Synthetic aperture radar imaging radio frequency interference detection method and system

Abstract

The application provides a synthetic aperture radar imaging radio frequency interference detection method and system, comprising the following steps: step S1: facing radio frequency interference feature collection, setting SAR working time sequence design; step S2: acquiring original echo through SAR satellite earth observation; step S3: according to the working time sequence of SAR, interference detection is carried out on the echo data corresponding to no transmission pulse of SAR, meanwhile, interference parameters are extracted, and a radio frequency interference signal model is established; step S4: according to the radio frequency interference signal model parameters and the original echo, interference detection and suppression are carried out again on the echo data corresponding to each transmission pulse; and step S5: outputting SAR echo data after interference suppression and carrying out focusing imaging processing. The application can effectively solve the problem of interference signal noise ratio faced by SAR satellite interference detection, improve interference detection and suppression capacity, and can provide important technical support for future SAR system design.

Description

Technical Field

[0001] This invention relates to the field of spaceborne radar system design and signal processing technology, specifically to a synthetic aperture radar (SAR) imaging radio frequency interference detection method and system. Background Technology

[0002] Spaceborne synthetic aperture radar (SAR) is an active microwave imaging sensor based on a satellite platform. It achieves high-resolution range imaging through the transmission of broadband frequency-modulated signals and pulse compression technology, and high-resolution azimuth imaging through azimuth virtual synthetic aperture technology. Spaceborne SAR images contain rich geometric, radiometric, and phase information, making it a primary technique for all-weather, all-day Earth observation. During SAR imaging, it is often affected by ground-based radio frequency interference. This interference can originate from various wireless communication devices, broadcast signals, or military radars. Radio frequency interference superimposed on the SAR echo signal causes noise, clutter, or target distortion in the image, severely affecting image quality and data resolution capabilities, posing significant security risks to applications such as resource surveys and emergency management. Therefore, researching and implementing effective anti-interference measures is crucial for improving the performance and reliability of SAR systems.

[0003] The published paper "SAR Radio Frequency Interference Suppression Method Based on Joint Filtering" (Wu Peng, Yang Lin, Zhang Yongsheng, et al. Radar Science and Technology, 2016, 14(3):225-230. DOI:10.3969 / j.issn.1672-2337.2016.03.001.) proposes an RFI suppression method based on joint filtering, taking into account the high power and narrow bandwidth characteristics of RFI signals. This method combines the advantages of traditional notch filtering and subspace projection methods in SAR radio frequency interference suppression. However, this method only considers signal processing anti-interference and does not consider the anti-interference design of SAR satellite systems.

[0004] Chinese patent document CN202210591783.X discloses a SAR radio frequency interference detection method. It analyzes the interference patterns and effects of different active noise interferences on spaceborne SAR images, determines the evaluation targets, establishes a SAR radio frequency interference image database, processes SAR interference images using anti-interference methods to form a comparative image database, establishes a SAR radio frequency interference image domain evaluation index system, classifies the evaluation indexes, analyzes the influence degree of each underlying index, and determines the weight of each underlying index. Step S5: Conducts image domain SAR radio frequency interference detection experiments and organizes and analyzes the detection results. However, this method only considers signal processing anti-interference and does not consider the anti-interference design of the SAR satellite system.

[0005] Chinese patent document CN202110313983.4 discloses a spaceborne SAR anti-jamming method based on frequency-modulated time-varying complex waveforms. It designs a composite modulation signal with low cross-correlation and high autocorrelation characteristics, which can be directly applied to deception interference suppression technology without iterative search. Simultaneously, by adding a random-phase transmission pulse sequence to periodic transmissions, the energy of the originally focused deception interference is dispersed across the range-azimuth two-dimensional plane, significantly improving the deception interference suppression capability. However, this method considers transmission signal encoding for anti-jamming but does not consider anti-jamming based on the timing design of the SAR satellite system.

[0006] The published paper "Research on Inter-Satellite Terrain Scattering Interference for Spaceborne SAR Systems" (Tao Mingliang, Sun Huanyu, Liu Yanyang, et al. Information Countermeasures Technology, 2023, 2(3):64-73.) introduces the inter-satellite terrain scattering interference patterns of spaceborne SAR systems, analyzes its existence conditions and mechanisms, constructs the geometric relationship of the interference propagation path, and derives the echo signal model after superimposed interference. Based on the differences between ground direct interference and inter-satellite scattering mutual interference signal models, the characteristic differences of the two types of interference in different signal characterization domains are compared and analyzed. However, this paper has not yet addressed the problem of inter-satellite direct wave interference suppression. This method only considers signal processing anti-interference, but does not consider the anti-interference design of SAR satellite systems.

[0007] Chinese patent document CN105974376B proposes a radio frequency interference (RF) suppression method using subspace projection. This method takes the echo signal of a range line from SAR data as input, constructs a phase space matrix based on the echo signal, and obtains the phase space matrix of the reference signal using subspace projection. A diagonal averaging method is then used to recover a one-dimensional reference signal from the reference signal phase space matrix. Based on the reference signal, a threshold for interfering signals is determined. Based on the determined interference threshold, the interfering frequency points present in the echo are identified and replaced with the average amplitude of the reference signal, thus completing the RF interference suppression for that range line. However, this method only considers signal processing anti-interference but does not consider the anti-interference design of the SAR satellite system.

[0008] In summary, current methods for SAR interference detection and suppression mainly involve signal encoding and processing the echoes in the signal domain. However, the use of SAR time-series design to obtain the electromagnetic spectrum of the observation area for interference detection and suppression has not yet been considered. This will lead to problems such as significant signal loss during interference suppression.

[0009] Therefore, a method and system for detecting radio frequency interference in synthetic aperture radar imaging is needed. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a synthetic aperture radar imaging radio frequency interference detection method and system.

[0011] A synthetic aperture radar imaging radio frequency interference detection method according to the present invention includes:

[0012] Step S1: Design the SAR working timing sequence for collecting radio frequency interference characteristics;

[0013] Step S2: Obtain the raw echo by observing the Earth through SAR satellites;

[0014] Step S3: Based on the SAR's operating timeline, perform interference detection on the echo data corresponding to the SAR's no-transmit pulse, extract interference parameters, and establish a radio frequency interference signal model.

[0015] Step S4: Based on the RF interference signal model parameters and the original echo, perform interference detection and suppression again on the echo data corresponding to each transmitted pulse;

[0016] Step S5: Output the interference-suppressed SAR echo data and perform focused imaging processing.

[0017] Preferably, step S1 includes:

[0018] Step S1.1: Generate a zebra pattern from the collected data, and set the radar working pulse repetition frequency and pulse width parameters based on the zebra pattern;

[0019] Step S1.2: Set the radar operating timing. Specifically, with M transmission pulses as the period, N radar transmission pulses are arbitrarily turned off in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

[0020] Preferably, step S3 includes:

[0021] Step S3.1: Determine the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range;

[0022] Specifically, the number of received radar echo signals for ground echoes without a main lobe is:

[0023]

[0024] In the formula, K is the pulse count corresponding to no pulse emission, R is the radar slant range, c is the speed of light, and PRF is the pulse repetition frequency. This is the floor operator;

[0025] Step S3.2: Convert the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detect the interference by the energy intensity of the spectrum in the frequency domain;

[0026] Step S3.3: Perform time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establish a radio frequency interference signal model S. RFI,i Where i represents the i-th type of interference.

[0027] Preferably, step S3.2 includes:

[0028] Step S3.2.1: Perform range-to-frequency domain transformation on the extracted radar echo signal;

[0029] Specifically, the frequency domain transformation is performed on the extracted L radar echoes. The radar echo corresponding to the l-th echo in the region without radar main lobe illumination is... The process of performing range-to-frequency domain transformation on the echo is as follows:

[0030]

[0031] In the formula, Represents the echo signal, FT{·} represents the Fourier transform, t a,l t represents the azimuth time corresponding to the l-th echo. r Where f is the distance sampling time, and f is the signal frequency;

[0032] Step S3.2.2: Set the first interference detection threshold and extract the distance cells with interference;

[0033] Specifically, the average spectral energy intensity of the L echoes Represented as

[0034]

[0035] First detection threshold T RFI for

[0036]

[0037] In the formula, α is the threshold coefficient; S range_comp,l This represents the signal of the l-th echo after range compression;

[0038] Step S3.2.3: Use the interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

[0039] Preferably, step S4 includes:

[0040] Step S4.1: Match the interference parameters of the radio frequency interference signal model with the original radar echo E0 one by one;

[0041] Specifically,

[0042]

[0043] In the formula, S rc,i (t a ,t r S(t) represents the matched filtered radar signal. a ,t r ) represents the original echo signal, S RFI,i Let i be the signal model for the i-th type of interference;

[0044] Step S4.2: Set a second detection threshold and perform detection. If the matched-filtered radar signal is greater than the second detection threshold, it is determined that there is radio frequency interference in the original echo E0, and proceed to step S4.3; if the matched-filtered radar signal does not exceed the second detection threshold, it is determined that there is no radio frequency interference in the original echo E0.

[0045] Step S4.3: Perform notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal S. notch,i (t a ,t r );

[0046] Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero:

[0047]

[0048] Repeat step S4.3 until all azimuth elements are zeroed, thus completing the notch filtering process.

[0049] Step S4.4: Perform inverse matched filtering on the radar signal after notch filtering to obtain the radar signal after interference suppression;

[0050] Specifically,

[0051]

[0052] In the formula, S filter,i (t a ,t r S represents the radar signal after suppressing the i-th type of interference. notch,i (t a ,t r () represents the radar signal after notch filtering.

[0053] A synthetic aperture radar imaging radio frequency interference detection system according to the present invention includes:

[0054] Module M1: Designed for SAR operating timing, focusing on radio frequency interference feature collection;

[0055] Module M2: Obtains raw echoes through SAR satellite Earth observation;

[0056] Module M3: Based on the SAR's operating timeline, it performs interference detection on the echo data corresponding to SAR without transmitted pulses, extracts interference parameters, and establishes a radio frequency interference signal model.

[0057] Module M4: Based on the RF interference signal model parameters and the original echo, perform interference detection and suppression again on the echo data corresponding to each transmitted pulse;

[0058] Module M5: Outputs interference-suppressed SAR echo data and performs focused imaging processing.

[0059] Preferably, the module M1 includes:

[0060] Module M1.1: Generates a zebra pattern from the collected data and sets the radar working pulse repetition frequency and pulse width parameters based on the zebra pattern;

[0061] Module M1.2: Sets the radar operating timing. Specifically, with M transmission pulses as the period, N radar transmission pulses are arbitrarily turned off in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

[0062] Preferably, the module M3 includes:

[0063] Module M3.1: Determine the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range;

[0064] Specifically, the number of received radar echo signals for ground echoes without a main lobe is:

[0065]

[0066] In the formula, K is the pulse count corresponding to no pulse emission, R is the radar slant range, c is the speed of light, and PRF is the pulse repetition frequency. This is the floor operator;

[0067] Module M3.2: Converts the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detects interference by the energy intensity of the spectrum in the frequency domain;

[0068] Module M3.3: Performs time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establishes a radio frequency interference signal model S. RFI,iWhere i represents the i-th type of interference.

[0069] Preferably, module M3.2 includes:

[0070] Module M3.2.1: Performs range-to-frequency domain transformation on the extracted radar echo signal;

[0071] Specifically, the frequency domain transformation is performed on the extracted L radar echoes. The radar echo corresponding to the l-th echo in the region without radar main lobe illumination is... The process of performing range-to-frequency domain transformation on the echo is as follows:

[0072]

[0073] In the formula, Represents the echo signal, FT{·} represents the Fourier transform, t a,l t represents the azimuth time corresponding to the l-th echo. r Where f is the distance sampling time, and f is the signal frequency;

[0074] Module M3.2.2: Set the first interference detection threshold and extract the distance cells where interference exists;

[0075] Specifically, the average spectral energy intensity of the L echoes Represented as

[0076]

[0077] First detection threshold T RFI for

[0078]

[0079] In the formula, α is the threshold coefficient; S range_comp,l This represents the signal of the l-th echo after range compression;

[0080] Module M3.2.3: Uses an interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

[0081] Preferably, the module M4 includes:

[0082] Module M4.1: Performs matched filtering on the interference parameters of the radio frequency interference signal model one by one with the original radar echo E0;

[0083] Specifically,

[0084]

[0085] In the formula, S rc,i (t a ,t r S(t) represents the matched filtered radar signal. a ,t r ) represents the original echo signal, S RFI,i Let i be the signal model for the i-th type of interference;

[0086] Module M4.2: Sets the second detection threshold and performs detection. If the matched-filtered radar signal is greater than the second detection threshold, it is determined that there is radio frequency interference in the original echo E0, and module M4.3 is triggered; if the matched-filtered radar signal does not exceed the second detection threshold, it is determined that there is no radio frequency interference in the original echo E0.

[0087] Module M4.3: Performs notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal S. notch,i (t a ,t r );

[0088] Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero:

[0089]

[0090] Repeat the execution of module M4.3 until all azimuth units are zeroed, thus completing the notch filtering process;

[0091] Module M4.4: Performs inverse matched filtering on the radar signal after notch filtering to obtain the radar signal after interference suppression;

[0092] Specifically,

[0093]

[0094] In the formula, S filter,i (t a ,t r S represents the radar signal after suppressing the i-th type of interference. notch,i (t a ,t r () represents the radar signal after notch filtering.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] 1. This invention is the first to design a SAR working timing sequence for collecting radio frequency interference features and to detect and suppress radio frequency interference. It uses radar recording signals without main lobe echo signals to sense radio frequency interference, and then uses the sensed radio frequency interference to detect and suppress radio frequency interference in the normally observed radar echo.

[0097] 2. This invention effectively solves the problem of low signal-to-interference ratio faced by existing radio frequency interference detection and suppression methods, improves interference detection and parameter estimation performance, and can provide important technical support for subsequent spaceborne SAR Earth imaging observation.

[0098] 3. The present invention employs a dual detection threshold (a first detection threshold and a second detection threshold), which improves the accuracy and robustness of interference detection.

[0099] 4. This invention improves the sensitivity of interference detection by matching the radio frequency interference signal model with the original echo through matched filtering technology; and by using notch filtering technology to set the range cells with interference to zero, it effectively suppresses the influence of radio frequency interference on radar signals while retaining useful signals. Attached Figure Description

[0100] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0101] Figure 1 This is a flowchart of a synthetic aperture radar imaging radio frequency interference detection method according to the present invention;

[0102] Figure 2 This is a schematic diagram of the SAR satellite inter-satellite direct wave interference detection and suppression process in Embodiment 1 of the present invention;

[0103] Figure 3 This is a SAR simulation image of Example 1 affected by radio frequency interference;

[0104] Figure 4 This is a comparison diagram of radar echoes with and without main lobe echo signals in Example 1.

[0105] Figure 5 This is a SAR simulation image after interference suppression according to Embodiment 1 of the present invention. Detailed Implementation

[0106] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0107] A synthetic aperture radar imaging radio frequency interference detection method according to the present invention includes:

[0108] Step S1: Design the SAR working timing sequence for collecting radio frequency interference characteristics;

[0109] Step S2: Obtain the raw echo by observing the Earth through SAR satellites;

[0110] Step S3: Based on the SAR's operating timeline, perform interference detection on the echo data corresponding to the SAR's no-transmit pulse, extract interference parameters, and establish a radio frequency interference signal model.

[0111] Step S4: Based on the RF interference signal model parameters and the original echo, perform interference detection and suppression again on the echo data corresponding to each transmitted pulse;

[0112] Step S5: Output the interference-suppressed SAR echo data and perform focused imaging processing.

[0113] Specifically, step S1 includes:

[0114] Step S1.1: Generate a zebra pattern from the collected data, and set the radar working pulse repetition frequency and pulse width parameters based on the zebra pattern;

[0115] Step S1.2: Set the radar operating timing. Specifically, with M transmission pulses as the period, N radar transmission pulses are arbitrarily turned off in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

[0116] Specifically, step S3 includes:

[0117] Step S3.1: Determine the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range;

[0118] Specifically, the number of received radar echo signals for ground echoes without a main lobe is:

[0119]

[0120] In the formula, K is the pulse count corresponding to no pulse emission, R is the radar slant range, c is the speed of light, and PRF is the pulse repetition frequency. This is the floor operator;

[0121] Step S3.2: Convert the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detect the interference by the energy intensity of the spectrum in the frequency domain;

[0122] Step S3.3: Perform time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establish a radio frequency interference signal model S. RFI,i Where i represents the i-th type of interference.

[0123] Specifically, step S3.2 includes:

[0124] Step S3.2.1: Perform range-to-frequency domain transformation on the extracted radar echo signal;

[0125] Specifically, the frequency domain transformation is performed on the extracted L radar echoes. The radar echo corresponding to the l-th echo in the region without radar main lobe illumination is... The process of performing range-to-frequency domain transformation on the echo is as follows:

[0126]

[0127] In the formula, Represents the echo signal, FT{·} represents the Fourier transform, t a,l t represents the azimuth time corresponding to the l-th echo. r Where f is the distance sampling time, and f is the signal frequency;

[0128] Step S3.2.2: Set the first interference detection threshold and extract the distance cells with interference;

[0129] Specifically, the average spectral energy intensity of the L echoes Represented as

[0130]

[0131] First detection threshold T RFI for

[0132]

[0133] In the formula, α is the threshold coefficient; S range_comp,l This represents the signal of the l-th echo after range compression;

[0134] Step S3.2.3: Use the interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

[0135] Specifically, step S4 includes:

[0136] Step S4.1: Match the interference parameters of the radio frequency interference signal model with the original radar echo E0 one by one;

[0137] Specifically,

[0138]

[0139] In the formula, S rc,i (t a ,t r S(t) represents the matched filtered radar signal. a ,t r ) represents the original echo signal, S RFI,i Let i be the signal model for the i-th type of interference;

[0140] Step S4.2: Set a second detection threshold and perform detection. If the matched-filtered radar signal is greater than the second detection threshold, it is determined that there is radio frequency interference in the original echo E0, and proceed to step S4.3; if the matched-filtered radar signal does not exceed the second detection threshold, it is determined that there is no radio frequency interference in the original echo E0.

[0141] Step S4.3: Perform notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal S. notch,i (t a ,t r );

[0142] Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero:

[0143]

[0144] Repeat step S4.3 until all azimuth elements are zeroed, thus completing the notch filtering process.

[0145] Step S4.4: Perform inverse matched filtering on the radar signal after notch filtering to obtain the radar signal after interference suppression;

[0146] Specifically,

[0147]

[0148] In the formula, S filter,i (t a ,t r S represents the radar signal after suppressing the i-th type of interference. notch,i (t a ,t r () represents the radar signal after notch filtering.

[0149] Example 1

[0150] A synthetic aperture radar (SAR) imaging radio frequency interference detection method according to the present invention includes:

[0151] Step S1: SAR timing design for radio frequency interference feature collection;

[0152] Step S2: SAR satellite Earth observation acquires raw echo E0;

[0153] Step S3: Use the echo data corresponding to the no-transmit pulse to perform interference detection and interference parameter extraction;

[0154] Step S4: Detect and suppress interference in the echo data corresponding to each transmitted pulse using the extracted interference information;

[0155] Step S5: Output the interference-suppressed SAR echo data and perform focused imaging processing.

[0156] Specifically, step S1, which focuses on the SAR operational timing design for interference feature collection, includes:

[0157] Step S1.1: Design the radar operating pulse repetition frequency and pulse width parameters based on the zebra diagram;

[0158] Step S1.2: To collect radio frequency interference data during pulse silence, the radar operating timing settings include using M transmission pulses as the period, and in each period, generating N random numbers from 1 to M to shut down the radar transmission pulse; in each pulse period, the radar normally receives and records ground echo signals; to ensure imaging quality, N must be less than M / 10.

[0159] Specifically, step S3 utilizes the echo data corresponding to the non-transmitted pulse to perform interference detection and interference parameter extraction, including:

[0160] Step S3.1: Based on the transmission timing and radar range, determine the radar signal with no main lobe ground echo. The pulse count corresponding to no pulse transmission is K, and the received echo count for no main lobe ground echo is...

[0161]

[0162] In the formula, K is the pulse count corresponding to no pulse emission, R is the radar slant range, c is the speed of light, and PRF is the pulse repetition frequency. This is the floor operator.

[0163] Step S3.2: Transform the extracted radar echo from the region without radar main lobe illumination to the frequency domain, and detect the interference according to the spectral energy intensity;

[0164] Step S3.3: Analyze the detected radio frequency interference using time-frequency analysis tools such as short-time Fourier transform to obtain the type and parameters of the radio frequency interference, and establish a radio frequency interference signal model S. RFI,i Here, the subscript i represents the i-th type of interference.

[0165] Specifically, step S3.2 includes:

[0166] Step S3.2.1: Perform frequency domain transformation on the extracted L radar echoes, and set the radar echo corresponding to the l-th echo in the region without radar main lobe illumination as... E0 represents the original echo, and the process of performing a range-to-frequency domain transformation on the echo can be expressed as follows:

[0167]

[0168] In the formula, Represents the echo signal, FT{·} represents the Fourier transform, t a,l t represents the azimuth time corresponding to the l-th echo. r Where f is the distance sampling time, and f is the signal frequency;

[0169] Step S3.2.2: Set the interference detection threshold according to the spectral energy intensity, and extract the range cells with interference, and calculate the average spectral energy intensity of the L echoes. It can be represented as

[0170]

[0171] Let the detection threshold T be... RFI It can be represented as

[0172]

[0173] In the formula, α is the threshold coefficient, which can be adjusted according to actual needs. Interference detection is performed using the set detection threshold. If the energy intensity is greater than the threshold value, the corresponding echo unit is considered to have radio frequency interference.

[0174] Specifically, step S4 utilizes the extracted interference information to perform interference detection and suppression on the echo data corresponding to each transmitted pulse, including:

[0175] Step S4.1: For all interference source parameters extracted in step S3, perform matched filtering on each of the original radar echoes.

[0176]

[0177] In the formula, S rc,i (t a ,t r S(t) represents the matched filtered radar signal.a ,t r ) represents the original echo signal, S RFI,i Let be the signal model for the i-th type of interference.

[0178] Step S4.2: Set the detection threshold T rc The detection process is the same as step S3.2. If the radar signal after matched filtering is greater than the threshold value, it is determined that there is radio frequency interference in the original echo, and then steps S4.3 and S4.4 are performed. If the radar signal after matched filtering does not exceed the second detection threshold value, it is determined that there is no radio frequency interference in the original echo E0.

[0179] Step S4.3: Perform notch filtering on the matched-filtered radar signal. The signal after notch filtering is denoted as S. notch,i (t a ,t r Let a certain azimuth unit be... The detected distance unit with radio frequency interference is The process of zeroing out distance cells subject to radio frequency interference can be expressed as follows:

[0180]

[0181] Perform the above processing on all azimuth units to complete the notch filtering process;

[0182] Step S4.4: Perform inverse matched filtering on the notch-filtered radar signal to obtain the radar signal after interference suppression:

[0183]

[0184] In the formula, S filter,i (t a ,t r S represents the radar signal after suppressing the i-th type of interference. notch,i (t a ,t r S represents the radar signal after notch filtering. RFI,i Let be the signal model for the i-th type of interference.

[0185] This invention significantly improves the quality and clarity of SAR imaging by performing inverse matched filtering and focused imaging processing on the radar signal after interference suppression. This method effectively reduces the negative impact of radio frequency interference on imaging results and is suitable for SAR imaging tasks in complex electromagnetic environments.

[0186] The present invention will now be described in detail with reference to the accompanying drawings.

[0187] The results of this invention are presented using raw echo data from the LuTan-1 01 satellite constellation, superimposed with inter-satellite direct wave interference. Here, it is assumed that a period of 256 transmitted pulses is used, with two transmitted pulses randomly shut down for simulation verification. The pulse repetition frequency of LuTan-1 is Hz, and the ground radio frequency interference is a linear frequency modulated signal with a bandwidth of 5MHz, a duration of 5 microseconds, and a repetition period of 5000Hz. Figure 3 The SAR image affected by interference is presented. Figure 4 A comparison chart of radar echoes with and without main lobe echo signals is presented. As can be seen from the chart, the interference-to-signal ratio (ISR) of radar echoes with no main lobe echo signals is significantly higher than that of radar echoes with main lobe echo signals. This provides important support for the detection and extraction of interference signals. Figure 5 The SAR image processed by the method of the present invention is shown. As can be seen from the figure, the interference signal is effectively suppressed.

[0188] The method of this invention successfully solves the problem of low signal-to-interference ratio in synthetic aperture radar (SAR) imaging radio frequency interference detection, and can provide important technical support for the design of subsequent spaceborne SAR systems.

[0189] This invention also provides a synthetic aperture radar (SAR) imaging radio frequency interference detection system. This system can be implemented by executing the steps of the synthetic aperture radar (SAR) imaging radio frequency interference detection method. That is, those skilled in the art can understand the synthetic aperture radar (SAR) imaging radio frequency interference detection method as a preferred embodiment of the synthetic aperture radar (SAR) imaging radio frequency interference detection system. The system includes:

[0190] Module M1: SAR timing design for collecting radio frequency interference features;

[0191] Module M2: Acquires raw echo E0 from SAR satellite Earth observation;

[0192] Module M3: Uses echo data corresponding to no transmitted pulses for interference detection and interference parameter extraction;

[0193] Module M4: Utilizes the extracted interference information to perform interference detection and suppression on the echo data corresponding to each transmitted pulse;

[0194] Module M5: Outputs interference-suppressed SAR echo data and performs focused imaging processing.

[0195] In one specific embodiment, a synthetic aperture radar imaging radio frequency interference detection system includes:

[0196] Module M1: Designs the SAR operating sequence for collecting radio frequency interference features; Module M2: Acquires raw echoes through SAR satellite Earth observation; Module M3: Detects interference in echo data corresponding to SAR pulses without transmission according to the SAR operating sequence, extracts interference parameters, and establishes a radio frequency interference signal model; Module M4: Performs interference detection and suppression again on echo data corresponding to each transmission pulse based on the radio frequency interference signal model parameters and the raw echoes; Module M5: Outputs the interference-suppressed SAR echo data and performs focused imaging processing.

[0197] Specifically, module M1 includes: module M1.1: forming a zebra pattern from the collected data, and setting the radar working pulse repetition frequency and pulse width parameters according to the zebra pattern; module M1.2: setting the radar working timing sequence, specifically, with M transmission pulses as the period, arbitrarily shutting down N radar transmission pulses in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

[0198] Specifically, module M3 includes: Module M3.1: determining the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range; specifically, the number of received radar echo signals without main lobe ground echo is:

[0199]

[0200] In the formula, K is the pulse count corresponding to no pulse emission, R is the radar slant range, c is the speed of light, and PRF is the pulse repetition frequency. The round-down operator is used; Module M3.2: Converts the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detects interference by the energy intensity of the spectrum in the frequency domain; Module M3.3: Performs time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establishes a radio frequency interference signal model S. RFI,i Where i represents the i-th type of interference.

[0201] Specifically, module M3.2 includes: Module M3.2.1: Performing range-to-frequency domain transformation on the extracted radar echo signals; specifically, performing frequency domain transformation on the extracted L echoes, where the radar echo corresponding to the l-th echo in the region without radar main lobe illumination is... The process of performing range-to-frequency domain transformation on the echo is as follows:

[0202]

[0203] In the formula, Represents the echo signal, FT{·} represents the Fourier transform, t a,l t represents the azimuth time corresponding to the l-th echo.r Where f is the range sampling time and f is the signal frequency; Module M3.2.2: Sets the first interference detection threshold and extracts the range cells with interference; specifically, the average spectral energy intensity of L echoes. Represented as

[0204]

[0205] First detection threshold T RFI for

[0206]

[0207] In the formula, α is the threshold coefficient; S range_comp,l This represents the signal after distance compression of the l-th echo; Module M3.2.3: Uses an interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

[0208] Specifically, module M4 includes: module M4.1: matching and filtering the interference parameters of the radio frequency interference signal model one by one with the original radar echo E0; specifically,

[0209]

[0210] In the formula, S rc,i (t a ,t r S(t) represents the matched filtered radar signal. a ,t r ) represents the original echo signal, S RFI,i Let be the signal model for the i-th type of interference; Module M4.2: Set a second detection threshold and perform detection. If the matched-filtered radar signal is greater than the second detection threshold, it is determined that there is radio frequency interference in the original echo E0, triggering module M4.3; if the matched-filtered radar signal does not exceed the second detection threshold, it is determined that there is no radio frequency interference in the original echo E0; Module M4.3: Perform notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal S. notch,i (t a ,t r Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero:

[0211]

[0212] Module M4.3 is executed repeatedly until all azimuth cells are zeroed, completing the notch filtering process; Module M4.4: performs inverse matched filtering on the notch-filtered radar signal to obtain the interference-suppressed radar signal; specifically,

[0213]

[0214] In the formula, S filter,i (t a ,t r S represents the radar signal after suppressing the i-th type of interference. notch,i (t a ,t r () represents the radar signal after notch filtering.

[0215] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0216] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for detecting radio frequency interference in synthetic aperture radar imaging, characterized in that, include: Step S1: Design the SAR working timing sequence for collecting radio frequency interference characteristics; Step S2: Obtain the raw echo by observing the Earth through SAR satellites; Step S3: Based on the SAR's operating timeline, perform interference detection on the echo data corresponding to the SAR's no-transmit pulse, extract interference parameters, and establish a radio frequency interference signal model. Step S4: Based on the RF interference signal model parameters and the original echo, perform interference detection and suppression again on the echo data corresponding to each transmitted pulse; Step S5: Output the interference-suppressed SAR echo data and perform focused imaging processing; Step S3 includes: Step S3.1: Determine the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range; Specifically, the number of received radar echo signals for ground echoes without a main lobe is: In the formula, K is the pulse count corresponding to no pulse emission. For radar slant range, At the speed of light, The pulse repetition frequency, This is the floor operator; Step S3.2: Convert the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detect the interference by the energy intensity of the spectrum in the frequency domain; Step S3.3: Perform time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establish a radio frequency interference signal model. ;in, Representing the Types of interference.

2. The synthetic aperture radar imaging radio frequency interference detection method according to claim 1, characterized in that, Step S1 includes: Step S1.1: Generate a zebra pattern from the collected data, and set the radar working pulse repetition frequency and pulse width parameters based on the zebra pattern; Step S1.2: Set the radar operating timing. Specifically, with M transmission pulses as the period, N radar transmission pulses are arbitrarily turned off in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

3. The synthetic aperture radar imaging radio frequency interference detection method according to claim 1, characterized in that, Step S3.2 includes: Step S3.2.1: Perform range-to-frequency domain transformation on the extracted radar echo signal; Specifically, regarding the extraction The radar echo of the first echo undergoes frequency domain transformation, and the area without radar main lobe illumination is the first... The radar echo corresponding to each echo is The process of performing range-to-frequency domain transformation on the echo is as follows: In the formula, Represents the echo signal. Represents Fourier transform, Representing the Each echo corresponds to a specific azimuth time. For distance sampling time, The signal frequency; Step S3.2.2: Set the first interference detection threshold and extract the distance cells where interference exists; Specifically, Average spectral energy intensity of each echo Represented as First detection threshold for In the formula, This is the threshold coefficient; Representing the The echo signal after distance compression; Step S3.2.3: Use the interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

4. The synthetic aperture radar imaging radio frequency interference detection method according to claim 1, characterized in that, Step S4 includes: Step S4.1: Compare the interference parameters of the radio frequency interference signal model with the original radar echo one by one. Perform matched filtering; Specifically, In the formula, The radar signal after matched filtering. The original echo signal, For the first Signal models of various types of interference; Step S4.2: Set a second detection threshold and perform detection. If the matched-filtered radar signal is greater than the second detection threshold, then the original echo is considered valid. If radio frequency interference is present, proceed to step S4.3; if the matched-filtered radar signal does not exceed the second detection threshold, the original echo is considered valid. There is no radio frequency interference. Step S4.3: Perform notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal. ; Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero, as follows: Repeat step S4.3 until all azimuth elements are zeroed, thus completing the notch filtering process. Step S4.4: Perform inverse matched filtering on the radar signal after notch filtering to obtain the radar signal after interference suppression; Specifically, In the formula, For the first radar signals after suppression of various types of interference. This is the radar signal after notch filtering.

5. A synthetic aperture radar imaging radio frequency interference detection system, characterized in that, include: Module M1: Designed for SAR operating timing, focusing on radio frequency interference feature collection; Module M2: Obtains raw echoes through SAR satellite Earth observation; Module M3: Based on the SAR's operating timeline, it performs interference detection on the echo data corresponding to SAR without transmitted pulses, extracts interference parameters, and establishes a radio frequency interference signal model. Module M4: Based on the RF interference signal model parameters and the original echo, perform interference detection and suppression again on the echo data corresponding to each transmitted pulse; Module M5: Outputs interference-suppressed SAR echo data and performs focused imaging processing; The module M3 includes: Module M3.1: Determine the radar echo signal without main lobe ground echo based on the SAR operating time sequence and radar range; Specifically, the number of received radar echo signals for ground echoes without a main lobe is: In the formula, K is the pulse count corresponding to no pulse emission. For radar slant range, At the speed of light, The pulse repetition frequency, This is the floor operator; Module M3.2: Converts the echo signal of the extracted radar main lobe-illuminated area into the frequency domain, and detects interference by the energy intensity of the spectrum in the frequency domain; Module M3.3: Performs time-frequency analysis on the detected radio frequency interference to obtain the type and parameters of the radio frequency interference, and establishes a radio frequency interference signal model. ;in, Representing the Types of interference.

6. The synthetic aperture radar imaging radio frequency interference detection system according to claim 5, characterized in that, The module M1 includes: Module M1.1: Generates a zebra pattern from the collected data and sets the radar working pulse repetition frequency and pulse width parameters based on the zebra pattern; Module M1.2: Sets the radar operating timing. Specifically, with M transmission pulses as the period, N radar transmission pulses are arbitrarily turned off in each period, while ensuring that ground echo signals can be received in each pulse period; where N is less than M / 10.

7. The synthetic aperture radar imaging radio frequency interference detection system according to claim 5, characterized in that, Module M3.2 includes: Module M3.2.1: Performs range-to-frequency domain transformation on the extracted radar echo signal; Specifically, regarding the extraction The radar echo of the first echo undergoes frequency domain transformation, and the area without radar main lobe illumination is the first... The radar echo corresponding to each echo is The process of performing range-to-frequency domain transformation on the echo is as follows: In the formula, Represents the echo signal. Represents Fourier transform, Representing the Each echo corresponds to a specific azimuth time. For distance sampling time, The signal frequency; Module M3.2.2: Set the first interference detection threshold and extract the distance cells where interference exists; Specifically, Average spectral energy intensity of each echo Represented as First detection threshold for In the formula, This is the threshold coefficient; Representing the The echo signal after distance compression; Module M3.2.3: Uses an interference detection threshold to perform interference detection on the extracted distance cells with interference. If the energy intensity is greater than the first detection threshold, the corresponding echo cell is considered to have radio frequency interference; if the energy intensity does not exceed the first detection threshold, the corresponding echo cell is considered not to have radio frequency interference.

8. The synthetic aperture radar imaging radio frequency interference detection system according to claim 5, characterized in that, The module M4 includes: Module M4.1: Compares the interference parameters of the radio frequency interference signal model with the original radar echo one by one. Perform matched filtering; Specifically, In the formula, The radar signal after matched filtering. The original echo signal, For the first Signal models of various types of interference; Module M4.2: Sets a second detection threshold and performs detection. If the matched-filtered radar signal is greater than the second detection threshold, the original echo is considered valid. Radio frequency interference is present, triggering module M4.3; if the matched-filtered radar signal does not exceed the second detection threshold, the original echo is considered valid. There is no radio frequency interference. Module M4.3: Performs notch filtering on the matched-filtered radar signal to obtain the notch-filtered signal. ; Specifically, the azimuth units are ordered according to a preset sequence, starting from the azimuth units. Initially, the corresponding distance unit with radio frequency interference was detected. Set the distance unit with radio frequency interference to zero, as follows: Repeat the execution of module M4.3 until all azimuth units are zeroed, thus completing the notch filtering process; Module M4.4: Performs inverse matched filtering on the radar signal after notch filtering to obtain the radar signal after interference suppression; Specifically, In the formula, For the first radar signals after suppression of various types of interference. This is the radar signal after notch filtering.

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