S.M. Shirokiy - Head of Sector of OJC «RPC «PSI» branch (Moscow region)
E.V. Titov - Ph. D. (Eng.), Head of Department, Main Product Engineer of OJC «RPC «PSI» branch (Moscow region)

At the current stage of GLONASS development, the accuracy level of consumer-s navigation support is mainly determined by the errors due to the space segment. However, in the near future the problem of high-precision navigation signals delay determination with the accuracy not exceeding 0.05−0.1 ns (1.5−3 cm) will be actual. Advanced technologies for accounting tropospheric refraction which used radiometric measurements are presented. The preliminary results of the experimental evaluation of the tropospheric delay accuracy using data from a prototype of the absolute water vapor radiometer colocated in «Svetloe» observatory of the «Quasar» radio interferometer network are presented. Envisaging further GLONASS development need to ensure high-precision estimation signals delay in Earth's troposphere. The solution of the problem among methods based on the use of radiometric measurements bearing the information about the structure and properties of the medium of propagation by measuring its photometric performance are obtained. The main contribution to the absorption coefficient of the signal in the atmosphere is belong to the lower troposphere (5−6 km) which contain most of the gaseous and condensed water vapor and are responsible for the delay variation. Water vapor radiometer (WVR) provides brightness temperature measurements on the two frequencies. The new parametric model, which is dependence the «wet» part of zenith tropospheric delay from the linearized values of the brightness temperature, are presented. Refinement of the model parameters is executed in regression analysis techniques, for which the measured values are estimates «wet» tropospheric delay, which a posteriori calculated in technologies SVOEVP (СВОЭВП). The following main results are received: 1. Models and methods to ensure estimation of the tropospheric delay GLONASS navigation signals based on WVR measurements are presented. Estimated model parameters are quite stable over time, which contributes to the finding of robust algorithms for their initialization and use in the GLONASS interests. 2. Accuracy of calculations the «wet» part of the troposphere delay based on the absolute WVR measurements is estimated at 3 mm (RMS). 3. In the case inhomogeneities in the WVR measurements error increases to 2−4 cm. When using the current values of the meteorological parameters during periods of restrictions on the use of WVR (rainfall) error in calculating the «wet» part of the tropospheric delay is increased to 10 cm. Compensation of WVR measurement errors is ensured by the inclusion of specialized devices (sensors).