jgg     2014 34 (3):  151-154    ISSN: 0412-1961  CN: 21-1139/TG COORDINATE SYSTEM CONVERSION OF GOCE GRADIENTS  DATA AND ERROR ANALYSIS Faculty of Geoscience and Environment Engineering，Southwest Jiaotong University，Chengdu 611756 Received: 2013-09-26  Revised: null  Online: 2014-05-28 Supporting info