Improved ambiguity resolution for URTK with dynamic atmosphere constraints   总被引：1，自引：0，他引：1  

Weiming Tang  Wenjian Liu  Xuan Zou  Zongnan Li  Liang Chen  Chenlong Deng  Chuang Shi 《Journal of Geodesy》2016,90(12):1359-1369

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Joint estimation of GPS/BDS real-time clocks and initial results     

Weixing Zhang  Yidong Lou  Shengfeng Gu  Chuang Shi  Jennifer S. Haase  Jingnan Liu 《GPS Solutions》2016,20(4):665-676

We present the joint estimation model for Global Positioning System/BeiDou Navigation Satellite System (GPS/BDS) real-time clocks and present the initial satellite clock solutions determined from 106 stations of the international GNSS service multi-GNSS experiment and the BeiDou experimental tracking stations networks for 1 month in December, 2012. The model is shown to be efficient enough to have no practical computational limit for producing 1-Hz clock updates for real-time applications. The estimated clocks were assessed through the comparison with final clock products and the analysis of post-fit residuals. Using the estimated clocks and corresponding orbit products (GPS ultra-rapid-predicted and BDS final orbits), the root-mean-square (RMS) values of coordinate differences from ground truth values are around 1 and 2–3 cm for GPS-only and BDS-only daily mean static precise point positioning (PPP) solutions, respectively. Accuracy of GPS/BDS combined static PPP solutions falls in between that of GPS-only and BDS-only PPP results, with RMS values approximately 1–2 cm in all three components. For static sites, processed in the kinematic PPP mode, the daily RMS values are normally within 4 and 6 cm after convergence for GPS-only and BDS-only results, respectively. In contrast, the combined GPS/BDS kinematic PPP solutions show higher accuracy and shorter convergence time. Additionally, the BDS-only kinematic PPP solutions using clock products derived from the proposed joint estimation model were superior compared to those computed using the single-system estimation model.  相似文献   

Enabling maps/location searches on mobile devices: constructing a POI database via focused crawling and information extraction     

Hsiu-Min Chuang  Ting-Yao Kao  Chung-Ting Cheng  Ya-Yun Huang  Kuo-Pin Cheong 《International journal of geographical information science》2016,30(7):1405-1425

With the popularity of mobile devices and smartphones, we have witnessed rapid growth in mobile applications and services, especially in location-based services (LBS). According to a mobile marketing survey, maps/location searches are among the most utilized services on smartphones. Points of interest (POIs), such as stores, shops, gas stations, parking lots, and bus stops, are particularly important for maps/location searches. Existing map services such as Google Maps and Wikimapia are constructed manually either professionally or with crowd sourcing. However, manual annotation is costly and limited in current POI search services. With the abundance of information on the Web, many store POIs can be extracted from the Web. In this paper, we focus on automatically constructing a POI database to enable store POI map searches. We propose techniques that are required to construct a POI database, including focused crawling, information extraction, and information retrieval techniques. We first crawl Yellow Page web sites to obtain vocabularies of store names. These vocabularies are then investigated with search engines to obtain sentences containing these store names from search snippets in order to train a store name recognition model. To extract POIs scattered across the Web, we propose a query-based crawler to find address-bearing pages that might be used to extract addresses and store names. We crawled 1.25 million distinct POI pairs scattered across the Web and implemented a POI search service via Apache Lucent’s search platform, called Solr. The experimental results demonstrate that the proposed geographical information retrieval model outperforms Wikimapia and a commercial app called ‘What’s the Number?’  相似文献   

不同霾识别方法对陕西霾判识的影响     

李星敏  董自鹏  赵奎锋  陈闯  彭艳 《气象》2022,48(5):647-657

利用2016年3月至2020年2月逐时气象和PM_2.5质量浓度观测资料,依据《霾的观测和预报等级（QX/T 113—2010）》（以下简称2010行标）和《霾的观测识别》（GB/T 36542—2018）(以下简称2018国标)两种标准规定的判识方法,分析了在不同标准下陕西省霾出现频率的差异。结果表明:采用2018国标判识的霾出现频率明显多于采用2010行标的霾出现频率,若均以霾现象持续6 h及以上作为判定标准,则两者得到的霾日数相当。在80%≤相对湿度<95%时,用2018国标判识的霾出现频率比采用2010行标多,湿度越大,增加越明显;气溶胶吸湿性参数对吸湿增长后气溶胶消光系数的计算影响较大,使用2018国标时应注意该参数在各地的差异。在PM_2.5≤75μg·m^-3时,采用2018国标仍能识别出霾,显现出湿度对能见度的影响;在PM_2.5>75μg·m^-3时,当空气污染达到中度及以上时,两者差异缩小。陕西省各地市霾发生频率的月变化均呈现出“冬高夏低”的“U型”分布,...  相似文献   

BeiDou phase bias estimation and its application in precise point positioning with triple-frequency observable   总被引：10，自引：5，他引：5  

Shengfeng Gu  Yidong Lou  Chuang Shi  Jingnan Liu 《Journal of Geodesy》2015,89(10):979-992

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基于小波去噪的高铁沉降预测模型研究     

刘闯  花向红  赵杰  王中华 《测绘信息与工程》2015,40(1)

以武汉市某高铁的沉降观测数据为基础,对小波去噪前后的观测数据分别采用非线性曲线拟合模型和时间序列分析模型进行建模预测,并与实测数据进行比较分析.结果表明,观测数据经小波去噪后再进行建模分析,两种方法的预测精度都有很大改善,对高铁沉降变形预报有一定的实用价值.  相似文献   

小波时变参数PGM(1,1)模型的工程应用研究     

袁达  邱卫宁  花向红  刘闯 《测绘信息与工程》2015,40(1)

首先阐述了小波去除数据噪声的方法及小波模型的选取问题,然后对GM(1,1)模型背景值生成序列进行改进,采用搜索法确定背景值最佳生成系数.考虑到模型中的灰参数会随时间而变化,采用多项式逼近模型灰参数,并通过最小二乘方法求解多项式的系数,最后形成了小波时变参数PGM(1,1)模型同时采用Runge-Kutta方法求解.通过武成城际铁路沉降监测数据的计算分析表明,小波时变参数PGM(1,1)在高铁沉降预测中具有较高的精度.  相似文献   

Real-time detection and repair of cycle slips in triple-frequency GNSS measurements   总被引：3，自引：1，他引：2  

Qile Zhao  Binzi Sun  Zhiqiang Dai  Zhigang Hu  Chuang Shi  Jingnan Liu 《GPS Solutions》2015,19(3):381-391

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云南怒江河流沉积物碎屑锆石LA-ICP-MS U-Pb年龄和Hf同位素组成及其地质意义     

包创  陈岳龙  步小飞  陈雪  李大鹏 《地质通报》2015,34(8):1413-1425

采用LA-MC-ICP-MS测定技术,对怒江河流沉积物中的碎屑锆石进行了U-Pb和Lu-Hf同位素测定。结果显示,碎屑锆石U-Pb年龄可分为6个组段:50~74Ma、84~235Ma、275~413Ma、451~569Ma、657~1429Ma和1602~3436Ma,其中最主要的年龄组段为50~74Ma和84~235Ma。50~74Ma的年龄段为新特提斯洋从俯冲到碰撞闭合的阶段,约65Ma的年龄峰值可能是印度大陆与欧亚大陆主体碰撞的远程地质记录。84~235Ma年龄段代表了中特提斯洋演化阶段,年龄峰值约为110Ma,可能指示羌塘地块与拉萨地块的碰撞拼接此时已经完成,通过U-Pb年龄分布对比,羌塘地块几乎没有给怒江河流沉积物提供物质。怒江河流沉积物中碎屑锆石的εHf(t)值介于-18.7~+11.7之间,模式年龄分布于0.65~4.05Ga之间,其中中生代碎屑锆石的εHf(t)值分布于-16.4~+2.9之间,与中拉萨地块有密切的亲缘性,同时含有少量北拉萨地块的特征。因此,怒江河流沉积物代表了中拉萨地块与北拉萨地块的特征。  相似文献   

GPS精密卫星钟差估计与分析   总被引：6，自引：1，他引：5  

楼益栋  施闯  周小青  叶世榕 《武汉大学学报(信息科学版)》2009,34(1)

探讨了GPS精密卫星钟差的估计方法,并分析了伪距与相位观测值对估计精度的影响。基于PAN-DA软件,采用全球均匀分布的40个IGS跟踪站的实测数据,对GPS精密钟差进行估计与分析。试验结果表明,目前采用PANDA软件估计的GPS精密卫星钟差与IGS事后精密卫星钟差比较,互差优于0.2 ns,与国际IGS各分析中心估计的卫星钟差精度相当。  相似文献