基于多轨道卫星观测数据分析尼泊尔地震长波辐射特征

综合已经在红外异常提取中应用的涡度和RST(Robust Satellite Technique)算法优点,提出了红外异常指数算法.并基于长时间尺度的中国静止卫星FY-2D和美国极轨卫星NOAA长波辐射数据,应用RST和异常指数算法,分别对2015年4月25日尼泊尔M_s8.1和5月12日M_s7.5地震前后卫星长波辐射变化特征进行了分析,开展了多轨道、多时空分辨率长波辐射同步地震热红外特征研究.结果表明,运用RST算法,两次地震前后,未能在震中周围发现明显的长波辐射异常.运用异常指数算法:(1)对于NOAA卫星,4月15日在M_s8.1地震震中以西出现热红外异常,到4月24日震中以西约100 km处出现异常最大值,随后逐渐消失.5月10日在M_s7.5地震震中以东约200 km发现异常;(2)在NOAA卫星长波辐射异常发现最大值当日,采用FY-2D卫星每3 h的数据分析可发现红外异常的动态演化过程,弥补NOAA卫星分辨率不足.以上结果为利用多轨道卫星监测地震热辐射变化提供了依据.     

Characterisation and multifaceted anisotropy assessment of Corvio sandstone for geological CO2 storage studies

We present a comprehensive characterisation of the physical, mineralogical, geomechanical, geophysical, and hydrodynamic properties of Corvio sandstone. This information, together with a detailed assessment of anisotropy, is needed to establish Corvio sandstone as a useful laboratory rock‐testing standard for well‐constrained studies of thermo–hydro–mechanical–chemical coupled phenomena associated with CO₂ storage practices and for geological reservoir studies in general. More than 200 core plugs of Corvio sandstone (38.1 and 50 mm diameters, 2:1 length‐to‐diameter ratio) were used in this characterisation study, with a rock porosity of 21.7 ± 1.2%, dry density 2036 ± 32 kg m^?3, and unconfined compressive and tensile strengths of 41 ± 3.28 and 2.3 ± 0.14 MPa, respectively. Geomechanical tests show that the rock behaves elastically between ～10 and ～18 MPa under unconfined conditions with associated Young's modulus and Poisson's ratio of 11.8 ± 2.8 GPa and 0.34 ± 0.01 GPa, respectively. Permeability abruptly decreases with confining pressure up to ～10 MPa and then stabilises at ～1 mD. Ultrasonic P‐ and S‐wave velocities vary from about 2.8–3.8 km s^?1 and 1.5–2.4 km s^?1, respectively, over confining and differential pressures between 0.1 and 35 MPa, allowing derivation of associated dynamic elastic moduli. Anisotropy was investigated using oriented core plugs for electrical resistivity, elastic wave velocity and attenuation, permeability, and tracer injection tests. Corvio sandstone shows weak transverse isotropy (symmetry axis normal to bedding) of <10% for velocity and <20% for attenuation.     

Uncertainty analysis and probabilistic segmentation of electrical resistivity images: the 2D inverse problem

In this paper, we present the uncertainty analysis of the 2D electrical tomography inverse problem using model reduction and performing the sampling via an explorative member of the Particle Swarm Optimization family, called the Regressive‐Regressive Particle Swarm Optimization. The procedure begins with a local inversion to find a good resistivity model located in the nonlinear equivalence region of the set of plausible solutions. The dimension of this geophysical model is then reduced using spectral decomposition, and the uncertainty space is explored via Particle Swarm Optimization. Using this approach, we show that it is possible to sample the uncertainty space of the electrical tomography inverse problem. We illustrate this methodology with the application to a synthetic and a real dataset coming from a karstic geological set‐up. By computing the uncertainty of the inverse solution, it is possible to perform the segmentation of the resistivity images issued from inversion. This segmentation is based on the set of equivalent models that have been sampled, and makes it possible to answer geophysical questions in a probabilistic way, performing risk analysis.     

The use of 3D modeling for the prediction of the seismic demands on the gravity dams

Seismic behavior of gravity dams has long been evaluated using a representative two‐dimensional (2D) system. Formulated for the gravity dams built in wide canyons, the assumption is nevertheless utilized extensively for almost all concrete dams due to the established procedures as well as the expected computational costs of a three‐dimensional model. However, a significant number of roller‐compacted concrete dams, characterized as such systems, do not conform to the basic assumptions of these methods by violating the conditions on canyon dimensions and joint‐spacing/details. Based on the premise that the 2D modeling assumption is overstretched for practical purposes in a variety of settings, the purpose of this study is to critically evaluate the use of 2D modeling for the prediction of the seismic demands on these systems. Using a rigorous soil–structure interaction approach, the difference between the two and three‐dimensional response for gravity dams was investigated first in the frequency domain for a range of canyon widths and foundation to dam moduli ratios. Then, the time domain differences between the crest displacements and the maximum principal stress were obtained using 70 different ground motions in order to show the possible bias introduced into the analysis results due to the modeling approach. The results of the study show that even for relatively wide canyons, the 2D analysis can lead to misleading predictions. Copyright © 2017 John Wiley & Sons, Ltd.     

结合ICESat-2和GEDI的中国东南丘陵地区ASTERGDEM高程精度评价与修正

星载激光雷达ICESat-2和GEDI可以为数字高程模型产品的精度评价与修正提供全球覆盖的、可靠的高精度参考数据源。然而,现有的DEM修正方法主要是针对DEM误差中的植被高信号且多采用线性回归模型。为此,本文分析了ASTER GDEM v3精度与土地覆盖类型、高程、坡度、起伏度及植被覆盖率的关系。在此基础上,提出了一种考虑上述多种精度影响因素并结合XGBoost和空间插值的DEM误差修正方法。结果分析表明:原始ASTER GDEM的误差整体呈正态分布,平均误差为-3.463 m,存在较大负偏差,高程精度随着高程、坡度、起伏度及植被覆盖率VCF的增大呈降低趋势;经过修正后,ASTER GDEM平均误差降低到了-0.233 m,负偏差得到有效改善,整体平均绝对误差降低了26.04%,整体均方差降低了23.56%,耕地、林地、草地、湿地、水域及人造地表的DEM平均绝对误差和均方差都有不同程度的降低;本文提出的方法对多种特征要素与地形误差间的非线性关系进行拟合建模,在研究区取得了较好的修正效果。     

湛江近海M2分潮的数值模拟

利用潮汐模型,在高分辨率的自适应曲线网格下,采用潮汐调和常数作为控制模拟精度的方法,模拟了洪江附近海域M2分潮的运动特征。模拟所得的潮汐调和常数同实测值相比,误差较小。根据模拟结果绘制的M2分潮的同潮图,揭示了湛江附近海域M2分潮振幅和迟角的分布特征以及M2分潮的传播和发展规律。模拟得到的M2分潮分别在涨憩、落憩、涨急和落急几个典型时刻的流场,揭示了湛江附近海域M2分潮潮流的分布特征及其运动规律。     

答“评‘紫坪铺水库造成孔隙弹性耦合变化及其对2008年汶川地震触发作用’二维模拟的局限性”

程惠红等(2015)在"评‘紫坪铺水库造成孔隙弹性耦合变化及其对2008年汶川地震触发作用’二维模拟的局限性"一文中提出,陶玮等(2014)采用二维模型模拟紫坪铺水库造成孔隙弹性耦合变化是一个不足,夸大了汶川地震震源处库仑应力增长值.我们认为采用二维模型模拟水库造成汶川地震震源处库仑应力变化确实可能存在一定偏差,但不会如程惠红等认为的"与三维模型相比夸大三倍".这是因为在程惠红等引用的论证中,二维模型计算中选取了接近水库最大剖面宽度而不是水库平均剖面宽度作为加载量参数,造成计算得到震源处库仑应力明显夸大.此外,陶玮等(2014)提出论断的主要依据不是"震源处"库仑应力值的大小,而是紫坪铺水库蓄水"由浅入深影响到整条断层,尤其对浅层范围的加载作用明显,达上百千帕,为整个断层面的失稳提供了基础".初始破裂的发生既可能是由水库蓄水引起,也可能是并非水库蓄水造成的一次普通构造小震,但其发生引发断层面上部已被水库蓄水弱化部分的连锁失稳而发生大震.即汶川地震既可能为直接触发也可能为间接触发,而我们的研究结果认为地震的发生完全可能由间接触发产生.若仅纠结于"震源处"的库仑应力变化,则忽视了水库蓄水影响的主体.水库蓄水对地震触发作用是一个复杂问题,相对这一问题所涉及的一系列不确定性因素来说,二维模拟的局限性所造成的影响并不很大也不是最大的,也不妨碍我们据此得出紫坪铺水库蓄水促进汶川地震发生的结论.     

短波红外CO2反演过程约束研究及初步反演结果

短波红外通道卫星CO2遥感是近年国际研究热点。首先,开展了卫星观测对气溶胶及大气温度的敏感性研究;其次,针对基于最优化理论的非线性迭代反演方法反演过程中的不收敛问题,提出了修正的阻尼牛顿方法(MDNM),并利用模拟数据评估了MDNM方法的有效性;最后,利用GOSAT卫星数据反演CO2的垂直混合比浓度,并与地基TCCON站点数进行比对。研究结果表明:短波近红外CO2卫星遥感受气溶胶散射及温度影响明显;通过地基比对初步验证了MDNM具有良好的精度,两者的相关性R2达到了0.729。     

顾及OSB改正的BDS-3新频点精密单点定位精度分析

基于武汉大学发布的BDS-2/3观测量偏差(OSB)改正产品,采用国内8个iGMAS测站1个月的观测数据,分析OSB改正前后对B1I/B3I旧频点及B1C/B2a新频点2种组合模式下BDS-2/3伪距单点定位(SPP)和精密单点定位(PPP)精度的影响。结果表明,B1I、B3I、B1C和B2a的OSB年均值为-80～70 ns,各频点OSB年稳定性分别为3.41 ns、5.87 ns、2.04 ns和2.32 ns。在BDS-2/3伪距单点定位方面,改正后B1I/B3I组合的3D方向定位精度优于2.53 m, B1C/B2a组合的3D方向定位精度优于3.84 m,二者精度提升均不明显。在BDS-2/3精密单点定位方面,B1I/B3I组合的3D方向定位精度优于7.7 cm,提升约20.6%,收敛时间约为38 min,提升约7.3%;B1C/B2a组合的3D方向定位精度优于3.7 cm,提升约11.9%,收敛时间约为36 min,提升约16.3%。     

金川二矿区地应力测量及研究新进展

金川镍矿是我国著名的有色金属矿山,工程地质条件复杂,矿山开采难度大。近年来由于矿山开发的深入,开采强度、深度、广度的增加,导致了各类工程地质问题恶化。地应力的测量与研究是进行工程地质问题研究的基础,本文总结了主力矿区二矿区地应力研究的历史,根据最新的实地测量数据,对于二矿区的地应力进行了系统研究与分析,总结了最新的矿区地应力分布规律,更新了应力与深度的计算公式,通过分析,1 000m水平为垂直应力逐渐占据主导地位的过渡带,主应力与最大水平应力增加的幅度变缓,带内的应力状况将变得十分复杂,同一深度,不同工程区域可能会出现不同的应力状态,并且随着最大主应力与最小主应力差值的增加,其剪应力将逐渐加大,这对于地下工程施工和采矿都是十分不利的。