For a horizontally stratified (isotropic) earth, the rms-velocity of a primary reflection is a key parameter for common-midpoint (CMP) stacking, interval-velocity computation (by the Dix formula) and true-amplitude processing (geometrical-spreading compensation), As shown here, it is also a very desirable parameter to determine the Fresnel zone on the reflector from which the primary zero-offset reflection results, Hence, the rms-velocity can contribute to evaluating the resolution of the primary reflection. The situation that applies to a horizontally stratified earth model can be generalized to three-dimensional (3-D) layered laterally inhomogeneous media. The theory by

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Three different theoretical approaches to amplitude‐preserving Kirchhoff depth migration are compared. Each of them suggests applying weights in the diffraction stack migration to correct for amplitude loss resulting from geometric spreading. The weight functions are given in different notations, but as is shown, all of these expressions are similar. A notation that is well suited for implementation is suggested: entirely in terms of Green's function quantities (amplitudes or point‐source propagators). For the most common prestack configurations (common‐shot and common‐offset) and 3-D, 2.5-D, and 2-D migrations, expressions of the weights are given in this notation. The quantities needed for calculation of the weights can be computed easily, e.g., by dynamic ray tracing.

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