1. Colombo, O.L. (1981). Numerical methods for harmonic analysis on the sphere, Report no. 310, Department of Geodetic Science, The Ohio State University..
2. Gaposchkin, E.M. (1980). Averaging on the surface of a sphere,. 1. Geophys. Res., 85 (B6), 3187–3193.
3. Jekeli, C. (1981). Alternative methods to smooth the earth’s gravity field, Report no. 327, Department of Geodetic Science and Surveying, Ohio State University.
4. Manuscripta Geodaetica;C Jekeli,1995
5. Moritz, H. (1989). Advanced Physical Geodesy, 2nd ed., Wichmann Verlag, Karlsruhe.