Deghosting and its Effect on Noise

Abstract

In marine seismic the ghost wavefield results in deep notches in the broadband frequency spectrum corresponding to the depth of the sources and detectors with respect to the sea surface. An inverse filter is used to remove these ghost effects. Application this filter has the consequence that the notch areas are amplified. In the presence of noise, the signal as well as the noise are amplified, which can lead to an unfavourable signal-tonoise ratio. Three methods are compared with respect to signal reconstruction and effect on noise. The first method, the non-causal method is exact for the signal outside the notches and inside the notch areas the noise is controlled with a ceiling applied to the inverse filter. The second method minimizes an objective function in order to indirectly calculate the ghost-free result without explicitly using the inverse filter. Finally, the hybrid method is a combination of these two. The methods are separately applied to a shot with and without noise. In order to quantify which method is most suited with respect to both signal reconstruction and noise suppression, a quantitative analysis is carried out. A constrained closed-loop method is the most accurate for this particular case.