HEISKANEN, WEIKKO ALEKSANTERI

(b. Kangaslampi, Finland, ca. 23 July 1895; d. Helsinki, Finland, 23 October 1971)

geodesy.

Theninth and youngest child of Heikki Heiskanen and Riikka Jurvanen, Heiskanen grew up on a small farm in eastern Finland. He was exceptionally energetic, generous in his opinions of others, and of a deep religious faith. In 1922 he married Kaarina Levanto; they had one daughter. From 1933 to 1936 Heiskanen was a member of the Finnish Diet, wherehe worked to improve the legal status of the Finnish language (Swedish was still the dominant language in some quarters). He also translated and wrote popular works on astronomy with the intent of widening the cultural sphere of his Finnish-speaking countrymen. His work in geodesy was recognized by memberships in seven different academies of science, including the American Academy of Arts and Sciences, and he was an honorary member of the Council of the International Association of Geodesy. The University of Bonn, the Helsinki University of Technology, the University of Uppsala, and Ohio State University awarded him honorary doctorates.

After three years of study, Heiskanen graduated with an M.S. degree from the University of Helsinki in 1919, with top honors in physics, mathematics, astronomy, political economy, and theoretical philosophy. With opportunities more promising in geodesy than in astronomy, his first love, he joined the Finnish Geodetic Institute in 1921 and produced a doctoral dissertation under Ilmari Bonsdorff, “Untersuchungen über Schwerkraft und Isostasie,” in 1924. Bonsdorff’s own studies on the isostatic equilibrium of the earth’s crust may well have provided the initial inspiration that led Heiskanen to become an expert in isostasy and a major figure in physical geodesy.

Heiskanen’s computational gravity calculations contributed to the development of methods for the isostatic reduction of gravity measurements, which were then used to compute the undulations of the geoid and eventually a worldwide geodetic system, the Columbus geoid. Outside of geodesy his work was important to the successful inertial guidance of the first United States satellites and missiles. which depended upon detailed knowledge of the gravity field, and important to geophysical studies of the structure of the earth’s crust. Heiskanen’s scientific career may be divided into three phases: his computations in the 1920’s in connection with the international gravity formula; his development and application of the Airy-Heiskanen hypothesis in isostasy in the 1930’s and 1940’s, most notably associated with the Isostatic Institute in Helsinki; and his program for the creation of a worldwide geodetic system, carried out after 1950 at Ohio State University.

The calculation of the geoid—the equipotential surface of the gravity field—was the central problem of classical geodesy. Thereferences surface was provided by the ellipsoid approved by the International Association of Geodesy in 1924, and the comparison of observed gravity values with it was based on the international gravity formula approved at the Stockholm congress of the association in 1930. Heiskanen first achieved international recognition when his value for gravity at the equator, γ=978.049 (1 + 0.0052884 sin² Φ–0.0000059 sin² 2 Φ)cm./sec.², was adopted by the congress as the first term, or idealized constant, of the formula. He had arrived at this figure on the basis of several thousand isostatically reduced gravity stations in all parts of the world.

From the beginning Heiskanen advocated the importance of the isostatic correction of gravity stations. His development of G.B. Airy’s less-favored hypothesis, according to which land masses float on a fluid base, like icebergs in the ocean, was to prove immensely fruitful in his own work; and present seismological findings would suggest that the AiryHeiskanen hypothesis prevails.

In 1928 Heiskanen began a twenty-one-year association with the Helsinki University of Technology. A research group of gifted students quickly gathered around him, and in 1936 that group was officially recognized by the International Association of Geodesy as the Isostatic Institute. Under Heiskanen’s guidance a simple cartographic method was developed for computing the topographic-isostatic effect, tables and maps for isostatic reduction were prepared, actual reductions of thousands of stations were carried out, the Undulations of the geoid were calculated over wide areas, and the problems of isostatic equilibrium and structure of the earth’s crust were studied.

After World War II several forces converged to bring Heiskanen to the United States. It was difficult to get the maps necessary for isostatic research in postwar Finland: and Heiskanen, appreciating the potential of improved gravimeters for extended gravity measurements, dreamed of a truly universal geodetic system that could replace the disparate regional and national systems of the time. Also at that time the United States government needed accurate gravity measurements to provide support to its rocket and satellite programs. In 1950 Heiskanen accepted a post at Ohio State University and for the next fifteen years spent most of the year in America, holding the post of director of the Finnish Geodetic Institute (1949–1962) mostly in absentia. For the first time courses in advanced geodesy were offered at an American university; they were heavily attended by U.S. Air Force officers. The Institute of Geodesy, Photogrammetry and Cartography, founded at Ohio State in 1951, was headed by Heiskanen from 1953 until 1965.

The program for the work at Ohio is laid out in Heiskanen’s On the World Geodetic System (1951). Gravity measurements from different systems, isostatically reduced, were to be used with George Stokes’s formula for computing the undulations of the geoid, and with Felix Vening Meinesz’s formulas for computing the absolute deflection of vertical components ξ and η. With this’ gravimetric’ method the absolute direction of the plumb line could be calculated for every point on earth; and thus every geodetic measurement, even measurements on different continents, could be incorporated into a uniform system. Theresult of the program, “The Columbus Geoid” (1957), was based on measurements collected from thirty-five countries, reduced for the first time by computer. Ironically, perhaps, this work appeared in the same year as the first satellite observations, which were to pave the way for the era of satellite geodesy. Heiskanen’s abilities as a teacher and administrator were such that Ohio State University quickly became the leading center for geodetic education in the United States, and perhaps half of the most prominent geodesists today were once his students.

BIBLIOGRAPHY

I. Original Works. Heiskanen’s “On the World Geodetic System” is in ’Suomen geodeettisen laitoksen julkaisuja (“Publications of the Finnish Geodetic Institute”), no. 39 (Helsinki, 1951), repr. in Publications of the Ohio State University, Institute of Geodesy, Photogrammetry and Cartography, no. 1 (Columbus, 1951). His other works include Gravity Survey of the State of Ohio (Columbus, 1956), written with U.A. Uotila; “The Columbus Geoid,” Transactions of the American Geophysical Union, 38, no. 6 (1957), 841–847; Size and Shape of the Earth: Symposium Held at the Ohio State University…November 13–15, 1956 (Columbus, 1957), as editor; The Earth and Its Gravity Field (New York, 1958), written with Felix Vening Meinesz; Assembly of Gravity Data (Columbus, 1959); Symposium on Geodesy in the Space Age… February 6–8, 1961 (Columbus, 1961), edited with Simo H. Laurila; and Physical Geodesy (San Francisco, 1967), written with Helmut Moritz.

II. Secondary Literature. A complete bibiography of Heiskanen’s writings is in “The Finnish Geodetic Institute 1918–1968,” in Suomen geodeettisen laitoksen julkaisuja, no. 65 (1969), 129–138. An account of his life and work is R.A. Hirvonen, in Proceedings of the Finnish Academy of Sciences and Letters for 1972 (1974), 75– 83.

Kathleen Ahonen