Airborne circular SAR imaging method and device

Abstract

The present invention relates to an airborne circular SAR imaging method and device. A specific implementation of the method includes: transforming the original SAR data into the range frequency domain, and then performing frequency demodulation processing to obtain phase history data; converting the phase history data in polar coordinate format into rectangular coordinate format through two-dimensional resampling; performing two-dimensional inverse Fourier transform on the two-dimensional resampled data to obtain a focused image; and performing geometric correction on the focused image to obtain the final circular SAR image. This implementation can obtain a two-dimensional high-resolution SAR image of the target with full viewing angle.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic scattering characteristic measurement, and in particular to an airborne circular SAR imaging method and device. Background Art

[0002] When performing airborne downward-looking SAR (Synthetic Aperture Radar) imaging measurements, a straight-line strip flight mode is often used. This mode can obtain SAR images of the target at a certain azimuth angle. However, if the target's surrounding environment is complex and there are obstructions or shadows on the target imaging in some directions, the target SAR imaging will be affected. Summary of the invention

[0003] In view of the defects in the prior art, the present invention provides an airborne circular SAR imaging method and device, which can obtain a two-dimensional high-resolution SAR image of the target with full viewing angle.

[0004] In order to solve the above technical problems, in one aspect, an embodiment of the present invention provides an airborne circular synthetic aperture radar SAR imaging method.

[0005] The airborne circular synthetic aperture radar (SAR) imaging method of the embodiment of the present invention comprises: transforming the original SAR data into the range frequency domain, and then performing frequency demodulation processing to obtain phase history data; converting the phase history data in polar coordinate format into rectangular coordinate format through two-dimensional resampling; performing two-dimensional inverse Fourier transform on the two-dimensional resampled data to obtain a focused image; and performing geometric correction on the focused image to obtain a final circular SAR image.

[0006] Optionally, the transforming of the original SAR data into the range frequency domain comprises: performing a range Fourier transform on the original SAR data and performing matched filtering to obtain a signal s(f r , t m )for:

[0007]

[0008] Among them, f r is the distance frequency, t m is the slow time, rect(·) is the rectangular window function, B is the transmit signal bandwidth, k r =4π(f c +f r ) / c is the wave number, f c is the center frequency, c is the speed of light, is the instantaneous slant range of the target, v is the antenna speed, R b is the shortest slant distance from the antenna phase center to the scene center, and (x, y) is the target coordinate.

[0009] Optionally, the demodulation process is performed to obtain phase history data, including: obtaining the phase history data s(f r , t m ):

[0010]

[0011] in, is the instantaneous slant distance from the antenna phase center to the scene center.

[0012] Optionally, the two-dimensional resampling includes distance resampling and azimuth resampling, wherein the distance resampling transforms the phase history data in polar coordinate format into a Keystone grid, and the signal s(k y , t m )for:

[0013]

[0014] Among them, k y is the distance wave number, θ a is the azimuth, k rc =4πf c / c is the wave number center, Δk r =4πB / c is the wave number bandwidth, ξ(·) is the second-order Taylor series expansion, and o(·) is the third-order and higher-order terms;

[0015] The azimuth resampling converts the data of the Keystone grid into a rectangular coordinate format. The azimuth resampled signal s(k x , k y )for:

[0016]

[0017] Among them, k x is the azimuth wave number.

[0018] Optionally, performing a two-dimensional inverse Fourier transform on the two-dimensionally resampled data to obtain a focused image includes: obtaining the focused image I(x, y) according to the following formula:

[0019]

[0020] Among them, Δk x is the azimuth wavenumber bandwidth.

[0021] Optionally, the geometric correction includes distortion correction, squint conversion and oblique ground conversion.

[0022] Optionally, the distortion correction is performed according to the following formula:

[0023]

[0024] The squint conversion is performed using the following formula:

[0025]

[0026] The skew-to-ground conversion is performed using the following formula:

[0027]

[0028] Among them, (x′, y′) is the corrected coordinate, θ sq is the slant angle, and β is the beam elevation angle.

[0029] In order to solve the above technical problem, on the other hand, an embodiment of the present invention provides an airborne circular SAR imaging device.

[0030] The airborne circular SAR imaging device of the embodiment of the present invention may include: a phase history acquisition unit, used to transform the original SAR data into the range frequency domain, and then perform frequency demodulation processing to obtain phase history data; a rectangular coordinate conversion unit, used to convert the phase history data in polar coordinate format into rectangular coordinate format through two-dimensional resampling; a focused image generation unit, used to perform two-dimensional inverse Fourier transform on the two-dimensional resampled data to obtain a focused image; and a correction unit, used to perform geometric correction on the focused image to obtain a final circular SAR image.

[0031] To achieve the above objective, according to another aspect of the present invention, an electronic device is provided.

[0032] An electronic device of the present invention comprises: one or more processors; a storage device for storing one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors implement the airborne circular track SAR imaging method provided by the present invention.

[0033] To achieve the above objective, according to yet another aspect of the present invention, a computer-readable storage medium is provided.

[0034] A computer-readable storage medium of the present invention stores a computer program, and when the program is executed by a processor, the airborne circular SAR imaging method provided by the present invention is implemented.

[0035] In the technical solution of the present invention, the acquired original SAR data is subjected to range transformation and frequency demodulation processing to obtain phase history data; polar coordinate processing is performed on the phase history data, that is, the phase history data in polar coordinate format is converted into rectangular coordinate format through two-dimensional resampling (specifically including range resampling and azimuth resampling); two-dimensional inverse Fourier transform is performed on the data in the rectangular coordinate format to obtain a focused image; geometric correction is performed on the focused image, including distortion correction, squint conversion and oblique ground conversion, to obtain the final circular SAR image. In this way, the airborne circular SAR can obtain a two-dimensional high-resolution SAR image of the target with a full-viewing angle range of 360°, which solves the problem that the two-dimensional imaging characteristics of the target in the traditional linear strip synthetic aperture radar can only be measured within a limited observation angle interval. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the main steps of the airborne circular SAR imaging method according to an embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of the geometric configuration of an airborne circular SAR according to an embodiment of the present invention;

[0038] Figure 3 is a schematic diagram of two-dimensional resampling based on distance and azimuth interpolation according to an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of grid output by polar coordinate algorithm under different oblique viewing angles according to an embodiment of the present invention;

[0040] Figure 5 is a schematic diagram of the final circular SAR image of an embodiment of the present invention;

[0041] Figure 6 Schematic diagram of components of an airborne circular SAR imaging device according to an embodiment of the present invention;

[0042] Figure 7 It is a schematic diagram of the structure of an electronic device used to implement the airborne circular SAR imaging method in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] As an emerging imaging mode, airborne circular SAR has the advantages of all-round observation, high spatial resolution and three-dimensional imaging. With the continuous development of circular SAR imaging technology, airborne circular SAR has gradually become one of the effective means to implement precise observation of key areas. Compared with linear trajectory SAR, circular SAR imaging has many unique advantages. First, in circular SAR imaging, the radar-carrying platform makes a 360° circular motion around the observation scene, and the antenna beam always points to the observation scene, which enables circular SAR to achieve a two-dimensional spatial resolution of up to sub-wavelength level, thereby obtaining more detailed observation target information; secondly, the circular imaging mode of circular SAR can obtain all-round scattering information of the observation target, which can avoid the phenomenon of target occlusion and shadow in conventional SAR imaging, thereby obtaining more comprehensive target imaging information; finally, compared with traditional SAR, circular SAR can realize three-dimensional image reconstruction of the observation target and obtain more dimensional target imaging information.

[0045] Figure 1 Schematic diagram of main steps of the airborne circular SAR imaging method according to an embodiment of the present invention.

[0046] like Figure 1 As shown, the airborne circular SAR imaging method according to the embodiment of the present invention can be specifically performed according to the following steps:

[0047] Step S101: transform the original SAR data into the range frequency domain, and then perform frequency demodulation processing to obtain phase history data.

[0048] Specifically, in this step, the original SAR data can be transformed into the range-frequency domain by the following steps:

[0049] The original SAR data is subjected to range Fourier transform and matched filtering to obtain the signal s(f r , t m )for:

[0050]

[0051] Among them, f r is the distance frequency, t m is the slow time, rect(·) is the rectangular window function, B is the transmit signal bandwidth, k r =4π(f c +f r ) / c is the wave number, f c is the center frequency, c is the speed of light, is the instantaneous slant range of the target, v is the antenna speed, R b is the shortest slant distance from the antenna phase center to the scene center, and (x, y) is the target coordinate.

[0052] The above demodulation frequency processing is then performed to obtain the phase history data, and the following steps can be specifically performed:

[0053] The phase history data s(f r , t m ):

[0054]

[0055] in, is the instantaneous slant distance from the antenna phase center to the scene center.

[0056] Step S102: converting the phase history data in polar coordinate format into rectangular coordinate format through two-dimensional resampling.

[0057] In this step, the two-dimensional resampling includes distance resampling and azimuth resampling. The distance resampling is achieved by distance difference, transforming the phase history data in polar coordinate format into a Keystone grid (trapezoidal network); the azimuth resampling is achieved by azimuth interpolation, converting the data of the Keystone grid into a rectangular coordinate format.

[0058] The distance resampled signal s(k y , t m )for:

[0059]

[0060] Among them, k y is the distance wave number, θ a is the azimuth, k rc =4πf c / c is the wave number center, Δk r =4πB / c is the wave number bandwidth, ξ(·) is the second-order Taylor series expansion, and o(·) is the third-order and higher-order terms;

[0061] The azimuth resampled signal s(k x , k y )for:

[0062]

[0063] Among them, k x is the azimuth wave number.

[0064] Step S103: performing a two-dimensional inverse Fourier transform on the two-dimensionally resampled data to obtain a focused image.

[0065] In this step, the focused image I(x, y) can be obtained according to the following formula:

[0066]

[0067] Among them, Δk x is the azimuth wavenumber bandwidth.

[0068] Step S104: performing geometric correction on the focused image to obtain a final circular SAR image.

[0069] In practical applications, the geometric correction may include distortion correction, squint conversion and oblique ground conversion. Each correction method is introduced below. In the following formula, (x′, y′) is the corrected coordinate.

[0070] First, distortion correction can be performed, and the correction amount is calculated using the following formula:

[0071]

[0072] Then, the squint conversion is performed. The specific method is as follows: when the target area is at different squint angles, it is necessary to establish a local rectangular coordinate system at different rotation angles. The local rectangular coordinate grid of polar coordinates causes the rotation of the imaged scene in the output image, and the rotation angle is equal to the squint angle θ sq Therefore, the rotation of the imaging scene is a significant feature of the polar coordinate algorithm, and the conversion relationship is:

[0073]

[0074] Finally, the above imaging processing is performed on an inclined plane, and an oblique-to-ground transformation is required to be performed to the ground plane coordinate system. The transformation relationship is:

[0075]

[0076] Among them, , β is the beam pitch angle.

[0077] After the above steps, the final airborne circular SAR image can be obtained. In this way, the present invention realizes circular SAR high-resolution imaging, and can obtain a two-dimensional high-resolution SAR image of the target with a full viewing angle range of 360°, solving the problem that the two-dimensional imaging characteristics of the target in the traditional linear strip synthetic aperture radar can only be measured within a limited observation angle interval.

[0078] Figure 2 FIG. 1 is a schematic diagram of the geometric configuration of an airborne circular SAR according to an embodiment of the present invention. Figure 2 As shown, the radar and the observation scene are both located in the xyz coordinate system, and the origin of the coordinate system is located at the center of the scene S. The antenna moves in a uniform linear motion with a speed v along the positive direction of the x-axis, R b is the shortest slant distance from the antenna phase center (APC) to the scene center S. Define the variable t m is the slow time, then the coordinates of APC are (vtm , R b ).θ a is the azimuth, point P represents any point target in the imaging scene; point O is a point in the direction of radar movement, which is closest to the center of the scene. Ra is the instantaneous slant distance from the antenna phase center (APC) to the center of the scene, and R represents the instantaneous slant distance from the antenna phase center (APC) to any point in the scene.

[0079] For a point target at (x, y), the instantaneous slant range from the APC to the point target is The echo signal s(τ, t m ) can be expressed as:

[0080]

[0081] Where τ is the fast time, c is the speed of light, T p is the pulse duration, γ is the linear modulation frequency, f c is the center frequency, rect(·) is the rectangular window function. Other parameters have been explained in the previous text and will not be repeated here.

[0082] Figure 3 is a schematic diagram of two-dimensional resampling based on distance and azimuth interpolation according to an embodiment of the present invention, such as Figure 3 As shown, the phase history data is arranged in polar coordinate format in Fourier space, that is, it is uniformly sampled in the radial and azimuthal directions (see Figure 3 If we want to use the two-dimensional Fourier transform to focus the image in the rectangular coordinate system, we first need to r , t m ) is used for polar coordinate processing, that is, the polar coordinate format data is converted into rectangular coordinate format through two-dimensional resampling. Range resampling is achieved through range interpolation, which transforms the polar coordinate format (Polar Grid) data into the Keystone grid (Keystone Grid). After range resampling, the phase history data is converted into a rectangular grid in k y Directions are uniformly sampled (see Figure 3 (middle figure). Azimuth resampling is achieved by cross-range interpolation, which converts the polar coordinate format data to a Cartesian grid. After azimuth resampling, the phase history data is realized in k x and k y Uniform sampling of directions (see Figure 3 right side of the figure).

[0083] Figure 4Schematic diagram of grid output by polar coordinate algorithm under different oblique viewing angles according to an embodiment of the present invention. Figure 4 As shown in , the (x′, y′) coordinate system used by the polar coordinate algorithm is a local rectangular coordinate system located in the target area, such as Figure 4 As shown in the chessboard-like rectangular grid in the figure, the focused image can be geometrically corrected by transformation.

[0084] Figure 5 It is a schematic diagram of the final circular SAR image of an embodiment of the present invention.

[0085] In summary, in the technical solution of the embodiment of the present invention, an airborne circular SAR signal model is used to propose an airborne circular SAR high-resolution imaging method, which can obtain the omnidirectional two-dimensional imaging features of the target, and solve the problem that the two-dimensional imaging features of the target in the traditional linear strip synthetic aperture radar can only be measured within a limited observation angle interval. The airborne circular SAR performs circular trajectory observation around the target area, and its observation angle range of 360° can solve the above problems and obtain a 360° omnidirectional two-dimensional high-resolution SAR image of the target.

[0086] It should be noted that, for the convenience of description, the aforementioned method embodiments are described as a series of action combinations, but those skilled in the art should be aware that the present invention is not limited by the described action sequence, and some steps can actually be performed in other sequences or simultaneously. In addition, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily necessary to implement the present invention.

[0087] In order to better implement the above-mentioned solution of the embodiment of the present invention, relevant devices for implementing the above-mentioned solution are also provided below.

[0088] See also Figure 6 As shown, the airborne circular SAR imaging device 600 provided by the embodiment of the present invention may include: a phase history acquisition unit 601 , a rectangular coordinate conversion unit 602 , a focused image generation unit 603 and a correction unit 604 .

[0089] Among them, the phase history acquisition unit 601 can be used to: transform the original SAR data into the range frequency domain, and then perform frequency demodulation processing to obtain the phase history data; the rectangular coordinate conversion unit 602 can be used to: convert the phase history data in the polar coordinate format into the rectangular coordinate format through two-dimensional resampling; the focused image generation unit 603 can be used to: perform two-dimensional inverse Fourier transform on the two-dimensional resampled data to obtain a focused image; the correction unit 604 can be used to: perform geometric correction on the focused image to obtain the final circular track SAR image.

[0090] In the embodiment of the present invention, the phase history acquisition unit 601 can be further used to: perform a range Fourier transform on the original SAR data, and perform matched filtering to obtain a signal s(f r , t m )for:

[0091]

[0092] Among them, f r is the distance frequency, t m is the slow time, rect(·) is the rectangular window function, B is the transmit signal bandwidth, k r =4π(f c +f r ) / c is the wave number, f c is the center frequency, c is the speed of light, is the instantaneous slant range of the target, v is the antenna speed, R b is the shortest slant distance from the antenna phase center to the scene center, and (x, y) is the target coordinate.

[0093] As a preferred solution, the phase history acquisition unit 601 can be further used to obtain the phase history data s(f r , t m ):

[0094]

[0095] in, is the instantaneous slant distance from the antenna phase center to the scene center.

[0096] Preferably, the two-dimensional resampling includes distance resampling and azimuth resampling, wherein the distance resampling transforms the phase history data in polar coordinate format into a Keystone grid, and the signal s(k y , t m )for:

[0097]

[0098] Among them, k y is the distance wave number, θ a is the azimuth, k rc =4πf c / c is the wave number center, Δk r =4πB / c is the wave number bandwidth, ξ(·) is the second-order Taylor series expansion, and o(·) is the third-order and higher-order terms;

[0099] The azimuth resampling converts the data of the Keystone grid into a rectangular coordinate format. The azimuth resampled signal s(k x , ky )for:

[0100]

[0101] Among them, k x is the azimuth wave number.

[0102] In a specific application, the focused image generation unit 603 can be further used to obtain the focused image I(x, y) according to the following formula:

[0103]

[0104] Among them, Δk x is the azimuth wavenumber bandwidth.

[0105] In practical applications, the geometric correction includes distortion correction, squint conversion and oblique ground conversion.

[0106] In addition, in the embodiment of the present invention, the distortion correction is performed by the following formula:

[0107]

[0108] The squint conversion is performed using the following formula:

[0109]

[0110] The skew-to-ground conversion is performed using the following formula:

[0111]

[0112] Among them, (x′, y′) is the corrected coordinate, θ sq is the oblique viewing angle, and Lu is the beam pitch angle.

[0113] In the technical solution of the embodiment of the present invention, an airborne circular SAR high-resolution imaging method is proposed by using an airborne circular SAR signal model, which can obtain the omnidirectional two-dimensional imaging features of the target, solving the problem that the two-dimensional imaging features of the target in the traditional linear strip synthetic aperture radar can only be measured within a limited observation angle interval. The airborne circular SAR performs circular trajectory observation around the target area, and its observation angle range of 360° can solve the above problems and obtain a 360° omnidirectional two-dimensional high-resolution SAR image of the target.

[0114] The present invention also provides an electronic device. The electronic device of an embodiment of the present invention includes: one or more processors; a storage device for storing one or more programs, when the one or more programs are executed by the one or more processors, the one or more processors implement the airborne circular SAR imaging method provided by the present invention.

[0115] Reference below Figure 7 , which shows a schematic diagram of the structure of a computer system 700 of an electronic device suitable for implementing an embodiment of the present invention. Figure 7 The electronic device shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present invention.

[0116] like Figure 7 As shown, the computer system 700 includes a central processing unit (CPU) 701, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 702 or a program loaded from a storage portion 708 into a random access memory (RAM) 703. Various programs and data required for the operation of the computer system 700 are also stored in the RAM 703. The CPU 701, the ROM 702, and the RAM 703 are connected to each other via a bus 704. An input / output (I / O) interface 705 is also connected to the bus 704.

[0117] The following components are connected to the I / O interface 705: an input section 706 including a keyboard, a mouse, etc.; an output section 707 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 708 including a hard disk, etc.; and a communication section 709 including a network interface card such as a LAN card, a modem, etc. The communication section 709 performs communication processing via a network such as the Internet. A drive 710 is also connected to the I / O interface 705 as needed. A removable medium 711, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 710 as needed so that a computer program read therefrom is installed into the storage section 708 as needed.

[0118] In particular, according to the embodiments disclosed in the present invention, the process described in the main step diagram above can be implemented as a computer software program. For example, the embodiments of the present invention include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program contains program code for executing the method shown in the main step diagram. In the above embodiment, the computer program can be downloaded and installed from the network through the communication part 709, and / or installed from the removable medium 711. When the computer program is executed by the central processing unit 701, the above functions defined in the system of the present invention are executed.

[0119] It should be noted that the computer-readable medium shown in the present invention may be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In the present invention, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, device or device. In the present invention, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, which carries a computer-readable program code. This propagated data signal may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. Computer readable signal media may also be any computer readable medium other than computer readable storage media, which may send, propagate or transmit a program for use by or in conjunction with an instruction execution system, apparatus or device. The program code contained on the computer readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wire, optical cable, RF, etc., or any suitable combination of the above.

[0120] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present invention. In this regard, each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the above-mentioned module, program segment or a part of a code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flow chart, and the combination of the boxes in the block diagram or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0121] The units involved in the embodiments of the present invention may be implemented by software or hardware. The units described may also be set in a processor, for example, it may be described as: a processor includes a phase history acquisition unit, a rectangular coordinate conversion unit, a focus image generation unit and a correction unit. The names of these units do not constitute a limitation on the units themselves in some cases, for example, the phase history acquisition unit may also be described as a "unit that provides phase history data to the rectangular coordinate conversion unit".

[0122] As another aspect, the present invention further provides a computer-readable medium, which may be included in the device described in the above embodiment; or may exist independently and not be assembled into the device. The above computer-readable medium carries one or more programs, and when the above one or more programs are executed by the device, the steps executed by the device include: transforming the original SAR data into the range frequency domain, and then performing frequency demodulation processing to obtain phase history data; converting the phase history data in polar coordinate format into rectangular coordinate format through two-dimensional resampling; performing two-dimensional inverse Fourier transform on the two-dimensional resampled data to obtain a focused image; performing geometric correction on the focused image to obtain the final circular track SAR image.

[0123] According to the technical solution of the embodiment of the present invention, an airborne circular SAR high-resolution imaging method is proposed by using an airborne circular SAR signal model, which can obtain the omnidirectional two-dimensional imaging features of the target, solving the problem that the two-dimensional imaging features of the target in the traditional linear strip synthetic aperture radar can only be measured within a limited observation angle interval. The airborne circular SAR performs circular trajectory observation around the target area, and its observation angle range of 360° can solve the above problems and obtain a 360° omnidirectional two-dimensional high-resolution SAR image of the target.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An airborne circular synthetic aperture radar SAR imaging method, characterized in that: include: The original SAR data is transformed into the range frequency domain, and then demodulated to obtain the phase history data; Converting the phase history data in polar coordinate format into rectangular coordinate format by two-dimensional resampling; Performing a two-dimensional inverse Fourier transform on the two-dimensionally resampled data to obtain a focused image; The focused image is geometrically corrected to obtain a final circular SAR image; the two-dimensional resampling includes range resampling and azimuth resampling, the range resampling transforms the phase history data in polar coordinate format to a Keystone grid, and the signal s(k y , t m )for: Among them, k y is the distance wave number, θ a is the azimuth, k rc =4πf c / c is the wave number center, Δk r =4πB / c is the wave number bandwidth, ξ(·) is the second-order Taylor series expansion, o(·) is the third-order and higher-order terms, f c is the center frequency, c is the speed of light, and (x, y) is the rectangular coordinate point in the Keystone grid; The azimuth resampling converts the data of the Keystone grid into a rectangular coordinate format. The azimuth resampled signal s(k x , k y )for: Among them, k x is the azimuthal wave number; The step of performing a two-dimensional inverse Fourier transform on the two-dimensionally resampled data to obtain a focused image includes: The focused image I(x, y) is obtained according to the following formula: Among them, Δk x is the azimuth wavenumber bandwidth.

2. The method according to claim 1, characterized in that: The step of transforming the original SAR data into the range frequency domain comprises: The original SAR data is subjected to range Fourier transform and matched filtering to obtain the signal s(f r , t m )for: Among them, f r is the distance frequency, t m is the slow time, rect(·) is the rectangular window function, B is the transmit signal bandwidth, k r =4π(f c +f r ) / c is the wave number, f c is the center frequency, c is the speed of light, is the instantaneous slant range of the target, v is the antenna speed, R b is the shortest slant distance from the antenna phase center to the scene center, and (x, y) is the target coordinate.

3. The method according to claim 2, characterized in that The demodulation frequency processing is then performed to obtain phase history data, including: The phase history data s(f r , t m ): in, is the instantaneous slant distance from the antenna phase center to the scene center.

4. The method according to claim 1, characterized in that: The geometric correction includes distortion correction, squint conversion and slant conversion.

5. The method according to claim 4, characterized in that The distortion correction is performed using the following formula: The squint conversion is performed using the following formula: The skew-to-ground conversion is performed using the following formula: Among them, (x′, y′) is the corrected coordinate, θ sq is the slant angle, and β is the beam elevation angle.

6. An airborne circular SAR imaging device, characterized in that: The airborne circular SAR imaging method as claimed in any one of claims 1 to 5 comprises: The phase history acquisition unit is used to: transform the original SAR data into the range frequency domain, and then perform frequency demodulation processing to obtain the phase history data; A rectangular coordinate conversion unit, used for: converting the phase history data in polar coordinate format into rectangular coordinate format by two-dimensional resampling; A focused image generating unit, used for: performing a two-dimensional inverse Fourier transform on the two-dimensionally resampled data to obtain a focused image; The correction unit is used to perform geometric correction on the focused image to obtain a final circular SAR image.

7. An electronic device, characterized in that: include: one or more processors; a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

Images