Louis Cagniard (1900-1971) was a French geophysicist who was noted for his seminal works in divergent branches of mathematical geophysics. His classic text Reflection and refraction of progressive seismic waves (1938) introduced a clever transformation in the Fourier-Laplace domain (later modified by A. de Hoop) that allows exact solutions of wave equations for multilayer media to be obtained analytically through a process of contour integration. Cagniard is also noted for his seminal 1953 paper which introduced the magnetotelluric prospecting method. Cagniard's work was in part based on the work of Russian geophysicist Andrey Nikolayevich Tikhonov.
Louis Cagniard graduated from the École Normale Supérieure, "Agrégé" of Physics in 1924, made his scientific debut as an assistant of the late physicist G. Bruhat.
After having received his Doctorate (Phd) in Physics (1928), he was appointed doctor of the Societe de Prospection Geophysique, a concern specializing in gravimetric and magnetic research work, which later, in 1936, united with the Compagnie Generale de Geophysique.
He received his Doctorate in mathematics in 1938, and put aside for awhile his activity in practical prospecting problems in order to teach Physics of the Earth in the Science Faculty at Strasbourg University. He was professor of Geophysics between 1939 and 1945 at the School and Observatory for Earth Science (EOST), relocated at Clermont Ferrand during the Second World War
Since 1946 he has been teaching Applied Geophysics in the Faculty of Science in Paris.
- Cagniard, L. (1962) Reflection and refraction of progressive seismic waves McGraw-Hill. Translation of Reflexion et refraction des ondes sismiques progressives" translation by Edward A. Flinn and C. Hewitt Dix
- Cagniard, L. (1953). ”BASIC THEORY OF THE MAGNETO‐TELLURIC METHOD OF GEOPHYSICAL PROSPECTING.” GEOPHYSICS, 18(3), 605–635.
- International Handbook of Earthquake & Engineering Seismology, Part 2 edited by William H.K. Lee, Hiroo Kanamori, Paul Jennings, Carl Kisslinger.
- Geophysics July 1953, Vol. XVII, No. 3.