Tor Hagfors, a world leader in the use of radar techniques to observe ionospheres, surfaces and interiors of planetary bodies, died of heart-failure on 17 January 2007, in Puerto Rico, at the age of 76. He was born on 8 December 1930, in Oslo, Norway, and received his education there and in Trondheim, where he graduated with exceptionally good grades with a degree in technical physics from the Norwegian Institute of Technology (NTH) in 1955.
Hagfors was then until 1963 employed at the Norwegian Defence Research Establishment (NDRE) where he worked mainly on scattering of high-frequency radio waves in the Earth's ionosphere. This work earned him a PhD in physics from the University of Oslo in 1959. With leave of absence from NDRE, he worked as a Research Associate at Stanford University in 1959/1960, developing a fundamental theory on incoherent scattering of radio waves from electrons in the ionosphere and also participating in radar studies of the Moon's surface in preparation for the later lunar landings.
Back in Norway Hagfors continued his scattering studies but, finding that the opportunities for experimental work were limited there, he accepted in 1963 a position at the Massachusetts Institute of Technology's Lincoln Laboratory where he stayed until 1971, interrupted by two years as Director of the Jicamarca Radio Observatory near Lima in Peru 1967-1969. There he gained a reputation as a very inspiring and efficient leader who handled difficult negotiations with the Peruvian military junta very well. In 1971 Hagfors was appointed Director of Operations of the Arecibo Radio Observatory in Puerto Rico, a position that he held and executed in an excellent way until 1973.
Although Tor had by now become a United States citizen with a brilliant scientific career, he chose to return to his alma mater, NTH, in Trondheim, where he worked as a Professor of Electronics between 1973 and 1982. From 1975 to 1982 he also served as Director of the European Incoherent Scatter Association (EISCAT) and was in charge of the construction of its radar facilities in Scandinavia. In 1982 Tor was back in USA as Director of the National Astronomy and Ionosphere Center (NAIC), which manages the Arecibo Observatory. At the same time he was Professor of both Astronomy and Electrical Engineering at Cornell University in Ithaca, New York.
In 1992 Hagfors accepted a call as Director of the Max-Planck Institut für Aeronomie in Lindau, Germany, where he remained until his retirement in 1998. During this period he was also Adjunct Professor at the Institute of Theoretical Astrophysics, University of Oslo, where he helped to start research projects in space research. The University of Tromsö, Norway; University of Nagoya, Japan; and University of Lancaster, UK, also benefited from visits by Tor as a Guest Professor.
Hagfors was widely valued as a member of many national and international scientific committees and unions, e. g., as head of a committee on space research for the Norwegian Research Council. He received many honors, notably the Van der Pol Gold Medal (1987), a Senior Humboldt Fellowship (1989), Membership in the Norwegian Academy of Science (1995), Extraordinary Membership in the Royal Astronomical Society (1998), the Sir Granville Beynon Medal (2002), a Doctorate Honoris Causa from the University of Oulu (2002), and a Honorary Doctorate from the University of Tromsö (2003).
Tor Hagfors had very wide interests; he was a brilliant researcher who published around 170 scientific papers. His many achievements in radio astronomy, in addition to what is already mentioned, included determination of the dielectric constant of the Moon's surface, radar mapping of the surfaces of Venus and of rapidly rotating planetary bodies, scattering studies of the surfaces of the Galilean satellites and of the interiors of comets and asteroids by radio sounding, and lastly the search for water on Mars by means of Mars Express data. He had a profound knowledge of not only the underlying physics of the phenomena that he studied, but was also a very skilled engineer who gave important contributions to antenna designs and equipment.
Tor was an inspiring scientist who gave generously of his time as teacher and adviser in fields such as information theory, plasma physics, radio astronomy, and antenna designs. He loved to socialize with friends and colleagues and he enjoyed outdoors activities, especially skiing. Despite his many accomplishments, he was a modest and friendly person who will be sorely missed.