(34) |

(35) |

(36) |

Equation (36) has the known general solution, expressed in terms of cylinder functions of complex order Watson (1952):

(37) |

In the general case of offset continuation, *C _{1}* and

(38) |

(39) |

The DMO operator now can be derived as the inversion of operator (39), which is a simple multiplication by . Therefore, offset continuation becomes a multiplication by (the cascade of two operators). This fact demonstrates an important advantage of moving to the log-stretch domain: both offset continuation and DMO are simple filter multiplications in the Fourier domain of the log-stretched time coordinate.

In order to compare operator (39) with the known versions of log-stretch DMO, it is necessary to derive its asymptotic representation for high frequencies . The required asymptotics follows directly from the definition of function in (40) and the known asymptotic representation for a Bessel function of high order Watson (1952):

(40) |

(41) |

(42) |

(43) |

Asymptotic representation (42) is valid for large frequency and . It can be shown that the phase function defined in (44) coincides precisely with the analogous term in Liner's ``exact log DMO'' Liner (1990), which was proven to provide the correct geometric properties of DMO. However, the amplitude term is different from that of Liner's DMO because of the difference in the amplitude preservation properties.

A number of approximate log DMO operators have been proposed in the literature. As shown by Liner, all of them but ``exact log DMO'' distort the geometry of reflection effects at large offsets. This fact is caused by the implied approximations of the true phase function . Bolondi's OC operator Bolondi et al. (1982) implies ; Notfors DMO Notfors and Godfrey (1987) implies ; and ``full DMO'' Bale and Jakubowicz (1987) has . All these approximations are valid for small (small offsets or small reflector dips) and have errors of the order of (Figure 2). The range of validity of Bolondi's operator is discussed in more detail in Fomel (1995).

offpha
Phase functions of the log DMO operators. Solid line: exact log DMO;
dashed line: Bolondi's OC; dashed-dotted line: Bale's full DMO; dotted
line: Notfors DMO.
Figure 2 |

In practice, seismic data are often irregularly sampled in space, but
regularly sampled in time. This makes it attractive to apply offset
continuation and DMO operators in the domain, where the
frequency corresponds to the log-stretched time, and *y* is
the midpoint coordinate. Performing the inverse Fourier transform on
the spatial frequency transforms the inverse DMO operator (39)
to the domain, where the filter multiplication becomes
a convolutional operator:

(44) |

(45) |

Figure 3

Inverting operator (45), we can obtain the DMO operator in the domain.

11/12/1997