SAR Imaging Based On the Range DopplerAlgorithmIntroductionAfter the course Radar Imaging, I did a simulation experiment in which I try to use Range Doppler Algorithm (RDA) for SAR Imaging. Here is my report for the experiment.In my simulation experiment, I got an ideal result of 3 point targets imaging based on the RDA on the condition of high squint.First of all, I would like to give the parameters used in my simulation.Then it is the flow chart of the algorithm.Raw radar dataResult Output Result analysis1.The echo signal2 (,)rect expexpcs t j kTjττπτ⎛-⎧⎫⎪⎪⎛=⋅-⎨⎬⎝⎪⎪⎪⎩⎭⎝⎭⎧⋅-⎨⎩This is the echo dataThis is the real part of the echo data2.Range compression and the SRCTo do range compression we can simply add a matched filter2()exp{}r rc r rj f H f K π=While the SRC filter is 2()exp{}r src r srcj f H f K π-=These two filters can be combined as one filter:2()exp{}r m r mj f H f K π=Where 1/rm r srcK K K K =-This is the signal after rangecompression and SRC.3. Range Cell Migration Correction (RCMC)The migration factor (,)a r D f V =()H j ω()()i i s t n t +()()o o s t n t +()h tThe phase multiplier 44exp{}exp{}(,)r c r crcmc a r j f R f o G D f V c cππ-=⋅Where c ois the range of the scene center.This is the signal after RCMC.4. Azimuth CompressionAfter RCMC, a matched filter is applied to focus the data in the azimuth direction.004(,)exp{}a r fa j R D f V f H cπ=The result is as follow:Data after azimuth compression.This is the required result. ConclusionAfter doing this simulation, I learned more on SAR imaging. It ’s the practical knowledge. I understood how to achieve the algorithm with IDL instead of just understanding it on the book. But I realize that no matterthe algorithm or the understanding of SAR, on which my study is still primary. I’m looking forward to access more and go deeper in this field.CODE;====矩形窗函数==================================function rect,tsizearr=size(t)ff=fltarr(sizearr(1))index=where(abs(t) le 0.5)ff(index)=1.return,ffend;;==========雷达参数================c=double(3.e8) ;光速lamd=double(0.03) ;波长fc=double(c/lamd) ;载频Br=double(1.e8) ;发射信号带宽Kr=double(1.5e13) ;距离调频率Tu=double(Br/Kr) ;发射脉冲时宽fs=double(Br*1.5) ;距离采样率PRF=double(300.0)Vr=double(100.0)Na=1024Nr=2048R0=double(2.e4)cita=double(20.*!pi/180) ;波束斜视角(radian)ta=(dindgen(Na)-Na/2)/PRF ;慢时间;=====================目标位置参数======================== xx=0yy=0x1=30y1=0;=====================雷达位置参数======================== x=vr*ta-R0*sin(cita) ;雷达方位位置y=R0*cos(cita) ;雷达距离位置dt=double(sqrt(x^2+y^2))Rref=dt ;参考目标实时距离oc=Rref[Na/2] ;场景中心距离;;================== 回波模拟======================= tr=(dindgen(Nr)-Nr/2)/fs+2*oc/crecord=dcomplexarr(Nr) ;一个脉冲记录data=dcomplexarr(Na,Nr) ;回波二维数组for ii=0LL,Na-1LL do beginrecord=dcomplexarr(Nr)Rt=sqrt((x(ii)-xx)^2+(y-yy)^2) ;目标到雷达瞬时距离Rt1=sqrt((x(ii)-x1)^2+(y-y1)^2)record0=rect((tr-2.*Rt/c)/Tu)*exp(dcomplex(0,!pi*kr*(tr-2.*Rt/c)^2))*exp(dcomplex(0,-4.*!pi/la md*Rt))record1=rect((tr-2.*Rt1/c)/Tu)*exp(dcomplex(0,!pi*kr*(tr-2.*Rt1/c)^2))*exp(dcomplex(0,-4.*!pi/ lamd*Rt1))data(ii,*)=record0+record1endforwindow,0contour,abs(data)window,10contour,real_part(shift(fft(data),Na/2,Nr/2));write_tiff,'d:\im3.tif',bytscl(abs(real_part(data)));write_tiff,'d:\im4.tif',bytscl(real_part(data));stop;===================== RD算法========================Fac=double(2*Vr*sin(cita)/lamd)Rc=dt[na/2]*cos(cita)fr=shift((dindgen(Nr)-Nr/2)*Fs/Nr,0/2);fa=shift((dindgen(Na)-Na/2)*PRF/Na,0/2)+Fac;D=sqrt(1-lamd^2*fa^2/4./Vr^2)Ksrc=2.*Vr^2*Fc^3*D^3/c/Rc/Fa^2;Hfr=exp(dcomplex(0,!pi*Fr^2/Kr));距离向匹配滤波器Hsrc=dcomplexarr(Na,Nr);for i=0,Na-1 do beginHsrc[i,*]=exp(dcomplex(0,-1*!pi*Fr^2/Ksrc[i]));endfor ;SRC滤波器for j=0,Nr-1 do begindata[*,j]=data[*,j]*exp(dcomplex(0,-2*!pi*Fac*ta));endfordata=shift(fft(data),Na/2,Nr/2);;=================距离压缩与二次距离压缩=============for i=0,Na-1 do begindata(i,*)=data(i,*)*exp(dcomplex(0,!pi*Fr^2/Kr))*Hsrc[i,*]endforwindow,1contour,abs(fft(data,1));;============距离徙动校正=============for i=0,Na-1 do beginrcmc=exp(dcomplex(0,4*!pi*Fr*Rc/d[i]/c))*exp(dcomplex(0,-4*!pi*Fr*oc/c)) ;dt[Na/2]-->o cdata[i,*]=fft(data[i,*]*rcmc,1)endforwindow,2contour,abs(data);;=================方位向压缩=============rt1=double(oc*cos(cita)+(i-Nr/2)*c/2./Fs);for i=0,Nr-1 do beginh_fa=exp(dcomplex(0,4*!pi*rt1*fc/c*D))*exp(dcomplex(0,-2*!pi*fa*oc*sin(cita)/Vr))data(*,i)=fft(data(*,i)*h_fa,1)endforwindow,3contour,abs(data)end。