VRS concept using NWP and Mod_Ion_FK : preliminary results in Brazil
Alves, Daniele Barroca Marra ... [et al.]
Nowadays, the use of multiple reference stations has had a great growth, mainly because this kind of procedure overcomes the limitations of standard real time kinematic (RTK) systems. Using multiple reference stations it is possible to model the atmospheric effects (troposphere refraction and ionosphere effect) and to reduce the satellite orbit errors. Another important question concerning this topic is related to the transmission of the network corrections to the users. There are some possibilities for this and an efficient one is the Virtual Reference Station (VRS) concept. In the VRS concept, a base station is generated near to the rover receiver (user). The preliminary results obtained from an in-house software which has been developed at SSo Paulo State University (UNESP), Brazil, are presented in this paper. In this software, it was used multiple reference stations data and atmosphere models developed by Brazilian researches to generate the VRS. In relation to the troposphere, it was used zenithal tropospheric delay (ZTD) predicted from a model of Numerical Weather Prediction (NWP) and the Niell mapping function. In relation to the satellite orbit, IGU precise ephemeredes provided by IGS were used to reduce orbit errors. Concerning the ionospheric effects, the Mod_Ion_FK model, developed at UNESP, has been used. Mod_Ion_FK and ZTD from NWP performance for network RTK using the VRS concept are the main topics of this paper. So far, no attempt was done for solving the ambiguities as fixed among the reference stations. The preliminary results provided accuracy of the order of 7.5 cm in the resultant processing the generated VRS in Precise Point Positioning (PPP) and 25 cm considering relative positioning between the VRS and the real file collected at the same position
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