CN104808204A - Moving-target detecting method and imaging method of stationary transmitter bistatic forward-looking synthetic aperture radar (SAR) - Google Patents

Abstract

The invention discloses a moving-target detecting method and imaging method of a stationary transmitter bistatic forward-looking synthetic aperture radar (SAR). According to the detecting method, ground static clutter that is represented by zero frequency images is removed in a frequency domain by means of differences among obtained complex images among all channels of a receiving station, moving-target echo that is represented by non-zero frequency images is reserved, and thereby, restraining of the ground static clutter and detection of a moving target can be finished. According to the imaging method, after detection of the moving target is finished, estimation of Doppler parameters of the moving target is achieved on basis of defocussed images of the moving target, thereby, focused imaging of the moving target is finished by means of the estimated Doppler parameters of the moving target, and influence of range migration and direction modulating signals caused by movement of the moving target on detection and imaging can be eliminated.

Description

A kind of fixed transmission station double-basis Forward-looking SAR moving target detection method and formation method

Technical field

The invention belongs to Radar Technology field, be specifically related to the fixed transmission station double-basis Forward-looking SAR moving target detection method in synthetic-aperture radar (Synthetic Aperture Radar, SAR) imaging technique and formation method.

Background technology

Synthetic-aperture radar (Synthetic Aperture Radar, SAR) be a kind of round-the-clock, round-the-clock modem high-resolution microwave remote sensing imaging radar, it utilizes the relative motion between radar antenna and target area to obtain the high resolving power in space.In fields such as military surveillance, topographic mapping, vegetational analysis, ocean and hydrologic observation, environment and disaster supervision, resource exploration and the micro-change detections of the earth's crust, synthetic-aperture radar has played more and more important effect.

Double-basis Forward-looking SAR is as emerging SAR technology, orthogonal line of equidistance-wait Doppler's line can be formed in receiver station forward vision areas, therefore imaging can be carried out to the positive forward vision areas of receiving station, compensate for a lot of deficiencies of single base SAR, in aircraft navigation, landing, cargo assault etc., have vital effect.Fixed transmission station double-basis Forward-looking SAR (SBF-SAR) is a kind of pattern of double-basis Forward-looking SAR, and its cell site is positioned at the static platform such as geostationary satellite or near space vehicle, and side-looking transmits; Receiving station is positioned on the airborne platform of motion, receives the echoed signal that region, dead ahead returns.

The detection of moving-target (MT) and imaging technique have huge application space in traffic control, battlefield monitoring, harbour monitoring etc.Therefore, fixed transmission station double-basis Forward-looking SAR moving target detect and imaging have very important Research Significance.

At document: Bistatic forward-looking SAR:Theory and challenges, J.Wu, J.Yang, Y.Huang, H, Yang and H.Wang, Radar Conference, 2009IEEE, 2009 and An omega-K imaging algorithm for bistatic forward-looking SAR with stationary transmitter, J.Wu, Y.Huang, J.Yang, P.Gao, a.W.L.Zhe Liu and H, Yang, Synthetic Aperture Radar (APSAR), 20113rd International Asia-Pacific Conference on, 2011, in pp.1-2, the formation method of static scene is studied.But for MT imaging, the orientation modulation signal of the unknown distance migration that the non-cooperation movement due to MT produces and superposition, the above-mentioned Theories and methods about preventing scene can not be applied to the MT imaging of SBF-SAR.

At document: Moving target imaging algorithm for SAR data, S.Werness, W.Carrara, L.Joyce, and D.Franczak, Aerospace and Electronic Systems, IEEE Transactions on, vol.26, no.1, pp.57-67, 1990, document: Theory of Synthetic Aperture Radar imaging of a moving target, J.K.Jao, Geoscience and Remote Sensing, IEEE Transactions on, vol.39, no.9, pp.1984-1992, 2001, and document: Ground moving targets imaging algorithm for Synthetic Aperture Radar, Aerospace and Electronic Systems, IEEE Transactions on, Vol.49, no.1, pp.462-477, in 2011, problem involved by moving target detect in single base SAR and imaging is studied, document: Space time adaptive processing for moving target detection and imaging in bistatic SAR, V.-T.Vu, T.Sjogren, and M.Pastina, Geoscience and Remote Sensing Symposium (IGASS), 2011IEEE International, 2011, pp.2828-2832, and document: Bistatic linear antenna array SAR for moving target detection, location, and imaging with two passive airborne radars, Geoscience and Remote Sensing, IEEE Transactions on, Vol.45, no.3, pp.554-565, in 2007, be studied for the problem involved by double-basis side-looking SAR moving target detect and imaging.But the method for above-mentioned document is not all suitable for moving target detect in SBF-SAR and imaging, because in the double-basis Forward-looking SAR of fixed transmission station, there is larger remaining range migration in MT echo, and MT motion is comparatively large on the impact of Doppler parameter, and azimuth spectrum exists the problems such as fuzzy.

Summary of the invention

The object of the invention is the defect existed for background technology, the MT detection method of a kind of SBF-SAR of research and design and formation method, fill up the blank of SBF-SAR in moving target detect and imaging field.

Technical scheme of the present invention is: a kind of SBF-SAR moving target detection method and formation method, specifically comprise the steps:

Step one: imaging system parameters initialization

If cell site's coordinate of SBF-SAR imaging system is (x _t, y _t, H _t), wherein, x _t, y _tand H _tbe respectively the x-axis, y-axis and z-axis coordinate of cell site; Receiving station forms receiving array antenna by M submatrix, and the distance between adjacent submatrix is d, and the flying height of receiving station is H _r, fly along y-axis with speed V, in η=0 moment orientation time, first position receiving submatrix antenna is (0,0, H _r), other M-1 receives submatrix antenna coordinate and is respectively (0, d, H _r), (0,2d, H _r) ..., (0, (M-1) d, H _r); Target P (x ₀, y ₀) be any one impact point of imaging region, wherein, x ₀, y ₀be respectively the x-axis of this target, y-axis coordinate; Target P (x ₀, y ₀) be v along the speed component of x-axis _x, the speed component along y-axis is v _y, work as v _x≠ 0 or v _ywhen ≠ 0, P (x ₀, y ₀) be moving-target, and work as v _x=v _ywhen=0, P (x ₀, y ₀) be Clutter; Cell site is to target P (x ₀, y ₀) distance be set to R _t; Receiving station m sub-array antenna in η moment orientation time to target P (x ₀, y ₀) oblique distance R _mR(η) can be expressed as:

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=\sqrt{{(x_0+v_x\mathrm{\η})}^2+{(y_0+(v_y-V)\mathrm{\η}-(M-1)d)}^2+H_R^2}$

Wherein, η represents the orientation time.

Step 2: obtain SBF-SAR echo expression formula, row distance of going forward side by side is to Fourier transform

If SBF-SAR transmits as linear FM signal:

s(τ)＝exp{j2πf _cτ+jπk _rτ ²}

Wherein, f _cfor carrier frequency, τ be distance to the time, k _rfor the chirp rate transmitted; Then receiving station m sub-array antenna receives from P (x ₀, y ₀) put the echoed signal expression formula that returns and can be expressed as:

$S_m(\mathrm{\η},\mathrm{\τ})=w(\mathrm{\η},{\mathrm{\η}}_{\mathrm{cb}})\exp \left[\mathrm{j\π}{k}_r{(\mathrm{\τ}-\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c})}^2\right]\×\exp [-j2\mathrm{\π}\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\mathrm{\λ}}]$

Wherein w () is orientation time window, η _cbfor the orient core moment, c is electromagnetic speed, λ=c/f _cfor wavelength.Carry out distance to echoed signal again can obtain to Fourier transform:

$S_m(\mathrm{\η},\mathrm{f\τ})=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\×\exp \{-j2\mathrm{\π}(f+f_c)\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c}\}$

Wherein, f be distance to frequency variable, S _t(f) spectrum expression formula for transmitting;

Again to R _mR(η) carry out Taylor expansion operation, can obtain

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=R_{\mathrm{mR}0}+R_{\mathrm{mR}}^{\text{'}}(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})+\frac{1}{2}{R}_{\mathrm{mR}}^{\text{'}\text{'}}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...$

Wherein, R _mR0for at η _cbreception station m sub-array antenna is to target P (x ₀, y ₀) distance, R ' _mRfor the once item of Taylor expansion, R " _mRfor the quadratic term of Taylor expansion.

Step 3: calculate impact point P (x ₀, y ₀) Azimuth Doppler Frequency of echo

Azimuth Doppler Frequency can be expressed as:

$f_d\left(\mathrm{\η}\right)=-\frac{1}{\mathrm{\λ}}\frac{\∂R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\∂\mathrm{\η}}\≈f_{D/\mathrm{radar}}+f_{D/t\arg \mathrm{et}}+(f_{R/\mathrm{radar}}+f_{R/t\arg \mathrm{et}})\mathrm{\η}$

Wherein, f _d/radarwith f _d/targetbe respectively the Doppler frequency center that radar motion and target travel produce, f _r/radarwith f _r/targetbe respectively the doppler frequency rate that radar motion and target travel produce.

Step 4: deblurring pre filtering operation, removes the doppler ambiguity of echoed signal

For removing the doppler ambiguity of SBF-SAR echoed signal, will following pre-filter function be built:

$H_{\mathrm{Dambiguity}}=\exp \left[j2\mathrm{\π}{f}_{D/\mathrm{fradar}}\frac{f+f_c}{f_c}\right]$

Wherein, f _d/fradarit is the Doppler frequency center of reference target.By S _m(η, f) and H _dambiguitybe multiplied, can obtain filtered signal is:

$\begin{array}{c}{S}_{m1}(\mathrm{\η},f)=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}\frac{f+f_c}{c}[R_{\mathrm{bi}0}+R_{\mathrm{mRres}}^{\text{'}}\mathrm{\η}-R_{\mathrm{mR}}^{\text{'}}{\mathrm{\η}}_{\mathrm{cb}}+\frac{1}{2}{R}_{\mathrm{mR}}^{\text{'}\text{'}}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...\left]\right\}\end{array}$

Wherein R _bi0=R _t+ R _mR0, R ' _mRres=R ' _mR-λ f _d/fradar.

Step 5: range migration school for the blind just with Range compress

Adopt following time-frequency coordinate transform to the school for the blind of MT range migration just to come at orientation time domain distance frequency domain, transformation relation is:

$\mathrm{\η}=\left(\frac{f_c}{f+f_c}\right){\mathrm{\η}}_k$

Wherein, η _kfor the orientation time new after time-frequency coordinate transform, after conversion, transient echo expression formula becomes:

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,f)=w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}(\frac{f+f_c}{c}{R}_{\mathrm{bi}0}+\frac{f_c}{c}{{R^{\text{'}}}_{\mathrm{mRres}}\mathrm{\η}}_k-\frac{f+f_c}{c}{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Utilize Range compress function to the data S after step 5 process _m2(η _k, f) carry out Range compress, wherein Range compress function is wherein, * represents complex conjugate operation; After Range compress, echo data is by distance to inverse Fourier transform to two-dimensional time-domain, and its data are designated as S _m2(η _k, τ):

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,\mathrm{\τ})={\mathrm{IFFT}}_{\mathrm{range}}[S_{m2}({\mathrm{\η}}_k,f)\·S_t^{*}\left(f\right)]\\ =w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})\sin c(\mathrm{\τ}-\frac{R_{\mathrm{bi}0}-{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}}{c})\{-j\frac{2\mathrm{\π}}{\mathrm{\λ}}(R_{\mathrm{bi}0}+{R^{\text{'}}}_{\mathrm{mRres}}{\mathrm{\η}}_k-{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Wherein, IFFT _range[] represents that distance is to inverse Fourier transform, and sinc () represents sinc function; After carrying out aforesaid operations, target P (x ₀, y ₀) be positioned at distance to in unit;

Step 6: orientation is balanced to Clutter doppler frequency rate, completes the focusing to Clutter

Can be obtained by step 5, after carrying out above-mentioned process, target P (x ₀, y ₀) be positioned at distance to in unit, if f _r/radar(x, y) for distance to unit internal coordinate is the doppler frequency rate of the target of (x, y), f _r/radar(x _ref, y _ref) be the doppler frequency rate of above-mentioned range unit internal reference target, wherein, x _reffor the x-axis coordinate of this reference target, y _reffor the y-axis coordinate of this reference target;

The difference calculating doppler frequency rate is again:

Δf _R/radar(x,y)＝f _R/radar(x,y)-f _R/radar(x _ref,y _ref)

To Δ f _r/radar(x, y) carries out quadratic integral along the orientation time, obtains the phase place of orientation to Clutter doppler frequency rate balance function, is designated as φ _nlcs(η _k), thus to obtain orientation to Clutter doppler frequency rate balance function be s _nlcs(η _k)=exp{j φ _nlcs(η _k);

By S _m2(η _k, τ) and s _nlcs(η _k) be multiplied, complete the equilibrium to Clutter doppler frequency rate in same range unit.Utilize same direction reference function, the focusing to Clutter can be completed, Fourier transform can be done on the basis of imaging clutter, simultaneously can clutter reduction and detect moving-target.

Step 7: obtain target P (x ₀, y ₀) bearing signal expression formula go forward side by side line phase compensate

After above-mentioned steps process, Clutter can focus on correct position, but moving-target P (x ₀, y ₀) still defocus and be positioned at orientation y ₀+ Δ position, wherein, Δ is the displacement produced due to target travel, can be expressed as:

$\mathrm{\Δ}=\frac{V\·f_{D/t\arg \mathrm{et}}}{f_{R/\mathrm{radar}}}$

For Clutter, Δ=0.

Moving-target P (x ₀, y ₀) bearing signal then can be expressed as S _m/p(x ₀, y ₀)

Wherein, m=1,2 ..., M, represent that the orientation of moving-target defocuses function, can be expressed as:

Wherein, rect [] is rectangular function, T _kfor the orientation extension width of moving-target out-of-focus image.

Utilize following phase compensation function to complete phase difference to producing due to the position difference between receiving station's subarray, penalty function can be expressed as:

$H_{\mathrm{Cphase}}=\exp \left[j\frac{2\mathrm{\π}}{\mathrm{\λ}}\sqrt{{(y_0+\mathrm{\Δ}-(m-1)d)}^2+H_R^2}\right]$

S _m/p(x ₀, y ₀) and penalty function H _cphaseafter being multiplied, can be expressed as:

Definition normalized frequency is then for ground static clutter, f _normalized=0, for MT, f _normalized≠ 0, then S _m/p2(x ₀, y ₀) can be expressed as:

Wherein, m=1,2 ..., M;

Step 8: extract transient echo, obtains the out-of-focus image of moving-target, completes the detection to moving-target

To S _m/p2(x ₀, y ₀) carry out discrete Fourier transformation along subarray image, obtain frequency domain SAR image, for ground static clutter, f _normalized=0, for MT, f _normalized≠ 0, therefore, the suppression that we have come opposite Clutter by removing the frequency domain SAR image of zero-frequency, then inverse discrete Fourier transform is done to the frequency domain SAR image of non-zero-frequency change, result is designated as S _defocus, be the out-of-focus image of MT, thus complete the detection to MT.

In order to solve the problem, based on above-mentioned SBF-SAR moving target detection method, the invention allows for a kind of SBF-SAR pre-filter method method, on the basis of said method step, also comprising the steps:

Step 9: based on the out-of-focus image of moving-target, estimating Doppler parameter

If the result S of step 8 _defocusin, MT diapoint is positioned at position of orientation η _c, out-of-focus image orientation extension width is T _k, then this MT out-of-focus image is utilized can to estimate Doppler frequency center f because target travel all produces _d/targetwith the doppler frequency rate f produced due to target travel _r/target:

f _D/target＝η _c·f _R/radar(x _ref,y _ref)

$f_{D/t\arg \mathrm{et}}=\frac{T_k\·f_{R/\mathrm{radar}}(x_{\mathrm{ref}},y_{\mathrm{ref}})}{T_s}$

Wherein, T _sfor the synthetic aperture time.

Step 10: moving-target Azimuth Compression, completes the focal imaging to moving-target

The direction reference function produced due to target travel can be expressed as:

$S_{\mathrm{ref}}({\mathrm{\η}}_k=w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}}))\exp \left\{j2\mathrm{\π}(f_{D/t\arg \mathrm{et}}{\mathrm{\η}}_k+\frac{1}{2}{f}_{R/t\arg \mathrm{et}}{\mathrm{\η}}_k^2)\right\}$

Then utilize S _ref(η _k) and MT out-of-focus image S _defocusbe multiplied at frequency domain, can complete the focal imaging to MT, imaging results is designated as S _image:

S _image＝IFFT _azimuth{FFT _azimuth[S _defocus]·FFT _azimuth[S _ref(η _k)]＝sinc(x-x ₀)sinc(y-y ₀)

Wherein, FFT _azimuth[] represents that orientation is to Fourier transform, IFFT _azimuth{ } represents that orientation is to inverse Fourier transform.

Beneficial effect of the present invention: the difference between the complex pattern that detection method of the present invention utilizes each interchannel of receiving station to obtain, the ground static clutter representated by zero-frequency image is removed at frequency domain, retain the transient echo representated by non-zero-frequency image, thus complete the ground prevention suppression of clutter and the detection to moving-target; Formation method of the present invention after completing moving target detect, then realizes estimation to moving-target Doppler parameter based on the out-of-focus image of moving-target, thus utilizes the Doppler parameter of the moving-target estimated to complete focal imaging to moving-target.

Accompanying drawing explanation

Fig. 1 is the schematic flow sheet of a kind of SBF-SAR moving target detection method of the present invention.

Fig. 2 is the schematic flow sheet of a kind of SBF-SAR pre-filter method method of the present invention.

Fig. 3 is the SBF-SAR geometrized structure graph that the specific embodiment of the invention adopts.

Fig. 4 is the SBF-SAR system parameter table that the specific embodiment of the invention adopts.

Fig. 5 is the target scene arrangenent diagram adopted in the specific embodiment of the invention.

Fig. 6 obtains SBF-SAR image after step 7.

Fig. 7 is the frequency domain figure picture of the Clutter target after step 10.

Fig. 8 is the MT frequency domain figure picture detected after step 10.

Fig. 9 is the imaging results to moving-target in the specific embodiment of the invention.

Embodiment

The present invention mainly adopts the mode of emulation experiment to verify, simulation and verification platform is Matlab2012.Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.

As shown in Figure 1, detailed process is as follows for the schematic flow sheet of a kind of SBF-SAR moving target detection method of the present invention and formation method:

Step one: imaging system parameters initialization

As shown in Figure 3, as shown in Figure 4, wherein, transmit the system parameter table adopted the SBF-SAR geometry that instantiation of the present invention adopts carrier frequency f _cfor 10GHz, carrier wavelength lambda is 0.03m, cell site coordinate (x _t, y _t, H _t) be (-20,10,3600) km; Receiving station speed V is 250m/s, and the receiving antenna submatrix number M of receiving station is 10, and the distance d between adjacent submatrix is the height H of 1m, receiving station _rfor 8km; Moving-target P (x ₀, y ₀) coordinate be (0,10) km; Moving-target P (x ₀, y ₀) along the speed component v of x-axis _xfor 11m/s, along the speed component v of y-axis _yfor 9m/s; Receiving station m sub-array antenna in η moment orientation time to target P (x ₀, y ₀) oblique distance R _mR(η) be:

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=\sqrt{{(x_0+v_x\mathrm{\η})}^2+{(y_0+(v_y-V)\mathrm{\η}-(M-1)d)}^2+H_R^2}$

Step 2: obtain SBF-SAR echo, row distance of going forward side by side is to Fourier transform

The target scene adopted in instantiation of the present invention is arranged as shown in Figure 5, wherein, and P ₁, P ₂, P ₃and P ₄for ground static clutter target, receiving station m sub-array antenna receives from P (x ₀, y ₀) put the echoed signal that returns and be:

$S_m(\mathrm{\η},\mathrm{\τ})=w(\mathrm{\η},{\mathrm{\η}}_{\mathrm{cb}})\exp \left[\mathrm{j\π}{k}_r{(\mathrm{\τ}-\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c})}^2\right]\×\exp [-j2\mathrm{\π}\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\mathrm{\λ}}]$

Wherein w () is orientation time window, η _cbfor the orient core moment, k _rfor the frequency modulation rate that transmits.Carry out distance to echoed signal again can obtain to Fourier transform:

$S_m(\mathrm{\η},\mathrm{f\τ})=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\×\exp \{-j2\mathrm{\π}(f+f_c)\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c}\}$

Wherein, f be distance to frequency variable, S _t(f) spectrum expression formula for transmitting.Again to R _mR(η) carry out Taylor expansion operation, can obtain

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=R_{\mathrm{mR}0}+R_{\mathrm{mR}}^{\text{'}}(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})+\frac{1}{2}{R}_{\mathrm{mR}}^{\text{'}\text{'}}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...$

Step 3: calculate impact point P (x ₀, y ₀) Azimuth Doppler Frequency of echo

Azimuth Doppler Frequency is:

$f_d\left(\mathrm{\η}\right)=-\frac{1}{\mathrm{\λ}}\frac{\∂R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\∂\mathrm{\η}}\≈f_{D/\mathrm{radar}}+f_{D/t\arg \mathrm{et}}+(f_{R/\mathrm{radar}}+f_{R/t\arg \mathrm{et}})\mathrm{\η}$

Wherein, f _d/radarwith f _d/targetbe respectively the Doppler frequency center that radar motion and target travel produce, f _r/radarwith f _r/targetbe respectively the doppler frequency rate that radar motion and target travel produce.

Step 4: deblurring pre filtering operation, removes the doppler ambiguity of echoed signal

Utilize following pre-filter function:

$H_{\mathrm{Dambiguity}}=\exp \left[j2\mathrm{\π}{f}_{D/\mathrm{fradar}}\frac{f+f_c}{f_c}\right]$

Remove the doppler ambiguity of echoed signal, filtered signal is:

$\begin{array}{c}{S}_{m1}(\mathrm{\η},f)=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}\frac{f+f_c}{c}[R_{\mathrm{bi}0}+R_{\mathrm{mRres}}^{\text{'}}\mathrm{\η}-R_{\mathrm{mR}}^{\text{'}}{\mathrm{\η}}_{\mathrm{cb}}+\frac{1}{2}{R}_{\mathrm{mR}}^{\text{'}\text{'}}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...\left]\right\}\end{array}$

Wherein R _bi0=R _t+ R _mR0, R ' _mRres=R ' _mR-λ f _d/fradar.

Step 5: range migration school for the blind just with Range compress

Adopt following time-frequency coordinate transform to the school for the blind of MT range migration just to come at orientation time domain distance frequency domain, transformation relation is:

$\mathrm{\η}=\left(\frac{f_c}{f+f_c}\right){\mathrm{\η}}_k$

Wherein, η _kfor the orientation time new after time-frequency coordinate transform, after conversion, transient echo expression formula becomes:

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,f)=w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}(\frac{f+f_c}{c}{R}_{\mathrm{bi}0}+\frac{f_c}{c}{{R^{\text{'}}}_{\mathrm{mRres}}\mathrm{\η}}_k-\frac{f+f_c}{c}{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Utilize Range compress function to the data S after step 5 process _m2(η _k, f) carry out Range compress, wherein Range compress function is after Range compress, echo data is by distance to inverse Fourier transform to two-dimensional time-domain, and its data are S _m2(η _k, τ):

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,\mathrm{\τ})={\mathrm{IFFT}}_{\mathrm{range}}[S_{m2}({\mathrm{\η}}_k,f)\·S_t^{*}\left(f\right)]\\ =w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})\sin c(\mathrm{\τ}-\frac{R_{\mathrm{bi}0}-{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}}{c})\{-j\frac{2\mathrm{\π}}{\mathrm{\λ}}(R_{\mathrm{bi}0}+{R^{\text{'}}}_{\mathrm{mRres}}{\mathrm{\η}}_k-{R^{\text{'}}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Step 6: orientation is balanced to Clutter doppler frequency rate, completes the focusing to Clutter

Can be obtained by step 5, after carrying out above-mentioned process, target P (x ₀, y ₀) be positioned at distance to in unit, if f _r/radar(x, y) for distance to unit internal coordinate is the doppler frequency rate of the target of (x, y), and the doppler frequency rate of reference target is f _r/radar(x _ref, y _ref);

The difference calculating doppler frequency rate is again:

Δf _R/radar(x,y)＝f _R/radar(x,y)-f _R/radar(x _ref,y _ref)

To Δ f _r/radar(x, y) carries out quadratic integral along the orientation time, obtains the phase place of orientation to Clutter doppler frequency rate balance function, is designated as φ _nlcs(η _k), thus to obtain orientation to Clutter doppler frequency rate balance function be s _nlcs(η _k)=exp{j φ _nlcs(η _k);

By S _m2(η _k, τ) and s _nlcs(η _k) be multiplied, complete the equilibrium to Clutter doppler frequency rate in same range unit.Utilize same direction reference function, the focusing to Clutter can be completed.Result as shown in Figure 6.

Step 7: obtain target P (x ₀, y ₀) bearing signal expression formula go forward side by side line phase compensate

After above-mentioned steps process, as shown in Figure 6, Clutter can focus on correct position to result, but moving-target P (x ₀, y ₀) still defocus and be positioned at orientation y ₀+ Δ position, wherein, Δ is due to f _d/targetand the displacement produced.Moving-target P (x ₀, y ₀) bearing signal be S _m/p(x ₀, y ₀)

Wherein, for the orientation of MT defocuses function, can be expressed as:

Wherein, rect [] is rectangular function, T _kfor the orientation extension width of moving-target out-of-focus image.

Utilize following phase compensation function to complete phase difference to producing due to the position difference between receiving station's subarray, penalty function is:

$H_{\mathrm{Cphase}}=\exp \left[j\frac{2\mathrm{\π}}{\mathrm{\λ}}\sqrt{{(y_0+\mathrm{\Δ}-(m-1)d)}^2+H_R^2}\right]$

S _m/p(x ₀, y ₀) and penalty function H _cphaseafter being multiplied, can be expressed as:

Normalized frequency then for ground static clutter, f _normalized=0, for MT, f _normalized≠ 0, then S _m/p2(x ₀, y ₀) be:

Step 8: extract transient echo, obtains the out-of-focus image of moving-target, completes the detection to moving-target

To S _m/p2(x ₀, y ₀) carry out discrete Fourier transformation along subarray image, obtain frequency domain SAR image, for ground static clutter, f _normalized=0, as shown in Figure 7; For MT, f _normalized≠ 0, as shown in Figure 8; Therefore, by removing the suppression that the frequency domain SAR image of zero-frequency has been come opposite Clutter, then do inverse discrete Fourier transform to the frequency domain SAR image of non-zero-frequency and change, result is designated as S _defocus, be the out-of-focus image of MT, thus complete the detection to MT.

Fig. 7 is the moving target detect result adopting method of the present invention to obtain in the present embodiment.Can be found out by the specific embodiment of the invention, the present invention can complete the suppression to ground Clutter, completes the detection to moving-target, thus solves the test problems of SBF-SAR moving-target.

Based on above-mentioned SBF-SAR moving target detection method, the invention allows for a kind of SBF-SAR pre-filter method method, as shown in Figure 2, on the basis of said method step, also comprise the steps:

Step 9: based on the out-of-focus image of moving-target, estimating Doppler parameter

The result S of step 8 _defocusin, MT diapoint is positioned at position of orientation η _c, out-of-focus image orientation extension width is T _k, utilize this MT out-of-focus image can estimate Doppler frequency center f because target travel all produces _d/targetwith the doppler frequency rate f produced due to target travel _r/target:

f _D/target＝η _c·f _R/radar(x _ref,y _ref)

$f_{D/t\arg \mathrm{et}}=\frac{T_k\·f_{R/\mathrm{radar}}(x_{\mathrm{ref}},y_{\mathrm{ref}})}{T_s}$

Step 10: moving-target Azimuth Compression, completes the focal imaging to moving-target

The direction reference function produced due to target travel is:

$S_{\mathrm{ref}}({\mathrm{\η}}_k=w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}}))\exp \left\{j2\mathrm{\π}(f_{D/t\arg \mathrm{et}}{\mathrm{\η}}_k+\frac{1}{2}{f}_{R/t\arg \mathrm{et}}{\mathrm{\η}}_k^2)\right\}$

Then utilize S _ref(η _k) and MT out-of-focus image S _defocusbe multiplied at frequency domain, can complete the focal imaging to MT, imaging results is designated as S _image:

S _image＝IFFT _azimuth{FFT _azimuth[S _defocus]·FFT _azimuth[S _ref(η _k)]}＝sinc(x-x ₀)sinc(y-y ₀)

Fig. 9 is the pre-filter method result adopting method of the present invention to obtain in the present embodiment.Can be found out by the specific embodiment of the invention, present invention achieves the focal imaging to moving-target, thus the invention solves the imaging problem of SBF-SAR moving-target.

Those of ordinary skill in the art will appreciate that, embodiment described here is to help reader understanding's principle of the present invention, should be understood to that protection scope of the present invention is not limited to so special statement and embodiment.Those of ordinary skill in the art can make various other various concrete distortion and combination of not departing from essence of the present invention according to these technology enlightenment disclosed by the invention, and these distortion and combination are still in protection scope of the present invention.

Claims (10)

1. a fixed transmission station double-basis Forward-looking SAR moving target detection method, specifically comprises the steps:

Step one: imaging system parameters initialization;

Step 2: obtain SBF-SAR echo expression formula, row distance of going forward side by side is to Fourier transform;

Step 3: calculate impact point P (x ₀, y ₀) Azimuth Doppler Frequency of echo;

Step 4: deblurring pre filtering operation, removes the doppler ambiguity of echoed signal;

Step 5: range migration school for the blind just with Range compress;

Step 6: orientation is balanced to Clutter doppler frequency rate, completes the focusing to Clutter;

Step 7: obtain target P (x ₀, y ₀) bearing signal expression formula go forward side by side line phase compensate;

Step 8: extract transient echo, obtains the out-of-focus image of moving-target, completes the detection to moving-target.

2. fixed transmission station as claimed in claim 1 double-basis Forward-looking SAR moving target detection method, it is characterized in that: in step one, the initialized specific implementation of imaging system parameters is: set cell site's coordinate of SBF-SAR imaging system as (x _t, y _t, H _t), wherein, x _t, y _tand H _tbe respectively the x-axis, y-axis and z-axis coordinate of cell site; Receiving station forms receiving array antenna by M submatrix, and the distance between adjacent submatrix is d, and the flying height of receiving station is H _r, fly along y-axis with speed V, in η=0 moment orientation time, first position receiving submatrix antenna is (0,0, H _r), other M-1 receives submatrix antenna coordinate and is respectively (0, d, H _r), (0,2d, H _r) ..., (0, (M-1) d, H _r); Target P (x ₀, y ₀) be any one impact point of imaging region, wherein, x ₀, y ₀be respectively the x-axis of this target, y-axis coordinate; Target P (x ₀, y ₀) be v along the speed component of x-axis _x, the speed component along y-axis is v _y, work as v _x≠ 0 or v _ywhen ≠ 0, P (x ₀, y ₀) be moving-target, and work as v _x=v _ywhen=0, P (x ₀, y ₀) be Clutter; Cell site is to target P (x ₀, y ₀) distance be set to R _t; Receiving station m sub-array antenna in η moment orientation time to target P (x ₀, y ₀) oblique distance R _mR(η) be:

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=\sqrt{{(x_0+v_x\mathrm{\η})}^2+(y_0+(v_y-V)\mathrm{\η}-{(M-1)d)}^2+H_R^2}$

Wherein, η represents the orientation time.

3. fixed transmission station as claimed in claim 2 double-basis Forward-looking SAR moving target detection method, is characterized in that: in step 2, and obtain SBF-SAR echo expression formula, row distance of going forward side by side is as follows to Fourier transform specific implementation:

If SBF-SAR transmits as linear FM signal:

s(τ)＝exp{j2πf _cτ+jπk _rτ ²}

Wherein, f _cfor carrier frequency, τ be distance to the time, k _rfor the chirp rate transmitted; Then receiving station m sub-array antenna receives from P (x ₀, y ₀) put the echoed signal expression formula that returns and be:

$S_m(\mathrm{\η},\mathrm{\τ})=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})\exp \left[\mathrm{j\π}{k}_r{(\mathrm{\τ}-\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c})}^2\right]\×\exp [-j2\mathrm{\π}\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\mathrm{\λ}}]$

Wherein w (.) is orientation time window, η _cbfor the orient core moment, c is electromagnetic speed, λ=c/f _cfor wavelength; Carry out distance to echoed signal again can obtain to Fourier transform:

$S_m(\mathrm{\η},f)=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\×\exp \{-j2\mathrm{\π}(f+f_c)\frac{R_T+R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{c}\}$

Wherein, f be distance to frequency variable, S _t(f) spectrum expression formula for transmitting;

Again to R _mR(η) carry out Taylor expansion operation, can obtain

$R_{\mathrm{mR}}\left(\mathrm{\η}\right)=R_{\mathrm{mR}0}+R_{\mathrm{mR}}^{\′}(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})+\frac{1}{2}{R}_{\mathrm{mR}}^{\′\′}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...$

Wherein, R _mR0for at η _cbreception station m sub-array antenna is to target P (x ₀, y ₀) distance, R ' _mRfor the once item of Taylor expansion, R ' ' _mRfor the quadratic term of Taylor expansion.

4. fixed transmission station as claimed in claim 3 double-basis Forward-looking SAR moving target detection method, is characterized in that: concrete calculating impact point P (x in step 3 ₀, y ₀) Azimuth Doppler Frequency of echo, as follows:

$f_d\left(\mathrm{\η}\right)=-\frac{1}{\mathrm{\λ}}\frac{\∂R_{\mathrm{mR}}\left(\mathrm{\η}\right)}{\∂\mathrm{\η}}\≈f_{D/\mathrm{radar}}+f_{D/t\arg \mathrm{et}}+(f_{R/\mathrm{radar}}+f_{R/t\arg \mathrm{et}})\mathrm{\η}$

Wherein, f _d/radarwith f _d/targetbe respectively the Doppler frequency center that radar motion and target travel produce, f _r/radarwith f _r/targetbe respectively the doppler frequency rate that radar motion and target travel produce.

5. fixed transmission station as claimed in claim 4 double-basis Forward-looking SAR moving target detection method, is characterized in that: for removing the doppler ambiguity of SBF-SAR echoed signal in step 4, build following pre-filter function:

$H_{\mathrm{Dambiguity}}=\exp \left[j2\mathrm{\π}{f}_{D/\mathrm{fradar}}\frac{f+f_c}{f_c}\right]$

Wherein, f _d/fradarit is the Doppler frequency center of reference target; By S _m(η, f) and H _dambiguitybe multiplied, can obtain filtered signal is:

$\begin{array}{c}{S}_{m1}(\mathrm{\η},f)=w(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}\frac{f+f_c}{c}[R_{\mathrm{bi}0}+R_{\mathrm{mRres}}^{\′}\mathrm{\η}-R_{\mathrm{mR}}^{\′}{\mathrm{\η}}_{\mathrm{cb}}+\frac{1}{2}{R}_{\mathrm{mR}}^{\′\′}{(\mathrm{\η}-{\mathrm{\η}}_{\mathrm{cb}})}^2+...\left]\right\}\end{array}$

Wherein, R _bi0=R _t+ R _mR0, R ' _mRres=R ' _mR-λ f _d/fradar.

6. fixed transmission station as claimed in claim 5 double-basis Forward-looking SAR moving target detection method, it is characterized in that: in step 5, range migration school for the blind with Range compress specific implementation is just: adopt following time-frequency coordinate transform to the school for the blind of moving-target range migration just to come at orientation time domain distance frequency domain, transformation relation is:

$\mathrm{\η}=\left(\frac{f_c}{f+f_c}\right){\mathrm{\η}}_k$

Wherein, η _kfor the orientation time new after time-frequency coordinate transform, after conversion, transient echo expression formula becomes:

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,f)=w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})S_t\left(f\right)\\ \×\exp \{-j2\mathrm{\π}(\frac{f+f_c}{c}{R}_{\mathrm{bi}0}+\frac{f_c}{c}{R^{\′}}_{\mathrm{mRres}}{\mathrm{\η}}_k-\frac{f+f_c}{c}{R^{\′}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Utilize Range compress function to transient echo S after change _m2(η _k, f) carry out Range compress, wherein Range compress function is wherein, * represents complex conjugate operation; After Range compress, echo data is by distance to inverse Fourier transform to two-dimensional time-domain, and its data are designated as S _m2(η _k, τ):

$\begin{array}{c}{S}_{m2}({\mathrm{\η}}_k,\mathrm{\τ})={\mathrm{IFFT}}_{\mathrm{range}}[S_{m2}({\mathrm{\η}}_k,f)\·S_t^{*}\left(f\right)]\\ =w({\mathrm{\η}}_k-{\mathrm{\η}}_{\mathrm{cb}})\sin c(\mathrm{\τ}-\frac{R_{\mathrm{bi}0}-{R^{\′}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}}{c})\{-j\frac{2\mathrm{\π}}{\mathrm{\λ}}(R_{\mathrm{bi}0}+{R^{\′}}_{\mathrm{mRres}}{\mathrm{\η}}_k-{R^{\′}}_{\mathrm{mR}}{\mathrm{\η}}_{\mathrm{cb}}+...)\}\end{array}$

Wherein, IFFT _range[] represents that distance is to inverse Fourier transform, and sinc () represents sinc function; After carrying out aforesaid operations, target P (x ₀, y ₀) be positioned at distance to in unit.

7. fixed transmission station as claimed in claim 6 double-basis Forward-looking SAR moving target detection method, is characterized in that: in step 6, and orientation to the balanced specific implementation of Clutter doppler frequency rate is: establish f _r/radar(x, y) for distance to unit internal coordinate is the doppler frequency rate of the target of (x, y), f _r/radar(x _ref, y _ref) be the doppler frequency rate of above-mentioned range unit internal reference target, wherein, x _reffor the x-axis coordinate of this reference target, y _reffor the y-axis coordinate of this reference target;

Then the difference of doppler frequency rate is:

Δf _R/radar(x，y)＝f _R/radar(x，y)-f _R/radar(x _ref，y _ref)

To Δ f _r/radar(x, y) carries out quadratic integral along the orientation time, obtains the phase place of orientation to Clutter doppler frequency rate balance function, is designated as φ _nlcs(η _k), thus to obtain orientation to Clutter doppler frequency rate balance function be s _nlcs(η _k)=exp{j φ _nlcs(η _k);

By S _m2(η _k, τ) and s _nlcs(η _k) be multiplied, complete the equilibrium to Clutter doppler frequency rate in same range unit; Utilize following direction reference function, can complete the focusing to Clutter, direction reference function can be expressed as:

$s_{\mathrm{ref}}\left({\mathrm{\η}}_k\right)=\exp \left\{\mathrm{j\π}{f}_{R/\mathrm{radar}}(x_{\mathrm{ref}},y_{\mathrm{ref}}){\mathrm{\η}}_k^2\right\}.$

8. fixed transmission station as claimed in claim 7 double-basis Forward-looking SAR moving target detection method, is characterized in that: in step 7, obtains target P (x ₀, y ₀) bearing signal expression formula go forward side by side line phase compensate specific implementation be: moving-target P (x ₀, y ₀) be defocus and be positioned at orientation y ₀+ Δ position, wherein, Δ is the displacement produced due to target travel, is expressed as:

$\mathrm{\Δ}=\frac{V\·f_{D/t\arg \mathrm{et}}}{f_{R/\mathrm{radar}}}$

For Clutter, Δ=0;

Moving-target P (x ₀, y ₀) bearing signal be expressed as S _m/p(x ₀, y ₀)

Wherein, m=1,2 ..., M, represent that the orientation of moving-target defocuses function, can be expressed as:

Wherein, rect [] is rectangular function, T _kfor the orientation extension width of moving-target out-of-focus image.

Utilize following phase compensation function to complete phase difference to producing due to the position difference between receiving station's subarray, penalty function is:

$H_{\mathrm{Cphase}}=\exp \left[j\frac{2\mathrm{\π}}{\mathrm{\λ}}\sqrt{{(y_0+\mathrm{\Δ}-(m-1)d)}^2+H_R^2}\right]$

S _m/p(x ₀, y ₀) and penalty function H _cphaseafter being multiplied:

Definition normalized frequency is then for ground static clutter, f _normalized=0, for moving-target, f _normalized≠ 0, then S _m/p2(x ₀, y ₀) be expressed as:

Wherein, m=1,2 ..., M.

9. fixed transmission station as claimed in claim 8 double-basis Forward-looking SAR moving target detection method, is characterized in that: in step 8, extracts transient echo, obtains the out-of-focus image of moving-target, completes to the specific implementation of the detection of moving-target to be: to S _m/p2(x ₀, y ₀) carry out discrete Fourier transformation, obtain frequency domain SAR image, for ground static clutter, f _normalized=0, for moving-target, f _normalized≠ 0, by removing the suppression that the frequency domain SAR image of zero-frequency has been come opposite Clutter, then do inverse discrete Fourier transform to the frequency domain SAR image of non-zero-frequency and change, result is designated as S _defocus, be the out-of-focus image of moving-target, thus complete the detection to moving-target.

10. a fixed transmission station double-basis Forward-looking SAR pre-filter method method, specifically comprises the steps:

Step one: imaging system parameters initialization;

Step 2: obtain SBF-SAR echo expression formula, row distance of going forward side by side is to Fourier transform;

Step 3: calculate impact point P (x ₀, y ₀) Azimuth Doppler Frequency of echo;

Step 4: deblurring pre filtering operation, removes the doppler ambiguity of echoed signal;

Step 5: range migration school for the blind just with Range compress;

Step 6: orientation is balanced to Clutter doppler frequency rate, completes the focusing to Clutter;

Step 7: obtain target P (x ₀, y ₀) bearing signal expression formula go forward side by side line phase compensate;

Step 8: extract transient echo, obtains the out-of-focus image of moving-target, completes the detection to moving-target;

Step 9: based on the out-of-focus image of moving-target, estimating Doppler parameter;

Step 10: moving-target Azimuth Compression, completes the focal imaging to moving-target.