Inferring Small-Scale Flatfields from Solar Rotation

We present a method to infer small-scale flatfields for imaging solar instruments using only regular-observation intensity images with a fixed field of view. The method is related to the flatfielding method developed by Kuhn, Lin, and Loranz (Publ. Astron. Soc. Pac. 103, 1097 – 1108, 1991), but does not require image offsets. Instead, it takes advantage of the fact that the solar image is changing in the CCD reference frame due to solar rotation. We apply the method to data sets of MDI filtergrams and compare the results to flat fields derived with other methods. Finally, we discuss the planned implementation of this method in the data processing for Helioseismic and Magnetic Imager on the Solar Dynamics Observatory.     

基于纠错编码的小波域自适应盲水印算法

提出了一种小波域自适应盲水印算法,并采用(7,4)汉明码技术进行纠错编码.以伪随机二值序列作为水印,采用中值系数抖动的方法将水印嵌入到小波变换后的低频分量,并且根据小波域系数间隔的大小自适应地确定水印量化步长,水印检测过程不需要原始图像的参与.实验结果表明,算法的自适应性强,具有较好的不可见性,且可以有效地抵抗JPEG压缩、锐化、加噪、模糊和缩放等攻击.     

地形抹平与半经验模型的Landsat TM/ETM+地形校正方法

地形校正可以减小地形起伏对地物光谱的影响,提高计算机分类在山区的精度。设计了针对全球土地覆盖分类的Landsat TM/ETM+数据地形校正方法 SCOS(Smoothed COS余弦),首先对地形的坡度角进行抹平处理,很大程度上削弱了地表非朗伯性对地形校正的影响,然后利用简单有效的余弦校正去除地形效应。该方法与其他常用地形校正算法的对比分析是通过对全球不同区域、不同地表覆盖的有代表性的6景Landsat TM/ETM+数据的试验,采用统计分析与目视判读的方式,从过度校正和类内均一性两个方面进行的。结果表明,该方法在目视效果和统计结果上优于常规方法,并且更加简单有效,无需复杂的大气参数及传感器参数,满足全球地表覆盖分类对地形校正的需求。     

Roughness effect on the correction factor of surface velocity for rill flows

Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) and interrill erosive phenomena. The dye tracer technique to measure surface flow velocity V_s is based on the measurement of the travel time of a tracer needed to cover a known distance. The measured V_s must be corrected to obtain the mean flow velocity V using a factor α_v = V/V_s which is generally empirically deduced. The V_s measurement can be influenced by the method applied to time the travel of the dye-tracer and α_v can vary in different flow conditions. Experiments were performed by a fixed bed small flume simulating a rill channel for two roughness conditions (sieved soil, gravel). The comparison between a chronometer-based (CB) and video-based (VB) technique to measure V_s was carried out. For each slope-discharge combination, 20 measurements of V_s, characterized by a sample mean V_m, were carried out. For both techniques, the frequency distributions of V_s/V_m resulted independent of slope and discharge. For a given technique, all measurements resulted normally distributed, with a mean equal to one, and featured by a low variability. Therefore, V_m was considered representative of surface flow velocity. Regardless of roughness, the V_m values obtained by the two techniques were very close and characterized by a good measurement precision. The developed analysis on α_v highlighted that it is not correlated with Reynolds number for turbulent flow regime. Moreover, α_v is correlated neither with the Froude number nor with channel slope. However, the analysis of the empirical frequency distributions of the correction factor demonstrated a slope effect. For each technique (CB, VB)-roughness (soil, gravel) combination, a constant correction factor was statistically representative even if resulted in less accurate V estimations compared to those yielded by the slope-specific correction factor.     

往复荷载作用下锈蚀钢筋混凝土柱黏结滑移模型及数值模拟研究

为实现地震作用下锈蚀钢筋混凝土柱精细化数值模拟分析,基于已有研究成果建立往复荷载作用下锈蚀钢筋与混凝土间的黏结滑移本构模型:结合课题组前期试验结果,采用ABAQUS有限元分析软件对建立的黏结滑移本构模型进行有效性验证,通过对数值计算结果与试验结果之间误差分析,进一步对黏结滑移模型中的摩擦黏结应力系数和退化系数进行修正,最终建立更为合理的锈蚀钢筋与混凝土间黏结滑移本构模型。通过数值计算结果与试验结果的再次比较,验证修正后黏结滑移本构模型的有效性。结果表明:修正后的锈蚀钢筋与混凝土间黏结滑移模型可更好地反映往复荷载作用下锈蚀钢筋混凝土柱的滞回性能。该成果可为地震作用下锈蚀钢筋混凝土结构的数值分析计算提供理论参考。     

土质边坡的饱和−非饱和渗流分析及特殊应力修正

基于连续多孔介质原理与混合体原理引入流?固耦合模型,采用FISH语言编制程序,建立了初始渗流场设置函数、饱和?非饱和渗流分析模块、特殊应力修正模块以及非饱和单元抗剪强度修正模块,实现了利用FLAC3D进行饱和?非饱和渗流分析,同时基于饱和?非饱和渗流场修正非饱和区土体单元的有效应力以及抗剪强度,完成了将FLAC3D中饱和土流?固耦合计算原理扩展到非饱和土中。在二次开发的分析模块基础上对Liakopoulos砂柱排水试验进行数值模拟,验证了计算模型和计算程序的正确性。同时也研究了降雨入渗对土质边坡的渗流场、位移场以及稳定性演变过程的影响,揭示了降雨诱发边坡失稳的机制。     

基于车载重力测量平台的城市地下空洞快速探测

为了解决现有静态重力测量在城市地下空洞探测时存在工作难度大、效率低等问题,本文提出了基于车载重力测量平台的城市地下空洞快速探测方法。采用国产高精度捷联式重力仪SAG搭建车载移动重力测量平台,在长春卫星广场附近进行动态重力测量试验。首先对测得数据进行楼房干扰校正;之后采用基于传统极值点深度估计(depth from extreme points,DEXP)方法改进的比值DEXP方法进行重力异常数据深度成像;最后采用Tilt梯度法对位场数据进行边界识别。选取轻轨站附近两条测线进行研究,得出测线在700～1 300m区域附近存在负值异常,在800和1 000m附近最佳深度分别是24和28m,构造指数分别为0.18和0.06;经分析符合实际地下轻轨站空洞类型和所在范围,验证了车载移动平台重力测量在城市地下空洞探测中展开的可能性和有效性。     

Stretching correction for amplitude-preserving vector wavefield reverse-time migration

The migration of multi-wave seismic data is aimed at obtaining the P- and S-wave imaging results of the amplitude preserving. But the P- and S-wave stretching effect produced by the reverse time migration of the elastic wave equation will not only reduce the vertical resolution of the migration results and the amplitude preserving of the large reflection angle. In this paper, the reverse time migration technique of amplitude preserving vector wave-field separating is used. Based on the analysis of the stretch mechanism and the influencing factors of stretch magnitude, the paper gave the stretch correcting factors. Then, realize the stretch correction method at the time that after the reverse extrapolation and before the imaging by solving the problem which is how to calculate the P-wave and Ps-wave propagation directions of imaging points at different times. The stretch correction method can improve the vertical resolution and amplitude fidelity of the imaging results and provide high fidelity input data for seismic data interpretation and inversion.© 2019 China Geology Editorial Office.     

双基雷达联合探测降水廓线的研究

利用1998年淮河流域能量和水循环试验(HUBEX)中的一次地面雷达与星载雷达(简称为双基雷达)联合探测雨强的资料,比较了现有的几种测雨雷达回波衰减订正方法.选取了一条比较有代表性的降水廓线,利用地基雷达数据对其进行衰减订正.结果表明,在雨区的中上部,星载雷达探测效果优于地基雷达;从"零度层亮带”往下至近地面,地基雷达探测效果优于星载雷达.     

SEISMIC GEOLOGY

正20141967An Zhanghui(Lanzhou Base of Institute of Earthquake Prediction,CEA,Lanzhou 730000,China);Du Xuebin Study onthe Geo-Electric Field Variation of Sichuan Lushan MS7.0and Wenchuan MS8.0Earthquake(Chinese Journal of Geophysics,ISSN0001-5733,CN11-2074/P,56(11),