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TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory 1
RAIN EFFECT ON POLARIMETRIC RAIN EFFECT ON POLARIMETRIC SAR OBSERVATIONSAR OBSERVATION
Hiroaki Yasuma and Hajime FukuchiTokyo Metropolitan UniversityDept. of Aerospace Engineering
July 28, 2010
RemoteTMU
Sensing Lab.RemoteTMU
Sensing Lab.RemoteTMU
Sensing Lab.RemoteTMU
Sensing Lab.RemoteTMU
Sensing Lab.RemoteTMU
Sensing Lab.
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INTRODUCTION (1)
Distortions in the SAR observational data come from various factors.
Absorptionby the atmosphere
( oxygen, water vapor, and so on. )
Scatteringby 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 )
ObservationFrequency
Example of SAR
MeteorologicalParticle FR
X-BandTerraSAR-X(9.65 GHz) Important
Negligible
Negligible
Important
C-BandRADARSAT-2
(5.405GHz)
L-BandPALSAR(1.27GHz)
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INTRODUCTION (2)
➣ High-frequency and high-resolution SAR such as TerraSAR-X (9.65GHz, 1m resolution) is successfulthese days.
➣ As frequency increases,
the rain effects cannot be ignored.
➣ Quantitative evaluations of these effects are scarce and thus needed.
TerraSAR-X. © EADS Astrium
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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.
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➣ 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
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POLSAR OBSERVATION MODEL
NTFPQSQPFRM t
The scattering matrix S sequentially receives turbulence in the propagation route.
t
Ice Layer P: Ice Distortion Matrix
Ionosphere F: Faraday Rotation
Receive Antenna RTransmit Antenna T
Rainfall Q: Rain Distortion Matrix
Land Surface S: Scattering Matrix
When rainfall isthe only error source
QSQM
VVVH
HVHH
VVVH
HVHH
VVVH
HVHH
VVVH
HVHH
QQQQ
SSSS
QQQQ
MMMM
If Q is computable with already known S,M can be obtained
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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.
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THE MAJOR THREE EFFECTS BY RAIN
1.Attenuation: |QHH|
Because of the scattering and absorption by the rain drops
2.Attenuation Ratio: |QVV /QHH|
Because of the non-spherical rain drop shape
3.Depolarization: |QHV /QHH|
Because of the non-spherical rain drop shape and
the canting angle of the rain drop
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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: |QVV /QHH|
Incident waves
Attenuated waves
H passes through the rain drop more than V.Rain drop
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DEPOLARIZATION
➣ The depolarization occurs because of the non-spherical rain drop shape and the canting angle of the rain drop.
➣ |QHV /QHH| represents the amount of this depolarization.
Incident wave
Attenuated wave
Canting angle
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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)
VVVH
HVHH
SSSS
1001
* 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. 41-51, 1977.
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0
1
2
3
4
5
6
7
0 20 40 60 80 100
Rain rate [mm/h]
13.9GHz9.65GHz5.405GHz
12
ESTIMATION RESULTS:RAIN-INDUCED ATTENUATION
Canting angle: 0°
➣ |QHH| represents the amount of the rain-induced attenuation.
Rai
n A
tten
uati
on [
dB/k
m]
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11.11.21.31.41.51.61.71.81.9
0 20 40 60 80 100Rain rate [mm/h]
Att
enua
tion
Rat
io 13.9GHz9.65GHz5.405GHz
13
ESTIMATION RESULTS: ATTENUATION RATIO
Canting angle: 0°
➣ |QVV /QHH| represents the attenuation ratio between H and V.
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0
0.1
0.2
0.3
0.4
0.5
0.6
0 20 40 60 80 100Rain rate [mm/h]
Dep
olar
izat
ion 13.9GHz
9.65GHz5.405GHz
14
ESTIMATION RESULTS: DEPOLARIZATION
Canting angle: 45°
➣ |QHV /QHH| represents the amount of the depolarization.
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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)
VVVH
HVHH
SSSS
1001
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Trihedral (or Plate) Reflector: S=
1001
Co-pol. Cross pol.Ideal
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Trihedral (or Plate) Reflector: S=
1001
5.405 [GHz]Co-pol. Cross pol.
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Trihedral (or Plate) Reflector: S=
1001
Co-pol. Cross pol.9.65 [GHz]
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Trihedral (or Plate) Reflector: S=
1001
Co-pol. Cross pol.13.9 [GHz]
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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.
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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. 3507-3518, 2009.
➣ 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. 41-51, 1977.