[PDF] Synthetic Aperture Radar (SAR): Principles and Applications

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MarwanYounis

GermanAerospaceCenter(DLR)

MicrowavesandRadarInstitute

82230Oberpfaffenhofen,Germany

e mail: marwan.younis@dlr.de/Web:www.dlr.de/HR

SyntheticApertureRadar(SAR):

Principles

andApplications slide 2German Aerospace CenterMicrowaves and Radar Institute

PART III

Theory: SAR Image Formation and

Image Properties

SAR Image Formation

z y x

Antenna

Azimuth

range

SAR Basic Principle

1) pulsed radar system

(PRF = Pulse Repetition Frequency)

2) two dimensional imaging

(range x azimuth)

3) range resolution

4) azimuth resolution

5) Radar system must be coherent!

T e L sa 2 a a d 2 o r p c B antenna > 100 Mbit/s kbit/s

SAR Data Flow

Transmitter

Receiver

Data

Recording

Range compression

Azimuth

compression Image evaluation Image interpretation

SAR raw data

SAR image data signal generator

Mixerpower

amplifierlow noise amplifier circulatorbase band signal I Q ADAD -90°

I/Q demodulator

Synthetic Aperture Radar (SAR)

ultra stable oscillator

Coherent Measurement Principle

transmit t (time)

Total time delay 1 =

1 o 2 . r c

Coherent demodulation

Received echo signal 1

phase change 1 1 4.. object phase r 1 4.. object phase r 1 A

Imaginary Part

Real Part

Coherent Measurement Principle

transmit

Total time delay 2 =

2 o 2 . r c

Coherent demodulation

2 4.. object phase r 2 4.. object phase r phase change 2 t (time)

Received echo signal 2

2 A

Imaginary Part

Real Part

I S I S o tfjAtfA 00

2exp2cos

complex representation: I jAexp after demodulation: A amplitude: 2 A intensity, power: phase: Every pixel of a complex SAR image consists of a real and an imaginary part, i.e. it is a phasor and contains amplitude and phase information. A

Phasor Representation of SAR Signal

4.. object r phase information

Imaginary Part

Real Part

o amplitude information backscattering coefficient r 0 velocity point target range / fast time antenna beam antenna azimuth / slow time pulse length illumination time / synthetic aperture length

2-D Raw Data Matrix

PRI

Number of Samples

for one point target

1500 azimuth

30000 range

T ill = 0.5 s L sa = 3.6 km = 100 s @ 20% dc

V= 7 km/s

d a = 5 m a = 0.35° @ 10 GHz = 600 km

Formation of Azimuth Chirp Signal

time azimuth azimuth signal

Number of Samples

for one point target

1500 azimuth

30000 range

time delay t=t 1

Synthetic Aperture Formation and Processing

Detection

convolution SAR processor point target responseresolution of synthetic aperturecoherent summation 12 point target flight direction beamwidth of real aperture antenna SAR sensor

Detection

convolution SAR processor received azimuth signal point target responseresolution of synthetic aperture phase corrections coherent summation

Synthetic Aperture Radar (SAR)

SAR Processing (Image Formation)

raw data

SAR image

quotesdbs_dbs23.pdfusesText_29

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