In this article, we present estimates of diurnal and semidiurnal harmonics of variations in integrated water vapor content (IWV) according to data from 16 GPS stations in the Volga–Ural region of Russia during 2013–2015. Amplitudes of diurnal harmonics are maximal in summer and reach values from 0.37 to 1.01 mm. Time at the maximum of diurnal harmonic is typically in the period from 14:00 to 17:00. Semidiurnal harmonics have the largest amplitudes in spring and autumn, but they do not exceed 0.19 mm. A comparison of the diurnal cycle from GPS data and ERA-Interim reanalysis has revealed significant differences in the phase. It is established that, as a result of evaporation from the underlying surface and convective lifting of moist air, the summer diurnal variations in IWV and surface density of water vapor are in antiphase. The diurnal cycle of IWV is determined by surface air temperature to be 88 % in summer and less than at 35 % in other seasons. It is noted that maximal amplitudes of diurnal harmonic of IWV are observed at stations located on the windward side of mountains.

The cross-comparison of different techniques for atmospheric integrated water vapour (IWV) measurements is the essential part of their quality assessment protocol. We inter-compare the synchronised data sets of IWV values measured by the Bruker 125 HR Fourier-transform infrared spectrometer (FTIR), RPG-HATPRO microwave radiometer (MW), and Novatel ProPak-V3 global navigation satellite system receiver (GPS) at the St. Petersburg site between August 2014 and October 2016. As the result of accurate spatial and temporal matching of different IWV measurements, all three techniques agree well with each other except for small IWV values. We show that GPS and MW data quality depends on the atmospheric conditions; in dry atmosphere (IWV smaller than 6 mm), these techniques are less reliable at the St. Petersburg site than the FTIR method. We evaluate the upper bound of statistical measurement errors for clear-sky conditions as 0.29 ± 0.02 mm (1.6 ± 0.3 %), 0.55 ± 0.02 mm (4.7 ± 0.4 %), and 0.76 ± 0.04 mm (6.3 ± 0.8 %) for FTIR, GPS, and MW methods, respectively. We propose the use of FTIR as a reference method under clear-sky conditions since it is reliable on all scales of IWV variability.

Variations in the atmospheric integrated water vapor obtained from the phase measurement by satellite navigation systems’ receivers are discussed. The comparison between numerical weather reanalysis fields and solar photometer measurements has shown an agreement with a relative deviation of less than 10%. Intraseasonal processes of 3–45 days in length significantly contribute to variations in the atmospheric integrated water vapor; their amplitude is 1–4 kg/m². Variations with periods from 3 to 10 days are the most frequent.

Based on two-frequency phase measurements of GNSS signals by ground-based receivers, zenith delays of radio signals in the troposphere are estimated. These estimates are compared with the NCEP/NCAR reanalysis data on weather fields. It is shown that the standard deviation in the values of zenith delays obtained in both ways is about 1 cm on average. According to our calculations, such a level of accuracy permits one to study the interday and intraday dynamics of the troposphere. The temporal resolution of estimates based on the GNSS data is 2 h, which makes it possible to organize atmosphere monitoring using a ground-based network of satellite tracking systems.