Synthetic aperture radar interference source positioning method based on time difference of arrival

Abstract

The invention discloses a synthetic aperture radar interference source positioning method based on time difference of arrival, and the method comprises the steps: firstly, estimating the time difference of arrival of a pulse transmitted by each interference source to an SAR through a received SAR echo signal, and then seeking a mapping relation between the coordinates of the interference source and TDOA; and finally, the interference source is positioned through a two-dimensional search method by using the mapping relation. The method is applicable to single-station SAR satellites, multi-station SAR satellites and single-station SAR satellites with multiple observations; according to the method, the reference signal is extracted from the SAR echo, so that the method is suitable for interference signals in any modulation form and has certain flexibility.

Description

Technical Field

[0001] The invention belongs to the field of interference source positioning, and in particular relates to a synthetic aperture radar interference source positioning method based on arrival time difference. Background Art

[0002] Due to the increasingly crowded electromagnetic environment, synthetic aperture radar (SAR) systems are often subject to radio frequency interference (RFI) generated by electronic devices operating in the same electromagnetic frequency band. These RFIs may cause artifacts such as haze or bright lines to appear in SAR images, seriously reducing the imaging quality and affecting subsequent signal and information processing based on SAR images. Therefore, the identification, location and suppression of RFI are crucial for SAR imaging.

[0003] Many researchers have proposed various interference source location methods based on spaceborne SAR platforms. For example, the RFI radiation source is located by cross-comparing the RFI images in two GRD images obtained by two satellites in ascending and descending orbits. However, this method relies on the long-term existence of the interference source and the estimation range is related to the synthetic aperture length. Some methods can only locate RFI interference sources with a fixed single waveform and lack flexibility. Some other methods assume too ideal conditions in the simulation, lack consideration of factors in actual situations, and lack actual data support. Summary of the invention

[0004] The purpose of the present invention is to provide a method for locating a synthetic aperture radar interference source based on arrival time difference, which can not only solve the problem of relying on the long-term existence of the RFI interference source, but also locate interference signals of various modulation forms, thereby improving the flexibility of locating the interference source.

[0005] The technical solution to achieve the purpose of the present invention is: a method for locating a synthetic aperture radar interference source based on time difference of arrival, comprising the following steps:

[0006] Establish the radiation source signal model received by SAR;

[0007] Extract the reference signal and perform correlation processing with the SAR echo signal;

[0008] Estimate the arrival time of each pulse;

[0009] Estimate the repetition period of the interference pulse of the radiation source;

[0010] Estimate the arrival time difference of each pulse;

[0011] Use the location information of the SAR satellite platform to perform coordinate transformation and interpolation, and divide the grid;

[0012] The obtained TDOA estimate is scanned against a two-dimensional grid using a grid search method.

[0013] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the computer program.

[0014] A computer-readable storage medium stores a computer program, which implements the steps of the above method when executed by a processor.

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] (1) The present invention estimates the interference source coordinates by the arrival time difference between the interference pulse and the SAR pulse in the SAR echo signal, is applicable to a single image or multiple images, and does not rely on the condition that the interference source persists;

[0017] (2) The reference signal in the present invention is a single pulse signal extracted from the original SAR echo, which is applicable to interference signals of any modulation form and has certain flexibility;

[0018] (3) The present invention is applicable to single-station SAR satellites, multi-station SAR satellites, and single-station SAR satellite platforms with multiple observations, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The flowchart of the synthetic aperture radar interference source positioning based on TDOA in the present invention.

[0020] Figure 2 It is a relationship diagram between parameters such as arrival time (TOA) and interference pulse repetition period in the TDOA estimation method of the present invention.

[0021] Figure 3 This is the positioning result using a single experimental data in the present invention.

[0022] Figure 4 This is the positioning result using a single experimental data in the present invention.

[0023] Figure 5 This is the positioning result based on the intersection of two intersecting lines using two experimental data in the present invention. DETAILED DESCRIPTION

[0024] In order to further explain the technical means and effects adopted by the present invention to achieve the purpose of the invention, a synthetic aperture radar interference source positioning method based on arrival time difference proposed by the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] See also Figure 1 , Figure 1This is a flowchart of establishing the relationship between the pulse arrival time difference (TDOA) in the SAR raw data and the ground RFI source coordinates provided by the implementation example of the present invention. The specific steps are as follows:

[0026] Step 1: Establish the radiation source signal model received by SAR. Based on the position coordinates (x0, y0, z0) of the ground stationary radiation source in the Earth-centered fixed coordinate system (ECG). Assume that the waveform parameters of the ground radiation source are as follows: i , pulse width T p , the pulse number k and the interference signal frequency function f(·), and construct the radiation source signal model i(t) received by SAR.

[0027]

[0028] Where t is time, τ(t) is signal delay, and t0 is the difference between the zero time of the ground radiation source and the zero time of the satellite.

[0029] Step 2: Extract the reference signal and perform correlation processing with the SAR echo signal.

[0030]

[0031] Where y(t) is the signal after correlation processing, r(t) is the received signal of SAR, s(t) is the extracted reference signal, h(t) is the impulse response of the matched filter, and h(t-τ)=s * (t'-t+τ) is the complex conjugate of the reference signal, R rs (t'-t) is r(t) and s * The cross-correlation function of (t'-t), a is a constant and t' is the correlation time.

[0032] The reference signal can be reconstructed using direct extraction and extraction parameter reconstruction methods. After the reference signal is extracted, it is cross-correlated with the original echo, the delay information is extracted from the cross-correlation function, and interpolation is used to improve the delay accuracy.

[0033] Step 3: Estimate the arrival time of each pulse. Based on the signal delay τ(t) and the difference t0 between the zero time of the ground radiation source and the zero time of the satellite, the arrival time (TOA) of each pulse is calculated based on the emission time of each pulse. represents the measured delay of the kth pulse received from the m(k)th PRI of the SAR. m(k) is the number of pulses of the satellite's own signal received when the satellite receives the kth pulse of the ground radiation source. The arrival time of the correlation peak in step 2 can be obtained

[0034] t TOA(k) = τ k +t0

[0035]

[0036] Among them, τ k is the time delay required for the kth pulse to reach the satellite, (x0, y0, z0) is the position of the ground stationary radiation source in the ground-fixed coordinate system, (x k ,y k ,z k ) is the position of the satellite when the kth pulse is emitted, and c is the speed of light.

[0037] Step 4: Estimate the repetition period of the interference pulse from the radiation source for The average of the observed arrival time differences between adjacent pulses can be used to obtain:

[0038]

[0039] Where N is the number of pulses taken for observation, The observed arrival time difference for each pulse.

[0040] Step 5: Estimate the arrival time difference of each pulse. Use the delay τ of the kth pulse k and the satellite position at the time of the kth pulse transmission (x k ,y k ,z k ), with the arrival time of the first pulse t TOA The time difference of arrival (TDOA) of each pulse is calculated based on (1) = τ1 + t0.

[0041] Since the radiation source is on the ground, in order to reduce the number of unknown parameters in the radiation source, the coordinate system of the radiation source target can be converted, and the position of the radiation source in the ground-fixed rectangular coordinate system can be converted into longitude and latitude as shown in formula (14). Where (L0, B0) is the longitude and latitude coordinates of the ground radiation source. Φ k (L0, B0) is a function related to the position where the kth pulse of the RFI source is received by the SAR.

[0042]

[0043] Since the original echo data of the SAR satellite is stored in the form of a matrix, it is represented by X∈C Nslow×Nfast , where N slow is the number of slow time sampling points, N fast is the number of sampling points corresponding to the pulse period emitted by the satellite. Since the SAR satellite intercepts the level 0 data during the signal transmission process, the final level 0 data we obtain can be expressed as X(1:N slow,N begin :N fast ). begin Indicates the starting point of each cycle without interception. Therefore, in actual measurement, It can be estimated as

[0044]

[0045] Where k∈Ω, Ω represents the set of observable pulses from ground-based radiation sources. x Represents the pulse repetition period of SAR. trun Indicates the length of time intercepted in each cycle. Figure 2 It includes the relationship between arrival time (TOA) and interference pulse repetition period and other parameters in the TDOA estimation method.

[0046] Step 6: Use the location information of the SAR satellite platform to perform coordinate conversion and interpolation, divide the image area into grids using latitude and longitude coordinates, define a set of two-dimensional grid points P, and represent each grid point as (L j, B j )∈P.

[0047] Step 7: Use the grid search method to scan the arrival time difference estimate obtained in step 5 with the two-dimensional grid. The positioning method can be described as:

[0048]

[0049] Among them, (L0′, B0′) is the calculated coordinates of the ground radiation source, (L j ,B j ) is the longitude and latitude coordinates of the jth grid point, φ k (L j ,B j ) is the theoretical TDOA of the jth grid point, and Ω represents the observable pulse number set of the ground radiation source.

[0050] This method can be extended from single-scan satellite data to multiple scans involving different tracks of a satellite or multiple satellites. The relationship between the loss calculated by equation (17) and the latitude and longitude of the RFI source is as follows: Figure 3 , Figure 4 The position that minimizes the loss corresponds to the location of the RFI source. Figure 3 and Figure 4 It can be clearly seen that the coordinate points with smaller losses are connected together to form a line. In essence, this line is formed by the intersection of the spatial hyperbola determined by TDOA and the search area.

[0051]

[0052] Q represents the number of passes of multiple SARs or multiple passes of a single SAR, Ω q represents the observable pulse number set of the ground radiation source at the qth pass, represents the arrival time difference observed for each pulse at the qth pass, represents the theoretical TDOA of the jth grid point during the qth pass.

[0053] like Figure 3 and Figure 4 As shown in , the large error of a single experimental data may be caused by the truncation of the original data, resulting in a large error in the TDOA estimation. The positioning using two sets of experimental data involves positioning based on the intersection of two intersecting lines, which can significantly reduce the error compared to using a single set of experimental data, such as Figure 5 shown.

Claims

1. A method for locating interference sources of synthetic aperture radar based on time difference of arrival, characterized in that: include: Establish the radiation source signal model received by SAR; Extract the reference signal and perform correlation processing with the SAR echo signal; Estimate the arrival time of each pulse; Estimate the repetition period of the interference pulse of the radiation source; Estimate the arrival time difference of each pulse; Use the location information of the SAR satellite platform to perform coordinate transformation and interpolation, and divide the grid; The obtained TDOA estimate is scanned against a two-dimensional grid using a grid search method.

2. The method for locating interference sources of synthetic aperture radar based on time difference of arrival according to claim 1, characterized in that: The established radiation source signal model i(t) received by SAR is: Where t is time, T i is the pulse repetition period, T p is the pulse width, k is the number of pulses, f(·) is the interference signal frequency function, τ(t) is the signal delay, and t0 is the difference between the zero time of the ground radiation source and the zero time of the satellite.

3. The method for locating interference sources of synthetic aperture radar based on time difference of arrival according to claim 1, characterized in that: Extract the reference signal and perform correlation processing with the SAR echo signal: Where y(t) is the signal after correlation processing, r(t) is the received signal of SAR, s(t) is the extracted reference signal, h(t) is the impulse response of the matched filter, and h(t-τ)=s * (t'-t+τ) is the complex conjugate of the reference signal, R rs (t'-t) is r(t) and s * The cross-correlation function of (t'-t), a is a constant and t' is the correlation time.

4. The method for locating a synthetic aperture radar interference source based on time difference of arrival according to claim 1, characterized in that: Estimate the arrival time t of each pulse TOA (k) t TOA (k)=τ k +t0 Among them, τ k is the time delay required for the kth pulse to reach the satellite, (x0, y0, z0) is the position of the ground stationary radiation source in the ground-fixed coordinate system, (x k ,y k ,z k ) is the position of the satellite when the kth pulse is emitted, and c is the speed of light.

5. The method for locating interference sources of synthetic aperture radar based on time difference of arrival according to claim 1, characterized in that: Estimate the repetition period of the interference pulse of the radiation source The repetition period is obtained using the average of the observed arrival time differences between adjacent pulses: Where N is the number of pulses taken for observation, The observed arrival time difference for each pulse.

6. The method for locating interference sources of synthetic aperture radar based on time difference of arrival according to claim 1, characterized in that: The first pulse arrives at time t TOA (1) = τ1 + t0 as the reference, the arrival time difference of each pulse is:

7. The method for locating a synthetic aperture radar interference source based on time difference of arrival according to claim 6, characterized in that: The position of the radiation source in the ground-fixed rectangular coordinate system is converted into longitude and latitude. The converted TDOA can be expressed as t TDOA (k)=φ k (L0,B0) Among them, (L0, B0) is the latitude and longitude coordinates of the ground radiation source, φ k (L0, B0) is a function related to the position where the kth pulse of the RFI source is received by the SAR.

8. The method for locating a synthetic aperture radar interference source based on time difference of arrival according to claim 1, characterized in that: Using the grid search method, the obtained TDOA estimate is scanned with a two-dimensional grid; In getting Finally, the grid search method is used to explore the area of ​​interest and find the target position that meets the above conditions based on the satellite's motion position information at each moment; Among them, (L0′, B0′) is the calculated coordinates of the ground radiation source, (L j ,B j ) is the longitude and latitude coordinates of the jth grid point, φ k (L j ,B j ) is the theoretical TDOA of the jth grid point, Ω represents the observable pulse number set of the ground radiation source; Q represents the number of passes of multiple SARs or multiple passes of a single SAR, Ω q represents the observable pulse number set of the ground radiation source at the qth pass, represents the arrival time difference observed for each pulse at the qth pass, represents the theoretical TDOA of the jth grid point during the qth pass.

9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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