基于SDR的GNSS接收机原理可视化教学平台

针对GNSS原理教学中,GNSS接收机原理部分缺乏直观的教学演示,提出了一种基于SDR的GNSS接收机原理可视化教学平台。通过这个平台,将封闭在硬件中的GNSS接收机实现方法直观地展现给学生,使学生加深了对GNSS接收机原理的认识。     

车载GNSS接收机多径抑制技术

在GNSS接收机的实际应用中,多径是影响定位精度的主要因素之一。在车载应用条件下,多径的影响由于快速的多径信道变化而变得更加明显,车载接收机的GNSS信号接收处理部分会受到包含周围运动车辆及其自身结构影响在内的复杂多径干扰。针对接收机的各个组成部分分析了天线设计、多径估计、多频测量、传感器融合等多种可用的多径抑制方法,并根据分析和比较结果指出:信号处理方法、基于导航的方法以及传感器融合方法是实现车载接收机多径消除的首选方法。     

《国家一、二等水准测量规范》新旧版本的比较

《国家一、二等水准测量规范》(GB/T12897-2006和GB12897-91)对建立一、二等水准网的布设原则、施测方法、精度指标和技术要求等环节做出了规定。从这些规定出发,对新、旧规范进行了分析,比较了两者之间的变化,进而说明新规范的发布和实施对今后水准测量的开展提供了新的技术方向指引和技术支持。     

Combining historical and new hydrographic data

The NOAA National Ocean Service hydrographic surveys run between 1930 and 1965 have been digitized from the paper smooth sheets. The surveys since 1965 have been collected, processed, and stored in digital form. The new multibeam systems have been used since 1984 to cover over 100,000 square nautical miles of the Exclusive Economic Zone with overlapping swaths of digital soundings. Each of these multibeam surveys may contain millions of soundings. None of the above data has been assigned quality control tags by NOS, but they are stored by survey number, with indexes showing what younger data are available to supersede older data in any area.

Large digital databases, such as the Master Seaftoor Digital Database, are planned in connection with the Defense Hydrographic Initiative. It will be necessary to assign quality control ratings to the soundings in the databases. The detailed survey data may be indexed in the master database but maintained in distributed databases. The databases could supply historical sounding data in digital form for the planning, collection, processing, and evaluation of new survey data.

During the compilation of some bathymetric maps and nautical charts, it is necessary to junction and combine the newer multibeam surveys having total bottom coverage, with the more widely spaced historical data. Precedence is given to the newer hydrographic data, with some older data being removed as needed in order to provide a smooth transition between data sets. In applying multibeam data to nautical charts, it is necessary that actual soundings be positioned properly with respect to bottom contours, which may have been drawn using gridded values. The junctioning of historical and newer data sets is expected to be aided by the use of interactive cartographic workstations.     

The morphotectonics and its evolutionary dynamics of the central Southwest Indian Ridge (49° to 51°E)

The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.     

投弃式温盐深测量仪在海底地形测量中的应用

介绍了投弃式温盐深测量仪(XCTD)的原理和特点,利用它获得的声速剖面数据与声速剖面仪测量的声速剖面数据进行了精度对比,论述了在特殊环境下,利用多波束测深系统进行海底地形测量时,使用XCTD进行声速剖面测量的优势,解决了测量船停车才能进行声速剖面测量的弊端,显著提高了多波束测深系统作业的效率。     

基于变异函数的多波束抽稀间距确定方法

在格网化抽稀方法中,抽稀间距的选取直接影响多波束测深数据抽稀结果和构建海底地形的表征能力。为了合理确定多波束测深数据抽稀间距,将地质统计学中的变异函数理论引入到多波束测深数据抽稀中,由水深变异函数估计海底DEM的精度,得出海底DEM精度与抽稀间距的关系。通过仿真计算表明:如果给定海底DEM的精度,再依据计算得到的拟合水深变异函数参数值,即可确定多波束测深数据抽稀网格间距的大小,该法适用于多波束测深数据抽稀的应用中。     

马里亚纳海沟“挑战者深渊”最深点水深探测

2011²012年,海洋六号船采用EM122多波束测深系统在马里亚纳海沟最深海域"挑战者深渊"进行的多波束水深测量,通过对测深资料进行分析处理,获得了高精度海底地形图,揭示了马里亚纳海沟挑战者深渊附近海底地形呈近东西向延伸,有西部、中部和东部三个洼地,它们由10800m等深线圈闭,长轴方向与海沟方向一致。洼地底部水深大于10900m,地形较为平坦。三个洼地最深区域分别由10916m、10904m和10915m等深线圈闭。三个洼地最大水深为10917m(误差小于20m),位于西部洼地内,中心位置为142°12.14'E,11°19.92'N。该处也是马里亚纳海沟最深点。     

基于多波束数据的网格水深模型内插方法精度分析

以多波束水深数据作为源数据,分析了网格水深建模中的数据内插,介绍了网格水深建模所用的常用内插方法,并从水深建模的精度和效率出发,计算分析了网格水深建模过程中内插方法的应用效果。实验结果表明:在当前网格水深建模常用的内插方法中,加权平均法是较适合多波束水深源数据内插网格水深模型点的方法,双线性曲面法是较适合网格水深模型点推估模型表面任意点水深的方法。     

多模卫星导航系统的RAIM算法研究

研究了多模卫星导航系统的RAIM（接收机完好性自主检测）算法,根据多模卫星导航系统的定位模型,基于最小二乘法的原理计算伪距残差,构造奇偶矢量进行故障检测和故障排除。在只有一个观测量出现粗差的前提下,仿真了GPS与多模GPS／GLONAss／Galileo系统下的卫星可见数和DOP（精度因子）,对比了衡量RAIM算法可用性的水平保护门限值（HPL）及这2种系统下的故障检测率与故障排除率。仿真结果表明：与GPS相比,多模导航系统具有更多的可见星,RAIM算法的可用性更高,并且其故障检测和故障排除的性能更好。因此,多模卫星导航系统不仅能为用户提供更高的定位精度,还能为用户提供更好的完好性保障。