国外几种星载光学遥感器的发展情况简介

文章介绍了国外空间对地观测的侦察相机、测绘相机以及其它星载光学遥感器的发展情况和近期态势。其中提到了它们在载体上对地观测的分辨率、光谱带宽、地面覆盖等性能指标,还介绍了相机或光学遥感器本身的性能参数。文章还对测绘相机专门提到了分类情况以及光学小卫星的发展态势,重点指出了不同光学遥感器所在卫星平台的姿态稳定性、指向和指向改变精度。     

印度第二代遥感卫星

IRS-1C/1D是印度空间研究组织研制的印度第二代遥感卫星,与第一代遥感卫星比较,不仅分辨率有所提高,而且还增加了遥感成像仪种类和扩大了光谱段。IRS-1C/1D卫星质量约为1250kg,它们携带的全色成像仪、多光谱成像仪和宽视场成像仪的分辨率分别可达到6m、23.6m和188m。文中对这种卫星的平台和有效载荷结构作了简要介绍。     

Orbview系列卫星介绍

文章介绍美国轨道成像公司研制并已经发射的Orbview-1和Orbview-2卫星和将要发射的Orbview-3和Orbview-4卫星的特性参数。     

微波和THz频段用于遥感标准的研发

美国国家标准和技术研究院(NIST)电磁部噪声规划提出了遥感应用例如卫星气象观测中的微波亮温度标准的研发。这个标准以现有波导系统电磁噪声基准为基础,与亮温度即辐射有关,借助一个特性很好的天线实现。热校准目标作为基准的补充,采用冗余测量的方式,用于检验或者减小不确定度。做过的26 GHz的初步测量表明所提出标准的可行性,同样太赫兹(THz)频率的研究也在进行中。对于THz噪声,用一个加热的目标作为噪声标准,虽然我们没有这么高频率的噪声基准。这个标准将与THz辐射计一起使用。辐射计基于一个接收机,该接收机采用了一个热电子测辐射热混频器,并被准光学适配器耦合到辐射中去。希望年底能够用这套系统进行THz噪声测量。     

利用GPS进行时间传递与频率比对

全面介绍了ＢＩＲＭＭ从１９８６～１９９２年间从事利用时间ＧＰＳ进行时间传递与频率比对技术研究方面的情况，包括所建立的ＣＰＳ定时校频系统、单站定时、ＳＡ对定时精度的影响、ＧＰＳ定时信号噪声模型、卡尔曼滤波、电离层时延估算、ＧＰＳ共视试验、ＣＰＳ校频、接收系统差测量等。     

卫星介质深层充电中的主要物理问题

卫星介质深层充电效应是诱发地球同步轨道卫星运行故障和异常的重要因素之一，通过计算机模拟对介质深层充电的时间常数、电场特征、以及屏蔽、介质厚度和接地方式对充电所致最大电场的影响等主要物理问题进行了详细的分析，并给出了初步的防护措施．     

中继卫星系统地面云存储架构设计

针对中继卫星系统日益增长的海量数据存储需求,探索将云技术应用于中继卫星地面存储系统中,研究并设计了适用于中继卫星系统的分布式云存储的体系架构.该架构通过分布式存储和存储虚拟化技术,对存储资源进行了整合,将分布在不同地理位置上的存储网络,集合成一个大规模广域云存储系统,可提供整体存储和访问的功能,并实现对数据的高效“存”、“取”、“管”.与传统NAS(Network Attached Storage,网络附加存储)架构分析比较,该架构从系统扩展性、可靠性和服务性等多个方面均更加具有优势,能够适应日益增长的中继卫星系统海量数据存储需求,解决中继卫星系统中大容量数据存储的瓶颈.     

Energy-optimal reconfiguration of satellite formation flying in the presence of uncertainties

In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances.     

Higher order ionospheric error correction in BDS precise orbit determination

The ionospheric error affects the accuracy of the Global Navigation Satellite Systems observation and precise orbit determination. Usually, only the first order ionospheric error is considered, which can be eliminated by the ionospheric-free linear combination observation. But the remaining higher order ionospheric error will affect the accuracy of observations and their applications. In this paper, the influence of the higher order ionospheric error have been studied by using the International Geomagnetic Reference Field 13 and the Global Ionosphere Maps model produced by the Center for Orbit Determination in Europe. Focus on ionospheric error, the experiment of paper at doy 302 in 2019, which show that the second order ionospheric error impacting BeiDou Navigation Satellite System (BDS) B1I and B3I observation is 6.3569 mm and 11.8484 mm, respectively. Whereas, the third order ionospheric error impacting BDS B1I and B3I observation is 0.1734 mm and 0.3977 mm, respectively. Due to the current measurement accuracy of BDS carrier-phase observation can reach 2 mm, the influence of high order ionospheric error on observation should be considered. For BDS precise orbit determination, the orbit overlapping results are indicated that its orbit accuracy can be improved approximately 5 mm with the higher order ionospheric error correction, which is also in agreement with the results of Satellite Laser Ranging in this work.     

Measuring atmospheric density using GPS–LEO tracking data

We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers.