Radon induced background processes in the KATRIN pre-spectrometer

The KArlsruhe TRItium Neutrino (KATRIN) experiment is a next generation, model independent, large scale tritium β-decay experiment to determine the effective electron anti-neutrino mass by investigating the kinematics of tritium β-decay with a sensitivity of 200 meV/c² using the MAC-E filter technique. In order to reach this sensitivity, a low background level of 10⁻² counts per second (cps) is required. This paper describes how the decay of radon in a MAC-E filter generates background events, based on measurements performed at the KATRIN pre-spectrometer test setup. Radon (Rn) atoms, which emanate from materials inside the vacuum region of the KATRIN spectrometers, are able to penetrate deep into the magnetic flux tube so that the α-decay of Rn contributes to the background. Of particular importance are electrons emitted in processes accompanying the Rn α-decay, such as shake-off, internal conversion of excited levels in the Rn daughter atoms and Auger electrons. While low-energy electrons (<100 eV) directly contribute to the background in the signal region, higher energy electrons can be stored magnetically inside the volume of the spectrometer. Depending on their initial energy, they are able to create thousands of secondary electrons via subsequent ionization processes with residual gas molecules and, since the detector is not able to distinguish these secondary electrons from the signal electrons, an increased background rate over an extended period of time is generated.     

数字锁相环变带宽滤波器的设计与仿真

对于确定参数的滤波器,快速的相位捕捉能力和高的噪声抑制能力是相互矛盾的。利用数字滤波器参数容易改变的特点,主要研究二阶锁相环环路中变带宽数字滤波器的设计,从而使锁相环路在初始阶段具备快速的捕捉能力和在锁定状态具备高的噪声抑制能力。对数字锁相环系统及滤波器在原理上进行了细致分析,之后给出软件实现该滤波器的算法,并用Matlab对系统进行仿真。     

基于随机模型改正的有色状态噪声处理新方法

控制有色状态噪声影响除了通过状态向量扩展的方法外,也可以通过修正随机模型.提出采用多项式长除法将有色状态噪声模型展开成无穷级数,截断取其有限项,进而求取有色状态噪声方差.利用该方差对随机模型进行修正,再结合现代时间序列分析方法,构造出新的ARMA新息模型,并根据该新息模型设计状态最优滤波器.为了说明该方法的正确性和合理性,将它与标准的Kalman滤波和状态向量扩展法进行分析和比较.结果证明利用该方法能有效地控制有色状态噪声的影响.     

滤波技术在煤田断层精细检测中的应用

中值滤波技术可以有效地去除随机噪声,增强水平同相轴的连续性,但其未考虑地层倾角的变化.断层/边缘增强滤波技术考虑到地层倾角的变化因素,能够突出细微差别,改善低信噪比资料,显著提高地震剖面质量.实践证明,断层/边缘增强滤波技术能更加突出地层接触关系,可以有效提高小断层的解释精度,提高煤田三维地震勘探资料解释的精度和准确性.     

Exploration of optimal time steps for daily precipitation bias correction: a case study using a single grid of RCM on the River Exe in southwest England

ABSTRACT

Bias correction is a necessary post-processing procedure in order to use regional climate model (RCM)-simulated local climate variables as the input data for hydrological models due to systematic errors of RCMs. Most of the present bias-correction methods adjust statistical properties between observed and simulated data based on a predefined duration (e.g. a month or a season). However, there is a lack of analysis of the optimal period for bias correction. This study attempted to address the question whether there is an optimal number for bias-correction groups (i.e. optimal bias-correction period). To explore this we used a catchment in southwest England with the regional climate model HadRM3 precipitation data. The proposed methodology used only one grid of RCM in the Exe catchment, one emissions scenario (A1B) and one member (Q0) among 11 members of HadRM3. We tried 13 different bias-correction periods from 3-day to 360-day (i.e. the whole of one year) correction using the quantile mapping method. After the bias correction a low pass filter was used to remove the high frequencies (i.e. noise) followed by estimating Akaike’s information criterion. For the case study catchment with the regional climate model HadRM3 precipitation, the results showed that a bias-correction period of about 8 days is the best. We hope this preliminary study on the optimum number bias-correction period for daily RCM precipitation will stimulate more research to improve the methodology with different climatic conditions. Future efforts on several unsolved problems have been suggested, such as how strong the filter should be and the impact of the number of bias correction groups on river flow simulations.

Editor M.C. Acreman Associate editor S. Kanae     

Baseflow separation in a small watershed in New Brunswick,Canada, using a recursive digital filter calibrated with the conductivity mass balance method

Baseflow separation is important for obtaining critical parameters for hydrological models. As measuring the baseflow component directly is difficult, various analytical and empirical baseflow separation methods have been developed and tested. The recursive digital filter (RDF) method is commonly used for baseflow separation due to its simplicity and low data requirement. However, parameters used in the RDF method are often determined arbitrarily, resulting in high uncertainty of the estimated baseflow rate. A more accurate method is the conductivity mass balance (CMB) method, which is established based on the differences in physical processes between baseflow and surface runoff. In this research, the output of the CMB method was used to calibrate the parameters of an RDF model, and the calibrated RDF model was used to estimate monthly, seasonal and annual baseflow rate and baseflow index for the past 19 years using streamflow discharge records. The characteristics of the baseflow hydrographs were found to be consistent with the hydrological and hydrogeological conditions of the research area. Research results indicated that the accuracy of the RDF model has been greatly enhanced after being calibrated with the CMB method so that the RDF model can provide more reliable baseflow separation results for a long‐term study. Copyright © 2012 John Wiley & Sons, Ltd.     

均值漂移粒子滤波的动态精密单点定位

粒子滤波以大量粒子计算为代价削弱动态精密单点定位的非线性方程线性化、非高斯噪声正态化造成的精度损失,这也带来计算效率较差的问题。针对计算效率低的问题,将均值漂移算法引入到粒子滤波,减少粒子选取个数,提高动态PPP中待估参数的计算效率。以某机载GPS数据为例,基于均值漂移算法的粒子滤波大大削减了粒子个数,计算效率有一定程度的提高。     

基于GRACE卫星RL05数据的南极冰盖质量变化分析

CSR(Centre for Space Research)最近发布了RL05数据,其空间分辨率、精度和周期变化特性等都优于RL04数据.本文采用300 km的扇形滤波及P5M11去相关滤波削弱南北条带等重力场模型误差,并采用Paulson2007模型进行冰川均衡模型改正,利用CSR RL05与RL04数据计算分析了南极2002年到2012年的质量变化序列及其变化趋势的空间分布特性,并选取8个特征点进一步分析了其质量变化序列.同时,对CSR、JPL(Jet Propulsion Laboratory)、GFZ (GeoForschungsZentrum)三个机构发布的RL05数据采用相同的滤波方法进行计算,得到整个南极的质量变化分别为-195.7±20.5 Gt/a、-203.8±23.1 Gt/a、-133.2±29.9 Gt/a,对全球海平面变化的影响分别为0.54±0.06 mm/a、0.56±0.06 mm/a、0.37±0.09 mm/a.     

基于相关迭代的非因果匹配滤波器多次波压制方法

针对常规多次波压制(SRME)方法存在的缺陷进行了改进.首先在多次波模型道预测阶段,采用数据相关和迭代更新的策略预测多次波模型道,该方法降低了SRME方法采用数据空间褶积对输入数据要求严格的限制,提高了对近偏移距缺失和空间假频数据的适应性.在匹配相减阶段,本文设计了一种非因果非平稳的匹配滤波器,该滤波器可以对整道多次波模型进行处理,而且当预测多次波模型道滞后于实际多次波时,也能够对多次波模型道进行很好的匹配.模型数据和实际数据试算证明该方法在多次波模型道预测和匹配相减阶段的优越性.     

耦合遥感观测和元胞自动机的城市扩张模拟

在传统元胞自动机(CA)模型中,静态的模型参数和模型误差不能释放是影响城市扩张模拟效果的两个重要原因。文中引入集合卡尔曼滤波方法到CA模型中,提出了基于联合状态矩阵的地理元胞自动机。该模型在模拟过程中可以通过同化遥感观测数据,动态地调整模型参数和纠正模拟结果,使模型参数能够反映转换规则的时空变化,同时也能较好地释放积累的模型误差。将模型应用于东莞市的城市扩张模拟中,实验结果表明,模型能够准确地调整模型参数使之符合城市发展模式,同时也能有效地控制模型误差,其模拟的空间格局与真实情况吻合。