1. Introduction to Synthetic Aperture Radar(SAR) Imaging
Jeong-Hee Choi, Ph.D.
Assistant Professor
Department of Computer and Communication
Taegu University
Tel : , Fax :
Web:

2. OVERVIEW
SAR System 개요
SAR Imaging System 특징
SAR 기술구성
SAR/ISAR System Classification
SAR System 구성도
Frequency Bands
SAR System Applications
Range/Cross range Imaging Raw-data Processing 원리
Existing SAR Systems
SAR Images

3. Imaging Geometry of a Radar Imaging System

4. Synthetic Aperture Radar의 특징장점
기존의 레이다와 비교하여 Cross Range의 해상도를 얻음으로써 영상정보추출 가능 : (Range • 파장) / Aperture size
카메라 영상이 단면 사진인데 반해 Topographic Image합성 가능
Active Instrument : 카메라 영상이 태양빛에 의존하는 반면 밤에도 촬영가능 ((Day or Night Imaging Capability)
Microwave 는 구름이나, 안개등에 무관하여 흐린 날이나 화산폭발장면도 촬영가능 (All weather Imaging Capability)
따라서 연속적인 환경 Monitoring 가능함 단점
단면 카메라 영상에 비해 해상도가 떨어짐. Eg) 나무, 차, 건물 등이 한 두개의 pixel로 나타남
정확한 Coherent Measurement가 필수 Suffer from Speckle

5. Synthetic Aperture Radar 기술 구성
Hardware
Radar Antenna
Phased Array
Local Oscillator
Pulse Generator
Analogue-to-Digital Converter, etc.
Multi-dimensional Signal Processing
Raw-data processing
Radiometric Calibration
Geometric Calibration
Modeling & Inversion
Image Enhancement
Sharpen Image for better Recognition
Image Transformation
Graphics/ Mapping
Image Interpretation

6. SAR Imaging System Classification
Relative Motion of Radar and Target area
SAR
ISAR
Mounting Vehicle
Spaceborne SAR
Airborne SAR
Radar Flight Motion
Linear SAR
Circular SAR
Beam Illumination
Spotlight Mode SAR
Stripmap Mode SAR
Transmitter/Receiver Status
Monostatic SAR
Bistatic SAR
Multistatic SAR
Advancement
Interferometric SAR
Polarimetric SAR

7. System Geometry for SAR Imaging

8. System Geometry for ISAR Imaging

9. System Geometry in Circular SAR Imaging
Side View
Top View

10. System Geometry in Stripmap SAR Imaging

11. Spotlight SAR : Electronic Beam Steering

12. Data Acquisition System for Quasi-Monostatic SAR/ISAR Imaging

13. Frequency Bands
Note : 파장(meter) = C/주파수(Hz=Cycles/sec), C = 광속

14. Applications of Synthetic Aperture maging
상용 시스템
지표면, 해표면, 해저면의 Topographic Image
농작물 분포 및 생태계 변화, Sea Ice, Oil Spill 등 환경 Monitoring
지하자원/유적 탐사
비행기 자동착륙 및 항공 Traffic Control
행성의 입체영상
군용 Radar 시스템
비행 정찰
미사일 탐지 및 추적 (ISAR)
FOPEN SAR
(Foliage Penetration SAR) 기타
Diagnostic medicine
기계 내부의 Non-destructive testing

15. Range Imaging 원리 • System Model ◦ Measured Echoed Signal
: Transmitted Radar Signal
: Target’s Reflectivity
: Target’s Range
: Propagation Speed
• Frequency Domain Representation

16. System Geometry for Range Imaging

18. Point Spread Function
• Target Reconstruction
where range mapping is defined by
• Reconstruction Via Matched Filtering

20. Signal Processing ◦ Frequency Domain Support Band of Radar signal
Dictates Time Domain Sampling
: Carrier Frequency
: Baseband Bandwidth
Range Resolution
Range Resolution을 좋게 하기위해서 송신신호의 대역폭이 넓을수록 유리함
따라서 레이다의 송신신호로 Chirp pulse 신호를 사용함.

22. ◦ Spatial Domain Support Band of Target Function
Dictates Time Domain Measurement Interval
: Radar Swath’s Mean Range
: Target Area’s Size
: Radar Signal Pulse Duration
Measuring Time Interval

23. Cross-Range Imaging 의 원리(Spotlight SAR예)
◦ Radar Distance from a Target at
◦ Measured Echoed Signal
◦ After Baseband Conversion
Cross-Range Imaging 의 원리(Spotlight SAR예)
◦ Consider Single Sinusoidal Source Signal,

24. Frequency Domain Representation of Measured Echoed Signal
Signature of Unit Reflector Target at
and its Fourier Transform

25. Finite Aperture Effect
만일 Synthesized Aperture 크기가 무한대라면 (L =  )
The support band of echoed data, in Doppler frequency domain
따라서 로 Band-limit된 신호의 Alias-free Sampling 간격 임.
실제로 Synthesized Aperture 는 유한하므로 n-th target에서 echo된
신호의 Doppler support 대역은
Finite Aperture Effect
Note :

26. ◦ Total Doppler Support Band of
◦ Cross-range Resolution
cf)
For Stripmap SAR
◦ Synthetic Aperture Domain Sampling
: Wavelength
◦ Pulse Repetition Interval =
Pulse Repetition Frequency(PRF)=1/PRI(Pulse Repetition Interval) =

27. Imaging System Geometry for Cross-range Imaging
(Broadside Target Area)

28. Imaging System Geometry for Cross-range Imaging
(Off-Broadside(Squint) Target Area)

29. Aspect Angle of a Target

30. Spotlight SAR Signal Spectrum Support

31. Slow-time Doppler Signature of a Target

32. Waveform approximation에 따른 SAR Image Reconstruction 기법들
Fresnel Approximation-based Reconstruction
: Range-Doppler Imaging
Plain Wave Approximation-based Reconstruction : Polar Format Processing
Wavefront (Spherical wave) reconstruction
* References :
 J. Curlander and R. McDonough, Synthetic Aperture Radar, Wiley, 1991
 M. Soumekh, Synthetic Aperture Radar Signal Processing with Matlab Algorithms, Wiley, 1999

33. SAR Imaging : Wavefront Reconstruction

34. (Fresnel Approximation-Based)
SAR Imaging : Range-Doppler Processing
(Fresnel Approximation-Based)

35. SAR Imaging : Polar Format Processing

38. Existed/Existing/Planned SAR Systems
군용 시스템
E-3 AWACS(Airborne Warning & Control System) : 걸프지역에서 공/해상의 Target Surveillance
E-8C joint STARS(Surveillance Target Attack Radar System):
걸프전에서 육상의 움직이는 Target Detection & Location
(NASA 의 우주선에 탑재한 것과 유사기종)
SEASAT
1978년 발사된 최초의 SAR 탑재 민간용 원격 탐사위성
L-band, HH polarized, 25m Az. Resolution, Incidence Angle :9-15도
SIR-A (Shuttle Imaging Radar):National Space Science Data Center/NASA
1981 Columbia 우주선 탑재, L-band, HH polarized
URL :

39. Existed/Existing/Planned SAR Systems (Cont.)
SIR-B, SIR-C (Radar Data Center, JPL)
1984 Challenger호 탑재, 1993년 이후 여러 우주선에 탑재,
L, C, and X-band, HH Polarized
URL :
JERS-1 : National Space Development Agency of Japan(NASDA)
1992년 위성탑재 SAR, L-band HH polarization, 18m Az. Resolution
Incidence Angle : 35도, URL :
ERS-1, ERS-2 : European Space Agency in Italy
1991, 1995년에 발사된 SAR 탑재위성, C-band, VV polarized,
30m Az. Resolution, Incidence Angle: 20-26도
URL :
Radarsat : Canada Center for Remote Sensing/Canadian Space Agency
1995 년 위성탑재 SAR, C-band, HH Polarization, m 해상도
Variable Incidence Angles : 도
URL :

40. Existed/Existing/Planned SAR Systems (Cont.)
NASA/JPL AIRSAR
DC-8 비행기에 탑재된 레이다
C, L, and P-band Inteferometric, Polarimetric SAR 시스템
0-70도의 큰 입사각 범위, 12m Az. Resolution
URL :
ENVISAT
2001년 6월 European Space Agency에 의해 발사/운용 예정인 위성탑재 레이다
URL :
ALOS(Advanced Land Observation System)
2002년 일본의 NASDA에 의해 발사 운용예정
L-band Full Polarimetric SAR 장착
URL :

41. Radar Image Distortion
Slant-range scale distortion
Foreshortening
Layover
Radar shadow