The growing demand for Global Navigation Satellite System (GNSS) technology has necessitated the establishment of a vast and ever-growing network of International GNSS Service (IGS) tracking stations worldwide. The IGS provides highly accurate and highly reliable daily time-series Zenith Tropospheric Delay (ZTD) products using data from the member sites towards the use of GNSS for precise geodetic, climatological, and meteorological applications. However, if for reasons like poor internet connectivity, equipment failure, and power outages, the IGS station is inaccessible or malfunctioning, and gaps are created in the data archive resulting in degrading the quality of the ZTD and precipitable water vapour (PWV) estimation. To address this challenge as a means of providing an alternative data source to improve the continuous availability of ZTD data and as a backup data in the event that the IGS site data are missing or unavailable in West Africa, this paper compares the sitewise operational Vienna Mapping Functions 3 (VMF3) ZTD product with the IGS final ZTD product over five IGS stations in West Africa. Eight different statistical evaluation metrics, such as the mean bias (MB), mean absolute error (MAE), root mean squared error (RMSE), Pearson correlation coefficient (r), coefficient of determination (r²), refined index of agreement (IA_r), Nash–Sutcliffe coefficient of efficiency (NSE), and the fraction of prediction within a factor of two (FAC2), are employed to determine the degree of agreement between the VMF3 and IGS tropospheric products. The results show that the VMF3-ZTD product performed excellently and matches very well with the IGS final ZTD product with an average MB, MAE, RMSE, r, r², NSE, IA_r, and FAC2 of 0.38 cm, 0.87 cm, 1.11 cm, 0.988, 0.976, 0.967, 0.992, and 1.00 (100%), respectively. This result is an indication that the VMF3-ZTD product is accurate enough to be used as an alternative source of ZTD data to augment the IGS final ZTD product for positioning and meteorological applications in West Africa.

中文翻译：

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利用GNSS观测值评估来自射线追踪的VMF3产品在西非地区的天顶对流层延迟

对全球导航卫星系统（GNSS）技术的需求不断增长，因此必须在全球范围内建立一个庞大且不断增长的国际GNSS服务（IGS）跟踪站网络。IGS使用来自会员站点的数据以及使用GNSS进行精确的大地，气候和气象应用，提供高度准确和高度可靠的每日时间序列天顶对流层延迟（ZTD）产品。但是，如果由于诸如互联网连接质量差，设备故障和停电等原因而无法访问IGS站或发生故障，并且在数据存档中创建了间隙，从而导致ZTD的质量和可沉淀水蒸气（PWV）估计下降。为了解决这一挑战，作为提供替代数据源以改善ZTD数据的连续可用性的方法，以及在西非缺少IGS站点数据或IGS站点数据不可用的情况下作为备用数据的方法，本文比较了按地点运行的Vienna Mapping功能3（VMF3）ZTD产品和IGS最终ZTD产品在西非的5个IGS站点上。八种不同的统计评估指标，例如平均偏差（MB），平均绝对误差（MAE），均方根误差（RMSE），皮尔逊相关系数（r），确定系数（r ²），精确的一致性指数（IA _r），纳什-萨特克利夫效率系数（NSE）以及预测系数在2的因子内（FAC2）用于确定程度VMF3和IGS对流层产品之间的协议。结果表明，VMF3-ZTD产品表现出色，并且与IGS最终ZTD产品非常匹配，平均MB，MAE，RMSE，r，r ²，NSE，IA _r和FAC2分别为0.38厘米，0.87厘米，1.11厘米，0.988、0.976、0.967、0.992和1.00（100％）。该结果表明，VMF3-ZTD产品足够准确，可以用作ZTD数据的替代来源，以增强IGS最终的ZTD产品，以用于西非的定位和气象应用。