jgg     2014 34 (2):  105-110    ISSN: 0412-1961  CN: 21-1139/TG ANALYSIS OF FACTORS AFFECTING ACCURACY OF GLOBAL  IONOSPHERIC GRID MODEL 1）College of Geomatics，Xi’an University of Science and Technology，Xi’an 710054 2）State Key Laboratory of Geodesy and Earth’s Dynamics，Wuhan 430077 3）School of Geodesy and Geomatics，Wuhan University，Wuhan 430079 Received: 2013-04-17  Revised: null  Online: 2014-04-21 Supporting info