Tor Hagfors, Cornell professor emeritus of astronomy and electrical engineering, died Jan. 17 in Puerto Rico of a heart attack. He was 76.

Hagfors was an internationally known pioneer in studies of the interaction of electromagnetic waves with ionized plasmas and solid surfaces. He was one of several people who independently developed the theory for incoherent scattering from magnetized plasmas, and he established many of the fundamental principles needed for radar astronomical observations of the moon and planets. His "Hagfors scattering law" describing the scattering of radar waves from planetary surfaces is still widely used, and his early radar studies of the properties of the lunar surface were an important contribution in preparation for the Apollo moon landings.

Hagfors published more than 200 scientific papers. His pioneering co-authored book "Radar Astronomy" (1968) is the primary reference for radar astronomers.

"Tor is widely known and respected in the international radio science community for his personal research achievements and his unselfish leadership efforts for the advancement of radio science," said Robert Brown, director of the National Astronomy and Ionosphere Center (NAIC) at Cornell, which manages the Arecibo Observatory in Puerto Rico for the National Science Foundation. "Much of the success of researchers at the NAIC Arecibo Observatory over the years is a direct result of Tor's insight and inspiration. His leadership, his wit and his wisdom are the legacy that will remain with his many friends forever."

After serving as director of operations for the NAIC at Arecibo from 1971 to 1973, Hagfors returned to his native Norway to found and direct the European Incoherent Scatter Association (EISCAT), where he was responsible for the construction and early operation of the EISCAT facility in Scandinavia. In 1982 he came to Cornell as professor and director of NAIC, initiating engineering studies and developing proposals that led to the second upgrading of the Arecibo telescope in the early 1990s. In 1992 he moved to Germany to direct the Max-Planck-Institute for Aeronomy, where he became involved in space missions to study the ionosphere and surface of Mars and the internal structure of comets. In recognition of his research achievements, the asteroid 1985 VD1 was named "Hagfors" in his honor.

His awards and honors include the van der Pol Gold Medal of the International Radio Union; the Senior Scientist Award of the Humboldt Society; and the Sir Granville Beynon Medal.

Hagfors is survived by his wife Hana, four children, a stepdaughter and eight grandchildren. A memorial service in Ithaca will be announced at a later date.