Method and system for calculating two-dimensional resolution and parameters of high squint spaceborne SAR

Abstract

The present invention provides a method and system for calculating the two-dimensional resolution and parameters of a high-squint satellite-borne SAR, including: calculating the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system according to the satellite-ground squint geometric relationship; calculating the support area range of the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system; calculating the two-dimensional spectrum width of the support area range of the wavenumber spectrum of the target point; calculating the two-dimensional resolution of the target point through the two-dimensional spectrum width according to the Fourier transform theory; and obtaining the design value of the synthetic aperture time and the signal bandwidth according to the coupling relationship between the two-dimensional resolution and the synthetic aperture time and the signal bandwidth. The present invention can obtain the support area range of the two-dimensional wavenumber spectrum of the target point by arranging the optimal ground rectangular coordinate system, and accurately obtain the two-dimensional resolution of the target point by directly calculating the two-dimensional spectrum width, which can solve the problem of decreased calculation accuracy caused by the coupling of the two-dimensional resolution under high squint in the existing method.

Description

Technical Field

[0001] The present invention relates to the field of radar signal processing technology, and in particular to a method and system for calculating two-dimensional resolution and parameters of a high-squint satellite-borne SAR. Background Art

[0002] Geometric resolution is a key factor in evaluating SAR image quality. In the early stages of SAR technology, the observation geometry of the radar was relatively simple, generally looking straight sideways, and the radar trajectory was approximately a straight line. At this time, the range resolution was determined by the transmission bandwidth of the signal, and the azimuth resolution was determined by the synthetic aperture time. However, as more and more spaceborne SARs work in the high squint mode, the two-dimensional resolution direction is coupled. At this time, the range and azimuth resolutions are not only affected by a single parameter, but are obtained by the coupling of multiple parameters. At the same time, with the increase of resolution and orbital altitude, the synthetic aperture time of spaceborne SAR increases, the impact of orbital curvature increases, and the error introduced by the linear approximation of the radar trajectory cannot be ignored.

[0003] Article 1 (Bao Min, Xu Gang, Li Yachao, et al. Research on Curved Trajectory Model and Imaging Algorithm of Geosynchronous Orbit SAR [J]. Acta Astronautics, 2011, 32(8):1769-1777) proposed a method for calculating the surface two-dimensional resolution under high-orbit circular orbit positive side-viewing SAR. This method can be applied to the surface two-dimensional resolution calculation under curved trajectory, but is not applicable to high squint observation geometry.

[0004] Article 2 (Long Jie, Yao Di, Sun Yingqin, et al. Resolution analysis method of forward slant SAR based on resolution ellipse [J]. Journal of Electronics, 2013, 41(12): 2493-2498.) proposed a resolution ellipse function calculation method for the case of straight-line trajectory dive squint. Although this method is suitable for squint observation geometry, it still has large errors under curved trajectory.

[0005] Article 3 (Wang J, Wang Y, Zhang J, Ge J. Resolution calculation and analysis in bistatic SAR with geostationary illuminator [J]. IEEE Transactions On Geoscience and Remote Sensing Letters, 2013, 10 (1): 194-198.) proposed a resolution calculation method based on fuzzy function polynomial approximation, which can accurately solve the resolution in any direction of the curve trajectory. However, this method cannot analytically characterize the relationship between resolution and system parameters, and therefore cannot guide system parameter design.

[0006] Article 4 (Liu Wenkang, Sun Guangcai, Chen Jianlai, et al. A design method for bandwidth and synthetic aperture time of high-orbit SAR [J]. Journal of Xidian University, 2017, 044(005): 58-63.) proposed a method for calculating the surface omnidirectional resolution ellipse based on satellite-ground geometric projection, and derived the relationship between the major and minor axes of the ellipse and the bandwidth and the synthetic aperture time. However, this method requires the radar trajectory to be a straight line, and the designed synthetic aperture time is usually too large.

[0007] Patent document CN115291179A discloses a method, electronic device and storage medium for analyzing the two-dimensional resolution of squint SAR. Based on the imaging result of the target point of squint SAR, the invention obtains the up-sampled result through two-dimensional spectrum interpolation and zero-filling processing, determines the two-dimensional sidelobe direction of the surface, calculates the two-dimensional direction angle through Radon transformation, and converts the two-dimensional direction to the vertical and horizontal axes through rotation transformation, and analyzes the two-dimensional resolution respectively. However, the patent document can only evaluate the two-dimensional resolution based on the SAR complex image after imaging, and cannot estimate the two-dimensional resolution index before imaging.

[0008] Patent document CN1133917418B discloses a method for evaluating the two-dimensional resolution of the ground plane of a squint satellite-borne SAR. The invention determines the three-dimensional coordinates of the imaging point and the normal vector of the slant range plane based on the squint SAR satellite-to-ground imaging geometry, and after determining the tangent plane based on the earth model, constructs the slant range vector. Then, the projection factor of the two-dimensional resolution is obtained based on the satellite-to-ground projection, and the two-dimensional resolution is calculated. However, the patent document calculates the two-dimensional resolution based on the satellite-to-ground geometry at the center moment. The accuracy is high under a straight trajectory, but the accuracy decreases under a curved trajectory. The resolution index calculation accuracy is not high, and it is not suitable for satellite-borne curved trajectories.

[0009] Patent document CN115291179A discloses a two-dimensional resolution analysis calculation method, electronic device and storage medium for squint SAR, which includes: obtaining the imaging area of ​​the target point after projection to the ground plane based on the squint SAR data; determining the ground azimuth sidelobes and ground range sidelobes of the target point, as well as the range of the ground azimuth angle and the ground range angle, and finally performing ground azimuth resolution analysis and range resolution analysis. However, the patent document can only perform two-dimensional resolution evaluation based on the SAR complex image after imaging, and cannot perform high-precision estimation of the resolution before imaging.

[0010] In summary, among the existing resolution calculation methods, there is no high-precision resolution calculation method specifically suitable for large squint of space-borne curved trajectories. There is a lack of analytical expressions for the resolution calculation method in this case, and the transfer relationship between system parameters and resolution cannot be obtained. However, it is known that the resolution calculation method for system parameter design usually uses a straight-line trajectory approximation, which has a large error under the space-borne SAR curved trajectory.

[0011] Therefore, it is necessary to design a new resolution calculation method, which can accurately calculate the two-dimensional resolution under large squint conditions of the satellite-borne curved trajectory, and can analytically characterize the relationship between the two-dimensional resolution and the signal bandwidth and synthetic aperture. Summary of the invention

[0012] In view of the defects in the prior art, the object of the present invention is to provide a method and system for calculating the two-dimensional resolution and parameters of a high-squint satellite-borne SAR.

[0013] A method for calculating two-dimensional resolution and parameters of a high-squint spaceborne SAR provided by the present invention comprises:

[0014] Step S1: Calculate the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system according to the satellite-ground squint geometric relationship;

[0015] Step S2: Calculate the support area range of the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system;

[0016] Step S3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area;

[0017] Step S4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width;

[0018] Step S5: According to the coupling relationship between the two-dimensional resolution and the synthetic aperture time and the signal bandwidth, the design values ​​of the synthetic aperture time and the signal bandwidth are obtained.

[0019] Preferably, the step S1 comprises:

[0020] Step S1.1: Establish the optimal ground rectangular coordinate system, the formula is as follows:

[0021]

[0022] Wherein, vector S represents the unit vector of the radar line of sight at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign.

[0023] Step S1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system, and the calculation formula is as follows:

[0024]

[0025] Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix.

[0026] Preferably, step S3 comprises:

[0027] Step S3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra It can be obtained through the geometric relationship between the satellite and the ground, and the calculation formula is as follows:

[0028]

[0029] Wherein, vector R represents the distance sidelobe direction vector;

[0030] Step S3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows:

[0031]

[0032] Where c is the speed of light, B is the signal bandwidth, and θ w Indicates the corner of the floor;

[0033] Step S3.3: Calculate the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows:

[0034]

[0035] Among them, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0036] Preferably, the step S4.1 comprises:

[0037] Step S4.1: Calculate the range resolution ρ r , the calculation formula is as follows:

[0038]

[0039] Among them, k r represents the distance weighting coefficient, which is caused by the imaging processor. When these broadenings are not considered, the coefficient is 0.886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle;

[0040] Step S4.2: Calculate the azimuth resolution ρ a , the calculation formula is as follows:

[0041]

[0042] Among them, k a represents the azimuth weighting factor, caused by the imaging processor, when these broadenings are not considered, the coefficient is 0.886. a represents the width of the azimuthal wavenumber spectrum, fc represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0043] Preferably, the step S5 comprises:

[0044] Step S5.1: Calculate the signal bandwidth design value B design , the formula is as follows:

[0045]

[0046] Among them, ρ r-design represents the required range resolution, k r represents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle;

[0047] Step S5.2: Calculate the synthetic aperture time, synthetic aperture time. The formula is as follows:

[0048]

[0049] Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f cIndicates the carrier frequency.

[0050] A high squint satellite-borne SAR two-dimensional resolution and parameter calculation system provided by the present invention comprises:

[0051] Module M1: Calculate the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system based on the satellite-ground oblique geometric relationship;

[0052] Module M2: Calculate the support area of ​​the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system;

[0053] Module M3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area;

[0054] Module M4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width;

[0055] Module M5: According to the coupling relationship between the two-dimensional resolution and the synthetic aperture time and the signal bandwidth, the design values ​​of the synthetic aperture time and the signal bandwidth are obtained.

[0056] Preferably, the module M1 comprises:

[0057] Module M1.1: Establish the optimal ground rectangular coordinate system, the formula is as follows:

[0058]

[0059] Wherein, vector S represents the unit vector of the radar line of sight at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign.

[0060] Module M1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system. The calculation formula is as follows:

[0061]

[0062] Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix.

[0063] Preferably, the module M3 comprises:

[0064] Module M3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra It can be obtained through the geometric relationship between the satellite and the ground, and the calculation formula is as follows:

[0065]

[0066] Wherein, vector R represents the distance sidelobe direction vector;

[0067] Module M3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows:

[0068]

[0069] Where c is the speed of light, B is the signal bandwidth, and θ w Indicates the corner of the floor;

[0070] Module M3.3: Calculation of the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows:

[0071]

[0072] Among them, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0073] Preferably, the module M4.1 comprises:

[0074] Module M4.1: Calculation of distance resolution ρ r , the calculation formula is as follows:

[0075]

[0076] Among them, k r represents the distance weighting coefficient, which is caused by the imaging processor. When these broadenings are not considered, the coefficient is 0.886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle;

[0077] Module M4.2: Calculation of azimuth resolution ρ a , the calculation formula is as follows:

[0078]

[0079] Among them, ka represents the azimuth weighting factor, caused by the imaging processor, when these broadenings are not considered, the coefficient is 0.886. a represents the width of the azimuthal wavenumber spectrum, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0080] Preferably, the module M5 comprises:

[0081] Module M5.1: Calculate the signal bandwidth design value B design , the formula is as follows:

[0082]

[0083] Among them, ρ r-design represents the required range resolution, k r represents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle;

[0084] Module M5.2: Calculate synthetic aperture time, synthetic aperture time. The formula is as follows:

[0085]

[0086] Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f c Indicates the carrier frequency.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] 1. The present invention can obtain the support area range of the two-dimensional wavenumber spectrum of the target point by arranging the optimal ground rectangular coordinate system, and accurately obtain the two-dimensional resolution of the target point by directly calculating the two-dimensional spectrum width, which can solve the problem of decreased calculation accuracy caused by the coupling of two-dimensional resolution under large squint in the existing method.

[0089] 2. The present invention can accurately analyze and characterize the relationship between two-dimensional resolution and signal bandwidth and synthetic aperture time. Therefore, appropriate signal bandwidth and synthetic aperture time can be designed according to resolution requirements. The obtained signal bandwidth and synthetic aperture time have higher accuracy and can be applied to the parameter design of satellite-borne SAR payload system and the analysis of satellite-ground integration indicators.

[0090] 3. The calculation process of the present invention does not have any approximation, so it can be applied to any radar trajectory, including space-borne SAR curve trajectory. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0092] Figure 1 It is a schematic diagram of the process of the present invention;

[0093] Figure 2 Schematic diagram of high squint observation geometry and optimal ground rectangular coordinate system;

[0094] Figure 3 It is a schematic diagram of the support area range and two-dimensional spectrum width of the two-dimensional wavenumber spectrum of the target point;

[0095] Figure 4 To simulate a target point focusing result and a two-dimensional profile;

[0096] Figure 5 To simulate the focusing results of two target points and the two-dimensional profile. DETAILED DESCRIPTION

[0097] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0098] The present invention calculates the support area range of the BP image two-dimensional wavenumber spectrum of the target point by arranging the optimal ground rectangular coordinate system, and then calculates the two-dimensional resolution according to the two-dimensional spectrum width, and simultaneously provides the design method of signal bandwidth and synthetic aperture time.

[0099] Embodiment 1

[0100] According to a method for calculating two-dimensional resolution and parameters of a high-squint satellite-borne SAR provided by the present invention, Figure 1 As shown, including:

[0101] Step S1: According to the radar position and target point coordinates in the WGS84 earth-fixed coordinate system, as well as the satellite-ground squint geometry relationship, the radar position and target point coordinates to be analyzed in the optimal ground rectangular coordinate system are calculated. The conversion matrix is ​​shown in S1.2. Specifically, the optimal ground rectangular coordinate system is established according to the conversion relationship between the satellite-ground squint geometry relationship and the WGS84 earth-fixed coordinate system. The step S1 includes:

[0102] Step S1.1: Establish the optimal ground rectangular coordinate system. Figure 2 As shown, the X-axis of the optimal ground rectangular coordinate system is determined by the azimuth unit direction vector A, the Z-axis is determined by the ground plane unit normal vector n corresponding to the target point, and the Y-axis is obtained by the right-hand rule, as shown in the following formula:

[0103]

[0104] Among them, vector S represents the unit vector of the radar line of sight direction at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign.

[0105] Step S1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system, and the calculation formula is as follows:

[0106]

[0107] Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix:

[0108] M r =[A n × A n]·I

[0109] Among them, I represents the unit matrix. It should be noted that in the rotation matrix expression at this time, each vector is expressed in the WGS84 earth-fixed coordinate system.

[0110] Step S2: Calculate the support area of ​​the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system. The calculation is performed according to the imaging theory of the back projection (BP) algorithm, and the calculation formula is as follows:

[0111]

[0112] Among them, K x and K y They represent the support range of the wavenumber spectrum in the azimuth and distance directions, respectively, and K r represents the wave number, (X(t a ),Y(t a ),Z(t a )) represents the radar position in the optimal ground rectangular coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth fixed coordinate system, t a Indicates the azimuth slow time, f c Indicates the carrier frequency, f r represents the distance frequency, and c represents the speed of light.

[0113] Step S3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area. Figure 3 As shown, the two-dimensional sidelobe angle of the target point is calculated according to the tilt of the image wave number spectrum, and the width of the two-dimensional wave number spectrum is further calculated. The step S3 includes:

[0114] Step S3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra It can be obtained through the geometric relationship between the satellite and the ground, and the calculation formula is as follows:

[0115]

[0116] Among them, vector R represents the range sidelobe direction vector, which can be obtained from the satellite velocity vector v and the radar line of sight direction vector S, and the formula is as follows:

[0117] R=(IS·S T )·v

[0118] Step S3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows:

[0119]

[0120] Where c is the speed of light, B is the signal bandwidth, and θ w Indicates the corner of the floor.

[0121] Step S3.3: Calculate the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows:

[0122]

[0123] Where fc represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(ts ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0124] Step S4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width.

[0125] The step S4.1 comprises:

[0126] Step S4.1: Calculate the range resolution ρ r , the calculation formula is as follows:

[0127]

[0128] Among them, k r represents the distance weighting coefficient, which is caused by the imaging processor. When these broadenings are not considered, the coefficient is 0.886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle.

[0129] Step S4.2: Calculate the azimuth resolution ρ a , the calculation formula is as follows:

[0130]

[0131] Among them, k a represents the azimuth weighting factor, caused by the imaging processor, when these broadenings are not considered, the coefficient is 0.886. a represents the width of the azimuthal wavenumber spectrum, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0132] Step S5: According to the coupling relationship between the two-dimensional resolution, the synthetic aperture time and the signal bandwidth, the design values ​​of the synthetic aperture time and the signal bandwidth are obtained. The step S5 includes:

[0133] Step S5.1: Calculate the signal bandwidth design value B design , the formula is as follows:

[0134]

[0135] Among them, ρ r-design represents the required range resolution, k rrepresents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle.

[0136] Step S5.2: Calculate the synthetic aperture time, synthetic aperture time. The formula is as follows:

[0137]

[0138] Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f c Indicates the carrier frequency.

[0139] The present invention aims to solve the problem that the prior art cannot accurately analyze and obtain the two-dimensional resolution under large squint and complex imaging geometry, resulting in insufficient accuracy of system parameter settings.

[0140] Embodiment 2

[0141] This embodiment is based on the simulation results of the first embodiment, and is a further verification of the effect of the first embodiment on the two-dimensional resolution and parameter calculation of the squint spaceborne SAR.

[0142] Simulation parameters, including orbit parameters and radar parameters, are shown in Table 1:

[0143] Table 1

[0144]

[0145] Using the high squint satellite-borne SAR two-dimensional resolution calculation method of the present invention, according to the simulation parameters given in the above table, the two-dimensional broadening coefficient is set to 0.886, and the theoretical resolution in the range direction is calculated to be 1.3632m, and the theoretical resolution in the azimuth direction is 1.2246m. At the same time, the BP algorithm is used to image the target point, and its two-dimensional side lobe is taken for 32 times upsampling interpolation, and its half-power point width is used as the true resolution, and the true resolution in the range direction is 1.3604m, and the true resolution in the azimuth direction is 1.2234m. Figure 4 As shown, according to the comparison between the theoretical resolution calculated by the present invention and the actual resolution, the error is less than 1%. Figure 4 From left to right in the figure, there are the imaging result of the target point BP algorithm, the azimuth profile after the target point is focused, and the distance profile after the target point is focused.

[0146] It can be found from the simulation results that the theoretical resolution obtained by the two-dimensional resolution calculation method of the high-squint spaceborne SAR proposed in the present invention has an error of less than 1% compared with the resolution of the real target point after imaging.

[0147] Embodiment 3

[0148] This embodiment is based on the simulation results of the first embodiment, and is a further verification of the effect of the first embodiment on the two-dimensional resolution and parameter calculation of the squint spaceborne SAR.

[0149] The simulation parameters include orbit parameters and radar parameters, as shown in Table 2:

[0150] Table 2

[0151]

[0152] Using the high squint satellite-borne SAR system parameter design method of the present invention, according to the simulation two parameters given in the table above, the two-dimensional required resolution is set to 1m, the designed signal bandwidth is 183MHz, and the synthetic aperture time is 1.7075s. At this time, the BP algorithm is used to image the target point, and its two-dimensional side lobes are taken for 32 times upsampling interpolation, and its half-power point width is used as the true resolution, and the true resolution in the range direction is 0.9984m, and the true resolution in the azimuth direction is 0.9938m. Figure 5 As shown, it can be seen that the system parameters calculated by the present invention can accurately achieve the index requirements. Figure 5 From left to right in the figure are the imaging result of the target point BP algorithm, the azimuth profile after the target point is focused, and the distance profile after the target point is focused.

[0153] According to the simulation results, it can be found that by adopting the high-squint satellite-borne SAR system parameter design method proposed in the present invention, the signal bandwidth and synthetic aperture time designed can accurately meet the index requirements for the two-dimensional resolution after imaging the target point.

[0154] Embodiment 4

[0155] The present invention also provides a high squint satellite-borne SAR two-dimensional resolution and parameter calculation system. The high squint satellite-borne SAR two-dimensional resolution and parameter calculation system can be realized by executing the process steps of the high squint satellite-borne SAR two-dimensional resolution and parameter calculation method, that is, those skilled in the art can understand the high squint satellite-borne SAR two-dimensional resolution and parameter calculation method as a preferred implementation of the high squint satellite-borne SAR two-dimensional resolution and parameter calculation system.

[0156] A high squint satellite-borne SAR two-dimensional resolution and parameter calculation system provided by the present invention comprises:

[0157] Module M1: Calculate the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system based on the satellite-ground oblique geometric relationship. Module M1 includes: Module M1.1: Establish the optimal ground rectangular coordinate system, the formula is as follows:

[0158]

[0159] Among them, vector S represents the unit vector of the radar line of sight direction at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign.

[0160] Module M1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system. The calculation formula is as follows:

[0161]

[0162] Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix.

[0163] Module M2: Calculate the support area of ​​the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system.

[0164] Module M3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area. Module M3 includes:

[0165] Module M3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra It can be obtained through the geometric relationship between the satellite and the ground, and the calculation formula is as follows:

[0166]

[0167] Wherein, vector R represents the distance sidelobe direction vector.

[0168] Module M3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows:

[0169]

[0170] Where c is the speed of light, B is the signal bandwidth, and θ w Indicates wiping corner.

[0171] Module M3.3: Calculation of the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows:

[0172]

[0173] Among them, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0174] Module M4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width.

[0175] Module M4.1 includes:

[0176] Module M4.1: Calculation of distance resolution ρ r , the calculation formula is as follows:

[0177]

[0178] Among them, k r represents the distance weighting coefficient, which is caused by the imaging processor. When these broadenings are not considered, the coefficient is 0.886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle.

[0179] Module M4.2: Calculation of azimuth resolution ρ a , the calculation formula is as follows:

[0180]

[0181] Among them, k a represents the azimuth weighting factor, caused by the imaging processor, when these broadenings are not considered, the coefficient is 0.886. a represents the width of the azimuthal wavenumber spectrum, f c represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively.

[0182] Module M5: According to the coupling relationship between the two-dimensional resolution, the synthetic aperture time and the signal bandwidth, the design values ​​of the synthetic aperture time and the signal bandwidth are obtained. Module M5 includes:

[0183] Module M5.1: Calculate the signal bandwidth design value B design , the formula is as follows:

[0184]

[0185] Among them, ρ r-design represents the required range resolution, k r represents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle.

[0186] Module M5.2: Calculate synthetic aperture time, synthetic aperture time. The formula is as follows:

[0187]

[0188] Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f c Indicates the carrier frequency.

[0189] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0190] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for calculating the two-dimensional resolution and parameters of a high-squint spaceborne SAR, characterized in that: include: Step S1: Calculate the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system according to the satellite-ground squint geometric relationship; Step S2: Calculate the support area range of the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system; Step S3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area; Step S4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width; Step S5: obtaining design values ​​of the synthetic aperture time and the signal bandwidth according to the coupling relationship between the two-dimensional resolution and the synthetic aperture time and the signal bandwidth; The step S3 comprises: Step S3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra , can be obtained through the satellite-ground geometric relationship, and the calculation formula is as follows: Wherein, vector R represents the distance sidelobe direction vector; Step S3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows: Where c is the speed of light, B is the signal bandwidth, and θ w Indicates the corner of the floor; Step S3.3: Calculate the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows: Where fc represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively; The step S4.1 comprises: Step S4.1: Calculate the range resolution ρ r , the calculation formula is as follows: Among them, k r It represents the distance weighting coefficient, which is caused by the imaging processor. When the broadening is not considered, the coefficient is 0.

886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle; Step S4.2: Calculate the azimuth resolution ρ a , the calculation formula is as follows: Among them, k a represents the azimuth weighting coefficient, which is caused by the imaging processor. When the broadening is not considered, the coefficient is 0.

886. Ba represents the width of the azimuth wavenumber spectrum, fc represents the carrier frequency, and X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively; The step S5 comprises: Step S5.1: Calculate the signal bandwidth design value B design , the formula is as follows: Among them, ρ r-design represents the required range resolution, k r represents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle; Step S5.2: Calculate the synthetic aperture time. The synthetic aperture time is calculated using the following formula: Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f c Indicates the carrier frequency.

2. The method for calculating two-dimensional resolution and parameters of high-squint spaceborne SAR according to claim 1, characterized in that: The step S1 comprises: Step S1.1: Establish the optimal ground rectangular coordinate system, the formula is as follows: Wherein, vector S represents the unit vector of the radar line of sight at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign. Step S1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system, and the calculation formula is as follows: Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix.

3. A high squint satellite-borne SAR two-dimensional resolution and parameter calculation system, characterized in that: include: Module M1: Calculate the radar position and the coordinates of the target point to be analyzed in the optimal ground rectangular coordinate system based on the satellite-ground oblique geometric relationship; Module M2: Calculate the support area of ​​the two-dimensional wavenumber spectrum of the image after the target point is focused in the optimal ground rectangular coordinate system; Module M3: Calculate the two-dimensional spectrum width of the target point wave number spectrum support area; Module M4: According to Fourier transform theory, the two-dimensional resolution of the target point is obtained by calculating the two-dimensional spectrum width; Module M5: according to the coupling relationship between the two-dimensional resolution, the synthetic aperture time and the signal bandwidth, the design values ​​of the synthetic aperture time and the signal bandwidth are obtained; The module M3 comprises: Module M3.1: Calculate the two-dimensional sidelobe angle θ of the target point ra , can be obtained through the satellite-ground geometric relationship, and the calculation formula is as follows: Wherein, vector R represents the distance sidelobe direction vector; Module M3.2: Calculate the width B of the distance wavenumber spectrum r , the calculation formula is as follows: Where c is the speed of light, B is the signal bandwidth, and θ w Indicates the corner of the floor; Module M3.3: Calculation of the width B of the azimuthal wavenumber spectrum a , the calculation formula is as follows: Where fc represents the carrier frequency, X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively; The module M4.1 includes: Module M4.1: Calculation of distance resolution ρ r , the calculation formula is as follows: Among them, k r It represents the distance weighting coefficient, which is caused by the imaging processor. When the broadening is not considered, the coefficient is 0.

886. B represents the signal bandwidth, c represents the speed of light, and θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle; Module M4.2: Calculation of azimuth resolution ρ a , the calculation formula is as follows: Among them, k a represents the azimuth weighting coefficient, which is caused by the imaging processor. When the broadening is not considered, the coefficient is 0.

886. Ba represents the width of the azimuth wavenumber spectrum, fc represents the carrier frequency, and X(t s ) and X(t e ) represent the X-axis position of the satellite at the start and end of the aperture in the optimal surface rectangular coordinate system, R(t s ) and R(t e ) represent the instantaneous slant distance at the start and end of the aperture, respectively; The module M5 comprises: Module M5.1: Calculate the signal bandwidth design value B design , the formula is as follows: Among them, ρ r-design represents the required range resolution, k r represents the distance weighting coefficient, c represents the speed of light, θ w represents the ground rubbing angle, θ ra represents the two-dimensional sidelobe angle; Module M5.2: Calculate the synthetic aperture time. The synthetic aperture time is calculated using the following formula: Among them, ρ a-design represents the required azimuth resolution, k1 represents Relative slow time t a The coefficient of the first-order term after Taylor expansion, f c Indicates the carrier frequency.

4. The high squint spaceborne SAR two-dimensional resolution and parameter calculation system according to claim 3, characterized in that: The module M1 comprises: Module M1.1: Establish the optimal ground rectangular coordinate system, the formula is as follows: Wherein, vector S represents the unit vector of the radar line of sight at the center moment. When the radar is looking right, vector A takes a positive sign, otherwise, vector A takes a negative sign. Module M1.2: Calculate the conversion relationship between the optimal ground rectangular coordinate system and the WGS84 earth fixed coordinate system. The calculation formula is as follows: Among them, (x i ,y i ,z i ) represents the coordinates of any point in the optimal ground rectangular coordinate system, (x e ,y e ,z e ) represents the coordinates of any point in the WGS84 earth-fixed coordinate system, (x0, y0, z0) represents the coordinates of the target point to be analyzed in the WGS84 earth-fixed coordinate system, M r Represents a rotation matrix.

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