jgg     2015 35 (5):  784-787    ISSN: 0412-1961  CN: 21-1139/TG Time Series Prediction Model of Ionospheric VTEC Improved by  Wavelet Decomposition Institude of Geospatial Information, Information Engineering University, 62 Kexue Road, Zhengzhou 450001,China Received: 2014-06-06  Revised: null  Online: 2015-10-10 Supporting info