The study of climate change is an important field of research. Monitoring of atmospheric variability especially the tropospheric precipitable water vapor (PWV) is a powerful way to investigate climate change. Global navigation satellite systems (GNSS) provide a good tool for studying atmospheric parameters as GNSS signals along its path from the satellites to the ground based receivers suffer a significant delay due to the refractivity of earth’s atmosphere. GNSS signals are not only delayed but also refracted in the neutral atmosphere. The zenith wet delays (ZWD) caused by the troposphere can be estimated during the geodetic processing of GNSS signals. Since the ZWD is tightly correlated to the PWV, GNSS observations can be used to study the changes of PWV. In this study GNSS data from the Egyptian permanent GNSS network (EPGN), International GNSS Service (IGS), EUREF Permanent Network (EPN) and Scripps Orbit and Permanent Array Center (SOPAC), for the years 2013 and 2014, were used. These GNSS stations provided a good geometrical coverage over the respective region. All GNSS data were processed using Bernese V 5.2 software. The needed product from GNSS data processing is the tropospheric zenith total delay (ZTD) over each GNSS site. The ZTD is divided based on physical parameters into zenith hydrostatic delay (ZHD) and zenith wet delay (ZWD). The ZWD is the basic observable used to calculate PWV. The values of the PWV were calculated and its variation over the study area was investigated. The quality of calculated PWV values from GNSS data evaluated against traditional Radiosonde (RS) measurements. The results of GNSS PWV showed good agreement with RS PWV when the PWV values were low, but this agreement became worse at high PWV values as the differences between the two techniques increased. The correlation coefficient between RS PWV and GNSS PWV varied from 0.31 to 0.84. Standard deviation of the differences between RS PWV and GNSS PWV ranged from 2.369 to 5.973 mm. The PWV estimated from GNSS observations had annual cycle, and its cycle in 2013 was different from that in 2014. The PWV differences between the 2 years clarified that the water vapor content over the east Mediterranean in most of 2014 days was higher than that in 2013. Furthermore, PWV variations were noted on both temporal and spatial scales. The highest temporal variation value was 25.41 mm whereas the maximum value of the spatial variation was 19.67 mm. The present study illustrated the importance of using geodetic networks to provide atmospheric information.

中文翻译：

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用GNSS评价东地中海的可沉淀水汽变化。

气候变化研究是重要的研究领域。监测大气变化，特别是对流层可沉淀水蒸气（PWV）是研究气候变化的有力方法。全球导航卫星系统（GNSS）为研究大气参数提供了一个很好的工具，因为GNSS信号从卫星到地面接收机的路径沿途，由于地球大气的折射率，它们遭受了严重的延迟。GNSS信号不仅会延迟，而且还会在中性大气中折射。由对流层引起的天顶湿延迟（ZWD）可以在GNSS信号的大地测量过程中估算。由于ZWD与PWV紧密相关，因此GNSS观测值可用于研究PWV的变化。在这项研究中，来自埃及永久性GNSS网络（EPGN）的GNSS数据，使用了2013年和2014年的国际GNSS服务（IGS），EUREF永久网络（EPN）和Scripps轨道与永久阵列中心（SOPAC）。这些GNSS站在相应区域提供了良好的几何覆盖。所有GNSS数据均使用Bernese V 5.2软件处理。GNSS数据处理所需的产品是每个GNSS站点上的对流层天顶总延迟（ZTD）。根据物理参数将ZTD分为天顶静水延迟（ZHD）和天顶湿延迟（ZWD）。ZWD是用于计算PWV的基本观测值。计算PWV的值，并研究其在研究区域内的变化。根据常规无线电探空仪（RS）测量评估的GNSS数据计算出的PWV值的质量。当PWV值较低时，GNSS PWV的结果显示出与RS PWV良好的一致性，但是当PWV值较高时，随着两种技术之间的差异增加，该一致性变得更差。RS PWV和GNSS PWV之间的相关系数在0.31至0.84之间变化。RS PWV和GNSS PWV之间差异的标准偏差范围为2.369至5.973 mm。根据GNSS观测估计的PWV具有年度周期，2013年的周期与2014年不同。两年之间的PWV差异表明，2014年大部分时间东地中海的水汽含量高于2013年此外，在时间和空间尺度上都记录了PWV变化。最高的时间变化值为25.41 mm，而空间变化的最大值为19.67 mm。