CN112649808B - Bistatic forward-looking SAR wave number domain imaging method based on shift configuration - Google Patents
Bistatic forward-looking SAR wave number domain imaging method based on shift configuration Download PDFInfo
- Publication number
- CN112649808B CN112649808B CN202011611367.9A CN202011611367A CN112649808B CN 112649808 B CN112649808 B CN 112649808B CN 202011611367 A CN202011611367 A CN 202011611367A CN 112649808 B CN112649808 B CN 112649808B
- Authority
- CN
- China
- Prior art keywords
- signal
- dimensional
- correction
- str
- azimuth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- 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
- G01S13/9043—Forward-looking SAR
-
- 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
Abstract
The invention discloses a bistatic forward-looking SAR wave number domain imaging method based on a shift configuration, which mainly solves the problems that the prior art is difficult to realize the accurate focusing of a large-scene target in a curve track state and the calculation amount is large. The implementation scheme is as follows: firstly, obtaining a two-dimensional frequency spectrum of a target echo signal; performing distance compression compensation correction on the two-dimensional frequency spectrum; designing an interpolation factor to interpolate the signal after the distance compression compensation correction; carrying out azimuth space-variant filtering correction on the interpolated signal; and performing orientation factor reconstruction, correction and focusing on the signals subjected to the orientation space-variant filtering correction to obtain a two-dimensional imaging image. The invention has the advantages of high imaging accuracy and small operand, and can be used for high-resolution imaging of the shift-variant double-base forward-looking SAR.
Description
Technical Field
The invention belongs to the technical field of radars, and further relates to a bistatic forward-looking SAR imaging method which can be used for high-resolution imaging of bistatic SAR under a shift-variable geometric configuration.
Background
One of the important applications of the bistatic synthetic aperture radar SAR is bistatic forward-looking SAR, under the configuration, the positions of a transmitting and receiving platform are separated, a receiver forwards looks to receive a target echo, the two-dimensional spatial resolution of the receiver in a forward-looking area is orthogonal or approximately orthogonal, and forward-looking two-dimensional imaging can be realized. The bistatic forward-looking SAR has great potential advantages in the aspect of high-resolution forward-looking two-dimensional imaging, and can be used for forward-looking imaging under aircraft blind landing and complex terrain backgrounds and the like. However, in the above-described situation, which has a velocity and an acceleration in a three-dimensional direction during flight, it is difficult to obtain an accurate echo two-dimensional spectrum. Therefore, various researchers at home and abroad propose various solutions for the problem of obtaining the bistatic SAR echo spectrum.
The heel-Sub Shin performs taylor expansion on the echo two-dimensional spectrum in a paper "Omega-K Algorithm for air bearing space initiative Bistatic Spotlight SAR imaging" (IEEE trans. Geosci. Remote sens., vol.47, no.1,238-250, jan.2009), performs approximate transformation, and equates the Bistatic parallel isovelocity SAR to a monostatic SAR, and finally performs imaging processing by using an Omega-K Algorithm. The method is only suitable for a level flight mode without acceleration, and bistatic SAR forward-looking imaging under a curve track cannot be realized.
Baochang Liu et al, in its published paper, "Bistatic SAR Data Focusing Using an Omega-K Algorithm Based on Method of Series conversion" (IEEE trans. Geosci. Remote Sens., vol.47, no.8,2899-2912, aug.2009), adopts a Series inversion Method to obtain a two-dimensional spectrum of a Bistatic SAR, and performs approximate processing in a beam pointing direction to realize linearization of the spectrum in a distance direction, and finally adopts an interpolation Method to realize Bistatic side view SAR imaging with a large squint angle and a wide field. The method has the advantages of low imaging precision and large computation amount, and is not suitable for the double-base model with the acceleration.
Disclosure of Invention
The invention aims to provide a bistatic forward-looking SAR wave number domain imaging method under a shift-variant geometric configuration, so that the wave number domain algorithm is combined with motion compensation, the constraint of acceleration is avoided, the bistatic SAR forward-looking two-dimensional high-resolution imaging is realized, and the operation amount is reduced.
In order to achieve the purpose, the technical scheme of the invention comprises the following steps:
(1) Obtaining a baseband echo signal, and performing linear walk correction and two-dimensional Fourier transform on the baseband echo signal to obtain a two-dimensional frequency spectrum S of a target echo signal r,a (f τ ,f η )，f τ Representing the range frequency, f η Representing the azimuth frequency;
(2) According to a correction factor H src (f τ ,f η ) For two-dimensional frequency spectrum S r,a (f τ ,f η ) Distance compression compensation correction is carried out to obtain a signal S after distance compression compensation correction cr,ca (f τ ,f η )；
(3) Design of interpolation factor f str Expressed as follows:
in the formula, E 2i ,E 3i ,E 4i I =1,2 are the signals S corrected for distance compression compensation, respectively cr,ca (f τ ,f η ) Second, third, and fourth order phase residue coefficients of (1) with respect to Δ R res Linear coefficient of construction of, Δ R res ＝R 0 -R s +ΔR，ΔR res Representing the target point bistatic slope distance and the compensated residual amount, R 0 Representing the sum of the two base skews of the target at the initial moment, R s Representing the sum of the dual base slant distances of the scene center reference point, ar representing the amount of residual distance warping, λ being the wavelength,
denotes the wave number, f c Carrier frequency, c is speed of light;
(4) Using interpolation factor f str Compensating the corrected signal S for distance compression cr,ca (f τ ,f η ) Two-dimensional linear interpolation is carried out to obtain an interpolated signal S str,r,a (f str ,f η )；
(5) For the interpolated signal S str,r,a (f str ,f η ) Performing orientation space-variant filtering correction to obtain the orientation space-variant filtered correctionSignal s s,r (t τ ,t η ) Wherein, t τ For a fast time, t η Is a slow time;
(6) Signal s corrected by space-variant filtering of the orientation s,r (t τ ,t η ) And performing azimuth reconstruction, correction and focusing to obtain a two-dimensional imaging image.
Compared with the prior art, the invention has the following advantages:
firstly, the invention realizes the imaging processing of the shift-configuration bistatic forward-looking SAR under the sub-aperture condition by two-dimensional interpolation and azimuth factor reconstruction correction focusing.
Secondly, the invention corrects the orientation space-variant of the Doppler frequency modulation coefficient, so that the wave number domain algorithm can be combined with motion compensation, and wave number domain focusing is adopted according to the characteristic of sub-aperture imaging, thereby avoiding the zero filling of the orientation of the traditional wave number domain algorithm, and reducing the operation amount compared with the traditional wave number domain imaging method.
Thirdly, the invention breaks through the limitation of acceleration on the wave number domain algorithm imaging, solves the two-dimensional space variation of the Doppler frequency modulation coefficient under the configuration of shift variation, effectively improves the focusing effect of a scene target point, and has good scene applicability.
Drawings
FIG. 1 is a flow chart of an implementation of the present invention;
FIG. 2 is an imaging geometry and scene layout diagram of a bistatic forward-looking SAR;
FIG. 3 is a graph of the results of imaging a point target using the method of the present invention;
FIG. 4 is a sectional view of the pulse pressure at each point of the imaging process using the prior Omega-K algorithm;
FIG. 5 is a cross-sectional view of the pulse pressure at each point of the imaging process using a prior art series inversion method;
FIG. 6 is a cross-sectional view of the pulse pressure at each point of the imaging process performed by the method of the present invention;
FIG. 7 is a two-dimensional contour map of points imaged using a prior Omega-K algorithm;
FIG. 8 is a two-dimensional contour plot of points imaged using a prior art series inversion method;
figure 9 is a two-dimensional contour plot of points imaged using the method of the present invention.
Detailed Description
The embodiments and effects of the present invention will be described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, the double-base forward-looking SAR wave number domain imaging method based on the shift configuration, provided by the invention, comprises the following implementation steps:
(1.1) the transmitted signal is a chirp signal, and for the convenience of description, the invention does not specifically analyze the change of the window function in the echo signal, so that the receiver obtains a baseband echo signal s after frequency mixing ta (t τ ,t η ) Expressed as follows:
s ta (t τ ,t η )＝exp(jπγ(t τ -τ(t η )) 2 )exp(-j2πf c τ(t η ))
where γ is the frequency modulation of the chirp signal, t τ For a fast time, t η Is a slow time, f c Is the carrier frequency, τ (t) η ) A target double-base echo time delay is obtained;
(1.2) for the base band echo signal s ta (t τ ,t η ) Carrying out range-to-Fourier transform to obtain an echo signal S of a range frequency domain-an azimuth time domain s (f τ ,t η )：
S s (f τ ,t η )＝exp[-j2πKcτ(t η )]
In the formula (I), the compound is shown in the specification,
denotes the wave number, f c Carrier frequency, c is speed of light;
(1.3) echo Signal S for distance frequency domain-azimuth time domain s (f τ ,t η ) The linear walking correction is carried out by using the Taylor first-order expansion coefficient mu of the slope distance model of the scene central reference point r1 Construction of a Linear correction Filter H l (f τ ,t η ) Expressed as follows:
H l (f τ ,t η )＝exp(2jπKμ r1 t η )；
(1.4) to the baseband echo signal s ta (t τ ,t η ) Linear walk correction is performed by applying a baseband echo signal s ta (t τ ,t η ) And a linear correction filter H l (f τ ,t η ) Multiplying to obtain a signal S after the linear walk correction is finished srl (f τ ,t η ) Comprises the following steps:
(1.5) Linear-Walking-corrected Signal S srl (f τ ,t η ) Performing azimuth Fourier transform to obtain two-dimensional frequency spectrum S of echo signal r,a (f τ ,f η )：
Wherein f is τ Representing the distance frequency, f η Representing the azimuth frequency, t n Is the target focusing time, R 0 Represents the target dual-base skew sum at the initial moment,
represents the wave number, mu 2 ,μ 3 ,μ 4 Each of f being formed by Taylor expansion coefficients of the target slope distance model η Second, third, and fourth order phase coefficients.
And 2, distance compression compensation correction.
(2.1) the following correction factor H is selected src (f τ ,f η )：
In the formula, f τ The frequency of the distance is represented by,μ′ 2 ,μ′ 3 ,μ′ 4 second, third and fourth phase correction coefficients R formed by Taylor expansion coefficients of the center reference point slope distance model respectively s The sum of the dual-base slant distance of the scene center reference point is shown;
(2.2) Using the correction factor H src (f τ ,f η ) For two-dimensional frequency spectrum S r,a (f τ ,f η ) Correction for distance compression compensation, i.e. two-dimensional spectrum S r,a (f τ ,f η ) And a correction factor H src (f τ ,f η ) Multiplying to obtain a compensated and corrected signal S cr,ca (f τ ,f η )：
In the formula,. DELTA.R res ＝R 0 -R s +ΔR，ΔR res Representing the biradical slope distance of the target point and the compensated residual amount, R 0 Representing the sum of the target bibase pitches at the initial time, Δ R representing the residual distance warping amount, Δ i I =2,3,4 denotes second, third and fourth order phase residue coefficients, respectively.
The subsequent imaging processing needs to compensate the corrected signal S for the distance compression cr,ca (f τ ,f η ) Interpolation is carried out to complete two-dimensional decoupling, however, under the condition of a large imaging scene, the two-dimensional space variation of Doppler frequency modulation characteristics in echo signals cannot be ignored, and the echo signals need to be subjected to space variation correction in the azimuth direction. In order to solve the problems existing in the traditional interpolation imaging method, an interpolation factor f needs to be redesigned str 。
(3.1) obtaining the distance compression compensated corrected signal S cr,ca (f τ ,f η ) Middle second, third and fourth phase residue coefficients delta 2 ,Δ 3 ,Δ 4 The residue delta R after the double base slope distance process with the target point is compensated res The linear relationship of (1):
signal S corrected by distance compression compensation cr,ca (f τ ,f η ) The phase residue coefficient in (1) is only related to the position between the transceiving platform of the bistatic SAR and the target point, and is related to delta R res There is no linear relationship between them, and the interpolation factor f is designed str The phase residue coefficient and Δ R must be obtained res Thus constructing a linear regression model as follows:
in the formula, E 2i ,E 3i ,E 4i I =1,2 are respectively the two-dimensional spectrum S after the distance compression compensation correction cr,ca (f τ ,f η ) Second, third, and fourth order phase residue coefficients of (1) with respect to Δ R res Linear construction coefficients of (a);
(3.2) substituting the linear regression model into the two-dimensional frequency spectrum signal S after the distance compression compensation correction cr,ca (f τ ,f η ) Obtaining a reconstructed two-dimensional spectrum S nr,na (f τ ,f η )：
(3.3) pair of the reconstructed two-dimensional spectrum signal S in (3.2) nr,na (f τ ,f η ) Extracting the formula S nr,na (f τ ,f η ) In the following expression form:
(3.4) suppose that the interpolation factor is f str Using a hypothetical interpolation factor f str For the two-dimensional spectrum signal S after the formula is extracted from (3.3) nr,na (f τ ,f η ) Interpolation is carried out to complete the solutionCoupling to obtain an interpolated signal S tr,ta (f τ ,f η ) Comprises the following steps:
in the formula (I), the compound is shown in the specification,
representing the wave number, f, of the electromagnetic radiation c Is the carrier frequency;
(3.5) extracting a formula from the two-dimensional spectrum signal S in the (3.3) nr,na (f τ ,f η ) And (3.4) interpolated signal S tr,ta (f τ ,f η ) By contrast derivation of the expression of (c), a factor f is obtained str The expression of (a) is:
and 4, performing two-dimensional linear interpolation.
Utilizing the interpolation factor f designed in the step 3 str Compensating the corrected signal S for distance compression cr,ca (f τ ,f η ) Two-dimensional interpolation is carried out, the envelope term and the azimuth phase term are separated, and a signal S after interpolation is obtained str,r,a (f str ,f η ) Comprises the following steps:
from the interpolated signal S str,r,a (f str ,f η ) It can be seen that the phase term exp (-j 2 π t) n f η ) Indicating the position of the target point at the azimuthal focusing instant. Phase term
Representing the focusing position of the target point in the distance direction, performing distance inverse Fourier transform on the signal to realize focusing in the distance direction, wherein the residual phase item comprises azimuth frequency f η Second and higher order terms of, tableAnd displaying the compensated azimuth residual frequency modulation item, wherein the item implies the azimuth space-variant of the Doppler frequency modulation item.
And 5, correcting the orientation space-variant filter.
Step 4, completing the two-dimensional decoupling operation in the imaging processing process, and interpolating the signal S str,r,a (f str ,f η ) The middle azimuth frequency modulation term coefficient is related to the position of the target point, namely, the Doppler frequency modulation two-dimensional space-variant characteristic exists. For the interpolated signal S str,r,a (f str ,f η ) To correct for space-variant, it is first necessary to correct the signal S str,r,a (f str ,f η ) Performing two-dimensional inverse Fourier transform to obtain a two-dimensional time domain signal s rt (t τ ,t η ) Then to a two-dimensional time-domain signal s rt (t τ ,t η ) The azimuth space-variant phase in (1) is subjected to azimuth space-variant filtering correction, and the method is realized as follows:
(5.1) on the interpolated signal S str,r,a (f str ,f η ) Performing two-dimensional inverse Fourier transform to obtain a two-dimensional time domain signal s rt (t τ ,t η )：
In the formula, t η Is a slow time, t τ For fast time, B is the transmission signal bandwidth, R bf For signal sampling position, f p For the focus position of the target point in the frequency domain, h j1 (ΔR res ) J =2,3,4 respectively indicate the space-variant part of the doppler frequency modulation term with distance with respect to the slow time t η Second, third, fourth order coefficients of (h) j2 (ΔR res ) J =2,3,4 respectively denote the doppler frequency modulation term with f p Linearly varying part with respect to slow time t η Second, third, and fourth order coefficients;
(5.2) for h j1 (ΔR res ) Partially correcting to construct an orientation space-variant filter H d (t η ) Comprises the following steps:
(5.3) converting the two-dimensional time domain signal s rt (t τ ,t η ) And azimuth space-variant filter H d (t η ) Multiplying to obtain a signal s after azimuth space-variant filtering correction s,r (t τ ,t η )：
And 6, reconstructing azimuth, correcting and focusing.
Signal s corrected by space-variant filtering s,r (t τ ,t η ) Middle h j2 (ΔR res ) J =2,3,4 denotes the doppler frequency modulation term with f p Linearly changing part, f p Representing the frequency domain focus position of the target point, which can be corrected by azimuth factor reconstruction, is implemented as follows:
(6.1) constructing an azimuth reconstruction relation as follows:
wherein, the first and the second end of the pipe are connected with each other,
representing the wave number, h, of the electromagnetic radiation j2 (ΔR res ) J =2,3,4 respectively denote the doppler frequency modulation term with f p Linearly varying part with respect to slow time t η Second, third and fourth order coefficients of (t) ηη Is an azimuth reconstruction factor;
(6.2) constructing a phase term exp (j 2 π f) using an orientation reconstruction relation p t ηη )；
(6.3) Filtering corrected Signal s for the space variant of the orientation s,r (t τ ,t η ) Performing azimuth factor reconstruction, namely using the phase term exp (j 2 pi f) constructed in (6.2) p t ηη ) Substitution s s,r (t τ ,t η ) The phase term in the method is used for obtaining a signal s after the azimuth factor is reconstructed s,a (t τ ,t ηη )：
s s,a (t τ ,t ηη )＝sinc(B(R bf -ΔR res ))exp{j2πf p t ηη }
In the formula, t τ For fast time, B is the transmission signal bandwidth, R bf For signal sampling position, f p The focusing position of the target point in the frequency domain;
(6.4) reconstructing the orientation factor of the signal s s,a (t τ ,t ηη ) And carrying out azimuth focusing to obtain a two-dimensional imaging image.
The effect of the present invention can be further illustrated by the following simulation experiments:
simulation conditions
The signal carrier frequency of the double-base forward-looking SAR radar system based on the shift configuration is set to be 17GHz, the pulse repetition frequency is set to be 10KHz, and both the receiver and the transmitter move along a curved track. The imaging geometry and scene layout of the bistatic forward-looking SAR are shown in fig. 2, wherein fig. 2 (a) is a three-dimensional schematic diagram of the imaging geometry of the bistatic forward-looking SAR, fig. 2 (b) is a schematic diagram of the scene layout, and as can be seen from fig. 2 (b), the initial layout of the imaging domain is a 5 × 5 rectangular lattice.
(II) simulation content
As can be seen from FIG. 3, the point target focusing effect is good, and meanwhile, the imaging result focused by the target points is a five-row five-column rectangular lattice, the transverse direction represents the distance direction, the longitudinal direction represents the azimuth direction, and the imaging result is consistent with the initial point distribution diagram, thereby proving the accuracy of the algorithm provided by the invention.
As can be seen from fig. 4, the edge points 1 and 3 of the scene processed by the existing Omega-K algorithm cannot be focused precisely in the azimuth direction, because when the echo is processed by the existing Omega-K algorithm, the dual-base platform has a velocity in the elevation direction and an acceleration in the three-dimensional direction, so that the linearization operation of the doppler frequency modulation term in the echo on the distance space-variant has a large phase error.
And 3, selecting edge points 1 and 3 and a center point 2 in an imaging scene, performing imaging simulation on the three points by using a grade inversion method provided by the literature 'missile-borne double-base forward-looking SAR extended imaging algorithm design', wherein an azimuth pulse pressure section diagram of each point obtained by simulation is shown in fig. 5, wherein fig. 5 (a) shows the azimuth pulse pressure section diagram of the edge point 1, fig. 5 (b) shows the azimuth pulse pressure section diagram of the center point 2, and fig. 5 (c) shows the azimuth pulse pressure section diagram of the edge point 3.
As can be seen from fig. 5, the azimuth peak-to-peak side lobe ratio of the scene edge points 1 and 3 imaged by the conventional series inversion method is too large, so that a defocus phenomenon exists, which indicates that when the scene width is large, the residual doppler modulation azimuth space-variant term is not negligible.
And 4, selecting edge points 1 and 3 and a central point 2 in an imaging scene, performing imaging simulation on the three points by using the method of the invention, and obtaining an azimuth pulse pressure cross-sectional view of each point through simulation as shown in fig. 6, wherein fig. 6 (a) shows the azimuth pulse pressure cross-sectional view of the edge point 1, fig. 6 (b) shows the azimuth pulse pressure cross-sectional view of the central point 2, and fig. 6 (c) shows the azimuth pulse pressure cross-sectional view of the edge point 3.
As can be seen from fig. 6, the distance space-variant characteristic and the azimuth space-variant item of the doppler frequency modulation item are considered in each target point subjected to the simulation processing by the algorithm provided by the present invention, the scene edge points 1 and 3 and the scene center point 2 both exhibit good focusing effects, the peak side lobes of each point are low, the main lobe and the first side lobe are clearly distinguished, and the focusing depth is good.
simulation 6, selecting edge points 1 and 3 and a center point 2 in an imaging scene, performing imaging simulation on the three points by using a grade inversion method provided by a literature 'missile-borne double-base forward-looking SAR extended imaging algorithm design', wherein a two-dimensional contour map of each point is shown in fig. 8, wherein fig. 8 (a) shows the two-dimensional contour map of the edge point 1; fig. 8 (b) shows a two-dimensional contour diagram of the center point 2; fig. 8 (c) shows a two-dimensional contour diagram of the edge point 3;
as can be seen from fig. 7 and 8, the two-dimensional main lobes at the edge points 1 and 3 are distorted, which indicates that there is a residual amount for the distance migration correction at these two points, and there is significant coupling between the main lobe and the side lobe.
Simulation 7, selecting edge points 1 and 3 and a center point 2 in an imaging scene, performing imaging simulation on the three points by using the method of the invention, and obtaining a two-dimensional contour map of each point as shown in fig. 9, wherein fig. 9 (a) shows the two-dimensional contour map of the edge point 1; fig. 9 (b) shows a two-dimensional contour diagram of the center point 2; fig. 9 (c) shows a two-dimensional contour diagram of the edge point 3;
as can be seen from fig. 9, both the scene edge points 1 and 3 and the scene center point 2 exhibit a good "cross" effect.
In conclusion, the method combines the wave number domain imaging algorithm and the motion compensation through two-dimensional interpolation and azimuth factor reconstruction correction focusing, realizes the accurate focusing of the double-base forward-looking SAR based on the shift configuration on the scene target point, and verifies the accuracy and the effectiveness of the method.
Claims (7)
1. A bistatic forward-looking SAR wave number domain imaging method based on a shift configuration is characterized by comprising the following steps:
(1) Obtaining a baseband echo signal, and performing linear walk correction and two-dimensional Fourier transform on the baseband echo signal to obtain a two-dimensional frequency spectrum S of a target echo signal r,a (f τ ,f η )，f τ Representing the range frequency, f η Representing the azimuth frequency;
(2) According to a correction factor H src (f τ ,f η ) For two-dimensional frequency spectrum S r,a (f τ ,f η ) Distance compression compensation correction is carried out to obtain a signal S after distance compression compensation correction cr,ca (f τ ,f η )；
(3) Design of interpolation factor f str The implementation is as follows:
(3a) A linear regression model was constructed, represented as follows:
in the formula,. DELTA. 2 ,Δ 3 ,Δ 4 Compensating the corrected signal S for distance compression cr,ca (f τ ,f η ) Second, third and fourth order phase residue coefficients;
(3b) Substituting a linear regression model into the distance compression compensation-corrected two-dimensional spectrum signal S cr,ca (f τ ,f η ) To obtain a reconstructed two-dimensional spectrum S nr,na (f τ ,f η ) Is represented as follows:
in the formula, t n Is the focus time of the target;
(3c) For the reconstructed two-dimensional frequency spectrum signal S nr,na (f τ ,f η ) Extracting the formula S nr,na (f τ ,f η ) In the following expression form:
(3d) Assuming an interpolation factor of f str Benefit fromBy a hypothetical interpolation factor f str For the two-dimensional frequency spectrum signal S after extracting the common factor nr,na (f τ ,f η ) Interpolation is carried out, decoupling is finished, and a signal S after interpolation is obtained tr,ta (f τ ,f η ) Comprises the following steps:
in the formula (I), the compound is shown in the specification,
representing the wave number, f, of the electromagnetic radiation c Is the carrier frequency;
(3e) By pair of signals S in (3 c) nr,na (f τ ,f η ) Signal S in (3 d) and (3 d) tr,ta (f τ ,f η ) Contrast derivation of expression to obtain interpolation factor f str The expression of (a) is:
in the formula, E 2i ,E 3i ,E 4i I =1,2 are respectively the signals S after the distance compression compensation correction cr,ca (f τ ,f η ) Second, third, and fourth order phase residue coefficients of (1) with respect to Δ R res Linear coefficient of construction of, Δ R res ＝R 0 -R s +ΔR，ΔR res Representing the biradical slope distance of the target point and the compensated residual amount, R 0 Representing the sum of the two base skews of the target at the initial moment, R s Representing the sum of the dual base slant distances of the scene center reference point, ar representing the amount of residual distance warping, λ being the wavelength,
represents wave number, f c Carrier frequency, c is speed of light;
(4) Using interpolation factor f str Compensating the corrected signal S for distance compression cr,ca (f τ ,f η ) Performing two-dimensional linear interpolation to obtain interpolated signal S str,r,a (f str ,f η )；
(5) For the interpolated signal S str,r,a (f str ,f η ) Performing azimuth space-variant filtering correction to obtain an azimuth space-variant filtered and corrected signal s s,r (t τ ,t η ) Wherein, t τ For a fast time, t η Is a slow time;
(6) Signal s corrected by space-variant filtering of the orientation s,r (t τ ,t η ) And performing azimuth reconstruction, correction and focusing to obtain a two-dimensional imaging image.
2. The method of claim 1, wherein the two-dimensional spectrum S of the target echo signal in (1) r,a (f τ ,f η ) Expressed as follows:
where γ is the frequency modulation of the chirp signal, t n Is the target focusing time, R 0 Represents the sum of the two base skews of the target at the initial moment, mu 2 ,μ 3 ,μ 4 Formed for f, respectively, taylor expansion coefficients of the target slope distance model η Second, third and fourth order phase coefficients of (f) η Indicating the azimuth frequency.
3. The method of claim 1, wherein the correction factor H in (2) src (f τ ,f η ) Expressed as follows:
where γ is the frequency modulation, μ, of the chirp signal 2 ′,μ 3 ′,μ 4 ' separately centered referenceSecond, third and fourth phase correction coefficients formed by Taylor expansion coefficients of the point slope distance model, R s Is the dual base slant sum of the scene center reference point.
4. The method of claim 1, wherein (2) is performed on a two-dimensional spectrum S r,a (f τ ,f η ) The distance compression compensation correction is carried out by converting the two-dimensional frequency spectrum S r,a (f τ ,f η ) And a correction factor H src (f τ ,f η ) Multiplying to obtain a signal S after distance compression compensation correction cr,ca (f τ ,f η )：
In the formula, t n Is the target focusing time, Δ j J =2,3,4 denotes second, third and fourth order phase residue coefficients, respectively.
5. The method of claim 1, wherein (4) utilizes an interpolation factor f str Compensating the corrected signal S for distance compression cr,ca (f τ ,f η ) Interpolation is carried out to obtain an interpolated signal S str,r,a (f str ,f η ) Is represented as follows:
in the formula, t n Is the time of focus of the object and,
representing the electromagnetic radiation wavenumber. />
6. The method of claim 1, wherein the interpolated signal S is paired in (5) str,r,a (f str ,f η ) Performing azimuth space-variant filtering correction to obtain an azimuth space-variant filtered and corrected signal s s,r (t τ ,t η )：
Where B is the transmission signal bandwidth and R bf For signal sampling position, f p For the focus position of the target point in the frequency domain,
representing the wave number, h, of the electromagnetic radiation j2 (ΔR res ) J =2,3,4 respectively denote the doppler frequency modulation term with f p Linearly varying part with respect to slow time t η Second, third, and fourth order coefficients.
7. The method of claim 1, wherein (6) the corrected signal s is filtered for space variant in orientation s,r (t τ ,t η ) And performing azimuth reconstruction, correction and focusing to obtain a two-dimensional imaging image, wherein the following steps are realized:
(6a) The structural orientation reconstruction relation is expressed as follows:
wherein the content of the first and second substances,
representing the wave number, h, of the electromagnetic radiation j2 (ΔR res ) J =2,3,4 respectively denote the doppler frequency modulation term with f p Linearly varying part with respect to slow time t η Second, third and fourth order coefficients of (f) p For the focus position of the target point in the frequency domain, t ηη Is an orientation reconstruction factor;
(6b) Construction of phase term exp (j 2 pi f) by using orientation reconstruction relation p t ηη )；
(6c) With the constructed phase term exp (j 2 π f) p t ηη ) Substitution of the azimuth space-variant filtered corrected signal s s,r (t τ ,t η ) Obtaining a signal s after the azimuth factor is reconstructed by the phase term in the s,a (t τ ,t ηη ) Is represented as follows:
s s,a (t τ ,t ηη )＝sinc(B(R bf -ΔR res ))exp{j2πf p t ηη }
where B is the transmission signal bandwidth and R bf Sampling a location for the signal;
(6d) Reconstructed signal s of orientation factor s,a (t τ ,t ηη ) And carrying out azimuth focusing to obtain a two-dimensional imaging image.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011611367.9A CN112649808B (en) | 2020-12-30 | 2020-12-30 | Bistatic forward-looking SAR wave number domain imaging method based on shift configuration |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011611367.9A CN112649808B (en) | 2020-12-30 | 2020-12-30 | Bistatic forward-looking SAR wave number domain imaging method based on shift configuration |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN112649808A CN112649808A (en) | 2021-04-13 |
| CN112649808B true CN112649808B (en) | 2023-04-07 |
Family
ID=75364182
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202011611367.9A Active CN112649808B (en) | 2020-12-30 | 2020-12-30 | Bistatic forward-looking SAR wave number domain imaging method based on shift configuration |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN112649808B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117665817B (en) * | 2024-02-01 | 2024-04-30 | 西安电子科技大学 | Complete real-time processable bistatic forward-looking SAR high-resolution imaging method |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5200754A (en) * | 1991-11-27 | 1993-04-06 | Hughes Aircraft Company | Fourth-order-product phase difference autofocus |
| CN101639530B (en) * | 2009-05-04 | 2011-09-07 | 北京交通大学 | SAR echo signal de-noising preprocessing method based on two-dimensional mixed transformation |
| CN102147469B (en) * | 2010-12-29 | 2012-11-07 | 电子科技大学 | Imaging method for bistatic forward-looking synthetic aperture radar (SAR) |
| CN103605118B (en) * | 2012-08-21 | 2016-01-20 | 中国科学院电子学研究所 | One utilizes polar region to visit ice radar and extracts ice layer of polar region method for position |
| CN103336280B (en) * | 2013-06-14 | 2014-10-29 | 电子科技大学 | Adjacent space slow platform synthetic aperture radar big scene imaging method |
| CN104898120A (en) * | 2015-06-12 | 2015-09-09 | 西安电子科技大学 | Double-base foresight high-mobility platform SAR imaging method based on echo simulation |
| CN106054183A (en) * | 2016-04-29 | 2016-10-26 | 深圳市太赫兹科技创新研究院有限公司 | Three-dimensional image reconstruction method and device based on synthetic aperture radar imaging |
| CN108490439A (en) * | 2018-03-20 | 2018-09-04 | 西安电子科技大学 | Bistatic arbitrary configuration SAR imaging methods based on equivalent oblique distance |
-
2020
- 2020-12-30 CN CN202011611367.9A patent/CN112649808B/en active Active
Non-Patent Citations (4)
| Title |
|---|
| A Frequency-Domain Imaging Algorithm for Translational Variant Bistatic Forward-Looking SAR;Haiwen Mei et al.;《IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING》;20191030;第58卷(第3期);全文 * |
| 双基前视SAR几何定位及同步误差分析;梅海文等;《电子与信息学报》;20180430;第40卷(第4期);全文 * |
| 基于瞬时多普勒频率的匀速移变双基SAR的二维频谱及其成像算法的应用;熊涛等;《电子与信息学报》;20120831;第34卷(第8期);全文 * |
| 移变模式双基地SAR的分辨特性及速度选择;仇晓兰等;《宇航学报》;20090731;第30卷(第7期);全文 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN112649808A (en) | 2021-04-13 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN101369018B (en) | Satellite machine combined double-base synthetic aperture radar frequency domain imaging method | |
| CN105259552A (en) | Synthetic aperture radar imaging method and device based on non-linear frequency-modulated signals | |
| CN103576147A (en) | Imaging method of synthetic aperture radar in large squint angle mode | |
| CN109738894B (en) | High squint multi-angle imaging method for large-field-of-view synthetic aperture radar | |
| CN110146889B (en) | Large-rotation-angle ISAR imaging method based on optimal echo sub-region selection | |
| CN108710111B (en) | Two-dimensional space-variant correction method for airborne bistatic forward-looking SAR azimuth phase | |
| CN110632594B (en) | Long-wavelength spaceborne SAR imaging method | |
| JP2019519784A (en) | SAR imaging method for interference analysis | |
| CN103760558A (en) | Terahertz radar ISAR imaging method | |
| CN108008387B (en) | Downward-looking three-dimensional imaging method for airborne array antenna | |
| CN115291212A (en) | Space variable nonlinear track expansion mapping high-resolution imaging method | |
| CN105204019A (en) | Stepped-frequency SAR imaging method based on wavenumber domain algorithm | |
| CN112649808B (en) | Bistatic forward-looking SAR wave number domain imaging method based on shift configuration | |
| CN110361733B (en) | Medium orbit SAR (synthetic aperture radar) large squint imaging method based on time-frequency joint resampling | |
| CN103630905A (en) | Antenna array SAR polar coordinate overlapped sub-aperture imaging method | |
| CN102759734B (en) | Imaging method with improved range migration algorithm (RMA) for high-resolution spaceborne synthetic aperture radar (SAR) | |
| CN113702974A (en) | Method for quickly optimizing airborne/missile-borne synthetic aperture radar image | |
| CN102608576A (en) | Geometric correction method for large rake forward synthetic aperture radar return image | |
| Liang et al. | Processing of very high resolution GF-3 SAR spotlight data with non-start–stop model and correction of curved orbit | |
| CN103630898A (en) | Method for estimating multi-baseline interferometry SAR phase bias | |
| CN103278819B (en) | Onboard high-resolution strabismus bunching synthetic aperture radar (SAR) imaging method based on sliding receiving window | |
| CN112415512B (en) | SAR moving target focusing method based on advance and retreat method and golden section method | |
| CN112285707B (en) | Passive multi-base high-resolution imaging method based on GPS navigation signals | |
| CN113466855A (en) | Signal reconstruction method and device | |
| CN103792534A (en) | SAR two-dimension autofocus method based on prior phase structure knowledge |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |