Scattering and Doppler Spectral Analysis for Two-Dimensional Linear and Nonlinear Sea Surfaces
Scattering and Doppler Spectral Analysis for Two-Dimensional Linear and Nonlinear Sea Surfaces
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二维线性和非线性海面的散射和多普勒频谱分析
DOI：
10.1109/tgrs.2010.2060204
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发表时间：
2011-02-01
影响因子：
8.2
通讯作者：
Xu, Xiaojian
中科院分区：
文献类型：
--
作者：
Li, Xiaofei;Xu, Xiaojian
将二维线性和二阶Creamer [Creamer（2）]非线性海面模型与二阶小斜率近似方法相结合，对比研究了海面的电磁散射和多普勒频谱特性。由于非线性流体动力学的影响，对于偏离镜面方向的散射角，Creamer（2）表面计算的双站归一化雷达散射截面（NRCS）略大于线性表面，Creamer（2）表面后向散射系数也随着风向角的增加而增加，而对于逆风方向，值得注意的是，观察结果是相反的。然而，正如Toporkov在一维表面情况下所指出的，非线性表面模型对平均NRCS的影响是微小的。特别是，后向散射回波的多普勒频谱比较线性和Creamer（2）表面在不同的入射角。正如所预期的那样，二维Creamer（2）曲面的多普勒频移和谱宽与线性曲面的多普勒频移和谱宽有很大不同，这与一维的情况是一致的。然而，对于较大的入射角，Creamer（2）表面的多普勒频谱展宽并不像以前使用全Creamer模型的一维研究中报告的那样严重。这种差异的原因似乎是克里默（2）近似的简化性质。此外，对不同风向下的多普勒特征的研究表明，非线性效应随着风向的改变而减弱。
Two-dimensional linear and second-order Creamer [Creamer (2)] nonlinear sea-surface models are combined with the second-order small-slope approximation method to comparatively study the electromagnetic scattering and the Doppler spectral characteristics from sea surfaces. Due to nonlinear hydrodynamics, the bistatic normalized radar cross section (NRCS) calculated from Creamer (2) surfaces is slightly larger than its linear surface counterpart for scattering angles departing from the specular direction, and the Creamer (2) surface backscattering coefficient increases as well for wind direction angles around upwind and downwind, whereas, for the crosswind direction, it is interesting to note that the observations are contrary. However, as was pointed out by Toporkov in a 1-D surface case, the effect of the nonlinear surface model on the average NRCS is minute. In particular, the Doppler spectra of the backscattered echoes are compared for the linear and Creamer (2) surfaces at various incident angles. It is seen, as expected, that the Doppler shifts and spectral widths of 2-D Creamer (2) surfaces exhibit different features compared with those of the linear surfaces, agreeing with the 1-D cases. However, for larger incident angles, the Doppler spectral broadening for Creamer (2) surfaces is not as severe as was reported in previous 1-D studies that used full Creamer model. The reason for this discrepancy appears to be the reduced nature of the Creamer (2) approximation. Moreover, studies of the Doppler characteristics for different wind directions demonstrate that nonlinear effects become weaker as the wind direction varies from upwind to crosswind.