利用国内VLBI网跟踪大椭圆轨道卫星

2004年7月,昆明VLBI站经过改造,由上海、乌鲁木齐和昆明站组成的中国VLBI网(CVN)采用统一的MARK4格式编制器和CVN硬盘记录系统,对大椭圆轨道卫星“探测1号”的2圈轨道的共同可视弧段进行了跟踪观测．软件相关处理程序已成功地用于检测卫星遥测信号的干涉条纹和数据相关处理．采用基于条纹幅度的加权最小二乘条纹拟合方法,获得了卫星VLBI观测量及其精度估计,完成了卫星VLBI观测量的3基线闭合误差检验．应用河外射电源校准方法和多频点相位校正信号提取方法,进行了台站钟差和仪器延迟等系统误差改正．经系统差改正后的卫星VLBI观测量序列已用于“探测1号”卫星的轨道确定．     

木星和土星冰卫星上的撞击坑分布:探寻外太阳系撞击体来源的钥匙

充分认识外太阳系撞击体的来源类型和分布特征,对认识外太阳系固态天体上撞击过程,明确外太阳系天体上的撞击坑生成率和撞击坑定年等诸多方面具有重要的意义.得益于海量高质量探测数据的获取,如今我们对内太阳系主要天体表面的撞击分布和来源已经有了较为深入的了解,但对外太阳系天体的撞击分布和来源还知之甚少.不同大小频率的撞击体会在外太阳系冰卫星表面形成不同大小频率分布的撞击坑,不同飞行速度的撞击体也会在同步自转的冰卫星上留下程度不同的前导-后随半球不对称分布的撞击坑,因此,对外太阳系冰卫星上撞击坑的大小频率分布和前导-后随半球不对称性分布的观测,可以用于反推外太阳系的主要撞击来源.木星系统中大坑(D＞10～30 km)的主要撞击来源是日心小天体(环绕太阳),但目前在木卫三和木卫四上观测到的前导-后随半球不对称性程度与黄道彗星引起的不对称性程度并不相符,更接近于近各向同性彗星(NICs)引起的不对称性,这与目前的天文观测和理论计算结果不一致;木卫二上的大坑稀少,小坑(D＜1 km)则主要受一次坑的溅射物影响.对土星系统,土卫五和土卫八的大坑(D＞20～30 km)分布更符合日心小天体来源;而土卫一、土卫四、土卫三上的分布则与行心碎屑物(以行星为中心)一致,尤其是小坑更可能来自以土星为中心的撞击体影响,例如大型盆地的溅射物或卫星碎片残骸.     

Availability of offloading from an LNG barge

Long-term data sets are discussed for three locations – a southern North Sea location, where sea states are typically dominated by wind-sea conditions, a Northwest Shelf of Australia location, where sea states are often a mix of wind-sea and swell conditions, and a Guinea Gulf location offshore Nigeria, where sea states are dominated by swell. Various types of sea state statistics that have application to availability studies are presented; but databases of these type that also include wind and current data can also be used to estimate response parameters, which can give a more direct assessment of availability, and some example statistics of these are also given. Finally, the availability of offloading an FLNG barge to carrier is evaluated for each of the data sets, for specific operability criteria. Two types of operability criteria are used in the availability evaluations, and the results compared.     

Carbon dioxide on planetary bodies: Theoretical and experimental studies of molecular complexes

An absorption band at ∼4.26 μm wavelength attributed to the asymmetric stretching mode of CO in CO₂ has been found on two satellites of Jupiter and several satellites of Saturn. The wavelength of pure CO₂ ice determined in the laboratory is 4.2675 μm, indicating that the CO₂ on the satellites occurs either trapped in a host material, or in a chemical or physical complex with other materials, resulting in a blue shift of the wavelength of the band. In frequency units, the shifts in the satellite spectra range from 3.7 to 11.3 cm⁻¹. We have performed ab initio quantum chemical calculations of CO₂ molecules chemically complexed with one, two, and more H₂O molecules and molecules of CH₃OH to explore the possibility that the blue shift of the band is caused by chemical complexing of CO₂ with other volatile materials. Our computations of the harmonic and anharmonic vibrational frequencies using high levels of theory show a frequency shift to the blue by 5 cm⁻¹ from pure CO₂ to CO-H₂O, and an additional 5 cm⁻¹ from CO₂-H₂O to CO₂-2H₂O. Complexing with more than two H₂O molecules does not increase the blue shift. Complexes of CO₂ with one molecule of CH₃OH and with one CH₃OH plus one H₂O molecule produce smaller shifts than the CO₂-2H₂O complex. Laboratory studies of CO₂:H₂O in a solid N₂ matrix also show a blue shift of the asymmetric stretching mode.     

Mass and interior of Enceladus from Cassini data analysis

Gravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be (1.0798±0.0016)×¹⁰²⁰ kg, which implies a density of . For a core made of hydrated silicates with a density of 2500 kg m⁻³ the core radius is ∼190 km and the quadrupole moment C₂₂∼1.4×¹⁰⁻³. If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin-orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained.     

厦门市房产测绘数据整理系统的研究与实现

对厦门市房产测绘数据进行了研究,介绍了厦门市房产测绘数据整理系统功能结构图,阐述了基于数组的比对分析输出算法,实现了厦门市房产测绘数据整理系统。实验数据表明,该算法有效地提高了测绘数据整理效率,加强了系统的可用性。     

GPS／GLoNASS／GALILEo组合导航DOP值及可用性分析

针对采用单卫星定位系统时,在城市高楼密集区和位于深山峡谷的水库、电站、矿山等环境下,GNSS用户接收到的卫星个数少且卫星分布不佳导致的可用性下降、定位精度较差的问题,提出多系统组合的定位方法。利用GPS、GLONASS及GALILE0系统的轨道参数模拟卫星星座,计算不同卫星高度角下单系统及组合系统的DOP值,根据DOP值分析其可用性。研究表明：在全球时空范围内、相同卫星高度角下,组合系统的可用性高于单系统,三系统组合的可用性高于双系统组合。     

Modeling of the radial and transverse components of the albedo function

In this work, we shall confine ourselves to solve analytically the integrals called , for the two components of albedo radiation pressure on an Earth’s satellite. When the Earth’s albedo is variable, as far as we know, this case has not been dealt with analytically. We shall solve these two integrals when the satellite’ horizon is illuminated and when the sun lies on the equator. This approach will facilitate the evaluation of the mentioned two equations. We will also compare our results with previous works obtained numerically.