浅析偏振光遥感的应用

偏振光遥感是近年来备受关注的一种新兴对地观测方法.早期的传感器多以目标的反射辐射或自身的辐射强度来推断目标的状态和性质,而把传感器接收信号中的偏振作为一种"噪音"来处理,随着空间遥感科学的发展,科学家们发现偏掁特性是一种良好的地表监测手段.     

Influence of resonances on the phase and the group refractive indices of air

The Barrell and Sears and Edlen formulae use the Sellmeier form away from resonances, which gives a “smooth” dependence within the visible and near-infrared spectra. All known atlases indicate numerous resonances in these regions, which cause local disturbance of the dispersion curve. Anomalous dispersion may be estimated from an absorption by the Kramer-Kronig ratios. It gives a change of phase refractive index of air in a range from several ppt to 1 ppb within narrow optical regions, causing large local dispersions. Computation of the group refractive index with the use of Rayleigh's ratio shows that the influence of resonance effects may be more than several ppm. For example, the error of the group refractive index for high-precision EDM using HeNe lasers (633 nm) varies between 0.2 and 0.7 ppm, depending on the laser stability. Received: 17 July 1996 / Accepted: 27 March 1997     

基于太赫兹时域光谱技术的白色软玉产地鉴定研究

不同产地的白色软玉组成矿物成分和结构构造十分相近,但价值差异很大。太赫兹(terahertz,THz)时域光谱技术可以提供物质的化学组成、结构及构像等信息,光谱指纹特征信息可用于物质鉴别。利用透射式太赫兹时域光谱技术分别对新疆、韩国、青海和俄罗斯这4个产地的白色软玉进行了测试,将得到的时域光谱进行快速傅里叶变换(fast Fourier transform,FFT)和计算后使用Savitzky-Golay(S-G)平滑处理进行降噪,得到4个产地白色软玉的0. 2～2. 5 THz频域内折射率和吸收系数。研究表明,4个产地白色软玉THz光谱折射率存在数值差异;不同产地太赫兹特征吸收峰的存在形式不同,新疆、青海的白色软玉在2. 0 THz波段有1个突出的小型特征吸收峰,而韩国和俄罗斯的白色软玉在1. 5～2. 0 THz波段有1个宽大的吸收包络。这些结果为进一步开发基于太赫兹时域光谱技术的白色软玉产地识别方法提供了基础数据。     

山基GPS掩星反演大气对流层折射率系统组成及其程序实现

山基GPS掩星技术因具有较强的实用功能成为目前反演大气研究的热点。结合雾灵山山基GPS掩星试验数据,研究了山基反演大气折射率的主要组成部分,并详细介绍了几个模块的实现过程,最后用程序解算了一段掩星数据。     

Long-term measurements of 36Cl to investigate potential solar influence on the decay rate

Recently, Jenkins et al. [6] reported on fluctuations in the detected decay events of ³⁶Cl which were measured with a Geiger–Müller counter. Experimental data of ³²Si measured by means of an end-window gas-flow proportional counter at the Brookhaven National Laboratory show similar periodicity, albeit a different amplitude. Jenkins et al. interpret the fluctuations as evidence of solar influence on the decay rates of beta-decaying radionuclides.In this work, liquid scintillation counting was used to check for potential variations in the ³⁶Cl decay rates. A custom-built counter with three photomultiplier tubes was used. In contrast to commercial counters, the relevant parameters of our system are well controlled and the discrimination threshold and HV setting can be adjusted and checked. The experimental data were analyzed by means of the triple-to-double coincidence ratio (TDCR) method which is a primary method for activity determination. Thus, our results do not depend on any other standard or reference source.Our data show fluctuations which are by more than one order of magnitude lower than those seen in the experiment using a Geiger–Müller counter. More importantly, no oscillation could be identified. Interestingly, our data overlap in time with those from Jenkins et al. [6]. We do not observe the phase and amplitude as seen by Jenkins and conclude that the fluctuations are not due to solar influence. This also implies that the interpretation by Jenkins et al. is false.     

Profile and Character of Atmospheric Structure Constant of Refractive Index Cn2

Random fluctuations of turbulence bring random fluctuations of the refractive index, making the atmosphere a random fluctuation medium that destroys the coherence of light-waves. Research in atmospheric turbulence is actually the investigation of the atmospheric refractive index. The atmospheric structure constant of refractive index, Cn2, is an important parameter denoting atmospheric turbulence. In this paper, Cn2 is measured during the day and at night and in all four seasons using a high sensitivity micro-thermal meter QHTP-2. The vertical profile of Cn2 in Hefei (0–30 km) is investigated by the analysis of experimental data. The average profile of Cn2 in Hefei exhibits conspicuous day and night differences with increased altitude. The distribution of log(Cn2) is nearly normal and has conspicuous seasonal differences.     

基于风廓线雷达的对流边界层高度的确定

大气边界层高度对于天气、气候和大气污染研究是一个至关重要的参量。对流边界层(Convective Boundary Layer,CBL)顶部的夹卷过程造成温度和湿度垂直梯度增强,导致这一层的折射率结构常数C■变高。C■的这种垂直分布特征经常被用来定位出CBL高度Z_i。本文利用2010年7—8月天津大港的风廓线雷达数据推断出CBL高度Z_i,对于多重C■峰值或不明确的C■峰值,本文改进了对Z_i的测定,分别讨论了C■最大后向散射法与C■和垂直速度方差(σ■)相结合的新方法的适用性。研究显示:(1)C■廓线具有单峰时,最大后向散射强度法能正确估计CBL高度,这种情况往往对应的是晴天。CBL上存在的残留层或云层引起的温湿起伏变化导致C■廓线具有双峰甚至多峰时,最大后向散射强度法可能会错误估计CBL高度;(2)C■和σ■结合的方法不仅与晴天时C■最大后向散射法有较好的一致性,而且可以将CBL造成的C■峰值从云层造成的C■峰值中区分出来,从而正确估计CBL高度;(3)一般而言,对流边界层中存在有明显的、破碎或者分散不明显的云时,C■和σ■结合的方法都能较好地识别出CBL对应的C■峰值。但由于边界层中的情况极为复杂,C■和σ■结合法也会因不同的原因而错误估计CBL高度。     

电磁波在电离层的传播特性研究

研究了折射率n与电子数浓度N_e及高度h之间的关系,并通过数值模拟对电子数浓度的高度剖面和折射率随高度的变化规律进行了分析.将模拟和实际观测出的频高图进行对比,发现在高电离层模拟值与实际值较相近,在低电离层则由于非线性关系及E_s层存在的效应,模拟值与实际值有较大的误差.     

Galileo改正电离层折射误差高阶项的方法

在研究电离层折射对Galileo测量的影响及电离层折射误差模型的基础上,针对Galileo系统中的4个频率,提出运用四频观测值将电离层折射误差改正至三阶项的方法,并推导了四频载波相位观测值无电离层折射组合方程,从而进一步提高了Galileo的定位精度。     

Geoneutrinos in Borexino

This paper describes the Borexino detector and the high-radiopurity studies and tests that are integral part of the Borexino technology and development. The application of Borexino to the detection and studies of geoneutrinos is discussed. Talk given by M.G. Giammarchi