频域叠加的大频偏导航信号捕获算法

在卫星导航接收机的设计和实现过程中,信号捕获是卫星信号同步的关键步骤。只有捕获到了正确的相位和多普勒信息,才能初始化跟踪环路,进而完成信号的同步。针对高动态接收机在大频偏条件下实现信号捕获需要进行多次频域搜索,计算量成倍增加的问题,该文以GPS系统为例,分析了多普勒频偏对相关峰的影响,利用频域叠加技术设计了在多普勒频移过大条件下的信号捕获方案。分析结果表明,该捕获方案可以完成大频偏下的信号捕获,降低了多次频域搜索带来的计算量,并且具有较好的捕获性能。     

GNSS双频兼容互操作接收机信号捕获方法

随着我国北斗导航系统“全球组网”序幕的拉开,设计实现接收机的兼容互操作功能已变成接收机设计领域的一个研究热点。文中针对GNSS双频兼容互操作接收机信号捕获环节设计中遇到的处理时间长、捕获精度低、硬件资源消耗大、兼容性差等问题,设计一种基于频域处理的信号捕获算法。该算法在传统频域捕获的基础上,优化频域转换资源利用与遍历方式,在能量累加方面加入相干与非相干累加方式,达到微弱信号捕获。借助Xilinx软件Vivado及其仿真工具,对整个捕获系统进行了仿真实现,验证了算法设计的准确性,本算法可以捕获信号功率-135 dB以上的信号,可捕获的载波多普勒频率范围满足实际工程需求。在实际工程验证中,本算法能较好地满足工程应用性能要求。      

基于预平均处理的导航信号捕获技术

针对传统导航信号捕获算法资源消耗大、多普勒分辨率低的问题,提出了一种基于预平均处理的变系数匹配滤波的快速捕获方法. 该方法将经过预平均处理后的导航中频信号和本地信号主码存入相应存储器,然后经变系数匹配滤波器完成相关累加,再经快速傅里叶变换(FFT)频率估计器完成数据的频谱分析,最后利用验证模块对FFT输出结果的最大值进行二次验证,完成捕获检测. 所提方法在达到相同积分时间的同时节省了50%硬件资源,能够提高捕获多普勒分辨率以提高转跟踪成功率,通过软件灵活配置可以实现多系统多频点全球卫星导航系统(GNSS)信号的兼容处理.      

基于复杂度与性能联合优化的卫星导航信号捕获方法

针对短突发信号捕获计算复杂度高的问题，提出了一种基于复杂度和性能联合优化的卫星导航信号捕获方法，推导分析采用并行频率搜索的分段相关-视频积累捕获算法的捕获性能和计算复杂度构建联合捕获优化因子.对不同频率搜索间隔、不同接收机灵敏度和不同相关器个数三种情况分别进行了优化设计，得到其计算复杂度和捕获性能联合最优的分段数，并与传统单一捕获性能优化方法对比，仿真实验结果表明：该设计值与载噪比(CNR)、频率搜索间隔等因素相关，可以有效控制捕获算法的计算复杂度；在输入CNR为45 dB-Hz、相关器个数为8、多普勒搜索间隔为2 000 Hz的情况下，相比于传统捕获优化方法，可降低21.2%的计算复杂度.     

基于正交子空间投影的伪卫星远近效应消除方法CSCD

针对地基伪卫星系统中接收机受到远近效应影响无法正确捕获远场伪卫星信号这一问题,引入了基于正交子空间投影算法的捕获优化方法.该方法应用于码分多址伪卫星信号,通过常规滑动相关法得到的强信号码相位和多普勒频移计算正交投影算子,将接收信号与其在强信号空间的投影相减得到弱信号空间并重新进行捕获,以消除强信号对弱信号的干扰.实验结果表明:强弱信号在小于30 dB的功率比范围内,应用正交子空间投影法可以有效改善弱信号捕获性能.这对拓宽地基伪卫星系统的有效工作范围、提升伪卫星接收机信号功率比容忍限度具有重大意义.     

改进差分相干累加算法的北斗卫星导航弱信号捕获

以提升北斗卫星导航能力为目的,设计了改进差分相干累加算法的北斗卫星导航弱信号捕获方法。该方法通过构建北斗卫星信号模型,利用该模型获得北斗卫星导航中频信号;然后以改进差分相干累加算法为基础,建立北斗卫星导航弱信号捕获模型,将北斗卫星导航中频信号作为该模型的输入,经过北斗卫星导航弱信号捕获模型对中频信号块实施累加处理和多普勒圆周位移搜索,以及快速傅里叶变换和反傅里叶变换等步骤后,通过判断北斗卫星导航弱信号捕获判决,输出北斗卫星导航弱信号捕获结果。实验结果表明：该方法在捕获北斗卫星导航弱信号时的运算量较小,可有效捕获-36 dB的北斗卫星导航弱信号,同时其捕获概率较高,应用效果较为显著。     

互相关干扰下微弱GPS信号的直接检测算法

微弱GPS信号的检测是当前的研究热点之一。基于GPS C/A码的互相关干扰理论模型,详细分析研究了强弱信号间的相对载波多普勒频移对互相关干扰的影响,在此基础上,研究了一种新的基于相对载波多普勒频移的微弱GPS信号直接检测算法,该算法不需要对互相干扰进行扣除,计算量小、便于工程实现,仿真结果表明:当干扰信号高出弱信号29dB时,该算法依然可以达到90%以上的检测成功概率。     

圆周移位在伪码补零BDS信号捕获算法中的应用

D1导航电文中加入了NH码,且D2导航电文的速率也比GPS信号的快很多,使得BDS的信号结构增加了捕获难度。采用伪码补零的方法可以对BDS信号进行有效捕获,但是该方法积分时间较长导致捕获耗时变长。本文提出了一种基于圆周移位的改进伪码补零算法,将搜索中复杂的载波剥离运算用计算量很小的频谱序列的搬移操作来代替,使算法复杂度大幅下降。试验结果表明,该方法可以有效减少运算量和捕获耗时。     

随机共振算法在北斗微弱信号捕获中的应用

为了提高北斗二代卫星接收机的捕获灵敏度,提出了一种基于自适应随机共振算法的微弱北斗信号捕获方法。将DBZP（Double Block Zero Padding）方法和自适应随机共振算法相结合,消除了导航数据位和NH码跳变的影响,显著提高了信噪比,能够实现微弱北斗信号的高灵敏度快速捕获。仿真结果验证和实际测试表明,该方法应用于微弱环境下的北斗信号捕获实时性好、灵敏度高,具有较高的应用价值。     

基于FPGA的GPS信号快速捕获方法实现

介绍了一种基于平均相关器的GPS信号快速捕获算法，通过VHDL语言描述在FPGA上实现了该算法。平均相关器是一种将输入的5000点GPS样本信号平均化为1024点样本，然后通过FFT方法实现GPS信号快速捕获的基带相关器。这种相关器可以一步搜索到所有可能的码相位偏移，大大提高了捕获速度，比较好地满足了实时处理的要求。     

阿克苏河-塔里木河水系水质污染遥感监测与评价

 采用Landsat TM数据分析了阿克苏河—塔里木河断面水质污染状况,通过波段的DN值和常规监测数据建立能反映水质状况的 污染物监测模型。结果发现,将2000年常规监测数据代入模型后,与遥感数据的结果基本吻合| 重建阿克苏河—塔里木河的连续水体 污染变化曲线,得出污染物浓度随着远离上游而增加。     

Monitoring drought dynamics in the Aravalli region (India) using different indices based on ground and remote sensing data

The hard-rock hilly Aravalli terrain of Rajasthan province of India suffers with frequent drought due to poor and delayed monsoon, abnormally high summer-temperature and insufficient water resources. In the present study, detailed analysis of meteorological and hydrological data of the Aravalli region has been carried out for the years 1984–2003. Standardised Precipitation Index (SPI) has been used to quantify the precipitation deficit. Standardised Water-Level Index (SWI) has been developed to assess ground-water recharge-deficit. Vegetative drought indices like Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) and Vegetation Health Index (VHI) have been computed using NDVI values obtained from Global Vegetation Index (GVI) and thermal channel data of NOAA AVHRR satellite. Detailed analyses of spatial and temporal drought dynamics during monsoon and non-monsoon seasons have been carried out through drought index maps generated in Geographic Information Systems (GIS) environment. Analysis and interpretation of these maps reveal that negative SPI anomalies not always correspond to drought. In the Aravalli region, aquifer-stress shifts its position time to time, and in certain pockets it is more frequent. In comparison to hydrological stress, vegetative stress in the Aravalli region is found to be slower to begin but quicker to withdraw.     

Landslide risk analysis between Giri and Tons Rivers in Himachal Himalaya (India)

The area around Sataun in the Sirmur district of Himachal Pradesh, India (falling between the rivers Giri and Tons; both tributaries of the Yamuna River) was studied for landslide vulnerability on behalf of the inhabitants. The study was made using extensive remote sensing data (satellite and airborne). It is well supported by field evidence, demographic and infrastructural details and aided by Geographic Information System (GIS) based techniques. Field observations testify that slope, aspect, geology, tectonic planes, drainage, and land use all influence landslides in the region. These parameters were taken into consideration using the statistical approach of landslide hazard zonation. Using the census data of 1991, vulnerability of the populace to the landslide hazard was accessed. As most of the infrastructure in the region is concentrated around population centres, population data alone was used for vulnerability studies.     

Gravity Changes Before Large Earthquakes in China: 1998-2005

Although it is well known that coseismic gravity changes take place during an earthquake, previous research has not yielded convincing evidence demonstrating that significant gravity changes occur before large earthquakes. Furthermore, even if we suspect that gravity changes occur before large earthquakes, we have yet to demonstrate how to consistently observe these changes for useful earthquake forecast that would bring benefits to society. We analyzed ground gravity survey data obtained in 1998, 2000, 200...     

GNSS系统及其技术的发展研究

阐述了国际上卫星导航系统的总体发展,对美、俄、欧、中的四大全球系统,以及相关的区域系统和增强系统进行了简单的介绍,研究分析了GNSS系统及其技术的发展趋势,同时分析了我国Compass全球系统面临的机遇和挑战,并提出了我国未来工作的建议.     

“4D”技术及其应用

介绍“４Ｄ”（即数字地面模型、数字正射影像、数字栅格地图和数字线划地图）系列产品的生产流程、关键技术、及其在耕地保护、防灾减灾救灾和城市规划等方面的应用方法。     

Virtual Australia: its key elements – know,think, communicate

Abstract

Virtual Australia is not a well-defined or agreed concept. This discussion paper conceptualises Virtual Australia as a ‘virtual [digital] model containing and representing all non-trivial objects and their contextual environment – from blue sky to bedrock – in real world Australia’. It describes a scenario for Virtual Australia, one or two decades from now, in which the locations and conditions of non-trivial objects and their environment are updated automatically through a combination of remote sensing and wireless communication technologies in support of a ‘Supranet’. It then examines the concept of the ‘Supranet’ – a pervasive information network based largely on wireless technology linking the physical world to a virtual model in real time – and develops and discusses three principal characteristics of the Supranet: the ability to have or collect specific information (know); the ability to process information (think); and the ability to communicate that information. If, in the near future, any or all non-trivial devices are to some extent able to know, think and communicate, the potential for object autonomy will be realised.     

Toward seamless indoor-outdoor applications: Developing stakeholder-oriented location-based services

Location-Based Services (LBS),an emerging new business based on smartphone and mobile networks,are becoming more and more popular.Most of these LBSs,however,only offer non-seamless indoor/outdoor applications and simple applications without giving stakeholders the chance to play an active role.Our specific aim is to solve these issues.This paper presents concepts to solve these issues by expanding the Open Location Services Interface Standard (OpenLS) to allow seamless indoor/outdoor positioning and to extend the content of the services to include information recommended by stakeholders.     

GIS空间数据的采集误差及其分析

本文详细阐述了GIS数据采集过程中的误差来源，重点分析了通过地图、遥感和摄影测量等方式采集数据所产生的误差及其特性，分析了其对GIS数据的影响与消减方法。     

地理数据库的关系模型及其实现

本文从以图论观点分析地理实体入手,系统阐述了地理数据库关系模型的设计法和过程。作者于1984年4～9月间在微型机上设计建立了关系型地理数据库的实方验系统(RGDB)。该系统采用了本文提出的关系模型,采用了可动态扩库的子库组合结构,这种结构具有灵活性和提高空间利用率的优点。RGDB含有多种功能的数据操作命令,除了具有一般检索功能外,还能进行“开窗”选取和十分“自由”的映象选取。本文对RGDB系统的主要性能和实现途径作了扼要介绍。