飞机总装数字化脉动生产线技术

飞机总装生产线作为新型生产组织模式,对提高飞机装配效率和质量,满足飞机批量生产要求具有重要作用.在分析总结国内外典型飞机总装生产线及其应用情况的基础上,对飞机数字化总装脉动生产线涉及的大部件数字化对接技术、数字化检测技术、精准移动技术、集成装配平台技术、物料精益配送技术等关键技术进行了探讨,为构建适合我国飞机总装配的脉动生产线提供思路.     

多模多频卫星导航系统码偏差统一定义与处理方法

精确处理和修正观测量偏差（OSB）是有效发挥多模多频优势,提升GNSS服务和应用效能的前提和基础，已成为国内外卫星导航高精度定位领域研究的热点问题之一。国际GNSS服务组织（IGS）和国际大地测量协会（IAG）专门成立了工作组推动相关工作。然而，目前有关观测量偏差处理的方法仍存在着定义不统一、求解不严密、使用不便捷等突出问题，给实时高精度定位应用带来诸多不利因素。针对此，首先阐述了中国科学院（CAS）电离层分析中心码偏差产品的定义、估计策略和使用方法，然后给出了部分精度评估和分析。结果表明：CAS、CODE和DLR发布的码偏差参数一致性优于0.30ns，CAS码偏差月稳定性优于0.15ns。相关工作对于推动多模多频GNSS在电离层监测、高精度定位和授时定时等领域的应用具有重要参考价值。     

Precise orbit determination for TH02-02 satellites based on BDS3 and GPS observations

The Tianhui-2 02 (TH02-02) satellite formation, as a supplement to the microwave mapping satellite system Tianhui-2 01 (TH02-01), is the first Interferometric Synthetic Aperture Radar (InSAR) satellite formation-flying system that supports the tracking of BeiDou global navigation Satellite system (BDS3) new B1C and B2a signals. Meanwhile, the twin TH02-02 satellites also support the tracking of Global Positioning System (GPS) L1&L2 and BDS B1I&B3I signals. As the spaceborne receiver employs two independent boards to track the Global Navigation Satellite System (GNSS) satellites, we design an orbit determination strategy by estimating independent receiver clock offsets epoch by epoch for each GNSS to realize the multi-GNSS data fusion from different boards. The performance of the spaceborne receiver is evaluated and the contribution of BDS3 to the kinematic and reduced-dynamic Precise Orbit Determination (POD) of TH02-02 satellites is investigated. The tracking data onboard shows that the average number of available BDS3 and GPS satellites are 8.7 and 9.1, respectively. The carrier-to-noise ratio and carrier phase noise of BDS3 B1C and B2a signals are comparable to those of GPS. However, strong azimuth-related systematic biases are recognized in the pseudorange multipath errors of B1C and B3I. The pseudorange noise of BDS3 signals is better than that of GPS after eliminating the multipath errors from specific signals. Taking the GPS-based reduced-dynamic orbit with single-receiver ambiguity fixing technique as a reference, the results of BDS3-only and BDS3 + GPS combined POD are assessed. The Root Mean Square (RMS) of orbit comparison of BDS3-based kinematic and reduced-dynamic POD with reference orbit are better than 7 cm and 3 cm in three-Dimensional direction (3D). The POD performance based on B1C&B2a data is comparable to that based on B1I&B3I. The precision of BDS3 + GPS combined kinematic orbit can reach up to 3 cm (3D RMS), which has a more than 25% improvement relative to the GPS-only solution. In addition, the consistency between the BDS3 + GPS combined reduced-dynamic orbit and the GPS-based ambiguity-fixed orbit is better than 1.5 cm (3D RMS).     

一种基于FPGA用游标法实现的时间间隔测定器

文中介绍时间间隔的测量原理和游标法的测时原理,针对一种基于FPGA的高精度测时系统,描述其硬件实现。该系统利用粗测与细测相结合来测量两个脉冲信号之间的时间间隔,其测时分辨率可达到1ns。系统具有精度高、功耗小及实现简便等优点。     

基于多模PPP-AR技术的大气水汽探测性能分析

精密单点定位（precise point positioning，PPP）反演大气可降水量（precipitable water vapor，PWV）具有精度高、实时性强等优点，能够在灾害监测、降雨预报及探测降水信息等方面发挥重要作用。为评估整周模糊度固定模式下PPP-AR（PPP ambiguity resolution）反演PWV的性能，选取全球范围16个MGEX站2022年4个时段的观测数据，采用最终精密星历解算，设置不同星座组合（GPS,BDS-3,GPS+BDS-3,GPS+GLO+GAL+BDS-3）获取对流层延迟（zenith total delay，ZTD）估值，并转换为PWV。从PPP-ZTD与IGS-ZTD的相关性、PPP-ZTD收敛时间、ZTD估值精度和PPP-PWV估值精度4个方面评价多模PPP-AR探测水汽的性能。结果表明，与单（G、C）、双系统（GC）固定解相比，多系统（GREC）固定解获取ZTD估值更加精确，相关系数更高。相较于单、双系统，多系统具有更快的收敛速度，收敛时间分别缩短了27%,25%和20%，多系统固定解与浮点解相比收敛时间缩短11%。此外，对GNSS PPP反演的PWV与探空站PWV（RS-PWV）进行对比，结果表明，WUH2站与HOB2站单、双、多系统固定解、多系统浮点解（float-GREC）的平均均方根误差分别为6.40 mm,6.48 mm,6.19 mm,6.17 mm,6.19 mm和5.82 mm,5.77 mm,5.72 mm,5.62 mm,5.70 mm。多模下得到的PWV估值精度最高，可为高精度的水汽反演提供支持。     

卫星与测站钟差支持条件下的GEO卫星精密定轨

在基于伪距的GEO卫星精密定轨中, GEO卫星的静地特性导致定轨解算无法对星地组合钟差进行有效估计, 需要独立的时间同步支持. 本文讨论了卫星和测站钟差支持条件下的GEO卫星定轨原理, 利用仿真数据系统地分析了中国区域网跟踪条件下GEO卫星的定轨精度, 从定性和定量角度分析了钟差二次项、星地时间同步精度、站间时间同步精度及系统差等因素对定轨精度的影响.     

Inter-agency comparison of TanDEM-X baseline solutions

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) is the first Synthetic Aperture Radar (SAR) mission using close formation flying for bistatic SAR interferometry. The primary goal of the mission is to generate a global digital elevation model (DEM) with 2 m height precision and 10 m ground resolution from the configurable SAR interferometer with space baselines of a few hundred meters. As a key mission requirement for the interferometric SAR processing, the relative position, or baseline vector, of the two satellites must be determined with an accuracy of 1 mm (1D RMS) from GPS measurements collected by the onboard receivers. The operational baseline products for the TanDEM-X mission are routinely generated by the German Research Center for Geosciences (GFZ) and the German Space Operations Center (DLR/GSOC) using different software packages (EPOS/BSW, GHOST) and analysis strategies. For a further independent performance assessment, TanDEM-X baseline solutions are generated at the Astronomical Institute of the University of Bern (AIUB) on a best effort basis using the Bernese Software (BSW).     

Ambiguity resolution in precise point positioning with hourly data for global single receiver

Integer ambiguity resolution (IAR) can improve precise point positioning (PPP) performance significantly. IAR for PPP became a highlight topic in global positioning system (GPS) community in recent years. More and more researchers focus on this issue. Progress has been made in the latest years. In this paper, we aim at investigating and demonstrating the performance of a global zero-differenced (ZD) PPP IAR service for GPS users by providing routine ZD uncalibrated fractional offsets (UFOs) for wide-lane and narrow-lane. Data sets from all IGS stations collected on DOY 1, 100, 200 and 300 of 2010 are used to validate and demonstrate this global service. Static experiment results show that an accuracy better than 1 cm in horizontal and 1–2 cm in vertical could be achieved in ambiguity-fixed PPP solution with only hourly data. Compared with PPP float solution, an average improvement reaches 58.2% in east, 28.3% in north and 23.8% in vertical for all tested stations. Results of kinematic experiments show that the RMS of kinematic PPP solutions can be improved from 21.6, 16.6 and 37.7 mm to 12.2, 13.3 and 34.3 mm for the fixed solutions in the east, north and vertical components, respectively. Both static and kinematic experiments show that wide-lane and narrow-lane UFO products of all satellites can be generated and provided in a routine way accompanying satellite orbit and clock products for the PPP user anywhere around the world, to obtain accurate and reliable ambiguity-fixed PPP solutions.     

Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

Low-Earth-Orbit(LEO) formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination(PROD) is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System(BDS) to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System(GPS) is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from9.71 to 21.58. Secondly, the results show that the 3-Dimensional(3 D) accuracy of PROD, based on BDS-only, GPS-only and BDS + GPS, is 0.74 mm, 0.66 mm and 0.52 mm, respectively. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit(GEO) satellites and Inclined Geosynchronous-Orbit(IGSO) satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision(ADOP), based on BDS + GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the SingleDifference(SD) ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit(MEO) satellites co-work with GEO satellites, the accuracy decreases by 17.02%.     

Towards PPP-RTK: Ambiguity resolution in real-time precise point positioning

Integer ambiguity resolution at a single station can be achieved by introducing predetermined uncalibrated phase delays (UPDs) into the float ambiguity estimates of precise point positioning (PPP). This integer resolution technique has the potential of leading to a PPP-RTK (real-time kinematic) model where PPP provides rapid convergence to a reliable centimeter-level positioning accuracy based on an RTK reference network. Nonetheless, implementing this model is technically subject to how rapidly we can fix wide-lane ambiguities, stabilize narrow-lane UPD estimates, and achieve the first ambiguity-fixed solution. To investigate these issues, we used 7 days of 1-Hz sampling GPS data at 91 stations across Europe. We find that at least 10 min of observations are required for most receiver types to reliably fix about 90% of wide-lane ambiguities corresponding to high elevations, and over 20 min to fix about 90% of those corresponding to low elevations. Moreover, several tens of minutes are usually required for a regional network before a narrow-lane UPD estimate stabilizes to an accuracy of far better than 0.1 cycles. Finally, for hourly data, ambiguity resolution can significantly improve the accuracy of epoch-wise position estimates from 13.7, 7.1 and 11.4 cm to 0.8, 0.9 and 2.5 cm for the East, North and Up components, respectively, but a few tens of minutes is required to achieve the first ambiguity-fixed solution. Therefore, from the timeliness aspect, our PPP-RTK model currently cannot satisfy the critical requirement of instantaneous precise positioning where ambiguity-fixed solutions have to be achieved within at most a few seconds. However, this model can still be potentially applied to some near-real-time remote sensing applications, such as the GPS meteorology.