《卫星定位与导航》教学研究与探索

总结了《卫星定位与导航》课程中实践教学环节存在的若干问题,通过对存在问题进行分析,提出了几点建议,使该课程实践教学体系与理论教学体系形成互促互动的良性关系,提高了测绘相关专业毕业生参与社会化生产的能力。     

全球定位系统的新进展(讲座) 第1讲 导航电文结构的变化和参数的精化——从导航电文的变化看GPS的进展

介绍了GPS现代化实施后调制在L2C码和L5码上的导航电文CNAV总体结构的变化情况,并对CNAV中部分参数的精化和扩充以及卫星历书的细化部分进行了详细阐述和分析。     

无地面控制点条件下卫星摄影测量的发展与现状

无地面控制点条件下, 卫星摄影测量研究与工程实践是世界各国在该领域中所面临的研究难点之一。本文介绍了在无地面控制条件下光学卫星摄影测量的研究发展和工程实践历程, 并对中国“天绘一号”卫星获取的影像实测结果进行分析, 结果表明, 中国在无地面控制条件下的卫星摄影测量研究与工程实践已居于国际领先地位。     

测绘卫星的姿态控制技术

通过分析测绘卫星的姿态控制要求, 研究了卫星姿态控制所涉及的主要误差源, 提出了相应的解决措施, 针对测绘卫星的需求进行了姿态控制系统方案设计。     

MODIS反照率产品在模拟黄河源区陆面过程和降水中的应用

地表反照率是陆面过程中一个重要的物理量, 其变化直接影响地表能量的收支状况, 进而可以影响气温和降水等其它气象要素。本文利用WRF (Weather Research and Forecasting) 模式, 通过两组数值模拟试验分别探讨了地表反照率改变在黄河源区不同下垫面情况下潜热、 感热的分配关系, 详细分析了地表反照率改变对降水变化的影响机制, 最后应用EOS/MODIS地表反照率产品替代原模式低时空分辨率的地表反照率。研究结果表明: (1)当地表反照率减少(增加)时, 模拟的区域平均地表温度、感热、潜热数值相应增大(减少)。当地表反照率减少0.1时, 地表温度上升约1.0 K, 感热和潜热量增量比约为3∶1。 (2) 地表反照率改变对降水量变化影响最大的区域是黄河源区下游的草场区域, 其次是黄河源头区域, 最小的是黄河源区北部的稀疏植被区域。地表反照率通过对大气动力、 热力以及水汽条件的影响, 使得降水发生的环境改变, 主要体现在: 当地表反照率减少时, 地表气压的减少使得大气低层的辐合气流增强, 有利于上升运动的发生; 2.0 m气温的升高增强了大气近地层的热力不稳定度; 2.0 m比湿的增加表明近地层空气水汽含量增加。 (3) 与实况对比分析发现, 使用卫星遥感产品后在月尺度上能够更准确地模拟降水量的变化过程。     

模糊优选神经网络模型在城市防洪规划方案优选中的应用

城市防洪规划方案的综合优选是一个涉及到政治、社会、经济、环境等多准则、多因素的复杂多目标决策问题.针对目前各种常用的综合优选模型应用中存在的指标权重选择及转换问题,利用模糊优选神经网络模型,构造了合理的网络拓扑结构并将模型应用于某城市的防洪规划方案综合优选中.实例结果表明,此模型不仅避免了对指标权重的处理问题,而且明显加快了BP网络的收敛速度.     

Rainfall yield characteristics of electrical storm observed in the Spanish Basque Country area during the period 1992–1996

This paper is focused on the study of rainfall yield characteristics of electrical storms observed over the Northern Iberian Peninsula during 1992–1996. To this aim Principal Components Analysis (PCA) and Self-Organizing Maps (SOM) method have been used. The SOM method is a group of artificial neural networks based on the topological properties of the human brain. Results clearly suggest that there exist three different meteorological patterns that are linked to the characteristics of electrical events found in the study area. In winter, most of the electrical events are formed under oceanic advection (NW air fluxes). On these cases, mean rainfall yield estimates reach values of 700 10⁴ m³ per cloud to ground lightning flash (CG flash). During summer most frequent electrical storms are associated to local instability shooting by surface heating with advection of humidity coming from the Iberian Peninsula. Under these meteorological situations, rain is scarcer if compared with oceanic events but lightning CG counts reach the maximum values found in the area (about 10 CG counts per 20 × 20 km² and day) giving this way the smallest rainfall yield with a mean value of 15 10⁴ m³ per CG flash. Iberian air fluxes associated with cold air in upper parts of the atmosphere represent the third meteorological pattern found. This pattern is most common in spring and autumn but is not unusual in the rest of the seasons. In those cases mean rainfall yield in the area is about 150 10⁴ m³ per CG flash. In all electrical episodes K instability index is greater than 15 °C but in the most lightning producing events, this index reaches in the area values greater than 24 °C. PCA results pointed out that there exists a relationship between rain and CG counts expressed by the first principal component computed from standardized data. However, we must notice that no event is solely linked to this axis, since a seasonal influence which decreases lightning production when rain increases is always present. Results found are of great interest for short term forecasting of flashfloods in mountainous areas like the Spanish Basque Country region.     

Scaling of tropical rainfall as observed by TRMM precipitation radar

We used a three-year (1998–2000) dataset of TRMM Precipitation Radar observations to investigate the scaling properties of spatial rainfall fields. This dataset allows consideration of spatial scales ranging from about 4.3 km to 138 km and short temporal scales corresponding to the sensor overpasses. The focus is on the marginal spatial moment scaling, which allows estimation of the scaling parameters from a single scene of data. Here we present a global perspective of the scaling properties of tropical rainfall in terms of its spatial variability, atmospheric forcing, predictability, and applicability. Our results reveal the following: 1) the scaling parameters exhibit strong variability associated with land/ocean contrast and mean precipitation at the synoptic scale; 2) there exists a one-to-one relationship between the scaling parameters and the large-scale spatial average rain rate of a universal functional form; 3) the majority of the scenes are consistent with the hypothesis of scale invariance at the moment orders of 0 and 2; 4) relatively there are more scale-invariant rain scenes over land than over ocean; and 5) for the scenes that are non-scale-invariant, deviation from scale-invariance mainly arises from the increasingly intermittent behavior of rainfall as spatial scale decreases. These results have important implications for the development and calibration of downscaling procedures designed to reproduce rainfall properties at different spatial scales and lead to a better understanding of the nature of tropical rainfall at various spatial resolutions.     

我国气象卫星及应用发展与展望

截止到2008年6月底,我国已成功发射了4颗风云一号极轨气象卫星、1颗风云三号极轨气象卫星和4颗风云二号静止气象卫星.目前,风云一号D星、风云二号C和D星在轨业务运行,风云三号A星正在在轨测试中.我国的气象卫星已初步实现了业务化、系列化,率先实现了国防科工委提出的我国遥感卫星从试验应用型向业务服务型转变的目标.同时,我国也已成为世界上同时拥有极轨和静止两个系列气象卫星的3个国家或国家集团之一.世界气象组织已将风云一号系列、风云二号系列和风云三号系列卫星纳入全球业务应用气象卫星序列,使我国风云卫星成为全球综合地球观测系统的重要成员.我国气象卫星在我国国民经济建设和防灾减灾中发挥了重要作用,也为区域,乃至全球许多国家的经济发展做出了重要贡献.回顾了我国气象卫星及地面应用系统的发展历程,简要总结了我国气象卫星应用所取得的重要成绩,同时对未来我国气象卫星的发展趋势和发展目标等进行了展望.     

利用TRMM卫星资料对人工增雨云系模式云微观场预报能力的检验

文中利用TRMM卫星测雨雷达探测反演的云水、雨水、云冰和降冰4种云参数产品及实况降水资料,对比检验该人工增雨云系业务模式对云微观场和地面降水场的预报能力.结果表明,人工增雨云系模式系统对降水的预报能力要略优于现行业务运行的GRAPES模式;人工增雨云系模式系统能较好地预报云系系统云物理微观量的垂直结构特征,模式预报的微观场与卫星监测吻合较好;在播撒窗区的水平分布上,模式预报的各水凝物分布形势和强中心位置与卫星监测一致,其大小也接近监测值;人工增雨云系模式能较好地预报云的微观场和天气形势场,可作为云系人工增雨条件决策的重要参考依据.