The effect of neglecting VLBI reference station clock offsets on UT1 estimates

Very Long Baseline Interferometry (VLBI) allows to monitor universal time (UT1) by conducting regular international experiments. Such dedicated observation networks are equipped with different hardware components, which require different processing strategies when the data are correlated. As the timing units at each stations are usually offset with respect to universal time (UTC) this effect should be considered during correlation processing. Thus, it is investigated how neglecting of these offsets theoretically impacts the estimation of UT1. Three different strategies for the proper handling of the timing offset will be discussed and their advantages/drawbacks will be pointed out. Moreover, it is studied how neglecting of these timing offsets affects UT1 time-series and how such a missing correction can be applied a posteriori. Although the discussed effect is for most of the UT1 experiments smaller than the formal error of the estimates, it is important to consider station clock offsets properly in next-generation VLBI systems, which are expected to improve accuracy of results by about one order of magnitude.     

一种双基站低轨道区域覆盖δ星座设计

在双基站理论研究基础上 ,进行了定倾角区域性覆盖双基站δ星座设计 ,采用倾角为 41°的回归轨道 ,用点覆盖数值仿真的方法设计了对地面站与空间站的一重覆盖与二重覆盖下的星座构型。且星座中各星之间 ,各星与空间站之间均可建立星际链路 ,保证数据在空间站、地面站及星座之间连续传递     

Star visibility and tracking from the Space Station

Purpose of the present study is to provide algorithms for and examples of how to simulate star visibility and tracking by a Telescope attached to the main truss of the International Space Station (ISS).     

Cosmic rays at High Mountain Observatories

The worldwide distribution of High Mountain Observatories provides a unique opportunity for performing contemporary measurements under different geomagnetic/altitude conditions and for collecting long-term data series. In this context, the history and some activities performed at two historical Research Stations are summarized: Chacaltaya Laboratory (Bolivia) and the Testa Grigia Research Station (Italy).     

Precise coseismic displacements from the GPS variometric approach using different precise products: Application to the 2008 MW 7.9 Wenchuan earthquake

The Global Positioning System (GPS) variometric approach has emerged as an attractive alternative to traditional well-developed positioning techniques including relative positioning and precise point positioning. Previous studies have demonstrated the capability of the variometric approach to retrieve coseismic displacements at centimeter-level precision, in a real-time manner using only readily available broadcast ephemeris. This study presents the first results comparing the performance of the variometric approach by using a variety of precise satellite orbit and clock products. Totally six kinds of products are included in our evaluation, namely the broadcast, IGS (International GNSS Service) ultra-rapid (predicted), ultra-rapid (observed), rapid, final (30-s clock) and CODE (Center for Orbit Determination in Europe) final (5-s clock) products. Static and dynamic experiments are conducted using 1-Hz GPS data covering a relatively large area in China during the 2008 Wenchuan M_W 7.9 earthquake. After removing the linear trend, the displacements using broadcast, ultra-rapid (predicted), ultra-rapid (observed) and rapid products reach nearly equivalent precisions at centimeter level. By using final and CODE final products, the precision of displacements can be significantly improved from 1.9–2.0 cm to 0.4–0.7 cm horizontally, and from 6.0–6.2 cm to 1.0–1.7 cm vertically for the dynamic experiments. The displacements using the CODE final products achieve the best precision, improved by more than 40% compared to those using the IGS final products. With the availability of IGS high-rate real-time precise products, this approach is promising to capture coseismic displacements more precisely in real time, which is crucial for earthquake and tsunami early warning.     

国际空间站上使用的两种计算机

欧空局为国际空间站研制了两个新型的计算机 :容错计算机 ( FTC)和标准有效载荷计算机 ( SPLC) ,它们可以满足空间站对计算机的需要 ,可以方便地构成各分种布式数据管理结构。文中介绍这两种不同类型的计算机设计     

“和平”号空间站自然舱介绍

“和平”号空间站由6个相继发射的舱体对接而成,其中的自然舱为一遥感舱,装有各种类型的遥感器,主要用来增强“和平”号空间站的地球遥感能力,研究地球生态状况。文章对这些仪器逐一介绍。     

区域导航陆基无线电导航系统自动选台和定位算法研究

针对利用陆基无线电导航系统实施区域导航运行时需要自动选择合理的导航台进行精确定位的要求,提出了一种陆基无线电导航系统自动选台和定位算法,并且采用上海虹桥机场到北京首都机场的RNAV航路和导航台信息进行了仿真实验,实验表明,提出的陆基无线电导航系统自动选台和定位算法可有效地选择较好的导航台,在及时切换为更好的导航台同时能避免导航台切换过于频繁,最终实现飞机的精确定位,确保DME/DME定位满足RNAV 2、VOR/DME定位满足RNAV 5的导航性能要求。