Global Geology     2015 18 (4):  245-    ISSN: 1673-9736:  CN: 22-1371/P Ｒesearch on ray tracing in VTI medium based on different models JI Songda, SUN Jianguo, GAO Zhenghui, SUN Hui, WANG Qianlong and HUANG Xinguo College of Geo- Exploration Science and Technology，Jilin University，Changchun 130026，China Received null  Revised null  Online 2015-12-25 Reference   Corresponding author: