In-situ observations of water vapour and atmospheric delay from the ground-based GNSS network from 1996 to present

This dataset provides estimates of water vapour derived from atmospheric delays in Global Navigation Satellite System
(GNSS) radio signals.
The initial data is collected from two in situ ground-based network of GNSS receivers – the International GNSS Service
(IGS) and EUREF Permanent Network (EPN). The IGS collects, archives, and freely distributes GNSS data from a
cooperatively operated global network of more than 500 ground-based GNSS stations since 1994. The EPN is a European
network of more than 300 continuously operating GNSS reference stations with precisely known coordinates.
The fundamental observable of ground-based GNSS is the Zenith Total Delay (ZTD). This observable represents the
propagation delay induced by the atmosphere on GNSS signals between the GNSS satellites and a GNSS receiver.
Using in-situ measurements of ZTD as well as ancillary meteorological data at the site, the vertically-integrated total
amount if water vapour in the air column can be retrieved. This integrated quantity is referred to as Total Column
Water Vapour (TCWV), or Precipitable Water Column (PWC), Total Precipitable Water (TPW),
or Integrated Precipitable Water (IPW), or also Integrated Water Vapour (IWV).
The TCWV values, with corresponding uncertainties, are available from the 2nd reprocessing campaign
of the EPN (EPN-repro2), the 3rd reprocessing campaign of the IGS (IGS-repro3), and the daily product of IGS.
All networks provide hourly records of ZTD as part of the products derived from GNSS data processing.
The GNSS TCWV derived from these ZTD data is a new product, made available exclusively for the Climate Data Store (CDS).
The data user must consider that while the EPN-repro2 and IGS-repro3 consist of tropospheric parameters derived from consistently
reprocessed data spanning multiple decades, the IGS daily product is a near real-time product which may contain jumps
in the time-series when a new processing model is introduced. Therefore, IGS daily ZTD and TCWV should not be considered
as reference products.
The method for retrieval of GNSS TCWV and details on the algorithms can be found in the documentation. For comparison,
TCWV values from the ECMWF ERA5 reanalysis are also made available for the user.
The datasets can be downloaded as NetCDF files (CDM-Obs-Core, see documentation) or as comma-separated values (CSV) files.

本数据集提供了由全球导航卫星系统（GNSS）无线电信号大气延迟得出的水汽估计值。初始数据收集自两个地面基于GNSS接收器的现场网络——国际GNSS服务（IGS）和欧洲参考框架永久网络（EPN）。自1994年以来，IGS收集、存档并免费分发来自全球超过500个地面GNSS站点的GNSS数据。EPN是一个包含超过300个持续运行的GNSS参考站点的欧洲网络，这些站点的坐标精确已知。地面GNSS的基本可观测量是仰角总延迟（ZTD）。该可观测量代表了大气对GNSS卫星与GNSS接收器之间GNSS信号传播延迟的影响。利用现场ZTD的测量值以及站点辅助气象数据，可以检索出大气柱内垂直积分的水汽总量。这个积分量被称为总柱水汽（TCWV），或可降水水柱（PWC）、总可降水（TPW）、积分可降水（IPW），或也称为积分水汽（IWV）。TCWV值及其对应的不确定性，可从EPN的第二次再处理活动（EPN-repro2）、IGS的第三次再处理活动（IGS-repro3）以及IGS的每日产品中获得。所有网络都提供ZTD的小时记录，作为从GNSS数据处理中派生出的产品的一部分。从这些ZTD数据中推导出的GNSS TCWV是一个新的产品，仅向气候数据存储（CDS）提供。数据用户必须考虑，虽然EPN-repro2和IGS-repro3由多个十年跨度的连续再处理数据得出的对流层参数组成，但IGS的每日产品是一个近实时产品，当引入新的处理模型时，时间序列中可能包含跳跃。因此，不应将IGS的每日ZTD和TCWV视为参考产品。GNSS TCWV的检索方法和算法的详细信息可以在文档中找到。为了比较，还向用户提供了ECMWF ERA5再分析中的TCWV值。数据集可以下载为NetCDF文件（CDM-Obs-Core，见文档）或逗号分隔值（CSV）文件。