An extension of general identities for 3D water-wave diffraction with application to the Diffraction Transfer Matrix

Interaction theories are used in numerous branches of physics to efficiently evaluate wave scattering by multiple obstacles. An example of these interaction theories is the direct matrix method introduced by Kagemoto and Yue [1], which enables fast computation of three-dimensional water-wave multiple-scattering problems. The building block of interaction theories is a mathematical operator that encapsulates the mapping between incident and scattered waves. This operator is generally referred to as T-matrix and satisfies both reciprocity and energy identities. In some branches of physics, such as acoustics and electromagnetism, these identities are well established; in hydrodynamics, however, they have only been derived for a T-matrix that maps two-dimensional incident and scattered water waves. In three dimensions, water waves can be represented as a series expansion of cylindrical eigenfunctions. In this paper, we use this representation of water waves to derive the reciprocity and energy identities satisfied by the T-matrix of the direct matrix method, known as Diffraction Transfer Matrix (dtm). The identities derived herein represent an extension of existing general relations between two diffraction solutions. We show that this extension can be applied to verify the accuracy of the dtm entries, thereby increasing the reliability of existing schemes for computing the dtm. We present results for the dtm of two geometrically different isolated obstacles, as well as for the dtm of an asymmetric array. Finally, we demonstrate that the results presented herein can be extended to floating bodies found in a wide range of ocean engineering problems.     

GNSS-R海面目标成像仿真方法研究

结合物理光学法及传统复合电磁散射计算模型中的"四路径"方法,以GNSS信号为信号源,提出了一种基于高频散射理论的GNSS-SAR成像模型,建模过程考虑了多路径散射、遮蔽、漫散射等效应,较好地描述了电磁散射效应对海面场景GNSS-SAR成像的影响。根据电磁散射效应,分析了海面风速对成像效果产生的干扰情况,发现在本文仿真场景下,9 m/s风速海背景下的目标能够被识别出来,17 m/s风速海背景下的目标几乎淹没在海杂波中。     

各向异性海面全极化微波双站散射的仿真与分析

为了解各向异性随机粗糙海面的微波双站散射机制及其特性,本文利用解析近似的积分方程模型以及一种改进的半经验海浪谱模型实现了对各向异性随机粗糙海面的全极化微波散射仿真模拟,并与卫星观测数据、经验的地球物理模式函数及已有的解析近似散射模型仿真结果进行了对比,验证了仿真结果的可行性和准确性。利用该模型分析了入射波频率、入射角、极化方式、海面风速及风向等参数对各向异性海面双站散射的影响。模拟结果表明,在不同的入射角、散射角及方位角等观测几何条件下,海面不同波段的双站散射表现出不同的空间散射特性,且对风速、风向等海面动力学参数表现出不同的敏感性,以L波段为例,海面向后半球双站散射在各个极化方式下都对风速较为敏感,而在同极化方式下,其对风向的响应在中低风速和高风速条件下相反,整体而言,低风速下海面双站散射对风向更为敏感。这表明对于海面动力参数的反演,双站散射可以提供比传统单站雷达后向散射更丰富的物理信息。本文探讨了各向异性海面微波双站散射特性,为基于主动式及分布式微波传感器的海洋动力参数遥感反演提供了理论分析基础。     

目标回波中的弹性信息提取方法研究

在主动声纳探雷识别中,弹性波提取方法一直是研究的难点。研究表明回波中,几何亮点主要表现为波形包络的强起伏的慢变化,在频域上属于低频,而弹性信息则隐含在包络中,其变化较快且能量微弱,相对于包络来说是比较弱的高频成份。运用中心差分的方法,可使高频成份得到较大的增强,从而实现弹性信息提取的目的。仿真和实验数据均取得了良好的效果。     

A general purpose exact Rayleigh scattering look-up table for ocean color remote sensing

1 Introduction In the total radiance received by an ocean color remote sensor, over 80% radiance is the contribution being scattered by air molecule and aerosol, and a wa- ter-leaving radiance carrying the ocean color informa- tion is only a small part. T…     

中国大陆余震序列类型的综合判定

在对中国大陆294次5级以上地震序列主震后不同时段、11个单项序列参数计算结果的基础上,分别建立不同时段、以不同序列参数为自变量的Fisher判别函数,用于序列类型的综合判定。在Fisher判别函数建立过程中,除以常规序列参数作为函数自变量输入外,还引入主震滑动角参数,以使判别函数在一定程度上包含主震破裂形式的信息。统计结果表明,序列类型识别正确率随资料长度(震后时段)增加而提高。不同类型序列的识别正确率不同,孤立型序列的识别正确率大于0.93,主余型序列的识别正确率为0.73~0.93,多震型序列的正确识别率为0.57~0.86,均明显高于随机投票0.33的自然对应率,因而其序列分类能力应得到正的评分。     

针对倾斜建筑物的四分量分解方法

经典的Freeman-Durden三分量分解模型存在着体散射能量过度估计的现象,这种现象易导致倾斜建筑物(即建筑物的排列方向与雷达飞行方向不平行)被错误解译为森林.虽然存在多种分解方法来避免倾斜建筑物的错误解译,但从非反射对称散射的角度来应对体散射能量过度估计目前研究仍较少.因此,提出一种新的四分量分解方法,可有效抑制...     

多元线性回归方法在地下水水位预测中的应用

在对已有长期开采资料的水源地进行资源评价时,充分利用长系列观测资料,可采用多元线性回归方法对地下水水位的变化规律进行研究对其变化趋势进行预测,本文重点对相关因素的确定和多元线性回归方法的应用进行了研究。     

A modelling study of aerosol processing by stratocumulus clouds and its impact on general circulation model parameterisations of cloud and aerosol

A model of the aqueous phase processing of an aerosol population undergoing multiple cycling through a stratocumulus (Sc) cloud layer is presented. Results indicate that a significant modification of the aerosol properties is achieved following the first cycle through cloud. In a polluted atmosphere, further modification in subsequent cycles is seen to be hydrogen peroxide limited unless there is a flux of ammonia entering the system through cloud base (CB). The modification of the aerosol population is seen to have little effect on the microphysics (specifically the cloud droplet concentration and effective radius) of the processing cloud. However, it enables processed aerosols to subsequently act as efficient cloud condensation nuclei (CCN) in less vigorous clouds (as a result of reducing the critical supersaturation required to activate them). The effects of variations in the internal mixture of soluble components of aerosols on the microphysics of clouds forming on them are also investigated using the cloud model. A (K2) parameterisation of the effects of variations in internally mixed nitrate loadings on the cloud droplet number concentration is presented. The effects of applying this K2 correction to the droplet number (derived from a parameterisation based on sulphate) for the presence of nitrate in aerosol have been investigated using the HadAM3 version of the Hadley Centre General Circulation Model (GCM). The effect on global annual mean simulations of the indirect forcing and effective radius is small, but more pronounced regionally. Suggestions (based on model results and observations) for parameterising the size distribution and in-cloud growth of aerosols for use in GCMs are presented.     

辽河盆地新生代多期构造热演化模拟

针对辽河盆地新生代拉张多期性的特点,提出一种适用于多期拉张盆地构造热演化模拟的纯剪切模型．该模型考虑了多期拉张的继承性、横向不均匀性以及拉张速率的可变性。通过几种拉张速率模式的对比,指出拉张速率模式的选择对模拟年轻盆地热演化过程具有重要意义．最后,利用该模型模拟研究了辽河盆地新生代的构造热演化历史．