TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 1 RAIN EFFECT ON POLARIMETRIC SAR OBSERVATION Hiroaki Yasuma and Hajime Fukuchi Tokyo Metropolitan University Dept. of Aerospace Engineering July 28, 2010

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 2 INTRODUCTION (1) Distortions in the SAR observational data come from various factors. Absorption by the atmosphere （ oxygen, water vapor, and so on. ） Scattering by the weather particle （ Rain, snow, fog, and hail, etc. ） It is essential to know the radio propagation characteristics. Faraday Rotation (FR) （ Phenomenon of polarization rotation ） Observation Frequency Example of SAR Meteorological Particle FR X-Band TerraSAR-X (9.65 GHz) Important Negligible Important C-Band RADARSAT-2 (5.405GHz) L-Band PALSAR (1.27GHz)

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 3 INTRODUCTION (2) ➣ High-frequency and high-resolution SAR such as TerraSAR-X (9.65GHz, 1m resolution) is successful these days. ➣ As frequency increases, the rain effects cannot be ignored. ➣ Quantitative evaluations of these effects are scarce and thus needed. TerraSAR-X. © EADS Astrium

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 4 IN CASE OF TerraSAR-X Excerpt from “On The Impact of Precipitation on Space-borne SAR Imaging: Recent Measurement with TerraSAR-X”, Andreas Danklmayer, Madhukar Chandra.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 5 ➣ Give the POLSAR observation model and estimate the effects at several conditions: PURPOSE OF RESEARCH Evaluate the effects of rain quantitatively ・ Observation frequency ・ Rainfall rate ・ Incident angle ・ Canting angle of rain drops ・ Rain area length

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 6 POLSAR OBSERVATION MODEL The scattering matrix S sequentially receives turbulence in the propagation route. Ice Layer P: Ice Distortion Matrix Ionosphere F: Faraday Rotation Receive Antenna R Transmit Antenna T Rainfall Q: Rain Distortion Matrix Land Surface S: Scattering Matrix When rainfall is the only error source If Q is computable with already known S, M can be obtained

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 7 THE RAIN EFFECT AREA ➣ The radio wave is absorbed and scattered by rain drops in area A. SAR Rainfall Area A Rain drops Rainfall SAR Area B ➣ Rain drops in area B promote the additional backscatter as well.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 8 THE MAJOR THREE EFFECTS BY RAIN 1.Attenuation: |Q HH | Because of the scattering and absorption by the rain drops 2.Attenuation Ratio: |Q VV /Q HH | Because of the non-spherical rain drop shape 3.Depolarization: |Q HV /Q HH | Because of the non-spherical rain drop shape and the canting angle of the rain drop

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 9 ATTENUATION RATIO ➣ The horizontal polarization (H) is attenuated more greatly than the vertical one (V) because of the non- spherical rain drop shape. ➣ Attenuation ratio between H and V: |Q VV /Q HH | Incident waves Attenuated waves H passes through the rain drop more than V. Rain drop

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 10 DEPOLARIZATION ➣ The depolarization occurs because of the non- spherical rain drop shape and the canting angle of the rain drop. ➣ |Q HV /Q HH | represents the amount of this depolarization. Incident wave Attenuated wave Canting angle

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 11 ESTIMATE THE RAIN DISTORTION MATRIX (Q) ➣ Calculation Condition: Derivation of Q: Oguchi’s method* Rain Shape: Pruppacher-and-Pitter Drop Size Distribution: Marshall-and-Palmer Rain Area Length: 5 km Incident Angle: 40° Canting Angle:0 ° or 45 ° Scattering Matrix : (Plate or Trihedral)       * Tomohiro Oguchi, “Scattering properties of Pruppacher-and-Pitter form rain drops and cross polarization due to rain: Calculation at 11, 13, 19.3 and 34.8GHz,” Radio Science, vol. 12, no. 1, pp , 1977.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 12 ESTIMATION RESULTS: RAIN-INDUCED ATTENUATION Canting angle: 0° ➣ |Q HH | represents the amount of the rain-induced attenuation. Rain Attenuation [dB/km]

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 13 ESTIMATION RESULTS: ATTENUATION RATIO Canting angle: 0° ➣ |Q VV /Q HH | represents the attenuation ratio between H and V.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 14 ESTIMATION RESULTS: DEPOLARIZATION Canting angle: 45° ➣ |Q HV /Q HH | represents the amount of the depolarization.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 15 ESTIMATION RESULTS: POLARIZATION SIGNATURE ➣ Calculation Condition: Rain rate: 50 [mm/h] Canting Angle:22.5° Derivation of Q: Oguchi’s method Rain Shape: Pruppacher-and-Pitter Drop Size Distribution: Marshall-and-Palmer Rain Area Length: 5 km Incident Angle: 40° Scattering Matrix : (Plate or Trihedral)       10 01

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 16 Trihedral (or Plate) Reflector: S= Co-pol.Cross pol. Ideal

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 17 Trihedral (or Plate) Reflector: S= [GHz] Co-pol.Cross pol.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 18 Trihedral (or Plate) Reflector: S= Co-pol.Cross pol [GHz]

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 19 Trihedral (or Plate) Reflector: S= Co-pol.Cross pol [GHz]

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 20 CONCLUSIONS ➣ The rain effect on POLSAR observation was quantitatively evaluated using the SAR observation model in non-spherical rain drop environments. ➣ The results show that the rain attenuation, the attenuation ratio and the depolarization increase as the frequency and rainfall rate increase, and that they also depend on the rain drop canting angle.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 21 REFERENCES ➣ Andreas Danklmayer, Madhukar Chandra, “On The Impact of Precipitation on Space-borne SAR Imaging: Recent Measurement with TerraSAR-X” ➣ Andreas Danklmayer, Bjorn J. Doring, Marco Schwerdt, and Madhu Chandra, “Assessment of Atmospheric Propagation Effects in SAR Images,” IEEE Trans. Geosci. Remote Sensing, vol. 47, pp , ➣ Tomohiro Oguchi, “Scattering properties of Pruppacher-and- Pitter form rain drops and cross polarization due to rain: Calculation at 11, 13, 19.3 and 34.8GHz,” Radio Science, vol. 12, no. 1, pp , 1977.