jgg     2009 29 (3):  80-83    ISSN: 0412-1961  CN: 21-1139/TG EFFECT OF HEIGHT DIFFERENCE ON GPS VERTICAL ACCURACY Dai Wujiao; Chen Zhaohua ;and Liang Ming Department of Survey Engineering and Geomatics, Central South University, Changsha 410083 Received: 1900-01-01  Revised: 1900-01-01  Online: null Supporting info null