CN116136590A - Method, device and storage medium for calibrating Doppler laser radar focal length - Google Patents
Method, device and storage medium for calibrating Doppler laser radar focal length Download PDFInfo
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Abstract
The invention discloses a method, a device and a storage medium for calibrating the focal length of a Doppler laser radar, wherein the method comprises the steps of obtaining echo signals detected horizontally by the coherent Doppler laser radar, and correcting the carrier-to-noise ratio of the echo signals by a distance and focusing function to obtain corrected signals; taking the logarithm of the correction signal, performing linear fitting, and respectively calculating fitting residual errors under the condition of different focal length parameters; according to the invention, according to the assumption of uniform aerosol horizontal distribution, the self calibration of a focusing function is realized by utilizing the horizontal detection echo of the coherent Doppler laser radar, and meanwhile, the dependence of the focal length parameter along with temperature is obtained, so that the guarantee is provided for further accurately inverting the backscattering coefficient and the extinction coefficient of the aerosol.
Description
Technical Field
The invention relates to a method, a device and a storage medium for calibrating a Doppler laser radar focal length, and belongs to the technical field of laser radars.
Background
Coherent doppler lidar can achieve velocity detection by detecting the doppler shift of echo signals of moving objects (e.g., atmospheric aerosols, clouds, hard objects, etc.). The method is widely used in the fields of aviation safety guarantee, wind power generation, air pollution monitoring and forecasting and the like.
In some research or application scenarios, information on aerosol concentration is currently of the same interest as the atmospheric wind speed. The current aerosol information is generally synchronously acquired through an aerosol laser radar working in a direct multimode detection mode, and the pulse energy, the system power consumption and the volume required by the existing direct detection aerosol laser radar are large, so that the existing direct detection aerosol laser radar is easily interfered by solar background radiation noise in daytime. Meanwhile, the common working wavelength (visible light or near infrared) of the fluorescent lamp poses a threat to human eye safety. The coherent laser radar adopts a middle infrared band with human eye safety, and the all-fiber system can ensure higher stability and integration level. However, because the coherent laser radar adopts single-mode detection, the detection efficiency is seriously affected by factors such as the focusing position of a laser beam, and the like, so that inversion of atmospheric parameters such as an aerosol extinction coefficient, a backscattering coefficient, and the like is difficult, and therefore, the intensity information of an echo signal of the coherent laser radar is often ignored.
In order to realize aerosol optical parameter inversion based on coherent Doppler laser radar, how to accurately predict the focusing position of a laser beam, so that the focusing function curve of the laser beam is accurately calibrated, which is a problem to be solved.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method, a device and a storage medium for calibrating the focal length of a Doppler laser radar, which realize self calibration of a focusing function by utilizing the horizontal detection echo of the coherent Doppler laser radar, so that parameters such as an aerosol backscattering coefficient, an extinction coefficient and the like can be inverted more accurately.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
in a first aspect, the present invention provides a method for calibrating a focal length of a doppler lidar, comprising:
acquiring an echo signal of the horizontal detection of the coherent Doppler laser radar, and correcting a distance and focusing function of the carrier-to-noise ratio of the echo signal to obtain a corrected signal;
taking the logarithm of the correction signal, performing linear fitting, and respectively calculating fitting residual errors under the condition of different focal length parameters;
and taking the focal length parameter corresponding to the minimum value of the fitting residual as the optimal focal length parameter.
Further, the formula of the carrier-to-noise ratio of the echo signal is as follows:
wherein E is T For the single pulse energy of the emergent laser, R is the distance between the target scatterer and the telescope, sigma is the atmospheric extinction coefficient, including atmospheric molecular extinction and aerosol extinction, beta is the aerosol backscattering coefficient, A r Is the effective receiving area of the telescope, c is the light velocity in the air, eta o For system efficiency, hv is photon energy, B is detector bandwidth, η h For coherent heterodyning efficiency, R represents the function argument on the path in the process from 0 to R.
Further, the formula of the focusing function is as follows:
wherein omega T E at telescope for outgoing Gaussian beam -2 Irradiance radius, lambda is laser wavelength, R f Is the focal length parameter, v 0 Is the transverse coherence length associated with turbulence.
Further, the performing linear fitting on the corrected signal after taking the logarithm, and calculating a fitting residual, includes:
the attenuated backscatter coefficients are defined as follows:
wherein ons is a constant factor related to system parameters;
the attenuated backscatter coefficients are logarithmically calculated to yield the formula:
lnβ'(R)＝lnβ-2σR (4)
i.e. lnβ' (R) is a linear function of the distance R, taking into account R f As variables, the following objective functions were constructed:
J(R f )＝MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)
wherein J (R) f ) To fit the residual, β' (R f R) is a correction signal, MSE represents root mean square, linear represents least squares linear fit.
Furthermore, multiple groups of focal length parameter-temperature data are obtained under different telescope temperatures, the dependence of focal length parameters along with the temperature is obtained through statistics fitting, and focusing function correction is carried out on echo signals according to telescope temperatures recorded in real time.
Further, acquiring echo signals of horizontal detection of a plurality of groups of coherent Doppler laser radars, and respectively calibrating the focal length by adopting the method for calibrating the focal length of the Doppler laser radars according to claim 1 to obtain corresponding optimal focal length parameters;
and taking the average value of all the optimal focal length parameters as the final focal length parameter.
In a second aspect, the present invention provides an apparatus for calibrating a focal length of a doppler lidar, comprising:
the correction signal acquisition module is used for acquiring echo signals horizontally detected by the coherent Doppler laser radar, and correcting the distance and focusing functions of the carrier-to-noise ratio of the echo signals to obtain correction signals;
the fitting residual error acquisition module is used for carrying out linear fitting on the corrected signals after taking logarithms, and calculating fitting residual errors respectively under the condition of giving different focal length parameters;
and the optimal focal length parameter acquisition module is used for selecting a focal length parameter corresponding to the minimum value of the fitting residual error as an optimal focal length parameter.
In a third aspect, the present invention provides an electronic device, comprising a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is operative according to the instructions to perform the steps of the method according to any one of the preceding claims.
In a fourth aspect, the present invention provides a computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of any of the methods described in the preceding claims.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method, a device and a storage medium for calibrating a focal length of a Doppler laser radar, which utilize a horizontal detection echo of the coherent Doppler laser radar to realize self calibration of a focusing function according to the assumption of uniform distribution of aerosol level, and obtain a dependence of focal length parameters along with temperature. This provides a guarantee for further accurate inversion of the aerosol backscattering coefficient and extinction coefficient.
Drawings
FIG. 1 is a graph of the carrier-to-noise ratio of a horizontal probe echo of a coherent Doppler lidar according to an embodiment of the present invention;
FIG. 2 is a distance correction curve obtained by performing a distance correction on the echo curve in FIG. 1;
FIG. 3 is a graph obtained by further performing focusing function correction according to the distance correction graph of FIG. 2, and a linear fitting result;
FIG. 4 is a statistical plot of focal length parameters obtained according to the method at different telescope temperatures, and a fitted relationship thereof;
fig. 5 is a flowchart of a method for calibrating a focal length of a doppler lidar according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
Example 1
As shown in fig. 5, this embodiment describes a method for calibrating a focal length of a doppler lidar, which includes:
acquiring an echo signal of the horizontal detection of the coherent Doppler laser radar, and correcting a distance and focusing function of the carrier-to-noise ratio of the echo signal to obtain a corrected signal;
taking logarithm of the correction signal, performing linear fitting, and calculating fitting residual errors;
under the condition of different focal length parameters, fitting residual errors are calculated respectively, and the focal length parameter corresponding to the minimum value of the residual errors is taken as the optimal focal length parameter.
The application process of the method for calibrating the Doppler laser radar focal length provided by the embodiment specifically relates to the following steps:
step one: selecting coherent Doppler laser radar level detection echo with uniform atmospheric aerosol distribution, weak turbulence and long detection distance, and performing distance and focusing function correction on the echo signal carrier-to-noise ratio to obtain a correction signal beta' (R) as shown in figure 1 f R); under the condition of no truncated Gaussian beam, the focusing function can be expressed as
Wherein omega T E at telescope for outgoing Gaussian beam -2 Irradiance radius, lambda is laser wavelength, R f Radius of curvature of the equiphase surface of the outgoing beam, i.e. focal length parameter ρ 0 For the transverse coherence length associated with turbulence, it is negligible in the case of weak turbulence.
Step two: and D, taking the logarithm of the corrected signal obtained in the step one, performing linear fitting, and calculating the fitting residual root mean square.
J(R f )＝MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)
Where MSE represents root mean square and Linear represents least squares linear fit. By global means at a given R f Calculation of J (R) in the value range f ) When it takes the minimum value, the corresponding R f The optimal focal length parameter is calculated.
Step three: and (5) counting the average value of a plurality of groups of results, and improving the inversion accuracy.
The description of the above embodiment will be made with reference to a preferred embodiment.
After the laser radar emits laser pulse into the atmosphere, the carrier-to-noise ratio of the received echo signal can be expressed as
Wherein E is T For the single pulse energy of the emergent laser, R is the distance between the target scatterer and the telescope, sigma is the atmospheric extinction coefficient, including atmospheric molecular extinction and aerosol extinction, beta is the aerosol backscattering coefficient, A r Is the effective receiving area of the telescope, c is the light velocity in the air, eta o For system efficiency, hv is photon energy, B is detector bandwidth, η h For coherent heterodyning efficiency (or focusing function), R represents the function argument on the path in the process from 0 to R. Under the condition of no truncated Gaussian beam, the focusing function can be expressed as
ω T E at telescope for outgoing Gaussian beam -2 Irradiance radius, lambda is laser wavelength, R f Radius of curvature ρ of the equiphase surface of the outgoing beam 0 For the transverse coherence length associated with turbulence, it is negligible in the case of weak turbulence.
Defining the attenuated backscattering coefficient
Wherein ons is a constant factor related to system parameters, it can be seen that the unknown variable related to distance is only the focusing function eta h (R). Under uniform distribution of aerosol levels, both σ and β are constants, so taking the logarithm of the attenuated backscatter coefficient can yield:
lnβ'(R)＝lnβ-2σR (4)
i.e. lnβ' (R) is a linear function of the distance R, taking into account R f As variables, the following objective functions were constructed:
J(R f )＝MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)
where MSE represents root mean square and Linear represents least squares linear fit. By global means at a given R f Calculation of J (R) in the value range f ) When it takes the minimum value, the corresponding R f The optimal focal length parameter is calculated. The corrected echo of the focusing function obtained based on the method and the linear fitting result thereof are given in fig. 3, and the corresponding optimal focal length parameter is 3km. In contrast, the echo curve is given in fig. 2 without correction of the focusing function.
Since the assumption of uniform distribution of aerosol levels is not always satisfied, inversion accuracy can be improved by counting the average of multiple sets of results. In addition, the telescope deformation caused by the temperature change can cause the change of focal length parameters, correction and compensation are needed according to the current telescope temperature information, and a focal length parameter statistical point diagram obtained according to the method at different telescope temperatures and fitting relations thereof are shown in fig. 4.
In the embodiment of the invention, according to the assumption of uniform aerosol level distribution, the self calibration of a focusing function is realized by utilizing the level detection echo of the coherent Doppler laser radar, and meanwhile, the dependence of focal length parameters on temperature is obtained. This provides a guarantee for further accurate inversion of the aerosol backscattering coefficient and extinction coefficient.
Example 2
The embodiment provides a device for calibrating a Doppler laser radar focal length, which comprises:
the correction signal acquisition module is used for acquiring echo signals horizontally detected by the coherent Doppler laser radar, and correcting the distance and focusing functions of the carrier-to-noise ratio of the echo signals to obtain correction signals;
the fitting residual error acquisition module is used for carrying out linear fitting on the corrected signals after taking logarithms, and calculating fitting residual errors respectively under the condition of giving different focal length parameters;
and the optimal focal length parameter acquisition module is used for selecting a focal length parameter corresponding to the minimum value of the fitting residual error as an optimal focal length parameter.
Example 3
The embodiment provides an electronic device, which comprises a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is operative according to the instructions to perform the steps of the method according to any one of embodiment 1.
Example 4
The present embodiment provides a computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of the method of any of embodiment 1.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (9)
1. A method of calibrating a focal length of a doppler lidar comprising:
acquiring an echo signal of the horizontal detection of the coherent Doppler laser radar, and correcting a distance and focusing function of the carrier-to-noise ratio of the echo signal to obtain a corrected signal;
taking the logarithm of the correction signal, performing linear fitting, and respectively calculating fitting residual errors under the condition of different focal length parameters;
and taking the focal length parameter corresponding to the minimum value of the fitting residual as the optimal focal length parameter.
2. The method of calibrating a focal length of a doppler lidar of claim 1, wherein the echo signal carrier-to-noise ratio is formulated as follows:
wherein E is T For emitting laser single pulse energy, R is target scattererDistance from telescope, sigma is atmospheric extinction coefficient, including atmospheric extinction and aerosol extinction, beta is aerosol backscattering coefficient, A r Is the effective receiving area of the telescope, c is the light velocity in the air, eta o For system efficiency, hv is photon energy, B is detector bandwidth, η h For coherent heterodyning efficiency, R represents the function argument on the path in the process from 0 to R.
3. A method of calibrating a focal length of a doppler lidar according to claim 2, wherein the focusing function is formulated as follows:
wherein omega T E at telescope for outgoing Gaussian beam -2 Irradiance radius, lambda is laser wavelength, R f As focal length parameter ρ 0 Is the transverse coherence length associated with turbulence.
4. A method of calibrating a focal length of a doppler lidar according to claim 3, wherein the performing a linear fit on the corrected signal after taking the logarithm and calculating a fit residual comprises:
the attenuated backscatter coefficients are defined as follows:
wherein ons is a constant factor related to system parameters;
the attenuated backscatter coefficients are logarithmically calculated to yield the formula:
lnβ'(R)＝lnβ-2σR (4)
i.e. lnβ' (R) is a linear function of the distance R, taking into account R f As variables, the following objective functions were constructed:
J(R f )＝MSE{lnβ'(R f ,R)-Linearfit[lnβ'(R f ,R)]} (5)
wherein J (R) f ) To fit the residual, β' (R f R) is a correction signal, MSE represents root mean square, linear represents least squares linear fit.
5. The method for calibrating the focal length of the Doppler laser radar according to claim 1, wherein a plurality of groups of focal length parameter-temperature data are obtained under different telescope temperatures, the dependence of the focal length parameter along with the temperature is obtained through statistics fitting, and the focusing function correction is carried out on the echo signals according to the telescope temperatures recorded in real time.
6. A method of calibrating a focal length of a Doppler lidar as claimed in claim 1,
acquiring echo signals of horizontal detection of a plurality of groups of coherent Doppler laser radars, and respectively calibrating the focal length by adopting the method for calibrating the focal length of the Doppler laser radars according to claim 1 to obtain corresponding optimal focal length parameters;
and taking the average value of all the optimal focal length parameters as the final focal length parameter.
7. A device for calibrating the focal length of a doppler lidar, comprising:
the correction signal acquisition module is used for acquiring echo signals horizontally detected by the coherent Doppler laser radar, and correcting the distance and focusing functions of the carrier-to-noise ratio of the echo signals to obtain correction signals;
the fitting residual error acquisition module is used for carrying out linear fitting on the corrected signals after taking logarithms, and calculating fitting residual errors respectively under the condition of giving different focal length parameters;
and the optimal focal length parameter acquisition module is used for selecting a focal length parameter corresponding to the minimum value of the fitting residual error as an optimal focal length parameter.
8. An electronic device, characterized in that: comprises a processor and a storage medium;
the storage medium is used for storing instructions;
the processor being operative according to the instructions to perform the steps of the method according to any one of claims 1 to 6.
9. A computer-readable storage medium having stored thereon a computer program, characterized by: which program, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 6.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116577899A (en) * | 2023-07-13 | 2023-08-11 | 中国科学技术大学 | Focal length adjusting system applied to wind-measuring laser radar |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116577899A (en) * | 2023-07-13 | 2023-08-11 | 中国科学技术大学 | Focal length adjusting system applied to wind-measuring laser radar |
| CN116577899B (en) * | 2023-07-13 | 2023-11-28 | 中国科学技术大学 | Focal length adjusting system applied to wind-measuring laser radar |
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