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

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

References

References

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

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 : http://southport.jpl.nasa.gov/nrc/chapter7.html

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 : http://southport.jpl.nasa.gov/nrc/chapter7.html

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° http://alos.nasda.go.jp/

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)

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

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

Wavelength Domain of Microwave 10GHz 1GHz 0.2mm 1.0mm 10mm 1mm 10cm 1m 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 1.0mm 10mm 1mm 10cm 1m wavelength Atmospheric penetration ratio

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`

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

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

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

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)

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

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

SAR History 1953 Carl Wiley (Good Year Corporation) invented SAR 1960s Civil application : archeology, real aperture interferometry 1978 SEASAT (NASA) : 25m resolution, L band 1980s ALMAZ (Soviet), Shuttle Imaging Radar (SIR)(NASA) 1991 ERS-1 (ESA), Interferometry, C band 1992 JERS-1 (JAXA), 12.5m resolution, L band 1995 RADARSAT (RSI) 1999 SRTM, single pass interferometry, 80% continental coverage 2002 ENVISAT (ESA) 2006 ALOS

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 793 - 821 km 799.8 km 691.65 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 9 - 48 degrees 13.5 - 39 degrees 10 - 51 degrees Incident angle 23 degrees 38.7 degrees 10 - 60 degrees 15 - 45 degrees 8 - 60 degrees Swap width 100 km 75 km 50 - 500 km 56.5 - 104.8 km 20 - 350 km Azimuth resolution 30 m 18 m (3 looks) 9 - 147 m 30 - 1000 m 10 - 100 m (2 looks) 7 - 100 m (multi looks) Range resolution 18 m 6 - 147 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 8.48 - 16 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

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)

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

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

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 0 2 4 6 8 10 12 14 16 18 20 22 24 time Pulse width τ （ｂ）Time flows of transmit & received signal

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

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

A B A B

DR ct q q earth’s surface q Dx

frequency MHz 1282.5 1275.0 Df=15 MHz 1267.5

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

L b=l/L R P d

Az Az t=0 t=0 R R Az t=0 R

R Az

Multi scattering length 3.910m (a) bridge’s architecture figure 2 1 Akasikaikyo bridge (http://www.oshimastudio.com) length 3.910m (a) bridge’s architecture figure 2 1 (b) SAR image’s signature 1 2 wire sea surface (c) scattering mechanism