1 Wave Polarization, Polarimetric SAR, and Polarimetric Scattering Models Yisok Oh Dept. of Radio Engineering, Hong-Ik University 다음은 PACRIM Training Course (Workshop) 의 강의 Note 중에서 1.1 Wave Properties 만을 발췌한 것으로, 전파의 성질을 이해하는데 도움이 될 것입니다. Seoul National University, February 16-19, 2000

2 Contents 1.Wave Polarization 1.1 Wave Properties 1.2 Polarization Synthesis 2.Polarimetric Radar System 2.1 A Scatterometer System 2.2 NASA/JPL POLSAR System 3.Polarimetric Scattering Models 3.1 Surface Scattering 3.2 Volume Scattering

3 1.1 Wave Properties -. What is the “ Field ” ? -. Waves : Electromagnetic Waves by Maxwell -. Planewave Propagation in free space -. Polarization : Basic concepts -. Microwave Generation : DC to AC -. Microwave Guidance by Waveguides/ Trans. lines -. Microwave Radiation by Antennas -. EM Wave Reflection from infinite planes -. Microwave Scattering from -. Point Targets -. Distributed Targets

4 Electromagnetic Fields Fields: Spatial distribution of a physical quantity. Static Fields No time-variation Separation of Electric Field and Magnetic Field Electromagnetic Fields Time-varying Fields Dynamic Fields Co-existence of Electric and Magnetic fields : DC: AC

5 Electrostatic Fields E : Electric Field (showing flux lines) Assuming infinite plates, V Conducting Plates E d +-+- Direction of E : From + charges to - charges

6 Magnetostatic Fields IEEE Emblem I : Current H : Magnetic Field (showing flux line) voltage current Electric Fields Magnetic Fields Assuming an infinite current line, I H Direction of H : Right-hand rule,

7 Dynamic (Time-Varying) Fields Electromotive Force (Voltage Source) Conduction Current Displacement Current Maxwell ’ s Equations Time-varying Electric Field E(r,t) Time-varying Magnetic Field H(r,t)

8 Waves Consider Water wave in a pond. Cut water surface at once (t=t 0 ) with Kwan-Woo ’ s Sword (청룡언월도) and look X (Spatial Displacement) Wave Height Log the height of Fishing Buoy (x=x 0 ) as a time function t (Time) Wave Height Even though the wave comes toward me, the water doesn ’ t !

9 Electromagnetic (EM) Waves An Example of an EM wave: Magnitude (source, distance, etc.) Sinusoidal Wave Time Variation Z-directed propagation Vector (Polarization) Time z, distance

10 Phase Velocity = constant Same Phase Assume these circles are surfing boards. Phase velocity = velocity of the equi-phase point Poynting Vector: : Real Power Flow (Magnitude and Direction)

11 Time-Harmonic Fields Time-harmonic Assumption: Time variation (Maxwell Equation) z : wave prop. direction (Phasor form)

12 Planewave Propagation x y z HyHy ExEx Planewave: wavefront is plane Spherical wave near an antenna Approximate Planewave in the Far-zone Z-directed propagating Linear polarized (x-direction) Wave

13 Polarization : shape of the locus of the E vector tip at a given point in space as a function of time. Polarization Linear Circular Elliptical Other Cases ConditionsExamples

14 Exercise (determination of polarization) Find polarization of the wave, Find instantaneous electric field: Plot electric field: Determine polarization 2 1 Ex Ey Linear pol. with

15 Polarization Ellipse Lin. Pol. Circular Pol. = Rotation Angle = Ellipticity Angle

16 Various Polarization States Left Circular pol. Wave directionThumb Electric FieldOther fingers of left hand

17 Microwave Generation Oscillators TubesSolid State Klystron TWT Magnetron Gunn Diode MESFET HEMT, etc. High Power Light, Cheap D.C. Power Microwave (A.C.) Instability Resonator Amplifying A MESFET Oscillator:

18 Microwave Guidance Two Conductors Single Conductor No Conductor ( Transverse ElectroMagnetic) Waveguides Coaxial Cable Two-wire Microstrip Rectangular, Circular Waveguides Dielectric Waveguide TEM wave TE, TM waves (Optical fibers) E H direction A Coaxial Cable :

19 Microwave Radiation Dipole Antenna : Transmission Line (Wave guider) Radiator (Discontinuity) * Current : temporal Variation of charges

20 Antennas Wire Antenna Aperture Antenna Reflector Antenna Printed Antenna Microstrip Antenna Coaxial Cable Electric Field Lines

21 EM Wave Reflection x z Perpendicular Polarization Electric field is perpendicular to the incidence plane x z Parallel Polarization Electric field is parallel to the incidence plane Horizontal Polarization Electric field is horizontal to Earth surface Vertical Polarization Magnetic field is horizontal to Earth surface Infinite plane

22 Microwave Scattering Radar System Radar System Point Target Distributed Target where : Radar Cross Section : Scattering Coefficient