jgg     2014 34 (2):  115-119    ISSN: 0412-1961  CN: 21-1139/TG ROBUST SPECTRAL ANALYSIS OF TIME SERIES OF GEO  IONOSPHERIC CORRECTION 1）College of Navigation & Aerospace Engineering，Information Engineering University，Zhengzhou 450052 2）State Key Laboratory of Geographic Information Engineering，Xi’an 710054 3）Xi’an Research Institute of Surveying and Mapping，Xi’an 710054 Received: 2013-12-04  Revised: null  Online: 2014-04-21 Supporting info