spotlight.rar_spotlight_合成孔径雷达_成像_聚束成像

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % PULSED SPOTLIGHT SAR SIMULATION AND RECONSTRUCTION % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% colormap(gray(256)) cj=sqrt(-1); pi2=2*pi; % c=3e8; % propagation speed f0=50e6; % baseband bandwidth is 2*f0 w0=pi2*f0; fc=200e6; % carrier frequency wc=pi2*fc; lambda_min=c/(fc+f0); % Wavelength at highest frequency lambda_max=c/(fc-f0); % Wavelength at lowest frequency kc=(pi2*fc)/c; % wavenumber at carrier frequency kmin=(pi2*(fc-f0))/c; % wavenumber at lowest frequency kmax=(pi2*(fc+f0))/c; % wavenumber at highest frequency % Xc=1000; % Range distance to center of target area X0=20; % target area in range is within [Xc-X0,Xc+X0] Yc=300; % Cross-range distance to center of target area Y0=60; % target area in cross-range is within % [Yc-Y0,Yc+Y0] % Case 1: L < Y0; requires zero-padding of SAR signal in synthetic % aperture domain % L=100; % synthetic aperture is 2*L % Case 2: L > Y0; slow-time Doppler subsampling of SAR signal spectrum % reduces computation % % L=400; % synthetic aperture is 2*L theta_c=atan(Yc/Xc); % Squint angle Rc=sqrt(Xc^2+Yc^2); % Squint radial range L_min=max(Y0,L); % Zero-padded aperture is 2*L_min % Xcc=Xc/(cos(theta_c)^2); % redefine Xc by Xcc for squint processing %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% u domain parameters and arrays for compressed SAR signal %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % duc=(Xcc*lambda_min)/(4*Y0); % sample spacing in aperture domain % for compressed SAR signal duc=duc/1.2; % 10 percent guard band; this guard band % would not be sufficient for targets % outside digital spotlight filter (use % a larger guard band, i.e., PRF) mc=2*ceil(L_min/duc); % number of samples on aperture uc=duc*(-mc/2:mc/2-1); % synthetic aperture array dkuc=pi2/(mc*duc); % sample spacing in ku domain kuc=dkuc*(-mc/2:mc/2-1); % kuc array % dku=dkuc; % sample spacing in ku domain %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% u domain parameters and arrays for SAR signal %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % if Yc-Y0-L < 0, % minimum aspect angle theta_min=atan((Yc-Y0-L)/(Xc-X0)); else theta_min=atan((Yc-Y0-L)/(Xc+X0)); end; theta_max=atan((Yc+Y0+L)/(Xc-X0)); % maximum aspect angle % du=pi/(kmax*(sin(theta_max)- ... sin(theta_min))); % sample spacing in aperture % domain for SAR signal du=du/1.4; % 20 percent guard band m=2*ceil(pi/(du*dku)); % number of samples on aperture du=pi2/(m*dku); % readjust du u=du*(-m/2:m/2-1); % synthetic aperture array ku=dku*(-m/2:m/2-1); % ku array %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Fast-time domain parmeters and arrays %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Tp=2.5e-7; % Chirp pulse duration alpha=w0/Tp; % Chirp rate wcm=wc-alpha*Tp; % Modified chirp carrier % if Yc-Y0-L < 0, Rmin=Xc-X0; else Rmin=sqrt((Xc-X0)^2+(Yc-Y0-L)^2); end; Ts=(2/c)*Rmin; % start time of sampling Rmax=sqrt((Xc+X0)^2+(Yc+Y0+L)^2); Tf=(2/c)*Rmax+Tp; % end time of sampling T=Tf-Ts; % fast-time interval of measurement Ts=Ts-.1*T; % start slightly earlier (10% guard band) Tf=Tf+.1*T; % end slightly later (10% guard band) T=Tf-Ts; Tmin=max(T,(4*X0)/(c*cos(theta_max))); % Minimum required T % dt=1/(4*f0); % Time domain sampling (guard band factor 2) n=2*ceil((.5*Tmin)/dt); % number of time samples t=Ts+(0:n-1)*dt; % time array for data acquisition dw=pi2/(n*dt); % Frequency domain sampling w=wc+dw*(-n/2:n/2-1); % Frequency array (centered at carrier) k=w/c; % Wavenumber array % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Resolution for Broadside: (x,y) domain rotated by theta_c % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% DX=c/(4*f0); % range resolution (broadside) DY=(Xcc*lambda_max)/(4*L); % cross-range resolution (broadside) %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Parameters of Targets %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % ntarget=9; % number of targets % Set ntarget=1 to see "clean" PSF of target at origin % Try this with other targets % xn: range; yn= cross-range; fn: reflectivity xn=zeros(1,ntarget); yn=xn; fn=xn; % Targets within digital spotlight filter % xn(1)=0; yn(1)=0; fn(1)=1; xn(2)=.7*X0; yn(2)=-.6*Y0; fn(2)=1.4; xn(3)=0; yn(3)=-.85*Y0; fn(3)=.8; xn(4)=-.5*X0; yn(4)=.75*Y0; fn(4)=1.; xn(5)=-.5*X0+DX; yn(5)=.75*Y0+DY; fn(5)=1.; % Targets outside digital spotlight filter % (Run the code with and without these targets) % xn(6)=-1.2*X0; yn(6)=.75*Y0; fn(6)=1.; xn(7)=.5*X0; yn(7)=1.25*Y0; fn(7)=1.; xn(8)=1.1*X0; yn(8)=-1.1*Y0; fn(8)=1.; xn(9)=-1.2*X0; yn(9)=-1.75*Y0; fn(9)=1.; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% SIMULATION %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % s=zeros(n,mc); % SAR signal array % for i=1:ntarget; % Loop for each target td=t(:)*ones(1,mc)-2*ones(n,1)*sqrt((Xc+xn(i)).^2+(Yc+yn(i)-uc).^2)/c; s=s+fn(i)*exp(cj*wcm*td+cj*alpha*(td.^2)).*(td >= 0 & td <= Tp & ... ones(n,1)*abs(uc) <= L & t(:)*ones(1,mc) < Tf); end; % s=s.*exp(-cj*wc*t(:)*ones(1,mc)); % Fast-time baseband conversion % User may apply a slow-time domain window, e.g., power window, on % simulated SAR signal array "s" here. G=abs(s)'; xg=max(max(G)); ng=min(min(G)); cg=255/(xg-ng); image(t,uc,256-cg*(G-ng)); axis('square');axis('xy') xlabel('Fast-time t, sec') ylabel('Synthetic Aperture (Slow-time) U, meters') title('Measured Spotlight SAR Signal') print P5.1.ps pause(1) % td0=t(:)-2*sqrt(Xc^2+Yc^2)/c; s0=exp(cj*wcm*td0+cj*alpha*(td0.^2)).*(td0 >= 0 & td0 <= Tp); s0=s0.*exp(-cj*wc*t(:)); % Baseband reference fast-time signal s=ftx(s).*(conj(ftx(s0))*ones(1,mc)); % Fast-time matched filtering % G=abs(iftx(s))'; xg=max(max(G)); ng=min(min(G)); cg=255/(xg-ng); tm=(2*Rc/c)+dt*(-n/2:n/2-1); % fast-time array after matched filtering image(tm,uc,256-cg*(G-ng)); axis('square');axis('xy') xlabel('Fast-time t, sec') ylabel('Synthetic Aperture (Slow-time) U, meters') title('SAR Signal after Fast-time Matched Filtering') print P5.2.ps pause(1) % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Slow-time baseband conversion for squint % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % kus=2*kc*sin(theta_c)*ones(1,n); % Doppler frequency shift in ku % domain due to squint % s=s.*exp(-cj*kus(:)*uc); % slow-time baseband conversion fs=fty(s); % Display aliased SAR spectrum % G=abs(fs)'; xg=max(max(G)); ng=min(min(G)); cg=255/(xg-ng); image(k*c/pi2,kuc,256-cg*(G-ng)); axis('square');axis('xy') xlabel('Fast-time Frequency, Hertz') ylabel('Synthetic Aperture (Slow-time) Frequency Ku, rad/m') title('Aliased Spotlight SAR Signal Spectrum') print P5.3.ps pause(1) % %%%%%%%%