Monitoring Zenithal Total Delays over the three different climatic zones from IGS GPS final products:A comparison between the use of the VMF1 and GMF mapping functions

The International GNSS Service(IGS) final products(ephemeris and clocks-correction) have made the GNSS an indispensable low-cost tool for scientific research, for example sub-daily atmospheric water vapor monitoring. In this study, we investigate if there is a systematic difference coming from the choice between the Vienna Mapping Function 1(VMF1) and the Global Mapping Function(GMF) for the modeling of Zenith Total Delay(ZTD) estimates, as well as the Integrated Precipitable Water Vapor(IPWV) estimates that are deduced from them. As ZTD estimates cannot be fully separated from coordinate estimates, we also investigated the coordinate repeatability between subsequent measurements.For this purpose, we monitored twelve GNSS stations on a global scale, for each of the three climatic zones(polar, mid-latitudes and tropical), with four stations on each zone. We used an automated processing based on the Bernese GNSS Software Version 5.2 by applying the Precise Point Positioning(PPP)approach, L3 Ionosphere-free linear combination, 7 cutoff elevation angle and 2 h sampling. We noticed an excellent agreement with the ZTD estimates and coordinate repeatability for all the stations w.r.t to CODE(the Center for Orbit Determination in Europe) and USNO(US Naval Observatory) products, except for the Antarctic station(Davis) which shows systematic biases for the GMF related results. As a final step, we investigated the effect of using two mapping functions(VMF1 and GMF) to estimate the IPWV,w.r.t the IPWV estimates provided by the Integrated Global Radiosonde Archive(IGRA). The GPS-derived IPWV estimates are very close to the radiosonde-derived IPWV estimates, except for one station in the tropics(Tahiti).

基于电网GNSS站的区域对流层延迟改正建模研究

基于全球卫星导航系统(global navigation satellite system, GNSS)的高精度定位技术是实现无人机自动巡检的基础条件。广东省地处南方沿海地区,大气水汽含量丰富,导致对流层天顶总延迟(zenith total delay, ZTD)在该地区短期变化剧烈;且常规ZTD经验模型在该区域精度较差,导致无人机自动巡检经常出现偏航等情况。对此基于广东电网自建地基增强系统,结合ERA5再分析资料和GNSS-ZTD解算结果,充分考虑ZTD在不同高程范围内的变化,通过分段函数对ERA5再分析资料进行拟合;并考虑年、半年和日周期变化的傅里叶级数来对分段拟合函数的系数进行时序分析,提出新区域ZTD格网模型;最后,使用96个广东电网GNSS站2023年1—3月的数据对所提出的模型进行验证,以其中31个站点作为基准站,以65个站点作为验证站进行模型验证。结果表明所提出的模型定位均方根误差为1.12 cm,远优于常规经验模型。

GNSS观测数据ZTD建模的质量控制方法

针对目前基于GNSS观测数据的对流层天顶总延迟(ZTD)模型缺乏有效质量控制手段的现状,提出了一套综合考虑数据量、网格分辨率以及模型稳定性的ZTD建模质量控制方法,并采用内华达大地测量实验室(NGL)解算的高空间分辨率GNSS对流层数据,选取了近十年德国及周边区域[47°N-55°N,5°E-15°E]183个测站的实测ZTD,对该方法进行了校验。实验结果表明:在该质量控制方法下建立的新模型精度稳定,平均均方根误差(RMS)为3.4 cm,相对于UNB3m、EGNOS、GPT2w+Saas平均改善了42.4%、35.8%、33.3%。本文提出的质量控制方法有效提升了基于GNSS观测数据的ZTD模型的性能,对于ZTD建模研究具有一定的参考价值。

Assessment of GNSS zenith tropospheric delay responses to atmospheric variables derived from ERA5 data over Nigeria

Tropospheric delay is a major error caused by atmospheric refraction in Global Navigation Satellite System(GNSS)positioning.The study evaluates the potential of the European Centre for Medium-range Weather Forecast(ECMWF)Reanalysis 5(ERA5)atmospheric variables in estimating the Zenith Tropospheric Delay(ZTD).Linear regression models(LRM)are applied to estimate ZTD with the ERA5 atmospheric variables.The ZTD are also estimated using standard ZTD models based on ERA5 and Global Pressure and Temperature 3(GPT3)atmospheric variables.These ZTD estimates are evaluated using the data collected from the permanent GNSS continuously operating reference stations in the Nigerian region.The results reveal that the Zenith Hydrostatic Delay(ZHD)from the LRM and the Saastamoinien model using ERA5 surface pressure are of identical accuracy,having a Root Mean Square(RMS)error of 2.3 mm while the GPT3-ZHD has an RMS of 3.4 mm.For the Zenith Wet Delay(ZWD)component,the best estimates are derived using ERA5 Precipitable Water Vapour(PWV).These include the ZWD derived by the LRM having an average RMS of 20.9 mm and Bevis equation having RMS of 21.1 mm and 21.0 mm for global and local weighted mean temperatures,respectively.The evaluation of GPT3-ZWD estimates gives RMS of 45.8 mm.This study has provided a valuable insight into the application of ERA5 data for ZTD estimation.In line with the fndings of the study,the ERA5 atmospheric variables are recommended for improving the accuracy in ZTD estimation,required for GNSS positioning.

天顶对流层延迟计算方法研究

依据精密单点定位(PPP)原理编写天顶对流层延迟估计程序,分别利用所编程序和GAMIT软件进行实测数据解算,将所得数据与IGS网站提供数据进行对比分析,结果显示PPP与双差法估计对流层延迟都有较高精度;但在双差法解算过程中发现,无远距离测站参与解算会影响对流层延迟估计的精度。

海潮对GNSS总天顶延迟量观测的影响

在顾及(方案Ⅰ)和不顾及(方案Ⅱ)海潮影响的情况下,利用中国地壳运动观测网络工程基准站观测数据分别计算总天顶延迟量,并对其进行比较。通过频谱特征分析,进一步研究了海潮对GNSS总天顶延迟量观测的影响,并得出了一些有益的结论。

基于最小二乘法无气象要素的PWV反演

提出了一种无需气象数据,直接用对流层天顶总延迟(zenith total delay,ZTD)推导大气可降水量(precipitable water vapor,PWV)的新方法。该方法从GPS反演大气水汽的反演方程出发,基于最小二乘法建立ZTD推算PWV的模型。结果表明,就BJFS测站而言,模型推算的PWV与GPS反演的PWV的均方根(root mean square,RMS)值为4.5 mm,两者存在一个微小的系统偏差,但相关系数高达0.982。在不研究其数值大小只研究其趋势变化时,可以用模型直接推算PWV,这可为气象学短期预报提供一定参考。

基于Matern^(5/2)核函数高斯过程回归算法的实时对流层内插模型研究

连续运行基准站(continuously operating reference station,CORS)网络是网络实时动态(real-time kinematic,RTK)必需的基础硬件设施,而网络RTK依然受站间距离增长所带来的非线性大气误差影响。而精密单点定位(precise point positioning,PPP)不需要额外的参考站,其通过对各类误差精确建模,解算用户位置信息,但由于先验对流层模型精度较差、卫星端和接收机端未校准相位延迟(uncalibrated phase delays,UPD)难以与模糊度有效分离,传统PPP收敛时间过长。结合两者的优势,基于PPP-RTK的思想,通过提取固定参考站位置处的实时天顶总延迟(zenith total delay,ZTD),并采用一种基于Matern^(5/2)核函数的非线性高斯过程回归模型,在线估计核函数超参数,从而对长间距基准站网络进行ZTD实时空域建模,为网内区域提供实时高精度的ZTD产品信息。采用中国湖北省CORS网2021年2月1日至4日共4天采样率为30 s的实时观测值数据对模型进行评估。实验结果表明,其在天顶方向收敛时间为17.5 min,定位精度为2.474 cm。与常规动态PPP解算结果相比,收敛时间提升10.26%,定位精度提升4.81%;与传统的线性插值算法相比,收敛时间提升7.89%,定位精度提升3.28%。且该模型具备较好的鲁棒性。