三道河水库浮游生物现状及其鱼产力的估算

本文报道1990年对三道河水库浮游生物现存量和浮游植物初级生产量的凋查结果。经初步鉴定,该水库浮蝣植物有8门39属,其中以绿藻门种类最多,占总属数的49％,其次为蓝藻和硅藻;浮游动物为37属,其中原生动物12属,轮虫13属,枝角类7属,桡足类5属。经测算,三道河水库1990年4—10月浮游植物数量和生物量分别为1139ind./L和2.085mg/L,浮游动物数量和生物量则分别为1253ind./L和1.327mg/L。浮游植物初级毛生产量平均为3.950g O_2/m~2·d。根据估算,该水库鲢鳙鱼产力为15×10~4kg左右。     

1960—2020年千岛湖流域蒸散发演变特征及驱动因素解析

为探究淡水湖库及其所属流域蒸散发演变特征,以及气象因子对蒸散发的影响规律。以长三角地区最大的淡水人工湖和重要的水源地——千岛湖为研究对象,采用Penman-Monteith等方法与WEP-L分布式水文模型,分别计算千岛湖流域1960—2020年潜在蒸散发(ET₀)与实际蒸散发(ET_a),分析二者年际变化趋势及突变年份;采用偏微分方法分析气象因子对ET₀的敏感性和贡献度;采用归因分析法分析突变前后气象因子对ET_a变化的贡献度,并利用蒸发表面水分指数(E_M1)解析流域蒸发互补关系。结果表明:ET₀与ET_a多年平均值分别为1021.7和857.5 mm,整体皆呈减少趋势,倾向率分别为-0.77和-1.03 mm/a,二者均在1980和2000年左右发生突变;ET₀对相对湿度变化最为敏感,ET₀增加的月份主要是由于相对湿度、平均气温的正贡献,风速呈负贡献但相对较小,ET₀减少的...     

基于地震探测的盐源盆地构造特征及动力学意义

基于覆盖盐源盆地的短周期天然地震台阵和布设的一条人工地震测线所获得的地震数据,从中提取地震能量属性,并通过地震层析成像获得该地区的浅部地震速度结构,继而对短周期地震台阵一个月的噪声数据进行互相关得到经验格林函数,再通过时频分析获得相速度频散曲线,反演获得不同深度的S波速度分布.研究结果显示,盐源盆地地震特征主要分为三层...     

Study and application of an improved four-dimensional variational assimilation system based on the physical-space statistical analysis for the South China Sea

The four-dimensional variational assimilation (4D-Var) has been widely used in meteorological and oceanographic data assimilation. This method is usually implemented in the model space, known as primal approach (P4D-Var). Alternatively, physical space analysis system (4D-PSAS) is proposed to reduce the computation cost, in which the 4D-Var problem is solved in physical space (i.e., observation space). In this study, the conjugate gradient (CG) algorithm, implemented in the 4D-PSAS system is evaluated and it is found that the non-monotonic change of the gradient norm of 4D-PSAS cost function causes artificial oscillations of cost function in the iteration process. The reason of non-monotonic variation of gradient norm in 4D-PSAS is then analyzed. In order to overcome the non-monotonic variation of gradient norm, a new algorithm, Minimum Residual (MINRES) algorithm, is implemented in the process of assimilation iteration in this study. Our experimental results show that the improved 4D-PSAS with the MINRES algorithm guarantees the monotonic reduction of gradient norm of cost function, greatly improves the convergence properties of 4D-PSAS as well, and significantly restrains the numerical noises associated with the traditional 4D-PSAS system.     

Research on the evolution law of permafrost under the influence of urbanization based on remote sensing technology

The permafrost of Mohe County and its suburbs in the Daxing′an Mountains has been influenced by the urbanization. Remote sensing, GIS technology and numerical simulation was used to study the temperature variations of permafrost with the changes in surface vegetation that cover Mohe County and suburban areas, and the law of permafrost degradation on the study area was analyzed. The research results show that the urban area of the study area increased 114.42%from 2000 to 2016, and the urbanization process is continuing to accelerate. The Normalized Difference Vegetation Index map of 2017 in Mohe County and its suburbs was studied and the maximum proportion of vegetation coverage was different in the four seasons. The numerical calculation model results show that the permafrost temperature change in the study area cyclically fluctuates in a cosine form. The annual variation curve of permafrost temperature gradually decreased and its accompanying phase lag increased with depth. The annual temperature change value with the different depths of the town was greater than the natural ground. The maximum permafrost thawing depths of the town and natural ground were 4.2 m and 2.82 m in 50 a, and the degradation rates of the two permafrost are, respectively, 0.88 cm/a and 0.46 cm/a. These results show that urbanization has accelerated the degradation of permafrost.     

Performance of rectangular closed diaphragm walls in gently sloping liquefiable deposits subjected to different earthquake ground motions

The performance of rectangular closed diaphragm walls(RCDW) subjected to earthquake ground motions is extremely complicated in gently sloping liquefiable deposits and requires further investigation. A nonlinear finite element(FE) model was developed to investigate the seismic performance of an RCDW in the OpenSees platform. Initially, the feasibility of the FE model to simulate the seismic behavior of the RCDW was validated by comparing the numerical results with the experimental data. The numerical results agree well with the centrifuge test data. Then, the calibrated model was used to study the seismic performance of the RCDW subjected to different ground motions in gently sloping liquefiable deposits.The numerical results indicate that the soil-RCDW system under near-fault ground motions is more likely to be damaged than that under far-fault ground motions. The difference between the maximum and minimum(D_(max-min)) the RCDW displacement and the maximum excess pore pressure in the soil core increased as the Arias intensity increased. The seismic response of the soil-RCDW system was strongly affected by the frequency content, durations, energy distribution and initial directions of the ground motions. Moreover, the modified specific energy density(MSED) has a good linear relationship with the D_(max-min) of the RCDW displacement.     

新区划图双参数调整对剪力墙结构土建成本的影响

考虑到《中国地震动参数区划图》(GB 18306—2015)(中华人民共和国国家质量监督检验检疫总局等,2016),提出了双参数调整原则,即对场地地震动峰值加速度和反应谱特征周期进行同时调整,以确定设计地震动反应谱,这势必会增加结构的土建成本.因此,基于Ⅱ类场地,对抗震设防烈度7度(0.15 g)的剪力墙结构在不同场地...     

基于视频监控图像的环巢湖蓝藻实时动态监测

蓝藻的防控与治理是湖泊水环境、水生态管理的重要内容,实时获取蓝藻的空间分布信息对于降低蓝藻灾害风险具有重要意义.针对地面调查费时费力、卫星遥感监测粒度较粗且时效性不强等问题,本文提出了一种基于视频监控网络的湖泊蓝藻实时监测技术.基于环巢湖视频监控网络的33个功能摄像机,研究如何从视频图像中实时、准确提取蓝藻的分布信息.为克服不同摄像头的观测角度不一致、光照强度和背景条件不一致等诸多挑战,在视频图像蓝藻表征分析的基础上,通过多尺度深度网络进行图像粗粒度分类,区分蓝藻与浑浊、阴影水体;基于随机森林进行蓝藻精细化识别,克服蓝藻的强异质性.最后以渔政站沿岸水域的日均蓝藻覆盖率和月均蓝藻覆盖率为统计单位,开展了巢湖沿岸蓝藻的动态监测.研究成果可为科学制定蓝藻治理方案提供技术支撑.     

应用卫星遥感技术监测大气痕量气体的研究进展

大气污染是全球环境变化的焦点,传统的地面定点监测大气污染技术已经越来越不能满足科学研究和国家决策的需求,大尺度卫星遥感大气污染技术作为一种新兴的研究手段,可以得到大尺度、长时间序列的污染物时空分布特征和变化趋势,进而研究大气化学变化对全球气候和生物地球化学循环的影响。对卫星遥感大气痕量气体科学领域的发展和国际上使用的各类大气痕量气体传感器以及所取得的科研成果进行了全面的综述,结合中国地区的自身特点,提出我国利用卫星遥感技术研究大气成分的思路和未来开展科研工作的方向。     

应用先进微波探测器AMSU资料遥感反演春季陆地表层湿度

利用先进微波探测器(AMSU)正演快速微波辐射传输模型,完成了AMSU 窗区通道亮温与地表温湿特征的相关性分析,根据模拟计算结果改进了现有业务上反演地表微波辐射率的统计分析方法,得到适用于我国非冻土积雪覆盖地区地表微波辐射率反演的指数分析模型;进一步通过地表微波辐射传输模型迭代反演得到土壤体积含水量信息.2001年相互匹配的AMSU资料和地面农业气象观测站地表相对湿度观测结果的对比分析表明二者间具有一定的相关性.利用2002年3月和2003年3月的AMSU资料,反演了我国陆地区域地表湿度;连续两年春季地表湿度反演结果的对比分析表明,与2002年春季相比,2003年我国北方沙尘暴发生源区地表湿度反演值普遍偏高,潮湿的下垫面特征与沙尘暴发生频次的减少之间有一定的对应关系.试验结果表明,利用AMSU遥感资料可以获取大范围陆地表层湿度信息,进行区域尺度陆地表层湿度特征的动态分析,为我国沙尘暴监测分析提供陆地表层湿度基础信息.