Chiba University Signal Processing Synthetic Aperture Radar Josaphat

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 n Microwave Sensor n Active Sensor n Imaging Radar 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 → In. SAR 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

Introduction SEASAT (1978) SIR-A (1981) SIR-B (1984) SIR-C (1994) 1 1, 5 Polarization HH HH, HV, VH, VV Look angle 20 o 50 o 20 o – 60 o Analog data Digital data Central Transmitter/ Receiver Distributed T/R modules Fixed antenna beam Mechanical beam steering Electronic beam steering Frequency (GHz) Pictures : http: //southport. jpl. nasa. gov/nrc/chapter 7. html

Introduction ERS-1 (1991) Frequency 5 (C band) (GHz) JERS-1 (1992) Radarsat (1995) 1. 275 (L band) 5 (C band) Polarizatio n VV HH HH Look angle 20 o 35 o 20 o – 60 o Pictures : http: //southport. jpl. nasa. gov/nrc/chapter 7. html

Introduction Specification of ALOS-PALSAR Main Observation Mode High Resolution Mode Observation Frequency SCAN SAR L-band(1. 27 GHz) Polarization HH, VV, HH&HV, VV&VH HH, VV Ground Resolution 10 m 100 m Look numbers 2 8 Swap area 70 km 250～ 350 km Off Nadir Angle 10～ 51° http: //alos. nasda. go. jp/

Satellite-onboard ＳＡＲ and flat-ground geometric system a enn sen rm tfo e dir so nt r/a hori ①： off-nadir angle zon tal d n ctio （look angle) irec t ion ②：depression angle ② pla ③：range beam width sla ① n ctio uth e dir an ge ③ ran ge dire m azi Grou nd r ange nt r ctio n ④ dir ec tio n ⑤：azimuth beam width ⑤ far range near range target JERS-1 SAR antenna ④：incidence angle 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 electric field time（ｔ） phase：f wavelength electric space （ｘ） field Time changing signal can be expressed as space function by using variable of amplitude and phase wave expression： F(t)=exp[2 pift] f : frequency df = f dt

Wavelength Domain of Microwave 10 GHz 0. 2 mm 1. 0 mm 1 mm 10 cm Visible IR 1 GHz 1 m Microwave NIR Ka. Ku. X C S L P Wavelength domain of electromagnetics and definition Atm. Pen. % 100 50 0 0. 2 mm 1. 0 mm 1 mm wavelength Atmospheric penetration ratio 10 cm 1 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

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

Reflection and Penetration of Microwave corner reflection water / sea surface : high dielectric constant perfectly scattering / reflection corner 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. 23 m, q=38 o 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

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

Scattering of microwave : surface scattering and volume scattering n Surface scattering (a) scattering on the boundary surface (different dielectric constant ) (b) scattered wave is reflected to different direction from incident wave n 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 volume scattering surface scattering dried sandy area surface scattering volume scattering surface scattering

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

SAR History 1953 Carl Wiley (Good Year Corporation) invented SAR 1960 s Civil application : archeology, real aperture interferometry 1978 SEASAT (NASA) : 25 m resolution, L band 1980 s ALMAZ (Soviet), Shuttle Imaging Radar (SIR)(NASA) 1991 ERS-1 (ESA), Interferometry, C band 1992 JERS-1 (JAXA), 12. 5 m 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. 3 GHz (C band) 5. 331 GHz ( C band) 1. 27 GHz (L band) Wavelength 5. 7 cm 23. 5 cm 5. 7 cm 5. 6 cm 23. 6 cm Polarization VV HH 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 Range resolution 30 m 18 m 6 - 147 m Peak Power 4. 8 k. W 325 W (1. 3 k. W spec) 5 k. W 1. 4 k. W 2. 3 k. W Bandwidth 19 MHz 15 MHz 11. 6/17. 3/30. 0 MHz 8. 48 - 16 MHz 14 MHz/28 MHz 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 30 - 1000 m 10 - 100 m (2 looks) 7 - 100 m (multi looks)

Basic Theory of SAR : Antenna wave illuminating pattern m b=2. 2 m L . 92 =11 ‘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. 3 o) b : half value in azimuth direction (JERS-1 : 1. 0 o)

Basic Theory of SAR : Antenna y Definition of half value : side lobe main lobe Po : power in the center of main lobe 1 1/2 x sensor/antenna L b 0 P 1 P 0 z L The half value is defined by ‘P 1 is attenuated to 3 d. B (equally 50%) of Po’. 10 log 10 Po/P 1=3 d. B y or P 1=0. 5 P 0 a 0 b P 1 : power in the peripheral of main lobe x

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

Pulse radar 0 22 1 20 21 18 2 19 20 17 18 16 sensor / antenna propagation of transmitted pulse 3 4 19 17 JERS-1 SAR antenna 5 18 15 6 16 17 7 14 15 16 8 13 14 9 15 12 13 10 14 11 11 12 13 10 12 11 12 tree house concrete （a）Pulse front wave building received signal Rn Transmitted pulse Rf Pulse power (Transmitted power） || peak power×pulse width 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) : 2 Rn/C Signal intensity Far range side (end of receiving) : 2 Rf/C+τ Continuity time of received pulse : concrete building’s echo house’s echo tree’s echo 0 2 Pulse width τ 4 6 8 10 12 14 16 18 20 T=(2 Rf /C+τ)-2 Rn/C 22 24 time （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

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

A B

q earth’s surface ct DR q q Dx

frequency MHz 1282. 5 1275. 0 1267. 5 Df=15 MHz

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

L b=l/L R P d

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

R Az

Multi scattering Akasikaikyo bridge (http: //www. oshimastudio. com) length 3. 910 m (a) bridge’s architecture figure 2 1 (b) SAR image’s signature 1 2 wire sea surface (c) scattering mechanism