Three-dimensional imaging method and system for helical motion trajectory sonar

Abstract

The application provides a three-dimensional imaging method and system of a spiral motion trajectory sonar, comprising the following steps: S1, collecting echo signals, and obtaining distance compressed signals according to the echo signals; S2, setting and dividing three-dimensional imaging grids based on the distance compressed signals, and obtaining a two-dimensional imaging result of a target height plane; and S3, superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result. Compared with a circular synthetic aperture sonar, the spiral motion trajectory sonar can obtain full-angle echo information and significantly improve the three-dimensional imaging height resolution.

Description

Technical Field

[0001] This invention belongs to the field of synthetic aperture sonar imaging technology, specifically relating to a three-dimensional imaging method and system for helical motion trajectory sonar. Background Technology

[0002] Synthetic aperture sonar imaging is an important method for detecting small underwater targets, as it can obtain high-resolution acoustic images of the detected target. However, conventional strip-type synthetic aperture sonar can only detect targets within a limited angular range, resulting in missed detections and overlay phenomena. To address these issues, circular synthetic aperture sonar has been proposed. Circular synthetic aperture sonar moves in a circle around the target at a fixed height plane to obtain full-angle echo signals. High-resolution acoustic images can be obtained through imaging algorithms such as the Fourier slice theorem and back projection. Although circular synthetic aperture sonar possesses three-dimensional imaging capabilities, single-baseline circular synthetic aperture sonar suffers from high-sidelobe effects in the height direction. To improve height resolution and suppress sidelobes, a spiral trajectory synthetic aperture sonar has been proposed.

[0003] Due to the unique characteristics of the helical motion trajectory, frequency domain algorithms are no longer suitable for this type of sonar imaging. In the time domain, the back projection method (BP) offers advantages such as high imaging accuracy and no trajectory limitations, making it suitable for synthetic aperture sonar imaging with helical motion trajectories. However, this algorithm suffers from high computational complexity and low imaging efficiency.

[0004] Patent document CN117930250A discloses a three-dimensional imaging method for circular synthetic aperture sonar based on FFBP. This method represents the echo signal received by the circular synthetic aperture sonar as g(τ, tm, h); where τ represents fast time, tm... m The slow time is represented by h, which represents the altitude of the received echo signal; range-directed matched filtering is performed on the echo signal to obtain the range-compressed signal s. r (τ, tm, h). Based on the slow time of the echo signal, the data is divided into altitude-range echo data. Altitude-based pixel-by-pixel focusing MVDR beamforming is then performed on the echo data. The altitude-compressed data is then re-divided according to altitude to obtain azimuth-range echo signals. FFBP imaging is then performed on the echo signals from different altitude directions to obtain the two-dimensional imaging result I. n This invention involves overlaying two-dimensional image sequences to obtain a three-dimensional image of the target region. It addresses the problems of existing synthetic aperture sonar technologies, such as difficulty in achieving three-dimensional imaging, slow data acquisition speed, high computational load in imaging algorithms, and low imaging efficiency. The proposed multi-baseline circular synthetic aperture sonar relies on beamforming methods to achieve high-dimensional imaging, resulting in low height-axis imaging resolution and making it unsuitable for sonar with helical motion trajectories. Summary of the Invention

[0005] In view of the defects in the prior art, the present application aims to provide a three-dimensional imaging method and system for a spiral motion trajectory sonar.

[0006] According to the present application, a three-dimensional imaging method for a spiral motion trajectory sonar is provided, comprising:

[0007] Step S1: collecting echo signals, and obtaining a range-compressed signal according to the echo signals;

[0008] Step S2: setting and dividing a three-dimensional imaging grid based on the range-compressed signal, and obtaining a two-dimensional imaging result of a target height plane;

[0009] Step S3: superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result.

[0010] Preferably, in the step S1, the range-compressed signal is obtained by matching filtering the echo signals based on a range direction.

[0011] Preferably, the echo signals are S rc (τ, θ), wherein τ represents a fast time, and θ represents an echo signal sampling direction; and the range-compressed signal is S r (τ, θ).

[0012] In the step S2, the following steps are included:

[0013] Step S2.1: setting a height and a bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding three-dimensional coordinate system; the three-dimensional coordinate system comprises a global cylindrical coordinate system;

[0014] Step S2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along a height direction;

[0015] Step S2.3: confirming a sub-aperture phase center position according to a sampling direction of the range-compressed signal, and then deriving a two-way delay between a pixel point of the two-dimensional imaging grid of the target height and the sub-aperture phase center position;

[0016] Step S2.4: coherently accumulating a projection of the echo signals based on the two-way delay to obtain a sub-image;

[0017] Step S2.5: interpolating and fusing the sub-image to obtain the two-dimensional imaging result.

[0018] Preferably, in the step S2.3, a mathematical expression of the two-way delay is as follows:

[0019] t = R ij / c

[0020] where t represents the double-path delay, c represents the sound speed in water, R ij represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position.

[0021] The R ij mathematical expression is:

[0022]

[0023] where (x i , y j ) represents the coordinates of the pixel point I0(i, j) in the local rectangular coordinate system ; L(θ L , r L , z L ) represents the position of the sonar position in the global cylindrical coordinate system; C(θ, r, z) represents the position of the sub-aperture phase center in the global coordinate system.

[0024] In the step S2.4, the mathematical expression of the sub-image is:

[0025]

[0026] where I0 represents the sub-image; n represents the starting azimuth angle of the sub-aperture, L min represents the azimuth sampling number of the sub-aperture, f c represents the signal carrier frequency; s r (τ, θ) represents the distance-compressed signal, where τ represents the fast time; exp represents the exponential function with the base e of the natural logarithm; j represents the imaginary unit; the symbol “·” represents the dot product;

[0027] In the step S2.5, the process of the interpolation fusion includes:

[0028] Step A1: according to the phase center positions of two adjacent sub-images of the k level, the two adjacent sub-images are fused into a new sub-image of the k-1 level; the new sub-image is I k-1 , and the corresponding phase center position is C k-1 (θ k-1 , r k-1 );

[0029] Step A2: based on the local polar coordinates of the pixels of the new sub-image, the coordinates of the pixels of the new sub-image in the global rectangular coordinate system are obtained, and then the corresponding sub-aperture beam center angle of the new sub-image is obtained.

[0030] Step A3: converting the coordinates in the global rectangular coordinate system into coordinates in a local coordinate system of the image of the previous level based on the central angle of the sub-aperture beam, to obtain a polar coordinate imaging result;

[0031] Step A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result;

[0032] Preferably, in the step A1, the phase center position of the new sub-image is mathematically expressed as:

[0033]

[0034] wherein θ k-1 and r k-1 respectively represent the horizontal coordinate and the vertical coordinate of the sub-aperture phase center corresponding to the k-1th sub-image I k-1 in the global polar coordinate system; and respectively represent the horizontal coordinate and the vertical coordinate of the sub-aperture phase center corresponding to the kth sub-image I in the global polar coordinate system; and respectively represent the horizontal coordinate and the vertical coordinate of the sub-aperture phase center corresponding to the kth sub-image I in the global polar coordinate system;

[0035] In the step A2, the local polar coordinate corresponding to the pixel of the new sub-image is The coordinates of the pixel of the new sub-image in the global rectangular coordinate system are [x k-1 , y k-1 ];

[0036] The coordinates of the pixel of the new sub-image in the global rectangular coordinate system are mathematically expressed as:

[0037]

[0038] wherein [θ k-1 , r k-1 ] represents the coordinates of the sub-aperture phase center corresponding to the sub-image I k-1 in the global polar coordinate system, represents the central angle of the sub-aperture corresponding to the new sub-image;

[0039] The central angle of the sub-aperture corresponding to the new sub-image is mathematically expressed as:

[0040]

[0041] In the step A3, the mathematical expression of the polar coordinate imaging result is:

[0042]

[0043] wherein, denotes a sub-image I k-1 pixel in the sub-image corresponding local polar coordinate system; [x k-1 , y k-1 ] denotes the coordinates of the pixel in the global rectangular coordinate system; k-1 denotes a sub-image I corresponding sub-aperture phase center.

[0044] According to the three-dimensional imaging system of the screw motion trajectory sonar provided by the application, comprising:

[0045] Module M1: collecting echo signals, and obtaining a range-compressed signal according to the echo signals;

[0046] Module M2: based on the range-compressed signal, setting and dividing a three-dimensional imaging grid to obtain a two-dimensional imaging result of a target height plane;

[0047] Module M3: superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result.

[0048] Preferably, in the module M1, the range-compressed signal is obtained by matching filtering the echo signals based on a range direction.

[0049] Preferably, the echo signals are S rc (τ, θ), wherein τ represents a fast time, and θ represents an echo signal sampling direction; and the range-compressed signal is S r (τ, θ).

[0050] In the module M2, comprising:

[0051] Module M2.1: setting the height and bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding three-dimensional coordinate system; the three-dimensional coordinate system comprises a global cylindrical coordinate system;

[0052] Module M2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along the height direction;

[0053] Module M2.3: confirming the sub-aperture phase center position according to the sampling direction of the range-compressed signal, and then deriving the two-way delay of the pixel point of the two-dimensional imaging grid of the target height and the sub-aperture phase center position;

[0054] Module M2.4: based on the two-way delay, coherently accumulating the projection of the echo signals to obtain a sub-image; ​

[0055] Module M2.5: interpolating and fusing the sub-images to obtain the two-dimensional imaging result.

[0056] Preferably, in the module M2.3, the mathematical expression of the two-way travel time is:

[0057] t = R / c ij / c

[0058] wherein t represents the two-way travel time, c represents the sound speed in water, R ij represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position;

[0059] The mathematical expression of the R ij is:

[0060]

[0061] wherein (x i , y j ) represents the coordinates of the pixel point I0(i, j) in the local rectangular coordinate system ; L(θ L , r L , z L ) represents the position of the sonar position in the global cylindrical coordinate system; C(θ, r, z) represents the position of the sub-aperture phase center in the global coordinate system;

[0062] In the module M2.4, the mathematical expression of the sub-image is:

[0063]

[0064] wherein I0 represents the sub-image; n represents the starting azimuth angle of the sub-aperture, L min represents the azimuth sampling number of the sub-aperture, f c represents the signal carrier frequency; s r (τ, θ) represents the signal after distance compression, wherein τ represents the fast time; exp represents the exponential function with the base e of natural logarithm; j represents the imaginary unit;

[0065] In the module M2.5, the process of interpolating and fusing includes:

[0066] Module A1: according to the phase center positions of k-level, two adjacent sub-images, fusing the two adjacent sub-images into a new sub-image of k-1 level; the new sub-image is I k-1 , and the corresponding phase center position is C k-1 (θ k-1 , r k-1 );

[0067] Module A2: based on the local polar coordinates corresponding to the pixels of the new sub-image, obtaining the coordinates of the pixels of the new sub-image in the global rectangular coordinate system, and further obtaining the sub-aperture beam center angle corresponding to the new sub-image;

[0068] Module A3: based on the sub-aperture beam center angle, converting the coordinates in the global rectangular coordinate system into coordinates in the local coordinate system of the previous level image, to obtain the polar coordinate imaging result;

[0069] Module A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result.

[0070] Preferably, in the module A1, the phase center position of the new sub-image is mathematically expressed as:

[0071]

[0072] Wherein, θ k-1 and r k-1 respectively represent the horizontal coordinate and the vertical coordinate of the phase center of the k-1 level sub-image I k-1 , that is, the horizontal coordinate and the vertical coordinate of the phase center of the corresponding sub-aperture of the new sub-image in the global polar coordinate system; and respectively represent the horizontal coordinate and the vertical coordinate of the phase center of the k level sub-image in the global polar coordinate system; and respectively represent the horizontal coordinate and the vertical coordinate of the phase center of the k level sub-image in the global polar coordinate system;

[0073] In the module A2, the local polar coordinates corresponding to the pixels of the new sub-image are The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are [x k-1 , y k-1 ];

[0074] The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are mathematically expressed as:

[0075]

[0076] Wherein, [θ k-1 , r k-1 ] represents the coordinates of the phase center of the sub-aperture corresponding to the sub-image I k-1 in the global polar coordinate system, represents the beam center angle of the sub-aperture corresponding to the new sub-image;

[0077] The beam center angle of the sub-aperture corresponding to the new sub-image is mathematically expressed as:

[0078]

[0079] In the module A3, the mathematical expression of the polar coordinate imaging result is:

[0080]

[0081] Wherein, represents the sub-image I k-1 pixel in the sub-image corresponding to the local polar coordinate system; [x k-1 , y k-1 ] represents the coordinates of the image I k-1 pixel in the global rectangular coordinate system; represents the sub-aperture phase center corresponding to the sub-image .

[0082] Compared with the prior art, the present application has the following beneficial effects:

[0083] 1. The spiral motion trajectory sonar provided by the present application can obtain full-angle echo information and significantly improve the height resolution of three-dimensional imaging compared with the circular periphery synthetic aperture sonar.

[0084] 2. The spiral motion trajectory provided by the present application includes standard circle, standard spiral, variable pitch spiral and variable radius spiral trajectory.

[0085] 3. The Fast Factorized BackProjection (FFBP) three-dimensional imaging method provided by the present application has the advantages of high imaging accuracy, simple imaging mode, easy motion compensation, and no motion trajectory restriction, and compared with the traditional back projection algorithm, the algorithm has smaller calculation amount and higher imaging efficiency under the same imaging resolution. BRIEF DESCRIPTION OF DRAWINGS

[0086] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the following drawings:

[0087] Figure 1 The spiral motion trajectory sonar imaging geometry three-dimensional schematic diagram provided by the present application;

[0088] Figure 2 The spiral motion trajectory sonar imaging geometry top view provided by the present application;

[0089] Figure 3 The motion trajectory schematic diagram of the sonar in the MATLAB simulation provided by the present application;

[0090] Figure 4 The detection point target diagram in the MATLAB simulation provided by the present application;

[0091] Figure 5 The three-dimensional imaging result diagram in the MATLAB simulation provided by the present application;

[0092] Figure 6 The two-dimensional imaging result diagram obtained after processing the simulation echo signal provided by the present application;

[0093] Figure 7 The two-dimensional imaging result diagram obtained after processing the simulation echo signal by the BP imaging method;

[0094] Figure 8 The imaging method flowchart provided by the present application. DETAILED DESCRIPTION

[0095] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These are within the scope of protection of the present application.

[0096] In order to speed up the imaging speed, the present application proposes a Fast Factorized Back Projection (FFBP) three-dimensional imaging method suitable for a helical motion trajectory sonar, which speeds up the three-dimensional imaging speed of the sonar under the premise of ensuring high imaging resolution, and has higher imaging efficiency.

[0097] The system proposed by the present application is composed of a transceiver combined sonar. In the surveying process, the sonar makes helical motion around the scene to be measured, and the sonar beam is always directed to the central axis of the scene to be measured.

[0098] Among them, the helical trajectory is a trajectory that can obtain full-angle echo signals and continuous sampling in the height direction, such as standard circle, standard helix, variable pitch helix and variable radius helix.

[0099] The imaging method proposed by the present application maps the echo data into different height imaging grids to obtain two-dimensional images at different heights, and finally superimposes the two-dimensional image sequence to obtain three-dimensional imaging results, realizing the expansion of the two-dimensional FFBP imaging algorithm to three-dimensional space.

[0100] The present application provides a FFBP three-dimensional imaging method and system suitable for a helical motion trajectory sonar. Here, taking the horizontal projection as a standard circle helical trajectory as an example, the three-dimensional image and the top view of the imaging geometry of the sonar are as followsFigure 1 、 Figure 2 as shown in the formula (1).

[0101] In hardware, the system is composed of a transceiver combined sonar. In the mapping process, the sonar is in spiral motion at the center of the measured scene, linear motion in the height direction, and circular motion in the horizontal direction, and the horizontal direction and the height direction are continuously and uniformly sampled. Assuming that the echo signal S rc (τ, θ) obtained by the sonar in the mapping process has L full sampling directions, and each direction has M distance sampling points, the echo signal can be represented as a matrix with a size of L full × M.

[0102] The three-dimensional imaging method provided by the application is a three-dimensional imaging method of a spiral motion trajectory sonar, and comprises the following steps:

[0103] Step 1: The echo signal received by the sonar system is represented as S rc (τ, θ). Wherein τ represents fast time, and θ represents echo signal sampling direction. The echo signal is subjected to distance direction matched filtering to obtain a distance compressed signal S r (τ, θ).

[0104] Step 2: Determine the imaging grid, divide the imaging grid along the height direction, and use the FFBP method to obtain the two-dimensional imaging result of each height plane. Specifically, the traditional FFBP method can only process the sonar data of straight line and standard circular motion trajectory, and the FFBP method provided by the application is an improved method, which can realize the imaging of sonar data of various motion trajectories.

[0105] Specifically, step 2 comprises two sub-steps of sub-aperture back projection and sub-aperture fusion, and taking the imaging in the imaging plane with a height of h as an example, comprising:

[0106] Step 2.1: Assuming that the three-dimensional imaging grid is a cylindrical space with a height of H and a radius of R, a global rectangular coordinate system and a corresponding global cylindrical coordinate system are established with the center of the grid as the origin. The three-dimensional imaging grid is divided into a plurality of two-dimensional imaging grids along the height direction, and a corresponding local polar coordinate system and a local rectangular coordinate system are established with the center of each two-dimensional imaging grid as the origin.

[0107] Assuming that the distance compressed signal S r (τ, θ) has L r sampling directions, and each direction has M distance sampling points. Specifically, the full-aperture data S (τ, θ) is divided into 2K K represents the decomposition layer number, and the number of sub-images combined in each level is 2. Assuming that there is a pixel point I0(i, j) in a two-dimensional imaging grid with a height of h. The position of the phase center of the sub-aperture is represented as C(θ, r, z), wherein the sonar position corresponding to an echo signal is represented as L(θ L , r L , z L ), the two-way time delay of the pixel point to the phase center is mathematically expressed as:

[0108] t=R ij / c

[0109] wherein t represents the two-way time delay, c represents the sound speed in water, and R ij represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position.

[0110] The mathematical expression of R ij is:

[0111]

[0112] wherein (x i , y j ) represents the coordinates of the pixel point I0(i, j) in the local rectangular coordinate system ; L(θ L , r L , z L ) represents the position of the sonar in the global cylindrical coordinate system; and C(θ, r, z) represents the position of the phase center of the sub-aperture in the global coordinate system.

[0113] The echo is back-projected to the scene for coherent accumulation to obtain a sub-image I0, and the mathematical expression is:

[0114]

[0115] wherein I0 represents the sub-image; n represents the starting azimuth angle of the sub-aperture, L min represents the number of azimuthal samples of the sub-aperture, f c represents the signal carrier frequency; s r (τ, θ) represents the distance-compressed signal, wherein τ represents the fast time; exp represents the exponential function with the base e as the base of the natural logarithm; j represents the imaginary unit; and the symbol “·” represents dot product;

[0116] Step 2.2: After BP imaging of the initial sub-aperture, a plurality of polar coordinate sub-images I0 on a specific height h plane are obtained, and two-dimensional interpolation fusion needs to be performed on the plurality of polar coordinate sub-images to obtain the final two-dimensional imaging result.

[0117] Specifically, in the process of interpolation fusion, first, the sub-aperture phase center of the next level sub-image is determined to determine the imaging grid of the new sub-image. Let two adjacent sub-images at the k level be denoted as The corresponding sub-image phase center position is and At this time, the new sub-image at the k.1 level formed by the fusion of the two sub-images can be expressed as I k-1 , and the corresponding phase center position C k-1 (θ k-1 , r k-1 ) and The corresponding phase center position The relationship between them is mathematically expressed as:

[0118]

[0119] Where C k-1 (θ k-1 , r k-1 ) represents the position of the sub-aperture phase center corresponding to the new sub-image I k-1 at the k-1 level, θ k-1 and r k-1 are the horizontal and vertical coordinates of the sub-aperture phase center in the global polar coordinate system, respectively; and represent the positions of the sub-aperture phase centers corresponding to the k level sub-images I and represent the horizontal and vertical coordinates of the sub-aperture phase center corresponding to the k level sub-image I , respectively; and represent the horizontal and vertical coordinates of the sub-aperture phase center corresponding to the k level sub-image I , respectively;

[0120] The local polar coordinates corresponding to the pixels of the image I k-1 are denoted as The coordinates of the image pixels in the global rectangular coordinate system can be expressed as [x k-1 , y k-1 ], and the calculation method is expressed as:

[0121]

[0122] Where [θ k-1 , r k-1 ] represents the coordinates of the sub-aperture phase center corresponding to the sub-image I k-1 in the global polar coordinate system, represents the sub-aperture phase center corresponding to the sub-image I​k-1 The corresponding beam center angle of the sub-aperture is mathematically expressed as:

[0123]

[0124] Then the coordinates in the global coordinate system need to be converted into the coordinates in the local coordinate system of the previous image, i.e. the local polar coordinates, which are converted to the image The corresponding local polar coordinates are mathematically expressed as:

[0125]

[0126] wherein, represents the pixel point in the sub-image I k-1 k-1 corresponding to the sub-aperture phase center in the local polar coordinate system; [x k-1 , y k-1 ] represents the coordinates of the pixel in the image I k-1 in the global rectangular coordinate system; represents the pixel point in the sub-image I corresponding to the sub-aperture phase center in the local polar coordinate system; [x k-1 , y k-1 ] represents the coordinates of the pixel in the image I k-1 in the global rectangular coordinate system;

[0127] Through the above coordinate conversion, the k-level sub-image interpolation fusion is obtained into the k-1-level sub-image. Through K-level interpolation, the polar coordinate imaging result can be obtained. Then the polar coordinate imaging result is interpolated into the global rectangular coordinate system to obtain the final two-dimensional imaging result.

[0128] Step 3: Superimpose the two-dimensional image sequence obtained in step 2, i.e. the two-dimensional imaging result, to obtain the three-dimensional imaging result.

[0129] In order to verify the correctness of the proposed FFBP-based circular synthetic aperture sonar three-dimensional imaging method, MATLAB is used to simulate the experiment. In this simulation scenario, the sonar motion trajectory is a standard circle in horizontal projection and a spiral trajectory upward, as shown in Figure 3 The sonar platform moves at a radius of 10 m from the height of Om to the height of 3 m. The simulation parameters are set as follows: the sound speed is 1500 m / s, the signal is a linear frequency modulation signal, the center frequency is 100 kHz, and the transmission pulse width is 5 ms. The detection targets are set as (-1, 1, 0.7), (-1, -1, 0.7), (1, 1, 0.2), (1, -1, 0.2), (-1, 1, -0.3), (-1, -1, -0.3), (1, 1, -0.8), (1, -1, -0.8), a total of 8 points, as shown in Figure 4

[0130] Figure 5The imaging results of the FFBP imaging method proposed in the application under the spiral trajectory are shown, and it can be concluded that the method can well reconstruct the imaging target.

[0131] Table 1 simulation parameter setting

[0132]

[0133]

[0134] In order to reflect the advantage of the FFBP algorithm in imaging efficiency, the FFBP algorithm and the BP algorithm proposed in the application are respectively used for two-dimensional imaging of the spiral echo signal in the plane with a height of 0.7, and the imaging results as shown in Figure 6 and Figure 7 are obtained. The imaging time of the FFBP algorithm is 2.258 seconds, and the imaging time of the BP algorithm is 136.5 seconds. In combination with the imaging time and the imaging results of Figure 6 , Figure 7 it can be seen that under the premise of similar imaging effect, the FFBP method proposed in the application has great advantage in operation efficiency.

[0135] The application further provides a three-dimensional imaging system of a spiral motion trajectory sonar, which can be realized by executing the flow steps of the three-dimensional imaging method of the spiral motion trajectory sonar, that is, the three-dimensional imaging method of the spiral motion trajectory sonar can be understood as the preferred embodiment of the three-dimensional imaging system of the spiral motion trajectory sonar by those skilled in the art.

[0136] According to the three-dimensional imaging system of the spiral motion trajectory sonar provided by the application, the three-dimensional imaging system of the spiral motion trajectory sonar comprises:

[0137] Module M1: collecting echo signals, and obtaining a distance compressed signal according to the echo signals;

[0138] Module M2: setting and dividing a three-dimensional imaging grid based on the distance compressed signal, and obtaining a two-dimensional imaging result of a target height plane;

[0139] Module M3: superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result.

[0140] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules implementing methods and structures within hardware components.

[0141] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other in any manner without conflict.

Claims

1. A method for three-dimensional imaging of a helical motion trajectory sonar, characterized in that, The method comprises: Step S1: collecting echo signals, and obtaining a range-compressed signal based on the echo signals; Step S2: setting and dividing a three-dimensional imaging grid based on the range-compressed signal, and obtaining a two-dimensional imaging result of a target height plane; Step S3: superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result; The echo signal is wherein, denotes fast time, denotes echo signal sample position; the range-compressed signal is ; In the step S2, the method comprises: Step S2.1: setting a height and a bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding three-dimensional coordinate system; the three-dimensional coordinate system comprises a global cylindrical coordinate system; Step S2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along a height direction; Step S2.3: confirming a sub-aperture phase center position according to a sampling direction of the range-compressed signal, and then obtaining a two-way delay between a pixel point of the two-dimensional imaging grid of the target height and the sub-aperture phase center position; Step S2.4: coherently accumulating projections of the echo signals based on the two-way delay to obtain a sub-image; Step S2.5: interpolating and fusing the sub-image to obtain the two-dimensional imaging result; In the step S2.3, a mathematical expression of the two-way delay is: wherein, denotes the two-way delay, denotes the speed of sound in water, denotes a pixel point in the sub-image the distance between the sonar position and the pixel point. The The mathematical expression is: wherein, represents a pixel point in a local rectangular coordinate system ; represents a position of the sonar in a global cylindrical coordinate system; represents a position of the sub-aperture phase center in a global coordinate system; In the step S2.4, a mathematical expression of the sub-image is: wherein, represents a sub-image; n represents a sub-aperture start azimuth, represents the number of azimuthal samples of a sub-aperture, represents a signal carrier frequency; represents a range-compressed signal, wherein, represents fast time; represents an exponential function with base e, the natural logarithm; represents the imaginary unit; the symbol "·" represents the dot product; In the step S2.5, the process of the interpolation and fusion comprises: Step A1: According to level, the phase center position of two adjacent sub-images, fusing the two adjacent sub-images into a new sub-image of level -1; the new sub-image is , and the corresponding phase center position is ; Step A2: obtaining coordinates of a pixel of the new sub-image in the global rectangular coordinate system based on a local polar coordinate corresponding to the pixel of the new sub-image, and then obtaining a sub-aperture beam center angle corresponding to the new sub-image; Step A3: converting the coordinates in the global rectangular coordinate system into coordinates in a local coordinate system of a previous image based on the sub-aperture beam center angle to obtain a polar coordinate imaging result; Step A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result.

2. The method of three-dimensional imaging of a helical motion trajectory sonar according to claim 1, characterized in that, In the step S1, the range-compressed signal is obtained by matching filtering the echo signals based on a distance direction.

3. The method of three-dimensional imaging of a helical motion trajectory sonar according to claim 2, characterized in that, In the step A1, a mathematical expression of the phase center position of the new sub-image is: wherein, denote denote level sub-images denote the horizontal and vertical coordinates in the global polar coordinate system of the sub-aperture phase center corresponding to the new sub-image; denote denote level sub-images horizontal and vertical coordinates; denote denote level sub-images horizontal and vertical coordinates in the global polar coordinate system of the sub-aperture phase center corresponding to the new sub-image; In the step A2, the local polar coordinates corresponding to the pixels of the new sub-image are ; and the coordinates of the pixels of the new sub-image in the global rectangular coordinate system are ; A mathematical expression of the coordinates of the pixel of the new sub-image in the global rectangular coordinate system is: wherein, representing a sub-image a coordinate of a corresponding sub-aperture phase center in global polar coordinates, representing a beam center angle of the sub-aperture corresponding to the new sub-image; A mathematical expression of the sub-aperture beam center angle corresponding to the new sub-image is: In the step A3, a mathematical expression of the polar coordinate imaging result is: wherein, represents a sub-image pixel in the sub-image corresponding local polar coordinate system; represents an image pixel in the global cartesian coordinate system; represents a sub-image corresponding sub-aperture phase center.

4. A three-dimensional imaging system for a helical motion trajectory sonar, characterized in that, The method comprises: Module M1: collecting echo signals, and obtaining a range-compressed signal based on the echo signals; Module M2: setting and dividing a three-dimensional imaging grid based on the range-compressed signal, and obtaining a two-dimensional imaging result of a target height plane; Module M3: superimposing the two-dimensional imaging result to obtain a three-dimensional imaging result; The echo signal is wherein, denotes the fast time, denotes the echo signal sample position; the range-compressed signal is ; In the module M2, the method comprises: Module M2.1: setting a height and a bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding three-dimensional coordinate system; the three-dimensional coordinate system comprises a global cylindrical coordinate system; Module M2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along a height direction; Module M2.3: confirming a sub-aperture phase center position according to a sampling position of the range-compressed signal, and further obtaining a two-way delay between a pixel point of the two-dimensional imaging grid of the target height and the sub-aperture phase center position; Module M2.4: based on the two-way delay, coherently accumulating projections of the echo signal to obtain a sub-image; Module M2.5: interpolating and fusing the sub-image to obtain the two-dimensional imaging result; In the module M2.3, a mathematical expression of the two-way delay is: wherein, denotes the two-way delay, denotes the speed of sound in water, denotes a pixel point in a sub-image the distance between the sonar position and the object. The The mathematical expression is: wherein, represents a pixel point in a local rectangular coordinate system ; and represents a position of the sonar in a global cylindrical coordinate system; represents a position of a sub-aperture phase center in a global coordinate system; In the module M2.4, a mathematical expression of the sub-image is: wherein, represents a sub-image; n represents a sub-aperture start azimuth, represents the number of azimuthal samples of a sub-aperture, represents a signal carrier frequency; represents a distance-compressed signal, wherein, represents fast time; represents an exponential function with base e, the natural logarithm; represents the imaginary unit; the symbol "·" represents the dot product; In the module M2.5, the process of the interpolation and fusion includes: Module A1: according to level, the phase center positions of two adjacent sub-images, fusing the two adjacent sub-images into a new sub-image of level -1; the new sub-image is , and the corresponding phase center positions are ; Module A2: based on local polar coordinates corresponding to pixels of the new sub-image, obtaining coordinates of the pixels of the new sub-image in a global rectangular coordinate system, and further obtaining a sub-aperture beam center angle corresponding to the new sub-image; Module A3: based on the sub-aperture beam center angle, converting the coordinates in the global rectangular coordinate system into coordinates in a local coordinate system of a previous image to obtain a polar coordinate imaging result; Module A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result.

5. The three-dimensional imaging system of a helical motion trajectory sonar according to claim 4, wherein, In the module M1, the range-compressed signal is obtained by matching filtering the echo signal based on a range direction.

6. The three-dimensional imaging system of a helical motion trajectory sonar according to claim 5, wherein, In the module A1, a mathematical expression of the phase center position of the new sub-image is: wherein, denote respectively level sub-images i.e. the horizontal and vertical coordinates in the global polar coordinate system of the sub-aperture phase center corresponding to said new sub-image; denote respectively level sub-images horizontal and vertical coordinates; denote respectively level sub-images horizontal and vertical coordinates in the global polar coordinate system of the sub-aperture phase center corresponding; In the module A2, the local polar coordinates corresponding to the pixels of the new sub-image are ; the coordinates of the pixels of the new sub-image in the global rectangular coordinate system are ; A mathematical expression of the coordinates of the pixels of the new sub-image in the global rectangular coordinate system is: wherein, representing sub-images coordinates of corresponding sub-aperture phase centers in global polar coordinates, representing a beam center angle of the sub-aperture corresponding to the new sub-image; A mathematical expression of the beam center angle of the sub-aperture corresponding to the new sub-image is: In the module A3, a mathematical expression of the polar coordinate imaging result is: wherein, representing a sub-image pixel in a sub-image corresponding coordinate in the local polar coordinate system; representing an image pixel in the global cartesian coordinate system; representing a sub-image corresponding sub-aperture phase center.

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