CN107918124A - Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant - Google Patents
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant 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
- G01S13/9041—Squint mode
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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
- G01S13/9004—SAR image acquisition techniques
- G01S13/9017—SAR image acquisition techniques with time domain processing of the SAR signals in azimuth
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Abstract
The invention discloses a kind of airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant, solves the problems, such as airborne big strabismus High Resolution SAR imaging because orientation piecemeal causes significant complexity, its realization includes：SAR echo signal Range Walk Correction；High order coupled phase and two-dimentional excess phase are compensated with higher order penalty function；Distance becomes to frequency modulation to be marked；Range compress and consistent curvature correction；Orientation higher order phase and excess phase compensation and frequency domain phase filtering；Orientation Non-linear chirp scaling；Azimuth Compression and the compensation of orientation order phase.The present invention is by without the coupling terms higher-order expansion in approximate two-dimensional frequency expression formula, improving the depth of focus；Piecemeal handles step-length bigger, and two-dimentional excess phase compensation, greatly reduces residual phase error.The present invention reduce imaging complexity, also weaken because distance to the asymmetric image fault of orientation secondary lobe, improve imaging and focusing performance, for it is airborne it is big strabismus High Resolution SAR imaging.
Description
Technical field
The invention belongs to Radar Signal Processing Technology field, more particularly to SAR (Synthetic Aperture Radar,
Synthetic aperture radar) imaging method is specifically a kind of airborne big strabismus High Resolution SAR imaging side with the correction of orientation space-variant
Method, for airborne big strabismus High Resolution SAR imaging.
Background technology
The appearance of synthetic aperture radar (Synthetic Aperture Radar, SAR), improves the bidimensional of conventional radar
Resolution ratio so that the information that radar obtains is more abundant.SAR has the advantages that two-dimensional optical imaging sensor does not possess, it can
With round-the-clock, all weather operations, and operating distance far and from the limitation of meteorological condition.SAR has been widely used at present
In every field, such as satellite remote sensing, mapping, investigates enemy, and the condition of a disaster is reported etc..With the development of digital processing technology,
More and more SAR imaging algorithms are suggested.The development of SAR imagings at present mainly has both direction：High-resolution and big strabismus
Angle, it is therefore desirable to propose corresponding algorithm for high-resolution and large slanting view angle machine.Big Squint SAR has the advantages that oneself is peculiar：
(1) information of objects ahead can be obtained in advance, and the Radar Cross Section (RCS) of (2) some targets is related with view angle, tiltedly
Depending on being more advantageous to obtaining target information, (3) can revisit area-of-interest.High resolution SAR can be obtained on mesh
Mark more information in region, improved while increasing target information to the resolution of Small object, be conducive to the detection of target with
Identification.
The difficult point of high squint SAR imaging is that the two dimension coupling of signal is more serious, and various imaging algorithms are both for such as
What effectively removes what two dimension coupling proposed.Processing accuracy is mainly improved in terms of two for high squint SAR imaging, first, oblique distance is public
Formula is unfolded, second, range migration correction.Current Squint SAR algorithm has the calculation of RD (Range-Doppler, range Doppler) class
Method, CS (Chirp-Scaling, frequency modulation become mark) class algorithm, (Nonlinear Chirp-Scaling, nonlinear frequency modulation become NCS
Mark) class algorithm, sub-aperture class algorithm etc..RD class algorithms are advanced row distance compressions, are then eliminated using secondary range compression
Two dimension coupling, then carries out range migration correction and orientation compression.CS classes algorithm is first removed in time domain and walked about, and then passes through tune
Frequency, which becomes, is marked on frequency domain removal bending, focuses on image finally by Range compress and Azimuth Compression, but do not account for distance and walk
The problem of azimuth focus depth of dynamic correction tape.NCS algorithms are when handling high squint SAR imaging with certain advantage, side
Position can release the limitation of Azimuth focus depth to NCS algorithms, and algorithm proposed by the invention is namely based on such.Sub-aperture class
Algorithm expands focal imaging region by being divided to aperture, but the algorithm needs the Duplication for improving data processing
Improve orientation imaging effect, complexity is higher.For the High Resolution SAR Imaging under the conditions of big strabismus, existing imaging side
Beam bunching mode is usually used to improve imaging resolution in method.Airborne big strabismus High Resolution SAR Imaging algorithm is introduced at present
Document is less.
Due in strabismus imaging greatly, general advanced row distance is walked about correction, therefore can bring orientation space-variant, and one
As be required for by the way of the processing of orientation piecemeal, and the complexity and the step-length of piecemeal of piecemeal processing are inversely proportional.Similar
Imaging method due to when two-dimensional frequency is unfolded exponent number it is not high enough, orientation space-variant correction can only meet orientation from reference center compared with
Near region, when target orientation from reference center farther out when, focusing performance is decreased obviously, thus orientation piecemeal processing
Step-length is smaller, therefore the complexity of imaging is larger.
The content of the invention
The purpose of the present invention is for it is airborne it is big strabismus High Resolution SAR imaging in due to orientation piecemeal step-length smaller strip come
The higher problem of complexity, propose that a kind of focusing performance is more preferable, the low orientation piecemeal step-length bigger of computation complexity carries
The airborne big strabismus High Resolution SAR imaging method of orientation space-variant correction.
The present invention is a kind of airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant, it is characterised in that
Include following steps：
Step 1, Range Walk Correction is carried out by SAR echo signal in a frequency domain：SAR echo signal is transformed into distance
Frequency domain, is corrected according to Range Walk Correction reference function, obtains the signal after Range Walk Correction；
Step 2, compensates high-order coupled phase and two-dimentional excess phase using the penalty function of higher order：Will
Signal after Range Walk Correction transforms to two-dimensional frequency, derives that high-order couples phase using without approximate two-dimensional frequency expression formula
Position compensation reference function and two-dimentional excess phase compensate reference function, obtain removing high-order coupled phase through overcompensation and residue is high
The signal of rank coupling terms；
Step 3, distance become mark processing to frequency modulation：The signal for removing high-order coupled phase and remaining high-order coupling terms is become
Range-Dopler domain is changed to, is multiplied by becoming scalar functions with linear range, the signal for the complementary range curvature that is eliminated；
Step 4, Range compress and consistent curvature correction：The signal for eliminating complementary range curvature is transformed into two-dimensional frequency,
By Range compress and consistent curvature correction, the signal after Range compress and after range curvature correction is obtained；
Step 5, phase compensation, the compensation of orientation excess phase and the filter of orientation frequency domain phase of orientation higher order
Ripple：Signal after Range compress and after range curvature correction is transformed to and ties up frequency domain apart from time domain side, passes through orientation higher order
Secondary phase compensation reference function and orientation excess phase compensate reference function, eliminate orientation quadravalence phase term, orientation
Five rank phase terms, three rank non-NULL variable of orientation and orientation excess phase, then be multiplied with orientation frequency domain filtering reference function,
Obtain removing the signal after high-order orientation phase term and orientation frequency domain filtering；
Step 6, the operation of orientation Non-linear chirp scaling：High-order orientation phase term and orientation frequency domain filtering will be removed
Signal afterwards transforms to two-dimensional time-domain, is multiplied with orientation Non-linear chirp scaling reference function, obtains orientation frequency and becomes mark
Signal afterwards；
Step 7, Azimuth Compression and the compensation of orientation order phase：By orientation frequency become mark after signal transform to away from
From Doppler domain, Azimuth Compression and the compensation of high-order orientation frequency plot are carried out, completes orientation compression and three rank of orientation and four
Rank phase compensation, finally does orientation inverse fourier transform, and can obtain SAR echo signal high-resolution after geometric correction gathers
Burnt image.
The present invention proposes a kind of improved to become the airborne big of mark and orientation Non-linear chirp scaling to frequency modulation based on distance
High Resolution SAR imaging method is squinted, advanced row distance is walked about correction, and using the 2-d spectrum expression formula of complete oblique distance, progress is more
High-order time series expansion obtains order phase compensation reference function and two-dimentional excess phase compensates reference function, by distance to tune
Frequency become mark processing realize distance to all targets accurate distance curvature correction, finally by orientation using extension it is non-
Linear frequency modulation becomes mark processing to solve the problems, such as the orientation depth of focus.
Compared with prior art, technical advantage of the invention：
1st, on the basis of use is without approximate two-dimensional frequency expression formula, by two-dimentional coupling terms higher-order expansion is obtained away from
Four items of off-frequency rate and five items of orientation frequency, therefore high-order coupled phase can be compensated when two-dimensional frequency is handled, this
Sample weakens distance to the figure brought with orientation secondary lobe asymmetry to greatest extent on the premise of computational complexity is not increased
Image distortion, while by the compensation of accurate two-dimentional excess phase, greatly reduce two-dimentional residual phase error, improve imaging
Focusing performance.
2nd, due to the expansion to two-dimentional coupling terms progress higher order, big Squint SAR is improved after Range Walk Correction
The depth of focus problem brought so that the step-length bigger of piecemeal processing is carried out in strabismus High Resolution SAR imaging contexts greatly, is reduced
The complexity of whole imaging.At the same time only comprising multiplying again and Fast Fourier Transform (FFT) and fast in whole imaging method process flow
Fast Fourier inversion computing, is not related to interpolation arithmetic, therefore be easy to Project Realization.
Brief description of the drawings
In order to illustrate more clearly about the embodiment of the present invention or technical scheme of the prior art, below will be to embodiment or existing
There is attached drawing needed in technology description to be briefly described, it should be apparent that, drawings in the following description are only this
Some embodiments of invention, for those of ordinary skill in the art, without creative efforts, can be with
Other attached drawings are obtained according to these attached drawings.
Fig. 1 is the imaging flow chart of the present invention；
Fig. 2 squints imaging geometry for carried SAR；
Fig. 3 is the setting of 3 point targets in scene；
Fig. 4 be the integration secondary lobe of the point A in Fig. 3 than curve, wherein figure (a) for distance to integration secondary lobe ratio,
Scheme the integration secondary lobe ratio that (b) is orientation；
Fig. 5 is the contour map of the point A in Fig. 3；
Fig. 6 be the integration secondary lobe of the point B in Fig. 3 than curve, wherein figure (a) be distance to integration secondary lobe than curve, scheme
(b) curve is compared for the integration secondary lobe of orientation；
Fig. 7 is the contour map of the point B in Fig. 3；
Fig. 8 is that the point C in Fig. 3 integrates secondary lobe than curve, wherein figure (a) be distance to integration secondary lobe than curve, scheme (b)
Compare curve for the integration secondary lobe of orientation；
Fig. 9 is the contour map of the point C in Fig. 3.
Embodiment
The present invention is described in detail below in conjunction with the accompanying drawings
Embodiment 1
In being handled in high squint SAR imaging, general advanced row distance is walked about correction, therefore can bring orientation sky
Become, be typically necessary by the way of the processing of orientation piecemeal, and the complexity of piecemeal processing and the step-length of piecemeal are inversely proportional.Class
As imaging method due to when two-dimensional frequency is unfolded exponent number it is not high enough, orientation space-variant correction orientation can only be met from reference
The nearer region of the heart, when target orientation from reference center farther out when, focusing performance is decreased obviously, so at orientation piecemeal
The step-length of reason is smaller, therefore the complexity of imaging is larger, it is difficult to engineering application.Present invention is specifically directed to this problem exhibition
Research has been opened, has proposed a kind of airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant, it may also be said to be to be based on
The airborne big strabismus High Resolution SAR imaging method of complete oblique distance or based on frequency modulation become the airborne big strabismus High Resolution SAR of target into
Image space method, for airborne big strabismus High Resolution SAR imaging, referring to Fig. 1, airborne big strabismus High Resolution SAR imaging process includes
Following steps：
Step 1, Range Walk Correction is carried out by SAR echo signal in a frequency domain：Because in big Squint SAR echo-signal
Distance is extremely serious to the coupling with orientation, so needing to first pass through this coupling of Range Walk Correction reduction.By SAR echoes
Signal first passes through quadrature demodulation and is changed into baseband signal, and baseband signal is passed through distance to quick Fu using digital signal processing device
In leaf transformation be transformed into apart from frequency domain, then multiply again into row matrix with Range Walk Correction reference function, obtain Range Walk Correction
Signal afterwards, so as to eliminate range walk, greatly reduces the distance of echo-signal to the coupling between orientation.
Step 2, compensates high-order coupled phase and two-dimentional excess phase using the penalty function of higher order：It is logical
Cross digital signal processing device and the signal after Range Walk Correction is transformed into two-dimentional frequency by orientation Fast Fourier Transform (FFT)
Domain, derives that high-order coupled phase compensation reference function and two-dimentional excess phase compensate using without approximate two-dimensional frequency expression formula
Reference function, uses unified reference oblique distance in high-order coupled phase compensates reference function, is typically chosen as radar to exposure field
The distance at scape center.By the signal in above two-dimensional frequency with compensating reference function and two-dimentional excess phase benefit apart from order phase
Repay reference function into row matrix again to multiply, obtain removing signal of the high-order apart from phase and high-order coupling terms through overcompensation.
Step 3, distance become mark processing to frequency modulation：High-order will be removed apart from phase and height by digital signal processing device
The signal of rank coupling terms is transformed into range-Dopler domain by distance to Fast Fourier Transform Inverse, is marked by becoming with linear range
Function multiplies again into row matrix, the signal for the complementary range curvature that is eliminated.
Step 4, Range compress and consistent curvature correction：Complementary range curvature will be eliminated by digital signal processing device
Signal be transformed into two-dimensional frequency to Fast Fourier Transform (FFT) by distance, with Range compress and consistent curvature correction reference function
Multiply again into row matrix, by Range compress and consistent curvature correction, obtain the signal after Range compress and after range curvature correction,
Complete distance to processing.
Step 5, phase compensation, the compensation of orientation excess phase and the filter of orientation frequency domain phase of orientation higher order
Ripple：Signal after Range compress and after range curvature correction is transformed to by range-Dopler domain by digital signal processing device,
Multiplied again into row matrix by compensating reference function with orientation higher order phase compensation reference function and orientation excess phase,
Orientation quadravalence phase term, five rank phase term of orientation, three rank non-NULL variable of orientation and orientation excess phase are eliminated, is
Enough coefficients are provided to orientation Non-linear chirp scaling, then are answered into row matrix with orientation frequency domain filtering reference function
Multiply, obtain removing the signal after high-order orientation phase term and orientation frequency domain filtering.
Step 6, the operation of orientation Non-linear chirp scaling：High-order orientation phase will be removed by digital signal processing device
Signal after position item and orientation frequency domain filtering is transformed into two-dimensional time-domain by orientation Fourier inversion, non-thread with orientation
Property frequency modulation become mark reference function multiply again into row matrix, obtain orientation frequency become mark after signal, so as to eliminate orientation space-variant
.
Step 7, Azimuth Compression and the compensation of orientation order phase：By digital signal processing device by orientation frequency
The signal become after mark is transformed into range-Dopler domain by orientation Fast Fourier Transform (FFT), carries out Azimuth Compression and high-order orientation
Frequency plot compensates, and completes orientation compression and three rank of orientation and quadravalence phase compensation, finally does orientation fast Flourier
Inverse transformation, can obtain the image of SAR echo signal high-resolution focusing after geometric correction.
The present invention has carried out high order approximation when two-dimensional frequency is unfolded, and reduces coupling secondary lobe, therefore improve distance reference
The focusing performance of center target farther out, increases to a length of synthetic aperture by the step-length that orientation piecemeal is handled, reduces into
As the complexity of processing.
Embodiment 2
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1, described in step 2
Use without approximate two-dimensional frequency expression formula, be specifically：
In formulaRepresent two-dimension spectrum coupling item, two dimension frequency
Domain coupling terms derivation does not contain approximation.
Wherein fτIt is distance to frequency (unit Hz), faFor orientation frequency (unit Hz), Wr(fτ) for distance to frequency
The amplitude in domain, Wa(fa) be orientation frequency domain amplitude, KrFor frequency modulation rate, XnRepresent that target exists with zero moment radar illumination center
(unit m), θ are angle of squint (unit rad) to distance in orientation, and c represents the light velocity (unit m/s), RnRepresent target
To the oblique distance of radar, (unit m), v are radar movable speed (unit m/s).
Higher accuracy and good focusing performance in order to obtain, the present invention is directed to two-dimension spectrum coupling item, first to it
Be unfolded on five class number of orientation frequency, then carry out frequency of distance item quadravalence series expansion, thus derive apart from high-order
Phase compensation reference function and two-dimentional excess phase compensate reference function, eliminate to greatest extent distance to orientation secondary lobe
Asymmetric phenomenon, also so that under strabismus High Resolution SAR imaging contexts greatly, greatly reduces two-dimentional residual phase error.
Embodiment 3
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-2, described in step 2
Use without approximate two-dimensional frequency expression formula derive apart from order phase compensate reference function, be specifically：
WhereinRnRepresent
Distance (unit m), f of the target to radarτIt is distance to frequency (unit Hz), faFor orientation frequency (unit Hz), θ
For angle of squint (unit rad), c represents the light velocity (unit m/s), and v is radar movable speed (unit m/s), fcFor radar
Launch signal carrier frequency (unit Hz).
Sensitiveness of the present invention for big strabismus High Resolution SAR imaging to order phase error, in distance to leading to during processing
Cross and two-dimentional coupled phase progress higher-order expansion is obtained into high-order coupled phase compensation reference function, utilize digital signal processing device
The 2D signal for removing range walk and high-order coupled phase compensation reference function are multiplied again into row matrix, compensation high-order coupling phase
Position, so as to weaken the image fault that distance is brought to secondary lobe asymmetry.
Embodiment 4
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-3, described in step 2
Use derive two-dimentional excess phase compensation reference function without approximate two-dimensional frequency expression formula, be specifically：
Wherein Δ Ψ=F (fτ,fa)-F(fτ,fa) ', represents two-dimentional excess phase, F (fτ,fa) ' be F (fτ,fa) on side
5 class number of bit frequency is unfolded, RnExpression target is to the distance of radar, and θ is angle of squint, and c represents the light velocity.
Sensitiveness of the present invention for big strabismus High Resolution SAR imaging to two-dimentional residual phase error, by by two-dimentional coupling
Close phase progress higher-order expansion and obtain two-dimentional excess phase compensation reference function, high-order will be compensated using digital signal processing device
The 2D signal of coupled phase compensates reference function with two-dimentional excess phase and multiplies again into row matrix to compensate two-dimentional excess phase, from
And greatly reduce two-dimentional residual phase error.
Embodiment 5
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-4, described in step 5
Orientation higher order phase compensation reference function, be specifically：
Wherein Rn'=Rn+XnSin θ, represents since the distance that Range Walk Correction is brought is to distortion, faFor orientation frequency
(unit Hz), RnRepresent that (unit m), θ are angle of squint (unit rad) to target, and λ is radar emission letter to the distance of radar
Number wavelength (unit m), XnRepresent that (unit m), v are thunders to target with distance of the zero moment radar illumination center in orientation
Up to translational speed (unit m).
Sensitiveness of the present invention for big strabismus High Resolution SAR imaging to order phase error, it is sharp when orientation is handled
With digital signal processing device square is carried out with orientation order phase compensation reference function by distance is completed to the 2D signal of processing
Battle array multiplies again, orientation order phase is compensated, so as to weaken the image fault that orientation secondary lobe asymmetry is brought.In addition this imaging side
Method only multiplies FFT/IFFT computings again comprising matrix, is not related to interpolation arithmetic, therefore be easy to Project Realization.
A comprehensive example is given below, and the present invention is further described
Embodiment 6
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-5, for airborne big oblique
Depending on the particularity of High Resolution SAR imaging, the present invention is improved based on airborne big strabismus stripmap SAR oblique distance model using one kind
The NCS airborne SAR in high squint mode extended based on distance to CS and orientation imaging method, use the 2-d spectrum of complete oblique distance
Expression formula, by CS processing realize distance to all targets accurate distance migration correct, then by being utilized in orientation
The Non-linear chirp scaling of extension is handled to solve the problems, such as the orientation depth of focus.Also by the simulating, verifying to on-board data
Effectiveness of the invention and accuracy.Many calculating and derivation are arrived involved in this example, is no longer done in detail for some conventionally calculations
Expansion.
Referring to Fig. 1, Irnaging procedures of the invention, which include, following realizes step：
1. two-dimentional coupling analysis is carried out to airborne big strabismus High Resolution SAR echo-signal first
1.1 imaging geometry models and echo signal model
Referring to Fig. 2, Fig. 2 show carried SAR strabismus imaging geometry model, and radar is flied at a constant speed with speed v, squinted
Angle is θ, flying height H, it is assumed that point O is slow time tmZero point, the distance of radar to antenna irradiation regional center is R0, point P
For zero moment antenna irradiation regional center, the distance of point P to target point A is X0,R(tm) for radar and target point A it is instantaneous tiltedly
Away from, alternatively referred to as instantaneous distance, also corresponded to radar and the geometrical model of target.
Instantaneous distance can be obtained according to the cosine law：
The transmitting of SAR antennas is linear frequency modulation (LFM) signal, then the fundamental frequency echo-signal that antenna receives is
Wherein A is signal strength, W related with the Radar Cross Section of targetr() and Wa() is the distance of signal
To being the fast time with orientation envelope, τ, KrFor the frequency modulation rate of LFM signals, λ is the wavelength of transmitting signal, and λ represents the light velocity, tcFor
Object time is passed through at radar beam center.
1.2 apart from expansion formula and range migration correction
In general imaging, by instantaneous oblique distance R (tm) it is deployed into tmCubic term obtain
In formula (3), Section 2 is range walk item, and Section 3 is range curvature to Section 4 is ranging offset item three times.
Under normal conditions, envelope approximation is arrived the second order term of orientation time by general algorithm, and phase approximation is arrived the orientation time
Three ranks, but for squinting airborne High Resolution SAR system greatly, due to more demanding resolution ratio, if calculated according to tradition
Oblique distance is carried out envelope Two-order approximation by method, and phase carries out three ranks approximation, can produce bigger error, can not obtain high-resolution
Target image, it is therefore desirable to the approximation of higher order or without approximate distance model.
To the echo-signal of reception into row distance to Fourier transformation FFT, can be obtained according to theorem in phase bit
Wherein fτIt is distance to frequency, tmOrientation time, fcTo launch signal carrier frequency.
Section 2 in formula (3) is walked about item for linear range, can be first corrected, corresponding reference function is
1.3 high-order coupled phases compensate and excess phase compensation
Formula (5) is multiplied with formula (4), using theorem in phase bit, orientation FFT is to product, converts the signal into two dimension
Frequency domain obtains
Wherein
Show that the calculating process of formula (6) is stringent, centre is without series approximate processing is used, F (fτ,fa) be launched on
fa5 class numbers, obtain
By (the f in formula (8)τ+fc)-1, (fτ+fc)-2, (fτ+fc)-3(fτ+fc)-4It is deployed on fτFour items obtain
Therefore remaining order phase can be obtained is
Δ Ψ=F (fτ,fa)-F′(fτ,fa) (10)
Formula (8) and formula (9) are substituted into formula (6) and obtain high-order coupled phase and remaining order phase compensation reference function
H1(fτ,fa)=H1a(fτ,fa)H1b(fτ,fa) (11)
Wherein
In above formula
2. distance is to processing
Compensating the two-dimensional representation that high-order coupled phase and remaining order phase obtain signal is
Wherein
From formula (14), comprehensive frequency modulation rate KmIt is distance R with range migration amountnWith orientation frequency faFunction, use
CS algorithms carry out range curvature correction.
By theorem in phase bit, distance is done to formula (15) to IFFT, range-Dopler domain is transformed into and obtains
Mark principle is become according to frequency modulation, obtains becoming mark equation
Hcs(τ,fa)=exp (j π Kmα(τ-τref)2) (16)
Wherein
τ in formularefFor reference distance, scene center is typically chosen as during zero moment to the distance of radar, does distance to becoming at mark
Reason operation, then do distance and obtain two-dimensional frequency signal to FFT
Wherein
Range compress is with consistent range migration correction reference function
By Range compress and consistent range migration correction, by theorem in phase bit, signal is obtained into row distance to IFFT
Range Doppler represents
3. orientation is handled
Target location from formula (21) it can be seen that by distance to after processing is Rn+XnSin θ, this is and target point side
A related variable of position position.It can be seen from the above that by distance to after processing, originally in same range cell and different azimuth
The point target of position, is compressed to different range cells now, this will cause distance, and to distorting, orientation frequency modulation rate goes out
Existing space-variant, causes orientation translation invariance to fail, it is impossible to carry out orientation again and be uniformly processed.
Following substitution of variable is used to formula (21), if
Rn'=Rn+Xnsinθ (22)
Then the range Doppler of the signal of formula (21) represents to be converted into
Wherein
It follows that it is now placed in same range cell Rn' point, quadratic term, cubic term, four items of orientation frequency
With five Xiang Douyu position of orientation XnRelated, i.e., orientation causes not carrying out orientation at unified focusing there are space-variant
Reason.4 rank of orientation and the phase very little of 5 ranks, can ignore the space-variant with orientation, and 3 rank phase space-variants cannot be ignored, will
3 rank polyphase decompositions are that non-space-variant part and space-variant part are
α3=a30+a31Xn (25)
Wherein
Analysis can eliminate 4 rank of orientation and 5 rank phase terms and 3 rank non-NULL variables more than, and compensate residue
Phase, corresponding reference function are
H3(τ,fa)=H3a(τ,fa)H3b(τ,fa) (27)
By formula (27) and the range Doppler domain representation of formula (23) mutually multiplied signal
Wherein
As can be seen that orientation frequency modulation rate is orientation moment t from formula (29)0Function, orientation frequency modulation rate use two
Rank approximation can obtain the precision of higher, especially in high-resolution imaging.Related t in orientation frequency modulation rate0Item be to need to eliminate
Dummy variable, these dummy variables influence azimuth focus depth, be given below it is a kind of eliminate space-variant method.
Enough coefficients, advanced line frequency domain phase filtering are provided in order to become mark to NCS, corresponding reference function is
Wherein γ ≠ 0.5, value cannot too greatly can not be too small, specific value is omitted.
Formula (31) is multiplied with formula (29), according to theorem in phase bit, ignores above phase effect three times, is orientation IFFT
The two-dimensional time-domain for obtaining signal represents
Three rank space-variant item of orientation frequency modulation rate and orientation, corresponding reference function are eliminated using the 4 rank NCS factors of orientation
For
Formula (33) is multiplied with formula (32), by orientation FFT transform to range-Dopler domain, is orientation compression and three
Secondary and four phase compensation, corresponding reference function are
Compressed by orientation and three times with four phase compensation, do the signal after orientation IFFT must be focused on
Finish after Range compress and phase compensation by orientation IFFT can be obtained by after geometric correction it is poly-
Burnt big strabismus High Resolution SAR image.
Due to expansion of the present invention to two-dimentional coupling terms higher order so that greatly strabismus High Resolution SAR imaging contexts when into
The step-length bigger of row piecemeal processing, reduces the complexity of imaging.At the same time only square is included in whole imaging method process flow
Battle array multiply again with FFT/IFFT computings, be not related to interpolation arithmetic, therefore be easy to Project Realization.
The present invention be proposed with reference to Range Walk Correction, distance to the NCS that CS and orientation extend it is a kind of airborne big oblique
Depending on High Resolution SAR imaging method.On the basis of completely without approximate instantaneous oblique distance model, by carrying out high-order in two-dimensional frequency
Approach unified elimination order phase.
The technique effect of the present invention is explained again below by emulation
Embodiment 7
For airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant with embodiment 1-6, Fig. 1 is the present invention
The flow chart of institute's extracting method, in order to verify the validity of institute's extracting method of the present invention, is imitated below by radar simulation data
Very.
The airborne big strabismus High Resolution SAR imaging parameters of table 1.
Table 1 is the parameter of carried SAR, referring to Fig. 3, it is assumed that has 3 target points in scene, respectively A, B, C, their seat
Mark difference (0,0),WrAnd LsRespectively strip width and length of synthetic aperture, θ are angle of squint, and height is believed
Do not marked in breath figure.Fig. 4 and Fig. 5 is the simulation result of target A points, and Fig. 6 and Fig. 7 is the simulation result of target B points, Fig. 8 and Fig. 9
For the simulation result of target C points.
Emulation content includes following simulation process：
1. Range Walk Correction：Echo-signal is multiplied by range walk reference function by distance to Fourier transformation
HLRWCIt can complete Range Walk Correction.
2. above-mentioned signal passed through orientation Fourier transformation, more than three ranks frequency of distance phase term and remaining is compensated
High-order two dimension coupled phase, reference function H1。
3. distance becomes mark processing to frequency modulation：By above-mentioned signal by distance to Fourier inversion, with range scaling function
HcsBe multiplied, then do distance to Fourier transformation, in two-dimensional frequency by with reference function H2Complete Range compress and disappear
Except remaining range curvature, distance is completed to processing.
4. the Non-linear chirp scaling processing of orientation extension：Above-mentioned signal is done into distance to Fourier inversion, with ginseng
Examine function H3It is multiplied, eliminates 4 rank phase term of orientation, 5 rank phase term of orientation, 3 rank non-NULL variable of orientation and remaining phase
Position, and for orientation extension Non-linear chirp scaling handle enough coefficients are provided, finally with reference function HancsIt is multiplied
Realize that orientation Non-linear chirp scaling is handled.
5. Azimuth Compression and excess phase compensation：Above-mentioned signal is done into orientation FFT, with reference function H4It is multiplied, realizes
Orientation is compressed and three times with four phase compensation functions, completes orientation processing.
Orientation IFFT is finally, the image that can be focused on after geometric correction.
The simulation result of A points：
Referring to Fig. 4, Fig. 4 be directed to Fig. 3 scenes in target A points peak sidelobe ratio curve, wherein Fig. 4 (a) for distance to
Peak sidelobe ratio curve, Fig. 4 (b) are orientation peak sidelobe ratio curve.As can be seen from the figure A point distances to peak side-lobe
Than near -13dB, and good symmetry being presented with orientation peak sidelobe ratio.
Referring to Fig. 5, Fig. 5 is the contour curve of A points, and as can be seen from the figure A points have obtained good focusing, so as to test
The good focusing effect of reference center acquisition can be directed to by demonstrate,proving big strabismus High Resolution SAR imaging method proposed by the present invention.
Embodiment 8
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-6, simulated conditions and imitative
True content is the same as embodiment 7.
The simulation result of B points：
Referring to Fig. 6, Fig. 6 be directed to Fig. 3 scenes in target B points peak sidelobe ratio curve, wherein Fig. 6 (a) for distance to
Peak sidelobe ratio curve, Fig. 6 (b) are orientation peak sidelobe ratio curve.As can be seen from the figure B point distances to peak side-lobe
Than near -13dB, and good symmetry being presented with orientation peak sidelobe ratio.
Referring to Fig. 7, Fig. 7 is the contour curve of B points, and as can be seen from the figure B points have obtained good focusing, so as to test
The good focusing effect of scene distalmost end acquisition can be directed to by demonstrate,proving big strabismus High Resolution SAR imaging method proposed by the present invention.
Embodiment 9
Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant is with embodiment 1-6, simulated conditions and imitative
True content is the same as embodiment 7.
The simulation result of C points：
Referring to Fig. 8, Fig. 8 be directed to Fig. 3 scenes in target C points peak sidelobe ratio curve, wherein Fig. 8 (a) for distance to
Peak sidelobe ratio curve, Fig. 8 (b) are orientation peak sidelobe ratio curve.As can be seen from the figure C point distances to peak side-lobe
Than near -13dB, and good symmetry being presented with orientation peak sidelobe ratio.
Referring to Fig. 9, Fig. 9 is the contour curve of C points, and as can be seen from the figure C points have obtained good focusing, so as to test
Orientation piecemeal can be increased to one length of synthetic aperture by demonstrate,proving big strabismus High Resolution SAR imaging method proposed by the present invention.
The above description is merely a specific embodiment, but protection scope of the present invention is not limited thereto, any
Those familiar with the art the invention discloses technical scope in, change or replacement can be readily occurred in, should all be contained
Cover within protection scope of the present invention.Therefore, protection scope of the present invention should be based on the protection scope of the described claims.
In brief, a kind of airborne big strabismus High Resolution SAR imaging side with the correction of orientation space-variant disclosed by the invention
Method, solves in airborne big strabismus High Resolution SAR imaging for the orientation piecemeal processing for overcoming azimuth focus depth and carrying out
Caused significant complexity problem, its realization include：SAR echo signal is subjected to Range Walk Correction in a frequency domain；Use
The penalty function of higher order compensates high-order coupled phase and two-dimentional excess phase；Distance becomes mark processing to frequency modulation；Away from
Tripping contracts and consistent curvature correction；Phase compensation, excess phase compensation and the frequency domain phase filtering of orientation higher order；Orientation
Operated to Non-linear chirp scaling；Azimuth Compression and the compensation of orientation order phase.The present invention is using without approximate two-dimensional frequency
Expression formula, carries out two-dimentional coupling terms the expansion of higher order, and improve that big Squint SAR brings after Range Walk Correction is poly-
Burnt depth problem so that the step-length bigger of piecemeal processing is carried out in strabismus High Resolution SAR imaging contexts greatly, reduces whole imaging
The complexity of processing.Distance is also weakened to greatest extent at the same time to the image fault brought with orientation secondary lobe asymmetry, is led to
The compensation of accurate two-dimentional excess phase is crossed, two-dimentional residual phase error is greatly reduced, improves the focusing performance of imaging.
Claims (5)
1. a kind of airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant, it is characterised in that include following
Step：
Step 1, Range Walk Correction is carried out by SAR echo signal in a frequency domain：SAR echo signal is transformed to apart from frequency domain,
It is corrected according to Range Walk Correction reference function, obtains the signal after Range Walk Correction；
Step 2, compensates high-order coupled phase and two-dimentional excess phase using the penalty function of higher order：By distance
The signal after correcting of walking about transforms to two-dimensional frequency, is mended using being derived without approximate two-dimensional frequency expression formula apart from order phase
Repay reference function and two-dimentional excess phase compensates reference function, obtain removing high-order coupled phase and remaining high-order coupling through overcompensation
Close the signal of item；
Step 3, distance become mark processing to frequency modulation：The signal for removing high-order coupled phase and remaining high-order coupling terms is transformed to
Range-Dopler domain, is multiplied by becoming scalar functions with linear range, the signal for the complementary range curvature that is eliminated；
Step 4, Range compress and consistent curvature correction：The signal for eliminating complementary range curvature is transformed into two-dimensional frequency, is passed through
Range compress and consistent curvature correction, obtain the signal after Range compress and after range curvature correction；
Step 5, phase compensation, excess phase compensation and the frequency domain phase filtering of orientation higher order：By after Range compress and
Signal after range curvature correction transforms to range-Dopler domain, passes through orientation higher order phase compensation reference function and side
Position compensates reference function to excess phase, and it is non-to eliminate orientation quadravalence phase term, five rank phase term of orientation, three rank of orientation
Space-variant item and orientation excess phase, then be multiplied with orientation frequency domain filtering reference function, obtain removing high-order orientation phase term
With the signal after orientation frequency domain filtering；
Step 6, the operation of orientation Non-linear chirp scaling：After high-order orientation phase term and orientation frequency domain filtering is removed
Signal transforms to two-dimensional time-domain, is multiplied with orientation Non-linear chirp scaling reference function, after obtaining orientation frequency change mark
Signal；
Step 7, Azimuth Compression and the compensation of orientation order phase：It is more that signal orientation frequency become after mark transforms to distance
General Le domain, carries out Azimuth Compression and the compensation of high-order orientation frequency plot, completes orientation compression and three rank of orientation and quadravalence phase
Position compensation, finally does orientation inverse fourier transform, and the focusing of SAR echo signal high-resolution is can obtain after geometric correction
Image.
2. the airborne big strabismus High Resolution SAR imaging method according to claim 1 with the correction of orientation space-variant, its feature
It is, the use described in step 2 is specifically without approximate two-dimensional frequency expression formula：
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Two-dimensional frequency coupling terms do not contain approximate processing, for two-dimensional frequency coupling terms, first it are carried out on 5 rank of orientation frequency
Series expansion, then carry out on 4 class number of frequency of distance item be unfolded, thus derive high-order coupled phase compensation reference function and
Two-dimentional excess phase compensates reference function.
3. the airborne big strabismus High Resolution SAR imaging method according to claim 1 with the correction of orientation space-variant, its feature
It is, the use described in step 2 derives that high-order coupled phase compensates reference function without approximate two-dimensional frequency expression formula,
Specifically
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4. the airborne big strabismus High Resolution SAR imaging method according to claim 1 with the correction of orientation space-variant, its feature
It is, the use described in step 2 derives two-dimentional excess phase compensation reference function without approximate two-dimensional frequency expression formula,
Specifically：
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5. the airborne big strabismus High Resolution SAR imaging method according to claim 1 with the correction of orientation space-variant, its feature
It is, the orientation higher order phase compensation reference function described in step 5, is specifically：
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Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201711012954.4A CN107918124A (en) | 2017-10-26 | 2017-10-26 | Airborne big strabismus High Resolution SAR imaging method with the correction of orientation space-variant |
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| Application Number | Priority Date | Filing Date | Title |
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| CN109613535A (en) * | 2018-12-12 | 2019-04-12 | 北京无线电测量研究所 | Orientation NCS imaging method, system, medium and equipment based on envelope correction |
| CN110596701A (en) * | 2019-07-01 | 2019-12-20 | 杭州电子科技大学 | Non-level-flight double-station SAR frequency domain FENLCS imaging method based on quadratic ellipse model |
| CN111175749A (en) * | 2020-01-19 | 2020-05-19 | 中国科学院电子学研究所 | Satellite-borne SAR imaging processing method |
| CN111679255A (en) * | 2020-06-19 | 2020-09-18 | 北京无线电测量研究所 | Method and device for correcting two-dimensional space-variant distance migration of squint airborne synthetic aperture radar |
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| CN114626006A (en) * | 2022-03-21 | 2022-06-14 | 电子科技大学 | FPGA (field programmable Gate array) realization method for real-time generation of CS (Circuit switched) algorithm compensation factor in radar imaging |
| CN116359863A (en) * | 2023-03-31 | 2023-06-30 | 中国人民解放军国防科技大学 | Compensation method for miniature unmanned aerial vehicle SAR course motion error |
| CN116500558A (en) * | 2023-03-13 | 2023-07-28 | 中南大学 | Airborne microwave photon SAR full aperture self-focusing method |
| CN116736304A (en) * | 2023-08-10 | 2023-09-12 | 西安电子科技大学 | Random frequency hopping signal imaging method based on linear frequency modulation signal |
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| CN109613535A (en) * | 2018-12-12 | 2019-04-12 | 北京无线电测量研究所 | Orientation NCS imaging method, system, medium and equipment based on envelope correction |
| CN109613535B (en) * | 2018-12-12 | 2022-05-13 | 北京无线电测量研究所 | Orientation NCS imaging method, system, medium and equipment based on envelope correction |
| CN110596701A (en) * | 2019-07-01 | 2019-12-20 | 杭州电子科技大学 | Non-level-flight double-station SAR frequency domain FENLCS imaging method based on quadratic ellipse model |
| CN111175749A (en) * | 2020-01-19 | 2020-05-19 | 中国科学院电子学研究所 | Satellite-borne SAR imaging processing method |
| CN111679255B (en) * | 2020-06-19 | 2023-03-28 | 北京无线电测量研究所 | Method and device for correcting two-dimensional space-variant distance migration of squint airborne synthetic aperture radar |
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| CN113189547B (en) * | 2021-04-20 | 2023-08-08 | 成都汇蓉国科微***技术有限公司 | SAR imaging method and system based on synthetic bandwidth frequency scaling |
| CN114626006B (en) * | 2022-03-21 | 2023-03-14 | 电子科技大学 | FPGA (field programmable Gate array) realization method for real-time generation of CS (Circuit switched) algorithm compensation factor in radar imaging |
| CN114626006A (en) * | 2022-03-21 | 2022-06-14 | 电子科技大学 | FPGA (field programmable Gate array) realization method for real-time generation of CS (Circuit switched) algorithm compensation factor in radar imaging |
| CN116500558A (en) * | 2023-03-13 | 2023-07-28 | 中南大学 | Airborne microwave photon SAR full aperture self-focusing method |
| CN116500558B (en) * | 2023-03-13 | 2023-09-19 | 中南大学 | Airborne microwave photon SAR full aperture self-focusing method |
| CN116359863A (en) * | 2023-03-31 | 2023-06-30 | 中国人民解放军国防科技大学 | Compensation method for miniature unmanned aerial vehicle SAR course motion error |
| CN116359863B (en) * | 2023-03-31 | 2024-02-06 | 中国人民解放军国防科技大学 | Compensation method for miniature unmanned aerial vehicle SAR course motion error |
| CN116736304A (en) * | 2023-08-10 | 2023-09-12 | 西安电子科技大学 | Random frequency hopping signal imaging method based on linear frequency modulation signal |
| CN116736304B (en) * | 2023-08-10 | 2023-10-20 | 西安电子科技大学 | Random frequency hopping signal imaging method based on linear frequency modulation signal |
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