Institute;
of;
Geodesy;
and;
Geophysics;
of;
Chinese;
Academy;
of;
Sciences,;
Wuhan;
430077,;
China;
Zhengzhou;
Information;
Engineering;
University,;
Zhengzhou;
450052,;
China;
Zhengzhou;
Information;
Engineering;
University,;
Zhengzhou;
450052,;
China;
Neumann; boundary; value; problem,; integral; solution,; gravity; disturbance.;