A method and system for experimentally determining a laser scattering matrix of a moving target

Abstract

The application provides a kind of experimental determination method and system of moving target laser scattering matrix, belong to laser multi-dimensional perception technical field.This method is realized the measurement and analysis of large field of view multi-angle light scattering matrix by the experimental determination device of moving target laser scattering matrix based on phase-locked amplification technology, to further in-depth study the light scattering characteristics of moving target and the inversion of surface reflectivity, provide guidance and support for the development of moving target remote detection identification technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser multi-dimensional sensing, and particularly relates to a moving target laser scattering matrix experimental determination method and system. BACKGROUND

[0002] In the aspect of measuring the light scattering characteristics of moving targets, the measurement has developed from simple scattered light intensity measurement and scattered light polarization degree measurement to light scattering matrix measurement. Although the light scattering matrix of different moving targets has been measured in the existing literature, there are still deficiencies in the completeness of the measured matrix elements and the accuracy of the measurement results.

[0003] The light scattering matrix is an important physical parameter for describing the scattering characteristics of a target scatterer. Through the study of the scattering matrix, all the light scattering intensity and polarization information of the scatterer, as well as the microscopic morphology structure and composition of the scatterer and other physical and chemical properties can be obtained. Therefore, the study of the light scattering characteristics of moving targets through the light scattering matrix and the study of the method for inverting the particle size distribution and the refractive index using the light scattering matrix will not only have important significance in the basic research of photoelectric remote target detection and identification application, but also have important application value in the above-mentioned fields such as space target optical measurement and atmospheric aerosol remote sensing.

[0004] When light passes through optical devices such as polarizing plates and wave plates, the intensity and polarization state of the light will change. Similar to the description of the scattering process by the scattering matrix, the change of the incident light state by the optical device can also be described by a 4x4 matrix, which is called the Muller matrix of the optical device.

[0005] Muller matrix of a polarizing plate is:

[0006]

[0007] Muller matrix of a 1 / 4 wave plate is:

[0008]

[0009] wherein, is the orientation angle, i.e. the included angle between the optical axis of the optical element and the reference plane (usually referred to as the scattering plane in the scattering measurement): , .

[0010] The Stokes vector of the incident light is known , and the Stokes vector of the outgoing light can be obtained by multiplying the Muller matrix M of the optical device by the Stokes vector of the incident light .

[0011] In the aspect of studying the inversion of the moving target's properties by using the light scattering matrix, the existing researches mainly use a single or two light scattering matrix elements for inversion, and the researches on simultaneous inversion of multiple scattering matrix elements are still rare. Therefore, it is necessary to further study the light scattering characteristics of the moving target and the inversion of the surface reflectivity by measuring and simulating the light scattering matrix of the moving target, and to provide guidance and support for the development of remote detection and identification technology of moving targets. SUMMARY

[0012] In view of the above technical problems, the present application aims to provide a moving target laser scattering matrix experimental determination method and system.

[0013] The first aspect of the present application discloses a moving target laser scattering matrix experimental determination system, which comprises a laser, a polarization modulation module, a frequency modulation module, a servo module, a dynamic detector, a static detector, a lock-in amplifier, a data acquisition device and a control calculator.

[0014] The laser emitted by the laser is subjected to polarization modulation by the polarization modulation module and frequency modulation by the frequency modulation module to form modulated polarized laser, which is irradiated onto the moving target.

[0015] The servo module drives the dynamic detector to rotate within an angle range of 5° to 175° with respect to the propagation direction of the modulated polarized laser on a circumference with the moving target as the center and a preset length as the radius, and the dynamic detector is used to receive the first direct current signal and the alternating current signal of the scattered light of the moving target.

[0016] The static detector is arranged at a fixed position and is used to fixedly receive the second direct current signal of the modulated polarized laser.

[0017] The control calculator controls the frequency modulation module to frequency modulate the polarized laser after polarization modulation through the lock-in amplifier, and after the servo module starts to rotate, the servo module generates an angle trigger signal and an angle synchronization signal; the generated angle trigger signal is sent to the lock-in amplifier and the data acquisition device; the generated angle synchronization signal is sent to the control calculator.

[0018] After receiving the angle trigger signal, the data acquisition device synchronously acquires the second direct current signal and the first direct current signal.

[0019] After receiving the angle trigger signal, the lock-in amplifier extracts the sine component amplitude aS and the cosine component amplitude bC of the alternating current signal in the dynamic detector according to the reference signal provided by the frequency modulation module.

[0020] The control calculator realizes data acquisition in each angle interval according to the angle synchronization signal, and further completes data normalization and Mueller matrix inversion; in each angle interval, the control calculator receives the second direct current signal and the first direct current signal sent by the data collector, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the phase-locked amplifier.

[0021] Optionally, the dynamic detector is integrated by a photomultiplier tube, a quarter-wave plate and a polarizer; and the static detector is a photomultiplier tube.

[0022] Optionally, the polarization modulation module is a polarizer; the control calculator solves scattering matrix elements under each angle by the least square method based on the normalized data and multi-angle linear equations, and completes Mueller matrix inversion; wherein, a coefficient matrix of the multi-angle linear equations is constructed by Mueller matrices of the polarizer, the polarizer and the quarter-wave plate.

[0023] Optionally, the frequency modulation module comprises an electro-optic modulator and a signal generator; wherein:

[0024] When the laser passes through the electro-optic modulator, the control calculator controls the signal generator to generate a driving voltage through the phase-locked amplifier, so as to drive the electro-optic modulator to generate modulated light with a modulation frequency of ω, and form the modulated polarized laser.

[0025] Optionally, the system further comprises: an optical filter wheel; wherein:

[0026] The optical filter wheel is arranged between the laser and the polarization modulation module, and is used for switching the laser wavelength.

[0027] The second aspect of the present application discloses a method for experimentally determining a laser scattering matrix of a moving target, which is realized by the system for experimentally determining a laser scattering matrix of a moving target according to any one of the above.

[0028] S1, the laser emitted by the laser passes through the polarization modulation module for polarization modulation, and the control calculator controls the frequency modulation module to modulate the polarized laser through the phase-locked amplifier, so as to form the modulated polarized laser and irradiate the moving target;

[0029] S2, the control calculator controls the servo module to start rotating, so as to drive the dynamic detector to rotate in an angle range of 5° to 175° with the propagation direction of the modulated polarized laser on a circumference with the moving target as the center and with a preset length as the radius, so that the dynamic detector receives the first direct current signal and the alternating current signal of the scattered light of the moving target;

[0030] S3, the second direct current signal of the modulated polarized laser is fixedly received by the static detector;

[0031] S4, after the control calculator controls the servo module to start rotating, the servo module generates an angle trigger signal and an angle synchronization signal; the generated angle trigger signal is sent to the lock-in amplifier and the data collector; the generated angle synchronization signal is sent to the control calculator;

[0032] S5, after the data collector receives the angle trigger signal, the second direct current signal and the first direct current signal are synchronously collected;

[0033] S6, after the lock-in amplifier receives the angle trigger signal, according to the reference signal provided by the frequency modulation module, the sine component amplitude aS and the cosine component amplitude bC of the alternating current signal in the dynamic detector are extracted;

[0034] S7, according to the angle synchronization signal, the control calculator realizes data collection in each angle interval, and then completes data normalization and Mueller matrix inversion; in each angle interval, the control calculator receives the second direct current signal and the first direct current signal sent by the data collector, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the lock-in amplifier.

[0035] Optionally, in step S4, the angle trigger signal is generated by the servo module at each rotation of a preset angle interval, and the trigger interval is 0.1° to 5°.

[0036] Optionally, in step S6, the lock-in amplifier demodulates the alternating current signal using a reference signal with a reference frequency of ω, and the sine component amplitude aS and the cosine component amplitude bC; wherein the reference frequency is consistent with the modulation frequency of the frequency modulation module.

[0037] Optionally, in step S7:

[0038] Data normalization is:

[0039] Divide the first direct current signal, the sine component amplitude aS and the cosine component amplitude bC by the second direct current signal to eliminate laser intensity fluctuations;

[0040] Mueller matrix inversion is:

[0041] Based on the normalized data and the multi-angle linear equation set, the scattering matrix elements under each angle are solved by the least square method, and the Mueller matrix inversion is completed.

[0042] Optionally, the method further comprises:

[0043] Switch the laser wavelength by the light filter wheel, and repeat steps S1-S7 to obtain the wavelength-dependent scattering matrix.

[0044] In summary, the scheme provided in the application has the following technical effects: the motion target remote matrix measuring device based on the phase-locked amplification technology has compact structure, high position accuracy and fast measuring speed, can extract weak laser scattering signals under fluctuating background noise, and can realize multi-angle motion target scattering matrix measurement and multi-wavelength motion target scattering matrix measurement. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0046] Figure 1 The figure is a principle block diagram of the motion target scattering matrix measuring system of the embodiment of the application.

[0047] Figure 2 The figure is a timing diagram of the laser scattering signal synchronous acquisition of the embodiment of the application.

[0048] Figure 3 The figure is a position signal and laser scattering signal acquisition block diagram of the embodiment of the application. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, the technical scheme in the embodiments of the application will be clearly and completely described below in combination with the drawings of the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0050] The purpose of the application is to provide a motion target Muller matrix experimental measuring device based on the phase-locked amplification technology, to realize the measurement and analysis of the large field of view multi-angle light scattering matrix, to further study the light scattering characteristics and surface reflectivity inversion of the motion target, and to provide guidance and support for the development of motion target remote detection and identification technology. Wherein:

[0051] ;

[0052] In the formula, and are the Muller matrices of the polarizing system and the detecting polarizing system respectively, is the scattering matrix of the sample to be measured. , , 、 and 、 、 、 respectively represent the Stokes Parameters of scattered light and incident light. These parameters are used to describe the polarization state of light, and are defined as follows:

[0053] • : total intensity of scattered light.

[0054] • : intensity difference between horizontal and vertical linear polarization components in scattered light.

[0055] • : intensity difference between 45° and 135° linear polarization components in scattered light.

[0056] • : intensity difference between right and left circular polarization components in scattered light.

[0057] • : total intensity of incident light.

[0058] • : horizontal and vertical linear polarization component difference of incident light.

[0059] • : 45° and 135° linear polarization component difference of incident light.

[0060] • : right and left circular polarization component difference of incident light.

[0061] by means of polarization modulation and other technical means and , a linear equation containing and other elements can be obtained, and the scattering angle and the numerical values of each scattering matrix element can be obtained by simple algebraic operation. The purpose of the present application is to propose a moving target Mueller matrix experimental determination system based on phase-locked amplification technology, to realize the measurement and analysis of large field of view multi-angle light scattering matrix, to further study the light scattering characteristics and surface reflectivity of moving targets, and to provide guidance and support for the development of moving target remote detection and identification technology.

[0062] The first aspect of the present application discloses a moving target laser scattering matrix experimental determination system, the system comprises: a laser, a polarization modulation module, a frequency modulation module, a servo module, a dynamic detector, a static detector, a phase-locked amplifier, a data collector and a control calculator, wherein,

[0063] The laser emitted by the laser is subjected to polarization modulation by a polarization modulation module and frequency modulation by a frequency modulation module to form modulated polarized laser which is irradiated on the moving target;

[0064] The servo module drives the dynamic detector to rotate on a circumference with the moving target as the center and with a preset length as the radius and within an angle range of 5° to 175° with the propagation direction of the modulated polarized laser, and the dynamic detector is used to receive a first direct current signal (direct current signal DCd) and an alternating current signal of the scattered light of the moving target;

[0065] The static detector is arranged at a fixed position and is used to fixedly receive a second direct current signal (direct current signal DCm) of the modulated polarized laser;

[0066] The control calculator controls the frequency modulation module to perform frequency modulation on the laser subjected to polarization modulation through a phase-locked amplifier, and after the servo module starts to rotate, the servo module generates an angle trigger signal and an angle synchronization signal; the generated angle trigger signal is sent to the phase-locked amplifier and the data collector; and the generated angle synchronization signal is sent to the control calculator;

[0067] After the data collector receives the angle trigger signal, the second direct current signal and the first direct current signal are synchronously collected;

[0068] After the phase-locked amplifier receives the angle trigger signal, according to a reference signal provided by the frequency modulation module, the phase-locked amplifier extracts a sine component amplitude aS and a cosine component amplitude bC of the alternating current signal in the dynamic detector;

[0069] According to the angle synchronization signal, the control calculator realizes data collection in each angle interval, and then completes data normalization and Mueller matrix inversion; in each angle interval, the control calculator receives the second direct current signal and the first direct current signal sent by the data collector, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the phase-locked amplifier.

[0070] Optionally, the dynamic detector is integrated by a photomultiplier tube, a quarter-wave plate and a polarizer; and the static detector is a photomultiplier tube. Since the output power of the laser may fluctuate due to factors such as temperature and power supply noise, the amplitude of the scattered signal is distorted. The present application synchronously collects the dynamic detection signal (DCd) and the static monitoring signal (DCm), and normalizes through ratio calculation (such as DCd / DCm), so as to eliminate the influence of laser intensity fluctuation on the scattering matrix measurement, and realize signal normalization and system stability calibration.

[0071] Optionally, the polarization modulation module is a polarizer; the control calculator solves the scattering matrix elements at each angle θ using the least squares method based on the normalized data and the multi-angle linear equation system to complete the Mueller matrix inversion; wherein, the coefficient matrix of the multi-angle linear equation system is constructed from the Mueller matrices of the polarizer, analyzer and quarter-wave plate.

[0072] Optionally, the frequency modulation module includes an electro-optic modulator and a signal generator;

[0073] When the laser passes through the electro-optic modulator, the controller uses a lock-in amplifier to control the signal generator to generate a driving voltage, which drives the electro-optic modulator to generate modulated light with a modulation frequency of ω, thus forming a modulated polarized laser.

[0074] Optionally, the system further includes: a filter wheel;

[0075] A filter wheel is positioned between the laser and the polarization modulation module to switch the laser wavelength.

[0076] like Figure 1 As shown, laser 1, after passing through a filter wheel 2, polarizer 3, electro-optic modulator 4, and aperture 6, illuminates the moving target 7 and finally stops at the light trap 12. During this process, the laser is frequency-modulated by the signal generator 5 when passing through the electro-optic modulator 4. Two detection devices are arranged on a circle with a radius of 0.5m centered on the moving target. The first photomultiplier tube 13 (PM monitor, static detector) is stationary at a certain position. The second photomultiplier tube 10 (with a quarter-wave plate 8 and analyzer 9 in front) receives the scattering information from the moving target. The servo motor controller 14 controls the servo motor 11 to rotate on a precision guide rail. The second photomultiplier tube 10 (PM detector), quarter-wave plate 8, and analyzer 9 form a whole (dynamic detector) that can rotate within an angle range of 5°-175° with respect to the beam propagation direction, and can complete the entire motion angle range within 5 seconds. During rotation, the DC detection signal DCm of PM monitor 13 and the first DC signal of PM detector 10 are directly acquired by data acquisition card 15 and transmitted to the computer, while the scattered signal in PM detector is expanded in series. and The amplitudes aS and bC are received through a lock-in amplifier 16, and the amplitude and phase information are transmitted to a computer 18 through a network switch 17.

[0077] Lock-in amplifier (LIA) is a kind of instrument specially used for extracting weak signal submerged in strong noise, its core principle is to separate the target signal from the noise by using the frequency and phase information of the reference signal through coherent detection technology. In the motion target laser scattering matrix measurement system of the application, the role of the lock-in amplifier is to extract the laser scattering signal (such as amplitude aS and bC) modulated by the electro-optical modulator, which is implemented as follows:

[0078] 1. Signal modulation and reference signal generation:

[0079] Electro-optical modulator 4: the light emitted by the laser passes through the electro-optical modulator and is modulated by the signal generator 5 at a frequency ω (for example, a sine wave or a square wave). The modulated laser carries a characteristic signal with a frequency of ω.

[0080] Reference signal: the signal generator 5 simultaneously provides a reference signal (frequency ω) with the same frequency and phase as the modulation signal for the lock-in amplifier, serving as the phase reference of the lock-in amplifier.

[0081] 2. Signal reception and mixing:

[0082] Probe signal: after the scattered light is received by the photomultiplier tube 10, the output signal contains:

[0083] Target signal: modulated scattering signal with a frequency of ω (weak and submerged in noise).

[0084] Noise: environmental light, detector thermal noise, circuit noise, etc. (wide frequency band).

[0085] The lock-in amplifier performs multiplication operation on the probe signal and the reference signal to realize mixing. After mixing, the signal is decomposed into high-frequency components and direct-current components. The high-frequency components contain noise, which can be filtered out by a low-pass filter. The direct-current component only retains the signal amplitude with the same frequency and phase (or fixed phase difference) as the reference signal. After passing through the low-pass filter, the output is a direct-current voltage proportional to the amplitude of the target signal aS and bC, and the noise is greatly suppressed. The lock-in amplifier can adjust the phase θ of the reference signal, and separate the real part and the imaginary part of the signal through quadrature detection, thereby obtaining the complete information of the scattering signal (such as aS and bC).

[0086] As shown in Figure 2 , the position signal is output by the servo motor, and the output pulse can be set in real time. The temporary adjustment range is 36KHz~360KHz, and the number of output pulses per half circle is 18KHz~180KHz.

[0087] As shown in Figure 3As shown, the data acquisition card and the lock-in amplifier work in the external trigger mode, and the external trigger signal is the position signal (servo motor output), which can output the zero position and two DC signals. The zero position is used for the lock-in amplifier to calculate the origin position of the laser modulation signal acquisition.

[0088] Figure 3 The synchronization acquisition process of the position signal and the laser scattering signal in the moving target laser scattering matrix measurement system is shown, and the sources, transmission paths and purposes of the signals are clarified.

[0089] 1. Signal source and purpose:

[0090] (1) Position signal (servo motor output);

[0091] Source:

[0092] Real-time generated by the rotary encoder of the servo motor 11, containing two types of signals:

[0093] A / B phase pulse: Determine the motor rotation angle and direction through pulse counting and phase difference.

[0094] Z-phase zero signal: Mark the mechanical origin of the motor (such as the position of θ=0°).

[0095] Purpose:

[0096] External trigger signal: The motor controller 14 converts the encoder pulse into a fixed angle interval trigger pulse (such as one pulse every 2°), sends it to the data acquisition card 15 and the lock-in amplifier 16, and synchronously starts data acquisition.

[0097] Angle synchronization signal: Real-time feedback of the current angle value (transmitted to the computer through RS-485 / EtherCAT), used to bind the scattering data with the angle position.

[0098] (2) Scattering laser signal:

[0099] Source:

[0100] PM detector (dynamic detection tube): Receive the scattered light of the moving target 7, output an electrical signal containing modulation frequency ω (including DCd, aS, bC components).

[0101] PM monitor (static monitoring tube): Detect the direct intensity of incident laser (DCm) for normalization.

[0102] Purpose:

[0103] DCd (dynamic DC signal): Reflects the total intensity of the scattered light, which needs to be normalized with DCm.

[0104] aS / bC (AC quadrature component): extracted by the phase-locked amplifier, used to calculate the non-diagonal elements of the Mueller matrix.

[0105] According to Figure 1 The workflow of the system is as follows:

[0106] Step 1: After power-on, the device components are adjusted to a good state, the power supply supplies power to each system module and component, the laser is first turned on for preheating, and the device state is continuously queried during the process, and the system preheating is waited to end;

[0107] Step 2: The computer sends a command to the phase-locked amplifier to start the electro-optical modulator to modulate the laser emitted by the laser, and waits for the modulation signal to be stable;

[0108] Step 3: The computer sends a command to the motor, and the motor starts to rotate, and the data acquisition card and the phase-locked amplifier start to wait for a trigger signal, and when the external trigger sampling clock signal is detected at the same time, the detector starts signal acquisition, at this time, the angle synchronization signal needs to be known to the computer at the same time, so that the computer can complete the data acquisition of each angle interval, and the DCm, DCd, aS and bC data can be matched with the angle, and the extraction of the signals required during the period is completed by the phase-locked and related circuits;

[0109] Step 4: In the single-cycle mode: after a cycle is completed, the acquisition is stopped and the computer is waited for further commands;

[0110] Step 5: After the state of the related device is changed, the next time is carried out, and the test is continued.

[0111] The second aspect of the present application discloses a kind of experimental determination methods of moving target laser scattering matrix, the method is realized by the moving target laser scattering matrix experimental determination system of any one described above, the method includes:

[0112] S1, the laser emitted by the laser passes through polarization modulation module and is polarized modulated, and the control calculator controls frequency modulation module to modulate the laser after polarization modulation by phase-locked amplifier, to form modulated polarized laser, and irradiate on moving target;

[0113] S2, control calculator controls servo module to start rotating, to drive dynamic detector on the circumference with moving target as center and with preset length as radius by servo module, and rotate in the angle range of 5 ° to 175 ° with the propagation direction of modulated polarized laser, to make dynamic detector receive the first direct current signal and AC signal of the scattered light of moving target;

[0114] S3, the second direct current signal of modulated polarized laser is fixedly received by static detector;

[0115] S4, after the control calculator controls the servo module to start rotating, the servo module generates an angle trigger signal and an angle synchronization signal; the generated angle trigger signal is sent to the phase-locked amplifier and the data collector; the generated angle synchronization signal is sent to the control calculator;

[0116] Optionally, in step S4, the angle trigger signal is generated by the servo module at every preset angle interval, and the trigger interval is 0.1° to 5°.

[0117] S5, after the data collector receives the angle trigger signal, the second direct current signal and the first direct current signal are synchronously collected;

[0118] S6, after the phase-locked amplifier receives the angle trigger signal, according to the reference signal provided by the frequency modulation module, the sine component amplitude aS and the cosine component amplitude bC of the alternating current signal in the dynamic detector are extracted;

[0119] Optionally, in step S6, the phase-locked amplifier demodulates the alternating current signal using the reference signal with a reference frequency of ω, and the sine component amplitude aS and the cosine component amplitude bC; wherein the reference frequency is consistent with the modulation frequency of the frequency modulation module.

[0120] S7, the control calculator realizes data collection in each angle interval according to the angle synchronization signal, and then completes data normalization and Mueller matrix inversion; in each angle interval, the control calculator receives the second direct current signal and the first direct current signal sent by the data collector, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the phase-locked amplifier.

[0121] Optionally, in step S7, the data normalization is:

[0122] The first direct current signal, the sine component amplitude aS and the cosine component amplitude bC are respectively divided by the second direct current signal to eliminate the fluctuation of laser intensity;

[0123] The Mueller matrix inversion is:

[0124] Based on the normalized data and the multi-angle linear equation set, the scattering matrix elements under each angle θ are solved by the least square method, and the Mueller matrix inversion is completed.

[0125] In the moving target laser scattering matrix measurement system, the computer gradually calculates the multi-angle and multi-wavelength Mueller matrix (scattering matrix) by combining the static monitoring signal (DCm), the dynamic scattering signal (DCd), the quadrature components (aS, bC) of the phase-locked amplifier, and the angle synchronization signal. The following is the specific data processing flow and algorithm implementation:

[0126] 1. Data preprocessing and normalization;

[0127] (1) Eliminate the fluctuation of laser intensity:

[0128] Normalized dynamic signal:

[0129] The static monitoring signal (DCm) reflects the real-time power fluctuation of the laser, and the dynamic scattering signal (DCd) needs to be divided by DCm to eliminate the instability of the light source:

[0130]

[0131] Inorm(θ) is the normalized dynamic signal. This step ensures that the data at different angles and wavelengths are comparable.

[0132] (2) Extract the modulation signal component:

[0133] The quadrature components aS and bC output by the lock-in amplifier have suppressed noise, but still need to be normalized:

[0134] ,

[0135] where the subscript norm represents normalization. These components carry polarization modulation information and are used to solve the non-diagonal elements of the Mueller matrix.

[0136] 2. Multi-angle scattering matrix calculation;

[0137] (1) Construct a linear equation set:

[0138] The Mueller matrix S(θ) is a 4×4 matrix that describes the scattering characteristics of the target at angle θ. By changing the state of the polarizer and the analyzer (such as rotating the wave plate angle), multiple equations can be established:

[0139]

[0140] where:

[0141] A is the known coefficient matrix, determined by the Mueller matrix of the optical device (polarizer, wave plate, etc.) and the modulation state.

[0142] N is the number of measurement angles (such as 5°–175°, with an interval of 2°, a total of 86 angles).

[0143] (2) Least squares solution:

[0144] Since the number of equations (4N) is usually much larger than the 16 unknown elements of the Mueller matrix, the least squares method is used for fitting:

[0145] This step is independently calculated for each angle θ, resulting in a complete angle-resolved Mueller matrix S(θ).

[0146] Optionally, the method further comprises:

[0147] Switch the laser wavelength by the filter wheel, and repeat steps S1-S7 to obtain the wavelength-dependent scattering matrix.

[0148] The multi-wavelength scattering matrix measurement includes:

[0149] (1) Switch the wavelength by the filter wheel;

[0150] The filter wheel (2) selects laser of different wavelengths (such as = 532 nm, = 1064 nm), and the above measurement process is repeated.

[0151] For each wavelength λ, DCm(λ), DCd(θ, λ), aS(θ, λ), and bC(θ, λ) are independently collected.

[0152] (2) Wavelength-dependent data processing;

[0153] For each wavelength λ, the normalized signal is calculated and S(θ, λ) is solved.

[0154] Finally, a three-dimensional data body S(θ, λ) (angle x wavelength x 16 matrix elements) is obtained.

[0155] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A system for experimentally determining the laser scattering matrix of a moving target, characterized in that, The system includes: a laser, a polarization modulation module, a frequency modulation module, a servo module, a dynamic detector, a static detector, a lock-in amplifier, a data acquisition unit, and a control calculator; wherein: The laser emitted by the laser undergoes polarization modulation by the polarization modulation module and frequency modulation by the frequency modulation module to form a modulated polarized laser, which then illuminates the moving target. The servo module drives the dynamic detector to rotate within an angle range of 5° to 175° with respect to the propagation direction of the modulated polarized laser on a circle with the moving target as the center and a preset length as the radius. The dynamic detector is used to receive the first DC signal and AC signal of the scattered light from the moving target. A static detector is positioned at a fixed location to receive the second DC signal of the modulated polarized laser. The control calculator controls the frequency modulation module to modulate the frequency of the polarization-modulated laser through a lock-in amplifier. After the control calculator starts controlling the servo module to start rotating, the servo module generates an angle trigger signal and an angle synchronization signal. The generated angle trigger signal is sent to the lock-in amplifier and the data acquisition unit. The generated angle synchronization signal is sent to the control calculator. After receiving the angle trigger signal, the data acquisition unit simultaneously acquires the second DC signal and the first DC signal; After receiving the angle trigger signal, the lock-in amplifier extracts the sine component amplitude aS and cosine component amplitude bC of the AC signal in the dynamic detector based on the reference signal provided by the frequency modulation module. The control calculator acquires data in each angle interval according to the angle synchronization signal, and then completes data normalization and Mueller matrix inversion. In each angle interval, the control calculator receives the second DC signal and the first DC signal sent by the data acquisition unit, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the lock-in amplifier.

2. The system according to claim 1, characterized in that, The dynamic detector is an integrated unit consisting of a photomultiplier tube, a quarter-wave plate, and an analyzer; the static detector is a photomultiplier tube.

3. The system according to claim 2, characterized in that, The polarization modulation module is a polarizer; the control calculator solves the scattering matrix elements at each angle using the least squares method based on the normalized data and the multi-angle linear equation system to complete the Mueller matrix inversion; the coefficient matrix of the multi-angle linear equation system is constructed from the Mueller matrices of the polarizer, analyzer and quarter-wave plate.

4. The system according to claim 1, characterized in that, The frequency modulation module includes an electro-optic modulator and a signal generator; wherein: When the laser passes through the electro-optic modulator, the controller uses a lock-in amplifier to control the signal generator to generate a driving voltage, which drives the electro-optic modulator to generate modulated light with a modulation frequency of ω, thus forming a modulated polarized laser.

5. The system according to claim 1, characterized in that, The system further includes: a filter wheel; wherein: The filter wheel is positioned between the laser and the polarization modulation module to switch the laser wavelength.

6. A method for experimentally determining the laser scattering matrix of a moving target, characterized in that, The method is implemented using the experimental measurement system for the laser scattering matrix of a moving target as described in any one of claims 1-5, and the method includes: S1, the laser emitted by the laser is polarized by the polarization modulation module, and the controller controls the frequency modulation module through the lock-in amplifier to modulate the frequency of the polarization-modulated laser to form a modulated polarized laser, which is then irradiated onto the moving target. S2, the controller controls the servo module to start rotating, so that the servo module drives the dynamic detector to rotate within an angle range of 5° to 175° with respect to the propagation direction of the modulated polarized laser on a circle with the moving target as the center and a preset length as the radius, so that the dynamic detector receives the first DC signal and AC signal of the scattered light of the moving target. S3 receives the second DC signal of the modulated polarized laser through a static detector; S4, after the control calculator starts controlling the servo module to start rotating, the servo module generates an angle trigger signal and an angle synchronization signal; the generated angle trigger signal is sent to the lock-in amplifier and the data acquisition unit; the generated angle synchronization signal is sent to the control calculator. S5, after the data acquisition unit receives the angle trigger signal, it simultaneously acquires the second DC signal and the first DC signal; S6, after receiving the angle trigger signal, the lock-in amplifier extracts the sine component amplitude aS and cosine component amplitude bC of the AC signal in the dynamic detector according to the reference signal provided by the frequency modulation module. S7 controls the calculator to acquire data in each angle interval according to the angle synchronization signal, and then completes data normalization and Mueller matrix inversion; in each angle interval, the calculator receives the second DC signal and the first DC signal sent by the data acquisition unit, and also receives the sine component amplitude aS and the cosine component amplitude bC sent by the lock-in amplifier.

7. The method according to claim 6, characterized in that, In step S4, the angle trigger signal is generated by the servo module at each preset angle interval, with the trigger interval being 0.1° to 5°.

8. The method according to claim 6, characterized in that, In step S6, the lock-in amplifier uses a reference signal with a reference frequency of ω to demodulate the AC signal, with the sine component amplitude aS and the cosine component amplitude bC; wherein the reference frequency is consistent with the modulation frequency of the frequency modulation module.

9. The method according to claim 6, characterized in that, In step S7: Data normalization is achieved by dividing the first DC signal, the amplitude of the sine component aS, and the amplitude of the cosine component bC by the second DC signal, respectively, to eliminate laser intensity fluctuations. The Mueller matrix inversion is performed by solving the scattering matrix elements at each angle using the least squares method based on the normalized data and the multi-angle linear equations.

10. The method according to claim 6, characterized in that, The method further includes: By switching the laser wavelength using a filter wheel and repeating steps S1–S7, a wavelength-dependent scattering matrix can be obtained.

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