A method for unwrapping phase in interferometric synthetic aperture sonar

Abstract

The present application relates to the technical field of interferometric synthetic aperture sonar signal, and particularly relates to a method for extracting a wrapped phase of interferometric synthetic aperture sonar, comprising: taking an arbitrary pixel point of a main image as a center pixel point, and intercepting a main window of a preset size; obtaining a maximum value of a local offset of an auxiliary window in a distance direction relative to the main window, calculating the size of each auxiliary window based on different offset values, and obtaining an auxiliary image; calculating a complex coherence coefficient of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offset values; taking an offset value corresponding to a maximum value of the amplitude of the complex coherence coefficient as an initial matching position of a complex image composed of the main image and the auxiliary image; and calculating a wrapped phase estimation value of the center pixel point of the main window. The method provided by the present application estimates the wrapped phase in a local window by using a coherence method, avoids mutual influence existing in a classical complex image registration global fitting method, and avoids significant errors of the wrapped phase.

Description

Technical Field

[0001] This invention relates to the field of interferometric synthetic aperture sonar signal technology, and in particular to a method for extracting the wrapped phase of interferometric synthetic aperture sonar. Background Technology

[0002] Interferometric synthetic aperture sonar (InSAS) and interferometric synthetic aperture radar (InSAR) operate on the same principle: both use the synthetic aperture principle to obtain two-dimensional high-resolution images and then use the interferometric principle to retrieve the elevation information of the imaging area.

[0003] Currently, elevation reconstruction mainly employs two methods: the time-delay method and the phase method. While the time-delay method is simple in principle, its distance difference estimation accuracy is limited. Using a large estimation window leads to a sharp increase in computational load and a decrease in elevation estimation accuracy. Introducing phase information improves estimation accuracy but introduces the phase entanglement problem. The InSAS elevation reconstruction method, based on phase information, also calculates the slant range difference through phase comparison, achieving wavelength-level accuracy. This significantly improves the accuracy of slant range difference measurement and greatly enhances the accuracy of digital elevation model reconstruction. High-quality entangled phase acquisition is crucial for the successful completion of elevation reconstruction in the phase method. In interferometric signal processing, entangled phase acquisition typically employs complex image registration methods, involving four main steps: control point pair selection, geometric transformation model construction, auxiliary image resampling, and interferometric phase extraction.

[0004] Currently, to improve the quality of the extracted interferometric phase, optimization is mainly achieved by improving the accuracy of control points and the geometric transformation model. However, all of these are based on the assumption that the imaging area is planar. When the terrain of the imaging area changes drastically, the extracted entangled phase exhibits significant errors.

[0005] Therefore, the current method still has shortcomings in the extraction of the entangled phase, which affects the efficient and high-precision elevation reconstruction of InSAS. Summary of the Invention

[0006] This invention provides a method for extracting the entangled phase of interferometric synthetic aperture sonar, which solves the problem of significant errors in the entangled phase extracted by existing technologies. It can estimate the entangled phase in a local window using the coherence method, avoiding the mutual influence of the classical complex image registration global fitting method.

[0007] This invention provides a method for entangled phase extraction in interferometric synthetic aperture sonar, comprising:

[0008] S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel.

[0009] S2 obtains the maximum value of the local offset of the auxiliary window relative to the main window in the distance direction based on the size of the main window, calculates the size of each auxiliary window based on the different offsets, and obtains the auxiliary image;

[0010] S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets;

[0011] S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image;

[0012] S5 calculates the estimated winding phase value of the center pixel of the main window.

[0013] According to the present invention, a method for extracting the entangled phase of an interferometric synthetic aperture sonar includes the following steps after step S5:

[0014] S6 repeats steps S1 to S5, selects other pixels of the main image as the center pixel, selects the main window and the auxiliary window, and calculates the estimated value of the entanglement phase of each pixel in the main image.

[0015] According to the present invention, a method for extracting the entangled phase of interferometric synthetic aperture sonar includes steps S1-S2 as follows:

[0016] A local window is set on the main image. After the main window is cropped, the offset range is obtained according to the maximum offset. The auxiliary window is then moved step by step on the auxiliary image.

[0017] The main window and the auxiliary window have the same center pixel. The main window and the auxiliary window have the same size in the orientation direction. The auxiliary window is offset to the left and right by a number of pixels in the distance direction from the main window.

[0018] According to the present invention, a method for extracting the entangled phase of an interferometric synthetic aperture sonar, in step S6, after obtaining the estimated entangled phase value of each pixel, further includes:

[0019] Each winding phase estimate is filtered using circumferential mean filtering and / or circumferential median filtering.

[0020] According to the present invention, a method for extracting the wrapped phase of an interferometric synthetic aperture sonar, step S5, includes calculating the estimated value of the wrapped phase of the center pixel of the main window, including:

[0021] Obtain the initial offset corresponding to the maximum value of the complex coherence coefficient, and obtain the complex correlation coefficients corresponding to the adjacent offsets of the initial offset;

[0022] Using the amplitude values ​​of each complex coherence coefficient as weights, the complex coherence coefficients corresponding to different offsets are superimposed to calculate the principal phase values ​​of each complex correlation coefficient.

[0023] The superimposed phase principal value is the estimated value of the wrapped phase of the center pixel of the main window.

[0024] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the winding phase extraction method for interferometric synthetic aperture sonar as described above.

[0025] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the winding phase extraction method for interferometric synthetic aperture sonar as described above.

[0026] The present invention provides a method for entangled phase extraction in interferometric synthetic aperture sonar, which has at least the following technical advantages:

[0027] This invention is based on the imaging principle of the InSAS system. By acquiring the wrapped phase based on the coherence method, the wrapped phase can be estimated in a local window using the coherence method without interpolation or other operations. Furthermore, the wrapped phase estimation process at different phase points is independent, making it suitable for parallel computing and more efficient. It avoids the mutual influence that exists in the classical global fitting method for complex image registration, and the calculation results are highly accurate and far superior to classical methods. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic flowchart of the winding phase extraction method for interferometric synthetic aperture sonar provided by the present invention;

[0030] Figure 2 This is a schematic diagram of the imaging geometry of the interferometric synthetic aperture sonar provided by the present invention;

[0031] Figure 3 This is a schematic diagram of the main image of the winding phase extraction method for interferometric synthetic aperture sonar provided by the present invention;

[0032] Figure 4 This is a schematic diagram of an auxiliary image of the winding phase extraction method for interferometric synthetic aperture sonar provided by the present invention;

[0033] Figure 5 A schematic diagram illustrating the entanglement phase generated by a pre-adjustment sonar system in the prior art;

[0034] Figure 6 This is a schematic diagram of the winding phase obtained after adjustments based on the classical methods of the prior art;

[0035] Figure 7 A schematic diagram of the entangled phase obtained after adjusting the entangled phase extraction method for the interferometric synthetic aperture sonar provided by the present invention;

[0036] Figure 8 A comparative schematic diagram of the winding phase extraction method for interferometric synthetic aperture sonar provided by the present invention and the one-dimensional phase obtained by the prior art;

[0037] Figure 9 A schematic diagram of the entanglement phase obtained by existing technology methods;

[0038] Figure 10 This is a schematic diagram of the entangled phase obtained by the entangled phase extraction method for interferometric synthetic aperture sonar provided by the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or modules is not limited to the steps or modules listed, but may optionally include steps or modules not listed, or may optionally include other steps or modules inherent to such process, method, product, or apparatus.

[0041] It should be noted that the terms "first" and "second" used in this invention merely distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first" and "second" can be interchanged in a specific order or sequence where permissible. It should be understood that the objects distinguished by "first" and "second" can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those described or illustrated herein.

[0042] In one embodiment, such as Figure 1 As shown, this invention provides a method for extracting the entangled phase of interferometric synthetic aperture sonar, comprising:

[0043] S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel.

[0044] S2 obtains the maximum value of the local offset of the auxiliary window relative to the main window in the distance direction based on the size of the main window, calculates the size of each auxiliary window based on the different offsets, and obtains the auxiliary image;

[0045] S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets;

[0046] S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image;

[0047] S5 calculates the estimated wrapping phase value of the center pixel of the main window;

[0048] It should be noted that interferometric synthetic aperture sonar uses phase images received by two receivers mounted on a platform at a known short distance apart to interfere with each other, generating a phase difference. The elevation of the target is then calculated from the interferogram, generating a high-precision underwater three-dimensional image.

[0049] As an example, such as Figure 2 The diagram shown illustrates the imaging geometry of interferometric synthetic aperture sonar. Figure 2 The coordinate system shown has the center pixel as the origin O and the corresponding left and right phase points P. l and P r The coordinates are (-Δx, 0) and (Δx, 0) respectively;

[0050] The baseline center is located at (x0, z0), with an inclination angle of θ and a length of B. The coordinates of the lower endpoint A1 are... The coordinates of the upper endpoint A2 are

[0051] P l Distance from points A1 and A2 and It can be represented as:

[0052]

[0053]

[0054] Distance difference between the two:

[0055]

[0056] Based on the equivalence principle, the approximation is as follows:

[0057]

[0058]

[0059] The point P on the right can be obtained using the same method. r The difference in distance between points A1 and A2:

[0060]

[0061] At this point, the gradient of the distance difference between the two phase points A1 and A2 is:

[0062]

[0063] As an example, the ChinSAS-150 system has a center frequency of 150kHz, a baseline length of 0.12m, and a tilt angle of 60°. When the sampling distance changes from 51m to 231m, and Δx = 0.5m, Δr changes from 0.0024m to 0.0005m, which are equivalent to 0.24 and 0.05 wavelengths respectively, and decreases linearly with Δx. Therefore, in a small local area, the distance difference can be considered negligible compared to the wavelength, and the center point distance difference can be used as an approximation.

[0064] According to the present invention, a method for extracting the entangled phase of an interferometric synthetic aperture sonar includes the following steps after step S5:

[0065] S6 repeats steps S1 to S5, selects other pixels of the main image as the center pixel, selects the main window and the auxiliary window, and calculates the estimated value of the entanglement phase of each pixel in the main image.

[0066] According to the present invention, a method for extracting the entangled phase of interferometric synthetic aperture sonar includes steps S1-S2 as follows:

[0067] A local window is set on the main image. After the main window is cropped, the offset range is obtained according to the maximum offset. The auxiliary window is then moved step by step on the auxiliary image.

[0068] The main window and the auxiliary window have the same center pixel point. The main window and the auxiliary window have the same size in the orientation direction. The auxiliary window is offset by a number of pixels to the left and right in the distance direction from the main window.

[0069] Specifically, assuming the size of the local main window is M×N, and the maximum offset of the auxiliary window relative to the main window in the distance direction is K, then the maximum size of the local auxiliary window is (M+2K)×N. The data of the local main window and the local auxiliary window are the same, and the size in the orientation direction is the same. The local auxiliary window is only extended by K pixels to the left and right in the distance direction.

[0070] Calculate the complex coherence coefficient of the secondary window image relative to the main window image at different offsets. The formula for calculating the complex coherence coefficient is:

[0071]

[0072] In the formula, m and n are the local center points of the main image, u and v are the pixel offsets in the azimuth and distance directions respectively, i and j are temporary variables, E(·) is the mean operation, and the local window size is (2L+1)×(2K+1).

[0073] The above formula is equivalent to:

[0074]

[0075] According to the present invention, a method for extracting the entangled phase of an interferometric synthetic aperture sonar, in step S6, after obtaining the estimated entangled phase value of each pixel, further includes:

[0076] Each entanglement phase estimate is filtered by circumferential mean filtering and / or circumferential median filtering to further improve the quality of the estimated interference phase.

[0077] According to the present invention, a method for extracting the wrapped phase of an interferometric synthetic aperture sonar, step S5, includes calculating the estimated value of the wrapped phase of the center pixel of the main window, including:

[0078] Obtain the initial offset corresponding to the maximum value of the complex coherence coefficient, and obtain the complex correlation coefficients corresponding to the adjacent offsets of the initial offset;

[0079] Using the amplitude values ​​of each complex coherence coefficient as weights, the complex coherence coefficients corresponding to different offsets are superimposed to calculate the principal phase values ​​of each complex correlation coefficient.

[0080] The superimposed phase principal value is the estimated value of the wrapped phase of the center pixel of the main window;

[0081] Using the magnitude of the coherence coefficient as a weight, the complex coherence coefficients corresponding to different offsets are superimposed, and the main phase value of the superimposed value is taken as the winding phase estimate of the center pixel. Since no interpolation operation is introduced in the entire calculation process, the winding phase estimation process of different phase points is independent, which is suitable for parallel computing, and the mutual influence between different phase points in the winding phase calculation process is eliminated.

[0082] In one embodiment, the i-th multiple correlation coefficient is denoted as A i >0, Let i represent the phase of the complex correlation coefficient, ranging from -K to K, where K represents the maximum offset. To improve the quality of phase estimation, the amplitude of the complex coherence coefficient is used as a weight to calculate the vector sum. (t is the exponent), and then its principal phase value is taken as the estimated winding phase value of the center pixel. This phase value reflects the phase difference caused by the distance difference between the center pixel and the upper and lower receiving arrays of the sonar within the captured local window.

[0083] In one embodiment, the simulation parameters of the sonar system are selected as shown in Table 1 below:

[0084] Table 1 Simulation System Parameters

[0085]

[0086] The effectiveness of the method provided by this invention on simulation data is compared with that of classical methods, and the results are as follows: Figure 3 , 4 As shown in Figures 5 and 6:

[0087] Figure 3 The preset main image, Figure 4 As a preset auxiliary image, Figure 5 To adjust the winding phase generated by the pre-adjustment sonar system, it is evident that the data has significant noise and low accuracy. Figure 6 The winding phase is obtained according to the classical method of the prior art. Figure 7 The winding phase is obtained after adjustment according to the method provided by the present invention; it can be seen that, relative to Figure 5 and 6 In other words, Figure 7 It significantly reduces data noise and effectively improves data accuracy;

[0088] Figure 8 The image shows a comparison of the one-dimensional phase obtained by the present invention and the prior art when the azimuth down is 100. Figure 8 The upper part is the one-dimensional phase obtained by the prior art, and the lower part is the one-dimensional phase obtained by the method according to the present invention. It can be seen that the phase accuracy obtained by the prior art is significantly lower than that of the method provided by the present invention.

[0089] Figures 9-10 The figures show a comparison of the residual phase diagrams obtained by the methods provided by the prior art and the methods provided by the present invention. It can be seen that the method provided by the present invention eliminates residual points and effectively improves the calculation accuracy compared with the prior art.

[0090] This invention also provides an electronic device, which may include: a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other via the communication bus. The processor can invoke logical instructions in the memory to execute a winding phase extraction method for interferometric synthetic aperture sonar provided by the above methods, including:

[0091] S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel.

[0092] S2 obtains the maximum value of the local offset of the auxiliary window relative to the main window in the distance direction based on the size of the main window, calculates the size of each auxiliary window based on the different offsets, and obtains the auxiliary image;

[0093] S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets;

[0094] S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image;

[0095] S5 calculates the estimated winding phase value of the center pixel of the main window.

[0096] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and sold or used as independent products, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0097] On the other hand, the present invention also provides a computer program product, the computer program product comprising a computer program stored on a non-transitory computer-readable storage medium, the computer program comprising program instructions, wherein when the program instructions are executed by a computer, the computer is able to execute a winding phase extraction method for interferometric synthetic aperture sonar provided by the above methods, comprising:

[0098] S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel.

[0099] S2 obtains the maximum value of the local offset of the auxiliary window relative to the main window in the distance direction based on the size of the main window, calculates the size of each auxiliary window based on the different offsets, and obtains the auxiliary image;

[0100] S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets;

[0101] S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image;

[0102] S5 calculates the wrapping phase estimate of the center pixel of the main window.

[0103] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a method for winding phase extraction of interferometric synthetic aperture sonar provided by the methods described above, comprising:

[0104] S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel.

[0105] S2 obtains the maximum value of the local offset of the auxiliary window relative to the main window in the distance direction based on the size of the main window, calculates the size of each auxiliary window based on the different offsets, and obtains the auxiliary image;

[0106] S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets;

[0107] S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image;

[0108] S5 calculates the estimated winding phase value of the center pixel of the main window.

[0109] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0110] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting the entangled phase of interferometric synthetic aperture sonar, characterized in that, include: S1 extracts a main window of a preset size based on the operating parameters of the sonar system and the size of the area to be processed, using any pixel in the main image as the center pixel. S2, based on the main window size, obtains the maximum local offset of the auxiliary window relative to the main window in the distance direction. Based on the different offsets, it calculates the size of each auxiliary window and obtains the auxiliary image. A local window is set on the main image. After cropping the main window, the offset range is obtained according to the maximum offset. The auxiliary window is moved step by step on the auxiliary image. The center pixel of the main window and the auxiliary window are the same. The size of the main window and the auxiliary window in the azimuth direction is the same. The auxiliary window is extended to the left and right by a number of pixels in the distance direction based on the main window. S3 calculates the complex coherence coefficients of the auxiliary image corresponding to the auxiliary window and the main image corresponding to the main window at different offsets; S4 uses the offset corresponding to the maximum amplitude of the complex coherence coefficient as the initial matching position of the complex image composed of the main image and the auxiliary image; S5 calculates the estimated wrapping phase value of the center pixel of the main window; including: Obtain the initial offset corresponding to the maximum value of the complex coherence coefficient, and obtain the complex correlation coefficients corresponding to the adjacent offsets of the initial offset; Using the amplitude values ​​of each complex coherence coefficient as weights, the complex coherence coefficients corresponding to different offsets are superimposed to calculate the principal phase values ​​of each complex correlation coefficient. The superimposed phase principal value is the estimated value of the wrapped phase of the center pixel of the main window.

2. The method for extracting the wound phase of interferometric synthetic aperture sonar according to claim 1, characterized in that, Step S5 and the following steps include: S6 repeats steps S1 to S5, selects other pixels of the main image as the center pixel, selects the main window and the auxiliary window, and calculates the estimated value of the entanglement phase of each pixel in the main image.

3. The method for extracting the wound phase of interferometric synthetic aperture sonar according to claim 2, characterized in that, After obtaining the wrapped phase estimate for each pixel, the process further includes: Each winding phase estimate is filtered using circumferential mean filtering and / or circumferential median filtering.

4. An electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the winding phase extraction method for interferometric synthetic aperture sonar as described in any one of claims 1 to 3.

5. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the winding phase extraction method for interferometric synthetic aperture sonar as described in any one of claims 1 to 3.

Images