多约束条件的全球定位系统单频单历元短基线定向技术与实现

通过研究全球定位系统(GPS)伪距测量精度对GPS载波相位差分技术在短基线定向问题中的影响,提出利用基线长度、基线俯仰、卫星之间几何关系的多约束最小二乘整周模糊度实时搜索算法,给出单频单历元进行短基线定向的具体过程和需要注意的关键问题.算法采用单历元解算,规避载波相位周跳问题,极大地减小初始化时间.静态和动态实验结果均表明:该方法快速有效,解算成功率高,具有较高的定向精度.     

High-precision orbit prediction and error control techniques for COMPASS navigation satellite

A new satellite orbit prediction method based on artificial neural network （ANN） model is proposed to improve the precision of orbit prediction. In order to avoid the difficulty of amending the dynamical model, it is attempted to use ANN model to learn the variation of orbit prediction error, and then the prediction result of ANN model is used to compensate the predicted orbit based on dynamic model to form a final predicted orbit. The experiment results showed that the orbit prediction error based on ANN model was less than that based on dynamical model, and the ent satellites and different improvement effects for differtime were different. The maximum rates of improvement of predicting 8, 15, 30 d were respectively 80 %, 77.77 %, 85 %. The orbit prediction error control technique based on the method of back overlap arc compare was brought forward to avoid the risk that the precision of predicted orbit is even worse after it is compensated by ANN model. The phenomena of failure were basically eliminated based on this technique, and the rate of failure was reduced from 30 % to 5 %. This technique could ensure that the engineering application of ANN model could come true.     

China＇s sizeable and uncertain carbon sink： a perspective from GOSAT

Despite the agreement that China’s terrestrial ecosystems can provide a carbon sink and offset carbon dioxide(CO2)emissions from fossil fuels,the magnitude and spatial distribution of the sink remain uncertain.Accurate quantification of the carbon sequestration capacity of China’s terrestrial ecosystems has profound scientific and policy implications.Here,we report on the magnitude and patterns of China’s terrestrial carbon sink using the global monthly CO2flux data product from the Greenhouse gases Observing SATellite(GOSAT),the world’s first satellite dedicated to global greenhouse gas observation.We use the first year’s data from GOSAT(June 2009–May2010)that are currently available to assess China’s biospheric carbon fluxes.Our results show that China’s terrestrial ecosystems provide a carbon sink of-0.21 Pg C a-1.The consumption of fossil fuels in China leads to carbon dioxide emissions of 1.90 Pg C a-1into the atmosphere,approximately 11.1%of which is offset by China’s terrestrial ecosystems.China’s terrestrial ecosystems play a significant role in offsetting fossil fuel emissions and slowing down the buildup of CO2in the atmosphere.Our analysis based on GOSAT data offers a new perspective on the magnitude and distribution of China’s carbon sink.Our results show that China’s terrestrial ecosystems provide a sizeable and uncertain carbon sink,and further research is needed to reduce the uncertainty in its magnitude and distribution.     

Variation of satellite transponder delay

For precise orbit determination of geosynchronous earth orbit(GEO)satellites using transfer ranging observations,it is generally assumed that the variation of the satellite transponder delay is very small and that it can be solved as a constant parameter together with satellite orbit parameters.However,this assumption is too general and it reduces the accuracy of orbit determination for GEO satellites.To study and analyse the impact of the satellite transponder delay on GEO satellites orbit determination,two schemes were proposed.First,the satellite transponder delay was eliminated by forming single-difference observations between two ground stations;second,the satellite transponder delay was described as a constant parameter.The preliminary results demonstrate a difference of about1–2 m between the two schemes when used for precise orbit determination of GEO satellites.By fixing the GEO satellite orbit and other relevant parameters estimated by single-difference model,we inversed the instantaneous transponder delay from non-difference observation.It was found that the satellite transponder delay has a distinct diurnal variation,with an amplitude of 3–4 m.The findings of this paper are helpful in establishing an accurate model of satellite transponder delay and in improving the accuracy of GEO satellites orbit determinations and predictions.     

中国走向极地考察“陆海空”时代

正作为中国第30次南极科考的一项重要任务和成果,2014年2月8日,中国南极泰山站正式建成开站,这是我国继长城站、中山站及昆仑站之后的第4个南极科考站。2015年,中国第5个南极科考站的建设也即将启动。泰山站:把科考能力"前移"数百公里泰山站得名于五岳之首的泰山,象征"坚实、稳固、庄严、国     

青藏高原上空对流云特征的初步分析

利用常规地面观测资料、高空资料以及卫星云图资料,通过2010年7月与2011年7月的云图对青藏高原及周边地区对流云和中尺度对流系统的活动进行初步研究,分析了青藏高原上空对流云的特征.结果表明:①青藏高原上的对流过程是在特定的环流背景下受西风带500 hPa低槽、700 hPa切变线、850 hPa低涡以及地面图上中尺度低涡和地面静止锋的共同影响造成的;②对流云产生不仅与水汽条件有关,还与不稳定层结条件和抬升力条件即触发机制有关;③对流云的发生发展具有明显的日变化.     

基于简化差分插值滤波的编队卫星相对导航

将一种基于Stirling内插公式的非线性差分插值滤波(Divided Difference Filter-DDF)算法的简化形式(Simplified Divided Difference Filter-SDDF)应用到编队卫星相对导航中.该算法通过对非线性系统方程进行多项式展开并取有限差分插值项进行近似.数值仿真结果表明:该算法相对于EKF(Extended Kalman Filter)算法有明显的优势,有较高的滤波精度、更快的收敛速度和较好的稳定性,其中相对位置估计相比EKF提高79%、相对速度提高52%,对编队卫星相对导航具有一定应用价值.     

热点排行

正(新闻时段20142014-11-01至20142014-11-10)1探月工程三期再入返回飞行试验圆满成功[核心媒体报道频次:22/30]1日06:42,再入返回飞行试验返回器在内蒙古四子王旗预定区域顺利着陆,我国探月工程三期再入返回飞行试验圆满成功,标志着我国已全面突破和掌握航天器以接近第二宇宙速度的高速再入返回关键技术,为确保嫦娥五号任务顺利实施和探月工程持续推进奠定了坚实基础。再入返回飞行试验器于10月24日在中国西昌卫星发射中心发射升空。2中国首辆永磁高铁下线最快3年商业化运营[核心媒体报道频次:22/30]     

GPS接收机中相位舍位噪声影响DDL的跟踪性能

为了解决在全球卫星定位系统(GPS)接收机中出现的阶梯状伪距测量结果的问题,在分析了接收机中伪码跟踪原理的基础上,找到了造成该问题的原因.通过研究数控振荡器(NCO)中相位舍位噪声的规律,得到了该噪声与数字中频采样率的关系,提出了基于减小相位舍位噪声的中频采样率优化方案.仿真结果显示: 选择高于且接近伪码速率整数倍的中频采样率能明显的抑止NCO相位舍位噪声.优选出的高分辨率、低漂移的数字中频采样率可以有效提高GPS接收机的跟踪精度.