Radio Sources and Scintillation

A review is given of the interplay between studies of compact radio sources and the scattering and scintillations that occur as the signals travel through the irregular refractive index of the interstellar and interplanetary plasmas. This revised version was published online in July 2006 with corrections to the Cover Date.     

相对湿度对大气气溶胶粒子短波辐射特性的影响

利用Mie散射原理和重庆实测气溶胶资料,详细计算了边界层内单个气溶胶粒子的光学特性参量,气溶胶粒子群体的散射、吸收、消光系数及不对称因子、散射比、光学厚度;进而采用二流近似和累加法计算了边界层内太阳短波辐射增温率。目的在于研究相对湿度对以上各特性参量的影响。结果表明,相对湿度在65%～95%之间变化时,对气溶胶粒子群体光学特性参数和太阳增温率的影响在量级上可与气溶胶粒子浓度成倍变化的影响相比拟。     

基于S波段双偏振雷达一次强雹暴过程观测分析

利用宁波S波段双偏振天气雷达资料、NCEP再分析资料、结合常规观测资料和实地冰雹调查资料,对2020年3月21日浙江省中北部一次强雹暴灾害过程(简称“03·21”过程)的天气背景和双偏振雷达回波演变特征进行分析。结果表明：(1)此次雹暴过程环流形势属于低层暖平流强迫类型,雹暴影响过程约4 h,雹暴A和B先以强的对流单体形态移动,在自西向东移动过程中分别加强为超级单体。(2)典型降雹时次具有明显的三体散射特征(TBSS),垂直剖面图上强回波(>50 dBz)伸展高度超过-20℃层,低层的弱回波,中高层悬垂回波明显。径向速度垂直剖面图上,雹暴低层辐合,其上叠加了辐散层,使得雹块得以继续形成和增长。(3)冰雹区出现了Z_DR冰雹信号,对应的反射率因子(Z_H)均大于65 dBz,差分反射率因子(Z_DR)介于-2.0～0 dB,相关系数(C_C)介于0.80～0.98;当结合Z_H、Z_DR、C_C综合判断云中有冰雹粒子,C_C...     

太湖水体吸收系数与散射系数的特征研究

湖泊水体光学特性是进行湖泊水体光学及水体光学遥感研究的基础。计算了太湖冬、夏季水体的吸收系数和散射系数,并在分析水体吸收特性的基础上对水体的光学类型进行了分类。结果表明:冬季太湖水体的光学类型属PY型(悬浮粒和黄质共同作用型),即水体的吸收特性受悬浮质和黄质的共同作用,而夏季则属CPY型(浮游藻类、悬浮粒和黄质共同作用型),即水体的吸收特性受悬浮质、黄质和浮游藻类三者的共同作用;不论冬季还是夏季,非色素悬浮粒是影响太湖水体散射特性的主要因子。     

长江三角洲地区大气气溶胶柱单次散射反照率特性研究

利用OMI卫星资料2006—2017年的483.5 nm波长的气溶胶柱单次散射反照率日均数据,分析了整层大气气溶胶单次散射反照率在长三角地区的时空分布特征,特别是其年际、月、季节变化特征.长江三角洲地区的大气气溶胶柱单次散射反照率越靠近海洋越大,而越靠近内陆越小.日均气溶胶柱单次散射反照率在0.881~0.971范围内变化,多年的平均值为0.939±0.024,最大分布概率出现在0.965~0.970区间,其值约为25％.长三角地区大气气溶胶柱单次散射反照率的年平均值集中于0.938~0.940之间,年际变化很小,变化值小于1％;月均柱单次散射反照率在6、8、9月有最大值,其值为0.968,而在2月有最小值,其值为0.915;季节平均单次散射反照率在夏季最大,其值为0.968,而在冬季最小,其值为0.919.     

基于逆散射理论的介质参数与其地震响应的尺度对应关系研究

在反演过程中进行频带控制是多尺度反演的重要策略,但数据频率成分与要反演的参数之间的尺度对应关系尚不清晰。本文利用Kormendi论文中的测井曲线模型,基于逆散射理论将地下介质参数的扰动分解为0-0-9-11 Hz、9-11-18-22 Hz、18-22-36-44 Hz和36-44-80-90 Hz共4个尺度,并利用反射率正演模拟方法生成4个尺度扰动成分的地震响应。通过对比地下介质参数不同尺度的扰动及其地震响应的频带成分,发现二者在4个扰动尺度上均具有一致性,由此得出介质参数与其地震响应具有定量尺度对应关系的结论。据此从介质扰动的尺度概念引申出反射系数的尺度概念,从逆散射理论角度探讨实验结果的理论依据,并对其在指导反演分频参数选取及薄互层解释等方面的应用展望进行讨论。     

Generalized Born scattering of elastic waves in 3-D media

It is well known that when a seismic wave propagates through an elastic medium with gradients in the parameters which describe it (e.g. slowness and density), energy is scattered from the incident wave generating low-frequency partial reflections. Many approximate solutions to the wave equation, e.g. geometrical ray theory (GRT), Maslov theory and Gaussian beams, do not model these signals. The problem of describing partial reflections in 1-D media has been extensively studied in the seismic literature and considerable progress has been made using iterative techniques based on WKBJ, Airy or Langer type ansätze. In this paper we derive a first-order scattering formalism to describe partial reflections in 3-D media. The correction term describing the scattered energy is developed as a volume integral over terms dependent upon the first spatial derivatives (gradients) of the parameters describing the medium and the solution. The relationship we derive could, in principle, be used as the basis for an iterative scheme but the computational expense, particularly for elastic media, will usually prohibit this approach. The result we obtain is closely related to the usual Born approximation, but differs in that the scattering term is not derived from a perturbation to a background model, but rather from the error in an approximate Green's function. We examine analytically the relationship between the results produced by the new formalism and the usual Born approximation for a medium which has no long-wavelength heterogeneities. We show that in such a case the two methods agree approximately as expected, but that in a media with heterogeneities of all wavelengths the new gradient scattering formalism is superior. We establish analytically the connection between the formalism developed here and the iterative approach based on the WKBJ solution which has been used previously in 1-D media. Numerical examples are shown to illustrate the examples discussed.     

起伏地表条件下的声波散射数值模拟的积分方程法

从散射理论的角度来看,起伏地表可以看作是一种特殊的扰动介质,因此应用散射积分方程求解起伏地表条件下的散射场在理论上是可行的。从三维频率域声波方程出发,由格林函数定理,得出起伏地表条件下的散射积分方程。散射积分方程为关于起伏地表的面积分和与速度扰动体有关的体积分之和,同时给出了格林函数在奇异点的积分方法。由于数值离散求解积分方程存在着计算时间太长和存储内存不足的问题,采用电磁散射积分方程的拟解析近似的方法。在假设反射函数为缓变函数的基础上,最终得到其近似表达式,因此散射场的数值求解不必再借助于代数方程组,只要进行数值积分即可。这种方法避开了传统数值计算方法存在的问题,为地震散射波场快速正演模拟打下了基础。理论分析表明,这种方法适用于小扰动的问题。当扰动较大时,拟解析近似会产生较大的误差。