CN101975948A - Imaging method for remote sensing satellite irradiation source forward-looking synthetic aperture radar - Google Patents

Abstract

The invention provides a frequency domain imaging method for a remote sensing satellite irradiation source forward-looking synthetic aperture radar (LSA-FBSAR). In the method, a nonlinear mapping relationship between range dimension space-variant range cell migration (RCM) and azimuth dimension space-variant RCM is acquired from the complex coupling relationship of a two-dimensional frequency spectrum by the resolution representation of the frequency spectrum of an LSA-FBSAR system and the characteristic of forward-looking work of a receiving platform. The conventional two-dimensional space-variant RCM compensation processing procedure is improved; the compensation of the target azimuth of a non-reference point and slant-range two-dimensional space-variant RCM is realized by scaled Fourier transform-phase multiplication technology and interpolation-phase multiplication technology; the problem of severe geometric distortion such as bending, distortion and the like of an imaging result caused by two-dimensional nonlinear space-variant RCM is effectively solved; and the method is suitable for realizing the high-resolution imaging of the LSA-FBSAR.

Description

A kind of remote sensing satellite irradiation source forward sight synthetic aperture radar image-forming method

Technical field

The invention belongs to the Radar Technology field, it is particularly related to remote sensing satellite irradiation source forward sight synthetic-aperture radar and (is called for short: imaging technique LSA-FBSAR).

Background technology

(be called for short: LSA-FBSAR) transmitter of system and receiver are placed in and hang down on rail remote sensing satellite, the aircraft platform remote sensing satellite irradiation source forward sight synthetic-aperture radar, the sending and receiving wave beam all points to the zone, dead ahead of aircraft platform, and to this zone emission broadband signal, receiver obtains the target scattering echo and carries out synthetic aperture processing, finally realizes the high-resolution two-dimensional imaging in receiver dead ahead.

The LSA-FBSAR system has abundant space, motion resource owing to the sending and receiving platform splits, can remove the remote sensing visual field restriction that traditional single base SAR forms because of the relative platform motion track symmetry in forward vision areas target location, thereby this system possesses the ability that breaks through traditional SAR system imaging blind area, can be applied to fields such as round-the-clock, round-the-clock aircraft independent landing, independent navigation, cargo assault, guided missile image matching guidance, for development and national economy and national security play an important role.

In addition, external exposure source Forward-looking SAR imaging system compared to other systems, adopt remote sensing satellite also to have following unique advantage as the LSA-FBSAR of irradiation source: (1), the relative target of spaceborne platform are with high-speed motion, the higher Doppler frequency bandwidth of relative target can be obtained, therefore meticulousr target information can be obtained; (2), compare transmitting of other purposes satellites, the frequency that remote sensing satellite transmits, polarization mode and signal bandwidth thereof etc. are more conducive to obtain high-resolution remote sensing images; (3), all can be used as the flat pad of system, system only need bear the cost of airboarne receiver, can significantly reduce system cost at the remote sensing satellite of rail work.This shows to have researching value as the LSA-FBSAR system of flat pad with low rail remote sensing radar satellite.

Yet work in positive forward sight owing to receiving platform in the LSA-FBSAR system, the distance and position of the relative target of receiver is symmetrical, the space-variant characteristic of short oblique distance changes so the forward sight mode of operation causes, (write a Chinese character in simplified form: space-variant characteristic RCM) causes its echoing characteristics and side-looking SAR system totally different also can to change SA-FBSAR system echoed signal middle distance unit migration accordingly; In addition, exist significant relative motion (flat pad typical rate: 7.4～7.6km/s between system's transmit-receive platform, receiving platform typical rate: 100m/s), cause relative position relation and system geometries between platform to change fast, the system complex degree increases, and therefore traditional SAR formation method and bistatic side-looking formation method are difficult to satisfy its high-quality imaging requirements.

The frequency domain imaging algorithm is the algorithm that a class imaging performance and operation efficiency have concurrently, is widely used in the SAR imaging.In the document of publishing at present, mainly contain at external exposure source Forward-looking SAR System imaging method: document 1:XiaoLan Q, Donghui H, Chibiao D.Some Reflections on Bistatic SAR ofForward-looking Configuration[J] .IEEE Geoscience and Remote Sensingletters, 2008,5 (4): from making up static irradiation source Forward-looking SAR System echo 2-d spectrum, proposed a kind of improved frequency domain imaging algorithm among the 735-739; Document 2:Hee-Sub S, Jong-Tae L.Omega-KAlgorithm for Airborne Forward-looking Bistatic Spotlight SAR Imaging[J] .IEEEGeoscience and Remote Sensing Letters, 2009,6 (2): 312-316.: utilize rotation of coordinate, approximate (the Extended Taylor Approximation) method of expansion Taylor expansion, forward sight receiving platform track in the system is rotated to be side-looking receive, then continue to use single base side-looking SAR frequency domain imaging algorithm and handle; Document 3:Haocheng W, Jianyu Y, Yulin H, Junjie W.Extended SIFFT Algorithm for BistaticForward-looking SAR[C] .Proc.of APSAR 2009.2 ^NdAsian-Pacific Conference onSynthetic Aperture Radar, 2009:955-959 receives Forward-looking SAR System, has proposed the imaging algorithm based on yardstick inverse Fourier transform (Inverse Scaled FourierTransform) at airborne irradiation source-airborne forward sight of parallel uniform flight.The method of these algorithm compensations two dimension space-variant range unit migrations is basic identical-and the first step is to implement the relevant RCM of distance and position (write a Chinese character in simplified form: RD-RCM) compensation, second step was to implement the relevant RCM of position of orientation (to write a Chinese character in simplified form: AD-RCM) compensation.

Yet present external exposure source Forward-looking SAR imaging algorithm is all at the Forward-looking SAR System of simple geometric structures such as static irradiation source and design, and LSA-FBSAR system architecture peace interstation kinematic relation is far beyond its complexity, echoed signal RCM characteristic changes, the respective imaging intractability is also bigger, and therefore existing traditional two-dimentional space-variant RCM compensation method and respective imaging method can't realize the LSA-FBSAR high-resolution imaging.

Summary of the invention

The objective of the invention is to overcome the deficiency that existing SAR frequency domain imaging technology can't be applied to LSA-FBSAR, provide the frequency domain imaging method of a kind of LSA-FBSAR of being applicable to system: a kind of remote sensing satellite irradiation source forward sight synthetic-aperture radar frequency domain imaging method, this formation method has taken into full account system's characteristics of LSA-FBSAR, not only can effectively compensate the echoed signal two dimension space-variant characteristic that causes because of system's transmit-receive platform speed difference, and can effectively proofread and correct the nonlinear geometry distortion distortion of introducing owing to the forward sight mode of operation, so this method can realize LSA-FB SAR high-resolution imaging efficiently.

Content of the present invention for convenience of description, at first make following term definition:

Definition 1, LSA-FBSAR system correlation parameter are described

Spaceborne platform oblique distance history

Airborne platform oblique distance history

LSA-FBSAR system oblique distance history

$R(t;r,T)=\sqrt{{(r_{0\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="HDA0000029836540000012.png,HDA0000029836540000021.png"\; state="\{\{state\}\}">S</figure-callout>}0}+r)}^2+v_S{(t-t_{0S})}^2}+\sqrt{r_{0\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="HDA0000029836540000012.png,HDA0000029836540000021.png"\; state="\{\{state\}\}">P</figure-callout>}0}^2+{(r/{\sin \mathrm{\&xi;}}_S)}^2+v_P{(t-t_{0P})}^2}$

Spaceborne platform phase place history φ _S(t)=kr _S(t)

Airborne platform phase place history φ _P(t)=kr _P(t)

LSA-FBSAR system phase history φ (t)=kR (t)+2 π f _dt

The t of time point in the phase bit of LSA-FBSAR system _kSatisfy φ ' (t _k)=0

The LSA-FBSAR system imaging as a result coordinate system (x, y), x=r/sin ξ wherein _S, y=v _ST _0S

Other parameters: τ is fast (oblique distance) time, and t is slow (orientation) time; v _S, v _PIt is respectively movement velocity size spaceborne and the relative target of airborne platform; Spaceborne and airborne platform is respectively at t _0S, t _0PConstantly nearest apart from forward sight scene arbitrary target P, and oblique distance is respectively r recently _0S, r _0Pt _0S0, t _0P0Be respectively that spaceborne, airborne platform is apart from reference target P ₀The nearest moment, r _0S0, r _0P0It is respectively spaceborne, airborne platform distance reference target P ₀Nearest oblique distance; R, T are respectively arbitrary target P and reference target P ₀Locus difference r=r _0S-r _0S0, T=t _0S-t _0S0F is the frequency corresponding to fast (oblique distance) time, and ω=2 π f are the angular frequency corresponding to fast (oblique distance) time, ω ₀Be the central angle frequency that transmits, f ₀Be the centre frequency that transmits,

C is the light velocity; f _dBe Doppler frequency corresponding to slow (orientation) time; ξ _SIt is the downwards angle of visibility of spaceborne platform.

Definition 2, range unit migration Nonlinear Two-Dimensional space-variant characteristic

The RCM that the non-linear space-variant characteristic of range unit migration is exactly an echoed signal is nonlinearities change with the variation of target two-dimensional space position.

For LSA-FBSAR, because the movement velocity between two platforms is unequal, orientation between two platforms changes in the process of motion to relative position relation, therefore except the intrinsic oblique distance space-variant problem of SAR, also has the orientation space-variant, be that system exists oblique distance dimension space-variant (to write a Chinese character in simplified form: RD-RCM), the azimuth dimension space-variant (writes a Chinese character in simplified form: AD-RCM) two-dimentional space-variant characteristic, must be proofreaied and correct respectively, just can be realized the high-quality imaging.

In addition, for LSA-FBSAR, because its airborne receiving platform works in forward-looking mode, the relative oblique distance of receiving platform flight path both sides target position symmetry, thereby cause its echoed signal oblique distance space-variant RCM to present significant nonlinear characteristic, promptly RD-RCM is nonlinearities change with the variation of target oblique distance locus.

Definition 3, air-phase time point t _b

Air-phase time point t _bFor satisfying the time point that following formula is set up

kr _S′(t _b)+2πf _d＝0

Find the solution this equation and can obtain t _bAnalytic solution: $t_b=t_{0S}-\frac{f_d{r}_{0S}}{v_S\sqrt{{\left(\frac{f+f_0}{c}{v}_S\right)}^2-f_d^2}}---\left(1\right)$

At this time point, the rate of change φ ' (t of system phase history _b) just equal the phase change rate kr ' of airborne platform _P(t _b), therefore claim that this time point is the air-phase time point.

The 2-d spectrum of definition 4, LSA-FBSAR system impulse response

According to the characteristics of LSA-FBSAR system, 2-d spectrum H (f, the f of definition LSA-FBSAR system impulse response _d) be

$H(f,f_d)=\exp \{-\mathrm{j\&phi;}\left(t_b\right)\}\&CenterDot;\exp \left\{j\frac{1}{2}\frac{{\left({\mathrm{\&phi;}}^{\&prime;}\left(t_b\right)\right)}^2}{{\mathrm{\&phi;}}^{\&prime;\&prime;}\left(t_b\right)}\right\}---\left(2\right)$

With two single station H of standard that exponential term is defined as 2-d spectrum respectively in the formula (2) _QM(f, f _d) and two station distortion term H _BD(f, f _d)

H _QM(f，f _d)＝exp{-jφ(t _b)}， $H_{\mathrm{BD}}(f,f_d)=\exp \left\{j\frac{1}{2}\frac{{\left({\mathrm{\&phi;}}^{\&prime;}\left(t_b\right)\right)}^2}{{\mathrm{\&phi;}}^{\&prime;\&prime;}\left(t_b\right)}\right\}---\left(3\right)$

Definition 5, contrary yardstick Fourier transform

The contrary yardstick Fourier transform ISFT (S (f)) of signal S (f) is

ISFT(S(f))＝∫S(f)exp(jaft)df (4)

Wherein a is a scale factor.The discrete representation form of contrary yardstick Fourier transform is

$\mathrm{ISFT}\left(S\left(n\right)\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}S\left(n\right)\&CenterDot;\exp (j\frac{2\mathrm{\&pi;a}}{N}\&CenterDot;n\&CenterDot;l),l=\mathrm{0,1},....---\left(5\right)$

Discrete contrary yardstick Fourier transform can realize that concrete enforcement can realize by twice phase multiplication and a convolution by the chirp transform.

The invention provides a kind of LSA-FBSAR frequency domain imaging method FB(flow block), as shown in Figure 1.In following each step explanation, identify the echo data frequency domain space at place after treatment with different subscripts: subscript τ-oblique distance frequency domain about formation method of the present invention; Subscript t-orientation frequency domain; Subscript τ, t-oblique distance frequency domain-orientation frequency domain.

A kind of remote sensing satellite irradiation source forward sight synthetic-aperture radar frequency domain imaging method provided by the invention, it comprises following steps:

Step 1, echoed signal are apart from compression

The original echo data s (τ of LSA-FBSAR system, t) deposit (M and N are positive integer) with the data matrix of the capable N row of M, original echo data s (τ, t) the every column data of data matrix is the sampling of depositing slow time t (orientation to) echoed signal, the deposit data of every row be the sampling of the fast time τ of monopulse (oblique distance to) echoed signal one by one;

Use s emission signal s ₀(τ) conduct is apart from the reference compression signal, s emission signal s ₀(τ) and original echoed signals s (τ t) obtains S respectively after transforming to the oblique distance frequency domain ₀(f) and S ^τ(f, t), then with S ₀(f) and S ^τ(f, t) conjugate multiplication realize the distance compression, are shown below

$S_{\mathrm{RC}}^{\mathrm{\&tau;}}(f,t)=S^{\mathrm{\&tau;}}(f,t)\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="HDA0000029836540000012.png,HDA0000029836540000021.png"\; state="\{\{state\}\}">S</figure-callout>}}_0^{*}\left(f\right)$

* represents complex conjugate in the following formula;

Step 2, fourier transform of azimuth

At the distance compressed echo signal

Each row in the data matrix are done Fourier transform and are obtained process apart from the compressed echo signal 2-d spectrum

Step 3, reference point phase compensation

According to reference point target P ₀Location parameter (r _0S=r _0S0, r _0P=r _0P0, t _0S=t _0S0, t _0P=t _0P0), utilize formula (1): $t_b=t_{0S}-\frac{f_d{r}_{0S}}{v_S\sqrt{{\left(\frac{f+f_0}{c}{v}_S\right)}^2-f_d^2}},$ Formula (2): $H(f,f_d)=\exp \{-\mathrm{j\&phi;}\left(t_b\right)\}\&CenterDot;\exp \left\{j\frac{1}{2}\frac{{\left({\mathrm{\&phi;}}^{\&prime;}\left(t_b\right)\right)}^2}{{\mathrm{\&phi;}}^{\&prime;\&prime;}\left(t_b\right)}\right\}$ , just can obtain the 2-d spectrum H of reference point target system impulse response ₀(f, f _d), with the 2-d spectrum H of reference point target system impulse response ₀(f, f _d) complex conjugate

With echoed signal apart from the compression after 2-d spectrum

The data matrix pointwise is multiplied each other and is obtained

Be shown below

$S_{\mathrm{RF}}^{\mathrm{\&tau;},t}(f,f_d)=S_{\mathrm{RC}}^{\mathrm{\&tau;},t}(f,f_d)\&CenterDot;H_0^{*}(f,f_d)$

Be 2-d spectrum through reference point phase compensation back echo signal, wherein in the formula (1), t _0SBe the satellite platform moment nearest apart from the distance target, r _0SThe nearest oblique distance of expression satellite platform distance objective, f ₀Be the centre frequency that transmits, v _SBe the movement velocity size of the relative target of satellite platform, f _dBe the Doppler frequency corresponding to slow (orientation) time t, f is the frequency corresponding to fast (oblique distance) time τ, r _0S0And r _0P0Be respectively satellite, aircraft platform relative reference target P ₀Nearest oblique distance, t _0S0And t _0P0Be respectively that satellite, aircraft platform are apart from reference target P ₀The nearest moment, φ (t in the formula (2) _b)=k[r _S(t _b)+r _P(t _b)]+2 π f _dT,

r _S(t _b) and r _P(t _b) be respectively air-phase time point t _bThe oblique distance size of moment satellite, aircraft platform distance objective;

Step 4, orientation space-variant characteristic compensation

To the 2-d spectrum after the phase compensation of process reference point

Each column data of matrix is done contrary yardstick Fourier transform, and the scale factor that conversion is adopted is a _ADThen, again will be through the signal times behind the contrary yardstick Fourier transform with phase factor

Just obtain the signal behind process side's space-variant characteristic compensation

Scale factor a _ADAnd phase factor

Obtain by following formula

Δ T=m/PRF wherein, m=0,1 ..., M-1, PRF are the pulse repetition raties of system's echoed signal, so far, have finished the compensation of each non-reference point target AD-RCM (being orientation space-variant characteristic) in the imaging scene;

Step 5, fourier transform of azimuth

To through the signal behind the orientation space-variant characteristic compensation

Each row of data matrix are done the 2-d spectrum after Fourier transform obtains orientation space-variant characteristic compensation

Step 6, oblique distance are to inverse fourier transform

To the 2-d spectrum behind the orientation space-variant characteristic compensation

Each row of matrix is done the data matrix that inverse Fourier transform obtains its oblique distance time domain-orientation frequency domain

Step 7, non-linear oblique distance space-variant characteristic compensation

Data matrix to oblique distance time domain-orientation frequency domain

Do interpolation processing; Again the data after the interpolation processing be multiply by phase factor

Obtain through the signal behind the two-dimentional space-variant characteristic compensation

Interpolation mapping-factor τ _RD(f _d) and phase factor

Obtain by following formula

Δ r=nc/Fsr wherein, n=0,1 ..., N-1, Fsr be the distance of echoed signal to sample frequency, c is a light velocity size;

So far, finish compensation to non-reference point target two-dimension non linearity space-variant characteristic in the imaging scene;

Step 8, orientation are to inverse Fourier transform

At the signal behind the two-dimentional space-variant characteristic compensation of process

Each row of data matrix are done inverse Fourier transform, then do coordinate transform: x=c τ, y=v _ST;

Handle through above-mentioned steps, just (τ obtains the target imaging result with high-resolution in t) to the target echo data s that can receive from the LSA-FBSAR system.

Need to prove:

Usually being chosen to image field scape central point is reference point target, because two station distortion term H in the imaging scene _BD(f, f _d) variation is less, so process step 1 promptly can be thought and finish the two station of whole imaging scene distortion term H to the processing of step 3 _BD(f, f _d) compensation.And the two-dimension non linearity space-variant characteristic of LSA-FBSAR system is mainly reflected in an accurate single station H _OM(f, f _d) in, through the processing of step 1 to step 3, still there is the part that is not compensated to RCM and orientation in the oblique distance of non-reference point target to RCM in the imaging scene, can't satisfy the requirement of high-resolution imaging, therefore needs step 4 to further compensation deals of step 8.

In addition, after step 4 is finished, because non-linear space-variant characteristic of oblique distance and orientation frequency f _dRelevant, corresponding RD-RCM compensation need be carried out in oblique distance time domain-orientation frequency domain.Therefore the present invention realized conversion between the territory in step 5, six before oblique distance space-variant characteristic compensation.

Essence of the present invention is to utilize the characteristics of LSA-FBSAR system to obtain the analytical expression of system's 2-d spectrum, and derives thus and obtain being applicable to the frequency domain imaging method of this system.Utilize the thought of ω-k algorithm, resolve statement, obtain the oblique distance dimension space-variant RCM of LSA-FBSAR, the Nonlinear Mapping relation of azimuth dimension space-variant RCM according to its 2-d spectrum; Based on these mapping relations, improved conventional two-dimensional space-variant RCM treatment for correcting flow process; And adopt the compensation that realizes non-reference point target two dimension space-variant linear R CM against yardstick Fourier transform-phase multiplication, interpolation-phase multiplication technology respectively, thereby serious geometric distortion problems such as the imaging results bending that effective correction causes because of two-dimension non linearity space-variant RCM, distortion.

Innovative point of the present invention is to utilize the characteristics of LSA-FBSAR system to obtain the analytical expression of system's 2-d spectrum, then utilizes the thought of ω-k algorithm, resolves statement according to 2-d spectrum, obtains the two-dimentional space-variant RCM mapping relations of LSA-FBSAR; By these mapping relations of research, improved conventional two-dimensional space-variant RCM treatment for correcting flow process at last; And realize compensation to this system's two-dimension non linearity space-variant characteristic by contrary yardstick Fourier transform-phase multiplication and interpolation-phase multiplication technology.

Ultimate principle of the present invention is to utilize the geometric model and the oblique distance model of LSA-FBSAR system, by analyzing the characteristics of property difference between this system platform and receiving platform forward sight mode of operation, come analytic representation LSA-FBSAR system impulse response 2-d spectrum with the air-phase time point; Then utilize LSA-FBSAR system impulse response 2-d spectrum, finish imaging scene internal reference point target two dimension space-variant characteristic compensation and orientation compression; By analysis of two-dimensional space-variant RCM mapping relations, be compensated the solution of non-reference point target two-dimension non linearity space-variant characteristic in the imaging scene again.

The technical matters that the present invention solves: only have the oblique distance space-variant in traditional single base SAR, the static irradiation source-forward sight double-base SAR, thereby its formation method can't solve orientation, oblique distance two dimension space-variant problem in the bistatic Forward-looking SAR imaging of star-machine; The two-dimentional space-variant that star-pusher side is looked in the double-base SAR is taken as the leading factor with its linear term, so its formation method is not suitable for the non-linear space-variant problem in the bistatic Forward-looking SAR of solution star-machine.The present invention utilizes the characteristics of LSA-FBSAR system, adopts rationally to be similar to, and obtains the high-precision two-dimensional frequency spectrum analytical expression of LSA-FBSAR system impulse response; Analytical expression by this 2-d spectrum can obtain two-dimentional space-variant RCM mapping relations and disposal route thereof, solved the two-dimentional space-variant problem in the LSA-FBSAR system, thereby can effectively proofread and correct because of serious geometric distortion phenomenon such as imaging results bending that two-dimension non linearity space-variant RCM causes, distortion.

Beneficial effect of the present invention: make full use of the characteristics of LSA-FBSAR system, simplified finding the solution of 2-d spectrum; From the coupled relation of this spectrum complex, detach and obtain its two-dimentional space-variant RCM Nonlinear Mapping relation, solved the difficult problem of two-dimension non linearity space-variant compensation in the LSA-FBSAR system.The present invention has filled up existing SAR frequency domain imaging technology can't be applied to this blank of LSA-FBSAR high-resolution imaging.

Description of drawings

Fig. 1 is a workflow block diagram of the present invention

Fig. 2 is nine point target relative position relation figure in the simulation imaging scene

P wherein ₀Be reference point target, P ₁～P ₈Be eight non-reference point target.

Fig. 3 is that (τ t) handles the back result through step 1 of the present invention to step 3 to the echo data s of LSA-FBSAR system

Wherein, transverse axis represent oblique distance to, the longitudinal axis represent the orientation to; P ₉～P ₁₆Be respectively corresponding to eight non-reference point target P ₁～P ₈Imaging results after echo is handled through step 1 of the present invention to step 3.

Fig. 4 is the echo data s of LSA-FBSAR system (τ, the imaging results after t) process step 1 of the present invention to step 8 is handled

Wherein, transverse axis represent oblique distance to, the longitudinal axis represent the orientation to; P ₁₇～P ₂₄Correspond respectively to eight non-reference point target P ₁～P ₈It is the imaging results after echo is handled through step 1 of the present invention to step 8.

The LSA-FBSAR system platform parameter of Fig. 5 for adopting in the embodiment of the invention.

Embodiment

The present invention mainly adopts the method for emulation experiment to verify, institute in steps, conclusion all on MATLAB 7.6 checking correct.

Present embodiment adopts TerraSAR-X satellite and airborne PAMIR as emission, receiving platform respectively, the parallel flight in the same way of two platforms, satellite platform is operated in steering spotlight pattern, and aircraft platform is operated under the forward-looking mode, and antenna beam speed is respectively 2100m/s and 700m/s.The centre frequency that transmits is 9.65GHz, and transmitted signal bandwidth is 60MHz, and pulse repetition rate is 2500Hz, and the echoed signal distance is 120MHz to sample frequency.Other system platform emulation parameter as shown in Figure 5.Comprise nine point targets in the simulation imaging scene, its relative position relation as shown in Figure 2, wherein reference point target is P ₀

Step 1, echoed signal are apart from compression

LSA-FBSAR echo signal data s (τ, t) deposit with the data matrix of one 1799 row 1024 row, wherein every column data is the sampling of depositing the slow time (orientation to) echoed signal, and the data of every row are the samplings of depositing the fast time (oblique distance to) monopulse echoed signal;

Apart from reference compression signal s ₀(τ) obtain reference signal frequency spectrum S as Fourier transform ₀(f), (τ t) does Fourier transform line by line and obtains S echoed signal s ^τ(f, t), with S ^τ(f, t) line by line with S ₀(f) conjugate multiplication obtains

Realize the distance compression, Fourier transform can pass through fast fourier transform (Fast FourierTransform is called for short FFT) to be realized;

Step 2, fourier transform of azimuth

At the echo data matrix after the distance compression

Each row do 2-d spectrum after FFT obtains distance compression

Step 3, reference point phase compensation

Be chosen to image field scape center point P ₀Be reference point target, satellite, aircraft platform are apart from reference point target P ₀Nearest oblique distance be respectively 896.1km, 3.0km, satellite platform is apart from reference point target P ₀The nearest moment is 1.461s.Utilize systematic parameter shown in Figure 5 and formula (1) Can obtain the air-phase point t of this system about reference point target _b, according to formula (2)

Can obtain the impulse response 2-d spectrum H of this system about reference point target ₀(f, f _d), with its conjugate matrices

With data matrix

Pointwise is multiplied each other and is obtained the 2-d spectrum data matrix of process reference point phase compensation back echo signal

Result as shown in Figure 3;

Step 4, orientation space-variant characteristic compensation

Obtain scale factor a according to formula (6) _AzAnd phase factor

To echoed signal 2-d spectrum matrix through reference point phase compensation

Each column data with scale factor a _ADDo contrary yardstick Fourier transform; Then, will multiply by phase factor through the data matrix behind the contrary yardstick Fourier transform again

Obtain through the data matrix behind the orientation space-variant characteristic compensation

Step 5, fourier transform of azimuth

To through the data matrix behind the orientation space-variant characteristic compensation

Each row do two-dimensional frequency data matrix after FFT obtains orientation space-variant RCM compensation

Step 6, oblique distance are to inverse Fourier transform

To the two-dimensional frequency data matrix after the orientation space-variant RCM compensation

Each row do the data matrix that fast adverse Fourier transform (Inverse Fast Fourier Transform, be called for short IFFT) obtains its oblique distance time domain-orientation frequency domain

Step 7, non-linear oblique distance space-variant characteristic compensation

Data matrix to oblique distance time domain-orientation frequency domain

Do the interpolation mapping, again the data after the interpolation processing be multiply by phase factor

Obtain through the signal behind the two-dimentional space-variant characteristic compensation

Step 8, orientation are to inverse Fourier transform

At the signal behind the two-dimentional space-variant characteristic compensation of process

Each row of data matrix are done the IFFT conversion, then do coordinate transform: x=c τ, y=v _ST;

Handle through above-mentioned steps, just can from LSA-FBSAR target echo data s (τ, obtain in t) complex pattern σ with high-resolution (x, y).

Fig. 3 is echo data s (τ, the imaging results after t) process above-mentioned steps 1 to step 3 is handled.As can be seen from Figure 3 owing to remove reference point P ₀Outside eight non-reference point target have AD-RCM and the RD-RCM that do not proofreaied and correct fully, therefore all there is non-linear oblique distance-orientation coupling in all the other four point targets except that reference point target, its imaging results malposition, serious two-dimension non linearity geometric distortion has appearred, can't satisfy the requirement of high-resolution imaging, need step 4 to step 8 further to handle.

Fig. 4 is echo data s (τ, the final imaging results after t) process above-mentioned steps 1 to step 8 is handled.Wherein, transverse axis represent oblique distance to, the longitudinal axis represent the orientation to, coordinate unit is rice, true origin is the reference point target position.As can be seen from Figure 4, adopt formation method provided by the invention to handle after, each point target is all well focused on, and the AD-RCM of non-reference point target and RD-RCM proofreaied and correct, each point target lays respectively at correct separately locus.Therefore, the invention provides frequency domain imaging method and be applicable to the LSA-FBSAR system, can effectively proofread and correct because of serious geometric distortion problem such as imaging results bending that two-dimension non linearity space-variant range unit migration causes, distortion, can be used for it and realize that its high-resolution imaging handles.

Claims (1)

1. remote sensing satellite irradiation source forward sight synthetic-aperture radar frequency domain imaging method is characterized in that it comprises following steps:

Step 1, echoed signal are apart from compression

The original echo data s (τ of remote sensing satellite irradiation source Forward-Looking SAR System, t) deposit with the data matrix of the capable N row of M, M and N are positive integer, original echo data s (τ, t) the every column data of data matrix is the sampling of depositing slow time t echoed signal, the deposit data of every row be the sampling of the fast time τ of monopulse echoed signal one by one; Slow time t be the orientation to, fast time τ be oblique distance to;

Use s emission signal s ₀(τ) conduct is apart from the reference compression signal, s emission signal s ₀(τ) and original echoed signals s (τ t) obtains S respectively after transforming to the oblique distance frequency domain ₀(f) and S ^τ(f, t), then with S ₀(f) and S ^τ(f, t) conjugate multiplication realize the distance compression, are shown below

$S_{\mathrm{RC}}^{\mathrm{\&tau;}}(f,t)=S^{\mathrm{\&tau;}}(f,t)\&CenterDot;S_0^{*}\left(f\right)$

* represents complex conjugate in the following formula;

Step 2, fourier transform of azimuth

At the distance compressed echo signal

Each row in the data matrix are done Fourier transform and are obtained process apart from the compressed echo signal 2-d spectrum

Step 3, reference point phase compensation

According to reference point target P ₀Location parameter (r _0S=r _0S0, r _0P=r _0P0, t _0S=t _0S0, t _0P=t _0P0),

Utilize formula (1): $t_b=t_{0S}-\frac{f_d{r}_{0S}}{v_S\sqrt{{\left(\frac{f+f_0}{c}{v}_S\right)}^2-f_d^2}},$

Formula (2): $H(f,f_d)=\exp \{-\mathrm{j\&phi;}\left(t_b\right)\}\&CenterDot;\exp \left\{j\frac{1}{2}\frac{{\left({\mathrm{\&phi;}}^{\&prime;}\left(t_b\right)\right)}^2}{{\mathrm{\&phi;}}^{\&prime;\&prime;}\left(t_b\right)}\right\}$

Just can obtain the 2-d spectrum H of reference point target system impulse response ₀(f, f _d); 2-d spectrum H with reference point target system impulse response ₀(f, f _d) complex conjugate

With echoed signal apart from the compression after 2-d spectrum

The data matrix pointwise is multiplied each other and is obtained

Be shown below

$S_{\mathrm{RF}}^{\mathrm{\&tau;},t}(f,f_d)=S_{\mathrm{RC}}^{\mathrm{\&tau;},t}(f,f_d)\&CenterDot;H_0^{*}(f,f_d)$

Be 2-d spectrum through reference point phase compensation back echo signal, wherein in the formula (1), t _0SBe the satellite platform moment nearest apart from the distance target, r _0SThe nearest oblique distance of expression satellite platform distance objective, f ₀Be the centre frequency that transmits, v _SBe the movement velocity size of the relative target of satellite platform, f _dBe the Doppler frequency corresponding to slow (orientation) time t, f is the frequency corresponding to fast (oblique distance) time τ, r _0S0And r _0P0Be respectively satellite, aircraft platform relative reference target P ₀Nearest oblique distance, t _0S0And t _0P0Be respectively that satellite, aircraft platform are apart from reference target P ₀The nearest moment, φ (t in the formula (2) _b)=k[r _S(t _b)+r _P(t _b)]+2 π f _dT,

r _S(t _b) and r _P(t _b) be respectively air-phase time point t _bThe oblique distance size of moment satellite, aircraft platform distance objective;

Step 4, orientation space-variant characteristic compensation

To the 2-d spectrum after the phase compensation of process reference point Each column data of matrix is done contrary yardstick Fourier transform, and the scale factor that conversion is adopted is a _ADThen, again will be through the signal times behind the contrary yardstick Fourier transform with phase factor

Just obtain the signal behind process side's space-variant characteristic compensation

Scale factor a _ADAnd phase factor

Obtain by following formula

Δ T=m/PRF wherein, m=0,1 ..., M-1, PRF are the pulse repetition raties of system's echoed signal, so far, have finished that each non-reference point target orientation space-variant characteristic is the compensation of AD-RCM in the imaging scene;

Step 5, fourier transform of azimuth

To through the signal behind the orientation space-variant characteristic compensation

Each row of data matrix are done the 2-d spectrum after Fourier transform obtains orientation space-variant characteristic compensation

Step 6, oblique distance are to inverse fourier transform

To the 2-d spectrum behind the orientation space-variant characteristic compensation

Each row of matrix is done the data matrix that inverse Fourier transform obtains its oblique distance time domain-orientation frequency domain

Step 7, non-linear oblique distance space-variant characteristic compensation

Data matrix to oblique distance time domain-orientation frequency domain

Do interpolation processing; Again the data after the interpolation processing be multiply by phase factor

Obtain through the signal behind the two-dimentional space-variant characteristic compensation Interpolation mapping-factor τ _RD(f _d) and phase factor Obtain by following formula

Δ r=nc/Fsr wherein, n=0,1 ..., N-1, Fsr be the distance of echoed signal to sample frequency, c is a light velocity size;

So far, finish compensation to non-reference point target two-dimension non linearity space-variant characteristic in the imaging scene;

Step 8, orientation are to inverse Fourier transform

At the signal behind the two-dimentional space-variant characteristic compensation of process

Each row of data matrix are done inverse Fourier transform, then do coordinate transform: x=c τ, y=v _ST;

Handle through above-mentioned steps, just (τ obtains high-resolution target imaging result in t) to the target echo data s that can receive from remote sensing satellite irradiation source forward sight synthetic-aperture radar abbreviation LSA-FBSAR system.

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