基于图像检索技术的岩石单轴压缩破坏过程CT描述

基于X射线的CT扫描技术,因其具有多层位、对同一岩石试件可连续、无损扫描等优点,在岩石力学与工程研究中得到了广泛应用。对岩石单轴压缩破坏过程进行实时CT扫描,也是岩石力学研究的重要内容之一。针对三维显微CT试验系统实时监测煤岩单轴压缩破坏过程中,因位移误差会引起扫描层定位不准确,进而影响试验结果这一基本问题,提出了基于图像检索技术的CT扫描图像处理方法。通过对煤岩试样在单轴载荷作用下破坏过程的CT实时监测,并引入基于Manhattan距离的相似性计算方法,检索出岩石试件同一层位在不同应力状态下的相似扫描层。结果表明,采用图像检索的方法,可以有效地减小煤岩在加载破坏过程中位移误差的影响,更好地通过CT图像来描述煤岩在不同应力状态下的微裂纹分布状况和演化规律,从而在细观层次上揭示岩石在单轴压缩条件下破坏的基本规律。     

水体石油类信息遥感提取模式研究

石油类是水体有机污染物中的一种,其对水体吸收系数的影响主要体现在有色可溶性有机物(chromophoric dissolved organic matter,CDOM)的光吸收特性上。在水色遥感领域,CDOM光吸收特性主要用其在参考波段的吸收系数和光谱斜率来表征。利用2008年5月、2009年8月和2010年6月在辽宁省盘锦市辽河油田境内获取的CDOM吸收系数、水体表观光学特性以及石油类污染浓度等试验数据,确定表征石油类污染水体CDOM吸收光谱特性的光谱斜率;根据光谱斜率以及表征CDOM浓度的440 nm参考波段吸收系数,建立遥感反演水体石油类污染浓度的模式,并利用31个野外现场实测值对模式精度进行了验证,结果表明,该模式的相对误差为7%;将该模式应用于国产卫星环境一号遥感数据,获取双台子河及辽东湾近岸水体石油类污染空间分布图。     

Assessment of total suspended sediment concentrations in Poyang Lake using HJ-1A/1B CCD imagery

We explored the potential of the environment and disaster monitoring and forecasting small satellite constellations (HJ-1A/1B satellites) charge-coupled device (CCD) imagery (spatial resolution of 30 m, revisit time of 2 days) in the monitoring of total suspended sediment (TSS) concentrations in dynamic water bodies using Poyang Lake, the largest freshwater lake in China, as an example. Field surveys conducted during October 17-26, 2009 showed a wide range of TSS concentration (3-524 mg/L). Atmospheric correction was implemented using the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) module in ENVI with the aid of aerosol information retrieved from concurrent Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) surveys, which worked well at the CCD bands with relatively high reflectance. A practical exponential retrieval algorithm was created between satellite remote sensing reflectance and in-situ measured TSS concentration. The retrieved results for the whole water area matched the in-situ data well at most stations. The retrieval errors may be related to the problem of scale matching and mixed pixel. In three selected subregions of Poyang Lake, the distribution trend of retrieved TSS was consistent with that of the field investigation. It was shown that HJ-1A/1B CCD imagery can be used to estimate TSS concentrations in Poyang Lake over synoptic scales after applying an appropriate atmospheric correction method and retrieval algorithm.     

Remote sensing retrieval of total absorption coefficient in the Bohai Sea

Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex.In this paper,we used 77 groups of field data of AOPs(apparent optical properties) and IOPs(inherent optical properties) collected in June,August,and September of 2005 in the Bohai Sea,to retrieve the spectral total absorption coefficient a(λ) with the quasi-analytical algorithm(QAA).For QAA implementation,different bands in the region 680-730 nm(in 5 nm intervals) were selected and compared,to determine the optimal band domain of the reference wavelength.On this basis,we proposed a new algorithm(QAA-Com),a combination of QAA-685 and QAA-715,according to turbidity characterized by a(440).The percentage difference of model retrievals in the visible domain was between 4.5%-45.1%,in average of 18.8% for a(λ).The QAA model was then applied to Medium Resolution Imaging Spectrometer(MERIS) radiometric products,which were temporally and spatially matched with in-situ optical measurements.Differences between MERIS retrievals and in-situ values were in the range 9.2%-27.8% for a(λ) in the visible domain.Major errors in satellite retrieval are attributable to uncertainties of QAA model parameters and in-situ measurements,as well as imperfect atmospheric correction of MERIS data by the European Space Agency(ESA).During a storm surge in April 2009,time series of MERIS images together with the QAA model were used to analyze spatial and temporal variability of the total absorption coefficient pattern in the Bohai Sea.It is necessary to collect more independent field data to improve this algorithm.     

Equipartitioning is not sufficient for Green's function extraction

The extraction of the Earth's Green's function from field fluctuations is a rapidly growing area of research.The principle of Green's function extraction is often related to the requirement of equipartitioning,which stipulates that the energy of field fluctuations is distributed evenly in some sense.We show the meaning of equipartitioning for a variety of different formulations for Green's function retrieval.We show that equipartitioning is not a sufficient condition,and provide several examples that illustrate this point.We discuss the implications of lack of equipartitioning for various schemes for the reconstruction of the Green's function in seismology.The theory for Green's function extraction is usually based on a statistical theory that relies on ensemble averages.Since there is only one Earth,one usually replaces the ensemble average with a time average.We show that such a replacement only makes sense when attenuation is taken into account,and show how the theory for Green's function extraction for oscillating systems can be extended to incorporate attenuation.     

太阳诱导叶绿素荧光的卫星遥感反演方法

利用卫星遥感探测区域和全球尺度太阳诱导叶绿素荧光SIF(Solar-Inducedchlorophyll Fluorescence)近年来成为研究热点。由于地球大气吸收和散射的影响,卫星尺度的SIF反演问题较为复杂,科学界对该问题一直存在争议,不同科学团队提出了众多方法。本文介绍了大气层顶SIF反演的机理、难点及思路,总结了近10年来最新发展的大气层顶SIF反演算法,并将这些算法归纳为3类:基于辐射传输方程的算法、简化的物理模型算法和数据驱动算法,分析讨论了各算法的特点及适用性;以应用最广泛的数据驱动算法为例,基于GOME-2数据详细介绍了算法的中间环节及注意事项;最后回顾了卫星遥感反演SIF的发展历程,汇总了目前及未来具有荧光探测能力的星载传感器,并依据数据源的特点相应地给出了适用的SIF反演算法,为今后基于航空和卫星高光谱数据的SIF反演提供了依据。     

一种改进的扇形波束旋转扫描散射计海面风矢量反演算法

扇形波束旋转扫描散射计（RFSCAT）是约十年前才被提出来的一种新型星载微波散射计。与其它旋转扫描散射计类似,其星下点附近区域和刈幅边缘区域的风场反演误差相对较大。在本文设定的参数条件下,RFSCAT散射计刈幅边缘区域的风向反演精度相对于轨道中间区域降低了约9°。针对这一问题,本文为RFSCAT散射计提出了一种改进的风矢量反演算法。新算法的主要特征是,根据风向反演偏差直方图,在整个刈幅区域内,对模糊解风向取值区间进行自适应扩展,以获取并保留更多可能风向解。利用模拟的100条轨道的L2A数据,对新算法进行反演验证。实验结果证明,新算法能够有效改善RFSCAT散射计星下点附近区域和轨道刈幅边缘区域的风向反演精度。星下点和刈幅边缘上的风矢量单元的风向反演精度相对于标准的MLE算法分别提高了1.6°和9°。     

Retrieving soil water contents from soil temperature measurements by using linear regression

A simple linear regression method is developed to retrieve daily averaged soil water content from diurnal variations of soil temperature measured at three or more depths. The method is applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 10, and 30 cm during 11-20 June 1995. The retrieved bulk soil water contents are compared with direct measurements for one pair of nearly collocated Mesonet and ARM stations and also compared with the retrievals of a previous method at 14 enhanced Oklahoma Mesonet stations. The results show that the current method gives more persistent retrievals than the previous method. The method is also applied to Oklahoma Mesonet soil temperature data collected at the depths of 5, 25, 60, and 75 cm from the Norman site during 20-30 July 1998 and 1-31 July 2000. The retrieved soil water contents are verified by collocated soil water content measurements with rms differences smaller than the soil water observation error (0.05m~3 m~(-3)). The retrievals are     

《大气、水灾害科技文献目录》检索系统

论述了《大气、水灾害科技文献目录》检索系统的数据来源、研制方式、文献分类和著录及社会效益