CN-122017875-A - Doppler tomography laser radar imaging device based on carrier phase noise compensation and optimization method

CN122017875ACN 122017875 ACN122017875 ACN 122017875ACN-122017875-A

Abstract

The invention relates to the technical field of coherent laser radar detection and imaging, in particular to a Doppler tomography laser radar imaging device based on carrier phase noise compensation and an optimization method. The phase noise is accurately estimated through the double-reference channel structure, and the image quality evaluation index is used as a parameter optimization basis and a judgment standard of the compensation effect, so that the target echo phase noise is accurately compensated, and the high-resolution Doppler tomography of the high-speed spin target with the rotating speed of 30Hz is realized under the condition that the optical path difference exceeds the laser coherence length by 80 times. The invention is designed for the echo signal wide spectrum characteristic of Doppler chromatography laser radar, and has the characteristics of high compensation precision, wide range of distance dynamic range, low manufacturing cost and the like.

Inventors

WEI KAI
LIU DENGFENG
YAO MULIN
LI JIAN
Song Anpeng

Assignees

浙江大学杭州国际科创中心

Dates

Publication Date: 20260512
Application Date: 20251225

Claims (10)

1. The Doppler chromatographic laser radar imaging device based on carrier phase noise compensation comprises a laser (2), a first optical splitter (3), an acousto-optic frequency shifter (4), a second optical splitter (5), a third optical splitter (9), a first optical coupler (10), a second optical coupler (15) and a signal acquisition and processing unit (19), wherein the input end of the first optical splitter (3) is connected to the output end of the laser (2), the first output end is connected to the input end of the third optical splitter (9), the second output end is connected to the input end of the acousto-optic frequency shifter (4), the input end of the second optical splitter (5) is connected to the output end of the acousto-optic frequency shifter (4), the first output end irradiates a target through a first collimating mirror (6), the second output end is connected to the signal input end of the second optical coupler (15) through a first delay optical fiber (13), the first output end of the third optical splitter (9) is connected to the input end of the first optical coupler (10), the second output end of the second optical splitter (9) is connected to the signal input end of the second optical coupler (10) through a local oscillator signal acquisition unit (19) through a first collimating mirror (7), the output end of the second optical coupler (15) is connected to a signal acquisition and processing unit (19) through a second balance detector (17); The imaging device is characterized by further comprising a second delay optical fiber (14), a third optical coupler (16) and a third balance detector (18), wherein the second optical beam splitter (5) and the third optical beam splitter (9) are three-output optical splitters, a third output end of the second optical beam splitter (5) is connected to a signal path input end of the third optical coupler (16), a third output end of the third optical beam splitter (9) is connected to a local oscillation path input end of the third optical coupler (16), and optical paths of the first delay optical fiber (13) and the second delay optical fiber (14) are different from each other.
2. A method of carrier phase noise compensation for a doppler-directed laser radar according to claim 1, characterized in that the optical path of the first delay fiber (13) is 3 to 10 times the optical path of the second delay fiber (14).
3. A carrier-phase noise compensation method for a doppler-chromatography laser radar according to claim 2, characterized in that the optical path of the first delay fiber (13) is 5 times the optical path of the second delay fiber (14).
4. A carrier-phase noise compensation method for a doppler-oriented tomography laser radar according to claim 1, characterized in that the signal acquisition and processing unit (19) is configured to perform the steps of: Extracting differential phase noise items based on heterodyne reference signals output by the second balance detector (17) and the third balance detector (18), and further reconstructing an estimated value matched with phase noise in the target mixed electric signal output by the first balance detector (11) as a noise estimated value; Noise cancellation is carried out by utilizing the noise estimation value and the target mixed frequency electric signal, so as to obtain a compensated target Doppler signal; and reconstructing an image based on the compensated target Doppler signal.
5. The method for carrier-phase noise compensation for Doppler computed tomography laser radar of claim 4, wherein the differential phase noise term is extracted based on heterodyne reference signals output by the second balanced detector (17) The method comprises the following steps: Wherein: For the carrier phase noise of the laser, Is that Delayed in time The phase of the post-phase is then, A fixed time delay introduced for the first delay fiber; extracting differential phase noise term based on heterodyne reference signal output by third balanced detector (18) The method comprises the following steps: Wherein: Is that Delayed in time The phase of the post-phase is then, A fixed time delay is introduced for the second delay fiber.
6. The method for compensating carrier phase noise for Doppler tomography laser radar of claim 4 wherein said noise estimate is obtained by constructing a digital delay adaptive filter and performing digital delay using a differential phase noise term to reconstruct an estimate matching the phase noise in the target mixed electrical signal as a noise estimate: Wherein: As an estimate of the noise value of the signal, In the form of a first adaptive filter, Is a second adaptive filter.
7. The method of carrier-phase noise compensation for a doppler-directed tomography laser of claim 6, wherein said first adaptive filter The method comprises the following steps: The second adaptive filter The method comprises the following steps: Wherein: for the delay of the received signal reflected by the target, Is closest to Is a whole number of (a) and (b), Is a unit impulse signal Through fixed time delay The delayed version of the latter is used to provide a new, Is closest to Is a whole number of (a) and (b), For the distance of the object to be a target, Is the speed of light, beta is And Is a ratio of (2).
8. The method for compensating carrier-phase noise for a doppler tomographic laser radar according to claim 6, wherein the compensated target doppler signal is: Wherein: In order to compensate for the post-compensation target doppler signal, The electrical signal is mixed for the target.
9. The method for compensating carrier phase noise of Doppler tomography laser radar according to claim 8, the method is characterized in that reconstructing an image based on the compensated target Doppler signal comprises: Based on the compensated target Doppler signal, carrying out short-time Fourier transform on the one-dimensional time domain signal to obtain an intensity image of the one-dimensional time domain signal; converting the intensity image from the time-frequency domain to the sinogram domain; And reconstructing an image based on the intensity image converted into the sinogram domain by using a filtering back projection algorithm.
10. A parameter optimization method of an image forming apparatus according to any one of claims 1 to 9, comprising: step A1, initializing the optical path length of a first delay optical fiber (13) and a second delay optical fiber (14); A2, obtaining a reconstructed image output by a signal acquisition and processing unit (19); step A3, calculating a quality evaluation index of the image: Wherein: For quality evaluation index, P is the height of the image, Q is the width of the image, The gray value of the pixel point with x +1 on the abscissa and y on the ordinate, The gray value of a pixel point with x on the abscissa and y on the ordinate, Gray values of pixel points with x abscissa and y+1 ordinate; And A4, changing the optical path lengths of the first delay optical fiber (13) and the second delay optical fiber (14), repeating the step A3 for a plurality of times, and taking the optical path lengths of the first delay optical fiber (13) and the second delay optical fiber (14) corresponding to the image with the optimal quality evaluation index as an optimization result.

Description

Doppler tomography laser radar imaging device based on carrier phase noise compensation and optimization method Technical Field The invention relates to the technical field of coherent laser radar detection and imaging, in particular to a Doppler tomography laser radar imaging device based on carrier phase noise compensation and an optimization method. Background The Doppler chromatographic laser radar is a single-frequency continuous wave laser radar based on laser coherent detection, obtains the spatial frequency spectrum of a high-speed spin target (such as an unmanned aerial vehicle rotor wing, a fan blade and the like) by a mode of incoherent superposition of Doppler projection information under multiple observation angles, and inverts the scattering characteristic of the target by utilizing a filtering back projection algorithm so as to reconstruct a two-dimensional velocity distribution or a spatial structure image of the target. The Doppler chromatographic laser radar has the advantages of simple structure and low hardware requirement, does not need a complex modulation module to generate high-repetition-frequency, high-linearity and high-bandwidth transmitting pulse, and can still obtain higher receiving signal-to-noise ratio. The technology can realize rapid high-resolution imaging of a remote high-speed rotating target in a target perception scene with limited resources, so that the technology has important application value in the fields of non-cooperative target recognition, space situation perception and the like. However, in a long-range detection scenario, the performance of doppler tomography lidar is severely limited by the laser carrier phase noise. According to the coherent detection principle, the effective detection distance is limited to be within the coherence length determined by the laser phase noise. When the target distance is increased, the optical path difference between the echo signal and the local oscillation light is increased, and the accumulated laser phase noise can lead to spectrum broadening of the beat signal and reduction of the signal to noise ratio, so that the reconstructed image is blurred and details are lost. This limits the spatial resolution and effective range of doppler radar, and cannot achieve effective target recognition, directly affecting the moving target detection performance of the system. Meanwhile, the current laser technology is difficult to realize low-cost balance between narrow linewidth and high power, and the high-power laser signal required by long-distance detection also can introduce extra noise to influence radar performance. Currently, existing laser carrier phase noise compensation techniques can be divided into two directions, hardware and algorithm. The hardware compensation technology can reduce the phase noise of the output signal of the laser from the source, such as an equal line width narrowing technology of an external cavity feedback technology and an equal phase locking technology of an optical phase-locked loop. But the system has complex structure and higher comprehensive cost, and is unfavorable for the miniaturization of equipment and the requirement of low cost. In addition, the time domain coherence of the signals can be improved by utilizing the mode of physically compensating the optical path difference by using the delay optical fiber, but the method is not applicable to remote motion non-cooperative targets and cannot flexibly match a larger distance dynamic range. On the other hand, the digital domain phase noise compensation algorithm can reduce the hardware requirement through calculation force configuration, and has strong flexibility and controllable cost. At present, the implementation and application of the phase noise compensation algorithm are concentrated in the fields of laser radars (such as inverse synthetic aperture laser radars) or optical fiber sensing (such as optical frequency domain reflectometers) of a frequency modulation continuous wave system, and the like, and the algorithms comprise phase digital delay, observation matrix generalized inverse and the like. However, the above methods have common defects, namely that the algorithm optimizing process and the effect evaluation depend on the sharpening degree of the signal spectrum, besides the characteristic problems of complex model, discontinuous phase and the like. Because the echo signal contains Doppler modulation information in the Doppler tomography system, the Doppler tomography system has wide spectrum characteristics, and the traditional signal layer evaluation index (such as a sharpening function) is difficult to be applicable. In addition, the phase noise compensation device based on the single auxiliary interferometer has good effect in a scene that the transmission optical path difference of the transmitted signal is an integral multiple of the delay difference of the auxiliary interferometer, but has the problem that the estimation