A method for detecting shipborne ground wave radar targets in maneuvering state

Abstract

A method for detecting a target by a shipborne ground wave radar in a maneuvering state includes obtaining the time domain data of each channel and the platform attitude data after the shipborne high-frequency ground wave radar distance demodulation; performing heading compensation and speed compensation; performing FFT processing on the compensated radar time domain data to obtain a space-time two-dimensional diagram of the distance unit to be measured; sequentially obtaining the maximum values ​​of all azimuths corresponding to a certain speed, forming a curve distributed with speed, finding the extreme point to construct a speed-azimuth two-dimensional binary vector of a suspected target; sequentially obtaining the maximum values ​​of all speeds corresponding to a certain azimuth, forming a curve distributed with azimuth, detecting the extreme point to construct a speed-azimuth two-dimensional binary vector of a suspected target; using the target speed distribution vector and the target azimuth distribution, calculating the number of targets that can be obtained at the same time and the azimuth and speed. The present invention improves the target detection performance and positioning accuracy in the case of a moving mobile platform by querying the extreme points on the azimuth dimension and speed dimension curves.

Description

Technical Field

[0001] The invention relates to a target detection method for a shipborne ground wave radar, and in particular to a target detection method for a shipborne ground wave radar in a maneuvering navigation state. Background Art

[0002] High-frequency ground wave radar, using the characteristics of vertically polarized electromagnetic waves in the 3-30MHz high-frequency band diffracting along the sea surface, can achieve large-scale, over-the-horizon continuous detection of sea surface ship targets. Compared with shore-based ground wave radars with fixed sites and limited detection areas, ship-borne ground wave radars can use the maneuverability of ship-borne platforms to expand their detection areas and increase the application range of ground wave radars. When the shipborne platform is in a navigation state, it will affect the target signal: when the shipborne platform is in uniform linear motion, since each detected ship target only appears in a certain azimuth cell, the movement of the shipborne platform only causes the target echo signal to shift in frequency, but not broaden, and the amplitude of the target echo signal remains unchanged; but when the speed or heading of the shipborne platform changes, the speed Doppler shift caused by the maneuvering change of the shipborne platform will also change, which will cause the target echo spectrum to broaden, and the signal amplitude and signal-to-noise ratio or signal-to-clutter ratio will also decrease, increasing the probability of missed detection of the target; similarly, the change of the target signal along the azimuth caused by the movement of the shipborne platform does not have the change law of the target signal of the shipborne ground wave radar under the conditions of shore-based and uniform linear motion, and the difficulty of target azimuth estimation is also increased. Even if the detection result is given, the target azimuth estimation error will increase. Therefore, in order to improve the target detection performance of the shipborne ground wave radar, it is necessary to consider the impact of the shipborne platform on the ground wave radar target signal and motion compensation processing, and develop a target detection method suitable for the movement of the mobile platform.

[0003] At present, the target detection process for shipborne ground wave radar is mainly to detect the target first and then estimate the target direction. In the target detection stage, the CFAR detection method similar to the shore-based ground wave radar is mainly used, and it is only suitable for the case where the shipborne platform is in uniform linear motion. When the shipborne platform is in a maneuvering change, the target signal is broadened, and this detection method is not applicable. In addition, for shipborne ground wave radar, domestic and foreign research on shipborne platform motion compensation methods has also been carried out. There are existing shipborne ground wave radar motion compensation methods for target detection, which mainly consider the platform motion compensation processing under uniform linear motion or periodic swaying motion. Its purpose is still mainly to eliminate the broadening or false peaks of sea clutter. In this process, the target signal is not fully considered; for the situation of mobile platform motion, there is currently no target detection method that combines motion characteristics. In addition, although there are many studies on motion compensation and target detection methods for mobile platform ground wave radar, their essence is to eliminate the broadening or false peaks caused by platform motion by suppressing sea clutter, and then perform target detection. This method is also not suitable for target detection and direction estimation under mobile platforms. Summary of the invention

[0004] The object of the present invention is to provide a method for detecting a target by a shipborne ground wave radar in a maneuvering state. The method uses real-time acquisition of radar data and shipborne platform attitude information, firstly eliminates the target signal broadening caused by the maneuvering motion of the shipborne platform through platform motion compensation, and then performs integrated detection and azimuth detection based on the compensated Doppler-azimuth dimension data, and simultaneously detects multiple targets and estimates the azimuth of the target, thereby improving the target detection performance and positioning accuracy in the case of maneuvering platform motion.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for detecting a target by a shipborne ground wave radar in a maneuvering state, characterized by comprising the following steps:

[0007] Step 1: First, obtain the time domain data x of each channel after the shipborne high-frequency ground wave radar distance demodulation all (t), and the attitude data of the shipborne platform P, including the navigation speed v P (t) and heading The x all (t)=[x1(t),x2(t),...,x N (t)] T , x n (t) = [x n1 , x n2 , ..., x nM ] T , v P (t) = [v1, v2, ..., vM ] T , in, N is the number of array element channels, M is the number of frequency sweep cycles;

[0008] Step 2: Calculate the heading compensation steering vector b(θ, t) of the beam angle θ, where θ is the set radar beam angle, and then perform heading compensation. The compensated radar time domain data is expressed as:

[0009] x all (t)′=x all (t)b(θ, t) T

[0010] Where b(θ, t) is the heading compensation steering vector of the beam angle θ at time t, x all (t) = [x1, x2, ..., x n ] T Represents radar time domain data of all channels;

[0011] Step 3: Use the shipborne platform speed information v P (t) Velocity compensation is performed on the radar time domain data after heading compensation to eliminate the offset caused by the change of platform velocity in azimuth θ. The radar time domain data after velocity compensation is expressed as:

[0012]

[0013] in is the phase quantity caused by the platform velocity at the beam angle θ, is the pitch angle at time t, λ is the radar wavelength;

[0014] Step 4: Perform FFT processing on the radar time domain data obtained after compensation for all azimuths to obtain a space-time two-dimensional image AD (i, k) of a certain range unit to be measured, where: represents the azimuth information of the compensated beam, bN is the number of beams, It indicates the speed information obtained by converting the frequency information obtained after FFT according to the radar parameters;

[0015] Step 5: Based on the obtained AD(i, k), find the maximum values ​​of all directions corresponding to a certain speed K in turn, and form a curve A distributed with speed K K (i) Then find the curve A along the velocity direction. K (i) and construct the speed-azimuth two-dimensional binary vector AA(i, K) of the suspected target based on the speed and corresponding azimuth of the extreme point:

[0016]

[0017] Step 6: Based on the obtained AD(i, k), find the maximum value of all velocities corresponding to a certain direction I in turn, and form a curve B distributed with direction I I (k), then detect the extreme point along the azimuth direction, and construct the speed-azimuth two-dimensional binary vector BB(I, k) of the suspected target according to the azimuth of the extreme point and the corresponding speed value:

[0018]

[0019] Step 7: Using the target velocity distribution vector AA(i, K) and the target azimuth distribution vector BB(I, k), calculate the number of targets that can be acquired at the same time, as well as their azimuth and velocity.

[0020] CC(i,k)=AA(i,K)∩BB(I,k)

[0021] When CC(i, k)=1, the corresponding i is the direction of the target, and the corresponding k is the speed of the target.

[0022] In step 2, the heading compensation steering vector b(θ, t) is calculated using the following method:

[0023] b(θ,t)=[e -j2πd′ / λ , e -j2π(d′+dsin(θ+β(t))) / λ , ..., e -j2π(d′+(N-1)dsin(θ+β(t))) / λ ] T ,

[0024] Where θ is the beam angle, is the heading change, d and d′ respectively represent the horizontal spacing between adjacent array elements before and after the heading change;

[0025] Compared with the prior art, the innovation of the present invention is embodied in the following aspects:

[0026] The present invention fully considers the target broadening characteristics of the shipborne platform in the case of maneuvering motion such as changes in speed and heading, and uses the attitude information of the shipborne platform to perform motion compensation processing of the radar signal, eliminating the radar broadening caused by the maneuvering motion of the shipborne platform. Moreover, the present invention adopts a different idea from the traditional shore-based ground wave radar or uniform linear motion shipborne ground wave radar to perform target detection in the two-dimensional RD spectrum, but to carry out integrated detection of target detection and azimuth estimation on the azimuth-Doppler two-dimensional spectrum at the same distance, and realizes the detection of multiple targets at the same distance by querying the extreme points on the azimuth dimension and velocity dimension (Doppler dimension) curve, and estimates the azimuth and velocity parameter information. The target detection performance and positioning accuracy under the condition of mobile platform movement are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a basic flow chart of the present invention.

[0028] Figure 2 It is an azimuth-Doppler (AD spectrum) diagram before motion compensation of the present invention.

[0029] Figure 3 It is the azimuth-Doppler (AD spectrum) diagram after motion compensation of the present invention.

[0030] Figure 4 This is a diagram of the extreme point detection result along the velocity distribution curve of the present invention (marked with "*").

[0031] Figure 5 This is a diagram of the extreme point detection result along the azimuth distribution curve of the present invention (marked with "O").

[0032] Figure 6 It is the result of superposition and simultaneous satisfaction of the two dimensional extreme value points of the present invention in the two dimensions of azimuth and velocity.

[0033] Figure 7 This is the target binary detection result diagram of the present invention.

[0034] Figure 8 yes Figure 7 The target binary detection result is superimposed on the azimuth-Doppler (AD spectrum) DETAILED DESCRIPTION

[0035] The method of the present invention is further described below in conjunction with the accompanying drawings.

[0036] A method for detecting shipborne ground wave radar targets in a maneuvering state, such as Figure 1 As shown, the following steps are included:

[0037] Step 1: First, obtain the time domain data of each channel after the shipborne high-frequency ground wave radar range demodulation and the attitude data of the shipborne platform P. The time domain data of all N channels of a range unit is recorded as x all (t)=[x1(t),x2(t),...,x N (t)] T , then the time domain sampling vector of any array element (channel) n is:

[0038] x n (t) = [x n1 , x n2 , ..., x nM ] T

[0039] in, N is the number of array element channels, M is the number of frequency sweep cycles, and the dimensions of all array element matrices are N*M.

[0040] For the attitude data of the shipborne platform P, its speed and radar heading are v P (t) = [v P1 , v P2 , ..., v PM ] T and

[0041] Step 2: Using platform attitude and heading data Calculate the heading compensation steering vector b(θ, t) of a certain beam angle θ at time t:

[0042] b(θ,t)=[e -j2πd′ / λ , e -j2π(d′+dsin(θ+β(t))) / λ ,…,e -j2π(d′+(N-1)dsin(θ+β(t))) / λ ] T ,

[0043] Where θ is the beam angle, is the heading change, d and d′ respectively represent the horizontal spacing between adjacent array elements before and after the heading change;

[0044] The multi-channel time domain data x is calculated by using the heading compensation steering vector b(θ, t). all (t) and make heading compensation:

[0045] x all (t)′=x all (t)b(θ, t) T

[0046] Step 3: Use the shipborne platform speed information v P (t) Perform velocity compensation on the heading-compensated radar time domain data to eliminate the offset caused by the change of platform velocity in azimuth θ;

[0047]

[0048] in is the phase quantity caused by the platform velocity at the beam angle θ, is the pitch angle at time t, and λ is the radar wavelength.

[0049] Azimuth-Doppler (AD spectrum) image before motion compensation Figure 2 As shown, the azimuth-Doppler (AD spectrum) after motion compensation is as follows Figure 3 shown.

[0050] Step 4: Perform FFT processing on the radar time domain data obtained after compensating for motion in all azimuths to obtain a two-dimensional azimuth-Doppler (velocity) map AD (i, k) of a certain range unit to be measured, where represents the azimuth information of the compensated beam, bN is the number of beams, It indicates the speed information obtained by converting the frequency information obtained after FFT according to the radar parameters.

[0051] Step 5: Based on the obtained AD(i, k), find the maximum value on all azimuth distribution curves corresponding to a certain speed (Doppler) K (the maximum value corresponds to the position of the target's possible location). The maximum values ​​of all speeds constitute the curve A distributed with speed. K (i) Find the extreme point in the curve, which is where the target's speed may be located; construct a set of suspected target coordinate values ​​AA(i, K) based on the speed and corresponding azimuth of the extreme point.

[0052] AA(i,K)=[(i,K)|i=arg ext max (A K (i))]

[0053] Among them, ext max (·) means taking the maximum value, arg(·) means taking the parameter value that satisfies the condition, A K =max(AD(:, K)), the colon refers to all values ​​in the domain, the extreme point A K (i) Satisfy A K (i)≥A K (i-1) and A K (i)≥A K (i+1); The extreme point detection result along the velocity distribution curve is shown in the figure Figure 4 shown.

[0054] Step 6: Find the maximum value on the velocity distribution curve for each direction. The maximum values ​​of all directions form the curve B with velocity distribution; find the extreme point B in the curve I (k), which is the direction where the target may exist; according to the direction of the extreme point and the corresponding speed value, a two-dimensional binary vector BB(I, k) of the suspected target direction distribution is constructed:

[0055] BB(I,k)=[(I,k)|k=arg ext max (B I (k))]

[0056] Among them, ext max (·) is the maximum value, B I=max(AD(I,:)), extreme point B I (k) Satisfy B I (k)≥B I (k-1) and B I (k)≥B I (k+1); The extreme point detection results along the azimuth distribution curve are shown in the figure Figure 5 shown.

[0057] Step 7: Use the target velocity distribution vector AA(i, K) and the target azimuth distribution vector BB(I, k) to calculate the number of targets, their azimuths and azimuths that can be acquired simultaneously.

[0058] CC(i,k)=AA(i,K)∩BB(I,k)

[0059] When CC(i, k) = 1, i is the target's position and k is the target's speed. The superposition of the two-dimensional extreme points in the two dimensions of position and speed and the simultaneous satisfaction of the results are as follows: Figure 6 shown.

[0060] at last, Figure 7 The target binary detection result diagram obtained by the method of the present invention is shown in FIG. Figure 8 shown.

Claims

1. A method for detecting a target by a shipborne ground wave radar in a maneuvering state, characterized in that The following steps are involved: Step 1: First, obtain the time domain data x of each channel after the shipborne high-frequency ground wave radar distance demodulation all (t), and the attitude data of the shipborne platform P, including the navigation speed v P (t) and heading The x all (t)=[x1(t),x2(t),…,x N (t)] T , x n (t) = [x n1 , x n2 , ..., x nM ] T ,v p (t) = [v1, v2, ..., v M ] T , in, N is the number of array element channels, M is the number of frequency sweep cycles; Step 2: Calculate the heading compensation steering vector b(θ,t) of the beam angle θ, where θ is the set radar beam angle, and then perform heading compensation. The compensated radar time domain data is expressed as: x all (t)'=x all (t)b(θ,t) T Where b(θ,t) is the heading compensation steering vector of the beam angle θ at time t, and x all (t)=[x1,x2,…,x n ] T Represents radar time domain data of all channels; Step 3: Use the shipborne platform speed information v P (t) Velocity compensation is performed on the radar time domain data after heading compensation to eliminate the offset caused by the change of platform velocity in azimuth θ. The radar time domain data after velocity compensation is expressed as: in is the phase quantity caused by the platform velocity at the beam angle θ, is the pitch angle at time t, λ is the radar wavelength; Step 4: Perform FFT processing on the radar time domain data obtained after compensation for all azimuths to obtain a space-time two-dimensional image AD (i, k) of a certain range unit to be measured, where: represents the azimuth information of the compensated beam, bN is the number of beams, It indicates the speed information obtained by converting the frequency information obtained after FFT according to the radar parameters; Step 5: Based on the obtained AD(i,k), find the maximum values ​​of all directions corresponding to a certain speed K in turn, and form a curve A distributed with speed K K (i) Then find the curve A along the velocity direction. K (i) and construct the speed-azimuth two-dimensional binary vector AA(i,K) of the suspected target based on the speed and corresponding azimuth of the extreme point: Step 6: Based on the obtained AD(i,k), find the maximum value of all velocities corresponding to a certain direction I in turn, and form a curve B distributed with direction I I (k), then detect the extreme point along the azimuth, and construct the speed-azimuth two-dimensional binary vector BB(I,k) of the suspected target according to the azimuth of the extreme point and the corresponding speed value: Step 7: Using the target velocity distribution vector AA(i, K) and the target azimuth distribution vector BB(I, k), calculate the number of targets that can be acquired at the same time, as well as their azimuth and velocity. CC(i,k)=AA(i,K)∩BB(I,k) When CC(i, k)=1, the corresponding i is the direction of the target, and the corresponding k is the speed of the target.

2. The method for detecting a target by a shipborne ground wave radar in a maneuvering state as claimed in claim 1, characterized in that In step 2, the heading compensation steering vector b(θ, t) is calculated using the following method: b(θ,t)=[e -j2πd′ / λ ,e -j2π(d′+ds(θ+β(t))) / λ ,…,e -j2π(d′+(N-1)dsin(θ+β(t))) / λ ] T , Where θ is the beam angle, is the heading change, d and d′ respectively represent the horizontal spacing between adjacent array elements before and after the heading change;

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