CN113933833B - High-speed target imaging method, system, computer equipment and processing terminal - Google Patents
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Abstract
The invention belongs to the technical field of radar imaging, and discloses a high-speed target imaging method, a system, computer equipment and a processing terminal, wherein the high-speed target imaging method comprises the following steps: establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z'; the radar receives the echo signal, and carries out de-wiring tone processing on the echo signal based on the reference signal to obtain a signal S dc(ts, l after the de-wiring tone processing; simplifying azimuth expression, combining ts phase items in echo signals to obtain preprocessed echo signals S (t s, l); realizing frequency modulation rate estimation of an S (t s, l) signal by using a segmented autocorrelation method and fractional Fourier change; using maximum likelihood estimation and minimum entropy estimation method to realize first order item parameter estimation; and respectively performing range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals to obtain two-dimensional vortex imaging of the compensated target. The high-speed target imaging method provided by the invention effectively improves the accuracy and quality of imaging.
Description
Technical Field
The invention belongs to the technical field of radar imaging, and particularly relates to a high-speed target imaging method, a system, computer equipment and a processing terminal.
Background
Currently, vortex electromagnetic waves refer to microwaves modulated with orbital angular momentum (orbital angularmomentum, OAM). Because of the modulation of the OAM to the phase, the wave front of the vortex electromagnetic wave presents a spiral ladder shape in the space distribution, and the surface of the vortex electromagnetic wave presents different reflection characteristics when the vortex electromagnetic wave irradiates a target object, which is equivalent to the beam diversity irradiation of the target; and because of the mutual orthogonality between the different vortex modes, this provides a modulation degree of freedom for information modulation other than amplitude, phase, frequency, space. Therefore, the transmission and information acquisition capabilities of the vortex electromagnetic waves are of great interest in the field of radar imaging, and a series of imaging algorithms based on vortex electromagnetic waves are proposed.
Document "Wang J,Liu K,Cheng Y,et al.Three-dimensional target imaging based on vortex stripmap SAR[J].IEEE Sensors Journal,2018,19(4):1338-1345" proposes a three-dimensional imaging method based on vortex electromagnetic waves and strip synthetic aperture radar.
Document "Jiang Y,Liu K,Wang H,et al.Orbital-angular-momentum-based ISAR imaging at terahertz frequencies[J].IEEE Sensors Journal,2018,18(22):9230-9235" proposes an Inverse Synthetic Aperture Radar (ISAR) algorithm based on vortex electromagnetic waves, which can implement high-resolution three-dimensional imaging of a target at terahertz frequencies.
The vortex synthetic aperture radar (SYNTHETIC APERTURE RADAR, SAR) imaging method proposed by the patent 'electromagnetic vortex wave-based synthetic aperture radar three-dimensional imaging method' (CN 110412571A) considers the imaging processing flow when the target moves at non-uniform speed.
Document "Bu X X,Zhang Z,Chen L Y,et al.Synthetic aperture radar interferometry based onvortex electromagnetic waves[J].IEEE Access,2019,7:82693-82700" proposes a synthetic aperture radar interferometry technique based on vortex electromagnetic waves, which can accurately obtain three-dimensional target information without a baseline.
Most of the vortex imaging technologies at present are based on a "stop-and-go" hypothesis model, and the speeds of Hypersonic missile weapons (Hypersonic cruise missile, HCM) and Hypersonic gliding aircraft (Hypersonic GLIDE VEHICLE, HGV) are generally between mach 5 and mach 10, so that not only the Zhongmeirush technology is pursued, but also the Hypersonic technology is greatly developed in countries such as india and australia due to the outstanding advantages of strong maneuverability, high movement speed and the like, and a new army competition involving Hypersonic speed can be seen. However, the traditional stop-and-go model is only suitable for low-speed and slow-speed targets, and when the model is applied to high-speed target imaging, mismatch filtering and Doppler coupling time shift caused by an intra-pulse Doppler term occur, namely, one-dimensional range profile broadening and displacement of the target are caused, and an azimuth angle image of the target coupled with a vortex mode l is blurred, so that the imaging quality is seriously reduced. Therefore, it is necessary to design a vortex electromagnetic wave imaging algorithm suitable for high-speed targets.
Through the above analysis, the problems and defects existing in the prior art are as follows:
(1) The existing vortex imaging technology is based on a 'stop-and-go' hypothesis model, and as the movement speed of an aircraft gradually increases, the movement of a target in a pulse cannot be ignored, and in this case, the traditional 'stop-and-go' hypothesis is not applicable any more.
(2) In the existing vortex imaging technology, a target range profile obtained based on a stop-and-go hypothesis model can deviate and broaden to a certain extent.
(3) In the existing vortex imaging technology based on the 'stop-and-go' hypothesis model, the target azimuth coupled with the OAM mode will also be blurred, which will lead to degradation of the target imaging quality.
The difficulty of solving the problems and the defects is as follows: after analysis of the motion state of the object, how to calculate and compensate for the additional phase term in the echo signal that causes the image quality to be reduced.
The meaning of solving the problems and the defects is as follows: the application range of the vortex radar can be effectively expanded by researching a vortex electromagnetic wave imaging algorithm aiming at a high-speed target, and the unique imaging dimension of the vortex radar can improve the detection capability of the high-speed moving target.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a high-speed target imaging method, a system, computer equipment and a processing terminal, in particular to a high-speed target imaging method, a system, computer equipment and a processing terminal based on vortex electromagnetic waves.
The invention is realized in that a high-speed target imaging method comprises the following steps:
Step one, a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z' are established;
step two, the radar receives an echo signal, and carries out de-wiring tone processing on the echo signal based on a reference signal to obtain a de-wiring tone post-signal S dc(ts, l), and the subsequent steps are mainly based on the signal S dc(ts, l) for operation;
Step three, simplifying an azimuth expression, combining t s phase items in the echo signals to obtain preprocessed echo signals S (t S, l), so that the preprocessed signals S (t S, l) can be analyzed to find out factors affecting imaging quality;
step four, combining the segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the modulation frequency of the echo signal S (t S, l), and providing data support for the next estimation step while finishing the range profile broadening compensation;
fifthly, a maximum likelihood estimation and minimum entropy estimation method is used for realizing first-order parameter estimation, so that compensation of range profile offset and azimuth profile blurring is completed;
And step six, respectively performing range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals to obtain two-dimensional vortex imaging of the compensated target.
Further, in the first step, the establishing the radar coordinate system O-xyz and the target relative coordinate system O '-x' y 'z' includes:
The radar is a uniform circular array UCA formed by N array elements, the center of the uniform circular array UCA is positioned at an origin O, and the target relative coordinate system O '-x' y 'z' is a rectangular coordinate system taking the equivalent phase center O 'of a target track as the origin, and the pointing direction of the target relative coordinate system O' -x 'y' z is consistent with the radar coordinate system O-xyz; by feeding each array element with corresponding phase excitation, vortex electromagnetic waves with the mode number of-l are formed, so that the target is irradiated;
The target consists of a plurality of scattering points, moves along a path with an included angle beta with the positive direction of the y axis at a speed v, and has an initial height R 0; the scattering point is denoted a' T(x'T,y'T,z'T) T.epsilon.1, 2, …, M in the relative coordinate system, a T(xT,yT,zT in the coordinate system O-xyz), and For the distance of the connecting line between the radar and the scattering point, the two satisfy the following relation:
Where t m is the slow time and t m＝mTR,TR is the pulse repetition frequency (Pulse Repetition Frequency, PRF) of the transmit signal.
Further, in the second step, the radar receives the echo signal, and performs a line-demodulation tone processing on the echo signal based on the reference signal to obtain a line-demodulation tone post-signal S dc(ts, l), including:
a chirp signal (Linear Frequency Modulation, LFM) is used to carry OAM to generate a vortex electromagnetic wave, and assuming that the target consists of M scattering points, the echo signal at one slow time instant is represented as:
wherein T p and K respectively represent the pulse width of the signal and the frequency modulation rate of the LFM, and f c is the center frequency of the signal Is a fast time; l is OAM mode, τ T＝2rT/c is echo delay corresponding to each scattering point,/>The last received echo signal is the fast time/>, which is the azimuth angle of the scattering point at the slow time t m Modality l-slow time t m three-dimensional radar echo data, namely a plurality of two-dimensional images according to slow time sequence;
because the Time-bandwidth product (Time-bandwidth Product, TBP) of the LFM signal is large, the echo signal is subjected to the line-splitting tone processing, and meanwhile, because the target distance and azimuth angle in a slow Time cannot be regarded as constants due to the high-speed motion of the target, the obtained line-splitting tone-post-signal is expressed as:
Wherein t s is a time variable taking the equivalent phase center O' as a reference point and satisfies Τ ΔT(ts)＝τT(ts)-τref is the relative echo delay in a slow time, τ ref＝2rref/c and r ref are the echo delay and distance between the radar and O', where each term can be expressed as:
Further, in the third step, the simplified azimuth expression combines the t s phase terms in the echo signal to obtain a preprocessed echo signal S (t s, l), which includes:
The expression of the signal after the line-separating tone shows that-2pi phi T(ts) is a first phase item, the echo signal is subjected to distance compression, and the item can cause the phenomenon of deviation and widening of the obtained one-dimensional distance image due to the influence of high-speed motion in the pulse, so that the imaging quality is reduced; as for the second phase term, since the azimuth coupled with the OAM mode l changes with time, the azimuth image of the target is also affected;
Azimuth angle Performing taylor polynomial expansion, and ignoring coefficients higher than second-order terms to obtain:
wherein, An initial azimuth of the target at the start time of each pulse;
Combining t s phase items in the echo signals to obtain processed echo signals:
wherein, F T is the center frequency for each component and K * is the corresponding tuning frequency; the first order term for t s will cause a shift in the target range profile and blurring of the azimuth profile, and the second order term for t s will widen the target range profile.
Further, in the fourth step, the frequency modulation rate estimation is implemented by using a piecewise autocorrelation method and fractional fourier transform, including:
estimating and compensating the second-order term coefficient to eliminate range profile broadening; the piecewise autocorrelation method has a small amount of computation, and is therefore used to determine the reference estimated frequency modulation value K', and the autocorrelation result is as follows:
Wherein Φ (T, P) =f Tτ+πK*τ2+φT-φP, the result after autocorrelation is composed of multiple components with frequencies of 2pi K * τ and 2pi K *τ+fT-fP, and the component with frequency of 2pi K * τ will occupy the main body when the sequence difference τ takes a proper value; the frequency modulation value K' is thus obtained by searching for the appropriate τ and performing a fast fourier transform FFT on R (τ) as follows:
for multi-component LFM signal frequency modulation rate estimation, K 'is used as a reference estimated frequency modulation value to restrict fractional Fourier change angle a' n, and the estimated frequency modulation rate is:
where N' is the number of sampling points and f s is the sampling rate. The echo signal can be obtained after compensation:
In the fifth step, the first-order term parameter estimation is implemented by using a maximum likelihood estimation method and a minimum entropy estimation method, including:
The relationship between the movement velocity v of the target and the estimated tuning frequency K' n is as follows:
K'n＝4πKv2/c2-4πKv/c；
selecting H echoes of a target, wherein the estimated speed estimation one-dimensional vector is v= [ v 1,v2,…,vk,…,vH]1×H ], and v k is the estimated speed of the kth echo; the noise distribution is generally considered to satisfy the gaussian white noise distribution, and the joint probability distribution with respect to the velocity vector v is:
Wherein μ and σ are the mean and variance of the gaussian distribution, respectively, the corresponding parameters are estimated by using the maximum likelihood estimation MLE, and μ is the target speed;
Compensating first order coefficients of t s to compensate for shift of the range profile and blur of the azimuth profile; since the entropy of the azimuth image is minimal when compensation is appropriate, the minimum entropy method is used to estimate the first order coefficients, and the compensated echo signal is as follows:
wherein,
The compensated echo signal is subjected to FFT in a fast time domain and an OAM mode domain, and the residual video phase term RVP and the oblique term are compensated to obtain the following components:
Wherein P a(fl) is the azimuthal image.
Another object of the present invention is to provide a high-speed target imaging system to which the high-speed target imaging method is applied, the high-speed target imaging system comprising:
The coordinate system construction module is used for establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z';
The line-demodulation frequency-modulation processing module is used for receiving echo signals through a radar, and performing line-demodulation frequency-modulation processing on the echo signals based on reference signals to obtain line-demodulation frequency-modulation post-signals S dc(ts, l);
The echo signal processing module is used for simplifying an azimuth angle expression, combining t s phase items in the echo signals and obtaining preprocessed echo signals S (t s, l);
The frequency modulation estimation module is used for realizing frequency modulation estimation by utilizing a segmentation autocorrelation method and fractional Fourier change after the echo signal is preprocessed;
The first-order item parameter estimation module is used for realizing first-order item parameter estimation by using a maximum likelihood estimation and minimum entropy estimation method;
And the imaging processing module is used for respectively carrying out range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals so as to obtain compensated two-dimensional vortex imaging of the target.
It is a further object of the present invention to provide a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of:
Establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z'; the radar receives the echo signal, and carries out de-wiring tone processing on the echo signal based on the reference signal to obtain a de-wiring tone post-signal S dc(ts, l); after simplifying the azimuth expression of the target, combining phase items related to time t s in the echo signals to obtain preprocessed echo signals S (t s, l); for the preprocessed echo signals, combining a segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the echo signal frequency modulation; according to the estimated value, a maximum likelihood estimation and a minimum entropy estimation method are used for realizing first-order item parameter estimation of the echo signal S (t s, l); and compensating the echo signals according to the estimated parameters, and finally performing range image compression and azimuth image compression to obtain the two-dimensional vortex imaging of the compensated target.
Another object of the present invention is to provide a computer readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:
Establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z'; the radar receives the echo signal, and carries out de-wiring tone processing on the echo signal based on the reference signal to obtain a de-wiring tone post-signal S dc(tS, l); after simplifying the azimuth expression of the target, combining phase items related to time t s in the echo signals to obtain preprocessed echo signals S (t S, l); for the preprocessed echo signals, combining a segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the echo signal frequency modulation; according to the estimated value, a maximum likelihood estimation and a minimum entropy estimation method are used for realizing first-order item parameter estimation of the echo signal S (t S, l); and compensating the echo signals according to the estimated parameters, and finally performing range image compression and azimuth image compression to obtain the two-dimensional vortex imaging of the compensated target.
Another object of the present invention is to provide an information data processing terminal for realizing the high-speed target imaging system.
By combining all the technical schemes, the invention has the advantages and positive effects that: the high-speed target imaging method provided by the invention effectively eliminates the phenomena of range profile shift broadening and azimuth angle image blurring existing when vortex electromagnetic waves image a high-speed moving target, and improves the imaging accuracy and quality.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a high-speed target imaging method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a high-speed target imaging method according to an embodiment of the present invention.
FIG. 3 is a block diagram of a high-speed target imaging system provided by an embodiment of the present invention;
In the figure: 1. a coordinate system construction module; 2. a wire-releasing tone processing module; 3. an echo signal acquisition module; 4. a frequency adjustment estimation module; 5. a first order item parameter estimation module; 6. and an imaging processing module.
Fig. 4 is a schematic diagram of an imaging model according to an embodiment of the present invention.
Fig. 5 is a simplified schematic diagram of an azimuthal expression provided by an embodiment of the present invention.
FIG. 6 is a schematic diagram of imaging an uncompensated target provided by an embodiment of the invention.
Fig. 7 is an imaging schematic of a compensated target provided by an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In view of the problems existing in the prior art, the present invention provides a high-speed target imaging method, a system, a computer device, and a processing terminal, and the present invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the high-speed target imaging method provided by the embodiment of the invention includes the following steps:
S101, establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z';
S102, receiving echo signals by a radar, performing line-demodulation tone processing on the echo signals based on reference signals to obtain line-demodulation tone-processed signals S dc(ts, l), and performing subsequent steps mainly based on the signals S dc(ts, I);
S103, simplifying an azimuth expression, combining t s phase items in the echo signals to obtain preprocessed echo signals S (t s, l), so that the preprocessed signals S (t s, l) can be analyzed to find out factors affecting imaging quality;
S104, combining a segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the modulation frequency of the echo signal S (t s, l), and providing data support for the next estimation step while finishing range profile broadening compensation;
s105, a maximum likelihood estimation and minimum entropy estimation method is used for realizing first-order parameter estimation, so that compensation of range profile offset and azimuth profile blurring is completed;
and S106, respectively performing range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals to obtain two-dimensional vortex imaging of the compensated target.
The schematic diagram of the high-speed target imaging method provided by the embodiment of the invention is shown in fig. 2.
As shown in fig. 3, a high-speed target imaging system provided by an embodiment of the present invention includes:
the coordinate system construction module 1 is used for establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z';
The de-line tone processing module 2 is used for receiving the echo signals through the radar, and performing de-line tone processing on the echo signals based on the reference signals to obtain de-line tone post-signal S dc(ts, l);
The echo signal processing module 3 is used for simplifying an azimuth angle expression, combining t s phase items in the echo signals to obtain preprocessed echo signals S dc(ts and l);
The frequency modulation rate estimation module 4 is used for realizing frequency modulation rate estimation by utilizing a segmentation autocorrelation method and fractional Fourier change after the echo signal is preprocessed;
the first-order item parameter estimation module 5 is used for realizing first-order item parameter estimation by using a maximum likelihood estimation method and a minimum entropy estimation method;
And the imaging processing module 6 is used for respectively carrying out range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals so as to obtain compensated two-dimensional vortex imaging of the target.
The technical scheme of the invention is further described below with reference to specific embodiments.
The scheme of the invention is approximately as follows:
Fig. 2 is a flowchart illustrating steps performed in the process.
1. First, a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z' are established. The radar is a Uniform Circular Array (UCA) formed by N array elements, the center of the radar is positioned at an origin O, and the target relative coordinate system O ' -x ' y ' z ' is a rectangular coordinate system taking the equivalent phase center O ' of a target track as the origin, and the pointing direction of the radar is consistent with the radar coordinate system O-xyz. By feeding each array element with a corresponding phase excitation, vortex electromagnetic waves with the mode numbers of-l can be formed, so that the target is irradiated.
2. The target is composed of a plurality of scattering points and moves along a path with an included angle beta with the positive direction of the y axis at a speed v, and the initial height is R 0. The scattering point can be represented in the relative coordinate system as a' T(x'T,y'T,z'T) T.epsilon.1, 2, …, M and in the coordinate system O-xyz as a T(xT,yT,zT), andFor the distance of the connecting line between the radar and the scattering point, the two satisfy the following relation:
Where t m is the slow time and t m＝mTR,TR is the pulse repetition frequency PRF of the transmit signal, fig. 4 is the corresponding target imaging model.
3. A chirped signal (LFM) is used to carry OAM to generate a vortex electromagnetic wave, and assuming that the target consists of M scattering points, the echo signal at one slow time instant can be expressed as:
wherein T p and K respectively represent the pulse width of the signal and the frequency modulation rate of the LFM, f c is the center frequency of the signal and Is a fast time. L is OAM mode, τ T＝2rT/c is echo delay corresponding to each scattering point,/>Is the azimuth of the scattering point at slow time t m. The last received echo signal is therefore fast time/>The modality l-slow time t m three-dimensional radar echo data can also be seen as a plurality of two-dimensional images in slow time order.
4. Because the Time Bandwidth Product (TBP) of the LFM signal is large, the echo signal is subjected to the line-demodulation tone processing to reduce the sampling rate requirement on the signal, and meanwhile, because the target distance and the azimuth angle in a slow time cannot be regarded as constants due to the high-speed movement of the target, the obtained line-demodulation tone-post-signal can be expressed as:
wherein t s is a time variable with the equivalent phase center O' as a reference point and satisfies Τ ΔT(ts)＝τT(ts)-τref is the relative echo delay in a slow time, τ ref＝2rref/c and r ref are the echo delay and distance between the radar and O', where each term can be expressed as:
5. It can be seen from the above that, -2pi phi T(ts) is the first phase term, and the echo signal is subjected to distance compression, so that the obtained one-dimensional range profile is offset and widened due to the influence of high-speed motion in the pulse, and the imaging quality is seriously reduced. As for the second phase term, since the azimuth angle coupled with the OAM mode l varies with time, the azimuth angle image of the target is also affected to some extent.
6. Azimuth angleThe taylor polynomial expansion is performed, and the coefficients higher than the second order term are ignored, so that the following can be obtained:
Wherein the method comprises the steps of Is the initial azimuth of the target at the beginning of the slow time. Fig. 5 is an error comparison of the true change in azimuth angle with the approximation over a slow time.
7. Combining the t s phase terms in the echo signals to obtain processed echo signals:
Wherein the method comprises the steps of F T is the center frequency for each component and K * is the corresponding tuning frequency. As can be seen from the above equation, the first term of t s will cause the shift of the target range profile and the blurring of the azimuth angle profile, and the second term of t s will widen the target range profile, fig. 6 (a) is the range profile and the azimuth angle profile of the target under a certain echo before compensation, and fig. 6 (b) is the two-dimensional imaging of the distorted target range profile.
8. The second order term coefficients are estimated and compensated to eliminate range profile broadening. The piecewise autocorrelation method has a small amount of computation, and is therefore used to determine the reference estimated fm value K', the autocorrelation result being as follows:
where Φ (T, P) =f Tτ+πK*τ2+φT-φP. It can be derived that the result after autocorrelation is made up of components with frequencies 2pi K * tau and 2pi K *τ+fT-fP, and that the component with frequency 2pi K * tau will occupy the main body when the sequence difference tau takes a suitable value. The frequency modulation value K' is thus obtained by searching for the appropriate τ and performing a Fast Fourier Transform (FFT) on R (τ) as follows:
For multi-component LFM signal frequency modulation rate estimation, fractional Fourier transform (FRFT) can effectively overcome cross interference, and has better accuracy, in order to reduce the operation amount requirement so as to improve the estimation speed, K 'is used as a reference estimated frequency modulation value to restrict fractional Fourier transform angle a' n, and the estimated frequency modulation rate is:
The echo signal can be obtained after compensation:
Where N' is the number of sampling points and f s is the sampling rate.
9. The motion velocity v of the target can be calculated by estimating the tuning frequency K' n:
K'n＝4πKv2/c2-4πKv/c；
And selecting H echoes of the target, wherein the estimated speed estimation one-dimensional vector is v= [ v 1,v2,…,vk,…,vH]1×H ], and v k is the estimated speed of the kth echo. The noise distribution is generally considered to satisfy the gaussian white noise distribution, and the joint probability distribution with respect to the velocity vector v is:
Where μ and σ are the mean and variance, respectively, of the gaussian distribution, the corresponding parameters are estimated using Maximum Likelihood Estimation (MLE), and μ is the target velocity sought.
10. The first order coefficients of t s are compensated to compensate for the shift of the range profile and the blurring of the azimuth profile. Since the entropy of the azimuth image is minimal when compensation is appropriate, the minimum entropy method is used to estimate the first order coefficients, and the compensated echo signal is as follows:
Wherein the method comprises the steps of
11. The compensated echo signal is subjected to FFT in a fast time domain and an OAM mode domain, and residual video phase terms (RVP) and diagonal terms are compensated to obtain the following components:
wherein P a(fl) is an azimuth image, fig. 7 (a) is a distance image and an azimuth image of the target after compensation, and fig. 7 (b) is a two-dimensional image of the target corresponding to the time, and compared with fig. 6 (a) and (b), it can be seen that the imaging quality is better improved.
In the above embodiments, it may be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When used in whole or in part, is implemented in the form of a computer program product comprising one or more computer instructions. When loaded or executed on a computer, produces a flow or function in accordance with embodiments of the present invention, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a computer network, or other programmable apparatus. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by a wired (e.g., coaxial cable, fiber optic, digital Subscriber Line (DSL), or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. that contains an integration of one or more available media. The usable medium may be a magnetic medium (e.g., floppy disk, hard disk, tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid state disk Solid STATE DISK (SSD)), etc.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.
Claims (10)
1. A high-speed target imaging method, characterized in that the high-speed target imaging method comprises the steps of:
Step one, a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z' are established;
step two, the radar receives an echo signal, and carries out de-wiring tone processing on the echo signal based on a reference signal to obtain a de-wiring tone post-signal S dc(ts, l), and the subsequent steps are mainly based on the signal S dc(ts, l) for operation;
Step three, simplifying an azimuth expression, combining t s phase items in the echo signals to obtain preprocessed echo signals S (t s, l), so that the preprocessed signals S (t s, l) can be analyzed to find out factors affecting imaging quality;
Step four, combining the segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the modulation frequency of the echo signal S (t s, l), and providing data support for the next estimation step while finishing the range profile broadening compensation;
fifthly, a maximum likelihood estimation and minimum entropy estimation method is used for realizing first-order parameter estimation, so that compensation of range profile offset and azimuth profile blurring is completed;
And step six, respectively performing range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals to obtain two-dimensional vortex imaging of the compensated target.
2. The method of high-speed object imaging according to claim 1, wherein in the first step, the establishing of the radar coordinate system O-xyz and the object relative coordinate system O '-x' y 'z' includes:
The radar is a uniform circular array UCA formed by N array elements, the center of the uniform circular array UCA is positioned at an origin O, and the target relative coordinate system O '-x' y 'z' is a rectangular coordinate system taking the equivalent phase center O 'of a target track as the origin, and the pointing direction of the target relative coordinate system O' -x 'y' z is consistent with the radar coordinate system O-xyz; by feeding each array element with corresponding phase excitation, vortex electromagnetic waves with the mode number of-l are formed, so that the target is irradiated;
The target consists of a plurality of scattering points, moves along a path with an included angle beta with the positive direction of the y axis at a speed v, and has an initial height R 0; scattering points are denoted a' T(x'T,y'T,z'T) T e1, 2 in the relative coordinate system, M, a T(xT,yT,zT in the coordinate system O-xyz), and For the distance of the connecting line between the radar and the scattering point, the two satisfy the following relation:
xT＝vtm+x′T.
yT＝R0+vtm/tan(β)+y′T.；
zT＝z′T.
Where t m is the slow time and t m＝mTR,TR is the pulse repetition frequency (Pulse Repetition Frequency, PRF) of the transmit signal.
3. The method of imaging a high-speed target according to claim 1, wherein in the second step, the radar receives an echo signal, and performs a line-removing tone processing on the echo signal based on a reference signal to obtain a line-removing tone post-signal S dc(ts, l), including:
a chirp signal (Linear Frequency Modulation, LFM) is used to carry OAM to generate a vortex electromagnetic wave, and assuming that the target consists of M scattering points, the echo signal at one slow time instant is represented as:
wherein T p and K respectively represent the pulse width of the signal and the frequency modulation rate of the LFM, and f c is the center frequency of the signal Is a fast time; l is OAM mode, τ T＝2rT/c is echo delay corresponding to each scattering point,/>The last received echo signal is the fast time/>, which is the azimuth angle of the scattering point at the slow time t m Modality l-slow time t m three-dimensional radar echo data, namely a plurality of two-dimensional images according to slow time sequence;
because the Time-bandwidth product (Time-bandwidth Product, TBP) of the LFM signal is large, the echo signal is subjected to the line-splitting tone processing, and meanwhile, because the target distance and azimuth angle in a slow Time cannot be regarded as constants due to the high-speed motion of the target, the obtained line-splitting tone-post-signal is expressed as:
Wherein t s is a time variable taking the equivalent phase center O' as a reference point and satisfies Τ ΔT(ts)＝τT(ts)-τref is the relative echo delay in a slow time, τ ref＝2rref/c and r ref are the echo delay and distance between the radar and O', where each term can be expressed as:
rT(ts)≈rT(tm)+vts
。
4. the method of claim 1, wherein in the third step, the simplified azimuth expression combines t s phase terms in the echo signals to obtain a preprocessed echo signal S (t s, l), which includes:
The expression of the signal after the line-separating tone shows that-2pi phi T(ts) is a first phase item, the echo signal is subjected to distance compression, and the item can cause the phenomenon of deviation and widening of the obtained one-dimensional distance image due to the influence of high-speed motion in the pulse, so that the imaging quality is reduced; as for the second phase term, since the azimuth coupled with the OAM mode l changes with time, the azimuth image of the target is also affected;
Azimuth angle Performing taylor polynomial expansion, and ignoring coefficients higher than second-order terms to obtain:
wherein, An initial azimuth of the target at the start time of each pulse;
Combining t s phase items in the echo signals to obtain processed echo signals:
wherein, F T is the center frequency for each component and K * is the corresponding tuning frequency; the first order term for t s will cause a shift in the target range profile and blurring of the azimuth profile, and the second order term for t s will widen the target range profile.
5. The method of high-speed object imaging according to claim 1, wherein in the fourth step, frequency modulation rate estimation is achieved by using a piecewise autocorrelation method and fractional fourier transform, comprising:
estimating and compensating the second-order term coefficient to eliminate range profile broadening; the piecewise autocorrelation method has a small amount of computation, and is therefore used to determine the reference estimated frequency modulation value K', and the autocorrelation result is as follows:
Wherein Φ (T, P) =f Tτ+πK*τ2+φT-φP, the result after autocorrelation is composed of multiple components with frequencies of 2pi K * τ and 2pi K *τ+fT-fP, and the component with frequency of 2pi K * τ will occupy the main body when the sequence difference τ takes a proper value; the frequency modulation value K' is thus obtained by searching for the appropriate τ and performing a fast fourier transform FFT on R (τ) as follows:
for multi-component LFM signal frequency modulation rate estimation, K 'is used as a reference estimated frequency modulation value to restrict fractional Fourier change angle a' n, and the estimated frequency modulation rate is:
wherein, N' is the sampling point number, f s is the sampling rate, and the echo signal can be obtained after compensation:
。
6. The method of claim 1, wherein in the fifth step, the first-order parameter estimation is implemented by using a maximum likelihood estimation method and a minimum entropy estimation method, and the method comprises:
The relationship between the movement velocity v of the target and the estimated tuning frequency K' n is as follows:
K'n＝4πKv2/c2-4πKv/c；
selecting H echoes of a target, wherein the estimated speed estimation one-dimensional vector is v= [ v 1,v2,…,vk,…,vH]1×H ], and v k is the estimated speed of the kth echo; the noise distribution is generally considered to satisfy the gaussian white noise distribution, and the joint probability distribution with respect to the velocity vector v is:
Wherein μ and σ are the mean and variance of the gaussian distribution, respectively, the corresponding parameters are estimated by using the maximum likelihood estimation MLE, and μ is the target speed;
Compensating first order coefficients of t s to compensate for shift of the range profile and blur of the azimuth profile; since the entropy of the azimuth image is minimal when compensation is appropriate, the minimum entropy method is used to estimate the first order coefficients, and the compensated echo signal is as follows:
wherein,
The compensated echo signal is subjected to FFT in a fast time domain and an OAM mode domain, and the residual video phase term RVP and the oblique term are compensated to obtain the following components:
Wherein P a(fl) is the azimuthal image.
7. A high-speed target imaging system that operates the high-speed target imaging method of any one of claims 1 to 6, characterized in that the high-speed target imaging system comprises:
The coordinate system construction module is used for establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z';
The de-frequency modulation processing module is used for receiving echo signals through a radar, and performing de-line frequency modulation processing on the echo signals based on reference signals to obtain de-line frequency modulated signals S dc(ts, l);
The echo signal processing module is used for simplifying an azimuth angle expression, combining t s phase items in the echo signals and obtaining preprocessed echo signals S (t s, l);
The frequency modulation estimation module is used for realizing frequency modulation estimation by utilizing a segmentation autocorrelation method and fractional Fourier change after the echo signal is preprocessed;
The first-order item parameter estimation module is used for realizing first-order item parameter estimation by using a maximum likelihood estimation and minimum entropy estimation method;
And the imaging processing module is used for respectively carrying out range image compression, azimuth image compression and intra-pulse motion compensation on the echo signals so as to obtain compensated two-dimensional vortex imaging of the target.
8. A computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of:
Establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z'; the radar receives the echo signal, and carries out de-wiring tone processing on the echo signal based on the reference signal to obtain a de-wiring tone post-signal S dc(ts, l); after simplifying the azimuth expression of the target, combining phase items related to time t s in the echo signals to obtain preprocessed echo signals S (t s, l); for the preprocessed echo signals, combining a segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the echo signal frequency modulation; according to the estimated value, a maximum likelihood estimation and a minimum entropy estimation method are used for realizing first-order item parameter estimation of the echo signal S (t s, l); and compensating the echo signals according to the estimated parameters, and finally performing range image compression and azimuth image compression to obtain the two-dimensional vortex imaging of the compensated target.
9. A computer readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:
Establishing a radar coordinate system O-xyz and a target relative coordinate system O '-x' y 'z'; the radar receives the echo signal, and carries out de-wiring tone processing on the echo signal based on the reference signal to obtain a de-wiring tone post-signal S dc(ts, l); after simplifying the azimuth expression of the target, combining phase items related to time t s in the echo signals to obtain preprocessed echo signals S (t s, l); for the preprocessed echo signals, combining a segmentation autocorrelation method with fractional Fourier change to realize efficient and accurate estimation of the echo signal frequency modulation; according to the estimated value, a maximum likelihood estimation and a minimum entropy estimation method are used for realizing first-order item parameter estimation of the echo signal S (t s, l); and compensating the echo signals according to the estimated parameters, and finally performing range image compression and azimuth image compression to obtain the two-dimensional vortex imaging of the compensated target.
10. An information data processing terminal for implementing the high-speed object imaging system according to claim 7.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8227735B1 (en) * | 2007-07-24 | 2012-07-24 | Lockheed Martin Coherent Technologies, Inc. | Combined active and passive imaging system with radiation source unit and detector |
| CN115336420B (en) * | 2013-08-30 | 2016-11-30 | 上海无线电设备研究所 | Integrated detection device for bottom view synthetic aperture and near-bottom view double-swath interference imaging |
| EP3144702A1 (en) * | 2015-09-17 | 2017-03-22 | Institute of Electronics, Chinese Academy of Sciences | Method and device for synthethic aperture radar imaging based on non-linear frequency modulation signal |
| CN108107430A (en) * | 2017-11-09 | 2018-06-01 | 北京理工大学 | A kind of Ship Target ISAR imaging methods based on fraction Fourier conversion |
-
2021
- 2021-09-11 CN CN202111065175.7A patent/CN113933833B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8227735B1 (en) * | 2007-07-24 | 2012-07-24 | Lockheed Martin Coherent Technologies, Inc. | Combined active and passive imaging system with radiation source unit and detector |
| CN115336420B (en) * | 2013-08-30 | 2016-11-30 | 上海无线电设备研究所 | Integrated detection device for bottom view synthetic aperture and near-bottom view double-swath interference imaging |
| EP3144702A1 (en) * | 2015-09-17 | 2017-03-22 | Institute of Electronics, Chinese Academy of Sciences | Method and device for synthethic aperture radar imaging based on non-linear frequency modulation signal |
| CN108107430A (en) * | 2017-11-09 | 2018-06-01 | 北京理工大学 | A kind of Ship Target ISAR imaging methods based on fraction Fourier conversion |
Non-Patent Citations (2)
| Title |
|---|
| 基于FRFT的一维距离像高速运动补偿;袁斌;唐鹏飞;徐世友;陈曾平;;雷达科学与技术;20120615(第03期);全文 * |
| 涡旋电磁波的理论与应用研究进展;李龙;薛皓;冯强;;微波学报;20180419(第02期);全文 * |
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