Method, system and satellite for determining doppler center of a spaceborne synthetic aperture radar

Abstract

The application discloses a kind of determination methods, systems and satellites of Doppler center of space-borne synthetic aperture radar, it is related to space-borne synthetic aperture radar technical field, method includes: obtaining and to the original data of satellite carried synthetic aperture radar in synthetic aperture time acquisition is parsed, obtains the Doppler frequency modulation slope and echo signal of synthetic aperture radar;According to Doppler frequency modulation slope and echo signal, the Doppler center of each distance unit of synthetic aperture radar is obtained;The Doppler center of all distance units is fitted, and the relationship curve between distance unit and Doppler center is obtained.The original data of satellite carried synthetic aperture radar in synthetic aperture time acquisition is analyzed by the application, the relationship curve between distance unit and Doppler center of synthetic aperture radar can be effectively obtained, based on the relationship curve, the SAR image with better focusing effect can be obtained.

Description

Technical Field

[0001] This invention relates to the field of spaceborne synthetic aperture radar technology, and in particular to a method, system, and satellite for determining the Doppler center of a spaceborne synthetic aperture radar. Background Technology

[0002] In SAR (Spaceborne Synthetic Aperture Radar) imaging processing, the Doppler center parameter is crucial for range migration calibration, azimuth focusing, and geometric calibration. Traditional methods for estimating the Doppler center parameter in spaceborne SAR are based on satellite attitude, orbit, and antenna beam pointing, requiring high accuracy of the measurement data. However, as SAR satellites reach the end of their operational lifespan, antenna patterns are prone to drift, meaning the antenna beam pointing deviates. In this situation, traditional Doppler center frequency calculation methods introduce angular errors, ultimately leading to defocusing and geometric distortion in the SAR image. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the shortcomings of existing technologies. Specifically, it provides a method, system, and satellite for determining the Doppler center of a spaceborne synthetic aperture radar, as detailed below:

[0004] 1) In a first aspect, the present invention provides a method for determining the Doppler center of a spaceborne synthetic aperture radar, the specific technical solution of which is as follows:

[0005] The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time is acquired and analyzed to obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar.

[0006] Based on the Doppler frequency modulation slope and echo signal, the Doppler center of each range cell of the synthetic aperture radar is obtained;

[0007] By fitting the Doppler centers of all distance cells, the relationship curve between the distance cells and the Doppler centers is obtained.

[0008] The beneficial effects of the method for determining the Doppler center of a spaceborne synthetic aperture radar provided by this invention are as follows:

[0009] When the antenna beam pointing of the synthetic aperture radar carried by the satellite deviates, by analyzing the raw data collected by the synthetic aperture radar during the synthetic aperture time, the relationship curve between the range cell and the Doppler center of the synthetic aperture radar can be effectively obtained. Based on this relationship curve, SAR images with better focusing effect can be obtained.

[0010] Based on the above scheme, the method for determining the Doppler center of a spaceborne synthetic aperture radar according to the present invention can be further improved as follows.

[0011] Furthermore, the process of obtaining the Doppler frequency modulation slope of the synthetic aperture radar includes:

[0012] The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time are analyzed to obtain the flight speed and orbital radius of the synthetic aperture radar.

[0013] The Doppler frequency modulation slope of the synthetic aperture radar is calculated based on its flight speed and trajectory radius.

[0014] Furthermore, based on the Doppler frequency modulation slope and echo signal, the Doppler center of each range cell of the synthetic aperture radar is obtained, including:

[0015] Construct a deslope function based on the Doppler frequency modulation slope;

[0016] The echo signal is de-skewing using a deskewing function to obtain the first signal;

[0017] The first signal is processed to obtain the Doppler center of each range cell of the synthetic aperture radar.

[0018] Furthermore, the Doppler centers of all range cells are fitted to obtain the relationship curves between the range cells and the Doppler centers, including:

[0019] Polynomial fitting is performed on the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers.

[0020] 2) Secondly, the present invention also provides a system for determining the Doppler center of a spaceborne synthetic aperture radar, the specific technical solution of which is as follows:

[0021] It includes a data parsing module, a Doppler center acquisition module, and a data fitting module;

[0022] The data parsing module is used to: acquire and parse the raw data collected by the synthetic aperture radar carried by the satellite during the synthetic aperture time, and obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar;

[0023] The Doppler center acquisition module is used to obtain the Doppler center of each range cell of the synthetic aperture radar based on the Doppler frequency modulation slope and the echo signal.

[0024] The data fitting module is used to fit the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers.

[0025] Based on the above scheme, the Doppler center determination system of a spaceborne synthetic aperture radar of the present invention can be further improved as follows.

[0026] Furthermore, the data parsing module is specifically used for:

[0027] The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time are analyzed to obtain the flight speed and orbital radius of the synthetic aperture radar.

[0028] The Doppler frequency modulation slope of the synthetic aperture radar is calculated based on its flight speed and trajectory radius.

[0029] Furthermore, the Doppler center acquisition module is specifically used for:

[0030] Construct a deslope function based on the Doppler frequency modulation slope;

[0031] The echo signal is de-skewing using a deskewing function to obtain the first signal;

[0032] The first signal is processed to obtain the Doppler center of each range cell of the synthetic aperture radar.

[0033] Furthermore, the data fitting module is specifically used to: perform polynomial fitting on the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers.

[0034] 3) In a third aspect, the present invention also provides a satellite, including an onboard processor, which is used to execute the method for determining the Doppler center of any of the above-described onboard synthetic aperture radars.

[0035] 4) In a fourth aspect, the present invention also provides an electronic device, the electronic device including a processor coupled to a memory, the memory storing at least one computer program, the at least one computer program being loaded and executed by the processor, so as to enable the electronic device to implement any of the above-mentioned methods for determining the Doppler center of a spaceborne synthetic aperture radar.

[0036] 5) In a fifth aspect, the present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements the method for determining the Doppler center of any of the above-mentioned spaceborne synthetic aperture radars.

[0037] It should be noted that the beneficial effects of the technical solutions of the second to fourth aspects of the present invention and their corresponding possible implementations can be found in the above description of the technical effects of the first aspect and its corresponding possible implementations, and will not be repeated here. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below:

[0039] Figure 1 This is a flowchart illustrating a method for determining the Doppler center of a spaceborne synthetic aperture radar according to an embodiment of the present invention.

[0040] Figure 2 This is a graph of data obtained by estimating Doppler center parameters using traditional methods;

[0041] Figure 3 This is a data graph of the Doppler center parameters obtained through this invention;

[0042] Figure 4 This is the curve showing the relationship between the distance unit and the Doppler center;

[0043] Figure 5 This is a SAR image obtained based on Doppler center parameters estimated using traditional methods.

[0044] Figure 6 This is a SAR image obtained based on Doppler center parameters estimated using traditional methods.

[0045] Figure 7 This is a schematic diagram of the structure of a Doppler center determination system for a spaceborne synthetic aperture radar according to an embodiment of the present invention;

[0046] Figure 8 This is a schematic diagram of the structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0047] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0048] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0049] like Figure 1 As shown in the figure, a method for determining the Doppler center of a spaceborne synthetic aperture radar according to an embodiment of the present invention includes the following steps:

[0050] S1 acquires and analyzes the raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time to obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar.

[0051] The process of obtaining the Doppler frequency modulation slope of the synthetic aperture radar includes:

[0052] S10. Analyze the raw data collected by the synthetic aperture radar (SAR) onboard the satellite during the synthetic aperture time to obtain the SAR's flight speed and orbital radius, specifically including:

[0053] S100. The raw data collected by the synthetic aperture radar onboard the satellite during the synthetic aperture time is analyzed to obtain the echo signal S(t). a ), and obtain the position of the synthetic aperture radar in the WGS84 coordinate system (S x ,S y ,S z ) and three velocity components (V x V y V z ), where S x Represents: The X-axis coordinate value of the synthetic aperture radar in the WGS84 coordinate system, S y Represents: The Y-axis coordinate value of the synthetic aperture radar in the WGS84 coordinate system, S z Represents: The Z-axis coordinate value of the synthetic aperture radar in the WGS84 coordinate system, V x Represents: the velocity component of the synthetic aperture radar along the X-axis in the WGS84 coordinate system, V y Represents: the velocity component of the synthetic aperture radar along the Y-axis in the WGS84 coordinate system, V z Represents the velocity component of the synthetic aperture radar in the Z-axis direction in the WGS84 coordinate system.

[0054] S101. Calculate the flight speed V of the synthetic aperture radar using the following formula. s :

[0055]

[0056] S102. Calculate the flight trajectory radius R of the synthetic aperture radar using the following formula. s :

[0057]

[0058] It should be noted that since the synthetic aperture radar is mounted on a satellite, the position and velocity of the synthetic aperture radar can be considered to be the same as the position and velocity of the satellite.

[0059] S11. Based on the flight speed and trajectory radius of the synthetic aperture radar, the Doppler frequency modulation slope of the synthetic aperture radar is calculated, specifically including:

[0060] S110. Calculate the equivalent velocity V of the synthetic aperture radar beam on the ground using the following formula. g :

[0061]

[0062] Among them, R e R0 represents the average radius of the Earth, R0 represents the distance between the synthetic aperture radar and the target to be imaged (i.e., the range cell), and θ represents the forward tilt angle of the synthetic aperture radar.

[0063] S111. Calculate the Doppler frequency modulation slope f′ of the synthetic aperture radar using the following formula. dr :

[0064]

[0065] Where λ represents the wavelength of the synthetic aperture radar, and θ r This indicates the equivalent forward slope angle of the ground.

[0066] S2. Based on the Doppler frequency modulation slope and echo signal, the Doppler center of each range cell of the synthetic aperture radar is obtained, specifically including:

[0067] S20. Construct a deslope function based on the Doppler frequency modulation slope. Deslope function S sl (t a The expression for ) is: Among them, t a The time indicates the moment, and j represents the imaginary part identifier.

[0068] S21. The echo signal is de-skewed using a de-skew function to obtain the first signal. In the first signal, at time t... a The amplitude S1(t) a )for:

[0069]

[0070] Where A0 represents the signal amplitude, f dc f represents the Doppler center frequency. dr Δf represents the azimuth frequency modulation slope of the echo signal. dr This represents the difference in azimuth frequency modulation slope in the echo signal at time t. a The amplitude is S(t) a ).

[0071] S22. Process the first signal to obtain the Doppler center of each range cell of the synthetic aperture radar, specifically including the following steps:

[0072] S220. Perform a Fast Fourier Transform (FFT) on the first signal to convert it to the range-Doppler (RD) domain, obtaining a second signal in the azimuth frequency domain (i.e., the azimuth frequency domain where the azimuth direction frequency is located). In the second signal, at the azimuth frequency η... a The amplitude is S1(η) a ):

[0073]

[0074] Where A0 represents the signal amplitude, f dc f represents the Doppler center frequency. dr Δf represents the azimuth frequency modulation slope of the echo signal. dr η represents the difference in azimuth frequency modulation slope. a Indicates the azimuth frequency.

[0075] S221. Upsample the second signal to obtain the third signal, specifically:

[0076] For η a Zero-padding is performed, and the frequency domain axis after zero-padding is represented as follows:

[0077] η′ a =[0 … 0 η a 0 … 0]

[0078] This yields the third signal, in which the azimuth frequency η′ is... a The amplitude is S1(η′) a ):

[0079]

[0080] Where A0 represents the signal amplitude, f dc f represents the Doppler center frequency. dr Δf represents the azimuth frequency modulation slope of the echo signal. dr η′ represents the difference in azimuth frequency modulation slope. a Indicates the azimuth frequency.

[0081] S222. Perform an inverse fast Fourier transform on the third signal to convert it to the two-dimensional time domain, obtaining the fourth signal. In the fourth signal, at time t′ a The amplitude is S1(t′) a ):

[0082] S1(t′ a )=A0exp(j2πf dc t′ a +jπΔf dr (t′ a ) 2 )

[0083] The time t′ of the fourth signal a Represented as: t′ a =(-Na′ / 2:1:Na′ / 2-1)·PRF′ / Na′.

[0084] Where Na′ represents the azimuth sampling number of the upsampled signal, i.e., the fourth signal, Na′=N·Na, where Na is a unified symbol, representing the azimuth sampling number of the first signal, and N represents the upsampling factor used when upsampling the second signal. For example, when η′ a =[0 η a When η' is 0, N = 3. a =[0 0 η a When N=5, PRF′ represents the pulse repetition frequency of the upsampled signal, i.e., the fourth signal. PRF′=N·PRF, where PRF represents the pulse repetition frequency of the first signal.

[0085] S223. Analyze the fourth signal to obtain the Doppler center of each range cell of the synthetic aperture radar, specifically including the following steps:

[0086] S2230. First, the fourth signal is processed to obtain the signal between two adjacent pulse repetition intervals (PRT). In the signal between two adjacent pulse repetition intervals, at time t′ a The amplitude is S2(t′) a ): S2(t′ a )=A0exp(j2πf dc (t′ a +τ)+jπΔf dr (t′ a +τ) 2 ), where τ=1 / PRF′, represents the time difference between the fourth signal and the signal between the repetition intervals of the two adjacent pulses.

[0087] Based on each time t′ a S1(t′) a ) and S2(t′ a ), thus obtaining the fifth signal, in which S1(t′) a ) and S2(t′ a The conjugate dot product result S3(t′) a ,τ) is:

[0088]

[0089] Wherein, conj(S2(t′) a )) means: for S2(t′ a Perform conjugation processing.

[0090] S2231. Then, the fifth signal is dephased, and the azimuth phase Φ of the echo signal is obtained using the following formula:

[0091] Φ=angle(S3(t′a ,τ))=2πf dc τ-πΔf dr τ 2

[0092] Here, angle(·) represents phase taking.

[0093] S2232. Differentiating the phase Φ, we obtain the Doppler center frequency of the current range cell:

[0094]

[0095] The Doppler center frequency corresponding to each distance cell was calculated using the method described above.

[0096] S3. Fit the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers, specifically:

[0097] Polynomial fitting is performed on the Doppler centers of all range cells to obtain the relationship curve between the range cells and the Doppler centers. SAR imaging is then performed based on the relationship curve between the range cells and the Doppler centers to obtain SAR images.

[0098] The beneficial effects of this invention are as follows:

[0099] 1) This invention utilizes deskewing processing to reduce the impact of Doppler frequency aliasing.

[0100] 2) This invention avoids introducing Doppler center ambiguity error through upsampling processing and directly obtains the true Doppler center estimate.

[0101] The technical effects of the present invention will be explained in the following manner:

[0102] The effectiveness and superiority of the spaceborne SAR Doppler center parameter estimation method based on echo data proposed in this patent are verified through two experiments. Experiment 1 compares the performance of the proposed Doppler center parameter estimation method with that of traditional estimation methods using Doppler center parameter curves. Experiment 2 directly performs SAR imaging processing using the Doppler center parameters estimated by the proposed method and the traditional method, respectively, and visually compares the imaging results. The experimental results are as follows: Figures 2 to 6 As shown, according to Figures 2 to 4 It can be seen that the method proposed in this invention can solve the problem of Doppler center winding along the distance direction. Figure 5 and Figure 6 It is known that traditional methods result in large errors in the estimated Doppler center parameters, leading to defocusing of the generated SAR images. The Doppler center parameters obtained using this invention have smaller errors, meeting SAR imaging requirements, and the generated SAR images meet design quality standards.

[0103] In the above embodiments, although the steps are numbered S1, S2, etc., they are only specific embodiments given by the present invention. Those skilled in the art can adjust the execution order of S1, S2, etc. according to the actual situation, which is also within the protection scope of the present invention. It can be understood that in some embodiments, some or all of the above embodiments may be included.

[0104] like Figure 7 As shown, an embodiment of the present invention provides a Doppler center determination system 200 for a spaceborne synthetic aperture radar, which includes a data parsing module 201, a Doppler center acquisition module 202, and a data fitting module 203.

[0105] The data parsing module 201 is used to: acquire and parse the raw data collected by the synthetic aperture radar carried by the satellite during the synthetic aperture time, and obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar;

[0106] The Doppler center acquisition module 202 is used to: obtain the Doppler center of each range cell of the synthetic aperture radar based on the Doppler frequency modulation slope and the echo signal;

[0107] The data fitting module 203 is used to: fit the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers.

[0108] Optionally, in the above technical solution, the data parsing module 201 is specifically used for:

[0109] The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time are analyzed to obtain the flight speed and orbital radius of the synthetic aperture radar.

[0110] The Doppler frequency modulation slope of the synthetic aperture radar is calculated based on its flight speed and trajectory radius.

[0111] Optionally, in the above technical solution, the Doppler center acquisition module 201 is specifically used for:

[0112] Construct a deslope function based on the Doppler frequency modulation slope;

[0113] The echo signal is de-skewing using a deskewing function to obtain the first signal;

[0114] The first signal is processed to obtain the Doppler center of each range cell of the synthetic aperture radar.

[0115] Optionally, in the above technical solution, the Doppler center acquisition module 202 is specifically used for:

[0116] The first signal is obtained by performing a frequency domain transformation on the complex signal.

[0117] Construct a deslope function based on the Doppler frequency modulation slope;

[0118] The first signal is de-scratched using a de-scratching function to obtain the second signal;

[0119] The second signal is processed to obtain the Doppler center of each range cell of the synthetic aperture radar.

[0120] Optionally, in the above technical solution, the data fitting module 203 is specifically used to: perform polynomial fitting on the Doppler centers of all distance units to obtain the relationship curve between the distance units and the Doppler centers.

[0121] It should be noted that the beneficial effects of the Doppler center determination system 200 for spaceborne synthetic aperture radar provided in the above embodiments are the same as those of the Doppler center determination method for spaceborne synthetic aperture radar described above, and will not be repeated here. Furthermore, the system provided in the above embodiments is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the system can be divided into different functional modules according to the actual situation to complete all or part of the functions described above. In addition, the system and method embodiments provided in the above embodiments belong to the same concept, and their specific implementation process is detailed in the method embodiments, and will not be repeated here.

[0122] The Doppler center determination system of the spaceborne synthetic aperture radar of the present invention can be a computer program (including program code) running on a computer device. For example, the Doppler center determination system of the spaceborne synthetic aperture radar of the present invention is an application software that can be used to execute the corresponding steps in the Doppler center determination method of the spaceborne synthetic aperture radar of the present invention.

[0123] In some embodiments, the Doppler center determination system of the spaceborne synthetic aperture radar of the present invention can be implemented in a combination of hardware and software. As an example, the Doppler center determination system of the spaceborne synthetic aperture radar of the present invention can be a processor in the form of a hardware decoding processor, which is programmed to execute the Doppler center determination method of the spaceborne synthetic aperture radar of the present invention. For example, the processor in the form of a hardware decoding processor can be one or more application-specific integrated circuits (ASICs), DSPs, programmable logic devices (PLDs), complex programmable logic devices (CPLDs), field-programmable gate arrays (FPGAs), or other electronic components.

[0124] The modules described in the embodiments of this invention can be implemented in software or hardware. The names of the modules are not, in some cases, limiting the scope of the module itself.

[0125] A satellite according to an embodiment of the present invention includes an onboard processor, which is used to execute any of the above-described methods for determining the Doppler center of an onboard synthetic aperture radar.

[0126] An electronic device according to an embodiment of the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements any of the above-described methods for determining the Doppler center of a spaceborne synthetic aperture radar. That is, an electronic device according to an embodiment of the present invention may include, but is not limited to: a processor and a memory; the memory is used to store the computer program; the processor is used to execute the method for determining the Doppler center of a spaceborne synthetic aperture radar as shown in any embodiment of the present invention by calling the computer program.

[0127] In one alternative embodiment, an electronic device is provided, such as Figure 8 As shown, Figure 8 The illustrated electronic device 4000 includes a processor 4001 and a memory 4003. The processor 4001 and the memory 4003 are connected, for example, via a bus 4002. Optionally, the electronic device 4000 may further include a transceiver 4004, which can be used for data interaction between the electronic device and other electronic devices, such as sending and / or receiving data. It should be noted that in practical applications, the transceiver 4004 is not limited to one type, and the structure of the electronic device 4000 does not constitute a limitation on the embodiments of the present invention.

[0128] Processor 4001 may be a CPU (Central Processing Unit), a general-purpose processor, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute the various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this invention. Processor 4001 may also be a combination that implements computational functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0129] Bus 4002 may include a path for transmitting information between the aforementioned components. Bus 4002 may be a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus, etc. Bus 4002 can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 8 The bus 4002 is represented by only one thick line, but this does not mean that there is only one bus or one type of bus.

[0130] The memory 4003 may be ROM (Read Only Memory) or other types of static storage devices capable of storing static information and instructions, RAM (Random Access Memory) or other types of dynamic storage devices capable of storing information and instructions, or EEPROM (Electrically Erasable Programmable Read Only Memory), CD-ROM (Compact Disc Read Only Memory) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto.

[0131] The memory 4003 stores the application code (computer program) for executing the present invention, and its execution is controlled by the processor 4001. The processor 4001 executes the application code stored in the memory 4003 to implement the content shown in the foregoing method embodiments.

[0132] Among them, electronic devices can also be terminal devices, which can be any device that can install applications, including at least one of smartphones, tablets, laptops, desktop computers, smart speakers, smartwatches, smart TVs, and smart in-vehicle devices.

[0133] It should be noted that, Figure 8 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0134] An embodiment of the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any of the above-described methods for determining the Doppler center of a spaceborne synthetic aperture radar.

[0135] Alternatively, the computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a compact disc read-only memory (CD-ROM), magnetic tape, a floppy disk, and an optical data storage device, etc.

[0136] In an exemplary embodiment, a computer program product or computer program is also provided, which includes computer instructions stored in a computer-readable storage medium. A processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform any of the aforementioned methods for determining the Doppler center of a spaceborne synthetic aperture radar.

[0137] Computer program code for performing the operations of this invention can be written in one or more programming languages ​​or a combination thereof. These programming languages ​​include object-oriented programming languages—such as Java, Smalltalk, and C++—and conventional procedural programming languages—such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0138] It should be understood that the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of methods and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0139] The computer-readable storage medium provided in this invention can be, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EEPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0140] The aforementioned computer-readable storage medium carries one or more programs, which, when executed by the electronic device, cause the electronic device to perform the method shown in the above embodiments.

[0141] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this invention is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this invention.

[0142] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and represent a limitation on a specific order or sequence. Where appropriate, the order of use for similar objects can be interchanged so that the embodiments of this application described herein can be implemented in an order other than that shown or described.

[0143] Those skilled in the art will recognize that this invention can be implemented as a system, method, or computer program product. Therefore, this invention can be specifically implemented in the following forms: it can be entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "system." Furthermore, in some embodiments, this invention can also be implemented as a computer program product contained in one or more computer-readable media, which includes computer-readable program code.

[0144] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the Doppler center of a spaceborne synthetic aperture radar, characterized in that, include: The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time is acquired and analyzed to obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar. The process of obtaining the Doppler center of each range cell of the synthetic aperture radar based on the Doppler frequency modulation slope and the echo signal includes: constructing a deskewing function based on the Doppler frequency modulation slope; performing deskewing processing on the echo signal using the deskewing function to obtain a first signal; performing a fast Fourier transform on the first signal to convert the first signal to the range-Doppler domain to obtain a second signal in the azimuth frequency domain; performing upsampling processing on the second signal to obtain a third signal; performing an inverse fast Fourier transform on the third signal to convert the third signal to the two-dimensional time domain to obtain a fourth signal; and analyzing the fourth signal to obtain the Doppler center of each range cell of the synthetic aperture radar. By fitting the Doppler centers of all distance cells, the relationship curve between the distance cells and the Doppler centers is obtained.

2. The method for determining the Doppler center of a spaceborne synthetic aperture radar according to claim 1, characterized in that, The process of obtaining the Doppler frequency modulation slope of the synthetic aperture radar includes: The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time are analyzed to obtain the flight speed and orbital radius of the synthetic aperture radar. The Doppler frequency modulation slope of the synthetic aperture radar is calculated based on its flight speed and trajectory radius.

3. The method for determining the Doppler center of a spaceborne synthetic aperture radar according to any one of claims 1 to 2, characterized in that, By fitting the Doppler centers of all range cells, the relationship curves between the range cells and the Doppler centers are obtained, including: Polynomial fitting is performed on the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers.

4. A system for determining the Doppler center of a spaceborne synthetic aperture radar, characterized in that, It includes a data parsing module, a Doppler center acquisition module, and a data fitting module; The data parsing module is used to: acquire and parse the raw data collected by the synthetic aperture radar carried by the satellite during the synthetic aperture time, and obtain the Doppler frequency modulation slope and echo signal of the synthetic aperture radar. The Doppler center acquisition module is used to: obtain the Doppler center of each range cell of the synthetic aperture radar based on the Doppler frequency modulation slope and the echo signal; The data fitting module is used to: fit the Doppler centers of all distance cells to obtain the relationship curve between the distance cells and the Doppler centers; The Doppler center acquisition module is specifically used to: construct a deslope function based on the Doppler frequency modulation slope; The echo signal is de-skewing using the de-skewing function to obtain a first signal. The first signal is then subjected to a Fast Fourier Transform (FFT) to convert it to the range-Doppler domain, resulting in a second signal in the azimuth frequency domain. The second signal is then upsampled to obtain a third signal. The third signal is then subjected to an Inverse Fast Fourier Transform (IFFT) to convert it to the two-dimensional time domain, resulting in a fourth signal. The fourth signal is then analyzed to obtain the Doppler center of each range cell of the synthetic aperture radar.

5. The system for determining the Doppler center of a spaceborne synthetic aperture radar according to claim 4, characterized in that, The data parsing module is specifically used for: The raw data collected by the synthetic aperture radar on the satellite during the synthetic aperture time are analyzed to obtain the flight speed and orbital radius of the synthetic aperture radar. The Doppler frequency modulation slope of the synthetic aperture radar is calculated based on its flight speed and trajectory radius.

6. A satellite, characterized in that, Includes a spaceborne processor for executing a method for determining the Doppler center of a spaceborne synthetic aperture radar as described in any one of claims 1 to 3.

7. An electronic device, characterized in that, The system includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements a method for determining the Doppler center of a spaceborne synthetic aperture radar as described in any one of claims 1 to 3.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements a method for determining the Doppler center of a spaceborne synthetic aperture radar as described in any one of claims 1 to 3.

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