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引用：https://zhuanlan.zhihu.com/p/3897812664
合成孔径雷达3种模式
SAR 模式“Stripmap”
传统的 SAR 带状映射模式采用固定的指向方向 的雷达天线宽侧到平台轨道。带状地图是 由 SAR 的条带形成的宽度并遵循长度的图像 平台本身的飞行线轮廓。详细说明 您可以在主题 SLAR 中找到。
图 1：SAR 模式的“带状图”
SAR 模式“Spotlight”
Spotlight-SAR 是一种用于获取高分辨率的 SAR 操作模式 通过转向雷达波束，使目标在波束内保持更长的时间 从而形成更长的合成孔径。Spotlight SAR 能够扩展 高分辨率 SAR 成像能力显着。随着使用脉冲数的增加， 方位角分辨率增加。这是通过将目标保持在 通过电子束对雷达波束进行更长时间的聚光灯照明 转向，从而产生更长的合成孔径。Spotlight SAR 操作模式 通常以牺牲空间覆盖率为代价，因为给定 当雷达波束时，SAR 的可达性条带无法被照亮 聚焦于特定目标区域。
图 2：SAR 模式“Spotlight”
SAR 模式“扫描”
一种合成孔径雷达，能够照亮多个子条带 通过将其天线从最低点扫描到不同的位置。这是 SAR 模式 “Scan”。
图 3：SAR 模式“扫描”
SAR 模式“扫描”
一种合成孔径雷达，能够照亮多个子条带 通过将其天线从最低点扫描到不同的位置。这是 SAR 模式 “Scan”。
图 3：SAR 模式“扫描”
主要原理
MATLAB代码
clear;clc;close all;%%================================================================%%Parameter--constantC=3e8; %propagation speed%%Parameter--radar characteristicsFc=1e9; %carrier frequency 1GHzlambda=C/Fc; %wavelength%%Parameter--target areaXmin=0; %target area in azimuth is within[Xmin,Xmax]Xmax=50;Yc=10000; %center of imaged areaY0=500; %target area in range is within[Yc-Y0,Yc+Y0]%imaged width 2*Y0%%Parameter--orbital informationV=100; %SAR velosity 100 m/sH=5000; %height 5000 mR0=sqrt(Yc^2+H^2);%%Parameter--antennaD=4; %antenna length in azimuth directionLsar=lambda*R0/D; %SAR integration lengthTsar=Lsar/V; %SAR integration time%%Parameter--slow-time domainKa=-2*V^2/lambda/R0; %doppler frequency modulation rateBa=abs(Ka*Tsar); %doppler frequency modulation bandwidthPRF=Ba; %pulse repitition frequencyPRT=1/PRF; %pulse repitition timeds=PRT; %sample spacing in slow-time domainNslow=ceil((Xmax-Xmin+Lsar)/V/ds); %sample number in slow-time domainNslow=2^nextpow2(Nslow); %for fftsn=linspace((Xmin-Lsar/2)/V,(Xmax+Lsar/2)/V,Nslow);%discrete time array in slow-time domainPRT=(Xmax-Xmin+Lsar)/V/Nslow; %refreshPRF=1/PRT;ds=PRT;%%Parameter--fast-time domainTr=5e-6; %pulse duration 10usBr=30e6; %chirp frequency modulation bandwidth 30MHzKr=Br/Tr; %chirp slopeFsr=3*Br; %sampling frequency in fast-time domaindt=1/Fsr; %sample spacing in fast-time domainRmin=sqrt((Yc-Y0)^2+H^2);Rmax=sqrt((Yc+Y0)^2+H^2+(Lsar/2)^2);Nfast=ceil(2*(Rmax-Rmin)/C/dt+Tr/dt);%sample number in fast-time domainNfast=2^nextpow2(Nfast); %for ffttm=linspace(2*Rmin/C,2*Rmax/C+Tr,Nfast); %discrete time array in fast-time domaindt=(2*Rmax/C+Tr-2*Rmin/C)/Nfast; %refresh%%%%%%%%%%%%%%%%%Fsr=1/dt;%%Parameter--resolutionDY=C/2/Br; %range resolutionDX=D/2; %cross-range resolution%%Parameter--point targetsNtarget=2; %number of targets%format [x, y, reflectivity]Ptarget=[Xmin,Yc,1 %position of targetsXmin,Yc+10*DY,1Xmin+20*DX,Yc+50*DY,1];disp('Parameters:')disp('Sampling Rate in fast-time domain');disp(Fsr/Br)disp('Sampling Number in fast-time domain');disp(Nfast)disp('Sampling Rate in slow-time domain');disp(PRF/Ba)disp('Sampling Number in slow-time domain');disp(Nslow)disp('Range Resolution');disp(DY)disp('Cross-range Resolution');disp(DX)disp('SAR integration length');disp(Lsar)disp('Position of targets');disp(Ptarget)%%================================================================%%Generate the raw signal dataK=Ntarget; %number of targetsN=Nslow; %number of vector in slow-time domainM=Nfast; %number of vector in fast-time domainT=Ptarget; %position of targetsSrnm=zeros(N,M);for k=1:1:Ksigma=T(k,3);Dslow=sn*V-T(k,1);R=sqrt(Dslow.^2+T(k,2)^2+H^2);tau=2*R/C;Dfast=ones(N,1)*tm-tau'*ones(1,M);%%%%%%%%%%%%%%%%%phase=pi*Kr*Dfast.^2-(4*pi/lambda)*(R'*ones(1,M));Srnm=Srnm+sigma*exp(j*phase).*(0<Dfast&Dfast<Tr).*((abs(Dslow)<Lsar/2)'*ones(1,M));%%%%%%%%%%%%%%%%%rangeend%%================================================================%%Range compressiontr=tm-2*Rmin/C;Refr=exp(j*pi*Kr*tr.^2).*(0<tr&tr<Tr);Sr=ifty(fty(Srnm).*(ones(N,1)*conj(fty(Refr))));Gr=abs(Sr);%%Azimuth compressionta=sn-Xmin/V;Refa=exp(j*pi*Ka*ta.^2).*(abs(ta)<Tsar/2);Sa=iftx(ftx(Sr).*(conj(ftx(Refa)).'*ones(1,M)));Ga=abs(Sa);%%================================================================%%draw the intensity image of signalcolormap(gray);figure(1)subplot(211);row=tm*C/2-2008;col=sn*V-26;%%%%%%%%%%%%%%%%%imagesc(row,col,255-Gr); %intensity image of Sraxis([Yc-Y0,Yc+Y0,Xmin-Lsar/2,Xmax+Lsar/2]);xlabel('\rightarrow\itRange in meters'),ylabel('\itAzimuth in meters\leftarrow'),title('Stripmap SAR after range compression'),subplot(212);imagesc(row,col,255-Ga); %intensity image of Saaxis([Yc-Y0,Yc+Y0,Xmin-Lsar/2,Xmax+Lsar/2]);xlabel('\rightarrow\itRange in meters'),ylabel('\itAzimuth in meters\leftarrow'),title('Stripmap SAR after range and azimuth compression'),%%================================================================%%draw 3D picturefigure(2)waterfall(real(Srnm((200:205),:)));axis tightxlabel('Range'),ylabel('Azimuth'),title('Real part of the raw signal'),figure(3)waterfall(Gr((200:205),(600:1000)));axis tight %%%%%%%%%%%%%%%%%how to choose200:205xlabel('Range'),ylabel('Azimuth'),title('Stripmap SAR after range compression'),figure(4)mesh(Ga((200:300),(750:860)));axis tightxlabel('Range'),ylabel('Azimuth'),title('Stripmap SAR after range and azimuth compression'),%%================================================================%%draw -3dB contourfigure(5)a=max(max(Ga));contour(row,col,Ga,[0.707*a,a],'b');grid onaxis([9995,10050,-20,20]),xlabel('\rightarrow\itRange in meters'),ylabel('\itAzimuth in meters\leftarrow'),title('Resolution Demo: -3dB contour');%%================================================================
