Abstract
We discuss an inverse problem of finding the sound speed c(x) and a damping coefficient σ( x ) in a second-order hyperbolic equation from two boundary observations. The coefficients are assumed to be unknown inside a ball in
Acknowledgements
This article was completed when as a Foreign Special Visiting Professor, the first author stayed at the Graduate School of Mathematical Sciences of the University of Tokyo from December 2002 till March 2003. He expresses his thanks to the University of Tokyo and the Japanese Ministry of Education, Culture, Sports, Science and Technology. The second author was supported partly by Grants 15340027 and 15654015 from the Japan Society for Promotion of Science.