Inverse Problems in the Measurement Technique by Scattering and Absorption Process

我们在1989年和1990年与华盛顿大学就多重散射和逆问题进行了合作研究。主要结果总结如下：1)神经网络在逆散射问题中的应用。应用神经网络技术求解逆散射问题。其基本思想是首先通过先验结果训练神经网络。该网络经过训练后，可以快速有效地求解逆问题。我们通过应用该技术从遥感数据中找到气溶胶的粒径分布，验证了该技术的有效性。2)多重散射效应。我们通过理论分析、数值模拟和毫米波实验对非常粗糙表面的散射进行了详细的研究。结果表明，后向散射增强对粗糙度谱很敏感。理论解提供了后向散射增强的物理解释，与数值结果吻合较好。提出了一种利用多重散射效应测量表面粗糙度的新方法。通过两次测量综合强度的二阶矩，可以唯一地确定均方根高度和相关长度两个粗糙度参数。我们还研究了一个由冰上两层雪组成的致密介质模型。结果表明，共极化截面是频率和雪粒大小的强函数。我们还发现，少量较大的雪粒对共偏振后向散射截面有显著贡献。电离层等离子体对高功率微波的散射。高功率微波可能被电离层等离子体散射，而电离层等离子体对弱微波是透明的。为实现弱微波的透明，进行了火箭实验。为研究高功率微波的非线性效应，进行了火箭实验。结果表明，微波可以激发电子回旋谐波。由于对波的激发机制还不太了解，我们已经开始开发计算机模拟代码。少

We have carried out a cooperative research with the University of Washington on multiple scatterings and inverse problems in 1989 and 1990. The major results are summarized in the followings.1) Application of Neural Network to Inverse Scattering Problems.The neural network technique has been applied to solve the inverse scattering problems. The fundamental idea is to first train the neural network by priori results. The network can speedily and efficiently solve the inverse problem, once it has been trained. We verified the validity of this technique by applying it to find particle-size distributions of aerosol from remote sensing data.2) Multiple Scattering Effects.We have made detailed studies of scattering by very rough surfaces by theoretical analyses, numerical simulations, and millimeter wave experiments. The results indicate that backscattering enhancement is sensitive to the roughness spectrum. The theoretical solutions provide a physical explanation of backscattering enhanceme … More nt and agree well with the numerical results.A new method has been proposed to measure the surface roughness by using multiple scattering effects. The two roughness parameters of rms heights and correlation lengths can be uniquely determined by twice measuring the second order moment of integrated intensities.We have also examined a dense medium model consisting of two layers of snow on top of ice. Our results show that the copolarized cross sections are strong functions of frequency and snow-grain size. We have also found that a small number of the larger snow grains contribute significantly to the copolarized backscattering cross section.3) Scattering of High Power Microwave by Ionospheric Plasma.High power microwave may be scattered by the ionospheric plasma, which is transparent for the weak microwave. A rocket experiment was carried out for transparent for the weak microwave. A rocket experiment was carried out for studying the nonlinear effects of high power microwave. It showed that the electron cyclotron harmonic waves are excited by the microwave. Since the wave excitation mechanism is not well-understood, we have started to develop the computer simulation codes. Less