Bistatic SAR phase synchronization method and device based on frequency scanning

Abstract

The invention provides a bistatic SAR (Synthetic Aperture Radar) phase synchronization method and device based on frequency scanning, and belongs to the technical field of bistatic SAR phase synchronization, and the method comprises the steps: constructing a transmitting signal model of an F-SCAN synchronization system, introducing transmitting delay into the transmitting signal model based on the characteristics of a frequency scanning signal, the description module is used for describing emission characteristics of signals under different beam pointing angles; f-SCAN represents frequency scanning; establishing a receiver of the F-SCAN synchronization system, receiving and demodulating the frequency scanning signal to obtain an expression of the demodulated signal, and extracting information including a synchronization phase from the expression; and performing pulse compression processing on the demodulated signal, realizing pulse compression of the signal through a frequency domain matched filter, and extracting a synchronous phase from a compression result to complete phase synchronization. According to the invention, the high signal-to-noise ratio of the synchronization signal in the whole orbit period is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of bistatic synthetic aperture radar (SAR) phase synchronization, and particularly to a bistatic SAR phase synchronization method and device based on frequency scanning. Background Art

[0002] The bistatic synthetic aperture radar (SAR) system is a special imaging technology, where the transmitter and receiver are respectively installed on two independent platforms. This system has significant advantages such as flexible baseline configuration, the ability to frequently revisit the target area, and obtaining multi-angle scattering information. However, the core technical problem lies in the phase synchronization between the two platforms. Since the data acquisition of the bistatic SAR system depends on different oscillators, and the deviation between the oscillators will cause phase errors during the demodulation of the echo signal, precise phase synchronization must be achieved to ensure the coherence of the data.

[0003] Currently, the phase synchronization methods for bistatic SAR systems are mainly divided into three categories: duplex communication methods (such as pulse pair transmission and MirrorLink scheme), simplex communication methods (such as direct wave synchronization and push-to-talk synchronization), and linkless methods (such as GPS-tamed clock and echo-based post-processing). However, each of these methods has its limitations. For example, direct wave synchronization is not applicable to spaceborne bistatic SAR systems; the accuracy of push-to-talk synchronization depends on the orbit measurement accuracy; the stability of the GPS-tamed clock is not sufficient to meet the high-precision requirements; and the echo-based post-processing method lacks sufficient robustness. In contrast, the pulse pair transmission scheme has become the most commonly used method due to its high technology maturity, strong engineering feasibility, and ability to meet the phase synchronization accuracy requirements. For example, the TanDEM-X system uses 6 dedicated horn antennas, while the LT-1 system uses 4 four-helix antennas to achieve phase synchronization, and these on-orbit distributed SAR systems all adopt the wide-beam synchronization system.

[0004] However, the existing technical solutions still have obvious drawbacks. The TanDEM-X and LT-1 dual-satellite systems adopt a dual-helix formation method, resulting in a large fluctuation in the signal-to-noise ratio (SNR) of the synchronization signal within the orbit period, thereby affecting the accuracy of phase synchronization. Taking the LT-1 system as an example, its orbit period is 97 minutes, while the synchronization process usually only lasts for 10 minutes. This means that the synchronization process may occur under low SNR conditions, thus generating large phase errors and ultimately affecting the subsequent imaging and interferometric measurement effects. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a bistatic SAR phase synchronization method and device based on frequency scanning, which is a phase synchronization scheme based on frequency scanning (F-SCAN). The F-SCAN technology and the corresponding signal model are introduced into the synchronization system to achieve dynamic scanning of narrow beams, transmit and receive synchronization signals with maximum gain, and ensure high SNR of the synchronization signals throughout the orbital period.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A bistatic SAR phase synchronization method based on frequency scanning includes the following steps:

[0008] Step 1: Construct the transmit signal model of the F-SCAN synchronization system. The transmit signal model is based on the characteristics of the frequency scanning signal and introduces transmit delay to describe the transmit characteristics of the signal at different beam pointing angles; F-SCAN represents frequency scanning.

[0009] Step 2: Establish the receiver of the F-SCAN synchronization system, receive and demodulate the frequency scanning signal, obtain the expression of the demodulated signal, and extract the information containing the synchronization phase from it.

[0010] Step 3: Perform pulse compression processing on the demodulated signal, implement signal pulse compression through a frequency domain matched filter, and extract the synchronization phase from the compression result to complete phase synchronization.

[0011] The present invention also provides a bistatic SAR phase synchronization device based on frequency scanning, including the following modules:

[0012] A transmit signal model construction module that constructs the transmit signal model of the F-SCAN synchronization system. The transmit signal model is based on the characteristics of the frequency scanning signal and introduces transmit delay to describe the transmit characteristics of the signal at different beam pointing angles; F-SCAN represents frequency scanning.

[0013] A receiver construction module that establishes the receiver of the F-SCAN synchronization system, receives and demodulates the frequency scanning signal, obtains the expression of the demodulated signal, and extracts the information containing the synchronization phase from it.

[0014] A phase synchronization module that performs pulse compression processing on the demodulated signal, implements signal pulse compression through a frequency domain matched filter, and extracts the synchronization phase from the compression result to complete phase synchronization.

[0015] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the steps of the above-mentioned bistatic SAR phase synchronization method based on frequency scanning.

[0016] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-described bistatic SAR phase synchronization method based on frequency scanning are implemented.

[0017] Beneficial effects:

[0018] 1. Significantly improve the signal-to-noise ratio: By introducing the frequency scanning technology and replacing the traditional wide-beam synchronization system with the dynamic scanning of narrow beams, the minimum signal-to-noise ratio of the synchronization signal can be significantly improved throughout the orbital period. For example, in the LT-1 system, the minimum signal-to-noise ratio is increased from 37.8049 dB to 54.2679 dB, effectively avoiding the synchronization error problem caused by low signal-to-noise ratio.

[0019] 2. Reduce the phase error: Due to the improvement of the signal-to-noise ratio, the phase synchronization error is greatly reduced. The simulation results show that the standard deviation of the residual phase error of the method of the present invention is only 0.0334°, compared with 0.6786° of the prior art, and the error is reduced by nearly 20 times. This enables the bistatic SAR system to obtain higher accuracy in imaging and interferometric measurement.

[0020] 3. Enhance the system robustness: The method of the present invention maintains a high signal-to-noise ratio throughout the orbital period, reduces the risk of synchronization failure caused by signal-to-noise ratio fluctuations, and improves the stability and reliability of the system.

[0021] 4. Strong compatibility: The processing flow of the method of the present invention is similar to the existing two-way pulse pair transmission scheme, and it is easy to be integrated into the existing bistatic SAR system without large-scale modification of the existing system, having good engineering feasibility.

[0022] Therefore, compared with the double-star pulse pair transmission synchronization scheme under the traditional wide-beam synchronization system, the present invention introduces the frequency scanning technology, replaces the original wide beam with the dynamic scanning of narrow beams, significantly improves the minimum signal-to-noise ratio of the synchronization signal within the orbital period, and reduces the phase error. Brief description of the drawings

[0023] Figure 1 is a flowchart of a bistatic SAR phase synchronization method based on frequency scanning according to the present invention;

[0024] Figure 2 is a graph of the change of the signal-to-noise ratio SNR of LT-1 and the present invention within the orbital period;

[0025] Figure 3 is a graph of the change of the phase synchronization error with the SNR;

[0026] Figure 4a , Figure 4b is a graph of the simulation results; wherein, Figure 4aThe synchronous simulation result of LT-1 Figure 4b The synchronous simulation result of the present invention

[0027] Figure 5 The figure shows a schematic diagram of a bistatic SAR phase synchronization device based on frequency scanning according to the present invention Specific implementation manners

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other

[0029] As Figure 1 shown, according to an embodiment of the present invention, a bistatic SAR phase synchronization method based on frequency scanning includes the following steps

[0030] Step 101: Establish a transmission signal model of the F-SCAN synchronization system to obtain a transmission signal

[0031] Due to the essential characteristics of frequency scanning, the F-SCAN signal introduces a transmission delay compared with the traditional LFM signal (linear frequency modulation signal). When the beam points to angle, the transmission signal can be expressed as

[0032] ;

[0033] ;

[0034] wherein, represents the frequency-scanned transmit antenna gain when the beam points to angle, is a rectangular window function, represents the fast time, represents the transmission delay, refers to the dwell time, represents the dwell coefficient, is the starting scan angle, is the scan angle range, j is the imaginary unit, exp{} represents the exponential function, represents the chirp rate of the synchronization signal, represents the pulse width of the synchronization signal, represents the carrier frequency of the synchronization signal

[0035] Step 102: Establish a receiver in the F-SCAN synchronization system, receive and demodulate to obtain a received signal

[0036] Based on the established transmission signal model above, the received signal of the F-SCAN synchronization system can be expressed as:

[0037] ;

[0038] wherein, represents the frequency-scanning receiving antenna gain at the beam pointing angle, is the one-way transmission delay between the slave satellite and the master satellite, is the distance between the master and slave satellites, represents the speed of light.

[0039] Subsequently, the received signal is demodulated by the local oscillator signal with a frequency of and further expressed after down-conversion as:

[0040] ;

[0041] wherein, is the received signal after down-conversion, and the intermediate parameter , j is the imaginary unit, is the residual modulation phase generated when is not exactly the same as during down-conversion, and it is also the synchronization phase to be extracted in the present invention for compensation during subsequent imaging. Since is amplitude modulation, it can be normalized, and this term may be ignored in the subsequent derivation. At this time, the received signal of the receiver of the F-SCAN synchronization system can be expressed as:

[0042] ;

[0043] Step 103: Perform pulse compression on the received signal received and demodulated by the receiver in the F-SCAN synchronization system, and extract the synchronization phase.

[0044] To extract the synchronization phase , it is necessary to perform pulse compression on the signal, and this step is usually carried out in the frequency domain.

[0045] First, use the principle of stationary phase (POSP) to convert the signal to the frequency domain:

[0046] ;

[0047] wherein, is the signal converted to the frequency domain, f represents the frequency, the center frequency , is the sign function, is the Fourier transform, is the dwell bandwidth of the frequency scan signal.

[0048] Matched filter for pulse compression In the frequency domain, it can be expressed as:

[0049] ;

[0050] where is the synchronization signal bandwidth.

[0051] Then the matched filter output is:

[0052] ;

[0053] After transforming back to the time domain, it is:

[0054] ;

[0055] where is the signal transformed back to the time domain, is the inverse Fourier transform.

[0056] It can be seen from the above formula that the received signal pulse of the F-SCAN synchronization system is compressed to At, the signal is sampled at to obtain the phase at the peak, and the phase can be obtained. Therefore, it is theoretically proved that the F-SCAN synchronization system can correctly extract the phase of the synchronization signal.

[0057] Example:

[0058] This example is based on the orbit parameters of LT-1. According to the synchronization antenna beam pattern and the SNR calculation formula, the SNR change of the synchronization signal within the orbit period before and after applying the method of the present invention is calculated, and then the influence of the SNR change on the phase synchronization error is obtained. The feasibility of the method proposed by the present invention is verified by comparison.

[0059] ;

[0060] where represents the peak power, is the distance between the master and slave satellites, is the transmitting antenna gain, is the receiving antenna gain, is the dwell pulse width of the frequency scan signal, is the Boltzmann constant, is the system temperature, is the wavelength corresponding to the carrier frequency, is the SNR of the frequency scan synchronization signal.

[0061] ;

[0062] wherein, represents the synchronization frequency, represents the noise spectrum. For additive white Gaussian noise, . is the azimuth transfer function for imaging processing, is the standard deviation of the theoretical phase error. As Figure 2 shows, when the frequency sweep scheme is not applied, the minimum SNR is 37.8049 dB and the maximum SNR is 65.2951 dB, indicating that the SNR of LT-1 varies significantly within the orbital period. Since the synchronization time of the LT-1 system within the orbital period does not exceed 10 minutes, there is a possibility of low signal-to-noise ratio during synchronization, which will lead to a large synchronization error and further affect the accuracy of imaging and interferometry.

[0063] After applying the frequency sweep scheme, although the maximum SNR of the synchronization signal within the orbital period decreases slightly due to the actual pulse width of the F-SCAN signal being smaller than that of the system signal, the minimum SNR is significantly increased from 37.8049 dB to 54.2679 dB. As Figure 3 can be seen, when SNR > 55 dB, the phase error is less than 0.05°, and further increasing the SNR has little effect on reducing the phase synchronization error; when SNR < 35 dB, the phase error exceeds 0.5°, and it is necessary to continue to increase the SNR. It can be seen that the method proposed in the present invention significantly reduces the phase error throughout the orbital period, and the following further verifies this result through simulation.

[0064] Taking the minimum possible SNR within the orbital period for the simulation experiment, the synchronization simulation results of LT-1 are as Figure 4a shown, where the std of the residual phase error is 0.6786°. The synchronization simulation results of the method proposed in the present invention are shown in Figure 4b, where the std of the residual phase error is 0.0334°. This verifies the superiority of the method proposed in the present invention and proves its potential for application in future bistatic SAR missions.

[0065] As Figure 5 shown, the present invention also provides a bistatic SAR phase synchronization device based on frequency scanning, including the following modules:

[0066] Transmitted signal model construction module, which constructs the transmitted signal model of the F-SCAN synchronization system. The transmitted signal model is based on the characteristics of the frequency sweep signal and introduces the transmission delay to describe the transmission characteristics of the signal at different beam pointing angles; F-SCAN represents frequency scanning;

[0067] The receiving mechanism building module builds a receiver for the F-SCAN synchronization system, receives and demodulates the frequency-scanned signal, obtains the expression of the demodulated signal, and extracts the information containing the synchronization phase from it;

[0068] The phase synchronization module performs pulse compression processing on the demodulated signal, realizes the pulse compression of the signal through a frequency-domain matched filter, and extracts the synchronization phase from the compression result to complete the phase synchronization.

[0069] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned dual-base SAR phase synchronization method based on frequency scanning are realized.

[0070] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned dual-base SAR phase synchronization method based on frequency scanning are realized.

[0071] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes. The solutions in the embodiments of the present invention can be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0072] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram can be realized by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the specified functions in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0073] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement the functions specified in the flowchart(s) Figure 1 a flowchart or flowcharts and / or block(s) Figure 1 a block or blocks.

[0074] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing steps for implementing the functions specified in the flowchart(s) Figure 1 a flowchart or flowcharts and / or block(s) Figure 1 a block or blocks.

[0075] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0076] It is apparent that those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A bistatic SAR phase synchronization method based on frequency scanning, characterized in that It includes the following steps: Step 1, construct the transmit signal model of the F-SCAN synchronization system. The transmit signal model is based on the characteristics of the frequency-scanned signal, introduces a transmit delay, and is used to describe the transmit characteristics of the signal at different beam pointing angles; F-SCAN represents frequency scanning. Step 2, establish the receiver of the F-SCAN synchronization system, receive and demodulate the frequency-scanned signal, obtain the expression of the demodulated signal, and extract the information containing the synchronization phase from it. Step 3, perform pulse compression processing on the demodulated signal, realize the pulse compression of the signal through a frequency-domain matched filter, and extract the synchronization phase from the compression result to complete phase synchronization.

2. A bistatic SAR phase synchronization method based on frequency scanning according to claim 1, characterized in that In the transmit signal model, the expression of the transmit signal includes the beam pointing angle, frequency-scanned transmit antenna gain, fast time, transmit delay, dwell time, dwell coefficient, starting scan angle, and scan angle range, which are used to accurately describe the transmit process of the frequency-scanned signal.

3. A bistatic SAR phase synchronization method based on frequency scanning according to claim 1, characterized in that The said Step 2 includes: Based on the transmit signal model in Step 1, the received signal is expressed as: ； Among them, represents the received signal, represents the beam pointing frequency-scanning receiving antenna gain at the angle, is the one-way transmission delay between the slave satellite and the master satellite, is the distance between the master and slave satellites, represents the speed of light, is the rectangular window function, represents the fast time, represents the transmission delay, refers to the dwell time, represents the dwell coefficient, is the starting scan angle, is the scan angle range, j is the imaginary unit, and exp{} represents the exponential function, represents the chirp rate of the synchronization signal, represents the pulse width of the synchronization signal, represents the carrier frequency of the synchronization signal.

4. A bistatic SAR phase synchronization method based on frequency scanning according to claim 3, characterized in that Received signal Demodulated by a local oscillator signal with a frequency of and further expressed as follows after downconversion: ； Among them, is the signal after receiving down-conversion, and the intermediate parameter , is the synchronization phase.

5. A bistatic SAR phase synchronization method based on frequency scanning according to claim 4, characterized in that Normalize the intermediate parameter so that the received signal of the receiver of the F-SCAN synchronization system is expressed as: 。 6. A bistatic SAR phase synchronization method based on frequency scanning according to claim 5, characterized in that The said Step 3 includes: Using the stationary phase principle, the received signal of the receiver in the F-SCAN synchronization system is transformed into the frequency domain: ； Among them, is the signal transformed into the frequency domain, f represents the frequency, and the center frequency , is the sign function, is the Fourier transform, is the dwell bandwidth of the frequency sweep signal.

7. A bistatic SAR phase synchronization method based on frequency scanning according to claim 6, characterized in that Perform pulse compression, and the matched filter for pulse compression Is represented in the frequency domain as: ； Among them, is the synchronization signal bandwidth; The matched filtering output is as follows: ； And then transform it back to the time domain as: ； Among them, is the signal transformed back to the time domain, is the inverse Fourier transform; The received signal pulse of the F-SCAN synchronization system is compressed to At this point, at The signal is sampled to obtain the signal , that is, the phase at the peak is obtained , that is, phase synchronization is achieved.

8. A bistatic SAR phase synchronization device based on frequency scanning, characterized in that It includes the following modules: A transmit signal model construction module, which constructs the transmit signal model of the F-SCAN synchronization system. The transmit signal model is based on the characteristics of the frequency-scanned signal, introduces a transmit delay, and is used to describe the transmit characteristics of the signal at different beam pointing angles; F-SCAN represents frequency scanning. A receiver construction module, which establishes the receiver of the F-SCAN synchronization system, receives and demodulates the frequency-scanned signal, obtains the expression of the demodulated signal, and extracts the information containing the synchronization phase from it. A phase synchronization module, which performs pulse compression processing on the demodulated signal, realizes the pulse compression of the signal through a frequency-domain matched filter, and extracts the synchronization phase from the compression result to complete phase synchronization.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the said program, it realizes the steps of a bistatic SAR phase synchronization method based on frequency scanning as described in any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When this computer program is executed by a processor, it realizes the steps of a bistatic SAR phase synchronization method based on frequency scanning as described in any one of claims 1 to 7.

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