基于GNSS的电离层形态监测与延迟模型研究
文献类型：学位论文
| 作者 | 霍星亮 |
| 学位类别 | 博士 |
| 答辩日期 | 2008-06 |
| 授予单位 | 中国科学院测量与地球物理研究所 |
| 授予地点 | 武汉 |
| 导师 | 欧吉坤 |
| 关键词 | 电离层形态 冬季异常 半年度异常 全球卫星定位系统(GPS) 伽利略导航卫星系统(GALILEO) 新一代导航卫星系统 电离层延迟 电离层电子总含量(TEC) 电离层模型 KLOBUCHAR模型 NeQuick模型 IGGSH模型 |
| 学位专业 | 大地测量学与测量工程 |
| 中文摘要 | 电离层形态监测有助于加深认识电离层活动规律及其变化机制。长期以来，人们对电离层形态的监测与研究主要借助于电离层测高仪、雷达以及探空火箭等观测仪器，并以电离层峰值电子密度(NmF2)、峰值高度(hmF2)以及临界频率(f0F2)为研究对象。近二十年来，以GPS为代表的全球导航卫星系统(GNSS)观测技术的兴起，以及全球分布的GPS跟踪站连续观测的海量数据的累积，使得利用GPS观测数据精确提取和测定电离层电子总含量(TEC)，进而定性/定量地研究电离层TEC变化活动规律成为可能。现有的研究表明，不同高度的电离层电子密度的变化活动存在较大差异。因此，研究比较TEC与以NmF2为代表的其它电离层参量呈现出的变化活动规律和内在联系机制，是我们关心的重要问题之一。本文重点利用GPS提取出高精度的电离层TEC信息，研究全球范围内电离层TEC冬季异常现象的区域性变化特征，并进一步分析了在不同地域TEC冬季异常现象形成的主导因素。同时，本文也分析研究了在春分点与秋分点TEC变化的不对称现象。 另一方面，电离层延迟是GNSS技术最严重、最棘手的误差源之一，能否有效地消除或减弱电离层延迟误差关系到众多单频GNSS接收机用户导航与定位的精度与可靠性。GPS/GALILEO导航卫星系统的广播电离层模型KLOBUCHAR/NeQuick可提供免费的电离层时延修正服务，但其对应的修正精度约为50％-60%左右，有时甚至更差；GPS广域增强系统(WAAS)可提供精度达80%以上的电离层时延修正服务，但其对应的软件与硬件设施要求高，用户使用该项服务的代价大。然而，目前有数量甚多的部分单频GNSS用户既不愿意付出高成本获取WAAS系统的高精度电离层时延修正服务，但卫星系统提供的免费的广播电离层时延修正服务又无法满足其导航与定位要求。因此，当前的电离层时延修正服务存在修正精度处于60-80%之间的服务空白区。此外，目前我国新一代卫星导航定位系统正处于大力推进与发展阶段，建立有效的广播电离层延迟改正模型也是我国新一代卫星导航系统建设的现实需求。本文在分析现有的广播电离层时延改正模型KLOBUCHAR/NeQuick优点与缺点的基础上，进一步开展研究一种新型的广播电离层延迟改正模型，力求使得其电离层延迟修正精度填补60-80%之间的服务空白区，实现无缝隙电离层延迟改正信息服务，为我国北斗等新一代卫星导航系统中广播电离层延迟改正模型的相关技术指标的制定和论证等，提供科学依据与参考。 针对上述内容，本文开展了以下几个方面的研究和探讨： ( I ) 基于GPS研究电离层TEC冬季异常现象 (1) 利用中国地壳运动观测网络GPS基准站的实测数据与电离层TEC球谐函数模型，可精确模拟中国区域及其邻域上空的电离层TEC周日演变活动，进而可提取出中国地域上空TEC的时间变化序列，实现有效监测中国地域TEC的冬季异常现象与半年度异常现象。 (2) 进一步分析电离层TEC冬季异常现象在全球不同地域的活动特征及讨论其相应的变化机制，本文利用全球分布的部分IGS GPS跟踪站全天候的实测资料，提取出各个测站上空的GPS TEC数据，结合NASA Goddard飞行中心提供的中心大气模型NRLMSISE-00给出的[O/N2]比例，定性地讨论不同区域的TEC季节性变化与中性大气原子分子比例-[O/N2]变化的相关性；再利用欧洲定轨中心(CODE)发布的IONEX格式的全球连续分布的格网电离层TEC数据(CODE TEC)与[O/N2]比例进行对比研究，定量地讨论全球范围内电离层TEC冬季异常现象的区域性变化特征；研究发现，不同区域的电离层TEC冬季异常程度存在明显的差异，结合前人关于电离层峰值电子密度NmF2的冬季异常变化与[O/N2]比例变化关系的研究成果的基础上，本文尝试解释了在不同区域的TEC冬季异常现象形成的主导因素。 ( II ) 基于GPS监测电离层TEC在春分点与秋分点的不对称性变化 首次利用GPS TEC数据与CODE TEC数据研究分析了白天的电离层TEC在春分点与秋分点的不对称性变化现象。研究结果表明，白天TEC在春分点大于秋分点，且其大小不对称性的程度随着太阳活动周期的变化而变化。进而，结合前人关于电子密度在春秋分点的不对称变化的研究成果，本文对在春秋分点TEC不对称变化的现象进行了初步解释。 ( III ) 基于GPS观测数据精化KLOBUCHAR电离层模型系数 电离层延迟是卫星定位系统的最主要误差源之一。为消除或减弱电离层延迟误差对卫星导航定位系统精度与可靠性的影响，GPS系统采用了广播电离层延迟模型-即KLOBUCHAR模型。然而，KLOBUCHAR模型的8参数函数无法有效模拟复杂多变的全球电离层TEC变化状态，加之，该模型实施期间相关的技术条件与电离层观测资料的限制，使得KLOBUCHAR模型的电离层延迟修正效果和精度受到较大的局限。事实上，研究也表明该模型仅达到50%左右的电离层时延修正效果。本文设计了一种精化KLOBUCHAR模型系数的方法，利用全球分布的IGS GPS跟踪站和中国地壳运动观测网络基准站的GPS实测数据，拟合生成了新的KLOBUCHAR-Self电离层模型系数。试算结果表明，新的KLOBUCHAR-Self模型系数可以更有效地修正电波传播时的电离层延迟影响，使得电离层延迟修正精度提高10%-15%左右。若采用新生成的KLOBUCHAR-Self系数作为卫星导航系统广播电离层延迟改正模型的发布系数，可使得广大的单频GPS接收机用户，在无须更新相关的软件与硬件的情况下，提高导航与定位结果的精度。 ( IV ) 提出一种新型的GNSS广播电离层延迟模型-IGGSH 与美国GPS/欧洲GALILEO导航卫星系统建设时分别采用了KLOBUCHAR/NeQuick广播电离层延迟模型类似，我国新一代导航卫星系统的建设，也要求对相关的广播电离层延迟模型的技术指标进行制定与论证，以及对模型方案的设计与实施提出依据与参考。本文在比较研究KLOBUCHAR与NeQuick模型的优点和不足的基础上，基于电离层球谐函数模型与快速傅立叶变换的方法，提出了一种新型的适合于广播发布的电离层延迟模型-IGGSH，并给出了其对应的实施构建方案。IGGSH广播电离层延迟模型既利用了球谐函数优良的数学结构可高精度地反演全球电离层TEC变化状态的优点，又在保持模型数学结构不被破坏的情况下大量减少需通过卫星发布的模型系数数目，且能够实时更新，具有良好的应用功能。研究表明，在相同条件下，IGGSH广播电离层模型的时延修正精度可达75%-80%左右，明显优于KLOBUCHAR和NeQuick模型的电离层时延修正精度 |
| 英文摘要 | Investigation on the ionospheric morphology is helpful for our understanding of the ionospheric behaviours. In the past decades, data from the ionospheric sounding, radar and rockets have been used to study the variations of peak electron density (NmF2), the F2 region maximum electron density height (hmF2) and critical frequency (f0F2). With the development of Global Navigation Satellite System (GNSS), more and more GNSS data have been collected from the global tracking stations, and the precise total electron content (TEC) of ionosphere can be estiamated using data from the global GNSS network. It is possible that the related phenomena of ionosphere are discussed with GNSS-derived TEC in term of qualitative/quantitative analysis. Some researches have pointed out that the climatology characteristics of electron density vary with the different ionospheric heights. Therefore, the connections and differences between ionospheric TEC variations and the variations of other ionospheric parameters including NmF2, hmF2 and f0F2 is the key issue we care. In this contribution, the precise TEC values are estimated using Global Positioning System (GPS) observations and the global-scale TEC winter anomaly is quantitatively addressed. Numerical results show that TEC winter anomaly in different regions of the world tends to be dominated by different factors. At the same time, the TEC equinoctial asymmetries in the northern and southern hemisphere are also presented. Additionally, the ionospheric delay is one of the major error resources for GNSS technique, and it will strongly affect the precise and reliability of positioning of single-frequency GNSS receivers. The broadcast ionospheric time-delay models, KLOBUCHAR and NeQuick, have been respectively adopted by GPS and GALILEO satellite system, and the free ionospheric delay information is sent as part of satellite broadcast messages. However, researchs have demonstrated that the KLOBUCHAR/NeQuick model can only account for approximately 50%-60% of the ionospheric delay. It also need to be pointed out that both wide area difference GPS (WADGPS) system and wide area augmentation system (WAAS), such as the FAA WAAS, EGNOS and MSAS, can provide an above 80% correction for the ionospheric range error, but the corresponding users must equip with special hard device, as well as improve hard-fixed software in receivers, for obtaining various differential corrections from WADGPS/WAAS. At present, a lot of single-frequency GNSS users would not like to obtain the ionospheric delay correction information from WADGPS/WAAS due to the high cost, but the ionospheric delay corrections from the broadcast ionospheric models-KLOBUCHAR and NeQuick cannot meet their requirements of navigation and positioning accuracies. Accordingly, there exists a blank of 60%-80% ionospheric correction accuracies for the single-frequency GNSS users. In addition, the next generation satellite navigation system that is the national strategic resource is being developed, and effective algorithms for ionospheric delay are essential for precise applications of satellite navigation system. For the purpose, major difficulties and key techniques related to the construction of new broadcast ionospheric time-delay model are investigated based on the analysis of advantage and disadvantage of KLOBUCHAR and NeQuick models in this paper. The improved new GNSS broadcast ionospheric time-delay algorithm may be considered as a value complementary ionospheric correction for the single-frequency GNSS users; meanwhile, the related results will also provide references for the next generation satellite navigation system. Major contributions of this dissertation are as follow: ( I ) Monitoring the winter anomaly of the ionospheric TEC based on GPS (1) With GPS observations from the Crustal Movement Observation Network of China (CMONOC) and the spherical harmonic (SH) function model, the diurnal variations of TEC above china and adjusted area are presented. Furthermore, time series of total electron content (TEC) above China is estimated, and the winter anomaly and semiannual of TEC above China are displayed. (2) The global-scale winter anomaly of ionospheric TEC is presented, and the regional characteristics of TEC winter anomaly in different regions are investigated in detail around the world. The correlation between the daytime TEC and the [O/N2] ratio is qualitatively studied using GPS observations from the worldwide IGS GPS ground stations and NRLMSIS-00 empirical atmosphere model from the NASA’s Goddard Space Flight Centre. Furthermore, the global-scale TEC winter anomaly is investigated in terms of quantitative analysis using the TEC maps in IONEX format from Centre for Orbit Determination in Europe (CODE) and [O/N2] ratio from the NRLMSIS-00 atmospheric model in this paper. Numerical results show that the winter anomaly of ionospheric TEC in different regions of the world tends to be dominated by different factors. According to the research findings proposed by others using the NmF2 winter anomaly and [O/N2] ratio, the possible reasons have been investigated to explain the TEC winter anomaly in different world regions. This is important for the understanding of ionospheric physical mechanism and establishing of ionospheric models. ( II ) Monitoring the TEC equinoctial asymmetries based on GPS The equinoctial asymmetry of TEC in the ionosphere is demonstrated using GPS TEC and CODE TEC maps. The related results show that the TEC values are stronger in March equinox than that in September equinox; meanwhile this phenomenon is subject to solar cycle modulation. This work is a complementarity on the asymmetry of electron density between March equinox and September equinox addressed by other researchers. ( III ) Refining the KLOBUCHAR coefficients based on GPS data Ionospheric delay is one of the major error sources in satellite navigation and positioning systems. The KLOBUCHAR model, as part of GPS broadcast messages, is widely used to correct for the ionospheirc delay for many real-time GPS navigation or positioning applications. However, because of the complexity of the ionosphere and the limitations of both the hardware related technologies, such as receiver performance and communication capability, and the ionosphere observation data in the mid 1970’s, the effectiveness, especially the correction accuracy, of the KLOBUCHAR model is greatly constrained. For this reason, GPS broadcast time-delay correction algorithm was designed for some single frequency users who may not have a requirement for nearly complete, automatic correction for ionospheric range and range rate errors, as dual frequency users provide, and only need to achieve a correction for approximately 50 percent rms of the ionospheric range error. In this contribution, a method is proposed to improve the GPS broadcast ionospheic time-delay correction accuracy, using GPS observation data from the globally distributed IGS observation stations and the Crust Movement Observation Network of China (CMONOC). A new set of KLOBUCHAR-Self coefficients is estimated using this method. Results demonstrate that the refined KLOBUCHAR-Self coefficients developed may provide better ionospheric delay corrections for single frequency GPS receivers and improve standard single point positioning accuracies. ( IV ) A new GNSS broadcast ionospheric time-delay model-IGGSH It is well known that KLOBUCHAR and NeQuick models have been respectively utilized in GPS and GALILEO system as broadcast ionospheric time-delay models. However, a new type of GNSS broadcast time-delay correction algorithm/model still need to be developed for the users of next generation navigation satellite system who wish to achieve about 75%-80% correction of the ionospheric delay. For this reason, an attempt has been made to develop a new GNSS broadcast ionospheric time–delay correction model, called the IGGSH model. This model should consider the following factors such as economical, computational and communication limitations, rather than a complicated art ionospheric model with many parameters or corrections. The IGGSH model is an improved version of the classic spherical harmonic function based on Fast Fourier Transformation (FFT). The IGGSH model parameters are determined by combining a solar cycle,.i.e.11years, of high precision GPS/GNSS data with the main ionopsheric TEC variations characteristics of different time/space scales such as day, month, season, half a year, year and solar cycle over different geographic locations including high, middle and low latitude areas. Experimental results demonstrate that the IGGSH model is available for relatively high accuracy ionospheric correction services, such as about 75%-80% range error correction, and its accuracy of ionospheric delay correction is better than that of KLOBUCHAR model and NeQuick model |
| 语种 | 中文 |
| 公开日期 | 2013-01-17 |
| 源URL | [http://ir.whigg.ac.cn//handle/342008/3690]  |
| 专题 | 测量与地球物理研究所_学生论文_学位论文 |
| 推荐引用方式 GB/T 7714 | 霍星亮. 基于GNSS的电离层形态监测与延迟模型研究[D]. 武汉. 中国科学院测量与地球物理研究所. 2008. |
入库方式： OAI收割
来源：测量与地球物理研究所
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