Abstract :
The inverse scattering problem for the wave equation ∂2tu=c(x, y)2 δx, yuis considered inRnx×R1y,n 2. The sound speed of the background medium,c0(y), takes different constant values on {y>0} and {y<0}. The exponentially decreasing perturbationc(x, y)−c0(y) is uniquely reconstructed from the scattering matrix of an arbitrarily fixed energy.