, and calculating fitting residuals under different focal length parameters; and taking the focal length parameter corresponding to the minimum fitting residual as the optimal focal length parameter. According to the assumption that the aerosol horizontal distribution is uniform, the focusing function is self-calibrated by using the horizontal detection echo of the coherent Doppler laser radar, and the dependence of the focal length parameter on temperature is obtained, which provides a guarantee for further accurately inverting the aerosol backscattering coefficient and the extinction coefficient.

Description

Technical Field

[0001] This invention relates to a method, apparatus, and storage medium for calibrating the focal length of a Doppler lidar, belonging to the field of lidar technology. Background Technology

[0002] Coherent Doppler lidar can detect velocity by detecting the Doppler frequency shift of echo signals from moving targets (such as atmospheric aerosols, clouds, and hard targets). It is currently widely used in fields such as aviation safety, wind power generation, and air pollution monitoring and forecasting.

[0003] Currently, aerosol concentration information is receiving the same level of attention as atmospheric wind speed in some research and application scenarios. Current aerosol information is generally acquired simultaneously using aerosol lidar operating on a direct multimode detection basis. However, existing direct aerosol lidar requires significant pulse energy, system power consumption, and size, and is susceptible to interference from solar background radiation noise during the day. Furthermore, its commonly used operating wavelengths (visible or near-infrared) pose a threat to human eye safety. Coherent lidar uses the eye-safe mid-infrared band, and its all-fiber system can ensure high stability and integration. However, because coherent lidar uses single-mode detection, its detection efficiency is severely affected by factors such as the laser beam focusing position, making it difficult to retrieve atmospheric parameters such as aerosol extinction coefficient and backscattering coefficient. Therefore, the intensity information of the coherent lidar echo signal is often ignored.

[0004] To achieve aerosol optical parameter inversion based on coherent Doppler lidar, the problem we need to solve is how to accurately predict the focusing position of the laser beam, and thus accurately calibrate the focusing function curve of the laser beam. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, device and storage medium for calibrating the focal length of a Doppler lidar. It utilizes the horizontal detection echo of a coherent Doppler lidar to achieve self-calibration of the focusing function, thereby enabling more accurate inversion of parameters such as aerosol backscattering coefficient and extinction coefficient.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a method for calibrating the focal length of a Doppler lidar, comprising:

[0008] The echo signal from the horizontal detection of the coherent Doppler lidar is acquired, and the carrier-to-noise ratio of the echo signal is corrected by range and focusing function to obtain the corrected signal.

[0009] The modified signal is logarithmically fitted and then linearly fitted. The fitting residuals are calculated for different focal length parameters.

[0010] The focal length parameter corresponding to the minimum value of the fitted residual is taken as the optimal focal length parameter.

[0011] Furthermore, the formula for the echo signal carrier-to-noise ratio is as follows:

[0012]

[0013] Among them, E T R is the single-pulse energy of the emitted laser, R is the distance between the target scatterer and the telescope, σ is the atmospheric extinction coefficient, including atmospheric molecular extinction and aerosol extinction, β is the aerosol backscattering coefficient, and A is the aerosol backscattering coefficient. r Let η be the effective receiving area of ​​the telescope, c be the speed of light in air, and η be the effective receiving area of ​​the telescope. o For system efficiency, hv is the photon energy, B is the detector bandwidth, and η is the system efficiency. h Let r represent the coherent heterodyne efficiency, and let r denote the function independent variable along the path from the integral at 0 to R.

[0014] Furthermore, the formula for the focusing function is as follows:

[0015]

[0016] Where, ω T For the output Gaussian beam at the telescope e -2 Irradiance radius, λ is the laser wavelength, R f is the focal length parameter, and v0 is the transverse coherence length related to turbulence.

[0017] Furthermore, the step of taking the logarithm of the corrected signal, performing linear fitting, and calculating the fitting residual includes:

[0018] The attenuation backscattering coefficient is defined by the following formula:

[0019]

[0020] Where cons. are constant factors related to the system parameters;

[0021] Taking the logarithm of the attenuation backscattering coefficient, we obtain the following formula:

[0022] lnβ'(R)=lnβ-2σR (4)

[0023] That is, lnβ'(R) is a linear function of the distance R. Consider R f For each variable, construct the following objective function:

[0024] J(R f )=MSE{lnβ'(R f ,R)-Linearfit[lnβ'(Rf ,R)]} (5)

[0025] Among them, J(R) f ) represents the fitting residual, β'(R) f R) represents the correction signal, MSE represents the root mean square, and Linearfit represents the least squares linear fitting.

[0026] Furthermore, multiple sets of focal length parameter-temperature data were obtained under different telescope temperatures, and the dependence of focal length parameters on temperature was statistically fitted. The focusing function of the echo signal was then corrected based on the real-time recorded telescope temperature.

[0027] Furthermore, multiple sets of echo signals from the horizontal detection of the coherent Doppler lidar were acquired, and the focal length was calibrated using the method for calibrating the focal length of the Doppler lidar to obtain the corresponding optimal focal length parameters.

[0028] The average value of each optimal focal length parameter is taken as the final focal length parameter.

[0029] Secondly, the present invention provides an apparatus for calibrating the focal length of a Doppler lidar, comprising:

[0030] The corrected signal acquisition module is used to acquire the echo signal from the horizontal detection of the coherent Doppler lidar, and to correct the carrier-to-noise ratio of the echo signal by range and focusing function to obtain the corrected signal;

[0031] The fitting residual acquisition module is used to perform linear fitting after taking the logarithm of the corrected signal, and to calculate the fitting residual under different focal length parameters.

[0032] The optimal focal length parameter acquisition module is used to select the focal length parameter corresponding to the minimum value of the fitting residual as the optimal focal length parameter.

[0033] Thirdly, the present invention provides an electronic device, including a processor and a storage medium;

[0034] The storage medium is used to store instructions;

[0035] The processor is configured to operate according to the instructions to perform the steps of the method according to any of the preceding claims.

[0036] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the preceding methods.

[0037] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0038] This invention provides a method, apparatus, and storage medium for calibrating the focal length of a Doppler lidar. Based on the assumption of a horizontally uniform aerosol distribution, the focusing function is self-calibrated using the horizontal detection echo of a coherent Doppler lidar, while simultaneously obtaining the dependence of the focal length parameter on temperature. This ensures the accurate inversion of the aerosol backscattering coefficient and extinction coefficient. Attached Figure Description

[0039] Figure 1 This is the carrier-to-noise ratio curve of the horizontal detection echo of the coherent Doppler lidar provided in the embodiments of the present invention;

[0040] Figure 2 Yes Figure 1 The distance correction curve obtained after distance correction of the mid-echo curve;

[0041] Figure 3 It is based on Figure 2 The mid-range correction curve is further corrected by the focusing function to obtain the curve, and the linear fitting result is also included.

[0042] Figure 4 It is a statistical point plot of focal length parameters obtained by the method under different telescope temperatures, and its fitting relationship;

[0043] Figure 5 This is a flowchart of a method for calibrating the focal length of a Doppler lidar according to an embodiment of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 5 As shown in the figure, this embodiment introduces a method for calibrating the focal length of a Doppler lidar, including:

[0047] The echo signal from the horizontal detection of the coherent Doppler lidar is acquired, and the carrier-to-noise ratio of the echo signal is corrected by range and focusing function to obtain the corrected signal.

[0048] After taking the logarithm of the corrected signal, perform linear fitting and calculate the fitting residuals;

[0049] Given different focal length parameters, calculate the fitting residuals respectively, and take the focal length parameter corresponding to the minimum residual as the optimal focal length parameter.

[0050] The method for calibrating the focal length of a Doppler lidar provided in this embodiment involves the following steps:

[0051] Step 1: Select a time when the atmospheric aerosol distribution is uniform, turbulence is weak, and the detection distance is long for the coherent Doppler lidar to detect the horizontal echo, such as... Figure 1 As shown, the corrected signal β'(R) is obtained by applying distance and focusing function correction to the echo signal carrier-to-noise ratio. f Under the condition of an untruncated Gaussian beam, the focusing function can be expressed as R);

[0052]

[0053] Where ω T For the output Gaussian beam at the telescope e -2 Irradiance radius, λ is the laser wavelength, R f ρ is the radius of curvature of the isophase surface of the outgoing beam, i.e., the focal length parameter, and ρ0 is the transverse coherence length related to turbulence, which can be ignored in the case of weak turbulence.

[0054] Step 2: Take the logarithm of the corrected signal obtained in Step 1 and perform linear fitting, then calculate the root mean square of the fitting residual.

[0055] J(R f )=MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)

[0056] Where MSE represents root mean square, and Linearfit represents least squares linear fitting. The global method is used to fit a given R... f Calculate J(R) within the range of values f When it reaches its minimum value, the corresponding R f This is the optimal focal length parameter we are looking for.

[0057] Step 3: Calculate the average of multiple sets of results to improve the accuracy of the inversion.

[0058] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0059] After a lidar emits a laser pulse into the atmosphere, the carrier-to-noise ratio of the received echo signal can be expressed as:

[0060]

[0061] Where E T R is the single-pulse energy of the emitted laser, R is the distance between the target scatterer and the telescope, σ is the atmospheric extinction coefficient, including atmospheric molecular extinction and aerosol extinction, β is the aerosol backscattering coefficient, and A is the aerosol backscattering coefficient. r Let η be the effective receiving area of ​​the telescope, c be the speed of light in air, and η be the effective receiving area of ​​the telescope. oFor system efficiency, hv is the photon energy, B is the detector bandwidth, and η is the system efficiency. h Let r be the coherent heterodyne efficiency (or focusing function), and r represent the independent variable of the function along the path from the integral at 0 to R. Under the condition of an untruncated Gaussian beam, the focusing function can be expressed as:

[0062]

[0063] ω T For the output Gaussian beam at the telescope e -2 Irradiance radius, λ is the laser wavelength, R f ρ is the radius of curvature of the isophase surface of the outgoing beam, and ρ0 is the transverse coherence length related to turbulence, which can be ignored in the case of weak turbulence.

[0064] Define the attenuation backscattering coefficient

[0065]

[0066] Where cons. represents constant factors related to system parameters, it can be seen that the only unknown variable related to distance is the focusing function η. h (R). Under the condition of a uniform horizontal distribution of aerosols, σ and β are both constants, therefore taking the logarithm of the attenuation backscattering coefficient yields:

[0067] lnβ'(R)=lnβ-2σR (4)

[0068] That is, lnβ'(R) is a linear function of the distance R. Consider R f For each variable, construct the following objective function:

[0069] J(R f )=MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)

[0070] Where MSE represents root mean square, and Linearfit represents least squares linear fitting. The global method is used to fit a given R... f Calculate J(R) within the range of values f When it reaches its minimum value, the corresponding R f This is the optimal focal length parameter we are looking for. Figure 3 The paper presents the corrected echo of the focusing function obtained based on the described method and its linear fitting results, with the corresponding optimal focal length parameter being 3km. For comparison, Figure 2 The image shows the echo curve without focusing function correction.

[0071] Since the assumption of a uniform horizontal distribution of aerosols is not always satisfied, averaging multiple sets of results is necessary to improve inversion accuracy. Furthermore, temperature variations cause telescope deformation, leading to changes in focal length parameters, which require correction and compensation based on current telescope temperature information. Figure 4 Statistical point plots of focal length parameters obtained by the method under different telescope temperatures are presented, along with their fitting relationships.

[0072] In this invention, based on the assumption of a horizontally uniform aerosol distribution, the focusing function is self-calibrated using the horizontal detection echo of a coherent Doppler lidar, while simultaneously obtaining the dependence of the focal length parameter on temperature. This provides a guarantee for further accurate inversion of the aerosol backscattering coefficient and extinction coefficient.

[0073] Example 2

[0074] This embodiment provides a device for calibrating the focal length of a Doppler lidar, comprising:

[0075] The corrected signal acquisition module is used to acquire the echo signal from the horizontal detection of the coherent Doppler lidar, and to correct the carrier-to-noise ratio of the echo signal by range and focusing function to obtain the corrected signal;

[0076] The fitting residual acquisition module is used to perform linear fitting after taking the logarithm of the corrected signal, and to calculate the fitting residual under different focal length parameters.

[0077] The optimal focal length parameter acquisition module is used to select the focal length parameter corresponding to the minimum value of the fitting residual as the optimal focal length parameter.

[0078] Example 3

[0079] This embodiment provides an electronic device, including a processor and a storage medium;

[0080] The storage medium is used to store instructions;

[0081] The processor is configured to operate according to the instructions to perform the steps of the method according to any one of Embodiment 1.

[0082] Example 4

[0083] This embodiment provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described in Embodiment 1.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for calibrating the focal length of a Doppler lidar, characterized in that, include: The echo signal from the horizontal detection of the coherent Doppler lidar is acquired, and the carrier-to-noise ratio of the echo signal is corrected by range and focusing function to obtain the corrected signal; The modified signal is logarithmically fitted and then the fitting residuals are calculated for different focal length parameters. The focal length parameter corresponding to the minimum value of the fitted residual is taken as the optimal focal length parameter. The formula for the echo signal carrier-to-noise ratio is as follows: （1） in, The single pulse energy of the emitted laser. The distance between the target scatterer and the telescope. This is the atmospheric extinction coefficient, which includes atmospheric molecular extinction and aerosol extinction. The aerosol backscattering coefficient is... The effective receiving area of ​​the telescope, The speed of light in air. For system efficiency, Photon energy, For detector bandwidth, For coherent heterodyne efficiency, Indicates the integral from 0 to The independent variables of the function along the path during the process; The formula for the focusing function is as follows: （2） in, For the output Gaussian beam at the telescope Irradiance radius, The wavelength of the laser. For focal length parameters, The transverse coherence length associated with turbulence; The process of taking the logarithm of the corrected signal, performing linear fitting, and calculating the fitting residual includes: The attenuation backscattering coefficient is defined by the following formula: （3） in These are constant factors related to system parameters; Taking the logarithm of the attenuation backscattering coefficient, we obtain the following formula: （4） Right now It is distance Consider a linear function. For each variable, construct the following objective function: （5） in, To fit the residuals, For the corrected signal, MSE represents the root mean square. This indicates a linear fit using the least squares method.

2. The method for calibrating the focal length of a Doppler lidar according to claim 1, characterized in that, Multiple sets of focal length parameter-temperature data were obtained under different telescope temperatures, and the dependence of focal length parameters on temperature was obtained by statistical fitting. The focusing function of the echo signal was corrected based on the telescope temperature recorded in real time.

3. The method for calibrating the focal length of a Doppler lidar according to claim 1, characterized in that, Multiple sets of echo signals from horizontal detection by coherent Doppler lidar are acquired, and the focal length is calibrated using the method for calibrating the focal length of Doppler lidar as described in claim 1, thereby obtaining the corresponding optimal focal length parameters. The average value of each optimal focal length parameter is taken as the final focal length parameter.

4. An apparatus for calibrating the focal length of a Doppler lidar, used to implement the method for calibrating the focal length of a Doppler lidar as described in any one of claims 1 to 3, characterized in that, include: The corrected signal acquisition module is used to acquire the echo signal from the horizontal detection of the coherent Doppler lidar, and to correct the carrier-to-noise ratio of the echo signal by range and focusing function to obtain the corrected signal; The fitting residual acquisition module is used to perform linear fitting after taking the logarithm of the corrected signal, and to calculate the fitting residual under different focal length parameters. The optimal focal length parameter acquisition module is used to select the focal length parameter corresponding to the minimum value of the fitting residual as the optimal focal length parameter.

5. An electronic device, characterized in that: Including processor and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1 to 3.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When executed by a processor, the program implements the steps of the method according to any one of claims 1 to 3.

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