Spaceborne sar full zero doppler guidance method, system, medium, and device

Abstract

The application provides a spaceborne SAR full zero Doppler guiding method, system, medium and equipment, comprising: step 1: establishing a small eccentricity SAR satellite orbit model, and deriving a Doppler center frequency mathematical expression at an arbitrary position of the orbit according to the relative position relationship between the satellite and the ground target; step 2: establishing the angle relationship between the Doppler center frequency and the two-dimensional electric scanning of the SAR system, and solving the scanning angle required for full zero Doppler guiding; and step 3: setting the wave positions in the azimuth direction and the range direction of the SAR system to realize full zero Doppler guiding control. The spaceborne SAR electric scanning full zero Doppler guiding method disclosed in the application can flexibly adapt to satellites of different scales and different orbits, realize decoupling control of the SAR load and other subsystems of the satellite, reduce the influence on other loads, and guarantee the SAR imaging effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of space-borne synthetic aperture radar, in particular to a space-borne SAR full zero Doppler guidance method, system, medium and equipment. BACKGROUND

[0002] Synthetic aperture radar (SAR) is an active remote sensor working in the microwave band, which can perform all-weather and all-day imaging and monitoring on the ground, and is one of the main development directions of satellite imaging remote sensing. The Doppler characteristic of space-borne SAR is the main factor determining the performance of the radar azimuth direction, which directly affects the radar azimuth resolution and the selection of PRF. Influenced by the motion of the satellite in orbit, the rotation of the earth, the eccentricity of the orbit and other factors, the beam pointing of the space-borne SAR antenna will deviate from the zero Doppler line, and distance migration will occur. If it is not corrected, a large error will be generated during azimuth compression, which will affect the image quality. Therefore, high-resolution SAR satellites must use Doppler guidance control to reduce the Doppler center frequency and simplify the image processing process.

[0003] At present, the SAR satellites in orbit all achieve the suppression of the Doppler center frequency through one-dimensional yaw maneuver guidance or two-dimensional pitch-yaw maneuver guidance, which has achieved good results. However, with the development of satellite systems towards larger weight and size, and more complex load configuration, the Doppler guidance achieved by maneuvering has certain bottlenecks.

[0004] The paper "Attitude Guidance Method of Low-Orbit Small-Elliptical-Orbit S-Band SAR Satellite" by Space East Satellite Co., Ltd. analyzes the residual Doppler center frequency after one-dimensional yaw traction under the approximate model of circular orbit, which is in the order of hundreds of Hz. Then a SAR satellite attitude guidance method for low-orbit small-elliptical-orbit is proposed, which uses the instantaneous elliptical orbit model to further reduce the residual Doppler center frequency. The technical approach of this method relies on satellite attitude maneuvering, which is completely different from the content described in the present application.

[0005] The patent CN201310687784.5 of the Institute of Electronics, Chinese Academy of Sciences discloses a space-borne synthetic aperture radar satellite 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 zero hertz or near zero hertz through attitude maneuvering under the condition of zero pitch angle or specific pitch angle. This method mainly aims at the requirements of load imaging on the pitch axis angle for improvement, which is different from the technical path and purpose of the present application.

[0006] CN201710292249.8 of Beijing Spacecraft General Design Department discloses a SAR satellite on-orbit performance improvement method based on electromechanical combined scanning, adopts electromechanical combined scanning, and uses the attitude maneuvering capability of the satellite and the load electric scanning capability as complementation, and the main purpose is to improve the image performance of the on-orbit phased array system satellite, which is different from the technical path and purpose of the present application.

[0007] CN202310050647.4 of the Chinese Academy of Sciences Aerospace Information Innovation Research Institute discloses a satellite-borne SAR Doppler guidance method independent of satellite attitude control, and the one-dimensional yaw maneuvering guidance of the traditional SAR system is equivalently replaced by electric scanning in the SAR azimuth direction and the pitch direction, which can effectively reduce the Doppler center frequency caused by the relative motion of the satellite and the ground target. However, due to the eccentricity of the SAR satellite orbit, the pitch attitude and speed at each position of the satellite flying on the elliptical orbit are different from those at the corresponding position on the circular orbit, except for the perigee and apogee, resulting in a large residual Doppler after yaw guidance. Therefore, the method has a large residual error, and the method is to transform the traditional maneuvering guidance law to form a control law suitable for electric scanning, but has the disadvantages of large calculation amount and being not conducive to real-time calculation on the satellite, which is completely different from the content of the present application.

[0008] The paper of Beijing University of Technology, "Electric Scanning Doppler Center Guidance Method for Strip SAR of Orderly Flying Double Station Small Satellite", proposes an electric scanning Doppler center guidance method for strip SAR of orderly flying double station small satellite. The method uses electric scanning to solve the Doppler center frequency, which is also a transformation of the traditional attitude guidance law, and has a large calculation amount and is prone to residual error, which is completely different from the content of the present application. SUMMARY

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

[0010] The satellite-borne SAR full zero Doppler guidance method provided by the present application comprises:

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

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

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

[0014] Preferably, the step 1 comprises:

[0015] Step 1.1: Establishing the position vector R of the satellite in the geocentric inertial coordinate system s and the velocity vector v s of the satellite, and the position vector R T and the velocity vector v T of the target point. e The slant range vector R between the satellite and the ground target, the angular velocity ω of the earth rotation, the satellite latitude amplitude u, the orbit inclination i, the eccentricity e, the semi-major axis a, and the perigee amplitude f are obtained.

[0016]

[0017] wherein R represents the slant range length between the satellite and the ground target; represents the first order differential of the slant range vector R with respect to time; and λ represents the wavelength.

[0018] Step 1.2: The pointing of the SAR antenna is established in the antenna coordinate system, the origin of which is located at the centroid of the antenna, the z-axis points to the geocenter, and the unit vector is i z ; the x-axis points to the satellite velocity direction, and the unit vector is i x , and thus:

[0019]

[0020] ω e = ω e (sin i cos u·i x -sin i·i y -cos i u·i z )

[0021] wherein R s represents the slant range length of the satellite position; v x represents the satellite velocity component in the i x direction; v z represents the satellite velocity component in the i z direction; μ represents the earth gravitational constant; ω e represents the earth rotation angular velocity; i x , i y , and i z are three unit vectors of the rectangular coordinate system.

[0022] Preferably, the step 2 comprises:

[0023] Step 2.1: After two-dimensional electric scanning, let the unit vector of the SAR antenna pointing direction be Then we have:

[0024]

[0025] Wherein, l, m, n are components on three coordinate axes;

[0026]

[0027] Step 2.2: To realize the full zero Doppler guidance, the Doppler center frequency f dc should be always 0, which can be satisfied by setting the beam scanning angles α and β, wherein the distance scanning angle α is set according to the field of view of the downward angle, and the azimuth scanning angle is obtained as:

[0028]

[0029] Preferably, a two-dimensional coordinate table of each T / R channel is formed, and the projection of each antenna element (x a , y b ) on the pointing angle relative to the coordinate origin is calculated by the following formula to obtain the wave positions of the SAR system in the azimuth and distance directions, so as to realize the full zero Doppler guidance of the spaceborne SAR electric scanning in two-dimensional electric scanning, and the calculation expression of the projection d a,b on the pointing angle is:

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

[0031] Wherein, x jk , y jk respectively represent the components of the coordinates of the antenna element in the jth row and kth column relative to the coordinate origin channel on the x-axis and y-axis.

[0032] According to the spaceborne SAR full zero Doppler guidance system provided by the application, comprising:

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

[0034] Module M2: establishing the angle relationship between the Doppler center frequency and the two-dimensional electric scanning of the SAR system, and solving the scanning angle required for the full zero Doppler guidance;

[0035] Module M3: realizing the full zero Doppler guidance control by setting the wave positions of the SAR system in the azimuth and distance directions.

[0036] Preferably, the module M1 comprises:

[0037] Module M1.1: Establishing the position vector R of the satellite in the geocentric inertial coordinate system s and the velocity vector v s , and the position vector R of the target point T and the velocity vector v T , the slant range vector R between the satellite and the ground target, the angular velocity ω of the earth rotation e , the satellite latitude amplitude u, the orbit inclination i, the eccentricity e, the semi-major axis a, the perigee amplitude f, the Doppler center frequency of the satellite, the expression is:

[0038]

[0039] wherein R represents the slant range length between the satellite and the ground target; represents the first order differential of the slant range vector R with respect to time; λ represents the wavelength;

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

[0041]

[0042] ω e = ω e (sin i cos u · i x -sin i · i y -cos i u · i z )

[0043] wherein R s represents the slant range length of the satellite position; v x represents the satellite velocity component in the i x direction; v z represents the satellite velocity component in the i z direction; μ represents the earth gravity constant; ω e represents the earth rotation angular velocity; i x , i y , i z are three unit vectors of the rectangular coordinate system.

[0044] Preferably, the module M2 comprises:

[0045] Module M2.1: After two-dimensional electrical scanning, the SAR antenna pointing unit vector is , then:

[0046]

[0047] wherein, l, m, n are components on three coordinate axes;

[0048]

[0049] Module M2.2: To achieve the full zero Doppler guidance, the Doppler center frequency f dc is always 0, and the requirements can be met by setting the beam scanning angles a and b, wherein the distance scanning angle a is set according to the field of view of the downward angle, and the azimuth scanning angle b is obtained as follows:

[0050]

[0051] Preferably, a two-dimensional coordinate table of each T / R channel is formed, and the projection of each antenna element (x a ,y b ) on the pointing angle relative to the coordinate origin is calculated to obtain the wave position of the azimuth and the distance of the SAR system, so as to realize the full zero Doppler guidance of the spaceborne SAR electric scanning by two-dimensional electric scanning, and the calculation expression of the projection d a,b on the pointing angle is as follows:

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

[0053] wherein, x jk , y jk represent the components of the coordinates of the antenna element in the jth row and the kth column relative to the coordinate origin on the x-axis and the y-axis, respectively.

[0054] The computer readable storage medium storing the computer program provided by the application, when the computer program is executed by the processor, realizes the steps of the spaceborne SAR full zero Doppler guidance method.

[0055] The electronic device provided by the application comprises a memory, a processor and a computer program stored on the memory and executable on the processor, and when the computer program is executed by the processor, realizes the steps of the spaceborne SAR full zero Doppler guidance method.

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

[0057] (1) The application can effectively reduce the information and function interaction between the spaceborne SAR load and the satellite platform during the working of the spaceborne SAR load, further realizes the decoupling of the spaceborne SAR load design and the satellite platform design, and does not interfere with the work of other loads on the satellite;

[0058] (2) The application can realize the full zero Doppler guidance for circular orbits or small eccentricity orbits, which is helpful to further improve the spaceborne SAR imaging resolution.

[0059] (3) The application reduces the requirement for the maneuverability of the satellite platform, helps to simplify the design, and does not need to specially consider the interference such as micro-vibration in the maneuvering state, and effectively guarantees the stability and other indexes of the SAR load during operation;

[0060] (4) The application can simultaneously inhibit the Doppler center frequency caused by the motion of the satellite in orbit, the rotation of the earth, the eccentricity of the orbit, the speed difference and other factors, and can provide technical support for the development of high-precision satellite SAR and multi-load satellites. BRIEF DESCRIPTION OF DRAWINGS

[0061] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0062] Figure 1 is a schematic diagram of the star-ground geometric relationship;

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

[0064] Figure 3 is an azimuth and range electric scanning angle diagram in a specific embodiment;

[0065] Figure 4 is a two-dimensional coordinate diagram of each T / R channel;

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

[0067] Figure 6 is a flowchart of the satellite-borne SAR full-zero Doppler guidance method of the application. DETAILED DESCRIPTION

[0068] The application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the application, a number of changes and improvements can be made. These all belong to the protection scope of the application.

[0069] Example 1

[0070] As Figure 6 , the application provides a satellite-borne SAR full-zero Doppler guidance method realized by electric scanning, comprising:

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

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

[0073] Step 3: By setting the wave position in the azimuth direction and the range direction of the SAR system, full zero Doppler guidance control is realized.

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

[0075] The Doppler center frequency of the satellite can be obtained as follows:

[0076]

[0077] The pointing direction of the SAR antenna is established in the satellite orbital coordinate system, with the origin at the satellite center of mass, the z-axis pointing to the Earth's center, and the unit vector i z , the x-axis pointing to the satellite velocity direction, and the unit vector i x , so we have:

[0078]

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

[0080] After two-dimensional electrical scanning, the SAR antenna points in the direction of the satellite and the target point, and the SAR antenna pointing unit vector is , so we have:

[0081]

[0082] To realize full zero Doppler guidance, it is necessary to ensure that f is always 0, which can be achieved by setting the beam scanning angles α and β. The range direction scanning angle α is set according to the field of view of the downward-looking angle, while the azimuth direction scanning angle β can be expressed as:

[0083]

[0084] The following parameters are used for the example.

[0085]

[0086]

[0087] The data in the table is substituted into the above formula, and the electrical scanning angle satisfying the full zero Doppler guidance is as shown in the following table. Figure 3

[0088] A two-dimensional coordinate table of each T / R channel is formed, as shown in the following table. Figure 4 The projection of each antenna element (x a ,y b ) on the pointing angle relative to the coordinate origin is calculated according to the following formula, so that the full zero Doppler guidance of the spaceborne SAR through electrical scanning is realized.The calculation expression of the projection d a,b on the pointing angle is d a,b =x jk l+y jk m. Figure 5 , and the Doppler center frequency after the electrical scanning guidance considering the antenna pointing error (0.02°) in the actual engineering is shown in the following table.

[0089] The distance electrical scanning angle of the present application is the same as the downward angle, and there is no angle change in the satellite yaw direction, so it does not interfere with the pointing angle of the SAR in the distance direction in the task planning, and can eliminate the difference between the task planning ground target and the actual imaging position caused by the traditional SAR guidance. The present application uses the earth inertial coordinate system in the elliptical orbit to derive the mathematical expression of the Doppler center frequency at any position on the orbit, which can accurately calculate the residual Doppler center frequency caused by the satellite radial velocity compared with the traditional circular orbit model, and provides a theoretical basis for realizing Doppler elimination. The present application does not need the satellite attitude control subsystem to provide the yaw and pitch attitude maneuvering, and can keep level flight during the load operation.

[0090] Embodiment 2

[0091] The present application also provides a spaceborne SAR full zero Doppler guidance system, which can be realized by executing the flow steps of the spaceborne SAR full zero Doppler guidance method, that is, the spaceborne SAR full zero Doppler guidance method can be understood by those skilled in the art as the preferred embodiment of the spaceborne SAR full zero Doppler guidance system.

[0092] The satellite-borne SAR full zero Doppler guiding system comprises: module M1: a small eccentricity SAR satellite orbit model is established, and a Doppler center frequency mathematical expression at an arbitrary position on the orbit is derived according to the relative position relationship between the satellite and the ground target; module M2: a relationship between the Doppler center frequency and the two-dimensional electric scanning angle of the SAR system is established, and a scanning angle required for full zero Doppler guiding is solved; and module M3: full zero Doppler guiding control is realized by setting the wave positions in the azimuth direction and the range direction of the SAR system.

[0093] The module M1 comprises:

[0094] Module M1.1: a position vector R of the satellite is established in the geocentric inertial coordinate system s and a velocity vector v s , a position vector R of the target point T and a velocity vector v T , an inclined moment vector R of the satellite and the ground target, an angular velocity ω of the earth rotation e , a satellite latitude amplitude angle u, an orbit inclination angle i, an eccentricity e, a semi-major axis a, and a perigee amplitude angle f, and a Doppler center frequency of the satellite is obtained, and the expression is:

[0095]

[0096] Wherein, R represents the inclined moment length of the satellite and the ground target; represents the first order differential of the inclined moment vector R with respect to time; and λ represents the wavelength.

[0097] Module M1.2: the pointing of the SAR antenna is established in the antenna coordinate system, the origin is located at the mass center of the antenna, the z-axis points to the geocenter, and the unit vector is i z ; the x-axis points to the satellite speed direction, and the unit vector is i x , and the following equation is obtained:

[0098]

[0099] ω e = ω e (sin i cos u · i x -sin i · i y -cos i sin u · i z )

[0100] Wherein, R s represents the inclined distance length of the satellite position; v x represents the satellite speed component in the i x direction; v z represents the satellite speed component in the i z direction; and μ represents the earth gravity constant; and ω edenotes the magnitude of the earth rotation angular velocity; i x y z are three unit vectors of the rectangular coordinate system.

[0101] The module M2 comprises:

[0102] Module M2.1: after two-dimensional electrical scanning, set the SAR antenna pointing unit vector as Then:

[0103]

[0104] wherein l, m, n are the components on three coordinate axes.

[0105]

[0106] Module M2.2: to realize the full zero Doppler guidance, the Doppler center frequency f dc must be always 0, which can be met by setting the beam scanning angles a and b, wherein the distance scanning angle a is set according to the field of view requirement of the downward angle, and the azimuth scanning angle b is obtained as:

[0107]

[0108] Form a two-dimensional coordinate table of each T / R channel, and calculate the projection of each antenna unit (x a , y b ) on the pointing angle relative to the coordinate origin to obtain the azimuth and range of the SAR system, so as to realize the full zero Doppler guidance of the spaceborne SAR electrical scanning by two-dimensional electrical scanning, and the calculation expression of the projection d a,b on the pointing angle is:

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

[0110] wherein x jk , y jk respectively represent the components of the coordinates of the jth row and kth column antenna unit relative to the coordinate origin channel on the x axis and y axis.

[0111] ​​Those skilled in the art know that, in addition to implementing the system, device and each module thereof provided by the present application in the form of pure computer readable program code, the same program can also be implemented in the form of logic gate, switch, special integrated circuit, programmable logic controller and embedded microcontroller, etc. by logically programming the method steps. Therefore, the system, device and each module thereof provided by the present application can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures in the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing methods and structures in the hardware component.

[0112] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily without conflict.

Claims

1. A spaceborne SAR all-zero Doppler guidance method, characterized in that, include: Step 1: Establish a small eccentricity SAR satellite orbit model. Based on the relative positional relationship between the satellite and the ground target, derive the mathematical expression for the Doppler center frequency at any position in the orbit. Step 2: Establish the relationship between the Doppler center frequency and the angle of the SAR system's two-dimensional electrical scan, and solve for the scanning angle required for all-zero Doppler guidance; Step 3: Achieve all-zero Doppler guidance control by setting the azimuth and range positions of the SAR system; Step 1 includes: 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, and the angular velocity ω of the Earth's rotation. e Given a satellite with latitude argument u, orbital inclination i, eccentricity e, semi-major axis a, and perigee argument f, the Doppler center frequency of the satellite is expressed as: Where R represents the slant length between the satellite and the ground target; λ represents the first derivative of the slope vector R in time; λ represents the wavelength. Step 1.2: The pointing of the SAR antenna is established in the antenna coordinate system, with the origin located at the antenna's centroid, the z-axis pointing towards the Earth's center, and the unit vector being i. z The x-axis points in the direction of the satellite's velocity, with a unit vector of i. x Then we have: ω e =ω e (synonymous·i x -here·i y -cosine·i z ) Among them, R s The slant range length representing the satellite's position; v x Indicate i x The satellite velocity component in the direction; v z Indicate i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the magnitude of the Earth's angular velocity of rotation; i x i y i z Three unit vectors in a rectangular coordinate system; Step 2 includes: Step 2.1: After using two-dimensional electronic scanning, let the SAR antenna point to the unit vector as... Then we have: Where l, m, and n are the components on the three coordinate axes; Step 2.2: To achieve all-zero Doppler guidance, the Doppler center frequency f must be guaranteed. dc The value is always 0. The 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. The azimuth scanning angle is then obtained as follows:

2. The spaceborne SAR all-zero Doppler guidance method according to claim 1, characterized in that, A two-dimensional coordinate table is generated for each T / R channel, and the coordinates of each antenna element (x) are calculated using the following formula. a ,y b The projection of the relative coordinate origin onto the pointing angle is used to obtain the azimuth and range positions of the SAR system. Two-dimensional electronic scanning is used to achieve zero-Doppler guidance for spaceborne SAR electronic scanning. The projection d onto the pointing angle is... a,b The calculation expression is: d a,b =x jk l+y jk m Where, x jk y jk These represent the x-axis and y-axis components of the coordinates of the antenna element in row j and column k relative to the origin channel, respectively.

3. A spaceborne SAR all-zero Doppler guidance system, characterized in that, include: Module M1: Establish a small eccentricity SAR satellite orbit model, and derive the mathematical expression for the Doppler center frequency at any position in 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 electrical scan, and solve for the scanning angle required for all-zero Doppler guidance; Module M3: Achieves all-zero Doppler guidance control by setting the azimuth and range positions of the SAR system; The module M1 includes: Module M1.1: 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, and the angular velocity ω of the Earth's rotation. e Given a satellite with latitude argument u, orbital inclination i, eccentricity e, semi-major axis a, and perigee argument f, the Doppler center frequency of the satellite is expressed as: Where R represents the slant length between the satellite and the ground target; λ represents the first derivative of the slope vector R in time; λ represents the wavelength. Module M1.2: The pointing of the SAR antenna is established in the antenna coordinate system, with the origin located at the antenna's centroid, the z-axis pointing towards the Earth's center, and the unit vector being i. z The x-axis points in the direction of the satellite's velocity, with a unit vector of i. x Then we have: ω e =ω e (synonymous·i x -here·i y -cosine·i z ) Among them, R s The slant range length representing the satellite's position; v x Indicate i x The satellite velocity component in the direction; v z Indicate i z The satellite velocity component in the direction; μ represents the Earth's gravitational constant; ω e Indicates the magnitude of the Earth's angular velocity of rotation; i x i y i z Three unit vectors in a rectangular coordinate system; The module M2 includes: Module M2.1: After adopting two-dimensional electronic scanning, let the SAR antenna point to the unit vector as... Then we have: Where l, m, and n are the components on the three coordinate axes; Module M2.2: To achieve all-zero Doppler guidance, the Doppler center frequency f must be guaranteed. dc The value is always 0. The 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. The azimuth scanning angle is then obtained as follows:

4. The spaceborne SAR all-zero Doppler guidance system according to claim 3, characterized in that, A two-dimensional coordinate table is generated for each T / R channel, and the coordinates of each antenna element (x) are calculated using the following formula. a ,y b The projection of the relative coordinate origin onto the pointing angle is used to obtain the azimuth and range positions of the SAR system. Two-dimensional electronic scanning is used to achieve zero-Doppler guidance for spaceborne SAR electronic scanning. The projection d onto the pointing angle is... a,b The calculation expression is: d a,b =x jk l+y jk m Where, x jk y jk These represent the x-axis and y-axis components of the coordinates of the antenna element in row j and column k relative to the origin channel, respectively.

5. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the spaceborne SAR all-zero Doppler guidance method as described in claim 1 or 2.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is executed by the processor, it implements the steps of the spaceborne SAR all-zero Doppler guidance method as described in claim 1 or 2.

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