利用层析成像方法反演近地表速度模型

由于地表条件复杂和近地表速度变化显著给近地表速度模型的反演工作带来了很大的困难。层析成像方法可以较好地模拟介质横向和纵向的速度变化,能同时考虑直达波、透射波、回折波、折射波等初至波,为确定近地表速度结构提供了有效的工具。主要介绍了层析成像的方法原理,并应用此方法反演了实际地震探区的近地表速度模型,取得了良好的应用效果。     

Deep-towed High Resolution multichannel seismic imaging

High Resolution (220–1050 Hz) seismic acquisition performed in deep water using deep-towed systems provides unrivalled lateral resolution when compared to conventional surface seismic. The lateral resolution of these acquisitions is controlled by the width of the first Fresnel zone, taking advantage of their positions close to the sea bottom. No current existing deep towed equipment can benefit from seismic imaging processing techniques to improve this resolution as a consequence of positioning inaccuracies. The technological developments of a digital deep-towed multichannel streamer are presented with a particular attention to positioning: each hydrophone incorporates a pitch, roll and heading sensor in order to monitor the constant deformation of the streamer in operation. The sea trials took place in July 2013 in the Mediterranean Sea. Pre-stack depth migration applied to the deep-towed multichannel data illustrates the potential of this emerging methodology in terms of penetration (12 dB improvement in Signal/Noise) and lateral resolution (mean signal wavelength: 3 m) when compared with deep-towed single-channel acquisition.     

Trends in the near-zero range of the minimum air-temperature distribution

This study estimated the trends in the number of days that fall within the near-zero (0?°C) range of the temperature continuum. This narrow range has importance for potential transportation hazards and freeze-thaw cycles. While the tails of the air-temperature distribution and their trends often are closely examined under the climate change context, the frequency and trend of other portions of the air-temperature distribution can be equally important, as many societal impacts are caused by events in the non-tail region, such as near-zero °C temperatures (NZT). Examining the trend of the number of NZT days over the conterminous USA for the period of 1948–1949 through 2010–2011, we found three distinct spatial clusters. The most distinctive spatial clusters are found along the West Coast (positive temperature trends leading to a decrease in NZT days), the High Plains and Northern Rockies (positive temperature trends leading to an increase in NZT days), and the southeastern USA (negative temperature trends leading to an increase in NZT days). While trends in the number of NZT days are linked to changes in mean minimum air temperature, increasing minimum temperature leads to a positive trend at NZT days only at some locations.     

A forestry GIS-based study on evaluating the potential of imaging spectroscopy in mapping forest land fertility

Fertility, or the availability of nutrients and water, controls forest productivity. It affects its carbon sequestration, and thus the forest's effect on climate, as well as its commercial value. Although the availability of nutrients cannot be measured directly using remote sensing methods, fertility alters several vegetation traits detectable from the reflectance spectra of the forest stand, including its pigment content and water stress. However, forest reflectance is also influenced by other factors, such as species composition and stand age. Here, we present a case study demonstrating how data obtained using imaging spectroscopy is correlated with site fertility. The study was carried out in Hyytiälä, Finland, in the southern boreal forest zone. We used a database of state-owned forest stands including basic forestry variables and a site fertility index. To test the suitability of imaging spectroscopy with different spatial and spectral resolutions for site fertility mapping, we performed two airborne acquisitions using different sensor configurations. First, the sensor was flown at a high altitude with high spectral resolution resulting in a pixel size in the order of a tree crown. Next, the same area was flown to provide reflectance data with sub-meter spatial resolution. However, to maintain usable signal-to-noise ratios, several spectral channels inside the sensor were combined, thus reducing spectral resolution. We correlated a number of narrowband vegetation indices (describing canopy biochemical composition, structure, and photosynthetic activity) on site fertility. Overall, site fertility had a significant influence on the vegetation indices but the strength of the correlation depended on dominant species. We found that high spatial resolution data calculated from the spectra of sunlit parts of tree crowns had the strongest correlation with site fertility.     

A multiple-point statistics algorithm for 3D pore space reconstruction from 2D images

Fluid flow behavior in a porous medium is a function of the geometry and topology of its pore space. The construction of a three dimensional pore space model of a porous medium is therefore an important first step in characterizing the medium and predicting its flow properties. A stochastic technique for reconstruction of the 3D pore structure of unstructured random porous media from a 2D thin section training image is presented. The proposed technique relies on successive 2D multiple point statistics simulations coupled to a multi-scale conditioning data extraction procedure. The Single Normal Equation Simulation Algorithm (SNESIM), originally developed as a tool for reproduction of long-range, curvilinear features of geological structures, serves as the simulation engine. Various validating criteria such as marginal distributions of pore and grain, directional variograms, multiple-point connectivity curves, single phase effective permeability and two phase relative permeability calculations are used to analyze the results. The method is tested on a sample of Berea sandstone for which a 3D micro-CT scanning image is available. The results confirm that the equi-probable 3D realizations obtained preserve the typical patterns of the pore space that exist in thin sections, reproduce the long-range connectivities, capture the characteristics of anisotropy in both horizontal and vertical directions and have single and two phase flow characteristics consistent with those of the measured 3D micro-CT image.     

Monitoring crack development in fiber concrete beam by using electrical resistivity imaging

Accurate detection of damaged concrete zones plays an important role in selecting the proper remedial technique. This study presents results from an application of the electrical imaging method to monitor the development of cracks in fiber concrete beams.The study showed that resistivity measurements on the concrete specimens were able to detect the increase of concrete resistivity with the curing time that reached about 65 Ωm after 28 days of curing. A similar development trend of concrete compressive strength was also found.Two types of cracks were investigated, i.e., artificial cracks made of plastic sheets inserted in concrete and cracks developed during a four-step loading test. A mini-electric imaging survey with Wenner array was conducted on the tension face of the beams. To deal with the effect of the beam size new procedures to correct resistivity measurements before inversion were proposed and successfully applied in this study. The results indicated that both crack direction and depth could be accurately determined in the inverted resistivity sections.     

PET/MRI新技术应用研究进展

PET/CT的广泛应用有力地促进了核医学的发展。MRI与CT相比有更高的软组织对比度和空间分辨率,且无电磁辐射,因此PET/MRI的研究成为近些年的热点,并已取得了初步的进展,虽然目前PET/MRI离广泛应用还存在一定距离,但已有的研究成果表明,PET/MRI具有广阔的发展空间,有望将分子影像技术的发展带入一个新的时代...     

云南岩溶石山区物探找水方法与实例分析

西南地区水资源短缺严重威胁到当地人民群众生活用水,也制约了本地区的经济发展。如何针对西南缺水地区水文地质特点,合理选择地球物理勘探综合技术方法寻找地下水,提高地下水勘查效率,是水文地质工作面临的十分重要问题。本文介绍了电导率成像系统和高密度电阻率法的基本原理、技术特点和适用范围,结合云南岩溶山区地下水勘查的应用实例,进行对比分析,圈定了含水岩溶带,确定了井位,有效解决了当地供水问题,说明了方法的有效性。提出西南地区地下水勘查建议,为今后的地下水资源利用工作提供借鉴。     

TEM虚拟波场三维连续速度分析及其在隧道超前预报中的应用

针对当前隧道超前地质预报工作中不能对于掌子面前方的水患进行有效预报的情况,笔者提出一种基于浮动薄板理论的隧道掌子面前方不良地质体的瞬变电磁波场变换延拓成像的超前预报有效方法,引入比较合适的三维的虚拟速度连续分析方法,解决了偏移成像中对实测资料的速度提取问题。给出了瞬变电磁方法在隧道中适用的工作方法。对理论模型和应用实例都进行了分析计算,得到的结果与实际情况相符合,表明该速度分析方法是切实有效的。     

支持向量机与微电阻率成像测井识别火山岩岩性

针对火山岩储层,从岩石化学成分分类和岩石结构分类两个角度出发,提出了一种利用测井资料识别火山岩岩性的方法。基于取芯薄片鉴定资料获得对应井段的常规测井数据,利用统计学习理论中的支持向量机方法对其处理,得到地质上按岩石化学成分分类的火山岩岩性类别。建立地层微电阻率成像测井图像与不同结构火山岩岩性之间的对应关系,归纳出典型的微电阻率图像模式,从而得到地质上按岩石结构分类的火山岩岩性类别,结合上述两者结论确定最终岩性,实现了运用支持向量机算法处理常规测井资料与微电阻率图像模式相结合的火山岩岩性测井识别新方法。