V. B. Kashkin - Dr.Sc. (Eng.), Professor, Siberian Federal University. E-mail: rtcvbk@rambler.ru
V. M. Vladimirov - Dr.Sc. (Eng.), Deputy Chairman of KSC Siberian Branch of RAS, Krasnoyarsk Scientific Center. E-mail: vlad@ksc.krasn.ru
A. O. Klykov - Postgraduate Student, Siberian Federal University. E-mail: shutnik@mail.ru

Signal delay in the troposphere is a source of error when measuring the real distance to the navigational satellite. Techniques for estimation the tropospheric delay by Saastamoinen and Hopfield are well known; they use operational terrestrial meteorological data at the location of the GNSS receiver and do not use the evidence on the vertical profiles of the atmosphere (VPT). It was found that the zenith tropospheric delay (ZTD), using these techniques, does not differ considerably from ZTD calculated for the standard model of the atmosphere in which the relative humidity is the same throughout the troposphere. The real profiles of temperature, pressure and humidity differ from models. It is necessary to know the meteorological parameters at the location of the GNSS receiver and information on VPT. The information can be obtained using satellites, for instance Meteor-M № 1 with MTVZA module or NOAA with ATOVS module. The zenith tropospheric delay (ZTD) was estimated using ATOVS VPT data at some latitudes at the North hemisphere. The result was compared with the result of Saasamoinen and Hopfield procedures. Delay determined with satellite VPT exceeds ZTD found by these techniques. This can be explained by the fact that satellite data ATOVS takes into account the actual distribution of temperature and water vapor, and not only on the surface, but also at the different isobaric levels. Another important advantage of satellite technology is the possibility to draw maps of the distribution of the tropospheric delay.