Aim. Identifying of reliable estimates of zenith tropospheric delay (ZTD) by the data of GNSS observations (remote monitoring of the troposphere) on the active reference stations of the west cross-border zone of Ukraine. Methods. The zenith tropospheric delays, and their direct link with integrated / precipitated water vapor are important products that are obtained in GNSS-meteorology. They allow to get the rapid information for numerical weather prediction. The reliability of the estimates of the integrated / precipitated water vapor from the GNSS data analysis is one of the main problems in the use of these results. Accordingly, strategy of analysis GNSS data should provide such ZTD estimations, which meet requirements of GNSS-meteorology. The determination of ZTD values was grounded traditionally on data analysis in the mode of packet network solution using least square method and observation technique which based on double differencing (DD) in the NRT mode. The absolute method of PPP which required precise corrections for satellite clocks together with predicted orbits, wasn’t applied practically. From point of view of analysis strategy of GNSS data the PPP method is popular thanks to creating by the International GNSS Service (IGS) and others institutions of a such products as accurate satellite orbits and clock corrections in RT mode. For comparing the ZTD data, obtained by the packages NRT-DD Bernese GNSS software and RT-PPP ALBERDING GNSS STATUS Software were selected for the February-March of 2016. The maximum amount of data at each observation station (2880 values) was by the selection criterion in this period. 17 GNSS stations were selected for comparison. The graphs of ZTD change over this period have been constructed for each station, as well as the hour changes of ZTD differences obtained by two packages. Results. Comparison results established the following: the use of different processing strategies GNSS data not significantly affect on the accuracy of zenith tropospheric delay. The obtained estimates of 1-2 cm fully satisfy the requirements for the indicated product in meteorology and climatology. Scientific novelty. The realized studies of two fundamentally different processing strategies GNSS data revealed the real accuracy of the zenith tropospheric delay, which allows to consider the results more reliable in comparison with results obtained by other researchers. Practical significance. Estimated values of ZTD obtained from a regional network of permanent GNSS stations of the western cross-border zone of Ukraine can become a valuable information in problems of numerical weather prediction.
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