A method for narrowband interference suppression in synthetic aperture radar based on notch detection

Abstract

This invention discloses a method for suppressing narrowband interference in synthetic aperture radar (SAR) based on notch detection. The method includes: for a received SAR signal contaminated by narrowband interference, accumulating along the azimuth dimension and then differentiating the result; subsequently, employing a two-stage notch detection method to detect and notch the narrowband and broadband interference separately. The first stage of notch detection determines the frequency of the narrowband interference and sets it to zero; the second stage of notch detection uses a sliding window to determine the frequency band contaminated by the broadband interference and sets it to zero. This invention innovatively uses a two-stage notch detection structure to achieve joint suppression of electromagnetic narrowband and broadband interference in SAR while effectively avoiding potential omissions and false detections due to the different characteristics of narrowband and broadband interference. Furthermore, it is computationally simple, has a fast response time, and meets the needs of practical applications.

Description

Technical Field

[0001] This invention relates to the field of synthetic aperture radar anti-jamming, and in particular to a method for narrow-bandwidth interference suppression of synthetic aperture radar based on detected notch waves. Background Technology

[0002] Synthetic Aperture Radar (SAR) is an active remote sensing radar system widely used in both military and civilian fields due to its all-weather, all-day operation. SAR can rapidly and accurately scan the ground using platforms such as satellites, obtaining high-resolution radar images of distant observation scenarios. Radio frequency (RF) interference is a special type of narrowband interference that significantly reduces the signal-to-interference-plus-noise ratio (SNR) of the echo, drowning out useful echo signals and causing the entire image to appear suppressed and contaminated, making SAR image texture completely invisible. Common RF interference is mainly divided into narrowband interference at a single frequency point and broadband interference occupying an entire frequency band. Common interference suppression methods typically utilize certain characteristics of RF interference in the time and frequency domains to suppress the interference.

[0003] Notch filtering is a widely used interference detection and suppression method in practical industrial products due to its excellent characteristics of high speed, low computational complexity, and stable performance. Since radio frequency interference energy is often about 20-30 dB higher than the useful signal, the common method is to set a threshold using a sliding window, considering frequencies with energy exceeding this threshold as interference-contaminated frequencies. This method is suitable for narrowband interference environments, but its performance is limited for broadband interference environments, and it is even less capable of handling radio frequency interference environments where both narrow and broadband interference coexist. Therefore, it is necessary to design a notch filtering method that fully considers the special properties of broadband interference, achieving notch filtering for broadband interference while retaining the excellent characteristics of traditional notch filtering methods. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for suppressing narrow-bandwidth interference in synthetic aperture radar (SAR) based on notch detection, in order to solve the problems of narrow-bandwidth mixed interference commonly encountered in existing SAR systems and the inability of existing detection methods to simultaneously detect the two types of interference. This invention achieves joint notch detection of narrow-bandwidth interference by differentiating and performing two detection notches targeting the respective characteristics of narrow-band and wide-bandwidth interference, thereby achieving SAR interference suppression.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for narrowband interference suppression in synthetic aperture radar based on detected notch waves, the method comprising the following steps:

[0007] Step S1: Convert the received time-domain synthetic aperture radar signal to the SAR image domain;

[0008] Step S2: Accumulate the SAR image signal obtained in step S1 along the azimuth dimension to obtain the received signal that is contaminated by interference in the frequency domain, and then differentiate the received signal to obtain the time difference result of the useful signal and the interference.

[0009] Step S3: A two-stage notch detection method is used to detect notches for narrowband interference and broadband interference respectively, which includes:

[0010] Step S301: In the first-stage detection notch filter, based on the characteristics of narrowband interference electromagnetic energy, mark its corresponding frequency point and set the frequency point to zero;

[0011] Step S302: In the second-stage detection notch filter, based on the characteristics of broadband interference electromagnetic energy, mark its corresponding frequency point; then, combining the sliding window method and the frequency point, determine the frequency band contaminated by broadband interference, and set the frequency band to zero.

[0012] Furthermore, in step S1, the received time-domain synthetic aperture radar signal is converted to the SAR image domain by performing Fourier transform and inverse Fourier transform.

[0013] Furthermore, in step S2, the SAR image signal is accumulated along the azimuth dimension to obtain the signal contaminated by interference in the frequency domain. Then, based on the slowly varying characteristics of the useful signal, a derivative operation is performed on the signal accumulated along the azimuth dimension, so that the interference signal and the useful signal can be distinguished by analyzing the energy level of the differentiated signal.

[0014] Furthermore, step S301 specifically includes:

[0015] The first stage of detection notch filtering is performed. Based on the characteristics of the narrowband interference electromagnetic energy after differentiation, an amplitude detection threshold is set. Frequency points with electromagnetic energy higher than the threshold are marked as frequencies contaminated by narrowband interference. The frequencies contaminated by narrowband interference are set to 0, thereby realizing the detection and suppression of narrowband interference.

[0016] Furthermore, step S302 specifically includes:

[0017] The second stage of sliding window detection notch filtering first establishes a second amplitude detection threshold based on the characteristics of broadband interference electromagnetic energy after differentiation. Frequency points exceeding this threshold are marked as potentially contaminated by broadband interference. Then, through a sliding window, frequencies exceeding the second amplitude detection threshold within the window are marked. Next, a judgment is made: if the percentage of marked frequency points to the total number of frequency points within the window exceeds a pre-set percentage threshold, then all frequency points within the window are judged as interfered frequencies. Finally, the interfered frequency points are set to 0, thus achieving the detection and suppression of broadband interference.

[0018] The beneficial effects of this invention are:

[0019] This invention is based on commonly used industrial interference energy detection methods. It achieves joint detection of narrowband and broadband hybrid electromagnetic interference by differentiating the interfered signal and using a detection notch for narrowband interference and a sliding window detection notch for broadband interference. The first part determines the frequency of the narrowband interference by detecting amplitude abrupt changes and applies a detection notch to that frequency based on the characteristic that narrowband interference only contaminates a single frequency. The second part determines the frequency band contaminated by the broadband interference using a sliding window approach and applies a detection notch to the window identified as contaminated by interference, based on the characteristic that broadband interference contaminates continuous frequency bands. This algorithm is simple to calculate, fast, and computationally inexpensive, showing promising prospects for practical applications. Attached Figure Description

[0020] Figure 1 The SAR image received in Example 1 is contaminated by narrowband and broadband interference;

[0021] Figure 2 This is the result of accumulating SAR images along the azimuth dimension in Example 1;

[0022] Figure 3 This is the result after differentiating the summed result in Example 1;

[0023] Figure 4 The notch detection results for narrowband interference in Example 1;

[0024] Figure 5 This is the notch detection result for broadband interference in Example 1;

[0025] Figure 6 This is a comparison chart of the notch detection results in Example 1 and the original data contaminated by interference. Figure 6 Figure a shows the original data that has been interfered with and contaminated. Figure 6 Figure b shows the results of notch detection. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] See Figures 1-6 This embodiment provides a method for narrow bandwidth interference suppression of synthetic aperture radar based on notch detection. The method specifically includes the following steps:

[0029] Step S1: Receive the time-domain synthetic aperture radar signal, and perform Fourier transform and inverse Fourier transform on it to convert the signal to the SAR image domain.

[0030] Specifically, in this embodiment, the SAR imaging results are as follows: Figure 1 As shown, the image is severely interfered with, and no useful surface information can be discerned from the image.

[0031] Step S2: Accumulate the SAR image signal obtained in step S1 along the azimuth dimension to obtain the received signal that is contaminated by interference in the frequency domain, and then differentiate the received signal to obtain the time difference result of the useful signal and the interference.

[0032] Specifically, in this embodiment, the useful signal obtained in step S2 is relatively smooth, as shown in the following example. Figure 2 and Figure 3 As shown, the Figure 2 To accumulate SAR image signals along the azimuth dimension and obtain the received signal contaminated by interference in the frequency domain; Figure 3 To obtain a smoother time difference result between the useful signal and the interference by taking the derivative.

[0033] More specifically, in this embodiment, in step S2, the SAR image signal is accumulated along the azimuth dimension to obtain the signal that is contaminated by interference in the frequency domain. Then, based on the slowly varying characteristics of the useful signal, a derivative operation is performed on the signal accumulated along the azimuth dimension, so that the interference signal and the useful signal can be distinguished by analyzing the energy level of the differentiated signal.

[0034] Step S3: A two-stage notch detection method is used to detect notches for narrowband interference and broadband interference respectively, which includes:

[0035] Step S301: Execute the first part of the notch detection. Based on the characteristics of the narrowband interference electromagnetic energy after differentiation, set a first amplitude detection threshold. Mark the frequency points with electromagnetic energy higher than the first amplitude detection threshold as the frequency points contaminated by narrowband interference. Set the frequency points contaminated by narrowband interference to 0 to realize the detection and suppression of narrowband interference.

[0036] Step S302: Perform the sliding window detection notch filtering in the second part. First, based on the characteristics of the broadband interference electromagnetic energy after differentiation, a second amplitude detection threshold is set, and frequency points higher than this threshold are marked as potentially contaminated by broadband interference. Then, through a sliding window, the frequency points in the window that are higher than the second amplitude detection threshold are marked. Next, a judgment is made: if the percentage of the number of marked frequency points to the total number of frequency points in the window is higher than a preset percentage threshold, then all frequency points in the window are judged as interfered frequency points. Finally, the interfered frequency points are set to 0, thereby realizing the detection and suppression of broadband interference.

[0037] Specifically, in step S3, narrowband interference suppression and broadband interference suppression are processed separately, making full use of the different characteristics of narrowband interference and broadband interference in the frequency domain. This ensures that frequency points contaminated by these two types of interference are not missed, and that frequency points containing only useful signals without interference are not misjudged as interference points.

[0038] In step S301, only frequency points contaminated by narrowband interference are marked, and based on the characteristics of narrowband interference, the data of these frequency points is set to 0 to protect as many useful signals as possible. More specifically, Figure 4 The results of notch filtering for narrowband interference detection.

[0039] In step S302, a sliding window method is used to mark windows where the proportion of the marked frequency point to the total window length is greater than a second proportional threshold as parts contaminated by broadband interference. The sliding window method utilizes the characteristic that broadband interference persists in a specific frequency band, ensuring that no broadband interference is missed during detection. More specifically, Figure 5 The results of notch filtering for detecting broadband interference.

[0040] After two notch tests, the following can be obtained: Figure 6 The diagram shows a comparison between the detected notch signal and the original data contaminated by interference. As can be seen from the diagram, this embodiment can perform joint notch detection of both narrowband and broadband interference without omissions or errors, and its performance is unaffected by the energy level of the original signal itself.

[0041] This invention addresses the limitations of existing synthetic aperture radar (SAR) systems, which often encounter narrow-bandwidth mixed interference, and the inability of existing detection methods to simultaneously detect both types of interference. It proposes a novel two-stage SAR narrow-bandwidth interference suppression method based on detection notch. By differentiating and performing two detection notches targeting the respective characteristics of narrow-band and broadband interference, a joint detection notch for narrow-bandwidth interference is achieved, thus suppressing SAR interference.

[0042] Any aspects of this invention not described in detail are well-known to those skilled in the art.

[0043] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for suppressing narrow bandwidth interference in synthetic aperture radar based on detected notch waves, characterized in that, The method includes the following steps: Step S1: Convert the received time-domain synthetic aperture radar signal to the SAR image domain; Step S2: Accumulate the SAR image signal obtained in step S1 along the azimuth dimension to obtain the received signal that is contaminated by interference in the frequency domain, and then differentiate the received signal to obtain the time difference result of the useful signal and the interference. Step S3: A two-stage notch detection method is used to detect notches for narrowband interference and broadband interference respectively, which includes: Step S301: In the first-stage detection notch filter, based on the characteristics of narrowband interference electromagnetic energy, the corresponding frequency point is marked and then set to zero; specifically, this includes: executing the first-stage detection notch filter, setting an amplitude detection threshold based on the characteristics of narrowband interference electromagnetic energy after differentiation, marking the frequency points with electromagnetic energy higher than the threshold as the frequency points contaminated by narrowband interference; and setting the frequency points contaminated by narrowband interference to 0, thereby realizing the detection and suppression of narrowband interference; Step S302: In the second-stage detection notch filter, based on the characteristics of broadband interference electromagnetic energy, the corresponding frequency points are marked; then, combined with the sliding window method and the frequency points, the frequency band contaminated by broadband interference is determined, and the frequency band is set to zero; specifically, this includes: performing the second-stage sliding window detection notch filter, firstly, based on the characteristics of broadband interference electromagnetic energy after differentiation, a second amplitude detection threshold is set, and frequency points higher than the threshold are marked as potentially contaminated by broadband interference; then, through the sliding window, the frequency points higher than the second amplitude detection threshold within the window are marked; next, a judgment is made: if the percentage of the number of marked frequency points to the total number of frequency points within the window is higher than a preset percentage threshold, then all frequency points within the window are judged as interfered frequency points; finally, the interfered frequency points are set to 0, thereby realizing the detection and suppression of broadband interference.

2. The method for narrow-bandwidth interference suppression of synthetic aperture radar based on detected notch waves according to claim 1, characterized in that, In step S1, the received time-domain synthetic aperture radar signal is converted to the SAR image domain by performing Fourier transform and inverse Fourier transform.

3. The method for narrow-bandwidth interference suppression of synthetic aperture radar based on detected notch waves according to claim 1, characterized in that, In step S2, the SAR image signal is accumulated along the azimuth dimension to obtain the signal that is contaminated by interference in the frequency domain. Then, based on the slowly varying characteristics of the useful signal, the derivative operation is performed on the signal accumulated along the azimuth dimension so that the interference signal and the useful signal can be distinguished by analyzing the energy level of the derivative signal.

Images