Same-orbit bistatic SAR ambiguity calculation method and system based on beam space synchronization

Abstract

The invention provides a same-orbit bistatic SAR ambiguity calculation method and system based on beam space synchronization, and the method comprises the steps: calculating a three-axis attitude angle based on the initial orbit parameters of a transmitting satellite and a receiving satellite; calculating azimuth angles and pitch angles of beam centers of the transmitting satellite and the receiving satellite in respective radar antenna coordinate systems; determining the value ranges of the range ambiguity order and the azimuth ambiguity order; traversing each group of range ambiguity order and azimuth ambiguity order, and calculating antenna gain and signal propagation distance; calculating the power ratio of each order fuzzy component to the main signal component to obtain the bistatic SAR ambiguity under the specified distance; and in a distance range corresponding to the wave position, selecting a plurality of distance points according to a preset step length, and calculating and outputting the bistatic SAR ambiguity of each distance point. By accurately modeling system geometry, signal propagation attenuation and antenna pattern influence, the accuracy of ambiguity prediction is effectively improved, and system optimization and imaging quality improvement are supported.

Description

Technical Field

[0001] This invention relates to the field of satellite overall design, and more specifically, to a method and system for calculating bistatic SAR ambiguity based on beam spatial synchronization. Background Technology

[0002] Synthetic Aperture Radar (SAR), as an active microwave remote sensing technology, possesses all-weather, all-day imaging capabilities, giving it irreplaceable advantages in surveying, disaster monitoring, and military reconnaissance. In recent years, bistatic SAR systems, due to their separate transmit and receive capabilities, can avoid the radio frequency interference and interception risks of monostatic systems. Furthermore, the flexible configuration of the transmit and receive platforms enhances imaging freedom, making it a research hotspot for new radar systems. Among these, co-orbital bistatic SAR (i.e., transmitting and receiving satellites are on the same orbital plane) has become the most engineering-feasible configuration due to its low orbital control complexity and relatively simple synchronization.

[0003] However, one of the core challenges facing co-orbit bistatic SAR systems is signal ambiguity. Ambiguity is a key factor affecting image quality. Ambiguity mainly includes range ambiguity and azimuth ambiguity, which can lead to false targets or signal superposition in the image, severely reducing image resolution and contrast, and affecting accurate target identification and analysis. In a bistatic configuration, ambiguous signals exhibit new characteristics: the separation of the transmitting and receiving platforms causes the spatial distribution of ambiguity cells to become asymmetrical, rendering traditional monostatic ambiguity calculation methods ineffective; to achieve beam spatial synchronization, the transmitting and receiving antennas need to dynamically adjust their attitudes so that the ambiguity signal intensity is modulated by the two-way antenna gain pattern; beam spatial synchronization requires that the beams of the transmitting and receiving satellites be precisely aligned with the same observation area, and the beam spatial synchronization state directly affects the target detection range, antenna gain distribution, and ambiguity characteristics. Therefore, accurately calculating the ambiguity of co-orbit bistatic SAR based on beam spatial synchronization is of great significance for optimizing system design and improving imaging quality.

[0004] The paper "Omnidirectional Ambiguity Characteristics and Calculation Methods of Spaceborne SAR" (Tao Manyi, Hu Guangqing, et al., *China Space Science and Technology*, 2022, 02) establishes an angle conversion model between arbitrary pointing angles of the radiation pattern and actual Earth observations. It also presents a method and steps for calculating omnidirectional ambiguity based on a two-dimensional radiation pattern. This method is only applicable to ambiguity analysis and calculation for low-Earth orbit monostatic spaceborne SAR. Monostatic SAR ambiguity calculation methods, based on monostatic geometric models and signal processing principles, are difficult to directly apply to co-orbit bistatic SAR systems.

[0005] The paper "Distributed GEO SAR Ambiguity Analysis" (Chen Zhiyang, Wang Tao, et al. Signal Processing, 2019, 06) proposes an approximate calculation method for the location of ambiguous regions in bistatic GEO SAR considering the Earth's spherical surface, and then provides the steps for calculating the ambiguity. This method is only applicable to high-orbit SAR ambiguity analysis and calculation; low-orbit imaging and orbital characteristics differ from high-orbit.

[0006] The paper "Research on Ambiguity Suppression of Slanting-Looking Spaceborne SAR Based on Beamforming Optimization Method" (Wang Changcheng, Zhang Yi, et al., Telecommunications Technology, 2024, 06) proposes a two-dimensional ambiguity (range and azimuth ambiguity) suppression method for spaceborne SAR based on planar array antenna beamforming. By adjusting the sidelobe amplitude corresponding to the ambiguity region, it flexibly suppresses the range and azimuth ambiguity of SAR slanting imaging, thereby improving the imaging quality of spaceborne SAR. This method improves ambiguity through beamforming optimization, but does not involve improving ambiguity by achieving beam spatial synchronization through joint control of satellite attitude and beam electronic scanning.

[0007] The paper "SAR Range Deambiguity Based on Element Pulse Coding" (Lan Lan, Liao Guisheng, et al., Telecommunications Technology, 2024, 06) proposes an element pulse coding (EPC) technique to achieve high-resolution wide-strip mapping (HRWS) SAR imaging, addressing the range ambiguity suppression problem in multiple-input multiple-output (MIMO) SAR. This method focuses on achieving high-resolution wide-strip mapping imaging by solving range ambiguity suppression, but does not address the issue of improving ambiguity through joint control of satellite attitude and beam electronic scanning to achieve beam spatial synchronization.

[0008] The patent "Method and System for Calculating Azimuth Ambiguity under Spaceborne Multi-channel SAR Error Conditions" (Patent No.: 202210857718.7) provides a method and system for calculating azimuth ambiguity under spaceborne multi-channel SAR error conditions. Based on echo simulation processing, it calculates the azimuth ambiguity of spaceborne multi-channel SAR and can superimpose various errors from the entire space-to-ground link, effectively solving the problem of the lack of an accurate error model for calculating azimuth ambiguity in spaceborne multi-channel SAR. This method is only applicable to azimuth ambiguity calculation in monostatic SAR and not to azimuth range ambiguity calculation in bistatic SAR.

[0009] Currently, research on ambiguity calculation for co-orbit bistatic SAR is still in the exploratory stage. Existing methods have shortcomings in considering the impact of beam spatial synchronization, accurately constructing antenna gain models, and solving ambiguities under complex geometric relationships. Therefore, to overcome the deficiencies of existing technologies, a method for ambiguity calculation is needed that can combine beam spatial synchronization characteristics and accurately consider the geometric relationships, signal propagation laws, and antenna characteristics of co-orbit bistatic SAR systems. This would improve the accuracy and reliability of ambiguity calculation and provide strong technical support for the design and application of co-orbit bistatic SAR systems. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for calculating bistatic SAR ambiguity based on beam spatial synchronization.

[0011] A method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to the present invention includes the following steps: Step S1: Calculate the three-axis attitude angles of the launching and receiving satellites based on their initial orbital parameters. Step S2: Based on the center slant range and center Doppler frequency, calculate the azimuth and elevation angles of the beam centers of the transmitting and receiving satellites in their respective radar antenna coordinate systems. Step S3: Determine the range of values ​​for the distance ambiguity order and the orientation ambiguity order; Step S4: Iterate through the range ambiguity order and azimuth ambiguity order of each group, and calculate the corresponding antenna gain and signal propagation distance; Step S5: Based on the antenna gain and signal propagation distance, calculate the power ratio of each order of ambiguity component to the main signal component to obtain the bistatic SAR ambiguity at the specified distance. Step S6: Within the distance range corresponding to the wave position, select multiple distance points according to a preset step size, repeat steps S2 to S5 for each distance point, calculate and output the bistatic SAR ambiguity corresponding to each distance point.

[0012] Preferably, step S1 includes: obtaining the initial orbital parameters of the launching satellite and the receiving satellite; simultaneously solving the bistatic distance equation and the bistatic zero-Doppler equation to obtain the position of the ground target point; and calculating the three-axis attitude angles of the launching satellite and the receiving satellite, including yaw, based on the position of the ground target point. , looking up and scrolling Based on the aforementioned three-axis attitude angles, the transformation matrix from the Earth-fixed coordinate system to the radar antenna coordinate system is obtained. :

[0013] in, It is a polar shift matrix. This is the Earth's rotation matrix. For nutation matrix, The precession matrix, Indicates rotation about the X-axis. Indicates rotation about the Y-axis. Indicates rotation about the Z-axis. Right ascension of the ascending node, For track inclination, Argument of latitude This refers to the angle at which the satellite flies.

[0014] Preferably, step S2 includes: based on the center slope distance and center Doppler frequency The location of the scene center in the Earth-fixed coordinate system is calculated by combining the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation. Establish transformation matrices from the Earth-fixed coordinate system to the radar antenna coordinates of the transmitting and receiving satellites, and calculate the azimuth angle of the beam center in the radar antenna coordinate system. and pitch angle :

[0015]

[0016] Where the X-axis represents the azimuth of the antenna, the Y-axis represents the elevation of the antenna, and the Z-axis represents the line-of-sight direction of the antenna. The distance from the target satellite to the antenna phase center. , This represents the satellite's position in the Earth-fixed coordinate system.

[0017] Preferably, step S3 includes: determining the range ambiguity order based on the detection range constraint corresponding to the near-end detection incident angle of the bistatic satellite. ,in, The offset represents an integer multiple of the pulse repetition interval; the azimuth ambiguity order is determined based on the antenna directional attenuation characteristics. ,in, This represents an integer multiple of the Doppler frequency offset.

[0018] Preferably, the step of determining the azimuth ambiguity order based on the antenna directional attenuation characteristics is described. This includes: the minimum value of the azimuth ambiguity order. The corresponding detection distance is greater than the minimum distance to the ground point under the constraint of the minimum incident angle of the two satellites in the same orbit:

[0019] in, This is the distance corresponding to the minimum incident angle of the SAR satellite. The distance from the satellite to the Earth's surface is the beam distance. At the speed of light, The pulse repetition frequency, It is a floor function, and the resulting order is an integer.

[0020] Preferably, step S4 includes: for each ground target point distance Doppler frequency The target position in the Earth-fixed coordinate system was obtained by using the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation, respectively. The line-of-sight vector between the target position and the phase centers of the launching and receiving satellite antennas is mapped to the azimuth angle of the launching satellite in the radar antenna coordinate system using a transformation matrix from the Earth-fixed coordinate system to the radar antenna coordinate system. and pitch angle azimuth angle of the received satellite and pitch angle Based on the azimuth and elevation angles of the transmitting and receiving satellites in the radar antenna coordinate system, and in conjunction with the corresponding radar antenna parameters, calculate the transmitting antenna gain respectively. Receiver antenna gain Target launch slant range and receiving slant range ;

[0021]

[0022]

[0023]

[0024] in, For the exponential parameters of the element radiation pattern, This represents the total number of antenna azimuth elements. This represents the total number of antenna elements in the elevation direction. Indicates the fuzzy order of the distance. Indicates the order of ambiguity. It is the imaginary unit. It is the wavelength of the radar signal. This refers to the azimuth unit spacing. The pitch element spacing is the unit spacing. Indicates the center azimuth angle of the transmitted beam. Indicates the center elevation angle of the transmitted beam. Indicates the center azimuth angle of the received beam. Indicates the center elevation angle of the receiving beam. This represents the position vector of the launched satellite in space. This represents the position vector of the receiving satellite in space, where, and The calculation formula is:

[0025]

[0026] in, This is the azimuth length of the antenna. This is the antenna's elevation length.

[0027] Preferably, for each ground target point distance Doppler frequency The target position in the Earth-fixed coordinate system was obtained by using the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation, respectively. ,include:

[0028]

[0029] in, The bibasic slope distance of the target point being processed. It's the speed of light. It is the distance fuzziness order. The pulse repetition frequency, It is the Doppler center frequency of the main signal. Indicates the first Frequency shift corresponding to azimuth ambiguity. SAR antenna bandwidth A certain frequency within; The bibase distance equation is:

[0030] in, and These are the phase center position vectors of the SAR antennas of the transmitting and receiving satellites, respectively. The Doppler equation is:

[0031] in, and These are the phase center velocity vectors of the SAR antennas of the launching and receiving satellites, respectively. Wavelength; The Earth ellipsoid model is as follows:

[0032] in, The radius is the equatorial radius. Ground elevation, The polar radius is .

[0033] Preferably, step S5 includes: calculating the antenna gain corresponding to each range ambiguity and azimuth ambiguity based on the bistatic ambiguity calculation formula and radar antenna parameters, to obtain the ambiguity at a specified distance.

[0034] in, The ambiguity order is the order of orientation ambiguity. This concludes the distance blurring. Center Doppler frequency, Indicates the first Frequency shift corresponding to azimuth ambiguity. Indicates the Doppler processing bandwidth. These represent the transmit and receive antenna gains, respectively. These represent the transmit and receive antenna gains at the main target, respectively. These represent the distance from the launching satellite to the ambiguous point and the distance from the ambiguous point to the receiving satellite, respectively. Indicates the bistatic distance of the primary target.

[0035] Preferably, step S6 includes: converting the wave position into a corresponding detection range, and selecting a step size as follows: .

[0036] This invention also provides a co-orbit bistatic SAR ambiguity calculation system based on beam spatial synchronization. This system can be implemented by executing the steps of the co-orbit bistatic SAR ambiguity calculation method based on beam spatial synchronization. That is, those skilled in the art can understand the co-orbit bistatic SAR ambiguity calculation method based on beam spatial synchronization as a preferred embodiment of the co-orbit bistatic SAR ambiguity calculation system based on beam spatial synchronization. The system includes: Module M1 calculates the three-axis attitude angles of the launching and receiving satellites based on their initial orbital parameters. Module M2, based on the center slant range and center Doppler frequency, calculates the azimuth and elevation angles of the beam centers of the transmitting and receiving satellites in their respective radar antenna coordinate systems. Module M3 determines the range of values ​​for the distance ambiguity order and the orientation ambiguity order; Module M4 iterates through the range ambiguity order and azimuth ambiguity order of each group and calculates the corresponding antenna gain and signal propagation distance. Module M5 calculates the power ratio of each order of ambiguity component to the main signal component based on the antenna gain and signal propagation distance, and obtains the bistatic SAR ambiguity at a specified distance. Module M6 selects multiple distance points within the distance range corresponding to the wave position according to a preset step size, and repeatedly triggers the operation of modules M2, M3, M4, and M5 for each distance point to calculate and output the bistatic SAR ambiguity corresponding to each distance point.

[0037] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for calculating bistatic SAR ambiguity based on beam spatial synchronization of the present invention, under the condition of simultaneously satisfying zero Doppler constraint and beam spatial synchronization coverage, determines the three-axis attitude angles of the launching satellite and the receiving satellite by solving the bistatic geometry and Doppler equations, including yaw angle, pitch angle and roll angle, so as to provide control basis for precise beam pointing. (2) This invention reasonably defines the order range of range ambiguity and azimuth ambiguity by using geometric constraints and antenna pattern characteristics. Under the premise of ensuring coverage of effective ambiguity units, it significantly reduces invalid calculations and achieves efficient and accurate ambiguity solution. (3) The method proposed in this invention has a clear structure and stable algorithm. It is applicable to co-orbit bistatic SAR systems with different orbital configurations and wave positions. It has good versatility and engineering applicability and has broad application prospects in SAR system design, performance evaluation and mission planning. Attached Figure Description

[0038] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 The flowchart illustrates a method for calculating bistatic SAR ambiguity based on beam spatial synchronization, as provided in this invention.

[0039] Figure 2 This is a schematic diagram of the spatial relationship between a bistatic SAR satellite and ground points provided in an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of spatial synchronization of beams of a bistatic SAR satellite provided in an embodiment of the present invention.

[0041] Figure 4 This is a schematic diagram illustrating the variation of bistatic ambiguity with intrawavelength detection distance, provided in an embodiment of the present invention. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0043] Figure 1 A flowchart of a co-orbit bistatic SAR ambiguity calculation method based on beam spatial synchronization provided by the present invention is shown below. Figure 1 As shown, it includes the following steps: Step 1: Based on the initial orbital parameters of the SAR satellites before and after co-orbiting, calculate the three-axis attitude angles of the transmitting and receiving satellites under beam spatial synchronization at a certain wave position.

[0044] Specifically, a schematic diagram of the spatial relationship between bistatic SAR satellites and ground points is shown below. Figure 2 As shown in the diagram, this is a schematic diagram of the spatial synchronization of beams from a co-orbital bistatic SAR satellite. Figure 3 As shown.

[0045] In this embodiment, the simulation start time is set to 12:00:00 on July 1, 2007 (UTC time). The orbital parameters of the preceding and following satellites are: semi-major axis 6978.14 km, eccentricity 0.001, inclination 97.7924°, perigee argument 90°, right ascension of ascending node 189.163°, mean perigee angles 0° and 356° respectively, and apparent skewness of 35° on the right side of the satellite. The calculated three-axis attitude angles of the launched satellite are: yaw. -12.73°, pitch -4.32°, rolling 4.03°; Received satellite three-axis attitude angle: yaw 15.06°, pitch 4.10°, rolling It is -3.01°.

[0046] Step 2: Based on the center slant range and center Doppler frequency, and combining the bistatic distance equation, Doppler equation, and Earth ellipsoid model equation, calculate the azimuth and elevation angles of the beam centers of the launching and receiving satellites in the radar antenna coordinate system.

[0047] In this embodiment, the center slope distance For 900km and center Doppler frequency The value is 0, and the azimuth angle of the transmitting satellite radar antenna coordinate system corresponding to the beam center is calculated. -20.24°, pitch angle The azimuth angle is 7.58°, which is the lower azimuth angle in the receiving satellite radar antenna coordinate system. 20.24°, pitch angle It is 0.27°.

[0048] Step 3: Determine the range of the range ambiguity order based on the range constraint of the near-end detection incident angle of the bistatic satellite in the same orbit, and determine the range of the azimuth ambiguity order based on the attenuation characteristics of the antenna pattern.

[0049] In this embodiment, the distance fuzziness order The lower ambiguity order is 3 at different distances. It can be 2 or 1.

[0050] Step 4: For each set of range and azimuth ambiguities, calculate the corresponding antenna gain and range. Specifically, the parameters for the transmitting and receiving satellite antennas are as follows: the azimuth antenna size is 10 meters, the elevation antenna size is 3 meters, the number of azimuth TR modules is 256, the number of elevation TR modules is 32, the bandwidth is 250Hz, the frequency is 1.2GHz, and the PRF is 2000Hz. For each set of range ambiguity and azimuth ambiguity, the corresponding antenna gain and the corresponding range are calculated.

[0051] Step 5: Calculate the bistatic SAR ambiguity at the specified distance.

[0052] Step 6: For the distance corresponding to the wave position range, take the calculation step size, calculate the bistatic ambiguity corresponding to each distance point and output it.

[0053] Specifically, the schematic diagram of the variation of bistatic ambiguity with intra-wavelength detection distance is shown below. Figure 4 As shown, the ambiguity variation curves for the beam within the range of 869km to 935km are obtained.

[0054] This invention also provides a co-orbit bistatic SAR ambiguity calculation system based on beam spatial synchronization. This system can be implemented by executing the steps of the co-orbit bistatic SAR ambiguity calculation method based on beam spatial synchronization. That is, those skilled in the art can understand the co-orbit bistatic SAR ambiguity calculation method based on beam spatial synchronization as a preferred embodiment of the co-orbit bistatic SAR ambiguity calculation system based on beam spatial synchronization. The system includes: Module M1 calculates the three-axis attitude angles of the launching and receiving satellites based on their initial orbital parameters. Module M2, based on the center slant range and center Doppler frequency, calculates the azimuth and elevation angles of the beam centers of the transmitting and receiving satellites in their respective radar antenna coordinate systems. Module M3 determines the range of values ​​for the distance ambiguity order and the orientation ambiguity order; Module M4 iterates through the range ambiguity order and azimuth ambiguity order of each group and calculates the corresponding antenna gain and signal propagation distance. Module M5 calculates the power ratio of each order of ambiguity component to the main signal component based on the antenna gain and signal propagation distance, and obtains the bistatic SAR ambiguity at a specified distance. Module M6 selects multiple distance points within the distance range corresponding to the wave position according to a preset step size, and repeatedly triggers the operation of modules M2, M3, M4, and M5 for each distance point to calculate and output the bistatic SAR ambiguity corresponding to each distance point.

[0055] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0056] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for calculating bistatic SAR ambiguity based on beam spatial synchronization, characterized in that, include: Step S1: Calculate the three-axis attitude angles of the launching and receiving satellites based on their initial orbital parameters. Step S2: Based on the center slant range and center Doppler frequency, calculate the azimuth and elevation angles of the beam centers of the transmitting and receiving satellites in their respective radar antenna coordinate systems. Step S3: Determine the range of values ​​for the distance ambiguity order and the orientation ambiguity order; Step S4: Iterate through the range ambiguity order and azimuth ambiguity order of each group, and calculate the corresponding antenna gain and signal propagation distance; Step S5: Based on the antenna gain and signal propagation distance, calculate the power ratio of each order of ambiguity component to the main signal component to obtain the bistatic SAR ambiguity at the specified distance. Step S6: Within the distance range corresponding to the wave position, select multiple distance points according to a preset step size, repeat steps S2 to S5 for each distance point, calculate and output the bistatic SAR ambiguity corresponding to each distance point.

2. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 1, characterized in that, Step S1 includes: Obtain the initial orbital parameters of the launching and receiving satellites; By simultaneously solving the bistatic distance equation and the bistatic zero-Doppler equation, the location of the ground target point can be obtained. Based on the location of the ground target point, calculate the three-axis attitude angles of the launching and receiving satellites, including yaw. , looking up and scrolling ; Based on the aforementioned three-axis attitude angles, the transformation matrix from the Earth-fixed coordinate system to the radar antenna coordinate system is obtained. : in, It is a polar shift matrix. This is the Earth's rotation matrix. For nutation matrix, The precession matrix, Indicates rotation about the X-axis. Indicates rotation about the Y-axis. Indicates rotation about the Z-axis. Right ascension of the ascending node, For track inclination, Argument of latitude This refers to the angle at which the satellite flies.

3. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 1, characterized in that, Step S2 includes: According to the central slope distance and center Doppler frequency The location of the scene center in the Earth-fixed coordinate system is calculated by combining the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation. ; Establish transformation matrices from the Earth-fixed coordinate system to the radar antenna coordinates of the transmitting and receiving satellites, respectively, and calculate the azimuth angle of the beam center in the radar antenna coordinate system. and pitch angle : Where the X-axis represents the azimuth of the antenna, the Y-axis represents the elevation of the antenna, and the Z-axis represents the line-of-sight direction of the antenna. The distance from the target satellite to the antenna phase center. , This represents the satellite's position in the Earth-fixed coordinate system.

4. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 1, characterized in that, Step S3 includes: The range ambiguity order is determined based on the detection range constraint corresponding to the near-end detection incident angle of a bistatic satellite in the same orbit. ,in, Indicates an offset that is an integer multiple of the pulse repetition interval; Determine the azimuth ambiguity order based on the antenna directional attenuation characteristics. ,in, This represents an integer multiple of the Doppler frequency offset.

5. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 4, characterized in that, The azimuth ambiguity order is determined based on the antenna directional attenuation characteristics. ,include: The minimum value of the orientation ambiguity order The corresponding detection distance is greater than the minimum distance to the ground point under the constraint of the minimum incident angle of the two satellites in the same orbit: in, This is the distance corresponding to the minimum incident angle of the SAR satellite. The distance from the satellite to the Earth's surface is the beam distance. At the speed of light, The pulse repetition frequency, It is a floor function, and the resulting order is an integer.

6. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 4, characterized in that, Step S4 includes: For each ground target point distance Doppler frequency The target position in the Earth-fixed coordinate system was obtained by using the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation, respectively. ; The line-of-sight vector between the target position and the phase centers of the launching and receiving satellite antennas is mapped to the azimuth angle of the launching satellite in the radar antenna coordinate system using a transformation matrix from the Earth-fixed coordinate system to the radar antenna coordinate system. and pitch angle azimuth angle of the received satellite and pitch angle ; Based on the azimuth and elevation angles of the transmitting and receiving satellites in the radar antenna coordinate system, and in conjunction with the corresponding radar antenna parameters, the transmitting antenna gain is calculated respectively. Receiver antenna gain Target launch slant range and receiving slant range ; in, For the exponential parameters of the element radiation pattern, This represents the total number of antenna azimuth elements. This represents the total number of antenna elements in the elevation direction. Indicates the fuzzy order of the distance. Indicates the order of ambiguity. It is the imaginary unit. It is the wavelength of the radar signal. This refers to the azimuth unit spacing. The pitch element spacing is the unit spacing. Indicates the center azimuth angle of the transmitted beam. Indicates the center elevation angle of the transmitted beam. Indicates the center azimuth angle of the received beam. Indicates the center elevation angle of the receiving beam. This represents the position vector of the launched satellite in space. This represents the position vector of the receiving satellite in space, where, and The calculation formula is: in, This is the azimuth length of the antenna. This is the antenna's elevation length.

7. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 6, characterized in that, The above for each ground target point distance Doppler frequency The target position in the Earth-fixed coordinate system was obtained by using the bistatic distance equation, the Doppler equation, and the Earth ellipsoid model equation, respectively. ,include: in, The bibasic slope distance of the target point being processed. It's the speed of light. It is the distance fuzziness order. The pulse repetition frequency, It is the Doppler center frequency of the main signal. Indicates the first Frequency shift corresponding to azimuth ambiguity. SAR antenna bandwidth A certain frequency within; The bibase distance equation is: in, and These are the phase center position vectors of the SAR antennas of the transmitting and receiving satellites, respectively. The Doppler equation is: in, and These are the phase center velocity vectors of the SAR antennas of the launching and receiving satellites, respectively. Wavelength; The Earth ellipsoid model is as follows: in, The radius is the equatorial radius. Ground elevation, The polar radius is .

8. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 1, characterized in that, Step S5 includes: Based on the bistatic ambiguity calculation formula and radar antenna parameters, the antenna gain corresponding to each range ambiguity and azimuth ambiguity is calculated to obtain the ambiguity at a specified range: in, The ambiguity order is the order of orientation ambiguity. This concludes the distance blurring. Center Doppler frequency, Indicates the first Frequency shift corresponding to azimuth ambiguity. Indicates the Doppler processing bandwidth. These represent the transmit and receive antenna gains, respectively. These represent the transmit and receive antenna gains at the main target, respectively. These represent the distance from the launching satellite to the ambiguous point and the distance from the ambiguous point to the receiving satellite, respectively. Indicates the bistatic distance of the primary target.

9. The method for calculating bistatic SAR ambiguity based on beam spatial synchronization according to claim 1, characterized in that, Step S6 includes: Convert the wave position to the corresponding detection range and select a step size as follows: .

10. A co-orbit bistatic SAR ambiguity calculation system based on beam spatial synchronization, characterized in that, include: Module M1 calculates the three-axis attitude angles of the launching and receiving satellites based on their initial orbital parameters. Module M2, based on the center slant range and center Doppler frequency, calculates the azimuth and elevation angles of the beam centers of the transmitting and receiving satellites in their respective radar antenna coordinate systems. Module M3 determines the range of values ​​for the distance ambiguity order and the orientation ambiguity order; Module M4 iterates through the range ambiguity order and azimuth ambiguity order of each group and calculates the corresponding antenna gain and signal propagation distance. Module M5 calculates the power ratio of each order of ambiguity component to the main signal component based on the antenna gain and signal propagation distance, and obtains the bistatic SAR ambiguity at a specified distance. Module M6 selects multiple distance points within the distance range corresponding to the wave position according to a preset step size, and repeatedly triggers the operation of modules M2, M3, M4, and M5 for each distance point to calculate and output the bistatic SAR ambiguity corresponding to each distance point.

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