An underwater correlation imaging system and method based on secondary modulation

Abstract

The present application discloses an underwater correlation imaging system and method based on secondary modulation, relating to the field of underwater optoelectronic imaging technology. In this system, an optical emission and guidance unit emits a laser signal, a signal receiving and processing unit generates a Hadamard matrix speckle sequence, and a control unit drives a swing mirror DMD modulation device to swing at a preset angle; the swing mirror DMD modulation device scans the detection target at a preset angle to determine sub-fields of view at different angles; a first reflected signal is modulated for the first time based on a reference Hadamard matrix speckle pattern to generate a first modulated light signal; the detection target is illuminated by the first modulated light signal, and a second modulated light signal reflected from the detection target is modulated for the second time based on a reference Hadamard inverse matrix speckle pattern to generate a second modulated light signal; the signal receiving and processing unit obtains a target image based on the second modulated light signal in each sub-field of view and the reference Hadamard matrix speckle pattern. The present application improves the signal-to-noise ratio of underwater correlation imaging.

Description

Technical Field

[0001] The present application relates to the field of underwater optoelectronic imaging technology, and in particular to an underwater correlation imaging system and method based on secondary modulation. Background Art

[0002] Traditional underwater imaging technologies, such as charge-coupled device (CCD) or intensified charge-coupled device (ICCD) cameras, have been widely used for detecting and imaging underwater targets. However, these technologies face significant limitations in underwater environments. First, optical effects such as scattering and absorption in water cause light waves to rapidly attenuate during propagation, resulting in a decrease in the intensity of the reflected light signal. This is particularly true in deep or turbid waters, where suspended particles and microorganisms complicate the light propagation path, significantly degrading image quality. CCD or ICCD cameras rely on changes in reflected light intensity to capture image information. However, in waters with strong scattering, background noise is high, reducing the contrast between the target and the background, ultimately compromising image clarity and accuracy. To overcome the bottlenecks of traditional underwater imaging, underwater correlation imaging (e.g., "ghost imaging" or quantum imaging) is an emerging imaging technique that has attracted increasing attention. Correlation imaging reconstructs images by detecting spatial intensity fluctuations in a light field. Unlike traditional light intensity detection, it uses a single-pixel detector to record the total intensity of the light field and reconstructs the target image by correlating it with the speckle field matrix of the illuminated object. This technique is highly adaptable to underwater environments and can reduce the effects of water scattering and refraction on the imaging process. It is particularly advantageous in low-light and long-distance detection. Although underwater correlation imaging overcomes the limitations of traditional CCD imaging technology to some extent, the strong scattering effect in water still significantly affects the signal-to-noise ratio in practical applications. In underwater environments, light waves are scattered and absorbed by particles, suspended matter, and dissolved matter during propagation, resulting in a significant amount of background noise in the detected echo signals. Especially in complex underwater environments, signal attenuation and noise interference significantly reduce the signal-to-noise ratio of underwater correlation imaging, blurring the contrast between the target object and the background, and affecting imaging accuracy and quality. Therefore, how to effectively reduce the impact of water scattering and improve the signal-to-noise ratio of underwater correlation imaging remains a key issue that needs to be urgently addressed in this technology.

[0003] Secondly, correlation imaging techniques (such as "ghost imaging" or quantum imaging) typically rely on laser light sources to illuminate the target object and detect the reflected light field. However, laser light sources suffer from a limited field of view in underwater environments. Laser beams are highly directional and typically form a highly concentrated, narrow beam, which limits their propagation range in water and prevents them from covering a wide detection field. Especially when the underwater target is far away or the water environment is uneven, the laser beam energy is easily affected by particles, suspended matter, or currents in the water, causing scattering and attenuation of the laser energy, resulting in insufficient beam intensity and thus affecting effective target detection. Furthermore, since laser beam propagation is affected by the optical properties of water, such as turbidity, temperature fluctuations, salinity, and current velocity, the laser's illumination angle and propagation path are unstable, further limiting its application underwater. Beam scattering and absorption are particularly significant in complex underwater environments, increasing the difficulty of imaging targets. As a result, detectors cannot effectively capture distant targets or obtain clear images in turbid waters. To address this issue, modern underwater imaging technologies have gradually attempted to improve the design of laser light sources, add multiple laser sources, or adopt multi-wavelength lasers to increase the coverage and penetration of the light source. However, although these methods can partially alleviate the problem of limited field of view, it is still difficult to achieve large-scale and efficient target detection in deep water or extremely turbid waters.

[0004] Therefore, it is necessary to provide an underwater correlation imaging system based on secondary modulation to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide an underwater correlation imaging system and method based on secondary modulation, which improves the signal-to-noise ratio of underwater imaging.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides an underwater correlation imaging system based on secondary modulation, the system comprising: an optical emission and guidance unit, a swing mirror DMD modulation device, a control unit, and a signal receiving and processing unit;

[0008] The optical emission and guidance unit is used to emit laser signals and guide the laser signals to the oscillating mirror DMD modulation device;

[0009] The signal receiving and processing unit is used to generate a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes multiple reference Hadamard matrix speckles;

[0010] The control unit is connected to the oscillating mirror DMD modulation device, and the control unit is used to drive the oscillating mirror DMD modulation device to oscillate according to a preset angle;

[0011] The oscillating mirror DMD modulation device is connected to the signal receiving and processing unit, and the oscillating mirror DMD modulation device is used to:

[0012] Scan the detection target at a preset angle to determine sub-fields of view at different angles; each sub-field of view corresponds to a reference Hadamard matrix speckle pattern;

[0013] For any sub-field of view, use any sub-field of view as the current sub-field of view:

[0014] Performing a first modulation on the first reflected signal based on a reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view;

[0015] Illuminating the detection target with the first modulated light signal in the current sub-field of view, receiving the light signal reflected by the detection target, and performing a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal in the current sub-field of view;

[0016] The signal receiving and processing unit is used to perform correlated imaging based on the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle to obtain a correlated reconstructed image of each sub-field of view, and to splice the correlated reconstructed images of all sub-fields of view of the detection target to obtain a target image.

[0017] In one embodiment, the optical emission and guidance unit includes: a laser, a reflector, and a beam splitter;

[0018] The laser signal emitted by the laser is reflected by the reflector and reaches the spectrometer, and the spectrometer guides the laser signal to the oscillating mirror DMD modulation device.

[0019] In one embodiment, the oscillating mirror DMD modulation device includes: an oscillating mirror and a digital micromirror device;

[0020] The digital micromirror device is connected to the signal receiving and processing unit and the control unit respectively, the swing mirror is connected to the control unit, and the digital micromirror device is fixed on the swing mirror;

[0021] The oscillating mirror scans the detection target at a preset angle to determine the sub-field of view at different angles;

[0022] The digital micromirror device performs a first modulation on the first reflected signal based on the reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated light signal in the current sub-field of view, and uses the first modulated light signal in the current sub-field of view to illuminate the detection target, receives the light signal reflected by the detection target, and performs a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal.

[0023] In one embodiment, the control unit comprises a microcontroller STM32;

[0024] The STM32 microcontroller is used to drive the oscillating mirror DMD modulation device to oscillate periodically according to the corresponding preset angle in the current sub-field of view.

[0025] In one embodiment, the control unit further comprises: a field programmable gate array;

[0026] The field programmable gate array is connected to the swing mirror and the digital micromirror device respectively;

[0027] Field Programmable Gate Arrays are used for:

[0028] A synchronous trigger signal is generated, and based on the synchronous trigger signal, the swinging of the swing mirror is controlled to be time-aligned with the modulation mode switching of the digital micromirror device; the modulation mode of the digital micromirror device is determined based on a reference Hadamard matrix speckle.

[0029] In one embodiment, the signal receiving and processing unit includes: an underwater wide-angle focusing lens assembly, a barrel detector, a data acquisition card, and a data processing unit;

[0030] The underwater wide-angle focusing lens group is used to expand the imaging field of view of the second modulated light signal after being transmitted by the optical emission and guidance unit in the current sub-field of view, and focus it on the barrel detector;

[0031] The bucket detector is used to obtain a light intensity signal in the current sub-field of view based on the second modulated light signal after focusing in the current sub-field of view;

[0032] The data acquisition card is used to store the light intensity signal under each sub-field of view;

[0033] The data processing unit is used to perform correlated imaging based on the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle to obtain a correlated reconstructed image of each sub-field of view, and to splice the correlated reconstructed images of all sub-fields of view of the detection target to obtain a target image.

[0034] In one embodiment, the signal receiving and processing unit further includes: an oscilloscope;

[0035] The oscilloscope is connected to the barrel detector and the data acquisition card respectively;

[0036] The oscilloscope is used to monitor the waveform and noise characteristics of the light intensity signal output by the bucket detector in the current sub-field of view in real time.

[0037] In one embodiment, the field programmable gate array is also connected to the bucket detector;

[0038] The field programmable gate array is also used to trigger the bucket detector to collect the light intensity signal under the current sub-field of view when the angle of the swing mirror is stabilized at a corresponding preset angle under the current sub-field of view.

[0039] In a second aspect, the present application provides an underwater correlation imaging method based on secondary modulation, the underwater correlation imaging method based on secondary modulation is based on the underwater correlation imaging system based on secondary modulation, and the underwater correlation imaging method based on secondary modulation includes:

[0040] Emitting laser signals and guiding the laser signals to the oscillating mirror DMD modulation device;

[0041] generating a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes a plurality of reference Hadamard matrix speckles;

[0042] Drive the oscillating mirror DMD modulation device to oscillate according to a preset angle;

[0043] Scan the detection target at a preset angle to determine sub-fields of view at different angles; each sub-field of view corresponds to a reference Hadamard matrix speckle pattern;

[0044] For any sub-field of view, use any sub-field of view as the current sub-field of view:

[0045] Performing a first modulation on the first reflected signal based on a reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view;

[0046] Illuminating the detection target with the first modulated light signal in the current sub-field of view, receiving the light signal reflected by the detection target, and performing a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal in the current sub-field of view;

[0047] Based on the correlation imaging of the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle, the correlated reconstructed image of each sub-field of view is obtained, and the correlated reconstructed images of all sub-fields of view of the detection target are spliced to obtain the target image.

[0048] In one embodiment, a spatial subdivision sparse reconstruction method is used to stitch the associated reconstructed images of all sub-fields of view to obtain a target image.

[0049] According to the specific embodiments provided in this application, this application has the following technical effects:

[0050] The present application discloses an underwater correlation imaging system and method based on secondary modulation, which utilizes a swing mirror DMD modulation device and combines the correlation imaging mechanism based on secondary modulation to modulate the target light information twice, effectively suppressing the noise and interference caused by water scattering, and greatly improving the signal-to-noise ratio of the target image finally obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0052] Figure 1 A schematic diagram of the structure of an underwater correlation imaging system based on secondary modulation provided in one embodiment of the present application;

[0053] Figure 2 A schematic flow chart of an underwater correlation imaging method based on secondary modulation provided in one embodiment of the present application;

[0054] Figure 3 Schematic diagram of a reference Hadamard speckle pattern generated by a 128×128-order Hadamard matrix according to an embodiment of the present application;

[0055] Figure 4 Schematic diagram of reference Hadamard inverse matrix speckle generated by a 128×128-order Hadamard inverse matrix provided in an embodiment of the present application.

[0056] Reference numerals:

[0057] Optical emission and guidance unit-1, laser-11, reflector-12, spectrometer-13; oscillating mirror DMD modulation device-2; control unit-3; signal receiving and processing unit-4, underwater wide-angle focusing lens group-41, bucket detector-42, data acquisition card-43, data processing unit-44, oscilloscope-45; detection target-5. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0059] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0060] In an exemplary embodiment, Figure 1 As shown, an underwater correlation imaging system based on secondary modulation is provided, which includes: an optical emission and guidance unit 1, a swing mirror DMD modulation device 2, a control unit 3 and a signal receiving and processing unit 4.

[0061] The optical emission and guidance unit 1 is used to emit laser signals and guide the laser signals to the oscillating mirror DMD modulation device 2 .

[0062] In one embodiment, if Figure 1 As shown, the optical emission and guidance unit 1 includes a laser 11 , a reflector 12 and a beam splitter 13 .

[0063] The laser signal emitted by the laser 11 is reflected by the reflector 12 and reaches the beam splitter 13 , and the beam splitter 13 guides the laser signal to the oscillating mirror DMD modulation device 2 .

[0064] Among them, the laser 11 adopts a 532nm laser, which emits a continuous laser with a wavelength of 532nm, providing an initial light source for illuminating the detection target 5; the reflector 12 is located between the laser 11 and the spectroscope 13, and is used to reflect the laser signal, adjust the optical path direction of the laser signal, and guide the laser signal to the oscillating mirror DMD modulation device 2; the spectroscope 13 realizes the separation and merging of the optical path, and divides the incident light (i.e., the laser signal) into two paths, one of which is first reflected to the oscillating mirror DMD modulation device 2 for the first modulation, and the other is transmitted to the barrel detector 42 after the second modulation (the transmitted light signal is Figure 1 medium blue light signal).

[0065] The signal receiving and processing unit 4 is used to generate a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes multiple reference Hadamard matrix speckles, such as Figure 1 shown.

[0066] The control unit is connected to the oscillating mirror DMD modulation device 2 , and the control unit is used to drive the oscillating mirror DMD modulation device 2 to oscillate according to a preset angle.

[0067] In one embodiment, the control unit includes: a microcontroller STM32.

[0068] The STM32 microcontroller drives the oscillating mirror DMD modulation device 2 to periodically oscillate at a preset angle within the current subfield of view. The STM32 synchronizes the oscillation angle of the oscillating mirror with the DMD modulation of the Hadamard speckle matrix, ensuring that each oscillating mirror angle corresponds to a subfield of view and a reference Hadamard matrix speckle pattern.

[0069] In one embodiment, the control unit further includes a Field-Programmable Gate Array (FPGA).

[0070] The field programmable gate array is connected with the swing mirror and the digital micromirror device respectively.

[0071] The field-programmable gate array (FPGA) generates a synchronous trigger signal and, based on it, controls the oscillation of the oscillating mirror, aligning it with the modulation mode switching of the digital micromirror device (DMD). This synchronizes the oscillating mirror angle with the DMD's (DMD) scanning. The DMD's modulation mode is determined based on a reference Hadamard matrix speckle pattern. The FPGA, a Xilinx Artix-7 XC7A100T, controls DMD mode switching in real time (1kHz refresh rate) and synchronizes the oscillating mirror angle with the 42-bit sampling of the bucket detector (latency <1μs).

[0072] Specifically, the oscillating mirror angle and DMD synchronize to control the scanning process, including:

[0073] 1) The oscillating mirror is driven by an STM32 microcontroller and periodically oscillates according to a preset angle sequence (e.g., 0°–60°, in 0.1° increments), dividing the large field of view into several sub-fields of view.

[0074] 2) Each swing mirror angle corresponds to a sub-field of view, and the DMD loads the Hadamard matrix pattern H that matches the spatial coordinates of the sub-field of view. i (x,y) (i.e., the reference Hadamard matrix speckle pattern corresponding to each sub-field of view), ensuring that the sub-field coverage is consistent with the DMD modulation area.

[0075] 3) FPGA is used to generate synchronous trigger signals to control the precise time alignment between the swing mirror swing and the DMD mode switching, with a delay error of less than 1μs.

[0076] The specific process is as follows: the FPGA receives the swing mirror angle feedback signal from the STM32 microcontroller, calls the pre-stored reference Hadamard matrix sequence according to the angle value, and drives the DMD to refresh the modulation mode; the actual swing mirror angle is monitored in real time through the photoelectric encoder deployed in the STM32 microcontroller and compared with the preset angle. If the deviation exceeds the threshold (such as ±0.05°), the drive voltage is adjusted through the PID algorithm to ensure the accuracy of the swing mirror angle.

[0077] The oscillating mirror DMD modulation device 2 is connected to the signal receiving and processing unit 4, and the oscillating mirror DMD modulation device 2 is used to:

[0078] The detection target 5 is scanned according to a preset angle to determine sub-fields of view at different angles; one sub-field of view corresponds to one reference Hadamard matrix speckle.

[0079] For any sub-field of view, use any sub-field of view as the current sub-field of view:

[0080] The first reflected signal is modulated for the first time based on the reference Hadamard matrix speckle in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view.

[0081] The detection target 5 is illuminated by the first modulated light signal in the current sub-field of view, and the light signal reflected by the detection target 5 is received. The light signal reflected by the detection target 5 is modulated for a second time based on the reference Hadamard matrix speckle in the current sub-field of view to generate a second modulated light signal in the current sub-field of view.

[0082] In one embodiment, the oscillating mirror DMD modulation device 2 includes an oscillating mirror and a digital micromirror device (DMD).

[0083] The digital micromirror device is connected to the signal receiving and processing unit 4 and the control unit respectively, the swing mirror is connected to the control unit, and the digital micromirror device is fixed on the swing mirror.

[0084] The oscillating mirror scans the detection target 5 according to a preset angle to determine sub-fields of view at different angles.

[0085] The digital micromirror device performs a first modulation on the first reflected signal based on the reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated light signal in the current sub-field of view, and uses the first modulated light signal in the current sub-field of view to illuminate the detection target 5, receives the light signal reflected by the detection target 5, and performs a second modulation on the light signal reflected by the detection target 5 based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal.

[0086] Specifically, the oscillating mirror DMD modulation device 2 quickly swings to scan the detection target 5, expands the field of view, divides the large field of view into multiple sub-fields of view, scans the detection target 5 in the current sub-field of view, and simultaneously Figure 1 During the first modulation process, the Hadamard matrix speckle pattern loaded by the DMD (ie, the reference Hadamard matrix speckle pattern, which is an orthogonal speckle pattern) is used to generate the first modulated optical signal.

[0087] The first modulated light signal in the current sub-field of view is reflected by the detection target 5 and returned to the oscillating mirror DMD modulation device 2 for a second modulation to generate the second modulated light signal in the current sub-field of view.

[0088] During the second modulation process, the DMD loads the corresponding reference Hadamard inverse matrix speckle pattern in each sub-field of view. The swing mirror angle and the DMD modulation mode are time-synchronized and controlled by the microcontroller STM32 and FPGA. The first modulated light signal is reflected by the detection target 5 and then reaches the DMD, where it undergoes a second modulation, further enhancing the target signal (i.e., the first reflected signal) while suppressing water scattered light.

[0089] The signal receiving and processing unit 4 is configured to perform correlated imaging based on the second modulated optical signal in each sub-field of view and the pre-modulated reference Hadamard matrix speckle pattern (i.e., the corresponding reference Hadamard matrix speckle pattern) to obtain a correlated reconstructed image of each sub-field of view, and to stitch the correlated reconstructed images of all sub-fields of view of the detection target 5 to obtain a target image.

[0090] In one embodiment, if Figure 1 As shown, the signal receiving and processing unit 4 includes: an underwater wide-angle focusing lens group 41, a bucket detector 42, a data acquisition card 43 and a signal receiving and processing unit 4.

[0091] The beam splitter 13, the underwater wide-angle focusing lens group 41, and the barrel detector 42 are located on the same optical path.

[0092] The underwater wide-angle focusing lens group 41 is used to expand the imaging field of view of the second modulated light signal after being transmitted by the optical emission and guidance unit 1 in the current sub-field of view, and focus it on the bucket detector 42. The underwater wide-angle focusing lens group 41 has a focal length of 50 mm and a field of view angle of 120°.

[0093] Bucket detector 42 is used to obtain the light intensity signal in the current sub-field of view based on the focused second modulated light signal. Bucket detector 42 has a bandwidth of 10 MHz and a sensitivity of 0.9 A / W (@532 nm). It replaces traditional CCDs and performs correlation calculations through single-pixel detection.

[0094] The data acquisition card 43 is used to store the light intensity signal under each sub-field of view, collect the electrical signal output by the corresponding barrel detector 42 under each sub-field of view, and transmit it to the signal receiving and processing unit 4.

[0095] The signal receiving and processing unit 4 is used to obtain a target image based on the light intensity signal in the current sub-field of view and the corresponding reference Hadamard matrix speckle pattern.

[0096] In one embodiment, the signal receiving and processing unit 4 further includes an oscilloscope 45 .

[0097] The oscilloscope 45 is connected to the barrel detector 42 and the data acquisition card 43 respectively.

[0098] The oscilloscope 45 is used to monitor in real time the waveform and noise characteristics of the light intensity signal in the current sub-field of view output by the bucket detector 42. The oscilloscope 45 has a sampling rate of 2 GS / s and a bandwidth of 200 MHz.

[0099] In one embodiment, the FPGA is also connected to the bucket detector 42 .

[0100] The field programmable gate array is also used to trigger the bucket detector 42 to collect the light intensity signal in the current sub-field of view when the angle of the swing mirror is stabilized at a corresponding preset angle in the current sub-field of view.

[0101] Based on the same inventive concept, embodiments of the present application also provide a method for underwater correlation imaging based on secondary modulation, based on the aforementioned underwater correlation imaging system. The solution provided by this method is similar to the solution described in the aforementioned system. Therefore, the specific limitations of one or more embodiments of the underwater correlation imaging method based on secondary modulation provided below can be found in the limitations of the underwater correlation imaging system based on secondary modulation above, and will not be repeated here.

[0102] In an exemplary embodiment, Figure 2 As shown, a method for underwater correlation imaging based on secondary modulation is provided, comprising the following steps:

[0103] Step S1: emitting a laser signal and guiding the laser signal to a oscillating mirror DMD modulation device.

[0104] Step S2: generating a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes a plurality of reference Hadamard matrix speckles.

[0105] Step S3: Drive the oscillating mirror DMD modulation device to oscillate according to a preset angle. The high-performance microcontroller STM32 and FPGA control the oscillating mirror and DMD to synchronously and dynamically scan and detect the target.

[0106] Step S4: Scan the detection target according to a preset angle to determine sub-fields of view at different angles; one sub-field of view corresponds to one reference Hadamard matrix speckle pattern.

[0107] For any sub-field of view, use any sub-field of view as the current sub-field of view:

[0108] Step S5: performing a first modulation on the first reflected signal based on the reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view.

[0109] Specifically, the reference Hadamard matrix speckle pattern under the current sub-field of view loaded by the DMD is The first reflected signal is modulated for the first time. The calculation formula for the first modulation is:

[0110] (1)

[0111] in, represents the first modulated light signal in any sub-field of view; represents the normalized Hadamard matrix speckle (i.e., the reference Hadamard matrix speckle), with dimension N×N, satisfying ; is the raw light intensity of the laser (unit: mW / cm²).

[0112] For example, select As a modulation matrix (i.e., reference Hadamard matrix speckle), the modulation process can be expressed as:

[0113] (2)

[0114] (3)

[0115] In formula (3), each row represents the speckle field distribution corresponding to a modulation mode; 、 、 and The columns represent the input light intensity at different locations (i.e., the intensity distribution of the original light field in the four sub-regions). Each row represents the speckle field encoding method corresponding to an orthogonal modulation mode. Due to the orthogonality of the Hadamard matrix, the noise projections between different modes cancel each other out, thereby improving the signal-to-noise ratio of the target signal.

[0116] Step S6: Use the first modulated light signal in the current sub-field of view to illuminate the detection target, receive the light signal reflected by the detection target, and perform a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal in the current sub-field of view.

[0117] Specifically, the target reflected light field (i.e., the light signal reflected by the target) after the target information light is modulated for the first time and detected is:

[0118] (4)

[0119] in, Represents the total light field after the target is reflected (i.e., the light signal reflected by the detection target), which includes the target signal and water scattering noise; represents the speckle light field generated after the first modulation (i.e., the first modulated light signal in any sub-field of view); Represents the target reflectivity distribution and carries the spatial information of the detected target; Represents water scattered light noise.

[0120] The speckle light field after the second modulation (i.e. the second modulated light signal):

[0121] (5)

[0122] in, represents the speckle light field after the second modulation (i.e., the second modulated light signal); represents the inverse matrix speckle of the Hadamard matrix speckle (for orthogonal matrices, here is the transposed matrix); since , the speckle light field after the second modulation is finally simplified to: target signal: With the noise term , where the noise term The statistical characteristics of are orthogonal to the target signal.

[0123] The inner product of the target signal and the noise term is:

[0124] (6)

[0125] in, Indicates the coordinates of the detected target; Coordinates representing the modulation pattern of noise or DMD; Indicates that in modulation mode ( k , l ) is the noise component introduced at .

[0126] because is a deterministic signal, and is zero-mean noise, then:

[0127] (7)

[0128] in, ; is the expected value operator; It is the inner product operation, which represents the dot product of the signal in the spatial domain.

[0129] The randomness of the noise causes it to have no correlation with the target signal, and the interference is canceled out under statistical averaging; the expectation of the inner product of the target signal and the noise term is zero, indicating that they are orthogonal in a statistical sense; the Hadamard matrix is equivalent to a set of orthogonal probes, the projection of the target signal on the probes is coherent, while the noise is random. The randomness of the noise causes the mean of its projection on different Hadamard matrix patterns to be zero. Correlation imaging suppresses the random contribution of noise and retains the deterministic information of the target signal through multiple measurements and statistical averaging.

[0130] Step S7: Correlation imaging is performed based on the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle pattern to obtain a correlated reconstructed image of each sub-field of view, and the correlated reconstructed images of all sub-fields of view of the detection target are spliced to obtain a target image.

[0131] In one embodiment, a spatial subdivision sparse reconstruction method is used to stitch the associated reconstructed images of all sub-fields of view to obtain a target image.

[0132] Specifically, the bucket detector and the data acquisition card detect and collect the light intensity signal corresponding to each sub-field of view; and each sub-field of view is independently reconstructed using the light intensity signal collected by the bucket detector and the corresponding reference Hadamard matrix speckle pattern.

[0133] The bucket detector signal (i.e., light intensity signal) in any sub-field of view is:

[0134] (8)

[0135] in, Indicates the i Bucket detector signal under the sub-field of view; Indicates the i The spatial area range of each sub-field of view; Indicates the second modulated optical signal at the spatial coordinate ( x , y ), ( x , y ) represents the two-dimensional position of a point in the sub-field of view, corresponding to the actual physical position of the detection target; Represents the integral over two-dimensional space coordinates.

[0136] The calculation method for independent reconstruction of any sub-field of view is as follows:

[0137] 1. Calculate the total light intensity in any sub-field of view:

[0138] (9)

[0139] in, Indicates the i The sub-field of view is in the spatial coordinate ( x , y ) is the intensity of the reconstructed image (i.e. i total light intensity within the sub-field of view); Indicates the i Under the sub-field of view, j The total light intensity signal of the bucket detector corresponding to the sub-modulation mode; M Indicates the total number of modulation modes (e.g., the number of rows in the reference Hadamard matrix, corresponding to the number of measurements); Indicates the i Sub-field of view M Average light intensity in sub-modulation mode; No. i The sub-field of view corresponds to the j The reference Hadamard matrix speckle is in the spatial coordinate ( x , y ) (the value is ±1).

[0140] 2. Splice the associated reconstructed images of each sub-field of view into a complete image, and apply weighted smoothing to the sub-field of view boundaries. The calculation method for weighted smoothing of any sub-field of view boundary is:

[0141] (10)

[0142] Where, represents the complete target image after stitching (i.e., the target image); Represents the spatial area in the sub-field of view , the boundary weight of the spatial coordinate (x, y); N is the total number of sub-fields of view; i Indicates the sequence number of the sub-field of view; Is the sub-field of view in the spatial region The internally reconstructed image information represents the target reflectivity or light intensity distribution of the sub-field of view; It means that the weighted results of all sub-fields of view are combined into a whole, that is, the contributions of the sub-fields of view are merged through the weight distribution of each spatial coordinate; where each spatial coordinate ( x , y ) is determined by the contributions of multiple sub-fields, satisfying the normalization condition:

[0143] (11)

[0144] 3. Optimize the sparsity of overlapping areas to ensure image consistency. This utilizes global sparse regularization and sub-field consistency optimization.

[0145] The global sparse regularization calculation formula is:

[0146] (12)

[0147] in, Represents the reconstructed global target image, which is composed of multiple sub-field images; Represents the L1 norm of the image, which represents the sum of the absolute values of all pixels and is used to enhance image sparsity (suppress noise); represents the regularization parameter, balancing sparsity and sub-field consistency; Indicates that for all adjacent sub-fields p and q sum; Represents a set of adjacent sub-fields of view; Indicates adjacent sub-fields of view p and q The sum of squared Euclidean distances in the overlapping areas ensures smooth stitching.

[0148] (13)

[0149] in, represents the overlapping area of sub-fields p and q; Indicates that the pth sub-field of view is at the coordinate ( x , y ) at the reconstruction intensity; Indicates that the qth sub-field of view is at the coordinate ( x , y ) at the reconstruction intensity.

[0150] Furthermore, Figure 3 and Figure 4 The modulation pattern of the reference Hadamard speckle generated by the 128×128 order reference Hadamard matrix is as follows: Figure 3 and Figure 4 As shown, the white area represents +1 and the black area represents -1. The orthogonality ensures the independence of different modes. These modulation modes are dynamically loaded by the DMD to achieve correlated modulation of the target area.

[0151] Furthermore, multiple sets of underwater image reconstruction results were obtained using different modulation systems (traditional Gaussian modulation pattern correlation imaging, Gaussian modulation computational correlation imaging, Hadamard modulation pattern correlation imaging, Hadamard modulation pattern computational correlation imaging, and underwater correlation imaging based on secondary modulation) at different sampling rates (ranging from 10% to 100%). The experimental results show that as the sampling rate increases, the image reconstruction effect changes in the following pattern: at low sampling rates, the reconstructed image is relatively blurry and the noise is more obvious; as the sampling rate increases, the image quality gradually improves and the noise is effectively suppressed. Ultimately, at a sampling rate of 100%, the image clarity and resolution reach optimal levels. In addition, the secondary modulation and sparse reconstruction techniques of this application have significant advantages in improving image quality and reducing noise.

[0152] Beneficial effects:

[0153] 1) Improved signal-to-noise ratio of underwater correlation imaging:

[0154] Traditional correlation imaging usually relies on only one modulation, which means that the optical signal is easily affected by water scattering and background noise during the acquisition process, resulting in a decrease in image quality. In contrast, the underwater correlation imaging system and method based on secondary modulation in the present application optimizes the correlation of the target light through two modulations. The first modulation produces a preliminary speckle pattern, and the second modulation further optimizes the target light information by adjusting the phase and intensity of the light, making the target light information more prominent in the image, while effectively suppressing the noise and interference caused by water scattering. Especially in strong underwater scattering environments, two modulations can greatly improve the signal-to-noise ratio of the image and avoid the noise interference problem common in single modulation methods. Through two modulations, not only the identifiability of the target is improved, but also the clarity and detail retention of the spliced image in complex underwater environments are ensured.

[0155] 2) Improved the system detection imaging field of view:

[0156] By introducing oscillating mirror DMD technology and spatial subdivision sparse reconstruction methods, image stitching technology is applied to underwater imaging systems, thereby expanding the imaging system's detection field of view. This not only increases the detection range, but also effectively enhances the imaging system's overall detection capabilities, especially in application scenarios such as large-scale detection and dynamic target capture.

[0157] 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, stored data, displayed data, 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 relevant data must comply with relevant regulations.

[0158] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. In particular, any reference to memory, database, 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 may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0159] The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processors involved in the various embodiments provided herein may include, but are not limited to, general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic units, data processing logic units based on quantum computing, and the like.

[0160] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, 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.

[0161] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the system, method, and core concept of this application. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of this application. In summary, the contents of this specification should not be construed as limiting this application.

Claims

1. An underwater correlation imaging system based on secondary modulation, characterized in that: The system comprises: an optical emission and guidance unit, a swing mirror DMD modulation device, a control unit and a signal receiving and processing unit; The optical emission and guidance unit is used to emit laser signals and guide the laser signals to the oscillating mirror DMD modulation device. The optical emission and guidance unit includes: a laser, a reflector and a spectroscope. The laser signal emitted by the laser is reflected by the reflector and reaches the spectroscope, and the spectroscope guides the laser signal to the oscillating mirror DMD modulation device. The signal receiving and processing unit is used to generate a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes multiple reference Hadamard matrix speckles; The control unit is connected to the oscillating mirror DMD modulation device, and the control unit is used to drive the oscillating mirror DMD modulation device to oscillate according to a preset angle; The oscillating mirror DMD modulation device is connected to the signal receiving and processing unit, and the oscillating mirror DMD modulation device is used to: Scan the detection target at a preset angle to determine sub-fields of view at different angles; each sub-field of view corresponds to a reference Hadamard matrix speckle pattern; For any sub-field of view, use any sub-field of view as the current sub-field of view: Performing a first modulation on the first reflected signal based on the reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view; the first reflected signal is an optical signal reflected by the spectroscope; Illuminating the detection target with the first modulated light signal in the current sub-field of view, receiving the light signal reflected by the detection target, and performing a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal in the current sub-field of view; The signal receiving and processing unit is used to perform correlated imaging based on the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle to obtain a correlated reconstructed image of each sub-field of view, and to splice the correlated reconstructed images of all sub-fields of view of the detection target to obtain a target image.

2. The underwater correlation imaging system based on secondary modulation according to claim 1, characterized in that: The swing mirror DMD modulation device includes: a swing mirror and a digital micromirror device; The digital micromirror device is connected to the signal receiving and processing unit and the control unit respectively, the swing mirror is connected to the control unit, and the digital micromirror device is fixed on the swing mirror; The oscillating mirror scans the detection target at a preset angle to determine the sub-field of view at different angles; The digital micromirror device performs a first modulation on the first reflected signal based on the reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated light signal in the current sub-field of view, and uses the first modulated light signal in the current sub-field of view to illuminate the detection target, receives the light signal reflected by the detection target, and performs a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal.

3. The underwater correlation imaging system based on secondary modulation according to claim 2, characterized in that: The control unit includes a microcontroller STM32; The STM32 microcontroller is used to drive the oscillating mirror DMD modulation device to oscillate periodically according to the corresponding preset angle in the current sub-field of view.

4. The underwater correlation imaging system based on secondary modulation according to claim 3, characterized in that: The control unit also includes: a field programmable gate array; The field programmable gate array is connected to the swing mirror and the digital micromirror device respectively; Field Programmable Gate Arrays are used for: A synchronous trigger signal is generated, and based on the synchronous trigger signal, the swinging of the swing mirror is controlled to be time-aligned with the modulation mode switching of the digital micromirror device; the modulation mode of the digital micromirror device is determined based on a reference Hadamard matrix speckle.

5. The underwater correlation imaging system based on secondary modulation according to claim 4, characterized in that: The signal receiving and processing unit includes: an underwater wide-angle focusing lens group, a barrel detector, a data acquisition card and a data processing unit; The underwater wide-angle focusing lens group is used to expand the imaging field of view of the second modulated light signal after being transmitted by the optical emission and guidance unit in the current sub-field of view, and focus it on the barrel detector; The bucket detector is used to obtain a light intensity signal in the current sub-field of view based on the second modulated light signal after focusing in the current sub-field of view; The data acquisition card is used to store the light intensity signal under each sub-field of view; The data processing unit is used to perform correlated imaging based on the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle to obtain a correlated reconstructed image of each sub-field of view, and to splice the correlated reconstructed images of all sub-fields of view of the detection target to obtain a target image.

6. The underwater correlation imaging system based on secondary modulation according to claim 5, characterized in that: The signal receiving and processing unit also includes: an oscilloscope; The oscilloscope is connected to the barrel detector and the data acquisition card respectively; The oscilloscope is used to monitor the waveform and noise characteristics of the light intensity signal output by the bucket detector in the current sub-field of view in real time.

7. The underwater correlation imaging system based on secondary modulation according to claim 5, characterized in that: The FPGA is also connected to the bucket detector; The field programmable gate array is also used to trigger the bucket detector to collect the light intensity signal under the current sub-field of view when the angle of the swing mirror is stabilized at a corresponding preset angle under the current sub-field of view.

8. An underwater correlation imaging method based on secondary modulation, characterized in that: The underwater correlation imaging method based on secondary modulation is based on the underwater correlation imaging system based on secondary modulation according to any one of claims 1 to 7, and the underwater correlation imaging method based on secondary modulation includes: Emitting laser signals and guiding the laser signals to the oscillating mirror DMD modulation device; generating a Hadamard matrix speckle sequence; the Hadamard matrix speckle sequence includes a plurality of reference Hadamard matrix speckles; Drive the oscillating mirror DMD modulation device to oscillate according to a preset angle; Scan the detection target at a preset angle to determine sub-fields of view at different angles; each sub-field of view corresponds to a reference Hadamard matrix speckle pattern; For any sub-field of view, use any sub-field of view as the current sub-field of view: Performing a first modulation on the first reflected signal based on a reference Hadamard matrix speckle pattern in the current sub-field of view to generate a first modulated optical signal in the current sub-field of view; Illuminating the detection target with the first modulated light signal in the current sub-field of view, receiving the light signal reflected by the detection target, and performing a second modulation on the light signal reflected by the detection target based on the reference inverse Hadamard matrix speckle pattern in the current sub-field of view to generate a second modulated light signal in the current sub-field of view; Based on the correlation imaging of the second modulated light signal in each sub-field of view and the corresponding reference Hadamard matrix speckle, the correlated reconstructed image of each sub-field of view is obtained, and the correlated reconstructed images of all sub-fields of view of the detection target are spliced to obtain the target image.

9. The underwater correlation imaging method based on secondary modulation according to claim 8, characterized in that: The spatial subdivision sparse reconstruction method is used to stitch the associated reconstructed images of all sub-fields of view to obtain the target image.

Images