Underwater double-pulse laser compression imaging method and system

Abstract

The invention discloses an underwater double-pulse laser compression imaging method and system, and the method comprises the steps: transmitting a double-pulse laser waveform containing different pulse widths through a double-pulse laser source, and irradiating a target region after the double-pulse laser waveform is collimated and expanded; focusing, modulating and collecting laser echoes of the target area; according to the collected laser echo waveform, distance and intensity information of the target area is obtained through cross-correlation calculation, and high-precision three-dimensional imaging of the underwater target area is carried out. According to the method and the system, non-scanning underwater laser imaging is realized by combining a double-pulse distance measurement method and a compression imaging method, and meanwhile, the intensity of an image and the distance reconstruction precision are remarkably improved by introducing cross-correlation calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of laser imaging systems, and in particular to an underwater double-pulse laser compression imaging method and system. Background Art

[0002] Underwater images are one of the means for humans to obtain effective underwater information. Laser imaging systems can simultaneously obtain the distance and reflectivity information of target objects, which is of great significance for application scenarios such as shallow sea topography mapping and bottom remote sensing. Existing underwater laser imaging systems mainly include range-gated and scanning types. Underwater laser imaging systems based on range-gated imaging technology have the following main disadvantages: 1. Since range gating only collects reflection signals near the target, it is necessary to pre-specify the working time of the image intensifier, and generally needs to rely on auxiliary equipment such as ultrasonic sensors to work; 2. Range-gated imaging technology relies on image intensifiers and CCDs to collect echo signals of targets. Each time slice requires high-repetition-rate acquisition to meet the exposure time requirements of the CCD, which ultimately leads to a significant increase in imaging time and cannot achieve a high range resolution; 3. Since range gating requires a high-repetition-rate shutter, the inconsistency of single exposure time will introduce additional errors to the system.

[0003] The main disadvantages of scanning underwater laser imaging systems include: 1. In order to obtain high-resolution images, the scanning underwater laser imaging system needs to obtain enough laser sampling points through a large number of repeated scans, which significantly reduces the imaging rate of the system; 2. The scanning field of view is a fan-shaped field of view, and the point cloud distribution is often non-uniform, so a large amount of calibration and post-correction is required to obtain the position information of the actual sampling points; 3. In order to suppress backscattering and noise, the CCD-based scanning underwater laser imaging system still needs to be combined with range gating technology, which results in it having the disadvantages of the above-mentioned range gating scheme.

[0004] The imaging method based on compressed sensing theory can obtain high-resolution images based on low-resolution imaging devices. It modulates the reflected signal of the target through a spatial light modulator and collects the corresponding echo pulses. After reconstruction calculation, the target image is finally obtained. The compressed imaging method can reduce the storage pressure of the system and increase the acquisition speed while improving the spatial resolution of the system. Since the detector can only obtain a single echo signal in a single measurement and cannot directly obtain the distance information of the entire target, the traditional compressed imaging method can only achieve two-dimensional image reconstruction. In addition, due to the backscattering problem of laser imaging in underwater environments, the echo signal will also contain stronger noise. Therefore, how to accurately extract the distance information of underwater targets from the echo signals of multiple measurements has become a key problem to be solved in compressed imaging. Summary of the invention

[0005] The purpose of the present invention is to provide an underwater dual-pulse laser compression imaging method and system, which realizes non-scanning underwater laser imaging by combining dual-pulse ranging and compression imaging methods, and significantly improves the image intensity and distance reconstruction accuracy by introducing cross-correlation calculation.

[0006] The objective of the present invention is achieved through the following technical solutions: An underwater double-pulse laser compression imaging method, the method comprising: Step 1: a dual-pulse laser source is used to emit a dual-pulse laser waveform with different pulse widths, and the dual-pulse laser waveform is collimated and expanded to irradiate the target area; Step 2, focusing, modulating and collecting the laser echo of the target area; Step 3: Based on the collected laser echo waveform, the distance and intensity information of the target area are obtained through cross-correlation calculation, and high-precision three-dimensional imaging of the underwater target area is performed.

[0007] An underwater double-pulse laser compression imaging system, the system comprises a laser emission module, an image acquisition module, and a control processing module, wherein: The laser emission module is used to emit a double-pulse laser waveform containing different pulse widths through a double-pulse laser source, and irradiate the target area after collimation and beam expansion; The image acquisition module is used to focus, modulate and acquire the laser echo of the target area; The control and processing module is used to obtain the distance and intensity information of the target area through cross-correlation calculation based on the collected laser echo waveform, and perform high-precision three-dimensional imaging of the underwater target area.

[0008] An electronic device comprises a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to execute the method.

[0009] A computer storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor and executing the method.

[0010] It can be seen from the technical solution provided by the present invention that the above method and system realize non-scanning underwater laser imaging by combining dual-pulse ranging and compressed imaging methods, and at the same time significantly improve the image intensity and distance reconstruction accuracy by introducing cross-correlation calculation, and can also complete high-precision three-dimensional imaging in the backscattering noise environment in underwater laser imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0012] Figure 1 A schematic diagram of the process flow of an underwater double-pulse laser compression imaging method provided by an embodiment of the present invention; Figure 2 The diagram is a schematic diagram of the architecture of the system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] like Figure 1 FIG. 1 is a flow chart of an underwater double-pulse laser compression imaging method provided by an embodiment of the present invention, wherein the method comprises: Step 1: a dual-pulse laser source is used to emit a dual-pulse laser waveform with different pulse widths, and the dual-pulse laser waveform is collimated and expanded to irradiate the target area; In this step, the dual-pulse laser source repeatedly emits a single laser waveform at a fixed frequency, and the laser waveform includes a wide pulse and a narrow pulse, and there is a certain interval time between the two pulses; The emitted laser waveform is shaped by the collimating and beam expanding lens and then irradiates the target area.

[0015] Step 2, focusing, modulating and collecting the laser echo of the target area; In this step, the laser echo of the target area is focused by a focusing lens and then projected onto the spatial optical modulator; The laser echo is modulated by a spatial optical modulator, the modulation templates are different rows of the measurement matrix, and the modulated waveform is projected onto the photosensitive surface of the detector; The modulated laser echo waveform is then collected by the detector.

[0016] During the acquisition of laser echo waveform: First, a standard double-pulse laser emission waveform p is collected and a random binary matrix of M×N dimensions is generated by calculation. As a measurement matrix for compressed sampling; Using a spatial optical modulator to project the i-th row of the measurement matrix as a modulation template, where i=1, 2, ..., M; and using the complete waveform of the laser echo signal as the i-th row of the sampling matrix Y; Repeat the operation until the projection of all rows in the measurement matrix is ​​completed, generating a complete sampling matrix Y of the laser echo waveform; Among them, M in the signal acquisition process is less than N, and the ratio M / N is the compression sampling rate in the compressed sensing theory.

[0017] Step 3: Based on the collected laser echo waveform, the distance and intensity information of the target area are obtained through cross-correlation calculation, and high-precision three-dimensional imaging of the underwater target area is performed.

[0018] In this step, according to the sampling matrix Y of the acquired laser echo waveform, the i-th column of the sampling matrix Y is extracted to generate a compressed sampling vector y under the time slice, where i=1,2,…,L; L is the number of elements in each row of the sampling matrix Y, that is, the number of columns of Y; The learned denoising-based approximate message passing algorithm LDAMP (Learned Denoising-based Approximate Message Passing) is used to Solution, For the generated M×N dimensional random binary matrix, the column vector reconstructed image x under the time slice is obtained; Repeat the operation until all columns of the sampling matrix Y are reconstructed, and splice the column vector reconstructed images x under all time slices into a complete N×L dimensional image matrix X; Extract the jth row of the image matrix X and find the maximum value a in the row vector max , and perform cross-correlation calculation on the row vector and the dual-pulse laser emission waveform vector p to obtain the cross-correlation vector r, where j = 1, 2, …, N; the process of cross-correlation calculation is as follows:

[0019] in, represents the kth element of the cross-correlation vector r; Represents the nth element of the jth row of the image matrix X; Represents the nkth element of the double-pulse laser emission waveform vector p, n=1,2,…,L; when nk≤0, =0; After the cross-correlation calculation is completed, find the position k where the maximum value in the cross-correlation vector r is located max , then the intensity corresponding to the jth pixel of the target 3D image to be reconstructed is a max , the corresponding distance d is calculated by the time-of-flight method: d=ckmax / 2f s , where c is the speed of light; f s is the A / D sampling rate of the system; Repeat the operation until all rows of the image matrix X are calculated; Then, by combining the distance and intensity information of all pixels in the target area, a visualization 3D model corresponding to the target area is rendered and generated. The specific rendering method may use MATLAB mesh or other software or algorithms that can achieve similar functions.

[0020] In a specific implementation, the LDAMP reconstruction algorithm can be replaced by methods such as TVAL3, COAST, or other methods based on iteration, denoising operators, or neural networks.

[0021] In addition, the dual-pulse laser source can be realized by using two lasers in conjunction with a delay control device, or by other hardware replacements that can achieve the same or similar functions.

[0022] Based on the above method embodiment, the embodiment of the present invention also provides an underwater double-pulse laser compression imaging system, such as Figure 2 FIG. 1 is a schematic diagram of the architecture of the system according to an embodiment of the present invention, wherein the system includes a laser emission module, an image acquisition module, and a control processing module, wherein: The laser emission module is used to emit a double-pulse laser waveform containing different pulse widths through a double-pulse laser source, and irradiate the target area after collimation and beam expansion; The image acquisition module is used to focus, modulate and acquire the laser echo of the target area; The control and processing module is used to obtain the distance and intensity information of the target area through cross-correlation calculation based on the collected laser echo waveform, and perform high-precision three-dimensional imaging of the underwater target area.

[0023] In a specific implementation, the control processing module is also responsible for the control and data exchange of each module of the system, as well as the storage of collected image data, wherein: The control processing module controls the switch and working state of the equipment in each module, and controls the image acquisition module to modulate and acquire the laser echo for each modulation template; and writes the corresponding laser echo data under all the acquired modulation templates into the storage device.

[0024] The implementation process of each module in the above system is described in the method embodiment.

[0025] An embodiment of the present invention further provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor is configured to run the computer program to execute each step in the method embodiment.

[0026] An embodiment of the present invention further provides a computer storage medium, wherein the computer storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor and executing each step in the method embodiment.

[0027] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professionals in the field. For example, the double-pulse laser waveform can also achieve similar effects by including three or more emission waveforms of pulses with different pulse widths.

[0028] In summary, the method and system described in the embodiments of the present invention have the following advantages: 1. By combining dual-pulse ranging and compressed imaging methods, non-scanning underwater laser imaging is achieved, and the image intensity and distance reconstruction accuracy are significantly improved by introducing cross-correlation calculation; 2. The use of spatial optical modulators can achieve non-scanning full-field high-speed data acquisition, and the imaging rate is significantly better than the existing scanning imaging system, and there is no need for complex point cloud processing; 3. Through the dual-pulse laser emission waveform, the wide pulse is used to provide more sampling points in the time domain for the reconstruction of compressed imaging, ensuring the reconstruction accuracy of the target intensity information; the narrow pulse is used in conjunction with the cross-correlation calculation to improve the reconstruction accuracy of the target distance information, so that this method can also complete high-precision three-dimensional imaging in the backscattering noise environment of underwater laser imaging.

[0029] 4. The method and system of the present invention do not require the assistance of other distance information acquisition equipment, and imaging can be performed within the detector response distance.

[0030] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. An underwater double-pulse laser compression imaging method, characterized in that: The method comprises: Step 1: a dual-pulse laser source is used to emit a dual-pulse laser waveform with different pulse widths, and the dual-pulse laser waveform is collimated and expanded to irradiate the target area; Step 2, focusing, modulating and collecting the laser echo of the target area; Step 3: Based on the collected laser echo waveform, the distance and intensity information of the target area are obtained through cross-correlation calculation, and high-precision three-dimensional imaging of the underwater target area is performed.

2. The underwater double-pulse laser compression imaging method according to claim 1, characterized in that: In step 1, The dual-pulse laser source repeatedly emits a single laser waveform at a fixed frequency, the laser waveform comprising a wide pulse and a narrow pulse, and a certain interval time between the two pulses; The emitted laser waveform is shaped by the collimating and beam expanding lens and then irradiates the target area.

3. The underwater double-pulse laser compression imaging method according to claim 1, characterized in that: In step 2, the laser echo of the target area is focused by a focusing lens and then projected onto a spatial optical modulator; The laser echo is modulated by a spatial optical modulator, the modulation templates are different rows of the measurement matrix, and the modulated waveform is projected onto the photosensitive surface of the detector; The modulated laser echo waveform is then collected by the detector.

4. The underwater double-pulse laser compression imaging method according to claim 3, characterized in that: During the acquisition of laser echo waveform: First, a standard double-pulse laser emission waveform p is collected and a random binary matrix of M×N dimensions is generated by calculation. As a measurement matrix for compressed sampling; Projecting the i-th row of the measurement matrix as a modulation template using a spatial optical modulator, where i=1, 2, ..., M; And the complete waveform of the laser echo signal is taken as the i-th row of the sampling matrix Y; Repeat the operation until the projection of all rows in the measurement matrix is ​​completed, generating a complete sampling matrix Y of the laser echo waveform; Among them, M in the signal acquisition process is less than N, and the ratio M / N is the compression sampling rate in the compressed sensing theory.

5. The underwater double-pulse laser compression imaging method according to claim 4, characterized in that: In step 3, According to the sampling matrix Y of the acquired laser echo waveform, the i-th column of the sampling matrix Y is extracted to generate the compressed sampling vector y under the time slice, where i=1,2,…,L; L is the number of elements in each row of the sampling matrix Y, that is, the number of columns of Y; Through the approximate message passing algorithm LDAMP based on learning denoising Solution, For the generated M×N dimensional random binary matrix, the column vector reconstructed image x under the time slice is obtained; Repeat the operation until all columns of the sampling matrix Y are reconstructed, and splice the column vector reconstructed images x under all time slices into a complete N×L dimensional image matrix X; Extract the jth row of the image matrix X and find the maximum value a in the row vector max , and perform cross-correlation calculation on the row vector and the dual-pulse laser emission waveform vector p to obtain the cross-correlation vector r, where j = 1, 2, …, N; the process of cross-correlation calculation is as follows: in, represents the kth element of the cross-correlation vector r; Represents the nth element of the jth row of the image matrix X; Represents the nkth element of the double-pulse laser emission waveform vector p, n=1,2,…,L; when nk≤0, =0; After the cross-correlation calculation is completed, find the position k where the maximum value in the cross-correlation vector r is located max , then the intensity corresponding to the jth pixel of the target 3D image to be reconstructed is a max , the corresponding distance d is calculated by the time-of-flight method: d=ck max / 2f s , where c is the speed of light; f s is the A / D sampling rate of the system; Repeat the operation until all rows of the image matrix X are calculated; Then, by combining the distance and intensity information of all pixels in the target area, a visual 3D model corresponding to the target area is rendered.

6. An underwater double-pulse laser compression imaging system, characterized in that: The system includes a laser emission module, an image acquisition module, and a control processing module, wherein: The laser emission module is used to emit a double-pulse laser waveform containing different pulse widths through a double-pulse laser source, and irradiate the target area after collimation and beam expansion; The image acquisition module is used to focus, modulate and acquire the laser echo of the target area; The control and processing module is used to obtain the distance and intensity information of the target area through cross-correlation calculation based on the collected laser echo waveform, and perform high-precision three-dimensional imaging of the underwater target area.

7. The underwater double-pulse laser compression imaging system according to claim 6, characterized in that: The control processing module is also responsible for the control and data exchange of each module of the system, as well as the storage of collected image data, wherein: The control processing module controls the switch and working state of the equipment in each module, and controls the image acquisition module to modulate and acquire the laser echo for each modulation template; and writes the corresponding laser echo data under all the acquired modulation templates into the storage device.

8. An electronic device, comprising a memory and a processor, characterized in that: A computer program is stored in the memory, and the processor is configured to run the computer program to perform the method according to any one of claims 1 to 5.

9. A computer storage medium, characterized in that The computer storage medium stores a plurality of instructions, and the instructions are suitable for being loaded by a processor and executing the method according to any one of claims 1 to 5.

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