range_doppler.rar_Range doppler sar_SAR_range_range doppler_sar

clear all; %====================================================================== %%% (I) parameters' definition %====================================================================== c=3e+8; % speed of light pi=3.1415926; % pi j00=sqrt(-1); % square root of -1 res_a=1; % required azimuth resolution res_r=1; % required range resolution k_a=1.2; % azimuth factor k_r=1.2; % range factor Ra=4000.; % radar working distance va=76.; % radar/platform forward velocity Tp=1.e-6; % transmitted pulse width fc=3e+9; % carrier frequency FsFactor = 1.2; theta=90*pi/180; % squint angle %====================================================================== lamda=c/fc; % wavelength Br=k_r*c/2./res_r; % required transmitted bandwidth Fs=Br*FsFactor; % A/D sampling rate bin_r=c/2./Fs; % range bin Kr=Br/Tp; % range chirp rate La=Ra*k_a*lamda/2/res_a/sin(theta); % required synthetic aperture length Ta=La/va; % required synthetic aperture time fdc=2*va*cos(theta)/lamda; % doppler centriod fdr=-2*(va*sin(theta)).^2/lamda/Ra; % doppler rate Bd=abs(fdr)*Ta; % doppler bandwidth prf=round(Bd*2); % PRF %====================================================================== %%%(II) echo return modelling (point target) %====================================================================== Na=fix(Ta*prf); % azimuth sampling number ta=((1:Na)-Na/2)/prf; % slow time along azimuth xa=va*ta-Ra*cos(theta); % azimuth location along flight track %x0=[ 0 0 0 0 0 ]; % define multi points if you want %R0=[-20 -10 0 10 20 ]; % x0: azimuth location (positive towards forward velocity) % R0: slant range location (positive towards far range) x0=[ 0 0 0 50]; R0=[ -200 -50 0 0]; Npt_num = length(x0); ra=zeros(Npt_num, length(xa)); % calculate every point target's slant range history for i=1:Npt_num ra(i,:)=sqrt((Ra*sin(theta)+R0(i)).^2+(xa+x0(i)).^2); end rmax=max(max(ra)); % max. slant range rmin=min(min(ra)); % min. slant range rmc=fix((rmax-rmin)/bin_r); % range sample number rg=0*ra; % initialize rg=fix((ra-rmin)/bin_r+1); % range gate index rgmax=max(max(rg)); rgmin=min(min(rg)); nr=round(Tp*Fs); % samples of a pluse tr=1:fix(nr)+1; tr=tr/Fs-Tp/2; % fast time within a pluse duration Nr=nr+rgmax; %====================================================================== %%%(II) echo return modelling (point target) %====================================================================== sig=zeros(Na,Nr); for i=1:Na for k=1:Npt_num sig(i,rg(k,i):rg(k,i)+nr)=sig(i,rg(k,i):rg(k,i)+nr)+exp(-j00*4*pi/lamda*ra(k,i))*exp(-j00*pi*Kr*(tr).^2); end end %====================================================================== % Range Doppler Algorithm %====================================================================== pre_filter=exp(-j00*2*pi*fdc*ta'); for i=1:Nr sig(:,i)=sig(:,i).*pre_filter; end disp('end of prefilter'); for i=1:Na sig(i,:)=fftshift(fft(sig(i,:))); end dfr=Fs/Nr; fr=((0:Nr-1)-Nr/2)*dfr; phase1=exp(-j00*pi*(fr).^2/Kr); for i=1:Na sig(i,:)=ifft(fftshift( sig(i,:).*phase1) ); end disp('end of range compression'); figure; colormap(gray); contour(abs(sig)); %%%=============================================================================== for i=1:Nr sig(:,i)=fftshift(fft(sig(:,i))); end disp('end of azimuth fft') dfa=prf/Na; fa=((0:Na-1)-Na/2)*dfa+fdc; figure; colormap(gray); contour(abs(sig)); %% RMC with interpolation rr=rmin+((1:Nr)-1)*bin_r-nr*bin_r/2; R=8; N_ex=2000; Up00=zeros(size(1:Nr*R+2*N_ex)); alpha_dc=1./sqrt(1-(lamda*fdc/2/va)^2); for i=1:Na Up00=0*Up00; Up00(N_ex+1:N_ex+Nr*R)=interp(sig(i,:),R); alpha_fx = 1./sqrt(1-(lamda*fa(i)/2/va)^2); dRa=rr*(alpha_fx-alpha_dc)*sin(theta); kpos=R*((1:Nr)-1)+round(R*dRa/bin_r)+N_ex; sig(i,:)=Up00(kpos); end disp('end of range motion correction') figure; colormap(gray); contour(abs(sig)); %%%=============================================================================== fa=fa-fdc; fdc=0; beta_dc = sqrt(1-(lamda*fdc/2/va).^2); delt_beta = sqrt(1-(lamda*fa/2/va).^2)-beta_dc; phase2 = exp((j00*4*pi*sin(theta)/lamda)*(delt_beta'*rr)); sig = sig.*phase2; for i=1:Nr sig(:,i)=ifft(fftshift(sig(:,i))); end disp('end of azimuth compression') figure; colormap(gray); contour(abs(sig));