基于GNSS的再分析资料对流层延迟精度评估

Assessments of global tropospheric delay retrieval from reanalysis based on GNSS data

对流层延迟对导航定位精度有着重要的影响,而再分析资料提供的高精度气象参数计算的对流层延迟可应用于定位过程中以提升定位精度.本文针对三种再分析资料计算的对流层延迟进行精度评估,并将其应用在精密单点定位中,分析其对定位精度的影响.首先,利用2020年全球范围内125个IGS(International GNSS Service)站的对流层天顶总延迟(Zenith Total Delay, ZTD)作为真值对三种再分析资料(ERA5、MERRA2、CRA40)计算的ZTD进行了精度评估,并分析其时空分布特性.研究结果表明:ERA5-ZTD的均方根误差(RMS)最小(12.1 mm),其次为CRA40-ZTD(15.8 mm)和MERRA2-ZTD(16.9 mm),整体上ERA5-ZTD的精度最高;据所选的IGS站点的比较结果发现赤道平均偏差(BIAS)呈现负值,在中高纬度地区CRA40的精度优于MERRA2,在低纬度地区则相反,而ERA5在各纬度平均精度均为最优;当考虑季节因素时,三者计算的ZTD-RMS在夏秋季较大,其中ERA5的RMS季节变化最稳定.之后还利用180个探空站点对三者计算的ZTD、天顶干延迟(Zenith Hydrostatic Delay, ZHD)、天顶湿延迟(Zenith Wet Delay, ZWD)进行了进一步精度评估,ERA5、MERRA2、CRA40的年均ZTD-RMS分别为13.2, 18.7, 14.9 mm.而年均ZHD-RMS分别为8.2, 8.5, 8.2 mm,差异较小,年均ZWD-RMS分别为9.3, 14.6, 11.6 mm,变化较大.最后,使用ERA5、MERRA2、CRA40计算的ZTD进行精密单点定位实验,结果显示,相对于Saastamoinen模型,其在N方向分别提升了59%、56%、47%、E方向提升了51%、47%、41%、U方向提升了81%、78%、75%.总体而言,ERA5对流层延迟精度在各方面表现均为最优.

The tropospheric delay has an important influence on the navigation and positioning process. The tropospheric delay calculated from the high-precision meteorological parameters provided by reanalysis data can be used in the positioning process to improve the positioning results. This paper evaluates the accuracy of tropospheric delay calculated from the three types of reanalysis data, and applies them to precise point positioning to analyze their impact on positioning results. First, using the ZTD(Zenith total delay) of 125 IGS(International GNSS Service) stations around the world in 2020 as the true value, the accuracy of the ZTD calculated by three reanalysis data(ERA5, MERRA2, CRA40) were evaluated, and their spatiotemporal distribution characteristics were analyzed. The research results show that the root mean square(RMS) of ERA5-ZTD is the smallest(12.1 mm), followed by CRA40-ZTD(15.8 mm) and MERRA2-ZTD(16.9 mm). The overall accuracy of ERA5-ZTD is the best. The tropical bias is negative, the accuracy of CRA40 is better than that of MERRA2 in the middle and high latitudes, and the opposite is true in low latitudes. The average accuracy of ERA5 at each latitude band is the best. When seasonal factors are considered, the ZTD-RMS of all three reanalyses is larger in summer and autumn, and the RMS seasonal variation of ERA5-ZTD is the most stable. After that, the ZTD, Zenith Hydrostatic Delay(ZHD), and Zenith Wet Delay(ZWD) were evaluated with 180 radiosonde stations. It is found that the annual average ZTD of ERA5, MERRA2, and CRA40 were 13.2, 18.7, 14.9 mm respectively. The annual average ZHD were 8.2, 8.5, 8.2 mm respectively, which difference is small, and ZWD were 9.3, 14.6, 11.6 mm respectively. ERA5 has again the highest correlation with radiosonde data. Finally, using the ERA5, MERRA2, and CRA40 calculated ZTD to do precise point positioning experiments, the results show that compared with the Saastamoinen model, its accuracy in the N direction is improved by 59%, 56%, 47% respectively, in the E directions 51%, 47%, 41% respectively, and U directions 81%, 78%, 75% respectively. In general, the accuracy of ERA5 tropospheric delays is the best in the three reanalysis data.