GNSS: status, modelagem atmosférica e métodos de posicionamento

GNSS has been widely used to realize positioning. Besides modernization of existent systems, like GPS (Global Positioning System) and GLONASS (Global'naya Navigatsionnaya Sputnikovaya Sistema), there are new initiatives, like GALILEO and Beidou/Compass. The purpose of this paper is present the “state of the art” of these systems. Besides, write about atmospheric effects that affect the GNSS signals propagation and consequently the positioning. This theme has great interest, Brazil has its territory in a privileged location, mainly concerning ionospheric effects. Finally, describe and present some results of GNSS positioning methods.