TROPOSPHERE MODELING IN LOCAL GPS NETWORK Jaroslaw Bosy, Andrzej Borkowski Department of Geodesy and Photogrammetry, Agricultural University, Grunwaldzka 53, PL - 50-357 Wroclaw, Poland bosy@kgf.ar.wroc.pl, borkowski@kgf.ar.wroc.pl Abstract Precise position determination of network points, particularly their vertical component is especially difficult in mountainous areas. Significant altitude differences and spatial variations of atmospheric parameters require the best possible approach to tropospheric delay (TD) estimation expressed by maximum reduction of systematic error caused by tropospheric refraction. The procedure of local meteorological parameters modelling (interpolation) in a GPS network area on the basis of meteorological observations, carried out concurrently to GPS measurements was introduced. The paper presents results of GPS data processing of local network KARKONOSZE (Sudetes, SW Poland) using different input data (standard atmosphere, MOPS model and ground meteorological data) and different methods of tropospheric delay estimation. INTRODUCTION The crucial factor for points altitude determination on the basis of GPS observations is tropospheric refraction (tropospheric delay). It may be easily noticed in case of local networks points situated in mountainous areas where great variability of atmospheric conditions is observed. (Borkowski et al., 2002; Bosy, 2005a). The tropospheric delay may be divided into two components, dry (hydrostatic) and wet. Approximately 90% of tropospheric delay caused by refraction is due to dry (hydrostatic) component of troposphere; it depends mainly on atmospheric pressure on the Earth surface and therefore it is easy to modelling. The hydrostatic component d T δ (Hydrostatic Delay) may be precisely determined on the strength of the ground meteorological measurements or the model of so-called standard atmosphere (Hugentobler et al., 2001). Remaining 10% of total tropospheric delay – wet component w T δ (Wet Delay) depends on the water vapour layout in the atmosphere and it is difficult to modelling (Mendes, 1999; Schüler, 2001; Bosy and Figurski, 2003). In this paper, comparative analysis of different models of tropospheric delay for dry and wet component are presented. Additionally, the procedure for building local troposphere model on the basis of meteorological conditions ground measurements, which were carried out simultaneously to GPS measurements within the whole network, was rendered. For the purpose of analysis, GPS and meteorological observations of the area covered with KARKONOSZE local network points (Kontny et al., 2002), situated in the mountainous area, were applied.