Data imaging method and device for space-borne SAR squint sliding spotlight mode

Abstract

The application relates to the technical field of signal processing, in particular to a data imaging method and device for a spaceborne SAR squint sliding spotlight mode. The method comprises the following steps: acquiring initial echo data and imaging parameters of a spaceborne SAR system, wherein the initial echo data is a set of echo data of multiple targets in a preset scene by the spaceborne SAR system; based on the imaging parameters, performing Doppler spectrum dealiasing on the initial echo data to obtain de-aliased data; based on the imaging parameters, performing focusing processing on the de-aliased data, and expanding the azimuth focusing depth by using an improved nonlinear frequency modulation algorithm to obtain a focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing high-order correction on a traditional nonlinear frequency modulation algorithm. The application can effectively focus the echo data of the large squint angle sliding spotlight mode, and the imaging precision is high.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and in particular to a data imaging method and apparatus for a spaceborne SAR oblique-looking sliding beamforming mode. Background Technology

[0002] In recent years, spaceborne SAR system technology has flourished, and its application areas have continued to expand. Complex and ever-changing observation tasks have placed increasingly stringent demands on spaceborne SAR systems. To meet users' needs for target feature representation, fine resolution, and high-precision positioning, the high-resolution operating mode of spaceborne SAR systems is gradually shifting from strip mode to sliding spotting mode, and from front-side viewing to oblique-viewing mode—specifically, oblique-view sliding spotting mode—to achieve clearer, finer, and more flexible observation of important ground scenes and targets.

[0003] However, compared to conventional front-side-view stripe pattern data, oblique-view sliding spotting pattern data faces challenges such as complex space-ground spatial geometry, two-dimensional depth coupling of echo signal azimuth / range, severe aliasing of signal azimuth spectrum, and two-dimensional spatial variation of imaging parameters. Classical imaging theories and methods are no longer applicable, and spaceborne SAR oblique-view sliding spotting pattern data faces numerous challenges in data imaging processing.

[0004] Therefore, there is an urgent need for a data imaging method and device for spaceborne SAR oblique-looking sliding beamforming mode to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a data imaging method and apparatus for spaceborne SAR oblique-view sliding spotting mode, which can effectively focus echo data of large oblique-view sliding spotting mode and achieve high imaging accuracy.

[0006] In a first aspect, embodiments of the present invention provide a data imaging method for a spaceborne SAR oblique-looking sliding spotting mode, comprising:

[0007] Acquire initial echo data and imaging parameters of the spaceborne SAR system, wherein the initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system;

[0008] Based on the imaging parameters, the initial echo data is subjected to Doppler spectrum dealiasing to obtain the dealiased data;

[0009] Based on the imaging parameters, the dealiased data is focused, and an improved nonlinear frequency modulation algorithm is used to extend the azimuth focusing depth to obtain a focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing a higher-order correction on a traditional nonlinear frequency modulation algorithm.

[0010] Secondly, embodiments of the present invention also provide a data imaging device for spaceborne SAR oblique-looking sliding beamforming mode, comprising:

[0011] The acquisition module is used to acquire initial echo data and imaging parameters of the spaceborne SAR system. The initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system.

[0012] The dealiasing module is used to perform Doppler spectrum dealiasing on the initial echo data based on the imaging parameters to obtain dealiased data;

[0013] The focusing module is used to focus the dealiased data based on the imaging parameters and extend the azimuth focusing depth using an improved nonlinear frequency modulation algorithm to obtain a focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing a high-order correction on a traditional nonlinear frequency modulation algorithm.

[0014] Thirdly, embodiments of the present invention also provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it implements the method described in any embodiment of this specification.

[0015] Fourthly, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the methods described in any embodiment of this specification.

[0016] This invention provides a data imaging method and apparatus for spaceborne SAR oblique-looking sliding spotting mode. By performing Doppler spectrum dealiasing on the initial echo data, the azimuth sampling rate can be expanded to obtain dealiased data, which is beneficial for subsequent focusing processing. By using an improved nonlinear frequency modulation algorithm to focus the dealiased data, the focusing depth can be improved and the imaging accuracy can be high. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the data imaging method of spaceborne SAR oblique-looking sliding beam-gathering mode provided in an embodiment of the present invention;

[0019] Figure 2This is a hardware architecture diagram of an electronic device provided in an embodiment of the present invention;

[0020] Figure 3 This is a structural diagram of a data imaging device for spaceborne SAR oblique-looking sliding beam-focusing mode provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of a simulation scenario of a spaceborne SAR system provided in an embodiment of the present invention;

[0022] Figure 5 This invention provides an embodiment of using the MCS method to... Figure 4 The SAR image is obtained by processing point P1 in the image.

[0023] Figure 6 This invention provides an embodiment of using the MCS method to... Figure 4 The SAR image is obtained by processing point P5 in the image.

[0024] Figure 7 This invention provides an embodiment of using the MCS method to... Figure 4 The SAR image is obtained by processing point P9 in the image.

[0025] Figure 8 This is an embodiment of the present invention that provides the method of the present invention for... Figure 4 The SAR image is obtained by processing point P1 in the image.

[0026] Figure 9 This is an embodiment of the present invention that provides the method of the present invention for... Figure 4 The SAR image is obtained by processing point P5 in the image.

[0027] Figure 10 This is an embodiment of the present invention that provides the method of the present invention for... Figure 4 The SAR image is obtained by processing point P9 in the image. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Please refer to Figure 1 This invention provides a data imaging method for spaceborne SAR oblique-looking sliding spotting mode, the method comprising:

[0030] Step 100: Obtain initial echo data and imaging parameters of the spaceborne SAR system. The initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system.

[0031] Step 102: Based on the imaging parameters, perform Doppler spectrum dealiasing on the initial echo data to obtain the dealiased data;

[0032] Step 104: Based on the imaging parameters, the dealiased data is focused, and an improved nonlinear frequency modulation algorithm is used to extend the azimuth focusing depth to obtain a focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing a high-order correction on a traditional nonlinear frequency modulation algorithm.

[0033] In this embodiment, by performing Doppler spectrum dealiasing on the initial echo data, the azimuth sampling rate can be expanded to obtain dealiased data, which is beneficial for subsequent focusing processing. By using an improved nonlinear frequency modulation algorithm to focus the dealiased data, the focusing depth can be improved, resulting in high imaging accuracy.

[0034] The following description Figure 1 The execution method of each step is shown.

[0035] First, regarding step 100, the imaging parameters of the spaceborne SAR system include:

[0036] Distance to point N r azimuth point number N a Signal sampling rate f s Pulse repetition frequency f prf Signal modulation frequency K r Operating wavelength λ, reference slant range r c Equivalent velocity v ref Equivalent oblique angle θ ref The mixing factor Y(r) at the reference slant distance c The orbital cubic compensation coefficient Δf3, and the Doppler center frequency f varying with distance r. d (r) and Doppler modulation frequency f r (r).

[0037] The initial echo data S0(τ,t;r,t) a The expression for ) is:

[0038]

[0039] In the formula, σ is the scattering coefficient of the target, rect[·] is the rectangular window function, τ is the range-fast time, t is the azimuth-slow time, c is the speed of light, and T is the pulse width. 3dBY(r) is the coherent accumulation time in the azimuth direction, and Y(r) is the mixing factor that varies with distance r, where r is the instantaneous distance between the satellite and the target.

[0040] The expression for Y(r) is:

[0041]

[0042] In the formula, R rot It is the shortest distance between the satellite and the rotation point, R(t; r,t). a R(t; r,t) represents the distance between the satellite and the target. a The expression for ) is:

[0043]

[0044] In the formula, v r For the satellite velocity, t a For the Doppler center time of the target, k i Let be the coefficients of the i-th order Taylor series expansion.

[0045] Then, regarding step 102, the step of performing Doppler spectral dealiasing on the initial echo data based on the imaging parameters to obtain dealiased data includes:

[0046] Step A1: Perform range compression and orbit higher-order term phase compensation on the initial echo data to obtain the first data;

[0047] Step A2: Perform linear distance movement correction and distance frequency-related derotation processing on the first data to obtain the second data;

[0048] Step A3: Perform Doppler frequency modulation compensation on the second data to obtain the dealiased data.

[0049] For step A1, the specific implementation process is as follows:

[0050] Step B1: Perform a range-to-Fourier transform on the initial echo data;

[0051] Step B2: Determine the first phase compensation factor based on the imaging parameters.

[0052] The specific determination process is as follows: based on the number of distance vector points N r azimuth point number N a Frequency modulation K r Pulse repetition frequency f prf Given the orbital cubic compensation coefficient Δf3, the operating wavelength λ, and the speed of light c, determine the first phase compensation factor H1(f τ ,t), its expression is:

[0053]

[0054] In the formula, f is the center frequency of the signal. τ For range frequency,

[0055] Step B3: Multiply the Fourier transform data by the first phase compensation factor to obtain the first data.

[0056] For step A2, the specific implementation process is as follows:

[0057] Step C1: Determine the second phase compensation factor based on the imaging parameters, and multiply the first data with the second phase compensation factor to obtain the data after linear distance travel correction.

[0058] The specific implementation process is as follows: based on the number of azimuth points N a Pulse repetition frequency f prf Reference slope distance r c Equivalent velocity v ref Equivalent oblique angle θ ref The mixing factor Y(r) at the reference slope distance c The second phase compensation factor is determined, and its expression is:

[0059]

[0060] The first data is multiplied by the second phase compensation factor to perform linear range walk correction (LRWC) on the first data, resulting in corrected data.

[0061] Step C2: Calculate the shortest distance R between the satellite at the reference slant range and the rotation point in the preset scenario. rot and the Deroation coefficient k w .

[0062] Among them, the closest distance R between the satellite and the rotation point rot It is calculated based on formula (2).

[0063] Deroation coefficient k w The expression is:

[0064]

[0065] Step C3, based on the nearest distance R rot and the Deroation coefficient k wA third phase compensation factor is determined, and the corrected data is multiplied by the third phase compensation factor to perform a third phase compensation. The third phase compensation factor H3(f) is... τ The expression for ,t) is:

[0066]

[0067] The corrected data is multiplied by the third phase compensation factor to complete the third phase compensation of the corrected data.

[0068] Step C4: Perform an azimuth-to-Fourier transform on the data after the third phase compensation.

[0069] Step C5, based on the Deroation coefficient k w Regarding the pulse repetition frequency f in the imaging parameters prf The pulse repetition frequency is updated to obtain the updated frequency.

[0070] The formula for updating the initial pulse repetition frequency is:

[0071]

[0072] In the formula, the left side of the equal sign is the updated pulse repetition frequency, and the right side of the equal sign is the initial pulse repetition frequency.

[0073] Step C6: Update the azimuth slow time in the imaging parameters based on the updated pulse repetition frequency to obtain the updated azimuth slow time.

[0074] The formula for updating the initial azimuth to slower time is:

[0075]

[0076] Step C7, determine the fourth phase compensation factor H4(f) based on the updated azimuth slow time. τ The data after azimuth-to-Fourier transform is multiplied by the fourth phase compensation factor to obtain the second data. The expression for the fourth phase compensation factor is:

[0077]

[0078] In the formula, t is the updated azimuth slow time.

[0079] For step A3, Doppler frequency modulation compensation is performed on the second data to obtain the dealiased data. The specific implementation process is as follows:

[0080] Based on the updated pulse repetition frequency f prf and the Deroation coefficient kw Determine the fifth phase compensation factor, and compare the second data with the fifth phase compensation factor H5(f τ ,f t Multiply by , and you get the de-aliased data.

[0081] Fifth compensation factor H5(f τ ,f t The expression for ) is:

[0082]

[0083] In the formula, f t For azimuth frequency,

[0084] In summary, step 102 utilizes a derotation factor related to the distance frequency to achieve a more thorough Doppler spectrum dealiasing.

[0085] Finally, regarding step 104, based on the imaging parameters, the dealiased data is focused, and an improved nonlinear frequency modulation algorithm is used to extend the azimuth focusing depth to obtain the focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing a higher-order correction on a traditional nonlinear frequency modulation algorithm.

[0086] In some implementation methods, the specific implementation process is as follows:

[0087] Step D1 involves focusing the target at the reference slant range to obtain the third data. The specific implementation process is as follows:

[0088] Perform an orientation-to-Fourier transform on the dealiased data;

[0089] Based on the reference slope range r c Equivalent velocity v ref and equivalent oblique angle θ ref Determine the compensation factor H at the reference slant distance. f0 (f t Its expression is:

[0090]

[0091] Based on the compensation factor H at the reference slant distance f0 (f t Determine the sixth phase compensation factor H6(f) τ ,f t Its expression is:

[0092]

[0093] By multiplying the dealiased data by the sixth phase compensation factor, the target at the reference slant range can be focused.

[0094] Step D2: Based on the third data, focus on targets other than the target at the reference slant range to obtain the fourth data. The specific implementation process is as follows:

[0095] (a) Perform range-to-inverse Fourier transform on the data after focusing on the target at the reference slant range;

[0096] (b) Using the Doppler center frequency f that varies with distance r d (r) and Doppler modulation frequency f r (r), calculate the satellite velocity v at each distance r. r (r) and oblique angle θ(r).

[0097] Satellite speed v r The formulas for calculating r and the oblique angle θ(r) are as follows:

[0098]

[0099]

[0100] In the formula, λ is the operating wavelength.

[0101] (c) Regarding the satellite velocity v r Taylor expansion is performed on (r) and the oblique angle θ(r), and the first-order coefficients are extracted. and k' θ .

[0102] (d) Based on first-order coefficients k' θ Compensation factor H at the reference slant distance f0 (f t The seventh phase compensation factor and the transformation factor of the Chirp-Z transform are determined.

[0103] Seventh phase compensation factor H7(τ,f) t The expression for ) is:

[0104]

[0105] In the formula,

[0106] The transformation factor H' of the Chirp-Z transform f (f t The expression for ) is:

[0107]

[0108] (e) Combine the data obtained after Fourier transform in step (a) with the seventh phase compensation factor H7(τ,f) t Multiply by , and you get the data after the seventh phase compensation.

[0109] (f) Perform a range-to-Chirp-Z transform on the data after the seventh phase compensation to transform the signal to the range frequency domain and obtain the fourth data.

[0110] It should be noted that after Chirp-Z transform, the range frequency f τ It will change, therefore, it needs to be updated using the following formula:

[0111] f τ =f τ ·H' f (f t (18)

[0112] In the formula, the left side of the equal sign is the updated range frequency, and the right side of the equal sign is the original range frequency. After the update, the influence of the Chirp-Z transform on the range frequency can be eliminated.

[0113] Step D3 involves performing distance-frequency related deramp processing on the fourth data to obtain the fifth data. The specific implementation process is as follows:

[0114] Based on the reference slope range r c Operating wavelength λ, equivalent velocity v ref Equivalent oblique angle θ ref The closest distance R between the satellite and the rotation point rot Determine the Deramp scaling factor k e and Deramp factor H8(f τ ,f t ).

[0115] The expression for the Deramp scaling factor is:

[0116]

[0117] The expression for the Deramp factor is:

[0118]

[0119] Multiplying the fourth data by the Deramp factor and then performing an azimuth-to-Fourier transform completes the distance-frequency related Deramp processing, yielding the fifth data.

[0120] Step D4: The improved nonlinear frequency modulation algorithm is used to perform frequency modulation processing on the fifth data to obtain the sixth data.

[0121] In this step, the improved nonlinear frequency modulation algorithm is obtained by re-deriving the perturbation coefficients of the traditional nonlinear frequency modulation algorithm using the second-order stationary phase point expression; wherein, the second-order stationary phase point expression is:

[0122] f tk =αk e ·(tt a )-(αk e ) 3 ·b3·(tt a ) 2 (twenty one)

[0123] In the formula, f tk This is the stationary phase point.

[0124] After re-derived, the coefficients of each order of the perturbation term in the improved nonlinear frequency modulation algorithm are as follows:

[0125]

[0126] In the formula, α ranges from [0.8, 1); l2 and l3 are the values ​​of l2 and l3 respectively, corresponding to the azimuth focusing time t. a The relevant second- and third-order residual space-varying phase coefficients; a4, b2, b3 and b4 are the time-domain fourth-order perturbation coefficients, frequency-domain second-order perturbation coefficients, third-order perturbation coefficients and fourth-order perturbation coefficients, respectively.

[0127] After obtaining the above coefficients, based on the Deramp scaling factor and the adjustable parameter α, the time-domain fourth-order perturbation factor H9(f) of the improved nonlinear frequency modulation algorithm is determined. τ ,t) and the fourth-order frequency domain perturbation factor H 10 (f τ ,f t The expressions for the two disturbance factors are as follows:

[0128]

[0129]

[0130] The fifth data is combined with the fourth-order time-domain perturbation factor H9(f) τ After multiplying by ,t), perform an azimuth-to-Fourier transform, and then multiply by the fourth-order frequency domain perturbation factor H. 10 (f τ ,f t Multiply by the fourth-order frequency domain perturbation factor H. 10 (f τ ,f t After multiplying, perform an inverse Fourier transform in the azimuth direction to complete the frequency modulation processing of the fifth data and obtain the sixth data.

[0131] Step D5 involves performing azimuth-focus position correction and range-direction inverse Fourier transform on the sixth data to obtain the final SAR image. The specific process is as follows:

[0132] Based on equivalent velocity v ref and equivalent oblique angle θ ref Determine the geometric correction phase factor H 13 (f τ ,t), its expression is:

[0133]

[0134] The sixth data is compared with the geometric correction phase factor H. 13 (f τ Multiply by ,t) to complete the azimuth-focus position correction process.

[0135] The sixth data is compared with the geometric correction phase factor H. 13 (f τ After multiplying by ,t, and then performing an inverse Fourier transform in the range direction, the focused SAR image can be obtained, which is the final SAR image.

[0136] It should be noted that the same characters in the above formulas have the same meaning, so this application will not repeat the explanation. When encountering characters with updated values, the corresponding formula shall be based on the updated values.

[0137] To demonstrate the imaging effect of the method of the present invention, the following is an example. Figure 4 Taking the simulated scenario of the spaceborne SAR system shown as an example, the MCS (Maximum Common Subgraph) method and the method of this invention are used to process it respectively, and the processing results are compared.

[0138] like Figure 4 As shown, nine equally spaced point targets were arranged in the scene, with a swath width of 5km × 5km (distance × azimuth). The imaging parameters are shown in Table 1.

[0139] Table 1 Imaging parameters

[0140] <![CDATA[Number of points in range direction N r > 16384 <![CDATA[Number of azimuth points N a > 65536 <![CDATA[Signal sampling frequency f s (MHz)]]> 300 <![CDATA[Pulse repetition frequency f prf (Hz)]]> 5000 <![CDATA[Chirp rate K r > 8e+13 Operating wavelength λ(m) 0.03 <![CDATA[Reference slant range r c (km)]]> 948.856 <![CDATA[Equivalent velocity v ref (m / s)]]> 7583.19 <![CDATA[Equivalent oblique viewing angle θ ref (°)]]> 20.0 <![CDATA[The mixing factor Y(r at the reference slant range c )]]> 0.3 <![CDATA[Third-order term compensation coefficient Δf3 of the rail]]> 3.98e-4

[0141] The MCS method was used to process the data, and the contour images of the focused points P1, P5, and P9 are shown below. Figures 5-7 As shown. Using the method of this invention, the contour diagrams of the focused results for point targets P1, P5, and P9 are obtained as follows. Figures 8-10 As shown.

[0142] from Figures 5-10The comparison results clearly show that the scene center point P5 can be well focused in both imaging methods; however, for the scene edge points P1 and P9, the MCS algorithm shows defocusing in the focusing results, while the method of this invention can effectively focus the sliding beam pattern data with a resolution of 0.5m and a swath width of 5km×5km (distance×azimuth) at an azimuth angle of 20 degrees.

[0143] Table 2 presents the imaging quality assessment results for the three point targets.

[0144] Table 2 Imaging quality assessment results

[0145]

[0146] As can be seen from Table 2, the method of the present invention has a good focusing effect.

[0147] like Figure 2 , Figure 3 As shown, this embodiment of the invention provides a data imaging device for spaceborne SAR oblique-looking sliding spotting mode. The device embodiment can be implemented through software, hardware, or a combination of both. From a hardware perspective, such as... Figure 2 The diagram shown is a hardware architecture diagram of an electronic device for a data imaging device in a spaceborne SAR oblique-looking sliding beam pattern according to an embodiment of the present invention. (Except for...) Figure 2 In addition to the processor, memory, network interface, and non-volatile memory shown, the electronic device in the embodiment may also include other hardware, such as a forwarding chip responsible for processing packets. Taking software implementation as an example, such as... Figure 3 As shown, a device in a logical sense is formed by the CPU of the electronic device in which it is located reading the corresponding computer program from the non-volatile memory into the memory for execution.

[0148] This embodiment provides a data imaging device for spaceborne SAR oblique-looking sliding spotting mode, comprising:

[0149] The acquisition module 300 is used to acquire initial echo data and imaging parameters of the spaceborne SAR system. The initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system.

[0150] The dealiasing module 302 is used to perform Doppler spectrum dealiasing on the initial echo data based on the imaging parameters to obtain dealiased data;

[0151] The focusing module 304, based on the imaging parameters, performs focusing processing on the dealiased data and utilizes an improved nonlinear frequency modulation algorithm to extend the azimuth focusing depth, thereby obtaining a focused SAR image. The improved nonlinear frequency modulation algorithm is obtained by performing a high-order correction on a traditional nonlinear frequency modulation algorithm.

[0152] In this embodiment of the invention, the acquisition module 300 can be used to execute step 102 in the above method embodiment, the dealiasing module 302 can be used to execute step 102 in the above method embodiment, and the focusing module 304 can be used to execute step 104 in the above method embodiment.

[0153] In some implementations, the dealiasing module 302 is used to perform the following operations:

[0154] Step E1: Perform range compression and orbit higher-order term phase compensation on the initial echo data to obtain the first data;

[0155] Step E2: Perform linear distance movement correction and distance frequency-related derotation processing on the first data to obtain the second data;

[0156] Step E3: Perform Doppler frequency modulation compensation on the second data to obtain the dealiased data.

[0157] In some implementations, the dealiasing module 302 performs the following operations during step E1:

[0158] Perform a range-to-Fourier transform on the initial echo data;

[0159] Based on the imaging parameters, a first phase compensation factor is determined;

[0160] The data after Fourier transform is multiplied by the first phase compensation factor to obtain the first data.

[0161] In some implementations, the dealiasing module 302 performs the following operations during step E2:

[0162] A second phase compensation factor is determined based on the imaging parameters, and the first data is multiplied by the second phase compensation factor to obtain the data after linear distance travel correction.

[0163] Calculate the closest distance between the satellite and the rotation point at the reference slant range in the preset scenario, as well as the Deroation coefficient;

[0164] A third phase compensation factor is determined based on the nearest distance and the Deroation coefficient, and the corrected data is multiplied by the third phase compensation factor to perform a third phase compensation.

[0165] Perform an azimuth-to-Fourier transform on the data after the third phase compensation.

[0166] The initial pulse repetition frequency in the imaging parameters is updated based on the Deroation coefficient to obtain the updated pulse repetition frequency;

[0167] The initial azimuth slow time in the imaging parameters is updated based on the updated pulse repetition frequency to obtain the updated azimuth slow time.

[0168] The fourth phase compensation factor is determined based on the updated azimuth slow time, and the data after azimuth Fourier transform is multiplied by the fourth phase compensation factor to obtain the second data.

[0169] In some implementations, the dealiasing module 302 performs the following operations during step E3:

[0170] Based on the updated pulse repetition frequency and the Deroation coefficient, a fifth phase compensation factor is determined, and the second data is multiplied by the fifth phase compensation factor to obtain the dealiased data.

[0171] In some implementations, the focusing module 304 is used to perform the following operations:

[0172] The target at the reference slant range is focused to obtain the third data.

[0173] Based on the third data, other targets besides the target at the reference slant range are focused to obtain the fourth data;

[0174] The fourth data is subjected to distance-frequency related Deramp processing to obtain the fifth data;

[0175] The improved nonlinear frequency modulation algorithm is used to perform frequency modulation processing on the fifth data to obtain the sixth data;

[0176] The sixth data is subjected to azimuth focus position correction and range inverse Fourier transform to obtain the final SAR image.

[0177] In some embodiments, the imaging parameters of the spaceborne SAR system include: number of range points, number of azimuth points, signal sampling rate, pulse repetition frequency, signal modulation frequency, operating wavelength, reference slant range, equivalent velocity, equivalent slant angle, mixing factor at the reference slant range, orbital cubic compensation coefficient, Doppler center frequency and Doppler modulation frequency varying with distance.

[0178] It is understood that the structures illustrated in the embodiments of the present invention do not constitute a specific limitation on a data imaging device for a spaceborne SAR oblique-looking sliding beamforming mode. In other embodiments of the present invention, a data imaging device for a spaceborne SAR oblique-looking sliding beamforming mode may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0179] The information interaction and execution process between the modules in the above-mentioned device are based on the same concept as the method embodiment of the present invention, and the specific details can be found in the description of the method embodiment of the present invention, and will not be repeated here.

[0180] This invention also provides an electronic device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements a data imaging method for a spaceborne SAR oblique-looking sliding beam pattern according to any embodiment of this invention.

[0181] This invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform a data imaging method for a spaceborne SAR oblique-looking sliding beam pattern according to any embodiment of this invention.

[0182] Specifically, a system or apparatus equipped with a storage medium may be provided, on which software program code implementing the functions of any of the embodiments described above is stored, and the computer (or CPU or MPU) of the system or apparatus may read and execute the program code stored in the storage medium.

[0183] In this case, the program code read from the storage medium can itself implement the function of any of the above embodiments, and therefore the program code and the storage medium storing the program code constitute part of the present invention.

[0184] Examples of storage media used to provide program code include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tapes, non-volatile memory cards, and ROMs. Alternatively, program code can be downloaded from a server computer via a communication network.

[0185] Furthermore, it should be clear that not only can the program code read by the computer be executed, but also the operating system or other components operating on the computer can be instructed based on the program code to perform some or all of the actual operations, thereby realizing the function of any of the embodiments described above.

[0186] Furthermore, it is understood that the program code read from the storage medium is written to the memory set in the expansion board inserted into the computer or to the memory set in the expansion module connected to the computer. Then, based on the instructions of the program code, the CPU or other components installed on the expansion board or expansion module execute some and all of the actual operations, thereby realizing the function of any of the above embodiments.

[0187] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0188] 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 data imaging method of a space-borne SAR squint sliding spotlight mode, characterized in that, include: Acquire initial echo data and imaging parameters of the spaceborne SAR system, wherein the initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system; Based on the imaging parameters, the initial echo data is subjected to Doppler spectrum dealiasing to obtain the dealiased data; Based on the imaging parameters, the dealiased data is focused, and the azimuth focusing depth is extended using an improved nonlinear frequency modulation algorithm to obtain a focused SAR image; wherein, the improved nonlinear frequency modulation algorithm is obtained by performing a high-order correction on the traditional nonlinear frequency modulation algorithm. The process of performing Doppler spectrum dealiasing on the initial echo data to obtain dealiased data includes: The initial echo data is subjected to range compression and higher-order orbit phase compensation to obtain the first data; The first data is subjected to linear distance movement correction and distance-frequency related derotation processing to obtain the second data; Doppler frequency modulation compensation is applied to the second data to obtain the dealiased data; The process of performing linear distance travel correction and distance-frequency related derotation processing on the first data to obtain the second data includes: A second phase compensation factor is determined based on the imaging parameters, and the first data is multiplied by the second phase compensation factor to obtain the data after linear distance travel correction. Calculate the closest distance between the satellite and the rotation point at the reference slant range in the preset scenario, as well as the Deroation coefficient; A third phase compensation factor is determined based on the nearest distance and the Deroation coefficient, and the corrected data is multiplied by the third phase compensation factor to perform a third phase compensation. Perform an azimuth-to-Fourier transform on the data after the third phase compensation. The initial pulse repetition frequency in the imaging parameters is updated based on the Deroation coefficient to obtain the updated pulse repetition frequency; The initial azimuth slow time in the imaging parameters is updated based on the updated pulse repetition frequency to obtain the updated azimuth slow time. The fourth phase compensation factor is determined based on the updated azimuth slow time, and the data after azimuth Fourier transform is multiplied by the fourth phase compensation factor to obtain the second data. The step of performing Doppler frequency modulation compensation on the second data to obtain dealiased data includes: Based on the updated pulse repetition frequency and the Deroation coefficient, a fifth phase compensation factor is determined, and the second data is multiplied by the fifth phase compensation factor to obtain the dealiased data.

2. The method of claim 1, wherein, The process of performing range compression and orbital higher-order phase compensation on the initial echo data to obtain first data includes: Perform a range-to-Fourier transform on the initial echo data; Based on the imaging parameters, a first phase compensation factor is determined; The data after Fourier transform is multiplied by the first phase compensation factor to obtain the first data.

3. The method of claim 1, wherein, The process of focusing the dealiased data and extending the azimuth focusing depth using an improved nonlinear frequency modulation algorithm to obtain a focused SAR image includes: The target at the reference slant range is focused to obtain the third data. Based on the third data, other targets besides the target at the reference slant range are focused to obtain the fourth data; The fourth data is subjected to distance-frequency related Deramp processing to obtain the fifth data; The improved nonlinear frequency modulation algorithm is used to perform frequency modulation processing on the fifth data to obtain the sixth data; The sixth data is subjected to azimuth focus position correction and range inverse Fourier transform to obtain the final SAR image.

4. The method according to claim 1, characterized in that, The imaging parameters of the spaceborne SAR system include: number of range points, number of azimuth points, signal sampling rate, pulse repetition frequency, signal modulation frequency, operating wavelength, reference slant range, equivalent velocity, equivalent slant angle, mixing factor at the reference slant range, orbital cubic compensation coefficient, Doppler center frequency and Doppler modulation frequency varying with distance.

5. A data imaging device for spaceborne SAR oblique-looking sliding beamforming mode, characterized in that, The apparatus for implementing the method as described in any one of claims 1-4 comprises: The acquisition module is used to acquire initial echo data and imaging parameters of the spaceborne SAR system. The initial echo data is a collection of echo data of multiple targets in a preset scene by the spaceborne SAR system. The dealiasing module is used to perform Doppler spectrum dealiasing on the initial echo data based on the imaging parameters to obtain dealiased data; The focusing module is used to focus the de-aliased data based on the imaging parameters and extend the azimuth focusing depth using an improved nonlinear frequency modulation algorithm to obtain a focused SAR image; wherein the improved nonlinear frequency modulation algorithm is obtained by performing a high-order correction on the traditional nonlinear frequency modulation algorithm.

6. A computing device comprising a memory and a processor, wherein the memory stores a computer program, and the processor, when executing the computer program, implements the method as described in any one of claims 1-4.

7. A computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the method of any one of claims 1-4.

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