jgg     2015 35 (1):  77-80    ISSN: 0412-1961  CN: 21-1139/TG The Influence of Satellite Clock Bias Sampling Intervals  on the Precision of High Frequency PPP-ZTD 1 Hunan Provincial Key Laboratory of Clean Coal Resources Utilization and Mine Eviromental Protection， Hunan University of Science and Technology， Taoyuan Road, Xiangtan 411201, China 2 Shanghai Astronomical Observatory，Chinese Academy of Sciences，80 Nandan Road, Shanghai 200030, China 3 The Climate Center of Hunan Province，196 South-Furong Road, Changsha 410119, China Received: 2013-09-30  Revised: null  Online: 2015-02-06 Supporting info