略论海洋测高卫星GPS厘米级定轨的实施基础

基于对多种飞机的机载GPS测量实践,认为我国HY-2海洋二号卫星实现厘米级精度的星载GPS定轨测量的基础是:选择适合天线,捕获多颗在视GPS卫星;注重天线安装位置,减弱多路径效应影响;选择适合GPS信号接收机,确保星载GPS测量数据优质。     

GPS卫星测量技术的新发展

在1991年初春的海湾战争中,以美国为首的多国部队给陆、海、空三军装备了17 000台GPS信号接收机;实战应用证明,GPS是作战武器的效率倍增器,GPS是赢得海湾战争胜利的重要技术条件之一。此后,世界上许多国家加速了GPS卫星信号的开发利用,以致GPS卫星测量技术迅速扩展了它的应用领域,本文主要综述了GPS技术的新发展。     

GPS反射信号的海洋应用

本文描述了全球定位导航系统(GPS)的在海面的反射信号在海洋领域的应用，同时建立了利用GPS前向散射信号测量海面粗糙度和海面地形(Topography)的反演算法；海面粗糙度与风速和风向有直接的关系，回波功率的前缘形状及时延与海面地形相关；利用卫星主动雷达和国外机载数据的结果分析比较表明，GPS反射计作为遥感工具有两个优点：即比传统微波主动雷达高的空间分辨率和快速的时间分辨率。     

基于空间交会GPS信号遮挡模型的建模与仿真

GPS应用于空间交会的相对导航具有广泛的应用前景,但两航天器相对运动时,航天器本身及地球曲率对GPS信号的遮挡是影响GPS相对导航可靠性的重要因素。研究了航天器单天线信号遮挡模型的双天线信号遮挡模型,通过数字仿真验证了数学模型的可行性,分析比较了两种数学模型在两航天器不同相对导航间距时GPS信号受遮挡情况,指出双天线相对导航系统相对于单天线相对导航系统性能的优越性。     

岸基GNSS反射信号延迟多普勒图变化特征分析

GNSS-R(Global Navigation Satellite System-Reflections)技术是一种可用于海面参数遥感探测的新兴技术,是当前国内外的研究热点之一。GNSS海面反射信号的延迟多普勒图像(DelayDoppler Map,DDM)是GNSS-R技术应用的重要理论基础。基于Z-V模型确定了岸基GNSS反射信号DDM的理论仿真方法和流程,并进行了实验验证,实验结果显示,仿真DDM与实测DDM之间具有很好的一致性。同时,全面系统地分析了风速、风向、接收天线高度和卫星仰角4个参数对DDM变化特征的影响规律,仿真结果显示:风速和接收天线高度的影响呈单调特性;风向的影响呈周期特性;卫星仰角的影响则比较特殊,在30°以下时呈现明显的单调性,大于30°时误差几乎相同,即具有窗函数选择特性,这种变化特征为利用DDM反演海面波浪、风场数和海面粗糙度等参数提供了理论依据和参考。     

GPS、Galileo、BDS、QZSS测距信号数据质量分析

基于多测站观测数据,采用伪距相位差组合和伪距多径组合方法,分析了GPS、Galileo、BDS和QZSS 4个系统伪距测量噪声和多径误差,比较了各系统内部信号数据质量以及系统间兼容信号数据质量。结果表明:GPS系统中L2C信号伪距测量精度要优于L2信号;Galileo系统中E5信号伪距测量精度最优,其E1和E5a信号伪距测量精度分别优于GPS/QZSS L1和L5信号;QZSS信号伪距测量精度与GPS信号基本一致;BDS系统三频信号伪距多径中均存在与高度角相关的系统性偏差,最大可达1m,且其三类卫星伪距测量精度有所差异,相同高度角条件下,GEO卫星伪距测量精度最优,IGSO卫星次之,MEO卫星最差。     

导航卫星反射信号的海冰特征模拟与分析

预防在我国北方寒冷冬季发生的海冰灾害,需要加强海冰的监测能力。作者为了探讨导航卫星反射信号监测海冰的能力,依据导航卫星反射信号的电磁波理论,尝试性地用FORTRAN90语言开发了模拟海冰反射信号的软件工具。本软件能够分析不同介电常数、不同介质厚度和不同卫星高度角下的海冰的反射信号特征。而且,为了验证模拟实验结果的可靠性,作者在天津海岸开展了1周的反射信号的海冰观测试验。通过观测实验和模拟结果对比分析,验证了反射信号模拟软件具有模拟海冰反射信号的能力。作者认为模拟软件可以用于解释观测试验数据的一些不确定性问题。     

利用伪卫星技术提高GPS定位质量的方法

差分GPS定位(DGPS)可显著提高GPS导航、定位的精度。但在卫星几何分布图形不良或个别方向卫星信号失锁的情况下,DGPS将失去其作用。若将发布差分改正信息的基准站看成伪GPS卫星(简称伪卫星),则可极大地改善差分定位的精度。本文结合国外的试验成果,将这一技术作一介绍,可对我国建立海上差分GPS观测模式时参考。     

基于GPS反射信号技术的渤海海冰实验

传统的海冰检测手段都存在着受天气影响或实时检测成本太高的缺点,为了更实时有效的检测海冰,减轻海冰灾害对于我国的影响,并达到防灾减灾的目的,本文研究了GPS反射信号(GPS-R)技术检测海冰的可能性。通过对2013年2月下旬在中国天津渤海湾的岸基架设GPS信号接收机所接收的观测数据进行分析,使用不同特性的反射海域(几乎全为海水或是海冰)的数据进行比对分析,其结果显示极化比值(反射左旋信号与直射右旋信号的比值)能够明显反演海冰密集度。本文首次将GPS-R技术应用于国内自主设计的渤海海冰检测实验中。     

GPS观测数据的建模与仿真

在研究GPS系统的基础上建立了GPS观测数据的仿真模型,编制了相应的计算机程序。仿真模型包括卫星参数模型、动力学模型和观测误差模型。仿真计算表明,卫星参数模型和动力学模型真实地反映了卫星的运动规律;误差模型反映了观测环境对信号传播的影响。同时可以调节和选择仿真模型的参数,仿真选择了地面静态和地面低动态的观测数据,这对于论证GPS定轨、导航算法、设计GPS接收机等有一定的实用价值。     

One-Centimeter Orbit Determination for Jason-1: New GPS-Based Strategies

The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1-2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone.     

One-Centimeter Orbit Determination for Jason-1: New GPS-Based Strategies

The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1–2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone.     

利用GPS高求取正常高的几种拟合方法

全面系统地研究了GPS点正常高的拟合方法,对平面拟合、二次多项式拟合、移动曲面拟合、多曲面拟合的GPS水准拟合方法,采用不同参数进行了论述。并结合实际测区,对GPS水准点进行了计算分析。提出了不同测区、不同地形、不同大地水准面的拟合方法,部分拟合方法已用于实际生产中,结果表明,这些方法是切实可行的。通过计算分析,得出结论：不同地形、不同面积的测区需要采用不同的拟合模型,并且拟合时采用的参数也不同。利用GPS高求定正常高,能够降低劳动强度和作业成本,提高作业效率。     

基于MapX的GPS位置信息实时标注系统

随着导航技术的发展,将GPS与GIS进行集成化开发,在电子地图中实时地标注GPS的位置等信息成为人们关注的热点。以MapX控件为图形平台,SerialPort控件为通信接口,在C#.net 2005环境下开发了一个小型GIS。针对GPS与GIS集成中的关键技术进行了研究,即GPS信号的接收和处理、GPS地理位置信息的实时显示。     

On Experience in using the remote acoustic method of partial reflections in studies of the lower troposphere

Using the phenomenon of the partial reflection of acoustic waves from anisotropic wind-velocity and temperature inhomogeneities in the lower troposphere is justified in determining the structure of these inhomogeneities. The data (obtained with the method of bistatic acoustic sounding) on signals reflected from stratified inhomogeneities in the lower 600-m layer of the troposphere are given. A detonation-type pulsed acoustic source was used. The methods of isolating a small (in amplitude) reflected signal against the background of noise and determining the reflecting-layer height and the partial-reflection coefficient from the measured parameters (time delay and amplitude) of a reflected signal are presented. The method of estimating the vertical gradients of the effective sound speed and the squared acoustic refractive index from the partial-reflection coefficient previously calculated is described on the basis of an Epstein transition-layer model. The indicated parameters are experimentally estimated for concrete cases of recording reflected signals. A comparison of our estimates with independent analogous data simultaneously obtained for the same parameters with monitoring instruments (a sodar and a temperature profiler) has yielded satisfactory results.     

Joint perturbation scattering characterization of a littoral oceanbottom reverberation: theory, scattering strength predictions, and datacomparisons

A joint surface roughness/volumetric perturbation scattering theory is utilized to characterize the reverberation from a littoral ocean bottom. The result is a reflected field spectrum that consists of specular and off-specular components. The predicted scattering strength from the off-specular component is shown to be comprised of interface roughness scattering, sediment inhomogeneity volumetric scattering, and interface roughness/sediment inhomogeneity correlation scattering. The sediment inhomogeneity volumetric scattering is shown to contain two contributions that are due to fractional variations in sediment densities and sound velocities. Both contributions are shown to be affected by the interface effect by a round-trip transmission coefficient factor. These two fractional variations are shown to contribute differently to scattering strength but similarly to backscattering strength. Inversely predicted roughness spectra from various sets of backscattering strength data are shown to be consistent with a generally known roughness spectrum. Both inversely predicted roughness and volumetric scattering physical property spectra are found to be self-consistent. However, the use of only ocean bottom backscattering strength data is found to be insufficient to judge whether the roughness or the volumetric scattering dominates. Reverberation characterizations using bistatic scattering strength data and signal spread data are planned for future studies