Method and device for extracting double-base multi-channel SAR (Synthetic Aperture Radar) synchronizing signal

Abstract

The invention discloses a bistatic multi-channel synthetic aperture radar (SAR) synchronous signal extraction method and device, and belongs to the technical field of synthetic aperture radar signal processing. According to the method, a bistatic SAR system with a plurality of receiving channels is constructed, and a synchronization signal and a scene echo signal are modeled into a linear mixed signal by using time delay and amplitude differences caused by physical position differences among the channels; a blind source separation algorithm based on high-order statistics is adopted to carry out centralization, whitening and joint diagonalization processing on multichannel received signals, and effective separation of synchronous signals and target echoes is realized. The method does not need to interrupt the imaging process, does not depend on priori knowledge or complex waveform design, remarkably improves the phase synchronization precision and the system flexibility, is suitable for various bistatic SAR systems, and has good practicability and universality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthetic aperture radar signal processing, and particularly relates to a bistatic multi-channel SAR synchronization signal extraction method and device. BACKGROUND

[0002] A synthetic aperture radar (SAR) system transmits electromagnetic waves and receives target echoes, forms a high-resolution image by using a synthetic aperture technology, and has important applications in fields such as military reconnaissance, topographic mapping and disaster monitoring. As an important branch of SAR, a bistatic SAR system places the transmitter and receiver on different platforms, can obtain more abundant target information, and has significant advantages in complex terrain detection and concealed target identification. However, the bistatic system also faces many challenges, and the phase synchronization problem is one of the key factors affecting the imaging quality.

[0003] In a bistatic SAR system, the frequency deviation of the transmitting and receiving platforms using independent frequency sources will introduce additional phase errors. The error mainly includes a linear term, a stationary random term, a random wandering term and a constant term. The linear phase error causes target Doppler shift and azimuth position deviation; the stationary random term causes sidelobe distortion and image defocus; and the random wandering term causes unconstrained phase drift over time, which seriously affects long-time coherent accumulation and imaging accuracy.

[0004] To address the above problems, various phase synchronization methods have been proposed in the prior art. Using a high-stability frequency source (such as an ultra-high-stability crystal oscillator or an optical clock) can effectively suppress the frequency deviation, but the cost is high and the environmental stability is strict. The direct wave synchronization scheme uses a direct wave signal to trigger the reception and compensate for the error, but the applicable scenarios are limited, and the receiving antenna must be located within the transmitting beam range. The two-way pulse pair transmission method achieves high-precision synchronization by mutual transmission of pulses between satellites, but it needs to interrupt the normal imaging process, resulting in data loss and sidelobe rise. The non-interrupt phase synchronization method (such as Kalman filter-based error compensation) does not need to interrupt the imaging, but the algorithm is complex, the system timing design constraints are strict, and the computing resource demand is large. In addition, the method based on waveform diversity and coherent accumulation has limited performance in a multipath environment.

[0005] In summary, the existing synchronization methods have obvious deficiencies in system applicability, implementation complexity, or data continuity, and there is an urgent need for a new synchronization signal extraction method that can balance high precision, strong adaptability, low complexity and non-interrupt operation. SUMMARY

[0006] To solve the above technical problems, the application provides a dual-baseline multi-channel SAR synchronization signal extraction method and device, which can extract the synchronization signal at the echo data level without any prior knowledge and system design constraints, thereby improving the synchronization accuracy, avoiding data loss, and adapting to different application scenarios.

[0007] To achieve the above object, the application adopts the following technical solutions:

[0008] A dual-baseline multi-channel SAR synchronization signal extraction method, the method comprising:

[0009] Step 1: Establish a dual-baseline multi-channel SAR system, the receiving antenna of the dual-baseline multi-channel SAR system comprises a plurality of receiving channels, and there is a time delay phase difference between the received echo signals of the plurality of receiving channels;

[0010] Step 2: Obtain the receiving signals of the plurality of receiving channels, the receiving signals being mixed signals of synchronization signals and scene point target echoes;

[0011] Step 3: Process the mixed signals using a joint approximate diagonalization blind source separation algorithm, including: constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signals into a plurality of independent source signal components, and extracting the synchronization signals from the plurality of independent source signal components.

[0012] Further, in step 1, the receiving antenna of the dual-baseline multi-channel SAR system is arranged with a plurality of receiving channels in the elevation direction, and the distribution difference of the plurality of receiving channels in the physical space causes a time delay phase difference between the echo signals received by different channels.

[0013] Further, in step 1, the dual-baseline multi-channel SAR system adopts a configuration mode in which the two satellites move along the azimuth direction at the same speed and in the same direction.

[0014] Further, in step 2, each receiving channel receives a linearly mixed signal of the synchronization signal and the scene point target echo signal with different weights.

[0015] Further, in step 3, before constructing the fourth-order cumulant matrix, the mixed signals are also preprocessed; the preprocessing includes centering processing and whitening processing; the centering processing is used to make the signal mean value zero, and the whitening processing is used to eliminate the second-order correlation between signals.

[0016] Further, the whitening processing is realized by calculating the autocorrelation matrix of the observed signal and performing eigenvalue decomposition, the purpose being to find a whitening matrix so that the autocorrelation matrix of the whitened signal is an identity matrix.

[0017] Further, in the step 3, the fourth-order cumulant matrix is constructed and joint diagonalization is performed, specifically: a fourth-order cumulant matrix is constructed for the preprocessed signal, eigenvalue decomposition is performed on the fourth-order cumulant matrix and a characteristic matrix corresponding to main eigenvalues is selected, and then a best unitary matrix is estimated through joint approximate diagonalization algorithm, and finally a separation matrix is obtained.

[0018] In another aspect, the application provides a dual-baseline multi-channel SAR synchronization signal extraction device, comprising:

[0019] A building module is configured to build a dual-baseline multi-channel SAR system, wherein the receiving antenna of the dual-baseline multi-channel SAR system comprises a plurality of receiving channels, and there is a time delay phase difference between the received echo signals of the plurality of receiving channels;

[0020] A receiving module is configured to obtain the receiving signals of the plurality of receiving channels, wherein the receiving signals are mixed signals of synchronization signals and scene point target echoes;

[0021] An extraction module is configured to process the mixed signals by using a joint approximate diagonalization blind source separation algorithm, comprising: constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signals into a plurality of independent source signal components, and extracting synchronization signals from the plurality of independent source signal components.

[0022] In a third aspect, the application provides an electronic device, comprising: one or more processors; a memory configured to store one or more programs; wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned dual-baseline multi-channel SAR synchronization signal extraction method.

[0023] In a fourth aspect, the application provides a computer-readable storage medium having stored executable instructions, which, when executed by a processor, enable the processor to implement the aforementioned dual-baseline multi-channel SAR synchronization signal extraction method.

[0024] The application has the following beneficial effects:

[0025] Non-interrupt continuous synchronization is achieved: the problem that the traditional two-way pulse pair transmission method needs to interrupt the imaging process is overcome, the continuity and data integrity of the SAR system are ensured, and data loss and sidelobe rise are avoided.

[0026] The system design and implementation complexity is reduced: the method does not need to rely on complex waveform design or strict constraints on signal transmission timing, only needs to process multi-channel receiving signals, simplifies the system design, and improves the flexibility and simplicity of engineering implementation.

[0027] Improved synchronization accuracy and applicability: The blind source separation method can effectively separate mixed signals, with high accuracy in extracting synchronization signals. It does not rely on high-cost, high-stability frequency sources or specific spatial geometry configurations, thus enhancing the applicability and robustness of the method in different application scenarios and system platforms. Attached Figure Description

[0028] Figure 1 This is a flowchart of a dual-base multi-channel SAR synchronization signal extraction method according to the present invention;

[0029] Figure 2 This is a schematic diagram of a bistatic multichannel SAR system in operation.

[0030] Figure 3 These are some parameters of the GF-3 system;

[0031] Figure 4 The amplitude spectrum of a separate synchronization signal after processing by an imaging algorithm;

[0032] Figure 5a The result of imaging processing of the signal from the first observation channel;

[0033] Figure 5b The result is the image processing of the signal from the second observation channel.

[0034] Figure 6a The image amplitude spectrum of the extracted scene echo signal;

[0035] Figure 6b The imaging amplitude spectrum of the extracted synchronization signal;

[0036] Figure 7a A two-dimensional contour map of point targets after upsampling;

[0037] Figure 7b This is a 3D schematic diagram after upsampling;

[0038] Figure 7c This is a range slice after upsampling;

[0039] Figure 7d This is an azimuth slice after upsampling. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] like Figure 1 As shown, the method for extracting bistatic multichannel SAR synchronization signals provided by the present invention includes:

[0042] Step 1: Establish a dual-baseline multi-channel SAR system, the receiving antenna of which contains multiple receiving channels, the difference in physical location of which causes different time delay phases between the received echo signals of different channels, and the dual satellites move along the azimuth direction at the same speed and in the same direction.

[0043] The receiving antenna of each satellite of the dual-baseline multi-channel SAR system contains multiple receiving channels in the elevation direction, the number of which determines the upper limit of the number of signals that can be separated, and the time delay and intensity difference between different channels due to the size of the antenna, so that each channel receives a linear mixture of synchronous signals and scene echo signals with different weights. This condition ensures the theoretical feasibility of blind source separation technology.

[0044] Step 2: Obtain the received signals of the multiple receiving channels, which are mixed signals of synchronous signals and scene point target echoes.

[0045] When the dual-baseline SAR system is working, the synchronous signal generated by the main satellite is transmitted at a certain time, and after a corresponding time delay, the auxiliary satellite receives and records the signal. The scene setting uses a non-interrupt phase synchronization method to transmit the synchronous signal, which does not cause data loss problems and avoids the problem of high azimuth side lobes, but the synchronous signal will be mixed with the scene point target echo. If a high-precision phase synchronization scheme is to be implemented, the extraction and separation of the synchronous signal must be accurately implemented. Assume that the receiving antenna of each system has receiving channels. Without considering noise, the received signal of each receiving channel can be represented as a linear weighted superposition of the synchronous signal and the echo signal of the observed scene , that is:

[0046] (1)

[0047] wherein represents the distance-time, represents the signal received by the system different channels, represents the weight of the scene echo signal corresponding to the receiving channels of the receiving antenna, represents the weight of the synchronous signal corresponding to the receiving channels of the receiving antenna. Assume that the transmitted linear frequency modulation signal can be represented as:

[0048] (2)

[0049] After scattering by a point target on the ground, the target echo signal received by the channel is:

[0050] (3)

[0051] where, , is the number of elevation channels, is the backscattering coefficient of the target, is the pulse duration, is the system operating frequency, is the frequency modulation rate, is the imaginary unit, is the rectangular window function, is the two-way propagation delay of the signal received by the th channel, and has the form:

[0052] (4)

[0053] is the time delay of the reference received signal. is the time delay difference between the th channel and the reference channel, and has the form:

[0054] (5)

[0055] where, , is the reference channel, is the channel height. is the target depression angle, is the antenna installation angle, is the electromagnetic wave propagation speed.

[0056] The echo signal of the th channel can be unfolded as:

[0057] (6)

[0058] Generally, the last two phase terms of the above equation can be neglected, and the signal envelope is considered to be the same. Therefore, the above equation can be re-expressed as:

[0059] (7)

[0060] where, , is the slant range history of the target relative to the reference channel, is the azimuth time. And the phase synchronization signal can be expressed as:

[0061] (8)

[0062] From the above equation, it can be seen that the synchronization signal is a linear frequency modulation signal, wherein represents the frequency modulation rate of the synchronization signal, represents the time delay of the synchronization signal transmitted by the primary satellite and received by the secondary satellite, represents the phase error caused by the frequency deviation of the satellite, represents an exponential function, represents an imaginary unit.

[0063] Step 3: processing the multi-channel mixed signal using a method based on fourth-order cumulant-based joint diagonalization, including constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signal into multiple independent source signal components, and extracting the synchronization signal from the multiple independent source signal components.

[0064] Based on the independent component analysis theory of high-order statistics, using the idea of optimized joint diagonalization, the separation and reconstruction of multiple mixed signals can be efficiently completed. Let the observation signal matrix composed of multi-channel mixed signals be:

[0065] (9)

[0066] wherein, represents the number of receiving channels, represents transposition, and the method can be specifically performed in the following steps.

[0067] First, the observation signal matrix is preprocessed, including centering and whitening. In terms of observation signals, centering is a basic preprocessing method. This processing process converts the processed observation signal into a zero-mean vector by subtracting the mean vector from the observation signal, thereby providing a standardized basis for subsequent data processing and analysis. Centering can be realized by the following formula:

[0068] (10)

[0069] wherein, represents the mean operation, represents the observation signal matrix after centering. Then, the centered observation signal matrix is whitened. The main goal of whitening is to eliminate the second-order statistical correlation between observation signals. In general, the whitened signal shows significant improvement in convergence performance and stability compared to the unwhitened signal. Specifically, it can be represented as finding a change matrix satisfying:

[0070] (11)

[0071] The autocorrelation matrix of the signal matrix after the action satisfies the following equation:

[0072] (12)

[0073] wherein, denotes the conjugate transpose operation, denotes the unit matrix, and in combination with the matrix decomposition theory, the above equation can be further derived as:

[0074] (13)

[0075] wherein, denotes the orthogonal matrix after the matrix decomposition, and denotes the corresponding diagonal matrix. Further, the change matrix can be solved, which can be expressed as:

[0076] (14)

[0077] For any random vector with a fourth-order cumulant, there exist characteristic matrices of dimensions and real numbers satisfying the following relationship:

[0078] (15)

[0079] wherein denotes a fourth-order cumulant, according to the above theory, for the pre-processed whitened signal matrix , given an arbitrary matrix , a fourth-order cumulant matrix of dimensions is constructed according to , wherein denotes the number of receiving channels, for the convenience of understanding, it is written as characteristic matrices of dimensions are expressed as follows:

[0080] (16)

[0081] wherein, denotes the operator for calculating the fourth-order cumulant, denotes the fourth-order cumulant of the first four components in the vector , and are all from 1 to integer, denotes an arbitrary matrix , the element in the th row and the th column of , and denotes the element in the th row and the th column of the fourth-order cumulant . Then, the fourth-order cumulant matrix is subjected to Eigen Value Decomposition (EVD) to obtain the following equation:

[0082] (17)

[0083] where is the corresponding eigenvector, is the eigenvalue matrix, the obtained eigenvalues are arranged in descending order, and the eigenvectors corresponding to the first eigenvalues are selected to form , and the subscript here only represents the corresponding variable of the matrix dimension, and the dimension is stacked as the characteristic matrix with the dimension of , and the eigenvalues and the corresponding characteristic matrix are combined to form a cumulant characteristic matrix set , which is expressed as follows:

[0084] (18)

[0085] where denotes a diagonal matrix, denotes a unitary matrix, and Givens rotation optimization of the above matrix set can obtain the estimation of the optimal unitary matrix . Finally, the whitening matrix and the jointly diagonalized unitary matrix are used to obtain the decomposition matrix :

[0086] (19)

[0087] The recovered signal matrix can be obtained by acting the decomposition matrix on the observation matrix :

[0088] (20)

[0089] where , represents the first source signal, in the above-mentioned scenario, the restored signal matrix mainly includes two parts of scene echo and synchronization signal, and the synchronization signal can be obtained based on the restored signal matrix.

[0090] Embodiments:

[0091] GF-3 system parameters are used as simulation parameters for simulation, a four-channel receiving antenna system is designed to verify the feasibility of the system and method, and a bistatic multi-channel SAR system schematic diagram is shown in Figure 2 , and part of the actual parameters of the GF-3 system are shown in Figure 3 .

[0092] The imaging scene is set to a three-point target scene, the three point targets are in the same range direction and different azimuth directions, the synchronization signal is a linear frequency modulation signal, and the frequency modulation rate, bandwidth and other parameters are consistent with the parameters of the linear frequency modulation signal transmitted by the system. The normalized amplitude spectrum of the synchronization signal after imaging algorithm processing is shown in Figure 4 , and the imaging results of the signals of the two observation channels of the echo signal mixed with the scene point target and the synchronization signal are shown in Figure 5a and Figure 5b , it can be seen that in addition to the set point target result, the synchronization signal is mixed, therefore, the method is adopted to extract the synchronization signal, and the separated two results are shown in Figure 6a and Figure 6b , which correspond to the imaging results of the separated scene point target echo and the processing results of the synchronization signal respectively. In order to measure the separation results, the center point target slice of the echo of the separated imaging scene is processed by upsampling and slice analysis, Figure 7a corresponding to the two-dimensional upsampling contour map, Figure 7b corresponding to the three-dimensional visualization effect, Figure 7c and Figure 7d corresponding to the distance and azimuth slices, it can be seen that the point target upsampling analysis result is ideal, and the echo of the scene point target and the synchronization signal are well separated.

[0093] On the other hand, the application provides a bistatic multi-channel SAR synchronization signal extraction device, each module included in the device can realize each step of the foregoing method, specifically, the device includes:

[0094] a building module for building a bistatic multi-channel SAR system, the receiving antenna of the bistatic multi-channel SAR system includes a plurality of receiving channels, and there is a time delay phase difference between the received echo signals of the plurality of receiving channels;

[0095] The receiving module is configured to acquire receiving signals of the multiple receiving channels, wherein the receiving signals are mixed signals of the synchronization signals and the scene point target echoes;

[0096] The extracting module is configured to process the mixed signals by using a joint approximate diagonalization blind source separation algorithm, including: constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signals into multiple independent source signal components, and extracting the synchronization signals from the multiple independent source signal components.

[0097] In a third aspect, the present application provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned dual-baseline multi-channel SAR synchronization signal extraction method.

[0098] In a fourth aspect, the present application provides a computer-readable storage medium having stored executable instructions, which, when executed by a processor, enable the processor to implement the aforementioned dual-baseline multi-channel SAR synchronization signal extraction method.

[0099] The above-described specific embodiments further illustrate the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are merely specific embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for extracting a dual-base multi-channel SAR synchronization signal, characterized in that, The method comprises: Step 1, establishing a dual-baseline multi-channel SAR system, wherein a receiving antenna of the dual-baseline multi-channel SAR system comprises a plurality of receiving channels, and a time delay phase difference exists between received echo signals of the plurality of receiving channels; Step 2, acquiring receiving signals of the plurality of receiving channels, wherein the receiving signals are mixed signals of synchronization signals and scene point target echoes; Step 3, processing the mixed signals by using a joint approximate diagonalization blind source separation algorithm, comprising: constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signals into a plurality of independent source signal components, and extracting synchronization signals from the plurality of independent source signal components.

2. The method according to claim 1, wherein, In the step 1, the receiving antenna of the dual-baseline multi-channel SAR system is arranged with a plurality of receiving channels in the elevation direction, and a distribution difference of the plurality of receiving channels in the physical space causes a time delay phase difference between echo signals received by different channels.

3. The method according to claim 1, wherein, In the step 1, the dual-baseline multi-channel SAR system adopts a configuration mode in which two satellites move along the azimuth direction at the same speed and in the same direction.

4. The method according to claim 1, wherein, In the step 2, each receiving channel receives a linear mixed signal of synchronization signals and scene point target echo signals with different weights.

5. The method according to claim 1, wherein, In the step 3, before the fourth-order cumulant matrix is constructed, the mixed signals are also preprocessed; the preprocessing comprises centralization processing and whitening processing; the centralization processing is used to make the signal mean value zero, and the whitening processing is used to eliminate the second-order correlation between signals.

6. The method according to claim 5, wherein, The whitening processing is realized by calculating the autocorrelation matrix of the observed signal and performing eigenvalue decomposition, and the purpose is to find a whitening matrix so that the autocorrelation matrix of the whitened signal is a unit matrix.

7. The method according to claim 1, wherein, In the step 3, the fourth-order cumulant matrix is constructed and joint diagonalization is performed, specifically: a fourth-order cumulant matrix is constructed for the preprocessed signal, eigenvalue decomposition is performed on the fourth-order cumulant matrix, and a feature matrix corresponding to the main eigenvalue is selected, then a best unitary matrix is estimated by using a joint approximate diagonalization algorithm, and finally a separation matrix is obtained.

8. A dual-base multi-channel SAR synchronization signal extraction apparatus, characterized by, Comprise: A establishing module is configured to establish a dual-baseline multi-channel SAR system, wherein a receiving antenna of the dual-baseline multi-channel SAR system comprises a plurality of receiving channels, and a time delay phase difference exists between received echo signals of the plurality of receiving channels; A receiving module is configured to acquire receiving signals of the plurality of receiving channels, wherein the receiving signals are mixed signals of synchronization signals and scene point target echoes; A extracting module is configured to process the mixed signals by using a joint approximate diagonalization blind source separation algorithm, comprising: constructing a fourth-order cumulant matrix and performing joint diagonalization, separating the mixed signals into a plurality of independent source signal components, and extracting synchronization signals from the plurality of independent source signal components.

9. An electronic device, comprising: Comprise: One or more processors; A memory is configured to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors are caused to implement the dual-baseline multi-channel SAR synchronization signal extraction method according to any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, A computer readable storage medium having stored thereon executable instructions that, when executed by a processor, enable the processor to implement a dual-base multi-channel SAR synchronization signal extraction method according to any one of claims 1-7.

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