CN107942340A - A kind of Terahertz SAR vibration compensation imaging methods - Google Patents
A kind of Terahertz SAR vibration compensation imaging methods 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
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
- G01S17/90—Lidar systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract
The present invention relates to a kind of Terahertz SAR vibration compensation imaging methods, including two-dimentional echo data is obtained, make Fourier transform to data by adjusting the distance, echo is gone to apart from frequency domain orientation time domain, carries out Range compress；Fourier transform is made to Data in Azimuth Direction, is walked about in two-dimensional frequency using Keystone conversion correction distances；Adjust the distance and make inverse Fourier transform to data, go to range-Dopler domain and carry out range curvature correction, and compensate orientation quadratic phase and residual video phase, main picture is corrected to pared echo in same distance door, complete the focusing of pared echo；Penalty function is constructed according to known vibration parameters, in range Doppler domain compensation Sine Modulated phase error as caused by vibration, realizes the suppression of pared echo, completes high-resolution two-dimension focusing imaging.Vibration error can be fully compensated in technical scheme, realize that the two-dimentional high-resolution of image focuses on.
Description
Technical field
The invention belongs to synthetic aperture radar video imaging field, and in particular to a kind of Terahertz SAR vibration compensations imaging
Method.
Background technology
Video Composition aperture radar (Video Synthetic Aperture Radar, ViSAR) system is as a kind of new
Technology, it is equal to the stationkeeping ability of target the positioning energy that infrared target system is provided when weather conditions are good through cloud layer
Power.The advantages of ViSAR, is the high aloof from politics and material pursuits two field picture for being capable of providing observation area, to track the maneuvering target on ground, meets
Maneuver warfare, the military requirement of quick response.Compared to traditional microwave band SAR system, THz wave is selected as carrier frequency
It can not only meet the requirement of high frame per second, moreover it is possible to obtain big signal bandwidth, while keep certain penetration capacity.Helicopter is not
Carry out one of main platform of ViSAR systems application.It is very sensitive to vibrating since the wavelength of THz wave is in millimeter magnitude.And
Fuselage shaking frequency caused by the rotary motion of helicopter blade be generally K Ω (Ω is the working speed frequency of rotor or tail-rotor,
K is the piece number of blade), while Oscillation Amplitude will increased dramatically with increasing for flying speed, can generally achieve millimeter magnitude, institute
Image can be caused serious defocus occur.It is the key for giving full play to ViSAR imaging advantages to design suitable imaging method.
At present still without the Terahertz SAR imaging methods of effective shaking platform.Foreign countries have researcher to propose application
In the imaging method of Vibration Targets, Keystone conversion (KT) methods and Doppler Keystone conversion (DKT) methods.Wherein
When Keystone converter techniques are used for motive target imaging, have very much for the Range Walk Correction under kinematic parameter unknown condition
Effect.Although traditional KT methods have been able to uncompensation distance and walk about, correction distance bending is unable to.Doppler Keystone becomes
The shortcomings that (DKT) method can make up KT methods is changed, it can just complete range migration correction in two-dimensional frequency.But with it is traditional
Linear movement platform is compared, and vibration causes that the difficulty of range migration correction will be increased there are Sine Modulated item in range migration curve
Degree.
The content of the invention
Present invention aims at a kind of Terahertz SAR vibration compensation imaging methods are provided, eliminate caused by Platform Vibration into
To echo, the focusing of image is completed, realizes high-resolution imaging.
A kind of Terahertz SAR vibration compensation imaging methods, specifically comprise the following steps：
Step (1)：Establish the two-dimentional echo signal model of Terahertz SAR imagings under shaking platform；
Step (2)：The two-dimentional echo-signal of collection；
Step (3)：Fourier transform is made to the two-dimentional echo-signal, two-dimentional echo-signal is gone to apart from frequency domain-side
Position time domain, into row distance pulse pressure；
Step (4)：Fourier transform is made to the two-dimentional echo-signal after pulse pressure, is utilized in two-dimensional frequency
Keystone conversion correction distances are walked about；
Step (5)：To the two-dimentional echo-signal after Keystone conversion in distance to inverse Fourier transform is made, apart from more
The general bending of Le domain correction distance, compensation quadratic phase and residual video phase, complete the focusing of pared echo；
Step (6)：Sine Modulated phase error compensation is carried out to the echo-signal after focusing, realizes the suppression of pared echo
System, completes two-dimension focusing imaging.
Further, the echo-signal in the step (1) is：
Wherein, wr() represents pulse envelope function, wa() is orientation envelope function, and R (t) is oblique distance, t0It is wave beam
Central instant, f0For radar carrier frequency, KrDistance is represented to frequency modulation rate, t is the orientation moment, and τ represents Distance Time, and c is the light velocity.
Further, in the step (2), the two dimension echo-signal includes distance to information and orientation information.
Further, the step (3)：Fourier transform is made to the two-dimentional echo-signal, echo is gone into distance frequency
Domain-orientation time domain, is specially into row distance pulse pressure：
By two-dimentional echo-signal along distance to obtaining sS (t, f after doing Fourier transformationr), wherein frRepresent frequency of distance, so
Laggard row distance pulse pressure.
Further, in the step (3), the matched filter formula apart from pulse pressure is as follows：
Wherein KrIt is distance to frequency modulation rate, frRepresent frequency of distance.
Further, the step (4)：Fourier transform is made to the two-dimentional echo-signal after pulse pressure, two
Dimension frequency domain is walked about using Keystone conversion correction distances and specifically included：
First by signal sS (t, the f after pulse pressurer) phase the form of Bessel function is resolved into along orientation, then
After orientation Fourier transformation, signal SS (f are obtaineda,fr), wherein faRepresent orientation frequency, then become using Keystone
Change to adjust the distance to walk about and be corrected, the signal after note correction is SS (fa′,fr)。
Further, in the step (4), the formula of Keystone conversion is
Wherein, f0Represent radar carrier frequency, faRepresent orientation frequency, fa' represent the orientation frequency after Keystone conversion, fr
Represent frequency of distance.
Further, the step (6) specifically includes：Echo-signal after focusing is multiplied by the filter of Sine Modulated phasing
Ripple device function is to carry out Sine Modulated phase error compensation.
Beneficial effect：
The present invention is carrying out Range compress apart from frequency domain-orientation time domain first；Then Keystone is utilized in two-dimensional frequency
Conversion correction distance is walked about；For the range curvature item that can not be fully compensated in two-dimensional frequency, it is more that echo is transformed into distance
General Le domain is corrected；Then orientation quadratic phase and residual video phase are compensated, realize distance to focusing；Finally compensate
The Sine Modulated phase error as caused by vibration, completes the suppression of pared echo, the image after being focused on.The present invention relative to
Traditional Keystone transform method can not only be in two-dimensional frequency full correction range walk, while can be fully compensated by vibrating
Sine Modulated item present in caused range migration curve, realizes that the two-dimentional high-resolution of image focuses on.
Brief description of the drawings
Fig. 1 is the process chart of the method for the present invention；
Fig. 2 is Terahertz SAR imaging geometry illustratons of model under shaking platform；
Fig. 3 is simulating scenes figure；
Fig. 4 is to complete the imaging results figure after pared echo focuses on using the method for the present invention；
Fig. 5 is to complete the imaging results figure after pared echo suppresses using the method for the present invention；
Fig. 6 is using ω K-method imaging results figures.
Embodiment
Do further details of explanation to technical scheme with specific embodiment below in conjunction with the accompanying drawings and say
It is bright.
Present invention aims at a kind of Terahertz SAR vibration compensation imaging methods are provided, eliminate caused by Platform Vibration into
To echo, the focusing of image is completed, realizes high-resolution imaging.As shown in Figure 1, the method for the present invention is realized in the following way：
The Terahertz SAR imaging signal models under shaking platform are initially set up, make Fourier change to data by adjusting the distance
Change, echo is gone to apart from frequency domain-orientation time domain, carries out Range compress；Then Fourier transform is made to Data in Azimuth Direction, two
Dimension frequency domain is walked about using Keystone conversion correction distances；Adjust the distance again and make inverse Fourier transform to data, how general go to distance
Strangle domain and carry out range curvature correction, and compensate orientation quadratic phase and residual video phase, make main picture with pared echo by school
Just arrive in same distance door, complete the focusing of pared echo；Penalty function finally is constructed according to known vibration parameters, it is more in distance
General Le domain compensation Sine Modulated phase error as caused by vibration, realizes the suppression of pared echo, completes two-dimension focusing imaging.
A kind of Terahertz SAR vibration compensation imaging methods, specifically include the following steps：
Step (1)：Establish the two-dimentional echo signal model of Terahertz SAR imagings under shaking platform；
As shown in Fig. 2, the Terahertz SAR imaging signal models under initially setting up shaking platform.P is a rest point on ground
Target, aircraft away from ground level be h it is aerial along OY axis with speed vaFlight.When point k is aperiodic motion error in phase
Position where the heart, point k ' is there are instantaneous phase center during periodic motion error.Will diagram coordinate system XYZO inverse times about the z axis
Pin rotates θ0, obtain a new coordinate system x ' y ' z ' k.Understand, the line segment of the phase center of carrier aircraft platform in plane x ' z ' k
On kk ' periodic motion, wherein φ are done centered on point k0For the angle of kk ' and kz '.Using shaking for simple harmonic oscillation analog platform
Dynamic, simple harmonic oscillation formula is as follows：
R (t)=Am·sinΦ
Wherein AmFor amplitude, Φ is vibration angle, fmFor vibration frequency,To vibrate first phase, t is the orientation moment.TsTo close
Into aperture time, when | fm·Ts| when >=1, the vibration of platform is dither.Oblique distance R (t) is derived using positive side perceived model,
Taylor expansion is carried out to R (t), while considers r (t) ＜ ＜ Rk(t), before reservation two obtain
WhereinBe it is without friction in the case of antenna in phase center k to point target P instantaneous oblique distance
Value, R0It is low coverage, vaFor speed, t is the orientation moment；A=CAmRepresenting equivalent vibration amplitude, wherein C is vibration amplitude constant,
AmFor amplitude, fmFor vibration frequency,To vibrate first phase.
Launch signal and use the pulse signal with linear FM characteristic, use f0Represent radar carrier frequency, KrRepresent distance to tune
Frequency, t are the orientation moment, and τ represents Distance Time, wr() represents pulse envelope function (being typically set to rectangle), must can launch
Signal s (τ)：
S (τ)=wr(τ)·exp{j(2πf0t+πKrτ2)}
Echo-signal expression formula after demodulated is：
Wherein, wr() represents pulse envelope function, wa() is orientation envelope function, and R (t) is oblique distance, t0It is wave beam
Central instant, f0For radar carrier frequency, KrDistance is represented to frequency modulation rate, t is the orientation moment, and τ represents Distance Time, and c is the light velocity.
Step (2)：The two-dimentional echo-signal of collection, wherein, the two dimension echo-signal includes distance to information and orientation
Information；
Step (3)：Fourier transform is made to the two-dimentional echo-signal, echo is gone to apart from frequency domain-orientation time domain, into
Row distance pulse pressure；
By two-dimentional echo-signal along distance to obtaining sS (t, f after doing Fourier transformationr), wherein, frRepresent frequency of distance,
Then it is as follows into row distance pulse pressure, the matched filter formula apart from pulse pressure：
Wherein KrIt is distance to frequency modulation rate, frRepresent frequency of distance.
Expression formula of the echo-signal after apart from pulse pressure be
Wherein, Wr(fr) it is apart from spectrum envelope function, frRepresent frequency of distance, wa() is orientation envelope function, t
It is the orientation moment, t0It is the beam center moment, f0Represent radar carrier frequency, c is the light velocity, and R (t) is oblique distance.
Step (4)：Fourier transform is made to the two-dimentional echo-signal after pulse pressure, is utilized in two-dimensional frequency
Keystone conversion correction distances are walked about；
First by signal sS (t, the f after pulse pressurer) phase the form of Bessel function is resolved into along orientation, then
After orientation Fourier transformation, signal SS (f are obtaineda,fr) (wherein faRepresent orientation frequency), then using Keystone
Conversion, which adjusts the distance to walk about, to be corrected, and the signal after note correction is SS (fa′,fr)。
Wherein, the formula of Keystone conversion is
Wherein, f0Represent radar carrier frequency, faRepresent orientation frequency, fa' represent the orientation frequency after Keystone conversion, fr
Represent frequency of distance.
The range walk item in signal can be completely eliminated by Keystone conversion, but range curvature item is still deposited
, and with time domain parameter R0Correlation, in the case where low coverage is unknown, range curvature item can not be fully compensated in two-dimensional frequency.
Step (5)：To the two-dimentional echo-signal after Keystone conversion in distance to inverse Fourier transform is made, apart from more
The general bending of Le domain correction distance, compensation quadratic phase and residual video phase, complete the focusing of pared echo；
By by the signal SS (f after correctiona′,fr) further transform to distance-Doppler domain come uncompensation distance bending item.
Ss is obtained into row distance to inverse Fourier transform1(fa', τ), the range curvature of track is then eliminated by interpolation correction.Wherein
The function of the interpolation correction is：
Wherein, fa' representing the orientation frequency after Keystone conversion, τ represents Distance Time, and c is the light velocity, R0It is low coverage, f0
For radar carrier frequency, vaFor speed.
By Ss1(fa', τ) with after interpolation correction function progress convolution, being seen in range-Dopler domain along orientation, point target
All on same straight line, it is corrected after signal energy all in same range gate.
Signal after correction range curvature is multiplied by orientation quadratic phase correcting filter function, for compensating secondary phase
Position.Wherein, the filter function formula is as follows：
Wherein R (τ)=c/2 τ represent oblique distance value, fa' representing the orientation frequency after Keystone conversion, τ represents distance
Time, c are the light velocity, f0For radar carrier frequency, vaFor speed.
So far the focusing of pared echo is completed.Distance is to there are still residual video phase error at this time, in order to follow-up
Parameter Estimation it must be compensated.It is ss that echo-signal after focusing is transformed to time domain1(t, τ), residual video phase
Position can be eliminated by time-domain filtering, and the formula of the residual video phase filter function is
sc=exp { j π Kat2]}
WhereinRepresent orientation frequency modulation rate, vaFor speed, λ is wavelength, R0It is low coverage, when t is orientation
Carve.By signal ss1(t, τ) is multiplied with residual video phase filter function to eliminate residual video phase, then is translated the signals into
Ss (f are expressed as to range-Dopler domaina′,τ)。
Step (6)：Sine Modulated phase error compensation is carried out to the echo-signal after focusing, realizes the suppression of pared echo
System, completes two-dimension focusing imaging.
By signal Ss (fa', τ) Sine Modulated phase-correction filter function is multiplied by, the formula of the filter function is as follows：
Wherein, A is equivalent vibration amplitude, fa' representing the orientation frequency after Keystone conversion, τ represents Distance Time, Ka
Represent orientation doppler frequency rate, fmFor vibration frequency,To vibrate first phase, λ is wavelength.
So far the suppression of pared echo is completed.
SAR image output finally is obtained as inverse Fourier transform to Data in Azimuth Direction, the SAR image formula of output is：
Wherein, t is the orientation moment, and τ represents Distance Time, and c is the light velocity, BrIt is transmitted signal bandwidth, R0For time domain parameter,
BaIt is doppler bandwidth, t0It is the beam center moment, f0For radar carrier frequency.
Simulating scenes in the present embodiment are as shown in figure 3, target is a static tank on ground.
Using the echo-signal of tank as input, to SAR echoes into row distance to FFT transform, go to apart from frequency domain-orientation
Time domain, into row distance pulse pressure；Orientation FFT transform is carried out, is walked about in two-dimensional frequency using Keystone conversion correction distances；Again
Adjust the distance and make inverse Fourier transform to data, go to range-Dopler domain and carry out range curvature correction, and it is secondary to compensate orientation
Phase and residual video phase, the focusing results for obtaining pared echo are as shown in Figure 4；
Finally in range Doppler domain compensation Sine Modulated phase error as caused by vibration, the suppression of pared echo is realized
System, it is as shown in Figure 5 to obtain two-dimension focusing imaging results.
In order to compare and analyze, same scene is given using the processing of ω K-methods as a result, as shown in Figure 6.By contrast
It can be seen that the imaging results obtained using ω K-methods can not resolution target tank position, and use the method for the present invention to handle
Target tank is high-visible afterwards.
In conclusion present invention is generally directed to the Terahertz SAR imagings under the shaking platforms such as helicopter, relative to tradition side
Method processing can cause image dispersion problem occur, and the present invention can not only be in two-dimensional frequency full correction range walk, while can
Sine Modulated error term present in the range migration curve as caused by vibration is fully compensated, realizes the two-dimentional high-resolution of image
Focus on.
Above-mentioned embodiment is only used for explanation and illustration technical scheme, but can not form and right is wanted
The protection and restriction asked.It will be apparent to those skilled in the art that carried out on the basis of technical scheme any simple
Deformation or replacement obtained from new technical solution, will fall under the scope of the present invention.
Claims (8)
1. a kind of Terahertz SAR vibration compensation imaging methods, it is characterised in that specifically comprise the following steps：
Step (1)：Establish the two-dimentional echo signal model of Terahertz SAR imagings under shaking platform；
Step (2)：The two-dimentional echo-signal of collection；
Step (3)：Fourier transform is made to the two-dimentional echo-signal, when two-dimentional echo-signal is gone to apart from frequency domain-orientation
Domain, into row distance pulse pressure；
Step (4)：Fourier transform is made to the two-dimentional echo-signal after pulse pressure, Keystone is utilized in two-dimensional frequency
Conversion correction distance is walked about；
Step (5)：To the two-dimentional echo-signal after Keystone conversion in distance to inverse Fourier transform is made, in range Doppler
Domain correction distance bending, compensation quadratic phase and residual video phase, complete the focusing of pared echo；
Step (6)：Sine Modulated phase error compensation is carried out to the echo-signal after focusing, realizes the suppression of pared echo, it is complete
It is imaged into two-dimension focusing.
2. the method as described in claim 1, it is characterised in that the echo-signal in the step (1) is：
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Wherein, wr() represents pulse envelope function, wa() is orientation envelope function, and R (t) is oblique distance, t0It is beam center
Moment, f0For radar carrier frequency, KrDistance is represented to frequency modulation rate, t is the orientation moment, and τ represents Distance Time, and c is the light velocity.
3. the method as described in claim 1, it is characterised in that in the step (2), the two dimension echo-signal includes distance
To information and orientation information.
4. the method as described in claim 1, it is characterised in that the step (3)：Fourier is made to the two-dimentional echo-signal
Conversion, echo is gone to apart from frequency domain-orientation time domain, is specially into row distance pulse pressure：
By two-dimentional echo-signal along distance to obtaining sS (t, f after doing Fourier transformationr), wherein frRepresent frequency of distance, Ran Houjin
Row distance pulse pressure.
5. the method as described in claim 1, it is characterised in that in the step (3), the matched filter apart from pulse pressure
Formula is as follows：
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Wherein KrIt is distance to frequency modulation rate, frRepresent frequency of distance.
6. the method as described in claim 1, it is characterised in that the step (4)：To the two-dimentional echo after pulse pressure
Signal makees Fourier transform, is walked about and specifically included using Keystone conversion correction distances in two-dimensional frequency：
First by signal sS (t, the f after pulse pressurer) phase the form of Bessel function is resolved into along orientation, then pass through
After orientation Fourier transformation, signal SS (f are obtaineda,fr), wherein faOrientation frequency is represented, then using Keystone conversion pair
Range walk is corrected, and the signal after note correction is SS (fa′,fr)。
7. such as the method any one of claim 1-6, it is characterised in that in the step (4), Keystone conversion
Formula is
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Wherein, f0Represent radar carrier frequency, faRepresent orientation frequency, fa' represent the orientation frequency after Keystone conversion, frRepresent away from
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8. such as the method any one of claim 1-7, it is characterised in that the step (6) specifically includes：After focusing on
Echo-signal be multiplied by Sine Modulated phase-correction filter function to carry out Sine Modulated phase error compensation.
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| CN114280055A (en) * | 2021-12-16 | 2022-04-05 | 北京工业大学 | Continuous terahertz wave synthetic aperture imaging system and method |
| CN114280055B (en) * | 2021-12-16 | 2024-02-23 | 北京工业大学 | Continuous terahertz wave synthetic aperture imaging system and method |
| CN114706078A (en) * | 2022-04-02 | 2022-07-05 | 南京航空航天大学 | Terahertz synthetic aperture radar imaging system and method based on digital signal processing |
| CN115982571A (en) * | 2023-01-12 | 2023-04-18 | 中国人民解放军军事科学院系统工程研究院 | Geometric representation method and device for space terahertz communication signals |
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