A single-pixel two-dimensional velocity measurement method suitable for dual-frequency continuous laser radar

Abstract

The present invention is a method for measuring the speed of a space object suitable for a single-pixel dual-frequency continuous laser radar. This method uses a compressed sensing (CS) algorithm, uses a digital microlens array (DMD) to encode the array echo signal, mixes the laser radar echo signal after AD conversion with the local oscillator signal and the reference signal respectively, and then integrates the sampling time length and performs bandpass filtering on the two mixed signals, and then performs compressed sensing recovery operations on the two processed signals to obtain two two-dimensional intensity distribution information. The Doppler frequency shift is obtained by calculating the inverse of the product of the corresponding pixel intensity ratio of the intensity distribution information obtained after recovery and the frequency difference between the reference signal frequency and the beat frequency. The speed of the space object is further obtained from the relationship between the Doppler frequency shift and the detection signal frequency.

Description

Technical field:

[0001] The present invention relates to a two-dimensional speed measurement technology of a single-pixel dual-frequency laser radar, and in particular to a two-dimensional speed measurement technology for obtaining a target motion speed by using Doppler frequency shift and compressed sensing single-pixel imaging technology. Background technology:

[0002] Speed ​​measurement is an important application in many fields such as aerospace, mechanical engineering, civil engineering, and biomedicine. Generally, there are three main methods for measuring the speed of a target object: mechanical measurement, optical measurement, and microwave measurement. Among them, optical measurement has excellent application prospects due to its non-contact, high precision, and wide range. The most commonly used method in optical measurement is laser Doppler technology, which uses the Doppler principle to analyze the frequency shift in the echo signal to invert the target's moving speed. At present, there are single-frequency laser Doppler technology and dual-frequency laser Doppler technology based on the light source used. The single-frequency laser is coherent with the signal light and the local oscillator light, so that the frequency shift signal is located in the mid-frequency band detectable by the detector. After demodulating the frequency, time-frequency analysis is performed to obtain the vibration information of the target. The dual-frequency laser overcomes the influence of atmospheric turbulence. At the same time, because the beat frequency of the dual-frequency laser is adjustable, it can cope with moving targets of different speeds by adjusting the beat frequency, and has a large dynamic range of speed measurement capabilities. However, the above-mentioned laser speed measurement applications are all one-dimensional single-point speed measurement. In addition, due to the difficulty and high cost of manufacturing area array detectors outside the visible light band, most common detectors are single-pixel or low-pixel area array detectors, and their resolution and detection frame rate are far lower than those of visible light area array detectors. At present, the detection technology of non-visible light bands, especially infrared bands, is relatively mature. Therefore, non-visible light area array detection is constrained to a certain extent. In order to solve the above problems, a two-dimensional target speed detection method using a single-pixel detector and a dual-frequency laser is proposed. The present invention utilizes methods such as Doppler frequency shift and compressed sensing single-pixel imaging technology, and uses a digital microlens array (DMD) to spatially encode the echo signal, and performs a recovery operation on the data group after mixing, filtering and integrating the echo signal with the local oscillator signal and the reference signal, and then obtains the two-dimensional target Doppler frequency shift through the relationship between the recovery result and the frequency difference between the local oscillator and the reference signal, and obtains the movement speed of the target on the two-dimensional plane through the relationship between the Doppler frequency shift and the detection wavelength and the moving speed. Summary of the invention:

[0003] The present invention utilizes compressed sensing single-pixel imaging technology to encode the dual-frequency laser radar echo signal through a digital microlens array (DMD), and utilizes FPGA and a multi-channel acquisition card to collect, digitally mix, bandpass filter and digitally integrate the echo signal to obtain a coded data group, and performs recovery operation on it. The Doppler frequency shift of an object in two-dimensional space is obtained according to the relationship between the recovery result and the frequency difference between the local oscillator and the reference signal, and then the movement speed of the object in two-dimensional space is obtained according to the relationship between the Doppler frequency shift and the detection wavelength and the moving speed.

[0004] The technical solution of the present invention is as follows:

[0005] S1: Split the single-frequency laser emitted by the seed laser source, and make one of the beams frequency modulated by an acousto-optic modulator, while the other laser beam is not processed; then combine the modulated laser beam with the other laser beam to obtain a dual-frequency laser source;

[0006] S2: The dual-frequency laser source obtained after beam combination is split again, and one of the beams is directly detected and received by the detector to obtain the local oscillator signal as follows:

[0007]

[0008] S3: According to the image size M×N, the required number of measurements K is calculated as required.

[0009] S4: Another dual-frequency laser beam is emitted through the power amplifier and the optical-mechanical system to illuminate the detection target. The optical-mechanical system receives the scattered and reflected light of the target and performs K spatial domain encoding through the DMD. Each encoding matrix is ​​c kij , where k = 1, 2, ..., K, i = 1, 2, ..., M, j = 1, 2, ..., N, the detector detects and receives to obtain the K groups of echo signals, where the kth group is:

[0010]

[0011] Where Δf ij is the Doppler shift of the pixel in the i-th row and j-th column.

[0012] S5: Mix the echo signal with the local oscillator signal and the reference signal respectively to obtain the following results:

[0013]

[0014]

[0015] S6: Integrate the above equations (3) and (4) for a time length of T to obtain the encoded data d1(k) and d2(k);

[0016] S7: Performing compressed sensing recovery operations on the d1(k) and d2(k) data obtained by K times of coding measurement to obtain recovery results r1(i, j) and r2(i, j);

[0017] S8: Calculate the moving speed of the detected target using the following formula:

[0018]

[0019] S9: According to the relationship between Doppler frequency shift, detection wavelength and object speed, the object speed v corresponding to each pixel is obtained. ij ;

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

[0021] The present invention provides a single-pixel two-dimensional velocity measurement method applied to a dual-frequency continuous laser radar. By using a compressed sensing single-pixel imaging method, the radar echo signal is spatially encoded, and the advantages of high precision of laser measurement and strong anti-atmospheric disturbance ability of dual-frequency laser are fully utilized. By using compressed sensing technology, the problem that infrared wavelength detectors cannot use infrared lasers for array velocity detection due to the manufacturing bottleneck of multi-pixel array detectors is solved. By spatially encoding the echo signal, mixing it with the local oscillator signal and the reference signal, and obtaining the recovery result through the recovery operation, the moving speed of the target on the two-dimensional plane can be accurately obtained by simple operations. This method has good accuracy and velocity resolution, low computational complexity, good development prospects, and can basically meet the needs of two-dimensional velocity measurement of single-pixel detectors in practice. Description of the drawings:

[0022] none. Specific implementation method:

[0023] The preferred embodiments of the present invention are described in detail below; this preferred embodiment is only to better illustrate the specific implementation of the present invention, and is not intended to limit the protection scope of the present invention.

[0024] The dual-frequency laser radar two-dimensional speed measurement method based on Doppler frequency shift and compressed sensing single pixel imaging technology used in the present invention comprises the following steps:

[0025] S1: Splitting the single-frequency laser emitted by the seed laser source, allowing one of the beams to be frequency modulated by an acousto-optic modulator, and the other laser beam is not processed; then combining the modulated laser beam with the other laser beam to obtain the dual-frequency laser source L1;

[0026] S2: The dual-frequency laser source obtained after beam combination is split again, and one of the beams is directly detected and received by the detector to obtain the local oscillator signal as follows:

[0027]

[0028] Where f1 is the local oscillator signal frequency, is the initial phase value of the eigensignal L2.

[0029] S3: According to the image size M×N, the required number of measurements K is calculated as required.

[0030] S4: Another dual-frequency laser beam is emitted through the power amplifier and the optical-mechanical system to illuminate the detection target. The optical-mechanical system receives the scattered and reflected light of the target and performs K spatial domain encoding through the DMD. Each encoding matrix is ​​c kij , where k = 1, 2, ..., K, i = 1, 2, ..., M, j = 1, 2, ..., N, the detector detects and receives to obtain the K groups of echo signals, where the kth group is:

[0031]

[0032] Where Δf ij is the Doppler shift of the pixel in the i-th row and j-th column.

[0033] S5: Mix the echo signal with the local oscillator signal and the reference signal respectively to obtain the following results:

[0034]

[0035] in, is the phase value corresponding to the echo of the pixel in the i-th row and j-th column in the target scene.

[0036] S6: Integrate the above equations (3) and (4) for a time length of T to obtain the encoded data d1(k) and d2(k);

[0037] S7: Performing compressed sensing recovery operations on the d1(k) and d2(k) data obtained by K times of coding measurement to obtain recovery results r1(i, j) and r2(i, j);

[0038] S8: Calculate the moving speed of the detected target using the following formula:

[0039]

[0040] Where f2 is the frequency of the target echo.

[0041] S9: According to the relationship between Doppler frequency shift, detection wavelength and object speed, the object speed v corresponding to each pixel is obtained. ij .

Claims

1. A method for measuring the motion speed of a two-dimensional object using a dual-frequency continuous laser radar based on Doppler frequency shift and compressed sensing single pixel imaging technology, characterized in that: The following steps are involved: S1: Split the single-frequency laser emitted by the seed laser source, and make one of the beams frequency modulated by an acousto-optic modulator, while the other laser beam is not processed; then combine the modulated laser beam with the other laser beam to obtain a dual-frequency laser source; S2: The dual-frequency laser source obtained after beam combination is split again, and one of the beams is directly detected and received by the detector to obtain the local oscillator signal as follows: S3: According to the image size M×N, the required number of measurements K is calculated according to the measurement needs; S4: Another dual-frequency laser beam is emitted through the power amplifier and the optical-mechanical system to illuminate the detection target. The optical-mechanical system receives the scattered and reflected light of the target and performs K spatial domain encoding through the DMD. Each encoding matrix is ​​c kij , where k = 1, 2, ..., K, i = 1, 2, ..., M, j = 1, 2, ..., N, the detector receives K coded echo signals, where the kth is: Where Δf ij is the Doppler frequency shift of the pixel in the i-th row and j-th column; S5: Mix the echo signal with the local oscillator signal and the reference signal respectively to obtain the following results: S6: Integrate the above equations (3) and (4) for a time length of T to obtain the encoded data d1(k) and d2(k); S7: Performing compressed sensing recovery operations on the d1(k) and d2(k) data obtained by K times of coding measurement to obtain recovery results r1(i, j) and r2(i, j); S8: Calculate the moving speed of the detected target using the following formula: S9: According to the relationship between Doppler frequency shift, detection wavelength and object speed, the object speed v corresponding to each pixel is obtained. ij .

2. The method for measuring the motion speed of a two-dimensional object using a dual-frequency continuous laser radar based on Doppler frequency shift and compressed sensing single pixel imaging technology according to claim 1 is characterized in that: The K-times encoded echo signal is obtained in the following way: S11: The local oscillator signal and the echo signal are firstly generated by a single-frequency laser source, and then one path is frequency-shifted by an acousto-optic frequency shifter after beam splitting, and then combined with the other path to obtain a dual-frequency laser source. The dual-frequency laser is then beam split again, and one path is emitted after passing through a power amplifier and an optical-mechanical system, irradiates the target, and returns to the optical-mechanical system, which is the echo signal; S12: placing a digital microlens array (DMD) on the optical path between the target and the optomechanical system, and performing spatial coding modulation on the echo signal through the DMD to obtain a coded echo signal; S13: According to the number of measurements K, the DMD array coding matrix is ​​transformed K times, each transformation will correspond to a coded echo signal, and after K times of transformation of the coding matrix and data collection, K coded echo signals are obtained.

3. The method for measuring the motion speed of a two-dimensional object using a dual-frequency continuous laser radar based on Doppler frequency shift and compressed sensing single pixel imaging technology according to claim 1 is characterized in that: The coded data d1(k) and d2(k) are obtained as follows: S21: Encoded data d1(k) is the sum of each encoded echo signal and the local oscillator signal Mixing, the signal after each mixing is integrated with a length of sampling time T; S22: Encoded data d2(k) is the sum of each encoded echo signal and the local oscillator signal Mixing, the signal after each mixing is integrated with a length of sampling time T to obtain.

4. The method for measuring the motion speed of a two-dimensional object using a dual-frequency continuous laser radar based on Doppler frequency shift and compressed sensing single pixel imaging technology according to claim 1, characterized in that: The compressed sensing recovery algorithms used in this method are basis pursuit algorithm, minimum total variation algorithm, and deep learning algorithm.

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