W. Keller, M. Kuhn, and W. Featherstone. Geodesy for the Planet Earth, volume 136 of International Association of Geodesy Symposia, page 527--537. Springer Berlin Heidelberg, (2011)
W. Keller. Geodesy Beyond 2000 -- The Challenges of the First Decade, volume 121 of International Association of Geodesy Symposia, page 208--213. Springer Berlin Heidelberg, (2000)
W. Keller. Gravity, Geoid and Geodynamics 2000, volume 123 of International Association of Geodesy Symposia, page 79--85. Springer Berlin Heidelberg, (2001)