SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics

Abstract

The invention discloses an SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics, and belongs to the technical field of radar signal processing, and the method comprises the steps: building an SAR echo model under the condition of NFM saturation interference, carrying out the short-time Fourier transform of the interfered SAR echo, carrying out the fundamental wave and high-order harmonic detection, carrying out the notch filtering in each STFT window, and carrying out the noise modulation saturation interference suppression. And converting back to an echo time domain, and finally obtaining SAR echo data after interference suppression. According to the method, NFM saturation interference can be effectively suppressed, the effectiveness of the proposed method is verified through semi-actual measurement data of Radarsat-1, and compared with a time domain cancellation method, the method has better saturation interference suppression capability.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a method for suppressing SAR noise frequency modulation saturation interference based on time-frequency characteristics. Background Art

[0002] Synthetic aperture radar (SAR) can use the relative motion between the radar and the target to obtain high-resolution surface images or data. SAR's all-day, all-weather imaging capabilities and high-resolution image quality make it a powerful remote sensing tool. SAR plays an important role in earth science, resource exploration, military applications, environmental monitoring and other fields. However, SAR is easily affected by radio frequency interference (RFI) in the same frequency band. There are many sources of RFI that may threaten SAR, such as communication equipment, radars operating in the same band, and jammers. High-power RFI can drown out the target echo, thereby seriously deteriorating the quality of SAR images. Usually, RFI appears as streaks on SAR images, obscuring the target of interest. Therefore, it is extremely important to study effective methods to suppress RFI in SAR systems.

[0003] To suppress RFI, researchers have studied it from different perspectives, including parametric methods, non-parametric methods, semi-parametric methods, and machine learning methods. Parametric methods involve building a parametric model of the interference signal and estimating the model parameters to estimate and extract the interference. Non-parametric methods use the difference in intensity characteristics between the interference and target echo signals to filter out the interference. Semi-parametric methods transform the complex signal separation problem into a hyperparameter optimization problem. The above interference suppression methods require specific analysis of specific environments, which leaves room for performance improvement. Machine learning methods can automatically extract the hierarchical features of targets in images and have been successfully applied in the field of computer vision.

[0004] Existing methods can achieve good suppression effects when dealing with various interferences. However, these methods often ignore saturation interference. Saturation caused by interference is not uncommon in synthetic aperture radars. These interferences are usually caused by radiation signals from co-frequency radars, jammers and other equipment at ground base stations. The power of these radiation sources is very strong, and the interference power directly reaching the SAR receiving end is only attenuated by the square of the distance, resulting in saturation of the SAR receiving channel and triggering nonlinear limiting distortion of the receiving channel. This nonlinear distortion causes the interference signal to be distorted in both time and frequency domain characteristics. In the time domain, the signal amplitude is truncated, causing amplitude and phase distortion. In the frequency domain, due to the nonlinear characteristics of saturation distortion, the interference spectrum produces false components. If we ignore the special characteristics of saturation interference and still use existing interference analysis and suppression methods, it will lead to a mismatch between the signal model and the suppression method, thereby deteriorating the interference suppression effect. Compared with other types of saturation interference, noise frequency modulation saturation interference not only has strong interference radiation power, but also has a wide spectrum and a small amplitude dynamic range. There is still a lot of room for research on the suppression method of noise frequency modulation saturation interference. Summary of the invention

[0005] The object of the present invention is to provide a SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics, which is used to suppress saturation interference and its high-order harmonics in a low intermediate frequency SAR receiver and effectively improve the imaging quality of SAR.

[0006] The technical solution to achieve the purpose of the present invention is: a method for suppressing SAR noise frequency modulation saturation interference based on time-frequency characteristics, comprising the following steps:

[0007] Step 1: Based on the low-IF SAR receiver response, establish the SAR echo model under NFM saturation interference;

[0008] Step 2: Analyze the time domain and frequency domain characteristics of single-frequency and broadband saturation interference, obtain the time domain and frequency domain characteristics of noise frequency modulation saturation interference, and determine the processing method for NFM interference suppression;

[0009] Step 3: Detection of saturation interference fundamental wave and high-order harmonics, determine the notch threshold of each short-time Fourier window, and eliminate the fundamental wave harmonics and high-order harmonics of saturation interference exceeding the threshold in each short-time Fourier window;

[0010] Step 4: Perform inverse STFT on the data to restore the interference-suppressed time-frequency domain signal to the time domain to obtain the interference-suppressed echo data.

[0011] 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.

[0012] A computer-readable storage medium stores a computer program, which implements the steps of the above method when executed by a processor.

[0013] A computer program product comprises a computer program, which implements the steps of the above method when executed by a processor.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention utilizes the harmonic characteristics of saturation interference to accurately detect the fundamental harmonics and high-order harmonics of NFM saturation interference in SAR echoes, thereby effectively suppressing NFM saturation interference; interference suppression is performed by notch filtering, which does not involve the matrix inversion operation of traditional algorithms and has higher efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of SAR noise FM saturation interference suppression based on time-frequency characteristics under the condition of low intermediate frequency SAR receiver.

[0016] Figure 2 It is the structural block diagram of low intermediate frequency SAR receiver.

[0017] Figure 3 This is a schematic diagram of single-frequency saturation interference.

[0018] Figure 4 These are the spectra of the single-frequency signal before and after saturation. (a) is the unsaturated spectrum of the single-frequency signal, and (b) is the saturated spectrum of the single-frequency signal.

[0019] Figure 5 This is the frequency spectrum of the LFM signal before and after saturation under the low intermediate frequency receiver. (a) is the non-saturated spectrum of the LFM signal, and (b) is the saturated spectrum of the LFM signal.

[0020] Figure 6 This is the time-frequency domain of the LFM signal before and after saturation under the low intermediate frequency receiver. (a) is the non-saturated time-frequency domain diagram of the LFM signal, and (b) is the saturated time-frequency domain diagram of the LFM signal.

[0021] Figure 7 These are the time-frequency domain diagrams of the NFM signal before and after saturation under the low-IF receiver. (a) is the time-frequency domain diagram of the non-saturated NFM signal, and (b) is the time-frequency domain diagram of the saturated NFM signal.

[0022] Figure 8 The figures are imaging effect diagrams of the frequency domain notch method and the method of the present invention, (a) is the imaging effect diagram of the method of the present invention, and (b) is the imaging effect diagram of the frequency domain notch method.

[0023] Fig. 9 The figures are partial enlarged images of ship targets of the imaging effect diagrams of the frequency domain notch method and the method of the present invention, (a) is a partial enlarged image of the method of the present invention, and (b) is a partial enlarged image of the frequency domain notch method. DETAILED DESCRIPTION

[0024] The invention belongs to the field of radar signal processing technology, and discloses a SAR noise frequency modulation (NFM) interference suppression method based on the time-frequency characteristics of saturated interference signals, including: establishing a SAR echo model under NFM saturated interference, performing short-time Fourier transform (STFT) on the interfered SAR echo, then performing fundamental wave and high-order harmonic detection, performing notch filtering in each STFT window, and then transforming back to the echo time domain, and finally obtaining SAR echo data after interference suppression. The invention can effectively suppress NFM saturated interference, and the effectiveness of the proposed method is verified by semi-actual measurement data of Radarsat-1. Compared with the time domain cancellation method, the method has better saturated interference suppression capability.

[0025] The present invention is further described in detail below with respect to specific implementation modes.

[0026] refer to Figure 1 The method for suppressing SAR noise frequency modulation saturation interference based on time-frequency characteristics provided by the present invention comprises the following steps:

[0027] Step 1, based on the low intermediate frequency SAR receiver response, establish the SAR echo model under NFM saturation interference;

[0028] The block diagram of the low intermediate frequency SAR receiver is shown in the attached figure. Figure 2 As shown, the low-IF receiver converts the echo signal to a lower IF, which is then converted into a digital signal through an analog-to-digital converter (ADC). Among them, the main function of the automatic gain control (AGC) and manual gain control (MGC) is to adjust the gain of the echo and amplify its power to an appropriate level to adapt to the intensity changes of the scene scattering. However, when faced with interference that is much stronger than the echo signal, this may exceed the dynamic range of the AGC or MGC, causing the signal power input to the ADC to exceed its sampling threshold, thereby causing saturation.

[0029] When using a low intermediate frequency SAR receiver, the NFM interference signal received by the receiver can be expressed as

[0030]

[0031] The amplitude A0 and the intermediate frequency f0 are constants, Δf represents the frequency deviation amplitude, and m(τ) is the modulation signal controlled by random noise. The randomness of m(τ) leads to random frequency deviation. Instead of the phase of the NFM interference signal, the NFM interference signal when the receiver is saturated is obtained.

[0032]

[0033] Among them A j (t) represents the nonlinear change of the NFM interference signal amplitude when the receiver is saturated. Assume that the signal input to the ADC is S in , then the output signal S out It can be expressed as

[0034] S out =A[sat(S in )]

[0035]

[0036] Where A[·] is the quantization model function, and sat(·) is the saturation function / saturation conversion model of the ADC. The dynamic range of the ADC is [-S a ,S a ], within this input range, the ADC works in a linear state. When the input signal amplitude exceeds this dynamic range, the ADC will work in a nonlinear state and the system will be saturated.

[0037] When saturation does not occur, the interference signal can be demodulated by orthogonal demodulation to obtain the following two baseband signals:

[0038]

[0039] Therefore, the process of interference signal passing through ADC and saturation and then orthogonal demodulation is equivalent to s I (t) and s Q (t) is input into the saturation transition model sat(·), and we can get the saturated signal

[0040]

[0041] Where C is the saturation coefficient, and C<1. When the received signal amplitude exceeds CA j (t), it indicates signal saturation.

[0042] Step 2: Analyze the time and frequency domain characteristics of single-frequency and broadband saturation interference, simulate the time and frequency domain characteristics of noise frequency modulation saturation interference, and determine the processing method for NFM interference suppression;

[0043] First, analyze the single-frequency saturation interference. Figure 3 As shown, single frequency saturation interference It is still a periodic signal, which can be expressed as

[0044]

[0045] Where T is the period and n is the count representing the period. is a constant, τ cIt is the moment when saturation occurs for the first time on the time axis. Single frequency interference signal It consists of two parts: one is the periodically modulated local sine / cosine function signal s1, which can be split into the product of a single frequency signal and a square wave signal s3; the other is a rectangular wave signal s2 with regular periodicity, such as Figure 3 As shown, the green part is s1 and the red part is s2, which can be expressed as

[0046]

[0047]

[0048] Expand s2 and s3 into Fourier series, and we get

[0049]

[0050] It can be seen that s2 contains only odd harmonic components, and s3 contains only even harmonic components. According to the properties of trigonometric functions, s3 and After multiplication, It only contains odd harmonic components. Therefore, it can be concluded that single-frequency saturation interference is composed of multiple high-order harmonics, and the frequency of the high-order harmonics is an odd multiple of the original signal frequency.

[0051] Next, we analyze the generalized form of broadband saturation interference. Broadband saturation interference cannot be directly compared with periodic single-frequency saturation interference, but the saturation function sat(·) can be approximated by the smooth non-affine function g(·).

[0052]

[0053] Taylor expansion of the function tanh(x) yields

[0054]

[0055] Among them B 2n is the Bernoulli number. It can be seen that the exponents of tanh(x) expansion are all odd terms, and do not contain even terms and DC components. Therefore, when using a low intermediate frequency SAR receiver, the unsaturated part of the received echo signal and its quadrature demodulation Respectively expressed as

[0056]

[0057] By reducing the high-order terms in the signal to a power and ignoring the constant term, we can obtain

[0058]

[0059] The results show that when the echo signal is saturated, high-order harmonics will be generated, and the frequencies of these harmonics are odd multiples of the original signal frequency, the intermediate frequencies of the high-order harmonics also become corresponding odd multiples, and the positive and negative frequency values ​​appear alternately. As the frequency multiples increase, the amplitude of the harmonics gradually decreases.

[0060] Figure 4 This is the spectrum of the single-frequency signal before and after saturation. It can be seen from the figure that the single-frequency signal only contains odd harmonic frequencies. Figure 5 The frequency spectrum of the LFM signal before and after saturation under the low intermediate frequency receiver. Figure 5 It can be seen from the figure that the bandwidth of the high-order harmonics of the broadband saturated interference signal and the corresponding relationship between the intermediate frequency and the fundamental harmonics, the saturated LFM signal becomes a combination of multiple LFM signals. The frequency center and bandwidth of these LFM signals are odd multiples of the original LFM signal, and the amplitude gradually decreases, which is consistent with the theoretical analysis. Figure 6 The figure shows the time-frequency domain of the LFM signal before and after saturation in the low-IF receiver. It can be seen from the figure that the saturated LFM signal generates multiple LFM harmonics. The modulation frequency of the harmonics is an odd multiple of the fundamental modulation frequency, and the positive and negative values ​​appear alternately. For example, the modulation frequencies of the 3rd and 5th harmonics are -3 times and 5 times the fundamental modulation frequency, respectively. Figure 7 is the time-frequency of the NFM signal before and after saturation under the low intermediate frequency receiver. Figure 7 (a) shows that the interference radiation power is strong, the spectrum is wide, and the frequency changes are relatively random. Figure 7 (b) shows that the saturated NFM FM interference has non-negligible high-order harmonics, especially the 3rd and 5th harmonics, but the amplitude of the high-order harmonics is weaker than the fundamental wave, and some instantaneous spectra have many spurs, and the harmonic position cannot be determined based on the amplitude, and can even be ignored. Therefore, it can be determined that the specific method of NFM interference suppression is to detect the fundamental wave and high-order harmonics of the interference separately, determine the notch threshold of each short-time Fourier window, and then perform notch filtering.

[0061] Step 3, saturated NFM interference fundamental wave and high-order harmonic detection, determine the notch threshold of each short-time Fourier window, and eliminate the fundamental wave harmonics and high-order harmonics of saturated interference exceeding the threshold in each short-time Fourier window;

[0062] Step 3.1, perform saturated NFM interference fundamental harmonic detection. Perform STFT on the i-th slow-time echo x[n] with interference, and the result is expressed as

[0063]

[0064] Where m represents the mth moment in the STFT result, and k represents X i The kth frequency in, w[·] represents the window function, N r Indicates the number of points in each STFT time window, Nfft Represents the number of FFT points in the time window. After executing STFT, the instantaneous frequency spectrum X corresponding to any time sample m is obtained. i [m,:]. Then, the interference in the instantaneous frequency spectrum is detected, and the adaptive threshold criterion of the maximum mean ratio (MMR) is expressed as

[0065]

[0066] Where R represents the root mean square error of MMSE estimation, T wide represents the interference detection threshold obtained adaptively, which is set to the sum of the mean and standard deviation of the instantaneous frequency spectrum. th (R th Indicates the tolerance to interference intensity, which is set by experience). It means there is no interference or the interference power is relatively low, and no interference suppression is required. th , indicating that there is relatively high-power interference and interference suppression is required. th When the instantaneous frequency spectrum is compared with the threshold value determined by the MMR criterion, if the frequency of the instantaneous frequency spectrum exceeds the threshold value, it is considered that there is interference on these frequencies. The frequencies that meet these conditions are recorded to obtain the position k of the interference fundamental frequency harmonic i Set, denoted as

[0067]

[0068] Step 3.2, perform saturated NFM interference high-order harmonic detection. It is known that in the instantaneous frequency spectrum of saturated interference, the center frequency and bandwidth of high-order harmonics are still odd multiples of the fundamental wave. Therefore, from The interference fundamental wave X can be directly obtained i [m,k i ], thereby deriving the position of the interfering high-order harmonics in the instantaneous frequency spectrum and obtaining the position set of the interfering qth harmonic Then the method of estimating the signal-to-interference ratio (ISR) of the interfering harmonic is used to determine whether to apply notch filtering. After obtaining the position of the interfering high-order harmonics in the instantaneous frequency spectrum, the SIR of the interfering harmonic can be expressed as

[0069]

[0070] in represents the power of the qth interfering harmonic, and P s Indicates the power of the useful signal. ISR (q)>0dB means that the power of the qth interfering harmonic exceeds the power of the signal. In this case, it is necessary to perform notch filtering on this interfering harmonic in the time-frequency domain. At the same time, the position set of interfering high-order harmonics that seriously affect the useful signal can be obtained, and this set can be combined with the position set of the interfering fundamental wave to obtain a comprehensive position set Ψ that requires notch filtering in the instantaneous spectrum. m .

[0071] Step 3.3, saturation NFM interference suppression, eliminates the fundamental harmonics and higher-order harmonics of the saturation interference exceeding the threshold in each short-time Fourier window.

[0072] According to step 3.2, the position set Ψ corresponding to the interference fundamental wave and high-order harmonics with larger power can be obtained. m . Through the location set Ψ m , a binary mask can be constructed for the instantaneous spectrum corresponding to time sample m, expressed as

[0073]

[0074] By combining the binary masks corresponding to each time sample, we can obtain a i [m,k] are of the same size. Then, by combining Q[m,k] with X i By multiplying [m,k], we can obtain the time-frequency spectrum without interfering fundamental waves and high-power harmonics. Expressed as

[0075]

[0076] Step 4: Perform inverse STFT on the data to obtain the interference suppressed time-frequency domain signal Restore to time domain Obtain the echo data after interference suppression. This process is expressed as

[0077]

[0078] The above process completes the suppression of saturated NFM interference and removes the interference fundamental wave and high-order harmonics caused by saturation.

[0079] According to the specific implementation method of the present invention, the interference is suppressed by using the frequency domain notch method and the SAR NFM saturation interference suppression method based on the time-frequency characteristics of the present invention, and the suppressed SAR echo data is imaged. The imaging result is as follows: Figure 8 shown.

[0080] The simulation experiment uses semi-measured SAR data and evaluates the interference suppression results through imaging results. The simulation experiment uses the measurement data of Radarsat-1 and manually adds saturated NFM interference. The specific parameters of the Radarsat-1 platform are: carrier frequency: 5.3GHz, transmission signal bandwidth: 30.116MHz, pulse width: 41.75us, flight platform speed: 7062m / s, range sampling rate: 32.317MHz, azimuth sampling rate: 1256.98MHz, azimuth frequency modulation rate 1733Hz / s. The specific parameters of the NFM interference signal are: frequency offset amplitude 0.63946MHz, time width 41.75us, signal-to-interference ratio is -27.6824dB.

[0081] Figure 8 In the imaging results shown, both the frequency domain notch method and the present invention can achieve a certain interference suppression effect. Fig. 9 The partial enlarged view shows that the ship display effect of the present invention is clearer and the interference suppression effect is better. It can be seen that under the same ISR conditions, the present invention can provide a much higher interference suppression effect than the traditional frequency domain notch method.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for suppressing SAR noise frequency modulation saturation interference based on time-frequency characteristics, characterized in that: The following steps are involved: Step 1: Based on the low-IF SAR receiver response, establish the SAR echo model under NFM saturation interference; Step 2: Analyze the time domain and frequency domain characteristics of single-frequency and broadband saturation interference, obtain the time domain and frequency domain characteristics of noise frequency modulation saturation interference, and determine the processing method for NFM interference suppression; Step 3: Detection of saturation interference fundamental wave and high-order harmonics, determine the notch threshold of each short-time Fourier window, and eliminate the fundamental wave harmonics and high-order harmonics of saturation interference exceeding the threshold in each short-time Fourier window; Step 4: Perform inverse STFT on the data to restore the interference-suppressed time-frequency domain signal to the time domain to obtain the interference-suppressed echo data.

2. The SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics according to claim 1 is characterized in that: Step 1 is as follows: Using a low IF SAR receiver, the received NFM interference signal is expressed as Wherein the amplitude A0 and the intermediate frequency f0 are constants, Δf represents the frequency offset amplitude, m(τ) is the modulation signal controlled by random noise, and the randomness of m(τ) leads to random frequency offset; Replace the phase of the NFM interference signal to obtain the NFM interference signal when the receiver is saturated Among them A j (t) represents the nonlinear change of the NFM interference signal amplitude when the receiver is saturated; assuming that the signal input to the ADC is S in , then the output signal S out Indicated as S out =A[sat(S in )] Where A[·] is the quantization model function, sat(·) is the saturation function / saturation conversion model of the ADC; the dynamic range of the ADC is [-S a ,S a ], within this input range, the ADC works in a linear state; when the input signal amplitude exceeds this dynamic range, the ADC will work in a nonlinear state and the system will be saturated; When saturation does not occur, the interference signal is demodulated through orthogonal demodulation to obtain the following two baseband signals: Therefore, the process of interference signal passing through ADC and saturation and then orthogonal demodulation is equivalent to s I (t) and s Q (t) is input into the saturation conversion model sat(·) to obtain the saturated signal and Where C is the saturation coefficient, and C<1; when the received signal amplitude exceeds CA j (t), it indicates signal saturation.

3. The SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics according to claim 2 is characterized in that: Step 2: Analyze the time and frequency domain characteristics of single-frequency and broadband saturation interference, simulate the time and frequency domain characteristics of noise frequency modulation saturation interference, and determine the processing method for NFM interference suppression, specifically: First, analyze the single-frequency saturation interference; single-frequency saturation interference is a periodic signal, specifically expressed as Where T represents the period, n represents the count of the period, and the initial phase is a constant, τ c is the moment when saturation first occurs on the time axis; single-frequency interference signal It consists of two parts: one is the periodically modulated local sine / cosine function signal s1, which can be split into the product of a single frequency signal and a square wave signal s3; the other is a rectangular wave signal s2 with a regular periodicity, which can be expressed as Expand s2 and s3 into Fourier series, and we get s2 contains only odd harmonic components, and s3 contains only even harmonic components. According to the properties of trigonometric functions, s3 and After multiplication, It only contains odd harmonic components; therefore, it is concluded that the single-frequency saturation interference is composed of multiple high-order harmonics, and the frequency of the high-order harmonics is an odd multiple of the original signal frequency; The saturation function sat(·) is approximated by a smooth non-affine function g(·): Taylor expansion of the function tanh(x) yields Among them B 2n is a Bernoulli number. The exponentials of tanh(x) expansion are all odd terms, and do not contain even terms and DC components. Therefore, when using a low intermediate frequency SAR receiver, the unsaturated part of the received echo signal and its quadrature demodulation Respectively expressed as Reduce the high-order terms in the signal to a power and ignore the constant term to obtain 4. The SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics according to claim 3 is characterized in that: Step 3: Detect the fundamental wave and high-order harmonics of saturated NFM interference, determine the notch threshold of each short-time Fourier window, and eliminate the fundamental wave harmonics and high-order harmonics of saturated interference that exceed the threshold in each short-time Fourier window; specifically: Step 3.1, perform saturated NFM interference fundamental harmonic detection; perform STFT on the i-th slow time echo x[n] with interference, and the result is expressed as Where m represents the mth moment in the STFT result, and k represents X i The kth frequency in, w[·] represents the window function, N r Indicates the number of points in each STFT time window, N fft Represents the number of FFT points in the time window; after executing STFT, the instantaneous frequency spectrum X corresponding to any time sample m is obtained i [m,:]; then detect the interference in the instantaneous frequency spectrum, the adaptive threshold criterion of the maximum average ratio is expressed as Where R represents the root mean square error of MMSE estimation, T wide represents the adaptively obtained interference detection threshold, which is set to the sum of the mean and standard deviation of the instantaneous frequency spectrum; when R<R th , no interference suppression is required, where R th Indicates the tolerance to interference intensity; when R ≥ R th , interference suppression is required; when R ≥ R th When the instantaneous frequency spectrum is compared with the threshold value determined by the MMR criterion, if the frequency of the instantaneous frequency spectrum exceeds the threshold value, it is considered that there is interference on these frequencies; the frequencies that meet these conditions are recorded to obtain the position k of the interference fundamental frequency harmonic i The collection of Step 3.2, perform saturated NFM interference high-order harmonic detection; it is known that in the instantaneous frequency spectrum of saturated interference, the center frequency and bandwidth of high-order harmonics are still odd multiples of the fundamental wave; therefore, from The interference fundamental wave X can be directly obtained from i [m,k i ], thereby deriving the position of the interfering high-order harmonics in the instantaneous frequency spectrum and obtaining the position set of the interfering qth harmonic Then, the method of estimating the interference-to-signal ratio of the interfering harmonic is used to determine whether to apply notch filtering; after obtaining the position of the interfering high-order harmonics in the instantaneous frequency spectrum, the interference-to-signal ratio of the interfering harmonic is expressed as in represents the power of the qth interfering harmonic, and P s Indicates the power of the useful signal; ISR (q) >0dB means that the power of the qth interfering harmonic exceeds the power of the signal; in this case, it is necessary to perform notch filtering on this interfering harmonic in the time-frequency domain; at the same time, the position set of interfering higher-order harmonics is obtained, and this set is combined with the position set of the interfering fundamental wave to obtain a comprehensive position set Ψ that requires notch filtering in the instantaneous spectrum m ; Step 3.3, saturation NFM interference suppression, eliminating the fundamental harmonics and high-order harmonics of the saturation interference exceeding the threshold in each short-time Fourier window; According to step 3.2, the position set Ψ corresponding to the interference fundamental wave and high-order harmonics with larger power is obtained. m ; Through the position set Ψ m , construct a binary mask for the instantaneous spectrum corresponding to time sample m, expressed as By combining the binary masks corresponding to each time sample, we obtain a i [m,k]; then, by combining Q[m,k] with X i [m,k] are multiplied to obtain the time-frequency spectrum without interfering fundamental waves and high-power harmonics Expressed as 5. The SAR noise frequency modulation saturation interference suppression method based on time-frequency characteristics according to claim 4 is characterized in that: Step 4: Perform inverse STFT on the data to obtain the interference suppressed time-frequency domain signal Restore to time domain Obtain the echo data after interference suppression, specifically:

6. 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 5 are implemented.

7. 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 5 are implemented.

8. 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 5 are implemented.

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