Elastic impedance normalization

The elastic impedance, or EI, function has enabled far-offset-angle stack data to be inverted using technology developed for acoustic impedance inversion. An undesirable feature of the EI function has been that its dimensionality varies with incidence angle θ and provides numerical values that change significantly with θ. These problems have been overcome by modifying the EI function with constants αo, βo, and ρo. These modifications allow for a direct comparison between elastic impedance values across a range of angles in a manner that was not available with the previous formulation. The modifications neither improve nor degrade the accuracy of the reflectivity that can be derived from the EI function.