1. Synthetic Aperture Radar
Chiba University
Signal Processing
Synthetic Aperture Radar
Josaphat Tetuko Sri Sumantyo, Ph.D
Center for Environmental Remote Sensing, Chiba University

2. Contents 1. Introduction of Synthetic Aperture Radar (SAR)
2. SAR Applications (History, Theory, Relationship with Remote Sensing etc)
3. Basic of Electromagnetic waves (Wave, Polarization, Absorption, Scattering etc)
4. Radar Equation and Microwave Scattering (Antenna Pattern)
5. Pulse Compression Technique and Image Production in Range Direction
6. Synthetic Aperture Technique and Image Production in Azimuth Direction
7. Basic of SAR Image Analysis

3. References

4. References

5. Introduction Microwave Sensor Active Sensor SAR and Definition
　　SAR (Synthetic Aperture Radar)
　　　　Satellite (sensor) itself illuminates microwave, then sensor receives
backscattered wave and processes this signal to be an image.
Benefit of SAR
　　　　All weather
　　　　Day and night time monitoring (Active sensor)
　　　　High coherency → InSAR applications
　　　　Polarization characteristics → Polarimetry
Lack of SAR
　　　　Analysis of backscattering Microwave Image  very complicated
　　　　　　(Different to the point of view in optical image analysis)
　　　　Image distortion (foreshortening, shadowing etc) caused by side looking
　Microwave Sensor
　Active Sensor
　Imaging Radar

6. Introduction
SEASAT (1978)
SIR-A (1981)
SIR-B (1984)
SIR-C (1994)
Frequency (GHz) 1
1, 5
Polarization HH
HH, HV, VH, VV
Look angle
20o
50o
20o – 60o
Analog data
Digital data
Central
Transmitter/
Receiver
Distributed
T/R modules
Fixed antenna beam
Mechanical
beam steering
Electronic
Pictures :

7. Introduction
ERS-1 (1991)
JERS-1 (1992)
Radarsat (1995)
Frequency (GHz)
5 (C band)
1.275 (L band)
Polarization VV HH
Look angle
20o
35o
20o – 60o
Pictures :

8. Specification of ALOS-PALSAR
Introduction
Specification of ALOS-PALSAR
Main Observation Mode
High Resolution Mode
SCAN SAR
Observation Frequency
L-band(1.27GHz)
Polarization
HH,VV,HH&HV,VV&VH
HH,VV
Ground Resolution
10m
100m
Look numbers 2 8
Swap area
70km
250～350km
Off Nadir Angle
10～51°

9. Satellite-onboard ＳＡＲ and flat-ground geometric system
sensor / antenna
①： off-nadir angle
　　（look angle)
②：depression angle
③：range beam width
④：incidence angle
⑤：azimuth beam width
horizontal direction
platform direction ② ① ③
slant range direction
range direction ⑤
azimuth direction ④
far range
near range
Ground range
target
JERS-1 SAR antenna
Pi-SAR (NICT/JAXA)

10. Optic sensor and microwave sensor
Optic sensor　 ：employed wavelength is recognized by human eyes
　　　　　　　　　　　　　　　　　　　Sun light scattering  easy to recognize
　Microwave sensor ：wavelength is cm order  difficult to recognize
　　　　　　　　　　　　　　　　　　　Mechanism of backscattering  complicated
　　　　　　　　　　　　　　　　　　　Image distortion
Mount Fuji : JERS-1 / OPS
Mount Fuji : JERS-1 / SAR

11. Microwave characteristics
Wave expression : phase and amplitude
Electromagnetic fields vibrate as the function of time when observed in one point in the space
Space distribution of electromagnetic fields is the function of space when time is fixed
amplitude
wavelength
electric field
electric field
time（ｔ）
phase：f
space （ｘ）
Time changing signal can be expressed as space function by using variable of amplitude and phase df
wave expression：　F(t)=exp[2pift] f : frequency　
= f dt

12. Wavelength Domain of Microwave
10GHz GHz
0.2mm mm mm mm cm m
Band
Wavelength （ｍｍ）
Frequency（ＧＨｚ） Ka
7.5 ~ 11.0
40.0 ~ 26.5 K
11.0 ~ 26.7
26.5 ~ 18.0 Ku
16.7 ~ 24.0
18.0 ~ 12.5 X
24.0 ~ 37.5
12.5 ~ 8.0 C
37.5 ~ 75.0
8.0 ~ 4.0 S
75.0 ~ 150
4.0 ~ 2.0 L
150 ~ 300
2.0 ~ 1.0 P
300 ~ 1000
1.0 ~ 0.3
Visible　　　 　　　　　　　　　　　　　　　　　　　　　　Microwave
IR NIR 　　　　　　　　　　　　　　　　　　　　　　　　　　　　KaKuX C S L P
Wavelength domain of electromagnetics and definition
100
Atm. Pen.　% 50
0.2mm mm mm mm cm m
wavelength
Atmospheric penetration ratio

13. Reflection and Penetration of Microwave
incident wave
scattering wave
Relationship of scattering and penetration q q
ratio of scattered and penetrated wave :　
effect of dielectric constant
mirror / corner reflection : 　
effect of surface roughness
penetrated wave q`

14. Reflection and Penetration of Microwave
corner reflection
water / sea surface :
high dielectric constant
perfectly scattering / corner reflection
black color on SAR image
Krakatau volcano complex, Indonesia

15. Reflection and Penetration of Microwave
Effect of earth’s surface :
　　　Ｒａｙｌｅｉｇｈ conditions ： h≦l/(8 cos q) →　standard of smooth surface
　　　　　　　　in case of ＪＥＲＳ－１： l=0.23m, q=38o
　　　　　　　　　　Conditions to satisfy ① ：　h≦3.65 cm
① smooth surface
② slightly rough surface
③ rough surface
Illustration of microwave scattering by earth’s surface

16. Krakatau volcano complex, Indonesia
③ rough surface
① smooth surface
② slightly rough surface
Krakatau volcano complex, Indonesia

17. Scattering of microwave : surface scattering and volume scattering
(a) scattering on the boundary surface (different dielectric constant )
(b) scattered wave is reflected to different direction from incident wave　　　　　　　　
　Volume scattering　　
(a) Penetrated electromagnetic wave is traped in the dielectical material
(b) Scattered wave in object on the earth’s surface (i.e. forest)

18. Scattering of microwave : surface and volume scatterings
Scattering Models
vegetation (forest)
icy river
surface scattering
surface scattering
volume scattering
volume scattering
surface scattering
surface scattering
dried sandy area
surface scattering
volume scattering
surface scattering

19. Polarizations Linier polarization Linier polarization
Horizontal polarization
Circular Pol.
Left handed circular polarization（ＬＨＣＰ）

20. SAR History 1953 Carl Wiley (Good Year Corporation) invented SAR
1960s Civil application : archeology, real aperture interferometry
SEASAT (NASA) : 25m resolution, L band
1980s ALMAZ (Soviet), Shuttle Imaging Radar (SIR)(NASA)
ERS-1 (ESA), Interferometry, C band
1992 JERS-1 (JAXA), 12.5m resolution, L band
RADARSAT (RSI)
1999 SRTM, single pass interferometry, 80% continental coverage
2002 ENVISAT (ESA)
2006 ALOS

21. SARs Specification ERS-1 JERS-1 RADARSAT ENVISAT ALOS Launched date
April 1991
February 1992
November 1995
March 2002
January 2006
Height
785 km
568 km km
799.8 km km
Inclination angle
98.5 degrees
97.7 degrees
98.6 degrees
98.55 degrees
98.16 degrees
Frequency
5.3 GHz (C band)
1.275 GHz (L band)
5.331 GHz ( C band)
1.27 GHz (L band)
Wavelength
5.7 cm
23.5 cm
5.6 cm
23.6 cm
Polarization VV HH
HH, VV, HH+VV, VV+VH, HH+HV
HH, VV, HH+HV, VV+VH, HH+VV+ HV+VH
Off-nadir angle
20 degrees
35 degrees
degrees
degrees
degrees
Incident angle
23 degrees
38.7 degrees
degrees
degrees
degrees
Swap width
100 km
75 km km km km
Azimuth resolution
30 m
18 m (3 looks) m m m
(2 looks) m
(multi looks)
Range resolution
18 m m
Peak Power
4.8 kW
325 W (1.3 kW spec)
5 kW
1.4 kW
2.3 kW
Bandwidth
19 MHz
15 MHz
11.6/17.3/30.0 MHz
MHz
14 MHz/28MHz
Antenna size
1 x 10 m
2.2 x 12 m
1.5 x 15 m
1.3 x 10 m
3.1 x 8.9 m

22. wave illuminating pattern
Basic Theory of SAR : Antenna
wave illuminating pattern
L=11.92 m
b=2.2 m
‘half value’
JERS-1 SAR antenna
b : antenna length in range direction
L : antenna length in azimuth direction
a : half value in range direction (JERS-1 : 5.3o)
b : half value in azimuth direction (JERS-1 : 1.0o)

23. Basic Theory of SAR : Antenna
sensor/antenna L P1 P0
side lobe
main lobe b0 1
1/2 y x z b a0
Definition of half value :
Po : power in the center of main lobe
P1 : power in the peripheral of main lobe
The half value is defined by ‘P1 is attenuated to 3 dB (equally 50%) of Po’.
10log10Po/P1=3 dB or
P1=0.5P0

24. Basic Theory of SAR : Radar Equation
To realize the relationship between radar received power and characteristic of scatterer.
A : effective surface of the receiver’s antenna
G : gain
: radar cross section or back scatterer surface
Pt : transmitted power
Ps : scattered power
Pr : received power
Pr=PsA/4pR2
Ps=PtG/4pR2s Pt
antenna R
attenuation by spreading of wave = 1/4pR2
PtG/4pR2
Scatterer
Pr=Ps A/4pR2=PtGAs/(4pR2)2

25. peak power×pulse width
Pulse radar
Pulse power
(Transmitted power） ||
peak power×pulse width
sensor / antenna 22 20 1 21 18 2 19 17 20 3 18 16 19 4 17 5
JERS-1 SAR antenna 15 18 16 6 17 14 15 7
propagation of transmitted pulse 16 13 8 14 15 9 12 13
Rn : slant range length at near range
Rf : slant range length at far range
Time to receive the pulse by antenna :
Near range side (start to receive) : 2Rn/C
Far range side (end of receiving) : 2Rf/C+τ
Continuity time of received pulse :
T=(2Rf /C+τ)-2Rn/C 14 10 11 12 13 11 10 11 12 12 Rn
tree
house Rf
concrete building
（a）Pulse front wave
Transmitted pulse
received signal
concrete building’s echo
Signal intensity
house’s echo
tree’s echo
time
Pulse width τ
（ｂ）Time flows of transmit & received signal

26. Flowchart of SAR Signal Processing
Start
Parameter calculation
Doppler center frequency
Range compression
Corner turn
Azimuth compression
Output image

27. range compressed image azimuth compressed image
Flowchart of SAR Signal Processing
Range
JERS-1 satellite
Azimuth
corner turn
North
raw data
range compressed image
North
sensor illumination
azimuth compressed image
rotated image

28. A B A B

29. DR ct q q
earth’s surface q Dx

31. frequency MHz
1282.5
1275.0
Df=15 MHz
1267.5

32. 1/Df 1/Df time t t reference signal output signal time
pulse length (t) A B C
transmitted pulse
received pulse
time t t
reference signal
output signal
1/Df
time A B C
1/Df

35. L
b=l/L R P d

40. Az Az
t=0
t=0 R R Az
t=0 R

42. R Az

55. Multi scattering length 3.910m (a) bridge’s architecture figure 2 1
Akasikaikyo bridge (
length 3.910m
(a) bridge’s architecture figure 2 1
(b) SAR image’s signature 1 2
wire
sea surface
(c) scattering mechanism