Method for planning imaging attitudes of main and auxiliary satellite platforms of distributed SAR (Synthetic Aperture Radar)

Abstract

The invention discloses a main and auxiliary satellite platform imaging attitude planning method of a distributed SAR (Synthetic Aperture Radar), and relates to the technical field of distributed satellite imaging. The equivalent virtual center satellite is introduced, a complete attitude traction correction scheme for transmitting the main satellite and receiving the auxiliary satellite of the distributed SAR system is given based on the equivalent virtual center satellite, and the purpose that the Doppler frequency of distributed SAR echoes is kept unchanged in the distance direction and is constantly zero is achieved. According to the method disclosed by the invention, the Doppler characteristic of the distributed SAR echo is ensured to have a zero value and is kept unchanged along the distance direction, and meanwhile, the high overlapping of footprint coverage areas of a transmitting beam and a receiving beam is ensured to be realized to the greatest extent; therefore, the gain loss caused by the offset of the transmitting and receiving beams is avoided, and the echo signal-to-noise ratio and the image quality of an observation scene can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed satellite imaging, and in particular to an imaging attitude planning method for a primary and secondary satellite platform of a distributed SAR. Background Art

[0002] Currently, Synthetic Aperture Radar (SAR), as an active remote sensing sensor, enables all-day, all-weather Earth observation and imaging, making it a crucial tool for addressing resource exploration, environmental protection, disaster warning, and national defense. As the demand for Earth observation continues to grow, SAR satellite applications are evolving from single-mission capabilities to multi-task capabilities such as high-resolution imaging, elevation inversion, and moving target tracking. However, the observation capabilities of traditional single-satellite SAR are limited, necessitating the use of distributed SAR to achieve these functions.

[0003] Distributed SAR places the SAR system's transmit and receive antennas on separate satellite platforms. Each satellite flies in a formation and works collaboratively. This system not only offers the all-day, all-weather Earth observation capabilities of single-satellite SAR, but also boasts the advantages of spatial dimensionality and information complementarity.

[0004] In the spatial dimension, distributed SAR can overcome the contradiction between range mapping width and azimuth resolution, obtaining high-resolution images of wide mapping scenes. Secondly, it can achieve three-dimensional terrain mapping in a single flight and obtain a digital elevation model (DEM) of the observed scene. Using tomography technology for distributed SAR, through flexible baseline configuration between satellites, can avoid the overlap effect in interferometric SAR (InSAR) technology and simultaneously achieve three-dimensional imaging. Combining tomography technology with compressed sensing (CS) technology can increase the high-dimensional resolution of traditional tomography SAR by an order of magnitude, which makes the application of distributed SAR in three-dimensional terrain mapping even broader.

[0005] In terms of information, distributed SAR can improve ground moving target detection (GMTI) performance. Because the echoes of GMTIs are obscured by ground clutter, single-satellite SAR is less effective in detecting slow-moving targets. However, distributed SAR utilizes multi-channel processing techniques, including clutter cancellation, spatiotemporal filtering, or spatial spectral processing, to significantly improve the signal-to-clutter-and-noise ratio (SCNR) of the echo signal. This reduces the minimum detectable velocity of GMTIs and increases the probability of detecting slow-moving targets. Secondly, distributed SAR has a higher spatial sampling rate, which facilitates the acquisition of more information about the target. Finally, through a multi-baseline configuration in range and azimuth, each satellite in the system can obtain non-backscattered signals from the same target from multiple perspectives. The spectrum in the range and azimuth directions exhibits a mutually expanding characteristic. This broadening of the signal spectrum translates to improved spatial resolution. Therefore, distributed SAR can achieve higher image resolution and achieve super-resolution imaging.

[0006] To effectively capture and realize the aforementioned advantages of distributed SAR, it is necessary to ensure the coordinated attitude of the transmitting and receiving satellites during imaging. Existing satellite platform yaw-pitch traction is typically for single-satellite SAR, which is not suitable for distributed SAR. Therefore, a joint attitude traction method for the transmitting and receiving platforms of distributed SAR is urgently needed. Summary of the Invention

[0007] Based on this, it is necessary to provide an imaging attitude planning method for the main and auxiliary satellite platforms of distributed SAR to address the above technical problems.

[0008] The present invention adopts the following technical solutions:

[0009] The present invention provides a distributed SAR primary and secondary satellite platform imaging attitude planning method, comprising:

[0010] Determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite;

[0011] According to the position vector and velocity vector of the equivalent virtual center satellite, the attitude traction three-axis Euler angle of the equivalent virtual center satellite corresponding to the sub-satellite point view of the observation scene under the satellite platform rotation is determined by the single-satellite SAR yaw traction method;

[0012] According to the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation, the three-axis pointing vector of the equivalent virtual center satellite is determined to determine the proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene;

[0013] According to the position vector, proximal vector, distal vector of the equivalent virtual central satellite and the position vector of the launching main satellite, the pitch plane of the launching main satellite's transmit beam covering the observation scene is determined to determine the three-axis pointing vector of the launching main satellite; according to the three-axis pointing vector, position vector and velocity vector of the launching main satellite, the three-axis Euler angle of the attitude traction of the launching main satellite is obtained;

[0014] Based on the position vector and three-axis pointing vector of the equivalent virtual center satellite, the azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite is determined. The target position is searched on the intersection line of the azimuth tangent plane and the earth's surface, with the Doppler frequency of the bistatic echo of the receiving beam of the auxiliary satellite covering the near and far ends of the observation scene being zero as a constraint.

[0015] With the constraint that the vector of the receiving auxiliary satellite pointing to the target position is within the pitch plane of the receiving auxiliary satellite, the three-axis pointing vector of the receiving auxiliary satellite is determined according to the target position and the position vector of the receiving auxiliary satellite; the attitude traction three-axis Euler angle of the receiving auxiliary satellite is obtained according to the three-axis pointing vector, position vector and velocity vector of the receiving auxiliary satellite.

[0016] Optionally, determining the position vector and velocity vector of an equivalent virtual central satellite of the transmitting primary satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting primary satellite and the position vector and velocity vector of the receiving auxiliary satellite specifically includes:

[0017] Determine the position vectors of the equivalent virtual central satellites of the transmitting main satellite and the receiving auxiliary satellite according to the arithmetic mean of the position vectors of the transmitting main satellite and the position vectors of the receiving auxiliary satellite;

[0018] The velocity vectors of the equivalent virtual central satellites of the transmitting main satellite and the receiving auxiliary satellite are determined according to the arithmetic mean of the position vector of the transmitting main satellite and the velocity vector of the receiving auxiliary satellite.

[0019] Optionally, the determining the three-axis pointing vector of the equivalent virtual center satellite according to the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation, so as to determine the proximal vector and the distal vector of the equivalent virtual center satellite pointing to the observation scene, specifically includes:

[0020] The three-axis pointing vector of the equivalent virtual center satellite is determined by the following formula based on the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation:

[0021]

[0022] The proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene are determined according to the three-axis pointing vector of the equivalent virtual center satellite using the following formula:

[0023]

[0024] in, and are the X-axis, Y-axis and Z-axis pointing vectors of the equivalent virtual center satellite in the LVLH coordinate system, M roll 、M pitch and M yaw are the roll, pitch and yaw rotation matrices of the equivalent virtual center satellite, θ roll is the roll traction angle of the equivalent virtual center satellite, θ pitch is the pitch pull angle of the equivalent virtual central satellite, θ yaw is the yaw pull angle of the equivalent virtual center satellite, is the proximal vector of the equivalent virtual center satellite pointing to the observation scene, is the far-end vector of the equivalent virtual central satellite pointing to the observation scene, θ n and θ f It is the offset angle of the sub-satellite point viewing angle at the near and far ends of the observation scene relative to the center of the observation scene.

[0025] Optionally, determining the pitch plane in which the transmit beam of the transmitting main satellite covers the observation scene based on the position vector, the proximal vector, the distal vector, and the position vector of the transmitting main satellite of the equivalent virtual central satellite specifically includes:

[0026] According to the position vector, the proximal vector and the distal vector of the equivalent virtual center satellite, the intersection points of the proximal vector and the distal vector with the earth's surface are determined;

[0027] Determine the vector from the launch main satellite to the two intersection points according to the position vector, the proximal vector and the distal vector of the launch main satellite pointing to the intersection points with the earth's surface respectively;

[0028] The vector from the launch main satellite to the two intersection points and the position vector of the launch main satellite are constrained to be within the pitch plane of the launch main satellite's transmission beam covering the observation scene, and the pitch plane of the launch main satellite's transmission beam covering the observation scene is determined.

[0029] Optionally, determining the three-axis pointing vector of the launching main satellite specifically includes:

[0030] With the constraint that the X-axis pointing vector of the launching main satellite in the LVLH coordinate system is perpendicular to the pitch plane of the launching main satellite's transmission beam covering the observation scene, the X-axis pointing vector corresponding to the launching main satellite operating in the left-side viewing condition or the right-side viewing condition is determined according to the vectors from the launching main satellite to the two intersection points.

[0031] The Z-axis pointing vector of the launched main satellite is determined by solving the problem of determining the Z-axis pointing vector of the launched main satellite, with the constraint that the intersection of the Z-axis pointing vector of the launched main satellite and the earth's surface is located in the antenna beam azimuth plane of the equivalent virtual central satellite.

[0032] According to the X-axis pointing vector and the Z-axis pointing vector of the launched main satellite, the Y-axis pointing vector of the launched main satellite is determined by the right-hand rule.

[0033] Optionally, determining the azimuth tangent planes of the equivalent virtual center satellite pointing to the near end and the far end of the observation scene according to the position vector and the three-axis pointing vector of the equivalent virtual center satellite specifically includes:

[0034] According to the viewing angle width of the observation scene and the three-axis pointing vector of the equivalent virtual center satellite, the normal vectors of the azimuth tangent planes of the equivalent virtual center satellite receiving beam at the near end and the far end of the observation scene are determined respectively;

[0035] The azimuth tangent plane pointing to the near end of the observation scene by the equivalent virtual center satellite is determined based on the constraints that the position vector of the equivalent virtual center satellite is located at the near end azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the near end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the near end of the observation scene.

[0036] With the constraints that the position vector of the equivalent virtual center satellite is located in the far azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the far end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the far end of the observation scene, the azimuth tangent plane pointing to the far end of the observation scene by the equivalent virtual center satellite is determined.

[0037] The present invention provides a distributed SAR primary and secondary satellite platform imaging attitude planning device, comprising:

[0038] An equivalent module is used to determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite;

[0039] The equivalent single-satellite traction module is used to determine the attitude traction three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation sequence corresponding to the sub-satellite point perspective of the observation scene through the single-satellite SAR yaw traction method based on the position vector and velocity vector of the equivalent virtual center satellite;

[0040] A vector determination module is used to determine the three-axis pointing vector of the equivalent virtual center satellite according to the attitude towing three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation sequence, so as to determine the proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene;

[0041] The first traction planning module is used to determine the pitch plane of the launch main satellite's transmit beam covering the observation scene based on the position vector, proximal vector, distal vector of the equivalent virtual central satellite and the position vector of the launch main satellite, so as to determine the three-axis pointing vector of the launch main satellite; and obtain the three-axis Euler angle of the attitude traction of the launch main satellite based on the three-axis pointing vector, position vector and velocity vector of the launch main satellite;

[0042] A search module is used to determine an azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite based on the position vector and the three-axis pointing vector of the equivalent virtual center satellite, and search for a target position on the intersection line of the azimuth tangent plane and the earth's surface, with the Doppler frequency of the bistatic echo of the receiving beam of the auxiliary satellite covering the near and far ends of the observation scene being zero as a constraint;

[0043] The second traction planning module is used to determine the three-axis pointing vector of the receiving auxiliary satellite according to the target position and the position vector of the receiving auxiliary satellite, with the vector of the receiving auxiliary satellite pointing to the target position being within the pitch plane of the receiving auxiliary satellite as a constraint; and obtain the three-axis Euler angle of the attitude traction of the receiving auxiliary satellite according to the three-axis pointing vector, position vector and velocity vector of the receiving auxiliary satellite.

[0044] The present invention provides a computer-readable storage medium, wherein the storage medium stores a computer program, and when the computer program is executed by a processor, the imaging attitude planning method of the primary and secondary satellite platforms of the distributed SAR is implemented.

[0045] The present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the imaging attitude planning method for the primary and secondary satellite platforms of the distributed SAR is implemented.

[0046] At least one of the above technical solutions adopted by the present invention can achieve the following beneficial effects:

[0047] The present invention introduces an equivalent virtual central satellite, and based on this, provides a complete distributed SAR system attitude traction correction scheme for the transmitting main satellite and the receiving auxiliary satellite, achieving the goal of keeping the Doppler frequency of the distributed SAR echo constant and constant at zero along the range direction, and realizing the maximum decoupling of the SAR echo in the range and azimuth directions. While ensuring that the Doppler characteristics of the distributed SAR echo have zero value and remain unchanged along the range direction, the present invention also ensures to the greatest extent that the high overlap of the footprint coverage area of the transmitting beam and the receiving beam is achieved, thereby avoiding the gain loss caused by the offset of the transmitting and receiving beams, and can greatly improve the echo signal-to-noise ratio and image quality of the observation scene. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0049] Figure 1 A schematic diagram of the yaw-pitch traction correction attitude of a satellite platform for a single-satellite SAR provided by the present invention;

[0050] Figure 2 A schematic flow chart of a method for imaging attitude planning of a primary and secondary satellite platform for a distributed SAR provided by the present invention;

[0051] Figure 3 A schematic diagram of the attitude traction design process of the transmitting main satellite and the receiving auxiliary satellite of the distributed SAR system provided by the present invention;

[0052] Figure 4 A schematic diagram of a design process for determining a three-axis attitude traction method for launching a main satellite provided by the present invention;

[0053] Figure 5 A schematic diagram of a design process for determining a three-axis attitude traction method for receiving an auxiliary satellite provided by the present invention;

[0054] Figure 6 A schematic diagram of the beam footprint of a transmitting and receiving antenna after attitude pulling of a transmitting and receiving main and auxiliary satellites provided by the present invention;

[0055] Figure 7 A schematic diagram of how the satellite latitude argument changes over time provided by the present invention;

[0056] Figure 8 A schematic diagram of the latitude argument of a selected track of data provided by the present invention;

[0057] Figure 9 A schematic diagram of a change in the number of six tracks within one track time provided by the present invention;

[0058] Figure 10 A schematic diagram of the attitude yaw and traction angle of an equivalent virtual central satellite provided by the present invention;

[0059] Figure 11 A schematic diagram of the attitude pitch tow angle of an equivalent virtual central satellite provided by the present invention;

[0060] Figure 12 A schematic diagram of the yaw attitude pull angle of a transmitting satellite and a receiving satellite designed based on the present invention is provided;

[0061] Figure 13A schematic diagram of the pitch attitude traction angle of a transmitting satellite and a receiving satellite designed based on the present invention is provided;

[0062] Figure 14 A schematic diagram of the roll attitude traction angle of a transmitting satellite and a receiving satellite designed based on the present invention is provided;

[0063] Figure 15 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 1 ;

[0064] Figure 16 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 1 ;

[0065] Figure 17 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 1 ;

[0066] Figure 18 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 2 ;

[0067] Figure 19 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 2 ;

[0068] Figure 20 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 2 ;

[0069] Figure 21 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 3 ;

[0070] Figure 22 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 3 ;

[0071] Figure 23 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 3 ;

[0072] Figure 24 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 4 ;

[0073] Figure 25 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 4 ;

[0074] Figure 26 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 4 ;

[0075] Figure 27 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 5 ;

[0076] Figure 28 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 5 ;

[0077] Figure 29 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 5 ;

[0078] Figure 30 The present invention provides a schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies. Figure 6 ;

[0079] Figure 31 The present invention provides a schematic diagram of a Doppler frequency of a transmitted and received echo. Figure 6 ;

[0080] Figure 32 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite provided by the present invention Figure 6 ;

[0081] Figure 33 A schematic diagram of an imaging attitude planning device for a primary and secondary satellite platform of a distributed SAR provided by the present invention;

[0082] Figure 34 A schematic diagram of a computer device for implementing a method for imaging attitude planning of primary and secondary satellite platforms of distributed SAR provided by the present invention. DETAILED DESCRIPTION

[0083] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0084] Currently, when using single-satellite SAR for Earth observation, in order to compensate for the Doppler shift effect caused by the Earth's rotation, the satellite platform needs to perform attitude traction correction in both yaw and pitch dimensions to ensure that the Doppler frequency of the echo is zero and does not change with distance, thereby improving the efficiency of ground imaging processing.

[0085] The yaw-pitch traction algorithm of the satellite platform of the single-star SAR is as follows. In the ECI coordinate system, the ground echo Doppler frequency f of the single-star SAR D It can be expressed as:

[0086]

[0087] Among them, λ r is the system wavelength, The satellite's location Pointing to ground targets A vector, which can be expressed as:

[0088]

[0089] for The rate of change over time, for The unit vector of , which can be expressed as:

[0090]

[0091] From the above formula (1), it can be seen that in order to ensure that the Doppler center f of the single-star SAR echo DC =0, the constraints that need to be met are:

[0092]

[0093] The speed of ground targets with the Earth's rotation in is the Earth's rotation angular velocity vector. Therefore, equation (4) can be expressed as:

[0094]

[0095] According to the conversion characteristics of vector cross product, formula (5) can be rewritten as:

[0096]

[0097] Will and Substituting into formula (6), we have:

[0098]

[0099] Here we define a satellite relative speed This speed is also the satellite speed in the ECF coordinate system. From equation (7), we can see that: in order to ensure that the Doppler center f of the echo signal is DC = 0, then the antenna beam center pointing vector Need and Therefore, it is necessary to adjust the attitude of the satellite platform in the yaw and pitch directions in the LVLH coordinate system, and finally adjust the X axis of the satellite platform to be perpendicular to the yaw direction and pitch direction. coincide with each other, then the YZ plane of the satellite platform coincides with perpendicular to each other, thus ensuring that the antenna beam center vector is located in this plane They are perpendicular to each other and do not change with the change of the viewing angle of the subsatellite point.

[0100] In the LVLH coordinate system, the relative speed of the satellite is The analytical expression can be expressed as:

[0101]

[0102] in and yes Three-axis components in the LVLH coordinate system. and is the unit vector of the three axes of the LVLH coordinate system. When the satellite platform does not perform attitude traction correction, the unit vector of the three axes of the satellite body is and The X axis of the satellite is aligned with the unit vector of the three axes of the LVLH coordinate system. The corresponding yaw traction angle α and pitch traction angle β are:

[0103]

[0104] The satellite platform yaw-pitch two-dimensional attitude traction of the single-star SAR realizes the X-axis of the satellite platform and The process of coincidence, and the corresponding yaw traction angle α and pitch traction angle β are as follows Figure 1 As shown, Figure 1 The figure is a schematic diagram of the yaw-pitch traction correction attitude of a satellite platform of a single-satellite SAR in the present invention.

[0105] For distributed spaceborne SAR, the echo's Doppler frequency is determined by the position and velocity of the transceiver platform. Furthermore, to ensure echo gain and system signal-to-noise ratio, the overlap of the transceiver beam footprints must be as high as possible. Therefore, based on these two constraints and building upon the single-satellite SAR satellite platform attitude pulling method, it is necessary to study a joint attitude pulling method for the transceiver platforms of distributed spaceborne SAR.

[0106] Unlike the self-transmitted and self-received echo Doppler frequency definition of the monostatic SAR in equation (1), the echo signal process of the distributed spaceborne SAR is "transmitting satellite → observation scene → receiving satellite". Therefore, the echo Doppler frequency in this system is determined by the position and velocity of the transmitting satellite and the position and velocity of the receiving satellite. Its expression f Bid for:

[0107]

[0108] in is the vector pointing from the launching satellite to the scene target yes The unit vector of is the vector pointing from the receiving satellite to the scene target yes The unit vector of

[0109] From formula (11), we can see that the Doppler frequency f of the distributed spaceborne SAR echo is Bid It consists of two independent parameters. The first is the transmit Doppler frequency f DTx , the second term is the received Doppler frequency f DRx Therefore, the distributed spaceborne SAR has the freedom to adjust the attitude of the two transmitting and receiving satellites. The goal of attitude pulling is to adjust the Doppler frequency f of the bistatic echo to the value of 0 under the premise of satisfying the overlap constraint of the transmit and receive beam footprints. Bid It is adjusted to a constant value and remains basically unchanged in the range direction, thereby achieving decoupling of the SAR scene echo signal in the azimuth and range directions, and achieving the purpose of improving imaging processing efficiency and accuracy.

[0110] In response to this demand, the present invention designs an attitude traction correction scheme for distributed satellites, provides a three-axis pointing algorithm and process for designing the transmitting main satellite and the receiving auxiliary satellite, and further derives the Euler angle value representing the satellite attitude based on the sequence definition.

[0111] The technical solutions provided by various embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0112] Figure 2This is a flow chart of a method for imaging attitude planning of a primary and secondary satellite platform for a distributed SAR in the present invention, which specifically includes the following steps:

[0113] S101: Determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite.

[0114] When planning the imaging attitude of the primary and secondary satellite platforms of the distributed SAR, the server of the business platform can comprehensively consider the constraints and goals of the attitude traction correction of the distributed spaceborne SAR satellite platform, such as Figure 3 As shown, Figure 3 This figure shows the design process for attitude traction between the transmitting primary satellite and the receiving auxiliary satellite in a distributed SAR system. The entire design process generally consists of five steps, with the required input parameters including the position and velocity vectors of the transmitting primary satellite, the position and velocity vectors of the receiving auxiliary satellite, and the viewing angle range of the sub-satellite point of the observation scene.

[0115] First, an equivalent virtual central satellite can be introduced based on the transmitting main satellite and the receiving auxiliary satellite, so that the attitude traction design of the transmitting main satellite and the receiving auxiliary satellite can be carried out with the help of the equivalent virtual central satellite.

[0116] Specifically, in one or more embodiments of the present invention, the server may transmit the position vector of the main satellite according to and the position vector of the receiving auxiliary satellite The arithmetic mean of the transmitting main satellite and the receiving auxiliary satellite is used to determine the position vector of the equivalent virtual central satellite And according to the position vector of the launching main satellite and receiving auxiliary satellites The arithmetic mean of the velocity vectors of the transmitting main satellite and the receiving auxiliary satellite is used to determine the velocity vector of the equivalent virtual central satellite As shown in formula (12) and formula (13):

[0117]

[0118] The server mentioned in the present invention can be a server set up on a business platform, or a device such as a desktop computer, a notebook computer, etc. that can execute the solution of the present invention. For the sake of convenience, the following description will only be made with the server as the execution subject.

[0119] S102: According to the position vector and velocity vector of the equivalent virtual center satellite, the attitude traction three-axis Euler angle of the equivalent virtual center satellite corresponding to the sub-satellite point perspective of the observation scene under the satellite platform rotation is determined by a single-satellite SAR yaw traction method.

[0120] Based on the above equivalent virtual center satellite, the server can further calculate the position vector of the equivalent virtual center satellite. and velocity vector The information can be used to obtain the yaw pull angle θ of the equivalent virtual center satellite by using the algorithm flow of the single-star SAR yaw pull (Equation (8) to Equation (10)). yaw and the pitch traction angle θ pitch Set the viewing angle of the sub-satellite point at the center of the observation scene to θ c , then under the YRP satellite platform transfer sequence, the corresponding attitude roll traction angle θ roll is: θ roll =θ c .

[0121] S103: Determine the three-axis pointing vector of the equivalent virtual center satellite according to the attitude towing three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation, so as to determine the proximal vector and the distal vector of the equivalent virtual center satellite pointing to the observation scene.

[0122] After obtaining the three-axis Euler angles of the attitude traction of the equivalent virtual center satellite under the satellite platform transition, the server can further determine the vectors pointing from the equivalent virtual center satellite to the near and far ends of the observation scene. In one or more embodiments of the present invention, the server can determine the three-axis pointing vectors of the equivalent virtual center satellite based on the three-axis Euler angles of the attitude traction of the equivalent virtual center satellite under the satellite platform transition using the following formula:

[0123]

[0124] Where, and are the X-axis, Y-axis and Z-axis pointing vectors of the equivalent virtual center satellite in the LVLH coordinate system, M roll 、M pitch and M yaw are the roll, pitch and yaw rotation matrices of the equivalent virtual center satellite, θ roll is the roll traction angle of the equivalent virtual center satellite, θ pitch is the pitch pull angle of the equivalent virtual central satellite, θ yaw is the yaw pull angle of the equivalent virtual center satellite.

[0125] The proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene are determined according to the three-axis pointing vector of the equivalent virtual center satellite using the following formula:

[0126]

[0127] Where, is the proximal vector of the equivalent virtual center satellite pointing to the observation scene, is the far-end vector of the equivalent virtual central satellite pointing to the observation scene, θ n and θ f It is the offset angle of the sub-satellite point viewing angle at the near and far ends of the observation scene relative to the center of the observation scene.

[0128] S104: Determine the pitch plane of the observation scene covered by the launch beam of the launch main satellite based on the position vector, proximal vector, distal vector of the equivalent virtual central satellite and the position vector of the launch main satellite, so as to determine the three-axis pointing vector of the launch main satellite; obtain the attitude traction three-axis Euler angle of the launch main satellite based on the three-axis pointing vector, position vector and velocity vector of the launch main satellite.

[0129] Position vector based on equivalent virtual center satellite And the equivalent virtual center satellite pointing to the near-end vector of the observation scene given by equations (16) and (17) With the distal vector Combined with the position and speed information of the launched main satellite, the three-axis attitude traction method of the launched main satellite can be determined. Figure 4 This is a schematic diagram of a design process for determining the three-axis attitude traction method for launching a main satellite in the present invention. Figure 4 It can be seen that this step may include 5 sub-parts.

[0130] 1. Determine the pitch plane ΔS for launching the main satellite el :

[0131] Specifically, in one or more embodiments of the present invention, the server may first determine the intersection points of the proximal vector and the distal vector with the earth's surface based on the position vector, proximal vector and distal vector of the equivalent virtual center satellite; determine the vector from the transmitting main satellite to the two intersection points based on the intersection points of the position vector, proximal vector and distal vector of the transmitting main satellite with the earth's surface; and determine the pitch plane of the transmitting main satellite's transmitting beam covering the observation scene with the constraint that the vectors from the transmitting main satellite to the two intersection points and the position vector of the transmitting main satellite are both within the pitch plane of the transmitting main satellite's transmitting beam covering the observation scene.

[0132] For example, the server can be based on the location of the equivalent virtual center satellite and the proximal vector pointing from the equivalent virtual center satellite to the observation scene With the distal vector The intersection of these two vectors with the earth's surface can be found and At this time, the position of the main satellite is used to launch The vector from the launch of the main satellite to these two intersection points can be obtained and

[0133]

[0134] Two vectors and and the launch location of the main satellite All located in ΔS el So ΔS el It can be defined by the constraints given by formula (20):

[0135]

[0136] The first term in formula (20) indicates the position coordinates of the transmitting main satellite Located in ΔS el The second term indicates that ΔS el To be perpendicular to and The determined cross product vector.

[0137] Then, the X-axis pointing vector of the launch satellite can be determined for both left-side and right-side viewing conditions, respectively, using the vectors from the launch satellite to the two intersection points, assuming the X-axis pointing vector of the launch satellite is perpendicular to the elevation plane of the launch satellite's transmit beam in the LVLH coordinate system. The Z-axis pointing vector of the launch satellite can be determined, assuming the intersection of the launch satellite's Z-axis pointing vector and the Earth's surface lies within the azimuth plane of the antenna beam of the equivalent virtual central satellite. The Y-axis pointing vector of the launch satellite can be determined using the right-hand rule based on the X- and Z-axis pointing vectors of the launch satellite. This is explained in detail below.

[0138] 2. Determine the X-axis unit pointing vector for launching the main satellite

[0139] X-axis pointing vector of the launch main satellite Should be perpendicular to the pitch plane ΔS el Therefore, it can be obtained by and To jointly determine. When the main satellite is launched and working in the left visual condition, It can be expressed as

[0140]

[0141] Where ||·|| is the vector modulus operator. When the main satellite is operating in the right view, It can be expressed as

[0142]

[0143] 3. Determine the Z-axis unit pointing vector for launching the main satellite

[0144] To ensure that the antenna beam of the main satellite can effectively cover the observation scene, the intersection of its Z-axis pointing vector and the earth's surface needs to be located in the antenna beam azimuth plane ΔM of the equivalent virtual center satellite. az According to this constraint, the Z-axis pointing vector of the launching main satellite can be established. Equation set. Let the Z axis point to the vector The intersection with the Earth is The coordinates of (x az ,y az ,z az ), can be solved by the following three equations:

[0145]

[0146] where R a =6378.137km and R b =6356.752km are the equatorial radius and polar radius respectively. Equation (23) constrains the Z-axis pointing vector of the launch main satellite Pointing vector with X axis are perpendicular to each other, and Equation (24) constrains Located in the azimuth plane of the equivalent virtual center satellite antenna beam, Equation (25) constrains Located on the surface of the Earth.

[0147] When using equations (23) to (25) we get After that, the Z-axis pointing vector of the main satellite can be obtained. for

[0148]

[0149] 4. Determine the Y-axis unit pointing vector for launching the main satellite

[0150] Based on the above and Using the right-hand rule, we can get the Y-axis pointing vector of the main satellite launch for:

[0151]

[0152] 5. Determine the three-axis Euler angles of the main satellite launch:

[0153] According to the three-axis pointing vector of the main satellite and and the location of the launch of the main satellite and speed The attitude traction Euler angle θ of the launch main satellite platform can be obtained yaw_Tx ,θpitch_Tx and θ roll_Tx .

[0154] S105: Based on the position vector and three-axis pointing vector of the equivalent virtual center satellite, determine the azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite, and use the Doppler frequency of the bistatic echo of the receiving beam of the auxiliary satellite covering the near and far ends of the observation scene to be zero as a constraint, and search for the target position on the intersection line of the azimuth tangent plane and the earth's surface.

[0155] S106: With the vector of the receiving auxiliary satellite pointing to the target position being constrained to be within the pitch plane of the receiving auxiliary satellite, determine the three-axis pointing vector of the receiving auxiliary satellite based on the target position and the position vector of the receiving auxiliary satellite; and obtain the three-axis Euler angles of the attitude traction of the receiving auxiliary satellite based on the three-axis pointing vector, position vector, and velocity vector of the receiving auxiliary satellite.

[0156] For the receiving auxiliary satellite, the auxiliary satellite attitude pulling method can be designed according to the following constraints: at the near and far ends of the observation scene covered by the receiving beam, the bistatic echo Doppler frequency is constrained to 0, as given by Equations (28) and (29).

[0157] f bi_near =0(28)

[0158] f bi_far =0(29)

[0159] Figure 5 This is a schematic diagram of a design process for determining the three-axis attitude traction method of the receiving auxiliary satellite in the present invention. Figure 5 It can be seen that it can be divided into 6 sub-parts.

[0160] 1. Determine the azimuth planes of the equivalent virtual center satellite at the near, center, and far ends of the observation scene:

[0161] In one or more embodiments of the present invention, the server may determine the normal vectors of the azimuth tangent planes of the equivalent virtual center satellite's receiving beam at the near and far ends of the observation scene based on the viewing angle width of the observation scene and the three-axis pointing vector of the equivalent virtual center satellite.

[0162] With the constraints that the position vector of the equivalent virtual center satellite is located in the proximal azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the proximal end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the proximal end of the observation scene, the azimuth tangent plane pointing to the proximal end of the observation scene by the equivalent virtual center satellite is determined.

[0163] With the constraints that the position vector of the equivalent virtual center satellite is located in the far azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the far end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the far end of the observation scene, the azimuth tangent plane pointing to the far end of the observation scene by the equivalent virtual center satellite is determined.

[0164] For example, the server can calculate the three-axis vector of the equivalent virtual center satellite and And the equivalent virtual center satellite position given by equations (12) and (13) and speed The azimuth plane ΔS of the equivalent virtual central satellite at the center of the observation scene az_cen Defined by the constraints given by formula (30)

[0165]

[0166] Assume that the viewing angle width of the observation scene is θ s , then the normal vectors of the azimuth tangent planes of the receiving beam at the near and far ends of the observation scene are given by equations (31) and (32).

[0167]

[0168] At this time, the azimuth section ΔS of the equivalent virtual center satellite at the near and far ends of the observation scene is az_near and ΔS az_far It can be defined by the constraints given by equations (33) and (34) respectively:

[0169]

[0170] In the result of ΔS az_near and ΔS az_far After the two azimuth planes are cut, the target position that satisfies equations (28) and (29) will be searched on the intersection of these two planes and the earth's surface.

[0171] 2. In ΔS az_near and ΔS az_far Search for the bistatic Doppler frequency f bistatic =0 position:

[0172] In the azimuth plane ΔS az_near In the formula (28), the constraint condition f is satisfied. bi_near =0 target position It can be solved by the equations given by (35) to (37).

[0173]

[0174] Equation (35) shows that the equivalent virtual center satellite position Point to the target location The vector of the plane and the normal vector of the plane perpendicular to each other; Equation (36) shows that the target position Located on the surface of the earth, formula (37) shows that The bistatic Doppler frequency f bi_near =0.

[0175] Similarly, the azimuth plane ΔS at the far end of the scene az_far Within, satisfying the constraint f bi_far =0 target position It can be solved by the equations given by (38) to (40).

[0176]

[0177] When the target position is obtained and After that, the three-axis vector of the receiving auxiliary satellite platform can be gradually determined.

[0178] 3. Determine the X-axis unit pointing vector of the receiving auxiliary satellite

[0179] To ensure that the bistatic echo Doppler frequency is always zero along the range direction within the antenna beam footprint, the elevation section of the receiving auxiliary satellite should contain and Two target points. Therefore, the vector from the receiving auxiliary satellite to these two target points and It should be located in the pitch plane of the receiving auxiliary satellite. Should be perpendicular to the pitch plane, so when receiving the observation from the right side of the auxiliary satellite, the X-axis pointing vector It can be determined by formula (41).

[0180]

[0181] When viewed from the left side, the X-axis pointing vector is

[0182]

[0183] Finally, the X-axis pointing vector is obtained for

[0184]

[0185] 4. Determine the Z-axis unit pointing vector of the receiving auxiliary satellite

[0186] When the elevation plane of the receiving auxiliary satellite is determined, the Z-axis pointing vector of the receiving auxiliary satellite will be located in the plane. In addition, to ensure that the receiving beam footprint can overlap with the transmitting beam and virtual beam footprint to the greatest extent, the intersection of the Z-axis pointing vector and the earth's surface is It should be located in the azimuth tangent plane of the equivalent virtual center satellite at the center of the scene. Based on the above analysis, in order to obtain the Z-axis pointing vector of the receiving auxiliary satellite, we must first obtain the intersection of this vector and the earth. The intersection position can be determined using the following set of equations.

[0187]

[0188] When obtained After receiving the Z-axis pointing vector of the auxiliary satellite It can be obtained from formula (47):

[0189]

[0190] Thus, the Z-axis pointing vector is obtained for:

[0191]

[0192] 5. Determine the Y-axis unit pointing vector of the receiving auxiliary satellite

[0193] When the X-axis pointing vector and the Z-axis pointing vector of the receiving auxiliary satellite are determined, the Y-axis pointing vector can be determined using the right-hand rule. This vector is the cross product of the Z-axis and X-axis pointing vectors, as shown in Equation (49).

[0194]

[0195] Figure 6 This is a schematic diagram of the transceiver antenna beam footprint after the attitude pulling of the main and auxiliary satellites in the present invention. Finally, it is necessary to ensure that the beam is along the Figure 6 The red dashed line in the middle shows the bistatic Doppler frequency f in the range direction of the receive beam footprint. bistatic =0.

[0196] based on Figure 2The present invention introduces an equivalent virtual central satellite and, based on this, provides a complete distributed SAR system attitude traction correction scheme for the transmitting primary satellite and receiving secondary satellite. This achieves the goal of maintaining the Doppler frequency of the distributed SAR echo constant at zero along the range direction, and achieves maximum decoupling of the SAR echo in the range and azimuth directions. While ensuring that the distributed SAR echo Doppler characteristic has zero value and remains constant along the range direction, the present invention also maximizes the overlap of the footprint coverage areas of the transmitting and receiving beams, thereby avoiding gain loss caused by transceiver beam offsets and significantly improving the echo signal-to-noise ratio and image quality of the observed scene. The present invention can utilize existing imaging algorithms for processing without the need for developing new algorithms, greatly improving the efficiency of ground imaging processing.

[0197] When applying the imaging attitude planning method of the main and auxiliary satellite platforms of the distributed SAR provided by the present invention, it is not necessary to Figure 2 The steps are executed in the order shown. The specific execution order of the steps can be determined according to needs, and the present invention does not limit this.

[0198] The present invention also provides an embodiment of the method. The effectiveness of the attitude pulling method for transmitting and receiving satellites provided by the present invention is verified below. Two co-orbital satellites separated by a certain distance in flight upwards are used as the transmitting and receiving satellites of a distributed spaceborne SAR system. The two satellites are located in the same orbital plane, with a flight time interval ΔT = 2s. The receiving satellite is located ahead of the transmitting satellite. The orbital parameters and system parameters required for other system simulations are listed in the following table:

[0199] Table 1 Orbit and system parameters of distributed spaceborne SAR system

[0200] Serial number System parameters Parameter value orbital mean semi-major axis 6871km mean orbital eccentricity 1.5×10-3 Average orbital inclination 97.39° Right ascension of the mean ascending node 179.52° Azimuth beamwidth of the transmitting antenna 1° Transmitting antenna elevation beamwidth 2° Azimuth beamwidth of the receiving antenna 1° Elevation beamwidth of the receiving antenna 2° System carrier frequency 9.8GHz The time interval between sending and receiving satellites 2s Subsatellite point viewing angle at the center of the observation scene 30°

[0201] Figure 7 Schematic diagram of the change of satellite latitude argument over time in the present invention. Figure 7 The change of satellite latitude argument over time based on the above orbital parameters is given. Since the change of satellite latitude argument is periodic, the complete data of one orbit is selected for analysis. The orbital time of this orbit is 4284s to 9963s. Within this orbital time range, the change of satellite latitude argument is as follows Figure 8 As shown, Figure 8 This is a schematic diagram of the latitude argument of one track of data selected in the present invention.

[0202] During this period of orbital time, the orbital semi-major axis, orbital inclination, orbital eccentricity, right ascension of ascending node, argument of perigee, and true anomaly change in the following ways: Figure 9 As shown, Figure 9 This is a schematic diagram of a change in the number of six tracks within one track time in the present invention. Figure 9 It can be seen that due to the influence of factors such as the Earth's oblateness J2 perturbation, the relevant parameters of the six orbital numbers, such as the semi-major axis, orbital inclination, right ascension of the ascending node, and argument of perigee, all change with time.

[0203] Since the transmitting satellite and the receiving satellite are in the same orbit and the orbital time interval differs by 2s, when the orbital time of the transmitting satellite is between 4284s and 9963s, the orbital time of the receiving satellite is between 4286s and 9965s. Using the six orbital numbers, the position and velocity information of the transmitting satellite and the receiving satellite can be calculated. According to equations (12) and (13), the position and velocity of the equivalent virtual center satellite can be further calculated, and the yaw and pitch traction angles of the single-satellite attitude obtained based on the equivalent virtual center satellite are as follows: Figure 10 and Figure 11 shown. Figure 10 This is a schematic diagram of the attitude yaw pull angle of an equivalent virtual central satellite in the present invention. Figure 11 This is a schematic diagram of the attitude pitch traction angle of an equivalent virtual central satellite in the present invention.

[0204] based on Figure 10 and Figure 11 The results of this paper can be used to deduce the attitude traction angles of the launching satellite and the pitching satellite in the YPR sequence within one orbital period. The corresponding simulation results are shown in Figure 2. Figure 12 、 13 As shown in 14, Figure 12 FIG1 is a schematic diagram of the yaw attitude pull angle of the transmitting satellite and the receiving satellite designed based on the present invention. Figure 13 Schematic diagram of the pitch attitude traction angle of the transmitting satellite and the receiving satellite designed based on the present invention. Figure 14 The figure below is a schematic diagram of the roll attitude pull angles for a transmitting and receiving satellite designed based on the present invention. Simulation results show that the yaw angles of the transmitting, receiving, and equivalent virtual center satellites are essentially identical. The largest difference in attitude between the transmitting and receiving satellites lies in their pitch angles. A "+" value for the transmitting satellite's pitch angle indicates forward-looking observation, while a "-" value for the receiving satellite's pitch angle indicates rearward-looking observation. Finally, the roll angles of the transmitting and receiving satellites are essentially consistent with the 30° subsatellite viewing angle of the observation scene, with a deviation of less than 0.004°.

[0205] according to Figure 10 and Figure 11 The simulation results show that the maximum, zero, and minimum moments of the yaw and pitch angles of the equivalent virtual center satellite are listed in Table 2. The effectiveness of the present invention will be verified using the six special moments in the table below.

[0206] Table 2 Peak and zero-value moments of the yaw and pitch angles of the equivalent virtual center satellite

[0207] Maximum moment Zero value moment Minimum moment Yaw angle 5326s 9582s 8163s Pitch angle 4903s 6783s 8598s

[0208] (1) The maximum yaw angle at time T = 5326s:

[0209] The satellite yaw angle θ at the equivalent virtual center yaw When the maximum value reaches 3.705°, the orbital time corresponding to the transmitting satellite is T = 5326s. At this time, the Doppler frequencies of the transmitting satellite and the receiving satellite, the Doppler frequency of the combined transmission and reception, and the transmission and reception beam footprints are as follows: Figures 15-17 As shown, Figure 15 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 1 , Figure 16 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 1 , Figure 17 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 1 From this result, it can be seen that since the observation mode of the transmitting satellite is forward squint and the receiving satellite is backward squint, the transmit and receive Doppler frequencies calculated in equation (11) are positive and negative respectively. The dual-base Doppler frequency result obtained by combining the two is as follows: Figure 16 As shown in Figure 1, it can be seen that the Doppler frequency of the echo signal is basically 0 and remains unchanged along the ground distance. The beam footprint coverage characteristics of the transmitting and receiving satellites and the equivalent virtual center satellite are shown in Figure 1. Figure 17 As shown, it can be seen that the three are basically overlapped. Based on the above results, it can be seen that the attitude traction method of the present invention for the transmitting and receiving satellites at this moment is effective.

[0210] (2) Yaw angle zero value time T = 9582s:

[0211] The satellite yaw angle θ at the equivalent virtual center yaw When it reaches zero, the orbital time corresponding to the transmitting satellite is T = 9582s. At this time, the Doppler frequencies of the transmitting satellite and the receiving satellite, the Doppler frequency of the combined transmission and reception, and the transmission and reception beam footprints are respectively as follows: Figures 18-20 As shown, Figure 18 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 2 , Figure 19 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 2 , Figure 20 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 2 .

[0212] Based on the synthetic Doppler frequency characteristics of transmission and reception (basically zero value and unchanged along the ground distance direction) and the beam footprint coverage characteristics (the transmitting and receiving beam footprints basically overlap), it can be considered that the attitude traction scheme of the transmitting satellite and the receiving satellite of the present invention is effective at this moment.

[0213] (3) The time when the yaw angle is minimum is T = 8163s:

[0214] The satellite yaw angle θ at the equivalent virtual center yaw When the minimum value is -3.705°, the orbital time corresponding to the transmitting satellite is T = 8163s. At this time, the Doppler frequencies of the transmitting and receiving satellites, the Doppler frequencies of the transmitting and receiving combined, and the footprints of the transmitting and receiving beams are as follows: Figures 21-13 As shown, Figure 21 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 3 , Figure 22 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 3 , Figure 23 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 3 .

[0215] Based on the synthetic Doppler frequency characteristics of transmission and reception (basically zero value and unchanged along the ground distance direction) and the beam footprint coverage characteristics (the transmitting and receiving beam footprints basically overlap), it can be considered that the attitude traction scheme of the transmitting satellite and the receiving satellite of the present invention is effective at this moment.

[0216] (4) The maximum yaw angle at time T = 4903s:

[0217] At the equivalent virtual center satellite elevation angle θ pitch When the minimum value reaches 0.08°, the orbital time corresponding to the transmitting satellite is T = 4903s. At this time, the Doppler frequencies of the transmitting and receiving satellites, the Doppler frequencies of the combined transmitting and receiving beams, and the footprints of the transmitting and receiving beams are as follows: Figures 24-26 As shown, Figure 24 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 4 , Figure 25 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 4 , Figure 26Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 4 .

[0218] Based on the synthetic Doppler frequency characteristics of transmission and reception (basically zero value and unchanged along the ground distance direction) and the beam footprint coverage characteristics (the footprints of the transmitting and receiving beams basically overlap), it can be considered that the attitude traction scheme of the transmitting satellite and the receiving satellite of the present invention is effective at this moment.

[0219] (5) The pitch angle zero value time T = 6783s:

[0220] At the equivalent virtual center satellite elevation angle θ pitch When it reaches zero, the orbital time corresponding to the transmitting satellite is T = 6783s. At this time, the Doppler frequencies of the transmitting satellite and the receiving satellite, the Doppler frequency of the combined transmission and reception, and the transmission and reception beam footprints are respectively as follows: Figures 27-29 As shown, Figure 27 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 5 , Figure 28 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 5 , Figure 29 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 5 .

[0221] Based on the synthetic Doppler frequency characteristics of transmission and reception (basically zero value and unchanged along the ground distance direction) and the beam footprint coverage characteristics (the footprints of the transmitting and receiving beams basically overlap), it can be considered that the attitude traction scheme of the transmitting satellite and the receiving satellite of the present invention is effective at this moment.

[0222] (6) The time when the pitch angle is minimum is T=8598s:

[0223] At the equivalent virtual center satellite elevation angle θ pitch When the minimum value is -0.08°, the orbital time corresponding to the transmitting satellite is T=8598s. At this time, the Doppler frequencies of the transmitting and receiving satellites, the Doppler frequencies of the combined transmitting and receiving beams, and the footprints of the transmitting and receiving beams are as follows: Figures 30-32 As shown, Figure 30 Schematic diagram of the Doppler frequencies of the transmitting and receiving satellites and the synthesized Doppler frequencies of the transmitting and receiving satellites in the present invention Figure 6 , Figure 31 A schematic diagram of the Doppler frequency of the echo transmitted and received in the present invention Figure 6 , Figure 32 Schematic diagram of the beam coverage footprint of a transceiver satellite and an equivalent virtual center satellite in the present invention Figure 6 .

[0224] Based on the synthetic Doppler frequency characteristics of transmission and reception (basically zero value and unchanged along the ground distance direction) and the beam footprint coverage characteristics (the transmitting and receiving beam footprints basically overlap), it can be considered that the attitude traction scheme of the transmitting satellite and the receiving satellite of the present invention is effective at this moment.

[0225] By analyzing the echo Doppler frequencies and the transmit and receive beam footprint coverage characteristics at the six special moments within the satellite's one orbit time, it can be considered that the solution of the present invention is effective within one orbit period.

[0226] Based on the attitude yaw traction of a single-satellite SAR, the present invention provides a platform attitude traction method for the transmitting satellite and receiving satellite of a distributed spaceborne SAR. In view of the multiple constraints of the attitude traction of the distributed SAR transceiver platform (the distributed echo Doppler frequency is 0 and remains unchanged along the range direction; the transmit and receive beam footprints must have a high degree of overlap), the design algorithms and processes for the attitude traction of the transmitting satellite and the receiving satellite are respectively provided to ensure that the above two constraints are met at the same time. The present invention has good technical scalability and can be expanded from the 1-transmitter-1-receiver distributed SAR system in the simulation example to the attitude traction design of more complex distributed spaceborne SAR systems such as 1-transmitter-multiple-receiver or multiple-transmitter-multiple-receiver.

[0227] The above is a method for imaging attitude planning of a primary and secondary satellite platform of a distributed SAR provided by one or more embodiments of the present invention. Based on the same idea, the present invention also provides a corresponding imaging attitude planning device for a primary and secondary satellite platform of a distributed SAR, such as Figure 33 shown.

[0228] Figure 33 A schematic diagram of a distributed SAR primary and secondary satellite platform imaging attitude planning device provided by the present invention includes:

[0229] The equivalent module 201 is configured to determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite;

[0230] The equivalent single-satellite traction module 202 is used to determine the attitude traction three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation sequence corresponding to the sub-satellite point perspective of the observation scene by using the single-satellite SAR yaw traction method according to the position vector and velocity vector of the equivalent virtual center satellite;

[0231] The vector determination module 203 is used to determine the three-axis pointing vector of the equivalent virtual center satellite according to the attitude towing three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation, so as to determine the proximal vector and the distal vector of the equivalent virtual center satellite pointing to the observation scene;

[0232] The first traction planning module 204 is configured to determine the pitch plane of the transmitted main satellite's transmit beam covering the observation scene based on the position vector, proximal vector, distal vector of the equivalent virtual central satellite, and the position vector of the transmitting main satellite, so as to determine the three-axis pointing vector of the transmitting main satellite; and obtain the three-axis Euler angles of the attitude traction of the transmitting main satellite based on the three-axis pointing vector, position vector, and velocity vector of the transmitting main satellite.

[0233] The search module 205 is configured to determine an azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite based on the position vector and the three-axis pointing vector of the equivalent virtual center satellite, and search for a target position on the intersection of the azimuth tangent plane and the Earth's surface, with the Doppler frequency of the bistatic echoes received by the auxiliary satellite covering the near and far ends of the observation scene being zero as a constraint;

[0234] The second traction planning module 206 is used to determine the three-axis pointing vector of the receiving auxiliary satellite based on the target position and the position vector of the receiving auxiliary satellite, with the vector of the receiving auxiliary satellite pointing to the target position being within the pitch plane of the receiving auxiliary satellite as a constraint; and obtain the three-axis Euler angle of the attitude traction of the receiving auxiliary satellite based on the three-axis pointing vector, position vector and velocity vector of the receiving auxiliary satellite.

[0235] Regarding the specific definition of the imaging attitude planning device of the primary and secondary satellite platforms of the distributed SAR, please refer to the definition of the imaging attitude planning method of the primary and secondary satellite platforms of the distributed SAR above, which will not be repeated here. The various modules in the above-mentioned imaging attitude planning device of the primary and secondary satellite platforms of the distributed SAR can be implemented in whole or in part by software, hardware and their combination. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0236] The present invention also provides a computer-readable storage medium, which stores a computer program, which can be used to execute the above Figure 2 The imaging attitude planning method of the main and auxiliary satellite platforms of distributed SAR is provided.

[0237] The present invention also provides Figure 34 The structural diagram of the computer equipment shown in FIG. Figure 34 As shown in the figure, at the hardware level, the computer device includes a processor, an internal bus, a network interface, a memory, and a non-volatile memory. Of course, it may also include other hardware required for the business. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it to achieve the above Figure 2 The imaging attitude planning method of the main and auxiliary satellite platforms of distributed SAR is provided.

[0238] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided by the present invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0239] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present invention.

Claims

1. A distributed SAR primary and secondary satellite platform imaging attitude planning method, characterized in that: include: Determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite; According to the position vector and velocity vector of the equivalent virtual center satellite, the attitude traction three-axis Euler angle of the equivalent virtual center satellite corresponding to the sub-satellite point view of the observation scene under the satellite platform rotation is determined by the single-satellite SAR yaw traction method; According to the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation, the three-axis pointing vector of the equivalent virtual center satellite is determined to determine the proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene; According to the position vector, proximal vector, distal vector of the equivalent virtual central satellite and the position vector of the launching main satellite, the pitch plane of the launching main satellite's transmit beam covering the observation scene is determined to determine the three-axis pointing vector of the launching main satellite; according to the three-axis pointing vector, position vector and velocity vector of the launching main satellite, the three-axis Euler angle of the attitude traction of the launching main satellite is obtained; Based on the position vector and three-axis pointing vector of the equivalent virtual center satellite, the azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite is determined. The target position is searched on the intersection line of the azimuth tangent plane and the earth's surface, with the Doppler frequency of the bistatic echo of the receiving beam of the auxiliary satellite covering the near and far ends of the observation scene being zero as a constraint. With the constraint that the vector of the receiving auxiliary satellite pointing to the target position is within the pitch plane of the receiving auxiliary satellite, the three-axis pointing vector of the receiving auxiliary satellite is determined according to the target position and the position vector of the receiving auxiliary satellite; the attitude traction three-axis Euler angle of the receiving auxiliary satellite is obtained according to the three-axis pointing vector, position vector and velocity vector of the receiving auxiliary satellite.

2. The imaging attitude planning method for the primary and secondary satellite platforms of the distributed SAR according to claim 1, characterized in that: The step of determining the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite specifically includes: Determine the position vectors of the equivalent virtual central satellites of the transmitting main satellite and the receiving auxiliary satellite according to the arithmetic mean of the position vectors of the transmitting main satellite and the position vectors of the receiving auxiliary satellite; The velocity vectors of the equivalent virtual central satellites of the transmitting main satellite and the receiving auxiliary satellite are determined according to the arithmetic mean of the position vector of the transmitting main satellite and the velocity vector of the receiving auxiliary satellite.

3. The imaging attitude planning method of the primary and secondary satellite platforms of the distributed SAR according to claim 1, characterized in that: The method of determining the three-axis pointing vector of the equivalent virtual center satellite according to the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform transition, so as to determine the proximal vector and the distal vector of the equivalent virtual center satellite pointing to the observation scene, specifically includes: The three-axis pointing vector of the equivalent virtual center satellite is determined by the following formula based on the attitude pulling three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation: The proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene are determined according to the three-axis pointing vector of the equivalent virtual center satellite using the following formula: in, and are the X-axis, Y-axis and Z-axis pointing vectors of the equivalent virtual center satellite in the LVLH coordinate system, M roll 、M pitch and M yaw are the roll, pitch and yaw rotation matrices of the equivalent virtual center satellite, θ roll is the roll traction angle of the equivalent virtual center satellite, θ pitch is the pitch pull angle of the equivalent virtual central satellite, θ yaw is the yaw pull angle of the equivalent virtual center satellite, is the proximal vector of the equivalent virtual center satellite pointing to the observation scene, is the far-end vector of the equivalent virtual central satellite pointing to the observation scene, θ n and θ f It is the offset angle of the sub-satellite point viewing angle at the near and far ends of the observation scene relative to the center of the observation scene.

4. The imaging attitude planning method for the primary and secondary satellite platforms of the distributed SAR according to claim 1, characterized in that: The step of determining the pitch plane in which the transmitting beam of the transmitting main satellite covers the observation scene according to the position vector, the proximal vector, the distal vector, and the position vector of the transmitting main satellite of the equivalent virtual central satellite specifically includes: According to the position vector, the proximal vector and the distal vector of the equivalent virtual center satellite, the intersection points of the proximal vector and the distal vector with the earth's surface are determined; Determine the vector from the launch main satellite to the two intersection points according to the position vector, the proximal vector and the distal vector of the launch main satellite pointing to the intersection points with the earth's surface respectively; The vector from the launch main satellite to the two intersection points and the position vector of the launch main satellite are constrained to be within the pitch plane of the launch main satellite's transmission beam covering the observation scene, and the pitch plane of the launch main satellite's transmission beam covering the observation scene is determined.

5. The imaging attitude planning method for the primary and secondary satellite platforms of the distributed SAR according to claim 4, characterized in that: The determining of the three-axis pointing vector of the launching main satellite specifically includes: With the constraint that the X-axis pointing vector of the launching main satellite in the LVLH coordinate system is perpendicular to the pitch plane of the launching main satellite's transmission beam covering the observation scene, the X-axis pointing vector corresponding to the launching main satellite operating in the left-side viewing condition or the right-side viewing condition is determined according to the vectors from the launching main satellite to the two intersection points. The Z-axis pointing vector of the launched main satellite is determined by solving the problem of determining the Z-axis pointing vector of the launched main satellite, with the constraint that the intersection of the Z-axis pointing vector of the launched main satellite and the earth's surface is located in the antenna beam azimuth plane of the equivalent virtual central satellite. According to the X-axis pointing vector and the Z-axis pointing vector of the launched main satellite, the Y-axis pointing vector of the launched main satellite is determined by the right-hand rule.

6. The imaging attitude planning method for the primary and secondary satellite platforms of the distributed SAR according to claim 1, characterized in that: The step of determining the azimuth tangent planes pointing to the near end and the far end of the observation scene by the equivalent virtual center satellite according to the position vector and the three-axis pointing vector of the equivalent virtual center satellite specifically includes: According to the viewing angle width of the observation scene and the three-axis pointing vector of the equivalent virtual center satellite, the normal vectors of the azimuth tangent planes of the equivalent virtual center satellite receiving beam at the near end and the far end of the observation scene are determined respectively; The azimuth tangent plane pointing to the near end of the observation scene by the equivalent virtual center satellite is determined based on the constraints that the position vector of the equivalent virtual center satellite is located at the near end azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the near end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the near end of the observation scene. With the constraints that the position vector of the equivalent virtual center satellite is located in the far azimuth tangent plane pointing to the observation scene by the equivalent virtual center satellite, and the normal vector of the azimuth tangent plane of the receiving beam of the equivalent virtual center satellite at the far end of the observation scene is perpendicular to the azimuth tangent plane of the equivalent virtual center satellite at the far end of the observation scene, the azimuth tangent plane pointing to the far end of the observation scene by the equivalent virtual center satellite is determined.

7. A distributed SAR primary and secondary satellite platform imaging attitude planning device, characterized in that: include: An equivalent module is used to determine the position vector and velocity vector of the equivalent virtual central satellite of the transmitting main satellite and the receiving auxiliary satellite according to the position vector and velocity vector of the transmitting main satellite and the position vector and velocity vector of the receiving auxiliary satellite; The equivalent single-satellite traction module is used to determine the attitude traction three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation sequence corresponding to the sub-satellite point perspective of the observation scene through the single-satellite SAR yaw traction method based on the position vector and velocity vector of the equivalent virtual center satellite; A vector determination module is used to determine the three-axis pointing vector of the equivalent virtual center satellite according to the attitude towing three-axis Euler angle of the equivalent virtual center satellite under the satellite platform rotation sequence, so as to determine the proximal vector and distal vector of the equivalent virtual center satellite pointing to the observation scene; The first traction planning module is used to determine the pitch plane of the launch main satellite's transmit beam covering the observation scene based on the position vector, proximal vector, distal vector of the equivalent virtual central satellite and the position vector of the launch main satellite, so as to determine the three-axis pointing vector of the launch main satellite; and obtain the three-axis Euler angle of the attitude traction of the launch main satellite based on the three-axis pointing vector, position vector and velocity vector of the launch main satellite; A search module is used to determine an azimuth tangent plane pointing to the near and far ends of the observation scene by the equivalent virtual center satellite based on the position vector and the three-axis pointing vector of the equivalent virtual center satellite, and search for a target position on the intersection line of the azimuth tangent plane and the earth's surface, with the Doppler frequency of the bistatic echo of the receiving beam of the auxiliary satellite covering the near and far ends of the observation scene being zero as a constraint; The second traction planning module is used to determine the three-axis pointing vector of the receiving auxiliary satellite according to the target position and the position vector of the receiving auxiliary satellite, with the vector of the receiving auxiliary satellite pointing to the target position being within the pitch plane of the receiving auxiliary satellite as a constraint; and obtain the three-axis Euler angle of the attitude traction of the receiving auxiliary satellite according to the three-axis pointing vector, position vector and velocity vector of the receiving auxiliary satellite.

8. A computer-readable storage medium, characterized in that The storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

9. A computer device, characterized in that: The method comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 1 to 6 when executing the program.

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