Satellite-borne SAR all-zero Doppler guidance method, system, medium and equipment

Abstract

The invention provides a satellite-borne SAR all-zero Doppler guidance method and system, a medium and equipment, and the method comprises the steps: 1, building a small eccentricity rate SAR satellite orbit model, and deducing a Doppler center frequency mathematical expression at any position of an orbit according to the relative position relation between a satellite and a ground target; 2, establishing an angle relation between Doppler center frequency and SAR system two-dimensional electric scanning, and solving a scanning angle required by all-zero Doppler guidance; and step 3, all-zero Doppler guidance control is realized by setting the wave positions in the azimuth direction and the distance direction of the SAR system. The spaceborne SAR electric scanning all-zero Doppler guidance method disclosed by the invention can flexibly adapt to satellites of different scales and different orbits, realizes decoupling control of SAR loads and other subsystems of the satellites, reduces the influence on other loads, and guarantees the SAR imaging effect.

Description

Technical Field

[0001] The present invention relates to the technical field of spaceborne synthetic aperture radar, and in particular to a spaceborne SAR full zero Doppler guidance method, system, medium and equipment. Background Art

[0002] Synthetic aperture radar (SAR) is an active remote sensor working in the microwave band. It can image and monitor the earth all day and all weather. It is one of the main development directions of satellite imaging remote sensing. The Doppler characteristic of satellite-borne SAR is the main factor that determines the azimuth performance of the radar, and directly affects the azimuth resolution and PRF selection of the radar. Affected by factors such as the satellite's motion in orbit, the earth's rotation, and the orbital eccentricity, the beam pointing of the satellite-borne SAR antenna will deviate from the zero Doppler line and produce range migration. If it is not corrected, large errors will occur during azimuth compression, affecting the image quality. Therefore, high-resolution SAR satellites must use Doppler guidance control to reduce the Doppler center frequency and simplify the post-image processing process.

[0003] Currently, all SAR satellites in orbit suppress Doppler center frequency through one-dimensional yaw maneuver guidance or two-dimensional pitch yaw maneuver guidance, and have achieved good results. However, as satellite systems develop towards larger weights and more complex payload configurations, there are certain bottlenecks in Doppler guidance achieved through maneuvers.

[0004] The paper "Research on the Attitude Guidance Method of S-band SAR Satellite in Low-orbit Small Elliptical Orbit" by Aerospace Dongfanghong Satellite Co., Ltd. analyzed that after one-dimensional yaw traction under the circular orbit approximation model, the Doppler center frequency residual is in the order of hundreds of Hz. Then a SAR satellite attitude guidance method for low-orbit small elliptical orbit was proposed, which uses an instantaneous elliptical orbit model to further reduce the Doppler center frequency residual. The technical approach of this method relies on satellite attitude maneuvers, which is completely different from the content described in this invention.

[0005] Patent No. CN201310687784.5 of the Institute of Electronics of the Chinese Academy of Sciences discloses a satellite-borne synthetic aperture radar attitude guidance method. Compared with the traditional two-dimensional attitude guidance method, this method can reduce the Doppler center frequency of the echo data to near zero Hz at zero pitch angle or at a specific pitch angle through attitude maneuvers. This method mainly improves the requirements of payload imaging for the pitch axis angle, which is different from the technical path and purpose of the present invention.

[0006] Patent No. CN201710292249.8 of Beijing Space Vehicle General Design Department discloses a method for improving the on-orbit performance of SAR satellites based on electromechanical joint scanning. The method adopts electromechanical joint scanning to complement the satellite's attitude maneuverability and payload electronic scanning capability. The main purpose is to improve the image performance of on-orbit phased array satellites, which is different from the technical path and purpose of the present invention.

[0007] Patent No. CN202310050647.4 of the Institute of Space Information Innovation of the Chinese Academy of Sciences discloses a satellite-borne SAR Doppler guidance method that does not rely on satellite attitude control. The electronic scanning in the azimuth and pitch directions of the SAR is equivalent to replacing the one-dimensional yaw maneuver guidance of the traditional SAR system, which can effectively reduce the Doppler center frequency caused by the relative motion between the satellite and the ground target. However, due to the common eccentricity of the SAR satellite orbit, except for the perigee and apogee, the pitch attitude and rate of the satellite flying on the elliptical orbit at each position are different from the pitch attitude and rate at the corresponding position on the circular orbit, resulting in a large Doppler residual after the yaw guidance. Therefore, in the same way, this method has a large residual error, and this method converts and calculates the traditional maneuver guidance law to form a control law suitable for electronic scanning, but it has the disadvantages of large calculation amount and is not conducive to the realization of real-time calculation on the satellite, which is completely different from the content described in the present invention.

[0008] The paper "Electronic Scanning Doppler Center Guidance Method for Short-flight Dual-station Small Satellite Strip SAR" by Beijing Institute of Technology proposes an electronic scanning Doppler center guidance method for short-flight dual-station small satellite strip SAR. In view of the limitations of traditional one-dimensional yaw guidance for dual-base satellites, electronic scanning is used to solve the Doppler center frequency. It also converts the traditional attitude guidance rules, which has a large amount of calculation and is prone to residual errors, which is completely different from the content described in the present invention. Summary of the invention

[0009] In view of the defects in the prior art, the object of the present invention is to provide a space-borne SAR full zero-Doppler guidance method, system, medium and equipment.

[0010] The spaceborne SAR full zero Doppler guidance method provided by the present invention comprises:

[0011] Step 1: Establish a small eccentricity SAR satellite orbit model, and derive the mathematical expression of the Doppler center frequency at any position on the orbit based on the relative position relationship between the satellite and the ground target;

[0012] Step 2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electronic scanning, and solve for the scanning angle required for full zero Doppler guidance;

[0013] Step 3: Achieve full zero Doppler guidance control by setting the wave position in the azimuth and range directions of the SAR system.

[0014] Preferably, the step 1 comprises:

[0015] Step 1.1: Establish the satellite's position vector R in the geocentric inertial coordinate system s With velocity vector v s , and the position vector R of the target point T With velocity vector v T , the slant moment vector R between the satellite and the ground target, the angular velocity of the earth's rotation ω e , the satellite latitude argument is u, the orbit inclination is i, the eccentricity is e, the semi-major axis is a, the perigee argument is f, and the Doppler center frequency of the satellite is expressed as:

[0016]

[0017] Where R represents the slant moment length between the satellite and the ground target; represents the first-order differential of the skew moment vector R in time; λ represents the wavelength;

[0018] Step 1.2: The SAR antenna is pointed in the antenna coordinate system, with the origin at the center of mass of the antenna, the z-axis pointing to the center of the earth, and the unit vector i z ; The x-axis points to the direction of the satellite velocity, and the unit vector is i x , then:

[0019]

[0020] ω e =ω e (sinicosu·i x -sini·i y -cosiniu·i z )

[0021] Among them, R s Indicates the slant range length of the satellite position; v x Indicates i x The satellite velocity component in the direction v z Indicates i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the angular velocity of the Earth's rotation; i x 、i y 、i z are three unit vectors in the rectangular coordinate system.

[0022] Preferably, step 2 comprises:

[0023] Step 2.1: After two-dimensional electronic scanning, assume that the SAR antenna points to the unit vector Then we have:

[0024]

[0025] Among them, l, m, and n are the components on the three coordinate axes;

[0026]

[0027] Step 2.2: To achieve full zero Doppler steering, the Doppler center frequency f dc It is always 0. The requirements can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the lower viewing angle. The azimuth scanning angle is obtained as follows:

[0028]

[0029] Preferably, a two-dimensional coordinate table of each T / R channel is formed, and the coordinates of each antenna unit (x a ,y b ) The projection of the relative coordinate origin on the pointing angle is used to obtain the wave position of the SAR system in the azimuth and range directions, and the space-borne SAR electronic scanning full zero Doppler guidance is realized by two-dimensional electronic scanning. The projection d on the pointing angle a,b The calculation expression is:

[0030] d a,b =x jk l+y jk m

[0031] Among them, x jk ,y jk They respectively represent the components of the coordinates of the antenna unit in row j and column k relative to the origin channel on the x-axis and the y-axis.

[0032] The spaceborne SAR full zero Doppler guidance system provided by the present invention comprises:

[0033] Module M1: Establish a small eccentricity SAR satellite orbit model, and derive the mathematical expression of the Doppler center frequency at any position on the orbit based on the relative position relationship between the satellite and the ground target;

[0034] Module M2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electronic scanning, and solve for the scanning angle required for full zero Doppler guidance;

[0035] Module M3: By setting the wave position in the azimuth and range directions of the SAR system, full zero Doppler guidance control is achieved.

[0036] Preferably, the module M1 comprises:

[0037] Module M1.1: Establishing the satellite position vector R in the geocentric inertial coordinate system s With velocity vector v s , and the position vector R of the target point T With velocity vector v T , the slant moment vector R between the satellite and the ground target, the angular velocity of the earth's rotation ω e , the satellite latitude argument is u, the orbit inclination is i, the eccentricity is e, the semi-major axis is a, the perigee argument is f, and the Doppler center frequency of the satellite is expressed as:

[0038]

[0039] Where R represents the slant moment length between the satellite and the ground target; represents the first-order differential of the skew moment vector R in time; λ represents the wavelength;

[0040] Module M1.2: The SAR antenna is pointed in the antenna coordinate system, with the origin at the center of mass of the antenna, the z-axis pointing to the center of the earth, and the unit vector i z ; The x-axis points to the direction of the satellite velocity, and the unit vector is i x , then:

[0041]

[0042] ω e =ω e (sinicosu·i x -sini·i y -cosiniu·i z )

[0043] Among them, R s Indicates the slant range length of the satellite position; v x Indicates i x The satellite velocity component in the direction v z Indicates i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the angular velocity of the Earth's rotation; i x 、i y 、i z are three unit vectors in the rectangular coordinate system.

[0044] Preferably, the module M2 comprises:

[0045] Module M2.1: After two-dimensional electronic scanning, assume that the SAR antenna points to the unit vector Then we have:

[0046]

[0047] Among them, l, m, and n are the components on the three coordinate axes;

[0048]

[0049] Module M2.2: To achieve full zero Doppler guidance, the Doppler center frequency f dc It is always 0. The requirements can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the lower viewing angle. The azimuth scanning angle is obtained as follows:

[0050]

[0051] Preferably, a two-dimensional coordinate table of each T / R channel is formed, and the coordinates of each antenna unit (x a ,y b ) The projection of the relative coordinate origin on the pointing angle is used to obtain the wave position of the SAR system in the azimuth and range directions, and the space-borne SAR electronic scanning full zero Doppler guidance is realized by two-dimensional electronic scanning. The projection d on the pointing angle a,b The calculation expression is:

[0052] d a,b =x jk l+y jk m

[0053] Among them, x jk ,y jk They respectively represent the components of the coordinates of the antenna unit in row j and column k relative to the origin channel on the x-axis and the y-axis.

[0054] According to the computer-readable storage medium storing a computer program provided by the present invention, when the computer program is executed by a processor, the steps of the space-borne SAR all-zero Doppler guidance method are implemented.

[0055] The electronic device provided according to the present invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, the steps of the spaceborne SAR all-zero Doppler guidance method are implemented.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) The present invention can effectively reduce the information and function interaction between the spaceborne SAR payload and the satellite platform during operation, further decouple the spaceborne SAR payload design from the satellite platform design, and does not interfere with the operation of other payloads on the satellite;

[0058] (2) The present invention can achieve full zero Doppler guidance for circular orbits or small eccentricity orbits, which helps to further improve the imaging resolution of spaceborne SAR;

[0059] (3) The present invention reduces the requirements for the maneuverability of the satellite platform, helps to simplify the design, and does not need to specifically consider interference such as micro-vibration in the maneuvering state, effectively ensuring the stability of the SAR payload during operation.

[0060] (4) The present invention can simultaneously suppress the Doppler center frequency caused by factors such as the satellite's on-orbit motion, the earth's rotation, orbital eccentricity, and speed differences, and can provide technical support for the development of high-precision spaceborne SAR and multi-payload satellites. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] 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:

[0062] Figure 1 This is a schematic diagram of the geometric relationship between the satellite and the earth;

[0063] Figure 2 It is a schematic diagram of the SAR antenna coordinate system;

[0064] Figure 3 It is a diagram of the electric scanning angles in the azimuth and range directions in a specific embodiment;

[0065] Figure 4 It is a schematic diagram of the two-dimensional coordinates of each T / R channel;

[0066] Figure 5 The Doppler center frequency after electronic scanning guidance in the ideal case and considering the antenna pointing error (0.02°) in actual engineering;

[0067] Figure 6 This is a flow chart of the spaceborne SAR full zero Doppler guidance method of the present invention. DETAILED DESCRIPTION

[0068] 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.

[0069] Example 1

[0070] like Figure 6 The present invention provides a spaceborne SAR full zero Doppler guidance method implemented by electronic scanning, comprising:

[0071] Step 1: Establish a small eccentricity SAR satellite orbit (including circular orbit) model and derive the mathematical expression of the Doppler center frequency at any position of the elliptical orbit;

[0072] Step 2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electronic scanning, and solve for the scanning angle required for full zero Doppler guidance;

[0073] Step 3: Achieve full zero Doppler guidance control by setting the wave position in the azimuth and range directions of the SAR system.

[0074] This example uses MATLAB programming software to implement the zero-Doppler guidance of spaceborne SAR through the above scheme. The position vector R of the satellite is established in the geocentric inertial coordinate system. s With velocity vector v s ,like Figure 1 and Figure 2 , and the position vector R of the target point T With velocity vector v T In addition, the angular velocity of the Earth's rotation ω e , the satellite's latitude argument is u, the orbital inclination is i, the eccentricity is e, the semi-major axis is a, and the perigee argument is f.

[0075] The Doppler center frequency of the available satellite is:

[0076]

[0077] The SAR antenna is pointed in the satellite orbit coordinate system, with the origin at the satellite center of mass, the z-axis pointing to the center of the earth, and the unit vector i z , the x-axis points to the direction of the satellite velocity, and the unit vector is i x , then:

[0078]

[0079] ω e =ω e (sinicosu·i x -sini·i y -cosiniu·i z )

[0080] After two-dimensional electronic scanning, the SAR antenna points to the slant moment R direction between the satellite and the target point, and the SAR antenna points to the unit vector: Then we have:

[0081]

[0082] To achieve full zero Doppler guidance, it is necessary to ensure that f is always 0. This requirement can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the downward viewing angle, and the azimuth scanning angle can be expressed as:

[0083]

[0084] The following parameters are used as examples.

[0085]

[0086]

[0087] Substituting the data in the table into the above formula, the electronic scanning angle that satisfies the full zero Doppler guidance can be obtained as follows: Figure 3 shown.

[0088] Form a two-dimensional coordinate table for each T / R channel, such as Figure 4 , and calculate the value of each antenna unit (x a ,y b ) relative to the projection of the origin of the coordinate system on the pointing angle, the full zero Doppler guidance of the spaceborne SAR can be achieved through electronic scanning. The projection on the pointing angle d a,b The calculation expression is: a,b =x jk l+y jk m. Figure 5 , which is the Doppler center frequency after electronic scanning guidance in the ideal case and considering the antenna pointing error (0.02°) in actual engineering.

[0089] The range electronic scanning angle of the present invention is the same as the downward viewing angle, and the yaw direction of the satellite has no angle change, so it does not interfere with the pointing angle of the SAR in the range direction in the mission planning, and can eliminate the difference between the mission planning ground target and the actual imaging position caused by the traditional SAR guidance. The present invention uses the earth inertial coordinate system under the elliptical orbit to derive the mathematical expression of the Doppler center frequency at any position of the orbit. Compared with the traditional circular orbit model, it can accurately calculate the residual Doppler center frequency caused by the radial velocity of the satellite, providing a theoretical basis for achieving Doppler elimination. The present invention does not require the satellite attitude and orbit control subsystem to provide attitude maneuvers in the yaw and pitch directions, and the payload can maintain level flight during operation.

[0090] Example 2

[0091] The present invention also provides a spaceborne SAR full zero Doppler guidance system, which can be implemented by executing the process steps of the spaceborne SAR full zero Doppler guidance method, that is, those skilled in the art can understand the spaceborne SAR full zero Doppler guidance method as a preferred implementation of the spaceborne SAR full zero Doppler guidance system.

[0092] The satellite-borne SAR full-zero Doppler guidance system provided by the present invention comprises: module M1: establishing a small eccentricity SAR satellite orbit model, and deriving a mathematical expression of the Doppler center frequency at any position of the orbit according to the relative position relationship between the satellite and the ground target; module M2: establishing an angular relationship between the Doppler center frequency and the two-dimensional electronic scanning of the SAR system, and solving the scanning angle required for full-zero Doppler guidance; module M3: realizing full-zero Doppler guidance control by setting the wave position in the azimuth and range directions of the SAR system.

[0093] The module M1 comprises:

[0094] Module M1.1: Establishing the satellite position vector R in the geocentric inertial coordinate system s With velocity vector v s , and the position vector R of the target point T With velocity vector v T , the slant moment vector R between the satellite and the ground target, the angular velocity of the earth's rotation ω e , the satellite latitude argument is u, the orbit inclination is i, the eccentricity is e, the semi-major axis is a, the perigee argument is f, and the Doppler center frequency of the satellite is expressed as:

[0095]

[0096] Where R represents the slant moment length between the satellite and the ground target; represents the first-order differential of the skew moment vector R in time; λ represents the wavelength;

[0097] Module M1.2: The SAR antenna is pointed in the antenna coordinate system, with the origin at the center of mass of the antenna, the z-axis pointing to the center of the earth, and the unit vector i z ; The x-axis points to the direction of the satellite velocity, and the unit vector is i x , then:

[0098]

[0099] ω e =ω e (sinicosu·i x -sini·i y -cosiniu·i z )

[0100] Among them, R s Indicates the slant range length of the satellite position; v x Indicates i x The satellite velocity component in the direction v z Indicates i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω eIndicates the angular velocity of the Earth's rotation; i x 、i y 、i z are three unit vectors in the rectangular coordinate system.

[0101] The module M2 comprises:

[0102] Module M2.1: After two-dimensional electronic scanning, assume that the SAR antenna points to the unit vector Then we have:

[0103]

[0104] Among them, l, m, and n are the components on the three coordinate axes;

[0105]

[0106] Module M2.2: To achieve full zero Doppler guidance, the Doppler center frequency f dc It is always 0. The requirements can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the lower viewing angle. The azimuth scanning angle is obtained as follows:

[0107]

[0108] Form a two-dimensional coordinate table for each T / R channel, and calculate each antenna unit (x a ,y b ) The projection of the relative coordinate origin on the pointing angle is used to obtain the wave position of the SAR system in the azimuth and range directions, and the space-borne SAR electronic scanning full zero Doppler guidance is realized by two-dimensional electronic scanning. The projection d on the pointing angle a,b The calculation expression is:

[0109] d a,b =x jk l+y jk m

[0110] Among them, x jk ,y jk They respectively represent the components of the coordinates of the antenna unit in row j and column k relative to the origin channel on the x-axis and the y-axis.

[0111] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program 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, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing the method and structures within the hardware component.

[0112] 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 spaceborne SAR full zero Doppler guidance method, characterized in that: include: Step 1: Establish a small eccentricity SAR satellite orbit model, and derive the mathematical expression of the Doppler center frequency at any position on the orbit based on the relative position relationship between the satellite and the ground target; Step 2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electronic scanning, and solve for the scanning angle required for full zero Doppler guidance; Step 3: Achieve full zero Doppler guidance control by setting the wave position in the azimuth and range directions of the SAR system.

2. The spaceborne SAR full zero Doppler guidance method according to claim 1, characterized in that: The step 1 comprises: Step 1.1: Establish the satellite's position vector R in the geocentric inertial coordinate system s With velocity vector v s , and the position vector R of the target point T With velocity vector v T , the slant moment vector R between the satellite and the ground target, the angular velocity of the earth's rotation ω e , the satellite latitude argument is u, the orbit inclination is i, the eccentricity is e, the semi-major axis is a, the perigee argument is f, and the Doppler center frequency of the satellite is expressed as: Where R represents the slant moment length between the satellite and the ground target; represents the first-order differential of the skew moment vector R in time; λ represents the wavelength; Step 1.2: The SAR antenna is pointed in the antenna coordinate system, with the origin at the center of mass of the antenna, the z-axis pointing to the center of the earth, and the unit vector i z ; The x-axis points to the direction of the satellite velocity, and the unit vector is i x , then: ω e =ω e (synonymous·i x -here·i y -cosine·i z ) Among them, R s Indicates the slant range length of the satellite position; v x Indicates i x The satellite velocity component in the direction v z Indicates i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the angular velocity of the Earth's rotation; i x 、i y 、i z are three unit vectors in the rectangular coordinate system.

3. The spaceborne SAR full zero Doppler guidance method according to claim 2, characterized in that: The step 2 comprises: Step 2.1: After two-dimensional electronic scanning, assume that the SAR antenna points to the unit vector Then we have: Among them, l, m, and n are the components on the three coordinate axes; Step 2.2: To achieve full zero Doppler steering, the Doppler center frequency f dc It is always 0. The requirements can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the lower viewing angle. The azimuth scanning angle is obtained as follows:

4. The spaceborne SAR full zero Doppler guidance method according to claim 3, characterized in that: Form a two-dimensional coordinate table for each T / R channel, and calculate each antenna unit (x a ,y b ) The projection of the relative coordinate origin on the pointing angle is used to obtain the wave position of the SAR system in the azimuth and range directions, and the space-borne SAR electronic scanning full zero Doppler guidance is realized by two-dimensional electronic scanning. The projection d on the pointing angle a,b The calculation expression is: d a,b =x jk l+y jk m Among them, x jk ,y jk They respectively represent the components of the coordinates of the antenna unit in row j and column k relative to the origin channel on the x-axis and the y-axis.

5. A spaceborne SAR full zero Doppler guidance system, characterized in that: include: Module M1: Establish a small eccentricity SAR satellite orbit model, and derive the mathematical expression of the Doppler center frequency at any position on the orbit based on the relative position relationship between the satellite and the ground target; Module M2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electronic scanning, and solve for the scanning angle required for full zero Doppler guidance; Module M3: By setting the wave position in the azimuth and range directions of the SAR system, full zero Doppler guidance control is achieved.

6. The spaceborne SAR full zero Doppler guidance system according to claim 5, characterized in that: The module M1 comprises: Module M1.1: Establishing the satellite position vector R in the geocentric inertial coordinate system s With velocity vector v s , and the position vector R of the target point T With velocity vector v T , the slant moment vector R between the satellite and the ground target, the angular velocity of the earth's rotation ω e , the satellite latitude argument is u, the orbit inclination is i, the eccentricity is e, the semi-major axis is a, the perigee argument is f, and the Doppler center frequency of the satellite is expressed as: Where R represents the slant moment length between the satellite and the ground target; represents the first-order differential of the skew moment vector R in time; λ represents the wavelength; Module M1.2: The SAR antenna is pointed in the antenna coordinate system, with the origin at the center of mass of the antenna, the z-axis pointing to the center of the earth, and the unit vector i z ; The x-axis points to the direction of the satellite velocity, and the unit vector is i x , then: ω e =ω e (synonymous·i x -here·i y -cosine·i z ) Among them, R s Indicates the slant range length of the satellite position; v x Indicates i x The satellite velocity component in the direction v z Indicates i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the angular velocity of the Earth's rotation; i x 、i y 、i z are three unit vectors in the rectangular coordinate system.

7. The spaceborne SAR full zero Doppler guidance system according to claim 6, characterized in that: The module M2 comprises: Module M2.1: After two-dimensional electronic scanning, assume that the SAR antenna points to the unit vector Then we have: Among them, l, m, and n are the components on the three coordinate axes; Module M2.2: To achieve full zero Doppler guidance, the Doppler center frequency f dc It is always 0. The requirements can be met by setting the beam scanning angles α and β. The range scanning angle α is set according to the field of view requirement of the lower viewing angle. The azimuth scanning angle is obtained as follows:

8. The spaceborne SAR full zero Doppler guidance system according to claim 7, characterized in that: Form a two-dimensional coordinate table for each T / R channel, and calculate each antenna unit (x a ,y b ) The projection of the relative coordinate origin on the pointing angle is used to obtain the wave position of the SAR system in the azimuth and range directions, and the space-borne SAR electronic scanning full zero Doppler guidance is realized by two-dimensional electronic scanning. The projection d on the pointing angle a,b The calculation expression is: d a,b =x jk l+y jk m Among them, x jk ,y jk They respectively represent the components of the coordinates of the antenna unit in row j and column k relative to the origin channel on the x-axis and the y-axis.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the spaceborne SAR all-zero Doppler guidance method according to any one of claims 1 to 4 are implemented.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the computer program is executed by a processor, the steps of the spaceborne SAR all-zero Doppler guidance method according to any one of claims 1 to 4 are implemented.

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