溢油海面微波散射场极化特征和频谱特性理论研究

The high false alarm rate due to look-alike oil spills, such as low wind speed area, upwelling and etc., is the main problem which puzzles the application of microwave sensors on the oil spill detection. Aiming at this issue, it is necessary to investigate the properties of microwave scattering from oil-covered sea surface based on the electromagnetic scattering theory. The polarization features of the microwave scattering are mainly related to the sea surface profile and the dielectric constant of sea water. On the other hand, the spectra of the microwave echoes reflect the motion characteristics of the sea waves. Because the sea surface profile and the motion of waves are both suppressed by the oil spill remarkably, the polarization properties and the spectral features would be affected by oil spill, too..In this project, based on the Navier-Stokes equation, boundary conditions of fluid dynamics and the wave action balance equation, a damping model of sea surface waves by oil film is proposed. And the influences of oil film parameters, such as the thickness, factional filling factor, viscosity, surface tension and etc., on the damping model are discussed in detail. Combining the damping model of sea surface waves with the numerical and the analytical method of electromagnetic scattering, the full- polarization scattering matrix of the microwave echo from oil-covered sea surface is evaluated. And then, the polarization features are studied using the polarimetric target decomposition theory. Meanwhile, the Doppler spectra of the echoes backscattered from oil-covered sea surface are also analyzed by periodogram method. Further, the dependences of polarization features and Doppler spectral characteristics on oil film parameters are investigated in order to find appropriate parameters for oil spill detection. The study in this project has great theoretical significance. Moreover, the results are also important to improve oil spill detection algorithm and decrease false alarm rate in practice.

疑似油膜导致的高虚警率问题一直困扰着微波传感器海上溢油探测技术的发展。鉴于此，有必要对油膜海面微波散射特征开展深入研究，其中，散射场极化特征主要与海表轮廓及海水介电常数有关，而频谱特性则反映了海浪运动状态。油膜对海浪的抑制作用不但会改变海表轮廓，也会改变海浪的运动状态，因此，必将对海面回波的极化特征和频谱特性产生影响。.针对以上问题，本项目拟基于N-S方程和海浪作用量平衡方程，建立一定厚度油膜对海浪的抑制模型，着重讨论油膜厚度、粘性等参数对该抑制模型的影响；结合该抑制模型，应用海面电磁散射数值/解析近似方法，求解油膜海面散射场；在此基础上，分别利用极化目标分解理论和周期图频谱分析方法求解油膜海面回波的极化特征和频谱特征，并分析这些特征对油膜的敏感性，为微波传感器海上溢油探测技术探索新的特征参数，降低溢油探测虚警率。本研究不但具有理论意义，而且对提高微波海上溢油探测能力也具有切实的探索价值。

基于Navier-Stokes方程、海浪作用量平衡方程、Lombardini模型和Jenkins模型分别研究了单分子油膜和有限厚度油膜对海浪谱的抑制，并利用不同的海浪谱采用一阶小斜率近似(SSA-1)开展了单站和双站情况下海面电磁散射研究。在此基础上，基于电磁散射近似方法从理论上推导了油膜覆盖海面的散射场，分析了不同雷达波段清洁海面和油膜覆盖海面的极化特性，并将理论结果与溢油SAR实测数据进行了比较。进一步，基于不同雷达波段的溢油SAR数据开展了极化特征分析，给出了适合溢油检测的雷达波段和极化特征。考虑到真实海面具有非线性特征，研究了非线性清洁海面及油膜覆盖海面的电磁散射场，并通过数值模拟对比了线性清洁海面和非线性清洁海面之间的差异；进一步讨论了油膜对偏度函数和峰度函数的影响以及油膜覆盖海面情况下非线性海面顺风和逆风的差异。最后，通过开展极化散射计水槽溢油实验与海上溢油SAR实验，获取了不同油膜厚度、不同油膜种类的散射场数据；分析了油膜厚度对不同极化通道散射系数的影响，并研究了油膜和海水的极化特性。. 本项目已按照前期计划开展研究，达到了预期研究目标。在本项目执行的四年期间，基于项目研究内容和所得结果在国内外知名学术期刊上发表或录用SCI/EI论文12篇，投稿论文2篇，待投稿论文2篇，参加IGRSS国际会议5人次，PIERS 会议3人次，ICCEM国际会议4人次，发表会议论文8篇。在该项目研究过程中，培养硕士研究生3名，博士研究生1名；培养青年教师3名。达到了预期目标。.