IGS精密钟差精度分析

对比了IGS官方提供的5 min和30 s间隔的精密钟差变化规律,分析了利用8阶滑动式Lagrange多项式插值和线性插值将精密钟差内插至30 s间隔的精度及可行性,得出了一些国内文献未论及的结论。     

精密卫星钟差两种插值方法的比较

介绍了两种GPS精密卫星钟差插值计算方法,采用实际数据进行了计算,与已知精密卫星钟差进行比较,结果显示线性插值方法略优于拉格朗日插值方法。     

A simplified yaw-attitude model for eclipsing GPS satellites

A simplified yaw-attitude modeling, consistent with Bar-Sever (1996), has been implemented and tested in the NRCan PPP software. For Block IIR GPS satellite it is possible to model yaw-attitude control during eclipsing periods by using the constant hardware yaw rate of 0.20°/s. The Block IIR satellites maintain the nominal yaw attitude even during a shadow crossing (Y. E. Bar-Sever, private communication, 2007), except for the noon and shadow midnight turn maneuvers, both of which can be modeled and last up to 15 min. Thus, for Block IIR satellites it is possible to maintain continuous satellite clock estimation even during eclipsing periods. For the Block II/IIA satellites, it is possible to model satisfactorily the noon turns and also shadow crossing, thanks to the permanent positive yaw bias of 0.5°, implemented in November 1995. However, in order to model the Block II/IIA shadow crossings, satellite specific yaw rates should be used, either solved for or averaged yaw-rate solutions. These yaw rates as estimated by the Jet Propulsion Laboratory (JPL) can differ significantly from the nominal hardware values. The Block II/IIA post-shadow recovery periods, which last about 30 min, should be considered uncertain and cannot be properly modeled. Data from post-shadow recovery periods should, therefore, not be used in precise global GPS analyses (Bar-Sever 1996). For high-precision applications, it is essential that users implement a yaw-attitude model, which is consistent with the generation of the satellite clocks. Initial testing and analyses, based on the IGS and AC Final orbits and clocks have revealed that during eclipsing periods, significant inconsistencies in yaw-attitude modeling still exist amongst the IGS Analyses Centers, which contribute to the errors of the IGS Final clock combinations.     

Can sandy beach molluscs show an endogenously controlled circatidal migrating behaviour? Hints from a swash rig experiment

Many macrofaunal species inhabiting exposed sandy beaches are dependent on the swash for their nutrition and migration and are highly adapted to the harsh physical conditions of the swash. The most important physical factors that determine the distribution and behaviour of swash related fauna, next to the swash itself, are sediment grain size and beach slope. Crucial swash parameters are swash period and swash velocity. Studying the influence of these factors on the animals in the field is often very difficult and it is almost impossible to identify which factor causes what effect. Crucial knowledge about the direct role of the swash itself is lacking. Therefore, a device that generates swash waves on an artificial beach under laboratory conditions was designed: the swash rig. In the swash rig, full and independent control on sediment grain size, beach slope, swash velocity and swash period is present. This will allow us to do a variety of experiments on the influence of each of these factors, independently or combined, on swash fauna. In one such experiment, Olivella semistriata – a dominant surfing gastropod on Ecuadorian sandy beaches – was placed in the swash rig during rising and falling tide and subjected – under constant conditions – to an equal wave regime. During falling tide, and in absence of any tidal cue, almost all specimens moved downshore, as they would in the field; hardly any specimens moved upshore. During upcoming tide, however, there was noticeable upward migration in the swash rig, and half of the runs showed a net upward migration. Contrary to the common understanding that the behaviour of sandy beach molluscs is entirely environmentally driven, this experiment hints at the presence of an endogenous circatidal clock, which is used to direct the tidal migration of the species.     

基于CPLD的数字移相分频钟

设计了一种数字移相分频钟 ,其中利用了先进的复杂可编程逻辑器件(CPLD -ComplexProgrammableLogicDevice)技术 ,将硬件电路模块化 ,把各功能模块集成在一个芯片中。与以往用分立元件设计硬件电路相比 ,具有电路简单 ,可靠性高 ,便于调试的特点     

GEO导航卫星定轨观测模型

根据GEO导航卫星的轨道特性,给出了严密的伪距观测和载波相位观测数学模型;讨论了其轨道和星钟差的解算条件,以及多星组差定轨的可行性。结果表明:在利用伪距时,如果测站钟差已知,需要4个以上站的数据才能进行定轨和星钟解算;如果站钟、星钟钟差已知,需要3个以上站的数据才能确定轨道。在利用站间组差伪距时,须有4个以上测站的钟差信息才能进行轨道和星钟解算;利用GEO卫星与MEO(IGSO)卫星组差定轨时,需要GEO卫星钟差已知且有3组星间组差数据。利用GEO卫星载波相位观测资料,不能单独解算轨道。     

Exposure of global mountain systems to climate warming during the 21st Century

We provide an assessment of surface temperature changes in mountainous areas of the world using a set of climate projections at a 0.5° resolution for two 30-year periods (2040–2069 and 2070–2099), using four Intergovernmental Panel for Climate Change (IPCC) emission scenarios and five AOGCM. Projected average temperature changes varied between +3.2 °C (+0.4 °C/per decade) and +2.1 °C (+0.26 °C/per decade) for 2055 and +5.3 °C (+0.48 °C/per decade) and +2.8 °C for 2085 (+0.25 °C/per decade). The temperature is expected to rise by a greater amount in higher northern latitude mountains than in mountains located in temperate and tropical zones. The rate of warming in mountain systems is projected to be two to three times higher than that recorded during the 20th century. The tendency for a greater projected warming in northern latitude mountain systems is consistent across scenarios and is in agreement with observed trends. In light of these projections, warming is considered likely to affect biodiversity (e.g., species extinctions, changes in the composition of assemblages), water resources (e.g., a reduction in the extent of glaciated areas and snow pack), and natural hazards (e.g., floods). Accurate estimate of the effects of climate change in mountain systems is difficult because of uncertainties associated with the climate scenarios and the existence of non-linear feedbacks between impacts.     

不同变质类型煤的XRD结构演化特征

通过对大别造山带前陆盆地石炭纪含煤岩系高煤级煤的X射线衍射分析,探讨了高煤级煤基本结构单元的演化特征及其影响因素。结果表明,构造应力作用提高了“煤晶核”BSU的延展度和堆砌度,使面网间距减小。      

一种卫星钟自相关的实时钟差预报算法

针对实时精密单点定位(RT-PPP)中实时数据流存在中断、延迟等问题,该文构建了顾及卫星钟自相关的随机模型,提出了一种基于方差分量估计的自适应卡尔曼滤波钟差超短期/短期预报算法,评估了连续27d实测法国空间研究中心(CNES)实时数据流CLK93产品完整率和精度水平,利用哈达玛方差对比分析了该实时产品与德国地学研究中心(GFZ)事后GBM产品的频率稳定性。利用本文算法与传统卡尔曼算法对两类产品进行预报,结果显示:CLK93产品BDS系统(C)、GPS系统(G)、GLONASS系统(R)、Galileo系统(E)30s和1min预报精度分别平均提升了8.50%、8.44%、7.20%、6.96%;GBM产品相应4个系统12h和24h预报精度分别平均提升了3.14%、3.53%、0.96%、10.01%。     

多GNSS系统组合PPP定位精度评估

采用MGEX网提供的GPS、GLONASS、BDS、GALILEO四系统双频观测数据,以CODE、GBM、WUM、GRG精密产品进行了静/准动态模式下多系统组合无电离层延迟PPP浮点解与整数钟法固定解实验。结果表明多系统的组合提升了定位精度,尤其是GLONASS的加入效果最明显,CODE与GBM产品的解算精度优于WUM、GRG产品。部分模糊度固定相比全模糊度固定的效果显著,模糊度固定明显缩短了PPP收敛时间,在静态模式下相对浮点解精度提升10%以内,动态模式下E方向与U方向精度提升效果最好。