Suppression of backscattered coherent noise by pre-stack partial migration

Abstract

Linear coherent noise frequently plagues marine seismic data in areas where the reflected energy is weak. This noise may arise in a number of different ways, but it has recently been suggested that the major culprits are diffractors located near, or at, the water bottom (Larner et al. 1983; Newman 1984). The diffraction patterns corresponding to such scatterers have stacking velocities that increase from the water velocity at the apex to very large values out on the limbs. As a result, the stacking velocity for the diffraction tails can coincide with that of deeper events at corresponding reflection times, and the tails of the diffractions will then stack coherently together with the deeper reflections. By contrast, since the diffractors can, in general, lie out of the plane of the survey, the apexes of the corresponding diffractions will appear below the water bottom and therefore be attenuated by stacking. The result is that the diffractions manifest themselves in the stacked data as the familiar strong linear events corresponding to diffraction hyperbolas without apexes.