利用多源数据构建全球天顶对流层延迟模型

Establishment of a global zenith tropospheric delay model using multi-source data

对流层延迟是无线电大地测量技术中的重要误差源,目前常用的对流层模型的建立均是基于单一数据源.本文按照直接对天顶对流层延迟建模的思路,采用格网化的GGOS Atmosphere的对流层数据和离散的IGS对流层产品联合建模,在利用IGS的高采样率对流层产品分析天顶对流层延迟的短周期变化特征的基础上,构建了一个多源数据的全球天顶对流层延迟模型.经过检验,多源模型的内符合精度为3.6 cm,表现出良好的拟合效果.使用未参与建模的IGS站进行外符合检验,统计结果显示多源模型的全球平均bias为?0.31 cm,全球平均RMS为4.16 cm,明显优于GZTD模型(bias为?0.48 cm;RMS为4.46 cm),且与目前精度最高的GPT2w模型(bias为?0.04 cm;RMS为4.14 cm)精度相当.多源模型的改正精度在空间和时间上具有良好的稳定性,同时多源模型在有IGS站支持的地区改正效果明显优于GZTD和GPT2w模型.多源模型具有全球适用、区域增强的优点.

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 GPT2 w 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.