Pressure-amplitude reflection coefficient
= Pressure-amplitude reflection coefficient
{title2=$r_p=(Z_2-Z_1)/(Z_2+Z_1)$}
The reflected-to-incident compressional <pressure> or normal-stress amplitude ratio at a planar interface. For normal incidence between lossless homogeneous media, the displayed expression uses <acoustic impedances> $Z_j=\rho_jV_{pj}$. The reflected <energy> fraction is $r_p^2$, while a same-coordinate particle-velocity reflection coefficient has the opposite sign.