An experimental system combining synchronous measurement of laser micro-doppler and polarization characteristics of space targets

Abstract

The application discloses a kind of experimental systems for combining synchronous measurement space target laser micro-doppler and polarization characteristics, the experimental system includes light source module, micro-doppler-polarization module, the emission light of light source module is branched after energy branching by optical fiber beam splitter, four-channel equal-energy distribution is realized by optical fiber beam splitter;Micro-doppler-polarization module uses coherent detection architecture, four-way local oscillator light and corresponding echo light of polarization state are respectively heterodyne mixed, the intensity of each polarization component in echo light is measured in real time, the micro-doppler frequency shift of target movement is obtained simultaneously, the attitude angle and depolarization degree of target are solved by algorithm, the depolarization degree collected under different materials, multiple incident attitude angles is statistically analyzed, and "incident attitude degree-depolarization degree" mapping database is established, which can provide a new dimension for unknown space target detection, and promote the development of space target detection technology to more refinement and intelligent direction.

Description

Technical Field

[0001] This invention belongs to the field of lidar applications and relates to an experimental system for measuring the laser micro-Doppler and polarization characteristics of space targets. Background Technology

[0002] With the increasing prevalence of human space activities, the number and types of space targets are becoming increasingly diverse, including both normal targets such as satellites, spacecraft, debris, and explosive fragments, as well as runaway targets. Achieving high-precision, real-time detection of various space targets has become a crucial issue in the development of modern aerospace technology. Optical polarization characteristics, as a fundamental physical quantity in the interaction between light and matter, can reflect differences in the optical constants, surface roughness, and coating properties of target materials. Therefore, utilizing the polarization characteristics of targets can add a new dimension to the detection, classification, and identification of space targets.

[0003] Laser micro-Doppler effect-based detection technology, with its advantages of high resolution and high detection sensitivity, is widely used in measuring the motion and geometric parameters of space targets. Among these, the attitude angle, as a key parameter describing the target's spatial orientation, not only determines the angle of polarization of the incident light on the target surface but also affects the change in the polarization characteristics of the echo light. By accurately estimating the target attitude angle, the contribution of inherent material properties to depolarization characteristics can be separated, thereby obtaining the "incident attitude angle-depolarization" relationship for different materials. This provides a new method for the accurate resolution and identification of space targets, improving the accuracy of detection technology.

[0004] In previous studies, micro-Doppler and polarization measurements were typically performed independently and in a time-division manner. This approach has two drawbacks: firstly, time-division measurement results in micro-Doppler and polarization parameters being acquired at different time points, making it impossible to truly align the physical states under the same observation conditions, which is detrimental to the rapid detection and accurate response of targets in high-speed motion; secondly, relying solely on either the micro-Doppler effect or polarization characteristics cannot provide a more comprehensive and accurate detection and identification of targets, thereby reducing the reliability of target detection and identification. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention provides an experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets. This system measures the intensity of each polarization component in the echo light in real time, and simultaneously obtains the micro-Doppler frequency shift of the target motion. The target's attitude angle and depolarization degree are calculated through an algorithm. Statistical analysis is performed on the depolarization degree collected under different materials and various incident attitude angles to establish an "incident attitude degree - depolarization degree" mapping database. This can provide a new dimension for the detection of unknown space targets and promote the development of space target detection technology towards a more refined and intelligent direction.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets includes a light source module, a micro-Doppler-polarization module, and a host computer, wherein:

[0008] The emitted light from the light source module is split into beams by a 1:9 fiber optic beam splitter. The local oscillator light with a 10% energy ratio is introduced into an 80MHz fundamental frequency modulation by an acousto-optic modulator and then distributed into four channels with equal energy through a 1:1:1:1 fiber optic beam splitter. These are referred to as local oscillator light 1, local oscillator light 2, local oscillator light 3 and local oscillator light 4.

[0009] The micro-Doppler polarization module uses a two-way polarization beam splitter to decouple the echo light into four linearly polarized lights of equal energy and polarization states of 0°, 90°, 45° and 135°, respectively, denoted as echo light 1, echo light 2, echo light 3 and echo light 4.

[0010] The micro-Doppler polarization module adopts a coherent detection architecture, which performs heterodyne mixing on the four local oscillator beams and the echo beams of the corresponding polarization states. After photoelectric conversion by a photodetector, the mixed output is used to realize real-time signal acquisition through a high-speed data acquisition card, which then transmits the acquired signal to the host computer.

[0011] After receiving the four mixed signals, the host computer calculates the energy corresponding to each polarization state, thereby obtaining the depolarization degree of the target echo light. Simultaneously, these four mixed signals are regarded as four laser micro-Doppler signals. Then, through digital filtering, time-frequency analysis, and parameter calculation steps, the incident attitude angle of the target is obtained, realizing the synchronous real-time measurement of the target's micro-Doppler and polarization characteristics. Based on this, the depolarization degree collected under different materials and multiple incident attitude angles is statistically analyzed to establish an "incident attitude angle - depolarization degree" mapping database, thereby realizing the joint application of micro-Doppler and polarization characteristics in the field of space target detection and identification.

[0012] The deflection degree D is expressed as:

[0013]

[0014] In the formula, P It is the degree of polarization. S 0 represents the total intensity of the light wave. S 1 represents the intensity difference of linearly polarized light in the x and y directions. S 2 represents the intensity difference of linearly polarized light in the 45° and 135° directions;

[0015] The incident attitude angle The extraction formula is:

[0016]

[0017] In the formula, Let be the distance from the vertex of the bottom face of the cube target to its center. , Let the target side length of the cube be... f max The maximum frequency shift of micro-Doppler, To emit laser wavelength, The target spin frequency is known.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention can measure the intensity of each polarization component in the echo light in real time, and simultaneously obtain the micro-Doppler frequency shift of the target motion. The target's attitude angle and depolarization degree are calculated synchronously through the algorithm.

[0020] 2. This invention can perform statistical analysis on the depolarization collected under different materials and various incident attitude angles, establish an "incident attitude angle - depolarization" mapping database, and combine micro-Doppler and polarization characteristics to form a multi-dimensional target detection, identification and classification method, providing a new dimension for the detection of targets in unknown space. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the principle of laser micro-Doppler detection of space targets;

[0022] Figure 2 This is a schematic diagram of the combined micro-Doppler and polarization detection experimental system;

[0023] Figure 3 This is a debiasing diagram of artificial composite materials compared to other materials;

[0024] Figure 4 It is the time spectrum of the synchronously measured micro-Doppler signal. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0026] This invention provides an experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of a space target. The system includes a light source module, a micro-Doppler-polarization module, a target module, and a host computer, wherein:

[0027] The light source module uses a fiber laser with a wavelength of 1064nm, which emits polarized light with a power of 100mW. After collimation, the spot diameter is 2cm.

[0028] The micro-Doppler-polarization module synchronously measures multiple polarization components in the echo light. Each polarization component can be regarded as a micro-Doppler signal, and the polarization characteristics and micro-Doppler characteristics are obtained in real time.

[0029] The target module includes natural biological materials and artificial composite materials. Natural biological materials cover various bird feathers, while artificial composite materials mainly include composite materials commonly used in space targets, as well as paper, wood boards, etc.

[0030] The emitted light from the light source module is split into four channels by a 1:9 fiber optic beam splitter. The local oscillator light, representing 10% of the energy, is modulated at an 80MHz fundamental frequency by an acousto-optic modulator and then distributed equally across four channels by a 1:1:1:1 fiber optic beam splitter, designated as Local Oscillator 1, Local Oscillator 2, Local Oscillator 3, and Local Oscillator 4. The micro-Doppler polarization module uses a two-way polarization beam splitter to decouple the echo light into four linearly polarized lights with equal energy and polarization states of 0°, 90°, 45°, and 135°, designated as Echo Light 1, Echo Light 2, Echo Light 3, and Echo Light 4. The micro-Doppler polarization module employs a coherent detection architecture, heterodyne mixing the four local oscillator lights with the corresponding polarization states of the echo light. The mixed output undergoes photoelectric conversion by a photodetector and is then acquired in real-time via a high-speed data acquisition card, which transmits the acquired signal to a host computer. After receiving the four mixed signals, the host computer calculates the energy corresponding to each polarization state, thereby obtaining the depolarization degree of the target echo light. These four mixed signals can also be considered as four laser micro-Doppler signals. Then, through digital filtering, time-frequency analysis, and parameter calculation, the target's characteristic parameters are obtained, with the incident attitude angle being the most relevant parameter. This achieves synchronous real-time measurement of the target's micro-Doppler and polarization characteristics. Based on this, statistical analysis is performed on the depolarization degrees collected under different materials and various incident attitude angles to establish an "incident attitude angle-depolarization degree" mapping database, thus realizing the joint application of micro-Doppler and polarization characteristics in the field of space target detection and identification.

[0031] In this invention, the polarization characteristics are measured as follows:

[0032] Stokes vectors are the most commonly used way to describe the polarization state of light waves. They can accurately and concisely represent fully polarized light, partially polarized light, and natural light.

[0033]

[0034] In the formula, and These represent the amplitudes of the electric vector in the x and y directions, respectively. This indicates averaging over time. This represents the phase difference between the x-direction and y-direction components of the electric vector.

[0035] We can obtain:

[0036]

[0037]

[0038]

[0039] Ultimately, we can obtain:

[0040]

[0041] From the above formula, we can obtain four Stokes parameters:

[0042]

[0043] In the formula, S 0 represents the total intensity of the light wave. S 1 represents the intensity difference of linearly polarized light in the x and y directions. S 2 represents the intensity difference of linearly polarized light in the 45° and 135° directions. S 3 represents the intensity difference between right-handed and left-handed circularly polarized light.

[0044] The circular polarization component of most polarized light is negligible within the instrument's detection range, therefore it is taken as... Degree of polarization P The proportion of linearly polarized light in the total light intensity can be represented by Stokes vector elements as follows:

[0045]

[0046] The debiasing degree D can be expressed as:

[0047]

[0048] In this invention, a cube is used as the detection target to analyze the micro-Doppler characteristics of a space target.

[0049] like Figure 1 As shown, the side length of the cube is... center of mass The intersection with the upper bottom surface is A vertex of the upper base is denoted as The attitude angle is The line-of-sight vector of the lidar is Let vector and The included angle is The distance from the target to the radar is denoted as .

[0050] vertex The range mode to the lidar is:

[0051]

[0052] Generally, the size of the target is much smaller than the distance between the target and the radar, further leading to:

[0053]

[0054] Cube vertices Around Axis spin, distance from the center of mass at each moment position vector for:

[0055]

[0056] The micro-Doppler frequency can be obtained as:

[0057]

[0058] Therefore, the maximum frequency shift of the micro-Doppler can be obtained as:

[0059]

[0060] When the target side length of the cube When known, It is also a known quantity. If the spin frequency of the target is known in advance, equation (13) has only one unknown parameter. .

[0061] The final formula for extracting the attitude angle is:

[0062]

[0063] Therefore, after obtaining the echo signal of the spatial target under an unknown attitude angle by the lidar, the echo signal is processed by short-time Fourier transform to obtain the corresponding time spectrum. Based on the edge peak of the time spectrum, when the side length and spin frequency of the target are known, the attitude angle can be solved by equation (14) to obtain the micro-Doppler characteristics of the target.

[0064] In this invention, the relationship between polarization characteristics and the laser micro-Doppler effect is as follows: Analysis based on the polarization principle shows that when the polarization state of the incident light is constant and the transmission medium remains unchanged, the depolarization degree of the target is mainly affected by its material properties and the incident attitude angle. Based on the micro-Doppler effect of space targets, the characteristic parameters of the target, including the target's attitude angle, are calculated from the time-frequency spectrum of the micro-Doppler signal. Given the target's attitude angle, the polarization characteristics of different targets are obtained by measuring their depolarization degrees, providing a new data dimension for subsequent target detection, identification, and classification.

[0065] Example:

[0066] In this embodiment, the principle of the micro-Doppler and polarization synchronization joint detection experimental system is as follows: Figure 2 As shown in the diagram, this system uses a 1064nm fiber laser as the seed source. The output optical signal is divided into two beams by a fiber beam splitter. The local oscillator beam, accounting for 10% of the energy, is modulated at a 70MHz fundamental frequency by an acousto-optic modulator and then distributed into four equal-energy channels (Local Oscillator 1, Local Oscillator 2, Local Oscillator 3, and Local Oscillator 4) by a 1:1:1:1 fiber beam splitter. Simultaneously, the signal beam accounting for 90% of the energy is amplified and projected onto the target area through the transmitter, where its reflected echo is received. This echo signal is decoupled into four linearly polarized beams of equal energy with polarization states of 0°, 90°, 45°, and 135° by a polarization beam splitter (Echo Beam 1, Echo Beam 2, Echo Beam 3, and Echo Beam 4). The system employs a coherent detection architecture, introducing the four local oscillator beams and their corresponding polarization-state echo beams into fiber couplers for heterodyne mixing. The mixed output undergoes photoelectric conversion by a photodetector and is then acquired in real-time via a high-speed data acquisition card. The deflection of the echo signal is calculated according to equation (8). Figure 3 The polarization response characteristics of artificial composite materials (such as epoxy carbon fiber, polyester carbon fiber, and plastics) and paper and wood panels reveal the essential differences in their optical field manipulation mechanisms. Specifically, within the incident angle range of 45°–90°, paper and wood panels exhibit significant depolarization, with an average depolarization degree exceeding 0.5. This phenomenon is likely closely related to the multi-layered rough structure and complex optical properties of these materials. In contrast, the depolarization degree of artificial composite materials (such as epoxy carbon fiber, polyester carbon fiber, and plastics) is generally below 0.5, possibly due to the higher surface smoothness of artificial materials, resulting in relatively weaker optical field manipulation capabilities. Figure 4 The time spectrum of the synchronously measured micro-Doppler signal.

Claims

1. An experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of a space target, characterized in that... The experimental system includes a light source module, a micro-Doppler-polarization module, and a host computer, wherein: The emitted light from the light source module is split into beams by a 1:9 fiber optic beam splitter. The local oscillator light with a 10% energy ratio is introduced into an 80MHz fundamental frequency modulation by an acousto-optic modulator and then distributed into four channels with equal energy through a 1:1:1:1 fiber optic beam splitter. These are referred to as local oscillator light 1, local oscillator light 2, local oscillator light 3 and local oscillator light 4. The micro-Doppler polarization module uses a two-way polarization beam splitter to decouple the echo light into four linearly polarized lights of equal energy and polarization states of 0°, 90°, 45° and 135°, respectively, denoted as echo light 1, echo light 2, echo light 3 and echo light 4. The micro-Doppler polarization module adopts a coherent detection architecture, which performs heterodyne mixing on the four local oscillator beams and the echo beams of the corresponding polarization states. After photoelectric conversion by a photodetector, the mixed output is used to realize real-time signal acquisition through a high-speed data acquisition card, which then transmits the acquired signal to the host computer. After receiving the four mixed signals, the host computer calculates the energy corresponding to each polarization state, thereby obtaining the depolarization degree of the target echo light. Simultaneously, these four mixed signals are regarded as four laser micro-Doppler signals. Then, through digital filtering, time-frequency analysis, and parameter calculation steps, the incident attitude angle of the target is obtained, realizing the synchronous real-time measurement of the target's micro-Doppler and polarization characteristics. Based on this, statistical analysis is performed on the depolarization degrees collected under different materials and multiple incident attitude angles to establish an "incident attitude angle - depolarization degree" mapping database, thereby realizing the joint application of micro-Doppler and polarization characteristics in the field of space target detection and identification.

2. The experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets according to claim 1, characterized in that... The light source module uses a fiber laser with a wavelength of 1064nm, which emits polarized light with a power of 100mW. After collimation, the spot diameter is 2cm.

3. The experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets according to claim 1, characterized in that... The targets include natural biomaterials and artificial composite materials.

4. The experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets according to claim 3, characterized in that... The natural biological material is bird feathers, and the artificial composite material is a composite material for space targets, paper, or wood.

5. The experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets according to claim 1, characterized in that... The deflection degree D is expressed as: In the formula, P is the degree of polarization, S0 is the total light intensity of the light wave, S1 is the intensity difference of linearly polarized light in the x and y directions, and S2 is the intensity difference of linearly polarized light in the 45° and 135° directions.

6. The experimental system for jointly and synchronously measuring the laser micro-Doppler and polarization characteristics of space targets according to claim 1, characterized in that... The incident attitude angle The extraction formula is: In the formula, Let be the distance from the vertex of the bottom face of the cube target to its center. , Let f be the target side length of the cube. max The maximum frequency shift of micro-Doppler, To emit laser wavelength, The target spin frequency is known.

Images