Inverse Problems for Wave Equations on a Riemannian Manifold

The main general subject of this chapter is an inverse problem of identifying unknown spatially varying coefficients of a wave equation from measurement data on a lateral boundary. This problem is of interest to many researchers working in various applied fields. For example, we can mention inverse problems related to non-destructive testing techniques and the geophysical problem of finding properties of geophysical media by observations of wave fields on a part of the surface of the earth.