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Recording geometries limit the maximum offset ray parameter.
However, our migration can put energy in part of the image gathers beyond this maximum aperture.
Therefore a mute needs to be applied to this part of the image gathers.
The maximum
*P*_{h} is a function of the coefficients on the right side of equation (1) and is given by equation (3):

| |
(3) |

where *h*_{max} is the maximum half offset, is the maximum expected geologic dip, *z* is depth,
and is the midpoint interval velocity function. This simple relation is a reasonable approximation,
but to truly define the migration aperture, ray-tracing needs to be used to account for the wavefield path above
the reflector. Figure 7 shows identical image gathers, with the right panel having the
mute applied. As expected, the deeper reflectors have a reduced maximum *P*_{h}.
The main use of this
mute is to zero points outside of the migration aperture so that they are not used in our
least-squares fit to find AVO intercept and AVO gradient Gratwick (2001).

**ph_mute
**

Figure 7 Identical image gathers. Right shows the result of
the *P*_{h} mute.

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** Up:** Gratwick: Amplitudes
** Previous:** CORRECTION FOR SYNTHETIC AMPLITUDE
Stanford Exploration Project

4/29/2001