CN107085213A - The moving target ISAR imaging methods designed based on random Based on Modulated Step Frequency Waveform - Google Patents
The moving target ISAR imaging methods designed based on random Based on Modulated Step Frequency Waveform Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/904—SAR modes
- G01S13/9064—Inverse SAR [ISAR]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/904—SAR modes
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Abstract
The invention belongs to the high-resolution imaging technical field in radar electronic warfare, a kind of disclosed moving target ISAR imaging methods designed based on random Based on Modulated Step Frequency Waveform, it is primarily based on phase cancellation and pulse recurrence interval is pre-designed and ISAR transmitted waveforms are designed, secondly subpulse compression processing is carried out using matched filtering, solution line frequency modulation or compression sensing method, obtains coarse resolution Range Profile Sequence；Then, equivalent measurement matrix is constructed, compression is handled between carrying out arteries and veins using compression sensing method, obtains the High Range Resolution of target.Obtain after the High Range Resolution sequence under different observation visual angles, orientation processing is carried out by compression sensing method, obtain the two-dimentional ISAR images of target.Present invention effectively prevents the influence that target motion synthesizes High Range Resolution compression arteries and veins, without the prior information of the parameters of target motion, the size of target velocity is insensitive to, image quality can be improved while data volume needed for reducing imaging.
Description
Technical field
The invention belongs to the high-resolution imaging technical field in radar electronic warfare random Based on Modulated Step Frequency Waveform is based on there is provided one kind
The moving target ISAR imaging methods of design, are particularly suitable for use in the high-resolution imaging of space/moving air target.
Background technology
ISAR (Inverse Synthetic Aperture Radar, ISAR) imaging technique is in radar mesh
Identify other field and play extremely important effect, particularly there is extensive in terms of space exploration, ballistic missile defense
Using.ISAR imagings obtain distance to high-resolution by being compressed to wideband radar echo, further using the rotation of target,
Orientation/pitching is realized to high-resolution using bore diameter synthesizing technology, is generally used for moving target such as aircraft, naval vessel, guided missile, defends
Star, celestial body etc. are imaged.In general, the high resolution radar imaging of moving target includes one-dimensional, two and three dimensions imaging, its
Middle one-dimensional range profile reflects projective distribution of the target scattering center in radar line of sight direction, is two and three dimensions high resolution radar
The basis of imaging.
High-resolution one-dimensional distance imaging method depends on the signal form that radar is used, the broadband being widely adopted in practice
The main linear FM signal of radar signal, stepped frequency radar and frequency modulation stepping (Chirp Frequency-Stepped,
CFS) signal.Under different signal systems, target moves different (the Hu Jiemin complexity fortune of influence degree to radar echo signal
Moving-target high resolution radar imaging technical research [D] Changsha:The National University of Defense Technology, 2011.).The conjunction of linear FM signal
It is a pulse time width into the Range Profile time, for the low-speed motion target such as aircraft, naval vessel, moves the distance-Doppler caused
Coupling can be ignored, the target (speed is up to km/second-time) for guided missile, satellite etc. with high-speed motion, and motion is caused
Influence can not ignore, it is believed that the target uniform motion in imaging time.The conjunction of stepped frequency radar and stepped-frequency chirp signal
It is a burst periods into the Range Profile time, it is more sensitive to target motion, it usually needs to consider target velocity and acceleration
Influence, that is, synthesize Range Profile when target motion can be approximately Secondary movement.
Each subpulse of stepped-frequency chirp signal is a Chirp signal, combines frequency step and linear frequency modulation two
The advantage of signal is planted, while high Range resolution is obtained, the requirement to digital signal processor instant bandwidth is reduced, simultaneously
Ensure that operating distance farther out, but the aggregate date rate of radar high-resolution imaging is still higher, between arteries and veins compression be sensitive to distance-
Doppler coupling (Long Teng, Mao Erke, what pendant a kind of jade Modulated Frequency Stepped Radar Signals analysis and processing [J] electronic letters, vols,
1998,26(12):84–88.).For the one-dimensional range profile composition problem of frequency modulation stepping radar moving target, existing method is mostly
Using the roadmap based on action reference variable and compensation, (Li Yachao, Liang Yi, Xing Mengdao wait to be based on linear modulated stepped frequency
ISAR parameter Estimations and imaging algorithm research [J] electronic letters, vols, 2008,36 (12):2464-2472.), this thinking is to echo
The quality of data requires higher, and calculates complicated, and estimated accuracy is difficult to meet sometimes to be required.Wideband radar high-resolution range Imaging
A kind of new way is that (Lin Yun, department's tin ability one kind changes by eliminating the influence of Doppler effect to the design of radar signal parameter
Stepped frequency radar signal performance evaluation [J] the aerospace journals entered, 2010,31 (10):2381-2387.), but current grind
Study carefully achievement only effective to conventional transmitting pulse, data user rate is relatively low.In addition, molecule pulse echo is lost in the middle part of a frame pulse string
When losing or producing wrong (contaminated), the Range Profile quality that conventional method is obtained will deteriorate.
Radar imaging method based on compressed sensing (Compressed Sensing, CS) is using less measurement data
Restructural go out target radar image (Li Shaodong, Yang Jun, Chen Wenfeng, wait radar imaging technologies of the based on compressive sensing theory with
Application study progress [J] electronics and information journal, 2016,38 (2):495-508.), to overcome above mentioned problem to provide possibility.
The principle of CS radar imagerys is, based on the openness of target echo signal, nonlinear optimization weight to be passed through using a small amount of incoherent measurement
Structure radar target image.Document " Compressive sensing and stretch processing " (Krichene HA,
Pekala M J,Sharp M D,et al.IEEE Radar Conference,Georgia,USA,2011:362-367.),
“Reconstruction ofMoving Target’sHRRP Using Sparse Frequency-Stepped Chirp
Signal”(Zhu F,Zhang Q,Lei Q,et al.IEEE Sensors Journal,2011,11(10):2327–
2334.), " A novel cognitive ISAR imaging method with random stepped frequency
chirp signal”(Zhu F,Zhang Q,Luo Y,et al.SCIECE CHINA Information Sciences,
2012,55(8):1910-1924.), " the high-resolution ISAR imaging methods based on random stepped-frequency chirp signal " (Lv Mingjiu, Lee is few
East, the electronics such as Yang Jun and information journal, 2016, Web publishing:http://www.cnki.net/kcms/detail/
11.4494.TN.20161017.1102.006.html) etc. the frequency modulation stepping ISAR imaging methods based on CS are studied,
But assume that echo has completed preferable motion compensation, influence of the target motion to synthesis Range Profile is not considered.Random frequency modulation step
Enter (Random CFS, RCFS) signal with stronger anti-interference and anti-intercepting and capturing ability, but the presence of radial velocity can cause mesh
The diverging of the broadening and energy of subject distance picture, makes target echo signal not sparse enough, and meeting directly is reconstructed to signal using CS
Bring reconstruction bias.Document " stochastic linear frequency modulation stepping radar Waveform Design and imaging algorithm research " (He Jing, Luo Ying, Zhang Qun,
Deng electronics and information journal, 2011,33 (9):2068-2075.), " the ISAR imagings based on sparse linear stepped-frequency chirp signal "
(Wang Hongxian, Liang Yi, Xing Mengdao wait Chinese sciences:Information science, 2011,41 (12):1529-1540.), " High-
Resolution ISAR Imaging With Sparse Stepped-Frequency Waveforms”(Zhang L,Qiao
Z J,Xing M D,et al.IEEE Trans.Geosci.Remote Sens.,2011,49(11):4630-4651.) etc. examine
Consider action reference variable and compensation problem, but principle is complex, realizes that step is comparatively laborious, and for high-speed motion feelings
Condition, validity is difficult to ensure that.In general, the high resolution radar imaging method currently for moving target need further to grind
Study carefully.
The content of the invention
The present invention is in view of the deficienciess of the prior art, propose a kind of motion designed based on random Based on Modulated Step Frequency Waveform
Target ISAR imaging methods, it is pre- using phase cancellation and pulse recurrence interval (Pulse Repetition Interval, PRI)
First designing technique eliminates influence of the target motion generated data arteries and veins, and makes full use of the advantage and radar mesh of CS information processings
The openness of scattered power distribution is marked, the deficiency that existing motive target imaging method is present is compensate for, solves frequency modulation stepping radar
The problem of aggregate date rate is higher, compression is sensitive to Doppler between arteries and veins, and without the prior information of the parameters of target motion.
The technical scheme is that：It is primarily based on phase cancellation and PRI is pre-designed principle, ISAR transmitted waveforms is entered
Row design, eliminate target motion influences on the high-order term that radar return is produced；Secondly using matched filtering, solution line frequency modulation or CS side
Method carries out subpulse compression processing to each subpulse echo, obtains coarse resolution Range Profile Sequence；By taking peak value or relevant summation
Handle and the data comprising target information are extracted from coarse resolution Range Profile for being compressed between arteries and veins；Then, based on CS principles, construction etc.
Calculation matrix is imitated, compression is handled between carrying out arteries and veins using CS algorithms, reconstructs the High Range Resolution of target.Obtain different observation visual angles
Under High Range Resolution sequence after, CS methods or conventional method can be selected to carry out orientation processing according to the actual requirements so that
Obtain the high-resolution two dimension ISAR pictures of target.
Technical scheme comprises the following steps：
The first step, is designed to ISAR transmitted waveforms
Random frequency modulation stepping (RCFS) signal waveform is designed according to radar return feature：When target uniform motion or acceleration
When size can be neglected, the high-order term that motion is produced to radar return is eliminated by phase cancellation or pulse recurrence interval designing technique
Influence；When the acceleration of target can not be ignored, combine and be pre-designed technology elimination motion to radar using phase cancellation and PRI
The high-order term influence that echo is produced.The main thought of Waveform Design is that subpulse carrier frequency and subpulse emission time are set
Meter.
(1) random stepped-frequency chirp signal echo modeling
If radar emission RCFS signals, a width of B of band that signal is occupied, per frame, transmitting pulse includes K Chirp subpulse,
The carrier frequency of k-th of subpulse is frk=f0+Γ(k)·Δf(0≤k≤K-1).Wherein, f0For the fundamental frequency of transmission signal, Δ f is
Subpulse bandwidth, B=N Δs f, Γ are a random subsets on [0, N-1], | Γ | the size table of=K, K≤N, K relative to N
The sparse degree of RCFS waveforms is levied.To ensure that signal covers the bandwidth B that conventional N number of subpulse is occupied, Γ (0)=0, Γ is made
(K-1) other elements in=N-1, Γ are a random subsets on [1, N-2].Then the time-domain expression of RCFS signals is
Wherein, w (t)=rect (t/Tp)·exp(jπγt2) it is Chirp subpulses, TpFor subpulse time width, γ=Δ
f/TpFor the chirp rate of subpulse, TkThe emission time of k-th of subpulse is represented, generally Tk=kTr, TrDuring to fix
Between parameter.Corresponding radar target is
Wherein, I is target scattering point number, and c is propagation velocity of electromagnetic wave, δiThe scattering strength of i-th of scattering point is represented,
Ri(t) represent the t scattering point to the radial distance of radar.The motion of target can be near when stepped-frequency chirp signal synthesizes Range Profile
It is seemingly Secondary movement, it is assumed that the initial distance of target centroid to radar is R0, the radial velocity and acceleration of target be respectively v and
A, riFor the radial distance of i-th of scattering point to target centroid, then
Ri(t)=R0+vt+0.5at2+ri (3)
By each subpulse echo and corresponding coherent local oscillation signal exp { j2 π (f0+ Γ (k) Δ f) t } mixing after can obtain
Video echo is
The compression process of subpulse is entered with conventional stepped-frequency chirp signal to the peak value of each coarse resolution Range Profile after pulse pressure
Row sampling, sampling instant tk=Tk+2R0/ c, then can obtain the data for synthesizing High Range Resolution：
Wherein, A is the fixed coefficient that pulse pressure is produced.
(2) Waveform Design (ignoring acceleration influence) based on phase cancellation
It is respectively T by PRI if every frame signal of radar emission includes two trains of pulserAnd 2TrRandom Chirp of K
Pulse is constituted, in addition to PRI is different, and two train of pulse remaining parameters are identical, and the emission time of its k-th of subpulse can be designated as respectively
Tk=kTr (6)
T′k=t0+2kTr (7)
Wherein, t0=KTr, the cycle of a corresponding frame pulse is Tb=3KTr。
According to formula (5), ignore acceleration influence, the echo-signal of two trains of pulse can be expressed as
Assuming that the relative position of target scattering point does not change in the synthesis Range Profile time, u is madec(k)=[u (k)]2/u′
(k), then
Wherein,Under normal circumstances, for
Space or aerial target, there is 2v/c ＜ ＜ 1, vt0＜ ＜ R0, therefore α1≈2ΔfR0/c.It can be seen that, after phase cancellation, echo middling speed
Degree-frequency couples the quadratic phase introduced and is eliminated, and effectively prevent the caused Range Profile of target motion and obscures and distortion.
It is pointed out that phase cancellation techniques are not only relevant with transmitted waveform, in addition it is also necessary to right during radar imagery
Echo carries out being not repeated to discuss in respective handling, follow-up image-forming step.
(3) Waveform Design (ignoring acceleration influence) being pre-designed based on PRI
Phase cancellation method needs to launch two trains of pulse every time, and subpulse number is more, and the data recording time is longer.To keep away
Exempt from the problem, the time interval for launching subpulse is redesigned, the random value in Γ is pressed into ascending order in design process
Arrangement.
From echo model (5), the coupled phase of target velocity-frequency is
The high-order term in phase of echo is eliminated, only the high-order term in φ need to be removed, make the emission time of k-th of subpulse
For
Then the cycle of a corresponding frame pulse isAnd
Obviously, φ no longer includes high-order term in formula (13).Formula (12) is substituted into formula (5) to obtain
Wherein,It can be seen that, pass through the pre- of PRI
First design, the phase term that speed is introduced only includes first order, eliminate influence of the target motion to synthesis Range Profile shape.
(4) Waveform Design (considering acceleration influence) that comprehensive utilization phase cancellation and PRI are pre-designed
If the acceleration of target can not be ignored, understood through deriving, being pre-designed by phase cancellation or PRI can not eliminate
The phase high-order term that acceleration is introduced.Further to eliminate the influence of acceleration, by phase cancellation method and the PRI sides of being pre-designed
Method is combined, so that obtaining a kind of new transmitting burst waveforms is used for high-resolution imaging.Every frame pulse of radar emission is by two
Individual random pulse train composition, each train of pulse includes K random Chirp subpulses, and the PRI of first train of pulse passes through formula (12)
Calculate, the PRI of second train of pulse is firstTimes, the emission time of its k-th of subpulse is
Wherein,The cycle of a corresponding frame pulse is
By with foregoing similar derivation it is seen that, two train of pulse echoes are carried out after phase cancellation processing, RCFS
The phase addition Item brought in radar return by target velocity and acceleration only includes first order, and high-order term is eliminated, synthesis away from
From as when can not consider the influence that brings of target motion.
Second step, subpulse compression processing
If the RCFS signals of radar emission design, for being compressed in the arteries and veins of Chirp subpulses, with conventional frequency modulation stepping letter
Number, polished, Xing Mengdao, Wang Tong radar imaging technology [M] Beijing (can be protected using matched filtering method or solution line frequency modulation method:
Electronic Industry Press, 2005.).For further reduction data transfer rate, the distance based on CS can also be utilized to compression method
(Ender J H G.On compressive sensing applied to radar[J].Signal Process.,2010,
90(5):1402-1414.), and because pulsewidth is smaller, without considering that target moves the influence to sub- pulse compression broadening.
As described in the modeling of first step echo, each subpulse echo is regarded with coherent local oscillation signal Frequency mixing processing first
Frequency echo, can be obtained after being then compressed to each subpulse echo
Wherein,The fixed coefficient produced for pulse pressure.The compression result of each subpulse is corresponded to
One width coarse resolution Range Profile of target.
3rd step, coarse resolution Range Profile information extraction
Generally consider that the radical length of target is less than not fuzzy distance siding-to-siding block length, i.e. target radial size and is less than subpulse
Range resolution unit c/2 Δs f situation, it is now single comprising mesh target area only one of which distance in each coarse resolution Range Profile
Member, the in theory sampling to the range cell contains the full detail of each scattering point in target.It is negligible for motion influence
Target for, the corresponding coarse resolution Range Profile of each subpulse will not produce spectral peaks to split phenomenon only comprising a peak value, close
Into can only take the information in coarse resolution Range Profile at amplitude maximum position during High Range Resolution.To each coarse resolution after pulse pressure
The peak value of Range Profile is sampled, as a result as shown in formula (5).
Influence of the Doppler effect to sub- pulse compression is mainly pulse pressure output peak value and shifting is produced between different subpulses
Dynamic, i.e., coarse resolution Range Profile produces displacement.In the case of random frequency modulation stepping, the coarse resolution Range Profile of k-th of subpulse is relative
In the 0th subpulse Range Profile envelope time shift be 2 (vTk+aTk 2/2)/c≈2vTk/ c, corresponding distance of walking about is vTk, it is maximum
Distance of walking about is vTb.When target speed is higher, the distance of walking about of subpulse Range Profile may surmount one even more than
Coarse resolution unit, presently, there are a variety of envelope alignment methods and (protects polished, Xing Mengdao, Wang Tong radar imaging technology [M] Beijing:Electricity
Sub- industry publishing house, 2005.) to eliminate influence of the envelope movement being compressed arteries and veins.However, subpulse Range Profile walk about away from
It is very possible to occur although target only occupies a coarse resolution unit in itself from the coarse resolution unit for being not necessarily integral multiple
Across the situation of two range cells, so as to cause energy leakage, peak-fall is exported, main lobe broadening now only takes amplitude most
Big range cell data will lost part target information, give compression strap between arteries and veins come larger error.To overcome this defect, root
The energy accumulation characteristic exported according to pulse pressure, the present invention proposes to carry out phase to each range cell data of each subpulse compression result
Dry summation, using summed result as the data source compressed between arteries and veins, improves the stability of synthesis High Range Resolution, this method need not
Envelope alignment processing.
According to above-mentioned analysis, when target velocity is smaller, the distance of walking about of each coarse resolution Range Profile is less than half of coarse resolution list
Member, i.e. vTbDuring ＜ c/4 Δ f, the peak cell data of coarse resolution Range Profile can be directly taken to be used to compress between arteries and veins；Work as target velocity
It is larger, i.e. vTbDuring >=c/4 Δ f, target main energetic is possible to be leaked to different range cells, and each subpulse can be compressed
Range cell data afterwards carry out relevant summation respectively, the data after coherent accumulation are used to compress between arteries and veins, so that it is guaranteed that extracting
Enough target informations.In theory, peak value processing is applied to low-speed motion target, with preferable noiseproof feature；Phase
Dry summation method is insensitive to the size of target velocity, but because noise energy is also accumulated in summation process, to noise
Robustness decrease.
4th step, High Range Resolution is synthesized based on CS algorithms
If radar emission signal is using conventional CFS signals, after PRI is pre-designed or phase cancellation is handled, to rough segmentation
Distinguish that the data after Range Profile information extraction carry out the High Range Resolution that inverse Fourier transform can obtain target, i.e. the data exist
The expression of Fourier embodies the radial distribution of target scattering rate, and it is sparse in Fourier to illustrate it.Institute in the present invention
The RCFS signals of design eliminate by target move bring phase high-order term influence, but due between subpulse carrier frequency increment be not
Uniformly, directly the data after coarse resolution Range Profile information extraction are made inverse Fourier transform can not obtain the high-resolution of target away from
From picture.
Understood according to formula (1), RCFS signals are the equal of the random contraction sampling to conventional CFS signals, its mechanism
It can be characterized with the fractional unit matrix Φ of K × N-dimensional, Φ row k correspondence unit matrix INΓ (k) row.According to target
It is openness that scattered power is distributed, and CS theories are introduced into the motive target imaging of RCFS signals by the present invention.Assuming that y={ uc(k)}
=[uc(0),uc(1),...,uc(K-1)]TFor the data arrow for being used to compress between arteries and veins obtained in launching pulse echo from every frame
Amount, target scattering rate radial distribution is σ, and Ψ is the normalization Fourier transform matrix of N × N-dimensional, then
Y=Φ Ψ σ (17)
Wherein, Φ={ Φk,n,
In formula (17), effective calculation matrix Θ=Φ Ψ are substantially a partial Fourier matrix, meet CS reconstruct
RIP conditions (Zhang L, Xing M D, Qiu C W, et al.Achieving Higher Resolution ISAR
Imaging With Limited Pulses via Compressed Sampling[J].IEEE Geosci.Remote
Sens.Lett.,2009,6(3):567-571.).Therefore, it is restructural mesh by nonlinear optimization based on echo model (17)
The projective distribution of scattered power diametrically is marked, that is, obtains High Range Resolution.Echo is not considered during due to construction sparse dictionary Ψ
The influence of a phase factor in model, therefore reconstruction result has cyclic shift, be the equal of make use of after cyclic shift away from
It is openness from picture, the cyclic shift of Range Profile can be eliminated by adjusting the shift amount of imaging window.
5th step, orientation compression processing
If desired the two-dimentional ISAR images of target are obtained, are obtained after the High Range Resolution sequence under different observation visual angles,
The processing of orientation is identical with other radar signals, can be selected according to the actual requirements between CS methods and conventional method,
Here repeat no more.Wherein, in CS methods orientation by receiving echo data or adjustment/reduction arteries and veins under a small amount of visual angle at random
Measurement is compressed in recurrence interval between group to realize, is also applied for partial distance picture and there is a situation where distortion, corresponding effective measurement
Matrix is partial Fourier matrix.
Due to using technical scheme as described above, the present invention brings following superiority：
1st, the present invention causes radar signal that there is stronger resisting to do in itself by being designed to ISAR transmitted waveforms, not only
Disturb with anti-intercepting and capturing ability, and effectively prevent the influence that target motion synthesizes High Range Resolution compression arteries and veins, and need not
The prior information of the parameters of target motion, is insensitive to the size of target velocity.
2nd, there is provided take at peak value and relevant two kinds of summation for influence of the present invention according to Doppler effect to sub- pulse compression
Reason mode extracts the target information included in coarse resolution Range Profile, improves the validity of high-resolution range Imaging and sane
Property.
3rd, the present invention reconstructs the High Range Resolution of target using CS algorithms, changes while data volume needed for reduction imaging
It has been apt to image quality.
4th, the High Range Resolution that obtains of the present invention, which has, protects phasic property, can be used in target identification or further two dimension,
Three-dimensional imaging is handled.
Brief description of the drawings
Fig. 1 is the moving target ISAR imaging method flow charts designed based on random Based on Modulated Step Frequency Waveform.
Routine CFS signals when Fig. 2 (a), Fig. 2 (b) and Fig. 2 (c) are respectively target velocity v=0, v=200 and v=2000
Subpulse compression result figure.
Fig. 3 (a), Fig. 3 (b) be respectively do not carry out routine CFS signals and RCFS signals in the case of waveform is pre-designed away from
From as composite result figure.
Fig. 4 is the High Range Resolution composite result figure being pre-designed based on waveform.Wherein, Fig. 4 (a), Fig. 4 (c) and Fig. 4
(e) the High Range Resolution synthesis based on phase cancellation method when being respectively target velocity v=200, v=2000 and v=3000
It is pre- based on PRI when result figure, Fig. 4 (b), Fig. 4 (d) and Fig. 4 (f) are respectively target velocity v=200, v=2000 and v=3000
The High Range Resolution composite result figure of first design method.
Fig. 5 (a), Fig. 5 (b) are respectively based on phase cancellation method and based on the PRI sides of being pre-designed under Low SNR
The Range Profile composite result figure of method.
Fig. 6 (a), Fig. 6 (b) and Fig. 6 (c) are respectively based on phase cancellation method, are pre-designed method based on PRI and are based on
The Range Profile composite result figure of the even accelerated motional objects of integrated approach.
Fig. 7 is the two-dimensional imaging result figure of emulation uniformly accelerated motion bullet target.Wherein, Fig. 7 (a), Fig. 7 (b) be based on
The two-dimensional imaging result figure of phase cancellation method, Fig. 7 (c), Fig. 7 (d) are the two-dimensional imaging result that method is pre-designed based on PRI
Figure, Fig. 7 (e), Fig. 7 (f) are the two-dimensional imaging result figure based on integrated approach.
Embodiment
Technical scheme for a better understanding of the present invention, herein below will be made with reference to accompanying drawing to embodiments of the present invention
Further describe.
Fig. 1 is the moving target ISAR imaging method flow charts designed based on random Based on Modulated Step Frequency Waveform.It is primarily based on phase
Position is offseted is pre-designed principle with PRI, and the ISAR random Based on Modulated Step Frequency Waveform launched is designed；Secondly each subpulse is returned
Ripple is compressed processing and obtains coarse resolution Range Profile Sequence；By taking peak value or relevant summation process to be carried from coarse resolution Range Profile
The data comprising target information are taken to be used for compression processing between arteries and veins；Then, the High Range Resolution of target is reconstructed using CS algorithms；Most
Afterwards, according to the actual requirements, selection CS methods or conventional method carry out orientation processing, so as to obtain the high-resolution two dimension of target
ISAR pictures.
The first step, is designed to ISAR transmitted waveforms
Random frequency modulation stepping (RCFS) signal waveform is designed according to radar return feature：When target uniform motion or acceleration
When size can be neglected, the high-order term that motion is produced to radar return is eliminated by phase cancellation or pulse recurrence interval designing technique
Influence；When the acceleration of target can not be ignored, combine and be pre-designed technology elimination motion to radar using phase cancellation and PRI
The high-order term influence that echo is produced.The main thought of Waveform Design is that subpulse carrier frequency and subpulse emission time are set
Meter.
(1) random stepped-frequency chirp signal echo modeling
If radar emission RCFS signals, a width of B of band that signal is occupied, per frame, transmitting pulse includes K Chirp subpulse,
The carrier frequency of k-th of subpulse is frk=f0+Γ(k)·Δf(0≤k≤K-1).Wherein, f0For the fundamental frequency of transmission signal, Δ f is
Subpulse bandwidth, B=N Δs f, Γ are a random subsets on [0, N-1], | Γ | the size table of=K, K≤N, K relative to N
The sparse degree of RCFS waveforms is levied.To ensure that signal covers the bandwidth B that conventional N number of subpulse is occupied, Γ (0)=0, Γ is made
(K-1) other elements in=N-1, Γ are a random subsets on [1, N-2].Then the time-domain expression of RCFS signals is
Wherein, w (t)=rect (t/Tp)·exp(jπγt2) it is Chirp subpulses, TpFor subpulse time width, γ=Δ
f/TpFor the chirp rate of subpulse, TkThe emission time of k-th of subpulse is represented, generally Tk=kTr, TrDuring to fix
Between parameter.Corresponding radar target is
Wherein, I is target scattering point number, and c is propagation velocity of electromagnetic wave, δiThe scattering strength of i-th of scattering point is represented,
Ri(t) represent the t scattering point to the radial distance of radar.The motion of target can be near when stepped-frequency chirp signal synthesizes Range Profile
It is seemingly Secondary movement, it is assumed that the initial distance of target centroid to radar is R0, the radial velocity and acceleration of target be respectively v and
A, riFor the radial distance of i-th of scattering point to target centroid, then
Ri(t)=R0+vt+0.5at2+ri (3)
By each subpulse echo and corresponding coherent local oscillation signal exp { j2 π (f0+ Γ (k) Δ f) t } mixing after can obtain
Video echo is
The compression process of subpulse is entered with conventional stepped-frequency chirp signal to the peak value of each coarse resolution Range Profile after pulse pressure
Row sampling, sampling instant tk=Tk+2R0/ c, then can obtain the data for synthesizing High Range Resolution：
Wherein, A is the fixed coefficient that pulse pressure is produced.
(2) Waveform Design (ignoring acceleration influence) based on phase cancellation
It is respectively T by PRI if every frame signal of radar emission includes two trains of pulserAnd 2TrRandom Chirp of K
Pulse is constituted, in addition to PRI is different, and two train of pulse remaining parameters are identical, and the emission time of its k-th of subpulse can be designated as respectively
Tk=kTr (6)
T′k=t0+2kTr (7)
Wherein, t0=KTr, the cycle of a corresponding frame pulse is Tb=3KTr。
According to formula (5), ignore acceleration influence, the echo-signal of two trains of pulse can be expressed as
Assuming that the relative position of target scattering point does not change in the synthesis Range Profile time, u is madec(k)=[u (k)]2/u′
(k), then
Wherein,Under normal circumstances, for
Space or aerial target, there is 2v/c ＜ ＜ 1, vt0＜ ＜ R0, therefore α1≈2ΔfR0/c.It can be seen that, after phase cancellation, echo middling speed
Degree-frequency couples the quadratic phase introduced and is eliminated, and effectively prevent the caused Range Profile of target motion and obscures and distortion.
It is pointed out that phase cancellation techniques are not only relevant with transmitted waveform, in addition it is also necessary to right during radar imagery
Echo carries out being not repeated to discuss in respective handling, follow-up image-forming step.
(3) Waveform Design (ignoring acceleration influence) being pre-designed based on PRI
Phase cancellation method needs to launch two trains of pulse every time, and subpulse number is more, and the data recording time is longer.To keep away
Exempt from the problem, the time interval for launching subpulse is redesigned, the random value in Γ is pressed into ascending order in design process
Arrangement.
From echo model (5), the coupled phase of target velocity-frequency is
The high-order term in phase of echo is eliminated, only the high-order term in φ need to be removed, make the emission time of k-th of subpulse
For
Then the cycle of a corresponding frame pulse isAnd
Obviously, φ no longer includes high-order term in formula (13).Formula (12) is substituted into formula (5) to obtain
Wherein,It can be seen that, pass through the pre- of PRI
First design, the phase term that speed is introduced only includes first order, eliminate influence of the target motion to synthesis Range Profile shape.
(4) Waveform Design (considering acceleration influence) that comprehensive utilization phase cancellation and PRI are pre-designed
If the acceleration of target can not be ignored, understood through deriving, being pre-designed by phase cancellation or PRI can not eliminate
The phase high-order term that acceleration is introduced.Further to eliminate the influence of acceleration, by phase cancellation method and the PRI sides of being pre-designed
Method is combined, so that obtaining a kind of new transmitting burst waveforms is used for high-resolution imaging.Every frame pulse of radar emission is by two
Individual random pulse train composition, each train of pulse includes K random Chirp subpulses, and the PRI of first train of pulse passes through formula (12)
Calculate, the PRI of second train of pulse is firstTimes, the emission time of its k-th of subpulse is
Wherein,The cycle of a corresponding frame pulse is
By with foregoing similar derivation it is seen that, two train of pulse echoes are carried out after phase cancellation processing, RCFS
The phase addition Item brought in radar return by target velocity and acceleration only includes first order, and high-order term is eliminated, synthesis away from
From as when can not consider the influence that brings of target motion.
Second step, subpulse compression processing
If the RCFS signals of radar emission design, for being compressed in the arteries and veins of Chirp subpulses, with conventional frequency modulation stepping letter
Number, polished, Xing Mengdao, Wang Tong radar imaging technology [M] Beijing (can be protected using matched filtering method or solution line frequency modulation method:
Electronic Industry Press, 2005.).For further reduction data transfer rate, the distance based on CS can also be utilized to compression method
(Ender J H G.On compressive sensing applied to radar[J].Signal Process.,2010,
90(5):1402-1414.), and because pulsewidth is smaller, without considering that target moves the influence to sub- pulse compression broadening.
As described in the modeling of first step echo, each subpulse echo is regarded with coherent local oscillation signal Frequency mixing processing first
Frequency echo, can be obtained after being then compressed to each subpulse echo
Wherein,The fixed coefficient produced for pulse pressure.The compression result of each subpulse is corresponded to
One width coarse resolution Range Profile of target.
3rd step, coarse resolution Range Profile information extraction
Generally consider that the radical length of target is less than not fuzzy distance siding-to-siding block length, i.e. target radial size and is less than subpulse
Range resolution unit c/2 Δs f situation, it is now single comprising mesh target area only one of which distance in each coarse resolution Range Profile
Member, the in theory sampling to the range cell contains the full detail of each scattering point in target.It is negligible for motion influence
Target for, the corresponding coarse resolution Range Profile of each subpulse will not produce spectral peaks to split phenomenon only comprising a peak value, close
Into can only take the information in coarse resolution Range Profile at amplitude maximum position during High Range Resolution.To each coarse resolution after pulse pressure
The peak value of Range Profile is sampled, as a result as shown in formula (5).
Influence of the Doppler effect to sub- pulse compression is mainly pulse pressure output peak value and shifting is produced between different subpulses
Dynamic, i.e., coarse resolution Range Profile produces displacement.In the case of random frequency modulation stepping, the coarse resolution Range Profile of k-th of subpulse is relative
In the 0th subpulse Range Profile envelope time shift be 2 (vTk+aTk 2/2)/c≈2vTk/ c, corresponding distance of walking about is vTk, it is maximum
Distance of walking about is vTb.When target speed is higher, the distance of walking about of subpulse Range Profile may surmount one even more than
Coarse resolution unit, presently, there are a variety of envelope alignment methods and (protects polished, Xing Mengdao, Wang Tong radar imaging technology [M] Beijing:Electricity
Sub- industry publishing house, 2005.) to eliminate influence of the envelope movement being compressed arteries and veins.However, subpulse Range Profile walk about away from
It is very possible to occur although target only occupies a coarse resolution unit in itself from the coarse resolution unit for being not necessarily integral multiple
Across the situation of two range cells, so as to cause energy leakage, peak-fall is exported, main lobe broadening now only takes amplitude most
Big range cell data will lost part target information, give compression strap between arteries and veins come larger error.To overcome this defect, root
The energy accumulation characteristic exported according to pulse pressure, the present invention proposes to carry out phase to each range cell data of each subpulse compression result
Dry summation, using summed result as the data source compressed between arteries and veins, improves the stability of synthesis High Range Resolution, this method need not
Envelope alignment processing.
According to above-mentioned analysis, when target velocity is smaller, the distance of walking about of each coarse resolution Range Profile is less than half of coarse resolution list
Member, i.e. vTbDuring ＜ c/4 Δ f, the peak cell data of coarse resolution Range Profile can be directly taken to be used to compress between arteries and veins；Work as target velocity
It is larger, i.e. vTbDuring >=c/4 Δ f, target main energetic is possible to be leaked to different range cells, and each subpulse can be compressed
Range cell data afterwards carry out relevant summation respectively, the data after coherent accumulation are used to compress between arteries and veins, so that it is guaranteed that extracting
Enough target informations.In theory, peak value processing is applied to low-speed motion target, with preferable noiseproof feature；Phase
Dry summation method is insensitive to the size of target velocity, but because noise energy is also accumulated in summation process, to noise
Robustness decrease.
4th step, High Range Resolution is synthesized based on CS algorithms
If radar emission signal is using conventional CFS signals, after PRI is pre-designed or phase cancellation is handled, to rough segmentation
Distinguish that the data after Range Profile information extraction carry out the High Range Resolution that inverse Fourier transform can obtain target, i.e. the data exist
The expression of Fourier embodies the radial distribution of target scattering rate, and it is sparse in Fourier to illustrate it.Institute in the present invention
The RCFS signals of design eliminate by target move bring phase high-order term influence, but due between subpulse carrier frequency increment be not
Uniformly, directly the data after coarse resolution Range Profile information extraction are made inverse Fourier transform can not obtain the high-resolution of target away from
From picture.
Understood according to formula (1), RCFS signals are the equal of the random contraction sampling to conventional CFS signals, its mechanism
It can be characterized with the fractional unit matrix Φ of K × N-dimensional, Φ row k correspondence unit matrix INΓ (k) row.According to target
It is openness that scattered power is distributed, and CS theories are introduced into the motive target imaging of RCFS signals by the present invention.Assuming that y={ uc(k)}
=[uc(0),uc(1),...,uc(K-1)]TFor the data arrow for being used to compress between arteries and veins obtained in launching pulse echo from every frame
Amount, target scattering rate radial distribution is σ, and Ψ is the normalization Fourier transform matrix of N × N-dimensional, then
Y=Φ Ψ σ (17)
Wherein, Φ={ Φk,n,
In formula (17), effective calculation matrix Θ=Φ Ψ are substantially a partial Fourier matrix, meet CS reconstruct
RIP conditions (Zhang L, Xing M D, Qiu C W, et al.Achieving Higher Resolution ISAR
Imaging With Limited Pulses viaCompressed Sampling[J].IEEE Geosci.Remote
Sens.Lett.,2009,6(3):567-571.).Therefore, it is restructural mesh by nonlinear optimization based on echo model (17)
The projective distribution of scattered power diametrically is marked, that is, obtains High Range Resolution.Echo is not considered during due to construction sparse dictionary Ψ
The influence of a phase factor in model, therefore reconstruction result has cyclic shift, be the equal of make use of after cyclic shift away from
It is openness from picture, the cyclic shift of Range Profile can be eliminated by adjusting the shift amount of imaging window.
5th step, orientation compression processing
If desired the two-dimentional ISAR images of target are obtained, are obtained after the High Range Resolution sequence under different observation visual angles,
The processing of orientation is identical with other radar signals, can be selected according to the actual requirements between CS methods and conventional method,
Here repeat no more.Wherein, in CS methods orientation by receiving echo data or adjustment/reduction arteries and veins under a small amount of visual angle at random
Measurement is compressed in recurrence interval between group to realize, is also applied for partial distance picture and there is a situation where distortion, corresponding effective measurement
Matrix is partial Fourier matrix.
Fig. 2~Fig. 7 is the simulation experiment result carried out in universal computer platform.
Fig. 2~Fig. 6 simulated conditions are set to：Radar emission RCFS signals, starting carrier frequency f0=10GHz, transmission signal
Bandwidth B=1GHz, subpulse bandwidth deltaf f=15MHz, subpulse time width Tp=5 μ s, sample frequency is 6.4MHz, set time
Parameter (being set to the PRI of conventional CFS signals, the two can be different in practice) Tr=250 μ s, launch in the case of conventional frequency modulation stepping
Subpulse number N=64, launches subpulse number K=32 in the case of random frequency modulation stepping.Target is made up of 5 scattering points, according to point
Scattering model generates echo data, and signal to noise ratio is 15dB.Subpulse is compressed using solution line frequency modulation processing mode, for ease of
Calculate, using zero padding processing has been carried out during compression synthesis Range Profile between FFT progress arteries and veins, (data length is changed into P=from 64 after zero padding
128) the effective calculation matrix dimension, constructed in CS imaging methods is K × P, using SL0 algorithms (Mohimani H, Babaie-
Zadeh M,Jutten C.A fast approach for overcomplete sparse decomposition based
on smoothedl0norm[J].IEEE Trans.Signal Process.,2009,57(1):289-301.) it is reconstructed.
In the case that Fig. 2 gives target velocity v=0, v=200m/s and v=2000m/s, the rough segmentation of conventional CFS signals
Distinguish Range Profile Sequence.It can be seen that, influence very little of the target velocity to sub- pulse compression shape；When target velocity is smaller, its antithetical phrase
The influence of pulse compression envelope displacement can be neglected substantially, when target velocity is larger, and subpulse Range Profile produces obvious
Envelope is walked about, and the main lobe energy of partial distance picture is distributed in two range cells, even across envelope alignment processing also without
Method eliminates this phenomenon, and now the peak cell of subpulse Range Profile can not cover the main energetic information of target.
Fig. 3 shows influence of the target velocity being compressed arteries and veins, wherein (a) is target velocity in the case of conventional frequency modulation stepping
FFT imaging results during v=0 and v=30m/s, (b) is the CS imaging results in the case of random frequency modulation stepping.For ease of observation,
The Range Profile cyclic shift that figure medium velocity is caused is not corrected.As can be seen that being compressed between the arteries and veins of CFS signals for Doppler's ratio
More sensitive, the movement velocity of target causes broadening and the translation of synthesis Range Profile, and corresponding CS reconstruction results are also due to openness
Significantly reduce and serious distortion.
Fig. 4 gives the CS reconstruction results being pre-designed based on phase cancellation under friction speed and based on PRI, every kind of condition
Under subpulse coarse resolution Range Profile be respectively adopted take peak value and the mode of relevant summation to be configured to synthesize High Range Resolution
Data.Reconstruction result shows, in the case that speed is relatively low, and peak cell data contain enough target informations, take peak value
Preferable quality reconstruction can be obtained with relevant summation, by contrast, the result secondary lobe for the summation that is concerned with is slightly higher, and this is due to ask
More noise energy is also superimposed while target energy is accumulated with process, so as to raise secondary lobe to a certain extent；Speed
In the case that degree is higher, each coarse resolution Range Profile peak cell data, which differ to establish a capital, contains enough target informations so that take
The reconstruction quality degradation of peak value, and relevant summation can then keep stability, therefore, preferably use relevant summed data to synthesize
High Range Resolution.Certainly, even if target velocity is higher, if can ensure that, the main scattering energy of target concentrates on coarse resolution distance
As in peak cell, then can still be by the High Range Resolution for taking peak value to obtain target, Fig. 4 (c) demonstrates this point.
Fig. 5 gives v=200m/s, CS reconstruction results when signal to noise ratio is 5dB.It is not difficult to find out, takes the processing knot of peak value
Fruit is better than the result based on phase cancellation better than the result of relevant summation based on the result that PRI is pre-designed, because
Noise energy is also accumulated in relevant summation process so that be difficult to obtain preferable reconstruction result when signal to noise ratio is relatively low, and phase
There is weak cross term influence in the cancellation process of position, therefore performance is also slightly worse.
Fig. 6 gives the CS method reconstruction results in the case of different acceleration.Assume that target does uniformly accelerated motion in emulation,
Initial radial velocity is v=3000m/s, using the relevant summed data of each subpulse coarse resolution picture, successively using based on phase
The method that offsets, carry out based on the PRI methods being pre-designed and integrated approach that both are combined compression synthesis target between arteries and veins
High Range Resolution.As seen from Figure 6, the motive target imaging method based on RCFS Waveform Designs is carried for high-speed motion
Even acceleration target be effective.When aimed acceleration is relatively low, using the CS side being pre-designed based on phase cancellation or based on PRI
Method compressed between arteries and veins, and the influence of weak cross term is not present in the latter, is using coarse resolution as the summed data that is concerned with
Under the conditions of have higher robustness；It is to be directed to even acceleration mesh that the CS methods being combined with phase cancellation are pre-designed based on PRI
Mark what model was proposed, be insensitive to the size of acceleration.
Putting forward High Range Resolution synthetic method for checking is used for the validity that two dimension ISAR is imaged, and does following emulation real
Test.If radar emission RCFS signals, signal relevant parameter ibid, launches M=128 frame pulses altogether.Bullet target is emulated to be dissipated by 7
Exit point is constituted, and target does uniformly accelrated rectilinear motion, kinematic parameter v=3000m/s, a=100m/s2, posture during radar observation
Angle excursion is [π/4, π/4+0.1], and echo data signal to noise ratio is 15dB.Imaging process middle-range descriscent uses CS methods, side
Position is to using traditional FFT methods.
Fig. 7 gives the ISAR imaging results under random Based on Modulated Step Frequency Waveform design condition, be followed successively by phase cancellation method,
PRI is pre-designed method and the CS reconstruction results of integrated approach, the peak cell number that every kind of scheme is successively compressed using subpulse
According to and relevant summed data be used for arteries and veins between compression handle, region shown in dotted line is scattering point focal position in figure.Experimental result table
Bright, the High Range Resolution that institute's extracting method is obtained can be imaged effective for the two-dimentional ISAR of moving target.Knowable to contrast, antithetical phrase
The processing mode of the relevant summation of pulse coarse resolution unit can obtain clearly target image, and imaging results have accurately reflected target and dissipated
The Two dimensional Distribution of exit point, and consider that the integrated approach quality reconstruction of acceleration influence is best.On the other hand, to sub- pulse compression knot
Fruit takes the processing mode of peak value poor due to there is energy leakage image quality, tight to occurring using distance during PRI design methods
Heavy defocuses and distortion, and in this case phase cancellation techniques are relatively excellent, because the target energy under set parameter
Leakage is less, and the influence to focusing performance is smaller, and this point has also embodied in Fig. 4 (e).
Claims (2)
1. a kind of moving target ISAR imaging methods designed based on random Based on Modulated Step Frequency Waveform, it is characterized in that：Its step is as follows：
The first step, is designed to ISAR transmitted waveforms
Random frequency modulation stepping RCFS signal waveforms are designed according to radar return feature, to subpulse carrier frequency and subpulse emission time
It is designed；
(1) random stepped-frequency chirp signal echo modeling
If radar emission RCFS signals, target includes I scattering point, and radar return is expressed as
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Chirp subpulses, TpFor subpulse time width, Δ f is subpulse bandwidth, γ=Δ f/Tp；f0For the fundamental frequency of transmission signal, k-th
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On a random subset, | Γ |=K, K≤N；TkThe emission time of k-th of subpulse is represented, generally Tk=kTr, Tr
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Radial distance of the scattering point to radar；
The motion of target is approximately Secondary movement when stepped-frequency chirp signal synthesizes Range Profile, it is assumed that target centroid to the initial of radar
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Ri(t)=R0+vt+0.5at2+ri (2)
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Phase cancellation techniques are not only relevant with transmitted waveform, in addition it is also necessary to carry out respective handling to echo during radar imagery,
It is not repeated in follow-up image-forming step；
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The subpulse number that the phase cancellation method requirement of use is launched every time is more, it is necessary to enter to the time interval for launching subpulse
Row is redesigned, and arranges the random value in Γ by ascending order in design process.Assuming that target uniform motion or acceleration influence
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The emission time for making k-th of subpulse is
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Wherein, It can be seen that, pass through setting in advance for PRI
Meter, the phase term that speed is introduced only includes first order, eliminates influence of the target motion to synthesis Range Profile shape；
(4) Waveform Design that comprehensive utilization phase cancellation and PRI are pre-designed, it is considered to which acceleration influences；
Phase cancellation method is pre-designed into method with PRI to be combined, so that obtaining a kind of new transmitting burst waveforms is used for
High-resolution imaging, if every frame pulse of radar emission is made up of two random pulse trains, each train of pulse is random comprising K
Chirp subpulses, the PRI of first train of pulse is calculated by formula (7), and the PRI of second train of pulse is firstTimes,
The emission time of its k-th of subpulse is
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Wherein,The cycle of a corresponding frame pulse is
By being carried out to two train of pulse echoes after phase cancellation processing, by target velocity and acceleration belt in RCFS radar returns
The phase addition Item come only includes first order, and high-order term is eliminated, and the shadow that target motion is brought can not be considered during synthesis Range Profile
Ring；
Second step, subpulse compression processing
If the RCFS signals of radar emission design, for being compressed in the arteries and veins of Chirp subpulses, with conventional stepped-frequency chirp signal,
Using matched filtering method or solution line frequency modulation method；For further reduction data transfer rate, also using based on compressed sensing (CS) away from
Descriscent compression method, and need not consider that target moves the influence to sub- pulse compression broadening；
Each subpulse echo is carried out to obtain after coherent mixing, pulse compression
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Wherein,The fixed coefficient produced for pulse pressure, the compression result of each subpulse has corresponded to target
A width coarse resolution Range Profile；
3rd step, coarse resolution Range Profile information extraction
Generally consider target radical length be less than not fuzzy distance siding-to-siding block length, i.e. target radial size be less than subpulse away from
From resolution cell c/2 Δs f situation, mesh target area only one of which range cell, reason are now included in each coarse resolution Range Profile
Sampling to the range cell on contains the full detail of each scattering point in target；Analysis knows, when target velocity is smaller, respectively
The distance of walking about of coarse resolution Range Profile is less than half of coarse resolution unit, i.e. vTbDuring ＜ c/4 Δ f, subpulse Range Profile is directly taken
Peak cell data are used to compress between arteries and veins；When target velocity is larger, i.e. vTbDuring >=c/4 Δ f, target main energetic is possible to let out
Reveal different range cells, the range cell data after being compressed to each subpulse carry out relevant summation respectively, by coherent accumulation
Data afterwards are used to compress between arteries and veins, so that it is guaranteed that extracting enough target informations；
4th step, High Range Resolution is synthesized based on CS algorithms
Analysis is known, in the case of conventional frequency modulation stepping, and after PRI is pre-designed or phase cancellation is handled, coarse resolution Range Profile is believed
It is sparse in Fourier to cease the data after extracting；Known according to formula (1), RCFS signals are the equal of to the random of CFS signals
Compression sampling, its mechanism is characterized with the fractional unit matrix Φ of K × N-dimensional, Φ row k correspondence unit matrix IN
Γ (k) rows；According to the openness of target scattering rate distribution, CS theories are introduced into the motive target imaging of RCFS signals；Assuming that y
={ uc(k) }=[uc(0),uc(1),...,uc(K-1)]TIt is used for what is compressed between arteries and veins for what is obtained in launching pulse echo from every frame
Data vector, target scattering rate radial distribution is σ, and Ψ is the normalization Fourier transform matrix of N × N-dimensional, then
Y=Φ Ψ σ (10)
Wherein, effective calculation matrix Θ=Φ Ψ are substantially a partial Fourier matrix, meet the condition of CS reconstruct；Cause
This, by nonlinear optimization is the projective distribution of restructural target scattering rate diametrically based on echo model (10), that is, obtains
High Range Resolution；The influence of a phase factor in echo model, therefore reconstruct are not considered during due to construction sparse dictionary Ψ
As a result there is cyclic shift, be the equal of make use of Range Profile after cyclic shift openness, by the shifting for adjusting imaging window
Measure to eliminate the cyclic shift of Range Profile in position；
5th step, orientation compression processing
If desired the two-dimentional ISAR images of target are obtained, are obtained after the High Range Resolution sequence under different observation visual angles, orientation
To processing it is identical with other radar signals, selected according to the actual requirements between conventional method and CS methods, thus
To the high-resolution two dimension ISAR pictures of target.
2. moving target ISAR imaging methods according to claim 1, it is characterised in that effective by RCFS Waveform Designs
The influence that target motion synthesizes High Range Resolution compression arteries and veins is avoided, and without the prior information of the parameters of target motion,
It is insensitive to the size of target velocity.
Moving target ISAR imaging methods according to claim 1, it is characterised in that by using designed RCFS ripples
Shape, the High Range Resolution of target is reconstructed based on CS algorithms, on the one hand can be improved while data volume needed for reducing imaging
Image quality, on the other hand improves anti-interference, the anti-intercepting and capturing ability of radar signal in itself.
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Application publication date: 20170822 |