基于STK跟踪与数据中继卫星轨道设计与仿真

发展跟踪与数据中继卫星对于构建天基测控网有着重要意义.概述了跟踪与数据中继卫星的定义与任务,阐述了跟踪与数据中继卫星通常选择的轨道,分析了地球静止轨道(GEO)中继卫星的地面覆盖特性和两颗GEO星组网的轨道覆盖盲区,以及中低轨卫星组网的步骤.提出了利用STK仿真分析中继卫星星座构形的方法,设计了基于STK的适合我国的地球静止轨道、大椭圆轨道、近圆轨道三种轨道的中继卫星星座与中低轨用户星的可见性仿真试验,通过对仿真结果的分析提出了我国中继卫星星座构形的初步设想.     

卫星组网可视化仿真系统设计与实现

卫星组网是满足未来空间通信需求的有效方式,为实现空间卫星组网的可视化,设计了一种卫星组网可视化仿真系统;系统由星座设计分系统、星座覆盖性能分析分系统、数据处理分系统和可视化分系统组成;在组网过程中,首先在星座设计分系统中设置星座的参数,根据轨道参数模型计算出星座中每颗卫星的轨道参数,并将计算结果输出给星座覆盖性能分析分系统,完成对纬度、区域和全球覆盖效果的分析、评估和显示;仿真结果表明:系统能够对卫星组网进行实时计算和显示,计算精度比STK仿真软件提高12%,系统运行稳定,界面良好。     

中继卫星和地面站多普勒频率研究

为实现用户卫星运动环境下信号的稳定跟踪[6]和精确测量[5],建立了用户卫星对中继卫星和地面测控站的多普勒频率及各阶导数的数学模型。根据数学模型推导计算公式,计算出理想运动模型的多普勒频率值。利用卫星仿真软件STK进行通信链路仿真,将仿真结果与理论计算结果进行比较。当用户卫星处于用户卫星和中继卫星星下点接近重合、用户卫星星下点和地面测控站接近重合的轨道时,多普勒频率及各阶导数仿真结果取得极大值。仿真结果表明,理论计算结果为多普勒频率和各阶导数的最大值,对接收机捕获范围和动态设计具有现实指导意义。     

北斗Ⅱ卫星导航系统星座仿真分析研究

针对北斗Ⅱ卫星导航星座中卫星位置不确定问题,改进并完善了正在筹建中的北斗Ⅱ卫星导航星座布局,在此基础上仿真分析了我国区域性导航系统以及北斗Ⅱ卫星导航星座的多星覆盖、位置精度衰减因子(position dilution of preci-sion,PDOP),给出了覆盖性能、导航定位精度等导航星座系统性能。仿真结果表明,北斗Ⅱ卫星导航系统多星覆盖及PDOP性能相对优于GPS导航星座,尤其适用于我国及周边地区。通过对不同最低仰角下北斗II导航星座及GPS星座多星覆盖变化分析,确定了各星座多星覆盖与仰角的关系以及变化特征,为北斗II导航系统组建工作以及应用终端设计提供了依据。     

侦察卫星地面机动目标覆盖特性分析与仿真

针对当前军用目标机动过程中易被卫星侦察的问题,对处于不同位置的机动目标进行侦察卫星覆盖特性分析,仿真其覆盖侦察过程.利用卫星工具软件包STK(Satellite Tool Kit)中先进的航天器系统分析软件,建立多摄动条件下侦察卫星星座运动学模型,调用STK的覆盖分析和虚拟现实模块,对卫星地面机动目标的覆盖算法和可视化技术进行研究.覆盖分析仿真结果表明:地面目标在机动过程中,侦察卫星对其实时位置的覆盖数据与目前采用的区域覆盖数据有一定差异,利用仿真结果能够有效减小覆盖预警数据的误差,且仿真结果与实际观测数据拟合良好.所提的方法处理地面机动目标侦察卫星覆盖情况准确度高,侦察卫星作战仿真过程逼真,具有很好的军事应用价值.     

星座覆盖性能评估的改进网格点仿真法

卫星星座覆盖性能指标评估的快速性对星座优化设计有重要的意义。根据改进的网格点仿真法,得到星座中每一颗卫星对地面点的覆盖时刻集;建立了一套卫星覆盖时刻集的合并方法,并给出了根据星座覆盖时刻集计算覆盖性能指标的方法。最后对Molniya轨道卫星星座进行了仿真,分析了星座在纬度线上的多重覆盖性能指标分布,以及不同数量卫星和网格点对计算时间的影响。仿真结果表明了改进网格点仿真的有效性和快速性。     

基于STK的靶标布设分析建模与仿真

由于靶标布设是航天测控的重要问题之一,覆盖分析为靶标布设提供重要的参考依据.为研究靶标布设的规律特点,提高测控质量,提出了利用STK进行仿真分析.针对某个工程中的靶标布设问题,采用卫星携带相机的侧摆情况和相机类型的情况,对卫星过境的覆盖品质进行了分析建模.并运用MATLAB与STK软件进行联合仿真,得出6种模式下的覆盖结果.仿真结果表明,无论是否侧摆还是相机类型不同的情况下,卫星过境时长均只与所处纬度有关,与经度无关,并且纬度越高,覆盖品质越好.     

无线传感器网络k重覆盖优化策略

为了实现无线传感器网络k重覆盖范围的最大化,提出了一种基于粒子群算法的无线传感器k重覆盖优化策略,提高了k重覆盖率,进而提高节点的利用率,延长无线传感器网络的寿命。同时,在保证网络覆盖精度的前提下,选择最合适的参数,这样既保证了最优的覆盖结果又最大限度地节约了计算量,延长了网络的寿命。通过仿真实验分析了粒子群算法的相关参数对覆盖性能指标的影响。实验结果表明,基于粒子群算法的k重覆盖策略有效地优化了网络的k重覆盖性能。     

多卫星非规则覆盖区域的通用求解算法

在综合考虑时间、空间、频谱、能量等几何和物理特性的条件下,复杂多卫星遥感系统对地球表面的覆盖区域呈非规则形状,采用解析方法难以求解和描述。为此,面向系统的综合性能和效能分析,基于点覆盖仿真方法,设计和实现了几种适合于任何瞬时覆盖条件和覆盖区形状的通用的覆盖点和覆盖区域边缘点的搜索算法,根据其特性,形象地称之为“池中投石法”、“油环点火法”和“逐步吸收法”等。该文首先介绍了生成地球表面网格点的两种基本方法一等经纬度法和等面积法,之后阐述了上述各种算法的主要设计思想和内容。     

STSS星座空间覆盖性能分析方法研究

弹道导弹中段是对抗集中体现的区域,美国计划研制空间跟踪与监视系统(STSS),以实现对于中段目标的探测和识别能力.主要针对STSS星座的全球空间覆盖性能开展研究.为了使卫星提供精确拦截导弹的信息,根据任务需求的角度分析了STSS可能的星座构型和参数,可通过分析STSS卫星的地球临边探测方式,提出了基于地心角的STSS星座空间覆盖性能仿真分析方法.并对其可能采取的星座构型分析了其空间覆盖能力进行仿真.仿真结果表明未来STSS星座将对弹道导弹中段突防构成严重威胁.     

面向减灾应用的光学成像静止卫星能力分析

静止卫星凭借其宽覆盖、高时效、机动灵活的特点,在国家减灾救灾业务中有着独特的应用优势。在回顾国内外静止卫星发展的基础上,总结其光学成像传感器在灾害监测预警中的应用现状和存在的问题。基于静止卫星及其载荷现有研制基础,从灾害管理各阶段应用需求出发,分析光学成像静止卫星在减灾中的应用潜力。根据减灾救灾实际业务和应用需求,分别从卫星工作模式、观测频次以及光学图像的几何性能、光谱范围、辐射性能等5个方面提出对静止卫星的技术指标要求,为推动我国的防灾减灾光学成像静止卫星建设提供借鉴。     

An efficient utilization of intermittent surface–satellite optical links by using mass storage device embedded in satellites

Recently, earth observation system by using satellite network has attracted much attention due to its wide coverage and disaster resistance. Although the system is useful for collecting various data, which have an effect on a natural disaster, ecology and so forth, earth observation satellite hardly send the collected observation data to the ground station. This is because that the earth observation satellite needs to orbit near surface of the earth to get high-precision data, and it limited the time that can be used to send the observed data traffic to the ground station. Additionally, the amount of the observed data drastically increase in these days. Thus, we focus on the data relay satellite using optical communication in this network. By relaying observed data to traffic to the relay satellite, which has geostationary orbit, it is possible to increase the chance of sending data for the observation satellite due to the wide coverage of the relay satellite. In addition, laser light that is used in optical communication in satellite network has high frequency and it can deliver large data compared with radio wave. However, laser light is greatly influenced by atmosphere, and optical link capacity between satellite and ground station drastically changes according to weather condition. Therefore, we propose a new data traffic control method to use the network constructed by satellites which has mass storage device effectively according to the condition of optical downlink between satellite and optical ground station. The effectiveness of the proposed method is evaluated with numerical result.     

基于MapObjects的在轨卫星运行仿真

卫星轨道预报技术是与卫星通信及卫星回收的关键技术。该文将卫星轨道预报技术和计算机仿真技术相结合,提出了在GIS控件——MapObjects上建立卫星在轨运行仿真平台的设计思想。在综合卫星的轨道计算、覆盖区域推导与地图投影的基础上,设计了基于二维实时动态显示技术的卫星轨道预报仿真平台。该平台可用于卫星轨道预报的地面测试及分析,应用数据库技术进行卫星及观察站点的管理。在实时显示卫星当前的参数的同时,利用二维显示技术动态仿真演示卫星的星下点轨迹及其覆盖区域和太阳的位置及其照亮区域的变化。     

面向异构通信卫星的地球站组网规划方法

经过多年的建设发展,卫星通信已经形成了多系列卫星并存、相互支撑、相互补充的通信系统。然而,由于各卫星系统建设时间跨度大,通信技术手段存在差异,如何高效利用异构的卫星通信资源成为了一个实际难题。为此,文中首次根据卫星与地球站的可互通条件构建了系统模型,并将其归结为线性约束下离散变量的非线性优化问题,优化目标是异构卫星波束间的负载均衡,并在此基础上设计了一种两阶段的启发式组网规划方法。最后,根据地球同步卫星网络特性设置了合理的仿真参数,利用Matlab平台进行仿真实验。仿真结果表明,所提方法在面对不同规模的地球站组网时,在平均负载和负载均衡性上均优于一般的枚举搜索和遗传优化算法,可以在短时间内对大规模的信道单元进行组网规划。     

Evaluation of remotely sensed actual evapotranspiration products from COMS and MODIS at two different flux tower sites in Korea

Estimating the evapotranspiration (ET) is a requirement for water resource management and agricultural productions to understand the interaction between the land surface and the atmosphere. Most remote-sensing-based ET is estimated from polar orbiting satellites having low frequencies of observation. However, observing the continuous spatio-temporal variation of ET from a geostationary satellite to determine water management usage is essential. In this study, we utilized the revised remote-sensing-based Penman–Monteith (revised RS-PM) model to estimate ET in three different timescales (instantaneous, daily, and monthly). The data from a polar orbiting satellite, the Moderate Resolution Imaging Spectroradiometer (MODIS), and a geostationary satellite, the Communication, Ocean, and Meteorological Satellite (COMS), were collected from April to December 2011 to force the revised RS-PM model. The estimated ET from COMS and MODIS was compared with measured ET obtained from two different flux tower sites having different land surface characteristics in Korea, i.e. Sulma (SMC) with mixed forest and Cheongmi (CFC) with rice paddy as dominant vegetation. Compared with flux tower measurements, the estimated ET on instantaneous and daily timescales from both satellites was highly overestimated at SMC when compared with the flux tower ET (Bias of 41.19–145.10 W m^?2 and RMSE of 69.61–188.78 W m^?2), while estimated ET results were slightly better at the CFC site (Bias of –27.28–13.24 W m^?2 and RMSE of 45.19–71.82 W m^?2, respectively). These errors in results were primarily caused due to the overestimated leaf area index that was obtained from satellite products. Nevertheless, the satellite-based ET indicated reasonable agreement with flux tower ET. Monthly average ET from both satellites showed nearly similar patterns during the entire study periods, except for the summer season. The difference between COMS and MODIS estimations during the summer season was mainly propagated due to the difference in the number of acquired satellite images. This study showed that the higher frequency of COMS than MODIS observations makes it more ideal to continuously monitor ET as a geostationary satellite with high spatio-temporal coverage of a geostationary satellite.     

LEO卫星网络中的一种分布式路由算法

在LEO卫星网络中，由于卫星高速运动导致的网络拓扑变化和不同卫星覆盖城内流量的非规整性给设计其特殊路由算法带来很大挑战。结合卫星网络的固有特点，本文提出一种基于路径信息压缩的分布式路由算法CPDR（Compressed Path Information based Distributed Routing）。该算法使用分布式分层链路状态收集策略和简洁的路径信息编码机制，能够在不引入额外信令开销基础之上提供多路径路由能力，实现卫星网路中的流量负载平衡、优化网络带宽应用、提高星际链路利用率。     

利用静止气象卫星监测浙江海上大雾

卫星遥感是监测大雾的重要手段,利用静止气象卫星监测海上大雾,可以得到时间分辨率比极轨卫星更高、空间覆盖比地面观测更连续的大雾产品。采用分级判识太阳高度角阈值和归一化大雾指数(NDFI)的方法,反演了2008年至今浙江海雾的逐时分布,并将静止卫星(MTSAT)遥感大雾监测结果与近5年地面大雾观测和2013年春季能见度自动观测记录作对比,结果显示遥感反演的总体精度分别为68.4%和69.6%,且空间分布上与地面观测相吻合。表明该方法可突出雾与其他地物的差异,且判识方法简单、实用性强、准确率较高;实时监测浙江海上大雾是可行的,具有良好的业务应用前景。不同时段正确率的验证结果显示,该方法更适用于海雾频发的冬春季以及白天的监测。     

A method for cross‐calibrating geostationary and polar orbiting satellite sensors in the infrared windows

The forward radiative transfer routine has been used to remove the artefact caused by modulation on meteorological satellite‐sensor responses. This paper describes a direct method where images observed by the infrared channels aboard the Multi‐functional Transport Satellite (MTSAT‐1R) and Fengyun‐2C (FY‐2C) geostationary satellites are compared with those by the Advanced Very High Resolution Radiometer (AVHRR) sensor aboard the National Oceanic and Atmospheric Administration (NOAA) polar‐orbiting satellites. The calibration differences between the polar orbiting and the geostationary satellites are found to be within 1 K of each other.     

Evapotranspiration monitoring with Meteosat Second Generation satellites: improvement opportunities from moderate spatial resolution satellites for vegetation

The Satellite Application Facility on Land Surface Analysis proposes a land evapotranspiration (ET) product, generated in near-real time. It is produced by an energy balance model forced by radiation components derived from data of the Spinning Enhanced Visible and Infrared Imager aboard Meteosat Second Generation geostationary satellites, at a spatial resolution of approximately 3 km at the equator and covering Europe, Africa, and South America. In this article, we assess the improvement opportunities from moderate spatial resolution satellites for ET monitoring at the Meteosat Second Generation satellite scale. Four variables, namely the land cover, the leaf area index (LAI), the surface albedo, and the open water fraction, derived from moderate-resolution satellites for vegetation monitoring are considered at two spatial resolutions, 1 km and 330 m, corresponding to the imagery provided by Satellite Pour l’Observation de la Terre (SPOT)-VEGETATION and future Project for On-Board Autonomy – Vegetation (PROBA-V) space-borne sensors. The variables are incorporated into the ET model, replacing or complementing input derived from the sensor aboard the geostationary satellite, and their relative effect on the model output is analysed. The investigated processes at small scales unresolved by the geostationary satellite are better taken into account in the final ET estimates, especially over heterogeneous and transition zones. Variables derived from sensors at 250–300 m are shown to have a noticeable effect on the ET estimates compared to the 1 km resolution, demonstrating the interest of PROBA-V 330 m-derived variables for the monitoring of ET at Meteosat Second Generation resolution.