Educational Objective

• Understand the SAR imaging process and SAR instrument operation modes

• Understand the relevant parameters of SAR systems

• Understand the basic SAR scattering process

• Understand the properties of SAR images

• Know some SAR satellites and their main properties

Tutorial

• Matlab codes

Synthetic ApertureRange ImagingIntroductionOverview Advanced SAR Modes Characteristics of SAR ImagesSAR Satellites

Angular Resolution of an Optical Imaging System

x

Ap

ertu

re D

Object spaceLensx

Diffraction limit (angle):

DRRx / ==Diffraction limit ():

R

→ Diffraction limits resolution of sensors and transmitters!Examples:Human eye: 1000 km * 500 nm/5 mm = 100 mSatellite dish antenna (Ku): 1000 km * 2 cm / 60 cm = 33 km (!)

D/

2/

SAR Imaging Geometry

radar

CSV /

swath width

BV

range: radar principle =scanning at speed of light

azimuth: scanning in flight directionat plus aperture synthesis(holography)

BV

coherent imaging: complex-valued pixelscontain amplitude (brightness)and phase information

for this lecture: straight flight path

VVV BCS == /

Radar transmits pulses and receives echoes at the rate of the pulse repetition frequency:PRF @ 1000 - 4000 Hz

Range Resolution( )

pulse length speed of light

2cos 2cos depression angler

cR

= =

Calculate Rr

Azimuth Resolution

slant range wavelength

antenna length

a

SR

L

=

BP SAR Functional Block Diagram

Pulse Compression

FFTDot

multiplicationIFFT

ADCBAQ/AGC

(12, 8, 6,or 4 bits)

Pixel slant range calculation

Back projection by range

(Interpolation)

SAR image energy

accumulationForm SAR images

SAR image parameters:SAR image center: (Rc, Xc,Zc)Range (DR) and X-range (DX) lengthRange(dR) and X-range (dX) resolutionTX waveform bandwidth (BW)Sampling rate (fs)PRFNavigation (lat, lon, and alt)

AForm SAR image

grid

QDDC

(fs/4) Baseband Conversion

Decimation FIRanalog signal

12-bit real data

BW and fs,Decimation factor = Df = floor(fs/4/BW)

20-bit complex

I & Q

4-bit complex

I & Q

fs fs/Df fs/Df

Pulse Compression (ping-pong process if needed)

FFTDot

multiplicationIFFT

Phase compensation

A

Data storage

Conjugated match filter

Back Projection SAR Functional Block Diagram

SIZE FSCM NO DWG NO REVDRAWN Charles Hsu BPSAR-001 01

ISSUED 1/17/2016 SCALE 1 : 1 SHEET 1 OF 1

Back Projection SAR Functional Block Diagram

Implemented in hardware

Under hardware development (?)

Implemented in MATLAB

Not implemented yet