Evaluation on real-time dynamic performance of BDS in PPP,RTK, and INS tightly aided modes

Since China’s BeiDou satellite navigation system (BDS) began to provide regional navigation service for Asia-Pacific region after 2012, more new generation BDS satellites have been launched to further expand BDS’s coverage to be global. In this contribution, precise positioning models based on BDS and the corresponding mathematical algorithms are presented in detail. Then, an evaluation on BDS’s real-time dynamic positioning and navigation performance is presented in Precise Point Positioning (PPP), Real-time Kinematic (RTK), Inertial Navigation System (INS) tightly aided PPP and RTK modes by processing a set of land-borne vehicle experiment data. Results indicate that BDS positioning Root Mean Square (RMS) in north, east, and vertical components are 2.0, 2.7, and 7.6?cm in RTK mode and 7.8, 14.7, and 24.8?cm in PPP mode, which are close to GPS positioning accuracy. Meanwhile, with the help of INS, about 38.8%, 67.5%, and 66.5% improvements can be obtained by using PPP/INS tight-integration mode. Such enhancements in RTK/INS tight-integration mode are 14.1%, 34.0%, and 41.9%. Moreover, the accuracy of velocimetry and attitude determination can be improved to be better than 1?cm/s and 0.1°, respectively. Besides, the continuity and reliability of BDS in both PPP and RTK modes can also be ameliorated significantly by INS during satellite signal missing periods.     

Displacement monitoring performance of relative positioning and Precise Point Positioning (PPP) methods using simulation apparatus

Besides the classical geodetic methods, GPS (Global Positioning System) based positioning methods are widely used for monitoring crustal, structural, ground etc., deformations in recent years. Currently, two main GPS positioning methods are used: Relative and Precise Point Positioning (PPP) methods. It is crucial to know which amount of displacement can be detected with these two methods in order to inform their usability according to the types of deformation. Therefore, this study conducted to investigate horizontal and vertical displacement monitoring performance and capability of determining the direction of displacements of both methods using a developed displacement simulator apparatus. For this purpose, 20 simulated displacement tests were handled. Besides the 24?h data sets, 12?h, 8?h, 4?h and 2?h subsets were considered to examine the influence of short time spans. Each data sets were processed using GAMIT/GLOBK and GIPSY/OASIS scientific software for relative and PPP applications respectively and derived displacements were compared to the simulated (true) displacements. Then statistical significance test was applied. Results of the experiment show that using 24?h data sets, relative method can determine up to 6.0?mm horizontal displacement and 12.3?mm vertical displacement, while PPP method can detect 8.1?mm and 19.2?mm displacements in horizontal and vertical directions respectively. Minimum detected displacements are found to grow larger as time spans are shortened.     

Near real-time BDS GEO satellite orbit determination and maneuver analysis with reversed point positioning

The Geostationary Earth Orbit (GEO) satellite is a crucial part of the BeiDou Navigation Satellite System (BDS) constellation. However, due to various perturbation forces acting on the GEO satellite, it drifts gradually over time. Thus, frequent orbit maneuvers are required to maintain the satellite at its designed position. During the orbit maneuver and recovery periods, the orbit quality of the maneuvered satellite computed with broadcast navigation ephemeris will be significantly degraded. Furthermore, the conventional dynamic Precise Orbit Determination (POD) approach may not work well, because of a lack of publicly available satellite information for modeling the thrust forces. In this paper, a near real-time approach free of thrust forces modeling is proposed for BDS GEO satellite orbit determination and maneuver analysis based on the Reversed Point Positioning (RPP). First, the station coordinates and receiver clock offsets are estimated by GPS/BDS combined Single Point Positioning (SPP) with single-frequency phase-smoothed pseudorange observations. Then, with the fixed station coordinates and receiver clock offsets, the RPP method can be conducted to determine the GEO satellite orbits. When no orbit maneuvers occur, the proposed method can obtain orbit accuracies of 0.92, 2.74, and 8.30?m in the radial, along-track, and cross-track directions, respectively. The average orbit-only Signal-In-Space Range Error (SISRE) is 1.23?m, which is slightly poorer than that of the broadcast navigation ephemeris. Using four days of GEO maneuvered datasets, it is further demonstrated that the derived orbits can be employed to characterize the behaviors of GEO satellite maneuvers, such as the time span of the maneuver as well as the satellite thrusting accelerations. These results prove the efficiency of the proposed method for near real-time GEO satellite orbit determination during maneuvers.     

图像信号预处理的一种算法

提出了针对含有斑、点目标的遥感图像进行有损压缩的一种方法,介绍了去局部均值算法原理,依据3σ准则推导了门限取值公式,给出了算法的流程。通过仿真实验,分析了算法的有效性。     

动背景中高速掠过点目标的双窗口捕捉算法

为解决动背景下高速掠过点目标的实时探测问题,探讨了一种新的算法：首先采用基于帧间差分向量一阶范数的目标检测算法对图象进行预处理,实现大面积背景抑制,提取可疑目标点;然后,对提取的可疑目标点采用双窗口搜索算法捕捉运动点目标。该算法简单,运算量小,易于实现。实验结果验证了算法的有效性。     

基于RTS滤波的GPS+BDS 非差非组合PPP/INS紧组合模型

GPS高精度定位技术在动态复杂环境中,其定位精度、可靠性和连续性因卫星信号频繁失锁而变差。为此,提出了采用基于RTS滤波(Rauch-Tung-Striebel Filter)的GPS+BDS非差非组合PPP(Precise Point Positioning)与INS(Inertial Navigation System)紧组合模型的策略来克服GPS在动态定位中的弱点。其中,采用GPS+BDS双系统观测数据,可提高PPP解算中的可用卫星数,改善星站间定位几何强度和提高PPP收敛速度;采用PPP/INS紧组合,利用INS的自主定位特性和短期高精度特性,可有效改善复杂环境下的定位精度和连续性;采用RTS滤波,可进一步提高PPP/INS紧组合性能。首先推导了GPS+BDS非差非组合函数模型、PPP/INS紧组合函数模型和RTS滤波函数模型,然后利用一组车载动态数据,对动态GPS PPP、GPS+BDS PPP、GPS/INS紧组合、GPS+BDS PPP/INS紧组合和基于RTS的GPS+BDS PPP/IMU紧组合的定位、测速和定姿性能进行分析。实验结果表明,该方案可有效提高定位(58%～72%)、测速(74%～82%)和定姿(4%～23%)精度,特别是对卫星失锁期间的定位性能改善尤为明显。     

GPS精密单点定位收敛性分析及改善措施

目前卫星定位技术中常用的高精度定位方法主要是相对定位和非差相位精密单点定位。非差相位精密单点定位无法像相对定位那样使用差分方式来消除定位中的某些误差,因而如何对影响定位的各个误差源进行准确地建模修正是提高非差相位精密单点定位精度和收敛速度的关键。本文从非差相位精密单点定位的3个关键环节入手,对影响定位收敛速度的因素进行简要分析,讨论了改善措施,并结合实际数据进行了相关验证。     

关于探测器定点在共线平动点附近的控制问题

对探测器定点在共线平动点附近的轨道控制提出了一种小推力方案,针对日-地（月）系的具体背景给出了数值模拟结果,并对其进行了相应的分析.     

已知最大定位误差的点特征松弛匹配

研究了在已知最大定位误差的情况下时，如何对基本点特征松弛匹配算法进行改进，以提高匹配性能。基本思想是利用已知的最大定位误差，确定两点对的最小匹配度量，从而减小虚假特征点对匹配结果的影响。采用针对模拟图像及实际卫片航片图像对的实验，比较了两种方法的性能。结果表明，在已知最大定位误差的情况下，该改进方法比基本点特征松弛匹配算法具有更好的匹配性能。     

概念设计阶段起落架接地点设计

针对现代民用飞机设计特点,尤其是某些新技术的应用和飞机系列化发展的需求,在充分吸收和借鉴传统飞机概念设计阶段起落架设计方法的基础上,从工程应用角度出发,总结并提出一套现代民用飞机概念设计阶段起落架接地点设计流程及方法。同时,按照设计流程将影响起落架接地点设计的限制因素划分为适航安全、性能、结构、空间布置、运营等影响因素,明晰各限制因素对设计产生的影响。