Assume that two media are laying in a half-space
and the interface wall is parallel to the boundary
of the half-space.
We can directly observe the data
near the boundary of the half-space,
but we cannot directly observe inside the half-space.
In this situation,
we try to identify these unknown things
by creating an artificial explosion
and observing on the boundary
the waves generated by the explosion.
In the previous works related to this problem,
only the speeds of the waves were treated,
but we also take into account the impedances of the media
in our setting.