Norwegian astronomer. Professional experience includes: Norwegian Defence Research Establishment (1955-1963); sabbatical, Stanford University (1959-1960); Lincoln Laboratory in Lexington, Massachusetts (1963-1967, 1969-1971); director, Jicamarca Radio Observatory (1967-1969); site director, Arecibo Observatory (1971-1973); lecturer in electrical engineering, NTH (1973-1982); first director, EISCAT scientific association (1975-1982); director of National Astronomy and Ionosphere Center (NAIC), professor of astronomy and electrical engineering, Cornell University (1982-1992); director, Max Planck Institute for Aeronomy in Lindau (Katlenburg-Lindau) in Germany (1992-1998).