[Find the paper and add this]
This formulation is from the Stanford Exploration Project, dated 6/8/2002.
Again, from SEP. Due to Fred Herkenhoff of Chevron. The stack amplitude is given by:
where and are the averages of sin2θ and tan2θ over the range of input angles to the stack.
According to SEP, "this form can now be inverted for the zero-offset reflectivity (RO) and the P-wave reflectivity (RP) without needing the interval velocities."
Implementation in Modelr
Implementation in Python
Bortfled's formula is implemented in bruges.