Yao Yibin

Multi-quadric Equations Interpolation and Its Applications to the Establishment of Crustal Movement Speed Field

In this paper, multiquadric equations interpolation is used to establish a widely covered and valuable speed field model, with which the crustal movement image is obtained.

Theoretic research on robustified least squares estimator based on equivalent variance-covariance

Depending on analyzing the abuse of equivalent weights, a set of self-contained theory system on robust estimation based on equivalent variance-covariance is established, which includes ϱ function, φ function, equivalent variance-covariance function, influence function and breakdown point. And an example is given to verify that the robust models proposed in this paper are reliable and correct.

On the non-linear motion of IGS station

With the daily SINEX files of the IGS, the time series of IGS stations are obtained using an independently developed software under generalized network adjustment models with coordinate patterns. From the time series, non-linear motions are found. With spectral analysis method, the variation frequency (annual period and semi-annual period) of the site velocity is found. Moreover, the empirical model of the velocity variation of the station has been established by regression analysis method based on the weekly solution coordinate series of the station. With respect to the velocity of the IGS tracking station, it was better to model the variation periodically or to give a velocity periodically using a piece-wise linear function rather than a linear variable to estimate its bias.

Establishment of a global zenith troposphericdelay model using multi-source data

Radio space-based geodesy techniques suffer from atmosphere propagation delays, of which the ionospheric delay can be largely eliminated by iono-free carrier phase combination techniques, and then the tropospheric delay becomes the main error source. In general, we project the slant delay to zenith direction with mapping function in GNSS navigation and positioning, so modeling the zenith tropospheric delay (ZTD) is a common method to reduce the tropospheric influence on signal travelling. Currently, the commonly used tropospheric delay models are all based on single data source. In this paper we initially used multi-source ZTD data to construct a tropospheric delay model. The ZTD data used for modeling are gridded data from GGOS Atmosphere and IGS troposphere products respectively. The Global Geodetic Observing System (GGOS) Atmosphere is a project that aims to establish atmospheric models. It provides gridded data of global zenith delays with temporal resolution of 6 h (0:00, 6:00, 12:00, 18:00UTC) and spatial resolution of 2.5°×2° (Lon× Lat), which are derived from the reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). IGS troposphere products are derived from position solutions of IGS stations with a high temporal resolution of 5 min and a high accuracy. Firstly, we used IGS ZTD data to analyze the characteristics of short periodic variations (diurnal cycle and semidiurnal cycle). Then, on basis of this analysis and previous researches on ZTD periodic variations conducted by other researchers, we combined GGOS ZTD data and IGS ZTD data to establish ZTD model in accordance with the idea of direct ZTD modeling. We obtained the temporal parameters via cycle fitting for ZTD data and saved the parameters in the form of global Delaunay triangles. For the proposed ZTD model, the ZTD values can be estimated by the methods of height reduction and linear triangle interpolation. The cycle fitting residuals of GGOS ZTD data and IGS ZTD data show that the internal accuracy are 3.62 and 3.60 cm respectively, indicating that our function model with diurnal cycle and semidiurnal cycle can well describe the temporal variations of ZTD. We validated the multi-source data model with respect to ZTD grid data from 94 globally distributed IGS stations during 2013, which were not involved in modeling. The obtained results show that the global average bias and RMS are - 0.31 cm and 4.16 cm respectively. Compared to other tropospheric delay models, multi-source data model is significantly superior to GZTD model (bias: - 0.48 cm; RMS: 4.46 cm) which ignores the short cycles of ZTD and is better than the GGrid model without IGS ZTD involved in modeling. With an accuracy reduce of only 0.2 mm, the multi-source data model is comparable to the most accurate and complicated GPT2w model (bias: - 0.04 cm; RMS: 4.14 cm). At the same time, we validated the stability of multi-source model in space and time, the testing results show the good correction performance and reliability. In addition to the globally applicable convenience, the multi-source model also show a characteristic of regional augmentation, which can greatly improve the tropospheric correction performances in areas around IGS sites. With the gradual increase of regional Continuously Operating Reference Stations (CORS) and global IGS stations and the development of meteorological data sources, how to assimilate diverse ZTD data sources to establish a more comprehensive global multi-source tropospheric delay needs more detailed and further study.

Earth Rotation Parameter Estimation by GPS Observations

The methods of Earth rotation parameter (ERP) estimation based on IGS SINEX file of GPS solution are discussed in detail. There are two different ways to estimate ERP: one is the parameter transformation method, and the other is direct adjustment method with restrictive conditions. By comparing the estimated results with independent copyright program to IERS results, the residual systemic error can be found in estimated ERP with GPS observations.

Crustal Movement Patterns of China Continent Measured by GPS

This paper uses multiquadric equations interpolation to establish a widely covered and valuable speed field model of China, with which the horizontal crustal movement patterns are obtained. The present-day vertical crustal movement velocity image of China is also expressed by GPS observation, from which we can know the vertical crustal movement patterns.