WE3.L09 - RAIN EFFECT ON POLARIMETRIC SAR OBSERVATION

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.


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)


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


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.


➣ 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


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


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.


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


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


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


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.

TOKYO METROPOLITAN UNIVERSITY Remote Sensing Laboratory

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]


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.


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.


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


Trihedral (or Plate) Reflector: S=

1001

Co-pol. Cross pol.Ideal



1001

5.405 [GHz]Co-pol. Cross pol.



1001

Co-pol. Cross pol.9.65 [GHz]



1001

Co-pol. Cross pol.13.9 [GHz]


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.


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.

WE3.L09 - RAIN EFFECT ON POLARIMETRIC SAR OBSERVATION

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