Seismic reflection coefficient ($R_{\sigma }=(Z_b-Z_a)/(Z_b+Z_a)$)

The ratio of reflected to incident wave amplitude under a stated physical-variable and polarity convention. For normal incidence between isotropic layers with impedances $Z_a,Z_b$, the stress-amplitude convention gives $R_{\sigma }=(Z_b-Z_a)/(Z_a+Z_b)$, while particle velocity gives $R_v=-R_{\sigma }$. The reflected energy fraction is $R_{\sigma }^2$ for a single lossless propagating mode. A receiver trace requires the relevant seismic wavelet, travel times and transmission factors as well as this local coefficient.