backscattering  from  sea  surface  with  precipitation

BACKSCATTERING FROM SEA SURFACE WITH PRECIPITATION

Saibun Tjuatja, Li Jiamei, Dong Xiaolong

Wave Scattering Research CenterThe University of Texas at Arlington

&Chinese Academy of Sciences Center for Space Science and Applied

ResearchMicrowave Remote Sensing Laboratory

July 25, 2011

This work is supported in parts by the Chinese Academy of Sciences Visiting Professorships for Senior International Scientists Program

Objectives of this study

– A physics based backscattering model that accounts for the vertical profile of the rain column

– Quantitative link between geophysical parameters and backscattering measurements

94 GHz Radar Reflectivity and Doppler Velocity from CRS measurements (Li et al., 2004)

Physics Based Forward Modeling:Microwave scattering from sea surface with precipitation

Physical Parameters Model Parameters

Physical Structure Model Structure

A Scattering Model for an Inhomogeneous Layer with Vertical Profile

Rain Layer Parameters

• Vertical profile– modeled with 12 sublayers

• Rain rate:– 10.48 mm/h and 22.80 mm/h

• Drop size distribution:– average drop size– volume fraction– Drop shape: spherical

Vertical Profile (Average Drop Size) of Rain Column

profile A: R = 10.48 mm h-1

Volume fraction: 0.7500E-05

profile B: R = 22.80 mm h-1

Volume fraction: 0.8000E-05

Rain Rate

where

R =6π10−4 N D( )

0

∞

∫ D 3vt D( )dD mm h−1⎡⎣ ⎤⎦

vt D( )≈3.80D 0.67 m s−1⎡⎣ ⎤⎦

Drop Size Distribution

Gamma distribution:

N D( )=N0D

me−λD mm−1 m−3⎡⎣ ⎤⎦

Volume fraction of rain drops:

v f =

π6

D 3N D( )0

∞

∫ dD

Other Model Parameters

• Sea surface roughness (IEM model)

• Rain drop relative permittivity (at 13.6 GHz):

ks =0.3, kL=3.8

e =55−j30

Model Analyses

• Effects of precipitation at C- and Ku-Band• Effects of rain rates• Effects of drop average drop size at constant R• Effects of volume fraction with a constant

average drop size• Effects of snow & melting layer

Effects of Precipitation (R=10.48mm h-1 ) at C- and Ku-Band

Effects of Rain Rate

Effects of Drop Size with Constant R

Effects of Volume Fraction with a Constant Drop Size

Vertical Profile with Snow & Melting Layer

Effects of snow & melting layer

Summary & Conclusion• A scattering model for rain column above sea surface

which accounts for vertical profile was developed and qualitatively validated.

• Model analyses show that at R=10.48 mm/h, the effects of precipitation at C-Band is negligible at small incident angles

• At Ku-Band, key features for differentiating backscattering from sea surface with and without precipitation include:– angular trend – separation between VV and HH

Thank you