Doppler laser velocimeter radar device and method

Abstract

This invention provides a device and method for a Doppler laser velocimetry radar. By simultaneously generating a pulse signal and a corresponding modulated local oscillator signal using an acousto-optic modulator, and adjusting the delay of the local oscillator signal, the rising edge of the reflected light pulse is aligned with the falling edge of the local oscillator signal. This allows for heterodyne interference to obtain a smaller amplitude intermediate frequency (IF) signal from the reflected light, avoiding the subsequent attenuation signal of tens of nanoseconds caused by the larger amplitude of the reflected IF signal. This eliminates the impact of increased noise in the low-frequency region of the spectrum caused by the attenuated signal on frequency estimation, improving the accuracy and reliability of velocity measurement. Furthermore, by extracting the initial phase of the smaller amplitude reflected IF signal, it is used for phase alignment of the atmospheric echo IF signal, achieving coherent accumulation of the atmospheric echo IF signal and improving the system's signal-to-noise ratio.

Description

Technical Field

[0001] This invention belongs to the field of lidar technology, specifically relating to a Doppler laser velocimetry radar device and method. Background Technology

[0002] When Doppler pulsed laser velocimetry radar is used for short-range speed measurement, such as measuring atmospheric data like aircraft vacuum speed and acquiring wind speed and direction near wind power generation devices, the short operating distance causes the intermediate frequency (IF) signal corresponding to the echo light signal generated by aerosol particles to be time-contiguous and even partially overlapped with the IF signal generated by the end-face reflection signal from the radar optical antenna. Furthermore, since the amplitude of the end-face reflected IF signal can reach several volts, far exceeding the millivolt level of the echo signal, it can cause the detector to enter a saturation state, exceeding the voltage range of the AD acquisition. In the digital signal acquired by the acquisition circuit, a high-amplitude end-face reflected IF signal is often followed by a low-amplitude echo IF signal. Due to the capacitance characteristics of the detection and acquisition circuit, a decaying signal with decreasing amplitude, lasting for tens of nanoseconds, is generated immediately after the end-face reflected IF signal. Figure 1 As shown. This attenuated signal manifests as low-frequency noise in the spectrum, covering a frequency range from one hertz to tens of megahertz. This significantly increases the amplitude of spectral noise, potentially even drowning out the actual Doppler signal and severely impacting the frequency estimation of the Doppler velocity signal. Figure 2 As shown.

[0003] Furthermore, if the generated end-face reflected intermediate frequency optical signal does not cause the detector to operate in the saturation region and the end-face reflected intermediate frequency electrical signal does not exceed the voltage range of the AD acquisition, then the phase alignment of the echo intermediate frequency signal can be achieved by extracting the frequency and phase information of the end-face reflected intermediate frequency signal, similar to the fully coherent radar of radio, thus realizing the time-domain coherent accumulation of the atmospheric echo pulse intermediate frequency signal of the lidar.

[0004] Furthermore, after performing spectral analysis on the echo signal to obtain the peak frequency, and then subtracting the fixed acousto-optic frequency shift, the Doppler frequency shift can be calculated. However, the acousto-optic frequency shift is determined by the frequency of the radio frequency signal generated by the circuit loaded on the acousto-optic modulator, the characteristics of the acousto-optic crystal and the transducer, and will change slightly with temperature. Therefore, this will bring about the calculation error of Doppler frequency shift and speed. Summary of the Invention

[0005] The objective of this invention is to provide a Doppler laser velocimetry radar device and method. By controlling the amplitude of the intermediate frequency (IF) signal reflected from the radar system's end face, the attenuation signal, which lasts for tens of nanoseconds and gradually decreases after the IF signal is reflected, is reduced or even eliminated, thereby eliminating the influence of this attenuation signal on spectrum estimation. Furthermore, the initial phase of the IF signal reflected from the end face can be extracted for phase alignment with the received atmospheric echo pulse IF signal, achieving coherent accumulation in the pulse time domain. Additionally, the frequency of the IF signal reflected from the end face represents the frequency shift of the signal light relative to the local oscillator light. By analyzing the spectrum of this relatively small amplitude IF signal reflected from the end face and extracting the peak frequency, it can be used as a reference value for the frequency shift of the radar system's optical path to calculate the Doppler frequency shift, reducing measurement errors caused by using a fixed frequency shift for calculation under varying temperature conditions.

[0006] The technical solution of the present invention: According to a first aspect of the present invention, a Doppler laser velocimetry radar device is provided, the device comprising: a seed laser 1, an acousto-optic modulator 2, an optical fiber amplifier module 4, a circulator module 5, and an optical antenna module 6 connected in sequence by optical fibers; The acousto-optic modulator 2 is also optically connected in sequence to the optical attenuator 7, the optical delay line 8, the coupler module 10, and the balanced photodetector module 11; the circulator module 5 is also optically connected to the coupler module 10. The signal processing module 12 is electrically connected to the acousto-optic modulator 2 and the balanced photodetector module 11, respectively. The signal processing module 12 is used to digitally acquire the signal sent by the balanced photodetector module 11, segment the obtained pulse digital intermediate frequency signal, and estimate the frequency of the signal after the intermediate frequency signal is reflected from the end face to obtain the laser line-of-sight velocity. The acousto-optic modulator 2 includes: an input optical fiber 21, an acousto-optic crystal 22, a transducer 23, a first coupling lens 24, a local oscillator output optical fiber 25, a second coupling lens 26, and a signal output optical fiber 27; the acousto-optic crystal 22 is coupled to the input optical fiber 21, the local oscillator output optical fiber 25, and the signal output optical fiber 27 respectively through optical elements, or directly coupled to them through optical fibers; the transducer 23 is tightly bonded to the acousto-optic crystal 22; The optical signal transmitted through the input optical fiber 21 enters the acousto-optic crystal 22 and generates acousto-optic diffraction, producing 0th-order output light and 1st-order output light. The 0th-order output light and 1st-order output light enter the local oscillator output optical fiber 25 and the signal output optical fiber 27, respectively. It also includes an intensity modulator 3, which is disposed between the acousto-optic modulator 2 and the fiber optic amplifier module 4, and is connected to the acousto-optic modulator 2 and the fiber optic amplifier module 4 respectively via optical fibers; the signal processing module 12 is electrically connected to the intensity modulator 3; It also includes a phase modulator module 9, which is disposed between the optical delay line 8 and the coupler module 10, and is connected to the optical delay line 8 and the coupler module 10 respectively via optical fibers; the signal processing module 12 is electrically connected to the phase modulator module 9; the phase modulator module 9 is connected between any two adjacent modules in the optical path formed by the acousto-optic modulator 2 to the optical delay line 8 to the coupler module 10, or between any two adjacent modules in the optical path formed by the acousto-optic modulator 2 to the circulator module 5 to the coupler module 10; The optical delay line 8 is used to delay the transmitted light and adjust the delay of the local oscillator light signal so that the rising edge of the end-face reflected light signal pulse is aligned with the falling edge of the local oscillator light pulse, thereby obtaining a smaller amplitude end-face reflected intermediate frequency signal through heterodyne interference.

[0007] In one possible embodiment, the fiber amplifier module 4 includes a fiber amplifier, the circulator module 5 includes a circulator, the optical antenna module 6 includes an optical antenna, the phase modulator module 9 includes a phase modulator, the coupler module 10 includes a coupler, and the balanced photodetector module 11 includes a balanced photodetector.

[0008] In one possible embodiment, the device further includes a first beam splitter 41 and a second beam splitter 42; The intensity modulator 3 and the fiber amplifier module 4 are connected by an optical fiber via a first beam splitter 41; the optical delay line 8 and the phase modulator module 9 are connected by an optical fiber via a second beam splitter 42. The fiber amplifier module 4 includes multiple fiber amplifiers, the circulator module 5 includes multiple circulators, the optical antenna module 6 includes multiple optical antennas, the phase modulator module 9 includes multiple phase modulators, the coupler module 10 includes multiple couplers, and the balanced photodetector module 11 includes multiple balanced photodetectors. Multiple fiber amplifiers, multiple circulators, and multiple optical antennas are connected sequentially in a one-to-one correspondence. Multiple phase modulators are connected in a one-to-one correspondence with multiple couplers and multiple balanced photodetectors; Multiple circulators are connected in a one-to-one correspondence with multiple couplers and multiple balanced photodetectors.

[0009] On the other hand, the present invention provides a Doppler laser velocimetry method, the method comprising: The laser emitted from the seed laser 1 undergoes acousto-optic diffraction after passing through the acousto-optic modulator 2, generating a local oscillator light and a signal light. The local oscillator light sequentially enters the optical attenuator 7, the optical delay line 8, and the coupler module 10. The signal light sequentially enters the fiber amplifier module 4 and the circulator module 5, and is emitted into the air through the optical antenna module 6. The optical antenna module 6 simultaneously receives the echo signal light scattered back by atmospheric aerosol particles. The echo signal light enters the coupler module 10 through the circulator module 5 and undergoes heterodyne interference with the local oscillator light. The heterodyne interference signal is detected by the balanced photodetector module 11, generating an intermediate frequency (IF) electrical signal. The signal processing module 12 acquires the detected IF electrical signal, quantizes it to obtain a digital IF signal, extracts the digital IF signal from the atmospheric echo, performs frequency estimation, and further calculates the velocity in the laser line-of-sight direction. By measuring the velocities in multiple laser line-of-sight directions, the three-axis velocity and velocity direction are calculated.

[0010] On the other hand, the present invention provides a method for implementing coherent accumulation, comprising the following steps: The laser emitted from seed laser 1 undergoes acousto-optic diffraction after passing through acousto-optic modulator 2. The 0th-order light does not produce frequency shift, while the 1st-order light produces a frequency shift equal to the applied radio frequency signal. The 0th-order light output serves as the local oscillator, and the 1st-order light output serves as the signal light. The local oscillator sequentially enters optical attenuator 7, optical delay line 8, and coupler module 10. The signal light sequentially enters fiber amplifier module 4 and circulator module 5, and is emitted into the air through optical antenna module 6. Optical antenna module 6 simultaneously receives the echo signal light scattered back by atmospheric aerosol particles. The echo signal light enters coupler module 10 through circulator module 5 and undergoes heterodyne interference with the local oscillator light. The heterodyne interference signal is detected by the balanced detector module, generating an intermediate frequency electrical signal. When the signal light is transmitted through the fiber end face of the circulator's two ports and the surface of the optical lens, it generates a reflected signal with an amplitude much larger than the atmospheric scattered echo signal. The AD converter acquires and quantizes the pulse intermediate frequency (IF) signal, extracts the end-face reflected IF digital signal with smaller amplitude, and obtains the frequency-amplitude spectrum and frequency-phase spectrum of this signal through FFT analysis. The frequency f0 corresponding to the maximum value of the amplitude spectrum is obtained, and the phase Φ0 in the phase spectrum corresponding to this frequency f0 is the initial phase of the extracted end-face reflected IF signal. Given a reference phase value for phase alignment, the difference between the obtained initial phase and the reference phase is calculated, and the number of data bits required to achieve phase alignment is calculated. By shifting the data, the phase of each IF pulse signal is aligned with the reference phase. After a certain number of IF pulse signals are phase aligned, these pulse signals are accumulated to achieve coherent accumulation.

[0011] On the other hand, the present invention provides a method for implementing coherent accumulation, comprising the following steps: Based on the intermediate frequency signal reflected from the end face, the signal processing module 12 calculates the phase adjustment amount and changes the phase shift of the phase modulator module 9 in real time, adjusting the initial phase of different echo intermediate frequency signals to a fixed value to meet the pulse coherent accumulation condition.

[0012] Advantages of this invention: This invention provides a device and method for a Doppler laser velocimetry radar suitable for short-range measurements. By simultaneously generating a pulse signal and a corresponding pulsed local oscillator signal through an acousto-optic modulator, and adjusting the delay of the local oscillator signal, the rising edge of the reflected light pulse is aligned with the falling edge of the local oscillator pulse. This allows for heterodyne interference to obtain a smaller amplitude intermediate frequency (IF) signal from the reflected light, avoiding the subsequent attenuation signal of tens of nanoseconds caused by the larger amplitude of the reflected IF signal. This eliminates the impact of increased noise in the low-frequency region of the spectrum caused by the attenuated signal on frequency estimation, improving the accuracy and reliability of velocity measurement. Furthermore, the initial phase of the smaller amplitude reflected IF signal can be extracted for phase alignment of the received atmospheric echo pulse IF signal, achieving coherent accumulation in the pulse time domain and improving the system's signal-to-noise ratio. Furthermore, the frequency of the intermediate frequency signal reflected from the end face can characterize the acoustic-optical frequency shift in real time. By analyzing the spectrum of the intermediate frequency signal reflected from the end face with a relatively small amplitude, the peak frequency can be extracted and used as the optical path frequency shift of the radar system to replace the fixed frequency shift for calculating the Doppler frequency shift. This reduces the measurement error caused by using a fixed frequency shift for calculation when the frequency shift changes under varying temperature conditions. Attached Figure Description Figure 1 To compare the ideal signal with the actual signal; Figure 2 Comparison of the spectrum of ideal signal and actual signal; Figure 3 A device for use as a Doppler laser velocimetry radar for short-range measurements; Figure 4 A schematic diagram of an acousto-optic modulator; Figure 5 Timing diagram for generating heterodyne intermediate frequency signals; Figure 6 This is a structural diagram of a scheme used for multi-channel Doppler laser velocimetry radar; Figure 7 Flowchart of the algorithm for implementing pulse coherent accumulation; Figure 8 Schematic diagrams of signal frequency-amplitude spectrum and frequency-phase spectrum; Figure 9 This is a schematic diagram of the signal processing module. Figure 10 A schematic diagram illustrating the method for achieving coherent accumulation; Explanation of reference numerals in the attached figures: 1-Seed laser, 2-Acousto-optic modulator, 3-Intensity modulator, 4-Fiber amplifier module, 5-Circulator module, 6-Optical antenna module, 7-Optical attenuator, 8-Optical delay line, 9-Phase modulator module, 10-Coupler module, 11-Balanced photodetector module, 12-Signal processing module, 21-Input fiber, 22-Acousto-optic crystal, 23-Transducer, 24-First coupling lens, 25-Local oscillator output fiber, 26-Second coupling lens, 27-Signal output fiber, 28-0th order output light, 29-1st order output light, 41-First beam splitter, 42-Second beam splitter. Detailed Implementation The present invention will now be described in further detail with reference to the accompanying drawings.

[0013] One aspect is to provide a Doppler laser velocimeter radar device, which can be referenced. Figure 3 The device includes: a seed laser 1, an acousto-optic modulator 2, an intensity modulator 3, an optical fiber amplifier module 4, a circulator module 5, and an optical antenna module 6 connected in sequence by optical fibers; the acousto-optic modulator 2 is connected in sequence by optical fibers to an optical attenuator 7, an optical delay line 8, a coupler module 10, and a balanced photodetector module 11; the circulator module 5 is connected by optical fibers to the coupler module 10. The signal processing module 12 is electrically connected to the acousto-optic modulator 2, the intensity modulator 3, and the balanced photodetector module 11. The signal processing module 12 is used to digitally acquire the signal sent by the balanced photodetector module 11, segment the obtained pulse digital intermediate frequency signal, and estimate the frequency of the signal after the intermediate frequency signal is reflected from the end face to obtain the laser line-of-sight velocity.

[0014] The pulse modulation signals loaded by the signal processing module 12 onto the acousto-optic modulator 2 and the intensity modulator 3 have the same repetition frequency and pulse width, and are guaranteed to be from the same source by frequency division of the same crystal oscillator. The two pulse signals have a certain delay to ensure that the pulse signal modulated by the acousto-optic modulator 2 is not truncated by the intensity modulator 3.

[0015] The intensity modulator 3 is not essential. Its purpose is to improve the extinction ratio of the generated pulse signal. It can be an electrically controlled optical switch of any principle, such as an electrically controlled MEMS optical switch, an electro-optic intensity modulator, a magneto-optic intensity modulator, an acousto-optic modulator, etc. It can also be an optical amplifier that can be used as an optical switch, such as a semiconductor optical amplifier, an EDFA, etc.

[0016] The phase modulator module 9 is not strictly necessary; its purpose is to adjust the phase value in real time to achieve coherent pulse accumulation. The phase modulator module 9 can be an electro-optic modulator composed of an electro-optic crystal, or a modulator capable of generating phase or optical path changes. The optical delay line 8 is used to delay the transmitted light for a certain period of time. It can be a length of optical fiber or a spatial folding optical path composed of a set of mirrors.

[0017] Optionally, the fiber amplifier module 4 includes a fiber amplifier, the circulator module 5 includes a circulator, the optical antenna module 6 includes an optical antenna, the coupler module 10 includes a coupler, and the balanced photodetector module 11 includes a balanced photodetector.

[0018] Optionally, you may refer to Figure 6 The device also includes a first beam splitter 41 and a second beam splitter 42; The intensity modulator 3 and the fiber amplifier module 4 are connected by an optical fiber via a first beam splitter 41; the optical delay line 8 and the coupler module 10 are connected by an optical fiber via a second beam splitter 42. The fiber optic amplifier module 4 includes multiple fiber optic amplifiers, the circulator module 5 includes multiple circulators, the optical antenna module 6 includes multiple optical antennas, the coupler module 10 includes multiple couplers, and the balanced photodetector module 11 includes multiple balanced photodetectors. Multiple fiber optic amplifiers, multiple circulators, and multiple optical antennas are connected sequentially in a one-to-one correspondence. Multiple circulators are connected in a one-to-one correspondence with multiple couplers and multiple balanced photodetectors.

[0019] For reference Figure 4 The acousto-optic modulator includes: an input optical fiber 21, an acousto-optic crystal 22, a transducer 23, a first coupling lens 24, a local oscillator output optical fiber 25, a second coupling lens 26, and a signal output optical fiber 27; the acousto-optic crystal 22 is coupled to the input optical fiber 21, the local oscillator output optical fiber 25, and the signal output optical fiber 27 respectively through optical elements such as lenses, or can be directly coupled to each other with optical fibers; the transducer 23 is tightly bonded to the acousto-optic crystal 22; The optical signal transmitted through the input optical fiber 21 enters the acousto-optic crystal 22 and generates acousto-optic diffraction, producing 0th-order output light 28 and 1st-order output light 29, which are at a certain angle. The size of the angle depends on the material properties and length of the acousto-optic crystal. The 0th-order output light 28 and the 1st-order output light 29 enter the local oscillator output optical fiber 25 and the signal output optical fiber 27, respectively. The signal processing module 12 is used to digitally acquire the heterodyne intermediate frequency signal sent by the balanced photodetector module 11, segment the obtained digital intermediate frequency signal, determine the initial phase of the echo pulse intermediate frequency signal based on the end face reflected intermediate frequency signal, calculate the phase change based on the obtained initial phase value, adjust the voltage value of the phase modulator module 9 in real time, generate a certain phase value to compensate for the initial phase change, and complete the phase alignment and coherent accumulation of the echo pulse digital intermediate frequency signal.

[0020] like Figure 9 As shown, the signal processing module 12 comprises a crystal oscillator, a clock management unit, an AD analog-to-digital converter, a coherent accumulation module, a frequency estimation module, a phase discrimination module, a phase-locked loop module, a phase signal generator, and a modulation signal / frequency shift signal generator; the generated modulation signal, frequency shift signal, and AD clock signal are all obtained from the same crystal oscillator after passing through the clock management unit.

[0021] On the other hand, a Doppler laser velocimetry method is provided, utilizing the measuring device described above, the method comprising: The laser emitted from the seed laser undergoes acousto-optic diffraction after passing through an acousto-optic modulator. The 0th-order light does not produce a frequency shift, while the 1st-order light produces a frequency shift equal to the applied radio frequency signal. The 0th-order light output serves as the local oscillator, and the 1st-order light output serves as the signal light. The local oscillator light sequentially enters the optical attenuator, optical delay line, and coupler module. The signal light sequentially enters the intensity modulator, fiber amplifier module, and circulator module, and is then emitted into the air through the optical antenna module. The optical antenna module simultaneously receives the echo signal light scattered back by atmospheric aerosol particles. The echo signal light enters the coupler module through the circulator module and undergoes heterodyne interference with the local oscillator light. The heterodyne interference signal is detected by the balanced detector module, generating an intermediate frequency (IF) electrical signal. The signal processing module acquires the detected IF electrical signal, quantizes it to obtain a digital IF signal, and extracts the digital IF signal from the atmospheric echo for frequency estimation. This allows for further calculation of the velocity along the laser line of sight. Measuring the velocities along multiple laser line of sight directions allows for the calculation of the three-axis velocity and velocity direction.

[0022] For reference Figure 5The acousto-optic modulator is loaded with a radio frequency signal and a pulse modulation signal with the required frequency shift. When the modulation signal is high, first-order diffraction light is generated, at which point the signal light power is maximum and the local oscillator light power is minimum. The magnitude of the local oscillator light can be adjusted by regulating the high level of the pulse modulation signal. When the modulation signal is zero, only 0th-order diffraction light is generated, at which point the local oscillator light power is maximum and the signal light power is minimum. When the signal light propagates through the fiber endface and optical lens surface at the two ports of the circulator, it generates a reflected signal (called the endface reflection signal) with an amplitude much larger than the atmospheric scattered echo signal. When the local oscillator light and the signal light output from the acousto-optic modulator reach the heterodyne interference of the coupler, the signal light's propagation time in the fiber is Δτ longer than that of the local oscillator light. By delaying the local oscillator light by Δτ time using an optical delay line, the rising edge of the endface reflection signal pulse is aligned with the falling edge of the local oscillator light pulse, thus obtaining a smaller amplitude endface reflection intermediate frequency signal through heterodyne interference. By adjusting the high-level value of the pulse modulation signal applied to the acousto-optic modulator, the amplitude of the endface reflection intermediate frequency signal can be adjusted, and its minimum value can be zero. Therefore, the large endface reflection intermediate frequency signal is avoided, which causes a continuous attenuation signal of tens of nanoseconds that follows, thus eliminating the influence of this attenuation signal on the spectrum estimation.

[0023] The reflected light signal reaching the end face of coupler module 10 can be expressed as:

[0024] in, For light wave frequency, The frequency shifter frequency is the frequency of the modulator. The phase generated by the transmission of the reflected signal light in the optical fiber path is the phase of the signal light. This refers to the phase change caused by the change in optical path length of the signal light transmitted through end-face reflection due to factors such as temperature, vibration, and stress variations.

[0025] The signal light emitted into the air interacts with atmospheric particles, producing a Doppler frequency shift. The atmospheric echo signal reaching coupler module 10 can be expressed as...

[0026] in, The phase generated by the transmission of signal light through the atmosphere. To account for the generated Doppler frequency shift, it is assumed here that the time difference between the end-face reflected signal light and the atmospheric echo signal light arriving at the coupler module 10 is very short, which can be considered as the optical path phase change caused by factors such as temperature, vibration, and stress variations. constant.

[0027] The optical signal of the local oscillator light, which is mixed with the reflected signal light from the end face, reaching the coupler module 10 can be expressed as follows:

[0028] in, The phase of the local oscillator light transmission is to be mixed with the signal light reflected from the end face. This refers to the phase change caused by variations in the optical path length of the local oscillator light due to factors such as temperature, vibration, and stress.

[0029] Similarly, it is believed that the phase change in the local oscillator optical path is caused by factors such as temperature, vibration, and stress variations. If the optical signal of the local oscillator light, which is mixed with the atmospheric echo signal light, reaches the coupler module 10, it can be expressed as follows:

[0030] in, The phase of the local oscillator light transmission is for mixing with the atmospheric echo signal light.

[0031] The intermediate frequency signal received by the balanced detector after heterodyne mixing of the signal light and the local oscillator light can be expressed as:

[0032] in, The initial phase of the intermediate frequency signal reflected from the end face. The phase of the optical path changes due to factors such as temperature, vibration, and stress.

[0033] The atmospheric echo intermediate frequency signal can be represented as

[0034] in, Compare the intermediate frequency signal reflected from the end face with the intermediate frequency signal of the atmospheric echo, and the phase difference between the two. It is a fixed value:

[0035] Therefore, by determining the initial phase of the intermediate frequency signal reflected from the end face, the phase alignment of the atmospheric echo intermediate frequency signal can be achieved, thereby enabling coherent accumulation of the echo intermediate frequency signal.

[0036] The method for achieving coherent accumulation can be described as follows: (Refer to...) Figure 7 The AD converter acquires and quantizes the pulse intermediate frequency signal, extracts the intermediate frequency digital signal of the end-face reflection with a smaller amplitude, and obtains the frequency-amplitude spectrum and frequency-phase spectrum of this signal segment through FFT analysis. (See [reference needed]). Figure 8The frequency f0 corresponding to the maximum value of the amplitude spectrum is obtained. The phase Φ0 in the phase spectrum corresponding to this frequency f0 is the initial phase of the extracted end-face reflection intermediate frequency signal. Alternatively, the initial phase can be corrected using a discrete spectrum correction method to improve the initial phase extraction accuracy. This initial phase has a fixed phase shift from the initial phase of the actual atmospheric echo intermediate frequency pulse signal. Given a reference phase value φ0 for phase alignment, the difference Δφ = φ0 - Φ0 between the calculated initial phase and this reference phase can be used to calculate the number of data bits required to achieve phase alignment. ,in F s The AD sampling frequency, f s This is the frequency of the echo intermediate frequency signal. f s It can be obtained through methods such as incoherent spectral accumulation and frequency estimation. This is achieved by shifting the intermediate frequency data of atmospheric echoes. n s The phase of a certain number of echo intermediate frequency pulse signals is aligned, and these shifted pulse intermediate frequency signals are accumulated to achieve coherent accumulation.

[0037] The coherent accumulation method can also be described as: finding the frequency corresponding to the maximum value of the amplitude spectrum. f 0, this frequency f The phase Φ0 in the phase spectrum corresponding to 0 is the initial phase of the extracted end-face reflected intermediate frequency signal. The phase-locked module provides an initial phase reference value and calculates the initial phase adjustment amount using methods such as proportional-integral (PI) control. This adjustment amount acts as a feedback quantity to the phase signal generator, which generates a voltage value for real-time adjustment of the phase modulator module 9. This causes the phase modulator module 9 to generate a certain phase shift, thereby compensating in real time for phase changes in the end-face reflected intermediate frequency signal caused by temperature, vibration, stress changes, etc., so that the initial phase is stabilized near the reference value. This achieves phase alignment of the echo pulse intermediate frequency signal, satisfies the coherent accumulation condition, and thus enables coherent accumulation of multiple different atmospheric echo pulse intermediate frequency signals in the same measurement area.

[0038] The method for achieving coherent accumulation can also be described as follows: (See also...) Figure 10 The RF signal 101 loaded onto the modulator module and the IF signal 102 detected by the balanced detector module are jointly loaded onto the phase-locked loop module 103, and the output signal 104 of the phase-locked loop module is loaded onto the phase modulator module 9. By changing the phase value of the phase modulator module 9, the phase of the end-face reflected IF signal is synchronized with the phase of the RF signal loaded onto the modulator module in real time, thereby achieving a fixed phase value for the end-face reflected IF signal. Therefore, the phase of the echo IF pulse signal is fixed, satisfying the coherent accumulation condition, thus enabling coherent accumulation of different echo pulse IF signals.

[0039] The pulse coherent accumulation process can be described as follows: N Time series corresponding to different pulses D ( n The time series is obtained by accumulating the corresponding sequence numbers. D A Represented as: in n This is the sequence number of the time series.

[0040] Time series after coherent accumulation D A Perform a Fast Fourier Transform (FFT) operation to obtain the frequency spectrum, then estimate the peak frequency to obtain the frequency corresponding to the spectral peak. f Subtract the frequency shift of the modulator module v M The Doppler frequency shift can be obtained. f - v M Therefore, the velocity in the laser line of sight can be calculated. λ is the laser wavelength.

[0041] Subtracting the acousto-optic frequency shift from the estimated peak frequency yields the Doppler frequency shift, which can then be used to calculate the laser line-of-sight velocity. However, since the acousto-optic frequency shift is determined by the frequency of the radio frequency signal applied to the acousto-optic modulator, the characteristics of the acousto-optic crystal and transducer, it undergoes slight changes with temperature. Subtracting a fixed frequency shift during temperature variations will introduce calculation errors. The frequency of the relatively small amplitude end-face reflected intermediate frequency signal can characterize the frequency shift generated by the acousto-optic modulator in real time. By analyzing the spectrum of this small amplitude end-face reflected intermediate frequency signal and extracting the peak frequency, it can be used as a reference value for the optical path frequency shift in the radar system to calculate the Doppler frequency shift, reducing measurement errors caused by using a fixed frequency shift under varying temperature conditions.

Claims

1. A Doppler laser velocimeter radar device, characterized in that, The device includes: a seed laser (1), an acousto-optic modulator (2), an optical fiber amplifier module (4), a circulator module (5), and an optical antenna module (6) connected in sequence by optical fibers. The acousto-optic modulator (2) is also optically connected to the optical attenuator (7), optical delay line (8), coupler module (10), and balanced photodetector module (11) in sequence; the circulator module (5) is also optically connected to the coupler module (10). The signal processing module (12) is electrically connected to the acousto-optic modulator (2) and the balanced photodetector module (11), respectively; The signal processing module (12) is used to digitally acquire the signal sent by the balanced photodetector module (11), segment the obtained pulse digital intermediate frequency signal, and estimate the frequency of the signal after the intermediate frequency signal is reflected from the end face to obtain the laser line of sight velocity. The acousto-optic modulator (2) includes: an input optical fiber (21), an acousto-optic crystal (22), a transducer (23), a first coupling lens (24), a local oscillator output optical fiber (25), a second coupling lens (26), and a signal output optical fiber (27); the acousto-optic crystal (22) is coupled to the input optical fiber (21), the local oscillator output optical fiber (25), and the signal output optical fiber (27) respectively through optical elements, or directly coupled to the optical fiber; the transducer (23) is tightly bonded to the acousto-optic crystal (22); The optical signal transmitted by the input optical fiber (21) enters the acousto-optic crystal (22) and will generate acousto-optic diffraction, producing 0th order output light and 1st order output light. The 0th order output light and 1st order output light enter the local oscillator output optical fiber (25) and the signal output optical fiber (27), respectively. It also includes an intensity modulator (3), which is disposed between the acousto-optic modulator (2) and the fiber amplifier module (4), and is connected to the acousto-optic modulator (2) and the fiber amplifier module (4) respectively via optical fibers; the signal processing module (12) is electrically connected to the intensity modulator (3). It also includes a phase modulator module (9), which is disposed between the optical delay line (8) and the coupler module (10) and is connected to the optical delay line (8) and the coupler module (10) respectively via optical fibers; the signal processing module (12) is electrically connected to the phase modulator module (9); the phase modulator module (9) is connected between any two adjacent modules in the optical path formed by the acousto-optic modulator (2) to the optical delay line (8) to the coupler module (10), or between any two adjacent modules in the optical path formed by the acousto-optic modulator (2) to the circulator module (5) to the coupler module (10); The optical delay line (8) is used to delay the transmitted light and adjust the delay of the local oscillator light signal so that the rising edge of the end-face reflected light signal pulse is aligned with the falling edge of the local oscillator light pulse, thereby obtaining a small amplitude end-face reflected intermediate frequency signal through heterodyne interference.

2. The Doppler laser velocimetry radar device according to claim 1, characterized in that, The fiber amplifier module (4) includes a fiber amplifier, the circulator module (5) includes a circulator, the optical antenna module (6) includes an optical antenna, the phase modulator module (9) includes a phase modulator, the coupler module (10) includes a coupler, and the balanced photodetector module (11) includes a balanced photodetector.

3. The Doppler laser velocimetry radar device according to claim 1, characterized in that, The device also includes a first beam splitter (41) and a second beam splitter (42). The intensity modulator (3) and the fiber amplifier module (4) are connected by an optical fiber via a first beam splitter (41); the optical delay line (8) and the phase modulator module (9) are connected by an optical fiber via a second beam splitter (42). The fiber amplifier module (4) includes multiple fiber amplifiers, the circulator module (5) includes multiple circulators, the optical antenna module (6) includes multiple optical antennas, the phase modulator module (9) includes multiple phase modulators, the coupler module (10) includes multiple couplers, and the balanced photodetector module (11) includes multiple balanced photodetectors. Multiple fiber amplifiers, multiple circulators, and multiple optical antennas are connected sequentially in a one-to-one correspondence. Multiple phase modulators are connected in a one-to-one correspondence with multiple couplers and multiple balanced photodetectors; Multiple circulators are connected in a one-to-one correspondence with multiple couplers and multiple balanced photodetectors.

4. A Doppler laser velocimeter method, employing the Doppler laser velocimeter radar device according to any one of claims 1-3, characterized in that, The method includes: The seed laser (1) emits laser light, which is then diffracted by the acousto-optic modulator (2) to generate local oscillator light and signal light. The local oscillator light enters the optical attenuator (7), optical delay line (8) and coupler module (10) in sequence. The signal light enters the fiber amplifier module (4) and circulator module (5) in sequence, and is emitted into the air through the optical antenna module (6). The optical antenna module (6) simultaneously receives the echo signal light scattered back by atmospheric aerosol particles. The echo signal light enters the coupler module (10) through the circulator module (5) and interferes heterodyne with the local oscillator light. The heterodyne interference signal is detected by the balanced photodetector module (11) to generate intermediate frequency electrical signal. The signal processing module (12) collects the detected intermediate frequency electrical signal, quantizes it to obtain digital intermediate frequency signal, extracts the digital intermediate frequency signal of atmospheric echo for frequency estimation, and further calculates the velocity in the laser line of sight direction. The three-axis velocity and velocity direction are calculated by measuring the velocities in multiple laser line of sight directions.

5. A method for achieving coherent accumulation, employing any one of the Doppler laser velocimetry radar devices according to claims 1-3, characterized in that, Includes the following steps: The laser emitted by the seed laser (1) undergoes acousto-optic diffraction after passing through the acousto-optic modulator (2). The 0th order light does not produce frequency shift, while the 1st order light produces a frequency shift equal to the frequency of the applied radio frequency signal. The 0th order light output serves as the local oscillator light, and the 1st order light output serves as the signal light. The local oscillator light sequentially enters the optical attenuator (7), the optical delay line (8), and the coupler module (10). The signal light sequentially enters the fiber amplifier module (4) and the circulator module (5), and is emitted into the air through the optical antenna module (6). The optical antenna module (6) simultaneously receives the echo signal light scattered back by atmospheric aerosol particles. The echo signal light enters the coupler module (10) through the circulator module (5) and interferes heterodyne with the local oscillator light. The heterodyne interference signal is detected by the balanced detector module, generating an intermediate frequency electrical signal. When the signal light is transmitted through the fiber end face of the circulator's two ports and the surface of the optical lens, it generates a reflected signal with an amplitude much greater than that of the atmospheric scattered echo signal. The AD acquires and quantizes the pulse intermediate frequency signal, extracts the end-face reflection intermediate frequency digital signal with smaller amplitude, and obtains the frequency-amplitude spectrum and frequency-phase spectrum of the signal through FFT analysis. The frequency f0 corresponding to the maximum value of the amplitude spectrum is obtained, and the phase Φ0 in the phase spectrum corresponding to the frequency f0 is the initial phase of the extracted end-face reflection intermediate frequency signal. Given a reference phase value for phase alignment, calculate the difference between the initial phase and the reference phase, and then calculate the number of data bits required to achieve phase alignment. By shifting the data, the phase of each intermediate frequency pulse signal is aligned with the reference phase. After a certain number of intermediate frequency pulse signals are phase aligned, these pulse signals are accumulated to achieve coherent accumulation.

6. A method for achieving coherent accumulation, employing any one of the Doppler laser velocimetry radar devices according to claims 1-3, characterized in that, Includes the following steps: Based on the intermediate frequency signal reflected from the end face, the signal processing module (12) calculates the phase adjustment amount and changes the phase shift of the phase modulator module (9) in real time, adjusting the initial phase of different echo intermediate frequency signals to a fixed value to meet the pulse coherent accumulation condition.

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