A method for identifying a flying object based on a coherent differential absorption lidar

Abstract

The application discloses a method for identifying flying targets based on coherent differential absorption laser radar, which comprises the following steps: alternately emitting laser pulses with different wavelengths into the atmosphere, obtaining Doppler spectrum information by coherently detecting echo signals; when the speed of the echo signal detection is different from the speed of the background aerosol, the Doppler spectrum shows a double-peak structure; according to the continuity of the speed of the background aerosol, judging the aerosol signal and other target signals in the double-peak signal; calculating the ratio of the echo signal strength of different wavelengths; according to the ratio result, distinguishing the flying target signal and the cloud signal outside the ambiguous distance. The application realizes the identification and distinction of the flying targets within the detection distance and the cloud signals outside the ambiguous distance based on the absorption depth difference of the echo signals by the specific gas, and realizes the detection of the concentration of the specific gas.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser radar, and relates to a method for identifying flying targets based on a coherent differential absorption laser radar. BACKGROUND

[0002] By analyzing the Doppler frequency shift of echo signals of moving targets (such as atmospheric aerosols, clouds, hard targets, etc.), a Doppler laser radar can realize the detection of the moving speed thereof. At present, the Doppler laser radar has been widely used in the fields of aviation safety guarantee, wind power generation, atmospheric pollution transmission monitoring, etc. According to different detection principles, the Doppler laser radar can be divided into a coherent detection Doppler laser radar and a direct detection Doppler laser radar. The coherent detection is to coherently beat the echo signal with the local laser to obtain an intermediate frequency current signal, and further to use a spectrum analysis method to inverse the Doppler frequency information. The direct detection is to use a frequency discriminator to convert the Doppler frequency shift information into the relative change of energy, so as to realize the detection of the speed of the target. Since the direct detection needs to assume a known spectrum shape, it is easily affected by atmospheric environmental factors, and the coherent Doppler laser radar can obtain accurate Doppler spectrum information, so the application of the coherent Doppler laser radar is more extensive.

[0003] For a coherent Doppler wind lidar taking aerosols as a medium, when there is a flying target (such as a bird, a drone, etc.) with a speed different from the background wind speed in the detection space, the echo signal strength of the flying target will be enhanced, and at the same time, two signal peaks will appear in the Doppler spectrum, which are respectively from the aerosols and the flying target; further extracting the two signal peaks can obtain the speed of the flying target, and according to the speed, the type of the flying target can be judged. However, due to the limitation of the maximum detection distance (blurring distance) of the laser radar, there is a possibility that the cloud signal outside the blurring distance will be mixed into the detection distance. Because the signals come from different distances, the speeds thereof are different, so the two peaks will also appear in the Doppler spectrum, which causes the problem that the flying target cannot be distinguished. SUMMARY

[0004] The purpose of the application is to overcome the deficiencies in the prior art, and to provide a method for identifying flying targets based on a coherent differential absorption laser radar, which realizes the identification of the flying targets in the detection distance and the cloud signals outside the blurring distance.

[0005] To achieve the above purpose, the application adopts the following technical scheme:

[0006] A method for identifying flying targets based on a coherent differential absorption laser radar, comprising the following steps:

[0007] Alternately emitting laser pulses with different wavelengths into the atmosphere, and obtaining Doppler spectrum information by coherently detecting echo signals;

[0008] The double-peak signal in the Doppler spectrum information is determined based on the characteristic that the Doppler spectrum shows a double-peak structure when the speed of the echo signal detected is different from the speed of the background aerosol;

[0009] The aerosol signal and the other target signal in the double-peak signal are determined according to the continuity of the background aerosol speed;

[0010] The echo signal intensity of the aerosol signal and the echo signal intensity of the other target signal are calculated according to the echo signal intensity of different wavelengths, and the echo signal intensity ratio of the aerosol signal and the echo signal intensity ratio of the other target signal are calculated;

[0011] The echo signal intensity ratio of the aerosol signal and the echo signal intensity ratio of the other target signal are compared, and it is determined that the other target signal is a flying target signal or a cloud signal outside the ambiguous distance.

[0012] Optionally, the wavelength of the emitted laser is within the gas absorption spectrum.

[0013] Optionally, the gas includes CO2, H2O, O3 and CH4.

[0014] Optionally, the number of laser pulses of different wavelengths is at least two.

[0015] Optionally, the ratio of the echo signals of different wavelengths includes the ratio of the direct Doppler spectrum or the ratio of the total intensity of each signal obtained by the double-peak separation method.

[0016] Optionally, when the echo signal intensity ratio of the other target signal is equal to the echo signal intensity ratio of the aerosol signal, the other target echo signal comes from a flying target; if not, the other target echo signal comes from a cloud outside the ambiguous distance.

[0017] Optionally, the echo signal intensity P i The expression of (R) is:

[0018]

[0019] Wherein, R is the distance between the atmospheric aerosol or other target and the coherent Doppler lidar, λ i is the wavelength of the laser, E0(λ i ) is the energy of the emitted laser pulse, c is the speed of light, A is the effective receiving area of the telescope, β(λ i , R) is the backscattering coefficient of the atmospheric aerosol at wavelength λ i , α(λ i , R) is the atmospheric extinction coefficient at wavelength λ i except the measured gas, N(r) is the concentration of the measured gas, and σ(λ i ) is the absorption cross section of the measured gas.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] The present application provides a method for identifying flying targets based on a coherent differential absorption lidar, which can simultaneously detect the gas concentration and Doppler velocity based on coherent detection; the absorption attenuation difference of the dual-wavelength echo signal of the coherent differential absorption lidar realizes the identification of the flying targets within the detection distance and the cloud signals outside the ambiguous distance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The present application provides a power spectrum diagram of the flying target signal within the ambiguous distance of the lidar.

[0023] Figure 2 The present application provides a power spectrum diagram of the cloud signal outside the ambiguous distance of the lidar. DETAILED DESCRIPTION

[0024] The present application will be further described below in conjunction with the accompanying drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0025] Example 1

[0026] The present application provides a method for identifying flying targets based on a coherent differential absorption lidar, which specifically includes the following steps:

[0027] S1, alternately emitting two laser pulses of different wavelengths into the atmosphere through the lidar, and obtaining the Doppler spectrum information through coherent detection of the echo signal; the wavelength of the emitted laser pulse is near the gas absorption spectrum line, and the gas includes but is not limited to common atmospheric gases such as CO2, H2O, O3 and CH4;

[0028] The received echo signal intensity P i The expression of R is:

[0029]

[0030] Wherein, R is the distance between the atmospheric aerosol or other targets and the coherent Doppler lidar, λ i represents the wavelength of the laser, E0(λ i ) represents the energy of the emitted laser pulse, c is the speed of light, A is the effective receiving area of the telescope, β(λ i , R) is the backscattering coefficient of atmospheric aerosol at wavelength λ i , α(λ i , R) is the atmospheric extinction coefficient at wavelength λ i except the measured gas, N(r) is the concentration of the measured gas, and σ(λi () represents the absorption cross section of the gas to be measured;

[0031] S2, When the velocity of the echo signal at a certain distance is different from the velocity of the background aerosol, the characteristic of the Doppler spectrum exhibiting a bimodal structure determines the bimodal signal in the Doppler spectrum information;

[0032] S3, based on the continuity of the background aerosol velocity, determine the aerosol signal and other target signals in the bimodal signal; such as Figure 1 The typical power spectrum example shown is that the signal with a velocity near 0 m / s is an aerosol signal, and the signal with a velocity near -5 m / s is a flight target signal.

[0033] S4. Calculate the echo signal intensity at different wavelengths based on Doppler spectral information. Then, calculate the ratio of the aerosol signal echo signal intensity to the echo signal intensity of other target signals based on the different wavelength echo signal intensities. Since wavelength λ... i The backscattering coefficient β(λ) at different wavelengths is selected near the absorption line of the gas to be measured. i The difference between R and E is very small, and the ratio of echo signal strength is 1:1. Based on the principle of differential absorption lidar, the gas concentration can be obtained.

[0034] S5, compare the echo signal intensity ratio of the aerosol signal with the echo signal intensity ratio of other target signals to determine whether the other target signals are flying target signals or cloud signals outside the ambiguous range;

[0035] For the signal of a flying target within the detection range, since the flying target and the background aerosol originate from the same location (denoted as R0), its echo signal undergoes the same absorption and attenuation as the aerosol echo. Therefore, the ratio of the two wavelengths of the flying target signal, T, is... t The ratio of the two wavelengths of the aerosol signal to T A Equal, i.e., T t (R0)=T A If (R0), then the echo signals from other targets originate from the flying target;

[0036] For cloud signals beyond the ambiguity distance, such as Figure 2 The example of a typical power spectrum is shown, since the cloud signal originates from the ambiguous distance R of the lidar. max In addition, its actual distance is R0 + M*R max M = 1, 2, ..., the echo signal undergoes absorption and attenuation differently from the aerosol echo, therefore the dual-wavelength ratio T of the cloud signal outside the ambiguity range is different. c The ratio of the two wavelengths of the aerosol signal to T a Not equal, i.e., T c (R0+M*R max )≠Ta (R0), then the other target echo signal comes from the cloud outside the ambiguous distance;

[0037] T(R) defined in the above description is the total echo intensity ratio integrated in Doppler domain, which needs to be calculated after the aerosol signal peak and the flying target or cloud signal peak outside the ambiguous distance are extracted respectively by using double peak fitting method or the like, or the echo ratio of double wavelengths can be directly calculated in Doppler domain, that is,

[0038]

[0039] wherein the superscript d represents Doppler domain, and v represents Doppler velocity, such as Figure 1 and Figure 2 As shown in the power spectrum diagrams of the flying target signal inside the ambiguous distance of the laser radar and the power spectrum diagram of the cloud signal outside the ambiguous distance of the laser radar provided by the embodiments of the present application, the present application realizes the identification of the flying target inside the detection distance and the cloud signal outside the ambiguous distance based on the absorption attenuation difference of the double-wavelength echo signals of the coherent differential absorption laser radar.

[0040] Embodiment two

[0041] The present application also provides a flying target identification system based on the coherent differential absorption laser radar and a computer readable storage medium, the flying target identification system comprising a processor and a storage medium, wherein the storage medium is used for storing instructions, and the processor is used for operating according to the instructions to perform the steps of a method for identifying a flying target based on the coherent differential absorption laser radar.

[0042] Embodiment three

[0043] The computer program stored on the computer readable storage medium is executed by the processor to realize the steps of a method for identifying a flying target based on the coherent differential absorption laser radar.

[0044] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system or a computer program product. Therefore, the present application can adopt a completely hardware embodiment, a completely software embodiment or an embodiment combining software and hardware aspects. Moreover, the present application can adopt a computer program product in the form of one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0045] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks.

[0046] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks.

[0047] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks.

[0048] The above only is the preferred embodiment of the present application, it should be pointed out that, for those skilled in the technical field, without departing from the technical principles of the present application, can also make a number of improvements and variations, these improvements and variations should also be considered as the protection scope of the present application.

Claims

1. A method for identifying flying targets based on coherent differential absorption lidar, characterized in that, Includes the following steps: Different wavelength laser pulses are alternately emitted into the atmosphere, and Doppler spectrum information is obtained by coherently detecting the echo signal; Based on the characteristic that the Doppler spectrum exhibits a bimodal structure when the velocity of the echo signal detection is different from the velocity of the background aerosol, the bimodal signal in the Doppler spectrum information is determined. Based on the continuity of the background aerosol velocity, determine the aerosol signal and other target signals in the bimodal signal; The echo signal intensity at different wavelengths is calculated based on Doppler spectral information, and the ratio of the echo signal intensity of the aerosol signal to that of other target signals is calculated based on the echo signal intensity at different wavelengths. The ratio of the echo signal intensity of the aerosol signal to the ratio of the echo signal intensity of other target signals is compared to determine whether the other target signals are flying target signals or cloud signals outside the ambiguous range. The wavelength of the laser pulse is within the gas absorption spectrum; If the ratio of the echo signal intensity of other target signals is equal to the ratio of the echo signal intensity of aerosol signals, then the echo signals of other targets come from flying targets; if they are not equal, then the echo signals of other targets come from clouds outside the ambiguity range.

2. The method for identifying flying targets based on coherent differential absorption lidar according to claim 1, characterized in that: The gases include CO2, H2O, O3, and CH4.

3. The method for identifying flying targets based on coherent differential absorption lidar according to claim 1, characterized in that: The number of laser pulses emitted at least two different wavelengths.

4. The method for identifying flying targets based on coherent differential absorption lidar according to claim 1, characterized in that: The ratio of echo signals of different wavelengths includes the ratio of direct Doppler spectra, or the ratio of the total intensity of each signal obtained by the double-peak separation method.

5. The method for identifying flying targets based on coherent differential absorption lidar according to claim 1, characterized in that, echo signal strength The expression is: in, This refers to the distance between atmospheric aerosols or other targets and the coherent Doppler lidar. Indicates the laser wavelength. Indicates the energy of the emitted laser pulse. At the speed of light, The effective receiving area of ​​the telescope, laser wavelength The atmospheric aerosol backscattering coefficient, It is the laser wavelength The atmospheric extinction coefficient excluding the gas being measured. It is the concentration of the gas to be measured. This represents the absorption cross section of the gas to be measured.

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