高纬度地区GPT2w模型的适应性分析

GPT2w模型是现有精度最高的天顶对流层模型，但是应用在高纬度地区时存在较大误差.为更好地保障卫星导航定位系统在高纬度地区的高精度应用，评定了GPT2w模型在高纬度地区的精度，获取天顶对流层湿延迟、干延迟和总延迟，探讨了GPT2w模型改正对精密单点定位的影响.试验结果表明: GPT2w模型在高纬度地区的精度为厘米级，优于其在中低纬度地区的精度；南北极地区天顶对流层呈现明显季节变化特征和区域一致性特征，夏季天顶对流层总延迟高于冬季，北极地区天顶对流层湿延迟明显高于南极地区，北极地区天顶对流层随季节的变化幅度大于南极地区.PPP试验结果表明，GPT2w模型能够有效改善定位精度，适应高纬度地区的高精度定位需求.      

卫星精密测定轨中的对流层延迟估算系统

基于V isual Basic编程,设计了卫星精密测定轨中的实时气象采集与对流层延迟估算系统。利用实时采集ZQZ-A型自动气象站的温度、相对湿度、大气压等气象要素,采用Saastamoinen模型进行估算天顶方向对流层静力延迟和湿延迟,同时采用地基双波段微波辐射计测量大气水汽总量和云液态水总量,进而估算更高精度的湿延迟,在其有效时与模型计算的静力延迟相加,得到天顶方向总延迟;无效时采用模型计算的总延迟。最后将其投影到卫星方向得到总延迟。实际应用表明,设计的对流层延迟估算系统人机界面友好,具有易用性,能实时、稳定地为卫星精密测定轨提供服务。     

基于日地月信息的航天器全弧段自主容积卡尔曼滤波导航

高精度全弧段航天器自主导航是航天应用技术的发展方向,是实现航天器在轨任务执行的前提和基础。文章对仅利用日、地、月等天文信息进行航天器全弧段自主导航方法进行了研究。首先,以航天器轨道动力学方程和航天器与日地月之间的夹角信息及地心距作为自主导航系统的状态模型和观测模型,构建了非线性导航系统模型。其次,给出了全弧段自主导航算法,在日月可见弧段采用非线性容积卡尔曼滤波实现航天器自主导航,在星蚀时段利用航天器轨道动力学模型进行高精度轨道预报。最后,给出了数值仿真算例。结果表明,基于日地月天文信息的航天器全弧段自主导航精度保持在2km以内,能够满足其自主导航的要求。     

一种高精度实时GPS卫星钟差预测算法

为获得高精度实时GPS卫星钟差,文章提出一种基于多项式和最小二乘支持向量机(Least Squares Support Vector Machines,LS-SVM)相结合的钟差预报方法.该方法采用国际GNSS服务发布的超快速观测星历建模进行短期预报,首先根据卫星钟的物理特性用附有周期项的多项式模型进行拟合以提取趋势项和周期项,然后用LS-SVM对多项式拟合残差进行建模预报,最后将预报结果加上趋势项和周期项,得到最终的钟差预报值.试验结果表明,所提算法能够实时有效地对GPS卫星钟差进行预报,且精度优于超快速预报星历.     

陆地生态系统碳监测卫星控制系统方案设计及在轨验证

陆地生态系统碳监测卫星(句芒号)主要用于陆地生态系统碳监测、陆地生态和资源调查监测、国家重大生态工程监测评价等,句芒号卫星控制分系统设计了高精度的姿态确定、高稳定的姿态控制算法和混合轨迹规划姿态机动算法.针对载荷对月定标的需求设计任意时刻经过任意惯性空间位置的惯性扫描模式,针对卫星自主任务规划的需求,设计一种基于地表模型图的星下点地表属性预报方法和高精度的火点视线指向地理经纬度计算方法,并为火点检测敏感器提供了太阳天顶角、卫星天顶角、相对方位角等云判辅助信息火点位置的实时动态预报,在轨实现了高可靠的敏感器火点指向计算和伪火点剔除.根据卫星在轨运行数据,给出相应指标实现情况,对姿态控制系统的方案和指标满足情况进行在轨验证.     

利用GPS技术实时监测上海区域电离层变化

基于GPS技术实时监测电离层变化原理, 利用载波平滑伪距观测值建立区域电离层模型的方法, 计算了电离层延迟量和硬件延迟, 根据硬件延迟值相对稳定的特点, 采取一定时段求解出硬件延迟量, 对实时硬件延迟量进行预报, 进而实时分离GPS信号传播路径上的垂直总电子含量VTEC. 利用上海区域内的GPS网的观测数据, 建立实时上海区域电离层延迟模型, 监测上海区域的电离层变化. 数据分析结果表明, 这种方法的内符合精度优于3 TECU.      

一种面向空间飞行器视觉导航的椭圆检测算法

基于椭圆特征的空间飞行器视觉导航技术是一种新颖的高精度空间探测自主导航方法,如何对空间目标的环形边缘进行精准提取和高效拟合是实现空间飞行器视觉导航的必要条件。针对该问题,提出一种面向空间飞行器视觉导航的椭圆检测算法。利用多项式逼近导航图像连续边缘段的方式提取椭圆弧段;通过基于极大似然假设检验理论构建的模型选择判据,对来自同一个椭圆的椭圆弧段进行准确合并;对合并后的椭圆弧段进行拟合,得到空间飞行器视觉导航的椭圆检测结果。大量的仿真实验表明：与传统的椭圆检测算法相比,所提算法具有较高的精度和更高的鲁棒性,可以广泛应用于空间飞行器视觉导航图像椭圆检测,为空间飞行器视觉导航算法提供精准的二次曲线输入。     

时间序列法在临近空间大气风场预报中的应用

受多种因素影响，临近空间大气环境要素复杂多变，预报难度很大.本文采用时间序列法中的自回归滑动平均（ARMA）模型对临近空间大气风场开展统计预报方法研究，基于廊坊（39.4°N，116.7°W）中频雷达在88km高度的大气纬向风数据开展预报试验.本次预报试验的样本数据为2015年9月24日至10月24日风场数据，利用过去7天数据对未来第8天风场数据进行预报.试验结果显示，ARMA模型对临近空间大气风场预报有一定的适用性.当风场变化规律性较强，即样本数据风场呈现出比较显著的24h周期性变化时，ARMA模型预报效果较好；当风场发生突变时，预报效果变差.与实测数据的对比结果表明，ARMA模型预报结果的误差在9~27m·s-1，预报效果优于同阶自回归（AR）模型，略优于高阶AR模型.      

北斗首颗备份卫星性能初步分析

主要从卫星钟差预报、轨道测定精度、伪距波动情况等角度分析了I6卫星与北斗卫星导航系统（BDS）其他现役倾斜地球同步轨道（IGSO）卫星的异同,并从位置精度因子（PDOP）和格网可用性评估了I6卫星入网对BDS的贡献。利用星地双向时频传递设备观测的星地钟差数据,评估了I6卫星星载原子钟的预报性能,结果表明,I6卫星发播的卫星钟参数外推5h预报误差的均方根误差（RMS）为232ns,外推1h预报误差的RMS为073ns,与现役IGSO卫星钟差预报水平相当;对多星联合精密定轨结果分析表明,与北斗现役I3卫星相比,姿态控制方式优化后的I6卫星在地影期间的轨道精度并未发生明显衰减,克服了现有北斗二号卫星在地影期间轨道精度下降,从而影响北斗服务的连续性、可用性问题;利用大口径抛物面天线采集到的数据对I6卫星的伪距波动进行了分析,结果表明I6卫星单个观测弧段内其伪距波动峰峰差约为1m,与其他IGSO卫星一致;进行PDOP仿真计算,结果表明I6卫星的加入使得喀什地区的PDOP最大值由1282下降为726,PDOP大于6的时段所占百分比由2911%下降为1721%;对格网电离层产品实施解算,结果表明I6卫星的加入使得6个电离层格网点的可用度提升至95%以上。     

一种一阶延迟惯性环节温控系统优化设计方法

为提高惯性仪表的温控精度,针对纯延迟环节对温控系统稳定性的影响,提出一种一阶延迟惯性环节温控系统的优化设计方法.该方法充分利用平衡电桥消除温度跟踪误差,设计脉冲宽度调制(PWM)控制方法提高加热效率,同时基于Ziegler-Nichols整定法进行PID控制器优化设计以提高温控系统的相角裕度,使得温控系统对仪表间参数差异的适应能力大大增强.试验表明,在实验室条件下和具有强制对流环境的温度循环试验条件下仪表温控精度为0.006℃(1σ).该方法简单有效,阻容参数易于选取,能够满足温度控制的高精度要求.     

Retrieval of the change of precipitable water vapor with zenith tropospheric delay in the Chinese mainland

As a preliminary step for assessing the impact of global positioning system (GPS) refractive delay data in numerical weather prediction (NWP) models, the GPS zenith tropospheric delays (ZTD) are analyzed from 28 permanent GPS sites in the Chinese mainland. The objectives are to estimate the GPS ZTD and their variability in this area. The differences between radiosonde precipitable water vapor (PWV) and GPS PWV have a standard deviation of 4 mm in delay, a bias of 0.24 mm in delay, and a correlation coefficient of 0.94. The correlation between GPS ZTD and radiosonde PWV amounts to 0.89, indicating that the variety of tropospheric zenith delay can reflect the change of precipitable water vapor. The good agreement also guarantees that the information provided by GPS will benefit the NWP models. The time series of GPS ZTD, which were derived continuously from 2002 to 2004, are used to analyze the change of precipitable water vapor in Chinese mainland. It shows that the general trend of GPS ZTD is diminishing from the south-east coastland to the north-west inland, which is in accordance with the distribution of Chinese annual amount of rainfall. The temporal distribution of GPS ZTD in the Chinese mainland is that the GPS ZTD reaches maximum in summer, and it reaches minimum in winter. The long term differences between the observational data sources require further study before GPS derived data become useful for climate studies.     

Temporal and spatial stochastic behaviour of high-frequency slant tropospheric delays from simulations and real GPS data

In this paper, a turbulence theory-based simulation procedure for slant tropospheric delay variations is presented. Based on this procedure tropospheric delay variations are simulated for three different geometric scenarios. The stochastic behaviour of the generated time series is assessed in terms of temporal structure functions. It is shown that the temporal structure functions – in general – follow a 5/3 to 2/3 power-law behaviour. Deviations from this behaviour due to the complex interaction between varying observation geometry and atmospheric/turbulent conditions are discussed.     

Improving the estimation of zenith dry tropospheric delays using regional surface meteorological data

Global Navigation Satellite Systems (GNSS) are emerging as possible tools for remote sensing high-resolution atmospheric water vapour that improves weather forecasting through numerical weather prediction models. Nowadays, the GNSS-derived tropospheric zenith total delay (ZTD), comprising zenith dry delay (ZDD) and zenith wet delay (ZWD), is achievable with sub-centimetre accuracy. However, if no representative near-site meteorological information is available, the quality of the ZDD derived from tropospheric models is degraded, leading to inaccurate estimation of the water vapour component ZWD as difference between ZTD and ZDD. On the basis of freely accessible regional surface meteorological data, this paper proposes a height-dependent linear correction model for a priori ZDD. By applying the ordinary least-squares estimation (OLSE), bootstrapping (BOOT), and leave-one-out cross-validation (CROS) methods, the model parameters are estimated and analysed with respect to outlier detection. The model validation is carried out using GNSS stations with near-site meteorological measurements. The results verify the efficiency of the proposed ZDD correction model, showing a significant reduction in the mean bias from several centimetres to about 5 mm. The OLSE method enables a fast computation, while the CROS procedure allows for outlier detection. All the three methods produce consistent results after outlier elimination, which improves the regression quality by about 20% and the model accuracy by up to 30%.     

CICQ结构中逼近work-conserving的分组调度算法

联合输入交叉点排队（CICQ）结构的分组调度算法是一个得到了充分研究的领域,但已有算法在吞吐率和分组平均时延方面与输出排队（OQ）的结果相比,依然不够令人满意,其关键在于OQ交换机可以工作于work-conserving状态。不同于已有的研究,本文提出了以使得交换机最大程度工作于work-conserving状态为目标的新的研究思路,给出并证明了CICQ交换机实现work-conserving状态的充分且必要条件。以此为基础,提出了一种新的CICQ输入调度的算法即交叉缓存队列均衡（CQB）算法,并将经典的最大队长优先（LQF）算法用于输出调度,结合得到CQB-LQF算法。仿真结果显示,与经典的及最新的CICQ分组调度算法相比,CQB-LQF算法显著提高了吞吐率及分组平均时延性能。      

Real-time zenith tropospheric delays in support of numerical weather prediction applications

The Geodetic Observatory Pecný (GOP) routinely estimates near real-time zenith total delays (ZTD) from GPS permanent stations for assimilation in numerical weather prediction (NWP) models more than 12 years. Besides European regional, global and GPS and GLONASS solutions, we have recently developed real-time estimates aimed at supporting NWP nowcasting or severe weather event monitoring. While all previous solutions are based on data batch processing in a network mode, the real-time solution exploits real-time global orbits and clocks from the International GNSS Service (IGS) and Precise Point Positioning (PPP) processing strategy. New application G-Nut/Tefnut has been developed and real-time ZTDs have been continuously processed in the nine-month demonstration campaign (February–October, 2013) for selected 36 European and global stations. Resulting ZTDs can be characterized by mean standard deviations of 6–10 mm, but still remaining large biases up to 20 mm due to missing precise models in the software. These results fulfilled threshold requirements for the operational NWP nowcasting (i.e. 30 mm in ZTD). Since remaining ZTD biases can be effectively eliminated using the bias-reduction procedure prior to the assimilation, results are approaching the target requirements in terms of relative accuracy (i.e. 6 mm in ZTD). Real-time strategy and software are under the development and we foresee further improvements in reducing biases and in optimizing the accuracy within required timeliness. The real-time products from the International GNSS Service were found accurate and stable for supporting PPP-based tropospheric estimates for the NWP nowcasting.     

一种飞轮密封罩优化设计方法

研究飞轮密封罩的结构优化设计方法.首先综合分析了利用凸弧和凹弧构建密封罩结构外形曲线的设计思路,在此基础上提出凹凸弧方案;进而据此推导出凹弧弓高极值,构建一系列飞轮密封罩结构模型;最后以某飞轮密封罩为分析对象,利用有限元技术研究其稳定性等性能随外形参数的变化规律.这种新的设计思路可对类似产品结构的设计提供指导.     

Near real-time estimation of tropospheric water vapour content from ground based GNSS data and its potential contribution to weather now-casting in Austria

The importance of high resolution meteorological analysis of the atmosphere increased over the past years. A detailed analysis of the humidity field is an important precondition for a better monitoring of local and regional extreme precipitation events and for forecasts with improved spatial resolution. For this reason, the Austrian Meteorological Agency (ZAMG) is operating the spatial and temporal high resolution INCA system (Integrated Now-casting through Comprehensive Analysis) since begin of 2005. Errors in this analysis occur mainly in the areas of rapidly changing and hard to predict weather conditions or rugged topography with extreme differences in height such as the alpine area of Austria. The aim of this work is to provide GNSS based measurements of the tropospheric water vapour content with a temporal resolution of 1 h and a temporal delay of less than 1 h to assimilate these estimates into the INCA system. Additional requirement is an accuracy of better than 1 mm of the precipitable water (PW) estimates.     

“嫦娥4号”中继星使命轨道段定轨计算与分析

"嫦娥4号"中继星是"嫦娥4号"探测器实现月球背面着陆与巡视的关键,目前正稳定运行在地-月L2点使命轨道上,该使命轨道为平均周期约14天的南族Halo轨道。因任务的需要,中继星本体系+Z轴需调整指向,处于正对太阳和非正对太阳两种状态。太阳光压在中继星+Z轴对日的情况下会加速卫星的角动量累积,增加卫星卸载喷气频次。基于中继星使命轨道段测控支持条件,采用重叠弧段法对两种状态下的中继星定轨精度进行分析与评估。结果表明,在中继星+Z轴非对日运行状态下,重叠弧段位置误差为1.6 km,速度误差为8 mm/s;在中继星+Z轴对日运行状态下,重叠弧段位置误差为0.6 km,速度误差为3 mm/s,这对中继星的长期运行具有重要参考价值。