中国历史时期土地覆被数据集地理空间重建进展评述

重建长时间序列具有空间属性的土地覆被数据集,对研究历史时期土地利用/土地覆被变化及其气候和生态效应具有重要意义。近年来,国内外学者就定量重建中国区域历史土地覆被数据集进行了积极探索。但由于历史时期土地利用数据来源多元、重建方法多样、验证方式各异等原因,不同学者的重建结果迥异,其中重建方法是导致差异形成的重要原因之一。本文从重建思路、假设和方法、结果验证等方面对覆盖中国区域的主要空间数据集进行了综合评述,结果表明：①基于历史记录的还原法和基于地理空间模型的重建法是历史土地覆被空间重建的主要方法,而根据建模过程,后者又可进一步分为“自上而下”的配置模型和“自下而上”的演化模型法。②基于数量重建进行空间重建是当前历史土地覆被数据集重建的主流,在缺少充分、客观历史数据的条件下,对基础数据、分布控制因素和限制因子进行合理假设是取得合理结果的重要条件。③为提高研究成果的解释力,需要对重建结果进行检验,直接验证法虽较为准确,但受时空尺度限制,具有显著的局限性,间接验证法可作为有效的补充。     

A three-dimensional variational data assimilation system for a size-resolved aerosol model: Implementation and application for particulate matter and gaseous pollutant forecasts across China

A three-dimensional variational(3DVAR) data assimilation(DA) system is presented here based on a size-resolved sectional aerosol model, the Model for Simulating Aerosol Interactions and Chemistry(MOSAIC) within the Weather Research and Forecasting model coupled to Chemistry(WRF-Chem) model. The use of this approach means that both gaseous pollutants such as SO_2, NO_2, CO, and O_3 as well as particulate matter(PM_(2.5), PM_(10)) observational data can be assimilated simultaneously.Two one-month parallel simulation experiments were conducted, one with the assimilation of surface hourly concentration observations of the above six pollutants released by the China National Environmental Monitoring Centre(CNEMC) and one without assimilation in order to verify the impact of assimilation on initial chemical fields and subsequent forecasts. Results show that, in the first place, use of the DA system can provide a more accurate model initial field. The root-mean-square error of PM_(2.5), PM_(10), SO_2, NO_2, CO, and O_3 mass concentrations in analysis field fell by 29.27 μg m~(-3)(53.5%), 34.5 μg m~(-3)(50.9%),30.36 μg m~(-3)(64.2%), 8.91 μg m~(-3)(39.5%), 0.46 mg m~(-3)(47.4%), and 15.11 μg m~(-3)(51.0%), respectively, compared to a background field without assimilation. At the same time, mean fraction error was reduced by 42.6%, 53.1%, 45.2%, 43.1%,69.9%, and 48.8%, respectively, while the correlation coefficient increased by 0.51, 0.55, 0.48, 0.38, 0.47, 0.65, respectively.Secondly, the results of this analysis reveal variable benefits from assimilation on different pollutants. DA significantly improves PM_(2.5), PM_(10), and CO forecasts leading to positive effects that last more than 48 h. The positive effects of DA on SO_2 and O_3 forecasts last up to 8 h but that remains relatively poor for NO_2 forecasts. Thirdly, the influence of assimilation varies in different areas. It is possible that the positive effects of DA on PM_(2.5) and PM_(10) forecasts can last more than 48 h across most regions of China. Indeed, DA significantly improves SO_2 forecasts within 48 h over north China, and much longer CO assimilation benefits(48 h) are found in most regions apart from north and east China and across the Sichuan Basin. DA is able to improve O_3 forecasts within 48 h across China with the exception of southwest and northwest regions and the O_3 DA benefits in southern China are more evident, while from a spatial distribution perspective, NO_2 DA benefits remain relatively poor.     

一次梅雨锋暴雨过程的中尺度对比模拟分析

使用新一代细网格WRF中尺度数值模式和MM5（V3）模式,对2003年7月4～6日发生在江淮流域的一次梅雨锋暴雨过程进行了数值模拟对比分析。结果表明：WRF和MM5都能较好的模拟这次暴雨过程雨带的分布和走向,而WRF能更好的模拟降水中心的位置和雨量;与暴雨过程相联系的低空急流和涡度场等分布特征的模拟,WRF模式亦优于MM5模式。此外,在云贵高原东麓山地,与WRF模式相比,MM5模式在低层模拟出虚假的低压环流,这可能与两模式所采用的垂直坐标差异有关。对WRF的模拟结果分析发现,700hPa湿位涡异常区与暴雨发生区对应很好。     

修正剑桥模型在DPC桩—土结构层中的应用分析

针对DPC桩-土结构层开展大型直剪试验,基于试验分析,在考虑DPC桩-土结构层注浆影响上引入临界应力比,构建了可描述应变软化的修正剑桥模型应力应变方程。直剪试验表明DPC桩-土结构层剪切特性表现为剪切软化,具有明显的峰值强度和残余强度,呈现出明显的结构性,其特征与超固结的黏土的剪切应力应变曲线特性类似。推导出的修正剑桥模型能较好的解释实验结果,所得出的结论对DPC桩的设计有一定的指导意义。      

Shifting Correlation Between Earthquakes and Electromagnetic Signals: A Case Study of the 2013 Minxian–Zhangxian ML 6.5 (MW 6.1) Earthquake in Gansu,China

The shifting correlation method (SCM) is proposed for statistical analysis of the correlation between earthquake sequences and electromagnetic signal sequences. In this method, the two different sequences were treated in units of 1 day. With the earthquake sequences fixed, the electromagnetic sequences were continuously shifted on the time axis, and the linear correlation coefficients between the two were calculated. In this way, the frequency and temporal distribution characteristics of potential seismic electromagnetic signals in the pre, co, and post-seismic stages were analyzed. In the work discussed in this paper, we first verified the effectiveness of the SCM and found it could accurately identify indistinct related signals by use of sufficient samples of synthetic data. Then, as a case study, the method was used for analysis of electromagnetic monitoring data from the Minxian–Zhangxian M_L 6.5 (M_W 6.1) earthquake. The results showed: (1) there seems to be a strong correlation between earthquakes and electromagnetic signals at different frequency in the pre, co, and post-seismic stages, with correlation coefficients in the range 0.4–0.7. The correlation was positive and negative before and after the earthquakes, respectively. (2) The electromagnetic signals related to the earthquakes might appear 23 days before and last for 10 days after the shocks. (3) To some extent, the occurrence time and frequency band of seismic electromagnetic signals are different at different stations. We inferred that the differences were related to resistivity, active tectonics, and seismogenic structure.     

Spatial-temporal pattern changes of main agriculture natural disasters in China during 1990-2011

China is a disaster prone country, and a comprehensive understanding of change of disasters is very important for China’s agricultural development. In this study, statistical techniques and geographic information system tools are employed to quantify the main agriculture disasters changes and effects on grain production in China during the period of 1990-2011. The results show that China’s grain production was severely affected by disasters including drought, flood, hail, frost and typhoon. The annual area covered by these disasters reached up to 48.7×10⁶ ha during the study period, which accounted for 44.8% of the total sown area, and about 55.1% of the per unit area grain yield change was caused by disasters. In addition, all of the disasters showed high variability, different changing trends, and spatial distribution. Drought, flood, and hail showed significantly decreasing trends, while frost and typhoon showed increasing trends. Drought and flood showed gradual changes and were distributed across the country, and disasters became more diversified from north to south. Drought was the dominated disaster type in northern China, while flood was the most important disaster type in the southern part. Hail was mainly observed in central and northern China, and frost was mainly distributed in southern China. Typhoon was greatly limited to the southeast coast. Furthermore, the resilience of grain production of each province was quite different, especially in several major grain producing areas, such as Shandong, Liaoning, Jilin and Jiangsu, where grain production was seriously affected by disasters. One reason for the difference of resilience of grain production was that grain production was marginalized in developed provinces when the economy underwent rapid development. For China’s agricultural development and grain security, we suggest that governments should place more emphasis on grain production, and invest more money in disaster prevention and mitigation, especially in the major grain producing provinces.     

利用CAP 方法快速计算云南地区中小地震震源机制解

地震的震源机制解是反应区域应力场的重要参数,充分利用数量众多的中小地震将有助于获得更高精度的区域应力场分布。本文以滇西地震预报实验场下关虚拟测震台网为例,介绍了利用虚拟台网产出数据,采用CAP 方法计算中小地震震源机制解的流程,并将该方法应用于计算云南地区2013 年2 月～ 2014 年2 月间MS≥3. 0 的64 次中小地震震源机制解。结果显示:①本文给出的方法为一种半自动处理方法,该方法可以在地震速报结果之后45 分钟之内给出震源机制解,分析认为影响震源机制解快速产出的主要因素是格林函数库的建立和编程实现标注P 波到时的全自动化;②云南地区中小地震震源机制解以走滑为主,但在香格里拉和洱源地区有少量正断层地震存在,位于研究区域内中小地震P 轴主应力方向在川滇菱形块体南部以北北西-南南东为主,而在印支板块则主要以北北东-南南西为主。     

地面三维激光扫描技术在变形监测中的应用

介绍了将地面三维激光扫描仪应用在变形监测中的数据处理流程和数据分析方法,并针对点云数据的特点,提出了点云和点云直接比较、点云生成模型后比较两种变形分析方法。在此基础上,编制了基于激光点云数据的变形分析软件,并设计了两组实验,验证了两种变形分析方法的有效性以及激光扫描技术应用于变形监测领域的可行性。     

滇西实验场地震中短临动态跟踪综合预测方案及其实践运用

对滇西实验场1992年以来地下流体前兆观测资料进行分析研究,选取应震效果通过R信度检验（对应MS≥5.0级地震）的8条单项前兆指标。综合考虑单项前兆指标虚报率和漏报率对指标信度的影响,对单项前兆指标利用数学模型进行综合处理,减少了虚报和漏报的次数,预测效果明显提高。利用分级预警模式分别建立了中期（T≤6个月）和短临（T≤3个月）预测模型。综合预测方案还提供了地点判定原则和震级估算原则。最终提供地震短临预测三要素。运用本综合预测方案对2011年腾冲5级双震、2013年洱源5级双震和德钦两次5级地震作用了较为成功的短临预测。     

卫星在轨颤动检测的可行性研究

卫星在轨颤动检测对CCD相机成像质量检测具有决定性,对图像应用潜力也是决定性的。利用快速小面阵CCD获取图像序列,提取任意时刻的参考图像与颤动图像进行SIFT初定位,利用RANSAC剔除SIFT位存在的粗差,结合图像运动模型,解算颤动状态参数。通过实验论证,此种方法检测在轨颤动是可行的、有效的。