【雷达】模拟合成孔径雷达(SAR)的点目标仿真

1 简介

基于理想情况下聚束式SAR点目标回波信号数学模型。

2 完整代码

%%IFFT in row of matrix
function s=ifty(fs);
s=fftshift(ifft(fftshift(fs.'))).';

%%FFT in column of matrix
function fs=ftx(s);
fs=fftshift(fft(fftshift(s)));%%IFFT in column of matrix
function s=iftx(fs);
s=fftshift(ifft(fftshift(fs)));%%FFT in row of matrix
function fs=fty(s);
fs=fftshift(fft(fftshift(s.'))).';%%================================================================
%%Filename: stripmapSAR.m
%%Help file: stripmapSAR.doc
%%Project: Stripmap SAR Simulation using point targets and Reconstrction
%%================================================================
clear;clc;close all;
%%================================================================
%%Parameter--constant
C=3e8; %propagation speed
%%Parameter--radar characteristics
Fc=1e9; %carrier frequency 1GHz
lambda=C/Fc; %wavelength
%%Parameter--target area
Xmin=0; %target area in azimuth is within[Xmin,Xmax]
Xmax=50;
Yc=10000; %center of imaged area
Y0=500; %target area in range is within[Yc-Y0,Yc+Y0]
%imaged width 2*Y0
%%Parameter--orbital information
V=100; %SAR velosity 100 m/s
H=5000; %height 5000 m
R0=sqrt(Yc^2+H^2);
%%Parameter--antenna
D=4; %antenna length in azimuth direction
Lsar=lambda*R0/D; %SAR integration length
Tsar=Lsar/V; %SAR integration time
%%Parameter--slow-time domain
Ka=-2*V^2/lambda/R0; %doppler frequency modulation rate
Ba=abs(Ka*Tsar); %doppler frequency modulation bandwidth
PRF=Ba; %pulse repitition frequency
PRT=1/PRF; %pulse repitition time
ds=PRT; %sample spacing in slow-time domain
Nslow=ceil((Xmax-Xmin+Lsar)/V/ds); %sample number in slow-time domain
Nslow=2^nextpow2(Nslow); %for fft
sn=linspace((Xmin-Lsar/2)/V,(Xmax+Lsar/2)/V,Nslow);%discrete time array in slow-time domain
PRT=(Xmax-Xmin+Lsar)/V/Nslow; %refresh
PRF=1/PRT;
ds=PRT;
%%Parameter--fast-time domain
Tr=5e-6; %pulse duration 10us
Br=30e6; %chirp frequency modulation bandwidth 30MHz
Kr=Br/Tr; %chirp slope
Fsr=3*Br; %sampling frequency in fast-time domain
dt=1/Fsr; %sample spacing in fast-time domain
Rmin=sqrt((Yc-Y0)^2+H^2);
Rmax=sqrt((Yc+Y0)^2+H^2+(Lsar/2)^2); %SAR姝ｅ鐩爣锛屾墍浠ヤ笌鏈?繙澶勭殑璺濈涓哄悎鎴愬瓟寰勯暱搴︾殑涓?崐
Nfast=ceil(2*(Rmax-Rmin)/C/dt+Tr/dt);%sample number in fast-time domain
Nfast=2^nextpow2(Nfast); %for fft
tm=linspace(2*Rmin/C,2*Rmax/C+Tr,Nfast); %discrete time array in fast-time domain
dt=(2*Rmax/C+Tr-2*Rmin/C)/Nfast; %refresh
Fsr=1/dt;
%%Parameter--resolution
DY=C/2/Br; %range resolution
DX=D/2; %cross-range resolution
%%Parameter--point targets
Ntarget=1; %number of targets
%format [x, y, reflectivity]
Ptarget=[Xmin,Yc,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 data
K=Ntarget; %number of targets
N=Nslow; %number of vector in slow-time domain
M=Nfast; %number of vector in fast-time domain
T=Ptarget; %position of targets
Srnm=zeros(N,M);
for k=1:1:K
sigma=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));
end
%%================================================================
%%Range compression
tr=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 compression
ta=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);
%%================================================================
%%graw the intensity image of signal
colormap(gray);
figure(1)
subplot(211);
row=tm*C/2-2008;col=sn*V-26;
imagesc(row,col,255-Gr); %intensity image of Sr
axis([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 Sa
axis([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 picture
figure(2)
waterfall(real(Srnm((200:205),:)));axis tight
xlabel('Range'),ylabel('Azimuth'),
title('Real part of the raw signal'),
figure(3)
waterfall(Gr((200:205),(600:1000)));axis tight
xlabel('Range'),ylabel('Azimuth'),
title('Stripmap SAR after range compression'),
figure(4)
mesh(Ga((200:300),(750:860)));axis tight
xlabel('Range'),ylabel('Azimuth'),
title('Stripmap SAR after range and azimuth compression'),
%%================================================================
%%draw -3dB contour
figure(5)
a=max(max(Ga));
contour(row,col,Ga,[0.707*a,a],'b');grid on
axis([9995,10050,-20,20]),
xlabel('\rightarrow\itRange in meters'),ylabel('\itAzimuth in meters\leftarrow'),
title('Resolution Demo: -3dB contour');
%%================================================================

3 仿真结果

4 参考文献

[1]吕守业, 龙腾, and 闫肃. "机载聚束式合成孔径雷达(SAR)点目标的仿真研究." 第十四届全国遥感技术学术交流会 0.

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