CN107271996A - A kind of airborne CSSAR Ground moving target imagings method - Google Patents
A kind of airborne CSSAR Ground moving target imagings method Download PDFInfo
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- CN107271996A CN107271996A CN201710413062.9A CN201710413062A CN107271996A CN 107271996 A CN107271996 A CN 107271996A CN 201710413062 A CN201710413062 A CN 201710413062A CN 107271996 A CN107271996 A CN 107271996A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/904—SAR modes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/904—SAR modes
- G01S13/9088—Circular SAR [CSAR, C-SAR]
Abstract
The invention provides a kind of airborne CSSAR Ground moving target imagings method, it is related to radar signal processing field.Airborne CSSAR receives the echo-signal of ground moving object, enter row distance to Fourier transformation and orientation Fourier transformation, in two-dimensional frequency construction range migration correction is carried out apart from matched filtering and range migration correction wave filter, then row distance is entered to inverse Fourier transform, construction Azimuth Compression wave filter group simultaneously carries out Azimuth Compression, and the peak power of the echo signal after computer azimuth compression, it is updated using the frequency modulation rate for causing the prominent Azimuth Compression wave filter of target peak after Azimuth Compression migration correcting filter of adjusting the distance, and the echo signal after migration correction of being adjusted the distance using the orientation compression filter carries out Azimuth Compression.The precision of the range migration correction of the present invention is very high, can be used for range resolution ratio very high system.
Description
Technical field
The present invention relates to radar signal processing field, especially a kind of synthetic aperture radar Ground moving target imaging side
Method.
Background technology
Airborne Circular test band synthetic aperture radar (Circular Stripmap Synthetic Aperture
Radar, CSSAR) it is a kind of new carried SAR developed in recent years, it has what wide coverage and periodicity were revisited
Feature, thus it is suitable for air to surface wide area scouting and time critical target (such as ground moving object) monitoring.
Because airborne CSSAR is a kind of new carried SAR for just occurring in recent years, people are to the ground under airborne CSSAR
It is also seldom that motive target imaging is studied.Document " Ground moving target imaging algorithm for
single channel airborne CSSAR”(Electronics Letters,2014,50:24) one kind is proposed first
Suitable for airborne single channel CSSAR Ground moving target imaging method, but to be only applicable to range resolution ratio relatively low for this method
System.When system range resolution ratio is higher, this method can not correctly correct the range migration of target, so as to can not realize to mesh
The high-quality imaging of target.
The content of the invention
In order to overcome the deficiencies in the prior art, the present invention proposes a kind of to be used for range resolution ratio very high airborne CSSAR
The Ground moving target imaging method of system.For existing airborne single channel CSSAR Ground moving target imaging methods in system
The problem of range resolution ratio can not correctly correct the range migration of target when higher, proposes a kind of improved imaging method, the ground
Face motive target imaging method can be used for range resolution ratio very high airborne CSSAR systems.
The problem of target range migration can not correctly being corrected for existing imaging method when system range resolution ratio is higher,
The present invention is improved to this method, proposes an iterative process flow to realize the precise calibration to the range migration of target.
The step of the technical solution adopted for the present invention to solve the technical problems is：
Step 1, airborne CSSAR receives the echo-signal of ground moving object, to the echo-signal point of the target received
Do not enter row distance to Fourier transformation and orientation Fourier transformation, echo signal is transformed into two-dimensional frequency, obtain two-dimentional frequency
Domain echo signal；
Step 2, in two-dimensional frequency construction apart from matched filter, by the two-dimensional frequency echo signal of step 1 with apart from
It is multiplied with wave filter and realizes Range compress into row distance to matched filtering；
Step 3, in two-dimensional frequency construction range migration correction wave filter Hrcmc(l), detailed step is as follows：
A) by the distance of step 2 to the echo signal S after matched filteringrc(fr,fa) be expressed as
Wherein, Wa() is orientation frequency envelope, Wr() is frequency of distance envelope, faFor base band orientation frequency, and it is full
Foot-PRF/2≤fa≤ PRF/2, PRF are the pulse recurrence frequency of radar, frFor frequency of distance, M is doppler ambiguity number, tacFor
At the time of target is passed through at radar beam center, RcFor tacMoment radar range-to-go, l1And l2Respectively target range equation
Monomial coefficient and secondary term coefficient, c is the light velocity, fcFor the carrier frequency of radar emission signal；
B) according to the expression formula of the echo signal after matched filtering, i.e. formula (1) constructs following range migration correction
Wave filter：
Wherein l is the range migration correction factor；
Step 4, by the two-dimensional frequency echo signal and H after Range compress in step 2rcmc(l) it is multiplied and carries out range migration
Correction, the echo signal after migration of then adjusting the distance correction enters row distance to inverse Fourier transform, after range migration correction
Echo signal transforms to range-Dopler domain from two-dimensional frequency, obtains range-Dopler domain echo signal；
Step 5, Azimuth Compression wave filter group is constructed, with each Azimuth Compression wave filter in Azimuth Compression wave filter group point
The other peak value that the echo signal after Azimuth Compression, and computer azimuth compression is carried out to range-Dopler domain echo signal in step 4
Power, detailed step is as follows：
A) range-Dopler domain echo signal s in step 4rcmc(tr,fa) be expressed as
Wherein, trFor apart from fast time, pr() is Range compress impulse response function；
B) according to the echo signal expression formula after range migration correction, i.e. formula (3), in Azimuth Compression wave filter group
I wave filter Hac,i(Ka,i) be configured to：
In formula (4),
Wherein, Ka,iFor the orientation frequency modulation rate of i-th of wave filter, the number of L wave filters for needed for, Ka,minAnd Ka,maxRespectively
For the minimum possible value and maximum value possible of the orientation frequency modulation rate of ground moving object interested, TaDuring for target synthetic aperture
Between,Expression rounds up；
By srcmc(tr,fa) and Hac,i(Ka,i) be multiplied, then orientation inverse Fourier transform is carried out, it can obtain i-th of filtering
Echo signal s after device Azimuth Compressionac,i(tr,ta) be：
WhereinRepresent to carry out orientation inverse Fourier transform；
C) the target peak power P after i-th of wave filter Azimuth CompressioniCalculated with equation below：
Wherein,Represent to obtain with trAnd taFor the binary function s of independent variableac,i(tr,ta) maximum
Value, | | expression takes absolute value；
Step 6, from the target peak power P after step 5 Azimuth CompressioniIn pick out maximum PqAnd corresponding orientation
Compression filter Hac,q(Ka,q)；
Step 7, judge whether l is equal to λ Ka,q/ 4, wherein λ are the wavelength of radar emission signal, Ka,qIt is Azimuth Compression filtering
Device Hac,q(Ka,q) frequency modulation rate, if it is, perform step 8, if it is not, then making l=λ Ka,q/ 4, update Hrcmc(l) returned after
Return to step 4；
Step 8, H is utilizedac,q(Ka,q) to the range-Dopler domain echo signal progress Azimuth Compression of step 4, complete to mesh
Target is imaged.
The beneficial effects of the invention are as follows due to carrying out range migration correction in the form of iterative processing, using causing orientation
The frequency modulation rate of the prominent Azimuth Compression wave filter of target peak migration correcting filter of adjusting the distance is updated after compression, energy
Enough it is substantially reduced the remaining range migration caused by frequency errors are adjusted in orientation.The precision of the range migration correction of the present invention is higher,
Range resolution ratio very high system can be used for.
Brief description of the drawings
Fig. 1 is the schematic flow sheet of the present invention.
Fig. 2 is airborne CSSAR observation geometries, wherein raThe radius of radar motion track, ω is the angular speed of radar, h
For radar altitude, vxAnd vyRespectively target is along x-axis and the speed of y-axis, r0And θ0For the distance of zero moment target to the origin of coordinates
With the azimuth of target.
Fig. 3 is Range compress result figure.
Fig. 4 is range migration correction simulation result figure, and wherein Fig. 4 (a) is document " Ground moving target
imaging algorithm for single channel airborne CSSAR”(Electronics Letters,
2014,50:24) the range migration correction result of method, Fig. 4 (b) is range migration correction result of the invention.
Fig. 5 is target imaging simulation result figure, and wherein Fig. 5 (a) is azimuthal section figure, and Fig. 5 (b) is distance profile figure, its
Middle IRW is response pulse duration (Impulse Response Width).
Embodiment
The present invention is further described with reference to the accompanying drawings and examples.
Fig. 1 is the schematic flow sheet of the present invention, and of the invention comprises the following steps that：
Step 1, airborne CSSAR receives the echo-signal of ground moving object, to the echo-signal point of the target received
Do not enter row distance to Fourier transformation and orientation Fourier transformation, echo signal is transformed into two-dimensional frequency, obtain two-dimentional frequency
Domain echo signal；
Fig. 2 is airborne single channel CSSAR observation geometries, and the movement locus of radar platform is that a radius is raCircle,
The angular speed of radar platform is ω, and flying height is h, and radar beam perpendicular to velocity attitude and points to the outer of movement locus all the time
Side.It is assumed that target linear uniform motion, and its speed along x-axis and y-axis is respectively vxAnd vy, in ta=0 moment (taFor orientation
The slow time), the coordinate of radar is (ra, 0, h), the coordinate of target is (r0cosθ0,r0sinθ0, 0), wherein, r0For ta=0 moment
Target is to the distance of the origin of coordinates, θ0For taThe azimuth of=0 moment target.
According to Fig. 2, target range equation is represented by
In formula (9),
Wherein, tacAt the time of target being passed through for radar beam center, RcFor ta=tacMoment radar range-to-go, rc
For ta=tacMoment target is to the distance of the origin of coordinates, θcFor ta=tacThe azimuth of moment target, l1And l2Respectively target away from
From the Monomial coefficient and secondary term coefficient of equation.
Assuming that the signal of radar emission is chirp pulse signal, then the target echo signal after demodulating is represented by：
Wherein, trFor apart from fast time, wr() is that c is the light velocity, w apart from envelopea() is orientation envelope, fcFor radar
The carrier frequency of transmission signal, KrFor the frequency modulation rate of radar emission signal.It is statement for the sake of simplicity, have ignored the normal of target echo signal
Number amplitude.
Two-dimensional Fourier transform is carried out to target echo signal, and utilizes principle in phase bit, the mesh of two-dimensional frequency can be obtained
Mark signal：
In formula (12),
Wherein, frFor frequency of distance, PRF is pulse recurrence frequency, faFor base band orientation frequency, and satisfaction-PRF/2≤fa
≤ PRF/2, Wa() is orientation frequency envelope, Wr(fr) it is frequency of distance envelope, M is doppler ambiguity number.Risen for statement is simple
See, have ignored the constant phase and amplitude in formula (12).
Due to fc＞ ＞ fr, approximate 1/ (fc+fr)≈1/fc-fr/fc 2Set up, therefore,It can be further represented as：
Therefore, the target echo signal of two-dimensional frequency is represented by：
Step 2, in two-dimensional frequency construction apart from matched filter, by the two-dimensional frequency echo signal of step 1 with apart from
It is multiplied with wave filter and realizes Range compress into row distance to matched filtering；
It can compensate the quadratic term of frequency of distance in echo signal phase at two-dimensional frequency by matched filtering, realize distance
Compression.According to the expression formula of the echo signal of two-dimensional frequency, it can be configured to apart from matched filter
By the target echo signal S (f of the two-dimensional frequency of formula (15)r,fa) and Hrc(fr) be multiplied, can obtain distance to
With filtered echo signal：
Step 3, in two-dimensional frequency construction range migration correction wave filter Hrcmc(l)；
For correction target range migration, need to compensate the coupling of frequency of distance and orientation frequency in echo signal phase to,
According to the expression formula of the echo signal after matched filtering, i.e. formula (1), following range migration correction wave filter is constructed：
Wherein l is the range migration correction factor.
Step 4, by the two-dimensional frequency echo signal and H after Range compress in step 2rcmc(l) it is multiplied and carries out range migration
Correction, the echo signal after migration of then adjusting the distance correction enters row distance to inverse Fourier transform, after range migration correction
Echo signal transforms to range-Dopler domain from two-dimensional frequency, obtains range-Dopler domain echo signal；
By Src(fr,fa) and Hrcmc(l) being multiplied to obtain：
To Src(fr,fa) enter row distance to inverse Fourier transform, obtain the range-Dopler domain mesh after range migration correction
Mark signal：
Wherein pr() is Range compress impulse response function.
From formula (3) as can be seen that also there is remaining range migration.When system range resolution ratio is very high, such as it is higher than
During 0.5m, the remaining range migration is likely to be more than half of Range resolution unit, therefore can not ignore.Therefore, one will be proposed
The iterative process flow of individual step 7 reduces the remaining range migration.
Step 5, Azimuth Compression wave filter group is constructed, with each Azimuth Compression wave filter in Azimuth Compression wave filter group point
The other peak value that the echo signal after Azimuth Compression, and computer azimuth compression is carried out to range-Dopler domain echo signal in step 4
Power, detailed step is as follows：
A) it is that Azimuth Compression is carried out to target, the quadratic term of orientation frequency in echo signal phase need to be compensated, it is contemplated that mesh
Target orientation frequency modulation rate is unknown, and the present invention carries out Azimuth Compression using an Azimuth Compression wave filter group.According to distance
I-th of wave filter H in echo signal expression formula after migration correction, Azimuth Compression wave filter groupac,i(Ka,i) be configured to：
In formula (4),
Wherein, Ka,iFor the orientation frequency modulation rate of i-th of wave filter, the number of L wave filters for needed for, Ka,minAnd Ka,maxRespectively
For the minimum possible value and maximum value possible of the orientation frequency modulation rate of ground moving object interested, TaDuring for target synthetic aperture
Between,Expression rounds up；
By srcmc(tr,fa) and Hac,i(Ka,i) be multiplied, then orientation inverse Fourier transform is carried out, it can obtain i-th of filtering
Echo signal s after device Azimuth Compressionac,i(tr,ta) be：
WhereinRepresent to carry out orientation inverse Fourier transform；
B) because the different azimuth compression filter in wave filter group uses different orientation frequency modulation rates, therefore these
Wave filter is different to the compression effectiveness of target.So that the prominent Azimuth Compression wave filter of target peak after Azimuth Compression
It is exactly the best wave filter of Azimuth Compression effect, that is, is ultimately used to carry out target the wave filter of Azimuth Compression.I-th of filter
Target peak power P after ripple device Azimuth CompressioniCalculated with equation below：
Wherein,Represent to obtain with trAnd taFor the binary function s of independent variableac,i(tr,ta) maximum
Value, | | represent modulus；
Step 6, from the target peak power P after step 5 Azimuth CompressioniIn pick out maximum PqAnd corresponding orientation
Compression filter Hac,q(Ka,q)；
Following mathematical operation is performed to determine to make the sequence number q of the prominent Azimuth Compression wave filter of target peak：
Then so that the prominent Azimuth Compression wave filter of target peak is exactly HAc, q(Ka,q)。
Step 7, judge whether l is equal to λ Ka,q/ 4, wherein λ are the wavelength of radar emission signal, Ka,qIt is Azimuth Compression filtering
Device Hac,q(Ka,q) frequency modulation rate, if it is, perform step 8, if it is not, then making l=λ Ka,q/ 4, update Hrcmc(l) returned after
Return to step 4；
Step 8, H is utilizedAc, q(Ka,q) to the range-Dopler domain echo signal progress Azimuth Compression of step 4, complete to mesh
Target is imaged.
By HAc, q(Ka,q) and srcmc(tr,fa) be multiplied and can obtain
To sac,q(tr,fa) carry out the echo signal after orientation inverse Fourier transform must can be imaged：
The effect of the present invention is further illustrated by following emulation experiment：
(1) range migration correction is emulated
Airborne single channel CSSAR systematic parameters are shown in Table 1, and target component is：vx=30m/s, vy=26m/s, r0=
23.81km, θ0=0.Fig. 3 is the target trajectory after Range compress, it can be seen that target has obvious range migration.Fig. 4 (a)
For document " Ground moving target imaging algorithm for single channel airborne
CSSAR”(Electronics Letters,2014,50:24) the range migration correction result of method, also in the presence of obvious
Range migration, this explanation this method can not full correction target range migration.Fig. 4 (b) is range migration correction of the invention
As a result, the track of target is vertical with distance axis, i.e., the range migration of target is corrected well, and this result illustrates this hair
It is bright correctly to correct the range migration of target.
The airborne CSSAR systematic parameters of table 1
| Radar platform speed | 150m/s |
| Flying radius | 3km |
| Radar platform height | 12km |
| Carrier frequency | 10GHz |
| Transmitted signal bandwidth | 150MHz |
| Sample frequency | 180MHz |
| Pulse recurrence frequency | 1000Hz |
| Azimuth beamwidth | 2° |
| Scene center incidence angle | 60° |
(2) target imaging is emulated
Parameter setting in this emulation is identical with the setting in emulation 1, and simulation result is shown in Fig. 5.Wherein, Fig. 5 (a) gives
The azimuthal section figure of target after imaging, and marked orientation response pulse duration (the Impulse Response of target
Width, IRW) broadening.Fig. 5 (b) give imaging after target distance profile figure, and marked target apart from IRW exhibitions
It is wide.It is seen from fig 5 that the orientation IRW broadenings of target are less than 2%, and it is zero apart from IRW broadenings, then illustrates the present invention
Target imaging be of high quality.
Claims (1)
1. a kind of airborne CSSAR Ground moving target imagings method, it is characterised in that comprise the steps：
Step 1, airborne CSSAR receives the echo-signal of ground moving object, and the echo-signal of the target to receiving is entered respectively
Line-spacing descriscent Fourier transformation and orientation Fourier transformation, two-dimensional frequency is transformed to by echo signal, obtains two-dimensional frequency mesh
Mark signal；
Step 2, in two-dimensional frequency construction apart from matched filter, by the two-dimensional frequency echo signal of step 1 with apart from matching filter
Ripple device is multiplied realizes Range compress into row distance to matched filtering；
Step 3, in two-dimensional frequency construction range migration correction wave filter Hrcmc(l), detailed step is as follows：
A) by the distance of step 2 to the echo signal S after matched filteringrc(fr,fa) be expressed as
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At the time of target being passed through up to beam center, RcFor tacMoment radar range-to-go, l1And l2Respectively target range equation
Monomial coefficient and secondary term coefficient, c are the light velocity, fcFor the carrier frequency of radar emission signal；
B) according to the expression formula of the echo signal after matched filtering, i.e. formula (1) constructs following range migration correction filtering
Device：
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Wherein l is the range migration correction factor；
Step 4, by the two-dimensional frequency echo signal and H after Range compress in step 2rcmc(l) it is multiplied and carries out range migration correction,
Then the echo signal after migration of adjusting the distance correction enters row distance to inverse Fourier transform, and the target after range migration correction is believed
Number range-Dopler domain is transformed to from two-dimensional frequency, obtain range-Dopler domain echo signal；
Step 5, Azimuth Compression wave filter group is constructed, it is right respectively with each Azimuth Compression wave filter in Azimuth Compression wave filter group
Range-Dopler domain echo signal carries out the peak power of the echo signal after Azimuth Compression, and computer azimuth compression in step 4,
Detailed step is as follows：
A) range-Dopler domain echo signal s in step 4rcmc(tr,fa) be expressed as
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Wherein, trFor apart from fast time, pr() is Range compress impulse response function；
B) according to the echo signal expression formula after range migration correction, i.e. formula (3), i-th in Azimuth Compression wave filter group
Wave filter Hac,i(Ka,i) be configured to：
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1
In formula (4),
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Wherein, Ka,iFor the orientation frequency modulation rate of i-th of wave filter, the number of L wave filters for needed for, Ka,minAnd Ka,maxRespectively feel
The minimum possible value and maximum value possible of the orientation frequency modulation rate of interest ground moving object, TaFor the target synthetic aperture time,
Expression rounds up；
By srcmc(tr,fa) and Hac,i(Ka,i) be multiplied, then orientation inverse Fourier transform is carried out, it can obtain i-th of wave filter orientation
Echo signal s after compressionac,i(tr,ta) be：
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WhereinRepresent to carry out orientation inverse Fourier transform；
C) the target peak power P after i-th of wave filter Azimuth CompressioniCalculated with equation below：
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Wherein,Represent to obtain with trAnd taFor the binary function s of independent variableac,i(tr,ta) maximum,
| | represent modulus；
Step 6, from the target peak power P after step 5 Azimuth CompressioniIn pick out maximum PqAnd corresponding Azimuth Compression
Wave filter Hac,q(Ka,q)；
Step 7, judge whether l is equal to λ Ka,q/ 4, wherein λ are the wavelength of radar emission signal, Ka,qIt is Azimuth Compression wave filter
Hac,q(Ka,q) frequency modulation rate, if it is, perform step 8, if it is not, then making l=λ Ka,q/ 4, update Hrcmc(l) returned after
To step 4；
Step 8, H is utilizedac,q(Ka,q) to the range-Dopler domain echo signal progress Azimuth Compression of step 4, complete to target
Imaging.
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| CN110187343A (en) * | 2019-05-28 | 2019-08-30 | 西北工业大学 | Airborne triple channel CSSAR moving-target Doppler's parameter estimate and ATI Method for Phase Difference Measurement |
| CN110471065A (en) * | 2018-05-11 | 2019-11-19 | 通用汽车环球科技运作有限责任公司 | For solving the filtering processing of range walk effect in range Doppler figure |
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| CN105891828A (en) * | 2016-04-22 | 2016-08-24 | 西安电子科技大学 | Airborne CSSAR radar moving-target detection method |
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| CN110471065A (en) * | 2018-05-11 | 2019-11-19 | 通用汽车环球科技运作有限责任公司 | For solving the filtering processing of range walk effect in range Doppler figure |
| CN110095774A (en) * | 2019-01-28 | 2019-08-06 | 南京航空航天大学 | A kind of circular track video SAR moving target detection method |
| CN110095774B (en) * | 2019-01-28 | 2022-04-15 | 南京航空航天大学 | Moving target detection method for circular track video SAR |
| CN110187343A (en) * | 2019-05-28 | 2019-08-30 | 西北工业大学 | Airborne triple channel CSSAR moving-target Doppler's parameter estimate and ATI Method for Phase Difference Measurement |
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