降雨对Ku波段旋转扇形波束散射计影响

星载散射计测量的归一化后向散射截面是有关海面毛细重力波的大小和方向的函数:散射计的回波强度与海面毛细重力波的振幅成正比;风向对后向散射系数具有调制作用。因此,可以利用散射计的数据,根据地球物理模型反演出具有高精确度、无雨和中低风速条件下的海面风场矢量。然而高达10%的散射计测量数据会受到降雨影响(Nie,etal.,2008),尤其工作在Ku波段的散射计。降雨对海面散射幅度的影响主要包括:(1)降雨对雷达波的衰减和散射;(2)降雨改变海洋水面形态和海面粗糙度。

Impact of rainfall on a Ku-band rotating fan-beam scatterometer

The effects of rainfall backscattering on space-borne rotating fan-beam scatterometer measurements at Ku-band were investigated in this study. A new scattering model based on Integral Equation Method (IEM) for sea surface with precipitation that accounts for the effects of rain column was presented. The relation between rain scattering and incidence was analyzed, and hence the rain effects on a rotating fan-beam scatterometer are obtained. The rain column is modeled as sublayers with different physical characteristics determined by the vertical profile of rainfall. Each sublayer is assumed to be statistically homogeneous, and the gamma distribution is used to model the drop size distribution within each sublayer. Sea surface is modeled as a rough surface, and its backscattering is calculated using the IEM model. Multiple scattering within and interactions between the rain layers and sea surface are accounted for in the matrix doubling formulation. The presented model is validated using published TRMM PR measurements. Results from model analyses show that rain effects are incident angle dependent, which can lead to non-uniform impacts within the footprint of a fan-beam scatterometer; these effects are strongly related to rain column vertical profile and rain rate, as different rain rate corresponds to different physical parameters.