State Key Laboratory of Lunar and Planetary Sciences;
Macau University of Science and Technology;
Macao 999078;
China;
China Deep Exploration Center-SinoProbe Center;
Chinese Academy of Geological Sciences;
Beijing 100037;
China;
School of Earth Sciences;
Key Laboratory of Mineral Resources in Western China;
Lanzhou University;
Lanzhou 730000;
China;
depth estimation; downward continuation; gravity data; continued fraction;