对流层延迟是卫星导航定位的主要误差源，GNSS广域增强需要高精度的对流层延迟产品进行误差修正。对流层延迟可通过GNSS进行实时估计，也可通过融合多源数据的数值气象预报模型获取。IGS发布的全球对流层天顶延迟产品由GNSS解算，其精度可达4mm，时间分辨率为5min，但其分布不均匀，在广袤的海洋区域无数据覆盖。GGOS Atmosphere基于ECMWF 40年再分析资料，可提供1979年以来时间分辨率为6h、空间分辨率为2.5°×2°的全球天顶对流层总延迟格网数据。本文通过2015年全球IGS测站的ZTD资料对GGOS的ZTD产品进行了评估，研究了GGOS Atmosphere 对流层延迟产品与IGS发布ZTD资料之间的系统差，通过线性拟合估计出每个测站GGOS-ZTD与IGS-ZTD系统差系数（包括比例误差a和固定误差b），然后对比例误差a、固定误差b进行球谐展开，建立了两种ZTD数据源之间的系统差模型。选取IGS测站和陆态网测站，对附加系统偏差改正后的GGOS-ZTD产品对PPP的收敛速度的影响进行研究。本文研究结果表明：GGOS-ZTD与IGS-ZTD间存在系统偏差，其bias平均为-0.54cm；两者之间较差的RMS平均为1.31cm，说明GGOS-ZTD产品足以满足广大GNSS导航定位用户对对流层延迟改正的需要。将改正了系统差后的GGOS-ZTD产品用于ALBH、DEAR、ISPA测站、PALM测站、ADIS测站、YNMH测站、WUHN测站进行PPP试验，发现可明显提高定位收敛速度，尤其是在U方向上，收敛速度分别提高10.58%、31.68%、15.96%、43.89%、51.46%、14.69%、18.40%。
The tropospheric delay is the main error source in satellite navigation, for which GNSS wide area augmentation needs ZTD product of high accuracy to correct error. The tropospheric delay can be simultaneously estimated by GNSS, and be also obtained from numerical meteorological forecast model based on multi-sources data. The global zenith tropospheric delay product published by IGS is resolved by GNSS, whose accuracy reaches 4 mm and time resolution is 5 minutes. However, the uneven-distributed IGS sites makes the vast ocean area without data coverage. Based on ECMWF re-analysis material for 40 years, GGOS Atmosphere provides global total zenith tropospheric delay grid data since 1979,whose time resolution is 6 h and spatial resolution is 2.5°×2°. The GGOS-ZTD product was assessed compared with ZTD material of global IGS sites in 2015 and the systematic difference between GGOS-ZTD and IGS-ZTD was researched.Systematic difference coefficients in every site (proportional error a and fixed error b) were estimated by linear fitting and then spherical harmonic expansion with a and b was made to build spherical harmonic expansion model for systematic difference coefficients (a and b).Finally the application effect of the GGOS Atmosphere ZTD product was analyzed with systematic difference eliminated in satellite navigation and positioning in IGS and CMONOC sites. The results prove that: there are systematic difference between GGOS-ZTD and IGS-ZTD. The mean bias is -0.54 cm and mean RMS of discrepancy is 1.31 cm, which is accurate enough to satisfy the ZTD correction needs of vast GNSS real-time navigation positioning users. The GGOS-ZTD product with its systematic difference corrected is used in the precise point positioning experiment in ALBH、DEAR、ISPA、PALM、ADIS、YNMH、WUHN sites. The result showed that the speed of convergence effectively is obviously advanced, especially in U direction(10.58%、31.68%、15.96%、43.89%、51.46%、14.69%、18.40% respectively).
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