基于高频稳度的接收机钟差建模方法及其在精密单点定位中的应用研究

Precise Point Positioning (PPP) has constantly been a research focus of the Global Navigation Satellite System (GNSS) community in the past decades. It has been demonstrated to be a powerful tool in geodesy and geodynamic applications such as precise orbit determination, precise timing, aerial photogrammetry, sea level monitoring, metrology and seismic hazard warning etc. However, the asymmetry of the observation geometry leads to strong mathematical correlations among the estimates of the receiver clock corrections, troposphere parameters, and the station height in PPP, which unfortunately degrades the height accuracy. This project intends to introduce the basic idea of de-correlation to separate the highly-correlated parameters among receiver clocks, zenith troposphere delays and height parameters. Therefore, the improved accuracy and time resolution of the height or troposphere delay may greatly enhance the performance of PPP in geosciences applications. Firstly, the characterizations of the frequency stability of high-precision oscillators are fully assessed from time domain and frequency domain. Then the theory and methodologies of receiver clock modeling are investigated including some key issues such as preprocessing schemes for abnormal clock data, modeling for both the systematic and random components of clocks, clock prediction and modeling errors etc. A clock model for use in Kalman filter is designed, in which a two-state model consisting of a time offset and frequency offset is employed to describe the behavior of the clock. Finally, the proposed clock modeling algorithms are verified and adopted in PPP solution. The performance of PPP with clock modeling and PPP with epoch-wise clock estimation are analyzed in detail.

针对当前精密单点定位（PPP）技术中测站高程分量、天顶对流层延迟与接收机钟差参数之间存在显著的数学相关性，由此导致PPP高程方向定位精度偏低、收敛速度较慢等问题，本项目拟引入降相关思想，提出适用于PPP的接收机钟差建模理论与方法，通过对一些性能（稳定度）较好的接收机钟差进行建模，降低高程分量参数、天顶对流层延迟参数与接收机钟差参数之间的相关性，改善PPP高程分量和天顶对流层延迟参数的估计精度，进而提升PPP技术在地学信号提取与地学现象解释等方面的能力。为此，本项目拟全面评估不同类型接收机钟的短期频稳度及钟差建模的可行性，突破接收机钟差建模中的异常数据处理、确定性分量与随机分量的模型表达、模型误差的推导、最佳预报时长的确定等若干关键问题，建立基于高频稳度的接收机钟差建模理论与方法，并将其应用于PPP中，实现快速、准确分离（估计）测站高程和天顶对流层延迟的目的。

鉴于当前许多IGS跟踪站均配置有高性能原子钟的现状，项目开展了基于钟差建的模精密单点定位（PPP）理论方法和应用研究。采用修正Allan方差法分析了不同IGS跟踪站的接收机钟随机噪声的时域特性，评估了不同类型接收机的短期稳定度及钟差建模的可行性，确定了分段线性钟差建模的有效时长；引入降相关思想，提出了适用于精密单点定位的接收机钟差建模方法，构建了钟差-钟速二维状态模型描述接收机钟差随机变化过程，推导了附有钟差建模的多系统组合PPP的数学模型；与传统的钟差逐历元参数估计方法相比，钟差建模方法降低了高程分量参数、天顶对流层延迟参数与接收机钟差参数之间的相关性，显著改善了GNSS高程分量的估计精度。项目成果对于提升精密单点定位（PPP）技术在地壳形变监测、低轨卫星定轨、水汽监测及预报等高精度GNSS地学领域的应用具有重要的科学意义。