1. China University of Geosciences, School of Computer Sciences, 430078 Wuhan, China
2. China University of Geosciences, Institute of Geophysics and Geomatics, 430074 Wuhan, China
3. Federal University of Goiás, Institute of Science and Technology, 74001-970 Goiás, Brazil
4. Aarhus University, Department of Geoscience, 8000 Aarhus C, Denmark