References

[1]
W. M. Kaula. Theory of satellite geodesy: applications of satellites to geodesy (Courier Corporation, 2013).
[2]
L. E. Cunningham. On the computation of the spherical harmonic terms needed during the numerical integration of the orbital motion of an artificial satellite. Celestial Mechanics, 207–216 (1970).
[3]
O. Montenbruck, E. Gill and F. Lutze. Satellite orbits: models, methods, and applications (Springer-Verlag, 2000).
[4]
F. Barthelmes. Definition of functionals of the geopotential and their calculation from spherical harmonic models, http://publications.iass-potsdam.de/pubman/item/escidoc (2013).