CN104166134A

CN104166134A - Real beam foresight scanning radar target two-dimension locating method

Info

Publication number: CN104166134A
Application number: CN201410422691.4A
Authority: CN
Inventors: 张寅�; 黄钰林; 王月; 李�杰; 武俊杰; 杨建宇; 李文超
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2014-08-25
Filing date: 2014-08-25
Publication date: 2014-11-26

Abstract

The invention discloses a real beam foresight scanning radar target two-dimension locating method which comprises the steps that S1. imaging system parameter initialization is carried out, the distance between an imaging system any point target and a moving platform is computed, and real beam scanning radar point target simulation parameters are set; S2. distance direction matched filtering is carried out; S3. distance direction moving compensation processing is carried out; S4. scanning radar orientation direction echo signals are subjected to modeling; S5. aweighting least square objective function is established; and S6. target orientation locating is carried out. According to the method, emitted signals and antenna direction image parameter information are used, a target range estimation problem is converted into the problem of a objective function optimal solution relative to a weighting vector wn, by solving the objective function optimal solution, the position information of a target orientation dimension is solved, the problem that a target orientation dimension locating accuracy in a moving platform foresight effect zone is low is effectively solved, and two-dimension accuracy locating of a moving platform foresight zone target distance dimension and an orientation dimension is achieved.

Description

Real-beam forward-looking scanning radar target two-dimensional positioning method

Technical Field

The invention belongs to the technical field of radars, and particularly relates to a real-beam forward-looking scanning radar target two-dimensional positioning method.

Background

The radar is not influenced by severe weather factors and can work all day long, so that the radar plays an indispensable role in military and civil fields such as military reconnaissance, marine and hydrological observation, land/sea tracking and rescue and the like. The method has important significance for realizing the accurate positioning of the target in the forward-looking area of the motion platform and realizing the functions of spying and detecting the enemy target, tracking and striking the target, searching and rescuing the sea target and the like.

The distance dimension high-precision positioning of the target in the forward-looking area of the moving platform can be realized by transmitting a linear frequency modulation signal with large bandwidth and processing the linear frequency modulation signal by using a pulse compression technology. However, for the azimuth dimension of the forward-looking imaging area, because the doppler frequency gradient generated by the relative motion of the platform and the target in the imaging area is almost zero, the existing imaging technologies such as synthetic aperture and the like are difficult to realize the accurate positioning of the azimuth dimension target and can only obtain the low-precision positioning result of the azimuth dimension target in a scanning imaging mode. Due to the fact that the accuracy of the positioning and amplitude estimation of the target position is low, the detection, monitoring, positioning and identification capabilities of the motion platform are seriously influenced.

Two methods are generally adopted for the problem of positioning a two-dimensional target in a forward-looking area of a motion platform, particularly how to improve the positioning capability of an orientation-dimensional target. One such method is disclosed in the following documents: blair W D, Brandt-Pearl M.monobulus DOA estimation of the magnitude of the unresolved Rayleigh targets [ J ]. Aerospace and Electronic Systems, IEEE Transactions on,2001,37(2):452- > 469. the orientation dimension is processed using the single-pulse technique. The technology is based on a single-pulse angle measurement principle, is mainly suitable for positioning a single strong point target, is effective for two point targets under specific conditions, but has serious deviation and even generates phenomena of false targets and the like when the target is positioned in a complex target environment with multiple scattering centers; the second is as in the literature: the method of Mahafza B R, Knight D L, Audeh N F. Forward-looking SAR imaging using a linear array with a translational motion [ C ]// Southeascon' 93, proceedings, IEEE.IEEE.1993: 4 p. However, the method needs linear arrays as long as possible to increase the aperture size, and meanwhile, because the Doppler bandwidth of the target in the forward-looking area is very small, the positioning accuracy of the target which can be obtained is still limited.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a real-beam forward-looking scanning radar target two-dimensional positioning method which solves the position information of a target azimuth dimension by solving the optimal solution of an objective function, effectively solves the problem of low positioning precision of the target azimuth dimension in a forward-looking action area of a motion platform and realizes two-dimensional accurate positioning of the target distance and the azimuth dimension in the forward-looking area of the motion platform.

The purpose of the invention is realized by the following technical scheme: a real beam forward-looking scanning radar target two-dimensional positioning method comprises the following steps:

s1: initializing parameters of an imaging system, calculating the distance between any point target in an imaging area and a motion platform, and setting simulation parameters of the point target of the real-beam scanning radar;

s2: distance direction matching filtering is carried out;

s3: performing distance direction motion compensation processing;

s4: modeling a scanning radar azimuth echo signal;

s5: constructing a weighted least square target function;

s6: and carrying out target azimuth positioning.

Further, the specific method for calculating the distance between the target at the arbitrary point of the imaging area and the motion platform in step S1 is as follows: the zero-time position of the moving platform is recorded as (0,0, h), the moving platform moves along the y axis, the moving speed is V, the azimuth angle of the target relative to the platform is recorded as q, and the lower view angle of the radar antenna is recorded as qThe scanning speed of the radar antenna is marked as omega; then the distance between the moving platform and the target in the scene at the time t is expressed as:

wherein, R0 is the initial distance between the motion platform and the target;

the specific method for setting the real beam scanning radar point target simulation parameters comprises the following steps: assuming that the amplitudes are all at different azimuth sampling positions at the same distance R in the scanning area, the position parameter of the target generating the motion amplitudes is set as theta (theta)₁,θ₂,...θ_N) The amplitude parameter is σ ═ (σ)₁,σ₂,...,σ_N) The radar emission signal is a chirp signal, and the echo of the scanning radar action area is recorded as S (t, tau) through coherent demodulation:

wherein tau is a distance direction time variable, rect (-) and a (-) respectively represent a distance time window and an orientation time window, K is a time frequency modulation slope of a transmitting signal, c is a light speed, and R (tau) represents a distance change between the moving platform and each target in the imaging area;

the azimuth time vector of the scanning radar imaging area is recorded as:

T_a＝[-PRI·N_a/2,-PRI·(N_a/2-1),…,PRI·(N_a/2-1)]

the distance time vector is:

T_r＝[-1/f_r·N_r/2,-1/f_r·(N_r/2-1),…,1f_r·(N_r/2-1)]

wherein f is_rFor range-wise sampling rate, PRI is the transmit signal pulse repetition interval, N_aNumber of sampling points in azimuth, N_rThe number of distance sampling points. .

Further, the distance direction matching filtering in step S2 specifically includes the following sub-steps:

s21: distance direction pulse compression processing is carried out on the echo S (t, tau) after coherent demodulation, distance dimension target high resolution is obtained, and distance direction frequency domain and azimuth direction time domain echo signals S (f) are obtained through distance direction FFT_r,τ)：

S22: constructing a distance matching filter function H (f)_r)：

S23: h (f)_r) With echo signal S (f)_rTau) to obtain echo signals S of the distance-direction frequency domain and the azimuth-direction time domain after distance compression₁(f_r,τ)：

Further, the distance motion compensation processing in step S3 specifically includes the following sub-steps:

s31: will be in step S1Performing Taylor expansion;

s32: neglecting the quadratic term in the expanded distance relational expression, simultaneously due to the sumIs small, socos θ ≈ 1, therefore, making R (x, y, t) ≈ R₀-Vt；

S33: structural range migration factor H (f)_r,t)：

S34: h (f)_rT) and S₁(f_rTau) multiplication is carried out to eliminate distance migration caused by radar platform movement, and distance-to-IFFT conversion is carried out to obtain two-dimensional time domain signal S with high distance positioning precision and low azimuth positioning precision₂(t,τ)：

Further, the specific method for modeling in step S4 is as follows: for each range unit, the echo model and processing mode of azimuth scanning imaging are the same, so that the echo data of any range unit is arbitrarily selected for signal modeling, and the azimuth echo signal vector y is expressed as:

y＝A(θ)x+n

wherein,is a direction matrix composed of direction vectors corresponding to the orientation sampling points, a (n) ═ a₁，…，a_N]∈R^L×1For an antenna pattern sequence, N is the number of sampling points for one beam width, x ═ x₁，...，x_N]Representing the amplitude information of the azimuth discrete target, wherein M is the number of azimuth sampling points, and y is [ y ═ y₁，...，y_M]For the azimuth received echo signal, n is the additive noise vector.

Further, the specific method for constructing the weighted least squares objective function in step S5 is as follows: for the nth target of the distance unit, a weighting vector w with dimension of M multiplied by 1 is constructed_nLet us orderAnd establishing a least square solution for solving a target function of the target amplitude:

where K is the number of times that the scanning radar sweeps through the target scene, x_nFor the amplitude of the nth target, the objective function is expanded to obtain:

wherein,

is a covariance matrix of the signal, order

The above equation is simplified to:

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n} .

further, the step S6 of locating the target position specifically includes the following sub-steps:

s61: solving equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

With respect to x_nAnd let its derivative be zero, get the derivative with respect to x_nAmplitude optimal estimation function:

{\hat{x}}_{n} = w_{n}^{H} g;

s62: will be equationSubstituting the target amplitude optimal estimation function into the formula

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In the middle, in an order

\hat{Q} = R - {gg}^{H},

Obtaining a reconstructed target function:

s63: calculating the objective function relation J₁(w) with respect to a weight vector w_nThe calculation method of the optimal solution comprises the following steps: calculating the objective function relation J₁(w) with respect to w_nAnd let it be zero, get the information about w_nThe optimal solution of (2):

s64: will w_nSubstituting the calculation result of (2) into the equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In (b), get about x_nThe amplitude of (d) is:

s65: and calculating all target amplitudes of the range cells by using the methods in the steps S63 and S64, positioning the angles of the targets, realizing the accurate positioning of the azimuth dimension of the targets, applying the algorithm to the whole scanning radar action area, processing the whole target scene by distance cells one by one, and realizing the two-dimensional accurate positioning of the targets in the imaging area.

Further, the method for calculating the number M of azimuth sampling points comprises the following steps:

wherein PRF is the pulse repetition frequency, ω is the scanning speed, and Φ is the scanning range.

The invention has the beneficial effects that: the method comprises the steps of adopting a real beam radar to work in a constant-speed scanning mode, transmitting linear frequency modulation signals by the radar, obtaining the precision positioning of a target distance dimension by matching and filtering the distance dimension of echo signals by utilizing transmitted signals and antenna directional diagram parameter information, then carrying out motion compensation to eliminate the influence of platform motion on the echo signals, realizing the high-precision positioning of the target distance dimension, then establishing a signal echo model of the real beam forward-looking scanning radar, constructing a target function for solving the position of an azimuth target based on a weighted least square criterion, and converting a target amplitude estimation problem into a target function about a weighted vector w_nSolving the position information of the target azimuth dimension by solving the optimal solution of the target function; the problem of low positioning precision of the target azimuth dimension in the forward-looking action area of the motion platform is effectively solved, two-dimensional accurate positioning of the target distance and the azimuth dimension of the forward-looking area of the motion platform is finally realized, and compared with the traditional two-dimensional target positioning method, the method has the advantages of higher positioning precision of the target azimuth dimension and more accurate amplitude restoration. The inventionThe method can be applied to the fields of moving target tracking, accurate guidance and the like.

Drawings

FIG. 1 is a flow chart of a positioning method of the present invention;

FIG. 2 is a block diagram of a real beam scanning radar imaging system employed in an embodiment of the present invention;

FIG. 3 is a diagram of a simulated target scene layout as employed by an embodiment of the present invention;

FIG. 4 is a two-dimensional echo signal generated according to system parameters in accordance with the present invention;

FIG. 5 is a Gaussian white noise graph with SNR of 20dB added to the data after pulse compression according to the embodiment of the present invention;

FIG. 6 is a cross-sectional view of distance-driven pulse data with 20dB Gaussian white noise along the azimuth direction according to an embodiment of the present invention;

FIG. 7 is a diagram illustrating the results of two-dimensional target positioning processing performed on the 9-point target in FIG. 3 according to an embodiment of the present invention;

FIG. 8 is a cross-sectional view of the process result of FIG. 6 taken along the azimuth direction in accordance with the present invention.

Detailed Description

The technical solutions of the present invention are further described below with reference to the drawings and the specific embodiments, but the present invention is not limited to the following descriptions.

As shown in fig. 1, a real beam forward-looking scanning radar target two-dimensional positioning method includes the following steps:

s2: distance direction matching filtering is carried out;

s3: performing distance direction motion compensation processing;

s4: modeling a scanning radar azimuth echo signal;

s5: constructing a weighted least square target function;

s6: and carrying out target azimuth positioning.

Further, the specific method for calculating the distance between the target at the arbitrary point of the imaging area and the motion platform in step S1 is as follows: the zero moment position of the moving platform is marked as (0,0, h), wherein 0,0 and h are respectively the x-axis, y-axis and z-axis coordinates of the receiving station; the moving platform moves along the y axis, the moving speed is V, the azimuth angle of the target relative to the platform is recorded as theta, and the lower view angle of the radar antenna is recorded as thetaThe scanning speed of the radar antenna is marked as omega; then the distance between the moving platform and the target in the scene at the time t is expressed as:

wherein R is₀Is the initial distance between the motion platform and the target;

the azimuth time vector of the scanning radar imaging area is recorded as:

T_a＝[-PRI·N_a/2,-PRI·(N_a/2-1),…,PRI·(N_a/2-1)]

the distance time vector is:

T_r＝[-1/f_r·N_r/2,-1/f_r·(N_r/2-1),…,1/f_r·(N_r/2-1)]

wherein f is_rFor range-wise sampling rate, PRI is the transmit signal pulse repetition interval, N_aNumber of sampling points in azimuth, N_rThe number of distance sampling points.

S22: constructing a distance matching filter function H (f)_r)：

s31: will be in step S1Performing Taylor expansion;

S33: structural range migration factor H (f)_r,t)：

S34: h (f)_rT) and S₁(f_rTau) multiplication to eliminate range migration caused by radar platform motion and proceeding range direction

IFFT (inverse fast Fourier transform) is used for obtaining two-dimensional time domain signal S with high distance positioning precision and low azimuth positioning precision₂(t,τ)：

y＝A(θ)x+n

wherein,is a direction matrix composed of direction vectors corresponding to the orientation sampling points, a (n) ═ a₁，…，a_N]∈R^L×1For an antenna pattern sequence, N is the number of sampling points for one beam width, x ═ x₁，...，x_N]Web representing azimuthally discrete objectsDegree information, M is the number of azimuth sampling points, y is [ y [ ]₁，...，y_M]For the azimuth received echo signal, n is the additive noise vector.

wherein,

is a covariance matrix of the signal, order

The above equation is simplified to:

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n} .

s61: solving equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

{\hat{x}}_{n} = w_{n}^{H} g;

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In the middle, in an order

\hat{Q} = R - {gg}^{H},

Obtaining a reconstructed target function:

s63: through the operation, the target amplitude estimation problem is converted into the objective function J₁(w) with respect to a weight vector w_nSolving the optimal solution problem, solving the objective function relation J₁(w) with respect to a weight vector w_nThe calculation method of the optimal solution comprises the following steps: calculating the objective function relation J₁(w) with respect to w_nAnd let it be zero, get the information about w_nThe optimal solution of (2):

s64: will w_nSubstituting the calculation result of (2) into the equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In (b), get about x_nThe amplitude of (d) is:

The technical scheme of the present invention is further described below with reference to specific embodiments, verification is mainly performed by using a simulation experiment method, and correctness is verified on Matlab2010 for all steps and conclusions.

The method comprises the following steps: for any point target in an imaging area, calculating the distance between the target and a moving platform, and setting real beam scanning radar point target simulation parameters.

Watch 1

Parameter(s)	Symbol	Numerical value
			Carrier frequency	f_c	10GHz
Bandwidth of	B	20MHz
			Transmission signal time width	T	50μs
Platform velocity	υ	150m/s
			Bandwidth of transmitted signal	B	40MHz
Height of platform	H	5Km

Pulse sampling frequency	PRF	1000Hz
			Scanning speed of antenna	ω	30°/s
Antenna beam width	θ	3°
			Scanning range	Φ	-8°～8°

An imaging scene adopted by the embodiment is shown in fig. 3, wherein dots are 3 × 3 dot targets arranged on the ground, the amplitudes of the dots are 1, 0.9 and 0.8 in sequence along the positive direction of the y axis, and the positions of the dot targets along the azimuth direction are-4 degrees, 2 degrees and 3.5 degrees respectively; the distance along the x-axis direction is 500m, the position coordinate of the radar platform at the initial moment is (0,0,5km), the target scattering function in the xoy plane is recorded as f (x, y), and the distance between a point (x, y) in the xoy plane and the radar platform d at the t moment is recorded as R (x, y, t).

Step two: generating an echo matrix S (t, tau) according to the imaging system parameters and the imaging scene set in the step one, and performing distance direction FFT to obtain S (f)_rTau), and constructing a distance-to-pulse pressure reference function in a frequency domain according to the frequency modulation slope K of the transmitting signal and the distance-to-reference time tau, and converting S (f)_rTau) and a pulse pressure reference function to complete the range-to-pulse compression, and the two-dimensional echo data of the range-to-frequency-domain azimuth-to-time domain after the pulse pressure is expressed as S₁(f_rτ) generated as shown in fig. 4.

Step three: the result R (x, y, t) is approximately equal to R according to the Taylor series expansion result R (x, y, t) of the slant distance history R (x, y, t) of the target in the forward-looking area₀Vt, to data S₁(f_rTau) carrying out scale transformation and eliminating range migration caused by radar platform movement, and carrying out range-to-IFFT transformation to obtain a two-dimensional time domain signal S₂(t, τ). To simulate the actual situation in the presence of noise, in the data S₂Gaussian white noise with SNR of 20dB is added to (t, τ), and the corresponding result is shown in fig. 5, and the profile along the azimuth direction is shown in fig. 6.

Step four: generating a direction vector a (theta) by using system parameters such as scanning speed, pulse repetition time, antenna beam width, etc. set by the system_k) And a direction matrix a.

Step five: from the generated echo signal, using a formula

And

respectively calculating covariance matrix R and vector g, and constructing weighted vector w with dimension of Mx 1_n。

Step six: for the nth target of the range unit, first, the covariance matrix R and the vector g calculated in the fifth step are substituted into the expressionMedium calculation matrixAnd the calculation result and the constructed direction vector h (theta)_n) Substituted into equation

Calculating the optimal weight vector w of the target amplitude_nW is to be_nSubstituting the calculation result into the equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

Middle calculation

And calculating the amplitude of the target and the position for positioning the target, and calculating the amplitude and the position of each target in the azimuth direction point by using the method.

And finally, processing the distance direction of the whole forward-looking action area of the scanning radar by distance units by using the method from the third step to the fifth step to obtain a two-dimensional positioning result of the target in the forward-looking imaging area of the scanning radar of the whole moving platform, wherein the imaging result is shown in fig. 7 and 8, in the diagram, the azimuth positioning positions of the three targets are respectively-4 degrees, 2.045 degrees and 3.459 degrees, and the positioning errors are respectively 0 degree, 0.045 degree and 0.041 degree. As can be seen from the figure, the invention can realize the two-dimensional target positioning processing of the forward-looking area of the scanning radar of the motion platform, can obviously improve the two-dimensional positioning precision of the real beam scanning radar target, has low positioning error, and has good improvement effect on the orientation dimension positioning of the target, the resolution of adjacent targets and the like of the processing result.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A real beam forward-looking scanning radar target two-dimensional positioning method is characterized by comprising the following steps: the method comprises the following steps:

s2: distance direction matching filtering is carried out;

s3: performing distance direction motion compensation processing;

s4: modeling a scanning radar azimuth echo signal;

s5: constructing a weighted least square target function;

s6: and carrying out target azimuth positioning.

2. The positioning method according to claim 1, characterized in that: the specific method for calculating the distance between the target at any point in the imaging area and the motion platform in step S1 is as follows: the zero-time position of the moving platform is recorded as (0,0, h), the moving platform moves along the y axis, the moving speed is V, the azimuth angle of the target relative to the platform is recorded as q, and the lower view angle of the radar antenna is recorded as qThe scanning speed of the radar antenna is marked as omega; then the distance between the moving platform and the target in the scene at the time t is expressed as:

the azimuth time vector of the scanning radar imaging area is recorded as:

T_a＝[-PRI·N_a/2,-PRI·(N_a/2-1),…,PRI·(N_a/2-1)]

the distance time vector is:

T_r＝[-1/f_r·N_r/2,-1/f_r·(N_r/2-1),…,1/f_r·(N_r/2-1)]

3. The positioning method according to claim 2, characterized in that: the distance direction matching filtering in step S2 specifically includes the following sub-steps:

S22: constructing a distance matching filter function H (f)_r)：

4. The positioning method according to claim 3, characterized in that: the distance motion compensation processing in step S3 specifically includes the following sub-steps:

s31: will be in step S1Performing Taylor expansion;

S33: structural range migration factor H (f)_r,t)：

5. The positioning method according to claim 4, characterized in that: the specific method for modeling in step S4 is as follows: for each range unit, the echo model and processing mode of azimuth scanning imaging are the same, so that the echo data of any range unit is arbitrarily selected for signal modeling, and the azimuth echo signal vector y is expressed as:

y＝A(θ)x+n

6. The positioning method according to claim 5, characterized in that: the specific method for constructing the weighted least squares objective function in step S5 is as follows: for the nth target of the distance unit, a weighting vector w with dimension of M multiplied by 1 is constructed_nLet us orderAnd establishing a least square solution for solving a target function of the target amplitude:

wherein,

is a covariance matrix of the signal, order

The above equation is simplified to:

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n} .

7. the positioning method according to claim 6, characterized in that: the step S6 of locating the target position specifically includes the following substeps:

s61: solving equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

{\hat{x}}_{n} = w_{n}^{H} g;

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In the middle, in an order

\hat{Q} = R - {gg}^{H},

Obtaining a reconstructed target function:

s64: will w_nIs calculated as a result ofEntry to equation

J (w) = w_{n}^{H} R w_{n} + {| x_{n} - w_{n}^{H} g |}^{2} - w_{n}^{H} g g^{H} w_{n}

In (b), get about x_nThe amplitude of (d) is:

8. The positioning method according to claim 5, characterized in that: the method for calculating the number M of the azimuth sampling points comprises the following steps: