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海面微波散射场多普勒谱特性研究
Investigation on Doppler spectra of microwave scattering from sea surface
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摘要: 基于粗糙面电磁散射双尺度模型推导给出了海面微波散射场多普勒谱频移和谱宽的理论公式，在该理论公式的推导过程中同时考虑了大尺度海浪的倾斜调制、遮蔽效应和曲率修正效应等因素的影响．文中将理论公式计算结果与精确数值结果进行了比较，并讨论了倾斜调制、遮蔽效应及曲率修正效应等因素对多普勒频移和谱宽的影响，发现倾斜调制使水平极化散射回波多普勒频移显著增大，从而导致水平极化回波多普勒频移比垂直极化回波多普勒频移大；在中等入射角度区域，遮蔽效应和曲率修正效应对多普勒谱并无显著影响，而在掠射条件下，遮蔽效应使得多普勒频移增大、谱宽变窄．本研究对深入理解动态海面散射场频谱特性具有一定参考意义．Abstract: Based on the composite surface scattering model, the analytical formulas for Doppler shift and bandwidth of radar echoes return from time-varying sea surface are derived. In our derivations, the influences of the tilt modulation, the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between the theoretical results and direct numerical simulations demonstrate that the analytical formulas can significantly improve the simulated results. And the effects of the tilt modulation, the shadow and the curvature on Doppler spectral properties are discussed in detail. From the simulated results, it is found that the predicted Doppler shifts are always larger in HH-polarization than in VV-polarization due to the tilt modulation of large-scale waves. In addition, at low-grazing angles, the shadow of large-scale waves results in a rapid increase of the predicted Doppler shift, and on the contrary maks the bandwidth narrower.
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