Sea surface low-speed target detection method based on Doppler characteristics and radar equipment

Abstract

The invention provides a sea surface slow-speed target detection method based on Doppler characteristics and radar equipment, and belongs to the field of radars, and the method comprises the steps: obtaining radar echoes, completing channel calibration and non-coherent accumulation, and obtaining a low-weight path, orientation and pitching spectrogram; carrying out land-sea separation on the low-weight sum path spectrogram to obtain a start detection range gate and an end detection range gate of a sea surface target, and carrying out sliding window detection on a sea surface target tracking center detection interval to obtain two-dimensional information and a signal-to-noise ratio of the sea surface target; solving azimuth and pitch angle errors of the low-weight time domain power spectrum; carrying out local coherent accumulation on the sea surface target tracking center detection interval to obtain a new low-weight path, orientation and pitching spectrogram; performing sliding window detection on the sea surface target tracking center detection interval of the new spectrogram to obtain new sea surface target two-dimensional information and a signal-to-noise ratio; solving azimuth and pitch angle errors of the new spectrogram; and carrying out information correlation and track correlation continuous measurement on the sea surface target, and maintaining target tracking.

Description

Technical Field

[0001] The present application belongs to the technical field of airborne radars, and in particular relates to a method and radar equipment for detecting slow targets on the sea surface based on Doppler characteristics. Background Art

[0002] When radar detects sea surface targets, it will be seriously interfered by the backscattering of radar signals by the sea surface. This interference is usually called sea clutter. Sea clutter has an amplitude distribution model for radar detection performance. However, even if the clutter model is given, it is still very difficult to evaluate radar detection performance. Sea clutter has a serious impact on radar detection performance when airborne radar tracks sea surface targets.

[0003] Therefore, there is a need for an engineering method that can effectively improve the success rate of slow target detection on the sea surface. Summary of the invention

[0004] The purpose of the present application is to provide a sea surface slow target detection method and radar equipment based on Doppler characteristics, so as to solve or alleviate at least one problem in the background technology.

[0005] On the one hand, the technical solution of the present application is: a method for detecting slow targets on the sea surface based on Doppler characteristics, comprising:

[0006] Get radar echo, complete channel calibration, non-coherent accumulation to get low-frequency and path spectrum map P Sum , azimuth spectrum diagram P Az and pitch spectrum P EI ;

[0007] For low-weight and road spectrum P Sum Separate land and sea to get the initial detection range gate N of the sea surface target r _Start and end detection distance gate N r _End two-dimensional information [N r _Start, N r _End] n (n=0,1,2…), the detection interval of the sea surface target tracking center [N r _Start, N r _End] Sliding window detection is performed to obtain the two-dimensional information of the sea surface target [N r , N f ] n (n=0,1,2…) and signal-to-noise ratio, where [N r _Start, N r _End]∈[N r , N f ] n (n=0,1,2…);

[0008] Obtain the low-repetition time domain power spectrum, and calculate the azimuth error Δθ according to the single pulse phase method. n,Az (n=0,1,2…) and pitch angle error Δθ n,EI (n=0,1,2…);

[0009] Perform local coherent accumulation on the detection interval of the sea target tracking center to obtain a new low-repetition and path spectrum map P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI , P' Sum =fft(IQData,FFT), where IQData is the time domain data and FFT is the number of accumulated points;

[0010] For the new low-weight and road spectrum P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI The sliding window detection is performed on the sea surface target tracking center detection interval to obtain the new two-dimensional information of the sea surface target [N r0 , N f0 ] n (n=0,1,2…) and signal-to-noise ratio;

[0011] For the new low-weight and road spectrum P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI Calculate the azimuth error Δθ' using the single pulse phase method n,Az (n=0,1,2…) and pitch angle error Δθ' n,EI (n=0,1,2…);

[0012] The two-dimensional information, signal-to-noise ratio, azimuth error, and pitch angle error of the sea surface target are correlated, and the track is continuously measured to maintain target tracking.

[0013] In an optional implementation manner of the present application, the process of performing information correlation on the frequency gate in the two-dimensional information of the sea surface target is:

[0014] Get the target speed by filtering the tracking track speed In the formula, R is the target distance, t is the filtering time;

[0015] Estimated Doppler frequency gate Where N is the fuzzy multiplicity, λ is the wavelength, and PRF is the pulse repetition frequency;

[0016] Target frequency gate for coherent accumulation|N f0 -N fiter |≤A, where A is the fault tolerance value caused by fuzzy multiplicity.

[0017] In an optional implementation manner of the present application, the process of correlating the range gate in the two-dimensional information of the sea surface target is as follows:

[0018] Determine the target range gate obtained by non-coherent accumulation detection Where R is the target distance, f s is the sampling rate, c is the speed of light;

[0019] The range gate N obtained by coherent accumulation r0 The target range gate N obtained by non-coherent accumulation detection r Perform correlation to satisfy N r0 =N r .

[0020] In an optional implementation manner of the present application, the process of performing information correlation on the signal-to-noise ratio of the sea surface target is:

[0021] Determine the signal-to-noise ratio of coherent integration: SNR = n p (SNR)1, where (SNR)1 represents the signal-to-noise ratio of a single pulse;

[0022] The empirical formula for determining the signal-to-noise ratio of non-coherent accumulation is:

[0023] Get the signal-to-noise ratio comparison threshold: k = SNR-SNR NCI

[0024] The signal-to-noise ratio difference ΔSNR=SNR0-SNR≤k.

[0025] In an optional implementation manner of the present application, the process of correlating the information of the sea surface target azimuth and pitch angle errors is as follows:

[0026] Construct the azimuth and elevation angle errors [Δθ n,Az , Δθ n,EI ](n=0,1,2…) and the azimuth and elevation angle errors obtained by coherent accumulation [Δθ' n,Az , Δθ' n,EI ](n=0,1,2…) to carry out relevant relationship;

[0027]

[0028] In the formula, Δβ i is the error of the i-th target, λ is the wavelength, d is the spacing between the oscillators, β is the top-down angle, e is a natural constant, E is the power function, j is a complex number, is the phase difference;

[0029] The coherently accumulated azimuth and elevation angle errors are selected in the frequency domain at the point where the CFAR target power is the largest (Nr,n , N f,n ), satisfying Δθ n,Az ≥Δθ' n,Az , Δθ n,EI ≥Δθ' n,EI (n=0,1,2…).

[0030] On the other hand, the technical solution provided by the present application is: a radar device, the radar device comprising a receiving antenna and a processing unit;

[0031] The receiving antenna is used to obtain radar echo;

[0032] The processing unit is used to execute any of the above methods for detecting slow sea surface targets based on Doppler characteristics.

[0033] Compared with the traditional method, the sea surface slow target detection method of the present application has greatly reduced the calculation steps of the clutter suppression algorithm, improved the operation speed, reduced the complexity, improved the reliability of the internal software operation of the radar system, can effectively eliminate sea clutter, improve the accuracy of target echo measurement, and can effectively suppress false targets caused by downward sea clutter. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solution provided by the present application, the following is a brief introduction to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present application.

[0035] Figure 1 This is a flow chart of the sea surface slow target detection method based on Doppler characteristics of this application.

[0036] Figure 2 This is the clutter area (elliptical part) when the airborne radar detects sea surface targets according to one embodiment of the present application.

[0037] Figure 3 This is a non-coherent accumulation target detection diagram of radar downward-looking sea surface echoes according to an embodiment of the present application.

[0038] Figure 4 This is a spectrum diagram of the local coherent accumulation and path spectrum of the radar downward-looking sea surface echo according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below in conjunction with the drawings in the embodiments of this application.

[0040] When the airborne radar looks down to track a target on the sea surface, the radar receives sea clutter and ground clutter at the same time. When the target is at a long distance, the sea wave conditions are unclear. The signal processing uses non-coherent accumulation. The sea clutter easily drowns the target echo and cannot be detected, resulting in a long period of no measurement and no correlation between the track. The track health time deteriorates and the target is easily lost.

[0041] In order to solve the above problems, this application proposes a sea surface slow target detection method based on Doppler characteristics, which can effectively suppress and eliminate sea clutter echoes, accurately detect sea surface targets, achieve track association continuity, and maintain stable tracking of sea surface targets.

[0042] like Figure 1 As shown, the sea surface slow target detection method based on Doppler characteristics provided by the present application removes sea clutter, accurately detects sea surface echoes, and stably tracks the target track according to the difference in Doppler characteristic expressions between sea clutter and target echoes. The method includes:

[0043] Step S10, in the radar detection situation environment for sea surface targets (radar beam inertial system pitch angle <0.5°), after receiving the radar echo, complete channel calibration, non-coherent accumulation and other processing to obtain the low-resonance and path spectrum map P Sum , azimuth spectrum diagram P Az and pitch spectrum P EI .

[0044] Step S20, based on the land-sea separation method of the digital map, the low-density and road spectrum map P Sum Separate and obtain the initial detection range gate N of the sea surface target r _Start and end detection distance gate N r _End two-dimensional information [N r _Start, N r _End] n (n=0,1,2…). After non-coherent accumulation, the detection interval of the sea surface target tracking center [N r _Start, N r _End] Sliding window detection is performed to obtain the two-dimensional information of the sea surface target [N r , N f ] n (n=0,1,2…), where N r is the distance gate, N f is the frequency gate, [N r _Start, N r _End]∈[N r , N f ] n (n=0,1,2…).

[0045] Step S30, obtaining a low-density time domain power spectrum, and calculating the azimuth error Δθ according to the single pulse phase method for the low-density time domain spectrum n,Az (n=0,1,2…) and pitch angle error Δθ n,EI (n=0,1,2…).

[0046] Step S40, perform local coherent accumulation on the sea surface target tracking center area to obtain a new low-resonance and path spectrum map P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI ,

[0047] The local coherent accumulation is: P' Sum =fft(IQData,FFT)

[0048] Where IQData is the time domain data and FFT is the number of accumulated points.

[0049] Step S50: the new low-frequency and high-frequency spectrum graph P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI The sea surface target tracking area is detected by sliding window to obtain new two-dimensional information of the sea surface target [N r0 , N f0 ] n (n=0,1,2…) and signal-to-noise ratio.

[0050] Step S60: compare the new low-frequency and high-frequency spectrum graph P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI The azimuth error Δθ' is obtained by using the single pulse phase method from the frequency domain data n,Az (n=0,1,2…) and pitch angle error Δθ' n,EI (n=0,1,2…).

[0051] Step S70, correlating the original sea surface target information with the new sea surface target information based on the Doppler characteristics, the sea surface target information includes two-dimensional sea surface target information, signal-to-noise ratio, azimuth error, and pitch angle error.

[0052] In this application, the tracking speed filter estimate is correlated with the target frequency gate obtained by coherent accumulation, so as to realize information correlation of the frequency gate in the two-dimensional information of the sea surface target. The specific process is as follows:

[0053] Get the target speed by filtering the tracking track speed In the formula, R is the target distance, t is the filtering time;

[0054] Estimated Doppler frequency gate Where N is the fuzzy multiplicity, λ is the wavelength, and PRF is the pulse repetition frequency;

[0055] Make the target frequency gate of the coherent accumulation satisfy: |N f0 -N fiter |≤A, where A is the fault tolerance value caused by fuzzy multiplicity.

[0056] In this application, the process of correlating the range gate in the two-dimensional information of the sea surface target is as follows:

[0057] Determine the target range gate obtained by non-coherent accumulation detection Where R is the target distance, f s is the sampling rate, c is the speed of light;

[0058] The target range gate N obtained by non-coherent accumulation detection r The target range gate N obtained by coherent accumulation detection r0 Correlate to satisfy N r0 =N r .

[0059] In this application, the process of information correlation of the signal-to-noise ratio of the sea surface target is:

[0060] Determine the signal-to-noise ratio of coherent integration: SNR = n p (SNR)1, where (SNR)1 represents the signal-to-noise ratio of a single pulse;

[0061] The signal-to-noise ratio of non-coherent integration is determined according to the empirical formula:

[0062] Construct signal-to-noise ratio correlation comparison threshold: k = SNR-SNR NCI ;

[0063] Make the signal-to-noise ratio difference satisfy: ΔSNR=SNR0-SNR≤k;

[0064] Generally, the signal-to-noise ratio difference ΔSNR fluctuates by 1 dB to 2 dB around the signal-to-noise ratio correlation comparison threshold K.

[0065] In this application, the process of information correlation of the sea surface target azimuth and pitch angle errors is as follows:

[0066] Construct the azimuth and elevation angle errors [Δθ n,Az , Δθ n,EI ](n=0,1,2…) and the azimuth and elevation angle errors obtained by coherent accumulation [Δθ' n,Az , Δθ' n,EI ](n=0,1,2…) to carry out relevant relationship;

[0067]

[0068] In the formula, Δβ i is the error of the i-th target, λ is the wavelength, d is the spacing between the oscillators, β is the top-down angle, e is a natural constant, E is the power function, j is a complex number, is the phase difference;

[0069] The non-coherent accumulation angle error of the conventional process is to select the maximum power point (N r , N f ) to obtain the angle error. This method is prone to selecting strong sea clutter, resulting in inaccurate angle error. In this application, the azimuth and pitch angle errors after coherent accumulation are selected in the frequency domain at the point where the CFAR (Constant False Alarm Rate) target power is the largest (N r,n , N f,n ) is theoretically the angular error of the target, satisfying Δθ n,Az ≥Δθ' n,Az , Δθ n,EI ≥Δθ' n,EI (n=0,1,2…).

[0070] The result of the coherent accumulation is that after the target information passes the above related conditions, it can be confirmed that it is the target CFAR (constant false alarm rate), the sea clutter is eliminated, the track is associated with continuous measurement, and the target is tracked.

[0071] The sea surface slow target detection method of the present application is based on the difference relationship between the Doppler of the sea surface reflection unit clutter and the target Doppler after coherent accumulation. The sea surface reflection unit contains sea clutter and ground clutter. The movement speed of these clutters is slower than that of the sea surface target, and the Doppler shift generated is small. When the number of accumulation points is large, the Doppler shift of the target and the Doppler shift of the clutter are relatively easy to distinguish. After the target is coherently accumulated, the signal-to-noise ratio is much stronger than that of the clutter, and it is easy to be detected. Based on this, the sea clutter and ground clutter are eliminated and false targets are suppressed.

[0072] like Figure 2 The figure shows a schematic diagram of the clutter area (the elliptical part between R1 and R2) when the airborne radar detects a sea surface target in an embodiment of the present application. The aircraft height H = 6000 meters, the aircraft speed V = 270 meters / second, and the distance range = 320 kilometers. When the aircraft beam pitch angle reaches the downward state, the detection of the slow sea surface target after non-coherent accumulation is as follows: Figure 3 As shown in Figure 2, the target at the range gate of 2604 was not detected. The frequency domain diagram of coherent integration under the slow target on the sea surface is shown in Figure 2. Figure 4 As shown, the target can be detected at a range gate of 2604. Through track-related continuous measurement, the target can be continuously detected and tracked.

[0073] Compared with the traditional method, the method of the present application has greatly reduced the calculation steps of the clutter suppression algorithm, improved the operation speed, reduced the complexity, improved the reliability of the internal software operation of the radar system, can effectively eliminate sea clutter, improve the accuracy of target echo measurement, and can effectively suppress false targets caused by downward-looking sea clutter.

[0074] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for detecting slow sea targets based on Doppler characteristics, characterized in that: include: Get radar echo, complete channel calibration, non-coherent accumulation to get low-frequency and path spectrum map P Sum , azimuth spectrum diagram P Az and pitch spectrum P EI ; For low-weight and road spectrum P Sum Separate land and sea to get the initial detection range gate N of sea surface targets r _Start and end detection distance gate N r _End two-dimensional information [N r _Start, N r _End] n (n=0,1,2…), the detection interval of the sea surface target tracking center [N r _Start, N r _End] Sliding window detection is performed to obtain the two-dimensional information of the sea surface target [N r , N f ] n (n=0,1,2…) and signal-to-noise ratio, where [N r _Start, N r _End]∈[N r , N f ] n (n=0,1,2…); Obtain the low-repetition time domain power spectrum, and calculate the azimuth error Δθ according to the single pulse phase method. n,Az (n=0,1,2…) and pitch angle error Δθ n,EI (n=0,1,2…); Perform local coherent accumulation on the detection interval of the sea target tracking center to obtain a new low-repetition and path spectrum map P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI , P' Sum =fft(IQData,FFT), where IQData is the time domain data and FFT is the number of accumulated points; For the new low-weight and road spectrum P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI The sliding window detection is performed on the sea surface target tracking center detection interval to obtain the new two-dimensional information of the sea surface target [N r0 , N f0 ] n (n=0,1,2…) and signal-to-noise ratio; For the new low-weight and road spectrum P' Sum , azimuth spectrum P' Az , Pitch spectrum P' EI Calculate the azimuth error Δθ' using the single pulse phase method n,Az (n=0,1,2…) and pitch angle error Δθ' n,EI (n=0,1,2…); The two-dimensional information, signal-to-noise ratio, azimuth error, and pitch angle error of the sea surface target are correlated, and the track is continuously measured to maintain target tracking.

2. The method for detecting slow sea targets based on Doppler characteristics as claimed in claim 1, characterized in that: The process of correlating the frequency gate in the two-dimensional information of the sea surface target is as follows: Get the target speed by filtering the tracking track speed In the formula, R is the target distance, t is the filtering time; Estimated Doppler frequency gate Where N is the fuzzy multiplicity, λ is the wavelength, and PRF is the pulse repetition frequency; Target frequency gate for coherent accumulation|N f0 -N fiter |≤A, where A is the fault tolerance value caused by fuzzy multiplicity.

3. The method for detecting slow sea surface targets based on Doppler characteristics as claimed in claim 1, characterized in that: The process of information correlation of the range gate in the two-dimensional information of the sea surface target is: Determine the target range gate obtained by non-coherent accumulation detection Where R is the target distance, f s is the sampling rate, c is the speed of light; The range gate N obtained by coherent accumulation r0 The target range gate N obtained by non-coherent accumulation detection r Perform correlation to satisfy N r0 =N r .

4. The method for detecting slow sea targets based on Doppler characteristics as claimed in claim 1, characterized in that: The process of information correlation of the signal-to-noise ratio of sea surface targets is: Determine the signal-to-noise ratio of coherent integration: SNR = n p (SNR)1, where (SNR)1 represents the signal-to-noise ratio of a single pulse; The empirical formula for determining the signal-to-noise ratio of non-coherent accumulation is: Get the signal-to-noise ratio comparison threshold: k = SNR-SNR NCI The signal-to-noise ratio difference ΔSNR=SNR0-SNR≤k.

5. The method for detecting slow sea targets based on Doppler characteristics as claimed in claim 1, characterized in that: The process of information correlation of sea surface target azimuth and pitch angle errors is as follows: Construct the azimuth and elevation angle errors [Δθ n,Az , Δθ n,EI ](n=0,1,2…) and the azimuth and elevation angle errors obtained by coherent accumulation [Δθ' n,Az , Δθ' n,EI ](n=0,1,2…) to carry out relevant relationship; In the formula, Δβ i is the error of the i-th target, λ is the wavelength, d is the spacing between the oscillators, β is the top-down angle, e is a natural constant, E is the power function, j is a complex number, is the phase difference; The coherently accumulated azimuth and elevation angle errors are selected in the frequency domain at the point where the CFAR target power is the largest (N r,n , N f,n ), satisfying Δθ n,Az ≥Δθ' n,Az , Δθ n,EI ≥Δθ' n,EI (n=0,1,2…).

6. A radar device, characterized in that: The radar device includes a receiving antenna and a processing unit; The receiving antenna is used to obtain radar echo; The processing unit is used to execute the sea surface slow target detection method based on Doppler characteristics as claimed in any one of claims 1 to 5.

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