Three-dimensional imaging method and system of spiral motion trail sonar

Abstract

The invention provides a three-dimensional imaging method and system for a spiral motion trail sonar, and the method comprises the steps: S1, collecting an echo signal, and obtaining a distance-compressed signal according to the echo signal; s2, based on the distance compressed signal, setting and dividing a three-dimensional imaging grid to obtain a two-dimensional imaging result of a target height plane; and S3, superposing the two-dimensional imaging result to obtain a three-dimensional imaging result. Compared with a circumferential synthetic aperture sonar, the spiral motion trail sonar provided by the invention can obtain full-angle echo information and significantly improve the three-dimensional imaging height resolution.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic aperture sonar imaging, and in particular, relates to a three-dimensional imaging method and system of a spiral motion trajectory sonar. Background Art

[0002] Synthetic aperture sonar imaging is an important means of detecting small underwater targets. Synthetic aperture sonar imaging can obtain high-resolution acoustic images of the detected target. However, conventional strip-type synthetic aperture sonar can only detect target objects within a limited angle range, and there are missed alarms and overlapping phenomena. In order to solve the above problems, a circular synthetic aperture sonar is proposed. The circular synthetic aperture sonar performs circular motion around the detected target in a fixed height plane to obtain full-angle echo signals. Through Fourier slice theorem, back projection and other imaging algorithm processing, a high-resolution acoustic image can be obtained. Although the circular synthetic aperture sonar has three-dimensional imaging capabilities, the single-baseline circular synthetic aperture sonar has an altitude sidelobe effect. In order to improve the altitude resolution and suppress the sidelobe, a spiral motion trajectory synthetic aperture sonar is proposed.

[0003] Due to the particularity of the spiral motion trajectory, the frequency domain algorithm is no longer applicable to the sonar imaging. In the time domain algorithm, the back projection method, namely Back Projection, referred to as BP, has the advantages of high imaging accuracy and no motion trajectory restriction, and can be used for spiral motion trajectory synthetic aperture sonar imaging. However, the algorithm has high computational complexity and low imaging efficiency.

[0004] Patent document CN117930250A discloses a 3D imaging method of circular synthetic aperture sonar based on FFBP. In this scheme, the echo signal received by the circular synthetic aperture sonar is represented as g(τ, tm, h); τ represents the fast time, t m represents the slow time, h represents the height of the received echo signal; the echo signal is subjected to range-matched filtering to obtain the range-compressed signal s r (τ, tm, h). According to the slow time of the echo signal, the data is divided into altitude-range echo data, and the echo data is subjected to altitude pixel-by-pixel focusing MVDR beamforming. The data compressed in altitude is re-divided according to altitude to obtain azimuth-range echo signals, and FFBP imaging is performed on the echo signals in different altitudes to obtain a two-dimensional imaging result I n . The two-dimensional image sequence is superimposed to obtain a three-dimensional image of the target area. This invention solves the problems in the prior art that synthetic aperture sonar is difficult to perform three-dimensional imaging, has slow data acquisition speed, large imaging algorithm calculation amount, and low imaging efficiency. The multi-baseline circular synthetic aperture sonar proposed in this scheme relies on the beamforming method to achieve altitude imaging, has low altitude imaging resolution, and cannot be applied to spiral motion trajectory sonar. Summary of the invention

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

[0006] A three-dimensional imaging method of a spiral motion trajectory sonar provided by the present invention comprises:

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

[0008] Step S2: Based on the distance compressed signal, set and divide the three-dimensional imaging grid to obtain a two-dimensional imaging result of the target height plane;

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

[0010] Preferably, in the step S1, the range-compressed signal is obtained by performing range-matched filtering on the echo signal.

[0011] Preferably, the echo signal is S rc (τ, θ), where τ represents the fast time and θ represents the sampling azimuth of the echo signal; the signal after range compression is S r (τ, θ);

[0012] In the step S2, it includes:

[0013] Step S2.1: 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 includes: a global cylindrical coordinate system;

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

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

[0016] Step S2.4: based on the round-trip delay, coherently accumulate the projection of the echo signal to obtain a sub-image;

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

[0018] Preferably, in step S2.3, the mathematical expression of the round-trip delay is:

[0019] t=R ij / c

[0020] Where t is the round trip delay, c is the speed of sound in water, and R ij Represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position.

[0021] The R ij The mathematical expression is:

[0022]

[0023]

[0024] Among them, (x i ,y j ) represents the pixel point I0(i, j) in the local rectangular coordinate system Coordinates in 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 subaperture phase center in the global coordinate system.

[0025] In step S2.4, the mathematical expression of the sub-image is:

[0026]

[0027] Where I0 represents the sub-image; n represents the starting azimuth of the sub-aperture, L min represents the number of azimuth sampling of the subaperture, f c Indicates the signal carrier frequency; s r (τ, θ) represents the signal after distance compression, where τ represents fast time; exp represents an exponential function with the base e of the natural logarithm as the base; j represents an imaginary unit; the symbol “·” represents a dot product;

[0028] In step S2.5, the interpolation fusion process includes:

[0029] Step A1: According to the phase center positions of two adjacent sub-images of level k, the two adjacent sub-images are fused into a new sub-image of level k-1; the new sub-image is I k-1 , the corresponding phase center position is C k-1 (θ k-1 , r k-1 );

[0030] Step A2: based on the local polar coordinates corresponding to 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 sub-aperture beam center angle corresponding to the new sub-image is obtained;

[0031] Step A3: based on the sub-aperture beam center angle, convert the coordinates in the global rectangular coordinate system into the coordinates of the local coordinate system of the previous level image to obtain a polar coordinate imaging result;

[0032] Step A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result;

[0033] Preferably, in the step A1, the phase center position of the new sub-image is expressed mathematically as follows:

[0034]

[0035] Among them, θ k-1 With r k-1 Represents the k-1 level sub-image I respectively k-1 , i.e., the abscissa and ordinate of the subaperture phase center corresponding to the new sub-image in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system;

[0036] In step A2, the local polar coordinates corresponding to the pixels of the new sub-image are The pixel coordinates of the new sub-image in the global rectangular coordinate system are [x k-1 ,y k-1 ];

[0037] The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are expressed mathematically as follows:

[0038]

[0039] Among them, [θ k-1 , r k-1 ] represents sub-image I k-1 The corresponding subaperture phase center coordinates in global polar coordinates, represents the beam center angle of the subaperture corresponding to the new sub-image;

[0040] The beam center angle of the subaperture corresponding to the new sub-image is expressed mathematically as follows:

[0041]

[0042] In step A3, the mathematical expression of the polar coordinate imaging result is:

[0043]

[0044] in, Represents sub-image I k-1 The pixel in the sub-image The corresponding coordinates in the local polar coordinate system; [x k-1 ,y k-1 ] represents image I k-1 The pixel's coordinates in the global rectangular coordinate system; Represents a sub-image The corresponding subaperture phase center.

[0045] A three-dimensional imaging system of a spiral motion trajectory sonar provided by the present invention comprises:

[0046] Module M1: collects echo signals, and obtains distance-compressed signals according to the echo signals;

[0047] Module M2: based on the distance compressed signal, setting and dividing the three-dimensional imaging grid to obtain the two-dimensional imaging result of the target height plane;

[0048] Module M3: superimpose the two-dimensional imaging results to obtain three-dimensional imaging results.

[0049] Preferably, in the module M1, the range-compressed signal is obtained by performing range-matched filtering on the echo signal.

[0050] Preferably, the echo signal is S rc (τ, θ), where τ represents the fast time and θ represents the sampling azimuth of the echo signal; the signal after range compression is S r (τ, θ);

[0051] The module M2 includes:

[0052] Module M2.1: Setting the height and bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding stereoscopic coordinate system; the stereoscopic coordinate system includes: a global cylindrical coordinate system;

[0053] Module M2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along the height direction;

[0054] Module M2.3: confirming the sub-aperture phase center position according to the sampling azimuth of the range-compressed signal, and then obtaining the round-trip delay between the pixel point of the two-dimensional imaging grid at the target height and the sub-aperture phase center position;

[0055] Module M2.4: based on the round-trip delay, coherently accumulate the projection of the echo signal to obtain a sub-image;

[0056] Module M2.5: interpolating and fusing the sub-images to obtain the two-dimensional imaging result.

[0057] Preferably, in the module M2.3, the mathematical expression of the round-trip delay is:

[0058] t=R ij / c

[0059] Where t is the round trip delay, c is the speed of sound in water, and R ij Represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position;

[0060] The R ij The mathematical expression is:

[0061]

[0062] Among them, (x i ,y j ) represents the pixel point I0(i, j) in the local rectangular coordinate system Coordinates in 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 subaperture phase center in the global coordinate system;

[0063] In the module M2.4, the mathematical expression of the sub-image is:

[0064]

[0065] Where I0 represents the sub-image; n represents the starting azimuth of the sub-aperture, L min represents the number of azimuth sampling of the subaperture, f c Indicates the signal carrier frequency; s r (τ, θ) represents the signal after distance compression, where τ represents the fast time; exp represents the exponential function with the base e of the natural logarithm as the base; j represents the imaginary unit;

[0066] In the module M2.5, the interpolation fusion process includes:

[0067] Module A1: According to the phase center positions of two adjacent sub-images of level k, the two adjacent sub-images are merged into a new sub-image of level k-1; the new sub-image is I k-1 , the corresponding phase center position is C k-1 (θ k-1 , r k-1 );

[0068] 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;

[0069] Module A3: based on the sub-aperture beam center angle, convert the coordinates in the global rectangular coordinate system into the coordinates of the local coordinate system of the previous level image to obtain a polar coordinate imaging result;

[0070] Module A4: interpolating the polar coordinate imaging result into the global rectangular coordinate system to obtain the two-dimensional imaging result.

[0071] Preferably, in the module A1, the phase center position of the new sub-image is expressed mathematically as follows:

[0072]

[0073] Among them, θ k-1 With r k-1 Represents the k-1 level sub-image I respectively k-1 , i.e., the abscissa and ordinate of the subaperture phase center corresponding to the new sub-image in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system;

[0074] In the module A2, the local polar coordinates corresponding to the pixels of the new sub-image are The pixel coordinates of the new sub-image in the global rectangular coordinate system are [x k-1 ,y k-1 ];

[0075] The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are expressed mathematically as follows:

[0076]

[0077] Among them, [θ k-1 , r k-1 ] represents sub-image I k-1 The corresponding subaperture phase center coordinates in global polar coordinates, represents the beam center angle of the subaperture corresponding to the new sub-image;

[0078] The beam center angle of the subaperture corresponding to the new sub-image is expressed mathematically as follows:

[0079]

[0080] In the module A3, the mathematical expression of the polar coordinate imaging result is:

[0081]

[0082] in, Represents sub-image I k-1 The pixel in the sub-image The corresponding coordinates in the local polar coordinate system; [x k-1 ,y k-1 ] represents image I k-1 The pixel's coordinates in the global rectangular coordinate system; Represents a sub-image The corresponding subaperture phase center.

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] 1. Compared with circular synthetic aperture sonar, the spiral motion trajectory sonar proposed in the present invention can obtain full-angle echo information and significantly improve the height resolution of three-dimensional imaging.

[0085] 2. The spiral motion trajectory provided by the present invention includes standard circle, standard spiral, variable pitch spiral and variable radius spiral trajectory.

[0086] 3. The factorized fast back-projection three-dimensional imaging method proposed in the present invention, namely Fast Factorized Back Projection, abbreviated as FFBP, has the advantages of high imaging accuracy, simple imaging mode, easy motion compensation, and no motion trajectory restriction. Compared with the traditional back-projection algorithm, the algorithm has smaller computational complexity and higher imaging efficiency at the same imaging resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0088] Figure 1 A three-dimensional schematic diagram of the spiral motion trajectory sonar imaging geometry provided by the present invention;

[0089] Figure 2 A geometric top view of the spiral motion trajectory sonar imaging provided by the present invention;

[0090] Figure 3 A schematic diagram of the motion trajectory of the sonar in the MATLAB simulation provided by the present invention;

[0091] Figure 4 A schematic diagram of a detection point target in a MATLAB simulation provided by the present invention;

[0092] Figure 5 A schematic diagram of the MATLAB simulation three-dimensional imaging results provided by the present invention;

[0093] Figure 6 A schematic diagram of a two-dimensional imaging result obtained after processing a simulated echo signal provided by the present invention;

[0094] Figure 7 It is a schematic diagram of the two-dimensional imaging result obtained after the simulated echo signal is processed by the BP imaging method;

[0095] Figure 8 This is a flow chart of the imaging method provided by the present invention. DETAILED DESCRIPTION

[0096] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0097] In order to speed up the imaging speed, the present invention proposes a factorized fast back projection three-dimensional imaging method suitable for spiral motion trajectory sonar, namely Fast Factorized Back Projection, referred to as FFBP. This method speeds up the sonar three-dimensional imaging speed while ensuring high imaging resolution, and has higher imaging efficiency.

[0098] The system proposed by the present invention is composed of a sonar with a transmitter and a receiver. During the surveying process, the sonar makes a spiral motion around the measured scene, and the sonar beam always points to the central axis of the measured scene.

[0099] Among them, the spiral trajectory includes standard circle, standard spiral, variable pitch spiral and variable radius spiral, etc., which can obtain full-angle echo signals and continuous sampling in height direction.

[0100] The imaging method proposed in the present invention maps echo data to imaging grids at different heights to obtain two-dimensional images at different heights, and finally superimposes the two-dimensional image sequence to obtain a three-dimensional imaging result, thereby realizing the extension of the two-dimensional FFBP imaging algorithm to three-dimensional space.

[0101] The embodiment of the present invention provides a FFBP three-dimensional imaging method and system suitable for spiral motion trajectory sonar. Here, a spiral trajectory with a horizontal projection as a standard circle is taken as an example. The three-dimensional diagram and top view of the sonar imaging geometry are shown in FIG. Figure 1 , Figure 2 shown.

[0102] In terms of hardware, the system consists of a sonar with a transmitter and receiver. During the surveying process, the sonar makes a spiral motion at the center of the scene being measured, a linear motion in the height direction, and a circular motion in the horizontal direction. The horizontal and height directions are sampled continuously and evenly. Assume that the echo signal S obtained by the sonar during the surveying process is rc (τ, θ) has L full sampling positions, each position has M distance sampling points, then the echo signal can be expressed as a L full ×M matrix.

[0103] The three-dimensional imaging method proposed by the present invention, that is, a three-dimensional imaging method of a spiral motion trajectory sonar provided by the present invention, comprises:

[0104] Step 1: The echo signal received by the sonar system is represented by S rc (τ, θ). τ represents the fast time, and θ represents the sampling direction of the echo signal. The echo signal is subjected to range-matched filtering to obtain the range-compressed signal S r (τ, θ).

[0105] 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 results of each height plane. Specifically, the traditional FFBP method can only process sonar data of straight lines and standard circular motion trajectories. The FFBP method provided by the present invention is an improved method that can realize the imaging of sonar data of various motion trajectories.

[0106] Specifically, step 2 includes two sub-steps: sub-aperture back projection and sub-aperture fusion. Taking imaging in an imaging plane with a height of h as an example, the step 2 includes:

[0107] Step 2.1: Assume that the 3D imaging grid is a cylindrical space with a height of H and a bottom radius of R. Establish a global rectangular coordinate system with the center of the grid as the origin. And the corresponding global cylindrical coordinate system The 3D imaging grid is divided into multiple 2D imaging grids along the height direction, and the corresponding local polar coordinate system is established with the center of each 2D imaging grid as the origin. and the local rectangular coordinate system

[0108] Assume that the signal S after distance compression is r (τ, θ) has sampling positions, and each position has M distance sampling points. Specifically, the full aperture data S r (τ, θ), divided into 2 according to the azimuthK sub-apertures. K represents the number of decomposition levels, and the number of sub-images merged at each level is 2. Assume that there is a pixel I0(i, j) in a two-dimensional imaging grid with a height of h. The position of the sub-aperture phase center is represented by C(θ, r, z), where the sonar position corresponding to an echo signal is represented by L(θ L , r L , z L ), then the two-way delay from the pixel to the phase center is expressed as:

[0109] t=R ij / c

[0110] Where t is the round trip delay, c is the speed of sound in water, and R ij Represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position.

[0111] The R ij The mathematical expression is:

[0112]

[0113] Among them, (x i ,y j ) represents the pixel point I0(i, j) in the local rectangular coordinate system Coordinates in 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 subaperture phase center in the global coordinate system.

[0114] The echo is back-projected to the scene for coherent accumulation to obtain the sub-image I0, the mathematical expression is:

[0115]

[0116] Where I0 represents the sub-image; n represents the starting azimuth of the sub-aperture, L min represents the number of azimuth sampling of the subaperture, f c Indicates the signal carrier frequency; s r (τ, θ) represents the signal after distance compression, where τ represents fast time; exp represents an exponential function with the base e of the natural logarithm as the base; j represents an imaginary unit; the symbol “·” represents a dot product;

[0117] Step 2.2: After BP imaging of the initial sub-aperture, several polar coordinate sub-images I0 on a plane at a specific height h are obtained. It is necessary to perform two-dimensional interpolation fusion on the obtained several polar coordinate sub-images to obtain the final two-dimensional imaging result.

[0118] Specifically, in the interpolation fusion process, first, the sub-aperture phase center of the next-level sub-image is determined to determine the imaging grid of the new sub-image. Assume that there are two adjacent sub-images at level k, which are represented as The corresponding sub-image phase center position is and At this time, the k.1-level new sub-image formed by the fusion of the two sub-images can be expressed as I k-1 , which corresponds to the phase center position C k-1 (θ k-1 , r k-1 )and The corresponding phase center position The relationship between them can be expressed mathematically as follows:

[0119]

[0120] Among them, C k-1 (θ k-1 , r k-1 ) represents the k-1 level sub-image I k-1 , that is, the position of the subaperture phase center corresponding to the new sub-image in the global polar coordinate system, θ k-1 With r k-1 are respectively the abscissa and ordinate of the subaperture phase center in the global polar coordinate system; Represents k-level sub-images respectively and The position of the corresponding subaperture phase center in the global polar coordinate system, and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system;

[0121] Image I k-1 The local polar coordinates corresponding to the pixel are expressed as The coordinates of image pixels in the global rectangular coordinate system can be expressed as [x k-1 ,y k-1 ], the calculation method is expressed as:

[0122]

[0123] Among them, [θ k-1 , r k-1 ] represents sub-image I k-1 The corresponding subaperture phase center coordinates in global polar coordinates, Represents sub-image Ik-1 The corresponding sub-aperture beam center angle is expressed mathematically as:

[0124]

[0125] Then the coordinates in the global coordinate system need to be converted to the coordinates in the local coordinate system of the previous level image, that is, the local polar coordinates. Here we convert to the image Taking the corresponding local polar coordinates as an example, the mathematical expression is:

[0126]

[0127] in, Represents sub-image I k-1 The pixel in the sub-image The corresponding coordinates in the local polar coordinate system; [x k-1 ,y k-1 ] represents image I k-1 The pixel's coordinates in the global rectangular coordinate system; Represents a sub-image The corresponding subaperture phase center.

[0128] Through the above coordinate transformation, the k-level sub-images are interpolated and fused into k-1-level sub-images. The polar coordinate imaging result can be obtained through K-level interpolation. Then the polar coordinate imaging result is interpolated into the global rectangular coordinate system to obtain the final two-dimensional imaging result.

[0129] Step 3: Superimpose the two-dimensional image sequence obtained in step 2, that is, the two-dimensional imaging result, to obtain a three-dimensional imaging result.

[0130] In order to verify the correctness of the proposed FFBP-based circular synthetic aperture sonar three-dimensional imaging method, MATLAB was used to simulate the method. In this simulation scenario, the sonar motion trajectory is a spiral trajectory with a standard circle as the horizontal projection and a straight line as the height upward, such as Figure 3 As shown in the figure, the sonar platform has a movement radius of 10m, and moves from an altitude of 0m to an altitude of 3m. The simulation parameters are set as follows: the sound speed is 1500m / s, the signal is a linear frequency modulation signal, the center frequency is 100kHz, and the transmission pulse width is 5ms. 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 the figure. Figure 4 shown.

[0131] Figure 5The imaging results of the FFBP imaging method proposed in this paper under the spiral trajectory are shown, and it can be concluded that this method can reconstruct the imaging target well. The 8 point targets are clearly visible, which verifies the effectiveness of the imaging method proposed in this paper.

[0132] Table 1 Simulation parameter settings

[0133]

[0134]

[0135] In order to reflect the advantage of FFBP algorithm in imaging efficiency, the FFBP algorithm and BP algorithm proposed in the present invention respectively perform two-dimensional imaging on the spiral echo signal in a plane with a height of 0.7, and obtain the following Figure 6 and Figure 7 The imaging results shown in the figure are shown in the figure. The imaging time of the FFBP algorithm is 2.258 seconds, and the imaging time of the BP algorithm is 136.5 seconds. Figure 6 , Figure 7 The imaging results show that under the premise of similar imaging effects, the FFBP method proposed in the present invention has great advantages in computational efficiency.

[0136] The present invention also provides a three-dimensional imaging system of a spiral motion trajectory sonar, which can be realized by executing the process steps of the three-dimensional imaging method of the spiral motion trajectory sonar, that is, those skilled in the art can understand the three-dimensional imaging method of the spiral motion trajectory sonar as a preferred implementation of the three-dimensional imaging system of the spiral motion trajectory sonar.

[0137] A three-dimensional imaging system of a spiral motion trajectory sonar provided by the present invention comprises:

[0138] Module M1: collects echo signals, and obtains distance-compressed signals according to the echo signals;

[0139] Module M2: based on the distance compressed signal, setting and dividing the three-dimensional imaging grid to obtain the two-dimensional imaging result of the target height plane;

[0140] Module M3: superimpose the two-dimensional imaging results to obtain three-dimensional imaging results.

[0141] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0142] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A three-dimensional imaging method of spiral motion trajectory sonar, characterized in that: include: Step S1: collecting echo signals, and obtaining distance-compressed signals according to the echo signals; Step S2: Based on the distance compressed signal, set and divide the three-dimensional imaging grid to obtain a two-dimensional imaging result of the target height plane; Step S3: superimposing the two-dimensional imaging results to obtain a three-dimensional imaging result.

2. The three-dimensional imaging method of spiral motion trajectory sonar according to claim 1, characterized in that: In the step S1, the range-compressed signal is obtained by performing range-matched filtering on the echo signal.

3. The three-dimensional imaging method of spiral motion trajectory sonar according to claim 1, characterized in that: The echo signal is S rc (τ, θ), where τ represents the fast time and θ represents the sampling azimuth of the echo signal; the signal after range compression is S r (τ, θ); In the step S2, it includes: Step S2.1: 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 includes: a global cylindrical coordinate system; Step S2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along the height direction; Step S2.3: confirming the sub-aperture phase center position according to the sampling azimuth of the range-compressed signal, and then obtaining the round-trip delay between the pixel point of the two-dimensional imaging grid at the target height and the sub-aperture phase center position; Step S2.4: based on the round-trip delay, coherently accumulate the projection of the echo signal to obtain a sub-image; Step S2.5: interpolating and fusing the sub-images to obtain the two-dimensional imaging result.

4. The three-dimensional imaging method of spiral motion trajectory sonar according to claim 3, characterized in that: In step S2.3, the mathematical expression of the round trip delay is: t=R ij / c Where t is the round trip delay, c is the speed of sound in water, and R ij Represents the distance between the pixel point I0(i, j) in the sub-image and the sonar position; The R ij The mathematical expression is: Among them, (x i ,y j ) represents the pixel point I0(i, j) in the local rectangular coordinate system Coordinates in 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 subaperture phase center in the global coordinate system; In step S2.4, the mathematical expression of the sub-image is: Where I0 represents the sub-image; n represents the starting azimuth of the sub-aperture, L min represents the number of azimuth sampling of the subaperture, f c Indicates the signal carrier frequency; s r (τ,θ) represents the signal after distance compression, where τ represents fast time; exp represents an exponential function with the base e of the natural logarithm as the base; j represents an imaginary unit; the symbol "·" represents a dot product; In step S2.5, the interpolation fusion process includes: Step A1: According to the phase center positions of two adjacent sub-images of level k, the two adjacent sub-images are fused into a new sub-image of level k-1; the new sub-image is I k-1 , the corresponding phase center position is C k-1 (θ k-1 ,r k-1 ); Step A2: based on the local polar coordinates corresponding to 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 sub-aperture beam center angle corresponding to the new sub-image is obtained; Step A3: based on the sub-aperture beam center angle, convert the coordinates in the global rectangular coordinate system into the coordinates of the local coordinate system of the previous level image 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.

5. The three-dimensional imaging method of spiral motion trajectory sonar according to claim 4, characterized in that: In step A1, the phase center position of the new sub-image is expressed as follows: Among them, θ k-1 With r k-1 Represents the k-1 level sub-image I respectively k-1 , i.e., the abscissa and ordinate of the subaperture phase center corresponding to the new sub-image in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; In step A2, the local polar coordinates corresponding to the pixels of the new sub-image are The pixel coordinates of the new sub-image in the global rectangular coordinate system are [x k-1 ,y k-1 ]; The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are expressed mathematically as follows: Among them, [θ k-1 ,r k-1 ] represents sub-image I k-1 The corresponding subaperture phase center coordinates in global polar coordinates, represents the beam center angle of the subaperture corresponding to the new sub-image; The beam center angle of the subaperture corresponding to the new sub-image is expressed mathematically as follows: In step A3, the mathematical expression of the polar coordinate imaging result is: in, Represents sub-image I k-1 The pixel in the sub-image The corresponding coordinates in the local polar coordinate system; [x k -1 ,y k-1 ] represents image I k-1 The pixel's coordinates in the global rectangular coordinate system; Represents a sub-image The corresponding subaperture phase center.

6. A three-dimensional imaging system of spiral motion trajectory sonar, characterized in that: include: Module M1: collects echo signals, and obtains distance-compressed signals according to the echo signals; Module M2: based on the distance compressed signal, setting and dividing the three-dimensional imaging grid to obtain the two-dimensional imaging result of the target height plane; Module M3: superimpose the two-dimensional imaging results to obtain three-dimensional imaging results.

7. The three-dimensional imaging system of spiral motion trajectory sonar according to claim 6, characterized in that: In the module M1, the range-compressed signal is obtained by performing range-matched filtering on the echo signal.

8. The three-dimensional imaging system of spiral motion trajectory sonar according to claim 6, characterized in that: The echo signal is S rc (τ,θ), where τ represents the fast time and θ represents the sampling azimuth of the echo signal; the signal after range compression is S r (τ,θ); The module M2 includes: Module M2.1: Setting the height and bottom surface of the three-dimensional imaging grid, establishing a global rectangular coordinate system and a corresponding stereoscopic coordinate system; the stereoscopic coordinate system includes: a global cylindrical coordinate system; Module M2.2: dividing the three-dimensional imaging grid into a plurality of two-dimensional imaging grids along the height direction; Module M2.3: confirming the sub-aperture phase center position according to the sampling azimuth of the range-compressed signal, and then obtaining the round-trip delay between the pixel point of the two-dimensional imaging grid at the target height and the sub-aperture phase center position; Module M2.4: based on the round-trip delay, coherently accumulate the projection of the echo signal to obtain a sub-image; Module M2.5: interpolating and fusing the sub-images to obtain the two-dimensional imaging result.

9. The three-dimensional imaging system of spiral motion trajectory sonar according to claim 8, characterized in that: In the module M2.3, the mathematical expression of the round trip delay is: t=R ij / c Where t is the round trip delay, c is the speed of sound in water, and R ij Represents the distance between the pixel point I0(i,j) in the sub-image and the sonar position. The R ij The mathematical expression is: Among them, (x i ,y j ) represents the pixel point I0(i,j) in the local rectangular coordinate system Coordinates in 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 subaperture phase center in the global coordinate system; In the module M2.4, the mathematical expression of the sub-image is: Where I0 represents the sub-image; n represents the starting azimuth of the sub-aperture, L min represents the number of azimuth sampling of the subaperture, f c Indicates the signal carrier frequency; s r (τ,θ) represents the signal after distance compression, where τ represents fast time; exp represents an exponential function with the base e of the natural logarithm as the base; j represents an imaginary unit; the symbol "·" represents a dot product; In the module M2.5, the interpolation fusion process includes: Module A1: According to the phase center positions of two adjacent sub-images of level k, the two adjacent sub-images are merged into a new sub-image of level k-1; the new sub-image is I k-1 , the corresponding phase center position is C k-1 (θ k-1 ,r k-1 ); 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; Module A3: based on the sub-aperture beam center angle, convert the coordinates in the global rectangular coordinate system into the coordinates of the local coordinate system of the previous level 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.

10. The three-dimensional imaging system of spiral motion trajectory sonar according to claim 9, characterized in that: In the module A1, the phase center position of the new sub-image is expressed as follows: Among them, θ k-1 With r k-1 Represents the k-1 level sub-image I respectively k-1 , i.e., the abscissa and ordinate of the subaperture phase center corresponding to the new sub-image in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; and Represents k-level sub-images respectively The horizontal and vertical coordinates of the corresponding subaperture phase center in the global polar coordinate system; In the module A2, the local polar coordinates corresponding to the pixels of the new sub-image are The pixel coordinates of the new sub-image in the global rectangular coordinate system are [x k-1 ,y k-1 ]; The coordinates of the pixels of the new sub-image in the global rectangular coordinate system are expressed mathematically as follows: Among them, [θ k-1 ,r k-1 ] represents sub-image I k-1 The corresponding subaperture phase center coordinates in global polar coordinates, represents the beam center angle of the subaperture corresponding to the new sub-image; The beam center angle of the subaperture corresponding to the new sub-image is expressed mathematically as follows: In the module A3, the mathematical expression of the polar coordinate imaging result is: in, Represents sub-image I k-1 The pixel in the sub-image The corresponding coordinates in the local polar coordinate system; [x k -1 ,y k-1 ] represents image I k-1 The pixel's coordinates in the global rectangular coordinate system; Represents a sub-image The corresponding subaperture phase center.

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