Citation of Professor Gedeon Dagan
at the Ceremony of Doctor Honoris Causa
at the University Pierre et Marie Curie-Paris VI
February 26, 1997
by
Professor G. de Marsily
Applied Geology Laboratory
University Pierre et Marie Curie-Paris VI

Mrs Rector, Mr. Vice-Chancellor, Mr. President, Mr. Dagan, dear colleagues, Mesdames, Monsieurs,

Having to present today the career of Mr. Gedeon Dagan, incumbent of the Raquel and Manuel Klachky Chair of Subsurface Hydrology at the Tel Aviv University, constitutes for me a real honor and great pleasure, that I want to share with you.

An honor, because first of all Mr. Dagan is a great man of science, and I thank the Council of the University Pierre and Marie Curie for choosing to distinguish him. You may have noticed that among all the Doctors that the University honors today, I believe Mr. Dagan is the only one having a chair in a Faculty of Engineering Sciences, as it was mentioned by the President Lemerle. Such Institutions are oriented toward applied rather than basic research; what I want to simply emphasize is that the quality of research in a discipline is not gauged by the objectives pursued, but by the quality of the individual and the originality of his pursuits.

Gedeon Dagan has studied first at the Bucharest University in the Faculty of Hydrotechnical Engineering and that of Applied Mathematics and Mechanics. After emigrating to Israel at the age of 30, he obtained shortly after the degree of Doctor of Science at the prestigious Technion in Haifa, the Israel Institute of Technology. His thesis dealt with problems of interface between fresh and salt waters in Coastal Aquifers and Professor Jacob Bear served as his advisor. He then assumed academic positions at the Technion and became a Professor in 1969, and subsequently moved to the chair in subsurface hydrology at Tel Aviv University, which he holds today. His academic career evolved in Israel, but with many visits to various Universities, including Paris, Berkeley, Santa Barbara, Ames (Iowa), Princeton, Padua, Rome and recently London. His achievements have led to numerous appointments of an academic or public nature in the area of water resources in Israel as well as UNESCO. He has also received many awards, including the prestigious Horton Award of the American Geophysical Union.

His collaboration with France is of long duration. I still remember our first contacts thirty years ago on the subject of interpretation of pumping tests in aquifers, up to recent frequent visits in Paris and participation in doctoral thesis committees. Our interests overlap because subsurface hydrology is taught in departments of Earth Sciences in France, whereas abroad it is found in Faculties of Civil or Hydraulic Engineering.

I shall discuss now the works of Mr. Dagan. I have for that to inflict upon you a few elementary notions of subsurface hydrology. Our discipline employs a large number of mathematical laws to characterize the velocities, transport and temperature of fluids that flow in the interconnected channels of porous media or fissured rocks. These laws obey the general principles of Fluid Mechanics, adapted to the porous structure. However, no matter how valid are these laws, we must recognize that we lack the means to characterize thoroughly the geometry of the paths followed by flowing water, and therefore that of the dimensions and intrinsic properties of porous structures. One of the major contributions of Gedeon Dagan to this discipline was to introduce the concept of random media in these problems. If the precise characterization of underground formations is a-priori impossible, he proposed to describe these media by random functions. These functions provide a measure of the uncertainty attached to any characterization of the properties of the medium. Gedeon Dagan undertook this task and contributed significantly to it, first to the notion of spatial covariance of properties, then to the inference of these statistical functions and subsequently to the conditioning of stochastic simulations by local measurements of variables like pressure, temperature and concentrations, that are easier to obtain. This process employed an arsenal of solutions of stochastic partial differential equations and inverse problems, but it is the scientist who developed new concepts that we honor today.

These works were published in more than one hundred articles in international journals, a monograph published in 1989 and at numerous conferences. Besides, Gedeon Dagan has had many students and a few have come from far away to honor him today. I would like to mention particularly Mr. Yoram Rubin, Professor at Berkeley, coming from the far California, to witness the friendship of Gedeon Dagan has developed with his students.

I will finish by mentioning that in order to take advantage of Mr. Dagan's visit to France, the University Paris VI organizes tomorrow and the day-after-tomorrow a seminar on Stochastic Hydrology, to which we have invited a small number of colleagues active in this field. The news has spread from mouth to ear, and numerous colleagues from all over the world expressed interest to come to Paris to present their works and to profit from discussions with Gedeon Dagan. Initially I was overwhelmed by this large number because of the small hall I reserved for the meeting, but eventually I secured the largest available one at Jussieu.

This event reflects better than my words the reputation of Gedeon Dagan, the esteem that his colleagues, who came here in large numbers and who I thank, hold him and the importance of his works. Many thanks again.!