In seismology, impedance of a rock layer is defined as,
the product of bulk density and P-wave velocity. The normal incidence (vertical) reflection coefficient between an upper layer 'i' and a lower layer 'i+1' is given by,
S-wave impedance is the product of bulk density and S-wave velocity
Elastic impedance (EI) is an offset (or angle) dependent property for non-normal angles of incidence. It was first described by Connolly, 1999.
P to S converted wave elastic impedance (PSEI)
Also called Shear wave impedance