变浅效应调制的近岸海面电磁散射多普勒谱特性研究

The nearshore region is the ocean area with the most frequent activities of human, thus the study on the Doppler spectra of electromagnetic (EM) backscattered echoes from nearshore sea surfaces is the urgent key issue need to be addressed. The traditional study on the EM scattering from sea surfaces often focuses on the deep sea, ignoring the influence of shoaling effect on the modeling of EM scattering. This project mainly focuses on the study of EM scattering from nearshore sea surfaces modulated by shoaling effect. Based on the nearshore finite-depth sea spectrum, hydrodynamic geometric modeling techniques and the improved second-order small slope approximation, the scattering characteristics of volume scattering source and its interaction with surface scattering is studied, with consideration of the shadow and curvature effect between sea waves under the circumstance of near-grazing incidence.Then, the statistical modeling of nearshore sea clutter is developped based on scattering mechanisms and models, the simulation of Doppler spectra of backscattered echoes from nearshore sea surfaces modulated by shoaling effect is successively presented, and the influences of radar and sea environmental parameters, especially the water depth, on scattering coefficient as well as Doppler shift and bandwidth are analyzed in detail, which provides a helpful theoretical reference for ocean remote sensing and related applications.

近岸海域是人类活动最为频繁的海洋范围，对近岸海面电磁散射回波的多普勒谱特性研究是海洋遥感领域急需解决的关键课题。传统的海面电磁散射研究往往针对深海展开，忽略了近岸变浅效应对电磁散射建模的影响。本项目重点开展变浅效应调制的近岸海面电磁散射机理研究，基于近岸有限水深风浪谱模型、水动力学几何建模技术和改进型二阶小斜率近似方法，兼顾考虑近掠入射情况下的海浪间遮挡效应和曲率调制效应，研究近岸有限水深海面上体散射源的散射特征及其与海面面散射的相互作用机理，建立基于散射机理和模型的近岸海杂波统计建模，实现变浅效应调制的海洋场景回波多普勒谱模拟，分析雷达参数和海环境参数尤其是海水深度对散射系数以及回波多普勒频移和谱展宽的影响，为我国近岸海洋遥感与相关应用提供有益的理论参考。

随着对海洋环境电磁散射特性分析的需求不断增长，近岸海域环境下海面电磁散射回波的多普勒谱特性研究成为了海洋遥感和目标检测等领域急需解决的关键课题。本项目重点对近岸海面电磁散射多普勒谱特性进行了研究，取得了以下研究成果：. 1）建立了相对高效和精确的变浅效应调制的近岸海面几何模型。通过合理考虑近岸浅水域波浪间频繁发生的非线性水动力效应，结合近岸浅水风浪谱和快速谱合成技术，使获得的建模结果与自然场景中的真实海面形态更加趋于一致。. 2）实现了针对独立近岸有限水深海面样本散射场的精确计算。讨论了海面上方风速、风向、水深和风区等海洋环境因素对散射结果的影响，提高了对深海和浅海环境散射回波特性差异的理解。. 3）进一步考虑了近岸海域海水深度逐渐变浅的环境因素，对相应海浪电磁散射特性的分析发现，水深的渐进变化效应反映出比固定水深情况下浅海波浪更加强烈的非线性作用。. 4）研究了更趋于实际情况的风浪和涌浪混合模式海浪电磁散射特性，通过对散射系数和散射回波多普勒谱的计算，对比分析了有效波高、谱峰周期、水深、风区和入射角等因素的影响，总结归纳了涌浪和风浪分别占主导地位时混合海浪的散射特性。. 5）引入了破碎波模型来考虑碎浪效应。基于复合表面模型研究了高频段碎浪对海面电磁散射的影响，获得含破碎波成分的复杂海面电磁散射预估。. 以上研究成果使得深入分析近岸海域复杂环境电磁散射特性成为可能，为后续的研究奠定了坚实的基础，并且在海洋遥感和海面及其上目标探测相关应用方面具有广泛的应用前景。