= Seismic reflection coefficient
{title2=$R_\sigma=(Z_b-Z_a)/(Z_b+Z_a)$}
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.
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