An underwater polarization ghost imaging method and device based on two-stage modulation

Abstract

The application discloses a two-stage modulation-based underwater polarization ghost imaging method and device, and relates to the fields of optical imaging and ocean detection. The method comprises the following steps: acquiring basic data of a target water area and constructing a backscattering point spread function; performing statistical decorrelation modulation on an original reference speckle sequence based on a first correlation coefficient, a second correlation coefficient and the backscattering point spread function, to obtain a primary modulation reference speckle distribution sequence; performing polarization space modulation on the primary modulation speckle sequence, to obtain a secondary modulation reference speckle distribution sequence; irradiating a target to be detected according to the secondary modulation reference speckle distribution sequence, acquiring a double-polarization bucket detection signal, and constructing a polarization difference signal sequence; and performing correlation reconstruction on the polarization difference signal sequence and the secondary modulation reference speckle distribution sequence, to obtain a reconstructed image. The application solves the problems of serious backscattering interference and insufficient imaging signal-to-noise ratio in a strong turbid underwater environment, and realizes high-quality underwater polarization ghost imaging.

Description

Technical Field

[0001] This application relates to the fields of optical imaging and marine exploration, and in particular to an underwater polarization ghost imaging method and apparatus based on two-level modulation. Background Technology

[0002] Underwater optical imaging technology plays an irreplaceable role in marine resource exploration, underwater archaeology, and environmental monitoring. However, due to the strong absorption and scattering of light by suspended particles, plankton, and water molecules in the water, especially the interference of backscattered light, the target reflection signal is submerged by strong background noise, severely limiting the detection range and imaging quality of traditional underwater imaging systems in turbid water. Related technologies mainly focus on the following directions: First, range-gated imaging technology, which filters out most of the backscattered light through time gating, but it requires extremely high synchronization control precision and is difficult to handle multiple scattering components; second, polarization imaging technology, which uses the difference in polarization characteristics between the target reflected light and the background scattered light to achieve separation; and third, ghost imaging technology, which achieves non-local imaging through correlation detection.

[0003] However, the aforementioned technologies still have significant shortcomings in practical applications. On the one hand, in underwater environments with strong scattering and high turbidity, multiple scattering of photons severely disrupts the polarization state of light, rendering the traditional polarization descattering method's assumption of "significant differences in the polarization states of the target light and the scattered light" invalid, leading to a sharp decline in the effectiveness of polarization imaging methods. On the other hand, underwater ghost imaging methods in these technologies typically use fixed or random speckle patterns to directly illuminate the target, failing to fully consider the statistical correlation between the speckle pattern itself and the backscattering noise of the water. Under strong background interference, the proportion of effective target information in the signal collected by the bucket detector is too low, resulting in insufficient signal-to-noise ratio in the reconstructed image, making it difficult to meet the needs of practical applications. Furthermore, these methods often simplify the polarization characteristics of the target itself to a constant value or ignore them directly, failing to flexibly and accurately separate the target signal from background scattering in complex underwater environments, and lacking an effective means to synergistically suppress backscattering from both the dimensions of "statistical correlation" and "spatial polarization distribution."

[0004] Therefore, there is an urgent need for an underwater polarization ghost imaging method based on two-level modulation that can effectively suppress water backscattering, extract target polarization information, and maintain high-quality imaging performance even in highly turbid environments. Summary of the Invention

[0005] The purpose of this application is to provide an underwater polarization ghost imaging method and device based on two-level modulation. It can use a two-level modulation architecture composed of statistical decorrelation modulation and polarization spatial modulation to synergistically suppress backscattering from two dimensions: statistical correlation and spatial polarization distribution. This solves the problems of severe backscattering interference, difficulty in target signal extraction, and poor imaging quality in correlation underwater imaging technology in strong scattering and high turbidity environments.

[0006] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides an underwater polarization ghost imaging method based on two-level modulation, comprising: Acquire basic data of the target water area and construct a backscattering point spread function; the basic data includes the background total barrel detection signal sequence under the condition of no target to be measured, the target total barrel detection signal sequence under the condition of the target to be measured, and the original reference speckle sequence used for the N irradiations, obtained from the target water area N times. Based on the aforementioned basic data, the backscattering noise sequence and the effective signal sequence of the target under test are determined, and the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test are calculated. Based on the first correlation coefficient, the second correlation coefficient, and the backscattering point diffusion function, the original reference speckle sequence is statistically decorrelated and modulated to obtain a first-modulated reference speckle distribution sequence. Based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, the polarization confidence map sequence is calculated, and based on the primary modulation reference speckle distribution sequence and the backscattering point diffusion function, the background prediction map sequence is calculated. The primary modulation reference speckle distribution sequence is polarized spatially modulated based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence to obtain the secondary modulation reference speckle distribution sequence. The target in the target water area is irradiated N times according to the secondary modulation reference speckle distribution sequence, and the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel are obtained for each irradiation. Based on the barrel detection signal from the parallel polarization channel and the barrel detection signal from the vertical polarization channel for each illumination, a polarization differential barrel detection signal sequence is obtained. By correlating and reconstructing the polarization differential barrel detection signal sequence with the secondary modulation reference speckle distribution sequence, a reconstructed image of the target in the target water area is obtained, realizing underwater polarization ghost imaging.

[0007] Secondly, this application provides an underwater polarization ghost imaging device based on two-level modulation, comprising: an optical emission and polarization guidance unit, a two-level modulation unit, a reference polarization measurement unit, a signal receiving unit, and a signal processing unit; The signal processing unit is connected to the two-stage modulation unit, the reference polarization measurement unit, and the signal receiving unit, respectively; the two-stage modulation unit is also connected to the optical emission and polarization guidance unit and the reference polarization measurement unit, respectively. The optical emission and polarization guiding unit is used to generate an illumination beam; The signal receiving unit is used to acquire the background barrel detection signal sequence of the target water area under the condition of no target and the target barrel detection signal sequence under the condition of target, and send the acquired background barrel detection signal sequence and target barrel detection signal sequence to the signal processing unit; simultaneously acquire the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel generated by the secondary modulated reference speckle distribution sequence illuminating the target, and send the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel to the signal processing unit; The signal processing unit generates an original reference speckle sequence and uses the original reference speckle sequence, the received background barrel detection signal sequence, and the target barrel detection signal sequence as basic data. Based on the basic data, it determines the backscattered noise sequence and the effective signal sequence of the target, calculates the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence, and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target. According to the first correlation coefficient, the second correlation coefficient, and the backscattered point spread function, it performs statistical decorrelation modulation on the original reference speckle sequence to obtain a first-modulated reference speckle distribution sequence, and controls two-stage modulation units to form the first-modulated reference speckle distribution sequence. Based on the equivalent response of the received first-modulated reference speckle distribution sequence under orthogonal polarization, it... The system calculates a polarization confidence map sequence based on the distribution, and calculates a background prediction map sequence based on the primary modulation reference speckle distribution sequence and the backscattering point spread function. It then calculates a secondary modulation function based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence, and performs polarization spatial modulation on the primary modulation reference speckle distribution sequence based on the secondary modulation function to obtain a secondary modulation reference speckle distribution sequence. Two-stage modulation units are then controlled to form the secondary modulation reference speckle distribution sequence. Finally, a polarization differential barrel detection signal sequence is obtained based on the received barrel detection signals from the parallel polarization channel and the vertical polarization channel. This sequence is then correlated with the secondary modulation reference speckle distribution sequence to reconstruct the image of the target in the target water area.

[0008] The two-stage modulation unit is used, under the control of the signal processing unit, to perform a first-stage statistical decorrelation modulation on the illumination beam output by the optical emission and polarization guidance unit to form a primary modulation reference speckle distribution sequence, and guide the primary modulation reference speckle distribution sequence to the reference polarization measurement unit; and to perform a second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence to form a secondary modulation reference speckle distribution sequence, and project the secondary modulation reference speckle distribution sequence as a light field onto the target in the target water area.

[0009] The reference polarization measurement unit is used to receive the primary modulation reference speckle distribution sequence sent by the two-stage modulation unit, obtain the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization state, and send it to the signal processing unit.

[0010] Thirdly, this application provides a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the underwater polarization ghost imaging method based on two-level modulation as described above.

[0011] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the underwater polarization ghost imaging method based on two-level modulation as described above.

[0012] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides an underwater polarization ghost imaging method and apparatus based on two-level modulation. By acquiring basic data of the target water area and constructing a backscattering point spread function, it solves the problem of lacking characterization of water scattering characteristics, realizing a quantitative description of the underwater backscattering process and providing a model foundation for subsequent decorrelation correction. By determining the backscattering noise sequence and the effective signal sequence of the target based on the basic data, and calculating the first and second correlation coefficients, it solves the problem of being unable to quantify the statistical relationship between the reference speckle pattern and noise / signal, achieving accurate characterization of the correlation between the speckle pattern and background noise. By statistically decorrelating the original reference speckle sequence based on the first and second correlation coefficients and the backscattering point spread function, a first-modulated reference speckle distribution sequence is obtained, solving the problem of indiscriminate correlation between the speckle pattern and backscattering noise, realizing that the reference speckle actively avoids the backscattering noise component in a statistical sense, fundamentally reducing the interference of background noise on correlation reconstruction. By calculating the polarization confidence map sequence based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, and calculating the background prediction map sequence based on the primary modulation reference speckle distribution sequence and the backscattering point diffusion function, the problem of being unable to identify target polarization information and background scattering intensity in the spatial domain is solved, achieving accurate positioning of the effective polarization information region of the target and the strong background scattering region. By performing polarization spatial modulation on the primary modulation reference speckle distribution sequence according to the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence, a secondary modulation reference speckle distribution sequence is obtained. This solves the problem of being unable to flexibly separate the target signal from background scattering in the spatial polarization dimension, achieving further enhancement of the effective polarization information of the target and suppression of residual background scattering in the spatial domain on the basis of decorrelation and noise suppression. By illuminating the target according to the secondary modulation reference speckle distribution sequence, barrel detection signals of the parallel polarization channel and the vertical polarization channel are obtained, and a polarization differential barrel detection signal sequence is constructed. This solves the problems of insufficient utilization of polarization information and large timing errors, achieving parallel acquisition and differential processing of dual polarization channels, and effectively extracting the target polarization features. By reconstructing the target image based on the correlation between the polarization difference barrel detection signal sequence and the secondary modulation reference speckle distribution sequence, the problem of insufficient signal-to-noise ratio in the correlation reconstruction method is solved, and high-quality polarization ghost imaging is achieved in a highly turbid underwater environment. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a flowchart illustrating an underwater polarization ghost imaging method based on two-level modulation, provided as an embodiment of this application.

[0015] Figure 2 This is a schematic diagram of the functional modules of an underwater polarization ghost imaging device based on two-level modulation, provided in an embodiment of this application.

[0016] Figure 3 This is a schematic diagram of the structure of a computer device provided in an embodiment of this application.

[0017] Reference numerals: 1-Optical emission and polarization guidance unit; 2-Two-stage modulation unit; 3-Reference polarization measurement unit; 4-Signal receiving unit; 5-Signal processing unit; 6-Laser; 7-Beam expander and collimator assembly; 8-Polarizer; 9-Polarization adjustment unit; 10-First spatial light modulator; 11-4f relay system; 12-Beam splitter; 13-Polarization-type transmission spatial light modulator; 14-Analyzer; 15-Projection lens; 16-First polarization beam splitter; 17-First charge-coupled device; 18-Second charge-coupled device; 19-Second polarization beam splitter; 20-First converging lens; 21-First barrel detector; 22-Second converging lens; 23-Second barrel detector; 24-Oscilloscope; 25-Data acquisition card; 26-Control processing unit. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] In one exemplary embodiment, such as Figure 1 As shown, an underwater polarization ghost imaging method based on two-level modulation is provided. This method is executed by a computer device, specifically by a terminal or server alone, or by both a terminal and a server. In this embodiment, it includes the following steps 101 to 108. Wherein: Step 101: Obtain basic data of the target water area and construct the backscattering point diffusion function; the basic data includes the background total barrel detection signal sequence under the condition of no target to be measured, the target total barrel detection signal sequence under the condition of the target to be measured, and the original reference speckle sequence used for the N irradiations, obtained from the target water area N times.

[0021] Step 102: Based on the basic data, determine the backscattering noise sequence and the effective signal sequence of the target under test, and calculate the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test.

[0022] Step 103: Statistical decorrelation modulation is performed on the original reference speckle sequence based on the first correlation coefficient, the second correlation coefficient, and the backscattering point diffusion function to obtain a first-modulated reference speckle distribution sequence.

[0023] Step 104: Based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, calculate the polarization confidence map sequence, and based on the primary modulation reference speckle distribution sequence and the backscattering point diffusion function, calculate the background prediction map sequence.

[0024] Step 105: Based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence, the primary modulation reference speckle distribution sequence is polarized spatially modulated to obtain the secondary modulation reference speckle distribution sequence.

[0025] Step 106: Irradiate the target in the target water area N times according to the secondary modulation reference speckle distribution sequence, and acquire the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel for each irradiation.

[0026] Step 107: Based on the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel for each illumination, a polarization differential barrel detection signal sequence is obtained.

[0027] Step 108: Based on the polarization differential barrel detection signal sequence and the secondary modulation reference speckle distribution sequence, a correlation reconstruction is performed to obtain a reconstructed image of the target in the target water area, thereby realizing underwater polarization ghost imaging.

[0028] By implementing steps 101 to 108 above, this application enables the reference speckle to actively avoid backscattering noise components in a statistical sense through the first decorrelation correction, thereby reducing the interference of background noise on correlation reconstruction from the source. Through the second polarization co-modulation, the effective polarization information of the target is further enhanced and residual background scattering is suppressed in the spatial domain by using the dual guidance of polarization confidence map and background prediction map. This achieves the synergistic optimization of statistical decorrelation and spatial polarization guidance, and significantly improves the imaging quality in highly turbid water bodies.

[0029] In another exemplary embodiment of this application, the backscattering point diffusion function is: .

[0030] in, Representing the plane of the object The backscattering point diffusion function at the point, the object plane refers to the plane where the target is located, that is, the plane on which the speckle pattern is projected and reflected by the target; This represents the Euclidean distance from the light source to the point of illumination on the object plane; Indicates the total attenuation coefficient; Indicates the empirical damping factor; The anisotropy factor of the Henyey-Greenstein phase function is represented; Indicates the water body decay term; Represents pi; The normalization factor represents the integral weight of the backscattering angle distribution; Indicates the scattering angle; Indicates the inverse Fourier transform; Indicates radial frequency; This represents the frequency domain attenuation term.

[0031] In another exemplary embodiment of this application, step 102 specifically includes: The background barrel detection signal sequence in the basic data is used as the backscattering noise sequence.

[0032] Subtract the target total barrel detection signals from the target total barrel detection signal sequence in the basic data and the corresponding background total barrel detection signals in the background total barrel detection signal sequence to obtain the effective signal sequence of the target to be tested.

[0033] The first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence, and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test are calculated using the following formulas: .

[0034] .

[0035] in, This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background barrel detection signal corresponding to the nth irradiation in the backscattered noise sequence; N represents the total number of irradiations. This represents the total light intensity scalar of the original reference speckle distribution corresponding to the nth illumination in the original reference speckle sequence. This represents the mean of the total light intensity scalar of the original reference speckle distribution corresponding to all illuminations in the original reference speckle sequence; This represents the mean of the background barrel detection signal corresponding to all illuminations in the backscattering noise sequence; Let represent the first, second, third, and fourth minimum regularization constants, respectively; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the mean of the effective signals of the target under test corresponding to all irradiations in the effective signal sequence of the target under test.

[0036] In another exemplary embodiment of this application, step 103 specifically includes: Based on the first and second correlation coefficients, the first decorrelation correction weights are calculated using the following formula: ; in, This indicates the first-order decorrelation correction weight; This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the fifth minimum regularization constant.

[0037] Based on the first-order decorrelation correction weights and the backscattering point spread function, the original reference speckle sequence is statistically decorrelated and modulated using the following formula to obtain the first-order modulated reference speckle distribution sequence: ; in, In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; This indicates that the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence is located on the object plane. The light intensity at that location; Indicates the global correction intensity coefficient; Representing the plane of the object Backscattering point diffusion function at the location; Represents a two-dimensional convolution operation; This represents the background scattering degradation term.

[0038] In another exemplary embodiment of this application, step 104 specifically includes: The polarization confidence map sequence is calculated using the following formula: ; in, This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; In a first-modulation reference speckle distribution sequence, the first... The primary modulation reference speckle distribution corresponding to the second irradiation, under parallel polarization analysis, on the object plane. The light intensity at that location; In a first-modulation reference speckle distribution sequence, the first... The first modulation reference speckle distribution corresponding to the second irradiation is analyzed under vertical polarization conditions on the object plane. The light intensity at that location; This represents the sixth minimum regularization constant.

[0039] The background prediction map sequence is calculated using the following formula: ; in, This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. Normalized light intensity at the location; Representing the plane of the object Backscattering point diffusion function at the location; In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; Represents a two-dimensional convolution operation; [ [Indicates taking the entire object plane] The maximum value; This represents the seventh minimum regularization constant.

[0040] In another exemplary embodiment of this application, step 105 specifically includes: The measurement quality factor sequence is calculated using the following formula based on the first and second correlation coefficients: ; in, Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; Represents a monotonic compression function; , , These represent the first weighting coefficient, the second weighting coefficient, and the third weighting coefficient, respectively. This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background total barrel detection signal corresponding to the nth illumination in the backscattering noise sequence; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the first [number] target in the total barrel detection signal sequence under the condition of having a target to be measured. Illuminate the corresponding target barrel detection signal; This represents the eighth minimum regularization constant.

[0041] The second-order modulation function is calculated using the following formula based on the measurement quality factor sequence, polarization confidence map sequence, and background prediction map sequence: ; in, Representing the plane of the object The second modulation function at the location; Indicates the polarization enhancement coefficient; Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; Indicates the background suppression coefficient; This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. Normalized light intensity at the location.

[0042] Based on the secondary modulation function, the polarization space modulation of the primary modulation reference speckle distribution sequence is performed, and the secondary modulation reference speckle distribution sequence is calculated using the following formula: ; In the formula, Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location.

[0043] In another exemplary embodiment of this application, step 108 specifically includes: The reconstructed image of the target in the target water area is obtained using the following formula: ; in, This represents the reconstructed image of the target in the target water area on the object plane. The pixel value at that location; N represents the total number of illuminations; This represents the polarization differential barrel detection signal corresponding to the nth illumination in the polarization differential barrel detection signal sequence; This represents the mean value of the polarization differential barrel detection signal corresponding to all illuminations in the polarization differential barrel detection signal sequence; Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; This indicates that the secondary modulation reference speckle distribution corresponding to all irradiations in the secondary modulation reference speckle distribution sequence is located on the object plane. The average light intensity at that location.

[0044] The following example illustrates this application using a specific underwater polarization ghost imaging process based on two-level modulation.

[0045] In one exemplary embodiment, an underwater polarization ghost imaging method based on two-level modulation is provided. First, in this embodiment, a 532nm wavelength laser is used as the illumination source (illumination beam). The illumination laser, after beam expansion and collimation, is incident on a first spatial light modulator (DMD, Digital Micromirror Device). The DMD is loaded with a pre-designed random speckle pattern to achieve amplitude modulation of the incident beam. Let the amplitude distribution of the collimated light field incident on the DMD surface be... , No. The original speckle sequence (pattern) loaded during the second irradiation was The optical field modulated by DMD can then be expressed as: (1).

[0046] In the formula, This represents the DMD plane during the nth irradiation. The complex amplitude distribution of the optical field after DMD modulation; Represents the spatial coordinates on the DMD plane; Indicates the first DMD plane during secondary irradiation The original speckle sequence loaded at that location.

[0047] The ideal reference speckle distribution of the nth element in the original reference speckle sequence on the object plane is calculated using the Fresnel diffraction formula for the nth irradiation. Let the equivalent propagation distance from the DMD to the target water surface be... , wavelength is Then we have: (2).

[0048] (3).

[0049] In the formula, Wave number; Indicates the first During the second irradiation, the original reference speckle propagates to the target plane (object plane). Complex amplitude distribution at the location; This indicates that the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence is located on the object plane. The light intensity at that point is the ideal reference speckle.

[0050] Since background scattering in turbid water can cause significant background noise to be received by the bucket detector, this embodiment uses an ideal reference speckle pattern. Based on this, a backscattering point diffusion function and a first decorrelation correction weight are introduced to first complete a statistical decorrelation modulation, and then polarization spatial modulation is completed based on the polarization confidence map sequence, the background prediction map sequence and the measurement quality factor, so as to obtain the second modulation reference speckle distribution sequence of the target to be measured for illuminating the target water area.

[0051] The following is a detailed explanation of steps S1 to S8.

[0052] Step S1: Obtain the background barrel detection signal sequence under the condition of no target to be measured, the target barrel detection signal sequence under the condition of target to be measured, and the original reference speckle sequence, and establish the backscattering point diffusion function expression based on the water scattering parameters.

[0053] This step is used to obtain the basic input quantities required for subsequent statistical decorrelation modulation and secondary polarization spatial modulation, including the original reference speckle sequence, the background barrel detection signal sequence, the target barrel detection signal sequence, and the backscattering point spread function.

[0054] In the absence of a target, the original reference speckle sequence consistent with the subsequent formal imaging is used. The background water area of ​​the target water body is illuminated frame by frame, and the background barrel detection signal of the parallel polarization channel corresponding to the nth illumination is recorded by the dual polarization barrel detection channel of the receiver. The background barrel detection signal of the vertical polarization channel corresponding to the nth illumination. And synthesized into the background barrel detection signal corresponding to the nth illumination in the background barrel detection signal sequence. : (4).

[0055] In the formula, This represents the background barrel detection signal (light intensity) measured by the parallel polarization channel corresponding to the nth illumination in the backscattered noise sequence (which is also the background barrel detection signal sequence). This represents the background barrel detection signal (light intensity) measured by the vertical polarization channel corresponding to the nth illumination in the backscattering noise sequence. This represents the background total barrel detection signal corresponding to the nth illumination in the backscattering noise sequence.

[0056] Under target conditions, the same set of original reference speckle sequences is used to illuminate the target area of ​​the target water body frame by frame. The target barrel detection signal of the parallel polarization channel corresponding to the nth illumination is recorded by the dual polarization barrel detection channel. The barrel detection signal and the vertical polarization channel corresponding to the nth illumination. The target barrel detection signals are combined into the target total barrel detection signal: (5).

[0057] In the formula, This represents the target barrel detection signal (light intensity) measured by the parallel polarization channel corresponding to the nth illumination in the target barrel detection signal sequence. This represents the target barrel detection signal (light intensity) measured by the vertical polarization channel corresponding to the nth illumination in the target barrel detection signal sequence. This represents the target barrel detection signal corresponding to the nth irradiation in the target barrel detection signal sequence.

[0058] Furthermore, the effective signal sequence of the target to be measured can be obtained from the target total barrel detection signal sequence and the background total barrel detection signal sequence: (6).

[0059] (7).

[0060] (8).

[0061] In the formula, This represents the effective signal component of the target measured by the parallel polarization channel corresponding to the nth irradiation in the effective signal sequence of the target; This represents the effective signal component of the target measured by the vertical polarization channel corresponding to the nth irradiation in the effective signal sequence of the target; This represents the effective signal of the target under test corresponding to the nth irradiation in the effective signal sequence of the target under test.

[0062] As an optional implementation, the backscattering point spread function Its expression can be written as: .

[0063] in, Indicates the empirical damping factor; This represents the Euclidean distance from the light source to the point of illumination on the object plane; , representing the total attenuation coefficient (unit: It consists of the absorption coefficient a and the scattering coefficient b; Represents radial frequency in cycles / radians; This represents the inverse Fourier transform. The phase function is expressed as: .

[0064] in, The anisotropy factor of the Henyey-Greenstein phase function is preferably satisfied with the backscattering dominance condition; The scattering angle is the angle between the scattering direction and the incident direction. .

[0065] In this case Representing the plane of the object The backscattering point diffusion function at that location is: .

[0066] object plane Backscattering point diffusion function at the location use The phase function represents, here, express Anisotropy factor of phase function, <0 indicates that backscattering is dominant; It is the normalization factor for the integral weight of the backscattering angle distribution, and its value depends on The following conditions must be met: .

[0067] Let be the azimuth angle, and the integral result is the normalized spherical solid angle.

[0068] S2: Based on the background total barrel detection signal sequence, the target total barrel detection signal sequence, and the original reference speckle sequence, determine the backscattering noise sequence and the effective signal sequence of the target to be measured, and calculate the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target to be measured.

[0069] This step is used to establish the statistical relationship between the original reference speckle and noise / signal, providing a basis for determining the subsequent decorrelation correction weights.

[0070] First, according to the formula Japanese style Obtain the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence. To facilitate statistical correlation analysis with the barrel detection signal sequence, each two-dimensional speckle pattern is converted into a total light intensity scalar, and a length equal to the total number of illuminations is constructed. One-dimensional speckle scalar sequence: (9).

[0071] In the formula, Indicates the target water area; This represents the total light intensity scalar of the original reference speckle distribution corresponding to the nth illumination in the original reference speckle sequence.

[0072] Further define the mean of each sequence: (10).

[0073] (11).

[0074] (12).

[0075] The first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence And the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test. The preferred method for calculation is to use the Pearson linear correlation coefficient based on ensemble averages. (13).

[0076] (14).

[0077] in, This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background barrel detection signal corresponding to the nth irradiation in the backscattered noise sequence; N represents the total number of irradiations. This represents the total light intensity scalar of the original reference speckle distribution corresponding to the nth illumination in the original reference speckle sequence. This represents the mean of the total light intensity scalar of the original reference speckle distribution corresponding to all illuminations in the original reference speckle sequence; This represents the mean of the background barrel detection signal corresponding to all illuminations in the backscattering noise sequence; These represent the first, second, third, and fourth minimum regularization constants, used to avoid zero denominators and ensure numerical stability. The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the mean of the effective signals of the target under test corresponding to all irradiations in the effective signal sequence of the target under test.

[0078] S3: Based on the first correlation coefficient between the original reference speckle sequence and the backscatter noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test, determine the first decorrelation correction weight; and based on the first decorrelation correction weight, the backscatter point spread function and the original reference speckle sequence, determine the first modulation reference speckle distribution sequence.

[0079] This step is used to determine the decorrelation correction weights based on the relative strength of noise correlation and signal correlation, and to complete the first speckle modulation.

[0080] As an optional implementation, one-time decorrelation correction weights The calculation formula can be expressed as: (15).

[0081] In the formula, This indicates the first-order decorrelation correction weight; This represents the fifth minimum regularization constant, used to avoid zero denominators and ensure numerical stability.

[0082] Based on this, the modulated reference speckle distribution after water backscattering degradation correction can be written as: (16).

[0083] in, In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; This indicates that the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence is located on the object plane. The light intensity at that location; Indicates the global correction intensity coefficient; Representing the plane of the object Backscattering point diffusion function at the location; Represents a two-dimensional convolution operation; This represents the background scattering degradation term predicted by the backscattering model.

[0084] S4: Based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under two orthogonal polarization analysis states, calculate the polarization confidence map sequence, and based on the primary modulation reference speckle distribution sequence and the backscattering point diffusion function, calculate the background prediction map sequence.

[0085] This step is used to further extract the effective spatial polarization information of the target and the distribution of strong background scattering regions from the primary modulation reference speckle, providing spatial guidance for secondary polarization spatial modulation.

[0086] As an optional implementation, after the first modulation reference speckle formation, the first modulation reference speckle distribution sequence is obtained through the reference polarization measurement branch. The primary modulation reference speckle distribution corresponding to the second irradiation, under parallel polarization analysis, on the object plane. Light intensity at the location ; Obtain the first modulated reference speckle distribution sequence The first modulation reference speckle distribution corresponding to the second irradiation is analyzed under vertical polarization conditions on the object plane. Light intensity at the location .

[0087] Based on the first modulation reference speckle distribution sequence, the first... The primary modulation reference speckle distribution corresponding to the second irradiation, under parallel polarization analysis, on the object plane. Light intensity at the location The first modulated reference speckle distribution sequence The first modulation reference speckle distribution corresponding to the second irradiation is analyzed under vertical polarization conditions on the object plane. Light intensity at the location Calculate the polarization confidence map sequence: (17).

[0088] in, This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; In a first-modulation reference speckle distribution sequence, the first... The primary modulation reference speckle distribution corresponding to the second irradiation, under parallel polarization analysis, on the object plane. The light intensity at that location; In a first-modulation reference speckle distribution sequence, the first... The first modulation reference speckle distribution corresponding to the second irradiation is analyzed under vertical polarization conditions on the object plane. The light intensity at that location; This represents the sixth minimum regularization constant, used to avoid zero denominators and ensure numerical stability.

[0089] At the same time, based on and Calculate the background prediction map sequence: (18).

[0090] in, This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. Normalized light intensity at the location; Representing the plane of the object Backscattering point diffusion function at the location; In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; Represents a two-dimensional convolution operation; [ [Indicates taking the entire object plane] The maximum value; This represents the seventh minimum regularization constant, used to avoid zero denominators and ensure numerical stability.

[0091] S5: Calculate the measurement quality factor sequence based on the first correlation coefficient of the background barrel detection signal sequence, the target barrel detection signal sequence, the original reference speckle sequence and the backscattering noise sequence, and the second correlation coefficient of the original reference speckle sequence and the effective signal sequence of the target under test; and determine the secondary modulation function based on the polarization confidence map sequence, the background prediction map sequence and the measurement quality factor sequence.

[0092] As an optional implementation method, the measurement quality factor sequence is calculated using the following formula: (19).

[0093] in, Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; Represents a monotonic compression function; , , These represent the first weighting coefficient, the second weighting coefficient, and the third weighting coefficient, respectively. This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background total barrel detection signal corresponding to the nth illumination in the backscattering noise sequence; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the first [number] target in the total barrel detection signal sequence under the condition of having a target to be measured. Illuminate the corresponding target barrel detection signal; This represents the eighth minimum regularization constant.

[0094] As an optional implementation, the secondary modulation function is calculated using the following formula based on the measurement quality factor sequence, polarization confidence map sequence, and background prediction map sequence: (20).

[0095] in, Representing the plane of the object The second modulation function at the location; Indicates the polarization enhancement coefficient; Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; Indicates the background suppression coefficient; This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. The normalized light intensity at that location. In this formula, Used to enhance the high polarization confidence region This is used to suppress high background prediction regions, thus enabling the second modulation to simultaneously enhance the effective information of the target and suppress background scattering.

[0096] S6: Based on the secondary modulation function and the primary modulation reference speckle distribution sequence, determine the secondary modulation reference speckle distribution sequence; and based on the secondary modulation reference speckle distribution sequence, illuminate the target under test to obtain the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel.

[0097] This step is used to construct a two-stage modulated reference speckle and to acquire a dual-polarization barrel detection signal under the illumination of this speckle.

[0098] As an optional implementation, the secondary modulation reference speckle distribution sequence is calculated using the following formula: (twenty one).

[0099] In the formula, Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location (secondary modulation reference speckle distribution).

[0100] For reflective targets, under illumination by a secondary modulated reference speckle distribution sequence, the barrel detection signal of the parallel polarization channel... Bucket detection signal of vertical polarization channel They can be represented as: (twenty two).

[0101] (twenty three).

[0102] In the formula, Representing the plane of the object The equivalent reflectivity distribution function under parallel polarization channel; Representing the plane of the object The equivalent reflectivity distribution function under the vertical polarization channel; Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location.

[0103] S7: Acquire dual-polarization barrel detection signals (barrel detection signals from the parallel polarization channel and the barrel detection signals from the vertical polarization channel) and construct polarization differential barrel detection signals.

[0104] This step is used to acquire the dual-polarization barrel detection signal of the target under illumination by a secondary modulated reference speckle distribution sequence, and to construct a polarization differential barrel detection signal sequence.

[0105] As an optional implementation, the polarization differential barrel detection signal sequence of the reflected laser from the target water area is calculated using the following formula: (twenty four).

[0106] In the formula, The polarization differential barrel detection signal corresponding to the nth irradiation in the polarization differential barrel detection signal sequence of the reflected laser from the target water area; The channel balance coefficient can be obtained during the target-free background measurement phase; where, This represents the average value of the background total barrel detection signal in the parallel polarization channel corresponding to the nth illumination in the backscattering noise sequence; This represents the average value of the background total barrel detection signal in the vertical polarization channel corresponding to the nth illumination in the backscattering noise sequence.

[0107] S8: Determine the reconstructed image of the target in the target water area based on the polarization differential barrel detection signal sequence and the secondary modulation reference speckle distribution sequence.

[0108] As an optional implementation, the mean value of the polarization differential barrel detection signal corresponding to all irradiations in the polarization differential barrel detection signal sequence and the mean value of the secondary modulation reference speckle distribution corresponding to all irradiations in the secondary modulation reference speckle distribution sequence on the object plane are calculated using the following formulas. The average light intensity at that location: (25).

[0109] (26).

[0110] In this implementation method, the reconstructed image of the target in the target water area is obtained using the following formula: (27).

[0111] in, This represents the reconstructed image of the target in the target water area on the object plane. The pixel value at that location.

[0112] In this embodiment, the first decorrelation modulation aims to minimize the strong correlation between the reference speckle and backscattering noise, while the second polarization-coordinated modulation aims to further bias the reference speckle towards the effective target information on the basis of decorrelation noise suppression. The two work together to achieve high-quality polarization ghost imaging in underwater strong scattering environments.

[0113] Based on the same inventive concept, this application also provides an underwater polarization ghost imaging device based on two-level modulation for implementing the underwater polarization ghost imaging method based on two-level modulation described above. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of the underwater polarization ghost imaging device based on two-level modulation provided below can be found in the limitations of the underwater polarization ghost imaging method based on two-level modulation above, and will not be repeated here.

[0114] In one exemplary embodiment, such as Figure 2As shown, an underwater polarization ghost imaging device based on two-stage modulation is provided, comprising: an optical emission and polarization guidance unit 1, a two-stage modulation unit 2, a reference polarization measurement unit 3, a signal receiving unit 4, and a signal processing unit 5.

[0115] The signal processing unit 5 is connected to the two-stage modulation unit 2, the reference polarization measurement unit 3, and the signal receiving unit 4, respectively; the two-stage modulation unit 2 is also connected to the optical emission and polarization guidance unit 1 and the reference polarization measurement unit 3, respectively.

[0116] The optical emission and polarization guiding unit 1 is used to generate an illumination beam.

[0117] The signal receiving unit 4 is used to acquire the background barrel detection signal sequence under the condition of no target and the target barrel detection signal sequence under the condition of target, and send the acquired background barrel detection signal sequence and target barrel detection signal sequence to the signal processing unit 5; simultaneously acquire the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel generated by the secondary modulated reference speckle distribution sequence illuminating the target, and send the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel to the signal processing unit 5.

[0118] The signal processing unit 5 is used to generate an original reference speckle sequence, and uses the original reference speckle sequence, the received background barrel detection signal sequence, and the target barrel detection signal sequence as basic data; based on the basic data, it determines the backscattering noise sequence and the effective signal sequence of the target to be tested, and calculates the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence, and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target to be tested; according to the first correlation coefficient, the second correlation coefficient, and the backscattering point spread function, it performs statistical decorrelation modulation on the original reference speckle sequence to obtain a first-modulation reference speckle distribution sequence, and controls the two-stage modulation unit to form the first-modulation reference speckle distribution sequence; according to the equivalent response of the received first-modulation reference speckle distribution sequence in the orthogonal polarization state... The system calculates a polarization confidence map sequence and a background prediction map sequence based on a primary modulation reference speckle distribution sequence and a backscattering point diffusion function. It then calculates a secondary modulation function based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence. The system then performs polarization spatial modulation on the primary modulation reference speckle distribution sequence using the secondary modulation function to obtain a secondary modulation reference speckle distribution sequence, and controls two-stage modulation units to form this secondary modulation reference speckle distribution sequence. Finally, it obtains a polarization differential barrel detection signal sequence based on the received barrel detection signals from the parallel polarization channel and the vertical polarization channel, and performs correlation reconstruction based on the polarization differential barrel detection signal sequence and the secondary modulation reference speckle distribution sequence to obtain a reconstructed image of the target in the target water area.

[0119] The two-stage modulation unit 2 is used, under the control of the signal processing unit, to perform a first-stage statistical decorrelation modulation on the illumination beam output by the optical emission and polarization guidance unit to form a primary modulation reference speckle distribution sequence, and guide the primary modulation reference speckle distribution sequence to the reference polarization measurement unit; and to perform a second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence to form a secondary modulation reference speckle distribution sequence, and project the secondary modulation reference speckle distribution sequence as a light field onto the target in the target water area.

[0120] The reference polarization measurement unit 3 is used to receive the first modulation reference speckle distribution sequence sent by the two-stage modulation unit 2, obtain the equivalent response distribution of the first modulation reference speckle distribution sequence under orthogonal polarization state, and send it to the signal processing unit 5.

[0121] As an optional implementation, the two-stage modulation unit 2 includes: a first spatial light modulator 10, a 4f relay system 11, a beam splitter 12, a polarization-type transmission spatial light modulator 13, an analyzer 14, and a projection lens 15.

[0122] The first spatial light modulator 10 is disposed on the output optical path of the optical emission and polarization guiding unit 1, and is used to perform first-stage statistical decorrelation modulation on the illumination beam under the control of the signal processing unit 5 to form a primary modulation reference speckle distribution sequence. The 4f relay system 11 is disposed on the output optical path of the first spatial light modulator 10, and is used to transmit the primary modulation reference speckle distribution sequence to the beam splitter 12.

[0123] The beam splitter 12 is disposed on the outgoing optical path of the 4f relay system 11 and is used to split the primary modulation reference speckle distribution sequence into a main optical path and a reference measurement optical path. The main optical path is output to the polarization-type transmission spatial light modulator 13, and the reference measurement optical path is output to the reference polarization measurement unit 3.

[0124] The polarization-type transmission spatial light modulator 13 is disposed on the main optical path of the beam splitter 12 and is used to perform second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence formed after the first-stage statistical decorrelation modulation under the control of the signal processing unit 5, so as to form a secondary modulation reference speckle distribution sequence.

[0125] The analyzer 14 is disposed on the output light path of the polarization-type transmission spatial light modulator 13 and is used to analyze the polarization of the primary modulation reference speckle distribution sequence that is subjected to polarization spatial modulation.

[0126] The projection lens 15 is disposed on the output light path of the analyzer 14 and is used to project the secondary modulation reference speckle distribution sequence formed after the second-stage polarization spatial modulation and analysis onto the target in the target water area.

[0127] As an optional implementation method, such as Figure 2 As shown, the optical emission and polarization guidance unit 1 includes a laser 6, a beam expander and collimator 7, a polarizer 8, and a polarization adjustment unit 9; the two-stage modulation unit 2 includes a first spatial light modulator 10, a 4f relay system 11, a beam splitter (BS) 12, a polarization-type transmission spatial light modulator (SLM) 13, an analyzer 14, and a projection lens 15; the reference polarization measurement unit 3 includes a polarizing beam splitter (PBS) 16, a first charge-coupled device (CCD) 17, and a second charge-coupled device 18; the signal receiving unit 4 includes a polarizing beam splitter 19, a first converging lens 20, a first barrel detector 21, a second converging lens 22, and a second barrel detector 23; and the signal processing unit 5 includes an oscilloscope 24, a data acquisition card 25, and a control processing unit 26.

[0128] As an optional implementation, the laser 6 in the optical emission and polarization guiding unit 1 is used to generate an illumination beam with stable intensity and good polarization characteristics; the beam expander and collimator 7 is disposed in the output optical path of the illumination beam to expand and collimate the incident beam, forming a parallel beam with a suitable aperture and uniform spatial distribution; the polarizer 8 is disposed in the output optical path of the beam expander and collimator 7 to shape the parallel beam into linearly polarized light with a defined polarization direction; and the polarization adjustment unit 9 is disposed in the output optical path of the polarizer 8 to adjust the polarization direction of the linearly polarized light to match the optimal working polarization direction of the subsequent polarization-type spatial light modulator.

[0129] In this implementation, the laser emitted by laser 6 is first expanded and collimated by beam expanding and collimating assembly 7 to form a parallel beam with a suitable aperture and relatively uniform spatial distribution. Subsequently, this parallel beam passes through polarizer 8 and is shaped into linearly polarized light with a defined polarization direction. Then, it passes through polarization adjustment unit 9 to adjust the polarization direction of the linearly polarized light to meet the requirements of the subsequent spatial light modulator. After the above processing, an incident beam with a known polarization state and suitable for subsequent two-stage modulation is obtained.

[0130] Laser 6 is preferably a 532nm laser, used to provide a stable intensity, good polarization characteristics, and suitable illumination source for underwater detection; beam expander and collimator 7 is used to improve the spatial consistency of the incident beam, providing a basis for the subsequent first spatial light modulator 10 to achieve uniform and high-contrast spatial coding modulation; polarizer 8 is used to ensure that the beam incident on the subsequent modulation system has a definite linear polarization direction; polarization adjustment unit 9 is used to further adjust the incident polarization direction to match the optimal working polarization direction of polarization-type transmission spatial light modulator 13.

[0131] The optical emission and polarization guidance unit 1 serves as the front end of the light source preparation for the entire device, providing incident light with a defined polarization state and stable beam quality for the subsequent two-stage modulation unit 2.

[0132] As an optional implementation, the first spatial light modulator 10 in the two-stage modulation unit 2 employs a digital micromirror device and is positioned on the output optical path of the polarization adjustment unit 9. Under the control of the signal processing unit 5, it performs spatial amplitude modulation on the incident illumination beam based on first-order decorrelation correction, forming a first-order modulation reference speckle distribution sequence. A 4f relay system 11 is positioned on the output optical path of the first spatial light modulator 10, used to stably and clearly transmit the first-order modulation reference speckle distribution sequence to subsequent modulation positions, ensuring a good spatial correspondence between the first-order modulation reference speckle distribution sequence and the subsequently formed second-order modulation reference speckle distribution sequence. A beam splitter 12 is positioned on the output optical path of the 4f relay system 11, used to divide the first-order modulation reference speckle distribution sequence into a main optical path and a reference measurement optical path. A polarization-type transmission spatial light modulator 13 is positioned on the main optical path of the beam splitter 12, used under the control of the signal processing unit 5 to modulate the first-order modulation reference speckle distribution sequence based on a second-order modulation function. The speckle distribution sequence is subjected to spatially varying polarization state modulation, phase delay modulation, or equivalent transmittance modulation; the analyzer 14, disposed on the output optical path of the second spatial light modulator 13, is used to polarize the modulated beam when the output of the second spatial light modulator 13 is a polarization state variation or phase delay variation, converting the spatially varying polarization state or phase delay into spatial intensity modulation corresponding to the secondary modulation function, so that the light field output by the analyzer 14 forms a secondary modulation reference speckle distribution sequence; the projection lens 15, disposed on the output optical path of the analyzer 14, is used to project the secondary modulation reference speckle distribution sequence onto the target in the target water area, thereby realizing the coded illumination of the target.

[0133] In this implementation, the incident light from the optical emission and polarization guiding unit 1 first enters the first spatial light modulator 10. Driven by the signal processing unit 5, the first spatial light modulator 10 outputs a primary modulation reference speckle distribution sequence. This primary modulation reference speckle distribution sequence then enters the 4f relay system 11. The 4f relay system 11 stably and clearly transmits the primary modulation reference speckle distribution sequence output by the first spatial light modulator 10 to the subsequent second modulation position, ensuring a good spatial correspondence between the primary and secondary modulation reference speckle distribution sequences.

[0134] A beam splitter 12 is installed after the 4f relay system 11. The beam splitter 12 divides the primary modulation reference speckle distribution sequence into two paths: one path serves as the main optical path, which continues to propagate to the polarization-type transmission spatial light modulator 13; the other path serves as the reference measurement optical path, which enters the reference polarization measurement unit 3 to obtain the equivalent reference response distribution of the primary modulation reference speckle distribution sequence under two orthogonal polarization analysis states.

[0135] The primary modulation reference speckle distribution sequence in the main optical path is incident on the polarization-type transmissive spatial light modulator 13. Under the control of the signal processing unit 5, the polarization-type transmissive spatial light modulator 13 performs polarization spatial modulation on the primary modulation reference speckle distribution sequence based on the secondary modulation function. Since the polarization-type transmissive spatial light modulator 13 is a polarization-type transmissive device, its modulation result usually manifests as a change in local polarization state or phase delay. Therefore, an analyzer 14 is set after it to convert the polarization change or phase delay change introduced by the polarization-type transmissive spatial light modulator 13 into an equivalent intensity modulation. The polarization-type transmissive spatial light modulator 13 and the analyzer 14 work together to form a secondary modulation reference speckle distribution sequence after the primary modulation reference speckle distribution sequence undergoes a second stage of polarization spatial modulation. The secondary modulation reference speckle distribution sequence is then projected onto the target in the target water area through the projection lens 15 to achieve coded illumination of the target.

[0136] In this system, the reference measurement branch split by beam splitter 12 is used to perform polarization reference measurement on the primary modulation reference speckle distribution sequence, while the main optical path is used to sequentially pass the primary modulation reference speckle distribution sequence through polarization-type transmission spatial light modulator 13 and analyzer 14 to form a secondary modulation reference speckle distribution sequence. With this structure, the system can achieve second-stage polarization-coordinated modulation while maintaining the spatial information of the first modulation optical field, thereby enhancing the ability to extract effective polarization information of the target and suppressing background scattering interference.

[0137] As an optional implementation, the reference polarization measurement unit 3 is disposed on the reference measurement optical path of the beam splitter 12 to obtain the equivalent reference response distribution of the first modulation reference speckle distribution sequence under two orthogonal polarization analysis states, providing raw data for constructing the polarization confidence map.

[0138] In this implementation, the reference light beam split by beam splitter 12 enters the reference polarization measurement unit 3 and is first incident on polarization beam splitter 16. Polarization beam splitter 16, based on its polarization selectivity, decomposes the reference light into two mutually orthogonal polarized beams, which are then directed to two independent exits. One parallel polarized beam is received by the first charge-coupled device 17, and the other orthogonally polarized beam is received by the second charge-coupled device 18.

[0139] The first charge-coupled device 17 is used to record the two-dimensional light intensity distribution of the first modulation reference speckle distribution sequence under parallel polarization analysis, and the second charge-coupled device 18 is used to record the two-dimensional light intensity distribution of the first modulation reference speckle distribution sequence under orthogonal polarization analysis. The two two-dimensional images correspond to the equivalent reference response distribution of the first modulation reference light field under the two orthogonal polarization analysis states, respectively, and can be used to construct polarization confidence maps.

[0140] In this embodiment, the reference polarization measurement unit 3 is located on the reference branch split by the beam splitter 12 in the two-stage modulation unit 2, preferably after the 4f relay system 11 and before the polarization-type transmission spatial light modulator SLM 13. This ensures that the reference measurement beam already contains the first layer of modulation information, but has not yet undergone the second layer of modulation, thereby more accurately reflecting the polarization response state of the primary modulation reference speckle distribution sequence.

[0141] The reference polarization measurement unit 3 does not directly participate in target illumination and target echo reception, but serves as a module for acquiring reference information required for the second modulation control, and is used to provide the signal processing unit 5 with the raw data required to construct the polarization confidence map.

[0142] As an optional implementation, the signal receiving unit 4 is disposed on the optical path of the target reflected echo and is used to synchronously and in parallel acquire the barrel detection signals of the parallel polarization channel and the vertical polarization channel in the target echo.

[0143] In this implementation, the echo beam reflected from the target detection area first enters the polarization beam splitter 19. The polarization beam splitter 19 decomposes the echo into two mutually orthogonal polarization components according to their polarization direction. One parallel polarized reflected beam is converged by the first converging lens 20 and enters the first barrel detector 21; the other orthogonally polarized reflected beam is converged by the second converging lens 22 and enters the second barrel detector 23. Thus, the first barrel detector 21 and the second barrel detector 23 simultaneously record the total light intensity signal of the two orthogonally polarized echoes.

[0144] In this embodiment, the first barrel detector 21 outputs a barrel detection signal in a parallel polarization channel, and the second barrel detector 23 outputs a barrel detection signal in a vertical polarization channel. Under target-free conditions, both channels output background barrel detection signals; under target-containing conditions, both channels output target barrel detection signals. Thus, the signal receiving unit 4 can provide raw data for subsequently constructing the background total barrel detection signal sequence, the target total barrel detection signal sequence, the effective signal sequence of the target under test, and the polarization differential barrel detection signal sequence.

[0145] This structure enables synchronous parallel acquisition of two orthogonal polarization components in the target echo, avoiding time errors caused by polarization time-division switching measurement and improving the synchronization and reliability of polarization ghost imaging data acquisition.

[0146] As an optional implementation, the signal processing unit 5 is connected to the first spatial light modulator 10, the polarization-type transmission spatial light modulator 13, the reference polarization measurement unit 3, and the signal receiving unit 4, respectively. It is used to generate an original reference speckle sequence, receive the background barrel detection signal sequence, the target barrel detection signal sequence, the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, and dual-polarization barrel detection data (barrel detection signals from the parallel polarization channel and the vertical polarization channel). It is also used to calculate the first correlation coefficient, the second correlation coefficient, the primary decorrelation correction weight, the polarization confidence map, the background prediction map, the measurement quality factor, and the secondary modulation function. It controls the first spatial light modulator 10 to form a primary modulation reference speckle distribution sequence, controls the polarization-type transmission spatial light modulator 13 and the analyzer 14 to form a secondary modulation reference speckle distribution sequence, and performs polarization difference correlation reconstruction based on the dual-polarization barrel detection data and the secondary modulation reference speckle distribution sequence, outputting a reconstructed image of the target in the target water area.

[0147] In this implementation, the oscilloscope 24 is connected to the first barrel detector 21 and the second barrel detector 23. Its function is to monitor the real-time waveform of the signals output from the dual-polarization barrel detection channels, facilitating observation and adjustment of the system's operating status, signal amplitude, noise level, and the synchronization characteristics of the two channels. Through the oscilloscope 24, it is possible to visually determine whether the outputs of the parallel polarization channel and the orthogonal polarization channel are stable, whether there is significant noise drift, and whether they meet the requirements for subsequent synchronous acquisition, thus providing a basis for system calibration and operational status diagnosis.

[0148] The data acquisition card 25 is used to synchronously acquire dual-polarization barrel detection signals from the first barrel detector 21 and the second barrel detector 23, and converts the acquired analog electrical signals into digital data streams before transmitting them to the control processing unit 26. Preferably, the outputs of the first barrel detector 21 and the second barrel detector 23 are simultaneously connected to the oscilloscope 24 and the data acquisition card 25 in a split or parallel manner. The oscilloscope 24 is used for real-time monitoring, and the data acquisition card 25 is used for formal synchronous acquisition, thereby ensuring that the barrel detection signal monitoring function and the data acquisition function are independent of each other and do not interfere with each other. This enables high-fidelity monitoring of the dual-polarization barrel detection signals and ensures the stability and synchronization of data acquisition during subsequent differential correlation calculations and parameter estimation.

[0149] The first charge-coupled device 17 and the second charge-coupled device 18 are preferably directly connected to the control processing unit 26. Specifically, the first charge-coupled device 17 outputs two-dimensional image data of the primary modulation reference speckle distribution sequence in the parallel polarization analysis state, and the second charge-coupled device 18 outputs two-dimensional image data of the primary modulation reference speckle distribution sequence in the vertical polarization analysis state. The control processing unit 26 directly receives and reads the image frame data uploaded by the two charge-coupled devices with USB 3.0 interfaces.

[0150] The control processing unit 26 is the core of the entire device for control and operation, and its main functions include: 1) First modulation control function: responsible for generating the original reference speckle sequence, and based on the backscattering point spread function and the first decorrelation correction weight, controlling the first spatial light modulator 10 to perform the first stage statistical decorrelation modulation on the incident illumination beam to form a first modulation reference speckle distribution sequence.

[0151] 2) Reference polarization analysis function: Receive two-dimensional image data from the first charge-coupled device 17 and the second charge-coupled device 18, extract the equivalent reference response distribution of the first modulation reference speckle distribution sequence under two orthogonal polarization analysis states, and construct a polarization confidence map accordingly.

[0152] 3) Second modulation control function: Combine the background prediction map and the measurement quality factor to calculate the secondary modulation function, and control the polarization-type transmission spatial light modulator 13 to perform second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence based on the secondary modulation function; after polarization projection by the analyzer 14, a secondary modulation reference speckle distribution sequence is formed.

[0153] 4) Dual-polarization barrel detection processing and reconstruction function: Receives dual-polarization barrel detection data from the first barrel detector 21 and the second barrel detector 23, calculates the barrel detection signal of the parallel polarization channel, the barrel detection signal of the vertical polarization channel, the target total barrel detection signal, the background total barrel detection signal, the effective signal of the target to be measured, and the polarization difference barrel detection signal, and performs polarization difference correlation reconstruction based on the secondary modulation reference speckle distribution sequence, and outputs the reconstructed image of the target to be measured in the target water area.

[0154] 5) Timing synchronization control function: used to uniformly control the working timing of the first spatial light modulator 10, polarization-type transmission spatial light modulator 13, first charge-coupled device 17, second charge-coupled device 18, first barrel detector 21, second barrel detector 23 and data acquisition card 25, to ensure strict synchronization of the first-level modulation, reference polarization measurement, second-level modulation and target echo acquisition at the frame level.

[0155] In summary, in this embodiment, the overall working process of the device is as follows: the laser output from laser 6 is collimated by beam expanding and collimating component 7, and then passes sequentially through polarizer 8 and polarization adjustment unit 9 to form incident polarized light that meets the working requirements of polarization-type transmission spatial light modulator 13. After the beam enters the first spatial light modulator 10, it undergoes first-stage statistical decorrelation modulation under the control of signal processing unit 5 to form a primary modulation reference speckle distribution sequence, which is then transmitted to beam splitter 12 via 4f relay system 11. Beam splitter 12 divides the primary modulation reference speckle distribution sequence into a main optical path and a reference optical path. The reference optical path enters the reference polarization measurement unit 3 and is split into two orthogonally polarized beams by polarization beam splitter 16. These beams are received by the first charge-coupled device 17 and the second charge-coupled device 18, respectively, to obtain the equivalent reference response of the primary modulation reference speckle distribution sequence under two orthogonal polarization analysis states. The main optical path continues to enter the polarization-type transmission spatial light modulator 13. Under the control of signal processing unit 5, the polarization-type transmission spatial light modulator 13 performs a second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence based on a secondary modulation function. Subsequently, polarization projection is performed by analyzer 14 to convert the polarization state change or phase delay change introduced by the polarization-type transmission spatial light modulator 13 into an equivalent intensity modulation. The polarization-type transmission spatial light modulator 13 and analyzer 14 work together to form a secondary modulation reference speckle distribution sequence after the primary modulation reference speckle distribution sequence undergoes the second-stage polarization spatial modulation. Finally, the projection lens 15 illuminates the target in the target water area.

[0156] The reflected echo from the target then enters the signal receiving unit 4, where it is decomposed into two mutually orthogonal polarization components by the polarization beam splitter 19. One parallel polarized reflected light passes through the first converging lens 20 and enters the first barrel detector 21; the other orthogonally polarized reflected light passes through the second converging lens 22 and enters the second barrel detector 23. The dual-polarization barrel detection signals output by the two barrel detectors are preferably connected simultaneously to the oscilloscope 24 and the data acquisition card 25 in a split or parallel manner. The oscilloscope 24 is used to monitor the waveform status of the dual polarization channels in real time, while the data acquisition card 25 is used to synchronously acquire the dual-polarization barrel detection signals and upload them to the control processing unit 26. Simultaneously, the reference polarization image data (equivalent response distribution of the first-modulated reference speckle distribution sequence under orthogonal polarization) output by the first charge-coupled device 17 and the second charge-coupled device 18 is directly uploaded to the control processing unit 26. Based on the above data, the control processing unit 26 performs the following operations: calculation of backscattering correlation parameters, construction of polarization confidence map, calculation of background prediction map, calculation of measurement quality factor, calculation of secondary modulation reference speckle distribution sequence, and polarization differential ghost imaging reconstruction. Finally, it outputs a reconstructed image of the target in the target water area.

[0157] Therefore, the device in this application constructs a two-stage modulation optical path by connecting a first spatial light modulator and a polarization-type transmission spatial light modulator in series. Combined with a beam splitter and a reference polarization measurement unit, it synchronously acquires the dual-polarization spatial distribution of the first modulation reference speckle distribution sequence obtained by statistical decorrelation modulation before the second modulation, enabling the construction of the secondary modulation function to have real-time polarization reference information. Simultaneously, it employs dual polarization barrel detection channels to acquire target echoes in parallel, avoiding timing errors caused by time-division measurement. Based on the decoupling and coordination of the two modulation functions, this device enhances the system's stability, synchronization, and engineering feasibility through an integrated architecture, ultimately achieving a comprehensive improvement in imaging quality and background interference resistance.

[0158] In summary, this application has the following beneficial effects: (1) By introducing a first-order decorrelation correction weight based on the backscattering point spread function and correlation coefficient in statistical decorrelation modulation, the limitation of speckle patterns and background noise being indiscriminately correlated in traditional ghost imaging is overcome. By utilizing the statistical correlation between the background barrel detection signal and the ideal reference speckle, the original speckle is subjected to the first adaptive correction, so that the modulated reference speckle actively "avoids" the backscattering noise component in a statistical sense, thereby reducing the interference of background noise on correlation reconstruction from the root and significantly improving the signal extraction capability under strong scattering environment.

[0159] (2) By introducing a dual guidance mechanism of polarization confidence map and background prediction map in polarization spatial modulation, fine-grained spatial domain modulation of primary modulation speckle is achieved. The polarization confidence map is constructed based on the equivalent response distribution of the first modulation field (the primary modulation reference speckle distribution sequence) under orthogonal polarization analysis, enabling precise localization of the spatial region where effective polarization information of the target is concentrated. The background prediction map is calculated by convolving the backscattering point diffusion function with the primary modulation reference speckle distribution sequence, identifying spatial locations prone to strong background scattering. Combined with the measurement quality factor, this method achieves differentiated modulation of the target enhancement region and the background suppression region, preserving target details while further suppressing residual backscattering, significantly improving imaging quality.

[0160] (3) By connecting the first decorrelation constraint and the second polarization co-modulation in series to form a two-stage modulation architecture, the statistical decorrelation of the first modulation and the spatial polarization co-optimization of the second modulation are organically combined, so that the speckle optimization process has the dual characteristics of statistical decorrelation and spatial polarization guidance. It effectively suppresses the interference of underwater backscattered light and significantly improves the target signal-to-noise ratio and anti-background interference ability of ghost imaging in turbid water.

[0161] (4) By setting up a beam splitter, a reference polarization measurement unit, and a polarization-type transmission spatial light modulator, an integrated optical path architecture of "first modulation reference light field dual polarization synchronous analysis - second modulation polarization cooperative coding" is constructed in the device. This structure achieves decoupling and coordination of the two modulation functions, and obtains the polarization spatial distribution of the first modulation light field in real time through the reference branch, so that the construction of the two-stage modulation does not depend on indirect estimation or offline calibration, which significantly improves the physical targeting and real-time performance of the modulation. The parallel acquisition design of the dual polarization barrel detection channel and the dual CCD reference measurement channel in the device fundamentally eliminates the timing error caused by time-division measurement, and enhances the overall stability and engineering feasibility of the system while improving data acquisition efficiency and synchronization.

[0162] In one exemplary embodiment, a computer device is provided, which may be a server or a terminal, and its internal structure diagram may be as follows. Figure 3 As shown, this computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The database stores underwater polarization ghost imaging processing data based on two-level modulation. The I / O interfaces are used for information exchange between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements an underwater polarization ghost imaging method based on two-level modulation.

[0163] Those skilled in the art will understand that Figure 3The structures shown are merely block diagrams of some structures related to the present application and do not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than shown in the figures, or combine certain components, or have different component arrangements. In an exemplary embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments. Furthermore, when the processor executes the computer program, it is also used to assign a frame number to each coded illumination process, and to bind the first modulation pattern, the second modulation pattern, the reference polarization measurement data, and the barrel detection signals of the parallel polarization channel and the vertical polarization channel under the same frame number accordingly; after confirming that the second modulation pattern has been loaded into the polarization-type transmissive spatial light modulator, the first spatial light modulator is triggered to output the first modulation pattern corresponding to the frame number, and the reference polarization measurement unit and the signal receiving unit are triggered to acquire the reference polarization measurement data and the dual polarization barrel detection signal respectively in the corresponding acquisition window, so that when the first modulation reference speckle distribution sequence reaches the polarization-type transmissive spatial light modulator, the polarization-type transmissive spatial light modulator is in the second modulation state corresponding to the frame number, and at the same time, the reference polarization measurement data and the dual polarization barrel detection signal are kept synchronized with the first modulation pattern and the second modulation pattern of the corresponding frame.

[0164] In one exemplary embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above-described method embodiments and performs the frame sequence number binding, second modulation pattern loading confirmation, and first spatial light modulator trigger control mentioned in the above-described computer device.

[0165] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0166] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0167] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0168] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0169] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An underwater polarization ghost imaging method based on two-level modulation, characterized in that, include: Acquire basic data of the target water area and construct a backscattering point spread function; the basic data includes the background barrel detection signal sequence under the condition of no target to be measured, the target barrel detection signal sequence under the condition of the target to be measured, and the original reference speckle sequence used for the N irradiations, obtained from the target water area N times. Based on the aforementioned basic data, the backscattering noise sequence and the effective signal sequence of the target under test are determined, and the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test are calculated. Based on the first correlation coefficient, the second correlation coefficient, and the backscattering point diffusion function, the original reference speckle sequence is statistically decorrelated and modulated to obtain a first-modulated reference speckle distribution sequence. Based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, the polarization confidence map sequence is calculated, and based on the primary modulation reference speckle distribution sequence and the backscattering point diffusion function, the background prediction map sequence is calculated. The polarization space modulation of the primary modulation reference speckle distribution sequence is performed based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence to obtain the secondary modulation reference speckle distribution sequence. The target in the target water area is irradiated N times according to the secondary modulation reference speckle distribution sequence, and the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel are obtained for each irradiation. Based on the barrel detection signal from the parallel polarization channel and the barrel detection signal from the vertical polarization channel for each illumination, a polarization differential barrel detection signal sequence is obtained. By correlating and reconstructing the polarization differential barrel detection signal sequence with the secondary modulation reference speckle distribution sequence, a reconstructed image of the target in the target water area is obtained, realizing underwater polarization ghost imaging.

2. The underwater polarization ghost imaging method based on two-level modulation according to claim 1, characterized in that, Based on the aforementioned fundamental data, the backscattering noise sequence and the effective signal sequence of the target under test are determined, and the first correlation coefficient between the original reference speckle sequence and the backscattering noise sequence and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test are calculated, specifically including: The background total barrel detection signal sequence in the basic data is used as the backscattering noise sequence; Subtract the target total barrel detection signals from the target total barrel detection signal sequence in the basic data and the corresponding background total barrel detection signals in the background total barrel detection signal sequence to obtain the effective signal sequence of the target to be tested; The first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence, and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target under test are calculated using the following formulas: ； ； in, This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background barrel detection signal corresponding to the nth irradiation in the backscattered noise sequence; N represents the total number of irradiations. This represents the total light intensity scalar of the original reference speckle distribution corresponding to the nth illumination in the original reference speckle sequence. This represents the mean of the total light intensity scalar of the original reference speckle distribution corresponding to all illuminations in the original reference speckle sequence; This represents the mean of the background barrel detection signal corresponding to all illuminations in the backscattering noise sequence; Let represent the first, second, third, and fourth minimum regularization constants, respectively; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the mean of the effective signals of the target under test corresponding to all irradiations in the effective signal sequence of the target under test.

3. The underwater polarization ghost imaging method based on two-level modulation according to claim 1, characterized in that, Based on the first correlation coefficient, the second correlation coefficient, and the backscattering point spread function, statistical decorrelation modulation is performed on the original reference speckle sequence to obtain a first-modulated reference speckle distribution sequence, specifically including: Based on the first and second correlation coefficients, the first decorrelation correction weights are calculated using the following formula: ； in, This indicates the removal of the relevant correction weights. This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; Denotes the fifth minimum regularization constant; Based on the first-order decorrelation correction weights and the backscattering point spread function, the original reference speckle sequence is statistically decorrelated and modulated using the following formula to obtain the first-order modulated reference speckle distribution sequence: ； in, In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; This indicates that the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence is located on the object plane. The light intensity at that location; Indicates the global correction intensity coefficient; Representing the object plane Backscattering point diffusion function at the location; Represents a two-dimensional convolution operation; This represents the background scattering degradation term.

4. The underwater polarization ghost imaging method based on two-level modulation according to claim 1, characterized in that, Based on the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization, a polarization confidence map sequence is calculated. Furthermore, based on the primary modulation reference speckle distribution sequence and the backscattering point spread function, a background prediction map sequence is calculated, specifically including: The polarization confidence map sequence is calculated using the following formula: ； in, This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; In a first-modulation reference speckle distribution sequence, the first... The primary modulation reference speckle distribution corresponding to the second irradiation, under parallel polarization analysis, on the object plane. The light intensity at that location; In a first-modulation reference speckle distribution sequence, the first... The first modulation reference speckle distribution corresponding to the second irradiation is analyzed under vertical polarization conditions on the object plane. The light intensity at that location; Represents the sixth minimum regularization constant; The background prediction map sequence is calculated using the following formula: ； in, This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. Normalized light intensity at the location; Representing the object plane Backscattering point diffusion function at the location; In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; Represents a two-dimensional convolution operation; [ [Indicates taking the entire object plane] The maximum value; This represents the seventh minimum regularization constant.

5. The underwater polarization ghost imaging method based on two-level modulation according to claim 1, characterized in that, The primary modulation reference speckle distribution sequence is polarization spatially modulated based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence to obtain the secondary modulation reference speckle distribution sequence, which specifically includes: The measurement quality factor sequence is calculated using the following formula based on the first and second correlation coefficients: ； in, Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; Represents a monotonic compression function; , , These represent the first weighting coefficient, the second weighting coefficient, and the third weighting coefficient, respectively. This represents the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence; This represents the original reference speckle distribution corresponding to the nth irradiation in the original reference speckle sequence; This represents the background barrel detection signal corresponding to the nth illumination in the backscattering noise sequence; The second correlation coefficient represents the original reference speckle sequence and the effective signal sequence of the target under test; This represents the effective signal of the target corresponding to the nth irradiation in the effective signal sequence of the target; This represents the first [number] target in the total barrel detection signal sequence under the condition of having a target to be measured. Illuminate the corresponding target barrel detection signal; This represents the eighth minimum regularization constant; The second-order modulation function is calculated using the following formula based on the measurement quality factor sequence, polarization confidence map sequence, and background prediction map sequence: ； in, Representing the object plane The second modulation function at the location; Indicates the polarization enhancement coefficient; Indicates the th in the measurement quality factor sequence The measurement quality factor corresponding to each irradiation; This indicates that the polarization confidence map corresponding to the nth illumination in the polarization confidence map sequence is located on the object plane. Confidence level at the location; Indicates the background suppression coefficient; This represents the normalized background prediction map on the object plane corresponding to the nth illumination in the background prediction map sequence. Normalized light intensity at the location; Based on the secondary modulation function, the polarization space modulation of the primary modulation reference speckle distribution sequence is performed, and the secondary modulation reference speckle distribution sequence is calculated using the following formula: ； In the formula, Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; In a first-modulation reference speckle distribution sequence, the first... The modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location.

6. The underwater polarization ghost imaging method based on two-level modulation according to claim 1, characterized in that, Based on the correlation and reconstruction of the polarization differential barrel detection signal sequence and the secondary modulation reference speckle distribution sequence, a reconstructed image of the target in the target water area is obtained, specifically including: The reconstructed image of the target in the target water area is obtained using the following formula: ； in, This represents the reconstructed image of the target in the target water area on the object plane. The pixel value at that location; N represents the total number of illuminations; This represents the polarization differential barrel detection signal corresponding to the nth illumination in the polarization differential barrel detection signal sequence; This represents the mean value of the polarization differential barrel detection signal corresponding to all illuminations in the polarization differential barrel detection signal sequence; Indicating the second modulated reference speckle distribution sequence, the first... The secondary modulation reference speckle distribution corresponding to the second irradiation is on the object plane. The light intensity at that location; This indicates that the secondary modulation reference speckle distribution corresponding to all irradiations in the secondary modulation reference speckle distribution sequence is located on the object plane. The average light intensity at that location.

7. An underwater polarization ghost imaging device based on two-level modulation, characterized in that, The underwater polarization ghost imaging device based on two-level modulation is used to implement the underwater polarization ghost imaging method based on two-level modulation as described in any one of claims 1-6. The underwater polarization ghost imaging device based on two-level modulation includes: an optical emission and polarization guidance unit, a two-level modulation unit, a reference polarization measurement unit, a signal receiving unit, and a signal processing unit. The signal processing unit is connected to the two-stage modulation unit, the reference polarization measurement unit, and the signal receiving unit, respectively; the two-stage modulation unit is also connected to the optical emission and polarization guidance unit and the reference polarization measurement unit, respectively. The optical emission and polarization guiding unit is used to generate an illumination beam; The signal receiving unit is used to acquire the background barrel detection signal sequence of the target water area under the condition of no target and the target barrel detection signal sequence under the condition of target, and send the acquired background barrel detection signal sequence and target barrel detection signal sequence to the signal processing unit; simultaneously acquire the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel generated by the secondary modulated reference speckle distribution sequence illuminating the target, and send the barrel detection signal of the parallel polarization channel and the barrel detection signal of the vertical polarization channel to the signal processing unit; The signal processing unit generates an original reference speckle sequence and uses the original reference speckle sequence, the received background barrel detection signal sequence, and the target barrel detection signal sequence as basic data. Based on the basic data, it determines the backscattered noise sequence and the effective signal sequence of the target, calculates the first correlation coefficient between the original reference speckle sequence and the backscattered noise sequence, and the second correlation coefficient between the original reference speckle sequence and the effective signal sequence of the target. According to the first correlation coefficient, the second correlation coefficient, and the backscattered point spread function, it performs statistical decorrelation modulation on the original reference speckle sequence to obtain a first-modulated reference speckle distribution sequence, and controls two-stage modulation units to form the first-modulated reference speckle distribution sequence. Based on the equivalent response of the received first-modulated reference speckle distribution sequence under orthogonal polarization, it... The system calculates a polarization confidence map sequence based on the distribution, and calculates a background prediction map sequence based on the primary modulation reference speckle distribution sequence and the backscattering point spread function. It then calculates a secondary modulation function based on the first correlation coefficient, the second correlation coefficient, the polarization confidence map sequence, and the background prediction map sequence, and performs polarization spatial modulation on the primary modulation reference speckle distribution sequence based on the secondary modulation function to obtain a secondary modulation reference speckle distribution sequence. Two-stage modulation units are then controlled to form the secondary modulation reference speckle distribution sequence. Finally, a polarization differential barrel detection signal sequence is obtained based on the received barrel detection signals from the parallel polarization channel and the vertical polarization channel. This sequence is then correlated with the secondary modulation reference speckle distribution sequence to reconstruct the image of the target in the target water area. The two-stage modulation unit, under the control of the signal processing unit, performs a first-stage statistical decorrelation modulation on the illumination beam output by the optical emission and polarization guidance unit to form a primary modulation reference speckle distribution sequence, and guides the primary modulation reference speckle distribution sequence to the reference polarization measurement unit; and performs a second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence to form a secondary modulation reference speckle distribution sequence, and projects the secondary modulation reference speckle distribution sequence as a light field onto the target in the target water area. The reference polarization measurement unit is used to receive the primary modulation reference speckle distribution sequence sent by the two-stage modulation unit, obtain the equivalent response distribution of the primary modulation reference speckle distribution sequence under orthogonal polarization state, and send it to the signal processing unit.

8. The underwater polarization ghost imaging device based on two-level modulation according to claim 7, characterized in that, The two-stage modulation unit includes: a first spatial light modulator, a 4f relay system, a beam splitter, a polarization-type transmission spatial light modulator, an analyzer, and a projection lens; The first spatial light modulator is disposed on the outgoing light path of the optical emission and polarization guiding unit, and is used to perform first-stage statistical decorrelation modulation on the illumination beam under the control of the signal processing unit to form a first-stage modulation reference speckle distribution sequence. The 4f relay system is set on the output optical path of the first spatial light modulator and is used to transmit the first modulation reference speckle distribution sequence to the beam splitter. The beam splitter is disposed on the outgoing optical path of the 4f relay system and is used to split the first modulation reference speckle distribution sequence into two paths: a main optical path and a reference measurement optical path. The main optical path outputs to the polarization-type transmission spatial light modulator, and the reference measurement optical path outputs to the reference polarization measurement unit. The polarization-type transmission spatial light modulator is disposed on the main optical path of the beam splitter and is used to perform second-stage polarization spatial modulation on the primary modulation reference speckle distribution sequence formed after the first-stage statistical decorrelation modulation under the control of the signal processing unit, so as to form a secondary modulation reference speckle distribution sequence. The polarizer is disposed on the output light path of the polarization-type transmission spatial light modulator and is used to analyze the polarization of the primary modulation reference speckle distribution sequence that is subjected to polarization spatial modulation. The projection lens is positioned on the output light path of the analyzer and is used to project the secondary modulation reference speckle distribution sequence formed after the second-stage polarization spatial modulation and analysis onto the target in the target water area.

9. A computer device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the computer program, it implements the underwater polarization ghost imaging method based on two-level modulation as described in any one of claims 1-6.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the underwater polarization ghost imaging method based on two-level modulation as described in any one of claims 1-6.

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