中国南海区1992-2012年的中尺度涡旋演化过程表达与统计分析

Automated identification and tracking of mesoscale ocean eddies has recently become one research hotspot in physical oceanography. Several methods have been developed and applied to survey the general kinetic and geometric characteristics of the ocean eddies in the South China Sea（SCS）. However, very few studies attempt to examine eddies＇ internal evolution processes. In this study, we reported a hybrid method to trace eddies＇ propagation in the SCS based on their internal structures, which are characterized by eddy centers, footprint borders, and composite borders. Eddy identification and tracking results were represented by a GIS-based spatiotemporal model. Information on instant states, dynamic evolution processes, and events of disappearance, reappearance, split, and mergence is stored in a GIS database. Results were validated by comparing against the ten Dongsha Cyclonic Eddies（DCEs） and the three long-lived anticyclonic eddies（ACEs） in the northern SCS, which were reported in previous literature. Our study confirmed the development of these eddies. Furthermore, we found more DCE-like and ACE-like eddies in these areas from 2005 to 2012 in our database. Spatial distribution analysis of disappearing, reappearing, splitting, and merging activities shows that eddies in the SCS tend to cluster to the northwest of Luzon Island, southwest of Luzon Strait, and around the marginal sea of Vietnam. Kuroshio intrusions and the complex sea floor topography in these areas are the possible factors that lead to these spatial clusters.     

北太平洋中尺度涡时空特征分析

利用1993~2011年19 a的AVISO卫星高度计资料研究了北太平洋(10°~60°N,120°E~100°W)中尺度涡的时空分布特征,结果表明:北太平洋每年约产生1 800余个涡旋,其中气旋涡稍多。北太平洋东部沿岸、西北沿岸、黑潮延伸体北侧、副热带逆流区是中尺度涡的高发区,春、冬季是涡旋的高发季节。涡极性分布以35°N为界,北部多反气旋涡,南部多气旋涡。涡旋半径以100 km左右为主,并且基本随纬度升高而减小,涡旋数量随着周期增长而急剧下降。反气旋涡的平均半径和周期均大于气旋涡。利用Argo浮标剖面资料分析的6个个例涡旋的垂直结构显示,每个涡旋都有其独特的冷暖核结构,深度不同。研究结果对于分析北太平洋涡动能分布及传输具有一定的参考价值。     

北京地区自动站降水特征的聚类分析

利用2007—2010年北京123个自动气象站逐时降水观测资料,采用聚类分析方法,对北京的主城区、西部和北部区、东北区、东南区共分为4个区域的逐时降水时空分布特征进行了分析。结果表明:通过与实际地形和下垫面类型比较,自动站分类较为合理,避免了在区域划分方面的主观因素影响。主城区降水集中时段最为突出,集中出现在7月逐日20—00时,且降水强度最强,降水量较大,降水小时数不多。西部和北部区降水集中出现在6月逐日18—20时、7月逐日23时至次日03时,降水小时数最多,降水强度不大,降水量不大。东北区降水主要集中出现在7月逐日00—08时和17—23时,降水小时数较多,降水强度不大,降水量最大;东南区降水主要集中出现在7月的逐日02—04时,降水小时数少,降水强度较大,降水量较大。     

利用静止气象卫星监测初生对流的研究进展

本文主要对近年来利用静止气象卫星监测、分析和研究对流初生的国内外若干研究结果和进展给予了简要综述。主要涉及对流的判识、对流的追踪技术、初生对流的多光谱云顶特征、初生对流的判据和问题与展望等方面的内容。总体而言,利用静止气象卫星监测初生对流,以及发展的对流,是目前国内外研究和探索的热点之一。研究表明,通过精心挑选对对流敏感的光谱通道、通道组合和时间演变判据,可以对初生对流进行监测,可比地面雷达更早地预警降雨系统的发展,显示出在临近预报中的应用潜力。监测对流初生的算法流程大体上分为目标判识、目标追踪和初生对流判识三个部分。国际上主要的一些与对流初生相关的成熟算法各具特色,如RDT(Rapidly Developing Thunderstorms)算法在对流判识中强调了垂直形态的峰值检测,追踪对流时利用了速度外推并检测重叠面积。ForTraCC(Forecasting and Tracking the Evolution of Cloud Clusters)算法关注活跃对流,一定程度上考虑了对流合并和分裂的情况,具有外推预报功能。GOES-R(The Geostationary Operational Environmental Satellite R-Series Program)算法特点是多光谱的使用,利用多光谱判识技术进行对流云顶检测,是面向下一代静止气象卫星探测能力的算法。UWCI(The University of Wisconsin Convective Initiation)构思巧妙,所提出的box-average技术简单易行,适合软件工程化。随着卫星传感器和探测能力的发展,以及计算机技术的快速发展,更多卫星资料将用于联合判识对流。同时,更新的计算机视觉、计算机图像处理和模式识别技术也将用来解决追踪中的复杂问题,进一步改进初生对流的判识准确率。     

基于MapReduce计算模型的气象资料处理调优试验

云计算技术使用分布式的计算技术实现了并行计算的计算能力和计算效率,解决了单机服务器计算能力低的问题。基于长序列历史资料所计算得出的气候标准值对于气象领域实时业务、准实时业务及科学研究中均具有重要的意义。由于长序列历史资料数据量大、运算逻辑较复杂,在传统单节点计算平台上进行整编计算耗时非常长。该文基于Hadoop分布式计算框架搭建了集群模式的云计算平台,以长序列历史资料作为源数据,基于MapReduce计算模型实现了部分整编算法,提高计算时效。同时,由于数据源本身具有文件个数多、单个文件小等特点,对数据源存储形式及数据文件大小进行改造,分别利用SequenceFile方式及文本文件合并方式对同一种场景进行计算时效对比测试,分别测试了10个文件合并、100个文件合并两种情况,使时效性得到了更大程度的提升。     

Automatic registration of optical imagery with 3D LiDAR data using statistical similarity

The development of robust and accurate methods for automatic registration of optical imagery and 3D LiDAR data continues to be a challenge for a variety of applications in photogrammetry, computer vision and remote sensing. This paper proposes a new approach for the registration of optical imagery with LiDAR data based on the theory of Mutual Information (MI), which exploits the statistical dependency between same- and multi-modal datasets to achieve accurate registration. The MI-based similarity measures quantify dependencies between aerial imagery, and both LiDAR intensity data and 3D point cloud data. The needs for specific physical feature correspondences, which are not always attainable in the registration of imagery with 3D point clouds, are avoided. Current methods for registering 2D imagery to 3D point clouds are first reviewed, after which the mutual MI approach is presented. Particular attention is given to adoption of the Normalised Combined Mutual Information (NCMI) approach as a means to produce a similarity measure that exploits the inherently registered LiDAR intensity and point cloud data so as to improve the robustness of registration between optical imagery and LiDAR data. The effectiveness of local versus global similarity measures is also investigated, as are the transformation models involved in the registration process. An experimental program conducted to evaluate MI-based methods for registering aerial imagery to LiDAR data is reported and the results obtained in two areas with differing terrain and land cover, and with aerial imagery of different resolution and LiDAR data with different point density are discussed. These results demonstrate the potential of the MI and especially the CMI methods for registration of imagery and 3D point clouds, and they highlight the feasibility and robustness of the presented MI-based approach to automated registration of multi-sensor, multi-temporal and multi-resolution remote sensing data for a wide range of applications.     

LiDAR点云数据的电力线3维重建

利用LiDAR数据进行电力设施提取与建模可以克服传统工程测量电力巡线工作量大,危险性高,效率低下等缺点,但现有的电力线提取研究主要集中在电力线的分离与提取,并且拟合的精度不高。针对此问题本文提出了一种精度较高的电力线拟合方法。首先,根据电力线两端悬挂、中间自然下垂的特点,求解电力线拟合的最佳几何模型;然后,通过电力线的走向和端点,建立电力线拟合的最佳平面坐标系;最后,采用基于二次多项式限制的最小二乘法拟合电力线,解算出最优参数,生成最终电力线模型。对真实数据的处理和精度评价表明,本文方法不仅能够实现电力线的快速3维重建,而且能够达到较高的拟合精度。     

Tetrolet域利用时空相关性的云图压缩感知重建

针对卫星云图数据量大,但传输通道和存储空间相对狭小的问题,本文基于Tetrolet变换,利用相邻时次云图的时空相关性,实现了一种高重构质量的卫星云图压缩感知方法。该方法将善于表达图像方向纹理及边缘信息的Tetrolet变换引入压缩感知的稀疏表示环节,从而很好地体现了卫星云图细节丰富、纹理结构复杂的特性;同时,考虑到卫星云图序列间的相关性,将时间相邻的卫星云图组成图像组,以中间时刻云图作为参考图像,计算其与相邻时次云图的差异,通过在参考图片及序列差异图片间合理分配采样率,获取测量数据,在压缩感知框架下,采用带平滑处理的投影Landweber算法,重构出相邻时次的图像组。实验结果表明,Tetrolet变换适用于卫星云图的稀疏表示,而且图像组时空相关性的利用可显著提高重构云图的视觉效果及客观评价指标;在采样率低于0.2时,红外1、水汽和可见光3个通道重构云图的峰值信噪比(PSNR)较传统方法平均提高了7.48 dB,13.51 dB和6.15 dB。由此可见,本文方法可以通过获取少数随机测量值,重构出高质量的卫星云图,不仅为云图数据的低比特率压缩提供了一种可行的解决方案,而且对于其他序列图像的压缩采样具有借鉴意义。     

The Characteristics of Atmospheric Ice Nuclei Measured at Different Altitudes in the Huangshan Mountains in Southeast China简

The concentration of ice nuclei （IN） and the relationship with aerosol particles were measured and analyzed using three 5-L mixing cloud chambers and a static diffusion cloud chamber at three altitudes in the Huangshan Mountains in Southeast China from May to September 2011.The results showed that the mean total number concentration of IN on the highest peak of the Huangshan Mountains at an activation temperature （Ta） of-20℃C was 16.6 L-1.When the supersaturation with respect to water （Sw） and with respect to ice （Si） were set to 5％,the average number concentrations of IN measured at an activation temperature of-20℃C by the static diffusion cloud chamber were 0.89 and 0.105 L-1,respectively.A comparison of the concentrations of IN at three different altitudes showed that the concentration of IN at the foot of the mountains was higher than at the peak.A further calculation of the correlation between IN and the concentrations of aerosol particles of different size ranges showed that the IN concentration was well correlated with the concentration of aerosol particles in the size range of 1.2-20 μtm.It was also found that the IN concentration varied with meteorological conditions,such as wind speed,with higher IN concentrations often observed on days with strong wind.An analysis of the backward trajectories of air masses showed that low IN concentrations were often related to air masses travelling along southwest pathways,while higher IN concentrations were usually related to those transported along northeast pathways.