一种提高我国空间站中继测控覆盖率的方法

根据中继卫星的定点位置,对我国中继卫星-空间站的几何覆盖率进行了分析,并对提高空间站中继测控覆盖率的途径进行了研究,提出了一种采用不同舱段的2副中继天线融合使用,并通过调整天线安装布局提高中继测控覆盖率的方法。经理论分析和仿真验证,该方法能够有效地提高空间站中继测控覆盖率,可为我国空间站中继天线的安装布局设计提供参考。     

Watershed image segmentation and cloud classification from multispectral MSG-SEVIRI imagery

In this work a technique for cloud detection and classification from MSG-SEVIRI (Meteosat Second Generation-Spinning Enhanced Visible and Infra-red Imager) imagery is presented. It is based on the segmentation of the multispectral images using order-invariant watershed algorithms, which are applied to the corresponding gradient images, computed by a multi-dimensional morphological operator. To reduce the over-segmentation produced by the watershed method, a RAG (Region Adjacency Graph) based region merging technique is applied, using region dissimilarity functions. Once the objects present in the image have been segmented, they are classified using a multi-threshold method based on physical considerations that takes into account the statistical parameters inside each region.     

中轨卫星移动通信系统小区驻留时间分布的研究

在中轨卫星移动通信系统中 ,确定小区驻留时间分布对于合理地规划切换策略具有十分重要的意义。文中指出了地球固定覆盖与卫星固定覆盖两种方式下小区驻留时间分布不同的原因。提出一种仿真计算卫星固定覆盖方式下小区驻留时间分布的方法 ,得出了数值结果 ,并与地球固定覆盖方式下的小区驻留时间分布作了比较     

Variation of rain drop size distribution with rain rate at a few coastal and high altitude stations in southern peninsular India

Rain drop size distribution (DSD) was measured at four places in Southern India {Thiruvananthapuram, Kochi, Munnar and Sriharikota (SHAR)} using a Joss–Waldvogel (JW) impact type disdrometer. The data for each minute were corrected for dead time errors and rain rate was computed from the corrected data. The data for a whole month were then sorted according to rain rate (R) into several classes ranging from 0.1 to >100 mm/h. The average DSD in each class was computed, and the lognormal distribution function was fitted to the average. In all the cases, the function fitted the data very well. The fit parameters were found to have dependence on rain rate. The total number of drops (N_T), the geometric mean diameter (D_g) and the standard geometric deviation (σ) were also computed from the fit parameters. The standard geometric deviation (σ) was found to be more or less constant with rain rate at all the sites and in all months. The other two parameters (N_T and D_g) were found to vary exponentially with rain rate except in Munnar, a high altitude station. At Thiruvananthapuram, in most of the months, N_T increased exponentially with rain rate up to some value of R, which was different in different months, and then remained more or less constant or decrease slightly. In all cases, the variation of N_T and D_g was such that N_TD_g³ increased linearly with rain rate.     

Introduction to global short message communication service of BeiDou-3 navigation satellite system

Short Message Communication (SMC) is a featured service of BeiDou Navigation Satellite System (BDS). After its successful deployment in 2003, Regional Short Message Communication (RSMC) service has been continuously serving China and its neighboring countries and regions, especially in life safety scenarios. In this paper, the architecture of the Global Short Message Communication (GSMC) system is proposed based on the medium earth orbit (MEO) constellation and the crosslinks of the global BeiDou navigation system (BDS-3). Three subtypes of GSMC service, i.e. positioning report, emergency search and rescue (SAR) and regular SMC are designed in accordance with the technical characteristic of integration of navigation and communication in BDS-3, which supports future wide applications of GSMC. The performance of the designed GSMC system is analyzed by numerical calculations. As BDS-3 was officially announced completion on July 31, 2020, GSMC has been providing initial service. First test results of the in orbit GSMC payloads are also presented in the paper to verify the designed capabilities. Preliminary results also show that the requirements of Global Maritime Distress and Safety System (GMDSS) can also be fulfilled.     

Using vegetation indices and texture measures to estimate vegetation fractional coverage (VFC) of planted and natural forests in Nanjing city,China

Vegetation fractional coverage (VFC) is an important vegetation parameter affecting exchanges of carbon, water, energy between the atmosphere and surface. In this study, the applicability of tonal and texture measures calculated using an IKONOS_2 image in retrieving VFC of forests was investigated in the urban area of Nanjing city, China. Four spectral vegetation indices (VI) and six texture measures (TEX) were related to VFCs acquired from in situ measurements. Models for estimating VFC based on VIs or/and TEXs were established and validated for planted low broad-leaf forest plots (PLB), planted mature forest plots (PMF), natural broad-leaf forest plots (NBF), and all forest plots (ALLv), respectively. The results show that high spatial resolution remote sensing data is applicable to estimate VFC in urban areas, and TEXs may act as effective supplements of vegetation indices (VIs) for the retrieval of VFC. VIs are suitable for VFC estimation of mature forests (such as NBF and PMF) with high vegetation density, and TEXs can yield a more accurate estimate for planted forests (such as PLB and PMF) with regular spatial distribution if they are calculated with proper parameters, such as window size. The combination of VIs and TEXs improve the estimation of VFC if forest types are not previously differentiated. The results can be used as a reference for determining effective spectral or texture parameters in VFC estimation under similar environmental conditions according to vegetation maturity and regularity.     

基于改进的NSGA-Ⅱ算法的区域覆盖卫星星座优化

对基于Pareto最优概念的非劣性分层遗传算法(NSGA-Ⅱ)进行了改进，与区域覆盖卫星星座的多目标优化设计相结合，提出基于改进的NSGA-Ⅱ算法的区域覆盖卫星星座优化设计方法，并利用多属性决策中的字典序法，根据目标的重要程度，在得到的Pareto解中进行选择．最后，利用STK和Matlab工具对遥感卫星星座进行了仿真，仿真结果表明该算法可以找到多个Pareto解，避免了传统的多目标优化求解方法的权值选择问题，并且比简单遗传算法具有更好的灵活性，从而解决了多目标优化的星座设计问题。     

面向导航增强的低轨星座设计与应用

随着传统产业升级和新兴技术的发展,社会生产和生活对分米级、厘米级的实时精准定位需求日益凸显。低轨卫星轨道高度低、信号强度大、短时间内几何构型变化快,因此应用低轨卫星开展导航增强服务成为研究热点。低轨卫星的增强服务性能依赖于星座的快速组网和设计,低轨卫星星座构型、轨道高度、轨道倾角等是影响其覆盖性能和增强性能的关键因素。全面分析了低轨星座设计的关键要素,包括轨道高度、轨道倾角和单星覆盖性、地面人口密度、空间环境等,在此基础上设计了单构型和复合构型低轨导航增强星座,并进一步分析低轨星座的覆盖性能。结果显示:复合低轨导航增强星座可以实现对全球的连续覆盖,同时满足极地高密度覆盖和低纬度的连续覆盖需求,对北斗导航系统的增强效果明显。     

基于组合赋权和云模型的遥测系统作战适用性评估研究

针对遥测系统作战适用性评估问题,构建了基于组合赋权和云模型的评估架构。采用AHP (Analytic Hierarchy Process,层次分析法)、改进变异系数法和最小鉴别信息原理确立指标综合权重;运用云模型理论,进行“黄金分割法”标准云设计和相似度匹配,确定指标等级差异,查找了装备作战适用性短板弱项所在,为遥测系统升级革新及新装备（软件定义遥测系统）研制开发提供依据遵循。评估方法可为遥测系统作战效能、体系适应性、在役适应性等类似评估提供参考借鉴,不断提高装备复杂环境下适应能力。     

地球资源卫星轨道设计

本文提出了满足设计要求的地球资源卫星轨道参数的计算方法。并且提出了使得地面轨迹形成覆盖循环所需要满足的简要公式。