A high-precision coherent wind measurement lidar system

Abstract

The present invention relates to the field of laser radar speed measurement, and specifically to a high-precision coherent wind measurement laser radar system. The system first obtains the intermediate frequency signal of the current measurement environment, performs frequency domain conversion on the portion of the intermediate frequency signal in each time period, obtains the frequency value of the intermediate frequency signal in each time period, and screens out the multiple scattering frequency value, performs wavelet decomposition on the intermediate frequency signal, and obtains the wavelet threshold of each sub-band signal; based on 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, the wavelet coefficient of the sub-band signal in each time period is adjusted, and combined with the wavelet function of the sub-band signal in each time period, an adjusted intermediate frequency signal is obtained, and based on the Doppler shift frequency of the adjusted intermediate frequency signal, the wind speed of the current measurement environment is calculated. The present invention can remove the multiple frequency shift effect in the intermediate frequency signal and improve the accuracy of wind speed measurement.

Description

Technical Field

[0001] The present invention relates to the field of laser radar speed measurement, and in particular to a high-precision coherent wind measurement laser radar 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 conduct real-time and high-precision measurements of wind fields. LiDAR is a method of detecting and measuring the relevant properties of target objects by emitting laser beams and then measuring the changes in the reflection and scattering of lasers after passing through the target objects. It has the advantages of high precision and high spatial resolution, especially coherent LiDAR, which is a LiDAR system based on coherent detection technology. It uses the Doppler effect and the coherence characteristics of lasers to measure wind speed by measuring the backscattered signal generated by the interaction between lasers and atmospheric aerosol particles.

[0003] In related technologies, wind speed measurement is usually achieved by detecting an intermediate frequency signal formed by mixing the laser signal after atmospheric scattering with the original laser signal, and using wavelet transform technology to decompose and reconstruct the intermediate frequency signal and perform Doppler frequency shift analysis on the signal. However, when there is severe weather such as heavy fog or haze in the measurement environment, the air contains a large number of tiny particles. These particles 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. The wavelet transform technology can only remove the multiple frequency shift effects at the corresponding level, but cannot remove the multiple frequency shift effects in the intermediate frequency signal, thereby reducing the accuracy of wind speed measurement. Summary of the Invention

[0004] In order to solve the technical problem that when there are a large number of tiny particles in the air, the wavelet transform technology can only remove the multiple frequency shift effects at the corresponding level, but cannot completely remove the multiple frequency shift effects in the intermediate frequency signal, thereby reducing the accuracy of wind speed measurement, the purpose of the present invention is to provide a high-precision coherent wind measurement lidar system. The technical solution adopted is as follows:

[0005] The present invention proposes a high-precision coherent wind measurement lidar system, which includes:

[0006] Signal acquisition module, used to obtain the intermediate frequency signal of the lidar in the current measurement environment;

[0007] The frequency shift analysis module is used to perform frequency domain conversion on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period; filter out multiple reference frequency values from all frequency values based on the number of times each frequency value appears in all time periods; and iteratively filter all the reference frequency values to obtain multiple scattering frequency values;

[0008] a decomposition and reconstruction module, configured to perform wavelet decomposition on the intermediate frequency signal to obtain a plurality of sub-band signals and a wavelet coefficient and a wavelet function of each sub-band signal in each time period, and obtain a wavelet threshold of each sub-band signal; obtain a retention degree of each sub-band signal in each time period based on a difference between the wavelet coefficient and the wavelet threshold of each sub-band signal in each time period, and a difference between the frequency value and the multiple scattering frequency value of the intermediate frequency signal in each time period; adjust the wavelet coefficient of each sub-band signal in each time period based on the retention degree of each sub-band signal in each time period, and obtain an adjusted intermediate frequency signal in combination with the wavelet function of each sub-band signal in each time period;

[0009] 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; and obtain the wind speed of the current measurement environment based on the Doppler shift frequency.

[0010] Furthermore, the step of selecting a plurality of reference frequency values from all frequency values includes:

[0011] Take any frequency value as the target frequency value, the number of time periods containing the target frequency value as the numerator, the number of all time periods as the denominator, and the ratio as the probability value of the target frequency value;

[0012] The average of the occurrence probability values of all frequency values is used as the screening threshold;

[0013] The frequency value whose occurrence probability value is greater than the screening threshold is used as the reference frequency value.

[0014] Furthermore, obtaining the multiple scattering frequency value includes:

[0015] Arranging all the reference frequency values in ascending order to obtain a reference frequency value sequence;

[0016] 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;

[0017] 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 is obtained. The calculation method of the frequency shift ratio of the reference frequency value sequence is:

[0018]

[0019] in, represents the frequency shift ratio of the reference frequency value sequence; Indicates the first The reference frequency shift ratio of the reference frequency value; represents an 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 ratio 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;

[0020] Initialize the reference frequency sequence to the current frequency value sequence;

[0021] 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, a plurality of reference frequency values are screened from the reference frequency value sequence and sorted in ascending order to obtain a frequency value sequence to be analyzed; and based on the method for obtaining the frequency shift ratio of the reference frequency value sequence, the frequency value sequence to be analyzed is analyzed to obtain the frequency shift ratio of the frequency value sequence to be analyzed;

[0022] Performing negative correlation normalization processing on the difference in the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence to obtain a similarity in the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence;

[0023] If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is less than a preset similarity threshold, the frequency value sequence to be analyzed is used as a new current frequency value sequence, and the iterative process is continued;

[0024] If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is not less than a preset similarity threshold, the iteration process is stopped, and all the reference frequency values in the frequency value sequence to be analyzed are used as multiple scattering frequency values.

[0025] Furthermore, obtaining the frequency value sequence to be analyzed includes:

[0026] 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;

[0027] A plurality of reference frequency values are screened out from the reference frequency value sequence and sorted in ascending order to obtain a frequency value sequence to be analyzed, wherein the ratio between the reference frequency value in the frequency value sequence to be analyzed and the frequent reference frequency value is equal to the frequency shift ratio of the current frequency value sequence. Power, where is an integer.

[0028] Furthermore, obtaining the retention degree of each subband signal in each time period includes:

[0029] Taking any sub-band signal as the target sub-band signal and any time period as the target time period;

[0030] 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 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 multiple scattering frequency values is used as the second difference value of the intermediate frequency signal in the target time period;

[0031] using the minimum value of the first difference value and the second difference value as the first retention parameter of the target time period;

[0032] Using an exponential function with a natural constant as a base, mapping the difference between the wavelet coefficient of the target subband signal in the target time period and the wavelet threshold of the target subband signal, to obtain a second retained parameter of the target subband signal in the target time period;

[0033] Normalizing the product of the first retention parameter and the second retention parameter to obtain a retention degree of the target subband signal in the target time period.

[0034] Furthermore, obtaining the adjusted intermediate frequency signal includes:

[0035] Taking the product value of the retention degree and the 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;

[0036] Combining the adjusted wavelet coefficients of each subband signal in each time period and the wavelet function to obtain an adjusted subband signal of each subband signal;

[0037] All adjusted sub-band signals of all sub-band signals are superimposed to obtain an adjusted intermediate frequency signal.

[0038] Furthermore, obtaining and adjusting the Doppler shift frequency of the intermediate frequency signal includes:

[0039] Performing Fourier transform on the adjusted intermediate frequency signal to obtain a frequency spectrum, and determining the Doppler shift frequency of the adjusted intermediate frequency signal in the frequency spectrum.

[0040] Furthermore, obtaining the wind speed of the current measurement environment includes:

[0041] The wind speed of the current measurement environment is obtained based on the calculation formula of the wind speed of the current measurement environment. The calculation formula of the wind speed of the current measurement environment is:

[0042]

[0043] in, Indicates the wind speed of the current measurement environment; Indicates the emission wavelength of the lidar; Indicates the Doppler shift frequency of the entire IF signal.

[0044] Furthermore, obtaining the frequency value of the intermediate frequency signal in each time period includes:

[0045] Perform Fourier transform on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period.

[0046] Furthermore, obtaining the wavelet threshold of each sub-band signal includes:

[0047] Based on the unbiased likelihood estimation SureShrink principle, the SURE value of the wavelet coefficient of each subband signal in each time period is calculated;

[0048] For each sub-band signal, the wavelet coefficient corresponding to the minimum SURE value is used as the wavelet threshold of each sub-band signal.

[0049] The present invention has the following beneficial effects:

[0050] The present invention takes into account 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, thereby reducing the accuracy of wind speed measurement. Therefore, the intermediate frequency signal of the laser radar in the current measurement environment is first obtained, and the multiple scattering frequency values that show multiple scattering characteristics are screened out 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 signal of the intermediate frequency signal after wavelet decomposition in each time period can be accurately analyzed, thereby constructing an adjusted intermediate frequency signal, removing the signal noise of the multiple Doppler frequency shifts caused by multiple scattering in the original intermediate frequency signal, and retaining only the frequency shift components generated by one scattering, thereby obtaining a more accurate Doppler frequency shift frequency, thereby improving the accuracy of wind speed measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0052] Figure 1 A block diagram of a high-precision coherent wind measurement lidar system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0053] To further illustrate the technical means and effectiveness of the present invention in achieving its intended objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation, structure, features, and effectiveness of a high-precision coherent wind measurement lidar system proposed in accordance with the present invention. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0054] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0055] The specific solution of a high-precision coherent wind measurement lidar system provided by the present invention is described in detail below with reference to the accompanying drawings.

[0056] See also Figure 1 , which shows a block diagram of a high-precision coherent wind measurement 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.

[0057] The signal acquisition module 101 is used to obtain the intermediate frequency signal of the laser radar in the current measurement environment.

[0058] The embodiment of the present invention first places a coherent lidar device in the current measurement environment, starts the coherent lidar device and emits a laser signal, and then receives the echo signal reflected or scattered back by aerosols or particulate matter in the atmosphere. 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 technical means well known to those skilled in the art and will not be elaborated here.

[0059] Among them, the laser in the coherent laser radar device used in the embodiment of the present invention is an all-fiber laser, the emission wavelength of the laser is set to 1.5 microns, and the pulse frequency is set to 20 Hz.

[0060] The frequency shift analysis module 102 is used to perform frequency domain conversion on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period; filter out multiple reference frequency values from all frequency values based on the number of times each frequency value appears in all time periods; and iteratively filter all reference frequency values to obtain multiple scattering frequency values.

[0061] When measuring wind speed in an open space, there are many tiny particles in the wind field, and the laser will be scattered and reflected when it hits these particles. Moreover, since the particles in the wind field have a certain speed, the reflected or scattered laser will produce Doppler shift. When the concentration of particles in the wind field is high, that is, the content of PM2.5, PM100, etc. in the atmosphere is too high, or when there is haze, after the laser is scattered by a particle, it will encounter other particles and be scattered again. After multiple scattering cycles, it will be received by the laser receiver in the radar. Since all particles are in the same In a wind field, the moving direction and speed are similar, which makes the frequency shift obtained by each scattering similar. The more times it is scattered, the more serious the frequency shift will be. There is a certain proportional relationship between the frequency shifts generated by different numbers of scattering, that is, each scattering will produce a frequency shift, and the proportion of each frequency shift is determined by the wind speed. Therefore, the distribution law of the spectrum obtained by multiple scattering can approximately determine the distribution law corresponding to each Doppler frequency shift, and then determine which signals are caused by multiple frequency shifts. Based on this, the multiple Doppler frequency shifts can be eliminated through wavelet transform in the subsequent process.

[0062] Because particles in the air scatter the laser an unknown number of times, 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, all detected signals include not only signals generated by single scattering, but also noise signals generated by other multiple scattering. Therefore, an embodiment of the present invention first performs frequency domain conversion on a portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period. In order to ensure that the signal portion of the intermediate frequency signal in each time period has only one frequency value, 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 one embodiment of the present invention, the length of each time period is set to 0.001 seconds. At this time, the intermediate frequency signal has a portion of the signal in each time period.

[0063] Preferably, in one embodiment of the present invention, Fourier transform can be performed on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period. Since the time period is set to be short, the intermediate frequency signal has only one frequency value in each time period. For example, the frequency value of the intermediate frequency signal in a certain time period is 10 Hz, wherein the portion of the intermediate frequency signal in each time period is explained as follows: the intermediate frequency signal is a time domain signal, which is distributed in the time domain. The portion of the intermediate frequency signal in each time period refers to the intermediate frequency signal being evenly divided into multiple time periods, and there is a portion of the intermediate frequency signal in each time period.

[0064] After obtaining the frequency value 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 screened out from all frequency values according to the number of times each frequency value appears in all time periods. The reference frequency value may be the frequency component formed by multiple scattering of the laser signal. Subsequently, the multiple scattering frequency values formed by multiple scattering can be further iteratively screened out from the reference frequency value, which is convenient for subsequent combination with wavelet transform to eliminate the signal noise of multiple Doppler frequency shifts generated by multiple scattering in the intermediate frequency signal, thereby improving the accuracy of wind speed measurement.

[0065] Preferably, in one embodiment of the present invention, the method for obtaining the reference frequency value specifically includes:

[0066] Take any frequency value as the target frequency value, take the number of time periods containing the target frequency value as the numerator, take the number of all time periods as the denominator, and take the ratio as the probability of occurrence of the target frequency value. The greater the overall level of the probability of occurrence of the target frequency value relative to the probability of occurrence of all frequency values, the more likely the target frequency value is to be a frequency component formed by multiple scatterings of the laser signal. Therefore, the average value of the probability of occurrence of all frequency values can be used as the screening threshold, and the frequency value with a probability of occurrence greater than the screening threshold can be used as the reference frequency value.

[0067] The signal generated by each frequency shift is only affected by the speed 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 wind speed, wind direction and other related characteristics of the wind field are stable and unchanged, so the frequency shift caused by scattering is only affected by the frequency of the initial laser. Every time the laser is scattered, it will produce a frequency shift, so in the final detected intermediate frequency signal, each time it is scattered, a frequency shift frequency will be generated, and each frequency shift is generated at a similar wind speed, which makes the ratio of each frequency shift similar. At the same time, the reference frequency values obtained above are not all frequency components formed by multiple scatterings of the laser signal. Therefore, the embodiment of the present invention also needs to iteratively screen all reference frequency values to screen out multiple scattering frequency values, which are frequency components formed by multiple scatterings of the laser signal.

[0068] Preferably, in one embodiment of the present invention, the method for obtaining the multiple scattering frequency value specifically includes:

[0069] First, all reference frequency values are arranged in ascending order to obtain a reference frequency value sequence, each reference frequency value in the reference frequency value sequence is used as the denominator, the next reference frequency value of each reference frequency value is used as the numerator, and the ratio is used as the reference frequency shift ratio of each reference frequency value in the reference frequency value sequence.

[0070] It should be noted that if there is no next reference frequency value for the last reference frequency value in the reference frequency value sequence, the average of the reference frequency shift ratios of all reference frequency values before the last reference frequency value can be used as the reference frequency shift ratio of the last reference frequency value.

[0071] Then, since the frequency shift is caused by the wind carrying particles and interfering with the laser, the ratio of 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 change caused by many scatterings, the higher the corresponding reference 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:

[0072]

[0073] in, represents the frequency shift ratio of the reference frequency value sequence; Indicates the first The reference frequency shift ratio of the reference frequency value; represents an 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 ratio 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, which is used for normalization.

[0074] Next, the reference frequency values in the reference frequency value sequence are iteratively screened. First, the reference frequency sequence is initialized and set to the current frequency value sequence.

[0075] 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, multiple reference frequency values are screened out from the reference frequency value sequence and sorted from small to large to obtain the frequency value sequence to be analyzed. Based on the method for obtaining the frequency shift ratio of the reference frequency value sequence, the frequency value sequence to be analyzed is analyzed to obtain the frequency shift ratio of the frequency value sequence to be analyzed.

[0076] Preferably, in one embodiment of the present invention, the method for obtaining the frequency value sequence to be analyzed specifically includes:

[0077] In the reference frequency value sequence, the reference frequency value corresponding to the maximum value of the 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 frequency value sequence to be analyzed, wherein the ratio between the reference frequency value in the frequency value sequence to be analyzed and the frequent reference frequency value is equal to the frequency shift ratio of the current frequency value sequence. Power, where is an integer.

[0078] Then, a negative correlation normalization process is performed on the difference in frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence to obtain the similarity of the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence.

[0079] In an embodiment of the present invention, the difference in frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence can be analyzed by calculating the absolute value of the difference in frequency shift ratio or the square of the difference, which is not limited here.

[0080] In the embodiment of the present invention, a negative exponential function with a natural constant as the base or The function form of , which realizes the normalization of negative correlation, is not limited here, where, Represents a normalization function for normalization processing. In one embodiment of the present invention, the normalization processing can be specifically, for example, maximum and minimum value normalization processing. In other embodiments of the present invention, other normalization methods can be selected according to the specific range of numerical values, which will not be described in detail.

[0081] As an example, in one embodiment of the present invention, the expression for the similarity of the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence can be specifically, for example, as follows:

[0082]

[0083] in, Indicates the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence; Represents the frequency shift ratio of the frequency value sequence to be analyzed; Indicates the frequency shift ratio of the current frequency value sequence; Expressed as a natural constant An exponential function with base .

[0084] If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is less than the preset similarity threshold, the frequency value sequence to be analyzed is used as the new current frequency value sequence and the iterative process is continued. The preset similarity threshold has a value range of In one embodiment of the present invention, the preset similarity threshold is set to 0.95. The preset similarity threshold can also be set by the implementer according to the specific implementation scenario and is not limited here.

[0085] If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is not less than a preset similarity threshold, the iteration process is stopped, and all reference frequency values in the frequency value sequence to be analyzed are used as multiple scattering frequency values.

[0086] An example 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 to the current frequency value sequence, that is, the current frequency value sequence is , at this time the frequency shift ratio of the current frequency value sequence is also 2, then the frequency value sequence to be analyzed is , if the frequency value sequence to be analyzed is and the current frequency value sequence If the similarity of the frequency shift ratio between the two is less than the preset similarity threshold, the frequency value sequence to be analyzed is As the new current frequency value sequence, the current frequency value sequence is , then, continue to calculate the current frequency value sequence The frequency shift ratio, assuming the calculated result is 3, the obtained frequency value sequence to be analyzed is , if the frequency value sequence to be analyzed is and the current frequency value sequence If the frequency shift ratio similarity between them is not less than the preset similarity threshold, the frequency value sequence to be analyzed is The reference frequency values 4, 12 and 36 in are used as the multiple scattering frequency values.

[0087] The decomposition and reconstruction module 103 is used to perform wavelet decomposition on the intermediate frequency signal to obtain multiple sub-band signals and 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 based on 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 based on the retention degree of each sub-band signal in each time period, and obtain the adjusted intermediate frequency signal in combination with the wavelet function of each sub-band signal in each time period.

[0088] In order to more effectively eliminate the signal noise of multiple Doppler frequency shifts caused by multiple scattering in the intermediate frequency signal, an embodiment of the present invention performs wavelet decomposition on the intermediate frequency signal to obtain multiple sub-band signals and wavelet coefficients and wavelet functions of each sub-band signal in each time period, and obtains the wavelet threshold of each sub-band signal, wherein the number of layers of wavelet decomposition is set to 3 to 6 layers. In one embodiment of the present invention, the number of layers of wavelet decomposition is set to 5 layers, and 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 technical means well known to those skilled in the art and will not be described in detail here.

[0089] After the intermediate frequency signal is decomposed by wavelet, a sub-band signal obtained can be represented by the wavelet coefficient and wavelet function of the sub-band signal in each time period:

[0090]

[0091] in, Represents the signal function corresponding to a certain sub-band signal; represents the constant of the wavelet function; Indicates that the subband signal is in Wavelet coefficients for each time period; Indicates that the subband signal is in Wavelet function of a time period; represents the scale parameter, Represents the translation parameter.

[0092] Preferably, in one embodiment of the present invention, the method for obtaining the wavelet threshold of each sub-band signal specifically includes:

[0093] Based on the unbiased likelihood estimation SureShrink principle, the SURE value of the wavelet coefficient of each subband signal in each time period is calculated. For each subband signal, the wavelet coefficient corresponding to the minimum SURE value is used as the wavelet threshold of each subband signal. The unbiased likelihood estimation SureShrink principle is a technical means well known to those skilled in the art and will not be elaborated here.

[0094] Since the above process obtains the multiple scattering frequency value, in order to remove the noise signals caused by multiple scattering, it is necessary to reduce its retention as much as possible. Conversely, the frequency shift frequency that may be caused by single scattering should be retained as much as possible. Considering that the frequency generated by single scattering is generally closest to the edge position, the retention degree of each sub-band signal in each time period can be obtained first according to the difference between the wavelet coefficient and the wavelet threshold of each sub-band signal in each time period, as well as the difference between the frequency value of the intermediate frequency signal in each time period and the multiple scattering frequency value. 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 multiple Doppler frequency shifts caused by multiple scattering in the original intermediate frequency signal.

[0095] Preferably, in one embodiment of the present invention, the method for obtaining the retention degree of each sub-band signal in each time period specifically includes:

[0096] Any sub-band signal is used as a target sub-band signal, and any time period is used as a target time period.

[0097] 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 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 multiple scattering frequency values is used as the second difference value of the intermediate frequency signal in the target time period.

[0098] 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.

[0099] An exponential function with a natural constant as the base is used to map the difference between the wavelet coefficient of the target subband signal in the target time period and the wavelet threshold of the target subband signal to obtain a second retention parameter of the target subband signal in the target time period.

[0100] Normalization is performed on the product value of the first retention parameter and the second retention parameter to obtain the retention degree of the target subband signal in the target time period.

[0101] As an example, in one embodiment of the present invention, the expression for the retention degree of the target subband signal in the target time period may be specifically, for example, as follows:

[0102]

[0103] in, Indicates the degree of retention of the target subband signal in the target time period; Indicates the frequency value of the intermediate frequency signal in the target time period; Represents the maximum value of all multiple scattering frequency values; Indicates the first difference value of the intermediate frequency signal in the target time period; Represents the minimum value of all multiple scattering frequency values; Indicates the second difference value of the intermediate frequency signal in the target time period; a first retention parameter representing a target time period; represents the minimum value function; Represents the wavelet coefficient of the target subband signal in the target time period; The wavelet threshold representing the target subband signal; A second reserved parameter representing the target subband signal in the target time period; Expressed as a natural constant An exponential function with base ; Represents the hyperbolic tangent function, which is used for normalization.

[0104] The same method as above can be used to obtain the retention degree of the target subband signal in each time period, as well as the retention degree of each subband signal in each time period. In order to retain the signal that has only undergone one frequency shift after one scattering as much as possible, it is necessary to retain the wavelet function and wavelet coefficients of the corresponding time period, and at the same time suppress the multiple frequency shift signals obtained by multiple scattering. Therefore, according to the retention degree of each subband signal in each time period, the wavelet coefficients of each subband signal in each time period can be adjusted, and combined with the wavelet function of each subband signal in each time period, the adjusted intermediate frequency signal can be obtained, thereby eliminating the signal noise of multiple Doppler frequency shifts caused by multiple scattering in the original intermediate frequency signal, thereby improving the accuracy of subsequent Doppler frequency shift frequency calculation and the accuracy of wind speed measurement.

[0105] Preferably, in one embodiment of the present invention, the method for adjusting the acquisition of the intermediate frequency signal specifically includes:

[0106] 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.

[0107] Combining the adjusted wavelet coefficients and wavelet functions of each sub-band signal in each time period, the 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:

[0108]

[0109] in, An adjusted sub-band signal representing a sub-band signal; represents the constant of the wavelet function; Indicates that the subband signal is in Adjusted wavelet coefficients for each time period; Indicates that the subband signal is in Wavelet function of a time period; represents the scale parameter, Represents the translation parameter.

[0110] All adjusted sub-band signals of all sub-band signals are superimposed to obtain an adjusted intermediate frequency signal.

[0111] As an example, in one embodiment of the present invention, the expression for adjusting the intermediate frequency signal may be specifically, for example, as follows:

[0112]

[0113] in, Indicates adjustment of the intermediate frequency signal; Indicates the An adjustment sub-band signal of a sub-band signal; Indicates the number of sub-band signals.

[0114] The wind speed measurement module 104 is configured to perform frequency domain conversion on the adjusted intermediate frequency signal to obtain the Doppler shift frequency of the adjusted intermediate frequency signal; and obtain the wind speed of the current measurement environment based on the Doppler shift frequency.

[0115] The signal noise of multiple Doppler frequency shifts generated by multiple scattering is removed from the adjusted intermediate frequency signal, and the adjusted intermediate frequency signal can be converted into the frequency domain to obtain the Doppler frequency 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 frequency shift frequency.

[0116] Preferably, in one embodiment of the present invention, the method for adjusting the acquisition of the Doppler shift frequency of the intermediate frequency signal specifically includes:

[0117] Perform Fourier transform on the adjusted intermediate frequency signal to obtain a spectrum diagram, and determine the Doppler shift frequency of the adjusted intermediate frequency signal in the spectrum diagram. Determining the Doppler shift frequency in the spectrum diagram is a technical means well known to those skilled in the art and will not be described in detail here.

[0118] Then, the wind speed of the current measurement environment can be obtained based on the Doppler shift frequency.

[0119] Preferably, in one embodiment of the present invention, the method for obtaining the wind speed of the current measurement environment specifically includes:

[0120] Based on the calculation formula of the wind speed of the current measurement environment, the wind speed of the current measurement environment is obtained. The calculation formula of the wind speed of the current measurement environment is:

[0121]

[0122] in, Indicates the wind speed of the current measurement environment; Indicates the emission wavelength of the lidar; It represents the Doppler shift frequency of the whole intermediate frequency signal. This formula is an existing formula and will not be described here.

[0123] It should be noted that the order in which the embodiments of the present invention are described above is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0124] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. A high-precision coherent wind measurement lidar system, characterized in that: The system comprises: Signal acquisition module, used to obtain the intermediate frequency signal of the lidar in the current measurement environment; The frequency shift analysis module is used to perform frequency domain conversion on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period; filter out multiple reference frequency values from all frequency values based on the number of times each frequency value appears in all time periods; and iteratively filter all the reference frequency values to obtain multiple scattering frequency values; a decomposition and reconstruction module, configured to perform wavelet decomposition on the intermediate frequency signal to obtain a plurality of sub-band signals and a wavelet coefficient and a wavelet function of each sub-band signal in each time period, and obtain a wavelet threshold of each sub-band signal; obtain a retention degree of each sub-band signal in each time period based on a difference between the wavelet coefficient and the wavelet threshold of each sub-band signal in each time period, and a difference between the frequency value and the multiple scattering frequency value of the intermediate frequency signal in each time period; adjust the wavelet coefficient of each sub-band signal in each time period based on the retention degree of each sub-band signal in each time period, and obtain an adjusted intermediate frequency signal in combination with the wavelet function of each sub-band signal in each time period; 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; and obtain the wind speed of the current measurement environment based on the Doppler shift frequency.

2. A high-precision coherent wind measurement lidar system according to claim 1, characterized in that: The step of selecting a plurality of reference frequency values from all frequency values includes: Take any frequency value as the target frequency value, the number of time periods containing the target frequency value as the numerator, the number of all time periods as the denominator, and the ratio as the probability value of the target frequency value; The average of the occurrence probability values of all frequency values is used as the screening threshold; The frequency value whose occurrence probability value is greater than the screening threshold is used as the reference frequency value.

3. A high-precision coherent wind measurement lidar system according to claim 2, characterized in that: The obtaining of the multiple scattering frequency value comprises: Arranging 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, the frequency shift ratio of the reference frequency value sequence is obtained. The calculation method of the frequency shift ratio of the reference frequency value sequence is: in, represents the frequency shift ratio of the reference frequency value sequence; Indicates the first The reference frequency shift ratio of the reference frequency value; represents an 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, a plurality of reference frequency values are screened from the reference frequency value sequence and sorted in ascending order to obtain a frequency value sequence to be analyzed; and based on the method for obtaining the frequency shift ratio of the reference frequency value sequence, the frequency value sequence to be analyzed is analyzed to obtain the frequency shift ratio of the frequency value sequence to be analyzed; Performing negative correlation normalization processing on the difference in the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence to obtain a similarity in the frequency shift ratio between the frequency value sequence to be analyzed and the current frequency value sequence; If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is less than a preset similarity threshold, the frequency value sequence to be analyzed is used as a new current frequency value sequence, and the iterative process is continued; If the frequency shift ratio similarity between the frequency value sequence to be analyzed and the current frequency value sequence is not less than a preset similarity threshold, the iteration process is stopped, and all the reference frequency values in the frequency value sequence to be analyzed are used as multiple scattering frequency values.

4. A high-precision coherent wind measurement lidar system according to claim 3, characterized in that: The obtaining of the frequency value sequence to be analyzed comprises: 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; A plurality of reference frequency values are screened out from the reference frequency value sequence and sorted in ascending order to obtain a frequency value sequence to be analyzed, wherein the ratio between the reference frequency value in the frequency value sequence to be analyzed and the frequent reference frequency value is equal to the frequency shift ratio of the current frequency value sequence. Power, where is an integer.

5. The high-precision coherent wind measurement lidar system according to claim 1, characterized in that: Obtaining the retention degree of each sub-band signal in each time period includes: Taking any sub-band signal as the target sub-band signal and any time period 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 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 multiple scattering frequency values is used as the second difference value of the intermediate frequency signal in the target time period; using the minimum value of the first difference value and the second difference value as the first retention parameter of the target time period; Using an exponential function with a natural constant as a base, mapping the difference between the wavelet coefficient of the target subband signal in the target time period and the wavelet threshold of the target subband signal, to obtain a second retained parameter of the target subband signal in the target time period; Normalizing the product of the first retention parameter and the second retention parameter to obtain a retention degree of the target subband signal in the target time period.

6. The high-precision coherent wind measurement lidar system according to claim 1, characterized in that: The obtaining and adjusting the intermediate frequency signal comprises: Taking the product value of the retention degree and the 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; Combining the adjusted wavelet coefficients of each subband signal in each time period and the wavelet function to obtain an adjusted subband signal of each subband signal; All adjusted sub-band signals of all sub-band signals are superimposed to obtain an adjusted intermediate frequency signal.

7. The high-precision coherent wind measurement lidar system according to claim 1, characterized in that: The obtaining and adjusting the Doppler shift frequency of the intermediate frequency signal comprises: Performing Fourier transform on the adjusted intermediate frequency signal to obtain a frequency spectrum, and determining the Doppler shift frequency of the adjusted intermediate frequency signal in the frequency spectrum.

8. The high-precision coherent wind measurement lidar system according to claim 1, characterized in that: Obtaining the wind speed of the current measurement environment includes: The wind speed of the current measurement environment is obtained based on the calculation formula of the wind speed of the current measurement environment. The calculation formula of the wind speed of the current measurement environment is: in, Indicates the wind speed of the current measurement environment; Indicates the emission wavelength of the lidar; Indicates the Doppler shift frequency of the entire IF signal.

9. The high-precision coherent wind measurement lidar system according to claim 1, characterized in that: Obtaining the frequency value of the intermediate frequency signal in each time period includes: Perform Fourier transform on the portion of the intermediate frequency signal in each time period to obtain the frequency value of the intermediate frequency signal in each time period.

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

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