Parameter estimation method of ground phase coding radar interference source based on SAR image

Abstract

The invention discloses a method for estimating parameters of a ground phase-coded radar interference source based on an SAR image. The method comprises the steps of deriving a corresponding relation between phase-coded interference parameters and SAR image features and estimating the parameters. According to the method, the corresponding relation between the pulse width, the bandwidth, the carrier frequency and the repetition frequency of the interference signal and the interference characteristics on the SAR image is determined according to the mathematical relation, the problems of unclear mathematical expression, unclear parameter corresponding relation and the like on the phase coding radio frequency interference SAR image are solved, and the interference fringe parameters on the SAR image are estimated and the corresponding relation is obtained through derivation, so that the interference fringe parameters on the SAR image are estimated. And inversion of interference source parameters of the ground phase-coded radar is realized. Simulation results show that parameters such as pulse width, bandwidth, carrier frequency, repetition frequency and the like of phase coding radio frequency interference can be accurately estimated; the method can be applied to estimating parameters such as pulse width, bandwidth, carrier frequency, repetition frequency and the like of a phase-coded signal from an SAR image interfered by a ground same-frequency phase-coded radar signal.

Description

Technical Field

[0001] The invention relates to the field of radar signal parameter estimation, in particular to a parameter estimation method for a ground phase coding radar interference source based on SAR images. Background Art

[0002] Synthetic Aperture Radar (SAR) is an active remote sensing radar system. With its unique synthetic aperture technology, it can achieve high-resolution imaging all day and all weather, and plays an important role in electronic warfare. However, SAR is often interfered by signals from other radio equipment, namely radio frequency interference (RFI), which seriously affects the imaging quality of SAR and reduces its target recognition ability. Studies have shown that SAR is more interfered by ground radar, and its interference signals mainly include linear frequency modulation signals and phase coded signals.

[0003] At present, the research on ground radar radio frequency interference is mainly focused on interference suppression. For example, the 2-D SPECralANaalysis (2-D SPECAN) filter proposed by Yang Huizhang et al. is used to remove the category of LFM RFI in level-1 SLC images, and can estimate the signal parameters of LFM RFI based on the characteristics of LFM RFI on the image. Lu Xingyu et al. proposed an effective solution to the interference suppression optimization problem based on the alternating direction multiplier method (ADMM), and Li Ning et al. proposed an improved feature subspace projection (ESP) method combined with the traditional notch filter method to alleviate mutual radio frequency interference (MRFI). However, there are relatively few studies on interference detection, especially interference source parameter estimation.

[0004] In terms of phase coding interference, it is difficult to estimate the parameters of phase coding interference from SAR images because its mathematical representation on SAR images is unclear and the corresponding relationship of parameters is unclear. Therefore, it is necessary to conduct in-depth research on the characteristics of phase coding interference on SAR images in order to achieve accurate estimation of its parameters. Summary of the invention

[0005] The purpose of the present invention is to provide a parameter estimation method for ground phase-coded radar interference source based on SAR images, by deriving the mathematical representation of phase-coded interference on SAR images, clarifying the corresponding relationship between its pulse width, bandwidth, carrier frequency, repetition rate and SAR image interference characteristics, thereby achieving accurate estimation of phase-coded interference parameters.

[0006] The technical solution to achieve the purpose of the present invention is: a parameter estimation method for ground phase coded radar interference source based on SAR image, comprising:

[0007] Establish SAR receiving signal model, ground radar transmitting phase coding signal model, and SAR radar imaging signal performance model;

[0008] Derive the mathematical representation of phase-coded interference on SAR images and the corresponding relationship between the pulse width, bandwidth, carrier frequency, repetition rate of phase-coded interference and SAR image characteristics;

[0009] The SAR echo data with interference is subjected to two-dimensional focusing imaging to obtain the SAR imaging diagram with interference. The single-range interference fringe width and fringe period as well as the bandwidth and carrier frequency in its spectrum are extracted. The pulse width, bandwidth, carrier frequency and repetition rate of phase-coded interference are calculated according to the corresponding relationship of parameters.

[0010] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the steps of the above method are implemented when the processor executes the program.

[0011] A computer-readable storage medium stores a computer program, which implements the steps of the above method when executed by a processor.

[0012] A computer program product comprises a computer program, which implements the steps of the above method when executed by a processor.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The present invention provides a method for estimating the parameters of ground phase-coded radar interference sources based on SAR images. According to the characteristics of the phase-coded interference after imaging, the specific manifestation of the phase-coded interference on the SAR image is mathematically derived for the first time, providing a theoretical basis for accurately estimating its parameters.

[0015] (2) The method for estimating the interference source parameters of ground phase-coded radar based on SAR images of the present invention can realize the effective estimation of phase-coded interference parameters by clarifying the correspondence between the interference signal pulse width, bandwidth, carrier frequency, repetition rate and the interference features on the SAR image, which helps to improve the performance of the SAR system in an interference environment.

[0016] (3) The present invention proposes a method for estimating the parameters of ground phase-coded radar interference sources based on SAR images. The method uses semi-measured data (clean SAR echo data + simulated interference) to conduct simulation experiments, which overcomes the difficulty in acquiring SAR echo data with interference. At the same time, it verifies the accuracy of the parameter estimation method and provides a reference for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flowchart of the method for estimating the parameters of the ground phase-coded radar interference source based on SAR images.

[0018] Figure 2 It is the manifestation of interference of different pulse widths on the SAR image.

[0019] Figure 3 It is the manifestation of interference of different bandwidths on SAR images.

[0020] Figure 4 It is the single-distance signal spectrum under different bandwidths.

[0021] Figure 5 It is the single-range signal spectrum under different carrier frequencies.

[0022] Figure 6 It is the manifestation of interference with different repetition frequencies on SAR images.

[0023] Figure 7 is the phase coding interference pulse width estimation error.

[0024] Figure 8 is the phase coding interference bandwidth estimation error.

[0025] Fig. 9 is the phase coded interference carrier frequency estimation error.

[0026] Fig.10 is the phase coding interference repetition frequency estimation error. DETAILED DESCRIPTION

[0027] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a parameter estimation method of a ground phase-coded radar interference source based on SAR images proposed by the present invention in combination with the accompanying drawings and specific implementation methods. The detailed steps are as follows:

[0028] Step 1: In the SAR image, if the echo from other radar signals is received, interference will occur. Considering that interference and noise exist at the same time, the received SAR signal is designed to be:

[0029] s(n,t)=x(n,t)+r(n,t)+g(n,t) (1)

[0030] Where t and η are fast time and slow time respectively, x(η,t) is the SAR echo signal, r(η,t) is the interference, and g(η,t) is the noise. The SAR echo signal model is used to simulate the actual received SAR signal.

[0031] Step 2: Establish the ground radar transmitting phase coded signal model as:

[0032]

[0033] Where rect(·) is the rectangular function, T i is the pulse duration of the interference, f c is the interference center frequency minus the SAR center frequency. The complex envelope function of the signal is in is the phase modulation function. For a two-phase coded signal, There are only two possible values, 0 and π, and the binary sequence can be used It can also be represented by a binary sequence The phase-coded signal model of ground radar transmission is used to analyze the influence of different parameters on the signal.

[0034] Step 3: Using the above ground radar transmission phase coded signal model, the N phase coded interference signals received in the SAR echo domain are expressed as:

[0035]

[0036] In the formula, a n is a complex number whose amplitude is related to the power level of the interference, δ(η) is the Dirac function, η n is the slow time of the nth interference pulse, t n is the propagation delay of the nth interference pulse. This signal model can describe the interference caused by ground radar signals to SAR satellites.

[0037] Step 4: SAR imaging is essentially a two-dimensional matched filtering process. The following formula is used to express the signal performance after imaging:

[0038]

[0039] In the formula, η' and t' are the azimuth time and distance time in the SAR image domain, h(η,t; η',t') is the time-varying convolution kernel, x(η',t'), r(η',t'), g(η',t') are the image signal after imaging, phase-coded interference signal and noise signal respectively. The phase-coded interference signal after imaging can be written as:

[0040]

[0041] The signal performance model after SAR radar imaging is used to analyze the characteristics of phase coded interference after imaging.

[0042] Step 5: Considering that the SAR system uses the LFM pulse signal as its transmission signal, on this basis, the two-dimensional LFM transmission signal can be expressed as:

[0043]

[0044] Where, T a and Tr They are the pulse repetition period and pulse width of the SAR system transmitting signal, η and t are the slow time and fast time, K a and K r They are the slow time FM slope and the fast time FM slope respectively.

[0045] Step 6: On this basis, using the stationary phase principle, the spectrum of an LFM transmission pulse signal can be expressed as:

[0046]

[0047] The spectrum of a phase-coded pulse signal can be expressed as:

[0048]

[0049] The signal spectrum after convolution is:

[0050]

[0051] Step 7: Order That is, the signal spectrum after convolution is inversely transformed. Using the principle of fast stationary phase, the time domain signal obtained by inverse Fourier transform (the time domain manifestation of phase coded interference on the SAR image) is:

[0052]

[0053] Where P is the number of code elements, τ is the code element width, c k is a coded binary sequence.

[0054] Similarly, the image response of n phase-coded interferences is expressed as:

[0055]

[0056] It can be deduced from the above formula that the phase coding interference parameters have a specific corresponding relationship with the interference features on the SAR image.

[0057] Step 8: From the above formula, we can know that the fast time of phase coding interference on SAR image is obtained by superimposing P sinc envelope signals with a spacing of τ. The width between the first sinc envelope peak and the Pth sinc envelope peak is Considering that the sinc envelope has a certain width, this time we take the first zero point of the sinc envelope as the boundary point, then the width of a sinc envelope is Therefore, the width of the phase-coded interference range stripes on the SAR image should be the sum of the above two widths, that is:

[0058]

[0059] Where T i is the pulse duration of the interference, T r is the pulse width of the SAR system transmitting signal, B r is the bandwidth of the SAR transmission signal, B i is the phase coded interference bandwidth.

[0060] Considering that the phase-coded interference signal is usually a narrowband signal, and the SAR system transmission signal is usually a broadband signal. According to the convolution theorem, time domain convolution is equal to frequency domain multiplication, so after imaging, the bandwidth of the range interference signal in the image is equal to the phase-coded interference bandwidth, that is:

[0061] B r '=B i (13)

[0062] As for the carrier frequency, it does not participate in the actual calculation before and after imaging, so the carrier frequency of the single-range interference signal in the image should remain unchanged after imaging. Since it is the interference center frequency minus the SAR center frequency, the carrier frequency of the single-range interference signal in the image is:

[0063]

[0064] Where fc r The center frequency of the SAR system transmitting signal;

[0065] Since the phase-coded interference is a pulse signal, the time difference between the interference fringes on the SAR image should be equal to the repetition period of the phase-coded interference pulse, that is, the repetition frequency of the interference fringes on the SAR image is equal to the repetition frequency of the phase-coded interference pulse, that is:

[0066] PRF r '=PRF i (15)

[0067] Where PRF i is the phase-coded interference pulse repetition frequency.

[0068] Step 9: See Figure 1 , Figure 1 This is a flow chart of parameter estimation of ground phase-coded radar interference sources based on SAR images. First, the SLC image of SAR is obtained. For the obtained imaging data, on the one hand, the interference fringe width and fringe spacing in the imaging image are measured. On the other hand, a set of single-range data with interference in the complex data obtained by two-dimensional focusing imaging is taken for FFT processing, and the spectrum of the interference signal after imaging can be obtained. Based on its spectrum, its bandwidth and carrier frequency can be extracted. The pulse width, bandwidth, carrier frequency and repetition rate of phase-coded interference are estimated based on the obtained parameters and the above-mentioned parameter correspondence.

[0069] Experiment 1: Change a certain parameter of the interference while keeping other parameters unchanged, and observe the corresponding relationship between the parameter and the interference characteristics of the SAR image. Figure 2 It is the manifestation of interference of different pulse widths on the SAR image. Figure 3 It is the manifestation of interference of different bandwidths on SAR images. Figure 4 It is the single-distance signal spectrum under different bandwidths. Figure 5 It is the single-range signal spectrum under different carrier frequencies. Figure 6 It is the manifestation of interference with different repetition rates on SAR images. It can verify the mathematical relationship between the pulse width, bandwidth, carrier frequency and repetition rate of interference before imaging and the interference characteristics after imaging.

[0070] Experiment 2: Estimate the pulse width, bandwidth, carrier frequency, and repetition rate of phase-coded RFI based on the interference features obtained on the SAR image, and calculate the estimation error. Figure 7 is the phase coding interference pulse width estimation error. Figure 8 is the phase coding interference bandwidth estimation error. Fig. 9 is the phase coded interference carrier frequency estimation error. Fig.10 is the phase coded interference repetition frequency estimation error. It can be seen that the estimated error is small, indicating that the pulse width, bandwidth, carrier frequency, repetition frequency and other parameters of phase coded RF interference can be estimated more accurately.

[0071] The parameter estimation method of the ground phase-coded radar interference source based on the SAR image in this embodiment not only mathematically derives the specific manifestation of phase-coded interference on the SAR image, but also clarifies the correspondence between the interference signal pulse width, bandwidth, carrier frequency, repetition frequency and the interference characteristics on the SAR image, and verifies the correctness of the derived correspondence through simulation experiments. The effective estimation of the phase-coded interference parameters is achieved, providing an effective solution to the parameter estimation problem of the ground phase-coded radar interference source in the SAR image under non-cooperative conditions.

[0072] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field of the present invention, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for estimating parameters of ground phase-coded radar interference sources based on SAR images, characterized in that: include: Establish SAR receiving signal model, ground radar transmitting phase coding signal model, and SAR radar imaging signal performance model; Derive the mathematical representation of phase-coded interference on SAR images and the corresponding relationship between the pulse width, bandwidth, carrier frequency, repetition rate of phase-coded interference and SAR image characteristics; The SAR echo data with interference is subjected to two-dimensional focusing imaging to obtain the SAR imaging diagram with interference. The single-range interference fringe width and fringe period as well as the bandwidth and carrier frequency in its spectrum are extracted. The pulse width, bandwidth, carrier frequency and repetition rate of phase-coded interference are calculated according to the corresponding relationship of parameters.

2. The method for estimating parameters of ground phase-coded radar interference sources based on SAR images according to claim 1, characterized in that: The establishment of the SAR receiving signal model is specifically as follows: In the SAR image, if the echo from other radar signals is received, interference will occur. Considering that interference and noise exist at the same time, the received SAR signal is designed to be: s(n,t)=x(n,t)+r(n,t)+g(n,t) (1) Where t and η are fast time and slow time respectively, x(η,t) is the SAR echo signal, r(η,t) is the interference, and g(η,t) is the noise.

3. The method for estimating parameters of ground phase-coded radar interference sources based on SAR images according to claim 1, characterized in that: The model of ground radar transmitting phase coded signal is established as: Where rect(·) is the rectangular function, T i is the pulse duration of the interference, f c is the interference center frequency minus the SAR center frequency; the complex envelope function of the signal is in is the phase modulation function, There are only two possible values: 0 and π.

4. The method for estimating parameters of ground phase-coded radar interference sources based on SAR images according to claim 1, characterized in that: Using the above one-dimensional phase-coded signal model, the N phase-coded interference signals received in the SAR two-dimensional echo domain are expressed as: In the formula, a n is a complex number whose amplitude is related to the power level of the interference, δ(η) is the Dirac function, η n is the slow time of the nth interference pulse, t n is the propagation delay of the nth interference pulse; this signal model describes the interference caused by the ground radar signal to the SAR satellite; SAR imaging is a two-dimensional matched filtering process, and the following formula is used to express the signal performance after imaging: Where η' and t' are the azimuth time and distance time in the SAR image domain, respectively; h(η, t; η', t') is the time-varying convolution kernel; x(η', t'), r(η', t'), and g(η', t') are the image signal, phase-coded interference signal, and noise signal after imaging, respectively; the phase-coded interference signal after imaging is written as:

5. The method for estimating parameters of ground phase-coded radar interference sources based on SAR images according to claim 1, characterized in that: The mathematical representation of phase coding interference on SAR images is derived as follows: The SAR system uses the LFM pulse signal as its transmission signal, and the two-dimensional LFM transmission signal is expressed as: Where, T a and T r They are the pulse repetition period and pulse width of the SAR system transmitting signal, η and t are the slow time and fast time, K a and K r They are the slow time FM slope and the fast time FM slope respectively; Using the stationary phase principle, the spectrum of an LFM transmission pulse signal is expressed as: The spectrum of a phase-coded pulse signal is expressed as: The signal spectrum after convolution is: make That is, the signal spectrum after convolution is inversely transformed. Using the principle of fast stationary phase, the time domain signal obtained by inverse Fourier transform is: Where P is the number of code elements, τ is the code element width, c k To encode binary sequence; The image response of n phase-coded interferences is expressed as: The above formula is the mathematical expression of phase coding interference on SAR images.

6. The method for estimating parameters of ground phase-coded radar interference sources based on SAR images according to claim 5, characterized in that: The corresponding relationship between the pulse width, bandwidth, carrier frequency, repetition frequency of phase coded interference and SAR image characteristics is derived as follows: The fast time performance of phase coded interference on SAR images is obtained by superimposing P sinc envelope signals with a spacing of τ. The width between the first sinc envelope peak and the Pth sinc envelope peak is Taking the first zero point of the sinc envelope as the boundary point, the width of a sinc envelope is At this time, the phase-coded interference range fringe width on the SAR image is the sum of the above two widths; the corresponding relationship of the pulse width is: Where T i is the pulse duration of the interference, T r is the pulse width of the SAR system transmitting signal, B r is the bandwidth of the SAR transmission signal, B i is the phase coded interference bandwidth; The corresponding relationship of the bandwidth is: B r '=B i The corresponding relationship of the carrier frequencies is: fc' r =fc r +f c Where fc r The center frequency of the SAR system transmitting signal; The corresponding relationship of the repetition frequency is: PRF r '=PRF i Where PRF i is the phase-coded interference pulse repetition frequency.

7. 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 program, the steps of the method according to any one of claims 1 to 6 are implemented.

8. 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 described in any one of claims 1 to 6 are implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

Images