Two-dimensional spatially variable motion compensation method, device, equipment and medium for airborne SAR

Abstract

This application relates to a two-dimensional space-variable motion compensation method, apparatus, device, and medium for airborne SAR. By setting an auxiliary point in the line-of-sight direction of the radar beam center in the motion error model, the range space-variable error and azimuth space-variable error are solved based on the positional geometric relationships between the auxiliary point, the target point, the ideal trajectory of the airborne SAR, and the actual trajectory. Correspondingly, range space-variable phase compensation functions and azimuth space-variable phase compensation functions are obtained. Then, after range compression of the echo data, range space-variable phase, range space-variable envelope, and azimuth space-variable phase compensation are performed sequentially to obtain two-dimensional space-variable motion-compensated echo data. This method can perform complex space-variable motion error compensation for ultra-high resolution airborne SAR.

Description

Technical Field

[0001] This application relates to the field of microwave remote sensing technology, and in particular to a method, apparatus, equipment and medium for two-dimensional spatially variable motion compensation of airborne SAR before range migration correction. Background Technology

[0002] SAR is a high-resolution Earth remote sensing technology applicable to all times and all weather conditions. Ideally, the high resolution of SAR in the azimuth direction depends on the platform moving in a uniform linear motion. However, in airborne SAR systems, the moving platform often deviates from the ideal linear trajectory due to atmospheric turbulence and other influences. The introduced motion errors result in range envelope errors and azimuth phase errors in the received echo data, thus reducing image quality.

[0003] As resolution increases, the impact of motion errors becomes more pronounced. Especially in ultra-high resolution scenarios (currently, researchers typically define ultra-high resolution SAR as a system with a resolution better than 0.1m, operating in the X band and above), motion errors exhibit greater spatial variability with the two-dimensional position of the target within the scene. This renders traditional two-step motion compensation methods based on beam center approximation ineffective, necessitating precise compensation to obtain well-focused SAR images. However, with increasing azimuth resolution, motion errors introduce additional envelope errors after range migration correction (RCMC), reducing the accuracy of motion compensation after RCMC.

[0004] Therefore, it is necessary to study a precise two-dimensional spatial motion compensation method that performs correction before RCMC. Summary of the Invention

[0005] Therefore, it is necessary to provide a two-dimensional airborne SAR method, device, equipment, and medium that can adapt to complex airborne motion errors in order to address the above-mentioned technical problems.

[0006] A two-dimensional spatially variable motion compensation method for airborne SAR, the method comprising:

[0007] Acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0008] In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly.

[0009] After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0010] At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0011] Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data through a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained.

[0012] In one embodiment, when solving for the range spatial variation error and the azimuth spatial variation error based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR, and the actual trajectory:

[0013] The actual slope distance of the auxiliary point is equal to the actual slope distance of the target point;

[0014] The instantaneous slope distance error of the target point is obtained based on the relationship between the actual slope distance of the auxiliary point, the slope distance corresponding to the ideal trajectory of the auxiliary point in the line of sight direction, and the slope distance corresponding to the ideal trajectory of the target point in the line of sight direction.

[0015] In one embodiment, the instantaneous slant range error of the target point includes the distance spatial variation error and the azimuth spatial variation error;

[0016] The distance spatial variation error is obtained by subtracting the slope distance of the auxiliary point from the slope distance of the auxiliary point on the ideal trajectory in the line of sight direction from the actual slope distance of the auxiliary point.

[0017] The azimuth spatial variation error is obtained by subtracting the slant distance of the target point from the slant distance of the auxiliary point on the ideal trajectory in the line of sight direction.

[0018] In one embodiment, when calculating the distance spatial variation error, the slant distance corresponding to the ideal trajectory of the auxiliary point in the line-of-sight direction is calculated using the following formula:

[0019]

[0020] When calculating the azimuth spatial variation error, since the distance spatial variation envelope correction has already been completed, the slant distance corresponding to the ideal trajectory of the auxiliary point in the line-of-sight direction is calculated using the following formula:

[0021]

[0022] in,

[0023] In the above formula, |BC| represents the slant distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction, Δy(t) a ) represents the distance error between the radar and the ideal position, r n The actual slant range of the target point is represented by Δz(t), where H represents the ideal radar altitude. a The height error of the radar at the ideal position is θ, where θ represents the oblique angle.

[0024] The slant distance of the target point along the ideal trajectory in the line-of-sight direction is calculated using the following formula:

[0025] |BP|=r n

[0026] In the above formula, |BP| represents the slant distance corresponding to the ideal trajectory of the target point in the line of sight direction.

[0027] In one embodiment, the step of performing azimuth phase compensation on the second intermediate echo data based on the azimuth spatially varying phase compensation function and using a frequency domain segmentation algorithm includes:

[0028] The azimuth spectrum of the second intermediate echo data is divided into multiple sub-band data according to the sub-band division constraint;

[0029] Each of the sub-band data is padded with zeros to match the length of the echo data, and then subjected to an inverse Fourier transform to the time domain to obtain the processed sub-band data.

[0030] The azimuth phase compensation function is used to perform azimuth phase compensation on each of the processed sub-generation data. The compensated sub-band data are then superimposed to obtain the two-dimensional spatial motion compensated echo data.

[0031] In one embodiment, the method further includes: after performing two-dimensional spatial motion compensation on the echo data, performing range migration correction and azimuth compression on the compensated echo data to obtain a high-resolution SAR target image.

[0032] A two-dimensional spatially variable motion compensation device for airborne SAR, the device comprising:

[0033] The echo data acquisition module is used to acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0034] The two-dimensional spatially variable motion compensation function construction module is used to set an auxiliary point in the line-of-sight direction of the radar beam center in the motion error model. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatially variable error and the azimuth spatially variable error are solved respectively, and the range spatially variable phase compensation function and the azimuth spatially variable phase compensation function are obtained accordingly.

[0035] The range-space-variable phase compensation module is used to perform range-space-variable phase error compensation on the range-compressed echo data after range compression, and then use the range-space-variable phase compensation function to obtain the first intermediate echo data.

[0036] The range-space-variable envelope compensation module is used to resample the range-space-variable envelope of the first intermediate echo data at each azimuth position using sinc interpolation to achieve range-space-variable envelope error compensation and obtain the second intermediate echo data.

[0037] The azimuth spatially variable phase compensation module is used to perform azimuth phase compensation on the second intermediate echo data based on the azimuth spatially variable phase compensation function and through a frequency domain segmentation algorithm, so as to obtain the echo data after two-dimensional spatially variable motion compensation.

[0038] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program performing the following steps:

[0039] Acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0040] In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly.

[0041] After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0042] At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0043] Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data through a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained.

[0044] A computer-readable storage medium having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0045] Acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0046] In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly.

[0047] After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0048] At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0049] Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data through a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained.

[0050] The aforementioned two-dimensional space-variable motion compensation method, device, equipment, and medium for airborne SAR, by setting an auxiliary point in the line-of-sight direction of the radar beam center in the motion error model, solves for range space-variable errors and azimuth space-variable errors based on the positional geometric relationships between the auxiliary point, the target point, the ideal trajectory of the airborne SAR, and the actual trajectory, and obtains the corresponding range space-variable phase compensation functions and azimuth space-variable phase compensation functions. Then, after range compression of the echo data, range space-variable phase, range space-variable envelope, and azimuth space-variable phase compensation are performed sequentially to obtain the two-dimensional space-variable motion-compensated echo data. This method can perform complex space-variable motion error compensation for ultra-high resolution airborne SAR. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating a two-dimensional spatially variable motion compensation method for airborne SAR in one embodiment;

[0052] Figure 2 This is a schematic diagram of the motion error model of the airborne platform's line of sight in one embodiment;

[0053] Figure 3This is a schematic diagram of the process of using a two-dimensional spatially variable motion compensation method for SAR imaging with airborne SAR in one embodiment;

[0054] Figure 4 This is the analysis data for three types of motion errors in a simulation experiment, where... Figure 4 (a) shows a schematic diagram of the slant distance error at different locations. Figure 4 (b) represents the distance null variable error. Figure 4 (c) indicates the azimuth space variable error.

[0055] Figure 5 This is a schematic diagram illustrating the variation of YZ axis trajectory deviation with azimuth and time in a simulation experiment.

[0056] Figure 6 This is a schematic diagram of the simulation results of a two-step traditional method for compensating point target 3 in a simulation experiment. Figure 6 (a) shows a schematic diagram of the simulation results for point target 3. Figure 6 (b) shows a schematic diagram of the distance profile corresponding to point target 3. Figure 6 (c) shows a schematic diagram of the azimuth profile corresponding to point target 3;

[0057] Figure 7 This is a schematic diagram of the simulation results of compensating point target 3 using this method in a simulation experiment. Figure 7 (a) shows a schematic diagram of the simulation results for point target 2. Figure 7 (b) shows a schematic diagram of the distance profile corresponding to point target 3. Figure 7 (c) shows a schematic diagram of the azimuth profile corresponding to point target 3;

[0058] Figure 8 This is a structural block diagram of a two-dimensional spatially variable motion compensation device for an airborne SAR in one embodiment;

[0059] Figure 9 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0061] Motion error can be decomposed into changes in heading speed and line-of-sight motion error. Changes in heading speed can be corrected through azimuth resampling; therefore, the derivation can focus only on line-of-sight motion error. After azimuth resampling and range compression, the motion error model for the airborne platform's line-of-sight direction is as follows: Figure 2As shown, the X-axis represents azimuth, the Y-axis represents distance, and the Z-axis represents altitude. Y and Z constitute the motion component along the line of sight. At azimuth t... a At time t, the carrier aircraft has motion errors Δy(t) along the Y and Z axes. a ) and Δz(t a For any point target P(x0,y0,0) in the scene, the airborne SAR echo signal can be represented as:

[0062]

[0063] In formula (1), B r For distance bandwidth; t a and t r These represent azimuth time and distance time, respectively; c is the speed of light; f c For carrier frequency; Let v be the slant distance corresponding to the ideal trajectory, and v be the ideal flight speed. Let H be the nearest slant distance to target P, and H be the platform height; ΔR(t) a x0, r0) represents the slant distance error, as shown in the attached figure. Figure 2 Therefore, the expression for the slant distance error is:

[0064]

[0065] From the perspective of motion compensation, the slant range error can be expressed as:

[0066] ΔR(t a ;x0,r0)=ΔR rc (t a ;x ref ,r ref )+ΔR rv (t a ;x ref ,r0)+ΔR av (t a ;x,r ref (3)

[0067] In formula (3), ΔR rc (t a ;x ref ,r ref ), ΔR rv (t a ;x ref ,r0),ΔR av (t a ;x,r ref ) represent the non-empty variable term, the distance empty variable term, and the azimuth empty variable term, respectively. ref ,r ref This indicates the slant distance and azimuth position of the target at the center of the scene.

[0068] The two-dimensional spatially variable nature of motion errors increases the difficulty of accurate motion compensation. In one embodiment, such as... Figure 1 As shown, a method for airborne SAR two-dimensional spatially variable motion compensation before RCMC is provided, including the following steps:

[0069] Step S100: Obtain the echo data of the target. The echo data is obtained by airborne SAR detection of the target.

[0070] In step S110, an auxiliary point is set in the line-of-sight direction of the radar beam center in the motion error model. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained.

[0071] Step S120: After range compression of the echo data, range-space-variable phase compensation function is used to compensate for range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0072] Step S130: At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0073] Step S140: Based on the azimuth spatially variable phase compensation function, the second intermediate echo data is subjected to azimuth phase compensation through a frequency domain segmentation algorithm to obtain the echo data after two-dimensional spatially variable motion compensation.

[0074] This embodiment proposes a two-dimensional spatially varying motion error compensation method for airborne SAR. This method compensates for the range spatially varying term through phase correction and range resampling before range migration correction, and uses a frequency domain segmentation algorithm to compensate for azimuth spatially varying phase errors, enabling it to adapt to more complex spatially varying motion errors. It should be noted that this method is implemented before range migration correction in the imaging of target echo data. Typical SAR imaging steps include range compression, RCMC, and azimuth compression, while spatially varying motion compensation is usually performed after RCMC. However, with increasing azimuth resolution, motion errors introduce additional envelope errors after RCMC, reducing the accuracy of motion compensation. This method, based on traditional error compensation methods, processes the range and azimuth spatially varying error terms separately before RCMC, quantitatively analyzes the magnitude of different types of errors, and can compensate for complex two-dimensional spatially varying motion errors.

[0075] In step S100, echo data is obtained by detecting the target point using high-resolution airborne SAR.

[0076] In step S110, construct as follows Figure 2 The motion error model is shown. In this model, a point C located in the line-of-sight direction of the radar beam center is introduced as an auxiliary point. The range spatial variation error and azimuth spatial variation error are solved according to the positional geometric relationship between the auxiliary point C, the target point P, the ideal trajectory of the airborne SAR, and the actual trajectory.

[0077] In this embodiment, the actual slant distance from auxiliary point C to point A on the actual radar trajectory is equal to the actual slant distance from target point P to point A on the actual radar trajectory. Thus, according to... Figure 2 The positional geometric relationship represented in the figure can be used to obtain the instantaneous slope distance error of the target point based on the relationship between the actual slope distance of the auxiliary point (the distance between point A and point C), the slope distance of the auxiliary point corresponding to the ideal trajectory in the line of sight (the distance between point C and point B), and the slope distance of the target point corresponding to the ideal trajectory in the line of sight (the distance between point P and point B).

[0078] Furthermore, the instantaneous slant distance error of the target point includes the distance spatial variation error and the azimuth spatial variation error. The distance spatial variation error can be obtained by subtracting the slant distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction from the actual slant distance of the auxiliary point, and the azimuth spatial variation error can be obtained by subtracting the slant distance of the target point corresponding to the ideal trajectory in the line of sight direction from the slant distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction.

[0079] Specifically, in the two-dimensional time domain, the position of each distance gate at each azimuth position x(i) can be represented as:

[0080]

[0081] In formula (4), r min f is the slope distance corresponding to the first sampling point, i.e., the nearest slope distance; s N represents the distance sampling frequency. r This indicates the distance points. At this point, the position r of the envelope of the target point P in the echo... n This corresponds to the slant range |AP| under the actual flight path. Let there be a point C in the line-of-sight direction at the beam center, whose actual slant range is the same as that of point P, i.e., |AC|=|AP|. Then the instantaneous slant range error of point P can be expressed as:

[0082]

[0083] In formula (5), |AC| represents the actual slope distance of the auxiliary point, |BC| represents the slope distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction, |BP| represents the slope distance of the target point corresponding to the ideal trajectory in the line of sight direction, and ΔR r (t a ;rn ) represents the spatially varying error in the distance from the beam center in the line-of-sight direction, ΔR a (t a ;r n ,x0) represents the azimuth spatial variation error of the target point P.

[0084] Furthermore, by calculating the actual slant distance of the auxiliary point, the slant distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction, and the slant distance of the target point corresponding to the ideal trajectory in the line of sight direction, the specific values ​​of the distance spatial variation error and the azimuth spatial variation error that need to be compensated are obtained.

[0085] In this embodiment, the actual slope distance of the auxiliary point is equal to the actual slope distance of the target point, so |AC|=r n It can be obtained through formula (4).

[0086] In this embodiment, when calculating the distance spatial variation error, the ground distance corresponding to the auxiliary point C when calculating the slant distance of the auxiliary point on the ideal trajectory in the line of sight direction can be expressed as:

[0087]

[0088] The slope distance of the auxiliary point corresponding to the ideal trajectory in the line of sight direction is calculated using the following formula:

[0089]

[0090] The range spatial variation term corresponding to the line-of-sight direction at the beam center is expressed as:

[0091]

[0092] According to formula (8), the range-space-variable phase compensation function in the two-dimensional time domain can be obtained, expressed as:

[0093]

[0094] Then, the azimuth spatial motion error is calculated using the following formula:

[0095] ΔR a (t a ;r n ,x0)=|BC|-|BP| (10)

[0096] In this embodiment, when calculating the azimuth spatial variation error, considering that the distance spatial variation term compensation has already been completed, the slant distance corresponding to the ideal trajectory of the auxiliary point in the line-of-sight direction is:

[0097]

[0098] have

[0099]

[0100] Based on the oblique angle, BF and FP in formula (11) can be solved:

[0101]

[0102] In formula (12), θ represents the angle of view. Here, the spatially variable phase error is expressed as a function of the angle of view θ. The relationship between the Doppler frequency and the instantaneous angle of view is as follows:

[0103]

[0104] In this embodiment, after completing the distance spatially varying envelope correction, the slant distance corresponding to the ideal trajectory of the target point in the line-of-sight direction is calculated using the following formula:

[0105] |BP|=r n (14)

[0106] In formula (14), |BP| represents the slant distance of the target point on the ideal trajectory in the line of sight direction after distance envelope correction.

[0107] Next, the azimuth spatial variation error of the target point P can be obtained according to formulas (11) and (14), and the corresponding azimuth spatial variation phase compensation function can be constructed based on the error.

[0108] In step S120, the range-space-variable phase error is compensated using the compensation function of formula (9) on the range-compressed echo data. Then, in step S130, the range-space-variable envelope is resampled at each azimuth position using sinc interpolation, thus completing the process.

[0109] R i (t a ;r n )+ΔR r (t a ;r n →R i (t a ;r n (15)

[0110] Next, in step S140, for the data after range spatial phase error compensation, azimuth phase error compensation is performed based on the azimuth spatial phase error compensation function. This includes: dividing the azimuth spectrum of the second intermediate echo data into multiple sub-band data according to the sub-band division constraint, zero-padding each sub-band data to match the length of the echo data, and performing an inverse Fourier transform to the time domain to obtain processed sub-band data. The azimuth spatial phase error compensation function is used to perform azimuth spatial phase error compensation on each processed sub-band data. The compensated sub-band data are then superimposed to obtain the echo data after two-dimensional spatial motion compensation.

[0111] Specifically, based on the frequency domain segmentation algorithm, the azimuth spectrum is first divided into multiple sub-band data, where the number of sub-bands N satisfies:

[0112]

[0113] In formula (16), θ a θ represents the azimuth beamwidth. sub This represents the sub-beamwidth. The number of sub-bands needs to satisfy the condition that each sub-band data can be considered a narrowband signal. On the one hand, since the center beam approximation is still used within the sub-beam, when dividing the spectrum, it is necessary to ensure that the error of the center approximation of each sub-spectrum is less than π / 4, that is, for θ... sub The size needs to meet the following requirements:

[0114]

[0115] On the other hand, the number of sub-bands cannot be too large, otherwise the time-bandwidth product (TBD) of the sub-beam signal will be too small. Let the center frequency corresponding to each sub-band be f. a,i The corresponding central oblique angle is:

[0116]

[0117] Then, each sub-band data is zero-padding to the original data size, and then Fourier transformed to the time domain. After that, the azimuth spatial variation phase error compensation function constructed in step S110 is used to compensate each sub-band data. Finally, the compensated data are superimposed to obtain the two-dimensional spatial variation motion compensated echo data.

[0118] The azimuth phase compensation function is expressed as follows:

[0119]

[0120] In this embodiment, after performing two-dimensional spatially variable motion compensation on the echo data, range migration correction and azimuth compression are then performed on the compensated echo data to obtain a high-resolution SAR target image. This completes the last two steps of the SAR imaging algorithm. Here, the wavenumber domain algorithm (WDA) can be directly used for imaging.

[0121] In this embodiment, when performing high-resolution airborne SAR imaging according to the method described herein, the following methods may also be used: Figure 3 The algorithm steps are shown.

[0122] This paper also provides experimental results obtained from simulations based on the proposed method to demonstrate the effectiveness of the proposed method.

[0123] In the experimental simulation, the magnitudes of three types of motion errors were quantitatively analyzed, as shown in Table 1, which presents the simulation parameters of the motion errors. Figure 4 As shown in (a), the slope distance error corresponds to different positions, such as Figure 4 (b) shows the distance spatial variable error, as follows: Figure 4 As shown in (c), the azimuth space variable error is as follows: Figure 5 As shown, the YZ axis trajectory deviation changes with azimuth and time.

[0124] It can be seen that the non-space-varying motion error is not negligible, the range-varying motion error exhibits an approximately linear change with the range direction, while the azimuth-varying motion term is less than half of the system's range resolution. Therefore, the influence of the azimuth motion term on the envelope can be ignored, but the phase error it introduces needs to be compensated for.

[0125] After compensation using the method presented in this paper, simulation evaluations were performed on three point targets at different distances from the same azimuth. Table 2 shows the evaluation results for the three point targets, all of which are close to the ideal performance. For comparison, Figure 6 An evaluation diagram after compensating for target 3 using a two-step method is also provided. For example... Figure 7 As shown, the simulation results of target 3 and the azimuth and range slices are displayed, with good focusing effect.

[0126] Table 1 Simulation System Parameter Settings

[0127] parameter value Distance resolution / m 0.1 Azimuth resolution / m 0.1 Flight altitude / km 4 Center slope distance / km 10 Carrier frequency / GHz 9.6 Bandwidth / MHz 1500 PRF / Hz 1200 Point target settings / m (0,9e3,0),(0,10e3,0),(0,11e3,0)

[0128] Table 2 Evaluation Results of Different Targets

[0129]

[0130] In the aforementioned two-dimensional spatially varying motion compensation method for airborne SAR, this method establishes a model based on the motion error caused by the airborne SAR moving platform, analyzes different types of errors, and determines the type of error that needs to be compensated based on the analysis results. Then, it processes the phase error of the range spatially varying error, compensates for the range spatially varying envelope error through range resampling, and finally compensates for the azimuth spatially varying phase error through a frequency domain segmentation algorithm. This method has good compensation effect and can perform higher-precision motion error compensation.

[0131] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0132] In one embodiment, such as Figure 8 As shown, a two-dimensional space-varying motion compensation device for airborne SAR is provided, comprising: an echo data acquisition module 200, a two-dimensional space-varying motion compensation function construction module 210, a range space-varying phase compensation module 220, a range space-varying envelope compensation module 230, and an azimuth space-varying phase compensation module 240, wherein:

[0133] The echo data acquisition module 200 is used to acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0134] The two-dimensional spatially variable motion compensation function construction module 210 is used to set an auxiliary point in the line-of-sight direction of the radar beam center in the motion error model, and solve the range spatially variable error and azimuth spatially variable error based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, and obtain the range spatially variable phase compensation function and the azimuth spatially variable phase compensation function accordingly.

[0135] The distance-space-variable phase compensation module 220 is used to perform distance-space-variable phase error compensation on the distance-compressed echo data after distance compression using the distance-space-variable phase compensation function, so as to obtain the first intermediate echo data.

[0136] The range spatially variable envelope compensation module 230 is used to resample the range spatially variable envelope of the first intermediate echo data at each azimuth position using sinc interpolation to achieve range spatially variable envelope error compensation and obtain the second intermediate echo data.

[0137] The azimuth spatial phase compensation module 240 is used to perform azimuth phase compensation on the second intermediate echo data based on the azimuth spatial phase compensation function and through the frequency domain segmentation algorithm to obtain the echo data after two-dimensional spatial motion compensation.

[0138] Specific limitations regarding the two-dimensional space-varying motion compensation device for airborne SAR can be found in the limitations of the two-dimensional space-varying motion compensation method for airborne SAR described above, and will not be repeated here. Each module in the aforementioned two-dimensional space-varying motion compensation device for airborne SAR can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independently of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the corresponding operations of each module.

[0139] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 9 As shown, the computer device includes a processor, memory, network interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The network interface is used to communicate with external terminals via a network connection. When the computer program is executed by the processor, it implements a two-dimensional spatially variable motion compensation method for airborne SAR. The display screen can be a liquid crystal display (LCD) or an e-ink display. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad mounted on the computer device casing, or an external keyboard, touchpad, or mouse.

[0140] Those skilled in the art will understand that Figure 9 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0141] In one embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0142] Acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0143] In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly.

[0144] After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0145] At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0146] Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data through a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained.

[0147] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program performing the following steps when executed by a processor:

[0148] Acquire the echo data of the target, which is obtained by airborne SAR detection of the target;

[0149] In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly.

[0150] After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data.

[0151] At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data.

[0152] Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data through a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained.

[0153] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0154] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0155] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A two-dimensional spatially variable motion compensation method for airborne SAR, characterized in that, The method includes: Acquire the echo data of the target, which is obtained by airborne SAR detection of the target; In the motion error model, an auxiliary point is set in the line-of-sight direction of the radar beam center. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatial variation error and the azimuth spatial variation error are solved respectively, and the range spatial variation phase compensation function and the azimuth spatial variation phase compensation function are obtained accordingly. After the echo data is range compressed, the range-space-variable phase compensation function is used to compensate for the range-space-variable phase error of the range-compressed echo data to obtain the first intermediate echo data. At each azimuth position, the range spatially variable envelope of the first intermediate echo data is resampled using sinc interpolation to achieve range spatially variable envelope error compensation, thereby obtaining the second intermediate echo data. Based on the azimuth spatially variable phase compensation function, and by performing azimuth phase compensation on the second intermediate echo data using a frequency domain segmentation algorithm, two-dimensional spatially variable motion-compensated echo data is obtained. Specifically, according to the sub-band division constraint, the azimuth spectrum of the second intermediate echo data is divided into multiple sub-band data. Each sub-band data is zero-padded to match the length of the echo data, and then subjected to an inverse Fourier transform to the time domain to obtain processed sub-band data. The azimuth spatially variable phase compensation function is used to perform azimuth phase compensation on each processed sub-band data. After superimposing the compensated sub-band data, the two-dimensional spatially variable motion-compensated echo data is obtained.

2. The two-dimensional spatial motion compensation method according to claim 1, characterized in that, When solving for the range spatial variation error and azimuth spatial variation error based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR, and the actual trajectory: The actual slope distance of the auxiliary point is equal to the actual slope distance of the target point; The instantaneous slope distance error of the target point is obtained based on the relationship between the actual slope distance of the auxiliary point, the slope distance corresponding to the ideal trajectory of the auxiliary point in the line of sight direction, and the slope distance corresponding to the ideal trajectory of the target point in the line of sight direction.

3. The two-dimensional spatial motion compensation method according to claim 2, characterized in that, The instantaneous slant range error of the target point includes the spatial variation error of distance and the spatial variation error of azimuth; The distance spatial variation error is obtained by subtracting the slope distance of the auxiliary point from the slope distance of the auxiliary point on the ideal trajectory in the line of sight direction from the actual slope distance of the auxiliary point. The azimuth spatial variation error is obtained by subtracting the slant distance of the target point from the slant distance of the auxiliary point on the ideal trajectory in the line of sight direction.

4. The two-dimensional spatial motion compensation method according to claim 3, characterized in that, When calculating the distance spatial variation error, the slant distance of the auxiliary point corresponding to the ideal trajectory in the line-of-sight direction is calculated using the following formula: When calculating the azimuth spatial variation error, since envelope correction has already been completed, the slant distance of the auxiliary point corresponding to the ideal trajectory in the line-of-sight direction is calculated using the following formula: in, In the above formula, This represents the slant distance of the auxiliary point along the ideal trajectory in the line of sight direction. This represents the distance error between the radar and the ideal position. This represents the actual slope distance of the target point. This indicates the ideal altitude of the radar. The altitude error of the radar relative to the ideal position. Indicates an oblique angle.

5. The two-dimensional spatial motion compensation method according to claim 4, characterized in that, The slant distance of the target point along the ideal trajectory in the line-of-sight direction is calculated using the following formula: In the above formula, This represents the slant distance corresponding to the ideal trajectory of the target point in the line-of-sight direction.

6. The two-dimensional spatial motion compensation method according to any one of claims 1-5, characterized in that, The method further includes: after performing two-dimensional spatial motion compensation on the echo data, performing range migration correction and azimuth compression on the compensated echo data to obtain a high-resolution SAR target image.

7. A two-dimensional spatially variable motion compensation device for airborne SAR, characterized in that, The device includes: The echo data acquisition module is used to acquire the echo data of the target, which is obtained by airborne SAR detection of the target; The two-dimensional spatially variable motion compensation function construction module is used to set an auxiliary point in the line-of-sight direction of the radar beam center in the motion error model. Based on the positional geometric relationship between the auxiliary point, the target point, the ideal trajectory of the airborne SAR and the actual trajectory, the range spatially variable error and the azimuth spatially variable error are solved respectively, and the range spatially variable phase compensation function and the azimuth spatially variable phase compensation function are obtained accordingly. The range-space-variable phase compensation module is used to perform range-space-variable phase error compensation on the range-compressed echo data after range compression, and then use the range-space-variable phase compensation function to obtain the first intermediate echo data. The range-space-variable envelope compensation module is used to resample the range-space-variable envelope of the first intermediate echo data at each azimuth position using sinc interpolation to achieve range-space-variable envelope error compensation and obtain the second intermediate echo data. The azimuth spatial-variable phase compensation module is used to perform azimuth phase compensation on the second intermediate echo data based on the azimuth spatial-variable phase compensation function and through a frequency domain segmentation algorithm to obtain two-dimensional spatial-variable motion-compensated echo data. Specifically, the azimuth spectrum of the second intermediate echo data is divided into multiple sub-band data according to the sub-band division constraint. Each sub-band data is zero-padded to match the length of the echo data and subjected to inverse Fourier transform to the time domain to obtain processed sub-band data. The azimuth spatial-variable phase compensation function is used to perform azimuth phase compensation on each processed sub-band data. The compensated sub-band data are then superimposed to obtain the two-dimensional spatial-variable motion-compensated echo data.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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