@unpublished{TUW-240698, author = {M{\"o}ller, Gregor and Maras, Jadre and Weber, Robert}, title = {Preconditions to GNSS Tomography of the Atmosphere}, year = {2015}, note = {poster presentation: IUGG 2015 General Assembly, Prag; 2015-06-22 -- 2015-07-02} }