A method for electrical imaging of underwater buried targets

Abstract

The present invention discloses an electrical imaging method for underwater buried targets, and belongs to the field of underwater buried target detection and imaging. First, a detection device is prepared, which includes two teams of transceiver electrodes, and then the array flow pattern and flow pattern matrix are obtained. The detection device is then used to perform a matrix scan on the detection area where the buried target is located to obtain a received signal matrix, and then the target width value and position corresponding to each row of the received signal matrix are obtained through spatial spectrum estimation and sliding window scanning, and finally inversion imaging is performed based on the width value and position. The present invention forms a virtual electrode array based on two pairs of moving transceiver electrodes, and has the advantages of low system complexity, low cost, fast imaging speed, and high accuracy.

Description

Technical Field

[0001] The invention belongs to the field of underwater buried target detection and imaging, and in particular relates to an underwater buried target electrical imaging method. Background Art

[0002] The acquisition, fusion and application of marine target information is currently a priority development area, and underwater buried target detection and imaging technology is also gaining increasing attention. Compared with other detection imaging technologies (such as synthetic aperture sonar detection technology and shallow layer profile detection technology), underwater buried target electrical imaging technology has the advantages of strong anti-interference ability, high accuracy, low cost and the ability to distinguish between metal and non-metal. It is widely used in submarine oil and gas pipeline detection, channel dredging, underwater unexploded ordnance detection and other fields.

[0003] Due to factors such as the undulating underwater topography and the position error of the electrode array, the existing electrical imaging methods have the following problems: First, the traditional detection imaging system usually uses a multi-electrode array, which greatly increases the complexity and cost of the detection imaging system. Second, due to the wide variety of buried targets, the complex boundary conditions of the underwater seabed, and the changes in the array posture, it is impossible to directly use analytical models to construct the array flow pattern. The solution is difficult and the calculation is large, resulting in slow imaging speed and low accuracy. Summary of the invention

[0004] The present invention proposes an underwater buried target electrical imaging method, the purpose of which is: 1. to solve the problem of complex structure and high cost of traditional multi-electrode array; 2. to solve the problem of high solution difficulty and large calculation amount of traditional methods.

[0005] The technical solution of the present invention is as follows:

[0006] A method for electrical imaging of underwater buried targets, comprising the following steps:

[0007] Step 1: prepare a detection device, wherein the detection device is arranged on a mobile carrier that can move underwater;

[0008] Step 2: Use the detection device to scan standard targets of different widths respectively, obtain the array flow patterns corresponding to each width, and construct a flow pattern matrix by splicing the array flow patterns of different widths in rows. ;

[0009] Step 3: Use the detection device to perform matrix scanning on the detection area where the buried target is located, and construct a receiving signal matrix based on the output signal of the detection device. ;

[0010] Step 4: Receive signal matrix The rows of Each row of the spatial spectrum is estimated to determine the received signal matrix Each row of corresponds to the closest array flow type, and then the received signal matrix is ​​determined according to the closest array flow type. The target width values ​​corresponding to each row of ;

[0011] Step 5: For the received signal matrix For each row of , the closest array flow pattern corresponding to the row is used for sliding window scanning, and local spatial spectrum estimation is performed during the sliding window scanning process to determine the received signal matrix The target position corresponding to each row of ;

[0012] Step 6: Based on the received signal matrix The target width values ​​and positions corresponding to all rows are inverted and imaged.

[0013] As a further improvement of the underwater buried target electrical imaging method: the detection device includes a pair of transmitting electrodes and a pair of receiving electrodes, the transmitting electrodes and the receiving electrodes are arranged in a line, and the two receiving electrodes are located on both sides of the two transmitting electrodes;

[0014] The transmitting electrode is used to transmit an active excitation electric field signal, which propagates in water and excites the target object to generate a secondary electric field. The electric field signal received by the receiving electrode includes the original electric field signal emitted by the transmitting electrode and the secondary electric field signal generated by the target object.

[0015] As a further improvement of the underwater buried target electrical imaging method: the distance between each receiving electrode and the transmitting electrode on the same side is equal.

[0016] As a further improvement of the underwater buried target electrical imaging method: before the detection device works, the transmitting electrode is driven to emit an electric field signal in a scene without a target object, and the electric field signal Sign_1 received by each receiving electrode at this time is recorded;

[0017] When the detection device is working, assuming that the electric field signal received by the receiving electrode is Sign_2, the secondary electric field signal part Sign_delta=Sign_2-Sign_1 is calculated for each receiving electrode, and finally the difference between the Sign_delta of the two receiving electrodes is used as the output signal of the detection device.

[0018] As a further improvement of the underwater buried target electrical imaging method, step 2 specifically includes:

[0019] Step 2-1, select standard targets with bars of different widths;

[0020] Step 2-2, use the detection device to scan the standard target body in the following way to obtain the array flow patterns corresponding to different widths: The standard target is placed on the first plane, and the detection device moves from one side of the standard target to the other side in a second plane parallel to the first plane and in a direction perpendicular to the standard target. Record the output signal of the detection device once, and take the part of the output signal sequence whose signal amplitude meets the preset requirements as the current width The corresponding array flow pattern;

[0021] Step 2-3: Connect the obtained array flow patterns row by row to obtain the flow pattern matrix , flow matrix Each row of corresponds to a width.

[0022] As a further improvement of the electrical imaging method for underwater buried targets, the matrix scanning in step 3 means: setting a plurality of equally spaced lateral paths in the detection area, scanning each row of lateral paths separately, and moving each lateral path by a preset spacing during the scanning process. Record the output signal of the primary detection device;

[0023] After completing the matrix scan, the receiving signal matrix is ​​constructed according to the recording position of the output signal ; Receive signal matrix Each row corresponds to each lateral path, and the arrangement order of each row is consistent with the arrangement order of the lateral paths in the detection area.

[0024] As a further improvement of the underwater buried target electrical imaging method, the specific process of step 4 is as follows:

[0025] Step 4-1: Calculate the flow matrix The projection matrix of each row;

[0026] Step 4-2: Calculate the received signal matrix The signal subspace of each row;

[0027] For the received signal matrix Any row of Line, record , the corresponding signal subspace is ;

[0028] Step 4-3: Traverse the received signal matrix For each row of : For any row, let it be row, respectively calculate the row and the flow matrix The spatial spectrum function between each row; for the flow matrix No. The spatial spectrum function is: ,in Represents the trace of the matrix; from the received signal matrix No. The set of all spatial spectrum functions corresponding to the row Find the maximum value in the flow matrix The corresponding row, flow matrix This row is the received signal matrix No. The closest array flow type corresponding to the row, and the flow type matrix The width of the row in the matrix is ​​the received signal matrix No. The target width value for the row.

[0029] As a further improvement of the underwater buried target electrical imaging method: in step 4-1, for the flow matrix No. OK , and its corresponding projection matrix is , superscript represents conjugate transpose;

[0030] In step 4-2, for , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript represents the conjugate transpose; then the covariance matrix Perform eigenvalue decomposition and obtain The diagonal matrix composed of eigenvalues; then The eigenvalues ​​are arranged in descending order. The eigenvalues ​​corresponding to the eigenvectors in order constitute the signal subspace .

[0031] As a further improvement of the underwater buried target electrical imaging method, the sliding window scanning process is as follows: assuming that the current receiving signal matrix No. OK , the number of output signals contained in this row is , the projection matrix corresponding to this row that is closest to the array flow type is , the length of the closest array flow pattern is ,and , then is the sliding window size Perform a scan with a step size of 1; for the first Sliding window, set The paragraph in the sliding window is , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript Represents the conjugate transpose, and then based on calculate The corresponding signal subspace , and then calculate the local spatial spectrum function corresponding to the sliding window ,in Represents the trace of the matrix.

[0032] As a further improvement of the underwater buried target electrical imaging method: in step 5, determine the received signal matrix The target position corresponding to each row of is as follows: for the received signal matrix For any row of , find the maximum value from all local spatial spectrum functions corresponding to the row, and use the center position of the sliding window corresponding to the maximum value as the target position corresponding to the row.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention uses two pairs of transmitting and receiving electrodes to form a detection device, and then performs matrix detection based on the detection device, thereby forming a virtual electrode array. Compared with the traditional multi-electrode array structure, it suppresses the position error of the array, increases the array aperture in disguise, and also reduces the structural complexity and cost of the imaging system.

[0035] 2. The present invention uses the twin modeling method to obtain the array flow pattern of target space focusing, and combines the subspace fitting algorithm and the sliding window algorithm to obtain the target width and position of each row, realizing linear imaging of buried targets. It no longer needs to adopt complex nonlinear iterative methods to achieve real-time two-dimensional imaging of buried targets, and has the advantages of fast imaging speed and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a front view when performing detection in a specific implementation mode;

[0037] Figure 2 A top view of a mobile carrier performing matrix detection in a specific implementation manner;

[0038] Figure 3 For the specific implementation step 2-2, different widths Array flow pattern curve below;

[0039] Figure 4 This is an inversion image obtained when the buried target object is a T-shaped pipe in a specific implementation manner;

[0040] Figure 5This is an inversion image obtained when the buried target is an S-shaped pipe in a specific implementation manner.

[0041] Reference numerals include:

[0042] 100. Mobile carrier, 101. Receiving electrode, 102. Transmitting electrode, 200. Target object. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0044] A method for electrical imaging of underwater buried targets, comprising the following steps:

[0045] Step 1: Prepare the detection device.

[0046] like Figure 1 The detection device includes a pair of transmitting electrodes 102 and a pair of receiving electrodes 101, the transmitting electrodes 102 and the receiving electrodes 101 are arranged in a line, and the two receiving electrodes 101 are located on both sides of the two transmitting electrodes 102. Preferably, the distance between each receiving electrode 101 and the transmitting electrode 102 on the same side is equal. In this embodiment, the distance between the transmitting electrodes 102 is 0.2m, and the distance between the receiving electrode 101 and the generating electrode on the same side is also 0.2m.

[0047] The transmitting electrode 102 is used to transmit an active excitation electric field signal, which propagates in the water and excites the target object 200 to generate a secondary electric field. The electric field signal received by the receiving electrode 101 includes the original electric field signal emitted by the transmitting electrode 102 and the secondary electric field signal generated by the target object 200.

[0048] Before the detection device works, the transmitting electrode 102 is driven to emit an electric field signal in a scene without a target object 200, and the electric field signal Sign_1 received by each receiving electrode 101 is recorded. When the detection device works, the electric field signal received by the receiving electrode 101 is set as Sign_2, and the secondary electric field signal part Sign_delta=Sign_2-Sign_1 is calculated for each receiving electrode 101, and finally the difference between the Sign_delta of the two receiving electrodes 101 is used as the output signal of the detection device.

[0049] Furthermore, the detection device is arranged on a mobile carrier 100 that can move underwater. In this embodiment, the mobile carrier 100 is an underwater vehicle (AUV).

[0050] Step 2: Use the detection device to scan standard targets of different widths respectively, obtain the array flow patterns corresponding to each width, and construct a flow pattern matrix by splicing the array flow patterns of different widths in rows. .

[0051] The specific process is:

[0052] Step 2-1, select standard targets of different widths. In this embodiment, the width selection range is 0.2m~4m, and a total of 20 standard targets are selected.

[0053] Step 2-2, use the detection device to scan the standard target body in the following way to obtain the array flow patterns corresponding to different widths: The standard target is placed on the first plane, and the detection device moves from one side of the standard target to the other side in a second plane parallel to the first plane and in a direction perpendicular to the standard target. Record the output signal of the detection device once, and take the part of the output signal sequence whose signal amplitude meets the preset requirements as the current width The corresponding array flow pattern.

[0054] In this embodiment, the above spacing The center of the standard target is taken as the origin of the moving axis. During scanning, the detection device moves from -6m to 6m. The array flow curves obtained at different widths are as follows: Figure 3 From the energy perspective, 95% of the energy is concentrated in the range of -3~3m, so only the output signal sequence within this range is retained as the array flow type.

[0055] Step 2-3: Connect the obtained array flow patterns row by row to obtain the flow pattern matrix , flow matrix Each row of corresponds to a width.

[0056] Step 3: Use the detection device to perform matrix scanning on the detection area where the buried target 200 is located, and construct a receiving signal matrix based on the output signal of the detection device. .

[0057] like Figure 1 and 2 The matrix scanning means: setting a plurality of equally spaced transverse paths in the detection area, scanning each row of transverse paths separately, and moving each transverse path by a preset spacing during the scanning process. Record the output signal of the primary detection device.

[0058] After completing the matrix scan, the receiving signal matrix is ​​constructed according to the recording position of the output signal . Receive signal matrix Each row corresponds to each lateral path, and the arrangement order of each row is consistent with the arrangement order of the lateral paths in the detection area.

[0059] Step 4: Receive signal matrix The rows of Each row of the spatial spectrum is estimated to determine the received signal matrix Each row of corresponds to the closest array flow type, and then the received signal matrix is ​​determined according to the closest array flow type. The target width values ​​corresponding to each row of .

[0060] The specific process is:

[0061] Step 4-1: Calculate the flow matrix The projection matrix for each row.

[0062] For the flow matrix No. OK , and its corresponding projection matrix is , superscript represents the conjugate transpose.

[0063] Step 4-2: Calculate the received signal matrix The signal subspace of each row.

[0064] For the received signal matrix Any row of Line, record , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript represents the conjugate transpose; then the covariance matrix Perform eigenvalue decomposition and obtain The diagonal matrix composed of eigenvalues; then The eigenvalues ​​are arranged in descending order. The eigenvalues ​​corresponding to the eigenvectors in order constitute the signal subspace .

[0065] Step 4-3: Traverse the received signal matrix For each row of : For any row, let it be row, respectively calculate the row and the flow matrix The spatial spectrum function between each row; for the flow matrix No. The spatial spectrum function is: ,in Represents the trace of the matrix; from the received signal matrix No. The set of all spatial spectrum functions corresponding to the row Find the maximum value in the flow matrix The corresponding row, flow matrix This row is the received signal matrix No. The closest array flow type corresponding to the row, and the flow type matrix The width of the row in the matrix is ​​the received signal matrix No. The target width value for the row.

[0066] At this point, the received signal matrix can be determined The target width value for all rows of the .

[0067] Step 5: For the received signal matrix For each row of , the closest array flow pattern corresponding to the row is used for sliding window scanning, and local spatial spectrum estimation is performed during the sliding window scanning process to determine the received signal matrix The target position corresponding to each row of .

[0068] The process of sliding window scanning is as follows: Assume that the current received signal matrix No. OK , the number of output signals contained in this row is , the projection matrix corresponding to this row that is closest to the array flow type is , the length of the closest array flow pattern is ,and , then is the sliding window size Perform a scan with a step size of 1; for the first Sliding window, set The paragraph in the sliding window is , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript Represents the conjugate transpose, and then based on calculate The corresponding signal subspace , and then calculate the local spatial spectrum function corresponding to the sliding window ,in Represents the trace of the matrix.

[0069] Determine the received signal matrix The target position corresponding to each row of is as follows: for the received signal matrix For any row of , find the maximum value from all local spatial spectrum functions corresponding to the row, and use the center position of the sliding window corresponding to the maximum value as the target position corresponding to the row.

[0070] Step 6: Based on the received signal matrix The target width values ​​and positions corresponding to all rows are inverted and imaged.

[0071] The above method is used to perform inversion imaging of underwater buried targets: Seawater medium conductivity 1Set to S / m, magnetic permeability of seawater Set to 1; burial target one is a "T" type pipeline, with specific parameters set to 0.5m burial depth, 4m widest, 1.5m narrowest, 11m total length, and 0.2m thickness; burial target two is an "S" type pipeline, with a burial depth of 0.5m, a pipeline width of 2m, and a thickness of 1m.

[0072] like Figure 4 and Figure 5 The blue border represents the actual outline and shape of the buried object. Comparing it with the inverted image, the outline and shape of the target in the inverted image are basically consistent with the actual target. Figure 4 and Figure 5 The "T" and "S" shapes of the buried targets are clearly presented, and the inversion graphics are relatively clear without distortion. In particular, the target size in the inversion graphics is basically consistent with the actual target size, and the error is kept within ±0.15m, which shows that the inversion accuracy of the present invention is high and relatively stable, the imaging results are relatively clear, and it can be well applied in practical engineering.

[0073] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. The scope of the present invention is defined by the claims rather than the above description.

Claims

1. A method for electrical imaging of underwater buried targets, characterized in that the steps include: Step 1: prepare a detection device, wherein the detection device is arranged on a mobile carrier that can move underwater; Step 2: Use the detection device to scan standard targets of different widths respectively, obtain the array flow patterns corresponding to each width, and construct a flow pattern matrix by splicing the array flow patterns of different widths in rows. ; Step 3: Use the detection device to perform matrix scanning on the detection area where the buried target is located, and construct a receiving signal matrix based on the output signal of the detection device. ; Step 4: Receive signal matrix The rows of Each row of the spatial spectrum is estimated to determine the received signal matrix Each row of corresponds to the closest array flow type, and then the received signal matrix is ​​determined according to the closest array flow type. The target width values ​​corresponding to each row of ; Step 5: For the received signal matrix For each row of , the closest array flow pattern corresponding to the row is used for sliding window scanning, and local spatial spectrum estimation is performed during the sliding window scanning process to determine the received signal matrix The target position corresponding to each row of ; Step 6: Based on the received signal matrix The target width values ​​and target positions corresponding to all rows are inverted and imaged.

2. The method for electrical imaging of underwater buried targets according to claim 1, characterized in that: The detection device comprises a pair of transmitting electrodes and a pair of receiving electrodes, the transmitting electrodes and the receiving electrodes are arranged in a line, and the two receiving electrodes are located on both sides of the two transmitting electrodes; The transmitting electrode is used to transmit an active excitation electric field signal, which propagates in water and excites the target object to generate a secondary electric field. The electric field signal received by the receiving electrode includes the original electric field signal emitted by the transmitting electrode and the secondary electric field signal generated by the target object.

3. The method for electrical imaging of underwater buried targets according to claim 2, characterized in that: The distance between each receiving electrode and the transmitting electrode on the same side is equal.

4. The method for electrical imaging of underwater buried targets as claimed in claim 2, characterized in that: Before the detection device works, it first drives the transmitting electrode to send out an electric field signal in a scene without a target object, and records the electric field signal Sign_1 received by each receiving electrode at this time; When the detection device is working, assuming that the electric field signal received by the receiving electrode is Sign_2, the secondary electric field signal part Sign_delta=Sign_2-Sign_1 is calculated for each receiving electrode, and finally the difference between the Sign_delta of the two receiving electrodes is used as the output signal of the detection device.

5. The method for electrical imaging of underwater buried targets according to claim 1, characterized in that: Step 2 specifically includes: Step 2-1, select standard targets with bars of different widths; Step 2-2, use the detection device to scan the standard target body in the following way to obtain the array flow patterns corresponding to different widths: The standard target is placed on the first plane, and the detection device moves from one side of the standard target to the other side in a second plane parallel to the first plane and in a direction perpendicular to the standard target. Record the output signal of the detection device once, and take the part of the output signal sequence whose signal amplitude meets the preset requirements as the current width The corresponding array flow pattern; Step 2-3: Connect the obtained array flow patterns row by row to obtain the flow pattern matrix , flow matrix Each row of corresponds to a width.

6. The method for electrical imaging of underwater buried targets according to claim 1, characterized in that: The matrix scanning in step 3 means: setting multiple equally spaced transverse paths in the detection area, scanning each row of transverse paths separately, and moving each transverse path by a preset spacing during the scanning process. Record the output signal of the primary detection device; After completing the matrix scan, the receiving signal matrix is ​​constructed according to the recording position of the output signal ; Receive signal matrix Each row corresponds to each lateral path, and the arrangement order of each row is consistent with the arrangement order of the lateral paths in the detection area.

7. The method for electrical imaging of underwater buried targets according to claim 1, characterized in that: The specific process of step 4 is as follows: Step 4-1: Calculate the flow matrix The projection matrix of each row; Step 4-2: Calculate the received signal matrix The signal subspace of each row; For the received signal matrix Any row of Line, record , the corresponding signal subspace is ; Step 4-3: Traverse the received signal matrix For each row of : For any row, let it be row, respectively calculate the row and the flow matrix The spatial spectrum function between each row; for the flow matrix No. The spatial spectrum function is: ,in represents the trace of the matrix, is the flow matrix No. The projection matrix corresponding to the row, superscript represents the conjugate transpose; from the received signal matrix No. The set of all spatial spectrum functions corresponding to the row Find the maximum value in the flow matrix The corresponding row, flow matrix This row is the received signal matrix No. The closest array flow type corresponding to the row, and the flow type matrix The width of the row in the matrix is ​​the received signal matrix No. The target width value for the row.

8. The method for electrical imaging of underwater buried targets as claimed in claim 7, characterized in that: In step 4-1, for the flow matrix No. OK , and its corresponding projection matrix is , superscript represents conjugate transpose; In step 4-2, for , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript represents the conjugate transpose; then the covariance matrix Perform eigenvalue decomposition and obtain The diagonal matrix composed of eigenvalues; then The eigenvalues ​​are arranged in descending order. The eigenvalues ​​corresponding to the eigenvectors in order constitute the signal subspace .

9. The method for electrical imaging of underwater buried targets according to claim 7 or 8, characterized in that: The process of sliding window scanning is as follows: Assume that the current received signal matrix No. OK , the number of output signals contained in this row is , the projection matrix corresponding to this row that is closest to the array flow type is , the length of the closest array flow pattern is ,and , then is the sliding window size Perform a scan with a step size of 1; for the first Sliding window, set The paragraph in the sliding window is , first calculate The covariance matrix of , Indicates the expected value of the calculation, the superscript Represents the conjugate transpose, and then based on calculate The corresponding signal subspace , and then calculate the local spatial spectrum function corresponding to the sliding window ,in Represents the trace of the matrix.

10. The method for electrical imaging of underwater buried targets according to claim 9, characterized in that: In step 5, determine the received signal matrix The target position corresponding to each row of is as follows: for the received signal matrix For any row of , find the maximum value from all local spatial spectrum functions corresponding to the row, and use the center position of the sliding window corresponding to the maximum value as the target position corresponding to the row.

Images