jgg     2013 33 (2):  49-53    ISSN: 0412-1961  CN: 21-1139/TG EFFECT OF DATA DEFECT ON ANALYZING GNSS TIME SERIES First Crust Monitoring and Application Center, CEA, Tianjin 300180 Received: 2012-10-12  Revised: null  Online: 2013-04-18 Supporting info