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This paper is an evaluation of the atmospheric water vapor remote sensing by GPS signals. The integrated water vapor (IWV) is calculated based on the measurement of the tropospheric zenith total delay (ZTD) effects on the microwave signals emitted by GPS satellites. The methodology proposed in this work is based on the combination of the global navigation satellite system (GNSS) observations and navigation data from the international GNSS service (IGS) products with meteorological data, measured at the stations level, to calculate the ZTD delay and estimate the integrated water vapor value. This work was carried out using data records from12 IGS stations distributed in seven countries in the four seasons of the year. The obtained results are compared with the values generated by Radiosonde measurement and MODIS satellite images level 2 (Water Vapor data product). In more than 90% of cases, the difference between the GPS and Radiosonde solutions is less than 3 mm with a monthly RMS less than 1.6 and a correlation of about 95%. The comparison between the GPS and MODIS shows that in more than 65 % of the time, the difference between the two solutions is less than 4 mm with a
monthly RMS less than 2.3, and the correlation is about 73%.