Performance of GPS and GPS/SINS navigation in the CE-5T1 skip re-entry mission

A CE-5T1 spacecraft completed a high-speed skip re-entry to the earth after a circumlunar flight on October 31, 2014. In addition to the strapdown inertial navigation system (SINS), a lightweight GPS receiver with rapid acquisition was developed as a navigation sensor in the re-entry capsule. The GPS receiver effectively solved the poor accuracy problem of long-term navigation using only the SINS. In contrast to ground users and low-earth-orbit spacecraft, numerous factors, including high altitude and kinetic characteristics in high-speed skip re-entry, are important for GPS positioning feasibility and were presented in accordance with the flight data. GPS solutions started at nearly 4900 km orbital altitude during the phases of re-entry process. These solutions were combined by an inertial measurement unit in a loosely coupled integrated navigation method and SINS navigation initialization. A simplified GPS/SINS navigation filter for limited resources was effectively developed and implemented on board for spacecraft application. Flight data estimation analyses, including trajectory, attitude, position distribution of GPS satellite, and navigation accuracy, were presented. The estimated accuracy of position was better than 42 m, and the accuracy of velocity was better than 0.1 m/s.     

Quality assessment of GNSS observations from an Android N smartphone and positioning performance analysis using time-differenced filtering approach

GPS Solutions - Tropical cyclones are a serious natural disaster concern in Australia due to El Niño and La Niña phenomena. However, little attention has been paid to the ionospheric...     

Mapping hourly dynamics of urban population using trajectories reconstructed from mobile phone records

Understanding the spatiotemporal dynamics of urban population is crucial for addressing a wide range of urban planning and management issues. Aggregated geospatial big data have been widely used to quantitatively estimate population distribution at fine spatial scales over a given time period. However, it is still a challenge to estimate population density at a fine temporal resolution over a large geographical space, mainly due to the temporal asynchrony of population movement and the challenges to acquiring a complete individual movement record. In this article, we propose a method to estimate hourly population density by examining the time‐series individual trajectories, which were reconstructed from call detail records using BP neural networks. We first used BP neural networks to predict the positions of mobile phone users at an hourly interval and then estimated the hourly population density using log‐linear regression at the cell tower level. The estimated population density is linearly correlated with population census data at the sub‐district level. Trajectory clustering results show five distinct diurnal dynamic patterns of population movement in the study area, revealing spatially explicit characteristics of the diurnal commuting flows, though the driving forces of the flows need further investigation.     

浅谈地理国情普查项目中控制点库的制作

数字正射影像数据是地理国情普查中主要的调查数据源,同时也是普查成果数据的重要组成部分。而控制点作为数字正射影像制作的基础数据也是普查成果中必不可少的一部分。本文就国情普查成果中影像控制点的采集与整理进行了探讨。     

高压输电线对GPS测量影响的测试与分析

对高压线下GPS测量数据进行了对比分析,得到高压输电线对GPS测量成果的定性结论:对于高压线下精度不高的定位测量,GPS定位技术是可以胜任的。     

地理国情普查基本统计专题地图实践与探讨

利用地理国情基本统计分析软件对地理国情普查预处理后数据进行基本统计分析。根据基本统计结果、基本统计汇总表及统计报告,制作行政区划四至点、高程分级、坡度分级、水域分布、水域统计、铁路与道路、行政村驻地分布图,并对地理国情普查成果及统计分析成果的应用推广服务提出建议。     

小冰期时中国南方地区降水模式的差异研究

小冰期是过去一千年中全球气候变化的重要事件之一。关于小冰期时中国季风区和西风影响区气候变化的对比研究众多,但是缺乏中国南方地区降水模式时空差异的研究,难以了解中国南方地区降水变化规律。为了系统地了解小冰期时中国南方地区降水的复杂性,本文将中国南方地区划分为东南—华南沿海地区、中部地区以及西南地区三个区域,总共选取了19条高分辨率的古气候记录进行对比研究,主要有以下几点认识:(1)相对于中世纪暖期而言,小冰期期间中国南方东南—华南沿海地区的气候偏湿,这可能与雨带在中国南方的滞留时间延长和沿海地区受台风的影响增强有关。(2)中国中部地区秦岭南麓和神农架高山林区在小冰期时期主要呈"冷湿"的模式,差异在于秦岭南麓区域主要在小冰期中后期偏湿,这与中部其他区域偏"冷干"的模式不同。这种区域差异可能是由于地形地势和大气环流的复杂性导致。(3)中国西南地区受印度夏季风和东亚夏季风的共同影响,且该区域地形复杂,其气候变化在小冰期时期存在更加明显的空间差异,没有呈现出比较一致的降水模式。与小冰期期间的降水变化不同的是,近30年东南—华南沿海地区除了台湾和雷州半岛,其他区域降水明显减少,可能受气温和人类活动等因素的影响。通过结合高分辨率的古气候记录,我们系统分析了中国南方小冰期的干湿模式在时空上的差异及其可能的影响因子,这对于认识小冰期时中国南方不同区域降水的复杂性及未来旱涝灾害的防控具有一定意义。     

城市轨道交通勘测大数据的集成与应用

正近年来,三维可视化技术日趋发展成熟,倾斜摄影技术、三维激光扫描技术等测绘新技术以及国内BIM技术的全面推广使用,使得建筑行业正在由二维设计建造向三维设计建造转变。由于城市轨道交通多建造在城市地下空间,与地上建筑相比,其在设计建造过程中面临着地下周边环境不可直观展示的困境,其更加迫切需要三维可视化技术来辅助地铁规划设计与建造施工。地质信息复杂多变,     

柴达木盆地鱼卡地区电磁场特征与铀成矿有利环境分析

正柴达木盆地是我国典型的多能源聚宝盆。自上世纪中期开展铀矿地质勘查工作以来,在盆地北缘中、下侏罗统地层中发现了一批砂岩型铀矿化点和异常带,基本证实了中、下侏罗统具备砂岩型铀成矿的基本地质条件(刘林等,2013)。其中,     

渤南洼陷沙四下亚段沉积时期古气候演化

正全球于古近纪发育PETM、ETM2、EECO、和MECO多个短期热气候事件(雷华蕊等,2018)。受热气候事件影响,渤南洼陷沙四下亚段沉积时期红层沉积发育并记录着热气候事件控制下古气候演化过程。立足于渤南洼陷沙四下亚段红层,恢复古气候演化过程,一方面可以点带面,揭示全球古近纪气候演化;另一方面为研究极端气候条件对湖盆沉积体系的控制作用奠定基础。