CN108490439A - Bistatic arbitrary configuration SAR imaging methods based on equivalent oblique distance - Google Patents
Bistatic arbitrary configuration SAR imaging methods based on equivalent oblique distance 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
- G01S13/9004—SAR image acquisition techniques
- G01S13/9011—SAR image acquisition techniques with frequency domain processing of the SAR signals in azimuth
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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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- 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
- G01S13/9058—Bistatic or multistatic SAR
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Abstract
The invention discloses a kind of bistatic arbitrary configuration SAR imaging methods based on equivalent oblique distance, realization step of the invention are：(1) biradical equivalent oblique distance model is built；(2) Range compress and non-space-variant error disturbance compensation；(3) orientation is gone tiltedly to handle；(4) distance for having distortion is imaged；(5) imaging results are carried out with the hybrid compensation of Spatially variant phase error and pattern distortion；(6) to there is the imaging of the distance of distortion to carry out distortion correction.The present invention has in the case where three axis of transmit-receive platform has speed and acceleration, can realize accurate phase and motion compensation to the processing of biradical synthetic aperture radar image-forming, obtain the biradical synthetic aperture radar image-forming result of higher focusing quality.
Description
Technical field
The invention belongs to field of communication technology, further relate to a kind of based on equivalent in Radar Signal Processing Technology field
Bistatic arbitrary configuration synthetic aperture radar (Synthetic Aperture Radar, SAR) imaging method of oblique distance.The present invention
The double-base SAR imaging that can be used for splitting the transmit-receive platform of arbitrary configuration curvilinear path, obtains undistorted double-base SAR distance
Figure is applied to the matching positioning of subsequent radar image.
Background technology
Double-base SAR imaging as a kind of new imaging detection system, by by transmitter with receiver wave beam to specific
Regional sustained is resident, can effectively promote radar and continue detectivity to the high-resolution of front Target under Complicated Background, in missile homing
Guidance, silent strike etc. have important application value in army.There are three larger axle speeds and acceleration for double-base SAR
Degree, flight path are curvilinear path, this makes the oblique distance model that traditional foundation uniform rectilinear track is established no longer be applicable in.
A kind of patent document " based on class list base equivalent double-base synthetic aperture radar of the University of Electronic Science and Technology in its application
Imaging method " (publication number：CN103033811A, application number：CN201210334076.9 it is disclosed in) a kind of based on class list base
The equivalent double-base SAR system imaging method in ground.This method the specific steps are：By by bistatic double joint oblique distance history etc.
Effect is the single oblique distance history in similar single base, obtains the analytical expression of the 2-d spectrum of system, simplifies bistatic double joint
Number Solve problems, the ripe single base imaging method of utilization, such as omega-K (wk) algorithm, range Doppler algorithm (RD
Algorithm), according to the expression formula of 2-d spectrum, the two-dimentional STOLT relationships of system are obtained, are finally become using the non-homogeneous Fourier of two dimension
Approximate two dimension STOLT interpolation is brought, the imaging to the system is completed.To largely reduce bistatic imaging algorithm
Complexity provides conveniently for follow-up imaging.Shortcoming existing for this method is, since the SAR imaging methods will be biradical
The double joint oblique distance history on ground is equivalent to the single oblique distance history in similar single base, and arbitrary configuration high-precision SAR is imaged, is existed
Larger approximate error can not achieve accurately phasing, influence the quality of target imaging.
A kind of patent document " fixed station double-base synthetic aperture radar imaging method " of the University of Electronic Science and Technology in its application
(publication number：CN102707283A, application number：CN201210198097.2 a kind of fixed station double-base SAR imaging is proposed in)
Method.A kind of double-base SAR system imaging method based on Doppler frequency expansion of the disclosure of the invention, by will be accurate double
Base SAR 2-d spectrums expression formula carries out Taylor expansion about Doppler frequency, simplifies and solves 2-d spectrum expression formula；It utilizes
The thought of omega-k algorithms obtains the two-dimentional STOLT relationships of system according to the expression formula of 2-d spectrum, finally by utilizing two
Dimension STOLT relationships complete the imaging of system using two-dimentional Nonuniform fast Fourier transform come approximate two dimension STOLT interpolation.Due to only
Consider Doppler frequency, largely reduces the complexity of bistatic imaging algorithm.Shortcoming existing for this method is,
In practical applications, double-base SAR and it is unsatisfactory for the bistatic imaging geometry configuration of fixed station of the invention, target can not be carried out
Effectively imaging.
Invention content
It is an object of the invention to the deficiency for above-mentioned prior art, a kind of bistatic based on equivalent oblique distance is proposed
Anticipate configuration SAR imaging methods, the distortionless SAR distances figure of acquisition, be suitable for arbitrary configuration curvilinear path double-base SAR at
Picture.
To achieve the purpose of the present invention, thinking of the invention is to pass through the double-base synthetic aperture thunder of structure arbitrary configuration
Up to the equivalent oblique distance model of SAR generalizations, non-space-variant error disturbance correction factor is obtained, non-space-variant error is disturbed with the correction factor
It is dynamic to compensate, rotation and interpolation are carried out to frequency spectrum using two dimensional separation interpolation method, using back mapping filtering and interpolation side
Method carries out hybrid compensation to Spatially variant phase error and pattern distortion and is transformed into distance plane using Sinc interpolation methods, obtains double
The undistorted distance figure of base synthetic aperture radar SAR signals.
The specific steps of the present invention include as follows：
(1) according to the following formula, the biradical synthetic aperture radar transmit-receive platform of arbitrary configuration is established to the equivalent oblique distance of target point
Model：
Wherein, R (tm) indicate in transmit-receive platform flight time tmMoment, the equivalent oblique distance model of transmit-receive platform to target point,
RTIndicate instantaneous oblique distance of the transmitter on female bullet relative to arbitrary target points in scene, RRIndicate that the receiver on bullet is opposite
The instantaneous oblique distance of arbitrary target points in scene, Σ indicate summation symbol, ARi(xp,yp) indicate coordinate of the transmitter to target point
Position (xp,yp) kinematic error ith coefficient of disturbance, ATi(xp,yp) indicate coordinate position (x of the receiver to target pointp,yp)
The ith coefficient of disturbance of kinematic error, the value of i are determined by imaging resolution；
(2) Range compress：
To the echo-signal that biradical synthetic aperture radar receives, Range compress processing is carried out, after obtaining Range compress
Echo-signal；
(3) kinematic error disturbs coarse compensation：
(3a) utilizes signal conversion formula, will be transformed to wave-number domain echo letter apart from frequency domain echo signal after Range compress
Number：
(3b), for reference point, correction factor and wave is disturbed with non-space-variant error with the scene center point (0,0) of imaging region
Number field echo-signal is multiplied to non-space-variant kinematic error disturbance compensation, obtains non-space-variant kinematic error disturbance compensation treated letter
Number：
(4) orientation is gone tiltedly to handle：
Echo-signal after coarse compensation is removed into oblique fac-tor with orientation, carrying out orientation to echo 2-d spectrum removes Xie Chu
Reason, obtains the compressed echo data of azimuth spectrum；
(5) by echo projection to distance plane：
Using projection transform formula, 2-d spectrum interpolation is carried out to the compressed echo data of azimuth spectrum, projects to distance
Plane obtains the distance echo data there are Spatially variant phase error and distortion：
(6) hybrid compensation of Spatially variant phase error and pattern distortion is carried out to echo：
(6a) is laid with the pixel network of one group and radar beam overlay area equal areas in ground level along X-axis, Y direction
Lattice, wherein pixel grid X to spacing be X to the spacing of π times of reciprocal 2 of wave-number domain width, Y-direction be Y-direction wave-number domain width
π times of reciprocal 2；
(6b) is multiplied by inclination of wave front compensating filter in two-dimentional wave-number domain, with the echo-signal after interpolation, and obtained product multiplies
With kinematic error residual compensation filter, inverse Fourier transform processing is carried out to the signal after compensation, the picture after being compensated is flat
Face focusedimage；
(7) correction distance figure distortion：
(7a) utilizes coordinate mapping equation, finds in the image plane after compensation and is sat with each ground pixel network lattice site
Mark the image plane pixel position coordinates after corresponding compensation；
8 × 8 pixels around each pixel in image plane after compensation are formed a picture element matrix by (7b)；
Each picture element matrix is multiplied by (7c) with 8 × 8 two-dimentional Sinc function interpolations template, obtains the new pixel of the element
Matrix adds up all elements value of each new picture element matrix, and each pixel corresponds on ground in the image plane after being compensated
Pixel value away from planar pixel grid；
(8) judge whether interpolation is complete for all ground level mesh points, if so, thening follow the steps (9), otherwise, execute step
(6)；
(9) distortionless double-base synthetic aperture radar SAR distance images are obtained.
The present invention compared with prior art, has the following advantages：
First, since the present invention is equivalent tiltedly by the SAR for building double-base SAR transmit-receive platform to the target point of arbitrary configuration
Away from model, the kinematic error disturbance term that acceleration is brought, without near linear oblique distance model separation, overcomes existing with double joint number
The problem of kinematic error is difficult to compensate for caused by arbitrary double-base SAR geometric configuration inaccuracy in technology so that of the invention
Equivalent oblique distance model accuracy higher, improves double-base SAR imaging precision.
Second, since the present invention uses back mapping interpolation, hybrid compensation is carried out to Spatially variant phase error and pattern distortion,
It overcomes double-base SAR image processing method in the prior art and there is the inclination of wave front of two-dimentional space-variant, movement after phase compensation
The problem of error disturbance residual and pattern distortion so that the present invention can meet three axis direction of Double tabletop and there is velocity and acceleration
The imaging configuration of movement improves the focusing performance of double-base SAR imaging result.
Description of the drawings
Fig. 1 is the flow chart of the present invention；
Fig. 2 be arbitrary configuration of the present invention double-base synthetic aperture radar SAR transmit-receive platforms to target point equivalent oblique distance
Model；
Fig. 3 is that the present invention emulates schematic diagram of layouting；
Fig. 4 is that the point of the prior art emulates azimuthal section figure；
Fig. 5 is that the point of the method for the present invention emulates azimuthal section figure；
Fig. 6 is the point focusing sectional view of the method for the present invention；
Fig. 7 is Spatially variant phase error of the present invention and the imaging results before and after pattern distortion hybrid compensation；
Fig. 8 is target point X-direction and Y-direction position deviation line chart after hybrid compensation of the present invention；
Specific implementation mode
The present invention will be further described below in conjunction with the accompanying drawings.
With reference to attached drawing 1, specific implementation step of the invention is as follows：
Step 1, equivalent oblique distance model is established.
Fig. 2 gives the equivalent oblique distance illustratons of model of SAR of double-base SAR transmit-receive platform to the target point of arbitrary configuration, in Fig. 2
X-axis indicate distance to coordinate, unit is rice, and Y-axis indicates that orientation coordinate, unit are rice, and Z axis indicates the height of transmit-receive platform
Degree, unit is rice.P (ρ, θ in Fig. 2p, 0) and indicate either objective point in imaging region, RTIndicate that the transmitter on female bullet is opposite
The instantaneous oblique distance of arbitrary target points, R in sceneRIndicate bullet on receiver relative in scene arbitrary target points it is instantaneous
Oblique distance, wherein R0TIndicate the transmitter bistatic instantaneous oblique distance corresponding with scene center point on female bullet, R0RIndicate connecing on bullet
Receipts machine bistatic instantaneous oblique distance corresponding with scene center point, θRIndicate the angle of receiver center oblique distance and Y-axis, θTIn transmitter
It is as follows to establish model according to Fig. 2 for the angle of heart oblique distance and Y-axis：
Wherein, R (tm) indicate in transmit-receive platform flight time tmMoment, the equivalent oblique distance moulds of SAR of transmit-receive platform to target point
Type, ARi(xp,yp) indicate coordinate position (x of the transmitter to target pointp,yp) kinematic error ith coefficient of disturbance, ATi(xp,
yp) indicate coordinate position (x of the receiver to target pointp,yp) kinematic error ith coefficient of disturbance, the value of i is by being imaged
What resolution ratio determined, arbitrary configuration refers to that the velocity variations in configuration have randomness and transmit-receive platform height, track angle can
Arbitrarily to select.
RR、RT、ARi(xp,yp) and ATi(xp,yp) be given by：
Wherein
In formula, (xR,yR,HR) indicate receiver tmPosition when=0 in coordinate system XOY, (xT,yT,HT) indicate tm=0
When position in coordinate system XOY, (vxR,vyR,vzR) indicate three axle speed vector of receiver, (vxT,vyT,vzT) indicate three axle speeds
Spend vector, (aRx,aRy,aRz) indicate receiver 3-axis acceleration vector, (aTx,aTy,aTz) indicate transmitting receipts machine 3-axis acceleration
Vector.
Step 2, Range compress.
To the echo-signal that double-base SAR receives, Range compress processing is carried out, obtains the letter of the echo after Range compress
Number.
Original echoed signals are as follows：
Wherein, Wr() indicates the frequency domain form apart from window function, frIt indicates apart from frequency domain, wa() indicates orientation window letter
Number forms of time and space, exp indicate that using natural logrithm as the index operation at bottom, j indicates that imaginary symbols, γ are indicated apart from frequency modulation rate, π tables
Show that pi, c indicate the light velocity, fcIndicate the carrier frequency of transmitter radar signal.
After Range compress, echo-signal is as follows
Step 3, non-space-variant kinematic error compensation.
Using following formula transformational relation, the echo-signal after Range compress is transformed to wave-number domain echo-signal：
Wherein, krIndicate imaging plane apart from wave number.
Wave-number domain echo-signal formula is as follows：
S=Wr(kr)wa(tm)exp(-jkrR(tm))
With the scene center point (0,0) of imaging region for reference point, correction factor and wave-number domain are disturbed with non-space-variant error
Echo-signal is multiplied to non-space-variant kinematic error disturbance compensation, obtains non-space-variant kinematic error disturbance compensation treated signal.
Non- space-variant error disturbance correction factor is as follows：
Wherein, HAccIndicate non-space-variant error disturbance correction factor, ARi0(0,0) seat of the transmitter to scene center point is indicated
Cursor position (xp,yp) kinematic error ith coefficient of disturbance, ATi0(0,0) coordinate position of the receiver to scene center point is indicated
(xp,yp) kinematic error ith coefficient of disturbance, coefficient of disturbance obtains by following formula：
After the processing of kinematic error disturbance compensation, echo-signal expression formula is as follows：
Wherein Di(xp,yp) andExpression it is as follows：
Wherein, first item is signal resolution item, represents double-base SAR phase of echo under conventional uniform rectilinear's configuration；Second
Item indicates secondary and kinematic error corrects residual item three times, equal related with aiming spot per term coefficient, shows kinematic error
There are two-dimensional position space-variants for residual phase；Item is remained for quadravalence after compensated acceleration correction factor and high-order space-variant.
Step 4, orientation is gone tiltedly to handle.
Echo-signal after coarse compensation is removed into oblique fac-tor with orientation, carrying out orientation to echo 2-d spectrum removes Xie Chu
Reason, obtains the compressed echo data of azimuth spectrum.
Orientation goes the oblique factor to be obtained by following formula：
Hdrp=exp (jkr(R0R+R0T))
Wherein, HdrpIndicate that the oblique factor is gone in orientation.
Step 5, distance planar imaging.
Using following transformational relation, 2-d spectrum interpolation is carried out to the compressed echo data of azimuth spectrum, projects to distance
Plane obtains the distance echo data there are Spatially variant phase error and distortion：
Wherein, kxIndicate the X of imaging localized ground to orientation wave number, krIndicate imaging plane apart from wave number, Γx(tm)
Indicate krTo kxConversion coefficient, kyIndicate the Y-direction orientation wave number of imaging localized ground, Γy(tm) indicate krTo kyConversion system
Number.
Conversion coefficient Γx(tm)、Γy(tm) as follows：
Wherein, cos indicates cosine operation, ψRIndicate instantaneous wiping ground of the receiver relative to the scene center point of imaging region
Angle, sin indicate sinusoidal operation, ψTIndicate instantaneous grazing angle of the transmitter relative to the scene center point of imaging region, the above change
Magnitude is obtained by following formula：
Echo polar form before interpolation is as follows：
The echo-signal phase of the signal is writeable as follows：
Wherein, Δ10、Δ11、Δ20、Δ21、Δ22It is obtained by following formula：
In formula, LiThe specific expression of (i=1,2 ..., 4) is as follows
The value that the above two formulas subscript includes the variable of c is corresponding instance variable in the slow time t in orientationmWhen=0
The value at quarter.
The echo carried out after two-dimensional interpolation is as follows：
Step 6, hybrid compensation is carried out to Spatially variant phase error and pattern distortion using back mapping interpolation.
The pixel grid of one group and radar beam overlay area equal areas is laid with along X-axis, Y direction in ground level,
Middle pixel grid X to spacing be 2 π/Δ kx, Y-direction spacing be 2 π/Δ ky。
In two-dimentional wave-number domain, it is multiplied by inclination of wave front compensating filter with the echo-signal after interpolation, obtained product is multiplied by fortune
Dynamic error residuals compensating filter carries out inverse Fourier transform processing, the focusedimage after being compensated to the signal after compensation.
Inclination of wave front compensating filter is as follows：
Kinematic error residual compensation filter is as follows：
Step 7, correction distance figure distortion.
Using the coordinate relationship of image plane and ground, finds in image plane and answered with each ground grid point locations coordinate pair
Image plane point position coordinates.
Image plane and the coordinate relationship on ground are：
Wherein, (ximg,yimg) indicate image plane coordinate position,Indicate receiver relative in the scene of imaging region
The instantaneous grazing angle of heart point, θRcIndicate the angle of receiver center oblique distance and Y-axis,Indicate transmitter relative to imaging region
Scene center point instantaneous grazing angle, θTcThe angle of transmitter center oblique distance and Y-axis.
By 8 × 8 pixels around each pixel in the image plane after compensation, a picture element matrix is formed；
Each picture element matrix is multiplied with 8 × 8 two-dimentional Sinc function interpolations template, obtains the new pixel square of the element
Battle array, all elements value of each new picture element matrix is added up, and each pixel is corresponded in distance in the image plane after being compensated
The pixel value of planar pixel grid；
Step 8, judge whether interpolation is complete for all ground level mesh points, if so, thening follow the steps (8), otherwise, execute step
(6)。
Step 9, distortionless biradical synthetic aperture radar distance image is obtained.
Emulate data processing experimental verification：
To verify the validity of the method for the present invention, the method for the present invention and class list base equivalent method are imitated in Matlab
Very, Fig. 3 gives the imaging region cloth point diagram of emulation, and X-axis indicates that target point X-direction coordinate, unit are rice in Fig. 3, and Y-axis indicates
Target point side's Y-direction coordinate, unit are rice.The midpoints Fig. 31 and point 3 are marginal points, and it is scene center point to put 2.β is indicated biradical in Fig. 3
Ditch, 3km indicate imaging region ground level along distance to length, 1.5km indicate imaging region ground level along orientation length
Degree, ground level azimuth resolution are 0.5m.Consider that platform has the speed and acceleration of three axis, emulates design parameter such as following table
It is shown：
1 radar simulation design parameter list of table
Fig. 4 is to emulate azimuthal section figure using the point of class list base equivalent method, and X-axis indicates frequency in Fig. 4, and unit is conspicuous
Hereby, Y-axis indicates normalization amplitude, and unit is decibel.Fig. 4 (a) is the imaging results edge obtained using class list base equivalent method
The azimuthal section figure of point 1, Fig. 4 (b) are the side of the imaging results scene center point 2 obtained using the method for class list base equivalent method
Position sectional view, Fig. 4 (c) is the azimuthal section figure for giving imaging results marginal point 3 obtained using class list base equivalent method.It is logical
Cross the azimuthal section for comparing 2 azimuthal section figure of Fig. 4 (b) Scenes central point and imaging results marginal point in Fig. 4 (a), Fig. 4 (c)
Figure, it is seen that there are a larger orientation phase errors for imaging results marginal point so that orientation defocuses, under azimuth resolution is serious
Drop.
Fig. 5 is to emulate azimuthal section figure using the point that the method for the present invention obtains, and X-axis indicates frequency in Fig. 5, and unit is conspicuous
Hereby, Y-axis indicates normalization amplitude, and unit is decibel.Fig. 5 (a) is the imaging results marginal point 1 obtained using the method for the present invention
Azimuthal section figure, Fig. 5 (b) are the azimuthal section figure of the imaging results scene center point 2 obtained using the method for the present invention, Fig. 5 (c)
Azimuthal section figure for the imaging results marginal point 3 obtained using the method for the present invention.By comparing Fig. 4 (a) and Fig. 5 (a), Fig. 4
(c) with Fig. 5 (c), it is seen that the first zero and the first secondary lobe of the imaging results marginal point 1 and point 3 that are obtained using the method for the present invention
It is pulled low, close to the secondary lobe of the scene center point 2 of imaging results, the method for the present invention is for imaging results marginal point space-variant phase
Error can compensate well.
Fig. 6 is the point simulation result two dimension contour map obtained using the method for the present invention, and X-axis indicates localizer unit in Fig. 6,
Unit is azimuth resolution, and Y-axis indicates range cell, and unit is distance resolution.Fig. 6 (a) is to be obtained using the method for the present invention
Imaging results marginal point 1 two-dimentional contour map, Fig. 6 (b) is the imaging results scene center obtained using the method for the present invention
The two-dimentional contour map of point 2, Fig. 6 (c) is the two-dimentional contour map of the imaging results marginal point 3 obtained using the method for the present invention.
Pass through the difference of comparison diagram 6 (b) and the two-dimentional contour map of Fig. 6 (a), Fig. 6 (c), it is seen that the principal subsidiary lobe of imaging results marginal point is bright
It is aobvious to separate, it is close with scene center point, demonstrate the validity of put forward the method for the present invention.
In order to further assess the performance of the method for the present invention, the imaging results midpoint obtained using two kinds of distinct methods is calculated
1,2,3 resolution ratio, peak sidelobe ratio, integral secondary lobe it is more as shown in table 2 below than index parameter, it can be seen that the method for the present invention at
Picture performance indicator result is coincide substantially with theoretical value, illustrates the validity of the method for the present invention.
The index parameter list of 2 simulated point of table
To verify the validity of the method for the present invention put forward Spatially variant phase error and geometric distortion hybrid compensation, on ground level edge
X-direction and Y-direction arrange that one group 11 × 11 of dot matrix, scene size are 1km × 1km, and distance grid spacing is 1m × 1m, is used
The method of the present invention carries out simulation imaging to echo.
Fig. 7 is Spatially variant phase error and the imaging results figure before and after geometric distortion hybrid compensation, and Fig. 7 (a) is space-variant phase
Error and the imaging results figure before geometric distortion hybrid compensation, after Fig. 7 (b) is Spatially variant phase error and geometric distortion hybrid compensation
Imaging results figure.By the imaging results figure of Fig. 7 (a) it is found that exist before Spatially variant phase error and geometric distortion hybrid compensation compared with
Big distortion, and imaging results marginal point is defocused there are a degree of, whole image is presented approximate " diamond shape ".By space-variant phase
For error with after pattern distortion hybrid compensation, " square " dot matrix for layouting consistent with emulation is presented in whole image.
Fig. 8 is the target point in Fig. 7 (b) in rectangle frame and the target point X-direction and Y-direction position deviation folding in distance figure
Line chart, X-axis indicates that target point serial number, Y-axis indicate the deviation of the coordinate and actual position coordinate in distance figure in Fig. 8.Fig. 8 (a)
For target point X-direction position deviation line chart, Fig. 8 (b) is target point Y-direction position deviation line chart, as shown in Figure 8, is passed through
After hybrid compensation correction, target point is much smaller than 1/4 resolution sizes in X to Y-direction deviation, and image is abnormal after illustrating hybrid compensation
Variable very little further demonstrates the validity of put forward hybrid compensation method.
Claims (6)
1. a kind of bistatic arbitrary configuration SAR imaging methods based on equivalent oblique distance, which is characterized in that this method is appointed by structure
The equivalent oblique distance model of double-base synthetic aperture radar SAR generalizations of meaning configuration obtains non-space-variant error disturbance correction factor, uses
The correction factor compensates the disturbance of non-space-variant error, and rotation and interpolation are carried out to frequency spectrum using two dimensional separation interpolation method,
Hybrid compensation is carried out to Spatially variant phase error and pattern distortion with interpolation method using back mapping filtering, using the interpolation sides Sinc
Method is transformed into distance plane, obtains the undistorted distance figure of double-base synthetic aperture radar SAR signals, and specific steps include such as
Under：
(1) according to the following formula, the double-base synthetic aperture radar SAR transmit-receive platforms of arbitrary configuration are established to the equivalent oblique distance of target point
Model：
Wherein, R (tm) indicate in transmit-receive platform flight time tmMoment, the equivalent oblique distance model of transmit-receive platform to target point, RTTable
Show instantaneous oblique distance of the transmitter relative to arbitrary target points in scene on female bullet, RRIndicate the receiver on bullet relative to field
The instantaneous oblique distance of arbitrary target points in scape, Σ indicate summation symbol, ARi(xp,yp) indicate coordinate position of the transmitter to target point
(xp,yp) kinematic error ith coefficient of disturbance, ATi(xp,yp) indicate coordinate position (x of the receiver to target pointp,yp) movement
The ith coefficient of disturbance of error, the value of i are determined by imaging resolution；
(2) Range compress：
To the echo-signal that double-base synthetic aperture radar SAR is received, Range compress processing is carried out, after obtaining Range compress
Apart from frequency domain echo signal；
(3) non-space-variant kinematic error compensation：
(3a) utilizes signal conversion formula, will be transformed to wave-number domain echo-signal apart from frequency domain echo signal after Range compress：
(3b), for reference point, correction factor and wave-number domain is disturbed with non-space-variant error with the scene center point (0,0) of imaging region
Echo-signal is multiplied to non-space-variant kinematic error disturbance compensation, obtains non-space-variant kinematic error disturbance compensation treated signal：
(4) orientation is carried out to echo 2-d spectrum to go tiltedly to handle：
Echo-signal after coarse compensation is removed into oblique fac-tor with orientation, carrying out orientation to echo 2-d spectrum goes tiltedly to handle, and obtains
To the compressed echo data of azimuth spectrum；
(5) by echo projection to distance plane：
Using projection transform formula, 2-d spectrum interpolation is carried out to the compressed echo data of azimuth spectrum, projects to distance plane,
Obtain the distance echo data there are Spatially variant phase error and distortion：
(6) hybrid compensation of Spatially variant phase error and pattern distortion is carried out to echo：
(6a) is laid with the pixel grid of one group and radar beam overlay area equal areas in ground level along X-axis, Y direction,
Middle pixel grid X to spacing be X to the spacing of π times of reciprocal 2 of wave-number domain width, Y-direction be the inverse of Y-direction wave-number domain width
2 π times；
(6b) is multiplied by inclination of wave front compensating filter in two-dimentional wave-number domain, with the echo-signal after interpolation, and obtained product is multiplied by fortune
Dynamic error residuals compensating filter carries out inverse Fourier transform processing to the signal after compensation, and the image plane after being compensated is poly-
Burnt image；
(7) correction distance figure distortion：
(7a) utilizes coordinate mapping equation, is found and each ground pixel network lattice site coordinate pair in the image plane after compensation
Image plane pixel position coordinates after the compensation answered；
8 × 8 pixels around each pixel in image plane after compensation are formed a picture element matrix by (7b)；
Each picture element matrix is multiplied by (7c) with 8 × 8 two-dimentional Sinc function interpolations template, obtains the new pixel square of the element
Battle array, all elements value of each new picture element matrix is added up, and each pixel is corresponded in distance in the image plane after being compensated
The pixel value of planar pixel grid；
(8) judge whether interpolation is complete for all ground level mesh points, if so, thening follow the steps (9), otherwise, execute step (6)；
(9) distortionless double-base synthetic aperture radar SAR distance images are obtained.
2. the bistatic arbitrary configuration SAR imaging methods according to claim 1 based on equivalent oblique distance, which is characterized in that
Arbitrary configuration described in step (1) refers to the configuration for meeting following three conditions simultaneously：
Condition 1, there is velocity amplitude in the velocity vector of transmit-receive platform in three axis directions in configuration；
Condition 2, there is acceleration value in the acceleration of transmit-receive platform in three axis directions in configuration；
Condition 3, the height of transmit-receive platform, track angle are without constraint in configuration.
3. the bistatic arbitrary configuration SAR imaging methods according to claim 1 based on equivalent oblique distance, which is characterized in that
Signal conversion formula described in step (3a) is as follows：
Wherein, krIndicate imaging plane apart from wave number, frIndicate that frequency of distance, π indicate that pi, c indicate the light velocity, fcIt indicates
The carrier frequency of transmitter radar signal.
4. the bistatic arbitrary configuration SAR imaging methods according to claim 1 based on equivalent oblique distance, which is characterized in that
Orientation described in step (4) goes the oblique factor to be obtained by following formula：
H=exp (jkr(R0R+R0T))
Wherein, H indicates that orientation goes the oblique factor, exp to indicate that, using natural logrithm as the index operation at bottom, j indicates imaginary symbols, R0TTable
Show transmitter bistatic instantaneous oblique distance corresponding with scene center point, R0RIndicate that receiver is corresponding with scene center point bistatic instantaneous
Oblique distance.
5. the bistatic arbitrary configuration SAR imaging methods according to claim 1 based on equivalent oblique distance, which is characterized in that
Projection transform formula described in step (5) is as follows：
Wherein, kxIndicate the X of distance plane to apart from wave number, krIndicate imaging plane apart from wave number, Γx(tm) indicate krTo kx
Conversion coefficient, kyIndicate the Y-direction orientation wave number on distance ground, Γy(tm) indicate krTo kyConversion coefficient.
6. the bistatic arbitrary configuration SAR imaging methods according to claim 1 based on equivalent oblique distance, which is characterized in that
Coordinate mapping equation described in step (7a) is as follows：
Wherein, ximgIndicate the X of corresponding pixel points in the image plane after compensation to coordinate, L3It indicates true by the target point of imaging region
Fixed constant,Indicate instantaneous grazing angle of the receiver relative to the scene center point of imaging region, θRcIndicate receiver center
The angle of oblique distance and Y-axis,Indicate instantaneous grazing angle of the transmitter relative to the scene center point of imaging region, θTcTransmitter
The angle of center oblique distance and Y-axis, yimgIndicate the Y-direction coordinate of corresponding pixel points in the image plane after compensation.
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