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
