摘要
随着GNSS在各个领域发挥愈来愈巨大的作用,很多国家和地区已经出现了数百个甚至上千个参考站的GNSS大型网络,如“中国大陆构造环境监测网络”工程就有260个参考站,其主要目的是监测中国大陆的地壳运动,以期能够监测一些同震活动。这种GNSS大型网络的出现给数据处理提出了新的挑战,特别是大网,同震监测所需要的实时解算仍然是一个难点。考虑到频繁发生的地震灾害已经对世界经济发展和人民生命财产安全造成了巨大的影响,同时也是危害我国公众安全的重要因素这一现状,因此利用“中国大陆构造环境监测网络”这类GNSS大型网络进行地震监测、提取地球物理信号是一项非常有意义的工作,将推动GNSS大网实时数据快速解算的理论、方法、技术的研究,同时也是当前国内外GNSS领域的一个研究热点。
本论文针对GNSS大网实时数据处理涉及的GNSS实时数据质量控制、实时卫星钟差估计、基于单站动态模式定位的GNSS大网模糊度固定、(改进)恒星日滤波等问题,进行了深入探讨与系统性研究,其主要研究内容和相关结论如下：
1.系统的研究了GNSS大网实时数据解算的方法与技术。从GNSS网络解算接近于0(n3)的处理时间不能满足实时解算这一问题,引出GNSS大网实时数据处理需要研究的几个关键技术：
研究了GNSS实时数据质量控制的方法与技术。1).通过对LG、MW组合的特性以及对周跳敏感度的分析,在其无法探测出某些周跳的情况下,提出利用验后残差分析进一步剔除粗差和周跳,增强实时质量控制的稳健性。2).研究了周跳修复的基本方法,提出利用“验后残差中误差最小”这一准则从备选周跳改正值中搜索最佳改正值的方法。
研究了实时卫星钟差估计的方法与技术。1).针对非差模式实时卫星钟差解算速度慢这一问题,提出使用历元间差分模式消除模糊度,大大提高解算速度。2).针对实时卫星钟差存在系统差,参考钟不稳定以及时延等问题,分别提出利用非差模式提供卫星钟差精确初值,拟稳基准以及外推卫星钟差等方法解决问题。3).提出“耗时率”这一概念对卫星钟差解算的实时性进行了分析,通过二次差法比较了卫星钟差的解算精度,并研究分析了外推卫星钟差对动态定位的影响。
研究了动态精密单点定位的方法与技术。研究分析了精密单点定位的主要误差源,并提出相应的处理方法；然后较为详细阐述了进行参数估计的平方根信息滤波的基本方法；最后通过GPS20Hz,1s,30s以及同震数据进行了测试与分析,验证了精密单点定位方法的正确性。
针对定位结果中依然残留与接收机卫星几何相关的误差(主要是多路径影响),并且考虑到地壳运动监测站的多天连续观测的特点,使用(改进)恒星日滤波进行时间序列平滑,进一步减弱多路径的影响,提高动态定位的精度。
2.进一步完善GNSS大网数据快速解算的方法与技术。1).较为深入的研究了基于单站动态模式定位进行模糊度固定的网解方法,进一步提高定位精度,具体流程为：组建双差模糊度,选择独立基线(双差模糊度),进行双差宽巷、窄巷模糊度固定,基于双差LC组合固定解约束的网平差。2).考虑到网平差非常费时,接近于0(n3)的处理时间。本文借鉴“不动点定理”,从理论上证明网平差的处理时间变为O(n)是可行的。3).通过算例分析可知,单站动态模式定位的精度通过模糊度固定可以得到提高,尤其是东方向,一般来说精度可以提高约10%-40%,并且验证了使用“不动点定理”的网解方法的处理时间为O(n),100个测站网解时间仅为一般方法的4%。对于100个IGS跟踪站进行模糊度固定的静态定位,在CPU2.8GHz的计算机上,本文所述的GNSS大网数据快速解算的方法只需要245.3s,仅为GAMIT处理时间6hour32min的1%。
3.研究了GNSS大网数据处理的改进算法。1).针对地壳运动监测站GNSS数据的特点,提出了自适应约束方法,使精密单点定位中模糊度能够快速收敛,并且定位结果能够真实反映监测站的形变。2).一般动态定位使用的是动态约束的这一方法,针对地壳运动监测站GNSS数据的特点,提出了先验坐标约束方法,通过实测数据对两种方法进行比较可知,在处理较好质量的观测数据时两种方法定位结果是一致的,观测噪声较大时,先验坐标约束能够适当提高解算精度。3).考虑到参与实时卫星钟差估计的区域站受到地震影响时所估卫星钟差出现较大偏差这一特殊情况,提出使用Helmert变换来消除或减弱动态定位结果中系统误差的方法,使定位结果依然正确。
4.设计与实现了GNSS精密单历元网解(PSENS)软件,并将其应用到实际工程中去。1).基于本文所述的理论、方法与技术,设计实现了GNSS精密单历元网解软件(PSENS),并介绍了该软件的总体框架、数据处理流程以及该软件的界面与特色。2).将PSENS软件应用到广州CORS系统以及中国大陆构造环境监测网络中去,进一步验证了该软件的实用性与稳健性；在应用中比较分析了对流层不同映射函数的差异,并且测试分析了时间序列平滑,海洋负荷潮汐改正,地球固体潮汐改正的效果。
With more and more importance of GNSS in different fields, many countries have built GNSS networks comprised of thousands of reference stations. One example is CMONOC of 260 stations, main purpose of which is to monitor China mainland plate motion for recovering co-seismic motion. Such GNSS networks, especially these large networks produce new challenges. Real-time estimation required by monitoring co-seismic motion is still a difficult issue. Considering the frequent earthquakes have caused large life and property loss and bad effects on world economy, it is meaningful to monitor earthquake and extract geophysical signals by such large networks such as CMONOC, while promoting the development, method and technique of real-time estimation. And it is also a hot topic in GNSS research field all over the world.
This paper deeply discusses and researches important issues in GNSS real-time data processing, including the GNSS real-time quality controlling, real-time satellite clock error estimation, GNSS large network ambiguity fixing based on single-station kinematics mode, modified sidereal filtering etc. The main contents and related conclusions including:
1. This paper researches method and technique of GNSS large network real-time data processing. As time needed by GNSS solution is about 0(n3), which could not satisfy the requirement of real-time processing, this paper studied several related key techniques:
This paper studied real-time quality control method. 1) By analyzing the characteristics of the combination of LG and MW and the sensitivity of cycle slipping, We remove gross error and cycle slips with a posteriori residuals to enhance the reliability of real-time quality control.2) We study cycle slips reparation method and propose a new method to search the best correction from all the possible cycle slips under the principle of minimum a posteriori standard error.
This paper studies real-time satellite clock error estimation method and technique. 1) As real-time satellite clock error estimation needs a lot of time, we resolve ambiguity based on epoch-difference method to improve processing speed.2) We determine satellite clock error precise initial value based on no-difference mode to eliminate the system errors of real-time satellite clock error; use quasi-stable datum and extrapolated satellite clock error in order to resolve the instability of reference clock and time delay. 3) We analyze the real-time characteristic of satellite clock error by the concept of time-consuming rate, and study satellite clock error precision and the effects of extrapolated satellite clock error on kinematics positioning by two-difference method.
This paper studies kinematics precise point positioning method and technique. We studies major error sources of precise point positioning and propose corresponding processing method. Then we discussed the basic method of parameter estimation with square root information filtering. Finally we use 20Hz, Is,30s GPS data and co-seismic data to test and analyze the method, which is demonstrated to be correct by the results.
Considering residuals from error related with receivers'geometry, and continuous observations of CMONOC stations, we use (filtered) sidereal filtering to smooth time series to weaken multi-path effects and improve positioning precision.
2. This paper improves quick estimation method and technique. 1) We deeply study network solution for ambiguity fixing based on single-station kinematics mode to improve positioning precision. The details are as the following:obtaining the double difference ambiguity, choosing independent baseline, fixing the double-difference ambiguity of wide-lane and narrow-lane, and network adjustment constrained by ambiguity-fixed estimation with double-difference LC combination. 2) Considering that network adjustment is time-consuming, approaching O(n3), this paper demonstrates it is feasible to reduce the network adjustment processing time to O(n) based on fixed point theory. 3) Tests show single station kinematics positioning precision could be improved, especially in the east direction, usually up to about 10%-40%. And the processing time is actually O(n) with network solution method based on fixed point theory, for example 100 stations using network solution method is only 4% of usual method. When using the method propose by this paper, static positioning for 100 IGS stations with fixed ambiguity on CPU2.8GHz only need 245.3s, about 1% of that of GAMIT time 6hour32min.
3.This paper studies modified algorithm for GNSS large network processing. 1) According to the characteristics of GNSS data of CMONOC stations, we propose adaptive constraints for quick ambiguity convergence of precision point positioning. 2) As kinematics constraints are usually used for kinematics positioning, we propose a priori coordinate constraint method. Comparison using real observations shows that these two methods are well-matched but a priori coordinate constraint method could improve precision in certain degree. 3) Considering large biases of satellite clock error when regional stations used for real-time satellite clock error estimation are affected by earthquake, this paper removes or eliminates system error of kinematics positioning by Helmert transformation.
4.This paper designs and realizes GNSS precise single epoch network solution (PSENS) software and employs it to actual project. 1) Based on the theory, method and technique in this paper, we design and realize PSENS software, and introduce the overall frame, data processing flow, interfaces and features of the software; 2) We employ PSENS software to Guangzhou CORS system and CMONOC to test the practicability and reliability. By these two projects, we analyze different troposphere mapping function and test the effects of time series smoothing, ocean loading correction, solid earth correction.
引文
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