High-precision coherent wind lidar system

Abstract

The invention relates to the field of laser radar speed measurement, in particular to a high-precision coherent wind measurement laser radar system. The system firstly obtains an intermediate frequency signal of a current measurement environment, carries out frequency domain conversion on a part of the intermediate frequency signal in each time period to obtain a frequency value of the intermediate frequency signal in each time period, screens out multiple scattering frequency values, carries out wavelet decomposition on the intermediate frequency signal, and obtains a wavelet threshold value of each sub-band signal; adjusting the wavelet coefficient of the sub-band signal in each time period according to the difference between the wavelet coefficient and the wavelet threshold of the sub-band signal in each time period and the difference between the frequency value and the multiple scattering frequency value of the intermediate frequency signal in each time period, and obtaining an adjusted intermediate frequency signal in combination with the wavelet function of the sub-band signal in each time period; and calculating the wind speed of the current measurement environment based on the Doppler frequency shift frequency of the adjusted intermediate frequency signal. According to the invention, multiple frequency shift effects in the intermediate frequency signals can be removed, and the accuracy of wind speed measurement is improved.

Description

Technical Field

[0001] The present invention relates to the field of lidar velocity measurement, and particularly to a high-precision coherent wind-measuring lidar system. Background Art

[0002] As a clean and sustainable form of energy, wind energy has attracted much attention. In order to more effectively develop and utilize wind energy resources, it is necessary to measure the wind field in real time and with high precision. A lidar is a device that emits a laser beam and then measures the changes in the laser after reflection, scattering, etc. by the target object to detect and measure the relevant properties of the target object. It has the advantages of high precision and high spatial resolution. In particular, a coherent lidar is a lidar system based on coherent detection technology. By using the Doppler effect and the coherent characteristics of the laser, it measures the backscattered signal generated by the interaction between the laser and atmospheric aerosol particles to measure the wind speed.

[0003] In related technologies, usually, the intermediate frequency signal formed by mixing the laser signal after atmospheric scattering with the original laser signal is detected, and the Doppler frequency shift analysis is performed on the signal after decomposition and reconstruction of the intermediate frequency signal by using wavelet transform technology, so as to realize the measurement of the wind speed. However, when there are severe weather conditions such as heavy fog or haze in the measurement environment, the air contains a large number of tiny particles, which will cause the laser emitted by the radar to be scattered multiple times, resulting in the intermediate frequency signal containing noise components with multiple Doppler frequency shifts. And the wavelet transform technology can only remove the multiple frequency shift effects at the corresponding level and cannot remove the multiple frequency shift effects in the intermediate frequency signal, reducing the accuracy of the wind speed measurement. Summary of the Invention

[0004] In order to solve the technical problem that when the air contains a large number of tiny particles, the wavelet transform technology can only remove the multiple frequency shift effects at the corresponding level and cannot completely remove the multiple frequency shift effects in the intermediate frequency signal, reducing the accuracy of the wind speed measurement, the purpose of the present invention is to provide a high-precision coherent wind-measuring lidar system, and the specific technical solution adopted is as follows: The present invention provides a high-precision coherent wind-measuring lidar system, and the system includes: A signal acquisition module, configured to obtain the intermediate frequency signal of the lidar in the current measurement environment; A frequency shift analysis module, configured to perform frequency domain conversion on a part of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period; screen out a plurality of reference frequency values from all the frequency values according to the number of times each frequency value appears in all the time periods; perform iterative screening on all the reference frequency values to obtain the multiple scattering frequency values; The decomposition and reconstruction module is used to perform wavelet decomposition on the intermediate frequency signal to obtain multiple sub-band signals, the wavelet coefficients and wavelet functions of each sub-band signal in each time period, and obtain the wavelet threshold of each sub-band signal; according to the difference between the wavelet coefficients and the wavelet threshold of each sub-band signal in each time period, and the difference between the frequency value and the multiple scattering frequency value of the intermediate frequency signal in each time period, obtain the retention degree of each sub-band signal in each time period; according to the retention degree of each sub-band signal in each time period, adjust the wavelet coefficients of each sub-band signal in each time period, and combine the wavelet functions of each sub-band signal in each time period to obtain the adjusted intermediate frequency signal. The wind speed measurement module is used to perform frequency domain conversion on the adjusted intermediate frequency signal to obtain the Doppler shift frequency of the adjusted intermediate frequency signal; based on the Doppler shift frequency, obtain the wind speed of the current measurement environment.

[0005] Further, the screening of multiple reference frequency values from all frequency values includes: Taking any one frequency value as the target frequency value, using the number of time periods containing the target frequency value as the numerator and the number of all time periods as the denominator, and taking the ratio as the occurrence probability value of the target frequency value; Taking the average value of the occurrence probability values of all frequency values as the screening threshold; Taking the frequency values with the occurrence probability value greater than the screening threshold as the reference frequency values.

[0006] Further, the obtaining of the multiple scattering frequency value includes: Sorting all the reference frequency values in ascending order to obtain a reference frequency value sequence; Taking each reference frequency value in the reference frequency value sequence as the denominator, taking the next reference frequency value of each reference frequency value as the numerator, and taking the ratio as the reference frequency shift ratio of each reference frequency value in the reference frequency value sequence; Based on the calculation method of the frequency shift ratio of the reference frequency value sequence, obtaining the frequency shift ratio of the reference frequency value sequence, and the calculation method of the frequency shift ratio of the reference frequency value sequence is: Wherein, represents the frequency shift ratio of the reference frequency value sequence; represents the reference frequency shift ratio of the th reference frequency value in the reference frequency value sequence; represents the average value of the reference frequency shift ratios of all reference frequency values in the reference frequency value sequence; represents the standard deviation of the reference frequency shift ratios of all reference frequency values in the reference frequency value sequence; represents the number of all reference frequency values in the reference frequency value sequence; represents the hyperbolic tangent function; Initialize the reference frequency sequence to the current frequency value sequence; Based on the frequency shift ratio of the current frequency value sequence and the occurrence probability value of each reference frequency value in the reference frequency value sequence, screen out multiple reference frequency values from the reference frequency value sequence, sort them from small to large to obtain the sequence of frequency values to be analyzed, and analyze the sequence of frequency values to be analyzed based on the method for obtaining the frequency shift ratio of the reference frequency value sequence to obtain the frequency shift ratio of the sequence of frequency values to be analyzed; Perform negative correlation normalization on the difference in the frequency shift ratio between the sequence of frequency values to be analyzed and the current frequency value sequence to obtain the similarity of the frequency shift ratio between the sequence of frequency values to be analyzed and the current frequency value sequence; If the similarity of the frequency shift ratio between the sequence of frequency values to be analyzed and the current frequency value sequence is less than the preset similarity threshold, then use the sequence of frequency values to be analyzed as the new current frequency value sequence and continue to execute the iterative process; If the similarity of the frequency shift ratio between the sequence of frequency values to be analyzed and the current frequency value sequence is not less than the preset similarity threshold, then stop the iterative process and use all the reference frequency values in the sequence of frequency values to be analyzed as the multiple scattering frequency values.

[0007] Further, the obtaining of the sequence of frequency values to be analyzed includes: In the reference frequency value sequence, use the reference frequency value corresponding to the maximum value of the occurrence probability value as the frequent reference frequency value; Screen out multiple reference frequency values from the reference frequency value sequence and sort them from small to large to obtain the sequence of frequency values to be analyzed, where the ratio between the reference frequency value in the sequence of frequency values to be analyzed and the frequent reference frequency value is equal to the power of the frequency shift ratio of the current frequency value sequence, where is an integer.

[0008] Further, the obtaining of the retention degree of each sub-band signal in each time period includes: Use any one sub-band signal as the target sub-band signal and any one time period as the target time period; Take the absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the maximum value of all multiple scattering frequency values as the first difference value of the intermediate frequency signal in the target time period, and take the absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the minimum value of all multiple scattering frequency values as the second difference value of the intermediate frequency signal in the target time period; Take the minimum value of the first difference value and the second difference value as the first retention parameter for the target time period; Use the exponential function with the natural constant as the base to map the difference between the wavelet coefficients of the target sub-band signal in the target time period and the wavelet threshold of the target sub-band signal, and obtain the second retention parameter of the target sub-band signal in the target time period; Normalize the product value of the first retention parameter and the second retention parameter to obtain the retention degree of the target sub-band signal in the target time period.

[0009] Further, the obtaining of the adjusted intermediate frequency signal includes: Take the product value of the retention degree and the wavelet coefficients of each sub-band signal in each time period as the adjusted wavelet coefficients of each sub-band signal in each time period; Combine the adjusted wavelet coefficients of each sub-band signal in each time period and the wavelet function to obtain the adjusted sub-band signal of each sub-band signal; Superimpose all the adjusted sub-band signals of all sub-band signals to obtain the adjusted intermediate frequency signal.

[0010] Further, the obtaining of the Doppler shift frequency of the adjusted intermediate frequency signal includes: Perform a Fourier transform on the adjusted intermediate frequency signal to obtain a spectrogram, and determine the Doppler shift frequency of the adjusted intermediate frequency signal in the spectrogram.

[0011] Further, the obtaining of the wind speed of the current measurement environment includes: Based on the calculation formula of the wind speed of the current measurement environment, obtain the wind speed of the current measurement environment. The calculation formula of the wind speed of the current measurement environment is: Wherein, represents the wind speed of the current measurement environment; represents the emission wavelength of the lidar; represents the Doppler shift frequency of the entire intermediate frequency signal.

[0012] Further, the obtaining of the frequency value of the intermediate frequency signal in each time period includes: Perform a Fourier transform on a part of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period.

[0013] Further, the obtaining of the wavelet threshold of each sub-band signal includes: Based on the unbiased likelihood estimation SureShrink principle, calculate the SURE value of the wavelet coefficients of each sub-band signal in each time period; For each sub-band signal, the wavelet coefficient corresponding to the minimum value of the SURE value is used as the wavelet threshold of each sub-band signal.

[0014] The present invention has the following beneficial effects: The present invention takes into account that when there are a large number of microparticles in the air, the wavelet transform technology can only remove the multiple frequency shift effects at the corresponding level, and cannot completely remove the multiple frequency shift effects in the intermediate frequency signal, reducing the accuracy of wind speed measurement. Therefore, the intermediate frequency signal of the lidar in the current measurement environment is first obtained, and the multiple scattering frequency values showing the characteristics of multiple scattering are selected from the frequency values of the intermediate frequency signal in all time periods. Subsequently, based on the multiple scattering frequency values, the retention degree of the sub-band signals obtained by wavelet decomposition of the intermediate frequency signal in each time period can be accurately analyzed, so as to construct an adjusted intermediate frequency signal, remove the signal noise of the multiple Doppler frequency shift generated by multiple scattering in the original intermediate frequency signal, and only retain the frequency shift components generated by single scattering, so as to obtain a more accurate Doppler frequency shift frequency and improve the accuracy of wind speed measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a block diagram of a high-precision coherent wind-measuring lidar system provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following will, in conjunction with the drawings and preferred embodiments, detail the specific implementation manner, structure, characteristics and effects of a high-precision coherent wind-measuring lidar system proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art belonging to the technical field of the present invention.

[0019] The following will specifically describe the specific solution of a high-precision coherent wind-measuring lidar system provided by the present invention in conjunction with the drawings.

[0020] Please refer to Figure 1, which shows a block diagram of a high-precision coherent wind lidar system provided by an embodiment of the present invention. The system includes: a signal acquisition module 101, a frequency shift analysis module 102, a decomposition and reconstruction module 103, and a wind speed measurement module 104.

[0021] The signal acquisition module 101 is used to obtain the intermediate frequency signal of the lidar in the current measurement environment.

[0022] In the embodiment of the present invention, first, a coherent lidar device is placed in the current measurement environment, the coherent lidar device is started and a laser signal is emitted, and then the echo signal reflected or scattered by aerosols or particulate matters in the atmosphere is received. The coherent lidar device mixes and interferes the echo signal with the local oscillation light generated inside the device to obtain an intermediate frequency signal. It should be noted that the acquisition of the intermediate frequency signal can be automatically completed by the coherent lidar device, which is a well-known technical means to those skilled in the art and will not be elaborated here.

[0023] Among them, the laser in the coherent lidar device used in the embodiment of the present invention is an all-fiber laser, and the emission wavelength of its laser is set to 1.5 microns, and the pulse frequency is set to 20 Hz.

[0024] The frequency shift analysis module 102 is used to perform frequency domain conversion on the part of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period; screen out multiple reference frequency values from all frequency values according to the number of times each frequency value appears in all time periods; perform iterative screening on all reference frequency values to obtain multiple scattering frequency values.

[0025] When measuring the wind speed on an open ground, since there are many tiny particles carried in the wind field, and in the wind field, when the laser irradiates these particles, scattering and reflection will occur. Moreover, since these particles in the wind field have a certain velocity, this causes the laser after reflection or scattering to produce a Doppler frequency shift phenomenon. When the particle concentration in the wind field is relatively high, that is, when the content of pm2.5, pm100, etc. in the atmosphere is too large, or in a haze weather, after the laser is scattered by one particle, it will encounter other particles and be scattered by them again. After experiencing multiple scatterings in this way, it is received by the laser receiver in the lidar. Since all the particles are in the same wind field, their moving directions and speeds are similar, which makes the frequency shift situations obtained by each scattering approximate. Then, the more times the scattering occurs, the more serious the frequency shift situation will be. There is a certain proportional relationship between the frequency shifts generated by different numbers of scatterings, that is, each scattering generates one frequency shift, and the ratio of each frequency shift is determined by the wind speed. Therefore, the distribution law on the spectrum obtained by multiple scatterings can approximately determine the distribution law corresponding to each Doppler frequency shift, and further determine which signals are caused by multiple frequency shifts. Based on this, multiple Doppler frequency shifts can be eliminated by wavelet transform in the subsequent process.

[0026] Due to the unknown number of scatterings of the laser by the particles in the air, it is difficult to determine whether the detected intermediate-frequency signal is the required single frequency shift. Considering that the laser is continuously emitted and detected, among all the detected signals, there are not only the signals generated by single scattering, but also the noise signals generated by other multiple scatterings. Therefore, in the embodiment of the present invention, the partial part of the intermediate-frequency signal in each time period is first subjected to frequency domain conversion to obtain the frequency value of the intermediate-frequency signal in each time period. In order to ensure that there is only one frequency value in the signal part of the intermediate-frequency signal in each time period, the length of the time period should be set shorter. The length of the time period is usually between 0.001 and 0.01 seconds. In an embodiment of the present invention, the length of each time period is set to 0.001 seconds. At this time, there is a part of the signal in the intermediate-frequency signal in each time period.

[0027] Preferably, in an embodiment of the present invention, the partial part of the intermediate-frequency signal in each time period can be subjected to Fourier transform to obtain the frequency value of the intermediate-frequency signal in each time period. Since the time period is set shorter, there is only one frequency value of the intermediate-frequency signal in each time period. For example, the frequency value of the intermediate-frequency signal in a certain time period is 10 Hz. Among them, the explanation of the partial part of the intermediate-frequency signal in each time period: the intermediate-frequency signal is a time-domain signal, which is distributed in the time domain. The partial part of the intermediate-frequency signal in each time period means that the intermediate-frequency signal is evenly divided by multiple time periods, and there is a part of the signal of the intermediate-frequency signal in each time period.

[0028] After obtaining the frequency values of the intermediate-frequency signal in each time period, the same frequency value may appear in multiple time periods. Therefore, multiple reference frequency values can be selected from all the frequency values according to the number of times each frequency value appears in all the time periods. The reference frequency values may be the frequency components formed by the laser signal after multiple scatterings. Subsequently, the multiple scattering frequency values formed by multiple scatterings can be further iteratively selected from the reference frequency values, which is convenient for subsequent combination with wavelet transform to eliminate the signal noise of the multiple Doppler frequency shifts generated by multiple scatterings in the intermediate-frequency signal and improve the accuracy of wind speed measurement.

[0029] Preferably, in an embodiment of the present invention, the method for obtaining the reference frequency value specifically includes: Taking any one frequency value as the target frequency value, taking the number of time periods containing the target frequency value as the numerator, taking the number of all time periods as the denominator, and taking the ratio as the occurrence probability value of the target frequency value. The larger the occurrence probability value of the target frequency value relative to the overall level of the occurrence probability values of all frequency values, the more likely the target frequency value is the frequency component formed by the laser signal after multiple scatterings. Therefore, the average value of the occurrence probability values of all frequency values can be used as the screening threshold, and the frequency values with occurrence probability values greater than the screening threshold are used as the reference frequency values.

[0030] The signal generated by each frequency shift is only affected by the velocity of the particles in the wind field and the frequency of the initial laser. However, since all the particles are in the same wind field, and in non-extreme weather, the relevant characteristics such as the wind speed and direction of the wind field are stable and unchanged. Therefore, the frequency shift caused by scattering is only affected by the frequency of the initial laser. Each time the laser is scattered, a frequency shift will occur. So, in the finally detected intermediate-frequency signal, each time there is a scattering, a frequency shift frequency will be generated, and each frequency shift is generated under similar wind speeds, which makes the ratio of each frequency shift similar. At the same time, not all of the above-obtained reference frequency values are frequency components formed by the laser signal after multiple scatterings. Therefore, the embodiments of the present invention also need to perform iterative screening on all the reference frequency values to screen out the multiple-scattering frequency values, and the multiple-scattering frequency values are the frequency components formed by the laser signal after multiple scatterings.

[0031] Preferably, in an embodiment of the present invention, the method for obtaining the multiple-scattering frequency values specifically includes: First, arrange all the reference frequency values in ascending order to obtain a reference frequency value sequence. Use each reference frequency value in the reference frequency value sequence as the denominator, and use the next reference frequency value of each reference frequency value as the numerator, and use the ratio as the reference frequency shift ratio of each reference frequency value in the reference frequency value sequence.

[0032] It should be noted that there is no next reference frequency value for the last reference frequency value in the reference frequency value sequence. At this time, the average value of the reference frequency shift ratios of all the reference frequency values before the last reference frequency value can be used as the reference frequency shift ratio of the last reference frequency value.

[0033] Then, since the frequency shift is generated by the wind carrying the particles to move and interfering with the laser, the ratio between the frequencies generated after two consecutive scatterings is similar. The closer the ratio of the frequency change caused by a certain scattering is to the overall level of the ratio of the frequency changes caused by many scatterings, the higher its corresponding reference value when calculating the frequency shift ratio caused by scattering. Therefore, based on the calculation method of the frequency shift ratio of the reference frequency value sequence, the frequency shift ratio of the reference frequency value sequence can be obtained. The calculation method of the frequency shift ratio of the reference frequency value sequence is: Among them, represents the frequency shift ratio of the reference frequency value sequence; represents the reference frequency shift ratio of the th reference frequency value in the reference frequency value sequence; represents the average value of the reference frequency shift ratios of all the reference frequency values in the reference frequency value sequence; The standard deviation of the reference frequency shift ratios of all reference frequency values in the reference frequency value sequence; Indicates the number of all reference frequency values in the reference frequency value sequence; Indicates the hyperbolic tangent function, which is used for normalization processing.

[0034] Next, iterative screening is performed on the reference frequency values in the reference frequency value sequence. First, the reference frequency sequence is initialized to the current frequency value sequence.

[0035] Based on the frequency shift ratio of the current frequency value sequence and the occurrence probability values of each reference frequency value in the reference frequency value sequence, multiple reference frequency values are screened out from the reference frequency value sequence and sorted from small to large to obtain the sequence of frequency values to be analyzed. Based on the method for obtaining the frequency shift ratio of the reference frequency value sequence, the sequence of frequency values to be analyzed is analyzed to obtain the frequency shift ratio of the sequence of frequency values to be analyzed.

[0036] Preferably, in an embodiment of the present invention, the method for obtaining the sequence of frequency values to be analyzed specifically includes: In the reference frequency value sequence, the reference frequency value corresponding to the maximum value of the occurrence probability value is used as the frequent reference frequency value. Multiple reference frequency values are screened out from the reference frequency value sequence and sorted from small to large to obtain the sequence of frequency values to be analyzed, where the ratio between the reference frequency value in the sequence of frequency values to be analyzed and the frequent reference frequency value is equal to the power of the frequency shift ratio of the current frequency value sequence, where is an integer.

[0037] Then, negative correlation normalization processing is performed on the difference in the frequency shift ratios between the sequence of frequency values to be analyzed and the current frequency value sequence to obtain the similarity of the frequency shift ratios between the sequence of frequency values to be analyzed and the current frequency value sequence.

[0038] In an embodiment of the present invention, the difference in the frequency shift ratios between the two can be analyzed by calculating the absolute value or the square value of the difference in the frequency shift ratios between the sequence of frequency values to be analyzed and the current frequency value sequence, which is not limited herein.

[0039] In an embodiment of the present invention, a negative exponential function with the natural constant as the base or in the form of a function can be used to achieve negative correlation normalization processing, which is not limited herein, where represents a normalization function for normalization processing. In an embodiment of the present invention, the normalization processing can specifically be, for example, maximum-minimum normalization processing. In other embodiments of the present invention, other normalization methods can be selected according to the specific range of values, which will not be elaborated herein.

[0040] As an example, in an embodiment of the present invention, the expression of the frequency shift ratio similarity between the sequence of frequency values to be analyzed and the current sequence of frequency values can be specifically, for example: Wherein, represents the frequency shift ratio similarity between the sequence of frequency values to be analyzed and the current sequence of frequency values; represents the frequency shift ratio of the sequence of frequency values to be analyzed; represents the frequency shift ratio of the current sequence of frequency values; represents the exponential function with the natural constant as the base.

[0041] If the frequency shift ratio similarity between the sequence of frequency values to be analyzed and the current sequence of frequency values is less than the preset similarity threshold, then the sequence of frequency values to be analyzed is used as the new current sequence of frequency values, and the iterative process is continued, wherein the value range of the preset similarity threshold is , in an embodiment of the present invention, the preset similarity threshold is set to 0.95, and the preset similarity threshold can also be set by the implementer according to the specific implementation scenario, which is not limited herein.

[0042] If the frequency shift ratio similarity between the sequence of frequency values to be analyzed and the current sequence of frequency values is not less than the preset similarity threshold, then the iterative process is stopped, and all the reference frequency values in the sequence of frequency values to be analyzed are used as the multiple scattering frequency values.

[0043] An example illustration of the iterative process: If the reference frequency value sequence is , and after calculation, assuming that the frequency shift ratio of the reference frequency value sequence is 2 and the frequent reference frequency value in the reference frequency value sequence is 12, first initialize the reference frequency sequence as the current sequence of frequency values, that is, the current sequence of frequency values is , at this time, the frequency shift ratio of the current sequence of frequency values is also 2, then the sequence of frequency values to be analyzed obtained is , if at this time the sequence of frequency values to be analyzed and the current sequence of frequency values the frequency shift ratio similarity between them is less than the preset similarity threshold, then the sequence of frequency values to be analyzed is used as the new current sequence of frequency values, at this time the current sequence of frequency values is , then, continue to calculate the frequency shift ratio of the current sequence of frequency values , assuming that the calculated result is 3, then the sequence of frequency values to be analyzed obtained is , if at this time the sequence of frequency values to be analyzed and the current sequence of frequency values the frequency shift ratio similarity between them is not less than the preset similarity threshold, then the sequence of frequency values to be analyzed The reference frequency values 4, 12, and 36 in are used as the multiple scattering frequency values.

[0044] The decomposition and reconstruction module 103 is configured to perform wavelet decomposition on the intermediate frequency signal to obtain a plurality of sub-band signals, the wavelet coefficients and wavelet functions of each sub-band signal in each time period, and obtain the wavelet threshold of each sub-band signal; according to the difference between the wavelet coefficients and wavelet thresholds of each sub-band signal in each time period, and the difference between the frequency value and the multiple scattering frequency value of the intermediate frequency signal in each time period, obtain the retention degree of each sub-band signal in each time period; according to the retention degree of each sub-band signal in each time period, adjust the wavelet coefficients of each sub-band signal in each time period, and combine the wavelet functions of each sub-band signal in each time period to obtain the adjusted intermediate frequency signal.

[0045] In order to more effectively eliminate the signal noise of the multiple Doppler frequency shift generated by multiple scattering in the intermediate frequency signal, the embodiment of the present invention performs wavelet decomposition on the intermediate frequency signal to obtain a plurality of sub-band signals, the wavelet coefficients and wavelet functions of each sub-band signal in each time period, and obtain the wavelet threshold of each sub-band signal. Among them, the number of layers of wavelet decomposition is set to 3 to 6 layers. In an embodiment of the present invention, the number of layers of wavelet decomposition is set to 5 layers, and the Symlets wavelet is selected for wavelet decomposition to suppress the pseudo-Gibbs phenomenon in coherent lidar signal processing, thereby improving the accuracy of wind speed measurement. Wavelet decomposition is a well-known technical means in the art and will not be elaborated here.

[0046] After the intermediate frequency signal is wavelet decomposed, a certain sub-band signal obtained can be represented by the wavelet coefficients and wavelet functions of the sub-band signal in each time period: Among them, represents the signal function corresponding to a certain sub-band signal; represents the constant of the wavelet function; represents the wavelet coefficient of the sub-band signal in the th time period; represents the wavelet function of the sub-band signal in the th time period; represents the scale parameter, represents the translation parameter.

[0047] Preferably, in an embodiment of the present invention, the method for obtaining the wavelet threshold of each sub-band signal specifically includes: Based on the unbiased likelihood estimation SureShrink principle, calculate the SURE value of the wavelet coefficients of each sub-band signal in each time period. For each sub-band signal, take the wavelet coefficient corresponding to the minimum value of the SURE value as the wavelet threshold of each sub-band signal. Among them, the unbiased likelihood estimation SureShrink principle is a well-known technical means in the art and will not be elaborated here.

[0048] Since the above process obtains multiple scattering frequency values, in order to remove the noise signals caused by multiple scattering, it is necessary to reduce its retention degree as much as possible. On the contrary, it is necessary to retain as much as possible the frequency shift frequencies that may be generated by single scattering. Considering that the frequencies generated by single scattering are generally closest to the edge positions, therefore, first, according to the difference between the wavelet coefficients and wavelet thresholds of each sub-band signal in each time period, and the difference between the frequency values of the intermediate frequency signal in each time period and the multiple scattering frequency values, obtain the retention degree of each sub-band signal in each time period. Subsequently, based on the retention degree of each sub-band signal in each time period, an adjusted intermediate frequency signal can be constructed to eliminate the signal noise of the multiple Doppler frequency shifts generated by multiple scattering in the original intermediate frequency signal.

[0049] Preferably, in an embodiment of the present invention, the method for obtaining the retention degree of each sub-band signal in each time period specifically includes: Take any sub-band signal as the target sub-band signal and any time period as the target time period.

[0050] Take the absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the maximum value of all multiple scattering frequency values as the first difference value of the intermediate frequency signal in the target time period, and take the absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the minimum value of all multiple scattering frequency values as the second difference value of the intermediate frequency signal in the target time period.

[0051] Take the minimum value of the first difference value and the second difference value as the first retention parameter of the target time period.

[0052] Use the exponential function with the natural constant as the base to map the difference between the wavelet coefficients of the target sub-band signal in the target time period and the wavelet threshold of the target sub-band signal to obtain the second retention parameter of the target sub-band signal in the target time period.

[0053] Normalize the product value of the first retention parameter and the second retention parameter to obtain the retention degree of the target sub-band signal in the target time period.

[0054] As an example, in an embodiment of the present invention, the expression of the retention degree of the target sub-band signal in the target time period can be specifically, for example: Among them, represents the retention degree of the target sub-band signal in the target time period; represents the frequency value of the intermediate frequency signal in the target time period; represents the maximum value of all multiple scattering frequency values; represents the first difference value of the intermediate frequency signal in the target time period; represents the minimum value of all multiple scattering frequency values; represents the second difference value of the intermediate frequency signal in the target time period; represents the first retention parameter of the target time period; represents the minimum value function; represents the wavelet coefficient of the target sub-band signal in the target time period; represents the wavelet threshold of the target sub-band signal; represents the second retention parameter of the target sub-band signal in the target time period; represents the natural constant as the base exponential function; represents the hyperbolic tangent function for normalization processing.

[0055] By the same method as above, the retention degree of the target sub-band signal in each time period and the retention degree of each sub-band signal in each time period can be obtained. In order to retain as much as possible the signal that has undergone only one scattering and one frequency shift, it is necessary to retain the wavelet function and wavelet coefficient in the corresponding time period, and at the same time suppress the signal with multiple frequency shifts obtained by multiple scatterings. Therefore, according to the retention degree of each sub-band signal in each time period, the wavelet coefficient of each sub-band signal in each time period can be adjusted, and combined with the wavelet function of each sub-band signal in each time period, an adjusted intermediate frequency signal is obtained, thereby eliminating the signal noise of the multiple Doppler frequency shifts generated by multiple scatterings in the original intermediate frequency signal, and improving the accuracy of subsequent Doppler frequency shift calculation and the accuracy of wind speed measurement.

[0056] Preferably, in an embodiment of the present invention, the method for obtaining the adjusted intermediate frequency signal specifically includes: Taking the product value of the retention degree and wavelet coefficient of each sub-band signal in each time period as the adjusted wavelet coefficient of each sub-band signal in each time period.

[0057] Combining the adjusted wavelet coefficient and wavelet function of each sub-band signal in each time period, an adjusted sub-band signal of each sub-band signal is obtained. The adjusted sub-band signal of each sub-band signal can be expressed as: Among them, represents the adjusted sub-band signal of a certain sub-band signal; represents the constant of the wavelet function; Indicates the adjusted wavelet coefficients of the subband signal in the th time period; Indicates the wavelet function of the subband signal in the th time period; Indicates the scale parameter, Indicates the translation parameter.

[0058] Superimpose all the adjusted subband signals of all subband signals to obtain an adjusted intermediate-frequency signal.

[0059] As an example, in an embodiment of the present invention, the expression of the adjusted intermediate-frequency signal can be specifically, for example: Wherein, Indicates the adjusted intermediate-frequency signal; Indicates the th adjusted subband signal of the subband signal; Indicates the number of subband signals.

[0060] The wind speed measurement module 104 is used to perform frequency-domain conversion on the adjusted intermediate-frequency signal to obtain the Doppler shift frequency of the adjusted intermediate-frequency signal; based on the Doppler shift frequency, obtain the wind speed of the current measurement environment.

[0061] The signal noise of multiple Doppler shifts generated by multiple scattering is removed from the adjusted intermediate-frequency signal, and then the frequency-domain conversion can be performed on the adjusted intermediate-frequency signal to obtain the Doppler shift frequency of the adjusted intermediate-frequency signal. Subsequently, the wind speed of the current measurement environment can be accurately calculated based on the Doppler shift frequency.

[0062] Preferably, in an embodiment of the present invention, the method for obtaining the Doppler shift frequency of the adjusted intermediate-frequency signal specifically includes: Perform Fourier transform on the adjusted intermediate-frequency signal to obtain a spectrogram, and determine the Doppler shift frequency of the adjusted intermediate-frequency signal in the spectrogram. Among them, determining the Doppler shift frequency in the spectrogram is a well-known technical means for those skilled in the art and will not be elaborated here.

[0063] Subsequently, the wind speed of the current measurement environment can be obtained based on the Doppler shift frequency.

[0064] Preferably, in an embodiment of the present invention, the method for obtaining the wind speed of the current measurement environment specifically includes: Based on the calculation formula of the wind speed of the current measurement environment, obtain the wind speed of the current measurement environment. The calculation formula of the wind speed of the current measurement environment is: Wherein, Indicates the wind speed of the current measurement environment; Represents the emission wavelength of the lidar; Represents the Doppler shift frequency of the intermediate frequency signal. This formula is an existing formula and will not be elaborated here.

[0065] It should be noted that the above-mentioned order of the embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. The processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0066] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. A high-precision coherent wind-measuring lidar system, characterized in that, The system includes: A signal acquisition module, configured to obtain an intermediate-frequency signal of a lidar in a current measurement environment; A frequency shift analysis module, configured to perform frequency-domain conversion on a part of the intermediate-frequency signal in each time period to obtain the frequency value of the intermediate-frequency signal in each time period; screen out a plurality of reference frequency values from all the frequency values according to the number of times each frequency value appears in all time periods; perform iterative screening on all the reference frequency values to obtain a multiple-scattering frequency value; A decomposition and reconstruction module, configured to perform wavelet decomposition on the intermediate-frequency signal to obtain a plurality of sub-band signals, the wavelet coefficients and wavelet functions of each sub-band signal in each time period, and obtain the wavelet threshold of each sub-band signal; obtain the retention degree of each sub-band signal in each time period according to the difference between the wavelet coefficients and the wavelet threshold of each sub-band signal in each time period, and the difference between the frequency value and the multiple-scattering frequency value of the intermediate-frequency signal in each time period; adjust the wavelet coefficients of each sub-band signal in each time period according to the retention degree of each sub-band signal in each time period, and combine the wavelet functions of each sub-band signal in each time period to obtain an adjusted intermediate-frequency signal; A wind speed measurement module, configured to perform frequency-domain conversion on the adjusted intermediate-frequency signal to obtain the Doppler shift frequency of the adjusted intermediate-frequency signal; obtain the wind speed of the current measurement environment based on the Doppler shift frequency.

2. The high-precision coherent wind-measuring lidar system according to claim 1, wherein The screening out a plurality of reference frequency values from all the frequency values includes: Taking any one frequency value as a target frequency value, using the number of time periods containing the target frequency value as the numerator and the number of all time periods as the denominator, and taking the ratio as the occurrence probability value of the target frequency value; Taking the average value of the occurrence probability values of all the frequency values as the screening threshold; Taking the frequency values whose occurrence probability values are greater than the screening threshold as reference frequency values.

3. The high-precision coherent wind-measuring lidar system according to claim 2, characterized in that, The obtaining the multiple-scattering frequency value includes: Sorting all the reference frequency values in ascending order to obtain a reference frequency value sequence; Taking each reference frequency value in the reference frequency value sequence as the denominator, taking the next reference frequency value of each reference frequency value as the numerator, and taking the ratio as the reference frequency shift ratio of each reference frequency value in the reference frequency value sequence; Obtaining the frequency shift ratio of the reference frequency value sequence based on the calculation method of the frequency shift ratio of the reference frequency value sequence, and the calculation method of the frequency shift ratio of the reference frequency value sequence is: Among them, represents the frequency shift ratio of the reference frequency value sequence; represents the reference frequency shift ratio of the th reference frequency value in the reference frequency value sequence; represents the average value of the reference frequency shift ratios of all reference frequency values in the reference frequency value sequence; represents the standard deviation of the reference frequency shift ratios of all reference frequency values in the reference frequency value sequence; represents the number of all reference frequency values in the reference frequency value sequence; represents the hyperbolic tangent function; Initializing the reference frequency sequence as the current frequency value sequence; Based on the frequency shift ratio of the current frequency value sequence and the occurrence probability value of each reference frequency value in the reference frequency value sequence, screening out a plurality of reference frequency values from the reference frequency value sequence and sorting them in ascending order to obtain a sequence of frequency values to be analyzed, and analyzing the sequence of frequency values to be analyzed based on the obtaining method of the frequency shift ratio of the reference frequency value sequence to obtain the frequency shift ratio of the sequence of frequency values to be analyzed; Performing negative-correlation normalization processing on the difference between the frequency shift ratios between the sequence of frequency values to be analyzed and the current frequency value sequence to obtain the frequency shift ratio similarity between the sequence of frequency values to be analyzed and the current frequency value sequence; If the similarity of the frequency shift ratio between the sequence of frequency values to be analyzed and the current sequence of frequency values is less than a preset similarity threshold, then the sequence of frequency values to be analyzed is used as the new current sequence of frequency values, and the iterative process is continued; If the similarity of the frequency shift ratio between the sequence of frequency values to be analyzed and the current sequence of frequency values is not less than the preset similarity threshold, then the iterative process is stopped, and all the reference frequency values in the sequence of frequency values to be analyzed are used as the multiple scattering frequency values.

4. A high-precision coherent wind lidar system according to claim 3, characterized in that, The obtaining of the sequence of frequency values to be analyzed includes: In the sequence of reference frequency values, the reference frequency value corresponding to the maximum value of the occurrence probability value is used as the frequent reference frequency value; Filter out multiple reference frequency values from the sequence of reference frequency values and sort them from smallest to largest to obtain a sequence of frequency values to be analyzed. Among them, the ratio between the reference frequency values in the sequence of frequency values to be analyzed and the frequently occurring reference frequency values is equal to the power of the frequency shift ratio of the current frequency value sequence, where is an integer.

5. A high-precision coherent wind-measuring lidar system according to claim 1, characterized in that, The obtaining of the retention degree of each sub-band signal in each time period includes: Any one sub-band signal is used as the target sub-band signal, and any one time period is used as the target time period; The absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the maximum value of all the multiple scattering frequency values is used as the first difference value of the intermediate frequency signal in the target time period, and the absolute value of the difference between the frequency value of the intermediate frequency signal in the target time period and the minimum value of all the multiple scattering frequency values is used as the second difference value of the intermediate frequency signal in the target time period; The minimum value of the first difference value and the second difference value is used as the first retention parameter of the target time period; Using the exponential function with the natural constant as the base, the difference between the wavelet coefficient of the target sub-band signal in the target time period and the wavelet threshold of the target sub-band signal is mapped to obtain the second retention parameter of the target sub-band signal in the target time period; The product value of the first retention parameter and the second retention parameter is normalized to obtain the retention degree of the target sub-band signal in the target time period.

6. A high-precision coherent wind lidar system according to claim 1, characterized in that, The obtaining of the adjusted intermediate frequency signal includes: The product value of the retention degree of each sub-band signal in each time period and the wavelet coefficient is used as the adjusted wavelet coefficient of each sub-band signal in each time period; Combining the adjusted wavelet coefficients of each sub-band signal in each time period and the wavelet function, the adjusted sub-band signal of each sub-band signal is obtained; All the adjusted sub-band signals of all the sub-band signals are superimposed to obtain the adjusted intermediate frequency signal.

7. A high-precision coherent wind-measuring lidar system according to claim 1, wherein The obtaining of the Doppler shift frequency of the adjusted intermediate frequency signal includes: The adjusted intermediate frequency signal is subjected to Fourier transform to obtain a spectrogram, and the Doppler shift frequency of the adjusted intermediate frequency signal is determined in the spectrogram.

8. A high-precision coherent wind lidar system according to claim 1, characterized in that The obtaining of the wind speed of the current measurement environment includes: Based on the calculation formula of the wind speed of the current measurement environment, the wind speed of the current measurement environment is obtained, and the calculation formula of the wind speed of the current measurement environment is: Among them, represents the wind speed of the current measurement environment; represents the emission wavelength of the lidar; represents the Doppler shift frequency of the intermediate frequency signal.

9. The high-precision coherent wind-measuring lidar system according to claim 1, wherein The obtaining of the frequency value of the intermediate frequency signal in each time period includes: The partial of the intermediate frequency signal in each time period is subjected to Fourier transform to obtain the frequency value of the intermediate frequency signal in each time period.

10. A high-precision coherent wind-measuring lidar system according to claim 1, characterized in that The obtaining of the wavelet threshold of each sub-band signal includes: Based on the unbiased likelihood estimation SureShrink principle, the SURE value of the wavelet coefficient of each sub-band signal in each time period is calculated; For each sub-band signal, the wavelet coefficient corresponding to the minimum value of the SURE value is used as the wavelet threshold of each sub-band signal.

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