On the recent global mean sea level changes: Trend extraction and El Niño's impact

The spatial sampling offered by TOPEX and Jason series of satellite radar altimeters and its continuity during the last twenty years are major assets to provide an improved vision of the global mean sea level (GMSL). The objective of this paper is to examine the recent GMSL variations (1993–2012) and to investigate the correlation between the GMSL and ENSO (El Niño-southern oscillation) episodes. For this purpose, a mean sea level anomalies time series, obtained from TOPEX, Jason-1 and Jason-2 measurements, is used to determine the trend of GMSL changes by using a simplified form of an unobserved components model (namely UCM). Then, to investigate the impact of the ENSO phenomenon on the GMSL changes, we considered the sea surface temperature anomalies (SSTA) index over the Niño3 region (5N–5S 150W–90W). Cross wavelet transform and wavelet coherence analysis are performed to expose common power between the GMSL changes and the SSTA index and their relative phase in the time–frequency space. The results indicate that there are in the estimated GMSL's trend a number of fluctuations over short periods that are least partly related to the El Niño/La Niña episodes. Cross wavelet transform and wavelet coherence analysis indicate that a significant correlation between GMSL and ENSO occurred during 1997–1998, 2006–2007, 2009–2010 El Niño events and 2007–2008 and 2010–2011 La Niña ones. All these areas show in-phase relationship, suggesting that GMSL and SSTA index vary synchronously.     

合成地震记录标定反射层位方法简析

地震层位的标定是地震勘探构造解释的基础,合成地震记录与井旁道对比是层位标定的一个主要方法。层位标定精度除了受地震资料本身的质量及测井资料质量影响之外,制作合成地震记录的准确性取决于地震剖面极性、反射系数、平均速度、地震子波等关键因素的精度。通过介绍确定各种参数的关键技术,提出了在标定地震发射层位中采用的具体方法和标准,如利用相关系数对比时相关系数应大于0.6;利用平均速度对比确定的人工合成地震记录与实际剖面形态差异较小;时深调整前后测井曲线在形态上不应存在差异等。另外为提高对比精度,对目的层段时深关系进行调整时,应结合其他资料,如电性曲线、岩性剖面及钻井地质分层等信息,使之符合地质规律。     

Fibre-reinforcement of granular materials: DEM visualisation and analysis

Mechanical properties of granular materials can be significantly improved by the inclusion of small amounts of short synthetic fibres. This phenomenon has been experimentally studied before by many researchers who have found that the shear strength of a granular material can be significantly improved. This study presents a visualisation of the phenomenon using discrete element method (DEM) simulations of direct shear tests conducted on mixtures of an idealised granular material and randomly oriented fibres. Snapshots showing the deformation of the samples, the velocity vectors of the particles and the force chains produced inside the samples are presented at different stages of the tests. Changes in shear strength and porosity are also illustrated. It was found that the reinforcement produced depends mostly on the rigidity of the fibres.     

基于小波核双重加权SVM模型的蓝藻水华识别与变化检测

以淀山湖为研究区域,利用Landsat系列遥感影像,提出了归化蓝藻指数的构建方法,结合波段组合和Gabor滤波器构建多特征空间,并基于变精度粗糙集和灰色关联决策相结合的方法进行特征空间的优化。在此基础上,采用小波核双重加权SVM分类模型,得到研究区蓝藻水华空间分布格局的识别与检测结果。以误差矩阵证明此分类模型能够较准确地识别出蓝藻水华覆盖区,满足环境调查的要求。研究成果为淀山湖蓝藻水华的防治和水生生态系统的保护提供了科学依据。     

庐枞火山岩盆地北部马鞭山铁矿床磁异常特征及找矿预测

马鞭山铁矿处于庐枞火山岩盆地北部边缘,其赋矿层位为东马鞍山(T2d)含铁质、钙质泥质粉砂岩。航磁为梯度带上叠加局部异常、局部异常形态规则,其走向与梯度带大致平行;地磁与航磁对应较好,异常未分解;地磁异常剖面曲线连续完整且正负伴生、具低缓特征。小波变换较好地分离出了矿致异常。盆地西侧和北侧二条航磁梯度带上局部低缓磁异常系寻找该类铁矿的重要指示信息。     

面向高光谱图像分类的超像素级Gabor特征融合方法研究

由于高光谱图像中的地物空间分布具有规整性和局部连续性,同时超像素分割是一种将空间图像分割成多个同质区域的有效方法,因此从超像素的角度进行高光谱图像分类将具有重要意义.本文提出了一种超像素级Gabor特征融合的高光谱图像分类方法,简称为SPGF.首先,使用一组预定义的二维Gabor滤波器与原始高光谱图像进行卷积运算,提取有效特征.同时,利用简单线性迭代聚类（简称SLIC）超像素分割方法将原始高光谱图像划分成互不重叠的超像素.然后,对于每个Gabor特征模块,利用支持向量机分类器进行分类,并使用多数投票策略实现各模块分类结果的融合.最后,使用通过SLIC算法得到的超像素图对分类结果进行修正.在2个真实高光谱数据集上的实验结果表明,本文提出的SPGF方法能够比领域内的一些经典算法获得更高的分类效果.     

小波去噪的灰色最小二乘支持向量机变形预测

针对变形监测数据的随机性和非平稳性,以及单一预测模型的不足,该文提出了基于小波去噪的灰色最小二乘支持向量机变形预测模型。采用小波去噪对原始数据进行降噪处理,减弱数据随机扰动的影响,建立灰色最小二乘支持向量机模型,并采用粒子群算法寻找最优参数。通过大坝位移监测数据实例对模型进行验证,并与灰色模型、最小二乘支持向量机以及灰色最小二乘支持向量机进行对比分析。实验结果证明,该模型预测精度更高、稳定性更强。     

基于视觉掩盖效应的自适应图像压缩算法

通过分析压缩过程中图像失真的产生机制，提出了一种基于视觉掩盖效应的自适应压缩算法。由于图像是一种非平稳信源，算法采用分块小波变换，并根据图像块的纹理复杂度进行自适应分解，以适应图像不同区域的统计特性。与JPEG2000的对比实验表明，该算法在高倍率压缩时可有效地提高解压图像的视觉质量，较好地保留了图像中的细节及微弱信息。     

Spatiotemporal environmental triggers of Ebola and Marburg virus transmission

Despite their fame, Ebola and Marburg viruses (family Filoviridae) remain mysterious. Filovirus outbreaks are restricted to tropical Africa, but their likely geographic extent has been outlined only recently, and their natural reservoir host(s) remains unidentified. If environmental conditions associated with outbreaks in space and time can be identified precisely, much could be learned about the ecology, evolution and transmission of these viruses. We examined five filovirus outbreaks for which time series of remotely sensed data (NDVI values) are available and for which the reservoir-to-human index case transmission timing and location are known. A wavelet analysis was used to detect anomalous behaviour in the NDVI signal across multiple time scales for each outbreak. Scale-wise anomalies were manifested at a 20-day scale, and were found in four of the five sites, one to three weeks preceding outbreaks, suggesting that filovirus-caused disease outbreaks may be associated with either behavioural shifts in a vertebrate host or changes in viral population dynamics. More generally, wavelet analysis offers a powerful tool for identifying temporal correlates of disease transmission events.     

Study of hydro-sedimentary variability of the Radicatel karst system influenced by climate signal fluctuations (Normandy,France)

ABSTRACT

This study relies on the use and analysis of hydro-meteorological variables, long turbidity time series (from 1988 to 2009, 21 years) and a sedimentary record to provide better understanding of the hydro-sedimentary variability of the karst system near the town of Radicatel, France. Wavelet analysis of rainfall, piezometric level and turbidity, as well as the sediment archive, show common modes of variability. A common spectral composition emphasizes the influence of climate controls. Comparison of the wavelet spectra with the North Atlantic Oscillation (NAO) spectrum clearly highlights the control of the latter on hydro-meteorological variables at the regional level. Climatic fluctuations are recorded in the turbidity signal and in sedimentary fill, as revealed by the 5- to 8-year frequency band, which is characteristic of the NAO index. A climatic signal is recorded in both rainfall events and piezometric levels, and also in sediment transport and deposition at the scale of the local karst system. The overall climate control is also present beyond the local variations and heterogeneities.

EDITOR D. Koutsoyiannis ASSOCIATE EDITOR D. Yang