Evaluation of atmospheric water vapour based on ERA5 Reanalysis Products and GNSS Observations in Algeria.

Tropospheric delay is one of the main sources of error affecting high-precision positioning and navigation and is a key parameter for detecting water vapour in the Global Navigation Satellite System (GNSS).

This delay is typically divided into wet and hydrostatic components. ZTD is described as the sum of the Zenith Hydrostatic Delay (ZHD) and the Zenith Wet Delay (ZWD) and can be combined with surface pressure and temperature to estimate the integrated content of water vapour above GNSS station.

In climate change context, the precipitable water vapour (PW) is key parameter of atmospheric process and dynamics and its variation is very high in space and time. Its accuracy is paramount for any geodetic or climatic study.

In recent years, data from atmospheric reanalysis products such as ERA-Interim, ERA5 (the fifth generation of reanalysis from the European Centre for Medium-Range Weather Forecasts) have been widely used to obtain information on tropospheric delay and water vapour   (Li et al., 2015; Zhou et al., 2020...)

The main objective of this study is to compute precipitable water vapour from ERA5 reanalysis for four stations in Algeria, which have different types of climate. We opt for using integration method for different level of pressure with ERA5.

The values of water vapour are also compared with radiosondes profiles and GNSS data. The results of this work shows good agreement with a correlation that is not less than not 0.95 and 0.70 compared as radiosondes profiles (Namaoui et al., 2022). The first results are encouraging, in particular for meteorological applications with good hope to introduce another dataset as GNSS to more understand the variation and behaviour of water vapour over a long period of observation.