Introduction to Imaging Radar INFGEO 4310€¦ · Svein-Erik Hamran INFGEO 4310 Svein-Erik Hamran...

18.09.2009

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Introduction to Imaging RadarINFGEO 4310

Svein-Erik HamranINFGEO 4310

Svein-Erik Hamran17.9.2009

Outline

• Introduction• Radar waveforms• Range Doppler Imaging• ISAR – Inverse Synthetic Aperture Imaging• Spotlight SAR – Synthetic Aperture Radar

St i SAR


• Stripmap SAR• Interferometric SAR• GPR – Ground Penetration Radar • Example of SAR systems

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RADAR = RAdio Detection And Ranging

1886 Heinrich Hertz confirmed radio wave propagation1904 Hülsmeyer patented ship collision-avoidance system1922 Ship detection methods at NRL (Taylor & Young,

700MHz)1930s England and Germany radar programs developed:

Chain Home early warning system (22-50 MHz)fire control systems

i ft i ti t


aircraft navigation systemscavity magnetron to transmit high-power microwaves

1940s Establishment of MIT Rad Lab (British + American) radar for tracking, U-boat detection

Multi disciplinary scienceElectromagneticscattering

Wave propagation

Antenna theory

Microwave andradio technique

Si l i


High speeddata collection

Signal processing

Visualisation

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Why Radar

• Works day or night (unlike optical imaging)• Works in all weather• Penetrates clouds and rain• Some radars can penetrate foliage, buildings, soil,

human tissue• Can provide very accurate distance measurements


• Can provide very accurate distance measurements• Sensitive to objects whose length scales are cm to m• Can measure velocities (Moving targets)

Electromagnetic Waves• An electromagnetic wave comprises two orthogonal vector

components:– Electric field intensity E– Magnetic field intensity H

• Sinusoidal EM wave:


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• Electric field oscillates back and forth.• EM wave propagation is in the direction orthogonal to oscillation of

both electric and magnetic fields.

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Radiation

E

E

H


7

H

The Radio-Frequency Spectrum


8

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Maxwell’s equations

0

=⋅∇

=×∇+∂∂

=×∇+∂∂

E

EHtE

EtH

fρε

σε

μWave equations

0

0

2

22

2

22

=∂∂

−∇

=∂∂

−∇

BB

tEE

εμ

εμ


9

0=⋅∇ Hf

μ2∂t

μ

Radar principle Waveform

AmplifierAWaveform

generator

Amplifier

Antenna

Mi


AmplifierMixerCorrelator

Radar range profileRadarprocessor

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Resolution – Bandwidth FB = 20%


Resolution – Bandwidth FB = 100%


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Range Resolution


Radar waveforms

• Gated-CW• Impulse• Noise radar• Chirp• FMCW

St f


• Step-frequency

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Impulse Radar


Sequential Sampling Receiver


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Block diagram of a noise radar


Analog correlation receiver


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Digital correlation receiver


Pulse Train Spectrum


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Step-frequency radar

ffrequency

B

Δf

SFCW


time

Step Frequency Waveform


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FMCW –Frequency Modulated Continous Wave


Chirp radar

Transmit uenc

y

Transmit Echo from 3 targetsTransmitand receive

time

freq

u

time

freq

uenc

yue

ncy

Localoscillatoroutput

Mixer


time

freq

uA

mpl

itude

f

output

Rangeresponse

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Classical radar image (PPI)


Range-Doppler Imaging

• The object rotation gives cross

Ω x

y

( , )x y0 0

r0

• The object rotation gives cross range resolution

r r x t y tr ya

a

= + +≈ +

0 0

0

sin cosΩ Ω• Range

D l


rra

f drdt

x t y t

x

d = = −

≈

2 2 2

2

0 0

0

λ λ λ

λ

ΩΩ

ΩΩ

Ω

cos sin

• Doppler:

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0

1

2

3

Ran

ge [m

]

Si l t t Ω 36º/

Range and Doppler

-3

-2

-1

R50

100

150

z]

Single target, Ω = 36º/s

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]

2

0

2

4

Ran

ge p

ositi

on [m

]


0 45 90 135 180 225 270 315 360-150

-100

-50

0

Angle [deg]

Dop

pler

[Hz

-4 -2 0 2 4-4

-2

Azimuth position [m]

R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

-4 -2 0 2 4-4

-2


R

ResolutioncBcy

2=ΔDistance (range)

Tfx

θλλλ

222=

Ω=Δ

Ω=Δ

Tf 1=ΔAzimut (Doppler)


pT θ222 ΩΩ

MHz800=BExample: cm75.18=Δy

s5s5.0cm,8.1

=°=Ω=

Tλ

°= 5.2pθ cm6.20=Δx

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ISAR• ISAR – Invers Synthetic

A t R d

HRR-profiles

Accurate tracking

Aperture Radar• Methode that is using the

targets motion• Relative motion makes a

change in aspect angle• Starts with range profiles• HRR – High Resolution Range

FFT

ISAR-image


• Main difficulty is accurate tracks

Simulation Example

• Frequency 1-2 GHz with 66 frequencies• Angular coverage step every 1 degree for total of 60

1

2

3

4

5

1

2

3

30

60

90

120

150

180


-5 -4 -3 -2 -1 0 1 2 3 4 5-5

-4

-3

-2

-1

0

210

240

270

300

330

180 0

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SAR bilde (J Moreira, Aerosensing)


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SAR-principle

rDL


Dλθ =

DRRx λθ ==Δ

L2λθ =′

22D

LRRx ==′=′Δλθ

x

Comparison of resolution

Distance: 10 kmAntenna: 1 mWavelenght: X-båndResolution: 300 m

SAR (Stripmap)Antenna: 1 mWavelenght: X-båndResolution: 0.5 m

Real aperture Synthetic aperture


Distance: 100 kmResolution: 3 km

Distance: 1000 kmResolution: 30 km

SAR (Spotlight)Theoretical Resolution: 7.5 mm

Independent of distance!

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Special effects in SAR-images

• Geometrical distortion – 3 types:– Foreshortening– Layover– Shadow

• All related to that the ground is not flat.• Can have a large influence for

i t t ti i h th


interpretation in areas where the topography is large.

• Speckle

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Foreshortening

ϑ

yΔrΔ

α

0 α ϑ< <

y y′Δ > Δ


y′Δ

Foreshortening

ϑ

rΔ

0ϑ α− < <

y y′Δ < Δy′Δ


yΔ α

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Layover

ϑ

α ϑ>



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Shadow

ϑ

α ϑ< −


α

MSTAR data (L Novak

MIT Lincoln Lab)


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Speckle

1 look 2 looks


3 looks 9 looks

Jakowatz & Co (1996)

SAR geometryx

rϑ

( )=T x r ϑ

ϕ


( , , )=T x r ϑ1 1 1 1( , , )=T x r ϑ

ϕ - Squint-angle

0=ϕ - Broad side

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SAR-principle

0 0( , )=P x y

0y

x

2 20 0( )= − +r x x y


2krϕ =

IEEE GRS Newsletter, Dec 2001.

SAR-modes

• Stripmap – antenna fixed side looking– Resolution given by antennas size: ~ d/2

• Spotlight – antenna is steered against the targetResolution given by angular coverage, max: λ/4 for 2π

• Stripmap is used to continous mapping with average reolution.

• Spotlight used to image areas of special interest


p g g pand with high resolution.

• ISAR – Invers SAR similar to spotlight but used to image moving targets

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Stripmap


Georef Stripmap


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Spotlight


PI-SAR (CRL/NASDA)


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PI-SAR



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PI-SAR


Interferometry

• Interferometry is a method that use the phase difference resulting from two measurements taken at different observation points

– General radar method not only usable for SAR– Very much used in SAR

• SAR-interferometry makes it possibly to resolve the altitude coordinate and thereby measure height.

Very sensitive since using the radar phase


– Very sensitive since using the radar phase– The radar system needs to be accurate and stable

• Makes GEOCODING possible, that is reference image pixels to geographical reference system.

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IFSAR2 1Δ = −ϕ ϕ ϕ

r1

r2

bd

h

2 12 ( )= −r rπλ

Relates to z


z

Cross-track interferometry (CTI)

Two or Single pass interferometry

IFSAR prosessering (DLRs SRTM-Web)


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LynxSAR, to-pass IFSAR


IFSAR2 1Δ = −ϕ ϕ ϕ

r1r2

2 12 ( )= −r rπλ

Relates to Δr


Along-track interferometry (ATI)

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AN/APY-6 GMTI og SAR (W Miceli, ONR)


Differential IFSAR – Time series


Andrew Hooper, Howard Zebker, Paul Segall, Bert Kampes, “A New Method for Measuring Deformation on Volcanoes and Other Natural Terrains Using InSAR Persistent Scatterers”, Geophysical Research Letters, (31) 23, 2004

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ExoMars Mission

• Scientific objectives are:T h f i f t d t lif– To search for signs of past and present life on Mars;

– To characterise the water/geochemical environment as a function of depth in the shallow subsurface;

– To study the surface environment and identify hazards to future missions;T i ti t th l t’ b f d


– To investigate the planet’s subsurface and deep interior to better understand the evolution and habitability of Mars.

• Pasteur Rover with instruments: Camera, Organics detector, Mass spectrometer, GPR, Raman/LIBS, Microscope, Drill.

• GEP: Met-sensors, Dust, GPR, Electric field

WISDOM GPR Prototype– Frequency [500 MHz – 3 GHz]

LO-frequencySynthesizer

Step-frequencySynthesizer

GatingSynthesizer

Master Clock

Tx-Front End

8 GHz

5-8 GHz

0.5-3 GHz

Tx-antenna

LO-frequencySynthesizer

Step-frequencySynthesizer

GatingSynthesizer

Master Clock

Tx-Front End

8 GHz

5-8 GHz

0.5-3 GHz

Tx-antenna


Rx-Front EndADCUSBPC

Rx-antenna

Rx-mixer

Rx-Front EndADCUSBPC

Rx-antenna

Rx-mixer

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Radar Prototype


Step Frequency Waveform Parameters• Number of Frequencies: 751• IF-Bandwidth: 500kHz• IF-Sampling Frequency 1 MHzIF Sampling Frequency 1 MHz • IF-Samples pr frequency: 10• Gating frequency: 5.12 MHz• Gating delay: 0 ns Tx and Rx• Gating

– Transmitting Power 0 dBm– Receiver Gain 60 dB


• CW– Transmitting Power -30 dBm– Receiver Gain 30 dB

• Sampling Along Profile: 10 cm• Time for each trace: 68 ms

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Radar Set UpRadar Electronics PC-Box


Antennas

Sampling Wheel


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• Mean annual air• Mean annual air temperature in NÅ is -6.3±C.

• Permafrost depth is ~100 m in costal areas and >500 m in mountainous areas.

• Active layer depth at the


y pfield site is believed to be ~2 m.

• This layer experiences thawing in the summer/autumn.

Aerial photographs


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Uversøyra Field Test Area


Sediment Layer on Top of Ice


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2 meter thick sediment layer

20 meter thick ice

L i i id th i


Layering inside the ice


Layers

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Interpretation

Glacier Ice

Permafrost Sediments


Moraine

50 to 80 meter along profile


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50 to 80 meter along profile


Kongsvegen Glacier Facies Characterization


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Radar Profile along stake line


Ablation ice Older SI Current SI Firn

Stake 5

Stake 6

Stake 7

C

DE

F


Stake 4

Stake 3

A

B

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Ablation zone


”Herring bone” zone


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Superimposed Ice Zone


Transition Zone


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Example 1 – Antarctica




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ENVISAT – ASAR

• ENVISAT is and ESA earth observation satellite • LAUNCH 28.02.2002, in orbit 03.04.2002• Instruments: ASAR, MERIS, RA-2, AATSR, MIPAS,

GOMOS, SCIAMACHY, MWR, DORIS• ASAR – Advanced Synthetic Aperture Radar


ENVISAT


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ASAR - antenna


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ASAR – Advanced Synthetic Aperture Radar• C-band 5.331 GHz (5.6 cm wavelenght)• Active phased array antenna 1.3 x 10 m• Elementene kan sende med horisontal (H) og

vertikal polarisasjon (V)• Bandwidth 200 kHz – 16 MHz, Transmits linear chirp• Nominel resolution 9 4 750 m products 30 x 30 m


• Nominel resolution 9.4 – 750 m, products 30 x 30 m up until 1 x 1 km

• Incidence angle 15-45º• Swath 56 – 105 km (405 km with ScanSAR)

ASAR – modes


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ERS2 – Wind field


Norut


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ASAR AP: Ottawa, Canada



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Fisheries protection zone

GREENLAND

SPITSBERGEN

NOVAYAZEMLYA

”LoopHole"

Fisheries zone

JAN MAYEN

ICELAND

"Greyzone"


FINLAND

SWEDEN

RUSSIANORWAY

GERMANY POLAND

UNITEDKINGDOM

ESTLAND

LATVIA

LITHAUENDENMARK

Barents Sea


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GA/SNL LynxSAR AN/APY-8

• Light weigth SAR-system with real time imaging

• Developed for UAVer: Predator, I-GNAT og Prowler II, weigth is 52 kg

• Four modes: Stripmap, spotlight, GMTI og CCD


LynxSAR parametere

- Frekvens: Ku-bånd 15.2 - 18.2 GHz- Båndbredde: 1 GHz, (15 cm nominell oppløsning)- Effekt: 350 W- Oppløsninger: 0.3 - 3 m stripmap

0.1 - 3 m spotlight- Rekkevidde: 7 - 30 km stripmap

4 - 25 km spotlight


- Sporbredde: 2600 piksel (934 m ved 0.3 m oppløsning, 45º)- Squint: ± 45º - 135º- GMTI: 3 m/s (ved 35 m/s), 4 - 25 km, 10 dBsm mål,

-10 dBsm/m2 clutter ,10 km sporbredde- CCD: Coherent Change Detection, Interferometri

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LynxSAR – UAV operations


Ground station Electronics andSignal processing


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Introduction to Imaging Radar INFGEO 4310€¦ · Svein-Erik Hamran INFGEO 4310 Svein-Erik Hamran...

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