GPS共视中电离层时延计算方法比较研究

为了更好地计算GPS CV（共视）时间传递中的电离层时延值（它是影响CPS CV比对结果精度的主要因素之一）,介绍了当前3种电离层时延的计算方法,并以NICT（National Institute of Information and Communications Technology）单站GPS比对数据及NICT与NTSC（National Time Service Center）的GPS共视比对数据为例,分析比较了不同的电离层时延计算方法对GPS时间比对结果精度的影响。计算结果表明：利用双频实测电离层时延和利用ICS（International GPS Service）提供的TEC（total electton content）map计算的电离层时延对GPS CV比对结果修正后的精度,比利用电离层改正模型的时延对比对结果修正后的精度分别提高30％～40％和20％～30％。     

IGS产品在GPS时间比对中的应用

在利用GPS CV(GPS Common View)技术进行高精度时间比对时，电离层和卫星位置误差对观测到的卫星信号的影响是不容忽视的，需要对它进行精确的估计和改正．讨论IGS精密星历和CODE全球总电子含量图(TECMAPs)在GPS时间传递中的应用．计算结果表明，采用IGS产品可有效提高单站定时和远距离时间传递的精度。     

电离层延迟改正模型综述

电离层延迟改正模型通常可以分为广播星历用的预报模型、广域差分用的实时模型、后处理模型3类,不同应用要求需要选择不同的模型。主要比较分析了几种常用的电离层延迟改正模型: 用于广域差分中生成格网模型的三角级数模型、多项式模型、低阶球谐函数模型等都可以获得很好的改正效果,且这3种模型基本上是等价的;电离层延迟谐函数展开模型可以用来分析电离层长时间系列的变化特征;国际电离层参考模型IRI的改正精度一般可以达到60％的效果;而GPS 星历采用的Klobuchar模型的参数设置存在一些不足,对此提出了一些改进措施。     

GPS共视时间比对中的电离层时延改正问题

众所周知，GPS共视是目前国际上主要的时间传递比对技术，其中扣除电离层时延是很重要的一个方面。介绍了如何采用国际GPS服务中心(IGS-International GPS Service)公布的电离总电子含量(TEC-Total Electron Content)图来进行电离层时延改正。结果表明：对于单频GPS接收机，采用TEC图作电离层时延改正后的单站定时和共视比对精度比用理论模型作改正的精度有很大的提高。通过比较还表明，亚太地区的时间实验室之室的时间传递精度比欧美地区的要低，这可能是因为亚太地区用于测量TEC的IGS测站少，因而导致该地区的TEC的精度较低。     

电离层对GPS测距的影响

利用单层电离层改正模型就GPS卫星高度角对测距的影响作了探讨。研究表明，通常采用的单层电离层改正模型中电离层高取均值对低高度角卫星测距的改正是不适应的，利用单层电离层模型改正时应顾及电离层高的变化。最后利用1986年武汉地区实测TEC数据进行了计算并将结果和IRI－90模型计算结果作了分析比较。     

在卫星授时中电离层误差实时改正的双极化方法

在卫星定位与授时中，电离层折射误差的影响是十分重要的．目前采用的主要改正方法是双频法，还有电离层模型法．双频法要求卫星发射两个工作频率，而电离层模型法的偏差又较大，这对于使用单频接收机的用户来讲，电离层折射改正就成为一个严重问题，笔者提出的双极化法正好可以解决单频接收机所遇到的问题．双极化法是基于电离层的双折射特性．一个线极化波在电离层中传播时被分裂成两个圆极化波，即左旋圆极化波和右旋圆极化波传播，左旋与右旋圆极化波在电离层中传播的速度不同，则到达接收点的时间也就不同，通过测量两个圆极化波到达接收点的传播时廷差，即可确定电离层折射误差的改正量．     

利用地基GPS网高精度实时监测电离层TEC

地基GPS网是监测电离层总电子含量(TEC)的有效手段之一,本文基于上海综合GPS应用网建立了高时空分辨率(0.5h×0.1°×0.1°)的垂直TEC格网模型,用于实时地监测该地区上空电离层TEC变化.该模型每30min给出一幅电离层TEC图,详细地反映了区域电离层分布和变化情况,并可用于实时地改正该地区单频GPS接收机的电离层延迟.     

GPS实时监测和预报电离层电子含量

GPS能高精度地实时监测电离层总电子含量(TEC)变化，对纠正单频GPS接收机电离层延迟和监测电离层活动及其所反映的太阳活动规律具有重要意义．上海地区GPS综合应用网的建立，为监测长江三角洲地区电离层变化提供了宝贵的资料，利用这些双频GPS接收机的连续观测资料，可近实时地监测和预报该地区电离层总电子含量，其内外符精度和外推预报30分钟的精度均优于0.4m．     

TAI 计算的变化

从1999年7月的资料开始,TAI 的计算中,对于长距离 GPS 共视比对结果将不再用电离层时延实测值,改用由国际 GPS 服务(IGS)提供的电离层模型。自 BIPM 采用 GPS 共视规范后,全球参加 TAI 计算的时间实验室的 GPS 共视观测资料按地区分别与 NIST、OP 和 CRL 进行比对(不作电离层改正)。该三站之间的     

GPS监测电离层活动的方法和最新进展

全球定位系统(GPS)可以快速、准确地提供电离层总电子含量(TEC)信息。简要介绍了GPS技术精确测量TEC、监测电离层的原理和方法，指出进行TEC绝对量估计时求解差分群延迟(DCB)的重要性，以及建立多层和实时电离层监测模型的必要性。分析了影响TEC估计的主要误差源，着重介绍了目前GPS监测电离层的最新成果和进展。     

Acceleration of Numerical Integration of the Equations of Motion of Asteroids

Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to...     

Observations of the intensity of the penumbra of sunspots

Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements.     

Equation of state and anisotropy of pressure of magnetars

Magnetars are the neutron stars with the highest magnetic fields up to 10¹⁵–10¹⁶ G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.     

A survey of orbits of co-orbitals of Mars

Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF₃₁, were discovered, librating about the L₅ Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ₇, to be a Trojan, associated with the L₄ Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND₄₃) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW₁₅ and 2000 TG₂, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion.     

Graphical representation of periodic motion of the line of nodes of the Moon

In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, , and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes.