Missile-borne large squint small-aperture multi-channel SAR imaging method
阅读说明：本技术 弹载大斜视小孔径多通道sar的成像方法 (Missile-borne large squint small-aperture multi-channel SAR imaging method ) 是由 邢孟道 侯雅昕 李宁 孙光才 于 2021-07-21 设计创作，主要内容包括：本发明涉及一种弹载大斜视小孔径多通道SAR的成像方法,该方法针对多通道回波,首先,在距离频域补偿场景中心非空变多通道相位差异,之后在距离时域补偿空变的通道相位差异项,随后,在距离时域方位频域进行多通道信号的重构,从而消除多通道存在的模糊。在二维频域中,进行距离徙动校正,通过改进的Stolt插值来获取目标距离向聚焦的信号,同时,方位时间谱压缩消除了信号在方位时间域的混叠,频域非线性变标消除了多普勒参数的空变性,方位向聚焦由SPECAN技术完成。本发明的方法更好的实时适应载有多通道的高机动运动轨迹,解决了通道间相位差异带来的无法联合处理的问题。(The invention relates to an imaging method of a missile-borne large squint small-aperture multi-channel SAR, which aims at multi-channel echo, firstly compensates non-space-variant multi-channel phase difference at the center of a scene in a distance frequency domain, then compensates a space-variant channel phase difference item in a distance time domain, and then reconstructs multi-channel signals in a distance time domain azimuth frequency domain, thereby eliminating ambiguity existing in multiple channels. In a two-dimensional frequency domain, range migration correction is carried out, signals of target range direction focusing are obtained through improved Stolt interpolation, meanwhile, aliasing of the signals in the range direction time domain is eliminated through azimuth time spectrum compression, space variability of Doppler parameters is eliminated through frequency domain nonlinear scaling, and azimuth direction focusing is completed through the SPECAN technology. The method of the invention is better suitable for the high maneuvering motion trail carrying multiple channels in real time, and solves the problem that the joint processing cannot be carried out due to the phase difference between the channels.)
1. A missile-borne large squint small-aperture multi-channel SAR imaging method is characterized by comprising the following steps:
s1: establishing a multi-channel large squint concentric circle skew distance model;
s2: acquiring a target echo signal;
s3: performing range pulse compression processing and range walk correction processing on the target echo signal to obtain a first correction signal;
s4: compensating a scene center non-space-variant multi-channel phase difference item and a space-variant multi-channel phase difference item of the first correction signal to obtain a compensation signal;
s5: performing multi-channel signal matrix reconstruction and Doppler spectrum reconstruction based on an improved steering matrix on the compensation signal to obtain a reconstructed signal;
s6: performing range migration correction processing and Stolt interpolation difference processing on the reconstructed signal to obtain a second correction signal;
s7: performing azimuth time spectrum compression processing and frequency domain nonlinear scaling processing on the second correction signal to obtain a two-dimensional time domain signal;
s8: carrying out azimuth SPECAN processing on the two-dimensional time domain signal to obtain a focusing signal;
s9: and carrying out geometric deformation interpolation correction processing on the focusing signal to obtain an SAR imaging image.
2. The imaging method of the missile-borne large-squint small-aperture multi-channel SAR (synthetic aperture radar) according to claim 1, wherein the instantaneous slant range of the multi-channel large-squint concentric circle slant range model comprises a fourth-order Taylor series of the slant range of the array center and a second-order Taylor series of the multi-channel difference, in the S1:
speed of radar platformAnd constant accelerationAlong the edgeCurve moves TaThe synthetic aperture time of (2) each channel on the radar platform is defined as CHmM is 1,2, …, M, when the radar is at azimuth time taWhen equal to 0, the central channel CH1The sub-satellite point is the origin of coordinates O, and the central channel beam is pointedDefine the X axis andis a yaw angle thetayawThe Q point is different in azimuth from the P pointA point of (1), wherein
Radar platform in curveWhen point C is above, the azimuth time is defined as taThe four-step Meglanlin series of the instantaneous slope distance is as follows:
wherein the content of the first and second substances,indicating radar center channel at taInstantaneous slope of time, taRepresenting azimuth time, i representing the expansion order, R representing the reference slope,coefficients representing the terms after Taylor expansion;
the instantaneous skew difference between the reference channel and the mth channel is expressed as:
wherein d ismDenotes the distance, R, of the mth channel from the reference channeld(dm,taR) represents the instantaneous slope difference, σ0(dmR) represents the zero-order coefficient, σ, after Taylor expansion1(dmR) represents the coefficient of the first order term after Taylor expansion, σ2(dmR) represents coefficients of quadratic terms after Taylor expansion;
the instantaneous skew of the mth channel is expressed as:
3. the imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 2, wherein the S2 comprises:
acquiring a first distance time domain and an orientation time domain signal A (t) of a target echo signalr,ta) For the first distance time domain and the azimuth time domain signal A (t)r,ta) Fourier transform of distance directionAnd obtaining a first distance frequency domain and azimuth time domain signal A' (f)r,ta) Wherein, in the step (A),
the first distance frequency domain and azimuth time domain signals A' (f)r,ta) Expressed as:
wherein, trRepresenting distance time, taIndicating the azimuth time, frDenotes the distance frequency, Wr(. represents the envelope of the distance to the frequency domain, wa(. for) the azimuth time-domain envelope, c the speed of light, fcRepresenting the carrier frequency and gamma representing the tuning frequency.
4. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 3, wherein the S3 comprises:
the first distance frequency domain and the azimuth time domain signal A' (f) are processedr,ta) Respectively and distance pulse compression function HRC(fr,ta) And distance walk correction function HRWC(fr,ta) Performing point multiplication to obtain a second distance frequency domain and orientation time domain signal B (f)r,ta) As the first correction signal, wherein,
the distance pulse compression function HRC(fr,ta) And the distance walk correction function HRWC(fr,ta) Respectively expressed as:
HRWC(fr,ta)＝exp(j4π(fc+fr)k10(Rs)ta/c)，
wherein R issDenotes the reference slope, k10(Rs) To representWhere R is RsAndthe value of time, j, represents the imaginary unit.
5. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 4, wherein the S4 comprises:
s41: the second distance frequency domain and the azimuth time domain signal B (f)r,ta) Non-space-variant multi-channel phase difference function H from scene center1(fr,ta) Multiplying to obtain a third distance frequency domain and azimuth time domain signal C (f)r,ta) Wherein, in the step (A),
the scene center non-space-variant multi-channel phase difference function H1(fr,ta) Expressed as:
wherein, Δ Rm(Rs,ta) Representing a non-space variant multi-channel reference slope distance difference;
s42: for the third distance frequency domain and the azimuth time domain signal C (f)r,ta) Performing inverse Fourier transform on the distance to obtain a second distance time domain and azimuth time domain signal C' (t)r,ta) Wherein, in the step (A),
the second distance and azimuth time domain signals C' (t)r,ta) Expressed as:
wherein R'm＝Rm-ΔRm(Rs,ta)-k1(Rs)ta；
S43: the second distance and azimuth time domain signals C' (t)r,ta) And space variant multi-channel phase difference function H2(tr,ta) Multiplying to obtain a third distance time domain and azimuth time domain signal C ″ (t)r,ta) As the compensation signal, there is, among others,
the space-variant multi-channel phase difference function H2(tr,ta) Expressed as:
wherein, Δ Rm(r,ta)＝ΔRm(R,ta)-ΔRm(Rs,ta) Multiple channel skew difference representing non-space variation of target, R ═ R-RsRepresenting the relative position of the target distance direction to the reference point.
6. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 5, wherein the S5 comprises:
s51: for the third distance time domain and the azimuth time domain signal C ″ (t)r,ta) Performing direction Fourier transform to obtain a first distance time domain and direction frequency domain signal D (t)r,fa)；
S52: for the first distance time domain and azimuth frequency domain signal D (t)r,fa) Performing multi-channel signal matrix reconstruction processing to obtain a second distance time domain and azimuth frequency domain signal D' (t)r,fb) Wherein, in the step (A),
the second distance time domain and azimuth frequency domain signals D' (t)r,fb) Expressed as:
wherein f isb∈[-PRF/2,PRF/2]After representation reconstructionAzimuth baseband frequency, I ∈ [ I ]min,Imax]Denotes faFuzzy number of faDenotes the azimuth frequency, H (r, d)m,fb+ i · PRF) represents the channel transfer function, PRF represents the pulse repetition frequency;
s53: for the second distance time domain and azimuth frequency domain signals D' (t)r,fb) Performing Doppler spectrum reconstruction based on the improved steering matrix to obtain a third distance time domain signal D ″ (t)r,fal) As the reconstructed signal, among others,
the third distance time domain and azimuth frequency domain signal D ″ (t)r,fal) Expressed as:
D”(tr,fal)＝Wopt(r,fb)·D′(tr,fb)，
wherein f isalRepresenting the azimuth frequency, W, after reconstruction of the Doppler spectrumopt(r,fb) Representing an improved weighting matrix based on digital beamforming;
the improved weighting matrix W based on digital beam formingopt(r,fb) Expressed as:
wherein R is-1Represents the inverse of the covariance of the slant-range matrix,denotes a steering matrix, and H denotes a conjugate transpose.
7. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 6, wherein the S6 comprises:
s61: for the third distance time domain and azimuth frequency domain signal D ″ (t)r,fal) Performing range Fourier transform to obtain a first range frequency domain and azimuth frequency domain signal E (f)r,fal) Wherein, in the step (A),
the first distance frequency domain and orientation frequency domain signals E (f)r,fal) Expressed as:
wherein f isalRepresenting the azimuth frequency, phi (r; f), after reconstruction of the Doppler spectrumr,fal) Representing the residual phase of the signal;
s62: the first distance frequency domain and the direction frequency domain signals E (f)r,fal) Distance migration correction function H which is not space-variant with distancercmc(fr,fal) Multiplying to obtain a second distance frequency domain and an azimuth frequency domain signal E' (f)r,fal) Wherein, in the step (A),
the distance non-space-variant distance migration correction function Hrcmc(fr,fal) Expressed as:
Hrcmc(fr,fal)＝exp(-jΦ0(Rs；fr,fal))，
wherein phi0(Rs；fr,fal) Representing a non-null variant item;
s63: for the second distance frequency domain and the direction frequency domain signals E' (f)r,fal) Performing improved Stolt interpolation to obtain third distance frequency domain and azimuth frequency domain signals E ″ (f)r,fal) Wherein, in the step (A),
the modified Stolt interpolation operation is represented as:
wherein f isr' represents the new range frequency after Stolt interpolation, phi1(fr,fal) Representing a space variant item;
s64: for the third distance frequency domain and the azimuth frequency domain signals E ″ (f)r,fal) Distance of travelPerforming inverse Fourier transform to obtain a fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) As the second correction signal, wherein,
the fourth distance time domain and orientation frequency domain signal E' "(t)r,fal) Expressed as:
therein, Ψ (r, f)al)＝Φ(r；fr＝0,fal)-Φ0(Rs；fr＝0,fal) And denotes the phase associated with azimuthal focusing, and λ denotes the carrier wavelength.
8. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as claimed in claim 7, wherein the S7 comprises:
s71: the fourth distance time domain and orientation frequency domain signal E' (t)r,fal) And a time dimension spectrum compression function HTSC(fal) Multiplying to obtain a fifth distance time domain and azimuth frequency domain signal F (t)r,fal) Wherein, in the step (A),
the time dimension spectrum compression function HTSC(fal) Expressed as:
HTSC(fal)＝exp(jΦ0(Rs；fr＝0,fal))；
s72: the fifth distance time domain and azimuth frequency domain signals F (t)r,fal) And frequency domain nonlinear scaling function HNCS(fal) Multiplying to obtain a sixth distance time domain and azimuth frequency domain signal F' (t)r,fal) Wherein, in the step (A),
the frequency domain nonlinear scaling function HNCS(fal) Expressed as:
wherein p represents a coefficient of a cubic term and q represents a coefficient of a cubic term;
s73: for the sixth distance time domain and azimuth frequency domain signal F' (t)r,fal) Performing orientation inverse Fourier transform to obtain the two-dimensional time domain signal F ″ (t)r,tal) Wherein, talIndicating the reconstructed azimuth time.
9. The imaging method of the missile-borne large squint small-aperture multi-channel SAR as recited in claim 8, wherein the S8 comprises:
s81: applying the two-dimensional time-domain signal F ″ (t)r,tal) And azimuth SPECAN function HSPE(tal) Multiplying to obtain a fourth distance time domain and azimuth time domain signal G (t)r,tal) Wherein, in the step (A),
the azimuth SPECAN function HSPE(tal) Expressed as:
wherein h is20Correspond toPhase of (a), h30Correspond toPhase of (a), h40Correspond toThe phase of (d);
s82: for the fourth distance time domain and azimuth time domain signal G (t)r,tal) Performing azimuth Fourier transform to obtain a focus signal H (t)r,fal) Wherein, in the step (A),
the focus signal H (t)r,fal) Expressed as:
H(tr,fal)＝σ0sinc(Br(tr-2k0/c))sinc(Ta(fal-h1/2π))，
wherein σ0Representing the backscattering coefficient, h, of a ground target1Coefficients representing the first order of the signal azimuth frequency domain, BrRepresenting the distance phase bandwidth, TaDenotes the synthetic aperture time, k0Indicating the target distance to the focus position.
Technical Field
The invention belongs to the technical field of radar signal processing, and particularly relates to an imaging method of a missile-borne large squint small-aperture multi-channel SAR.
Background
Synthetic Aperture Radar (SAR) is a practical imaging Radar, can work all day long and all day long, and is widely applied to ground scene observation, ocean remote sensing and other aspects. With the development of synthetic aperture radars, the SAR is also applied to many new platforms, such as missiles, fighters and the like, and due to the characteristics of multiple tracks, advanced image acquisition, real-time imaging and the like, the large squint SAR is also widely applied to high-speed maneuvering platforms.
Under the condition that the actual resolution requirement is not high, imaging can be performed by using echo signals in a small section of aperture so as to improve the real-time performance, but when the small-aperture SAR is applied to a wide scene, the imaging effect is seriously influenced by the blurring of the azimuth direction and the distance direction. APC (Azimuth Phase Coding) can effectively solve the problem of range ambiguity, but since the filter can only move the doppler spectrum to within the Pulse Repetition Frequency (PRF), the compression effect depends greatly on the resampling rate, which also affects the real-time performance of the imaging process.
Compared with the conventional small-aperture SAR imaging, the missile-borne large-squint small-aperture multi-channel SAR is suitable for the conditions of high maneuverability and wide imaging of a maneuvering platform. Research and application of multi-channel SAR imaging algorithms mainly focus on satellite-borne and straight-line trajectory airborne aspects. For distance blurring of multi-channel SAR data, firstly, all channel signals are compensated to a phase center, then a guide matrix is established by combining a digital beam forming method, multi-channel signal joint deblurring is completed by reconstructing a Doppler spectrum, and then focusing imaging is completed by matched filtering.
However, in combination with a large squint small aperture of a maneuvering platform, the channel pointing vector in the multi-channel SAR is space-variant and the included angle with the platform velocity vector is also space-variant, which will cause the problems of nonlinearity of each channel signal spectrum and doppler spectrum aliasing.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an imaging method of a missile-borne large squint small-aperture multi-channel SAR. The technical problem to be solved by the invention is realized by the following technical scheme:
the invention provides a missile-borne large squint small-aperture multi-channel SAR imaging method, which comprises the following steps:
s1: establishing a multi-channel large squint concentric circle skew distance model;
s2: acquiring a target echo signal;
s3: performing range pulse compression processing and range walk correction processing on the target echo signal to obtain a first correction signal;
s4: compensating a scene center non-space-variant multi-channel phase difference item and a space-variant multi-channel phase difference item of the first correction signal to obtain a compensation signal;
s5: performing multi-channel signal matrix reconstruction and Doppler spectrum reconstruction based on an improved steering matrix on the compensation signal to obtain a reconstructed signal;
s6: performing range migration correction processing and Stolt interpolation difference processing on the reconstructed signal to obtain a second correction signal;
s7: performing azimuth time spectrum compression processing and frequency domain nonlinear scaling processing on the second correction signal to obtain a two-dimensional time domain signal;
s8: carrying out azimuth SPECAN processing on the two-dimensional time domain signal to obtain a focusing signal;
s9: and carrying out geometric deformation interpolation correction processing on the focusing signal to obtain an SAR imaging image.
In one embodiment of the present invention, the instantaneous slope distance of the multi-channel large squint concentric circle slope distance model includes a fourth order taylor series of the slope distance of the array center and a second order taylor series of the multi-channel difference, in the S1:
speed of radar platformAnd constant accelerationAlong the edgeCurve moves TaThe synthetic aperture time of (2) each channel on the radar platform is defined as CHmM1, 2, …, M, when the radar is in azimuthTime taWhen equal to 0, the central channel CH1The sub-satellite point is the origin of coordinates O, and the central channel beam is pointedDefine the X axis andis a yaw angle thetayawThe Q point is different in azimuth from the P pointA point of (1), wherein
Radar platform in curveWhen point C is above, the azimuth time is defined as taThe four-step Meglanlin series of the instantaneous slope distance is as follows:
wherein the content of the first and second substances,indicating radar center channel at taInstantaneous slope of time, taRepresenting azimuth time, i representing the expansion order, R representing the reference slope,coefficients representing the terms after Taylor expansion;
the instantaneous skew difference between the reference channel and the mth channel is expressed as:
wherein d ismDenotes the distance, R, of the mth channel from the reference channeld(dm,taR) represents the instantaneous slope difference, σ0(dmR) represents the zero-order coefficient, σ, after Taylor expansion1(dmR) represents the coefficient of the first order term after Taylor expansion, σ2(dmR) represents coefficients of quadratic terms after Taylor expansion;
the instantaneous skew of the mth channel is expressed as:
in an embodiment of the present invention, the S2 includes:
acquiring a first distance time domain and an orientation time domain signal A (t) of a target echo signalr,ta) For the first distance time domain and the azimuth time domain signal A (t)r,ta) Fourier transform of distance direction is carried out to obtain a first distance frequency domain and azimuth time domain signal A' (f)r,ta) Wherein, in the step (A),
the first distance frequency domain and azimuth time domain signals A' (f)r,ta) Expressed as:
wherein, trRepresenting distance time, taIndicating the azimuth time, frDenotes the distance frequency, Wr(. represents the envelope of the distance to the frequency domain, wa(. for) the azimuth time-domain envelope, c the speed of light, fcRepresenting the carrier frequency and gamma representing the tuning frequency.
In an embodiment of the present invention, the S3 includes:
the first distance frequency domain and the azimuth time domain signal A' (f) are processedr,ta) Respectively and distance pulse compression function HRC(fr,ta) And distance walk correction function HRWC(fr,ta) Performing dot multiplication to obtain a second distance frequency domainAnd an azimuth time domain signal B (f)r,ta) As the first correction signal, wherein,
the distance pulse compression function HRC(fr,ta) And the distance walk correction function HRWC(fr,ta) Respectively expressed as:
HRWC(fr,ta)＝exp(j4π(fc+fr)k10(Rs)ta/c)，
wherein R issDenotes the reference slope, k10(Rs) To representWhere R is RsAndthe value of time, j, represents the imaginary unit.
In an embodiment of the present invention, the S4 includes:
s41: the second distance frequency domain and the azimuth time domain signal B (f)r,ta) Non-space-variant multi-channel phase difference function H from scene center1(fr,ta) Multiplying to obtain a third distance frequency domain and azimuth time domain signal C (f)r,ta) Wherein, in the step (A),
the scene center non-space-variant multi-channel phase difference function H1(fr,ta) Expressed as:
wherein, Δ Rm(Rs,ta) Representing a non-space variant multi-channel reference slope distance difference;
s42: for the third distance frequency domain and the azimuth time domain signalC(fr,ta) Performing inverse Fourier transform on the distance to obtain a second distance time domain and azimuth time domain signal C' (t)r,ta) Wherein, in the step (A),
the second distance and azimuth time domain signals C' (t)r,ta) Expressed as:
wherein R'm＝Rm-ΔRm(Rs,ta)-k1(Rs)ta；
S43: the second distance and azimuth time domain signals C' (t)r,ta) And space variant multi-channel phase difference function H2(tr,ta) Multiplying to obtain a third distance time domain and azimuth time domain signal C' (t)r,ta) As the compensation signal, there is, among others,
the space-variant multi-channel phase difference function H2(tr,ta) Expressed as:
wherein, Δ Rm(r,ta)＝ΔRm(R,ta)-ΔRm(Rs,ta) Multiple channel skew difference representing non-space variation of target, R ═ R-RsRepresenting the relative position of the target distance direction to the reference point.
In an embodiment of the present invention, the S5 includes:
s51: for the third range and azimuth time domain signals C' (t)r,ta) Performing direction Fourier transform to obtain a first distance time domain and direction frequency domain signal D (t)r,fa)；
S52: for the first distance time domain and azimuth frequency domain signal D (t)r,fa) Carrying out multi-channel signal matrix reconstruction processing to obtainSecond distance time domain and azimuth frequency domain signals D' (t)r,fb) Wherein, in the step (A),
the second distance time domain and azimuth frequency domain signals D' (t)r,fb) Expressed as:
wherein f isb∈[-PRF/2,PRF/2]Representing the reconstructed azimuth baseband frequency, I ∈ [ I ∈ [ ]min,Imax]Denotes faFuzzy number of faDenotes the azimuth frequency, H (r, d)m,fb+ i · PRF) represents the channel transfer function, PRF represents the pulse repetition frequency;
s53: for the second distance time domain and azimuth frequency domain signals D' (t)r,fb) Performing Doppler spectrum reconstruction based on the improved steering matrix to obtain a third distance time domain signal D '(t) and an azimuth frequency domain signal D' (t)r,fal) As the reconstructed signal, among others,
the third distance time domain and azimuth frequency domain signal D' (t)r,fal) Expressed as:
D″(tr,fal)＝Wopt(r,fb)·D′(tr,fb)，
wherein f isalRepresenting the azimuth frequency, W, after reconstruction of the Doppler spectrumopt(r,fb) Representing an improved weighting matrix based on digital beamforming;
the improved weighting matrix W based on digital beam formingopt(r,fb) Expressed as:
wherein R is-1Represents the inverse of the covariance of the slant-range matrix,representing steering matrices, H tablesThe conjugate transpose is shown.
In an embodiment of the present invention, the S6 includes:
s61: for the third distance time domain and azimuth frequency domain signal D' (t)r,fal) Performing range Fourier transform to obtain a first range frequency domain and azimuth frequency domain signal E (f)r,fal) Wherein, in the step (A),
the first distance frequency domain and orientation frequency domain signals E (f)r,fal) Expressed as:
wherein f isalRepresenting the azimuth frequency, phi (r; f), after reconstruction of the Doppler spectrumr,fal) Representing the residual phase of the signal;
s62: the first distance frequency domain and the direction frequency domain signals E (f)r,fal) Distance migration correction function H which is not space-variant with distancercmc(fr,fal) Multiplying to obtain a second distance frequency domain and an azimuth frequency domain signal E' (f)r,fal) Wherein, in the step (A),
the distance non-space-variant distance migration correction function Hrcmc(fr,fal) Expressed as:
Hrcmc(fr,fal)＝exp(-jΦ0(Rs；fr,fal))，
wherein phi0(Rs；fr,fal) Representing a non-null variant item;
s63: for the second distance frequency domain and the direction frequency domain signals E' (f)r,fal) Performing improved Stolt interpolation to obtain a third distance frequency domain and azimuth frequency domain signal E' (f)r,fal) Wherein, in the step (A),
the modified Stolt interpolation operation is represented as:
wherein f isr' represents the new range frequency after Stolt interpolation, phi1(fr,fal) Representing a space variant item;
s64: for the third distance and azimuth frequency domain signals E' (f)r,fal) Performing inverse Fourier transform on the distance to obtain a fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) As the second correction signal, wherein,
the fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) Expressed as:
therein, Ψ (r, f)al)＝Φ(r；fr＝0,fal)-Φ0(Rs；fr＝0,fal) And denotes the phase associated with azimuthal focusing, and λ denotes the carrier wavelength.
In an embodiment of the present invention, the S7 includes:
s71: the fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) And a time dimension spectrum compression function HTSC(fal) Multiplying to obtain a fifth distance time domain and azimuth frequency domain signal F (t)r,fal) Wherein, in the step (A),
the time dimension spectrum compression function HTSC(fal) Expressed as:
HTSC(fal)＝exp(jΦ0(Rs；fr＝0,fal))；
s72: the fifth distance time domain and azimuth frequency domain signals F (t)r,fal) And frequency domain nonlinear scaling function HNCS(fal) Multiplying to obtain a sixth distance time domain and azimuth frequency domain signal F' (t)r,fal) Wherein, in the step (A),
the frequency domain nonlinear scaling function HNCS(fal) Expressed as:
wherein p represents a coefficient of a cubic term and q represents a coefficient of a cubic term;
s73: for the sixth distance time domain and azimuth frequency domain signal F' (t)r,fal) Performing the direction inverse Fourier transform to obtain the two-dimensional time domain signal F' (t)r,tal) Wherein, talIndicating the reconstructed azimuth time.
In an embodiment of the present invention, the S8 includes:
s81: the two-dimensional time domain signal F' (t)r,tal) And azimuth SPECAN function HSPE(tal) Multiplying to obtain a fourth distance time domain and azimuth time domain signal G (t)r,tal) Wherein, in the step (A),
the azimuth SPECAN function HSPE(tal) Expressed as:
wherein h is20Correspond toPhase of (a), h30Correspond toPhase of (a), h40Correspond toThe phase of (d);
s82: for the fourth distance time domain and azimuth time domain signal G (t)r,tal) Performing azimuth Fourier transform to obtain a focus signal H (t)r,fal) Wherein, in the step (A),
the focus signal H (tr,fal) Expressed as:
H(tr,fal)＝σ0sinc(Br(tr-2k0/c))sinc(Ta(fal-h1/2π))，
wherein σ0Representing the backscattering coefficient, h, of a ground target1Coefficients representing the first order of the signal azimuth frequency domain, BrRepresenting the distance phase bandwidth, TaDenotes the synthetic aperture time, k0Indicating the target distance to the focus position.
Compared with the prior art, the invention has the beneficial effects that:
1. the imaging method of the missile-borne large-squint small-aperture multi-channel SAR takes a maneuvering platform as a background, establishes a multi-channel large-squint concentric circle slant range model, adopts four-order Taylor series approximate instantaneous slant range for the center of an array, adopts second-order Taylor series expansion for multi-channel difference, reduces the error of reference slant range in the imaging process of the multi-channel SAR, and better adapts to a multi-channel-loaded high maneuvering motion track in real time.
2. The imaging method of the missile-borne large-squint small-aperture multi-channel SAR disclosed by the invention solves the problem that joint processing cannot be carried out due to the phase difference between channels by a method of compensating the non-space-variant multi-channel phase difference through a distance frequency domain and compensating the space-variant multi-channel phase difference through a distance time domain.
3. The missile-borne large squint small-aperture multi-channel SAR imaging method solves the problem of insufficient azimuth bandwidth of a large squint small-aperture motorized platform through multi-channel signal matrix reconstruction and Doppler spectrum reconstruction based on an improved guide matrix, completes the reconstruction of multi-channel SAR signals, and has good effect and application value in the large squint SAR imaging of the motorized platform.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.
Drawings
Fig. 1 is a block flow diagram of an imaging method of a missile-borne large squint small-aperture multi-channel SAR according to an embodiment of the present invention;
fig. 2 is a schematic flowchart of an imaging method of a missile-borne large squint small-aperture multi-channel SAR according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a large squint multi-channel concentric circle slant range model provided by an embodiment of the invention;
FIG. 4 is a schematic diagram of time-frequency line analysis of a multi-channel phase difference correction effect according to an embodiment of the present invention;
FIG. 5 is a diagram of an azimuth time-domain spectrum compression time-frequency analysis provided in an embodiment of the present invention;
FIG. 6 is a schematic diagram of a simulated target distribution according to an embodiment of the present invention;
fig. 7 is a schematic diagram illustrating analysis of a simulated target range migration correction result according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of an analysis of a simulation target time domain spectrum compression process according to an embodiment of the present invention;
fig. 9 is a contour diagram of a simulation target according to an embodiment of the present invention.
Detailed Description
In order to further explain the technical means and effects of the present invention adopted to achieve the predetermined object, the following describes in detail an imaging method of a missile-borne large squint small aperture multi-channel SAR according to the present invention with reference to the accompanying drawings and the detailed description.
The foregoing and other technical matters, features and effects of the present invention will be apparent from the following detailed description of the embodiments, which is to be read in connection with the accompanying drawings. The technical means and effects of the present invention adopted to achieve the predetermined purpose can be more deeply and specifically understood through the description of the specific embodiments, however, the attached drawings are provided for reference and description only and are not used for limiting the technical scheme of the present invention.
Example one
Referring to fig. 1 and fig. 2 collectively, fig. 1 is a block flow diagram of an imaging method of a missile-borne large squint small-aperture multi-channel SAR according to an embodiment of the present invention; fig. 2 is a schematic flow diagram of an imaging method of a missile-borne large squint small-aperture multi-channel SAR according to an embodiment of the present invention. As shown in the figure, the imaging method of the present embodiment includes:
s1: establishing a multi-channel large squint concentric circle skew distance model;
in the present embodiment, the instantaneous slope distance of the multi-channel large squint concentric circle slope distance model includes a fourth order taylor series of the slope distance of the array center and a second order taylor series of the multi-channel difference.
Referring to fig. 3, fig. 3 is a schematic diagram of a large squint multi-channel concentric circle slant-distance model according to an embodiment of the present invention. As shown in the figure, the multi-channel large squint concentric circle slant-distance model of the present embodiment is a time-frequency spectrum reconstructed large squint imaging geometric model of the maneuvering trajectory, and specifically, in S1:
setting the synthetic aperture time T of a radar platformaInner curveAt a velocity vectorAnd constant acceleration vectorAnd (6) moving. An antenna array of M channels, each channel defined as CH, is provided on a radar platformmAnd M is 1,2, …, M. Each channel on the antenna can receive signals, and the central channel CH1Transmitting chirp signals, i.e. CH1Also as signal transmission channels (fig. 2 shows only three channels for simplicity of illustration).
The orientation of the array of channels is time-varying, when the radar is at azimuth time taWhen equal to 0, the radar platform is located at position B and the central channel CH1The sub-satellite point is the origin of coordinates O, and the central channel beam is pointedDefine the X axis andis the yaw angle theta of the radar systemyaw. Point P is any point on the yaw line and is a distance R from the radar platform position at time zero. The point Q is any point on the ring equidistant from P, so OP ═ OQ, the azimuth angle between themThat is, the Q point is different in azimuth from the P pointA point of (1), wherein
When radar platform is at azimuth time taTime arrives at point C, signal transmission channel CH1The instantaneous slope distance can be expanded to a fourth-order craolins series:
wherein the content of the first and second substances,indicating radar center channel at taInstantaneous slope of time, taRepresenting azimuth time, i representing the expansion order, R representing the reference slope,coefficients representing the terms after taylor expansion,is shown at taThe i-th derivative at 0;
it can be seen that each sub-term coefficientAbout a reference slope distance R and an azimuth angleTwo-dimensional space-variant parameters, so coefficientCan be arranged inCarrying out Mefroline expansion:
wherein i is 1,2,3,4, j is 0,1, … 4-i, kij(R) is represented inThe derivatives of the orders of (a).
The instantaneous skew of the mth lane can then be expressed as:
wherein the content of the first and second substances,representing a unit vector co-directional with the channel spacing.
Since the platform track and the channel position can be obtained by the inertial navigation system, the signal transmitting channel CH1The difference in skew from the mth channel can be expressed as azimuth time taA second order polynomial of:
wherein d ismDenotes the distance, R, of the mth channel from the reference channeld(dm,taR) represents the instantaneous slope difference, σ0(dmR) represents the zero-order coefficient, σ, after Taylor expansion1(dmR) represents the coefficient of the first order term after Taylor expansion, σ2(dmR) represents coefficients of quadratic terms after Taylor expansion;
it should be noted that, in this embodiment, the signal transmission channel CH1As a reference channel.
In the present embodiment, the coefficient σi(dmR), i ═ 0,1,2 can be obtained by curve fitting, so the two-step development instant slope distance of the mth channel is:
as can be seen from the above formula, the signal transmission channel CH1The skew distance between the m-th channel is distance-coupled and orientation space-variant.
S2: acquiring a target echo signal;
in the embodiment, the SAR radar is in the signal transmission channel CH1Transmitting a chirp signal from each channel CHmReceiving a target echo signal, specifically, S2 includes:
acquiring a first distance time domain and an orientation time domain signal A (t) of a target echo signalr,ta) It can be expressed as:
wherein, wrDenotes the distance time-domain envelope, wa(. x) denotes azimuth time-domain envelope, c denotes speed of light, λ denotes carrier wavelength, j denotes imaginary unit, tmIndicating the azimuth time.
For the first distance time domain and the azimuth time domain signal A (t)r,ta) Fourier transform of distance direction is carried out to obtain a first distance frequency domain and azimuth time domain signal A' (f)r,ta) Wherein, in the step (A),
first distance frequency domain and azimuth time domain signals A' (f)r,ta) Expressed as:
wherein, trRepresenting distance time, taIndicating the azimuth time, frDenotes the distance frequency, Wr(. represents the envelope of the distance to the frequency domain, wa(. X) denotes azimuth time-domain envelope, c denotes speed of light, fcRepresenting the carrier frequency and gamma representing the tuning frequency.
It should be noted that in this example, the conventional reconstruction means is used to convert the skew distance into:
wherein, Δ Rm(R,ta) Representing the varying and time-varying portions of the multi-channel phase difference that need to be compensated for.
S3: performing range pulse compression processing and range walk correction processing on the target echo signal to obtain a first correction signal;
specifically, S3 includes:
the first distance frequency domain and the azimuth time domain signal A' (f) are processedr,ta) Respectively and distance pulse compression function HRC(fr,ta) And distance walk correction function HRWC(fr,ta) Performing point multiplication to obtain a second distance frequency domain and orientation time domain signal B (f)r,ta) As a first correction signal, in which,
distance pulse compression function HRC(fr,ta) And distance walk correction function HRWC(fr,ta) Respectively expressed as:
wherein R issDenotes the reference slope, k10(Rs) To representWhere R is RsAndthe value of time, j, represents the imaginary unit.
It should be noted that, in this embodiment, because a large squint angle generates a large doppler center, and the doppler spectrum width also exceeds the azimuth beam width, the envelope of one target will be distributed within a plurality of range units, so that the range walk correction function is proposed in this embodiment to solve the problem caused by the large squint angle.
S4: compensating a scene center non-space-variant multi-channel phase difference item and a space-variant multi-channel phase difference item for the first correction signal to obtain a compensation signal;
specifically, S4 includes:
s41: the second distance frequency domain and the azimuth time domain signal B (f)r,ta) Non-space-variant multi-channel phase difference function H from scene center1(fr,ta) Multiplying to obtain a third distance frequency domain and azimuth time domain signal C (f)r,ta) Wherein, in the step (A),
scene center non-space-variant multi-channel phase difference function H1(fr,ta) Expressed as:
wherein, Δ Rm(Rs,ta) Indicating a non-space variant multi-channel reference slope difference, i.e. when R-RsΔ R of (g)m(R,ta) (ii) a After this step, the non-space-variant multi-channel phase differences in the signal that are independent of distance are eliminated.
S42: for the third distance frequency domain and the azimuth time domain signal C (f)r,ta) Performing inverse Fourier transform on the distance to obtain a second distance time domain and azimuth time domain signal C' (t)r,ta) Wherein, in the step (A),
second range and azimuth time domain signals C' (t)r,ta) Expressed as:
wherein R'm＝Rm-ΔRm(Rs,ta)-k1(Rs)ta；
S43: the second distance time domain and azimuth time domain signals C' (t)r,ta) And space variant multi-channel phase difference function H2(tr,ta) Multiplying to obtain a third distance time domain and azimuth time domain signal C' (t)r,ta) As a compensation signal, among other things,
space-variant multi-channel phase difference function H2(tr,ta) Expressed as:
wherein, Δ Rm(r,ta)＝ΔRm(R,ta)-ΔRm(Rs,ta) Multiple channel skew difference representing non-space variation of target, R ═ R-RsRepresenting the relative position of the target distance direction to the reference point.
It should be noted that, because the large squint multi-channel small-aperture SAR mounted on the mobile platform has a short synthetic aperture time, the signals of a single target will be gathered in the same range unit after the range walk correction, so that the space-variant multi-channel phase difference function H can be used2(tr,ta) To correct for. By step S4, the distance-varying and time-varying multi-channel phase differences are compensated, so that spectral reconstruction can be done within a single distance cell.
S5: performing multi-channel signal matrix reconstruction and Doppler spectrum reconstruction based on the improved steering matrix on the compensation signal to obtain a reconstructed signal;
specifically, S5 includes:
s51: for the third distance time domain and azimuth time domain signal C' (t)r,ta) Performing direction Fourier transform to obtain a first distance time domain and direction frequency domain signal D (t)r,fa)；
Specifically, after multi-channel phase difference compensation, the skew distance of the mth channel can be expressed as:
wherein R isref(ta) Represents the reference channel slope distance after the distance walk correction, so the doppler spectrum of the mth channel can be represented as:
Dm(tr,fa)＝Sref(r,fa)H(r,dm,fa) (14)，
channel transfer function H (r, d) in Doppler spectrumm,fa) Can be expressed as:
it can be seen that the steering vector index phase and the azimuth frequency faTherefore, after the compensation of the multi-channel phase difference, please refer to fig. 4, where fig. 4 is a schematic diagram of time-frequency line analysis of the multi-channel phase difference correction effect provided in the embodiment of the present invention, in which (a) represents a time-frequency diagram before the multi-channel phase difference correction, and (b) represents a time-frequency diagram after the multi-channel phase difference correction, and as shown in (b) of fig. 4, a curve of the time-frequency line becomes a straight line.
S52: for the first distance time domain and the azimuth frequency domain signal D (t)r,fa) Performing multi-channel signal matrix reconstruction processing to obtain a second distance time domain and azimuth frequency domain signal D' (t)r,fb) Wherein, in the step (A),
second distance time domain and azimuth frequency domain signals D' (t)r,fb) Expressed as:
wherein f isb∈[-PRF/2,PRF/2]Representing the reconstructed azimuth baseband frequency, I ∈ [ I ∈ [ ]min,Imax]Denotes faFuzzy number of faDenotes the azimuth frequency, H (r, d)m,fb+ i · PRF) represents the channel transfer function, PRF represents the pulse repetition frequency;
then the Doppler spectrum of all channels is relative to the azimuth baseband frequency fbCan be expressed as:
wherein, S (r, f)b) Is an m × 1 signal vector, N (r, f)b) Is an m × 1 noise vector.
S53: for the second distance time domain and azimuth frequency domain signal D' (t)r,fb) Performing Doppler spectrum reconstruction based on the improved steering matrix to obtain a third distance time domain signal D '(t) and an azimuth frequency domain signal D' (t)r,fal) As a reconstructed signal, among others,
third distance time domain and azimuth frequency domain signal D' (t)r,fal) Expressed as:
D″(tr,fal)＝Wopt(r,fb)·D′(tr,fb) (18)，
wherein f isalRepresenting the azimuth frequency, W, after reconstruction of the Doppler spectrumopt(r,fb) Representing an improved weighting matrix based on digital beamforming;
improved weighting matrix W based on digital beam formingopt(r,fb) Expressed as:
wherein R is-1Represents the inverse of the covariance of the slant-range matrix,denotes a steering matrix, and H denotes a conjugate transpose.
In this embodiment, to reconstruct the blurred doppler spectrum, the steering matrix may be constructed as:
wherein A (r, f)b) Is a m × 1 vector, ai(r) is the steering vector expressed as:
while the blurred portion of the reference channel may be expressed as:
combining equations (16-17) and (20-22), the signal matrix can be represented as:
S(r,fb)＝A(r,fb)·Sref(r,fb)+N(fb) (23)，
since the present embodiment utilizes the algorithm of Doppler spectrum reconstruction, S is determined byref(r,fb) The fuzzy part of the signal is compensated to obtain equivalent single-channel non-fuzzy signal, and the azimuth sampling rate is improved by N times, namely the PRF of the new signalII-PRF, wherein I-Imax-Imin+1 is the doppler ambiguity number.
S6: performing range migration correction processing and Stolt interpolation difference processing on the reconstructed signal to obtain a second correction signal;
specifically, S6 includes:
s61: for the third distance time domain and azimuth frequency domain signal D' (t)r,fal) Performing range Fourier transform to obtain a first range frequency domain and azimuth frequency domain signal E (f)r,fal) Wherein, in the step (A),
first distance frequency domain and azimuth frequency domain signals E (f)r,fal) Expressed as:
wherein f isalRepresenting the azimuth frequency, phi (r; f), after reconstruction of the Doppler spectrumr,fal) Representing the residual phase of the signal;
in addition, the signal residual phase phi (r; f)r,fal) Expressed as:
wherein the content of the first and second substances,indicating the reference azimuth phase center.
In the embodiment, the range migration of the range space-variant can be solved by the block range migration correction, so the azimuth space-variant of the range migration in the range-oriented processing can be ignored, and only the linear range space-variant needs to be considered. Therefore, the coefficient in the pitch model of the present embodiment may be R ═ RsThe Taylor expansion is:
s62: the first distance frequency domain and the direction frequency domain signal E (f)r,fal) Distance migration correction function H which is not space-variant with distancercmc(fr,fal) Multiplying to obtain the second distance frequency domain and the azimuth frequency domainNumber E' (f)r,fal) Wherein, in the step (A),
in this embodiment, to resolve range migration, the signal is left in the remaining phase Φ (r; f)r,fal) The deployment is in two parts:
Φ(r；fr,fal)＝Φ0(Rs；fr,fal)+Φ1(fr,fal)r (27)，
wherein phi0(Rs；fr,fal) Representing non-space-variant terms,. phi1(fr,fal) Representing a null term.
Therefore, in this embodiment, the range non-space-varying range migration correction function Hrcmc(fr,fal) Expressed as:
Hrcmc(fr,fal)＝exp(-jΦ0(Rs；fr,fal)) (28)，
s63: for the second distance frequency domain and the direction frequency domain signal E' (f)r,fal) Performing improved Stolt interpolation to obtain a third distance frequency domain and azimuth frequency domain signal E' (f)r,fal) Wherein, in the step (A),
the modified Stolt interpolation operation is represented as:
wherein f isr' represents the new range frequency after Stolt interpolation;
s64: for the third distance frequency domain and the azimuth frequency domain signal E' (f)r,fal) Performing inverse Fourier transform on the distance to obtain a fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) As the second correction signal, wherein,
fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) Expressed as:
therein, Ψ (r, f)al) Indicating the phase associated with the azimuthal focus, and lambda the carrier wavelength, specifically,
Ψ(r,fal)＝Φ(r；fr＝0,fal)-Φ0(Rs；fr＝0,fal) (31)。
it should be noted that since the targets share the reference tilt focused on the same range bin on the same concentric circle, the parameters of the azimuth process can be updated according to each range bin.
S7: carrying out azimuth time spectrum compression processing and frequency domain nonlinear scaling processing on the second correction signal to obtain a two-dimensional time domain signal;
specifically, S7 includes:
s71: a fourth distance time domain and azimuth frequency domain signal E' (t)r,fal) And a time dimension spectrum compression function HTSC(fal) Multiplying to obtain a fifth distance time domain and azimuth frequency domain signal F (t)r,fal)，
Specifically, for small synthetic aperture data, the azimuth should focus the target in the azimuth frequency domain using a time dimension spectral analysis (SPECAN) approach. However due to the superposition of the reference phases in equation (28). Referring to fig. 5, fig. 5 is a diagram of an azimuthal time-domain spectrum compression time-frequency analysis according to an embodiment of the present invention, where (a) shows a result diagram of time-frequency lines of different targets rotated by an angle α, (b) shows a time-frequency diagram of a time-domain spectrum compression function, and (c) shows a result diagram of time-domain spectrum compression, where as shown in (b) of fig. 5, time-frequency lines of different targets are rotated by an angle α, that is, time-dimensional spectrum expansion is generated. Without the zero-padding operation, the signal will produce aliasing in the azimuth time domain. Therefore, a time-dimension spectrum compression function is proposed to solve the problem of azimuth time-domain aliasing.
Wherein, the time dimension spectrum compression function HTSC(fal) Expressed as:
HTSC(fal)＝exp(jΦ0(Rs；fr＝0,fal)) (32)；
in the present embodiment, after the signal is multiplied by the time-dimensional spectrum compression function, as shown in (c) of fig. 5, the time-frequency spectrum of each target is rotated by an angle α, so that the problem of aliasing of the azimuth time-domain spectrum is solved.
S72: the fifth distance time domain and azimuth frequency domain signal F (t)r,fal) And frequency domain nonlinear scaling function HNCS(fal) Multiplying to obtain a sixth distance time domain and azimuth frequency domain signal F' (t)r,fal)。
The phase of the signal after the azimuth time domain spectrum compression can be expressed as:
wherein f isdr＝2(k1-k10) And/λ, which represents the doppler center of the azimuthal space variation. In order to correct the direction space variation of the Doppler center, the implementation provides a frequency domain nonlinear scaling function HNCS(fal) Expressed as:
wherein p represents a coefficient of a cubic term and q represents a coefficient of a cubic term;
after the azimuth inverse fourier transform, the phase of the signal is represented in the time domain as:
wherein h is1taIThe linear term representing the phase represents the position of the focus, and other terms affect the focusing effect in higher order. In order to obtain specific coefficients of the frequency domain nonlinear scaling function, coefficients of the quadratic term in the higher-order term may again be related to azimuth angleThe expansion is as follows:
space variant term h in orientation time quadratic term21And h22When the value is zero, a coefficient p of the cubic term and a coefficient q of the cubic term can be obtained, specifically:
s73: for the sixth distance time domain and azimuth frequency domain signal F' (t)r,fal) Performing the direction inverse Fourier transform to obtain a two-dimensional time domain signal F' (t)r,tal) Wherein, talIndicating the reconstructed azimuth time.
S8: carrying out azimuth SPECAN processing on the two-dimensional time domain signal to obtain a focusing signal;
specifically, S8 includes:
s81: two-dimensional time domain signal F' (t)r,tal) And azimuth SPECAN function HSPE(tal) Multiplying to obtain a fourth distance time domain and azimuth time domain signal G (t)r,tal) Wherein, in the step (A),
azimuth SPECAN function HSPE(tal) Expressed as:
wherein h is20Correspond toPhase of (a), h30Correspond toPhase of (a), h40Correspond toThe phase of (d);
s82: for the fourth distance time domain and the azimuth time domain signal G (t)r,tal) Performing azimuth Fourier transform to obtain a focus signal H (t)r,fal) Wherein, in the step (A),
focus signal H (t)r,fal) Expressed as:
H(tr,fal)＝σ0sinc(Br(tr-2k0/c))sinc(Ta(fal-h1/2π)) (39)，
wherein σ0Representing the backscattering coefficient, h, of a ground target1Coefficients representing the first order of the signal azimuth frequency domain, BrRepresenting the distance phase bandwidth, TaDenotes the synthetic aperture time, k0Indicating the target distance to the focus position.
S9: and carrying out geometric deformation interpolation correction processing on the focusing signal to obtain an SAR radar imaging image.
The imaging method of the missile-borne large-squint small-aperture multi-channel SAR in the embodiment is characterized in that a multi-channel large-squint concentric circle slant range model is established by taking a maneuvering platform as a background, a four-order Taylor series approximate instantaneous slant range is adopted for the center of an array, and a second-order Taylor series expansion is adopted for multi-channel difference, so that the error of a reference slant range in the multi-channel SAR imaging process is reduced, and the multi-channel high-maneuvering motion track is better adapted in real time.
Moreover, the problem that joint processing cannot be carried out due to the phase difference between the channels is solved by a method for compensating the non-space-variant multi-channel phase difference through the distance frequency domain and compensating the space-variant multi-channel phase difference through the distance time domain. By multi-channel signal matrix reconstruction and Doppler spectrum reconstruction based on the improved guide matrix, the problem of insufficient azimuth bandwidth of the large squint small-aperture mobile platform is solved, multi-channel SAR signal reconstruction is completed, and the method has good effect and application value in large squint SAR imaging of the mobile platform.
Example two
In this embodiment, simulation experiment verification is performed on the missile-borne large squint small-aperture multi-channel SAR imaging method of the first embodiment.
1. Simulation conditions
The experimental simulation parameters are shown in table 1, the distance direction width and the azimuth direction width are respectively 3km and 6km, the distribution of point targets is shown in fig. 6, and fig. 6 is a simulated target distribution schematic diagram provided by the embodiment of the invention.
TABLE 1 SAR simulation parameters
2. Simulation content and result analysis
Simulation 1:
referring to fig. 7, fig. 7 is a schematic diagram illustrating analysis of a simulated target range migration correction result according to an embodiment of the present invention. The left graph in fig. 7 shows the result of range migration correction in a conventional manner, the right graph shows the result of range migration correction in this embodiment, and (a) in fig. 7 shows an object a1The distance migration correction result of (a), FIG. 7 is a target B2The distance migration correction result of (a), FIG. 7 (C) is a target C3And (4) a distance migration correction result. As can be seen from the figure, the result graph on the right side has better focusing effect in the distance direction than the result graph in the left conventional mode, and therefore, the effectiveness of the improved Omega-K mode for correcting the distance migration is proved.
Referring to fig. 8, fig. 8 is a schematic diagram of analysis of a time domain spectrum compression process of a simulation target according to an embodiment of the present invention, where fig. 8 (a) is a time-frequency line before time-dimension spectrum compression, it can be seen that aliasing is generated in an azimuth time domain by a target, and target points that should be distributed on two sides are folded to the middle due to insufficient azimuth time spectrum. Fig. 8 (b) is a time-frequency line after time-dimension spectrum compression, and it can be seen that aliasing of the target in the azimuth time domain is eliminated, and signals of each point are sequentially arranged in the frequency spectrum. Therefore, the effectiveness of the time-dimensional spectrum compression of the present embodiment in solving the azimuth time-domain aliasing is proved.
Referring to fig. 9, fig. 9 is a contour diagram of a simulation target according to an embodiment of the present invention, and fig. 9 shows a two-dimensional cross-sectional view of nine points located at different positions and different distances. FIG. 9 (a) shows three points A located on the same distance ring in the order from left to right1，B1And C1A cross-sectional view of the simulation result of (1); the diagram (b) in FIG. 9 shows three points A located on the distance ring from the center of the scene in sequence from left to right2，B2And C2A cross-sectional view of the simulation result of (1); in FIG. 9, (c) shows three points A located on the distant ring in the order from left to right3，B3And C3Cross-sectional view of the simulation result.
As can be seen from the figure, the quality of the target of the imaging point obtained by the method proposed in this embodiment is good, and in order to further evaluate the performance of the proposed focusing algorithm, the present embodiment lists the measurement parameters of the target in table 2, and the windowless ideal values of the Peak side lobe Ratio (PSLR, Peak Sidelobe Ratio) and the Integrated Sidelobe Ratio (ISLR) are-13.26 dB and-10.8 dB, respectively, so that the focusing performance of the method proposed in this embodiment approaches the ideal value.
TABLE 2 Point target Focus Performance evaluation
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or device that comprises a list of elements does not include only those elements but may include other elements not expressly listed. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of additional like elements in the article or device comprising the element.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：一种斜视聚束SAR成像的频域自聚焦方法